National Library of Energy BETA

Sample records for arsenide gaas gypsum

  1. Ohmic contact formation process on low n-type gallium arsenide (GaAs) using indium gallium zinc oxide (IGZO)

    SciTech Connect (OSTI)

    Yang, Seong-Uk; Jung, Woo-Shik; Lee, In-Yeal; Jung, Hyun-Wook; Kim, Gil-Ho; Park, Jin-Hong

    2014-02-01

    Highlights: We propose a method to fabricate non-gold Ohmic contact on low n-type GaAs with IGZO. 0.15 A/cm{sup 2} on-current and 1.5 on/off-current ratio are achieved in the junction. InAs and InGaAs formed by this process decrease an electron barrier height. Traps generated by diffused O atoms also induce a trap-assisted tunneling phenomenon. - Abstract: Here, an excellent non-gold Ohmic contact on low n-type GaAs is demonstrated by using indium gallium zinc oxide and investigating through time of flight-secondary ion mass spectrometry, X-ray photoelectron spectroscopy, transmission electron microscopy, JV measurement, and H [enthalpy], S [entropy], Cp [heat capacity] chemistry simulation. In is diffused through GaAs during annealing and reacts with As, forming InAs and InGaAs phases with lower energy bandgap. As a result, it decreases the electron barrier height, eventually increasing the reverse current. In addition, traps generated by diffused O atoms induce a trap-assisted tunneling phenomenon, increasing generation current and subsequently the reverse current. Therefore, an excellent Ohmic contact with 0.15 A/cm{sup 2} on-current density and 1.5 on/off-current ratio is achieved on n-type GaAs.

  2. Simple intrinsic defects in GaAs : numerical supplement.

    SciTech Connect (OSTI)

    Schultz, Peter Andrew

    2012-04-01

    This Report presents numerical tables summarizing properties of intrinsic defects in gallium arsenide, GaAs, as computed by density functional theory. This Report serves as a numerical supplement to the results published in: P.A. Schultz and O.A. von Lilienfeld, 'Simple intrinsic defects in GaAs', Modelling Simul. Mater. Sci Eng., Vol. 17, 084007 (2009), and intended for use as reference tables for a defect physics package in device models. The numerical results for density functional theory calculations of properties of simple intrinsic defects in gallium arsenide are presented.

  3. The comparison between gallium arsenide and indium gallium arsenide as materials for solar cell performance using Silvaco application

    SciTech Connect (OSTI)

    Zahari, Suhaila Mohd; Norizan, Mohd Natashah; Mohamad, Ili Salwani; Osman, Rozana Aina Maulat; Taking, Sanna

    2015-05-15

    The work presented in this paper is about the development of single and multilayer solar cells using GaAs and InGaAs in AM1.5 condition. The study includes the modeling structure and simulation of the device using Silvaco applications. The performance in term of efficiency of Indium Gallium Arsenide (InGaAs) and GaAs material was studied by modification of the doping concentration and thickness of material in solar cells. The efficiency of the GaAs solar cell was higher than InGaAs solar cell for single layer solar cell. Single layer GaAs achieved an efficiency about 25% compared to InGaAs which is only 2.65% of efficiency. For multilayer which includes both GaAs and InGaAs, the output power, P{sub max} was 8.91nW/cm with the efficiency only 8.51%. GaAs is one of the best materials to be used in solar cell as a based compared to InGaAs.

  4. Outdoor Performance of a Thin-Film Gallium-Arsenide Photovoltaic Module

    SciTech Connect (OSTI)

    Silverman, T. J.; Deceglie, M. G.; Marion, B.; Cowley, S.; Kayes, B.; Kurtz, S.

    2013-06-01

    We deployed a 855 cm2 thin-film, single-junction gallium arsenide (GaAs) photovoltaic (PV) module outdoors. Due to its fundamentally different cell technology compared to silicon (Si), the module responds differently to outdoor conditions. On average during the test, the GaAs module produced more power when its temperature was higher. We show that its maximum-power temperature coefficient, while actually negative, is several times smaller in magnitude than that of a Si module used for comparison. The positive correlation of power with temperature in GaAs is due to temperature-correlated changes in the incident spectrum. We show that a simple correction based on precipitable water vapor (PWV) brings the photocurrent temperature coefficient into agreement with that measured by other methods and predicted by theory. The low operating temperature and small temperature coefficient of GaAs give it an energy production advantage in warm weather.

  5. Structure and electrical characterization of gallium arsenide nanowires with different V/III ratio growth parameters

    SciTech Connect (OSTI)

    Muhammad, R.; Ahamad, R.; Ibrahim, Z.; Othaman, Z.

    2014-03-05

    Gallium arsenide (GaAs) nanowires were grown vertically on GaAs(111)B substrate by gold-assisted using metal-organic chemical vapour deposition. Field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and conductivity atomic force microscopy (CAFM) analysis were carried out to investigate the effects of V/III ratio on structural properties and current-voltage changes in the wires. Results show that GaAs NWs grow preferably in the wurtzite crystal structure than zinc blende crystal structure with increasing V/III ratio. Additionally, CAFM studies have revealed that zincblende nanowires indicate ohmic characteristic compared to oscillation current occurred for wurtzite structures. The GaAs NWs with high quality structures are needed in solar cells technology for trapping energy that directly converts of sunlight into electricity with maximum capacity.

  6. Optoelectronic simulation of GaAs solar cells with angularly selective filters

    SciTech Connect (OSTI)

    Kraus, Tobias Hhn, Oliver; Hauser, Hubert; Blsi, Benedikt

    2014-02-07

    We discuss the influence of angularly selective filters on thin film gallium arsenide solar cells. For this reason, the detailed balance model was refined to fit our needs with respect to Auger recombination, reflection, transmission, and realistic absorption. For calculating real systems, an approach was made to include optical effects of angularly selective filters into electron-hole dynamic equations implemented in PC1D, a one dimensional solar cell calculation tool. With this approach, we find a relative V{sub oc} increase of 5% for an idealized 100?nm GaAs cell, including Auger recombination.

  7. Pure silver ohmic contacts to N- and P- type gallium arsenide materials

    DOE Patents [OSTI]

    Hogan, Stephen J. (Golden, CO)

    1986-01-01

    Disclosed is an improved process for manufacturing gallium arsenide semiconductor devices having as its components an n-type gallium arsenide substrate layer and a p-type gallium arsenide diffused layer. The improved process comprises forming a pure silver ohmic contact to both the diffused layer and the substrate layer, wherein the n-type layer comprises a substantially low doping carrier concentration.

  8. Process for forming pure silver ohmic contacts to N- and P-type gallium arsenide materials

    DOE Patents [OSTI]

    Hogan, S.J.

    1983-03-13

    Disclosed is an improved process for manufacturing gallium arsenide semiconductor devices having as its components a n-type gallium arsenide substrate layer and a p-type gallium arsenide diffused layer. The improved process comprises forming a pure silver ohmic contact to both the diffuse layer and the substrate layer wherein the n-type layer comprises a substantially low doping carrier concentration.

  9. Inhalation developmental toxicology studies: Gallium arsenide in mice and rats

    SciTech Connect (OSTI)

    Mast, T.J.; Greenspan, B.J.; Dill, J.A.; Stoney, K.H.; Evanoff, J.J.; Rommereim, R.L.

    1990-12-01

    Gallium arsenide is a crystalline compound used extensively in the semiconductor industry. Workers preparing solar cells and gallium arsenide ingots and wafers are potentially at risk from the inhalation of gallium arsenide dust. The potential for gallium arsenide to cause developmental toxicity was assessed in Sprague- Dawley rats and CD-1 (Swiss) mice exposed to 0, 10, 37, or 75 mg/m{sup 3} gallium arsenide, 6 h/day, 7 days/week. Each of the four treatment groups consisted of 10 virgin females (for comparison), and {approx}30 positively mated rats or {approx}24 positively mated mice. Mice were exposed on 4--17 days of gestation (dg), and rats on 4--19 dg. The day of plug or sperm detection was designated as 0 dg. Body weights were obtained throughout the study period, and uterine and fetal body weights were obtained at sacrifice (rats, 20 dg; mice, 18 dg). Implants were enumerated and their status recorded. Live fetuses were sexed and examined for gross, visceral, skeletal, and soft-tissue craniofacial defects. Gallium and arsenic concentrations were determined in the maternal blood and uterine contents of the rats (3/group) at 7, 14, and 20 dg. 37 refs., 11 figs., 30 tabs.

  10. Preliminary survey report: control technology for gallium arsenide processing at Morgan Semiconductor Division, Garland, Texas

    SciTech Connect (OSTI)

    Lenihan, K.L.

    1987-03-01

    The report covers a walk through survey made of the Morgan Semiconductor Facility in Garland, Texas, to evaluate control technology for gallium-arsenide dust in the semiconductor industry. Engineering controls included the synthesis of gallium-arsenide outside the crystal pullers to reduce arsenic residues in the pullers, also reducing worker exposure to arsenic during cleaning of the crystal pullers.

  11. Heat load of a P-doped GaAs photocathode in SRF electron gun

    SciTech Connect (OSTI)

    Wang, E.; Ben-Zvi, I.; Kewisch, J.; Burrill, A.; Rao, T.; Wu, Q.; Jain, A.; Gupta, R.; Holmes, D.

    2010-05-23

    Many efforts were made over the last decades to develop a better polarized electron source for the high energy physics. Several laboratories operate DC guns with the Gallium-Arsenide photo-cathode, which yield a highly polarized electron beam. However, the beam's emittance might well be improved using a Superconducting RF electron gun, which delivers beams of higher brightness than DC guns does, because the field gradient at the cathode is higher. SRF guns with metal cathodes and CsTe cathodes have been tested successfully. To produce polarized electrons, a Gallium-Arsenide photo-cathode must be used: an experiment to do so in a superconducting RF gun is under way at BNL. Since the cathode will be normal conducting, the problem about the heat load stemming from the cathode arises. We present our measurements of the electrical resistance of GaAs at cryogenic temperatures, a prediction of the heat load and the verification by measuring the quality factor of the gun with and without cathode.

  12. Temperature dependence of carrier capture by defects in gallium arsenide

    SciTech Connect (OSTI)

    Wampler, William R.; Modine, Normand A.

    2015-08-01

    This report examines the temperature dependence of the capture rate of carriers by defects in gallium arsenide and compares two previously published theoretical treatments of this based on multi phonon emission (MPE). The objective is to reduce uncertainty in atomistic simulations of gain degradation in III-V HBTs from neutron irradiation. A major source of uncertainty in those simulations is poor knowledge of carrier capture rates, whose values can differ by several orders of magnitude between various defect types. Most of this variation is due to different dependence on temperature, which is closely related to the relaxation of the defect structure that occurs as a result of the change in charge state of the defect. The uncertainty in capture rate can therefore be greatly reduced by better knowledge of the defect relaxation.

  13. Ultra-thin GaAs single-junction solar cells integrated with a reflective back scattering layer

    SciTech Connect (OSTI)

    Yang, Weiquan; Becker, Jacob; Liu, Shi; Kuo, Ying-Shen; Li, Jing-Jing; Zhang, Yong-Hang; Landini, Barbara; Campman, Ken

    2014-05-28

    This paper reports the proposal, design, and demonstration of ultra-thin GaAs single-junction solar cells integrated with a reflective back scattering layer to optimize light management and minimize non-radiative recombination. According to our recently developed semi-analytical model, this design offers one of the highest potential achievable efficiencies for GaAs solar cells possessing typical non-radiative recombination rates found among commercially available III-V arsenide and phosphide materials. The structure of the demonstrated solar cells consists of an In{sub 0.49}Ga{sub 0.51}P/GaAs/In{sub 0.49}Ga{sub 0.51}P double-heterostructure PN junction with an ultra-thin 300?nm thick GaAs absorber, combined with a 5??m thick Al{sub 0.52}In{sub 0.48}P layer with a textured as-grown surface coated with Au used as a reflective back scattering layer. The final devices were fabricated using a substrate-removal and flip-chip bonding process. Solar cells with a top metal contact coverage of 9.7%, and a MgF{sub 2}/ZnS anti-reflective coating demonstrated open-circuit voltages (V{sub oc}) up to 1.00?V, short-circuit current densities (J{sub sc}) up to 24.5?mA/cm{sup 2}, and power conversion efficiencies up to 19.1%; demonstrating the feasibility of this design approach. If a commonly used 2% metal grid coverage is assumed, the anticipated J{sub sc} and conversion efficiency of these devices are expected to reach 26.6?mA/cm{sup 2} and 20.7%, respectively.

  14. Thermal influence on charge carrier transport in solar cells based on GaAs PN junctions

    SciTech Connect (OSTI)

    Osses-Mrquez, Juan; Caldern-Muoz, Williams R.

    2014-10-21

    The electron and hole one-dimensional transport in a solar cell based on a Gallium Arsenide (GaAs) PN junction and its dependency with electron and lattice temperatures are studied here. Electrons and heat transport are treated on an equal footing, and a cell operating at high temperatures using concentrators is considered. The equations of a two-temperature hydrodynamic model are written in terms of asymptotic expansions for the dependent variables with the electron Reynolds number as a perturbation parameter. The dependency of the electron and hole densities through the junction with the temperature is analyzed solving the steady-state model at low Reynolds numbers. Lattice temperature distribution throughout the device is obtained considering the change of kinetic energy of electrons due to interactions with the lattice and heat absorbed from sunlight. In terms of performance, higher values of power output are obtained with low lattice temperature and hot energy carriers. This modeling contributes to improve the design of heat exchange devices and thermal management strategies in photovoltaic technologies.

  15. GaAs photoconductive semiconductor switch

    DOE Patents [OSTI]

    Loubriel, Guillermo M. (Sandia Park, NM); Baca, Albert G. (Albuquerque, NM); Zutavern, Fred J. (Albuquerque, NM)

    1998-01-01

    A high gain, optically triggered, photoconductive semiconductor switch (PCSS) implemented in GaAs as a reverse-biased pin structure with a passivation layer above the intrinsic GaAs substrate in the gap between the two electrodes of the device. The reverse-biased configuration in combination with the addition of the passivation layer greatly reduces surface current leakage that has been a problem for prior PCSS devices and enables employment of the much less expensive and more reliable DC charging systems instead of the pulsed charging systems that needed to be used with prior PCSS devices.

  16. Recovery of chemical values from waste gypsum. Final report, December 1989-August 1992

    SciTech Connect (OSTI)

    Paisley, M.A.; Litt, R.D.

    1992-10-15

    A two-stage, two reactor process is being developed to recover sulfur or sulfuric acid and lime from waste gypsum. Waste gypsum is produced by a variety of industries including chemical, fertilizer and electric utilities. Current environmental regulations are increasing the landfill disposal cost to $30/ton or more depending on specific local conditions. These costs are expected to increase and the quantity of waste gypsum is also expected to increase. The two-stage gypsum recovery process uses two separate fluidized bed reactors to (1) reduce the gypsum to calcium sulfide (CaS) and then (2) roast the sulfide with air producing a SO2-rich gas and regenerated CaO. Fluidization and elutriation problems in the first stage were overcome to achieve up to 85 percent conversion of gypsum to CaS. Reducing gas composition, temperature, and solids residence time were shown to be the primary parameters affecting the reactions. Additional work is needed to achieve even greater conversion and to demonstrate the integrated 2-stage operation. A preliminary economic evaluation indicated a 3-year payback could be achieved for a 1000 ton/day plant. The capital cost was estimated to be $8.5 million. Operating cost savings were based on reduced disposal cost, use/sale of sulfuric acid and use/sale of lime.

  17. Photoluminescence from GaAs nanodisks fabricated by using combination...

    Office of Scientific and Technical Information (OSTI)

    GaAs nanodisks fabricated by using combination of neutral beam etching and atomic hydrogen-assisted molecular beam epitaxy regrowth Citation Details In-Document Search Title:...

  18. Dynamics of formation of photoresponse in a detector structure made of gallium arsenide

    SciTech Connect (OSTI)

    Ayzenshtat, G. I., E-mail: ayzen@mail.tomsknet.ru; Lelekov, M. A.; Tolbanov, O. P. [Tomsk State University (Russian Federation)

    2008-04-15

    The influence of capture effects on the characteristics of detectors of the ionizing radiation based on semi-insulating gallium arsenide is considered. Generation of nonequilibrium electrons and holes along the entire thickness of the active region was performed under illumination with an infrared light-emitting diode with a wavelength of 0.9 {mu}m. In this case, the situation emerging in the device structure under the effect of X-ray radiation or a high-energy electron beam was simulated. It is shown that the variation in the shape of the output signal with time in this case is caused by variation in the electric field profile due to the capture of holes at deep centers in gallium arsenide. An absolutely different distribution of the electric field emerges in the structure under irradiation of a semitransparent cathode of the structure with a red light-emitting diode, emission of which penetrates into the active region for mere 1 {mu}m. In this case, the transformation of the electric field is caused by the capture of electrons. Under the prolonged effect of such radiation, a space-charge-limited current mode emerges in the device.

  19. Au impact on GaAs epitaxial growth on GaAs (111){sub B} substrates in molecular beam epitaxy

    SciTech Connect (OSTI)

    Liao, Zhi-Ming; Chen, Zhi-Gang; Xu, Hong-Yi; Guo, Ya-Nan; Sun, Wen; Zhang, Zhi; Yang, Lei; Lu, Zhen-Yu; Chen, Ping-Ping; Lu, Wei; Zou, Jin; Centre for Microscopy and Microanalysis, The University of Queensland, St. Lucia, Queensland 4072

    2013-02-11

    GaAs growth behaviour under the presence of Au nanoparticles on GaAs {l_brace}111{r_brace}{sub B} substrate is investigated using electron microscopy. It has been found that, during annealing, enhanced Ga surface diffusion towards Au nanoparticles leads to the GaAs epitaxial growth into {l_brace}113{r_brace}{sub B} faceted triangular pyramids under Au nanoparticles, governed by the thermodynamic growth, while during conventional GaAs growth, growth kinetics dominates, resulting in the flatted triangular pyramids at high temperature and the epitaxial nanowires growth at relatively low temperature. This study provides an insight of Au nanoparticle impact on GaAs growth, which is critical for understanding the formation mechanisms of semiconductor nanowires.

  20. Gypsum treated fly ash as a liner for waste disposal facilities

    SciTech Connect (OSTI)

    Sivapullaiah, Puvvadi V.; Baig, M. Arif Ali

    2011-02-15

    Fly ash has potential application in the construction of base liners for waste containment facilities. While most of the fly ashes improve in the strength with curing, the ranges of permeabilities they attain may often not meet the basic requirement of a liner material. An attempt has been made in the present context to reduce the hydraulic conductivity by adding lime content up to 10% to two selected samples of class F fly ashes. The use of gypsum, which is known to accelerate the unconfined compressive strength by increasing the lime reactivity, has been investigated in further improving the hydraulic conductivity. Hydraulic conductivities of the compacted specimens have been determined in the laboratory using the falling head method. It has been observed that the addition of gypsum reduces the hydraulic conductivity of the lime treated fly ashes. The reduction in the hydraulic conductivity of the samples containing gypsum is significantly more for samples with high amounts of lime contents (as high as 1000 times) than those fly ashes with lower amounts of lime. However there is a relatively more increase in the strengths of the samples with the inclusion of gypsum to the fly ashes at lower lime contents. This is due to the fact that excess lime added to fly ash is not effectively converted into pozzolanic compounds. Even the presence of gypsum is observed not to activate these reactions with excess lime. On the other hand the higher amount of lime in the presence of sulphate is observed to produce more cementitious compounds which block the pores in the fly ash. The consequent reduction in the hydraulic conductivity of fly ash would be beneficial in reducing the leachability of trace elements present in the fly ash when used as a base liner.

  1. Photoeffects in WO{sub 3}/GaAs electrode

    SciTech Connect (OSTI)

    Yoon, K.H.; Lee, J.W.; Cho, Y.S.; Kang, D.H.

    1996-12-01

    Photoeffects of a {ital p}-type GaAs coated with WO{sub 3} thin film have been investigated as a function of film thickness and photoresponse transients of the WO{sub 3}/GaAs electrode were studied. Also, these results were compared to those for a single {ital p}-type GaAs electrode. The photocurrent of the WO{sub 3}/GaAs electrode depended on the film thickness of the WO{sub 3}, showing an optimum photon efficiency for specimens of 800 A thickness. This is due to the existence of an effective interface state within the band gap which reduces trapping of carriers and facilitates carrier movement. For an 800-A-thick WO{sub 3} thin film deposited {ital p}-GaAs photoelectrode, the photogenerated electrons were found to move to an electrolyte at a higher positive onset potential compared with that of single {ital p}-type GaAs, which was confirmed as a result of transient behavior. {ital I}{endash}{ital V} and {ital C}{endash}{ital V} characteristics of the WO{sub 3}/GaAs electrode were also compared with those of a single {ital p}-type GaAs electrode. {copyright} {ital 1996 American Institute of Physics.}

  2. Analysis of Nitrogen Incorporation in Group III-Nitride-Arsenide Materials Using a Magnetic Sector Secondary-Ion Mass Spectrometry (SIMS) Instrument: Preprint

    SciTech Connect (OSTI)

    Reedy, R. C.; Geisz, J. F.; Kurtz, S. R.; Adams, R. O.; Perkins, C. L.

    2001-10-01

    Presented at the 2001 NCPV Program Review Meeting: Group III-nitride-arsenide materials were studied by SIMS, XRD, and Profiler to determine small amounts of nitrogen that can lower the alloys bandgap significantly.

  3. Localized corrosion of GaAs surfaces and formation of porous GaAs

    SciTech Connect (OSTI)

    Schmuki, P.; Vitus, C.M.; Isaacs, H.S.; Fraser, J.; Graham, M.J.

    1995-12-01

    The present work deals with pitting corrosion of p- and n-type GaAs (100). Pit growth can be electrochemically initiated on both conduction types in chloride-containing solutions and leads after extended periods of time to the formation of a porous GaAs structure. In the case of p-type material, localized corrosion is only observed if a passivating film is present on the surface, otherwise -- e.g. in acidic solutions -- the material suffers from a uniform attack (electropolishing) which is independent of the anion present. In contrast, pitting corrosion of n-type material can be triggered independent of the presence of an oxide film. This is explained in terms of the different current limiting factor for the differently doped materials (oxide film in the case of the p- and a space charge layer in the case of the n-GaAs). The porous structure was characterized by SEM, EDX and AES, and consists mainly of GaAs. From scratch experiments it is clear that the pit initiation process is strongly influenced by surface defects. For n-type material, AFM investigations show that light induced roughening of the order of several hundred nm occurs under non-passivating conditions. This nm- scale roughening however does not affect the pitting process.

  4. Calculation of infrared plasma reflection spectra of inhomogeneously doped P-type gallium arsenide

    SciTech Connect (OSTI)

    CHEN Wei-xi; LI Guo-hua; NIU Jin-zhen; GUO Chang-zhi

    1982-01-01

    The influence of the surface concentration and concentration profile of free carriers, the layer thickness and free carrier concentration of the homogeneous substrate on the infrared plasma reflection spectra of inhomogeneously doped P-type GaAs layers is analyzed by computer solutions of differential equations for the optical admittance. Computed spectra are reported for four different profiles and several substrate concentrations. Methods for evaluation of the measured reflection spectra and the limitation of this technique are discussed.

  5. Application of the bounds-analysis approach to arsenic and gallium antisite defects in gallium arsenide

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Wright, A. F.; Modine, N. A.

    2015-01-23

    The As antisite in GaAs (AsGa) has been the subject of numerous experimental and theoretical studies. Recent density-functional-theory (DFT) studies report results in good agreement with experimental data for the +2, +1, and 0 charge states of the stable EL2 structure, the 0 charge state of the metastable EL2* structure, and the activation energy to transform from EL2* to EL2 in the 0 charge state. However, these studies did not report results for EL2* in the -1 charge state. In this paper, we report new DFT results for the +2, +1, 0, and -1 charge states of AsGa, obtained usingmore » a semilocal exchange-correlation functional and interpreted using a bounds-analysis approach. In good agreement with experimental data, we find a -1/0 EL2* level 0.06 eV below the conduction-band edge and an activation energy of 0.05 eV to transform from EL2* to EL2 in the -1 charge state. While the Ga antisite in GaAs (GaAs) has not been studied as extensively as AsGa, experimental studies report three charge states (-2, -1, 0) and two levels (-2/-1, -1/0) close to the valence-band edge. Recent DFT studies report the same charge states, but the levels are found to be well-separated from the valence-band edge. To resolve this disagreement, we performed new DFT calculations for GaAs and interpreted them using a bounds analysis. The analysis identified the -1 and 0 charge states as hole states weakly bound to a highly-localized -2 charge state. Moreover, the -2/-1, -1/0 levels were found to be near the valence-band edge, in good agreement with the experimental data.« less

  6. Modeling the VOC emissions from interior latex paint applied to gypsum board

    SciTech Connect (OSTI)

    Guo, Z.; Fortmann, R.; Marfiak, S.; Tichenor, B.; Sparks, L.

    1997-09-01

    The paper discusses modeling volatile organic compound (VOC) emissions from indoor latex paint applied to gypsum board. An empirical source model for a porous substrate was developed that takes both the wet- and dry-stage emission into consideration. Tests in the U.S. EPA`s Source Characterization Laboratory showed that common interior surfaces such as gypsum board and carpet could absorb significant amounts of latex paint VOCS from the air, and that they were re-emitted very slowly. An indoor air quality model incorporating the source model, an irreversible sink model, and the air movement data obtained from tracer gas tests made satisfactory predictions for the VOC levels in a test house.

  7. In-Plane Electronic Anisotropy of Underdoped ___122___ Fe-Arsenide Superconductors Revealed by Measurements of Detwinned Single Crystals

    SciTech Connect (OSTI)

    Fisher, Ian Randal

    2012-05-08

    The parent phases of the Fe-arsenide superconductors harbor an antiferromagnetic ground state. Significantly, the Neel transition is either preceded or accompanied by a structural transition that breaks the four fold symmetry of the high-temperature lattice. Borrowing language from the field of soft condensed matter physics, this broken discrete rotational symmetry is widely referred to as an Ising nematic phase transition. Understanding the origin of this effect is a key component of a complete theoretical description of the occurrence of superconductivity in this family of compounds, motivating both theoretical and experimental investigation of the nematic transition and the associated in-plane anisotropy. Here we review recent experimental progress in determining the intrinsic in-plane electronic anisotropy as revealed by resistivity, reflectivity and ARPES measurements of detwinned single crystals of underdoped Fe arsenide superconductors in the '122' family of compounds.

  8. Bismuth-induced phase control of GaAs nanowires grown by molecular...

    Office of Scientific and Technical Information (OSTI)

    Bismuth-induced phase control of GaAs nanowires grown by molecular beam epitaxy Citation Details In-Document Search Title: Bismuth-induced phase control of GaAs nanowires grown by ...

  9. Transport-reaction model for defect and carrier behavior within displacement cascades in gallium arsenide

    SciTech Connect (OSTI)

    Wampler, William R.; Myers, Samuel M.

    2014-02-01

    A model is presented for recombination of charge carriers at displacement damage in gallium arsenide, which includes clustering of the defects in atomic displacement cascades produced by neutron or ion irradiation. The carrier recombination model is based on an atomistic description of capture and emission of carriers by the defects with time evolution resulting from the migration and reaction of the defects. The physics and equations on which the model is based are presented, along with details of the numerical methods used for their solution. The model uses a continuum description of diffusion, field-drift and reaction of carriers and defects within a representative spherically symmetric cluster. The initial radial defect profiles within the cluster were chosen through pair-correlation-function analysis of the spatial distribution of defects obtained from the binary-collision code MARLOWE, using recoil energies for fission neutrons. Charging of the defects can produce high electric fields within the cluster which may influence transport and reaction of carriers and defects, and which may enhance carrier recombination through band-to-trap tunneling. Properties of the defects are discussed and values for their parameters are given, many of which were obtained from density functional theory. The model provides a basis for predicting the transient response of III-V heterojunction bipolar transistors to pulsed neutron irradiation.

  10. Polycrystalline MBE-grown GaAs for solar cells

    SciTech Connect (OSTI)

    Friedman, D.J.; Kurtz, S.R.; Kibbler, A.E.; Al-Jassim, M.; Jones, K.; Keyes, B.; Matson, R.

    1997-02-01

    This paper will discuss initial studies of thin-film GaAs grown by molecular-beam epitaxy for use in developing a thin-film GaAs solar cell. Photocurrent and photoluminescence intensity are related to the material morphology as a function of growth conditions. Growth temperature and V/III ratio have a dramatic effect on the photocurrent. However, it seems likely that even after optimizing such growth parameters, it will be necessary to provide substrates that can provide templates to enhance grain size from the start of thin-film growth. {copyright} {ital 1997 American Institute of Physics.}

  11. Polycrystalline MBE-grown GaAs for solar cells

    SciTech Connect (OSTI)

    Friedman, D. J.; Kurtz, Sarah R.; Kibbler, A. E.; Al-Jassim, M.; Jones, K.; Keyes, B.; Matson, R.

    1997-02-15

    This paper will discuss initial studies of thin-film GaAs grown by molecular-beam epitaxy for use in developing a thin-film GaAs solar cell. Photocurrent and photoluminescence intensity are related to the material morphology as a function of growth conditions. Growth temperature and V/III ratio have a dramatic effect on the photocurrent. However, it seems likely that even after optimizing such growth parameters, it will be necessary to provide substrates that can provide templates to enhance grain size from the start of thin-film growth.

  12. Electronic contribution to friction on GaAs

    SciTech Connect (OSTI)

    Applied Science and Technology Graduate Group, UC Berkeley; Dept. of Materials Sciences and Engineering, UC Berkeley; Salmeron, Miquel; Qi, Yabing; Park, J.Y.; Hendriksen, B.L.M.; Ogletree, D.F.; Salmeron, Miquel

    2008-04-15

    The electronic contribution to friction at semiconductor surfaces was investigated by using a Pt-coated tip with 50nm radius in an atomic force microscope sliding against an n-type GaAs(100) substrate. The GaAs surface was covered by an approximately 1 nm thick oxide layer. Charge accumulation or depletion was induced by the application of forward or reverse bias voltages. We observed a substantial increase in friction force in accumulation (forward bias) with respect to depletion (reverse bias). We propose a model based on the force exerted by the trapped charges that quantitatively explains the experimental observations of excess friction.

  13. Radiation damage of GaAs thin-film solar cells on Si substrates

    SciTech Connect (OSTI)

    Itoh, Y.; Yamaguchi, M.; Nishioka, T.; Yamamoto, A.

    1987-01-15

    1-MeV electron irradiation damages in GaAs thin-film solar cells on Si substrates are examined for the first time. Damage constant for minority-carrier diffusion length in GaAs heteroepitaxial films on Si substrates is found to be the same as that in GaAs homoepitaxial films on GaAs substrates. This agreement suggests that GaAs/Si has the same defect introduction rate with radiation as GaAs/GaAs. The degradation of GaAs solar cells on Si with electron irradiation is less than that of GaAs solar cells on GaAs, because in the present, GaAs films on Si substrates have lower minority-carrier diffusion length compared to GaAs films on GaAs and these films are insensitive to radiation. The p/sup +/-p/sup +/-n AlGaAs-GaAs heteroface solar cell with junction depth of about 0.3 ..mu..m is concluded to be useful for a high-efficiency and radiation-resistant solar cell fabricated on a Si substrate.

  14. Testing a GaAs cathode in SRF gun

    SciTech Connect (OSTI)

    Wang, E.; Kewisch, J.; Ben-Zvi, I.; Burrill, A.; Rao, T.; Wu, Q.; Holmes, D.

    2011-03-28

    RF electron guns with a strained superlattice GaAs cathode are expected to generate polarized electron beams of higher brightness and lower emittance than do DC guns, due to their higher field gradient at the cathode's surface and lower cathode temperature. We plan to install a bulk GaAs:Cs in a SRF gun to evaluate the performance of both the gun and the cathode in this environment. The status of this project is: In our 1.3 GHz 1/2 cell SRF gun, the vacuum can be maintained at nearly 10{sup -12} Torr because of cryo-pumping at 2K. With conventional activation of bulk GaAs, we obtained a QE of 10% at 532 nm, with lifetime of more than 3 days in the preparation chamber and have shown that it can survive in transport from the preparation chamber to the gun. The beam line has been assembled and we are exploring the best conditions for baking the cathode under vacuum. We report here the progress of our test of the GaAs cathode in the SRF gun. Future particle accelerators, such as eRHIC and the ILC require high-brightness, high-current polarized electrons. Strained superlattice GaAs:Cs has been shown to be an efficient cathode for producing polarized electrons. Activation of GaAs with Cs,O(F) lowers the electron affinity and makes it energetically possible for all the electrons, excited into the conduction band that drift or diffuse to the emission surface, to escape into the vacuum. Presently, all operating polarized electron sources, such as the CEBAF, are DC guns. In these devices, the excellent ultra-high vacuum extends the lifetime of the cathode. However, the low field gradient on the photocathode's emission surface of the DC guns limits the beam quality. The higher accelerating gradients, possible in the RF guns, generate a far better beam. Until recently, most RF guns operated at room temperature, limiting the vacuum to {approx}10{sup -9} Torr. This destroys the GaAs's NEA surface. The SRF guns combine the excellent vacuum conditions of DC guns and the high accelerating gradient of the RF guns, potentially offering a long lived cathode with very low emittance. Testing this concept requires preparation of the cathode, transportation to the SRF gun and evaluation of the performance of the cathode and the gun at cryogenic temperatures. In our work at BNL, we successfully activated the bulk GaAs in the preparation chamber. The highest quantum efficient was 10% at 532 nm that fell to 0.5% after 100 hours. We explored three different ways to activate the GaAs. We verified that the GaAs photocathode remains stable for 30 hours in a 10{sup -11} Torr vacuum. Passing the photocathode through the low 10{sup -9} Torr transfer section in several seconds caused the QE to drop to 0.8%. The photocathode with 0.8% QE can be tested for the SRF gun. The gun and beam pipe were prepared and assembled. After baking at 200 C baking, the vacuum of the gun and beam pipe can sustain a low 10{sup -11} Torr at room temperature. The final test to extract electrons from the gun is ongoing. In this paper, we discuss our progress with this SRF gun and the results of the photocathode in preparation chamber and in magnet transfer line.

  15. Formation and properties of porous GaAs

    SciTech Connect (OSTI)

    Schmuki, P.; Lockwood, D.J.; Fraser, J.W.; Graham, M.J.; Isaacs, H.S.

    1996-06-01

    Porous structures on n-type GaAs (100) can be grown electrochemically in chloride-containing solutions. Crystallographic etching of the sample is a precursor stage of the attack. Polarization curves reveal the existanece of a critical onset potential for por formation (PFP). PFP is strongly dependent on the doping level of the sample and presence of surface defects. Good agreement between PFP and breakdown voltage of the space charge layer is found. Surface analysis by EDX, AES, and XPS show that the porous structure consists mainly of GaAs and that anion uptake in the structure can only observed after attackhas been initiated. Photoluminescence measurements reveal (under certain conditions) visible light emission from the porous structure.

  16. An experiment to test the viability of a gallium-arsenide cathode in a SRF electron gun

    SciTech Connect (OSTI)

    Kewisch,J.; Ben-Zvi, I.; Rao, T.; Burrill, A.; Pate, D.; Wu, Q.; Todd, R.; Wang, E.; Bluem, H.; Holmes, D.; Schultheiss, T.

    2009-05-04

    Strained gallium arsenide cathodes are used in electron guns for the production of polarized electrons. In order to have a sufficient quantum efficiency lifetime of the cathode the vacuum in the gun must be 10{sup -11} Torr or better, so that the cathode is not destroyed by ion back bombardment or through contamination with residual gases. All successful polarized guns are DC guns, because such vacuum levels can not be obtained in normal conducting RF guns. A superconductive RF gun may provide a sufficient vacuum level due to cryo-pumping of the cavity walls. We report on the progress of our experiment to test such a gun with normal GaAs-Cs crystals.

  17. Polycrystalline GaAs solar cells on low-cost Silicon-Film{trademark} substrates

    SciTech Connect (OSTI)

    Mauk, M.G.; Feyock, B.W.; Hall, R.B.; Cavanaugh, K.D.; Cotter, J.E.

    1997-12-31

    The authors assess the potential of a low-cost, large-area Silicon-Film{trademark} sheet as a substrate for thin-film polycrystalline GaAs solar cells. Silicon-Film is a relatively inexpensive material on which large-grain (>2 mm) polycrystalline GaAs films can be formed. The GaAs epitaxial layers are grown by a simple close-spaced vapor transport (CSVT) technique using water vapor as a transport agent. A recrystallized Ge{sub 1{minus}x}Si{sub x} buffer layer between the GaAs epilayer and Silicon-Film substrate can facilitate growth of the GaAs. Selective epitaxy on patterned, oxide-masked substrates is effective in reducing thermal stress effects.

  18. Quantum effects in electron beam pumped GaAs

    SciTech Connect (OSTI)

    Yahia, M. E.; National Institute of Laser Enhanced Sciences , Cairo University ; Azzouz, I. M.; Moslem, W. M.

    2013-08-19

    Propagation of waves in nano-sized GaAs semiconductor induced by electron beam are investigated. A dispersion relation is derived by using quantum hydrodynamics equations including the electrons and holes quantum recoil effects, exchange-correlation potentials, and degenerate pressures. It is found that the propagating modes are instable and strongly depend on the electron beam parameters, as well as the quantum recoil effects and degenerate pressures. The instability region shrinks with the increase of the semiconductor number density. The instability arises because of the energetic electron beam produces electron-hole pairs, which do not keep in phase with the electrostatic potential arising from the pair plasma.

  19. Boron, bismuth co-doping of gallium arsenide and other compounds for photonic and heterojunction bipolar transistor devices

    DOE Patents [OSTI]

    Mascarenhas, Angelo

    2015-07-07

    Isoelectronic co-doping of semiconductor compounds and alloys with acceptors and deep donors is sued to decrease bandgap, to increase concentration of the dopant constituents in the resulting alloys, and to increase carrier mobilities lifetimes. For example, Group III-V compounds and alloys, such as GaAs and GaP, are isoelectronically co-doped with, for example, B and Bi, to customize solar cells, and other semiconductor devices. Isoelectronically co-doped Group II-VI compounds and alloys are also included.

  20. Coal fly ash and phospho-gypsum mixture as an amendment to improve rice paddy soil fertility

    SciTech Connect (OSTI)

    Lee, Y.B.; Ha, H.S.; Lee, C.H.; Kim, P.J.

    2008-04-15

    Rice is a plant that requires high levels of silica (Si). As a silicate NOD source to rice, coal fly ash (hereafter, fly ash), which has an alkaline pH and high available silicate and boron (B) contents, was mixed with phosphor-gypsum (hereafter, gypsum, 50%, wt wt{sup -1}), a by-product from the production of phosphate fertilizer, to improve the fly ash limitation. Field experiments were carried out to evaluate the effect of the mixture on soil properties and rice (Oryza sativa) productivity in silt loam (SiL) and loamy sand (LS) soils to which 0 (FG 0), 20 (FG 20), 40 (FG 40), and 60 (FG 60) Mg ha{sup -1} were added. The mixture increased the amount of available silicate and exchangeable calcium (Ca) contents in the soils and the uptake of silicate by rice plant. The mixture did not result in accumulation of heavy metals in soil and an excessive uptake of heavy metals by the rice grain. The available boron content in soil increased with the mixture application levels up to 1.42 mg kg{sup -1} following the application of 60 Mg ha{sup -1} but did not show toxicity. The mixture increased significantly rice yield and showed the highest yields following the addition of 30-40 Mg ha{sup -1} in two soils. It is concluded that the fly ash and gypsum mixture could be a good source of inorganic soil amendments to restore the soil nutrient balance in rice paddy soil.

  1. Sulfur-mediated palladium catalyst immobilized on a GaAs surface

    SciTech Connect (OSTI)

    Shimoda, M. [Surface Physics and Structure Unit, Surface Physics Group, National Institute for Materials Science, 1-2-1, Sengen, Tsukuba, Ibaraki 305-0047 (Japan); Konishi, T. [Anan National College of Technology, 265 Aoki, Minobayashi-cho, Anan, Tokushima 774-0017 (Japan); Nishiwaki, N. [School of Environmental and Engineering, Kochi University of Technology, Tosayamada, Kami, Kochi 782-8502 (Japan); Yamashita, Y.; Yoshikawa, H. [Synchrotron X-ray Station at SPring-8, National Institute for Materials Science, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148 (Japan)

    2012-06-15

    We present a hard x-ray photoelectron spectroscopy study on the preparation process of palladium catalyst immobilized on an S-terminated GaAs(100) surface. It is revealed that Pd(II) species are reduced on the GaAs surface and yield Pd nanoparticles during the process of Pd immobilization and the subsequent heat treatment. A comparison with the results on GaAs without S-termination suggests that the reduction of Pd is promoted by hydroxy groups during the Pd immobilization and by S during the heat treatment.

  2. Spire Semiconductor formerly Bandwidth Semiconductor LLC | Open...

    Open Energy Info (EERE)

    Zip: 3051 Product: Spire-owned US-based manufacturer of gallium-arsenide (GaAs) cells; offers design and manufacturing capabilities of concentrator cells. References: Spire...

  3. Photovoltaic Single-Crystalline, Thin-Film Cell Basics

    Broader source: Energy.gov [DOE]

    Single-crystalline thin films are made from gallium arsenide (GaAs), a compound semiconductor that is a mixture of gallium and arsenic.

  4. GaAs Blocked-Impurity-Band Detectors for Far-Infrared Astronomy

    SciTech Connect (OSTI)

    Cardozo, Benjamin Lewin

    2004-12-21

    High-purity and doped GaAs films have been grown by Liquid-phase epitaxy (LPE) for development of a blocked impurity band (BIB) detector for far-infrared radiation. The film growth process developed has resulted in the capability to grow GaAs with a net active impurity concentration below 1 x 10{sup 13} cm{sup -3}, ideal for the blocking layer of the BIB detector. The growth of n-type LPE GaAs films with donor concentrations below the metal-insulator transition, as required for the absorbing layer of a BIB detector, has been achieved. The control of the donor concentration, however, was found to be insufficient for detector production. The growth by LPE of a high-purity film onto a commercially grown vapor-phase epitaxial (VPE) n-type GaAs doped absorbing layer resulted in a BIB device that showed a significant reduction in the low-temperature dark current compared to the absorbing layer only. Extended optical response was not detected, most likely due to the high compensation of the commercially grown GaAs absorbing layer, which restricts the depletion width of the device.

  5. MOCVD growth of GaAs solar cells on silicon substrates

    SciTech Connect (OSTI)

    Vernon, S.M.; Haven, V.E.; Geoffroy, L.M.; Sanfacon, M.M.; Mastrovito, A.L. )

    1992-12-01

    This paper reports advances in the development of solar cells made from GaAs-on-Si structures prepared by metalorganic chemical vapor deposition (MOCVD). The use of concentrator cells, operating at [similar to]200 suns, has led to the efficiency achievements of 21.3% (AM1.5D) for a GaAs-on-Si solar cell, and 27.6 (AM1.5D) for a homoepitaxial GaAs cell. The development of epitaxial multilayer dielectric mirrors (Bragg reflectors), as back-surface reflectors in thin-film GaAs cells, on both Si and GaAs substrates, is shown to lead to modest efficiency increases, over that of conventional designs.

  6. Numerical analysis for high-efficiency GaAs solar cells fabricated on Si substrates

    SciTech Connect (OSTI)

    Yamaguchi, M.; Amano, C.; Itoh, Y.

    1989-07-15

    This paper describes some recent developments in GaAs thin-film solar cells fabricated on Si substrates by metalorganic chemical vapor deposition and numerically analyzes them.GaAs solar cells with efficiency of more than 18% are successfully fabricated on Si substrates by reducing the dislocation density. Photovoltaic properties of GaAs/Si cells are analyzed by considering the effect of nonuniform dislocation distribution on recombination properties of GaAs thin films on Si substrates. Numerical analysis shows that the effect of majority-carrier trapping must be considered. High efficiency GaAs solar cells with total-area efficiency of over 20% on Si substrates can be realized if dislocation density can be reduced to less than 5/times/10/sup 5/ cm/sup /minus/2/.

  7. Efficiency considerations for polycrystalline GaAs thin-film solar cells

    SciTech Connect (OSTI)

    Yamaguchi, M.; Itoh, Y.

    1986-07-01

    The effect of grain boundaries upon the efficiency of polycrystalline GaAs thin-film solar cells is analyzed. Solar-cell properties are calculated on a simple model where grain boundaries act as recombination centers to reduce the minority-carrier diffusion length in the solar cell's active layer and increase the space-charge layer recombination current. An effective diffusion length is expressed in terms of grain size, allowing the calculation of short-circuit current density and open-circuit voltage. Excellent agreement is obtained between theory and experiment. The fabrication of thin-film GaAs solar cells with an efficiency greater than 18% appears to be possible if the grain size in the thin-film GaAs layer with thickness of 3 ..mu..m is larger than 1000 ..mu..m.

  8. Double Power Output for GaAs Solar Cells Embedded in Luminescent Waveguides

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    Power Output for GaAs Solar Cells Embedded in Luminescent Waveguides Work w as p erformed a t U niversity o f I llinois X. S heng, L . S hen, T . K im, L . L i, X . W ang, R . D owdy, P . F roeter, K . S higeta, X . L i, R.G. N uzzo, N .C. G iebink, a nd J .A. R ogers, A dv. E nergy M ater., i n p ress ( 2013) GaAs cell transfer printed on a free standing LSC with a diffuse BSR separated by an air gap Scientific Achievement Double power output of bifacial thin-film GaAs microscale solar cells is

  9. High-Efficiency GaAs Thin-Film Solar Cell Reliability | Department of

    Office of Energy Efficiency and Renewable Energy (EERE) Indexed Site

    Energy GaAs Thin-Film Solar Cell Reliability High-Efficiency GaAs Thin-Film Solar Cell Reliability Presented at the PV Module Reliability Workshop, February 26 - 27 2013, Golden, Colorado PDF icon pvmrw13_ps2_alta_li.pdf More Documents & Publications Agenda for the PV Module Reliability Workshop, February 26 - 27 2013, Golden, Colorado Sensitivities of I-V Parameters in C-Si PV Modules of Hygrothermal Stress The Acceleration of Degradation by HAST and Air-HAST in c-Si PV Modules

  10. Electron-limiting defect complex in hyperdoped GaAs: The D D X center

    Office of Scientific and Technical Information (OSTI)

    (Journal Article) | DOE PAGES Electron-limiting defect complex in hyperdoped GaAs: The D D X center « Prev Next » Title: Electron-limiting defect complex in hyperdoped GaAs: The D D X center Authors: Ma, Jie ; Wei, Su-Huai Publication Date: 2013-03-29 OSTI Identifier: 1103991 Type: Publisher's Accepted Manuscript Journal Name: Physical Review B Additional Journal Information: Journal Volume: 87; Journal Issue: 11; Journal ID: ISSN 1098-0121 Publisher: American Physical Society Sponsoring

  11. Analysis of defects in GaAsN grown by chemical beam epitaxy on high index GaAs substrates

    SciTech Connect (OSTI)

    Bouzazi, Boussairi; Kojima, Nobuaki; Ohshita, Yoshio; Yamaguchi, Masafumi

    2013-09-27

    The lattice defects in GaAsN grown by chemical beam epitaxy on GaAs 311B and GaAs 10A toward [110] were characterized and discussed by using deep level transient spectroscopy (DLTS) and on the basis of temperature dependence of the junction capacitances (C{sub J}). In one hand, GaAsN films grown on GaAs 311B and GaAs 10A showed n-type and p-type conductivities, respectively although the similar and simultaneous growth conditions. This result is indeed in contrast to the common known effect of N concentration on the type of conductivity, since the surface 311B showed a significant improvement in the incorporation of N. Furthermore, the temperature dependence of C{sub J} has shown that GaAs 311B limits the formation of N-H defects. In the other hand, the energy states in the forbidden gap of GaAsN were obtained. Six electron traps, E1 to E6, were observed in the DLTS spectrum of GaAsN grown on GaAs 311B, with apparent activation energies of 0.02, 0.14, 0.16, 0.33, 0.48, and 0.74 eV below the bottom edge of the conduction band, respectively. In addition, four hole traps, H1 to H4, were observed in the DLTS spectrum of GaAsN grown on GaAs 10A, with energy depths of 0.13, 0.20, 0.39, and 0.52 eV above the valence band maximum of the alloy, respectively. Hence, the surface morphology of the GaAs substrate was found to play a key factor role in clarifying the electrical properties of GaAsN grown by CBE.

  12. The Morphology and Microstructure of Thin-Film GaAs on Mo Substrates

    SciTech Connect (OSTI)

    Jones, K. M.; Al-Jassim, M. M.; Hasoon, F. S.; Venkatasubramanian, R.

    1999-04-26

    The growth of GaAs thin films on Molybdenum foils was investigated in an attempt to find a low-cost substrate for GaAs. The films were grown by metalorganic chemical vapor deposition (MOCVD). The film thickness was in the 2-4{micro}m range, while the deposition temperature was in the 650-825 C range. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to investigate the film morphology and microstructure, respectively. The film morphology in general, and the grain size in particular, were found to be strongly dependent on the growth temperature. However, the defect structure observed in these films was relatively insensitive to the growth conditions.

  13. Strain-driven growth of GaAs(111) quantum dots with low fine structure splitting

    SciTech Connect (OSTI)

    Yerino, Christopher D.; Jung, Daehwan; Lee, Minjoo Larry; Simmonds, Paul J.; Liang, Baolai; Huffaker, Diana L.; Schneider, Christian; Unsleber, Sebastian; Vo, Minh; Kamp, Martin; Hfling, Sven

    2014-12-22

    Symmetric quantum dots (QDs) on (111)-oriented surfaces are promising candidates for generating polarization-entangled photons due to their low excitonic fine structure splitting (FSS). However, (111) QDs are difficult to grow. The conventional use of compressive strain to drive QD self-assembly fails to form 3D nanostructures on (111) surfaces. Instead, we demonstrate that (111) QDs self-assemble under tensile strain by growing GaAs QDs on an InP(111)A substrate. Tensile GaAs self-assembly produces a low density of QDs with a symmetric triangular morphology. Coherent, tensile QDs are observed without dislocations, and the QDs luminescence at room temperature. Single QD measurements reveal low FSS with a median value of 7.6??eV, due to the high symmetry of the (111) QDs. Tensile self-assembly thus offers a simple route to symmetric (111) QDs for entangled photon emitters.

  14. Growth and properties of crystalline barium oxide on the GaAs(100) substrate

    SciTech Connect (OSTI)

    Yasir, M.; Dahl, J.; Lng, J.; Tuominen, M.; Punkkinen, M. P. J.; Laukkanen, P. Kokko, K.; Kuzmin, M.; Ioffe Physical-Technical Institute, Russian Academy of Sciences, St. Petersburg 194021 ; Korpijrvi, V.-M.; Polojrvi, V.; Guina, M.

    2013-11-04

    Growing a crystalline oxide film on III-V semiconductor renders possible approaches to improve operation of electronics and optoelectronics heterostructures such as oxide/semiconductor junctions for transistors and window layers for solar cells. We demonstrate the growth of crystalline barium oxide (BaO) on GaAs(100) at low temperatures, even down to room temperature. Photoluminescence (PL) measurements reveal that the amount of interface defects is reduced for BaO/GaAs, compared to Al{sub 2}O{sub 3}/GaAs, suggesting that BaO is a useful buffer layer to passivate the surface of the III-V device material. PL and photoemission data show that the produced junction tolerates the post heating around 600?C.

  15. Epitaxial two-dimensional nitrogen atomic sheet in GaAs

    SciTech Connect (OSTI)

    Harada, Yukihiro, E-mail: y.harada@eedept.kobe-u.ac.jp; Yamamoto, Masuki; Baba, Takeshi; Kita, Takashi [Department of Electrical and Electronic Engineering, Graduate School of Engineering, Kobe University, 1-1 Rokkodai, Nada, Kobe 657-8501 (Japan)

    2014-01-27

    We have grown an epitaxial two-dimensional nitrogen (N) atomic sheet in GaAs by using the site-controlled N ?-doping technique. We observed a change of the electronic states in N ?-doped GaAs from the isolated impurity centers to the delocalized impurity band at 1.49?eV with increasing N-doping density. According to the excitation-power- and temperature-dependent photoluminescence (PL) spectra, the emission related to localized levels below the impurity band edge was dominant at low excitation power and temperature, whereas the effects of the localized levels can be neglected by increasing the excitation power and temperature. Furthermore, a clear Landau shift of the PL-peak energy was observed at several Tesla in the Faraday configuration, in contrast to the case in the impurity limit.

  16. Patterned Exfoliation of GaAs Based on Masked Helium Implantation and Subsequent Rapid Thermal Annealing

    SciTech Connect (OSTI)

    Woo, H. J.; Choi, H. W.; Kim, G. D.; Hong, W.; Kim, J. K.

    2009-03-10

    A method of patterning single crystal GaAs based on ion implantation induced selective area exfoliation is suggested. Samples were implanted with 200-500 keV helium ions to a fluence range of 2-4x10{sup 16} He{sup +}/cm{sup 2} at room temperature through masks of Ni mesh (40 {mu}m opening) or stainless steel wire (50 {mu}m in diameter), and subsequent rapid thermal annealing at 350-500{open_square} resulted in expulsion of ion beam exposed material. The influences of ion energy, ion fluence, implantation temperature, subsequent annealing conditions (temperature and ramp rate), and mask pattern and its orientation with GaAs lattice on the patterned exfoliation were examined.

  17. Molecular Beam Epitaxial Growth of GaAs on (631) Oriented Substrates

    SciTech Connect (OSTI)

    Cruz Hernandez, Esteban; Rojas Ramirez, Juan-Salvador; Contreras Hernandez, Rocio; Lopez Lopez, Maximo; Pulzara Mora, Alvaro; Mendez Garcia, Victor H.

    2007-02-09

    In this work, we report the study of the homoepitaxial growth of GaAs on (631) oriented substrates by molecular beam epitaxy (MBE). We observed the spontaneous formation of a high density of large scale features on the surface. The hilly like features are elongated towards the [-5, 9, 3] direction. We show the dependence of these structures with the growth conditions and we present the possibility of to create quantum wires structures on this surface.

  18. Static atomic displacements in a CdTe epitaxial layer on a GaAs substrate

    SciTech Connect (OSTI)

    Horning, R.D.; Staudenmann, J.

    1987-05-25

    A (001)CdTe epitaxial layer on a (001)GaAs substrate was studied by x-ray diffraction between 10 and 360 K. The CdTe growth took place at 380 /sup 0/C in a vertical gas flow metalorganic chemical vapor deposition reactor. Lattice parameters and integrated intensities of both the substrate and the epitaxial layer using the (00l) and (hhh) Bragg reflections reveal three important features. Firstly, the GaAs substrate does not exhibit severe strain after deposition and it is as perfect as a bulk GaAs. Secondly, the CdTe unit cell distorts tetragonally with a/sub perpendicular/>a/sub parallel/ below 300 K. The decay of the (00l) reflection intensities as a function of the temperature yields a Debye temperature of 142 K, the same value as for bulk CdTe. Thirdly, a temperature-dependent isotropic static displacement of the Cd and the Te atoms is introduced to account for the anomalous behavior of the (hhh) intensities.

  19. Final report on LDRD project 105967 : exploring the increase in GaAs photodiode responsivity with increased neutron fluence.

    SciTech Connect (OSTI)

    Blansett, Ethan L.; Geib, Kent Martin; Cich, Michael Joseph; Wrobel, Theodore Frank; Peake, Gregory Merwin; Fleming, Robert M.; Serkland, Darwin Keith; Wrobel, Diana L.

    2008-01-01

    A previous LDRD studying radiation hardened optoelectronic components for space-based applications led to the result that increased neutron irradiation from a fast-burst reactor caused increased responsivity in GaAs photodiodes up to a total fluence of 4.4 x 10{sup 13} neutrons/cm{sup 2} (1 MeV Eq., Si). The silicon photodiodes experienced significant degradation. Scientific literature shows that neutrons can both cause defects as well as potentially remove defects in an annealing-like process in GaAs. Though there has been some modeling that suggests how fabrication and radiation-induced defects can migrate to surfaces and interfaces in GaAs and lead to an ordering effect, it is important to consider how these processes affect the performance of devices, such as the basic GaAs p-i-n photodiode. In this LDRD, we manufactured GaAs photodiodes at the MESA facility, irradiated them with electrons and neutrons at the White Sands Missile Range Linac and Fast Burst Reactor, and performed measurements to show the effect of irradiation on dark current, responsivity and high-speed bandwidth.

  20. High mobility single-crystalline-like GaAs thin films on inexpensive flexible metal substrates by metal-organic chemical vapor deposition

    SciTech Connect (OSTI)

    Dutta, P. Rathi, M.; Gao, Y.; Yao, Y.; Selvamanickam, V.; Zheng, N.; Ahrenkiel, P.; Martinez, J.

    2014-09-01

    We demonstrate heteroepitaxial growth of single-crystalline-like n and p-type doped GaAs thin films on inexpensive, flexible, and light-weight metal foils by metal-organic chemical vapor deposition. Single-crystalline-like Ge thin film on biaxially textured templates made by ion beam assisted deposition on metal foil served as the epitaxy enabling substrate for GaAs growth. The GaAs films exhibited strong (004) preferred orientation, sharp in-plane texture, low grain misorientation, strong photoluminescence, and a defect density of ?10{sup 7?}cm{sup ?2}. Furthermore, the GaAs films exhibited hole and electron mobilities as high as 66 and 300?cm{sup 2}/V-s, respectively. High mobility single-crystalline-like GaAs thin films on inexpensive metal substrates can pave the path for roll-to-roll manufacturing of flexible III-V solar cells for the mainstream photovoltaics market.

  1. Band Structure of Strain-Balanced GaAsBi/GaAsN Super-lattices on GaAs

    SciTech Connect (OSTI)

    Hwang, J.; Phillips, J. D.

    2011-05-31

    GaAs alloys with dilute content of Bi and N provide a large reduction in band-gap energy with increasing alloy composition. GaAsBi/GaAsN heterojunctions have a type-II band alignment, where superlattices based on these materials offer a wide range for designing effective band-gap energy by varying superlattice period and alloy composition. The miniband structure and effective band gap for strain-balanced GaAsBi/GaAsN superlattices with effective lattice match to GaAs are calculated for alloy compositions up to 5% Bi and N using the kp method. The effective band gap for these superlattices is found to vary between 0.89 and 1.32 eV for period thickness ranging from 10 to 100 . The joint density of states and optical absorption of a 40/40 GaAs0.96Bi0.04/GaAs0.98N0.02 superlattice are reported demonstrating a ground-state transition at 1.005 eV and first excited transition at 1.074 eV. The joint density of states is similar in magnitude to GaAs, while the optical absorption is approximately one order of magnitude lower due to the spatially indirect optical transition in the type-II structure. The GaAsBi/GaAsN system may provide a new material system with lattice match to GaAs in a spectral range of high importance for optoelectronic devices including solar cells, photodetectors, and light emitters.

  2. Optical properties of GaAs 2D hexagonal and cubic photonic crystal

    SciTech Connect (OSTI)

    Arab, F. Assali, A.; Grain, R.; Kanouni, F.

    2015-03-30

    In this paper we present our theoretical study of 2D hexagonal and cubic rods GaAs in air, with plan wave expansion (PWE) and finite difference time domain (FDTD) by using BandSOLVE and FullWAVE of Rsoft photonic CAD package. In order to investigate the effect of symmetry and radius, we performed calculations of the band structures for both TM and TE polarization, contour and electromagnetic propagation and transmission spectra. Our calculations show that the hexagonal structure gives a largest band gaps compare to cubic one for a same filling factor.

  3. Comparison of binary collision approximation and molecular dynamics for displacement cascades in GaAs.

    SciTech Connect (OSTI)

    Foiles, Stephen Martin

    2011-10-01

    The predictions of binary collision approximation (BCA) and molecular dynamics (MD) simulations of displacement cascades in GaAs are compared. There are three issues addressed in this work. The first is the optimal choice of the effective displacement threshold to use in the BCA calculations to obtain the best agreement with MD results. Second, the spatial correlations of point defects are compared. This is related to the level of clustering that occurs for different types of radiation. Finally, the size and structure of amorphous zones seen in the MD simulations is summarized. BCA simulations are not able to predict the formation of amorphous material.

  4. Perpendicularly magnetized {tau}-MnAl (001) thin films epitaxied on GaAs

    SciTech Connect (OSTI)

    Nie, S. H.; Zhu, L. J.; Lu, J.; Pan, D.; Wang, H. L.; Yu, X. Z.; Xiao, J. X.; Zhao, J. H.

    2013-04-15

    Perpendicularly magnetized {tau}-MnAl films have been epitaxied on GaAs (001) by molecular-beam epitaxy. Crystalline quality and magnetic properties of the samples were strongly dependent on growth temperature. The highest coercivity of 10.7 kOe, saturation magnetization of 361.4 emu/cm{sup 3}, perpendicular magnetic anisotropy constant of 13.65 Merg/cm{sup 3}, and magnetic energy product of 4.44 MGOe were achieved. These tunable magnetic properties make MnAl films valuable as excellent and cost-effective alternative for not only high density perpendicular magnetic recording storage and spintronics devices but also permanent magnets.

  5. Magnetism and transport properties of epitaxial Fe-Ga thin films on GaAs(001)

    SciTech Connect (OSTI)

    Duong Anh Tuan; Shin, Yooleemi; Cho, Sunglae; Dang Duc Dung; Vo Thanh Son

    2012-04-01

    Epitaxial Fe-Ga thin films in disordered bcc {alpha}-Fe crystal structure (A2) have been grown on GaAs(001) by molecular beam epitaxy. The saturated magnetization (M{sub S}) decreased from 1371 to 1105 kA/m with increasing Ga concentration from 10.5 to 24.3 % at room temperature. The lattice parameter increased with the increase in Ga content because of the larger atomic radius of Ga atom than that of Fe. The increase in carrier density with Ga content caused in lower resistivity.

  6. Origins of ion irradiation-induced Ga nanoparticle motion on GaAs surfaces

    SciTech Connect (OSTI)

    Kang, M.; Wu, J. H.; Chen, H. Y.; Thornton, K.; Goldman, R. S. [Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109-2136 (United States)] [Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109-2136 (United States); Sofferman, D. L. [Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109-2136 (United States) [Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109-2136 (United States); Department of Physics, Adelphi University, Garden City, New York 11530-0701 (United States); Beskin, I. [Department of Physics, University of Michigan, Ann Arbor, Michigan 48109-1040 (United States)] [Department of Physics, University of Michigan, Ann Arbor, Michigan 48109-1040 (United States)

    2013-08-12

    We have examined the origins of ion irradiation-induced nanoparticle (NP) motion. Focused-ion-beam irradiation of GaAs surfaces induces random walks of Ga NPs, which are biased in the direction opposite to that of ion beam scanning. Although the instantaneous NP velocities are constant, the NP drift velocities are dependent on the off-normal irradiation angle, likely due to a difference in surface non-stoichiometry induced by the irradiation angle dependence of the sputtering yield. It is hypothesized that the random walks are initiated by ion irradiation-induced thermal fluctuations, with biasing driven by anisotropic mass transport.

  7. Rigid-body translation and bonding across l brace 110 r brace antiphase boundaries in GaAs

    SciTech Connect (OSTI)

    Rasmussen, D.R.; McKernan, S.; Carter, C.B. )

    1991-05-20

    A transmission-electron-microscope strong-beam technique is used to investigate the rigid-body translation across {l brace}110{r brace} antiphase boundaries in GaAs. The results show a translation in the {l angle}001{r angle} direction parallel to the plane of the boundary. The magnitude of the translation is determined, and the antisite bond lengths are discussed in terms of the tetrahedral radii of Ga and As. Given this knowledge of the rigid-body translation, the absolute polarity of a GaAs grain can be determined immediately from a bright-field image of the {l brace}110{r brace} antiphase boundary.

  8. GaAs buffer layer technique for vertical nanowire growth on Si substrate

    SciTech Connect (OSTI)

    Xu, Xiaoqing Parizi, Kokab B.; Huo, Yijie; Kang, Yangsen; Philip Wong, H.-S.; Li, Yang

    2014-02-24

    Gold catalyzed vapor-liquid-solid method is widely applied to IIIV nanowire (NW) growth on Si substrate. However, the easy oxidation of Si, possible Si contamination in the NWs, high defect density in the NWs, and high sensitivity of the NW morphology to growth conditions largely limit its controllability. In this work, we developed a buffer layer technique by introducing a GaAs thin film with predefined polarity as a template. It is found that samples grown on these buffer layers all have high vertical NW yields in general, due to the single-orientation of the buffer layers. Low temperature buffer with smoother surface leads to highest yield of vertical NWs, while high temperature (HT) buffer with better crystallinity results in perfect NW quality. The defect-free property we observed here is very promising for optoelectronic device applications based on GaAs NW. Moreover, the buffer layers can eliminate Si contamination by preventing Si-Au alloy formation and by increasing the thickness of the Si diffusion barrier, thus providing more flexibility to vertical NW growth. The buffer layer technique we demonstrated here could be easily extended to other III-V on Si system for electronic and photonic applications.

  9. Doped Contacts for High-Longevity Optically Activated, High Gain GaAs Photoconductive Semiconductor Switches

    SciTech Connect (OSTI)

    MAR,ALAN; LOUBRIEL,GUILLERMO M.; ZUTAVERN,FRED J.; O'MALLEY,MARTIN W.; HELGESON,WESLEY D.; BROWN,DARWIN JAMES; HJALMARSON,HAROLD P.; BACA,ALBERT G.; THORNTON,R.L.; DONALDSON,R.D.

    1999-12-17

    The longevity of high gain GaAs photoconductive semiconductor switches (PCSS) has been extended to over 100 million pulses. This was achieved by improving the ohmic contacts through the incorporation of a doped layer that is very effective in the suppression of filament formation, alleviating current crowding. Damage-free operation is now possible with virtually infinite expected lifetime at much higher current levels than before. The inherent damage-free current capacity of the bulk GaAs itself depends on the thickness of the doped layers and is at least 100A for a dopant diffusion depth of 4pm. The contact metal has a different damage mechanism and the threshold for damage ({approx}40A) is not further improved beyond a dopant diffusion depth of about 2{micro}m. In a diffusion-doped contact switch, the switching performance is not degraded when contact metal erosion occurs, unlike a switch with conventional contacts. This paper will compare thermal diffusion and epitaxial growth as approaches to doping the contacts. These techniques will be contrasted in terms of the fabrication issues and device characteristics.

  10. Growing antiphase-domain-free GaAs thin films out of highly ordered planar nanowire arrays on exact (001) silicon

    SciTech Connect (OSTI)

    Li, Qiang; Ng, Kar Wei; Lau, Kei May

    2015-02-16

    We report the use of highly ordered, dense, and regular arrays of in-plane GaAs nanowires as building blocks to produce antiphase-domain-free GaAs thin films on exact (001) silicon. High quality GaAs nanowires were grown on V-grooved Si (001) substrates using the selective aspect ratio trapping concept. The 4.1% lattice mismatch has been accommodated by the initial GaAs, a few nanometer-thick with high density stacking faults. The bulk of the GaAs wires exhibited smooth facets and a low defect density. An unusual defect trapping mechanism by a tiara-like structure formed by Si undercuts was discovered. As a result, we were able to grow large-area antiphase-domain-free GaAs thin films out of the nanowires without using SiO{sub 2} sidewalls for defect termination. Analysis from XRD ?-rocking curves yielded full-width-at-half-maximum values of 238 and 154?arc sec from 900 to 2000?nm GaAs thin films, respectively, indicating high crystalline quality. The growth scheme in this work offers a promising path towards integrated III-V electronic, photonic, or photovoltaic devices on large scale silicon platform.

  11. PROJECT PROFILE: 2D Materials for Low Cost Epitaxial Growth of Single Sun

    Office of Energy Efficiency and Renewable Energy (EERE) Indexed Site

    Gallium Arsenide (GaAs) Photovoltaics | Department of Energy 2D Materials for Low Cost Epitaxial Growth of Single Sun Gallium Arsenide (GaAs) Photovoltaics PROJECT PROFILE: 2D Materials for Low Cost Epitaxial Growth of Single Sun Gallium Arsenide (GaAs) Photovoltaics Funding Opportunity: SuNLaMP SunShot Subprogram: Photovoltaics Location: National Renewable Energy Laboratory, Golden, CO SunShot Award Amount: $125,000 Low-cost III-V cells will result in a breakthrough in photovoltaic (PV)

  12. Efficiency calculations of thin-film GaAs solar cells on Si substrates

    SciTech Connect (OSTI)

    Yamaguchi, M.; Amano, C.

    1985-11-01

    Dislocation effect upon the efficiency of single-crystal thin-film AlGaAs-GaAs heteroface solar cells on Si substrates is analyzed. Solar-cell properties are calculated based on a simple model; in the model, dislocations act as recombination centers to reduce the minority-carrier diffusion length in each layer and increase the space-charge layer recombination current. Numerical analysis is also carried out to optimize thin-film AlGaAs-GaAs heteroface solar-cell structures. The fabrication of thin-film AlGaAs-GaAs heteroface solar cells with a practical efficiency larger than 18% on Si substrates appears possible if the dislocation density in the thin-film GaAs layer is less than 10/sup 6/ cm/sup -2/.

  13. Thin film GaAs solar cells on glass substrates by epitaxial liftoff

    SciTech Connect (OSTI)

    Lee, X.Y.; Goertemiller, M.; Boroditsky, M.; Ragan, R.; Yablonovitch, E.

    1997-02-01

    In this work, we describe the fabrication and operating characteristics of GaAs/AlGaAs thin film solar cells processed by the epitaxial liftoff (ELO) technique. This technique allows the transfer of these cells onto glass substrates. The performance of the lifted-off solar cell is demonstrated by means of electrical measurements under both dark and illuminated conditions. We have also optimized the light trapping conditions in this direct-gap material. The results show that good solar absorption is possible in active layers as thin as 0.32 {mu}m. In such a thin solar cell, the open circuit voltage would be enhanced. We believe that the combination of an epitaxial liftoff thin GaAs film, and nano-texturing can lead to record breaking performance. {copyright} {ital 1997 American Institute of Physics.}

  14. GaAs micro-pyramids serving as optical micro-cavities

    SciTech Connect (OSTI)

    Karl, M.; Beck, T.; Li, S.; Hu, D. Z.; Schaadt, D. M.; Kalt, H.; Hetterich, M.

    2010-01-04

    An efficient light-matter coupling requires high-quality (Q) micro-cavities with small mode volume. We suggest GaAs micro-pyramids placed on top of AlAs/GaAs distributed Bragg reflectors to be promising candidates. The pyramids were fabricated by molecular-beam epitaxy, electron-beam lithography and a subsequent wet-chemical etching process using a sacrificial AlAs layer. Measured Q-factors of optical modes in single pyramids reach values up to 650. A finite-difference time-domain simulation assuming a simplified cone-shaped geometry suggests possible Q-factors up to 3600. To enhance the light confinement in the micro-pyramids we intend to overgrow the pyramidal facets with a Bragg mirror--results of preliminary tests are given.

  15. Evolution of superclusters and delocalized states in GaAs1–xNx

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Fluegel, B.; Alberi, K.; Beaton, D. A.; Crooker, S. A.; Ptak, A. J.; Mascarenhas, A.

    2012-11-21

    The evolution of individual nitrogen cluster bound states into an extended state infinite supercluster in dilute GaAs1–xNx was probed through temperature and intensity-dependent, time-resolved and magnetophotoluminescence (PL) measurements. Samples with compositions less than 0.23% N exhibit PL behavior that is consistent with emission from the extended states of the conduction band. Near a composition of 0.23% N, a discontinuity develops between the extended state PL peak energy and the photoluminescence excitation absorption edge. The existence of dual localized/delocalized state behavior near this composition signals the formation of an N supercluster just below the conduction band edge. The infinite supercluster ismore » fully developed by 0.32% N.« less

  16. Fano Resonance in GaAs 2D Photonic Crystal Nanocavities

    SciTech Connect (OSTI)

    Valentim, P. T.; Guimaraes, P.S. S.; Luxmoore, I. J.; Szymanski, D.; Whittaker, D. M.; Fox, A. M.; Skolnick, M. S.; Vasco, J. P.; Vinck-Posada, H.

    2011-12-23

    We report the results of polarization resolved reflectivity experiments in GaAs air-bridge photonic crystals with L3 cavities. We show that the fundamental L3 cavity mode changes, in a controlled way, from a Lorentzian symmetrical lineshape to an asymmetrical form when the linear polarization of the incident light is rotated in the plane of the crystal. The different lineshapes are well fitted by the Fano asymmetric equation, implying that a Fano resonance is present in the reflectivity. We use the scattering matrix method to model the Fano interference between a localized discrete state (the cavity fundamental mode) and a background of continuum states (the light reflected from the crystal slab in the vicinity of the cavity) with very good agreement with the experimental data.

  17. Large area, low capacitance, GaAs nanowire photodetector with a transparent Schottky collecting junction

    SciTech Connect (OSTI)

    Seyedi, M. A. Yao, M.; O'Brien, J.; Dapkus, P. D.; Wang, S. Y.; Nanostructured Energy Conversion Technology and Research , Advanced Studies Laboratories, University of California, Santa Cruz, California 95064, USA and NASA Ames Research Center, Moffett Field, California 94035

    2013-12-16

    We present experimental results on a GaAs/Indium-Tin-Oxide Schottky-like heterojunction photodetector based on a nanowire device geometry. By distributing the active detecting area over an array of nanowires, it is possible to achieve large area detection with low capacitance. Devices with bare GaAs and passivated AlGaAs/GaAs nanowires are fabricated to compare the responsivity with and without surface passivation. We are able to achieve responsivity of >0.5A/W and Signal-Noise-Ratio in excess of 7?dB for 2?V applied reverse bias with passivated nanowire devices. Capacitance-voltage measurement yields <5?nF/cm{sup 2}, which shows a strong possibility for high-speed applications with a broad area device.

  18. Epitaxial lift-off of quantum dot enhanced GaAs single junction solar cells

    SciTech Connect (OSTI)

    Bennett, Mitchell F.; Bittner, Zachary S.; Forbes, David V.; Hubbard, Seth M.; Rao Tatavarti, Sudersena; Wibowo, Andree; Pan, Noren; Chern, Kevin; Phillip Ahrenkiel, S.

    2013-11-18

    InAs/GaAs strain-balanced quantum dot (QD) n-i-p solar cells were fabricated by epitaxial lift-off (ELO), creating thin and flexible devices that exhibit an enhanced sub-GaAs bandgap current collection extending into the near infrared. Materials and optical analysis indicates that QD quality after ELO processing is preserved, which is supported by transmission electron microscopy images of the QD superlattice post-ELO. Spectral responsivity measurements depict a broadband resonant cavity enhancement past the GaAs bandedge, which is due to the thinning of the device. Integrated external quantum efficiency shows a QD contribution to the short circuit current density of 0.23?mA/cm{sup 2}.

  19. Suitability of epitaxial GaAs for x-ray imaging

    SciTech Connect (OSTI)

    Sun, G.C.; Talbi, N.; Verdeil, C.; Bourgoin, J.C.

    2004-09-20

    Because the rate of indirect photon-electron conversion for scintillator materials coupled with arrays of photodiodes is at least 25 times smaller than the rate of direct conversion, we examine the conditions to be fulfilled by semiconductors undergoing such direct conversion to be applied to x-ray imaging. Bulk grown materials are not well suited to this application, because large defect concentrations give rise to strongly nonuniform electronic properties. We argue that only epitaxial layers are suitable for use as imaging devices and we illustrate our argument using the case of thick epitaxial GaAs layers. Detectors made with such layers exhibit a good energy resolution, a charge collection efficiency which approaches 1, linearity over more than three orders of amplitude, no afterglow (a response time shorter than 20 {mu}s), and no charge-induced polarization effects.

  20. Simulation of quantum dots size and spacing effect for intermediate band solar cell application based on InAs quantum dots arrangement in GaAs

    SciTech Connect (OSTI)

    Hendra, P. I. B. Rahayu, F. Darma, Y.

    2014-03-24

    Intermediate band solar cell (IBSC) has become a promising technology in increasing solar cell efficiency. In this work we compare absorption coefficient profile between InAs quantum dots with GaAs bulk. We calculate the efficiency of GaAs bulk and GaAs doped with 2, 5, and 10 nm InAs quantum dot. Effective distances in quantum dot arrangement based on electron tunneling consideration were also calculated. We presented a simple calculation method with low computing power demand. Results showed that arrangement of quantum dot InAs in GaAs can increase solar cell efficiency from 23.9 % initially up to 60.4%. The effective distance between two quantum dots was found 2 nm in order to give adequate distance to prevent electron tunneling and wave functions overlap.

  1. Energy distribution of nonequilibrium electrons and optical phonons in GaAs under band-to-band pumping by intense short pulses of light

    SciTech Connect (OSTI)

    Altybaev, G. S.; Kumekov, S. E. Mahmudov, A. A.

    2009-03-15

    Deviation from the Fermi distribution of nonequilibrium electrons and distribution of 'hot' optical phonons in GaAs under band-to-band pumping by picosecond pulses of light are calculated.

  2. Doping and electronic properties of GaAs grown by close-spaced vapor transport from powder sources for scalable III–V photovoltaics

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Ritenour, Andrew J.; Boucher, Jason W.; DeLancey, Robert; Greenaway, Ann L.; Aloni, Shaul; Boettcher, Shannon W.

    2014-09-01

    We report the use of a simple close-spaced vapor transport technique for the growth of high-quality epitaxial GaAs films using potentially inexpensive GaAs powders as precursors. The free carrier type and density (1016 to 1019 cm–3) of the films were adjusted by addition of Te or Zn powder to the GaAs source powder. We show using photoelectrochemical and electron beam-induced current analyses that the minority carrier diffusion lengths of the n- and p-GaAs films reached ~3 μm and ~8 μm, respectively. Hall mobilities approach those achieved for GaAs grown by metal–organic chemical vapor deposition, 1000–4200 cm2 V–1 s–1 for n-GaAsmore » and 50–240 cm V–1 s–1 for p-GaAs depending on doping level. We conclude that the electronic quality of GaAs grown by close-spaced vapor transport is similar to that of GaAs made using conventional techniques and is thus sufficient for high-performance photovoltaic applications.« less

  3. Doping and electronic properties of GaAs grown by close-spaced vapor transport from powder sources for scalable IIIV photovoltaics

    SciTech Connect (OSTI)

    Ritenour, Andrew J.; Boucher, Jason W.; DeLancey, Robert; Greenaway, Ann L.; Aloni, Shaul; Boettcher, Shannon W.

    2014-09-01

    We report the use of a simple close-spaced vapor transport technique for the growth of high-quality epitaxial GaAs films using potentially inexpensive GaAs powders as precursors. The free carrier type and density (1016 to 1019 cm3) of the films were adjusted by addition of Te or Zn powder to the GaAs source powder. We show using photoelectrochemical and electron beam-induced current analyses that the minority carrier diffusion lengths of the n- and p-GaAs films reached ~3 ?m and ~8 ?m, respectively. Hall mobilities approach those achieved for GaAs grown by metalorganic chemical vapor deposition, 10004200 cm2 V1 s1 for n-GaAs and 50240 cm V1 s1 for p-GaAs depending on doping level. We conclude that the electronic quality of GaAs grown by close-spaced vapor transport is similar to that of GaAs made using conventional techniques and is thus sufficient for high-performance photovoltaic applications.

  4. Deep level defects in n-type GaAsBi and GaAs grown at low temperatures

    SciTech Connect (OSTI)

    Mooney, P. M.; Watkins, K. P.; Jiang, Zenan; Basile, A. F.; Lewis, R. B.; Bahrami-Yekta, V.; Masnadi-Shirazi, M.; Beaton, D. A.; Tiedje, T.

    2013-04-07

    Deep level defects in n-type GaAs{sub 1-x}Bi{sub x} having 0 < x < 0.012 and GaAs grown by molecular beam epitaxy (MBE) at substrate temperatures between 300 and 400 Degree-Sign C have been investigated by Deep Level Capacitance Spectroscopy. Incorporating Bi suppresses the formation of an electron trap with activation energy 0.40 eV, thus reducing the total trap concentration in dilute GaAsBi layers by more than a factor of 20 compared to GaAs grown under the same conditions. We find that the dominant traps in dilute GaAsBi layers are defect complexes involving As{sub Ga}, as expected for MBE growth at these temperatures.

  5. Highly uniform, multi-stacked InGaAs/GaAs quantum dots embedded in a GaAs nanowire

    SciTech Connect (OSTI)

    Tatebayashi, J. Ota, Y.; Ishida, S.; Nishioka, M.; Iwamoto, S.; Arakawa, Y.

    2014-09-08

    We demonstrate a highly uniform, dense stack of In{sub 0.22}Ga{sub 0.78}As/GaAs quantum dot (QD) structures in a single GaAs nanowire (NW). The size (and hence emission energy) of individual QD is tuned by careful control of the growth conditions based on a diffusion model of morphological evolution of NWs and optical characterization. By carefully tailoring the emission energies of individual QD, dot-to-dot inhomogeneous broadening of QD stacks in a single NW can be as narrow as 9.3?meV. This method provides huge advantages over traditional QD stack using a strain-induced Stranski-Krastanow growth scheme. We show that it is possible to fabricate up to 200 uniform QDs in single GaAs NWs using this growth technique without degradation of the photoluminescence intensity.

  6. Proposed measurement of spin currents in a GaAs crystal using the electro-optical Pockels effect

    SciTech Connect (OSTI)

    Zhang, Xingchu; Zheng, Yongjun; She, Weilong

    2014-07-14

    A new method for measuring spin currents is proposed, based on the linear electro-optic (Pockels) effect caused by the additional second-order nonlinear electric susceptibility (electro-optic tensor) generated by the spin currents. The non-zero elements of electro-optic tensor induced by spin currents in GaAs crystal are calculated, and the wave coupling theory of linear electro-optic effect is used to analyze the polarization change of a probe beam. The numerical results show that, for a linearly polarized probe beam with a frequency close to the band gap of GaAs crystal, its polarization rotation can be as large as 14 μrad under an applied electric field of about 350 V/mm. This effect should offer an alternative detection method for spintronics.

  7. Atomic-scale observation of parallel development of super elasticity and reversible plasticity in GaAs nanowires

    SciTech Connect (OSTI)

    Bao, Peite; Du, Sichao; Zheng, Rongkun; Wang, Yanbo; Liao, Xiaozhou; Cui, Xiangyuan; Yen, Hung-Wei; Kong Yeoh, Wai; Ringer, Simon P.; Gao, Qiang; Hoe Tan, H.; Jagadish, Chennupati; Liu, Hongwei; Zou, Jin

    2014-01-13

    We report the atomic-scale observation of parallel development of super elasticity and reversible dislocation-based plasticity from an early stage of bending deformation until fracture in GaAs nanowires. While this phenomenon is in sharp contrast to the textbook knowledge, it is expected to occur widely in nanostructures. This work indicates that the super recoverable deformation in nanomaterials is not simple elastic or reversible plastic deformation in nature, but the coupling of both.

  8. The influence of electron irradiation on electron holography of focused ion beam milled GaAs p-n junctions

    SciTech Connect (OSTI)

    Cooper, David; Twitchett-Harrison, Alison C.; Midgley, Paul A.; Dunin-Borkowski, Rafal E.

    2007-05-01

    Electron beam irradiation is shown to significantly influence phase images recorded from focused ion beam milled GaAs p-n junction specimens examined using off-axis electron holography in the transmission electron microscope. Our results show that the use of improved electrical connections to the specimen overcomes this problem, and may allow the correct built in potential across the junction to be recovered.

  9. Quantum efficiency temporal response and lifetime of a GaAs cathode in SRF electron gun

    SciTech Connect (OSTI)

    Wang, E.; Ben-Zvi, I.; Kewisch, J.; Burrill, A.; Rao, T.; Wu, Q.; Holmes, D.

    2010-05-23

    RF electron guns with a strained super lattice GaAs cathode can generate polarized electron beam of higher brightness and lower emittance than do DC guns, due to their higher field gradient at the cathode's surface. In a normal conducting RF gun, the extremely high vaccum required by these cathodes can not be met. We report on an experiment with a superconducting SRF gun, which can maintain a vacuum of nearly 10-12 torr because of cryo-pumping at the temperature of 4.2K. With conventional activation, we obtained a QE of 3% at 532 nm, with lifetime of nearly 3 days in the preparation chamber. We plan to use this cathode in a 1.3 GHz 1/2 cell SRF gun to study its performance. In addition, we studied the multipacting at the location of cathode. A new model based on the Forkker-Planck equation which can estimate the bunch length of the electron beam is discussed in this paper. Future particle accelerators such as eRHIC and ILC require high brightness, high current polarized electrons Recently, using a superlattice crystal, the maximum polarization of 95% was reached. Activation with Cs,O lowers the electron affinity and makes it energetically possible for all the electrons excited in to the conduction band and reach the surface to escape into the vacuum. Presently the polarized electron sources are based on DC gun, such as that at the CEBAF at Jlab. In these devices, the life time of the cathode is extended due to the reduced back bombardment in their UHV conditions. However, the low accelerating gradient of the DC guns lead to poor longitudinal emittance. The higher accelerating gradient of the RF gun generates low emittance beams. Superconducting RF guns combine the excellent vacuum conditions of the DC guns with the higher accelerating gradients of the RF guns and provide potentially a long lived cathode with very low transverse and longitudinal emittance. In our work at BNL, we successfully activated the GaAs. The quantum efficient is 3% at 532 nm and is expected to improve further. In addition, we studied the multipacting at the location of cathode. A new model based on the Forkker-Planck equation which can estimate the bunch length of the electron beam is discussed in this paper.

  10. Characterization of the CEBAF 100 kV DC GaAs Photoelectron Gun Vacuum System

    SciTech Connect (OSTI)

    M.L. Stutzman; P. Adderley; J. Brittian; J. Clark; J. Grames; J. Hansknecht; G.R. Myneni; M. Poelker

    2007-05-01

    A vacuum system with pressure in the low ultra-high vacuum (UHV) range is essential for long photocathode lifetimes in DC high voltage GaAs photoguns. A discrepancy between predicted and measured base pressure in the CEBAF photoguns motivated this study of outgassing rates of three 304 stainless steel chambers with different pretreatments and pump speed measurements of non-evaporable getter (NEG) pumps. Outgassing rates were measured using two independent techniques. Lower outgassing rates were achieved by electropolishing and vacuum firing the chamber. The second part of the paper describes NEG pump speed measurements as a function of pressure through the lower part of the UHV range. Measured NEG pump speed is high at pressures above 510^?11 Torr, but may decrease at lower pressures depending on the interpretation of the data. The final section investigates the pump speed of a locally produced NEG coating applied to the vacuum chamber walls. These studies represent the first detailed vacuum measurements of CEBAF photogun vacuum chambers.

  11. Local Structures and Interface Morphology of InGaAsN Thin Films Grown on GaAs

    SciTech Connect (OSTI)

    Allerman, A.A.; Chen, J.G.; Geisz, J.F.; Huang, S.; Hulbert, S.L.; Jones, E.D.; Kao, Y.H.; Kurtz, S.; Kurtz, S.R.; Olson, J.M.; Soo, Y.L.

    1999-02-23

    The compound semiconductor system InGaAsN exhibits many intriguing properties which are particularly useful for the development of innovative high efficiency thin film solar cells and long wavelength lasers. The bandgap in these semiconductors can be varied by controlling the content of N and In and the thin films can yet be lattice-matched to GaAs. In the present work, x-ray absorption fine structure (XAFS) and grazing incidence x-ray scattering (GIXS) techniques have been employed to probe the local environment surrounding both N and In atoms as well as the interface morphology of InGaAsN thin films epitaxially grown on GaAs. The soft x-ray XAFS results around nitrogen K-edge reveal that N is in the sp{sup 3} hybridized bonding configuration in InGaAsN and GaAsN, suggesting that N impurities most likely substitute for As sites in these two compounds. The results of In K-edge XAFS suggest a possible trend of a slightly larger coordination number of As nearest neighbors around In atoms in InGaAsN samples with a narrower bandgap whereas the In-As interatomic distance remains practically the same as in InAs within the experimental uncertainties. These results combined suggest that N-substitution of the As sites plays an important role of bandgap-narrowing while in the meantime counteracting the compressive strain caused by In-doping. Grazing incidence x-ray scattering (GIXS) experiments verify that InGaAsN thin films can indeed form very smooth interfaces with GaAs yielding an average interfacial roughness of 5-20{angstrom}.

  12. Multi-junction, monolithic solar cell using low-band-gap materials lattice matched to GaAs or Ge

    DOE Patents [OSTI]

    Olson, Jerry M. (Lakewood, CO); Kurtz, Sarah R. (Golden, CO); Friedman, Daniel J. (Lakewood, CO)

    2001-01-01

    A multi-junction, monolithic, photovoltaic solar cell device is provided for converting solar radiation to photocurrent and photovoltage with improved efficiency. The solar cell device comprises a plurality of semiconductor cells, i.e., active p/n junctions, connected in tandem and deposited on a substrate fabricated from GaAs or Ge. To increase efficiency, each semiconductor cell is fabricated from a crystalline material with a lattice constant substantially equivalent to the lattice constant of the substrate material. Additionally, the semiconductor cells are selected with appropriate band gaps to efficiently create photovoltage from a larger portion of the solar spectrum. In this regard, one semiconductor cell in each embodiment of the solar cell device has a band gap between that of Ge and GaAs. To achieve desired band gaps and lattice constants, the semiconductor cells may be fabricated from a number of materials including Ge, GaInP, GaAs, GaInAsP, GaInAsN, GaAsGe, BGaInAs, (GaAs)Ge, CuInSSe, CuAsSSe, and GaInAsNP. To further increase efficiency, the thickness of each semiconductor cell is controlled to match the photocurrent generated in each cell. To facilitate photocurrent flow, a plurality of tunnel junctions of low-resistivity material are included between each adjacent semiconductor cell. The conductivity or direction of photocurrent in the solar cell device may be selected by controlling the specific p-type or n-type characteristics for each active junction.

  13. Highly polarized emission in spin resolved photoelectron spectroscopy of alpha-Fe(001)/GaAs(001)

    SciTech Connect (OSTI)

    Tobin, James; Yu, Sung Woo; Morton, Simon; Waddill, George; Thompson, Jamie; Neal, James; Spangenberg, Matthais; Shen, T.H.

    2009-05-19

    Highly spin-polarized sources of electrons, Integrated into device design, remain of great interest to the spintronic and magneto-electronic device community Here, the growth of Fe upon GaAs(001) has been studied with photoelectron spectroscopy (PES), including Spin Resolved PES. Despite evidence of atomic level disorder such as intermixing, an over-layer with the spectroscopic signature of alpha-Fe(001), with a bcc real space ordering, Is obtained The results will be discussed in light of the possibility of using such films as a spin-polarized source in device applications.

  14. Effect of Bi isovalent dopants on the formation of homogeneous coherently strained InAs quantum dots in GaAs matrices

    SciTech Connect (OSTI)

    Peleshchak, R. M.; Guba, S. K.; Kuzyk, O. V.; Kurilo, I. V.; Dankiv, O. O.

    2013-03-15

    The distribution of hydrostatic strains in Bi{sup 3+}-doped InAs quantum dots embedded in a GaAs matrix are calculated in the context of the deformation-potential model. The dependences of strains in the material of spherical InAs quantum dots with substitutional (Bi {yields} As) and interstitial (Bi) impurities on the quantum-dot size are derived. The qualitative correlation of the model with the experiment is discussed. The data on the effect of doping on the morphology of self-assembled InAs:Bi quantum dots in a GaAs matrix are obtained.

  15. National Gypsum | Open Energy Information

    Open Energy Info (EERE)

    About Partnership with NREL Partnership with NREL Yes Partnership Type Test & Evaluation Partner Partnering Center within NREL Electricity Resources & Building Systems...

  16. Outdoor Testing of GaInP2/GaAs Tandem Cells with Top Cell Thickness Varied

    SciTech Connect (OSTI)

    McMahon, W. E.; Emergy, K. E.; Friedman, D. J.; Ottoson, L.; Young, M. S.; Ward, J. S.; Kramer, C. M.; Duda, A.; Kurtz, S.

    2005-08-01

    In this study, we measure the performance of GaInP2/GaAs tandem cells under direct beam sunlight outdoors in order to quantify their sensitivity to both spectral variation and GaInP2 top-cell thickness. A set of cells with five different top-cell thicknesses was mounted on a two-axis tracker with the incident sunlight collimated to exclude all except the direct beam. Current-voltage (I-V) curves were taken throughout the course of several days, along with measurements of the direct solar spectrum. Our two major conclusions are: (1) GaInP2/GaAs tandem cells designed for either the ASTM G-173 direct (G-173D) spectrum or the "air mass 1.5 global" (AM1.5G) spectrum perform the best, and (2) cells can be characterized indoors and modeled using outdoor spectra with the same result. These results are equally valid for GaInP2/GaAs/Ge triple-junction cells.

  17. Interface composition between Fe{sub 3}O{sub 4} nanoparticles and GaAs for spintronic applications

    SciTech Connect (OSTI)

    Hihath, Sahar; Kiehl, Richard A.; Benthem, Klaus van

    2014-08-28

    Recent interest in spintronic applications has necessitated the study of magnetic materials in contact with semiconductor substrates; importantly, the structure and composition of these interfaces can influence both device functionality and the magnetic properties. Nanoscale ferromagnet/semiconductor structures are of particular interest. In this study, the interface structure between a monolayer of ferromagnetic magnetite (Fe{sub 3}O{sub 4}) nanoparticles and a GaAs substrate was studied using cross-sectional transmission electron microscopy techniques. It was found that a continuous amorphous oxide interface layer separates the nanoparticles from the GaAs substrate, and that iron diffused into the interface layer forming a compositional gradient. Electron energy-loss near-edge fine structures of the O K absorption edge revealed that the amorphous oxide is composed of γ-Fe{sub 2}O{sub 3} directly underneath the Fe{sub 3}O{sub 4} nanoparticles, followed by a solid solution of Ga{sub 2}O{sub 3} and FeO and mostly Ga{sub 2}O{sub 3} when approaching the buckled oxide/substrate interface. Real-space density functional theory calculations of the dynamical form factor confirmed the experimental observations. The implication of the findings on the optimization of these structures for spin injection is discussed.

  18. First-principles studies on molecular beam epitaxy growth of GaAs1-xBix

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Luo, Guangfu; Yang, Shujiang; Li, Jincheng; Arjmand, Mehrdad; Szlufarska, Izabela; Brown, April S.; Kuech, Thomas F.; Morgan, Dane

    2015-07-14

    We investigate the molecular beam epitaxy (MBE) growth of GaAs1-xBix film using density functional theory with spin-orbit coupling to understand the growth of this film, especially the mechanisms of Bi incorporation. We study the stable adsorption structures and kinetics of the incident molecules (As? molecule, Ga atom, Bi atom, and Bi? molecule) on the (2 x 1)-Gasub||Bi surface and a proposed q(1 x 1)-Gasub||AsAs surface has a quasi-(1 x 1) As layer above the Ga-terminated GaAs substrate and a randomly oriented As dimer layer on top. We obtain the desorption and diffusion barriers of the adsorbed molecules and also themorereaction barriers of three key processes related to Bi evolution, namely, Bi incorporation, As/Bi exchange, and Bi clustering. The results help explain the experimentally observed dependence of Bi incorporation on the As/Ga ratio and growth temperature. Furthermore, we find that As? exchange with Bi of the (2 x 1)-Gasub||Bi surface is a key step controlling the kinetics of the Bi incorporation. Finally, we explore two possible methods to enhance the Bi incorporation, namely, replacing the MBE growth mode from codeposition of all fluxes with a sequential deposition of fluxes and applying asymmetric in-plane strain to the substrate.less

  19. Towards low-cost high-efficiency GaAs photovoltaics and photoelectrodes grown via vapor transport from a solid source

    SciTech Connect (OSTI)

    Boucher, Jason; Ritenour, Andrew; Boettcher, Shannon W.

    2013-04-29

    Towards low-cost high-efficiency GaAs photovoltaics and photoelectrodes grown via vapor transport from a solid source GaAs is an attractive material for thin-film photovoltaic applications, but is not widely used for terrestrial power generation due to the high cost of metal-organic chemical vapor deposition (MOCVD) techniques typically used for growth. Close space vapor transport is an alternative that allows for rapid growth rates of III-V materials, and does not rely on the toxic and pyrophoric precursors used in MOCVD. We characterize CSVT films of GaAs using photoelectrochemical current-voltage and quantum efficiency measurements. Hole diffusion lengths which exceed 1.5 um are extracted from internal quantum efficiency measurements using the Gartner model. Device physics simulations suggest that solar cells based on these films could reach efficiencies exceeding 24 %. To reach this goal, a more complete understanding of the electrical properties and characterization of defects will be necessary, including measurements on complete solid-state devices. Doping of films is achieved by using source material containing the desired impurity (e.g., Te or Zn). We discuss strategies for growing III-V materials on inexpensive substrates that are not lattice-matched to GaAs.

  20. Mechanisms Determining the Structure of Gold-Catalyzed GaAs Nanowires Studied by in Situ X-ray Diffraction

    SciTech Connect (OSTI)

    Takahasi, Masamitu; Kozu, Miwa; Sasaki, Takuo; Hu, Wen

    2015-09-02

    The evolution of polytypism during GaAs nanowire growth was investigated with in situ X-ray diffraction. The growth of nanowires was found to start with the formation of zincblende structure, followed by the growth of wurtzite structure. The growth process was well reproduced by a simulation based on a layer-by-layer nucleation model. The good agreement between the measured and simulated results confirms that nucleation costs higher energy for the stackings changing the crystal structure than for those conserving the preceding structure. The transition in prevalent structure can be accounted for by the change of local growth conditions related to the shape of triple phase line rather than by the change in supersaturation level, which quickly reaches steady state after starting growth.

  1. Strong enhancement of terahertz emission from GaAs in InAs/GaAs quantum dot structures

    SciTech Connect (OSTI)

    Estacio, Elmer; Pham, Minh Hong; Takatori, Satoru; Cadatal-Raduban, Marilou; Nakazato, Tomoharu; Shimizu, Toshihiko; Sarukura, Nobuhiko; Somintac, Armando; Defensor, Michael; Awitan, Fritz Christian B.; Jaculbia, Rafael B.; Salvador, Arnel; Garcia, Alipio

    2009-06-08

    We report on the intense terahertz emission from InAs/GaAs quantum dot (QD) structures grown by molecular beam epitaxy. Results reveal that the QD sample emission was as high as 70% of that of a p-type InAs wafer, the most intense semiconductor emitter to date. Excitation wavelength studies showed that the emission was due to absorption in strained undoped GaAs, and corresponds to a two order-of-magnitude enhancement. Moreover, it was found that multilayer QDs emit more strongly compared with a single layer QD sample. At present, we ascribe the intense radiation to huge strain fields at the InAs/GaAs interface.

  2. Metamorphic approach to single quantum dot emission at 1.55 {mu}m on GaAs substrate

    SciTech Connect (OSTI)

    Semenova, E. S.; Hostein, R.; Patriarche, G.; Mauguin, O.; Largeau, L.; Robert-Philip, I.; Beveratos, A.; Lemaitre, A.

    2008-05-15

    We report on the fabrication and the characterization of InAs quantum dots (QDs) embedded in an indium rich In{sub 0.42}Ga{sub 0.58}As metamorphic matrix grown on a GaAs substrate. Growth conditions were chosen so as to minimize the number of threading dislocations and other defects produced during the plastic relaxation. Sharp and bright lines, originating from the emission of a few isolated single quantum dots, were observed in microphotoluminescence around 1.55 {mu}m at 5 K. They exhibit, in particular, a characteristic exciton/biexciton behavior. These QDs could offer an interesting alternative to other approaches as InAs/InP QDs for the realization of single photon emitters at telecom wavelengths.

  3. Magnetic anisotropies in epitaxial Fe{sub 3}O{sub 4}/GaAs(100) patterned structures

    SciTech Connect (OSTI)

    Zhang, W. Zhang, D.; Yuan, S. J.; Huang, Z. C.; Zhai, Y.; Wong, P. K. J.; Wu, J.; Xu, Y. B.

    2014-10-15

    Previous studies on epitaxial Fe{sub 3}O{sub 4} rings in the context of spin-transfer torque effect have revealed complicated and undesirable domain structures, attributed to the intrinsic fourfold magnetocrystalline anisotropy in the ferrite. In this Letter, we report a viable solution to this problem, utilizing a 6-nm-thick epitaxial Fe{sub 3}O{sub 4} thin film on GaAs(100), where the fourfold magnetocrystalline anisotropy is negligible. We demonstrate that in the Fe{sub 3}O{sub 4} planar wires patterned from our thin film, such a unique magnetic anisotropy system has been preserved, and relatively simple magnetic domain configurations compared to those previous reports can be obtained.

  4. Mechanisms Determining the Structure of Gold-Catalyzed GaAs Nanowires Studied by in Situ X-ray Diffraction

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Takahasi, Masamitu; Kozu, Miwa; Sasaki, Takuo; Hu, Wen

    2015-09-02

    The evolution of polytypism during GaAs nanowire growth was investigated with in situ X-ray diffraction. The growth of nanowires was found to start with the formation of zincblende structure, followed by the growth of wurtzite structure. The growth process was well reproduced by a simulation based on a layer-by-layer nucleation model. The good agreement between the measured and simulated results confirms that nucleation costs higher energy for the stackings changing the crystal structure than for those conserving the preceding structure. The transition in prevalent structure can be accounted for by the change of local growth conditions related to the shapemore » of triple phase line rather than by the change in supersaturation level, which quickly reaches steady state after starting growth.« less

  5. Monolithically interconnected GaAs solar cells: A new interconnection technology for high voltage solar cell output

    SciTech Connect (OSTI)

    Dinetta, L.C.; Hannon, M.H.

    1995-10-01

    Photovoltaic linear concentrator arrays can benefit from high performance solar cell technologies being developed at AstroPower. Specifically, these are the integration of thin GaAs solar cell and epitaxial lateral overgrowth technologies with the application of monolithically interconnected solar cell (MISC) techniques. This MISC array has several advantages which make it ideal for space concentrator systems. These are high system voltage, reliable low cost monolithically formed interconnections, design flexibility, costs that are independent of array voltage, and low power loss from shorts, opens, and impact damage. This concentrator solar cell will incorporate the benefits of light trapping by growing the device active layers over a low-cost, simple, PECVD deposited silicon/silicon dioxide Bragg reflector. The high voltage-low current output results in minimal 12R losses while properly designing the device allows for minimal shading and resistance losses. It is possible to obtain open circuit voltages as high as 67 volts/cm of solar cell length with existing technology. The projected power density for the high performance device is 5 kW/m for an AMO efficiency of 26% at 1 5X. Concentrator solar cell arrays are necessary to meet the power requirements of specific mission platforms and can supply high voltage power for electric propulsion systems. It is anticipated that the high efficiency, GaAs monolithically interconnected linear concentrator solar cell array will enjoy widespread application for space based solar power needs. Additional applications include remote man-portable or ultra-light unmanned air vehicle (UAV) power supplies where high power per area, high radiation hardness and a high bus voltage or low bus current are important. The monolithic approach has a number of inherent advantages, including reduced cost per interconnect and increased reliability of array connections. There is also a high potential for a large number of consumer products.

  6. Impact of artificial lateral quantum confinement on exciton-spin relaxation in a two-dimensional GaAs electronic system

    SciTech Connect (OSTI)

    Kiba, Takayuki Murayama, Akihiro; Tanaka, Toru; Tamura, Yosuke; Higo, Akio; Thomas, Cedric; Samukawa, Seiji

    2014-10-15

    We demonstrate the effect of artificial lateral quantum confinement on exciton-spin relaxation in a GaAs electronic system. GaAs nanodisks (NDs) were fabricated from a quantum well (QW) by top-down nanotechnology using neutral-beam etching aided by protein-engineered bio-nano-templates. The exciton-spin relaxation time was 1.4 ns due to ND formation, significantly extended compared to 0.44 ns for the original QW, which is attributed to weakening of the hole-state mixing in addition to freezing of the carrier momentum. The temperature dependence of the spin-relaxation time depends on the ND thickness, reflecting the degree of quantum confinement.

  7. Atomic and electronic structures of SrTiO3/GaAs heterointerfaces: An 80-kV atomic-resolution electron energy-loss spectroscopy study

    SciTech Connect (OSTI)

    Qiao, Q.; Klie, Robert F; Ogut, Serdar; Idrobo Tapia, Juan C

    2012-01-01

    We have examined the atomic and electronic structures of epitaxially grown, ultrathin SrTiO{sub 3} (100) films on GaAs (001) using 80-kV aberration-corrected atomic-resolution Z-contrast imaging and electron energy-loss spectroscopy (EELS) to develop a fundamental understanding of the interfacial structure-property relationships. We find that the interface is atomically abrupt and no surface reconstruction of the GaAs (001) surface is observed. Using atomic-column resolved EELS, we examine the oxygen vacancy and Ti concentrations in the SrTiO{sub 3} film and across the heterointerface. We show that Ti diffuses into the first few monolayers of GaAs. Using a combination of EELS and first-principles calculations, we present evidence for the formation of As oxides at the interface depending on the thin-film growth conditions. These findings are used to explain the differences in the transport behavior of the films.

  8. Charge and fluence lifetime measurements of a dc high voltage GaAs photogun at high average current

    SciTech Connect (OSTI)

    J. Grames, R. Suleiman, P.A. Adderley, J. Clark, J. Hansknecht, D. Machie, M. Poelker, M.L. Stutzman

    2011-04-01

    GaAs-based dc high voltage photoguns used at accelerators with extensive user programs must exhibit long photocathode operating lifetime. Achieving this goal represents a significant challenge for proposed high average current facilities that must operate at tens of milliamperes or more. This paper describes techniques to maintain good vacuum while delivering beam, and techniques that minimize the ill effects of ion bombardment, the dominant mechanism that reduces photocathode yield of a GaAs-based dc high voltage photogun. Experimental results presented here demonstrate enhanced lifetime at high beam currents by: (a) operating with the drive laser beam positioned away from the electrostatic center of the photocathode, (b) limiting the photocathode active area to eliminate photoemission from regions of the photocathode that do not support efficient beam delivery, (c) using a large drive laser beam to distribute ion damage over a larger area, and (d) by applying a relatively low bias voltage to the anode to repel ions created within the downstream beam line. A combination of these techniques provided the best total charge extracted lifetimes in excess of 1000 C at dc beam currents up to 9.5 mA, using green light illumination of bulk GaAs inside a 100 kV photogun.

  9. Methylthiol adsorption on GaAs(100)-(2 x 4) surface: Ab initio quantum-chemical analysis

    SciTech Connect (OSTI)

    Lebedev, M. V.

    2008-09-15

    Quantum-chemical cluster calculations within the density functional theory are performed to study the mechanism of adsorption of the methylthiol molecule CH{sub 3}SH on an As-As dimer on a GaAs (100) surface. It is shown that the adsorption of the molecule can proceed through dissociation of either the S-H or C-S bond. The lowest energy has the state of dissociative adsorption with the rupture of the C-S bond resulting in the formation of a methane molecule and sulfur adatom incorporated between surface arsenic atoms constituting the dimer. A somewhat higher energy has the state of dissociative adsorption with the rupture of the S-H bond. In this state the CH{sub 3}S-radical is adsorbed at an arsenic atom constituting dimer and the hydrogen atom is adsorbed at a gallium atom bonded to this arsenic atom. These two states provide chemical and electronic passivation of the semiconductor surface.

  10. 20% (AM1.5) efficiency GaAs solar cells on sub-mm grain-size poly-Ge and its transition to low-cost substrates

    SciTech Connect (OSTI)

    Venkatasubramanian, R.; O`Quinn, B.C.; Siivola, E.; Keyes, B.; Ahrenkiel, R.

    1997-12-31

    Some of the key material and device issues related to the development of GaAs solar cells on poly-Ge substrates, including the dark-current reduction mechanism with an undoped spacer at the p{sup +}-n depletion layer, are discussed. Device-structure optimization studies that have led the authors to achieve an AM1.5 efficiency of {approximately}20% for a 4-cm{sup 2}-area GaAs cell on sub-mm grain-size poly-Ge and an efficiency of {approximately}21% for a 0.25-cm{sup 2}-area cell are presented. This successful demonstration of high-efficiency GaAs cells on sub-mm grain-size poly-Ge substrates have motivated us to consider the development of high-quality GaAs materials on significantly lower-cost substrates such as glass and moly foils. To date, the authors have achieved a best minority-carrier lifetime of 0.41 nsec in an n-GaAs thin-film on moly. The role of Group-VI dopant in the possible passivation of grain-boundaries in poly-GaAs is discussed. Development of PV-quality GaAs material, with minority-carrier lifetime of 1 to 2 nsec, on los-cost moly foils can significantly impact both the terrestrial and the space PV applications.

  11. The arsenides LnPd{sub 3}As{sub 2} (Ln = La-Nd, Sm, Gd) and structure refinement of CePd{sub 2-x}As{sub 2} with the ThCr{sub 2}Si{sub 2} structure

    SciTech Connect (OSTI)

    Quebe, P.; Jeitschko, W.

    1995-02-15

    The title compounds were prepared in well-crystallized form by annealing the corresponding binary arsenides in a NaCl/KCl flux. The compounds LnPd{sub 3}As{sub 2} crystallize with a new monoclinic structure type, which was determined from single-crystal X-ray data of GdPd{sub 3}As{sub 2}: C2/m, a = 1656.3(6) pm, b = 404.6(2) pm, c = 993.7(4) pm, {beta} = 107.85(2){degrees}, Z = 6, R = 0.025 for 1728 structure factors and 58 variable parameters. These arsenides belong to a large structural family with a metal to metalloid ratio of 2:1. Somewhat unusual features in the structure of GdPd{sub 3}As{sub 2} are the (distorted) octahedral coordination of one gadolinium site and the square-planar coordination of arsenic atoms around two palladium sites. All of these, however, are also observed for the corresponding atoms in the previously reported, closely related structure of Th{sub 5}Fe{sub 19}P{sub 12}. CePd{sub 2-x}As{sub 2} has the tetragonal ThCr{sub 2}Si{sub 2} structure (a = 425.1(2) pm, c = 1026.1(6)pm, R = 0.023 for 244 F values and 11 variables) with an As-As distance of 247.1(1) pm. The refinement of the occupancy parameter of the palladium position resulted in a value of 87.9(2)% corresponding to the formula CePd{sub 1.758(4)}As{sub 2}. It is argued that the formation of these defects reduces antibonding (destabilizing) Pd-Pd interactions.

  12. Metal organic chemical vapor deposition of 111-v compounds on silicon

    DOE Patents [OSTI]

    Vernon, Stanley M.

    1986-01-01

    Expitaxial composite comprising thin films of a Group III-V compound semiconductor such as gallium arsenide (GaAs) or gallium aluminum arsenide (GaAlAs) on single crystal silicon substrates are disclosed. Also disclosed is a process for manufacturing, by chemical deposition from the vapor phase, epitaxial composites as above described, and to semiconductor devices based on such epitaxial composites. The composites have particular utility for use in making light sensitive solid state solar cells.

  13. InGaAsN Solar Cells with 1.0eV Bandgap, Lattice Matched to GaAs

    SciTech Connect (OSTI)

    Allerman, A.A.; Banas, J.J.; Gee, J.M.; Hammons, B.E.; Jones, E.D.; Kurtz, S.R.

    1998-11-24

    The design, growth by metal-organic chemical vapor deposition, and processing of an In{sub 0.07}Ga{sub 0.93}As{sub 0.98}N{sub 0.02} solar Al, with 1.0 ev bandgap, lattice matched to GaAs is described. The hole diffusion length in annealed, n-type InGaAsN is 0.6-0.8 pm, and solar cell internal quantum efficiencies > 70% arc obwined. Optical studies indicate that defects or impurities, from InGAsN doping and nitrogen incorporation, limit solar cell performance.

  14. Final Technical Progress Report: High-Efficiency Low-Cost Thin-Film GaAs Photovoltaic Module Development Program; July 14, 2010 - January 13, 2012

    SciTech Connect (OSTI)

    Mattos, L.

    2012-03-01

    This is the final technical progress report of the High-Efficiency Low-Cost Thin-Film GaAs Photovoltaic Module Development Program. Alta Devices has successfully completed all milestones and deliverables established as part of the NREL PV incubator program. During the 18 months of this program, Alta has proven all key processes required to commercialize its solar module product. The incubator focus was on back end process steps directed at conversion of Alta's high quality solar film into high efficiency 1-sun PV modules. This report describes all program deliverables and the work behind each accomplishment.

  15. Localization-delocalization transition of electrons at the percolation threshold of semiconductor GaAs1–xNx alloys: The appearance of a mobility edge

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Alberi, K.; Fluegel, B.; Beaton, D. A.; Ptak, A. J.; Mascarenhas, A.

    2012-07-09

    Electrons in semiconductor alloys have generally been described in terms of Bloch states that evolve from constructive interference of electron waves scattering from perfectly periodic potentials, despite the loss of structural periodicity that occurs on alloying. Using the semiconductor alloy GaAs₁₋xNx as a prototype, we demonstrate a localized to delocalized transition of the electronic states at a percolation threshold, the emergence of a mobility edge, and the onset of an abrupt perturbation to the host GaAs electronic structure, shedding light on the evolution of electronic structure in these abnormal alloys.

  16. Magneto-transport properties of InAs nanowires laterally-grown by selective area molecular beam epitaxy on GaAs (110) masked substrates

    SciTech Connect (OSTI)

    Akabori, M.; Yamada, S.

    2013-12-04

    We prepared InAs nanowires (NWs) by lateral growth on GaAs (110) masked substrates in molecular beam epitaxy. We measured magneto-transport properties of the InAs NWs. In spite of parallel-NW multi-channels, we observed fluctuating magneto-conductance. From the fluctuation, we evaluated phase coherence length as a function of measurement temperature, and found decrease in the length with increase in the temperature. We also evaluate phase coherence length as a function of gate voltage.

  17. Controllable growth and optical properties of InP and InP/InAs nanostructures on the sidewalls of GaAs nanowires

    SciTech Connect (OSTI)

    Yan, Xin; Zhang, Xia Li, Junshuai; Cui, Jiangong; Ren, Xiaomin

    2014-12-07

    The growth and optical properties of InP and InP/InAs nanostructures on GaAs nanowires are investigated. InP quantum well and quantum dots (QDs) are formed on the sidewalls of GaAs nanowires successively with increasing the deposition time of InP. The GaAs/InP nanowire heterostructure exhibits a type-II band alignment. The wavelength of the InP quantum well is in the range of 857892?nm at 77?K, which means that the quantum well is nearly fully strained. The InP quantum dot, which has a bow-shaped cross section, exhibits dislocation-free pure zinc blende structure. Stranski-Krastanow InAs quantum dots are subsequently formed on the GaAs/InP nanowire core-shell structure. The InAs quantum dots are distributed over the middle part of the nanowire, indicating that the In atoms contributing to the quantum dots mainly come from the vapor rather than the substrate. The longest emission wavelength obtained from the InAs QDs is 1039?nm at 77?K. The linewidth is as narrow as 46.3?meV, which is much narrower than those on planar InP substrates and wurtzite InP nanowires, suggesting high-crystal-quality, phase-purity, and size-uniformity of quantum dots.

  18. Optical properties of multi-stacked InGaAs/GaNAs quantum dot solar cell fabricated on GaAs (311)B substrate

    SciTech Connect (OSTI)

    Shoji, Yasushi; Akimoto, Katsuhiro; Okada, Yoshitaka

    2012-09-15

    Quantum dot solar cells (QDSCs) comprised of 10 stacked pairs of strain-compensated InGaAs/GaNAs QD structure have been fabricated by atomic hydrogen-assisted molecular beam epitaxy. A homogeneous and high-density QD array structure with improved in-plane ordering and total density of {approx}10{sup 12} cm{sup -2} has been achieved on GaAs (311)B grown at 460 Degree-Sign C after stacking. The external quantum efficiency (EQE) of InGaAs/GaNAs QDSC increases in the longer wavelength range due to additive contribution from QD layers inserted in the intrinsic region. The short-circuit current density measured for QDSC is 17.2 mA/cm{sup 2} compared to 14.8 mA/cm{sup 2} of GaAs reference cell. Further, an increase in EQE due to photocurrent production by 2-step photon absorption has been observed at room temperature though it is still small at around 0.1%.

  19. Npn double heterostructure bipolar transistor with ingaasn base region

    DOE Patents [OSTI]

    Chang, Ping-Chih; Baca, Albert G.; Li, Nein-Yi; Hou, Hong Q.; Ashby, Carol I. H.

    2004-07-20

    An NPN double heterostructure bipolar transistor (DHBT) is disclosed with a base region comprising a layer of p-type-doped indium gallium arsenide nitride (InGaAsN) sandwiched between n-type-doped collector and emitter regions. The use of InGaAsN for the base region lowers the transistor turn-on voltage, V.sub.on, thereby reducing power dissipation within the device. The NPN transistor, which has applications for forming low-power electronic circuitry, is formed on a gallium arsenide (GaAs) substrate and can be fabricated at commercial GaAs foundries. Methods for fabricating the NPN transistor are also disclosed.

  20. Spatially resolved study of polarized micro-photoluminescence spectroscopy on single GaAs nanowires with mixed zincblende and wurtzite phases

    SciTech Connect (OSTI)

    Mukherjee, Amlan; Ghosh, Sandip; Breuer, Steffen; Jahn, Uwe; Geelhaar, Lutz; Grahn, Holger T.

    2015-02-07

    Localized and polarized photoluminescence spectra are observed in single GaAs nanowires with mixed zincblende and wurtzite phases, grown using molecular beam epitaxy. For low excitation intensities, the photoluminescence emission exhibits narrow spectral features predominantly polarized perpendicular to the nanowire axis. For high excitation intensities, the photoluminescence spectra transform into dominant broadened features, which exhibit different peak energies and polarization properties. The strongly polarized emission at high excitation intensities is identified as being due to a spatially direct transition in wurtzite sections of the nanowires. The analysis, including band structure calculations suggests that carriers in the wurtzite sections diffuse into regions where the average low-temperature peak emission energy and crystal field parameter are 1.535?eV and 20?meV, respectively.

  1. Independent dynamic acousto-mechanical and electrostatic control of individual quantum dots in a LiNbO{sub 3}-GaAs hybrid

    SciTech Connect (OSTI)

    Pustiowski, Jens; Mller, Kai; Bichler, Max; Koblmller, Gregor; Finley, Jonathan J.; Wixforth, Achim; Krenner, Hubert J.

    2015-01-05

    We demonstrate tuning of single quantum dot emission lines by the combined action of the dynamic acoustic field of a radio frequency surface acoustic wave and a static electric field. Both tuning parameters are set all-electrically in a LiNbO{sub 3}-GaAs hybrid device. The surface acoustic wave is excited directly on the strong piezoelectric LiNbO{sub 3} onto which a GaAs-based p-i-n photodiode containing a single layer of quantum dots was epitaxially transferred. We demonstrate dynamic spectral tuning with bandwidths exceeding 3?meV of single quantum dot emission lines due to deformation potential coupling. The center energy of the dynamic spectral oscillation can be independently programmed simply by setting the bias voltage applied to the diode.

  2. Multi-spectral optical absorption in substrate-free nanowire arrays

    SciTech Connect (OSTI)

    Zhang, Junpeng; Chia, Andrew; Boulanger, Jonathan; LaPierre, Ray; Dhindsa, Navneet; Khodadad, Iman; Saini, Simarjeet

    2014-09-22

    A method is presented of fabricating gallium arsenide (GaAs) nanowire arrays of controlled diameter and period by reactive ion etching of a GaAs substrate containing an indium gallium arsenide (InGaP) etch stop layer, allowing the precise nanowire length to be controlled. The substrate is subsequently removed by selective etching, using the same InGaP etch stop layer, to create a substrate-free GaAs nanowire array. The optical absorptance of the nanowire array was then directly measured without absorption from a substrate. We directly observe absorptance spectra that can be tuned by the nanowire diameter, as explained with rigorous coupled wave analysis. These results illustrate strong optical absorption suitable for nanowire-based solar cells and multi-spectral absorption for wavelength discriminating photodetectors. The solar-weighted absorptance above the bandgap of GaAs was 94% for a nanowire surface coverage of only 15%.

  3. InGaAs/GaAsP strain balanced multi-quantum wires grown on misoriented GaAs substrates for high efficiency solar cells

    SciTech Connect (OSTI)

    Alonso-lvarez, D.; Thomas, T.; Fhrer, M.; Hylton, N. P.; Ekins-Daukes, N. J.; Lackner, D.; Philipps, S. P.; Bett, A. W.; Sodabanlu, H.; Fujii, H.; Watanabe, K.; Sugiyama, M.; Nasi, L.; Campanini, M.

    2014-08-25

    Quantum wires (QWRs) form naturally when growing strain balanced InGaAs/GaAsP multi-quantum wells (MQW) on GaAs [100] 6 misoriented substrates under the usual growth conditions. The presence of wires instead of wells could have several unexpected consequences for the performance of the MQW solar cells, both positive and negative, that need to be assessed to achieve high conversion efficiencies. In this letter, we study QWR properties from the point of view of their performance as solar cells by means of transmission electron microscopy, time resolved photoluminescence and external quantum efficiency (EQE) using polarised light. We find that these QWRs have longer lifetimes than nominally identical QWs grown on exact [100] GaAs substrates, of up to 1??s, at any level of illumination. We attribute this effect to an asymmetric carrier escape from the nanostructures leading to a strong 1D-photo-charging, keeping electrons confined along the wire and holes in the barriers. In principle, these extended lifetimes could be exploited to enhance carrier collection and reduce dark current losses. Light absorption by these QWRs is 1.6 times weaker than QWs, as revealed by EQE measurements, which emphasises the need for more layers of nanostructures or the use light trapping techniques. Contrary to what we expected, QWR show very low absorption anisotropy, only 3.5%, which was the main drawback a priori of this nanostructure. We attribute this to a reduced lateral confinement inside the wires. These results encourage further study and optimization of QWRs for high efficiency solar cells.

  4. Current flow and potential efficiency of solar cells based on GaAs and GaSb p-n junctions

    SciTech Connect (OSTI)

    Andreev, V. M.; Evstropov, V. V.; Kalinovsky, V. S. Lantratov, V. M.; Khvostikov, V. P.

    2009-05-15

    Dependence of the efficiency of single-junction and multijunction solar cells on the mechanisms of current flow in photoactive p-n junctions, specifically on the form of the dark current-voltage characteristic J-V, has been studied. The resistanceless J-V{sub j} characteristic (with the series resistance disregarded) of a multijunction solar cell has the same shape as the characteristic of a single-junction cell: both feature a set of exponential portions. This made it possible to develop a unified analytical method for calculating the efficiency of singlejunction and multijunction solar cells. The equation relating the efficiency to the photogenerated current at each portion of the J-V{sub j} characteristic is derived. For p-n junctions in GaAs and GaSb, the following characteristics were measured: the dark J-V characteristic, the dependence of the open-circuit voltage on the illumination intensity P-V{sub OC}, and the dependence of the luminescence intensity on the forward current L-J. Calculated dependences of potential efficiency (under idealized condition for equality to unity of external quantum yield) on the photogenerated current for single-junction GaAs and GaSb solar cells and a GaAs/GaSb tandem are plotted. The form of these dependences corresponds to the shape of J-V{sub j} characteristics: there are the diffusion- and recombination-related portions; in some cases, the tunneling-trapping portion is also observed. At low degrees of concentration of solar radiation (C < 10), an appreciable contribution to photogenerated current is made by recombination component. It is an increase in this component in the case of irradiation with 6.78-MeV protons or 1-MeV electrons that brings about a decrease in the efficiency of conversion of unconcentrated solar radiation.

  5. Theory of the electronic structure of dilute bismide and bismide-nitride alloys of GaAs: Tight-binding and k.p models

    SciTech Connect (OSTI)

    Usman, Muhammad; Broderick, Christopher A.; O'Reilly, Eoin P.

    2013-12-04

    The addition of dilute concentrations of bismuth (Bi) into GaAs to form GaBi{sub x}As{sub 1?x} alloys results in a large reduction of the band gap energy (E{sub g}) accompanied by a significant increase of the spin-orbit-splitting energy (?{sub SO}), leading to an E{sub g} < ?{sub SO} regime for x ? 10% which is technologically relevant for the design of highly efficient photonic devices. The quaternary alloy GaBi{sub x}N{sub y}As{sub 1?x?y} offers further flexibility for band gap tuning, because both nitrogen and bismuth can independently induce band gap reduction. This work reports sp{sup 3}s* tight binding and 14-band k?p models for the study of the electronic structure of GaBi{sub x}As{sub 1?x} and GaBi{sub x}N{sub y}As{sub 1?x?y} alloys. Our results are in good agreement with the available experimental data.

  6. Direct observation of oxygen-vacancy-enhanced polarization in a SrTiO3-buffered ferroelectric BaTiO3 film on GaAs

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Qiao, Q.; Zhang, Y.; Contreras-Guerrero, Rocio; Droopad, Ravi; Pantelides, S. T.; Pennycook, Stephen J.; Ogut, Serdar; Klie, Robert F.

    2015-11-16

    The integration of functional oxide thin-films on compound semiconductors can lead to a class of reconfigurable spin-based optoelectronic devices if defect-free, fully reversible active layers are stabilized. However, previous first-principles calculations predicted that SrTiO3 thin filmsgrown on Si exhibit pinned ferroelectric behavior that is not switchable, due to the presence of interfacial vacancies. Meanwhile, piezoresponse force microscopy measurements have demonstrated ferroelectricity in BaTiO3 grown on semiconductor substrates. The presence of interfacial oxygen vacancies in such complex-oxide/semiconductor systems remains unexplored, and their effect on ferroelectricity is controversial. We also use a combination of aberration-corrected scanning transmission electron microscopy and first-principles densitymore » functional theory modeling to examine the role of interfacial oxygen vacancies on the ferroelectricpolarization of a BaTiO3 thin filmgrown on GaAs. Moreover, we demonstrate that interfacial oxygen vacancies enhance the polar discontinuity (and thus the single domain, out-of-plane polarization pinning in BaTiO3), and propose that the presence of surface charge screening allows the formation of switchable domains.« less

  7. Structural and band alignment properties of Al{sub 2}O{sub 3} on epitaxial Ge grown on (100), (110), and (111)A GaAs substrates by molecular beam epitaxy

    SciTech Connect (OSTI)

    Hudait, M. K.; Zhu, Y.; Maurya, D.; Priya, S.; Patra, P. K.; Ma, A. W. K.; Aphale, A.; Macwan, I.

    2013-04-07

    Structural and band alignment properties of atomic layer Al{sub 2}O{sub 3} oxide film deposited on crystallographically oriented epitaxial Ge grown in-situ on (100), (110), and (111)A GaAs substrates using two separate molecular beam epitaxy chambers were investigated using cross-sectional transmission microscopy (TEM) and x-ray photoelectron spectroscopy (XPS). High-resolution triple axis x-ray measurement demonstrated pseudomorphic and high-quality Ge epitaxial layer on crystallographically oriented GaAs substrates. The cross-sectional TEM exhibited a sharp interface between the Ge epilayer and each orientation of the GaAs substrate as well as the Al{sub 2}O{sub 3} film and the Ge epilayer. The extracted valence band offset, {Delta}E{sub v}, values of Al{sub 2}O{sub 3} relative to (100), (110), and (111) Ge orientations using XPS measurement were 3.17 eV, 3.34 eV, and 3.10 eV, respectively. Using XPS data, variations in {Delta}E{sub v} related to the crystallographic orientation were {Delta}E{sub V}(110)Ge>{Delta}E{sub V}(100)Ge{>=}{Delta}E{sub V}(111)Ge and the conduction band offset, {Delta}E{sub c}, related to the crystallographic orientation was {Delta}E{sub c}(111)Ge>{Delta}E{sub c}(110)Ge>{Delta}E{sub c}(100)Ge using the measured {Delta}E{sub v}, bandgap of Al{sub 2}O{sub 3} in each orientation, and well-known Ge bandgap of 0.67 eV. These band offset parameters are important for future application of Ge-based p- and n-channel metal-oxide field-effect transistor design.

  8. The currentvoltage and capacitancevoltage characteristics at high temperatures of Au Schottky contact to n-type GaAs

    SciTech Connect (OSTI)

    zerli, Halil; Karteri, ?brahim; Karata?, ?kr; Altindal, ?emsettin

    2014-05-01

    Highlights: The electronic parameters of the diode under temperature were investigated. The barrier heights have a Gaussian distribution. Au/n-GaAs diode exhibits a rectification behavior. - Abstract: We have investigated the temperature-dependent currentvoltage (IV) and capacitancevoltage (CV) characteristics of Au/n-GaAs Schottky barrier diodes (SBDs) in the temperature range of 280415 K. The barrier height for the Au/n-type GaAs SBDs from the IV and CV characteristics have varied from 0.901 eV to 0.963 eV (IV) and 1.234 eV to 0.967 eV (CV), and the ideality factor (n) from 1.45 to 1.69 in the temperature range 280415 K. The conventional Richardson plots are found to be linear in the temperature range measured. Both the ln(I{sub 0}/T{sup 2}) versus (kT){sup ?1} and ln(I{sub 0}/T{sup 2}) versus (nkT){sup ?1} plots gives a straight line corresponding to activation energies 0.773 eV and 0.870 eV, respectively. A ?{sub b0} versus 1/T plot was drawn to obtain evidence of a Gaussian distribution of the BHs, and values of ?{sup }{sub b0} = 1.071 eV and ?{sub 0} = 0.094 V for the mean BH and zero-bias standard deviation have been obtained from this plot.

  9. Molecular beam epitaxial growth of Bi{sub 2}Te{sub 3} and Sb{sub 2}Te{sub 3} topological insulators on GaAs (111) substrates: a potential route to fabricate topological insulator p-n junction

    SciTech Connect (OSTI)

    Zeng, Zhaoquan; Morgan, Timothy A.; Li, Chen; Hirono, Yusuke; Hu, Xian; Hawkridge, Michael E.; Benamara, Mourad; Salamo, Gregory J.; Fan, Dongsheng; Yu, Shuiqing; Department of Electrical Engineering, University of Arkansas, Fayetteville, AR 72701 ; Zhao, Yanfei; Lee, Joon Sue; Wang, Jian; The Center for Nanoscale Science and Department of Physics, The Pennsylvania State University, University Park, PA 16802 ; Wang, Zhiming M.; State Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science and Technology of China, Chengdu 610054; Engineering Research Center for Semiconductor Integrated Technology, Institute of Semiconductors, Chinese Academy of Science, Beijing 100083

    2013-07-15

    High quality Bi{sub 2}Te{sub 3} and Sb{sub 2}Te{sub 3} topological insulators films were epitaxially grown on GaAs (111) substrate using solid source molecular beam epitaxy. Their growth and behavior on both vicinal and non-vicinal GaAs (111) substrates were investigated by reflection high-energy electron diffraction, atomic force microscopy, X-ray diffraction, and high resolution transmission electron microscopy. It is found that non-vicinal GaAs (111) substrate is better than a vicinal substrate to provide high quality Bi{sub 2}Te{sub 3} and Sb{sub 2}Te{sub 3} films. Hall and magnetoresistance measurements indicate that p type Sb{sub 2}Te{sub 3} and n type Bi{sub 2}Te{sub 3} topological insulator films can be directly grown on a GaAs (111) substrate, which may pave a way to fabricate topological insulator p-n junction on the same substrate, compatible with the fabrication process of present semiconductor optoelectronic devices.

  10. Fabrication and characterisation of gallium arsenide ambipolar quantum point contacts

    SciTech Connect (OSTI)

    Chen, J. C. H. Klochan, O.; Micolich, A. P.; Hamilton, A. R.; Das Gupta, K.; Sfigakis, F.; Ritchie, D. A.; Trunov, K.; Wieck, A. D.; Reuter, D.

    2015-05-04

    We show that ballistic one-dimensional channels can be formed in an ambipolar device fabricated on a high mobility Al{sub 0.34}Ga{sub 0.66}As/GaAs heterostructure. Both electron and hole quantised conductances can be measured in the same one-dimensional channel. We have used this device to compare directly the subband spacings of the two charge carriers in the same confining potential and used this to compare the electron and hole effective masses.

  11. Impact of stress relaxation in GaAsSb cladding layers on quantum dot creation in InAs/GaAsSb structures grown on GaAs (001)

    SciTech Connect (OSTI)

    Bremner, S. P.; Ban, K.-Y.; Faleev, N. N.; Honsberg, C. B.; Smith, D. J.

    2013-09-14

    We describe InAs quantum dot creation in InAs/GaAsSb barrier structures grown on GaAs (001) wafers by molecular beam epitaxy. The structures consist of 20-nm-thick GaAsSb barrier layers with Sb content of 8%, 13%, 15%, 16%, and 37% enclosing 2 monolayers of self-assembled InAs quantum dots. Transmission electron microscopy and X-ray diffraction results indicate the onset of relaxation of the GaAsSb layers at around 15% Sb content with intersected 60 dislocation semi-loops, and edge segments created within the volume of the epitaxial structures. 38% relaxation of initial elastic stress is seen for 37% Sb content, accompanied by the creation of a dense net of dislocations. The degradation of In surface migration by these dislocation trenches is so severe that quantum dot formation is completely suppressed. The results highlight the importance of understanding defect formation during stress relaxation for quantum dot structures particularly those with larger numbers of InAs quantum-dot layers, such as those proposed for realizing an intermediate band material.

  12. Effect of spacer layer thickness on multi-stacked InGaAs quantum dots grown on GaAs (311)B substrate for application to intermediate band solar cells

    SciTech Connect (OSTI)

    Shoji, Yasushi; Narahara, Kohei; Okada, Yoshitaka; Tanaka, Hideharu; Kita, Takashi; Akimoto, Katsuhiro

    2012-04-01

    We have investigated the properties of multi-stacked layers of self-organized In{sub 0.4}Ga{sub 0.6}As quantum dots (QDs) on GaAs (311)B grown by molecular beam epitaxy. We found that a high degree of in-plane ordering of QDs structure with a six-fold symmetry was maintained though the growth has been performed at a higher growth rate than the conventional conditions. The dependence of photoluminescence characteristics on spacer layer thickness showed an increasing degree of electronic coupling between the stacked QDs for thinner spacer layers. The external quantum efficiency for an InGaAs/GaAs quantum dot solar cell (QDSC) with a thin spacer layer thickness increased in the longer wavelength range due to additive contribution from QD layers inserted in the intrinsic region. Furthermore, a photocurrent production by 2-step photon absorption has been observed at room temperature for the InGaAs/GaAs QDSC with a spacer layer thickness of 15 nm.

  13. InGaAsN/GaAs heterojunction for multi-junction solar cells

    DOE Patents [OSTI]

    Kurtz, Steven R. (Albuquerque, NM); Allerman, Andrew A. (Albuquerque, NM); Klem, John F. (Albuquerque, NM); Jones, Eric D. (Edgewood, NM)

    2001-01-01

    An InGaAsN/GaAs semiconductor p-n heterojunction is disclosed for use in forming a 0.95-1.2 eV bandgap photodetector with application for use in high-efficiency multi-junction solar cells. The InGaAsN/GaAs p-n heterojunction is formed by epitaxially growing on a gallium arsenide (GaAs) or germanium (Ge) substrate an n-type indium gallium arsenide nitride (InGaAsN) layer having a semiconductor alloy composition In.sub.x Ga.sub.1-x As.sub.1-y N.sub.y with 0GaAs layer, with the InGaAsN and GaAs layers being lattice-matched to the substrate. The InGaAsN/GaAs p-n heterojunction can be epitaxially grown by either molecular beam epitaxy (MBE) or metalorganic chemical vapor deposition (MOCVD). The InGaAsN/GaAs p-n heterojunction provides a high open-circuit voltage of up to 0.62 volts and an internal quantum efficiency of >70%.

  14. Microfabricated wire arrays for Z-pinch. (Technical Report) ...

    Office of Scientific and Technical Information (OSTI)

    ...cathode connections in Z. Electroplated gold wire arrays with integrated anodecathode ... GALLIUM ARSENIDES; ALUMINIUM ARSENIDES; GOLD; ELECTROPLATING; COPPER; PLATINUM; ...

  15. Analysis of gallium arsenide deposition in a horizontal chemical vapor deposition reactor using massively parallel computations

    SciTech Connect (OSTI)

    Salinger, A.G.; Shadid, J.N.; Hutchinson, S.A.

    1998-01-01

    A numerical analysis of the deposition of gallium from trimethylgallium (TMG) and arsine in a horizontal CVD reactor with tilted susceptor and a three inch diameter rotating substrate is performed. The three-dimensional model includes complete coupling between fluid mechanics, heat transfer, and species transport, and is solved using an unstructured finite element discretization on a massively parallel computer. The effects of three operating parameters (the disk rotation rate, inlet TMG fraction, and inlet velocity) and two design parameters (the tilt angle of the reactor base and the reactor width) on the growth rate and uniformity are presented. The nonlinear dependence of the growth rate uniformity on the key operating parameters is discussed in detail. Efficient and robust algorithms for massively parallel reacting flow simulations, as incorporated into our analysis code MPSalsa, make detailed analysis of this complicated system feasible.

  16. NMR evidence for inhomogeneous glassy behavior driven by nematic fluctuations in iron arsenide superconductors

    SciTech Connect (OSTI)

    Dioguardi, A. P.; Lawson, M. M.; Bush, B. T.; Crocker, J.; Shirer, K. R.; Nisson, D. M.; Kissikov, T.; Ran, S.; Bud'ko, S. L.; Canfield, P. C.; Yuan, S.; Kuhns, P. L.; Reyes, A. P.; Grafe, H. -J.; Curro, N. J.

    2015-10-16

    We present 75As nuclear magnetic resonance spin-lattice and spin-spin relaxation rate data in Ba(Fe1xCox)2As2 and Ba(Fe1xCux)2As2 as a function of temperature, doping, and magnetic field. The relaxation curves exhibit a broad distribution of relaxation rates, consistent with inhomogeneous glassy behavior up to 100 K. The doping and temperature response of the width of the dynamical heterogeneity is similar to that of the nematic susceptibility measured by elastoresistance measurements. In this study, we argue that quenched random fields which couple to the nematic order give rise to a nematic glass that is reflected in the spin dynamics.

  17. NMR evidence for inhomogeneous glassy behavior driven by nematic fluctuations in iron arsenide superconductors

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Dioguardi, A. P.; Lawson, M. M.; Bush, B. T.; Crocker, J.; Shirer, K. R.; Nisson, D. M.; Kissikov, T.; Ran, S.; Bud'ko, S. L.; Canfield, P. C.; et al

    2015-10-16

    We present 75As nuclear magnetic resonance spin-lattice and spin-spin relaxation rate data in Ba(Fe1–xCox)2As2 and Ba(Fe1–xCux)2As2 as a function of temperature, doping, and magnetic field. The relaxation curves exhibit a broad distribution of relaxation rates, consistent with inhomogeneous glassy behavior up to 100 K. The doping and temperature response of the width of the dynamical heterogeneity is similar to that of the nematic susceptibility measured by elastoresistance measurements. In this study, we argue that quenched random fields which couple to the nematic order give rise to a nematic glass that is reflected in the spin dynamics.

  18. Accelerated aging of GaAs concentrator solar cells

    SciTech Connect (OSTI)

    Gregory, P.E.

    1982-04-01

    An accelerated aging study of AlGaAs/GaAs solar cells has been completed. The purpose of the study was to identify the possible degradation mechanisms of AlGaAs/GaAs solar cells in terrestrial applications. Thermal storage tests and accelerated AlGaAs corrosion studies were performed to provide an experimental basis for a statistical analysis of the estimated lifetime. Results of this study suggest that a properly designed and fabricated AlGaAs/GaAs solar cell can be mechanically rugged and environmentally stable with projected lifetimes exceeding 100 years.

  19. Defect production during ion implantation of various A/sub III/B/sub V/ semiconductors

    SciTech Connect (OSTI)

    Wesch, W.; Wendler, E.; Goetz, G.; Kekelidse, N.P.

    1989-01-15

    The present paper gives a survey about the defect generation caused by ion implantation of GaAs, InAs, GaP, and InP. By combining Rutherford backscattering spectrometry, optical spectroscopy, and transmission electron microscopic methods, further information concerning the kinetics of the defect production as well as the type of defects created is obtained. Generally, the defect concentration in the region of implantation parameters investigated can be described by the energy density deposited into nuclear processes. Below critical values of the nuclear deposited energy density in GaAs weakly damaged layers containing point defects and point defect clusters are produced. With increasing nuclear deposited energy density an increasing number of amorphous zones is created due to manifold overlap of the initial defect clusters. The results indicate that in GaAs and InAs already at relatively low implantation temperatures, the amorphization occurs via homogeneous defect nucleation. The results obtained for GaP and InP, on the other hand, point at a remarkable contribution of heterogeneous defect nucleation already at room temperature, leading to amorphization at markedly lower nuclear deposited energy densities in spite of nearly identical values of the nuclear deposited energy. It is therefore concluded that defect recombination and annealing at room temperature is much less pronounced in the phosphides than in the arsenides.

  20. Recent developments in high-efficiency PV cells

    SciTech Connect (OSTI)

    Deb, S.

    2000-05-22

    Enormous progress has been made in recent years on a number of photovoltaic (PV) materials and devices in terms of conversion efficiencies. Ultrahigh-efficiency (>30{percent}) PV cells have been fabricated from gallium arsenide (GaAs) and its ternary alloys such as gallium indium phosphide (GaInP{sub 2}). The high-efficiency GaAs-based solar cells are being produced on a commercial scale, particularly for space applications. Efficiencies in the range of 18{percent} to 24{percent} have been achieved in traditional silicon-based devices fabricated from both multicrystalline and single-crystal materials. Major advances in efficiency have also been made on various thin-film solar cells based on amorphous silicon (aSi:H), copper gallium indium diselenide (CIGS), and cadmium telluride materials. This paper gives a brief overview of the recent progress in PV cell efficiencies based on these materials and devices.

  1. Micro-cooler enhancements by barrier interface analysis

    SciTech Connect (OSTI)

    Stephen, A.; Dunn, G. M.; Glover, J.; Oxley, C. H.; Bajo, M. Montes; Kuball, M.; Cumming, D. R. S.; Khalid, A.

    2014-02-15

    A novel gallium arsenide (GaAs) based micro-cooler design, previously analysed both experimentally and by an analytical Heat Transfer (HT) model, has been simulated using a self-consistent Ensemble Monte Carlo (EMC) model for a more in depth analysis of the thermionic cooling in the device. The best fit to the experimental data was found and was used in conjunction with the HT model to estimate the cooler-contact resistance. The cooling results from EMC indicated that the cooling power of the device is highly dependent on the charge distribution across the leading interface. Alteration of this charge distribution via interface extensions on the nanometre scale has shown to produce significant changes in cooler performance.

  2. High-efficiency solar cell and method for fabrication

    DOE Patents [OSTI]

    Hou, H.Q.; Reinhardt, K.C.

    1999-08-31

    A high-efficiency 3- or 4-junction solar cell is disclosed with a theoretical AM0 energy conversion efficiency of about 40%. The solar cell includes p-n junctions formed from indium gallium arsenide nitride (InGaAsN), gallium arsenide (GaAs) and indium gallium aluminum phosphide (InGaAlP) separated by n-p tunnel junctions. An optional germanium (Ge) p-n junction can be formed in the substrate upon which the other p-n junctions are grown. The bandgap energies for each p-n junction are tailored to provide substantially equal short-circuit currents for each p-n junction, thereby eliminating current bottlenecks and improving the overall energy conversion efficiency of the solar cell. Additionally, the use of an InGaAsN p-n junction overcomes super-bandgap energy losses that are present in conventional multi-junction solar cells. A method is also disclosed for fabricating the high-efficiency 3- or 4-junction solar cell by metal-organic chemical vapor deposition (MOCVD). 4 figs.

  3. High-efficiency solar cell and method for fabrication

    DOE Patents [OSTI]

    Hou, Hong Q.; Reinhardt, Kitt C.

    1999-01-01

    A high-efficiency 3- or 4-junction solar cell is disclosed with a theoretical AM0 energy conversion efficiency of about 40%. The solar cell includes p-n junctions formed from indium gallium arsenide nitride (InGaAsN), gallium arsenide (GaAs) and indium gallium aluminum phosphide (InGaAlP) separated by n-p tunnel junctions. An optional germanium (Ge) p-n junction can be formed in the substrate upon which the other p-n junctions are grown. The bandgap energies for each p-n junction are tailored to provide substantially equal short-circuit currents for each p-n junction, thereby eliminating current bottlenecks and improving the overall energy conversion efficiency of the solar cell. Additionally, the use of an InGaAsN p-n junction overcomes super-bandgap energy losses that are present in conventional multi-junction solar cells. A method is also disclosed for fabricating the high-efficiency 3- or 4-junction solar cell by metal-organic chemical vapor deposition (MOCVD).

  4. Synthesis, Crystal and Electronic Structures of the Pnictides AE3TrPn3 (AE = Sr, Ba; Tr = Al, Ga; Pn = P, As)

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Stoyko, Stanislav; Voss, Leonard; He, Hua; Bobev, Svilen

    2015-09-24

    New ternary arsenides AE3TrAs3 (AE = Sr, Ba; Tr = Al, Ga) and their phosphide analogs Sr3GaP3 and Ba3AlP3 have been prepared by reactions of the respective elements at high temperatures. Single-crystal X-ray diffraction studies reveal that Sr3AlAs3 and Ba3AlAs3 adopt the Ba3AlSb3-type structure (Pearson symbol oC56, space group Cmce, Z = 8). This structure is also realized for Sr3GaP3 and Ba3AlP3. Likewise, the compounds Sr3GaAs3 and Ba3GaAs3 crystallize with the Ba3GaSb3-type structure (Pearson symbol oP56, space group Pnma, Z = 8). Both structures are made up of isolated pairs of edge-shared AlPn4 and GaPn4 tetrahedra (Pn = pnictogen, i.e.,more » P or As), separated by the alkaline-earth Sr2+ and Ba2+ cations. In both cases, there are no homoatomic bonds, hence, regardless of the slightly different atomic arrangements, both structures can be rationalized as valence-precise [AE2+]3[Tr3+][Pn3-]3, or rather [AE2+]6[Tr2Pn6]12-, i.e., as Zintl phases.« less

  5. Observed damage during Argon gas cluster depth profiles of compound semiconductors

    SciTech Connect (OSTI)

    Barlow, Anders J. Portoles, Jose F.; Cumpson, Peter J.

    2014-08-07

    Argon Gas Cluster Ion Beam (GCIB) sources have become very popular in XPS and SIMS in recent years, due to the minimal chemical damage they introduce in the depth-profiling of polymer and other organic materials. These GCIB sources are therefore particularly useful for depth-profiling polymer and organic materials, but also (though more slowly) the surfaces of inorganic materials such as semiconductors, due to the lower roughness expected in cluster ion sputtering compared to that introduced by monatomic ions. We have examined experimentally a set of five compound semiconductors, cadmium telluride (CdTe), gallium arsenide (GaAs), gallium phosphide (GaP), indium arsenide (InAs), and zinc selenide (ZnSe) and a high-? dielectric material, hafnium oxide (HfO), in their response to argon cluster profiling. An experimentally determined HfO etch rate of 0.025?nm/min (3.95??10{sup ?2}?amu/atom in ion) for 6?keV Ar gas clusters is used in the depth scale conversion for the profiles of the semiconductor materials. The assumption has been that, since the damage introduced into polymer materials is low, even though sputter yields are high, then there is little likelihood of damaging inorganic materials at all with cluster ions. This seems true in most cases; however, in this work, we report for the first time that this damage can in fact be very significant in the case of InAs, causing the formation of metallic indium that is readily visible even to the naked eye.

  6. Recent improvements in materials for thin GaAs and multibandgap solar cells

    SciTech Connect (OSTI)

    Benner, J.P.

    1985-05-01

    The High Efficiency Concepts Program at SERI supports research on III-V compound semiconductors with the objective of achieving the maximum attainable photovoltaic conversion efficiencies for terrestrial solar electric power. The outcome of this research may also affect the future of space photovoltaic cells. While the interest in thin-film, high-efficiency solar cells for terrestrial applications is driven principally by consideration of system costs, such cells would also improve the power density of space power arrays.

  7. ESR Detection of optical dynamic nuclear polarization in GaAs...

    Office of Scientific and Technical Information (OSTI)

    ESR Detection of optical dynamic nuclear polarization in GaAsAlsub xGasub 1-xAs ... Citation Details In-Document Search Title: ESR Detection of optical dynamic nuclear ...

  8. Antimonide-Based Long-Wavelength Lasers on GaAs Substrates

    SciTech Connect (OSTI)

    KLEM,JOHN F.; Blum, O.

    2000-08-17

    We have investigated the use of GaAsSb in edge-emitting laser active regions, in order to obtain lasing near 1.3 {micro}m. Single quantum well GaAsSb devices display electroluminescence at wavelengths as long as 1.34 {micro}m, but substantial blueshifts occur under high injection conditions. GaAsSb single quantum well edge emitters have been obtained which lase at 1.275 {micro}m with a room-temperature threshold current density as low as 535 A/cm{sup 2}. Modification of the basic GaAsSb/GaAs structure with the addition of InGaAs layers results in a strongly type-II band alignment which can be used to further extend the emission wavelength of these devices. Using GaAsSb/InGaAs active regions, lasers emitting at 1.17 {micro}m have been obtained with room-temperature threshold current densities of 120 A/cm{sup 2}, and devices operating at 1.29 {micro}m have displayed thresholds as low as 375 A/cm{sup 2}. Characteristic temperatures for devices employing various GaAsSb-based active regions have been measured to be 60-73 K.

  9. Two dimensional electron transport in modulation-doped In{sub...

    Office of Scientific and Technical Information (OSTI)

    of Publication: United States Language: English Subject: 77 NANOSCIENCE AND NANOTECHNOLOGY; ALUMINIUM ARSENIDES; ANTIMONIDES; COMPARATIVE EVALUATIONS; DOPED MATERIALS;...

  10. Gamma ray measurements with photoconductive detectors using a...

    Office of Scientific and Technical Information (OSTI)

    AND TECHNOLOGY; ARGON; BREMSSTRAHLUNG; DEUTERIUM; DIAMONDS; GALLIUM ARSENIDES; GAMMA DETECTION; GAMMA RADIATION; HYDROGEN; MEV RANGE; NEON; PHOTOCONDUCTORS; PHOTOMULTIPLIERS;...

  11. Production development and utilization of Zimmer Station wet FGD by-products. Final report. Volume 3, Product development of gypsum, Phase 1

    SciTech Connect (OSTI)

    Smith, Kevin; Beeghly, Joel H.

    2000-11-30

    In the way of background information about 30 electric utility units with a combined total of 15,000 MW utilize magnesium enhanced lime flue gas desulfurization (FGD) systems. The first generation process begun in 1973, called the Thiosorbic® Process, was a technical breakthrough that offered significantly improved operating and performance characteristics compared with competing FGD technologies. The process is described as Flow Diagram "A" in Figure 1. A disadvantage of this and other inhibited or natural oxidation wet FGD systems is the capital and operating cost associated with landfill disposal of the calcium sulfite based solids. Fixation to stabilize the sludge solids for compunction in a landfill also consumes fly ash that otherwise may be marketable.

  12. Electron emitting device and method of making the same

    DOE Patents [OSTI]

    Olsen, Gregory Hammond; Martinelli, Ramon Ubaldo; Ettenberg, Michael

    1977-04-19

    A substrate of single crystalline gallium arsenide has on a surface thereof a layer of single crystalline indium gallium phosphide. A layer of single crystalline gallium arsenide is on the indium gallium phosphide layer and a work function reducing material is on the gallium arsenide layer. The substrate has an opening therethrough exposing a portion of the indium gallium phosphide layer.

  13. Integrated three-dimensional photonic nanostructures for achieving near-unity solar absorption and superhydrophobicity

    SciTech Connect (OSTI)

    Kuang, Ping; Lin, Shawn-Yu; Hsieh, Mei-Li

    2015-06-07

    In this paper, we proposed and realized 3D photonic nanostructures consisting of ultra-thin graded index antireflective coatings (ARCs) and woodpile photonic crystals. The use of the integrated ARC and photonic crystal structure can achieve broadband, broad-angle near unity solar absorption. The amorphous silicon based photonic nanostructure experimentally shows an average absorption of ∼95% for λ = 400–620 nm over a wide angular acceptance of θ = 0°–60°. Theoretical studies show that a Gallium Arsenide (GaAs) based structure can achieve an average absorption of >95% for λ = 400–870 nm. Furthermore, the use of the slanted SiO{sub 2} nanorod ARC surface layer by glancing angle deposition exhibits Cassie-Baxter state wetting, and superhydrophobic surface is obtained with highest water contact angle θ{sub CB} ∼ 153°. These properties are fundamentally important for achieving maximum solar absorption and surface self-cleaning in thin film solar cell applications.

  14. The efficiency limit of CH{sub 3}NH{sub 3}PbI{sub 3} perovskite solar cells

    SciTech Connect (OSTI)

    Sha, Wei E. I.; Ren, Xingang; Chen, Luzhou; Choy, Wallace C. H.

    2015-06-01

    With the consideration of photon recycling effect, the efficiency limit of methylammonium lead iodide (CH{sub 3}NH{sub 3}PbI{sub 3}) perovskite solar cells is predicted by a detailed balance model. To obtain convincing predictions, both AM 1.5 spectrum of Sun and experimentally measured complex refractive index of perovskite material are employed in the detailed balance model. The roles of light trapping and angular restriction in improving the maximal output power of thin-film perovskite solar cells are also clarified. The efficiency limit of perovskite cells (without the angular restriction) is about 31%, which approaches to Shockley-Queisser limit (33%) achievable by gallium arsenide (GaAs) cells. Moreover, the Shockley-Queisser limit could be reached with a 200?nm-thick perovskite solar cell, through integrating a wavelength-dependent angular-restriction design with a textured light-trapping structure. Additionally, the influence of the trap-assisted nonradiative recombination on the device efficiency is investigated. The work is fundamentally important to high-performance perovskite photovoltaics.

  15. High Efficiency Nanostructured III-V Photovoltaics for Solar Concentrator Application

    SciTech Connect (OSTI)

    Hubbard, Seth

    2012-09-12

    The High Efficiency Nanostructured III-V Photovoltaics for Solar Concentrators project seeks to provide new photovoltaic cells for Concentrator Photovoltaics (CPV) Systems with higher cell efficiency, more favorable temperature coefficients and less sensitivity to changes in spectral distribution. The main objective of this project is to provide high efficiency III-V solar cells that will reduce the overall cost per Watt for power generation using CPV systems.This work is focused both on a potential near term application, namely the use of indium arsenide (InAs) QDs to spectrally "tune" the middle (GaAs) cell of a SOA triple junction device to a more favorable effective bandgap, as well as the long term goal of demonstrating intermediate band solar cell effects. The QDs are confined within a high electric field i-region of a standard GaAs solar cell. The extended absorption spectrum (and thus enhanced short circuit current) of the QD solar cell results from the increase in the sub GaAs bandgap spectral response that is achievable as quantum dot layers are introduced into the i-region. We have grown InAs quantum dots by OMVPE technique and optimized the QD growth conditions. Arrays of up to 40 layers of strain balanced quantum dots have been experimentally demonstrated with good material quality, low residual stain and high PL intensity. Quantum dot enhanced solar cells were grown and tested under simulated one sun AM1.5 conditions. Concentrator solar cells have been grown and fabricated with 5-40 layers of QDs. Testing of these devices show the QD cells have improved efficiency compared to baseline devices without QDs. Device modeling and measurement of thermal properties were performed using Crosslight APSYS. Improvements in a triple junction solar cell with the insertion of QDs into the middle current limiting junction was shown to be as high as 29% under one sun illumination for a 10 layer stack QD enhanced triple junction solar cell. QD devices have strong potential for net gains in efficiency at high concentration.

  16. Efficient Schottky-like junction GaAs nanowire photodetector with 9?GHz modulation bandwidth with large active area

    SciTech Connect (OSTI)

    Seyedi, M. A. Yao, M.; O'Brien, J.; Wang, S. Y.; Dapkus, P. D.

    2014-07-28

    Efficient, low capacitance density GaAs/Indium-Tin-Oxide Schottky-like junction photodetectors with a 50??m square active are fabricated for operation in the gigahertz range. Modulation bandwidth is experimentally measured up to 10?GHz at various applied reverse biases and optical intensities to explore the effects of photo-generated carrier screening on modulation bandwidth. Last, the bandwidth dependence on applied reverse bias and optical intensity is simulated as a means to quantify average carrier velocities in nanowire material systems.

  17. Passivation of deep level states caused by misfit dislocations in InGaAs on patterned GaAs

    SciTech Connect (OSTI)

    Matragrano, M.J.; Watson, G.P.; Ast, D.G. ); Anderson, T.J.; Pathangey, B. )

    1993-03-22

    Deep level transient spectroscopy (DLTS) and cathodoluminescence (CL) were used to study the hydrogen passivation of misfit dislocations in In[sub 0.06]Ga[sub 0.94]As/GaAs heterostructures. The CL observations indicate that hydrogen plasma exposure passivates most, but not all, of the dark line defects existing in the specimen prior to hydrogenation. The concentration of deep level defect states that cannot be passivated is below the detection limit of the DLTS instrument (approximately 4[times]10[sup 12] cm[sup [minus]3]). We find the passivation is stable after anneals at temperatures as high as 600 [degree]C, indicating that hydrogen passivation of misfit dislocations is at least as stable as that of the isolated point defect studied previously with DLTS [W. C. Dautremont-Smith, J. C. Nabity, V. Swaminathan, M. Stavola, J. Chevalier, C. W. Tu, and S. J. Pearton, Appl. Phys. Lett. [bold 49] 1098 (1986)].

  18. Search for: All records | SciTech Connect

    Office of Scientific and Technical Information (OSTI)

    (5) indium arsenides (5) layers (4) molecular beam epitaxy (4) substrates (4) ... transport, materials and chemistry by design, optics, synthesis (novel materials), ...

  19. The role of screening of the electron-phonon interaction in relaxation of photoexcited electron-hole plasma in semiconductors

    SciTech Connect (OSTI)

    Kumekov, S. E.

    2008-08-15

    The role of screening of the interaction of the electron-hole plasma with optical phonons is analytically evaluated by the example of gallium arsenide.

  20. Bilayer Graphene Gets a Bandgap

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    nanoelectronics. This is a narrower bandgap than common semiconductors like silicon or gallium arsenide, and it could enable new kinds of optoelectronic devices for generating,...

  1. Search for: All records | SciTech Connect

    Office of Scientific and Technical Information (OSTI)

    arsenides (1) antennas (1) applied life sciences (1) biological functions (1) brain (1) computerized simulation (1) copper (1) copper plating. (1) deformation (1) design ...

  2. Effects of strain and quantum confinement in optically pumped nuclear magnetic resonance in GaAs: Interpretation guided by spin-dependent band structure calculations

    SciTech Connect (OSTI)

    Wood, R. M.; Saha, D.; McCarthy, L. A.; Tokarski, III, J. T.; Sanders, G. D.; Kuhns, P. L.; McGill, S. A.; Reyes, A. P.; Reno, J. L.; Stanton, C. J.; Bowers, C. R.

    2014-10-29

    A combined experimental-theoretical study of optically pumped NMR (OPNMR) has been performed in a GaAs/Al0.1Ga0.9As quantum well film with thermally induced biaxial strain. The photon energy dependence of the Ga-71 OPNMR signal was recorded at magnetic fields of 4.9 and 9.4 T at a temperature of 4.8-5.4 K. The data were compared to the nuclear spin polarization calculated from differential absorption to spin-up and spin-down states of the conduction band using a modified Pidgeon Brown model. Reasonable agreement between theory and experiment is obtained, facilitating assignment of features in the OPNMR energy dependence to specific interband transitions. Despite the approximations made in the quantum-mechanical model and the inexact correspondence between the experimental and calculated observables, the results provide insight into how effects of strain and quantum confinement are manifested in OPNMR signals

  3. Effects of strain and quantum confinement in optically pumped nuclear magnetic resonance in GaAs: Interpretation guided by spin-dependent band structure calculations

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Wood, R. M.; Saha, D.; McCarthy, L. A.; Tokarski, III, J. T.; Sanders, G. D.; Kuhns, P. L.; McGill, S. A.; Reyes, A. P.; Reno, J. L.; Stanton, C. J.; et al

    2014-10-29

    A combined experimental-theoretical study of optically pumped NMR (OPNMR) has been performed in a GaAs/Al0.1Ga0.9As quantum well film with thermally induced biaxial strain. The photon energy dependence of the Ga-71 OPNMR signal was recorded at magnetic fields of 4.9 and 9.4 T at a temperature of 4.8-5.4 K. The data were compared to the nuclear spin polarization calculated from differential absorption to spin-up and spin-down states of the conduction band using a modified Pidgeon Brown model. Reasonable agreement between theory and experiment is obtained, facilitating assignment of features in the OPNMR energy dependence to specific interband transitions. Despite the approximationsmore » made in the quantum-mechanical model and the inexact correspondence between the experimental and calculated observables, the results provide insight into how effects of strain and quantum confinement are manifested in OPNMR signals« less

  4. Oxygen vacancy induced magnetization switching in Fe{sub 3}O{sub 4} epitaxial ultrathin films on GaAs(100)

    SciTech Connect (OSTI)

    Huang, Zhaocong; Chen, Qian; Zhai, Ya E-mail: jlwang@seu.edu.cn; Wang, Jinlan E-mail: jlwang@seu.edu.cn; Xu, Yongbing; Wang, Baoping

    2015-05-04

    The magnetic and transport properties of half metallic Fe{sub 3}O{sub 4}, which are sensitive to the stoichiometry, are the key issue for applications in spintronics. An anomalous enlargement of the saturation magnetic moment is found in a relatively thick sample of epitaxial Fe{sub 3}O{sub 4} film by post-growth oxidation method. The investigation of the thickness dependence of magnetic moment suggests that the enhanced magnetism moment may come from the existence of oxygen vacancies. First-principles calculations reveal that with oxygen vacancies in Fe{sub 3}O{sub 4} crystal the spin of Fe ions in the tetrahedron site near the vacancy is much easier to switch parallel to the Fe ions in the octahedron site by temperature disturbance, supported by the temperature dependence of magnetic moment of Fe{sub 3}O{sub 4} films in experiment.

  5. GaAs, AlGaAs and InGaP Tunnel Junctions for Multi-Junction Solar Cells Under Concentration: Resistance Study

    SciTech Connect (OSTI)

    Wheeldon, Jeffrey F.; Valdivia, Christopher E.; Walker, Alex; Kolhatkar, Gitanja; Hall, Trevor J.; Hinzer, Karin; Masson, Denis; Riel, Bruno; Fafard, Simon; Jaouad, Abdelatif; Turala, Artur; Ares, Richard; Aimez, Vincent

    2010-10-14

    The following four TJ designs, AlGaAs/AlGaAs, GaAs/GaAs, AlGaAs/InGaP and AlGaAs/GaAs are studied to determine minimum doping concentration to achieve a resistance of <10{sup -4} {omega}{center_dot}cm{sup 2} and a peak tunneling current suitable for MJ solar cells up to 1500-suns concentration (operating current of 21 A/cm{sup 2}). Experimentally calibrated numerical models are used to determine how the resistance changes as a function of doping concentration. The AlGaAs/GaAs TJ design is determined to require the least doping concentration to achieve the specified resistance and peak tunneling current, followed by the GaAs/GaAs, and AlGaAs/AlGaAs TJ designs. The AlGaAs/InGaP TJ design can only achieve resistances >5x10{sup -4} {omega}cm{sup 2}.

  6. NREL preprints for the 23rd IEEE Photovoltaic Specialists Conference

    SciTech Connect (OSTI)

    Fitzgerald, M.

    1993-05-01

    Topics covered include various aspects of solar cell fabrication and performance. Aluminium-gallium arsenides, cadmium telluride, amorphous silicon, and copper-indium-gallium selenides are all characterized in their applicability in solar cells.

  7. SolarTec AG | Open Energy Information

    Open Energy Info (EERE)

    SolarTec AG Place: Munich, Bavaria, Germany Product: Developing a technology it calls Sol*Con- 700x Fresnel concentrators for use with gallium arsenide or germanium cells, also...

  8. Weyl Fermions Discovered After 85 Years

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    theorized 85 years ago: the Weyl fermion. It was detected as an emergent quasiparticle in synthetic crystals of the semimetal, tantalum arsenide (TaAs). Using angle-resolved...

  9. Buildings Energy Data Book: 1.6 Embodied Energy of Building Assemblies

    Buildings Energy Data Book [EERE]

    6 Embodied Energy of Commercial Interior Wall Assemblies in the U.S. Embodied Energy CO2 Equivalent Interior Wall Type (2) (MMBtu/SF) (1) Emissions (lbs/SF) 2x4 wood stud (16" OC) + gypsum board (3) 0.03 2.84 2x4 wood stud (24" OC) + gypsum board (3) 0.03 2.78 2x4 wood stud (24" OC) + 2 gypsum boards (4) 0.04 4.45 Steel stud (16" OC) + gypsum board (4) 0.04 3.99 Steel stud (24" OC) + gypsum board (4) 0.04 3.64 Steel stud (24" OC) + 2 gypsum boards 0.05 5.31 6"

  10. Building America Research-to-Market Plan

    Office of Energy Efficiency and Renewable Energy (EERE) Indexed Site

    ... Levy, E., M. Mullens, E. Tompos, B. Kessler, P. Rath. Expert Meeting Report: Advanced ... US Gypsum Company. "Moisture, Mold, and Construction Practices." 2007. Wiehagen, J., and ...

  11. Eagle County, Colorado: Energy Resources | Open Energy Information

    Open Energy Info (EERE)

    Colorado Edwards, Colorado El Jebel, Colorado Gypsum, Colorado Minturn, Colorado Red Cliff, Colorado Vail, Colorado Retrieved from "http:en.openei.orgw...

  12. Building America Technlogy Solutions for New and Existing Homes...

    Office of Energy Efficiency and Renewable Energy (EERE) Indexed Site

    to improve performance and mitigate moisture issues: dimple mat; spray polyurethane foam insulation; moisture and thermal management systems for the floor; and paperless gypsum...

  13. Luminescence properties of light-emitting diodes based on GaAs with the up-conversion Y{sub 2}O{sub 2}S:Er,Yb luminophor

    SciTech Connect (OSTI)

    Gruzintsev, A. N. [Russian Academy of Sciences, Institute of Problems of Microelectronics Technology (Russian Federation)], E-mail: gran@ipmt-hpm.ac.ru; Barthou, C.; Benalloul, P. [Institute des NanoSciences (France)

    2008-03-15

    Y{sub 2}O{sub 2}S luminophors doped with Er{sup 3+} and Yb{sup 3+} ions are produced by means of solid-phase synthesis and deposited onto standard AL123A infrared light-emitting diodes. When excited with 940 nm radiation from a light-emitting diode, the structures exhibit intense visible up-conversion luminescence. A maximal brightness of 2340 cd/m{sup 2} of green and red up-conversion luminescence at corresponding wavelengths around 550 and 600 nm is observed for the Y{sub 2}O{sub 2}S compound doped with 2 at % Er{sup 3+} ions and 6 at % Yb{sup 3+} ions. The ratio of the intensity of green (or red) up-conversion luminescence to the intensity of infrared Stokes luminescence increases with increasing applied voltage. The efficiency of visible emission of the light-emitting diode structures is {eta} = 1.2 lm/W at an applied voltage of 1.5 V.

  14. Recent Progress toward Robust Photocathodes

    SciTech Connect (OSTI)

    Mulhollan, G. A.; Bierman, J. C. [Saxet Surface Science, Austin, TX 78744 (United States)

    2009-08-04

    RF photoinjectors for next generation spin-polarized electron accelerators require photo-cathodes capable of surviving RF gun operation. Free electron laser photoinjectors can benefit from more robust visible light excited photoemitters. A negative electron affinity gallium arsenide activation recipe has been found that diminishes its background gas susceptibility without any loss of near bandgap photoyield. The highest degree of immunity to carbon dioxide exposure was achieved with a combination of cesium and lithium. Activated amorphous silicon photocathodes evince advantageous properties for high current photoinjectors including low cost, substrate flexibility, visible light excitation and greatly reduced gas reactivity compared to gallium arsenide.

  15. Clean process to destroy arsenic-containing organic compounds with recovery of arsenic

    DOE Patents [OSTI]

    Upadhye, Ravindra S. (Pleasanton, CA); Wang, Francis T. (Danville, CA)

    1996-01-01

    A reduction method is provided for the treatment of arsenic-containing organic compounds with simultaneous recovery of pure arsenic. Arsenic-containing organic compounds include pesticides, herbicides, and chemical warfare agents such as Lewisite. The arsenic-containing compound is decomposed using a reducing agent. Arsine gas may be formed directly by using a hydrogen-rich reducing agent, or a metal arsenide may be formed using a pure metal reducing agent. In the latter case, the arsenide is reacted with an acid to form arsine gas. In either case, the arsine gas is then reduced to elemental arsenic.

  16. Clean process to destroy arsenic-containing organic compounds with recovery of arsenic

    DOE Patents [OSTI]

    Upadhye, R.S.; Wang, F.T.

    1996-08-13

    A reduction method is provided for the treatment of arsenic-containing organic compounds with simultaneous recovery of pure arsenic. Arsenic-containing organic compounds include pesticides, herbicides, and chemical warfare agents such as Lewisite. The arsenic-containing compound is decomposed using a reducing agent. Arsine gas may be formed directly by using a hydrogen-rich reducing agent, or a metal arsenide may be formed using a pure metal reducing agent. In the latter case, the arsenide is reacted with an acid to form arsine gas. In either case, the arsine gas is then reduced to elemental arsenic. 1 fig.

  17. Low dimensional GaAs/air vertical microcavity lasers

    SciTech Connect (OSTI)

    Gessler, J.; Steinl, T.; Fischer, J.; Hfling, S.; Schneider, C.; Kamp, M.; Mika, A.; S?k, G.; Misiewicz, J.

    2014-02-24

    We report on the fabrication of gallium arsenide (GaAs)/air distributed Bragg reflector microresonators with indium gallium arsenide quantum wells. The structures are studied via momentum resolved photoluminescence spectroscopy which allows us to investigate a pronounced optical mode quantization of the photonic dispersion. We can extract a length parameter from these quantized states whose upper limit can be connected to the lateral physical extension of the microcavity via analytical calculations. Laser emission from our microcavity under optical pumping is observed in power dependent investigations.

  18. Profiling the Built-In Electrical Potential in III-V Multijunction Solar Cells (Poster)

    SciTech Connect (OSTI)

    Jiang, C.-S.; Friedman, D. J.; Moutinho, H. R.; Al-Jassim, M. M.

    2006-05-01

    We have observed three electrical potentials at the top, tunneling, and bottom junctions of GnInP{sub 2}/GaAs tandem-junction solar cells, by performing the UHV-SKPM measurement. The effect of laser illumination was avoided by using GaAs laser with photon energy of 1.4 eV for the AFM operation. We also observed higher potentials at the atomic steps than on the terraces for both p-type GaInP{sub 2} epitaxial layer and p-type GaAs substrate, and found that the potential at steps of GaAs substrate depends on the step directions.

  19. MANUSCRIPT PREPARATION TEMPLATE FOR THE 35TH IEEE PHOTOVOLTAIC...

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    few micrometers. GaAs is used extensively as one of the primary junctions for multi- junction photovoltaic (PV) cells for space applications and concentrator modules. Despite the...

  20. Technology Solutions Case Study: Interior Foundation Insulation Upgrade-Minneapolis Residence

    SciTech Connect (OSTI)

    2013-10-01

    This interior foundation project employed several techniques to improve performance and mitigate moisture issues: dimple mat; spray polyurethane foam insulation; moisture and thermal management systems for the floor; and paperless gypsum board and steel framing.

  1. Environmental chamber measurements of mercury flux from coal utilization by-products

    SciTech Connect (OSTI)

    Pekney, Natalie J.; Martello, Donald; Schroeder, Karl; Granite, Evan

    2009-05-01

    An environmental chamber was constructed to measure the mercury flux from coal utilization by-product (CUB) samples. Samples of fly ash, FGD gypsum, and wallboard made from FGD gypsum were tested under both dark and illuminated conditions with or without the addition of water to the sample. Mercury releases varied widely, with 7- day experiment averages ranging from -6.8 to 73 ng/m(2) h for the fly ash samples and -5.2 to 335 ng/m(2) h for the FGD/wallboard samples. Initial mercury content, fly ash type, and light exposure had no observable consistent effects on the mercury flux. For the fly ash samples, the effect of a mercury control technology was to decrease the emission. For three of the four pairs of FGD gypsum and wallboard samples, the wallboard sample released less (or absorbed more) mercury than the gypsum.

  2. Environmental chamber measurements of mercury flux from coal utilization by-products

    SciTech Connect (OSTI)

    Pekney, N.J.; Martello, D.V.; Schroeder, K.T.; Granite, E.J.

    2009-05-01

    An environmental chamber was constructed to measure the mercury flux from coal utilization by-product (CUB) samples. Samples of fly ash, FGD gypsum, and wallboard made from FGD gypsum were tested under both dark and illuminated conditions with or without the addition of water to the sample. Mercury releases varied widely, with 7-day experiment averages ranging from -6.8 to 73 ng/m2 h for the fly ash samples and -5.2 to 335 ng/m2 h for the FGD/wallboard samples. Initial mercury content, fly ash type, and light exposure had no observable consistent effects on the mercury flux. For the fly ash samples, the effect of a mercury control technology was to decrease the emission. For three of the four pairs of FGD gypsum and wallboard samples, the wallboard sample released less (or absorbed more) mercury than the gypsum.

  3. bedka_turner_poster.ppt

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    especially for the kaolinite+gypsum retrievals. Questions or comments? sarahb@ssec.wisc.edu, dturner@ssec.wisc.edu The 3 periods have significant diurnal variations in surface...

  4. Resume 11-25-94

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    fly ash and flue-gas gypsum: Intact soil cores and repacked columns. Water, Air Soil Pollution. 134:285-303 (SREL 2586). Vulava, V.M., E.B. Perry, C.S. Romanek, and J.C. Seaman....

  5. Preliminary materials assessment for the Satellite Power System (SPS)

    SciTech Connect (OSTI)

    Teeter, R.R.; Jamieson, W.M.

    1980-01-01

    Presently, there are two SPS reference design concepts (one using silicon solar cells; the other using gallium arsenide solar cells). A materials assessment of both systems was performed based on the materials lists set forth in the DOE/NASA SPS Reference System Report: Concept Development and Evaluation Program. This listing identified 22 materials (plus miscellaneous and organics) used in the SPS. Tracing the production processes for these 22 materials, a total demand for over 20 different bulk materials (copper, silicon, sulfuric acid, etc.) and nealy 30 raw materials (copper ore, sand, sulfur ore, etc.) was revealed. Assessment of these SPS material requirements produced a number of potential material supply problems. The more serious problems are those associated with the solar cell materials (gallium, gallium arsenide, sapphire, and solar grade silicon), and the graphite fiber required for the satellite structure and space construction facilities. In general, the gallium arsenide SPS option exhibits more serious problems than the silicon option, possibly because gallium arsenide technology is not as well developed as that for silicon. Results are presented and discussed in detail. (WHK)

  6. Resonant Spin Excitation in the High Temperature Superconductor Ba0.6K0.4Fe2As2

    SciTech Connect (OSTI)

    Christianson, Andrew D; Goremychkin, E. A.; Osborn, R.; Rosenkranz, Stephen; Lumsden, Mark D; Malliakas, C.; Todorov, L.; Claus, H.; Chung, D.Y.; Kanatzidis, M.; Bewley, Robert I.; Guidi, T.

    2008-12-18

    A new family of superconductors containing layers of iron arsenide has attracted considerable interest because of their high transition temperatures (T{sub c}), some of which are >50 K, and because of similarities with the high-{sub c} copper oxide superconductors. In both the iron arsenides and the copper oxides, superconductivity arises when an antiferromagnetically ordered phase has been suppressed by chemical doping. A universal feature of the copper oxide superconductors is the existence of a resonant magnetic excitation, localized in both energy and wavevector, within the superconducting phase. This resonance, which has also been observed in several heavy-fermion superconductors is predicted to occur when the sign of the superconducting energy gap takes opposite values on different parts of the Fermi surface, an unusual gap symmetry which implies that the electron pairing interaction is repulsive at short range. Angle-resolved photoelectron spectroscopy shows no evidence of gap anisotropy in the iron arsenides, but such measurements are insensitive to the phase of the gap on separate parts of the Fermi surface. Here we report inelastic neutron scattering observations of a magnetic resonance below T{sub c} in Ba{sub 0.6}K{sub 0.4}Fe{sub 2}As{sub 2}, a phase-sensitive measurement demonstrating that the superconducting energy gap has unconventional symmetry in the iron arsenide superconductors.

  7. Simple intrinsic defects in InAs : numerical predictions.

    SciTech Connect (OSTI)

    Schultz, Peter Andrew

    2013-03-01

    This Report presents numerical tables summarizing properties of intrinsic defects in indium arsenide, InAs, as computed by density functional theory using semi-local density functionals, intended for use as reference tables for a defect physics package in device models.

  8. Method of making suspended thin-film semiconductor piezoelectric devices

    DOE Patents [OSTI]

    Casalnuovo, Stephen A.; Frye-Mason, Gregory C.

    2001-01-01

    A process for forming a very thin suspended layer of piezoelectric material of thickness less than 10 microns. The device is made from a combination of GaAs and AlGaAs layers to form either a sensor or an electronic filter. Onto a GaAs substrate is epitaxially deposited a thin (1-5 micron) sacrificial AlGaAs layer, followed by a thin GaAs top layer. In one embodiment the substrate is selectively etched away from below until the AlGaAs layer is reached. Then a second selective etch removes the sacrificial AlGaAs layer, that has acted here as an etch stop, leaving the thin suspended layer of piezoelectric GaAs. In another embodiment, a pattern of small openings is etched through the thin layer of GaAs on top of the device to expose the sacrificial AlGaAs layer. A second selective etch is done through these openings to remove the sacrificial AlGaAs layer, leaving the top GaAs layer suspended over the GaAs substrate. A novel etchant solution containing a surface tension reducing agent is utilized to remove the AlGaAs while preventing buildup of gas bubbles that would otherwise break the thin GaAs layer.

  9. Low-cost, high-efficiency solar cells utilizing GaAs-on-Si technology

    SciTech Connect (OSTI)

    Vernon, S.M. )

    1993-04-01

    This report describes work to develop technology to deposit GaAs on Si using a nucleation layer of atomic-layer-epitaxy-grown GaAs or AlAs on Si. This ensures two-dimensional nucleation and should lead to fewer defects in the final GaAs layer. As an alternative, we also developed technology for depositing GaAs on sawtooth-patterned Si. Preliminary studies showed that this material can have a very low defect density, [approximately] 1 [times] 10[sup 5] cm[sup [minus]5], as opposed to our conventionally grown GaAs on SL which has a typical defect density of over 1 [times]10[sup 7] cm[sup [minus]2]. Using these two now methods of GaAs-on-Si material growth, we made solar cells that are expected to show higher efficiencies than those of previous cells.

  10. Low-cost, high-efficiency solar cells utilizing GaAs-on-Si technology. Annual subcontract report, 1 August 1991--31 July 1992

    SciTech Connect (OSTI)

    Vernon, S.M.

    1993-04-01

    This report describes work to develop technology to deposit GaAs on Si using a nucleation layer of atomic-layer-epitaxy-grown GaAs or AlAs on Si. This ensures two-dimensional nucleation and should lead to fewer defects in the final GaAs layer. As an alternative, we also developed technology for depositing GaAs on sawtooth-patterned Si. Preliminary studies showed that this material can have a very low defect density, {approximately} 1 {times} 10{sup 5} cm{sup {minus}5}, as opposed to our conventionally grown GaAs on SL which has a typical defect density of over 1 {times}10{sup 7} cm{sup {minus}2}. Using these two now methods of GaAs-on-Si material growth, we made solar cells that are expected to show higher efficiencies than those of previous cells.

  11. Monolithic high voltage nonlinear transmission line fabrication process

    DOE Patents [OSTI]

    Cooper, G.A.

    1994-10-04

    A process for fabricating sequential inductors and varistor diodes of a monolithic, high voltage, nonlinear, transmission line in GaAs is disclosed. An epitaxially grown laminate is produced by applying a low doped active n-type GaAs layer to an n-plus type GaAs substrate. A heavily doped p-type GaAs layer is applied to the active n-type layer and a heavily doped n-type GaAs layer is applied to the p-type layer. Ohmic contacts are applied to the heavily doped n-type layer where diodes are desired. Multiple layers are then either etched away or Oxygen ion implanted to isolate individual varistor diodes. An insulator is applied between the diodes and a conductive/inductive layer is thereafter applied on top of the insulator layer to complete the process. 6 figs.

  12. Monolithic high voltage nonlinear transmission line fabrication process

    DOE Patents [OSTI]

    Cooper, Gregory A. (346 Primrose Dr., Pleasant Hill, CA 94523)

    1994-01-01

    A process for fabricating sequential inductors and varactor diodes of a monolithic, high voltage, nonlinear, transmission line in GaAs is disclosed. An epitaxially grown laminate is produced by applying a low doped active n-type GaAs layer to an n-plus type GaAs substrate. A heavily doped p-type GaAs layer is applied to the active n-type layer and a heavily doped n-type GaAs layer is applied to the p-type layer. Ohmic contacts are applied to the heavily doped n-type layer where diodes are desired. Multiple layers are then either etched away or Oxygen ion implanted to isolate individual varactor diodes. An insulator is applied between the diodes and a conductive/inductive layer is thereafter applied on top of the insulator layer to complete the process.

  13. DEDALOS NREL: Cooperative Research and Development Final Report, CRADA Number CRD-07-237

    SciTech Connect (OSTI)

    Friedman, D.

    2013-06-01

    Currently High Concentration Photovoltaic (HCPV) terrestrial modules are based on the combination of optic elements that concentrate the sunlight into much smaller GaAs space cells to produce electricity. GaAs cell technology has been well developed for space applications during the last two decades, but the use of GaAs cells under concentrated sunlight in terrestrial applications leaves unanswered questions about performance, durability and reliability. The work to be performed under this CRADA will set the basis for the design of high-performance, durable and reliable HCPV terrestrial modules that will bring down electricity production costs in the next five years.

  14. Comparison of steady-state and transient characteristics of lattice-matched and strained InGaAs-AlGaAs (on GaAs) and InGaAs-AlInAs (on InP) quantum-well lasers

    SciTech Connect (OSTI)

    Lam, Y.; Singh, J. ); Loehr, J.P. )

    1992-05-01

    This paper reports on numerical techniques to study the output spectra and to solve the multimode coupled rate equations including TE and TM propagations for In{sub x}Ga{sub 1{minus}x}As-Al{sub 0.3}Ga{sub 0.7}As and In{sub 0.53+x}Ga{sub 0.47{minus}x}As-Al{sub 0.48}In{sub 0.52}As quantum well lasers. Optical properties are calculated from a 4 {times} 4 k {center dot} p bandstructure and strain effects are included with the deformation potential theory. The authors find that an introduction of 1.4% compressive strain to the quantum well results in roughly 3-4 times improvement in the intrinsic static characteristics in terms of lower threshold current, greater mode suppression, and lower nonlashing photon population in the laser cavity. The authors also identify the role of strain on the large signal temporal response. If the laser is switched from the off state to a given photon density in the lasing mode, then the strained system exhibits a faster intrinsic time response. However, if the lasers are switched to equal total photon density, then the strained system has a slower time response. The authors also include calculated CHSH Auger rates in our model and find that the main effect of Auger recombination is to greatly increase the threshold current and to shorten the response time to large signal switching.

  15. Summer 2011 Intern Project- Eric Ling | Center for Energy Efficient

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    Materials Eric Ling THERMOELECTRIC PROPERTIES OF DOPED InGaAs Eric Ling Physics and Mathamatics UC Santa Barbara Mentor: Borzoyeh Shojaei Faculty Advisor: Chris Pamlstrom Department: Electrical and Computer Engineering In recent history, thermeoelectrics have shown to be promising materials for energy conversion via wasted heat to electricity. One such material, indium gallium arsenide (InGaAs), may possess a high electrical conductivity term in the thermoelectric figure of merit when doped

  16. Weyl Fermions Discovered After 85 Years

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    Weyl Fermions Discovered After 85 Years Print An international team led by Princeton University scientists has discovered an elusive massless particle first theorized 85 years ago: the Weyl fermion. It was detected as an emergent quasiparticle in synthetic crystals of the semimetal, tantalum arsenide (TaAs). Using angle-resolved photoemission spectroscopy (ARPES), the researchers studied the surface and bulk band structure of TaAs. The results exhibit the features-cones, nodes, and arcs-that

  17. Weyl Fermions Discovered After 85 Years

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    Weyl Fermions Discovered After 85 Years Print An international team led by Princeton University scientists has discovered an elusive massless particle first theorized 85 years ago: the Weyl fermion. It was detected as an emergent quasiparticle in synthetic crystals of the semimetal, tantalum arsenide (TaAs). Using angle-resolved photoemission spectroscopy (ARPES), the researchers studied the surface and bulk band structure of TaAs. The results exhibit the features-cones, nodes, and arcs-that

  18. Weyl Fermions Discovered After 85 Years

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    Weyl Fermions Discovered After 85 Years Weyl Fermions Discovered After 85 Years Print Wednesday, 09 December 2015 00:00 An international team led by Princeton University scientists has discovered an elusive massless particle first theorized 85 years ago: the Weyl fermion. It was detected as an emergent quasiparticle in synthetic crystals of the semimetal, tantalum arsenide (TaAs). Using angle-resolved photoemission spectroscopy (ARPES), the researchers studied the surface and bulk band structure

  19. Weyl Fermions Discovered After 85 Years

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    Weyl Fermions Discovered After 85 Years Print An international team led by Princeton University scientists has discovered an elusive massless particle first theorized 85 years ago: the Weyl fermion. It was detected as an emergent quasiparticle in synthetic crystals of the semimetal, tantalum arsenide (TaAs). Using angle-resolved photoemission spectroscopy (ARPES), the researchers studied the surface and bulk band structure of TaAs. The results exhibit the features-cones, nodes, and arcs-that

  20. Weyl Fermions Discovered After 85 Years

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    Weyl Fermions Discovered After 85 Years Print An international team led by Princeton University scientists has discovered an elusive massless particle first theorized 85 years ago: the Weyl fermion. It was detected as an emergent quasiparticle in synthetic crystals of the semimetal, tantalum arsenide (TaAs). Using angle-resolved photoemission spectroscopy (ARPES), the researchers studied the surface and bulk band structure of TaAs. The results exhibit the features-cones, nodes, and arcs-that

  1. Weyl Fermions Discovered After 85 Years

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    Weyl Fermions Discovered After 85 Years Print An international team led by Princeton University scientists has discovered an elusive massless particle first theorized 85 years ago: the Weyl fermion. It was detected as an emergent quasiparticle in synthetic crystals of the semimetal, tantalum arsenide (TaAs). Using angle-resolved photoemission spectroscopy (ARPES), the researchers studied the surface and bulk band structure of TaAs. The results exhibit the features-cones, nodes, and arcs-that

  2. Weyl Fermions Discovered After 85 Years

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    Weyl Fermions Discovered After 85 Years Print An international team led by Princeton University scientists has discovered an elusive massless particle first theorized 85 years ago: the Weyl fermion. It was detected as an emergent quasiparticle in synthetic crystals of the semimetal, tantalum arsenide (TaAs). Using angle-resolved photoemission spectroscopy (ARPES), the researchers studied the surface and bulk band structure of TaAs. The results exhibit the features-cones, nodes, and arcs-that

  3. Advanced Flue Gas Desulfurization (AFGD) demonstration project: Volume 2, Project performance and economics. Final technical report

    SciTech Connect (OSTI)

    1996-04-30

    The project objective is to demonstrate removal of 90--95% or more of the SO{sub 2} at approximately one-half the cost of conventional scrubbing technology; and to demonstrate significant reduction of space requirements. In this project, Pure Air has built a single SO{sub 2} absorber for a 528-MWe power plant. The absorber performs three functions in a single vessel: prequencher, absorber, and oxidation of sludge to gypsum. Additionally, the absorber is of a co- current design, in which the flue gas and scrubbing slurry move in the same direction and at a relatively high velocity compared to conventional scrubbers. These features all combine to yield a state- of-the-art SO{sub 2} absorber that is more compact and less expensive than conventional scrubbers. The project incorporated a number of technical features including the injection of pulverized limestone directly into the absorber, a device called an air rotary sparger located within the base of the absorber, and a novel wastewater evaporation system. The air rotary sparger combines the functions of agitation and air distribution into one piece of equipment to facilitate the oxidation of calcium sulfite to gypsum. Additionally, wastewater treatment is being demonstrated to minimize water disposal problems inherent in many high-chloride coals. Bituminous coals primarily from the Indiana, Illinois coal basin containing 2--4.5% sulfur were tested during the demonstration. The Advanced Flue Gas Desulfurization (AFGD) process has demonstrated removal of 95% or more of the SO{sub 2} while providing a commercial gypsum by-product in lieu of solid waste. A portion of the commercial gypsum is being agglomerated into a product known as PowerChip{reg_sign} gypsum which exhibits improved physical properties, easier flowability and more user friendly handling characteristics to enhance its transportation and marketability to gypsum end-users.

  4. Buildings Energy Data Book: 9.4 High Performance Buildings

    Buildings Energy Data Book [EERE]

    4 Case Study, The Philip Merrill Environmental Center, Annapolis, Maryland (Office) Building Design Floor Area: 31,000 SF Floors: 2 Footprint: 220 ft. x (1) 2 Floors of open office space Attached pavilion containing: Meeting space Kitchen Staff dining Conference room Shell Windows U-Factor SHGC (2) Type: Double Pane, Low-e, Argon Filled Insulating Glass 0.244 0.41 Wall/Roof Material Effective R-Value Interior Wall plywood, gypsum, SIP foam, and sheathing 28.0 Exterior Wall gypsum and insulated

  5. Ferromagnetic thin films

    DOE Patents [OSTI]

    Krishnan, K.M.

    1994-12-20

    A ferromagnetic [delta]-Mn[sub 1[minus]x]Ga[sub x] thin film having perpendicular anisotropy is described which comprises: (a) a GaAs substrate, (b) a layer of undoped GaAs overlying said substrate and bonded thereto having a thickness ranging from about 50 to about 100 nanometers, (c) a layer of [delta]-Mn[sub 1[minus]x]Ga[sub x] overlying said layer of undoped GaAs and bonded thereto having a thickness ranging from about 20 to about 30 nanometers, and (d) a layer of GaAs overlying said layer of [delta]-Mn[sub 1[minus]x]Ga[sub x] and bonded thereto having a thickness ranging from about 2 to about 5 nanometers, wherein x is 0.4[+-]0.05. 7 figures.

  6. Search for: All records | SciTech Connect

    Office of Scientific and Technical Information (OSTI)

    Reabsorption of Soft X-Ray Emission at High X-Ray ... absorption (TPA) of below-band-gap radiation in CdSe QDs. ... and ultrafast pumpprobe processes in semiconductors (GaAs). ...

  7. Cyrium Technologies Inc | Open Energy Information

    Open Energy Info (EERE)

    Place: Ottowa, Ontario, Canada Zip: K1A 0R6 Product: Canadian manufacturer of GaAs photovoltaic (PV) cells for terrestrial and space use. Coordinates: 38.554325, -121.784714...

  8. Photonic Power Systems Inc | Open Energy Information

    Open Energy Info (EERE)

    Zip: 95014-2305 Product: Provider of GaAs and InP-based solutions for delivering electrical power over fibre for numerous electronic applications. Coordinates: 37.31884,...

  9. AIXTRON AG | Open Energy Information

    Open Energy Info (EERE)

    industry. Their equipment is used in the manufacture of LEDs, germanium and GaAs solar cells and OLEDs. Coordinates: 50.778138, 6.088498 Show Map Loading map......

  10. Investigation of the GaN-on-GaAs interface for vertical power device applications

    SciTech Connect (OSTI)

    Mreke, Janina Uren, Michael J.; Kuball, Martin; Novikov, Sergei V.; Foxon, C. Thomas; Hosseini Vajargah, Shahrzad; Wallis, David J.; Humphreys, Colin J.; Haigh, Sarah J.; Al-Khalidi, Abdullah; Wasige, Edward; Thayne, Iain

    2014-07-07

    GaN layers were grown onto (111) GaAs by molecular beam epitaxy. Minimal band offset between the conduction bands for GaN and GaAs materials has been suggested in the literature raising the possibility of using GaN-on-GaAs for vertical power device applications. I-V and C-V measurements of the GaN/GaAs heterostructures however yielded a rectifying junction, even when both sides of the junction were heavily doped with an n-type dopant. Transmission electron microscopy analysis further confirmed the challenge in creating a GaN/GaAs Ohmic interface by showing a large density of dislocations in the GaN layer and suggesting roughening of the GaN/GaAs interface due to etching of the GaAs by the nitrogen plasma, diffusion of nitrogen or melting of Ga into the GaAs substrate.

  11. Search for: All records | SciTech Connect

    Office of Scientific and Technical Information (OSTI)

    ... adsorb on the GaAs(111)sub B surface compared to the liquid gold catalyst surface and the interface between the gold catalyst droplet and the nanowire, andmore these adsorbed ...

  12. SolFocus Inc | Open Energy Information

    Open Energy Info (EERE)

    Inc Place: California Zip: 94043 Product: California-based developer of high concentration PV (CPV) technology using triple junction GaAs cells. References: SolFocus Inc1...

  13. Technical Session II Talks | U.S. DOE Office of Science (SC)

    Office of Science (SC) Website

    Print Text Size: A A A FeedbackShare Page Detector R&D at LBNL (Denes) .pdf file (6.2MB) GaAs Detector (Durbin) .pdf file (450KB) Advanced Neutron Detectors (Smith) .pdf file ...

  14. Reply to “Comment on ‘Optically pumped spin-exchange polarized-electron source’ ”

    SciTech Connect (OSTI)

    Pirbhai, M.; Knepper, J.; Litaker, E. T.; Tupa, D.; Gay, T. J.

    2015-05-26

    In the proceeding Comment [1] on our recent report of a Rb spin-exchange polarized-electron source [2], Williams et al. contend: (a) that our source is poorly characterized compared with modern GaAs sources, (b) that we have overstated the difficulties of using GaAs photoemission sources, and (c) that our explanation of various physics issues related to the source's operating principles are not cogent.

  15. Reply to “Comment on ‘Optically pumped spin-exchange polarized-electron source’ ”

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Pirbhai, M.; Knepper, J.; Litaker, E. T.; Tupa, D.; Gay, T. J.

    2015-05-26

    In the proceeding Comment [1] on our recent report of a Rb spin-exchange polarized-electron source [2], Williams et al. contend: (a) that our source is poorly characterized compared with modern GaAs sources, (b) that we have overstated the difficulties of using GaAs photoemission sources, and (c) that our explanation of various physics issues related to the source's operating principles are not cogent.

  16. New GaInP/GaAs/GaInAs, Triple-Bandgap, Tandem Solar Cell for High-Efficiency Terrestrial Concentrator Systems

    SciTech Connect (OSTI)

    Kurtz, S.; Wanlass, M.; Kramer, C.; Young, M.; Geisz, J.; Ward, S.; Duda, A.; Moriarty, T.; Carapella, J.; Ahrenkiel, P.; Emery. K.; Jones, K.; Romero, M.; Kibbler, A.; Olson, J.; Friedman, D.; McMahon, W.; Ptak, A.

    2005-11-01

    GaInP/GaAs/GaInAs three-junction cells are grown in an inverted configuration on GaAs, allowing high quality growth of the lattice matched GaInP and GaAs layers before a grade is used for the 1-eV GaInAs layer. Using this approach an efficiency of 37.9% was demonstrated.

  17. Cavity-enhanced single photon emission from site-controlled In(Ga)As quantum dots fabricated using nanoimprint lithography

    SciTech Connect (OSTI)

    Tommila, J.; Hakkarainen, T. V.; Schramm, A. Guina, M.; Belykh, V. V.; Sibeldin, N. N.; Heinonen, E.

    2014-05-26

    We report on the emission dynamics of single In(Ga)As quantum dots formed in etched GaAs pits and integrated into micropillar cavities. The site-controlled quantum dots were fabricated by molecular beam epitaxy on nanoimprint lithography patterned GaAs(001) surfaces. Triggered single photon emission confirmed by photon autocorrelation measurements is demonstrated. Time-resolved photoluminescence experiments clearly show an effect of the cavity on the spontaneous emission rate of the quantum dot.

  18. Carbon doping of III-V compound semiconductors

    SciTech Connect (OSTI)

    Moll, A.J.

    1994-09-01

    Focus of the study is C acceptor doping of GaAs, since C diffusion coefficient is at least one order of magnitude lower than that of other common p-type dopants in GaAs. C ion implantation results in a concentration of free holes in the valence band < 10% of that of the implanted C atoms for doses > 10{sup 14}/cm{sup 2}. Rutherford backscattering, electrical measurements, Raman spectroscopy, and Fourier transform infrared spectroscopy were amonth the techniques used. Ga co-implantation increased the C activation in two steps: first, the additional radiation damage creates vacant As sites that the implanted C can occupy, and second, it maintains the stoichiometry of the implanted layer, reducing the number of compensating native defects. In InP, the behavior of C was different from that in GaAs. C acts as n-type dopant in the In site; however, its incorporation by implantation was difficult to control; experiments using P co-implants were inconsistent. The lattice position of inactive C in GaAs in implanted and epitaxial layers is discussed; evidence for formation of C precipitates in GaAs and InP was found. Correlation of the results with literature on C doping in III-V semiconductors led to a phenomenological description of C in III-V compounds (particularly GaAs): The behavior of C is controlled by the chemical nature of C and the instrinsic Fermi level stabilization energy of the material.

  19. Petrology of lower and middle Eocene carbonate rocks, Floridan aquifer, central Florida

    SciTech Connect (OSTI)

    Thayer, P.A.; Miller, J.A.

    1984-09-01

    Study of cores from a US Geological Survey test well near Polk City, Florida, indicates that the Avon Park-Lake City (Claibornian) and Oldsmar (Sabinian) Limestones, which comprise most of the Floridan aquifer in central Florida, can be divided into six microfacies: foraminiferal mudstone, foraminiferal wackestone-packstone, foraminiferal grainstone, nodular anhydrite, laminated dolomicrite, and replacement dolomite. Dolomite containing variable amounts of nodular anhydrite forms more than 90% of the Avon Park-Lake city interval, whereas thte Oldsmar is chiefly limestone. Several episodes of dolomite formation are recognized. Laminated dolomicrite formed syngenetically in a supratidal-sabhka environment. Crystalline dolomite with nodular anhydrite formed early by replacement of limestone through reflux of dense, magnesium-rich brines. Replacement dolomite not associated with evaporites and containing limpid crystals probably formed later by a mixed-water process in the subsurface environment. Late diagenetic processes affecting crystalline dolomites include hydration of anhydrite to gypsum, partial dissolution of gypsum, minor alteration of gypsum to calcite, and dissolution of calcian dolomite cores in stoichiometric crystals. Crystalline dolomite and grainstone are the only rock types that have high enough porosities and permeabilities to provide significant yields of water. Medium and finely crystalline dolomites show best values of porosity and permeability because they have high percentages of intercrystal and moldic pores that are well connected. Filling of pores by anhydrite or gypsum can significantly reduce porosity and permeability.

  20. Effect of curing conditions on the geotechnical and geochemical properties of CFBC ashes

    SciTech Connect (OSTI)

    Bland, A.E.

    1999-07-01

    Western Research Institute, in cooperation with the US Department of Energy Federal Energy Technology Center, initiated a multi-year program to examine the relationship between CFBC ash chemistry and geotechnical properties as they relate to ash disposal and utilization. Four CFBC facilities supplied ash from their units for the study representing high-sulfur (4%) and medium-sulfur (1.8%) bituminous coal. Sub-bituminous coal (0.9% sulfur) and petroleum coke (5--6% sulfur) fired ashes were also included in the study. The ashes were composed principally of large quantities of anhydrite (CaSO{sub 4}) and lime (CaO) and minor amounts of calcite (CaCO{sub 3}). The ash curing study addressed the impact of curing conditions (sealed and saturated curing and 23 C and 5 C curing temperature) on the geochemical and geotechnical properties of the ash. The strength development and expansion varied with the type and characteristics of the ashes. The expansion appeared to be inversely related to strength development. As the strength decreased under saturated curing, the expansion increased significantly. The application of 5 C saturated curing resulted in further strength loss and increased expansion. The hydration reaction products appeared to be principally the hydration of lime (CaO) to portlandite (Ca[OH]{sub 2}), the hydration of anhydrite (CaSO{sub 4}) to gypsum (CaSO{sub 4} {center{underscore}dot} 2H{sub 2}O), and the precipitation of ettringite (Ca{sub 6}Al{sub 2}[SO{sub 4}]{sub 3}[OH]{sub 12} {center{underscore}dot} 26H{sub 2}O) from the soluble calcium, sulfates and alumina. No thaumasite was noted in the specimens. The ashes appeared to follow one of several hydration reaction trends: (1) ettringite-only development, (2) ettringite and/or gypsum early followed by later gypsum formation, or (3) gypsum-only formation. Testing confirmed that the hydration reaction chemistry was related to geotechnical properties of the ashes. Strength development and expansion appeared to be related to ettringite and/or gypsum formation. The expansion increased with saturated curing and appeared to be predominantly gypsum based. A pore filling model was found to be consistent with the observed relationships between hydration phases (ettringite and gypsum) and strength development and expansion, as well as SEM observations and void reduction observations.

  1. The state of the art of thin-film photovoltaics

    SciTech Connect (OSTI)

    Surek, T.

    1993-10-01

    Thin-film photovoltaic technologies, based on materials such as amorphous or polycrystalline silicon, copper indium diselenide, cadmium telluride, and gallium arsenide, offer the potential for significantly reducing the cost of electricity generated by photovoltaics. The significant progress in the technologies, from the laboratory to the marketplace, is reviewed. The common concerns and questions raised about thin films are addressed. Based on the progress to date and the potential of these technologies, along with continuing investments by the private sector to commercialize the technologies, one can conclude that thin-film PV will provide a competitive alternative for large-scale power generation in the future.

  2. New Solar Cells to Boost Satellite Power

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    Solar Cells to Boost Satellite Power For more information contact: George Douglas (303) 275-4096 e:mail: george_douglas@nrel.gov TECSTAR SIGNS PATENT AGREEMENT WITH NREL Golden, Colo., May 7, 1998 — New solar cells that provide as much as 50 percent more power for satellites are orbiting Earth, helping flash back telephone and television signals. These cells are based on the two-junction, gallium indium phosphide on gallium arsenide designs developed at the U.S. Department of Energy's National

  3. Search for: All records | SciTech Connect

    Office of Scientific and Technical Information (OSTI)

    Switch to Detail View for this search SciTech Connect Search Results Page 1 of 4 Search for: All records Creators/Authors contains: "Lu, Hong" × Sort by Relevance Sort by Date (newest first) Sort by Date (oldest first) Sort by Relevance « Prev Select page number Go to page: 1 of 4 1 » Next » Everything34 Electronic Full Text3 Citations31 Multimedia0 Datasets0 Software0 Filter Results Filter by Subject materials science (7) applied life sciences (5) gallium arsenides (5) indium

  4. The Story of a Cutting-Edge Solar Startup | Department of Energy

    Office of Energy Efficiency and Renewable Energy (EERE) Indexed Site

    The Story of a Cutting-Edge Solar Startup The Story of a Cutting-Edge Solar Startup June 20, 2012 - 9:40am Addthis Erin R. Pierce Erin R. Pierce Former Digital Communications Specialist, Office of Public Affairs What does this project do? Watch the video to learn how Alta Devices manufacturers high performance solar cells at a low cost. Alta Devices is rethinking how high performance solar cells are made. The Silicon Valley startup has taken gallium arsenide -- an expensive semiconductor

  5. Search for: All records | SciTech Connect

    Office of Scientific and Technical Information (OSTI)

    Switch to Detail View for this search SciTech Connect Search Results Page 2 of 4 Search for: All records Creators/Authors contains: "Lu, Hong" × Sort by Relevance Sort by Date (newest first) Sort by Date (oldest first) Sort by Relevance « Prev Select page number Go to page: 2 of 4 2 » Next » Everything34 Electronic Full Text3 Citations31 Multimedia0 Datasets0 Software0 Filter Results Filter by Subject materials science (7) applied life sciences (5) gallium arsenides (5) indium

  6. Intense terahertz emission from molecular beam epitaxy-grown GaAs/GaSb(001)

    SciTech Connect (OSTI)

    Sadia, Cyril P.; Laganapan, Aleena Maria; Agatha Tumanguil, Mae; Estacio, Elmer; Somintac, Armando; Salvador, Arnel; Que, Christopher T.; Yamamoto, Kohji; Tani, Masahiko

    2012-12-15

    Intense terahertz (THz) electromagnetic wave emission was observed in undoped GaAs thin films deposited on (100) n-GaSb substrates via molecular beam epitaxy. GaAs/n-GaSb heterostructures were found to be viable THz sources having signal amplitude 75% that of bulk p-InAs. The GaAs films were grown by interruption method during the growth initiation and using various metamorphic buffer layers. Reciprocal space maps revealed that the GaAs epilayers are tensile relaxed. Defects at the i-GaAs/n-GaSb interface were confirmed by scanning electron microscope images. Band calculations were performed to infer the depletion region and electric field at the i-GaAs/n-GaSb and the air-GaAs interfaces. However, the resulting band calculations were found to be insufficient to explain the THz emission. The enhanced THz emission is currently attributed to a piezoelectric field induced by incoherent strain and defects.

  7. Band structure of the epitaxial Fe/MgO/GaAs(001) tunnel junction studied by x-ray and ultraviolet photoelectron spectroscopies

    SciTech Connect (OSTI)

    Lu, Y.; Le Breton, J. C.; Turban, P.; Lepine, B.; Schieffer, P.; Jezequel, G.

    2006-10-09

    The electronic band structure in the epitaxial Fe/MgO/GaAs(001) tunnel junction has been studied by x-ray and ultraviolet photoelectron spectroscopy measurements. The Schottky barrier height (SBH) of Fe on MgO/GaAs heterostructure is determined to be 3.3{+-}0.1 eV, which sets the Fe Fermi level at about 0.3 eV above the GaAs valence band maximum. This SBH is also exactly the same as that measured from Fe on MgO monocrystal. After Fe deposition, no band bending change is observed in MgO and GaAs underlayers. On the contrary, Au and Al depositions led to clear variation of the band bending in both MgO and GaAs layers. This effect is analyzed as a fingerprint of defect states at the MgO/GaAs interface.

  8. Evidence of a New Hydrogen Complex in Dilute Nitride Alloys

    SciTech Connect (OSTI)

    Bisognin, G.; De Salvador, D.; Napolitani, E.; Berti, M.; Polimeni, A.; Felici, M.; Capizzi, M.; Guengerich, M.; Klar, P. J.; Bais, G.; Jabeen, F.; Piccin, M.; Rubini, S.; Martelli, F.; Franciosi, A.

    2007-04-10

    By means of high resolution x-ray diffraction and photoluminescence measurements we demonstrate that, as a result of hydrogen irradiation of GaAs1-xNx/GaAs, the original tensile strain of the as-grown material is reversed into a compressive one and that, at the same time, N atoms are electronically passivated. We show that the amount of compressive strain is determined exclusively by N concentration. This compressive strain is caused by the formation of peculiar N-H complexes and disappears after moderate annealing, while N electronic passivation still holds. These experimental results demonstrate that the lattice properties of fully-hydrogenated GaAs1-xNx/GaAs are ruled by a H complex which is different and less stable than that responsible for electronic passivation of N in GaAs1-xNx/GaAs.

  9. Solid-state lighting :lamp targets and implications for the semiconductor chip.

    SciTech Connect (OSTI)

    Tsao, Jeffrey Yeenien

    2003-01-01

    Once again GaAs MANTECH (with III-Vs Review acting as media sponsor) promises to deliver high quality papers covering all aspects of compound semiconductor manufacturing, with speakers from leading-edge equipment, epiwafer, and device suppliers. Since its launch in 1986, GaAs MANTECH has consistently been one of the highlight events of the conference calendar. Coverage includes all compound-based semiconductors, not just GaAs. With an excellent technical program comprising of almost 80 papers and expanded workshop sessions, the 2003 event should prove the best ever. As in previous years, an Interactive Forum and Ugly Picture Contest will be included. A major attraction will be the associated exhibition, with more than 70 suppliers expected to participate.

  10. Three-junction solar cells comprised of a thin-film GaInP/GaAs tandem cell mechanically stacked on a Si cell

    SciTech Connect (OSTI)

    Yazawa, Y.; Tamura, K.; Watahiki, S.; Kitatani, T.; Ohtsuka, H.; Warabisako, T.

    1997-12-31

    Three-junction tandem solar cells were fabricated by mechanical stacking of a thin-film GaInP/GaAs monolithic tandem cell and a Si cell. The epitaxial lift-off (ELO) technique was used for the thinning of GaInP/GaAs tandem cells. Both spectral responses of the GaInP top cell and the GaAs middle cell in the thin-film GaInP/GaAs monolithic tandem cell were conserved. The Si cell performance has been improved by reducing the absorption loss in the GaAs substrate.

  11. Observation of the Kondo effect in a spin-3/2 hole quantum dot

    SciTech Connect (OSTI)

    Klochan, O.; Micolich, A. P.; Hamilton, A. R.; Trunov, K.; Reuter, D.; Wieck, A. D.

    2013-12-04

    We report the observation of the Kondo effect in a spin-3/2 hole quantum dot formed near pinch-off in a GaAs quantum wire. We clearly observe two distinctive hallmarks of quantum dot Kondo physics. First, the zero-bias peak in the differential conductance splits an in-plane magnetic field and the splitting is independent of gate voltage. Second, the splitting rate is twice as large as that for the lowest one-dimensional subband. We show that the Zeeman splitting of the zero-bias peak is highly anisotropic and attribute this to the strong spin-orbit interaction for holes in GaAs.

  12. Isoelectronic co-doping

    DOE Patents [OSTI]

    Mascarenhas, Angelo

    2004-11-09

    Isoelectronic co-doping of semiconductor compounds and alloys with deep acceptors and deep donors is used to decrease bandgap, to increase concentration of the dopant constituents in the resulting alloys, and to increase carrier mobilities lifetimes. Group III-V compounds and alloys, such as GaAs and GaP, are isoelectronically co-doped with, for example, N and Bi, to customize solar cells, thermal voltaic cells, light emitting diodes, photodetectors, and lasers on GaP, InP, GaAs, Ge, and Si substrates. Isoelectronically co-doped Group II-VI compounds and alloys are also included.

  13. Strength of semiconductors, metals, and ceramics evaluated by a microscopic cleavage model with Morse-type and Lennard-Jones-type interaction

    SciTech Connect (OSTI)

    Hess, Peter

    2014-08-07

    An improved microscopic cleavage model, based on a Morse-type and Lennard-Jones-type interaction instead of the previously employed half-sine function, is used to determine the maximum cleavage strength for the brittle materials diamond, tungsten, molybdenum, silicon, GaAs, silica, and graphite. The results of both interaction potentials are in much better agreement with the theoretical strength values obtained by ab initio calculations for diamond, tungsten, molybdenum, and silicon than the previous model. Reasonable estimates of the intrinsic strength are presented for GaAs, silica, and graphite, where first principles values are not available.

  14. Current-matched high-efficiency, multijunction monolithic solar cells

    DOE Patents [OSTI]

    Olson, Jerry M.; Kurtz, Sarah R.

    1993-01-01

    The efficiency of a two-junction (cascade) tandem photovoltaic device is improved by adjusting (decreasing) the top cell thickness to achieve current matching. An example of the invention was fabricated out of Ga.sub.0.52 In.sub.0.48 P and GaAs. Additional lattice-matched systems to which the invention pertains include Al.sub.x Ga.sub.1-x /GaAS (x= 0.3-0.4), GaAs/Ge and Ga.sub.y In.sub.l-y P/Ga.sub.y+0.5 In.sub.0.5-y As (0

  15. Absorption enhancement through Fabry-Prot resonant modes in a 430?nm thick InGaAs/GaAsP multiple quantum wells solar cell

    SciTech Connect (OSTI)

    Behaghel, B.; Tamaki, R.; Watanabe, K.; Sodabanlu, H.; Vandamme, N.; Dupuis, C.; Bardou, N.; Cattoni, A.; Okada, Y.; Sugiyama, M.; Collin, S.; Guillemoles, J.-F.

    2015-02-23

    We study light management in a 430?nm-thick GaAs p-i-n single junction solar cell with 10 pairs of InGaAs/GaAsP multiple quantum wells (MQWs). The epitaxial layer transfer on a gold mirror improves light absorption and increases the external quantum efficiency below GaAs bandgap by a factor of four through the excitation of Fabry-Perot resonances. We show a good agreement with optical simulation and achieve around 10% conversion efficiency. We demonstrate numerically that this promising result can be further improved by anti-reflection layers. This study paves the way to very thin MQWs solar cells.

  16. Recovery Act : Near-Single-Crystalline Photovoltaic Thin Films on Polycrystalline, Flexible Substrates

    SciTech Connect (OSTI)

    Venkat Selvamanickam; Alex Freundlich

    2010-11-29

    III-V photovoltaics have exhibited efficiencies above 40%, but have found only a limited use because of the high cost of single crystal substrates. At the other end of the spectrum, polycrystalline and amorphous thin film solar cells offer the advantage of low-cost fabrication, but have not yielded high efficiencies. Our program is based on single-crystalline-like thin film photovoltaics on polycrystalline substrates using biaxially-textured templates made by Ion Beam-Assisted Deposition (IBAD). MgO templates made by IBAD on flexible metal substrate have been successfully used for epitaxial growth of germanium films. In spite of a 4.5% lattice mismatch, heteroepitaxial growth of Ge was achieved on CeO2 that was grown on IBAD MgO template. Room temperature optical bandgap of the Ge films was identified at 0.67 eV indicating minimal residual strain. Refraction index and extinction coefficient values of the Ge films were found to match well with that measured from a reference Ge single crystal. GaAs has been successfully grown epitaxially on Ge on metal substrate by molecular beam epitaxy. RHEED patterns indicate self annihilation of antiphase boundaries and the growth of a single domain GaAs. The GaAs is found to exhibit strong photoluminescence signal and, an existence of a relatively narrow (FWHM~20 meV) band-edge excitons measured in this film indicates a good optoelectronic quality of deposited GaAs. While excellent epitaxial growth has been achieved in GaAs on flexible metal substrates, the defect density of the films as measured by High Resolution X-ray Diffraction and etch pit experiments showed a high value of 5 * 10^8 per cm^2. Cross sectional transmission electron microscopy of the multilayer architecture showed concentration of threading dislocations near the germanium-ceria interface. The defect density was found decrease as the Ge films were made thicker. The defects appear to originate from the MgO layer presumably because of large lattice mismatches between the various layers. The defect density in GaAs was reduced by a factor of five by adding a step of in-situ deposition of Ge by MBE on the sputtered Ge prior to GaAs growth. We have investigated device design strategies that would support development of high-efficiency devices in presence of dislocation densities of 10^8 cm^-2 present in our epitaxial GaAs films. Results from modeling work show that with a proper emitter, base and doping selection, the modeled efficiency of a GaAs cells with dislocation densities of 10^9 and 10^8 cm^-2 could be increased from 1% and 7% to 11% and 17% respectively. Under AM0, this single junction GaAs solar cell, has optimized value of emitter and base thickness of around 0.7 and 1.7 microns respectively, to give a maximum efficiency of 24.2%. We have fabricated complete GaAs solar cells using our Ge films on metal substrates. Pattern resolution of few microns with well-defined grid line of 30 microns has been realized on few cm square flexible templates. The ability to grow single-crystalline-like Ge films on flexible, polycrystalline substrates by reel-to-reel tape processing now provides an immense potential to fabricate high quality III-V photovoltaics on flexible, inexpensive substrates.

  17. Building America Top Innovations Hall of Fame Profile … Attic Air Sealing Guidelines

    Energy Savers [EERE]

    Terminology Air Barrier Material (ABM) --- A does not allow air to pass throu plywood/OSB, foam board, duc lumber. Backing --- Any material that s be sprayed so as to provide an glass batts. Baffle (B) --- Manufactured chu direct ventilation air flow up an foam board or cardboard. Thermal Blocking --- Any rigid heat sources like chimneys or metal and gypsum board. Fasteners --- Staples, screws o attach Thermal Blocking or AB Sealant --- Any flexible produc or more materials will adhere a Detail

  18. Experimental and Analytical Research on Fracture Processes in ROck

    SciTech Connect (OSTI)

    Herbert H.. Einstein; Jay Miller; Bruno Silva

    2009-02-27

    Experimental studies on fracture propagation and coalescence were conducted which together with previous tests by this group on gypsum and marble, provide information on fracturing. Specifically, different fracture geometries wsere tested, which together with the different material properties will provide the basis for analytical/numerical modeling. INitial steps on the models were made as were initial investigations on the effect of pressurized water on fracture coalescence.

  19. Tricalcium aluminate hydration in additivated systems. A crystallographic

    Office of Scientific and Technical Information (OSTI)

    study by SR-XRPD (Journal Article) | SciTech Connect SciTech Connect Search Results Journal Article: Tricalcium aluminate hydration in additivated systems. A crystallographic study by SR-XRPD Citation Details In-Document Search Title: Tricalcium aluminate hydration in additivated systems. A crystallographic study by SR-XRPD Synchrotron radiation X-ray powder diffraction has been used to monitor the evolution of ettringite in C3A-gypsum synthetic mixture and in commercial cement systems

  20. Coal combustion products 2007 production and use report

    SciTech Connect (OSTI)

    2009-07-01

    The American Coal Ash Association's 2007 Annual Coal Combustion Products (CCP) are derived from data from more than 170 power plants. The amount of CCPs used was 40.55%, a decrease of 2.88% from 2006, attributed to reduced fuel burn and a decrease in demand in the building industry. Figures are given for the production of fly ash, flue gas desulfurization gypsum, bottom ash, FBC ash and boiler slag. The article summarises results of the survey. 1 ref., 1 tab.

  1. Analytical determination of critical crack size in solar cells

    SciTech Connect (OSTI)

    Chen, C.P.

    1988-05-01

    Although solar cells usually have chips and cracks, no material specifications concerning the allowable crack size on solar cells are available for quality assurance and engineering design usage. Any material specifications that the cell manufacturers use were developed for cosmetic reasons that have no technical basis. Therefore, the Applied Solar Energy Corporation (ASEC) has sponsored a continuing program for the fracture mechanics evaluation of GaAs. Fracture mechanics concepts were utilized to develop an analytical model that can predict the critical crack size of solar cells. This model indicates that the edge cracks of a solar cell are more critical than its surface cracks. In addition, the model suggests that the material specifications on the allowable crack size used for Si solar cells should not be applied to GaAs solar cells. The analytical model was applied to Si and GaAs solar cells, but it would also be applicable to the semiconductor wafers of other materials, such as a GaAs thin film on a Ge substrate, using appropriate input data.

  2. Deep-level transient spectroscopy of InAs/GaAs quantum dot superlattices

    SciTech Connect (OSTI)

    Sobolev, M. M.; Nevedomskii, V. N.; Zolotareva, R. V.; Vasil'ev, A. P.; Ustinov, V. M.

    2014-02-21

    Deep level transient spectroscopy (DLTS) has been applied to study the carrier emission from states of a 10-layer system of tunnel-coupled vertically correlated quantum dots (VCQDs) in p-n InAs/GaAs heterostructures with different widths of GaAs spacers under varied reverse bias (U{sub r}) and filling voltage pulse U{sub f}.

  3. Optically-initiated silicon carbide high voltage switch

    DOE Patents [OSTI]

    Caporaso, George J. (Livermore, CA); Sampayan, Stephen E. (Manteca, CA); Sullivan, James S. (Livermore, CA); Sanders, David M. (Livermore, CA)

    2012-02-28

    An improved photoconductive switch having a SIC or other wide band gap substrate material, such as GaAs and field-grading liners composed of preferably SiN formed on the substrate adjacent the electrode perimeters or adjacent the substrate perimeters for grading the electric fields.

  4. Optically initiated silicon carbide high voltage switch

    DOE Patents [OSTI]

    Caporaso, George J. (Livermore, CA); Sampayan, Stephen E. (Manteca, CA); Sullivan, James S. (Livermore, CA); Sanders; David M. (Livermore, CA)

    2011-02-22

    An improved photoconductive switch having a SiC or other wide band gap substrate material, such as GaAs and field-grading liners composed of preferably SiN formed on the substrate adjacent the electrode perimeters or adjacent the substrate perimeters for grading the electric fields.

  5. Profiling the Built-in Electrical Potential in III-V Multijunction Solar Cells: Preprint

    SciTech Connect (OSTI)

    Jiang, C.-S.; Friedman, D. J.; Moutinho, H. R.; Al-Jassim, M. M.

    2006-05-01

    We report on a direct measurement of the electrical potential on cross-sections of GaInP2/GaAs multiple-junction solar cells by using an ultrahigh-vacuum scanning Kelvin probe microscope (UHV-SKPM). The UHV-SKPM allows us to measure the potential without air molecules being adsorbed on the cross-sectional surface. Moreover, it uses a GaAs laser with photon energy of 1.4 eV for the atomic force microscope (AFM) operation. This eliminated the light-absorption-induced bottom-junction flattening and top-junction enhancement, which happened in our previous potential measurement using a 1.85-eV laser for the AFM operation. Three potentials were measured at the top, tunneling, and bottom junctions. Values of the potentials are smaller than the potentials in the bulk. This indicates that the Fermi level on the UHV-cleaved (110) surface was pinned, presumably due to defects upon cleaving. We also observed higher potentials at atomic steps than on the terraces for both GaInP2 epitaxial layer and GaAs substrate. Combining scanning tunneling microscopy (STM) and SKPM measurements, we found that the potential height at steps of the GaAs substrate depends on the step direction, which is probably a direct result of unbalanced cations and anions at the steps.

  6. Optically enhanced photon recycling in mechanically stacked multijunction solar cells

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Steiner, Myles A.; Geisz, John F.; Ward, J. Scott; Garcia, Ivan; Friedman, Daniel J.; King, Richard R.; Chiu, Philip T.; France, Ryan M.; Duda, Anna; Olavarria, Waldo J.; et al

    2015-11-09

    Multijunction solar cells can be fabricated by mechanically bonding together component cells that are grown separately. Here, we present four-junction four-terminal mechanical stacks composed of GaInP/GaAs tandems grown on GaAs substrates and GaInAsP/GaInAs tandems grown on InP substrates. The component cells were bonded together with a low-index transparent epoxy that acts as an angularly selective reflector to the GaAs bandedge luminescence, while simultaneously transmitting nearly all of the subbandgap light. As determined by electroluminescence measurements and optical modeling, the GaAs subcell demonstrates a higher internal radiative limit and, thus, higher subcell voltage, compared with GaAs subcells without the epoxy reflector.more » The best cells demonstrate 38.8 ± 1.0% efficiency under the global spectrum at 1000 W/m2 and ~ 42% under the direct spectrum at ~100 suns. As a result, eliminating the series resistance is the key challenge for further improving the concentrator cells.« less

  7. Profiling the Built-In Electrical Potential in III-V Multijunction Solar Cells

    SciTech Connect (OSTI)

    Jiang, C.-S.; Friedman, D. J.; Moutinho, H. R.; Al-Jassim, M. M.

    2006-01-01

    We report on a direct measurement of the electrical potential on cross-sections of GaInP{sub 2}/GaAs multiple-junction solar cells by using an ultrahigh-vacuum scanning Kelvin probe microscope (UHV-SKPM). The UHV-SKPM allows us to measure the potential without air molecules being adsorbed on the cross-sectional surface. Moreover, it uses a GaAs laser with photon energy of 1.4 eV for the atomic force microscope (AFM) operation. This eliminated the light-absorption-induced bottom-junction flattening and top-junction enhancement, which happened in our previous potential measurement using a 1.85-eV laser for the AFM operation. Three potentials were measured at the top, tunneling, and bottom junctions. Values of the potentials are smaller than the potentials in the bulk. This indicates that the Fermi level on the UHV-cleaved (110) surface was pinned, presumably due to defects upon cleaving. We also observed higher potentials at atomic steps than on the terraces for both GaInP2 epitaxial layer and GaAs substrate. Combining scanning tunneling microscopy (STM) and SKPM measurements, we found that the potential height at steps of the GaAs substrate depends on the step direction, which is probably a direct result of unbalanced cations and anions at the steps.

  8. Electrically active Er doping in InAs, In{sub 0.53}Ga{sub 0.47...

    Office of Scientific and Technical Information (OSTI)

    Electrically active Er doping in InAs, Insub 0.53Gasub 0.47As, and GaAs Citation Details In-Document Search Title: Electrically active Er doping in InAs, Insub 0.53Gasub ...

  9. Field Testing of Nano-PCM Enhanced Building Envelope Components

    SciTech Connect (OSTI)

    Biswas, Kaushik; Childs, Phillip W; Atchley, Jerald Allen

    2013-08-01

    The U.S. Department of Energy s (DOE) Building Technologies Program s goal of developing high-performance, energy efficient buildings will require more cost-effective, durable, energy efficient building envelopes. Forty-eight percent of the residential end-use energy consumption is spent on space heating and air conditioning. Reducing envelope-generated heating and cooling loads through application of phase change material (PCM)-enhanced envelope components can facilitate maximizing the energy efficiency of buildings. Field-testing of prototype envelope components is an important step in estimating their energy benefits. An innovative phase change material (nano-PCM) was developed with PCM encapsulated with expanded graphite (interconnected) nanosheets, which is highly conducive for enhanced thermal storage and energy distribution, and is shape-stable for convenient incorporation into lightweight building components. During 2012, two test walls with cellulose cavity insulation and prototype PCM-enhanced interior wallboards were installed in a natural exposure test (NET) facility at Charleston, SC. The first test wall was divided into four sections, which were separated by wood studs and thin layers of foam insulation. Two sections contained nano-PCM-enhanced wallboards: one was a three-layer structure, in which nano-PCM was sandwiched between two gypsum boards, and the other one had PCM dispersed homogeneously throughout graphite nanosheets-enhanced gypsum board. The second test wall also contained two sections with interior PCM wallboards; one contained nano-PCM dispersed homogeneously in gypsum and the other was gypsum board containing a commercial microencapsulated PCM (MEPCM) for comparison. Each test wall contained a section covered with gypsum board on the interior side, which served as control or a baseline for evaluation of the PCM wallboards. The walls were instrumented with arrays of thermocouples and heat flux transducers. Further, numerical modeling of the walls containing the nano-PCM wallboards were performed to determine their actual impact on wall-generated heating and cooling loads. The models were first validated using field data, and then used to perform annual simulations using Typical Meteorological Year (TMY) weather data. This article presents the measured performance and numerical analysis to evaluate the energy-saving potential of the nano-PCM-enhanced building components.

  10. APPLIED PHYTO-REMEDIATION TECHNIQUES USING HALOPHYTES FOR OIL AND BRINE SPILL SCARS

    SciTech Connect (OSTI)

    M.L. Korphage; Bruce G. Langhus; Scott Campbell

    2003-03-01

    Produced salt water from historical oil and gas production was often managed with inadequate care and unfortunate consequences. In Kansas, the production practices in the 1930's and 1940's--before statewide anti-pollution laws--were such that fluids were often produced to surface impoundments where the oil would segregate from the salt water. The oil was pumped off the pits and the salt water was able to infiltrate into the subsurface soil zones and underlying bedrock. Over the years, oil producing practices were changed so that segregation of fluids was accomplished in steel tanks and salt water was isolated from the natural environment. But before that could happen, significant areas of the state were scarred by salt water. These areas are now in need of economical remediation. Remediation of salt scarred land can be facilitated with soil amendments, land management, and selection of appropriate salt tolerant plants. Current research on the salt scars around the old Leon Waterflood, in Butler County, Kansas show the relative efficiency of remediation options. Based upon these research findings, it is possible to recommend cost efficient remediation techniques for slight, medium, and heavy salt water damaged soil. Slight salt damage includes soils with Electrical Conductivity (EC) values of 4.0 mS/cm or less. Operators can treat these soils with sufficient amounts of gypsum, install irrigation systems, and till the soil. Appropriate plants can be introduced via transplants or seeded. Medium salt damage includes soils with EC values between 4.0 and 16 mS/cm. Operators will add amendments of gypsum, till the soil, and arrange for irrigation. Some particularly salt tolerant plants can be added but most planting ought to be reserved until the second season of remediation. Severe salt damage includes soil with EC values in excess of 16 mS/cm. Operators will add at least part of the gypsum required, till the soil, and arrange for irrigation. The following seasons more gypsum will be added and as the soil EC is reduced, plants can be introduced. If rapid remediation is required, a sufficient volume of topsoil, or sand, or manure can be added to dilute the local salinity, the bulk amendments tilled into the surface with added gypsum, and appropriate plants added. In this case, irrigation will be particularly important. The expense of the more rapid remediation will be much higher.

  11. Experimental study of the proposed super-thermal-conductor: BAs

    SciTech Connect (OSTI)

    Lv, Bing; Lan, Yucheng; Zhang, Qian; Ren, Zhifeng E-mail: cwchu@uh.edu; Wang, Xiqu; Jacobson, Allan J.; Hu, Yongjie; Chen, Gang; Broido, David; Chu, Ching-Wu E-mail: cwchu@uh.edu

    2015-02-16

    Recent calculations predict a super-thermal-conductivity of ?2000?Wm{sup ?1} K{sup ?1}, comparable to that of diamond, in cubic boron arsenide (BAs) crystals, which may offer inexpensive insulators with super-thermal-conductivity for microelectronic device applications. We have synthesized and characterized single crystals of BAs with a zinc blende cubic structure and lattice parameters of a?=?4.7830(7) . A relatively high thermal conductivity of ?200?Wm{sup ?1} K{sup ?1} is obtained, close to those of best non-carbon crystal insulators, such as SiC, although still an order of magnitude smaller than the value predicted. Based on our XPS, X-ray single crystal diffraction, and Raman scattering results, steps to achieve the predicted super-thermal conductivity in BAs are proposed.

  12. Interplay of light transmission and catalytic exchange current in photoelectrochemical systems

    SciTech Connect (OSTI)

    Fountaine, Katherine T.; Lewerenz, Hans J.; Atwater, Harry A.

    2014-10-27

    We develop an analytic current-voltage expression for a variable junction photoelectrochemical (PEC) cell and use it to investigate and illustrate the influence of the optical and electrical properties of catalysts on the optoelectronic performance of PEC devices. Specifically, the model enables a simple, yet accurate accounting of nanostructured catalyst optical and electrical properties through incorporation of an optical transmission factor and active catalytic area factor. We demonstrate the utility of this model via the output power characteristics of an exemplary dual tandem solar cell with indium gallium phosphide and indium gallium arsenide absorbers with varying rhodium catalyst nanoparticle loading. The approach highlights the importance of considering interactions between independently optimized components for optimal PEC device design.

  13. Semiconductor Device Analysis on Personal Computers

    Energy Science and Technology Software Center (OSTI)

    1993-02-08

    PC-1D models the internal operation of bipolar semiconductor devices by solving for the concentrations and quasi-one-dimensional flow of electrons and holes resulting from either electrical or optical excitation. PC-1D uses the same detailed physical models incorporated in mainframe computer programs, yet runs efficiently on personal computers. PC-1D was originally developed with DOE funding to analyze solar cells. That continues to be its primary mode of usage, with registered copies in regular use at more thanmore » 100 locations worldwide. The program has been successfully applied to the analysis of silicon, gallium-arsenide, and indium-phosphide solar cells. The program is also suitable for modeling bipolar transistors and diodes, including heterojunction devices. Its easy-to-use graphical interface makes it useful as a teaching tool as well.« less

  14. Mixed-RKDG Finite Element Methods for the 2-D Hydrodynamic Model for Semiconductor Device Simulation

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Chen, Zhangxin; Cockburn, Bernardo; Jerome, Joseph W.; Shu, Chi-Wang

    1995-01-01

    In this paper we introduce a new method for numerically solving the equations of the hydrodynamic model for semiconductor devices in two space dimensions. The method combines a standard mixed finite element method, used to obtain directly an approximation to the electric field, with the so-called Runge-Kutta Discontinuous Galerkin (RKDG) method, originally devised for numerically solving multi-dimensional hyperbolic systems of conservation laws, which is applied here to the convective part of the equations. Numerical simulations showing the performance of the new method are displayed, and the results compared with those obtained by using Essentially Nonoscillatory (ENO) finite difference schemes. Frommore » the perspective of device modeling, these methods are robust, since they are capable of encompassing broad parameter ranges, including those for which shock formation is possible. The simulations presented here are for Gallium Arsenide at room temperature, but we have tested them much more generally with considerable success.« less

  15. Products of an Artificially Induced Hydrothermal System at Yucca Mountain

    SciTech Connect (OSTI)

    S. Levy

    2000-08-07

    Studies of mineral deposition in the recent geologic past at Yucca Mountain, Nevada, address competing hypotheses of hydrothermal alteration and deposition from percolating groundwater. The secondary minerals being studied are calcite-opal deposits in fractures and lithophysal cavities of ash-flow tuffs exposed in the Exploratory Studies Facility (ESF), a 7.7-km tunnel excavated by the Yucca Mountain Site Characterization Project within Yucca Mountain. An underground field test in the ESF provided information about the minerals deposited by a short-lived artificial hydrothermal system and an opportunity for comparison of test products with the natural secondary minerals. The heating phase lasted nine months, followed by a nine-month cooling period. Natural pore fluids were the only source of water during the thermal test. Condensation and reflux of water driven away from the heater produced fluid flow in certain fractures and intersecting boreholes. The mineralogic products of the thermal test are calcite-gypsum aggregates of less than 4-micrometer crystals and amorphous silica as glassy scale less than 0.2 mm thick and as mounds of tubules with diameters less than 0.7 micrometers. The minute crystal sizes of calcite and gypsum from the field test are very different from the predominantly coarser calcite crystals (up to cm scale) in natural secondary-mineral deposits at the site. The complex micrometer-scale textures of the amorphous silica differ from the simple forms of opal spherules and coatings in the natural deposits, even though some natural spherules are as small as 1 micrometer. These differences suggest that the natural minerals, especially if they were of hydrothermal origin, may have developed coarser or simpler forms during subsequent episodes of dissolution and redeposition. The presence of gypsum among the test products and its absence from the natural secondary-mineral assemblage may indicate a higher degree of evaporation during the test than during the deposition of natural calcite-opal deposits.

  16. TECHNICAL REPORT

    Office of Scientific and Technical Information (OSTI)

    TECHNICAL REPORT September 1 through November 30, 1994 Project Title: MANUFACTURE OF AMMONIUM SULFATE FERTILIZER FROM FGD-GYPSUM ICCI Project Number: Principal Investigator: Other Investigators: Project Manager; DOE Cooperative Agreement Number: DE-FC22-92PC9252 1 (Year 3) 94-1/3.1B-3M M.4.M. Chou, Illinois State Geological Survey (ISGS) M. Rostam-Abadi and J.M. Lytle, ISGS R. Hoeft, University of Illinois; EZ. Blevins, Allied Signal-Chemicals; F. Achron, Southeast Marketing Chemical Process

  17. Beneficial use of coal combustion products continues to grow

    SciTech Connect (OSTI)

    MacDonald, M.

    2008-07-01

    In August 2007 the American Coal Ash Association (ACAA) released results of the Coal Combustion Products Production (CCP) and use survey. Production was 124,795,000 tons while beneficial use was 54,203,000 tons, a utilization rate of over 43%, 3% higher than in 2005. The article includes graphs of 40 years of CCP production and use and projected trade of CCP utilization until 2011. It also gives 2006 figures for Production and use of fly ash, bottom ash, boiler slag, FGD gypsum and other FGD products, and FBC ash. 3 refs., 3 figs.

  18. ACAA 2006 fall meeting

    SciTech Connect (OSTI)

    2006-07-01

    The seven presentations (in pdf format) on the CD-ROM are: Amended Silicates{trademark}: mercury control without harming fly ash (J. Butz and others); benefits of gypsum in agriculture (L.D. Norton); co-firing biomass in pc fired units (C. Meijer and others); minimizing the impact of air pollution control equipment retrofits on saleability of fly ash (C.Weilert); new power plant construction - CCP readiness (T. Jansen); recent utilization of fly ash in coal plant construction (J. Liljegren and T. Hart); and resource conservation challenge (C. McLaughlin).

  19. LOS ALAMOS, N.M., January 15, 2013-Researchers from Los Alamos National

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    follows the 'Yellowknife Road' to Martian wet area January 15, 2013 Instrument confirms presence of gypsum and related minerals LOS ALAMOS, N.M., January 15, 2013-Researchers from Los Alamos National Laboratory and the French Space Agency have tracked a trail of minerals that point to the prior presence of water at the Curiosity rover site on Mars. Researchers from the Mars Science Laboratory's ChemCam team today described how the laser instrument aboard the Curiosity Rover-an SUV-sized vehicle

  20. Deep level centers and their role in photoconductivity transients of InGaAs/GaAs quantum dot chains

    SciTech Connect (OSTI)

    Kondratenko, S. V. Vakulenko, O. V.; Mazur, Yu. I. Dorogan, V. G.; Marega, E.; Benamara, M.; Ware, M. E.; Salamo, G. J.

    2014-11-21

    The in-plane photoconductivity and photoluminescence are investigated in quantum dot-chain InGaAs/GaAs heterostructures. Different photoconductivity transients resulting from spectrally selecting photoexcitation of InGaAs QDs, GaAs spacers, or EL2 centers were observed. Persistent photoconductivity was observed at 80?K after excitation of electron-hole pairs due to interband transitions in both the InGaAs QDs and the GaAs matrix. Giant optically induced quenching of in-plane conductivity driven by recharging of EL2 centers is observed in the spectral range from 0.83?eV to 1.0?eV. Conductivity loss under photoexcitation is discussed in terms of carrier localization by analogy with carrier distribution in disordered media.

  1. Origins of interlayer formation and misfit dislocation displacement in the vicinity of InAs/GaAs quantum dots

    SciTech Connect (OSTI)

    Huang, S.; Kim, S. J.; Pan, X. Q.; Goldman, R. S.

    2014-07-21

    We have examined the origins of interlayer formation and misfit dislocation (MD) displacement in the vicinity of InAs/GaAs quantum dots (QDs). For QDs formed by the Stranski-Krastanov mode, regularly spaced MDs nucleate at the interface between the QD and the GaAs buffer layer. In the droplet epitaxy case, both In island formation and In-induced “nano-drilling” of the GaAs buffer layer are observed during In deposition. Upon annealing under As flux, the In islands are converted to InAs QDs, with an InGaAs interlayer at the QD/buffer interface. Meanwhile, MDs nucleate at the QD/interlayer interface.

  2. Impact of the modulation doping layer on the ν = 5/2 anisotropy

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Shi, X.; Pan, W.; Baldwin, K. W.; West, K. W.; Pfeiffer, L. N.; Tsui, D. C.

    2015-03-30

    We have carried out a systematic study of the tilted magnetic field induced anisotropy at the Landau level filling factor ν = 5/2 in a series of high quality GaAs quantum wells, where the setback distance (d) between the modulation doping layer and the GaAs quantum well is varied from 33 to 164 nm. We have observed that in the sample of the smallest d, electronic transport is anisotropic when the in-plane magnetic field (Bip) is parallel to the [1–10] crystallographic direction, but remains more or less isotropic when Bip // [110]. In contrast, in the sample of largest d,more » electronic transport is anisotropic in both crystallographic directions. Lastly, our results clearly show that the modulation doping layer plays an important role in the tilted field induced ν = 5/2 anisotropy.« less

  3. Non-Destructive Spent Fuel Characterization with Semi-Conducting Gallium Arsinde Neutron Imaging Arrays

    SciTech Connect (OSTI)

    Douglas S. McGregor; Holly K. Gersch; Jeffrey D. Sanders; John C. Lee; Mark D. Hammig; Michael R. Hartman; Yong Hong Yang; Raymond T. Klann; Brian Van Der Elzen; John T. Lindsay; Philip A. Simpson

    2002-01-30

    High resistivity bulk grown GaAs has been used to produce thermal neutron imaging devices for use in neutron radiography and characterizing burnup in spent fuel. The basic scheme utilizes a portable Sb/Be source for monoenergetic (24 keV) neutron radiation source coupled to an Fe filter with a radiation hard B-coated pixellated GaAs detector array as the primary neutron detector. The coated neutron detectors have been tested for efficiency and radiation hardness in order to determine their fitness for the harsh environments imposed by spent fuel. Theoretical and experimental results are presented, showing detector radiation hardness, expected detection efficiency and the spatial resolution from such a scheme. A variety of advanced neutron detector designs have been explored, with experimental results achieving 13% thermal neutron detection efficiency while projecting the possibility of over 30% thermal neutron detection efficiency.

  4. Advanced materials development for multi-junction monolithic photovoltaic devices

    SciTech Connect (OSTI)

    Dawson, L.R.; Reno, J.L.

    1996-07-01

    We report results in three areas of research relevant to the fabrication of monolithic multi-junction photovoltaic devices. (1) The use of compliant intervening layers grown between highly mismatched materials, GaAs and GaP (same lattice constant as Si), is shown to increase the structural quality of the GaAs overgrowth. (2) The use of digital alloys applied to the MBE growth of GaAs{sub x}Sb{sub l-x} (a candidate material for a two junction solar cell) provides increased control of the alloy composition without degrading the optical properties. (3) A nitrogen plasma discharge is shown to be an excellent p-type doping source for CdTe and ZnTe, both of which are candidate materials for a two junction solar cell.

  5. Band filling effects on temperature performance of intermediate band quantum wire solar cells

    SciTech Connect (OSTI)

    Kunets, Vas. P. Furrow, C. S.; Ware, M. E.; Souza, L. D. de; Benamara, M.; Salamo, G. J.; Mortazavi, M.

    2014-08-28

    Detailed studies of solar cell efficiency as a function of temperature were performed for quantum wire intermediate band solar cells grown on the (311)A plane. A remotely doped one-dimensional intermediate band made of self-assembled In{sub 0.4}Ga{sub 0.6}As quantum wires was compared to an undoped intermediate band and a reference p-i-n GaAs sample. These studies indicate that the efficiencies of these solar cells depend on the population of the one-dimensional band by equilibrium free carriers. A change in this population by free electrons under various temperatures affects absorption and carrier transport of non-equilibrium carriers generated by incident light. This results in different efficiencies for both the doped and undoped intermediate band solar cells in comparison with the reference GaAs p-i-n solar cell device.

  6. Method of manufacturing flexible metallic photonic band gap structures, and structures resulting therefrom

    DOE Patents [OSTI]

    Gupta, Sandhya (Bloomington, MN); Tuttle, Gary L. (Ames, IA); Sigalas, Mihail (Ames, IA); McCalmont, Jonathan S. (Ames, IA); Ho, Kai-Ming (Ames, IA)

    2001-08-14

    A method of manufacturing a flexible metallic photonic band gap structure operable in the infrared region, comprises the steps of spinning on a first layer of dielectric on a GaAs substrate, imidizing this first layer of dielectric, forming a first metal pattern on this first layer of dielectric, spinning on and imidizing a second layer of dielectric, and then removing the GaAs substrate. This method results in a flexible metallic photonic band gap structure operable with various filter characteristics in the infrared region. This method may be used to construct multi-layer flexible metallic photonic band gap structures. Metal grid defects and dielectric separation layer thicknesses are adjusted to control filter parameters.

  7. Towards a graphene-based quantum impedance standard

    SciTech Connect (OSTI)

    Kalmbach, C.-C.; Schurr, J. Ahlers, F. J.; Mller, A.; Novikov, S.; Lebedeva, N.; Satrapinski, A.

    2014-08-18

    Precision measurements of the quantum Hall resistance with alternating current (ac) in the kHz range were performed on epitaxial graphene in order to assess its suitability as a quantum standard of impedance. The quantum Hall plateaus measured with alternating current were found to be flat within one part in 10{sup 7}. This is much better than for plain GaAs quantum Hall devices and shows that the magnetic-flux-dependent capacitive ac losses of the graphene device are less critical. The observed frequency dependence of about ?8??10{sup ?8}/kHz is comparable in absolute value to the positive frequency dependence of plain GaAs devices, but the negative sign is attributed to stray capacitances which we believe can be minimized by a careful design of the graphene device. Further improvements thus may lead to a simpler and more user-friendly quantum standard for both resistance and impedance.

  8. Wavelength controlled multilayer-stacked linear InAs quantum dot arrays on InGaAsP/InP (100) by self-organized anisotropic strain engineering: A self-ordered quantum dot crystal

    SciTech Connect (OSTI)

    Sritirawisarn, N.; Otten, F. W. M. van; Eijkemans, T. J.; Noetzel, R.

    2008-09-29

    Multilayer-stacked linear InAs quantum dot (QD) arrays are created on InAs/InGaAsP superlattice templates formed by self-organized anisotropic strain engineering on InP (100) substrates in chemical beam epitaxy. Stacking of the QD arrays with identical emission wavelength in the 1.55 {mu}m region at room temperature is achieved through the insertion of ultrathin GaAs interlayers beneath the QDs with increasing interlayer thickness in successive layers. The increment in the GaAs interlayer thickness compensates the QD size/wavelength increase during strain correlated stacking. This is the demonstration of a three-dimensionally self-ordered QD crystal with fully controlled structural and optical properties.

  9. Growth, steady-state, and time-resolved photoluminescence study of CdTe/MgCdTe double heterostructures on InSb substrates using molecular beam epitaxy

    SciTech Connect (OSTI)

    DiNezza, Michael J.; Liu, Shi; Kirk, Alexander P.; Zhang, Yong-Hang; School of Electrical, Computer and Energy Engineering, Arizona State University, Tempe, Arizona 85287 ; Zhao, Xin-Hao; School for Engineering of Matter, Transport and Energy, Arizona State University, Tempe, Arizona 85287

    2013-11-04

    CdTe/MgCdTe double heterostructures (DHs) are grown on InSb substrates using molecular beam epitaxy and reveal strong photoluminescence with over double the intensity of a GaAs/AlGaAs DH with an identical layer structure design grown on GaAs. Time-resolved photoluminescence of the CdTe/MgCdTe DH gives a Shockley-Read-Hall recombination lifetime of 86 ns, which is more than one order of magnitude longer than that of typical polycrystalline CdTe films. These findings indicate that monocrystalline CdTe/MgCdTe DHs effectively reduce surface recombination, have limited nonradiative interface recombination, and are promising for solar cells that could reach power conversion efficiencies similar to that of GaAs.

  10. Progress on a cryogenically cooled RF gun polarized electron source

    SciTech Connect (OSTI)

    Fliller, R.P., III; Edwards, H.; /Fermilab

    2006-08-01

    RF guns have proven useful in multiple accelerator applications. An RF gun capable of producing polarized electrons is an attractive electron source for the ILC or an electron-ion collider. Producing such a gun has proven elusive. The NEA GaAs photocathode needed for polarized electron production is damaged by the vacuum environment in an RF gun. Electron and ion back bombardment can also damage the cathode. These problems must be mitigated before producing an RF gun polarized electron source. In this paper we report continuing efforts to improve the vacuum environment in a normal conducting RF gun by cooling it with liquid nitrogen after a high temperature vacuum bake out. We also report on a design of a cathode preparation chamber to produce bulk GaAs photocathodes for testing in such a gun. Future directions are also discussed.

  11. Multi-phonon-assisted absorption and emission in semiconductors and its potential for laser refrigeration

    SciTech Connect (OSTI)

    Khurgin, Jacob B.

    2014-06-02

    Laser cooling of semiconductors has been an elusive goal for many years, and while attempts to cool the narrow gap semiconductors such as GaAs are yet to succeed, recently, net cooling has been attained in a wider gap CdS. This raises the question of whether wider gap semiconductors with higher phonon energies and stronger electron-phonon coupling are better suitable for laser cooling. In this work, we develop a straightforward theory of phonon-assisted absorption and photoluminescence of semiconductors that involves more than one phonon and use to examine wide gap materials, such as GaN and CdS and compare them with GaAs. The results indicate that while strong electron-phonon coupling in both GaN and CdS definitely improves the prospects of laser cooling, large phonon energy in GaN may be a limitation, which makes CdS a better prospect for laser cooling.

  12. Impact of the modulation doping layer on the ? = 5/2 anisotropy

    SciTech Connect (OSTI)

    Shi, X.; Pan, W.; Baldwin, K. W.; West, K. W.; Pfeiffer, L. N.; Tsui, D. C.

    2015-03-30

    We have carried out a systematic study of the tilted magnetic field induced anisotropy at the Landau level filling factor ? = 5/2 in a series of high quality GaAs quantum wells, where the setback distance (d) between the modulation doping layer and the GaAs quantum well is varied from 33 to 164 nm. We have observed that in the sample of the smallest d, electronic transport is anisotropic when the in-plane magnetic field (Bip) is parallel to the [110] crystallographic direction, but remains more or less isotropic when Bip // [110]. In contrast, in the sample of largest d, electronic transport is anisotropic in both crystallographic directions. Lastly, our results clearly show that the modulation doping layer plays an important role in the tilted field induced ? = 5/2 anisotropy.

  13. Electron Traps Detected in p-type GaAsN Using Deep Level Transient Spectroscopy

    SciTech Connect (OSTI)

    Johnston, S.; Kurtz, S.; Friedman, D.; Ptak, A.; Ahrenkiel, R.; Crandall, R.

    2005-01-01

    The GaAsN alloy can have a band gap as small as 1.0 eV when the nitrogen composition is about 2%. Indium can also be added to the alloy to increase lattice matching to GaAs and Ge. These properties are advantageous for developing a highly-efficient, multi-junction solar cell. However, poor GaAsN cell properties, such as low open-circuit voltage, have led to inadequate performance. Deep-level transient spectroscopy of p-type GaAsN has identified an electron trap having an activation energy near 0.2 eV and a trap density of at least 1016 cm-3. This trap level appears with the addition of small amounts of nitrogen to GaAs, which also corresponds to an increased drop in open-circuit voltage.

  14. Beyond Silicon: Cutting the Costs of Solar Power | U.S. DOE Office of Science (SC)

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    Beyond Silicon: Cutting the Costs of Solar Power Stories of Discovery & Innovation Beyond Silicon: Cutting the Costs of Solar Power Enlarge Photo Courtesy of University of Illinois Mechanically flexible, high efficiency solar module that uses an interconnected array of microscale GaAs photovoltaic cells, grown in a multilayer stack on a wafer and then printed onto a sheet of plastic. Enlarge Photo 04.15.11 Beyond Silicon: Cutting the Costs of Solar Power New method of fabricating

  15. Beam driven upper-hybrid-wave instability in quantized semiconductor plasmas

    SciTech Connect (OSTI)

    Jamil, M.; Rasheed, A.; Rozina, Ch.; Moslem, W. M.; Centre for Theoretical Physics, The British University in Egypt , El-Shorouk City, Cairo ; Salimullah, M.

    2014-02-15

    The excitation of Upper-Hybrid waves (UHWs) induced by electron beam in semiconductor plasma is examined using quantum hydrodynamic model. Various quantum effects are taken into account including recoil effect, Fermi degenerate pressure, and exchange-correlation potential. The bandwidth of the UHWs spectrum shows that the system supports purely growing unstable mode. The latter has been studied for diversified parameters of nano-sized GaAs semiconductor.

  16. Manufacturing of ultra-high efficiency thin-film concentrator cells

    SciTech Connect (OSTI)

    Gale, R. )

    1992-02-01

    This report describes a research project to study developments required to expedite commercializing the GaAs solar cell concentrator technology. We baseline the GaAs concentrator cell and 1000X module design into pilot operation at Kopin Corporation. To attain these improvements, we will use Kopin's existing pilot line to produce cleavage of lateral epitaxial film for transfer (CLEFT) GaAs solar cells; these cells already exhibit efficiencies of about 24% at air mass 1.5. We will modify the CLEFT cell to form concentrators that perform well at 500--1000 suns. We will derive the know-how for this modification from an integration of Kopin and VS Corporation technologies. The pilot line will be broadened to include cell receiver and module assembly, using VS Corporation technology obtained from Varian as a baseline. A second-generation design will be formulated to address improvements in the module, and these will be incorporated into the pilot line along with the CLEFT concentrator cell. In parallel, we integrate Kopin's CLEFT GaAs cell technology with the advanced AlGaAs and InGaAs material technology obtained by VS Corporation from Varian to develop a near-term, two-junction mechanical stack with an efficiency of 35%. The receiver thus developed will be compatible with a three-junction approach that has been proposed elsewhere by Kopin. Using a three-junction stack can yield an efficiency of over 40%, and when such cells become available, the pilot line process will have been designed to use them. 11 refs.

  17. Laboratory Testing at STC | Department of Energy

    Office of Energy Efficiency and Renewable Energy (EERE) Indexed Site

    Laboratory Testing at STC Laboratory Testing at STC Presented at the PV Module Reliability Workshop, February 26 - 27 2013, Golden, Colorado PDF icon pvmrw13_ps1_pearl_propst.pdf More Documents & Publications PID Failure of c-Si and Thin-Film Modules and Possible Correlation with Leakage Currents High-Efficiency GaAs Thin-Film Solar Cell Reliability Salvage Values Determines Reliability of Used Photovoltaics

  18. Heterojunction solar cell

    DOE Patents [OSTI]

    Olson, Jerry M. (Lakewood, CO)

    1994-01-01

    A high-efficiency single heterojunction solar cell wherein a thin emitter layer (preferably Ga.sub.0.52 In.sub.0.48 P) forms a heterojunction with a GaAs absorber layer. The conversion effiency of the solar cell is at least 25.7%. The solar cell preferably includes a passivating layer between the substrate and the absorber layer. An anti-reflection coating is preferably disposed over the emitter layer.

  19. Current and lattice matched tandem solar cell

    DOE Patents [OSTI]

    Olson, Jerry M. (Lakewood, CO)

    1987-01-01

    A multijunction (cascade) tandem photovoltaic solar cell device is fabricated of a Ga.sub.x In.sub.1-x P (0.505.ltoreq.X.ltoreq.0.515) top cell semiconductor lattice matched to a GaAs bottom cell semiconductor at a low-resistance heterojunction, preferably a p+/n+ heterojunction between the cells. The top and bottom cells are both lattice matched and current matched for high efficiency solar radiation conversion to electrical energy.

  20. 1.3??m photoluminescence of Ge/GaAs multi-quantum-well structure

    SciTech Connect (OSTI)

    Aleshkin, V. Ya.; Dubinov, A. A. Kudryavtsev, K. E.; Rumyantsev, V. V.; Tonkikh, A. A.; Zakharov, N. D.; Zvonkov, B. N.

    2014-01-28

    In this paper, we report on photoluminescence studies of a multiple quantum well Ge/GaAs heterostructure grown by laser-assisted sputtering. A broad luminescence peak is found at about 1.3??m at room temperature. We attribute this peak to the direct band gap transitions between ?-valley electrons in the GaAs matrix and valence band heavy holes in Ge quantum wells.

  1. Heterojunction solar cell

    DOE Patents [OSTI]

    Olson, J.M.

    1994-08-30

    A high-efficiency single heterojunction solar cell is described wherein a thin emitter layer (preferably Ga[sub 0.52]In[sub 0.48]P) forms a heterojunction with a GaAs absorber layer. The conversion efficiency of the solar cell is at least 25.7%. The solar cell preferably includes a passivating layer between the substrate and the absorber layer. An anti-reflection coating is preferably disposed over the emitter layer. 1 fig.

  2. High-efficiency, thin-film solar cells. Annual subcontractor report, 1 July 1991--30 June 1992

    SciTech Connect (OSTI)

    Gale, R.P.

    1994-01-01

    This report describes work on a 3-year research program to investigate thin-film GaAs/GaInP cells using the cleavage of lateral epitaxial film for transfer (CLEFT) technique, and to determine the process to enable overgrowth of GaAs films using organometallic chemistry. Application of the CLEFT thin-film technique to GaInP/GaAs solar cells and organometallic overgrowth was investigated. A problem of alloy contamination was identified and controlled, leading to higher quality layers. Solar cell structures were grown and fabricated using previously determined growth parameters for GaAs and GaInP. With the improved materials developed significant improvements were made in solar cell performance. Conditions for in-situ overgrowth by organometallic chemical vapor deposition (OMCVD) were determined and continuous GaAs layers were grown over a separation mask layer. The layers were successfully separated from their substrate using the CLEFT process, demonstrating the application of overgrowth using OM chemistry with HCl.

  3. Variation of lattice constant and cluster formation in GaAsBi

    SciTech Connect (OSTI)

    Puustinen, J.; Schramm, A.; Guina, M.; Wu, M.; Luna, E.; Laukkanen, P.; Laitinen, M.; Sajavaara, T.

    2013-12-28

    We investigate the structural properties of GaAsBi layers grown by molecular beam epitaxy on GaAs at substrate temperatures between 220315 C. Irrespective of the growth temperature, the structures exhibited similar Bi compositions, and good overall crystal quality as deduced from X-Ray diffraction measurements. After thermal annealing at temperatures as low as 500 C, the GaAsBi layers grown at the lowest temperatures exhibited a significant reduction of the lattice constant. The lattice variation was significantly larger for Bi-containing samples than for Bi-free low-temperature GaAs samples grown as a reference. Rutherford backscattering spectrometry gave no evidence of Bi diffusing out of the layer during annealing. However, dark-field and Z-contrast transmission electron microscopy analyses revealed the formation of GaAsBi clusters with a Bi content higher than in the surrounding matrix, as well as the presence of metallic As clusters. The apparent reduction of the lattice constant can be explained by a two-fold process: the diffusion of the excess As incorporated within As{sub Ga} antisites to As clusters, and the reduction of the Bi content in the GaAs matrix due to diffusion of Bi to GaAsBi clusters. Diffusion of both As and Bi are believed to be assisted by the native point defects, which are present in the low-temperature as-grown material.

  4. ILC @ SLAC R&D Program for a Polarized RF Gun

    SciTech Connect (OSTI)

    Clendenin, J.E.; Brachman, A.; Dowell, D.H.; Garwin, E.L.; Ioakemidi, K.; Kirby, R.E.; Maruyama, T.; Miller, R.A.; Prescott, C.Y.; Wang, J.W.; Lewellen, J.W.; Prepost, R.; /Wisconsin U., Madison

    2006-01-25

    Photocathode rf guns produce high-energy low-emittance electron beams. DC guns utilizing GaAs photocathodes have proven successful for generating polarized electron beams for accelerators, but they require rf bunching systems that significantly increase the transverse emittance of the beam. With higher extraction field and beam energy, rf guns can support higher current densities at the cathode. The source laser system can then be used to generate the high peak current, relatively low duty-factor micropulses required by the ILC without the need for post-extraction rf bunching. The net result is that the injection system for a polarized rf gun can be identical to that for an unpolarized rf gun. However, there is some uncertainty as to the survivability of an activated GaAs cathode in the environment of an operating rf gun. Consequently, before attempting to design a polarized rf gun for the ILC, SLAC plans to develop an rf test gun to demonstrate the rf operating conditions suitable for an activated GaAs cathode.

  5. Activation Layer Stabilization of High Polarization Photocathodes in Sub-Optimal RF Gun Environments

    SciTech Connect (OSTI)

    Gregory A. Mulhollan

    2010-11-16

    Specific activation recipes for bulk, 100 nm thick MBE grown and high polarization III-V photocathode material have been developed which mitigate the effects of exposure to background gasses. Lifetime data using four representative gasses were acquired for bulk GaAs, 100 nm unstrained GaAs and strained superlattice GaAs/GaAsP, all activated both with Cs and then Cs and Li (bi-alkali). Each photoemitter showed marked resilience improvement when activated using the bi-alkali recipe compared to the standard single alkali recipe. A dual alkali activation system at SLAC was constructed, baked and commissioned with the purpose of performing spin-polarization measurements on electrons emitted from the bi-alkali activated surfaces. An end station at SSRL was configured with the required sources for energy resolved photoemission measurements on the bi-alkali activated and CO2 dosed surfaces. The bi-alkali recipes were successfully implemented at SLAC/SSRL. Measurements at SLAC of the photoelectron spin-polarization from the modified activation surface showed no sign of a change in value compared to the standard activated material, i.e., no ill effects. Analysis of photoemission data indicates that the addition of Li to the activation layer results in a multi-layer structure. The presence of Li in the activation layer also acts as an inhibitor to CO2 absorption, hence better lifetimes in worse vacuum were achieved. The bi-alkali activation has been tested on O2 activated GaAs for comparison with NF3 activated surfaces. Comparable resilience to CO2 exposure was achieved for the O2 activated surface. An RF PECVD amorphous silicon growth system was modified to allow high temperature heat cleaning of GaAs substrates prior to film deposition. Growth versus thickness data were collected. Very thin amorphous silicon germanium layers were optimized to exhibit good behavior as an electron emitter. Growth of the amorphous silicon germanium films on the above substrates was fine tuned with respect to time and power to moderate plasma damage to the photo-generating layer. Auger electron spectroscopy was used to analyze the composition and thickness of the emitter layers. AFM studies showed conformal growth on the GaAs substrates. Measurements at SLAC on the photoemitted electrons from high polarization substrates coated with amorphous silicon germanium indicated an ~10% relative drop in spin-polarization at the wavelength corresponding to the maximum spin-polarization when compared to the uncoated material,

  6. The effect of cure conditions on the stability of cement waste forms after immersion in water

    SciTech Connect (OSTI)

    Siskind, B.; Adams, J.W.; Clinton, J.H.; Piciulo, P.L.; McDaniel, K.

    1988-01-01

    We investigated the effects of curing conditions on the stability of cement-solidified ion-exchange resins after immersion in water. The test specimens consisted of partially depleted mixed-bed bead resins solidified in one of three vendor-supplied Portland I cement formulations, in a reference cement formulation, or in a gypsum-based binder formulation. We cured samples prepared using each formulation in sealed containers for periods of 7, 14, or 28 days as well as in air or with an accelerated heat cure prior to 90-day immersion in water. Two cement formulations exhibited apparent Portland-cement-like behavior, i.e., compressive strength increased or stabilized with increasing cure time. Two cement formulations exhibited behavior apparently unlike that of Portland cement, i.e., compressive strength decreased with increasing cure time. Such non-Portland-cement-like behavior is correlated with higher waste loadings. The gypsum-based formulation exhibited approximately constant compressive strength with cure time. Accelerated heat cures may not give compressive strengths representative of real-time cures. Some physical deterioration (cracking, spalling) of the waste form occurs during immersion.

  7. Setting and stiffening of cementitious components in Cast Stone waste form for disposal of secondary wastes from the Hanford waste treatment and immobilization plant

    SciTech Connect (OSTI)

    Chung, Chul-Woo; Chun, Jaehun, E-mail: jaehun.chun@pnnl.gov; Um, Wooyong; Sundaram, S.K.; Westsik, Joseph H.

    2013-04-01

    Cast Stone is a cementitious waste form, a viable option to immobilize secondary nuclear liquid wastes generated from the Hanford Waste Treatment and Immobilization Plant. However, no study has been performed to understand the flow and stiffening behavior, which is essential to ensure proper workability and is important to safety in a nuclear waste field-scale application. X-ray diffraction, rheology, and ultrasonic wave reflection methods were used to understand the specific phase formation and stiffening of Cast Stone. Our results showed a good correlation between rheological properties of the fresh mixture and phase formation in Cast Stone. Secondary gypsum formation was observed with low concentration simulants, and the formation of gypsum was suppressed in high concentration simulants. A threshold concentration for the drastic change in stiffening was found at 1.56 M Na concentration. It was found that the stiffening of Cast Stone was strongly dependent on the concentration of simulant. Highlights: A combination of XRD, UWR, and rheology gives a better understanding of Cast Stone. Stiffening of Cast Stone was strongly dependent on the concentration of simulant. A drastic change in stiffening of Cast Stone was found at 1.56 M Na concentration.

  8. Setting and Stiffening of Cementitious Components in Cast Stone Waste Form for Disposal of Secondary Wastes from the Hanford waste treatment and immobilization plant

    SciTech Connect (OSTI)

    Chung, Chul-Woo; Chun, Jaehun; Um, Wooyong; Sundaram, S. K.; Westsik, Joseph H.

    2013-04-01

    Cast stone is a cementitious waste form, a viable option to immobilize secondary nuclear liquid wastes generated from Hanford vitrification plant. While the strength and radioactive technetium leaching of different waste form candidates have been reported, no study has been performed to understand the flow and stiffening behavior of Cast Stone, which is essential to ensure the proper workability, especially considering necessary safety as a nuclear waste form in a field scale application. The rheological and ultrasonic wave reflection (UWR) measurements were used to understand the setting and stiffening Cast Stone batches. X-ray diffraction (XRD) was used to find the correlation between specific phase formation and the stiffening of the paste. Our results showed good correlation between rheological properties of the fresh Cast Stone mixture and phase formation during hydration of Cast Stone. Secondary gypsum formation originating from blast furnace slag was observed in Cast Stone made with low concentration simulants. The formation of gypsum was suppressed in high concentration simulants. It was found that the stiffening of Cast Stone was strongly dependent on the concentration of simulant. A threshold concentration for the drastic change in stiffening was found at 1.56 M Na concentration.

  9. Composite materials for thermal energy storage

    DOE Patents [OSTI]

    Benson, D.K.; Burrows, R.W.; Shinton, Y.D.

    1985-01-04

    A composite material for thermal energy storage based upon polyhydric alcohols, such as pentaerythritol, trimethylol ethane (also known as pentaglycerine), neopentyl glycol and related compounds including trimethylol propane, monoaminopentaerythritol, diamino-pentaerythritol and tris(hydroxymethyl)acetic acid, separately or in combinations, which provide reversible heat storage through crystalline phase transformations. These PCM's do not become liquid during use and are in contact with at least one material selected from the group consisting of metals, carbon, siliceous, plastic, cellulosic, natural fiber, artificial fiber, concrete, gypsum, porous rock, and mixtures thereof. Particulate additions such as aluminum or graphite powders, as well as metal and carbon fibers can also be incorporated therein. Particulate and/or fibrous additions can be introduced into molten phase change materials which can then be cast into various shapes. After the phase change materials have solidified, the additions will remain dispersed throughout the matrix of the cast solid. The polyol is in contact with at least one material selected from the group consisting of metals, carbon, siliceous, plastic, cellulosic, natural fiber, artificial fiber, concrete, gypsum, and mixtures thereof.

  10. Composite materials for thermal energy storage

    DOE Patents [OSTI]

    Benson, David K. (Golden, CO); Burrows, Richard W. (Conifer, CO); Shinton, Yvonne D. (Northglenn, CO)

    1986-01-01

    The present invention discloses composite material for thermal energy storage based upon polyhydric alcohols, such as pentaerythritol, trimethylol ethane (also known as pentaglycerine), neopentyl glycol and related compounds including trimethylol propane, monoaminopentaerythritol, diamino-pentaerythritol and tris(hydroxymethyl)acetic acid, separately or in combinations, which provide reversible heat storage through crystalline phase transformations. These phase change materials do not become liquid during use and are in contact with at least one material selected from the group consisting of metals, carbon siliceous, plastic, cellulosic, natural fiber, artificial fiber, concrete, gypsum, porous rock, and mixtures thereof. Particulate additions, such as aluminum or graphite powders, as well as metal and carbon fibers can also be incorporated therein. Particulate and/or fibrous additions can be introduced into molten phase change materials which can then be cast into various shapes. After the phase change materials have solidified, the additions will remain dispersed throughout the matrix of the cast solid. The polyol is in contact with at least one material selected from the group consisting of metals, carbon siliceous, plastic, cellulosic, natural fiber, artificial fiber, concrete, gypsum, and mixtures thereof.

  11. Multiphase flow and multicomponent reactive transport model of the ventilation experiment in Opalinus clay

    SciTech Connect (OSTI)

    Zheng, L.; Samper, J.; Montenegro, L.; Major, J.C.

    2008-10-15

    During the construction and operational phases of a high-level radioactive waste (HLW) repository constructed in a clay formation, ventilation of underground drifts will cause desaturation and oxidation of the rock. The Ventilation Experiment (VE) was performed in a 1.3 m diameter unlined horizontal microtunnel on Opalinus clay at Mont Terri underground research laboratory in Switzerland to evaluate the impact of desaturation on rock properties. A multiphase flow and reactive transport model of VE is presented here. The model accounts for liquid, vapor and air flow, evaporation/condensation and multicomponent reactive solute transport with kinetic dissolution of pyrite and siderite and local-equilibrium dissolution/precipitation of calcite, ferrihydrite, dolomite, gypsum and quartz. Model results reproduce measured vapor flow, liquid pressure and hydrochemical data and capture the trends of measured relative humidities, although such data are slightly overestimated near the rock interface due to uncertainties in the turbulence factor. Rock desaturation allows oxygen to diffuse into the rock and triggers pyrite oxidation, dissolution of calcite and siderite, precipitation of ferrihydrite, dolomite and gypsum and cation exchange. pH in the unsaturated rock varies from 7.8 to 8 and is buffered by calcite. Computed changes in the porosity and the permeability of Opalinus clay in the unsaturated zone caused by oxidation and mineral dissolution/precipitation are smaller than 5%. Therefore, rock properties are not expected to be affected significantly by ventilation of underground drifts during construction and operational phases of a HLW repository in clay.

  12. Production development and utilization of Zimmer Station wet FGD by-products. Final report. Volume 1, Executive summary

    SciTech Connect (OSTI)

    Smith, Kevin; Beeghly, Joel H.

    2000-11-30

    About 30 electric utility units with a combined total of 15,000 MW utilize magnesium enhanced lime flue gas desulfurization (FGD) systems. A disadvantage of this and other inhibited or natural oxidation wet FGD systems is the capital and operating cost associated with landfill disposal of the calcium sulfite based solids. Fixation to stabilize the solids for compaction in a landfill also consumes fly ash that otherwise may be marketable. This Executive Summary describes efforts to dewater the magnesium hydroxide and gypsum slurries and then process the solids into a more user friendly and higher value form. To eliminate the cost of solids disposal in its first generation Thiosorbic® system, the Dravo Lime Company developed the ThioClear® process that utilizes a magnesium based absorber liquor to remove S02 with minimal suspended solids. Magnesium enhanced lime is added to an oxidized bleed stream of thickener overflow (TOF) to produce magnesium hydroxide [Mg(OH)2] and gypsum (CaS04 • 2H20), as by-products. This process was demonstrated at the 3 to 5 MW closed loop FGD system pilot plant at the Miami Fort Station of Cinergy, near Cincinnati, Ohio with the help of OCDO Grant Agreement CDO/D-91-6. A similar process strictly for'recovery and reuse of Mg(OH)2 began operation at the Zimmer Station of Cinergy in late 1994 that can produce 900 pounds of Mg(OH)2 per hour and 2,600 pounds of gypsum per hour. This by-product plant, called the Zimmer Slipstream Magnesium Hydroxide Recovery Project Demonstration, was conducted with the help of OCDO Grant Agreement CDO/D-921-004. Full scale ThioClear® plants began operating in 1997 at the 130 MW Applied Energy Services plant, in Monaca, PA, and in year 2000 at the 1,330 MW Allegheny Energy Pleasants Station at St. Marys, WV.

  13. An inverted AlGaAs/GaAs patterned-Ge tunnel junction cascade concentrator solar cell. Final subcontract report, 1 January 1991--31 August 1992

    SciTech Connect (OSTI)

    Venkatasubramanian, R.

    1993-01-01

    This report describes work to develop inverted-grown Al{sub 0.34}Ga{sub 0.66}As/GaAs cascades. Several significant developments are reported on as follows: (1) The AM1.5 1-sun total-area efficiency of the top Al{sub 0.34}Ga{sub 0.66}As cell for the cascade was improved from 11.3% to 13.2% (NREL measurement [total-area]). (2) The ``cycled`` organometallic vapor phase epitaxy growth (OMVPE) was studied in detail utilizing a combination of characterization techniques including Hall-data, photoluminescence, and secondary ion mass spectroscopy. (3) A technique called eutectic-metal-bonding (EMB) was developed by strain-free mounting of thin GaAs-AlGaAs films (based on lattice-matched growth on Ge substrates and selective plasma etching of Ge substrates) onto Si carrier substrates. Minority-carrier lifetime in an EMB GaAs double-heterostructure was measured as high as 103 nsec, the highest lifetime report for a freestanding GaAs thin film. (4) A thin-film, inverted-grown GaAs cell with a 1-sun AM1.5 active-area efficiency of 20.3% was obtained. This cell was eutectic-metal-bonded onto Si. (5) A thin-film inverted-grown, Al{sub 0.34}Ga{sub 0.66}As/GaAs cascade with AM1.5 efficiency of 19.9% and 21% at 1-sun and 7-suns, respectively, was obtained. This represents an important milestone in the development of an AlGaAs/GaAs cascade by OMVPE utilizing a tunnel interconnect and demonstrates a proof-of-concept for the inverted-growth approach.

  14. An inverted AlGaAs/GaAs patterned-Ge tunnel junction cascade concentrator solar cell

    SciTech Connect (OSTI)

    Venkatasubramanian, R. )

    1993-01-01

    This report describes work to develop inverted-grown Al[sub 0.34]Ga[sub 0.66]As/GaAs cascades. Several significant developments are reported on as follows: (1) The AM1.5 1-sun total-area efficiency of the top Al[sub 0.34]Ga[sub 0.66]As cell for the cascade was improved from 11.3% to 13.2% (NREL measurement [total-area]). (2) The cycled'' organometallic vapor phase epitaxy growth (OMVPE) was studied in detail utilizing a combination of characterization techniques including Hall-data, photoluminescence, and secondary ion mass spectroscopy. (3) A technique called eutectic-metal-bonding (EMB) was developed by strain-free mounting of thin GaAs-AlGaAs films (based on lattice-matched growth on Ge substrates and selective plasma etching of Ge substrates) onto Si carrier substrates. Minority-carrier lifetime in an EMB GaAs double-heterostructure was measured as high as 103 nsec, the highest lifetime report for a freestanding GaAs thin film. (4) A thin-film, inverted-grown GaAs cell with a 1-sun AM1.5 active-area efficiency of 20.3% was obtained. This cell was eutectic-metal-bonded onto Si. (5) A thin-film inverted-grown, Al[sub 0.34]Ga[sub 0.66]As/GaAs cascade with AM1.5 efficiency of 19.9% and 21% at 1-sun and 7-suns, respectively, was obtained. This represents an important milestone in the development of an AlGaAs/GaAs cascade by OMVPE utilizing a tunnel interconnect and demonstrates a proof-of-concept for the inverted-growth approach.

  15. Observation of dynamic water microadsorption on Au surface

    SciTech Connect (OSTI)

    Huang, Xiaokang, E-mail: xiaokang.huang@tqs.com; Gupta, Gaurav; Gao, Weixiang; Tran, Van; Nguyen, Bang; McCormick, Eric; Cui, Yongjie; Yang, Yinbao; Hall, Craig; Isom, Harold [TriQuint Semiconductor, Inc., 500 W Renner Road, Richardson, Texas 75080 (United States)

    2014-05-15

    Experimental and theoretical research on water wettability, adsorption, and condensation on solid surfaces has been ongoing for many decades because of the availability of new materials, new detection and measurement techniques, novel applications, and different scales of dimensions. Au is a metal of special interest because it is chemically inert, has a high surface energy, is highly conductive, and has a relatively high melting point. It has wide applications in semiconductor integrated circuitry, microelectromechanical systems, microfluidics, biochips, jewelry, coinage, and even dental restoration. Therefore, its surface condition, wettability, wear resistance, lubrication, and friction attract a lot of attention from both scientists and engineers. In this paper, the authors experimentally investigated Au{sub 2}O{sub 3} growth, wettability, roughness, and adsorption utilizing atomic force microscopy, scanning electron microscopy, reflectance spectrometry, and contact angle measurement. Samples were made using a GaAs substrate. Utilizing a super-hydrophilic Au surface and the proper surface conditions of the surrounding GaAs, dynamic microadsorption of water on the Au surface was observed in a clean room environment. The Au surface area can be as small as 12??m{sup 2}. The adsorbed water was collected by the GaAs groove structure and then redistributed around the structure. A model was developed to qualitatively describe the dynamic microadsorption process. The effective adsorption rate was estimated by modeling and experimental data. Devices for moisture collection and a liquid channel can be made by properly arranging the wettabilities or contact angles of different materials. These novel devices will be very useful in microfluid applications or biochips.

  16. Structural, morphological, and magnetic characterization of In{sub 1-x}Mn{sub x}As quantum dots grown by molecular beam epitaxy

    SciTech Connect (OSTI)

    Ferri, F. A.; Marega, E. Jr.; Coelho, L. N.; Kunets, V. P.; Salamo, G. J.

    2012-08-01

    In this paper, we present a method to order low temperature (LT) self-assembled ferromagnetic In{sub 1-x}Mn{sub x}As quantum dots (QDs) grown by molecular beam epitaxy (MBE). The ordered In{sub 1-x}Mn{sub x}As QDs were grown on top of a non-magnetic In{sub 0.4}Ga{sub 0.6}As/GaAs(100) QDs multi-layered structure. The modulation of the chemical potential, due to the stacking, provides a nucleation center for the LT In{sub 1-x}Mn{sub x}As QDs. For particular conditions, such as surface morphology and growth conditions, the In{sub 1-x}Mn{sub x}As QDs align along lines like chains. This work also reports the characterization of QDs grown on plain GaAs(100) substrates, as well as of the ordered structures, as function of Mn content and growth temperature. The substitutional Mn incorporation in the InAs lattice and the conditions for obtaining coherent and incoherent structures are discussed from comparison between Raman spectroscopy and x-ray analysis. Ferromagnetic behavior was observed for all structures at 2 K. We found that the magnetic moment axis changes from [110] in In{sub 1-x}Mn{sub x}As over GaAs to [1-10] for the ordered In{sub 1-x}Mn{sub x}As grown over GaAs template.

  17. A noninvasive bunch length monitor for femtosecond electron bunches

    SciTech Connect (OSTI)

    Wang, D.X.; Kraft, G.A.; Price, E.; Wood, P.A.; Porterfield, D.W.; Crowe, T.W.

    1997-01-01

    A bunch length monitor for ultrashort (90 fs to 1 ps) electron bunches using a coherent synchrotron radiation detection techniques has been developed in a collaboration between the Thomas Jefferson National accelerator Facility (Jefferson Lab) and the University of Virginia. The noninvasive, high-resolution, high-sensitivity, low-noise monitor employs a state-of-the-art {open_quotes}bandpass{close_quotes} GaAs Schottky whisker diode operated at room temperature. This letter presents the monitor{close_quote}s performance. {copyright} {ital 1997 American Institute of Physics.}

  18. Atomic moments in Mn2CoAl thin films analyzed by X-ray magnetic circular dichroism

    SciTech Connect (OSTI)

    Jamer, M. E.; Assaf, B. A.; Sterbinsky, G. E.; Arena, D. A.; Heiman, D.

    2014-12-05

    Spin gapless semiconductors are known to be strongly affected by structural disorder when grown epitaxially as thin films. The magnetic properties of Mn2CoAl thin films grown on GaAs (001) substrates are investigated here as a function of annealing. This study investigates the atomic-specific magnetic moments of Mn and Co atoms measured through X-ray magnetic circular dichroism as a function of annealing and the consequent structural ordering. Results indicate that the structural distortion mainly affects the Mn atoms as seen by the reduction of the magnetic moment from its predicted value.

  19. InAs quantum dot growth on Al{sub x}Ga{sub 1?x}As by metalorganic vapor phase epitaxy for intermediate band solar cells

    SciTech Connect (OSTI)

    Jakomin, R.; Kawabata, R. M. S.; Souza, P. L.; Mouro, R. T.; Pires, M. P.; Micha, D. N.

    2014-09-07

    InAs quantum dot multilayers have been grown using Al{sub x}Ga{sub 1?x}As spacers with dimensions and compositions near the theoretical values for optimized efficiencies in intermediate band photovoltaic cells. Using an aluminium composition of x?=?0.3 and InAs dot vertical dimensions of 5?nm, transitions to an intermediate band with energy close to the ideal theoretical value have been obtained. Optimum size uniformity and density have been achieved by capping the quantum dots with GaAs following the indium-flush method. This approach has also resulted in minimization of crystalline defects in the epilayer structure.

  20. Understanding polarization properties of InAs quantum dots by atomistic modeling of growth dynamics

    SciTech Connect (OSTI)

    Tasco, Vittorianna; Todaro, Maria Teresa; De Giorgi, Milena; Passaseo, Adriana; Usman, Muhammad

    2013-12-04

    A model for realistic InAs quantum dot composition profile is proposed and analyzed, consisting of a double region scheme with an In-rich internal core and an In-poor external shell, in order to mimic the atomic scale phenomena such as In-Ga intermixing and In segregation during the growth and overgrowth with GaAs. The parameters of the proposed model are derived by reproducing the experimentally measured polarization data. Further understanding is developed by analyzing the strain fields which suggests that the two-composition model indeed results in lower strain energies than the commonly applied uniform composition model.

  1. Atomic moments in Mn2CoAl thin films analyzed by X-ray magnetic circular dichroism

    SciTech Connect (OSTI)

    Jamer, M.; Sterbinsky, G.; Assaf, B.; Arena, D.; Heiman, D.

    2014-12-05

    Spin gapless semiconductors are known to be strongly affected by structural disorder when grown epitaxially as thin films. The magnetic properties of Mn2CoAl thin films grown on GaAs (001) substrates are investigated here as a function of annealing. This study investigates the atomic-specific magnetic moments of Mn and Co atoms measured through X-ray magnetic circular dichroism as a function of annealing and the consequent structural ordering. The results indicate that the structural distortion mainly affects the Mn atoms as seen by the reduction of the magnetic moment from its predicted value. (auth)

  2. DC characteristics of OMVPE-grown N-p-n InGaP/InGaAsN DHBTs

    SciTech Connect (OSTI)

    Li, N.Y.; Chang, P.C.; Baca, A.G.; Xie, X.M.; Sharps, P.R.; Hou, H.Q.

    2000-01-04

    The authors demonstrate, for the first time, a functional N-p-n heterojunction bipolar transistor using a novel material, InGaAsN, with a bandgap energy of 1.2eV as the p-type base layer. A 300{angstrom}-thick In{sub x}Ga{sub 1-x}As graded layer was introduced to reduce the conduction band offset at the p-type InGaAsN base and n-type GaAs collector junction. For an emitter size of 500 {mu}m{sup 2}, a peak current gain of 5.3 has been achieved.

  3. Photovoltaic Manufacturing Technology report, Phase 1

    SciTech Connect (OSTI)

    Mason, A.V.; Lillington, D.R.

    1992-10-01

    This report describes subcontracted research by Spectrolab, Inc., to address tasks outlined in the National Renewable Energy Laboratory's (NREL) Letter of solicitation RC-0-10057. These tasks include the potential of making photovoltaics (PV) a more affordable energy source, as set forth in the goal of the PVMaT project. Spectrolab believes that the DOE cost goals can be met using three different types of cells: (1) silicon concentrator cells, (2) high efficiency GaAs concentrator cells, and (3) mechanically stacked multijunction cells.

  4. Bismuth nano-droplets for group-V based molecular-beam droplet epitaxy

    SciTech Connect (OSTI)

    Li, C.; Zeng, Z. Q.; Hirono, Y.; Morgan, T. A.; Hu, X.; Salamo, G. J.; Fan, D. S.; Wu, J.; Yu, S. Q.; Wang, Zh. M.

    2011-12-12

    Self-assembly of bismuth droplets at nanoscale on GaAs(100) surface using molecular beam epitaxy was demonstrated. Fine control of density and size was achieved by varying growth temperature and total bismuth deposition. Droplet density was tuned by roughly 3 orders of magnitude, and the density-temperature dependence was found to be consistent with classical nucleation theory. These results may extend the flexibility of droplet epitaxy by serving as templates for group V based droplet epitaxy, which is in contrast to conventional group III based droplet epitaxy and may encourage nanostructure formation of bismuth-containing materials.

  5. Photoluminescence studies of individual and few GaSb/GaAs quantum rings

    SciTech Connect (OSTI)

    Young, M. P.; Woodhead, C. S.; Roberts, J.; Noori, Y. J.; Noble, M. T.; Krier, A.; Hayne, M.; Young, R. J.; Smakman, E. P.; Koenraad, P. M.

    2014-11-15

    We present optical studies of individual and few GaSb quantum rings embedded in a GaAs matrix. Contrary to expectation for type-II confinement, we measure rich spectra containing sharp lines. These lines originate from excitonic recombination and are observed to have resolution-limited full-width at half maximum of 200 ?eV. The detail provided by these measurements allows the characteristic type-II blueshift, observed with increasing excitation power, to be studied at the level of individual nanostructures. These findings are in agreement with hole-charging being the origin of the observed blueshift.

  6. The progress of funnelling gun high voltage condition and beam test

    SciTech Connect (OSTI)

    Wang, E.; Ben-Zvi, I.; Gassner, D. M.; Lambiase, R.; Meng, W.; Rahman, O.; Pikin, A.; Rao, T.; Sheehy, B.; Skaritka, J.; Pietz, J.; Ackeret, M.; Yeckel, C.; Miller, R.; Dobrin, E.; Thompson, K.

    2015-05-03

    A prototype of a high average current polarized electron funneling gun as an eRHIC injector has been built at BNL. The gun was assembled and tested at Stangenes Incorporated. Two beams were generated from two GaAs photocathodes and combined by a switched combiner field. We observed the combined beams on a YAG crystal and measured the photocurrent by a Faraday cup. The gun has been shipped to Stony Brook University and is being tested there. In this paper we will describe the major components of the gun and recent beam test results. High voltage conditioning is discussed as well.

  7. Effect of exciton oscillator strength on upconversion photoluminescence in GaAs/AlAs multiple quantum wells

    SciTech Connect (OSTI)

    Kojima, Osamu, E-mail: kojima@phoenix.kobe-u.ac.jp; Okumura, Shouhei; Kita, Takashi [Department of Electrical and Electronic Engineering, Graduate School of Engineering, Kobe University, 1-1 Rokkodai, Nada, Kobe 657-8501 (Japan); Akahane, Kouichi [National Institute of Information and Communications Technology, 4-2-1 Nukui-kitamachi, Koganei, Tokyo 184-8795 (Japan)

    2014-11-03

    We report upconversion photoluminescence (UCPL) in GaAs/AlAs multiple quantum wells. UCPL from the AlAs barrier is caused by the resonant excitation of the excitons in the GaAs well. When the quantum well has sufficient miniband width, UCPL is hardly observed because of the small exciton oscillator strength. The excitation-energy and excitation-density dependences of UCPL intensity show the exciton resonant profile and a linear increase, respectively. These results demonstrate that the observed UCPL caused by the saturated two-step excitation process requires a large number of excitons.

  8. Wafer-Bonded Internal Back-Surface Reflectors for Enhanced TPV Performance

    SciTech Connect (OSTI)

    C.A. Wang; P.G. Murphy; P.W. O'Brien; D.A. Shiau; A.C. Anderson; Z.L. Liau; D.M. Depoy; G. Nichols

    2002-08-12

    This paper discusses recent efforts to realize GaInAsSb/GaSb TPV cells with an internal back-surface reflector (BSR). The cells are fabricated by wafer bonding the GaInAsSb/GaSb device layers to GaAs substrates with a dielectric/Au reflector, and subsequently removing the GaSb substrate. The internal BSR enhances optical absorption within the device while the dielectric layer provides electrical isolation. This approach is compatible with monolithic integration of series-connected TPV cells and can mitigate the requirements of filters used for front-surface spectral control.

  9. Transport Experiments on 2D Correlated Electron Physics in Semiconductors

    SciTech Connect (OSTI)

    Tsui, Daniel

    2014-03-24

    This research project was designed to investigate experimentally the transport properties of the 2D electrons in Si and GaAs, two prototype semiconductors, in several new physical regimes that were previously inaccessible to experiments. The research focused on the strongly correlated electron physics in the dilute density limit, where the electron potential energy to kinetic energy ratio rs>>1, and on the fractional quantum Hall effect related physics in nuclear demagnetization refrigerator temperature range on samples with new levels of purity and controlled random disorder.

  10. Thermally stimulated 315 THz emission at plasmon-phonon frequencies in polar semiconductors

    SciTech Connect (OSTI)

    Poela, J., E-mail: pozela@pfi.lt; Poela, K.; il?nas, A.; irmulis, E.; Kaalynas, I.; Jucien?, V.; Venckevi?ius, R. [Center for Physical Sciences and Technology, Semiconductor Physics Institute (Lithuania)

    2014-12-15

    The possibilities of distinguishing highly coherent terahertz emission at a specified frequency from the incoherent thermal emission of a hot body are considered. It is experimentally shown that the smooth planar surface (with no diffraction guides) of heated GaAs and AlGaAs wafers emits directed continuous-wave (cw) terahertz radiation at coupled surface plasmon-phonon vibrational frequencies. The recording of terahertz reflectance spectra is demonstrated as a method for the identification of plasmons, optical phonons, and coupled plasmon-phonon vibrations in semiconductors.

  11. Heterojunction solar cell with passivated emitter surface

    DOE Patents [OSTI]

    Olson, Jerry M. (Lakewood, CO); Kurtz, Sarah R. (Golden, CO)

    1994-01-01

    A high-efficiency heterojunction solar cell wherein a thin emitter layer (preferably Ga.sub.0.52 In.sub.0.48 P) forms a heterojunction with a GaAs absorber layer. A passivating window layer of defined composition is disposed over the emitter layer. The conversion efficiency of the solar cell is at least 25.7%. The solar cell preferably includes a passivating layer between the substrate and the absorber layer. An anti-reflection coating is preferably disposed over the window layer.

  12. Optical spectroscopy of quantum confined states in GaAs/AlGaAs quantum well tubes

    SciTech Connect (OSTI)

    Shi, Teng; Fickenscher, Melodie; Smith, Leigh; Jackson, Howard; Yarrison-Rice, Jan; Gao, Qiang; Tan, Hoe; Jagadish, Chennupati; Etheridge, Joanne; Wong, Bryan M.

    2013-12-04

    We have investigated the quantum confinement of electronic states in GaAs/Al{sub x}Ga{sub 1?x}As nanowire heterostructures which contain radial GaAs quantum wells of either 4nm or 8nm. Photoluminescence and photoluminescence excitation spectroscopy are performed on single nanowires. We observed emission and excitation of electron and hole confined states. Numerical calculations of the quantum confined states using the detailed structural information on the quantum well tubes show excellent agreement with these optical results.

  13. Atomic moments in Mn2CoAl thin films analyzed by X-ray magnetic circular dichroism

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Jamer, M. E.; Assaf, B. A.; Sterbinsky, G. E.; Arena, D. A.; Heiman, D.

    2014-12-05

    Spin gapless semiconductors are known to be strongly affected by structural disorder when grown epitaxially as thin films. The magnetic properties of Mn2CoAl thin films grown on GaAs (001) substrates are investigated here as a function of annealing. This study investigates the atomic-specific magnetic moments of Mn and Co atoms measured through X-ray magnetic circular dichroism as a function of annealing and the consequent structural ordering. Results indicate that the structural distortion mainly affects the Mn atoms as seen by the reduction of the magnetic moment from its predicted value.

  14. Electro optical tuning of Tamm-plasmon exciton-polaritons

    SciTech Connect (OSTI)

    Gessler, J.; Baumann, V.; Emmerling, M.; Amthor, M.; Winkler, K.; Schneider, C.; Kamp, M.; Hfling, S.

    2014-11-03

    We report on electro optical tuning of the emission from GaAs quantum wells resonantly coupled to a Tamm-plasmon mode in a hybrid metal/dielectric structure. The structures were studied via momentum resolved photoluminescence and photoreflectance spectroscopy, and the surface metal layer was used as a top gate, which allowed for a precise tuning of the quantum well emission via the quantum confined Stark effect. By tuning the resonance, we were able to observe the characteristic anticrossing behavior of a polaritonic emission in the strong light-matter coupling regime, yielding a Rabi splitting of (9.2??0.2) meV.

  15. Magneto-exciton-polariton condensation in a sub-wavelength high contrast grating based vertical microcavity

    SciTech Connect (OSTI)

    Fischer, J.; Brodbeck, S.; Worschech, L.; Kamp, M.; Schneider, C.; Hfling, S.; Zhang, B.; Wang, Z.; Deng, H.

    2014-03-03

    We comparably investigate the diamagnetic shift of an uncoupled quantum well exciton with a microcavity exciton-polariton condensate on the same device. The sample is composed of multiple GaAs quantum wells in an AlAs microcavity, surrounded by a Bragg reflector and a sub-wavelength high contrast grating reflector. Our study introduces an independent and easily applicable technique, namely, the measurement of the condensate diamagnetic shift, which directly probes matter contributions in polariton condensates and hence discriminates it from a conventional photon laser.

  16. Technical Session II Talks | U.S. DOE Office of Science (SC)

    Office of Science (SC) Website

    II Talks Scientific User Facilities (SUF) Division SUF Home About User Facilities Projects Accelerator & Detector Research Science Highlights Principal Investigators' Meetings BES Home 2011 Accelerator Detector RD PI Meeting files Technical Session II Talks Print Text Size: A A A FeedbackShare Page Detector R&D at LBNL (Denes) .pdf file (6.2MB) GaAs Detector (Durbin) .pdf file (450KB) Advanced Neutron Detectors (Smith) .pdf file (818KB) Neutron Imaging System (Bingham) .pdf file (1.1MB)

  17. Magnetic and transport properties of Mn{sub 2}CoAl oriented films

    SciTech Connect (OSTI)

    Jamer, Michelle E.; Assaf, Badih A.; Devakul, Trithep; Heiman, Don

    2013-09-30

    The structure, magnetic, and transport properties of thin films of the Heusler ferrimagnet Mn{sub 2}CoAl have been investigated for properties related to spin gapless semiconductors. Oriented films were grown by molecular beam epitaxy on GaAs substrates and the structure was found to transform from tetragonal to cubic for increasing annealing temperature. The anomalous Hall resistivity is found to be proportional to the square of the longitudinal resistivity and magnetization expected for a topological Berry curvature origin. A delicate balance of the spin-polarized carrier type when coupled with voltage gate-tuning could significantly impact advanced electronic devices.

  18. Atomic moments in Mn{sub 2}CoAl thin films analyzed by X-ray magnetic circular dichroism

    SciTech Connect (OSTI)

    Jamer, M. E.; Assaf, B. A.; Heiman, D.; Sterbinsky, G. E.; Arena, D. A.

    2014-12-07

    Spin gapless semiconductors are known to be strongly affected by structural disorder when grown epitaxially as thin films. The magnetic properties of Mn{sub 2}CoAl thin films grown on GaAs (001) substrates are investigated here as a function of annealing. This study investigates the atomic-specific magnetic moments of Mn and Co atoms measured through X-ray magnetic circular dichroism as a function of annealing and the consequent structural ordering. The results indicate that the structural distortion mainly affects the Mn atoms as seen by the reduction of the magnetic moment from its predicted value.

  19. Localization-delocalization transition of electrons at the percolation threshold of semiconductor GaAs1xNx alloys: The appearance of a mobility edge

    SciTech Connect (OSTI)

    Alberi, K.; Fluegel, B.; Beaton, D. A.; Ptak, A. J.; Mascarenhas, A.

    2012-07-09

    Electrons in semiconductor alloys have generally been described in terms of Bloch states that evolve from constructive interference of electron waves scattering from perfectly periodic potentials, despite the loss of structural periodicity that occurs on alloying. Using the semiconductor alloy GaAs??xNx as a prototype, we demonstrate a localized to delocalized transition of the electronic states at a percolation threshold, the emergence of a mobility edge, and the onset of an abrupt perturbation to the host GaAs electronic structure, shedding light on the evolution of electronic structure in these abnormal alloys.

  20. Suppression of the thermal hysteresis in magnetocaloric MnAs thin film by highly charged ion bombardment

    SciTech Connect (OSTI)

    Trassinelli, M. Marangolo, M.; Eddrief, M.; Etgens, V. H.; Gafton, V.; Hidki, S.; Lacaze, E.; Lamour, E.; Prigent, C.; Rozet, J.-P.; Steydli, S.; Zheng, Y.; Vernhet, D.

    2014-02-24

    We present the investigation on the modifications of structural and magnetic properties of MnAs thin film epitaxially grown on GaAs induced by slow highly charged ions bombardment under well-controlled conditions. The ion-induced defects facilitate the nucleation of one phase with respect to the other in the first-order magneto-structural MnAs transition, with a consequent suppression of thermal hysteresis without any significant perturbation on the other structural and magnetic properties. In particular, the irradiated film keeps the giant magnetocaloric effect at room temperature opening new perspective on magnetic refrigeration technology for everyday use.

  1. Spin and charge transport in double-junction Fe/MgO/GaAs/MgO/Fe heterostructures

    SciTech Connect (OSTI)

    Wolski, S. Szczepa?ski, T.; Dugaev, V. K.; Barna?, J.; Landgraf, B.; Slobodskyy, T.; Hansen, W.

    2015-01-28

    We present theoretical and experimental results on tunneling current in single Fe/MgO/GaAs and double Fe/MgO/GaAs/MgO/Fe tunnel junctions. The charge and spin currents are calculated as a function of external voltage for different sets of parameters characterizing the semiconducting GaAs layer. Transport characteristics of a single Fe/MgO/GaAs junction reveal typical diode as well as spin diode features. The results of numerical calculations are compared with current-voltage characteristics measured experimentally for double tunnel junction structures, and a satisfactory agreement of the theoretical and experimental results has been achieved.

  2. InGaP/GaAs Inverted Dual Junction Solar Cells For CPV Applications Using Metal-Backed Epitaxial Lift-Off

    SciTech Connect (OSTI)

    Bauhuis, Gerard J.; Mulder, Peter; Haverkamp, Erik J.; Schermer, John J.; Nash, Lee J.; Fulgoni, Dominic J. F.; Ballard, Ian M.; Duggan, Geoffrey

    2010-10-14

    The epitaxial lift-off (ELO) technique has been combined with inverted III-V PV cell epitaxial growth with the aim of employing thin film PV cells in HCPV systems. In a stepwise approach to the realization of an inverted triple junction on a MELO platform we have first grown a GaAs single junction PV cell to establish the basic layer release process and cell processing steps followed by the growth, fabrication and test of an inverted InGaP/GaAs dual junction structure.

  3. High-power InGaAs/GaAs quantum-well laser with enhanced broad spectrum of stimulated emission

    SciTech Connect (OSTI)

    Wang, Huolei; Yu, Hongyan; Zhou, Xuliang; Kan, Qiang; Yuan, Lijun; Wang, Wei; Pan, Jiaoqing; Chen, Weixi; Ding, Ying

    2014-10-06

    We report the demonstration of an InGaAs/GaAs quantum well (QW) broadband stimulated emission laser with a structure that integrated a GaAs tunnel junction with two QW active regions. The laser exhibits ultrabroad lasing spectral coverage of ?51?nm at a center wavelength of 1060?nm with a total emission power of 790 mW, corresponding to a high average spectral power density of 15.5 mW/nm, under pulsed current conditions. Compared to traditional lasers, this laser with an asymmetric separate-confinement heterostructure shows broader lasing bandwidth and higher spectral power density.

  4. 80th Annual Conference of the DPG & DPG Spring Meeting (Regensburg,

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    Germany) - JCAP 80th Annual Conference of the DPG & DPG Spring Meeting (Regensburg, Germany) 80th Annual Conference of the DPG & DPG Spring Meeting (Regensburg, Germany) Sun, Mar 6, 2016 11:30am 11:30 Fri, Mar 11, 2016 12:30pm 12:30 Regensburg Germany Matthias Richter, "Probing the TiO2/Liquid Interface of a Photoelectrochemical Cell by X-Ray Photoelectron Spectroscopy" Amorphous TiO2 coatings can stabilize semiconductor photoanodes such as Si, GaAs, and GaP that are

  5. A

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    have demonstrated that very high efficiencies, up to 38%, may be achievable using r ay o p&cal a ngle r estric&on i n u ltrathin (50nm) GaAs cells. Light trapping cell geometry a nd a n e xcellent b ack r eflector a re key t o t he h ighest e fficiencies. Significance and Impact The high efficiencies and thin cells that are possible in this regime could allow for significantly reduced PV cost per waO and with r educed m aterials u sage. Research D etails - Used detailed balance modeling

  6. The effect of interelement dipole coupling in patterned ultrathin single crystal Fe square arrays

    SciTech Connect (OSTI)

    Sun Li; Zhai Ya; Wong Pingkwanj; Zhang Wen; Xu Yongbing; Zou Xiao; Wu Jing; Luo Linqiang; Zhai Hongru

    2011-02-01

    The correlation between the magnetic properties and the interelement separation in patterned arrays of ultrathin single crystal Fe films of 12 monolayers (ML) grown on GaAs(100) has been studied. The critical condition to form single domain remanent states in the square elements was found to be 10 {mu}m in size and 20 {mu}m for the interelement separation. The coercivity was also found to increase with the increasing interelement separation in the patterned arrays. These results are attributed to the competition between the large in-plane uniaxial anisotropy, the demagnetizing field, and interelement dipole coupling as determined semiqualitatively by the ferromagnetic resonance measurements.

  7. Temperature dependence of the dielectric response of AlSb

    SciTech Connect (OSTI)

    Jung, Y. W.; Kim, T. J.; Kim, Y. D.; Shin, S. H.; Kim, S. Y.; Song, J. D.

    2011-12-23

    Spectroscopic ellipometry was used to determine the optical response of an intrinsic AlSb film as a function of temperature. The 1.5 {mu}m thick film was grown on a (001) GaAs substrate by molecular beam epitaxy. Measurements were done at temperatures from 300 K to the growth temperature of 800 K over a spectral range of 0.7 to 5.0 eV. To avoid oxidation artifacts, measurements were done with the film in situ. The data were analyzed using a parametric semiconductor model for its temperature dependence.

  8. Current- and lattice-matched tandem solar cell

    DOE Patents [OSTI]

    Olson, J.M.

    1985-10-21

    A multijunction (cascade) tandem photovoltaic solar cell device is fabricated of a Ga/sub x/In/sub 1-x/P (0.505 equal to or less than x equal to or less than 0.515) top cell semiconductor lattice-matched to a GaAs bottom cell semiconductor at a low resistance heterojunction, preferably a p/sup +//n/sup +/ heterojunction between the cells. The top and bottom cells are both lattice-matched and current-matched for high efficiency solar radiation conversion to electrical energy.

  9. Heterojunction solar cell with passivated emitter surface

    DOE Patents [OSTI]

    Olson, J.M.; Kurtz, S.R.

    1994-05-31

    A high-efficiency heterojunction solar cell is described wherein a thin emitter layer (preferably Ga[sub 0.52]In[sub 0.48]P) forms a heterojunction with a GaAs absorber layer. A passivating window layer of defined composition is disposed over the emitter layer. The conversion efficiency of the solar cell is at least 25.7%. The solar cell preferably includes a passivating layer between the substrate and the absorber layer. An anti-reflection coating is preferably disposed over the window layer. 1 fig.

  10. Daily Fill Factor Variation as a Diagnostic Probe of Multijunction Concentrator Systems During Outdoor Operation

    SciTech Connect (OSTI)

    McMahon, W. E.; Emery, K. E.; Friedman, D. J.; Ottoson, L.; Young, M. S.; Ward, J. S.; Kramer, C. M.; Duda, A.; Kurtz, S.

    2007-01-01

    The work presented here is for GaInP2/GaAs tandem cells, but the conclusions are equally valid for GaInP2/GaAs/Ge triple-junction cells. Optimizing a concentrator system which uses multijunction solar cells is challenging because: (a) the conditions are variable, so the solar cells rarely operate under optimal conditions and (b) the conditions are not controlled, so any design problems are difficult to characterize. Any change in the spectral content of direct-beam sunlight as it passes through the concentrator optics is of particular interest, as it can reduce the performance of multijunction cells and is difficult to characterize.

  11. Light-splitting photovoltaic system utilizing two dual-junction solar cells

    SciTech Connect (OSTI)

    Xiong, Kanglin; Yang, Hui; Lu, Shulong; Dong, Jianrong; Zhou, Taofei; Wang, Rongxin; Jiang, Desheng

    2010-12-15

    There are many difficulties limiting the further development of monolithic multi-junction solar cells, such as the growth of lattice-mismatched material and the current matching constraint. As an alternative approach, the light-splitting photovoltaic system is investigated intensively in different aspects, including the energy loss mechanism and the choice of energy bandgaps of solar cells. Based on the investigation, a two-dual junction system has been implemented employing lattice-matched GaInP/GaAs and InGaAsP/InGaAs cells grown epitaxially on GaAs and InP substrates, respectively. (author)

  12. Oil shale potential of the Heath and Tyler formations, Central Montana

    SciTech Connect (OSTI)

    Cox, W.E.; Cole, G.A.

    1981-01-01

    The units in the middle of the Heath formation below the gypsum beds were found to have the highest oil yields. That interval was generally 25 to 50 ft (7.6 to 15.2 m) thick. The upper portion of the Heath formation yielded as much as 9.8 gal/ton in section 9, and 14.9 gal/ton in section 10. The Tyler formation was determined to have very low oil potential, with the maximum yield being 2.2 gal/ton. The instability of some of the Heath slopes could present problems in the mining of oil shale. Specific stratigraphic horizons in which zones of high and low oil and metal contents occur would be extremely difficult to map in areas where the units have been displaced by landslide movement.

  13. Petrographic report on clay-rich samples from Permian Unit 4 salt, G. Friemel No. 1 well, Palo Duro Basin, Deaf Smith County, Texas: unanalyzed data

    SciTech Connect (OSTI)

    Fukui, L M

    1983-09-01

    This report presents the results of mineralogic and petrographic analyses performed on five samples of clay-rich rock from salt-bearing Permian strata sampled by drill core from G. Friemel No. 1 Well, Deaf Smith County, Texas. Five samples of clay-rich rock from depths of about 2457, 2458, 2521, 2548, and 2568 feet were analyzed to determine the amounts of soluble phase (halite) and the amounts and mineralogy of the insoluble phases. The amounts of halite found were 59, 79, 47, 40, and 4 weight percent, respectively, for the samples. The insoluble minerals are predominately clay (20 to 60 volume percent) and anhydrite (up to 17 volume percent), with minor (about 1.0%) and trace amounts of quartz, dolomite, muscovite, and gypsum. The clays include illite, chlorite, and interstratified chlorite-smectite. The results presented in this petrographic report are descriptive, uninterpreted data. 2 references, 7 tables.

  14. A comparison of solidification media for the stabilization of low- level radioactive wastes

    SciTech Connect (OSTI)

    Cowgill, M.G.

    1991-10-01

    When requirements exist to stabilize low-level radioactive waste (LLW) prior to disposal, efforts to achieve this stability often center on the mixing of the waste with a solidification medium. Although historically the medium of choice has been based on the use of portland cement as the binder material, several other options have been developed and subsequently implemented. These include thermoplastic polymers, thermosetting polymers and gypsum. No one medium has thus far been successful in providing stability to all forms of LLW. The characteristics and attributes of these different binder materials are reviewed and compared. The aspects examined include availability of information, limitations to use, sensitivity to process or waste chemistry changes, radionuclide retention ability, modeling of radionuclide release processes, ease and safety of use, and relative costs.

  15. Incorporation of titanium dioxide nanoparticles in mortars - Influence of microstructure in the hardened state properties and photocatalytic activity

    SciTech Connect (OSTI)

    Lucas, S.S.

    2013-01-15

    The environmental pollution in urban areas is one of the causes for poor indoor air quality in buildings, particularly in suburban areas. The development of photocatalytic construction materials can contribute to clean the air and improve sustainability levels. Previous studies have focused mainly in cement and concrete materials, disregarding the potential application in historic buildings. In this work, a photocatalytic additive (titanium dioxide) was added to mortars prepared with aerial lime, cement and gypsum binders. The main goal was to study the way that microstructural changes affect the photocatalytic efficiency. The photocatalytic activity was determined using a reactor developed to assess the degradation rate with a common urban pollutant, NO{sub x}. The laboratory results show that all the compositions tested exhibited high photocatalytic efficiency. It was demonstrated that photocatalytic mortars can be applied in new and old buildings, because the nanoadditives do not compromise the mortar hardened state properties.

  16. Characterization of patinas by means of microscopic techniques

    SciTech Connect (OSTI)

    Vazquez-Calvo, C.

    2007-11-15

    Many stone-made historic buildings have a yellowish layer called 'patina' on their external surface. In some cases, it is due to the natural ageing of the stone caused by chemical-physical reactions between the surface of the stone and the environment, and in other cases it is the result of biological activity. The origin of these patinas can be also be due to ancient protective treatments. The use of organic additives, such as protein-based compounds, in lime or gypsum-based patinas is a traditional technique, which has been used in past centuries for the conservation and protection of stone materials. The thinness of the patinas ensures that microscopic techniques are irreplaceable for their analysis. Optical Microscopy, Fluorescence Microscopy, Scanning Electron Microscopy together with an Energy Dispersive X-ray Spectrometer, and Electron Microprobe are the microscopic techniques used for the characterization of these coverings, providing very useful information on their composition, texture and structure.

  17. Buildings Energy Data Book: 1.6 Embodied Energy of Building Assemblies

    Buildings Energy Data Book [EERE]

    7 Embodied Energy of Floor Structures in the U.S. Floor Structure with Interior Ceiling Finish of Gypsum Board, Latex Paint Embodied Energy CO2 Equivalent (MMBtu/SF) (1) Emissions (lbs/SF) Glulam joist and plank decking 0.04 3.06 Precast Hollowcore 0.05 13.43 Wood I-joist 0.02 2.03 Open-web Steel Joist 0.06 7.94 Open-web Steel Joist with concrete topping 0.07 12.30 Precast Double-T 0.04 11.38 Precast Double-T with concrete topping 0.06 16.45 Steel Joist 0.06 8.82 Steel Joist with plywood decking

  18. Carbon Capture and Water Emissions Treatment System (CCWESTRS) at Fossil-Fueled Electric Generating Plants

    SciTech Connect (OSTI)

    P. Alan Mays; Bert R. Bock; Gregory A. Brodie; L. Suzanne Fisher; J. Devereux Joslin; Donald L. Kachelman; Jimmy J. Maddox; N. S. Nicholas; Larry E. Shelton; Nick Taylor; Mark H. Wolfe; Dennis H. Yankee; John Goodrich-Mahoney

    2005-08-30

    The Tennessee Valley Authority (TVA), the Electric Power Research Institute (EPRI), and the Department of Energy-National Energy Technologies Laboratory (DOE-NETL) are evaluating and demonstrating integration of terrestrial carbon sequestration techniques at a coal-fired electric power plant through the use of Flue Gas Desulfurization (FGD) system gypsum as a soil amendment and mulch, and coal fly ash pond process water for periodic irrigation. From January to March 2002, the Project Team initiated the construction of a 40 ha Carbon Capture and Water Emissions Treatment System (CCWESTRS) near TVA's Paradise Fossil Plant on marginally reclaimed surface coal mine lands in Kentucky. The CCWESTRS is growing commercial grade trees and cover crops and is expected to sequester 1.5-2.0 MT/ha carbon per year over a 20-year period. The concept could be used to meet a portion of the timber industry's needs while simultaneously sequestering carbon in lands which would otherwise remain non-productive. The CCWESTRS includes a constructed wetland to enhance the ability to sequester carbon and to remove any nutrients and metals present in the coal fly ash process water runoff. The CCWESTRS project is a cooperative effort between TVA, EPRI, and DOE-NETL, with a total budget of $1,574,000. The proposed demonstration project began in October 2000 and has continued through December 2005. Additional funding is being sought in order to extend the project. The primary goal of the project is to determine if integrating power plant processes with carbon sequestration techniques will enhance carbon sequestration cost-effectively. This goal is consistent with DOE objectives to provide economically competitive and environmentally safe options to offset projected growth in U.S. baseline emissions of greenhouse gases after 2010, achieve the long-term goal of $10/ton of avoided net costs for carbon sequestration, and provide half of the required reductions in global greenhouse gases by 2025. Other potential benefits of the demonstration include developing a passive technology for water treatment for trace metal and nutrient release reductions, using power plant by-products to improve coal mine land reclamation and carbon sequestration, developing wildlife habitat and green-space around production facilities, generating Total Maximum Daily Load (TMDL) credits for the use of process water, and producing wood products for use by the lumber and pulp and paper industry. Project activities conducted during the five year project period include: Assessing tree cultivation and other techniques used to sequester carbon; Project site assessment; Greenhouse studies to determine optimum plant species and by-product application; Designing, constructing, operating, monitoring, and evaluating the CCWESTRS system; and Reporting (ongoing). The ability of the system to sequester carbon will be the primary measure of effectiveness, measured by accessing survival and growth response of plants within the CCWESTRS. In addition, costs associated with design, construction, and monitoring will be evaluated and compared to projected benefits of other carbon sequestration technologies. The test plan involves the application of three levels each of two types of power plant by-products--three levels of FGD gypsum mulch, and three levels of ash pond irrigation water. This design produces nine treatment levels which are being tested with two species of hardwood trees (sweet gum and sycamore). The project is examining the effectiveness of applications of 0, 8-cm, and 15-cm thick gypsum mulch layers and 0, 13 cm, and 25 cm of coal fly ash water for irrigation. Each treatment combination is being replicated three times, resulting in a total of 54 treatment plots (3 FGD gypsum levels X 3 irrigation water levels x 2 tree species x 3 replicates). Survival and growth response of plant species in terms of sequestering carbon in plant material and soil will be the primary measure of effectiveness of each treatment. Additionally, the ability of the site soils and unsaturated zone subsurface m

  19. Utilization of municipal solid waste incineration fly ash for sulfoaluminate cement clinker production

    SciTech Connect (OSTI)

    Wu Kai; Shi Huisheng; Guo Xiaolu

    2011-09-15

    Highlights: > The replacement can be taken up to 30% of MSWI fly ash in the raw mix. > The novelty compositional parameters were defined, their optimum values were determined. > Expansive property of SAC is strongly depended on gypsum content. > Three leaching test methods are used to assess the environmental impact. - Abstract: The feasibility of partially substituting raw materials with municipal solid waste incineration (MSWI) fly ash in sulfoaluminate cement (SAC) clinker production was investigated by X-ray diffraction (XRD), compressive strength and free expansion ratio testing. Three different leaching tests were used to assess the environmental impact of the produced material. Experimental results show that the replacement of MSWI fly ash could be taken up to 30% in the raw mixes. The good quality SAC clinkers are obtained by controlling the compositional parameters at alkalinity modulus (C{sub m}) around 1.05, alumina-sulfur ratio (P) around 2.5, alumina-silica ratio (N) around 2.0{approx}3.0 and firing the raw mixes at 1250 deg. C for 2 h. The compressive strengths of SAC are high in early age while that develop slowly in later age. Results also show that the expansive properties of SAC are strongly depended on the gypsum content. Leaching studies of toxic elements in the hydrated SAC-based system reveal that all the investigated elements are well bounded in the clinker minerals or immobilized by the hydration products. Although some limited positive results indicate that the SAC prepared from MSWI fly ash would present no immediate thread to the environment, the long-term toxicity leaching behavior needs to be further studied.

  20. Groundwater geochemical modeling and simulation of a breached high-level radioactive waste repository in the northern Tularosa Basin, New Mexico

    SciTech Connect (OSTI)

    Chappell, R.W.

    1989-01-01

    The northern Tularosa Basin in south-central New Mexico was ranked favorably as a potential location for a high-level radioactive waste repository by a US Geological Survey pilot screening study of the Basin and Range Province. The favorable ranking was based chiefly on hydrogeologic and descriptive geochemical evidence. A goal of this study was to develop a methodology for predicting the performance of this or any other basin as a potential repository site using geochemical methods. The approach involves first characterizing the groundwater geochemistry, both chemically and isotopically, and reconstructing the probable evolutionary history of, and controls on the ground water chemistry through modeling. In the second phase of the approach, a hypothetically breached repository is introduced into the system, and the mobility of the parent radionuclide, uranium, in the groundwater is predicted. Possible retardation of uranium transport in the downgradient flow direction from the repository by adsorption and mineral precipitation is then considered. The Permian Yeso Formation, the primary aquifer in the northern Tularosa Basin, was selected for study, development and testing of the methodology outlined above. The Yeso Formation contains abundant gypsum and related evaporite minerals, which impart a distinctive chemical signature to the ground water. Ground water data and solubility calculations indicate a conceptual model of irreversible gypsum and dolomite dissolution with concomitant calcite precipitation. Recharge areas are apparent from temperature, {delta}{sup 18}O and {delta}{sup 2} H, and {sup 3}H trends in the aquifer. Corrected {sup 14}C ages range between modern and 31,200 years, and suggest an average ground water velocity of 0.83 m/yr.

  1. Inverted Metamorphic Multijunction (IMM) Cell Processing Instructions

    SciTech Connect (OSTI)

    Duda, A.; Ward, S.; Young, M.

    2012-02-01

    This technical report details the processing schedule used to fabricate Inverted Metamorphic Multijunction (IMM) concentrator solar cells at The National Renewable Energy Laboratory (NREL). These devices are used as experimental test structures to support the research at NREL that is focused on increasing the efficiency of photovoltaic power conversion. They are not intended to be devices suitable for deployment in working concentrator systems primarily because of heat sinking issues. The process schedule was developed to be compatible with small sample sizes and to afford relatively rapid turn-around times, in support of research efforts. The report describes the use of electro deposition of gold for both the back and front contacts. Electro-deposition is used because of its rapid turn around time and because it is a benign metallization technique that is seldom responsible for damage to the semiconductors. The layer transfer technique is detailed including the use of a commercially available adhesive and the etching away of the parent gallium arsenide substrate. Photolithography is used to define front contact grids as well as the mesa area of the cell. Finally, the selective wet chemical etchant system is introduced and its use to reveal the back contact is described.

  2. Importance of the Fermi-surface topology to the superconducting state of the electron-doped pnictide Ba(Fe1-xCox)?As?

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Liu, Chang; Palczewski, A. D.; Dhaka, R. S.; Kondo, Takeshi; Fernandes, R. M.; Mun, E. D.; Hodovanets, H.; Thaler, A. N.; Schmalian, J.; Budko, S. L.; et al

    2011-07-25

    We used angle-resolved photoemission spectroscopy and thermoelectric power to study the poorly explored, highly overdoped side of the phase diagram of Ba(Fe1-xCox)?As? high-temperature superconductor. Our data demonstrate that several Lifshitz transitionstopological changes of the Fermi surfaceoccur for large x. The central hole barrel changes to ellipsoids that are centered at Z at x~0.11 and subsequently disappear around x~0.2; changes in thermoelectric power occur at similar x values. Tc decreases and goes to zero around x~0.15between the two Lifshitz transitions. Beyond x=0.2 the central pocket becomes electron-like and superconductivity does not exist. Our observations reveal the importance of the underlying Fermiologymorein electron-doped iron arsenides. We speculate that a likely necessary condition for superconductivity in these materials is the presence of the central hole pockets rather than nesting between central and corner pockets.less

  3. PVT -- A photovoltaic/thermal concentrator total energy system: Final phase 1 project report. Building opportunities in the U.S. for photovoltaics (PV:BONUS) Two

    SciTech Connect (OSTI)

    1998-12-31

    United Solar completed its Phase 1 report and its proposal for Phase 2 of the PVBONUS Two program at the end of March 1998. At the same time, it also completed and submitted a proposal to the California Energy Commission PIER program for additional funding to cost-share development and testing of a pre-production model of the PVT-14. It was unsuccessful in both of these proposed efforts. While waiting for the proposal decisions, work continued in April and May to analyze the system design and component decisions described below. This document is a final summation report on the Phase 1 effort of the PVBONUS Two program that describes the key technical issues that United Solar and its subcontractor, Industrial Solar Technology Corporation, worked on in preparation of a Phase 2 award. The decisions described were ones that will guide the design and fabrication of a pre-production prototype of a 1500:1 mirrored concentrator with gallium arsenide cells when United solar resumes its development work. The material below is organized by citing the key components that underwent a design review, what the company considered, what was decided, the name of the expected supplier, if not to be produced in-house, and some information about expected costs. The cost figures given are usually budgetary estimates, not the result of firm quotations or extensive analysis.

  4. Environmental assessment for the satellite power system concept development and evaluation program: atmospheric effects

    SciTech Connect (OSTI)

    Rote, D.M.; Brubaker, K.L.; Lee, J.L.

    1980-11-01

    The US Department of Energy (DOE) has undertaken a preliminary, three-year program to investigate the impacts of the construction and operation of a satellite power system, of unprecedented scale. The Department of Energy's program, titled The Concept Development and Evaluation Program, focused its investigations on a Reference System description that calls for the use of either silicon (Si) or gallium aluminum-arsenide (GaAlAs) photovoltaic cells on 60 satellites to be constructed in GEO over a 30-yr period. Rectennas would be constructed on the ground to receive microwave energy from the satellites. Each satellite-rectenna pair is designed to produce 5 GW of power on an essentially continuous basis for use as a baseload power source for an electric power distribution system. The environmental assessment part of the program was divided into five interdependent task areas. The present document constitutes the final technical report on one of the five task areas, the Assessment of the Atmospheric Effects, and as such presents an in-depth summary of work performed during the assessment program. The issues associated with SPS activities in the troposphere are examined. These include tropospheric weather modification related to rectenna operations and rocket launches, and air quality impacts related to rocketlaunch ground clouds. Then progressing upward through the various levels of the atmosphere, the principal middle and upper atmospheric effects associated with rocket effluents are analyzed. Finally, all of the potential SPS atmospheric effects are summarized.

  5. Method of and apparatus for measuring vapor density

    DOE Patents [OSTI]

    Nelson, Loren D. (Morrison, CO); Cerni, Todd A. (Littleton, CO)

    1989-01-01

    Apparatus and method determine the concentration of an individual component, such as water vapor, of a multi-component mixture, such as a gaseous mixture for cooling a nuclear reactor. A hygrometer apparatus includes an infrared source for producing a broadband infrared energy beam that includes a strong water vapor absorption band and a weak water vapor absorption region. The beam is chopped to select infrared pulses. A temporally first pulse has a wavelength in the weakly absorbing region, a temporally second pulse has a wavelength in the strong band and a temporally third pulse has a wavlength in the weakly absorbing region. A fourth reference pulse representing background radiation is interposed in such chopped pulses. An indium arsenide infrared sensor is responsive to the pulses for generating an output signal in proportion to: ##EQU1## where N1 is proportional to the transmission through the sample of the first signal, N4 is related to the background radiation, and [K2 (N2-N4)+K3 (N3-N4)] is the time-weighted average of the transmission through the sample of the second and third pulses applicable at the time of the second pulse, with the reference pulse N4 being subtracted in each case to render the ratio independent of variations in the background radiation.

  6. Method of and apparatus for measuring vapor density

    DOE Patents [OSTI]

    Nelson, L.D.; Cerni, T.A.

    1989-10-17

    Apparatus and method are disclosed which determine the concentration of an individual component, such as water vapor, of a multi-component mixture, such as a gaseous mixture for cooling a nuclear reactor. A hygrometer apparatus includes an infrared source for producing a broadband infrared energy beam that includes a strong water vapor absorption band and a weak water vapor absorption region. The beam is chopped to select infrared pulses. A temporally first pulse has a wavelength in the weakly absorbing region, a temporally second pulse has a wavelength in the strong band and a temporally third pulse has a wavelength in the weakly absorbing region. A fourth reference pulse representing background radiation is interposed in such chopped pulses. An indium arsenide infrared sensor is responsive to the pulses for generating an output signal in proportion to an equation given in the patent where N1 is proportional to the transmission through the sample of the first signal, N4 is related to the background radiation, and [K2 (N2-N4) + K3 (N3-N4)] is the time-weighted average of the transmission through the sample of the second and third pulses applicable at the time of the second pulse, with the reference pulse N4 being subtracted in each case to render the ratio independent of variations in the background radiation. 11 figs.

  7. Method of making an icosahedral boride structure

    DOE Patents [OSTI]

    Hersee, Stephen D.; Wang, Ronghua; Zubia, David; Aselage, Terrance L.; Emin, David

    2005-01-11

    A method for fabricating thin films of an icosahedral boride on a silicon carbide (SiC) substrate is provided. Preferably the icosahedral boride layer is comprised of either boron phosphide (B.sub.12 P.sub.2) or boron arsenide (B.sub.12 As.sub.2). The provided method achieves improved film crystallinity and lowered impurity concentrations. In one aspect, an epitaxially grown layer of B.sub.12 P.sub.2 with a base layer or substrate of SiC is provided. In another aspect, an epitaxially grown layer of B.sub.12 As.sub.2 with a base layer or substrate of SiC is provided. In yet another aspect, thin films of B.sub.12 P.sub.2 or B.sub.12 As.sub.2 are formed on SiC using CVD or other vapor deposition means. If CVD techniques are employed, preferably the deposition temperature is above 1050.degree. C., more preferably in the range of 1100.degree. C. to 1400.degree. C., and still more preferably approximately 1150.degree. C.

  8. Production data on 0.55 eV InGaAs thermophotovoltaic cells

    SciTech Connect (OSTI)

    Wojtzuk, S.; Colter, P.; Charache, G.; Campbell, B.

    1996-05-01

    Low bandgap 0.55 eV (2.25 {micro}m cutoff wavelength) indium gallium arsenide (In{sub 0.72}Ga{sub 0.28}As) thermophotovoltaic (TPV) cells use much more of the long wavelength energy emitted from low temperature (< 1,200 C) thermal sources than either Si or GaSb cells. Data are presented on a statistically significant number (2,500) of these TPV cells, indicating the performance obtainable in large numbers of cells. This data should be useful in the design and modeling of TPV system performance. At 1.2 A/cm{sup 2} short-circuit current, an average open-circuit voltage of 283 mV is obtained with a 60% fill factor. The peak external quantum efficiency for uncoated cells is 65% and is over 50% from 1.1 to 2.2 {micro}m. Internal quantum efficiency is over 76% in this range assuming an estimated 34% reflectance loss.

  9. Systematics of the temperature-dependent interplane resistivity in Ba(Fe1-xMx)?As? (M=Co, Rh, Ni, and Pd)

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Tanatar, M. A.; Ni, N.; Thaler, A.; Budko, S. L.; Canfield, P. C.; Prozorov, R.

    2011-07-27

    Temperature-dependent interplane resistivity ?c(T) was measured systematically as a function of transition-metal substitution in the iron-arsenide superconductors Ba(Fe1-xMx)?As?, M=Ni, Pd, Rh. The data are compared with the behavior found in Ba(Fe1-xCox)?As?, revealing resistive signatures of pseudogap. In all compounds we find resistivity crossover at a characteristic pseudogap temperature T* from nonmetallic to metallic temperature dependence on cooling. Suppression of T* proceeds very similarly in cases of Ni and Pd doping and much faster than in similar cases of Co and Rh doping. In cases of Co and Rh doping an additional minimum in the temperature-dependent ?c emerges for high dopings,morewhen superconductivity is completely suppressed. These features are consistent with the existence of a charge gap covering part of the Fermi surface. The part of the Fermi surface affected by this gap is notably larger for Ni- and Pd-doped compositions than in Co- and Rh-doped compounds.less

  10. An Efficient Molecular Dynamics Scheme for Predicting Dopant Implant Profiles in Semiconductors

    SciTech Connect (OSTI)

    Beardmore, K.M.; Gronbech-Jensen, N.

    1998-09-15

    The authors present a highly efficient molecular dynamics scheme for calculating the concentration profile of dopants implanted in group-IV alloy, and III-V zinc blende structure materials. The program incorporates methods for reducing computational overhead, plus a rare event algorithm to give statistical accuracy over several orders of magnitude change in the dopant concentration. The code uses a molecular dynamics (MD) model, instead of the binary collision approximation (BCA) used in implant simulators such as TRIM and Marlowe, to describe ion-target interactions. Atomic interactions are described by a combination of 'many-body' and screened Coulomb potentials. Inelastic energy loss is accounted for using a Firsov model, and electronic stopping is described by a Brandt-Kitagawa model which contains the single adjustable parameter for the entire scheme. Thus, the program is easily extensible to new ion-target combinations with the minimum of tuning, and is predictive over a wide range of implant energies and angles. The scheme is especially suited for calculating profiles due to low energy, large angle implants, and for situations where a predictive capability is required with the minimum of experimental validation. They give examples of using their code to calculate concentration profiles and 2D 'point response' profiles of dopants in crystalline silicon, silicon-germanium blends, and gallium-arsenide. They can predict the experimental profiles over five orders of magnitude for <100> and <110> channeling and for non-channeling implants at energies up to hundreds of keV.

  11. Predicting Low Energy Dopant Implant Profiles in Semiconductors using Molecular Dynamics

    SciTech Connect (OSTI)

    Beardmore, K.M.; Gronbech-Jensen, N.

    1999-05-02

    The authors present a highly efficient molecular dynamics scheme for calculating dopant density profiles in group-IV alloy, and III-V zinc blende structure materials. Their scheme incorporates several necessary methods for reducing computational overhead, plus a rare event algorithm to give statistical accuracy over several orders of magnitude change in the dopant concentration. The code uses a molecular dynamics (MD) model to describe ion-target interactions. Atomic interactions are described by a combination of 'many-body' and pair specific screened Coulomb potentials. Accumulative damage is accounted for using a Kinchin-Pease type model, inelastic energy loss is represented by a Firsov expression, and electronic stopping is described by a modified Brandt-Kitagawa model which contains a single adjustable ion-target dependent parameter. Thus, the program is easily extensible beyond a given validation range, and is therefore truly predictive over a wide range of implant energies and angles. The scheme is especially suited for calculating profiles due to low energy and to situations where a predictive capability is required with the minimum of experimental validation. They give examples of using the code to calculate concentration profiles and 2D 'point response' profiles of dopants in crystalline silicon and gallium-arsenide. Here they can predict the experimental profile over five orders of magnitude for <100> and <110> channeling and for non-channeling implants at energies up to hundreds of keV.

  12. High-Efficiency GaInP/GaAs Tandem Solar Cells

    SciTech Connect (OSTI)

    Bertness, K. A.; Friedman, D. J.; Kurtz, S. R.; Kibbler, A. E.; Cramer, C.; Olson, J. M.

    1996-09-01

    GaInP/GaAs tandem solar cells have achieved efficiencies between 25.7-30.2%, depending on illumination conditions. The efficiencies are the highest confirmed two-terminal values measured for any solar cell within each standard illumination category. The monolithic, series-connected design of the tandem cells allows them to be substituted for silicon or gallium arsenide cells in photovoltaic panel systems with minimal design changes. The advantages of using GaInP/GaAs tandem solar cells in space and terrestrial applications are discussed primarily in terms of the reduction in balance-of-system costs that accrues when using a higher efficiency cell. The new efficiency values represent a significant improvement over previous efficiencies for this materials system, and we identify grid design, back interface passivation, and top interface passivation as the three key factors leading to this improvement. In producing the high-efficiency cells, we have addressed nondestructive diagnostics and materials growth reproducibility as well as peak cell performance.

  13. High-efficiency GaInP/GaAs tandem solar cells

    SciTech Connect (OSTI)

    Bertness, K.A.; Friedman, D.J.; Kurtz, S.R.; Kibbler, A.E.; Kramer, C.; Olson, J.M.

    1994-12-01

    GaInP/GaAs tandem solar cells have achieved new record efficiencies, specifically 25.7% under air-mass 0 (AM0) illumination, 29.5% under AM 1.5 global (AM1.5G) illumination, and 30.2% at 140-180x concentration under AM 1.5 direct (AM1.5D) illumination. These values are the highest two-terminal efficiencies achieved by any solar cell under these illumination conditions. The monolithic, series-connected design of the tandem cells allows them to be substituted for silicon or gallium arsenide cells in photovoltaic panel systems with minimal design changes. The advantages of using GaInP/GaAs tandem solar cells in space and terrestrial applications are discussed primarily in terms of the reduction in balance-of-system costs that accrues when using a higher efficiency cell. The new efficiency values represent a significant improvement over previous efficiencies for this materials system, and we identify grid design, back interface passivation, and top interface passivation as the three key factors leading to this improvement. In producing the high-efficiency cells, we have addressed nondestructive diagnostics and materials growth reproducibility as well as peak cell performance. 31 refs.

  14. The polarized SRF gun experiment.

    SciTech Connect (OSTI)

    Kewisch,J.; Ben-Zvi, I.; Rao, T.; Burrill, A.; Pate, D.; Grover, R.; Todd, R.; Bluem, H.; Holmes, D.; Schultheiss, T.

    2007-09-10

    RF electron guns are capable of producing electron bunches with high brightness, which outperform DC electron guns and may even be able to provide electron beams for the ILC without the need for a damping ring. However, all successful existing guns for polarized electrons are DC guns because the environment inside an RF gun is hostile to the GaAs cathode material necessary for polarization. While the typical vacuum pressure in a DC gun is better than 10{sup -11} torr the vacuum in an RF gun is in the order of 10{sup -9} torr. Experiments at BINP Novosibirsk show that this leads to strong ion back-bombardment and generation of dark currents, which destroy the GaAs cathode in a short time. The situation might be much more favorable in a (super-conducting) SRF gun. The cryogenic pumping of the gun cavity walls may make it possible to maintain a vacuum close to 10{sup -12} torr, solving the problem of ion bombardment and dark currents. Of concern would be contamination of the gun cavity by evaporating cathode material. This report describes an experiment that Brookhaven National Laboratory (BNL) in collaboration with Advanced Energy Systems (AES) is conducting to answer these questions.

  15. Development of an IR-transparent, inverted-grown, thin-film, Al[sub 0. 34]Ga[sub 0. 66]As/GaAs cascade solar cell

    SciTech Connect (OSTI)

    Venkatasubramanian, R.; Timmons, M.L.; Sharps, P.R.; Colpitts, T.S.; Hills, J.S.; Hancock, J.; Hutchby, J.A. )

    1992-12-01

    Inverted growth and the development of associated cell processing, are likely to offer a significant degree of freedom for improving the performance of many III-V multijunction cascades and open new avenues for advanced multijunction concepts. This is especially true for the development of high-efficiency Al[sub 0.37]Ga[sub 0.63]As/GaAs cascades where the high growth temperatures required for the AlGaAs top cell growth can cause the deterioration of the tunnel junction interconnect. In the approach of inverted-grown AlGaAs/GaAs cascade cells, the AlGaAs top cell is grown first at 780 [degree]C and the GaAs tunnel junction and bottom cell are grown at 675 [degree]C. After the inverted growth, the AlGaAs/GaAs cascade structure is selectively removed from the parent substrate. The feasibility of inverted growth is demonstrated by a fully-processed, inverted-grown, thin film GaAs cell with a 1-sun AM1.5 efficiency of 20.3%. Also, an inverted-grown, thin-film, Al[sub 0.34]Ga[sub 0.66]As/GaAs cascade with AM1.5 efficiencies of 19.9% and 21% at 1-sun and 7-suns, respectively, has been obtained.

  16. Enhancement of current collection in epitaxial lift-off InAs/GaAs quantum dot thin film solar cell and concentrated photovoltaic study

    SciTech Connect (OSTI)

    Sogabe, Tomah Shoji, Yasushi; Tamayo, Efrain; Okada, Yoshitaka; Mulder, Peter; Schermer, John

    2014-09-15

    We report the fabrication of a thin film InAs/GaAs quantum dot solar cell (QD cell) by applying epitaxial lift-off (ELO) approach to the GaAs substrate. We confirmed significant current collection enhancement (?0.91?mA/cm{sup 2}) in the ELO-InAs QD cell within the wavelength range of 700?nm900?nm when compared to the ELO-GaAs control cell. This is almost six times of the sub-GaAs bandgap current collection (?0.16?mA/cm{sup 2}) from the wavelength range of 900?nm and beyond, we also confirmed the ELO induced resonance cavity effect was able to increase the solar cell efficiency by increasing both the short circuit current and open voltage. The electric field intensity of the resonance cavity formed in the ELO film between the Au back reflector and the GaAs front contact layer was analyzed in detail by finite-differential time-domain (FDTD) simulation. We found that the calculated current collection enhancement within the wavelength range of 700?nm900?nm was strongly influenced by the size and shape of InAs QD. In addition, we performed concentrated light photovoltaic study and analyzed the effect of intermediate states on the open voltage under varied concentrated light intensity for the ELO-InAs QD cell.

  17. Infrared-sensitive photocathode

    DOE Patents [OSTI]

    Mariella, Jr., Raymond P. (Danville, CA); Cooper, Gregory A. (Pleasant Hill, CA)

    1995-01-01

    A single-crystal, multi-layer device incorporating an IR absorbing layer that is compositionally different from the Ga.sub.x Al.sub.1-x Sb layer which acts as the electron emitter. Many different IR absorbing layers can be envisioned for use in this embodiment, limited only by the ability to grow quality material on a chosen substrate. A non-exclusive list of possible IR absorbing layers would include GaSb, InAs and InAs/Ga.sub.w In.sub.y Al.sub.1-y-w Sb superlattices. The absorption of the IR photon excites an electron into the conduction band of the IR absorber. An externally applied electric field then transports electrons from the conduction band of the absorber into the conduction band of the Ga.sub.x Al.sub.1-x Sb, from which they are ejected into vacuum. Because the band alignments of Ga.sub.x Al.sub.1-x Sb can be made the same as that of GaAs, emitting efficiencies comparable to GaAs photocathodes are obtainable. The present invention provides a photocathode that is responsive to wavelengths within the range of 0.9 .mu.m to at least 10 .mu.m.

  18. Infrared-sensitive photocathode

    DOE Patents [OSTI]

    Mariella, R.P. Jr.; Cooper, G.A.

    1995-04-04

    A single-crystal, multi-layer device is described incorporating an IR absorbing layer that is compositionally different from the Ga{sub x}Al{sub 1{minus}x}Sb layer which acts as the electron emitter. Many different IR absorbing layers can be envisioned for use in this embodiment, limited only by the ability to grow quality material on a chosen substrate. A non-exclusive list of possible IR absorbing layers would include GaSb, InAs and InAs/Ga{sub w}In{sub y}Al{sub 1{minus}y{minus}w}Sb superlattices. The absorption of the IR photon excites an electron into the conduction band of the IR absorber. An externally applied electric field then transports electrons from the conduction band of the absorber into the conduction band of the Ga{sub x}Al{sub 1{minus}x}Sb, from which they are ejected into vacuum. Because the band alignments of Ga{sub x}Al{sub 1{minus}x}Sb can be made the same as that of GaAs, emitting efficiencies comparable to GaAs photocathodes are obtainable. The present invention provides a photocathode that is responsive to wavelengths within the range of 0.9 {mu}m to at least 10 {mu}m. 9 figures.

  19. Experimental observation of spin-dependent electron many-body effects in CdTe

    SciTech Connect (OSTI)

    Horodysk, P.; N?mec, P. Novotn, T.; Trojnek, F.; Mal, P.

    2014-08-07

    In semiconductors, the spin degree of freedom is usually disregarded in the theoretical treatment of electron many-body effects such as band-gap renormalization and screening of the Coulomb enhancement factor. Nevertheless, as was observed experimentally in GaAs, not only the single-particle phase-space filling but also many-body effects are spin sensitive. In this paper, we report on time- and polarization-resolved differential transmission pump-probe measurements in CdTe, which has the same zincblende crystal structure but different material parameters compared to that of GaAs. We show experimentally that at room temperature in CdTeunlike in GaAsthe pump-induced decrease of transmission due to the band-gap renormalization can even exceed the transmission increase due to the phase-space filling, which enables to measure directly the spin-sensitivity of the band-gap renormalization. We also observed that the influence of the band-gap renormalization is more prominent at low temperatures.

  20. Proposal of high efficiency solar cells with closely stacked InAs/In{sub 0.48}Ga{sub 0.52}P quantum dot superlattices: Analysis of polarized absorption characteristics via intermediateband

    SciTech Connect (OSTI)

    Yoshikawa, H. Kotani, T.; Kuzumoto, Y.; Izumi, M.; Tomomura, Y.; Hamaguchi, C.

    2014-07-07

    We present a theoretical study of the electronic structures and polarized absorption properties of quantum dot superlattices (QDSLs) using widegap matrix material, InAs/In{sub 0.48}Ga{sub 0.52}P QDSLs, for realizing intermediateband solar cells (IBSCs) with twostep photonabsorption. The planewave expanded BurtForeman operator ordered 8band kp theory is used for this calculation, where strain effect and piezoelectric effect are taken into account. We find that the absorption spectra of the second transitions of twostep photonabsorption can be shifted to higher energy region by using In{sub 0.48}Ga{sub 0.52}P, which is latticematched material to GaAs substrate, as a matrix material instead of GaAs. We also find that the transverse magnetic polarized absorption spectra in InAs/In{sub 0.48}Ga{sub 0.52}P QDSL with a separate IB from the rest of the conduction minibands can be shifted to higher energy region by decreasing the QD height. As a result, the second transitions of twostep photonabsorption by the sunlight occur efficiently. These results indicate that InAs/In{sub 0.48}Ga{sub 0.52}P QDSLs are suitable material combination of IBSCs toward the realization of ultrahigh efficiency solar cells.

  1. Development of 1.25 eV InGaAsN for triple junction solar cells

    SciTech Connect (OSTI)

    LI,N.Y.; SHARPS,P.R.; HILLS,J.S.; HOU,H.; CHANG,PING-CHIH; BACA,ALBERT G.

    2000-05-16

    Development of next generation high efficiency space monolithic multifunction solar cells will involve the development of new materials lattice matched to GaAs. One promising material is 1.05 eV InGaAsN, to be used in a four junction GaInP{sub 2}/GaAs/InGaAsN/Ge device. The AMO theoretical efficiency of such a device is 38--42%. Development of the 1.05 eV InGaAsN material for photovoltaic applications, however, has been difficult. Low electron mobilities and short minority carrier lifetimes have resulted in short minority carrier diffusion lengths. Increasing the nitrogen incorporation decreases the minority carrier lifetime. The authors are looking at a more modest proposal, developing 1.25 eV InGaAsN for a triple junction GaInP{sub 2}/InGaAsN/Ge device. The AMO theoretical efficiency of this device is 30--34%. Less nitrogen and indium are required to lower the bandgap to 1.25 eV and maintain the lattice matching to GaAs. Hence, development and optimization of the 1.25 eV material for photovoltaic devices should be easier than that for the 1.05 eV material.

  2. Final Report: Tunable Narrow Band Gap Absorbers For Ultra High Efficiency Solar Cells

    SciTech Connect (OSTI)

    Bedair, Salah M.; Hauser, John R.; Elmasry, Nadia; Colter, Peter C.; Bradshaw, G.; Carlin, C. Z.; Samberg, J.; Edmonson, Kenneth

    2012-07-31

    We report on a joint research program between NCSU and Spectrolab to develop an upright multijunction solar cell structure with a potential efficiency exceeding the current record of 41.6% reported by Spectrolab. The record efficiency Ge/GaAs/InGaP triple junction cell structure is handicapped by the fact that the current generated by the Ge cell is much higher than that of both the middle and top cells. We carried out a modification of the record cell structure that will keep the lattice matched condition and allow better matching of the current generated by each cell. We used the concept of strain balanced strained layer superlattices (SLS), inserted in the i-layer, to reduce the bandgap of the middle cell without violating the desirable lattice matched condition. For the middle GaAs cell, we have demonstrated an n-GaAs/i-(InGaAs/GaAsP)/p-GaAs structure, where the InxGa1-xAs/GaAs1-yPy SLS is grown lattice matched to GaAs and with reduced bandgap from 1.43 eV to 1.2 eV, depending upon the values of x and y.

  3. The impact of monolayer coverage, barrier thickness and growth rate on the thermal stability of photoluminescence of coupled InAs/GaAs quantum dot hetero-structure with quaternary capping of InAlGaAs

    SciTech Connect (OSTI)

    Mandal, A.; Verma, U.; Halder, N.; Chakrabarti, S.

    2012-03-15

    Highlight: Black-Right-Pointing-Pointer Coupled InAs/GaAs MQDs with (In{sub 0.21}Al{sub 0.21}Ga{sub 0.58}As + GaAs) caps are considered. Black-Right-Pointing-Pointer Monolayer coverage, barrier thickness and growth rate of the dots are the factors. Black-Right-Pointing-Pointer PL peaks for the samples are within 1.1-1.3 {mu}m; significant for IBSCs and lasers. Black-Right-Pointing-Pointer NPTP (non-resonant multi-phonon assisted tunneling process) effect on FWHM of PL. -- Abstract: The self-assembled InAs/GaAs MQDs are widely investigated for their potential application in optoelectronic devices like lasers and photovoltaics. We have explored the effect of QD growth rate and structural parameters like capping layer thickness on the morphology and optical properties of the MQD heterostructures overgrown with a combination capping of InAlGaAs and GaAs. The growth rate of the seed layers in the MQD samples is also varied to investigate its effect in the vertical stacking of the islands. The change in the morphology and the optical properties of the samples due to variation in growth and structural parameters are explained by the presence of strain in the QD structures, which arises due to lattice mismatch.

  4. GaInP/GaAs/GaInAs Monolithic Tandem Cells for High-Performance Solar Concentrators

    SciTech Connect (OSTI)

    Wanlass, M. W.; Ahrenkiel, S. P.; Albin, D. S.; Carapella, J. J.; Duda, A.; Emery, K.; Geisz, J. F.; Jones, K.; Kurtz, S.; Moriarty, T.; Romero, M. J.

    2005-08-01

    We present a new approach for ultra-high-performance tandem solar cells that involves inverted epitaxial growth and ultra-thin device processing. The additional degree of freedom afforded by the inverted design allows the monolithic integration of high-, and medium-bandgap, lattice-matched (LM) subcell materials with lower-bandgap, lattice-mismatched (LMM) materials in a tandem structure through the use of transparent compositionally graded layers. The current work concerns an inverted, series-connected, triple-bandgap, GaInP (LM, 1.87 eV)/GaAs (LM, 1.42 eV)/GaInAs (LMM, {approx}1 eV) device structure grown on a GaAs substrate. Ultra-thin tandem devices are fabricated by mounting the epiwafers to pre-metallized Si wafer handles and selectively removing the parent GaAs substrate. The resulting handle-mounted, ultra-thin tandem cells have a number of important advantages, including improved performance and potential reclamation/reuse of the parent substrate for epitaxial growth. Additionally, realistic performance modeling calculations suggest that terrestrial concentrator efficiencies in the range of 40-45% are possible with this new tandem cell approach. A laboratory-scale (0.24 cm2), prototype GaInP/GaAs/GaInAs tandem cell with a terrestrial concentrator efficiency of 37.9% at a low concentration ratio (10.1 suns) is described, which surpasses the previous world efficiency record of 37.3%.

  5. Isotropic Hall effect and ''freeze-in'' of carriers in the InGaAs self-assembled quantum wires

    SciTech Connect (OSTI)

    Kunets, Vas. P.; Prosandeev, S.; Mazur, Yu. I.; Ware, M. E.; Teodoro, M. D.; Dorogan, V. G.; Lytvyn, P. M.; Salamo, G. J.

    2011-10-15

    Using molecular beam epitaxy, we prepared an anisotropic media consisting of InGaAs quantum wires epitaxially grown on GaAs (311)A. Anisotropy is observed in the lateral conductivity and photoluminescence polarization. However, an isotropic Hall effect is observed in the same samples. We show that the Hall effect in this anisotropic heterostructure remains isotropic regardless of the change of the doping in GaAs barriers and regardless of the InGaAs coverage, whereas the conductivity anisotropy experiences a strong change under these actions. In addition, we observed an anomalous increase in carrier density, ''freeze-in,'' at low temperatures. In order to explain this, we generalized the theory of Look [D. C. Look, Phys. Rev B 42, 3578 (1990)] by considering the low field magneto-transport in anisotropic media. This theory confirms that the Hall constant remains isotropic in anisotropic semiconductor heterostructures, agreeing with our experiment and explains the anomalous behavior of carriers as a result of multi-band conductivity.

  6. Low Cost High Efficiency InP-Based Solar Cells: Cooperative Research and Development Final Report, CRADA Number CRD-09-344

    SciTech Connect (OSTI)

    Wanlass, M.

    2012-07-01

    NREL will develop a method of growing and fabricating single junction InP solar cells on 2-inch InP substrates on which a release layer has been deposited by MicroLink Devices. NREL will transfer to MicroLink the details of the InP solar cell layer structure and test results in order that the 2-inch results can be replicated on 4-inch InP substrates. NREL will develop a method of growing and fabricating single junction InP solar cells, including a metamorphic layer, on 2-inch GaAs substrates on which a release layer has been deposited by MicroLink Devices. NREL will transfer to MicroLink the details of the InP solar cell layer structure and test results in order that the 2-inch results can be replicated on 6-inch GaAs substrates. NREL will perform characterization measurements of the solar cells, including I-V and quantum efficiency measurements at AM1.5 1-sun.

  7. Effect of CoFe insertion in Co{sub 2}MnSi/CoFe/n-GaAs junctions on spin injection properties

    SciTech Connect (OSTI)

    Ebina, Yuya; Akiho, Takafumi; Liu, Hong-xi; Yamamoto, Masafumi; Uemura, Tetsuya

    2014-04-28

    The CoFe thickness (t{sub CoFe}) dependence of spin injection efficiency was investigated for Co{sub 2}MnSi/CoFe/n-GaAs junctions. The ?V{sub NL}/I value, which is a measure of spin injection efficiency, strongly depended on t{sub CoFe}, where ?V{sub NL} is the amplitude of a nonlocal spin-valve signal, and I is an injection current. Importantly, the maximum value of ?V{sub NL}/I for a Co{sub 2}MnSi/CoFe/n-GaAs junction was one order of magnitude higher than that for a CoFe/n-GaAs junction, indicating that a Co{sub 2}MnSi electrode works as a highly polarized spin source. No clear spin signal, on the other hand, was observed for a Co{sub 2}MnSi/n-GaAs junction due to diffusion of Mn atoms into the GaAs channel. Secondary ion mass spectrometry analysis indicated that the CoFe insertion effectively suppressed the diffusion of Mn into GaAs, resulting in improved spin injection properties compared with those for a Co{sub 2}MnSi/n-GaAs junction.

  8. Simulations for preliminary design of a multi-cathode DC electron gun for eRHIC

    SciTech Connect (OSTI)

    Wu, Q.; Ben-Zvi, I.; Chang, X.; Skaritka, J.

    2010-05-23

    The proposed electron ion collider, eRHIC, requires a large average polarized electron current of 50 mA, which is more than 20 times higher than the present experimental output of a single, highly polarized electron source, based on cesiated super-lattice GaAs. To meet eRHIC's requirement for current, we designed a multicathode DC electron gun for injection. The twenty-four GaAs cathodes emit electrons in sequence, then are combined on axis by a rotating field (or 'funnelled'). In addition to its ultra-high vacuum requirements, the multicathode DC electron gun will place high demand on the electric field symmetry, the magnetic field shielding, and on preventing arcing. In this paper, we discuss our results from a 3D simulation of the latest model for this gun. The findings will guide the actual design in future. Their preliminary design of a multi-cathode electron source for eRHIC demonstrated tolerable fields and reasonable results in both field and particle simulations.

  9. Bandgap and optical absorption edge of GaAs{sub 1?x}Bi{sub x} alloys with 0?

    SciTech Connect (OSTI)

    Masnadi-Shirazi, M.; Lewis, R. B.; Bahrami-Yekta, V.; Tiedje, T.; Chicoine, M.; Servati, P.

    2014-12-14

    The compositional dependence of the fundamental bandgap of pseudomorphic GaAs{sub 1?x}Bi{sub x} layers on GaAs substrates is studied at room temperature by optical transmission and photoluminescence spectroscopies. All GaAs{sub 1?x}Bi{sub x} films (0???x???17.8%) show direct optical bandgaps, which decrease with increasing Bi content, closely following density functional theory predictions. The smallest measured bandgap is 0.52?eV (?2.4??m) at 17.8% Bi. Extrapolating a fit to the data, the GaAs{sub 1?x}Bi{sub x} bandgap is predicted to reach 0?eV at 35% Bi. Below the GaAs{sub 1?x}Bi{sub x} bandgap, exponential absorption band tails are observed with Urbach energies 36 times larger than that of bulk GaAs. The Urbach parameter increases with Bi content up to 5.5% Bi, and remains constant at higher concentrations. The lattice constant and Bi content of GaAs{sub 1?x}Bi{sub x} layers (0?

  10. Manufacturing of High-Efficiency Bi-Facial Tandem Concentrator Solar Cells: February 20, 2009--August 20, 2010

    SciTech Connect (OSTI)

    Wojtczuk , S.

    2011-06-01

    Spire Semiconductor made concentrator photovoltaic (CPV) cells using a new bi-facial growth process and met both main program goals: a) 42.5% efficiency 500X (AM1.5D, 25C, 100mW/cm2); and b) Ready to supply at least 3MW/year of such cells at end of program. We explored a unique simple fabrication process to make a N/P 3-junction InGaP/GaAs/InGaAs tandem cells . First, the InGaAs bottom cell is grown on the back of a GaAs wafer. The wafers are then loaded into a cassette, spin-rinsed to remove particles, dipped in dilute NH4OH and spin-dried. The wafers are then removed from the cassette loaded the reactor for GaAs middle and InGaP top cell growth on the opposite wafer face (bi-facial growth). By making the epitaxial growth process a bit more complex, we are able to avoid more complex processing (such as large area wafer bonding or epitaxial liftoff) used in the inverted metamorphic (IMM) approach to make similar tandem stacks. We believe the yield is improved compared to an IMM process. After bi-facial epigrowth, standard III-V cell steps (back metal, photolithography for front grid, cap etch, AR coat, dice) are used in the remainder of the process.

  11. Microstructural evaluation of Sb-adjusted Al{sub 0.5}Ga{sub 0.5}As{sub 1{minus}y}Sb{sub y} buffer layer systems for IR applications

    SciTech Connect (OSTI)

    Chen, E.; Paine, D.C.; Uppal, P.; Ahearn, J.S.; Nichols, K.; Charache, G.W.

    1998-06-01

    The authors report on a transmission electron microscopy (TEM) study of Sb-adjusted quaternary Al{sub 0.5}Ga{sub 0.5}As{sub 1{minus}y}Sb{sub y} buffer-layers grown on <001> GaAs substrates. A series of structures were grown by MBE at 470 C that utilize a multilayer grading scheme in which the Sb content of Al{sub 0.5}Ga{sub 0.5}As{sub 1{minus}y}Sb{sub y} buffer-layers grown on <001> GaAs substrates. A series of structures were grown by MBe at 470 C that utilize a multilayer grading scheme in which the Sb content of Al{sub 0.5}Ga{sub 0.5}As{sub 1{minus}y}Sb{sub y} is successively increased in a series of 125 nm thick layers. Post growth analysis using conventional bright field and weak beam dark field imaging of these buffer layers in cross-section reveals that the interface misfit dislocations are primarily of the 60{degree} type and are distributed through out the interfaces of the buffer layer. When optimized, the authors have shown, using plan view and cross-sectional TEM, that this approach can reduce the threading defect density to below the detectability limit of TEM (< 10{sup 5}/cm{sup 2}) and preserve growth surface planarity. The Sb-graded approach was used to fabricate two 2.2 {micro}m power converter structures fabricated using InGaAs grown on Sb-based buffer layers on GaAs substrates. A microstructural and electrical characterization was performed on these device structures and the results are contrasted with a sample in which InP was selected as the substrate. Microstructure, defect density and device performance in these not-yet-optimized Sb-based buffer layers compares favorably to equivalent devices fabricated using InP substrates.

  12. Experimental and theoretical studies of band gap alignment in GaAs{sub 1?x}Bi{sub x}/GaAs quantum wells

    SciTech Connect (OSTI)

    Kudrawiec, R. Kopaczek, J.; Polak, M. P.; Scharoch, P.; Gladysiewicz, M.; Misiewicz, J.; Richards, R. D.; Bastiman, F.; David, J. P. R.

    2014-12-21

    Band gap alignment in GaAs{sub 1?x}Bi{sub x}/GaAs quantum wells (QWs) was studied experimentally by photoreflectance (PR) and theoretically, ab initio, within the density functional theory in which the supercell based calculations are combined with the alchemical mixing approximation applied to a single atom in a supercell. In PR spectra, the optical transitions related to the excited states in the QW (i.e., the transition between the second heavy-hole and the second electron subband) were clearly observed in addition to the ground state QW transition and the GaAs barrier transition. This observation is clear experimental evidence that this is a type I QW with a deep quantum confinement in the conduction and valence bands. From the comparison of PR data with calculations of optical transitions in GaAs{sub 1?x}Bi{sub x}/GaAs QW performed for various band gap alignments, the best agreement between experimental data and theoretical calculations has been found for the valence band offset of 52??5%. A very similar valence band offset was obtained from ab initio calculations. These calculations show that the incorporation of Bi atoms into GaAs host modifies both the conduction and the valence band. For GaAs{sub 1?x}Bi{sub x} with 0?GaAs in the range of ?60%40% (?40%60%), which is in good agreement with our conclusion derived from PR measurements.

  13. Electrical and optical performance characteristics of 0.74eV p/n InGaAs monolithic interconnected modules

    SciTech Connect (OSTI)

    Wilt, D.M.; Weizer, V.G.; Fatemi, N.S.; Jenkins, P.P.; Hoffman, R.W. Jr.; Jain, R.K.; Murray, C.S.; Riley, D.R.

    1997-06-01

    There has been a traditional trade-off in thermophotovoltaic (TPV) energy conversion development between system efficiency and power density. This trade-off originates from the use of front surface spectral controls such as selective emitters and various types of filters. A monolithic interconnected module (MIM) structure has been developed which allows for both high power densities and high system efficiencies. The MIM device consists of many individual indium gallium arsenide (InGaAs) cells series-connected on a single semi-insulating indium phosphide (InP) substrate. The MIM is exposed to the entire emitter output, thereby maximizing output power density. An infrared (IR) reflector placed on the rear surface of the substrate returns the unused portion of the emitter output spectrum back to the emitter for recycling, thereby providing for high system efficiencies. Initial MIM development has focused on a 1 cm{sup 2} device consisting of eight series interconnected cells. MIM devices, produced from 0.74 eV InGaAs, have demonstrated V{sub oc} = 3.2 volts, J{sub sc} = 70 mA/cm{sup 2} and a fill factor of 66% under flashlamp testing. Infrared (IR) reflectance measurements (> 2 {micro}m) of these devices indicate a reflectivity of > 82%. MIM devices produced from 0.55 eV InGaAs have also been demonstrated. In addition, conventional p/n InGaAs devices with record efficiencies (11.7% AM0) have been demonstrated.

  14. Investigation of Tunable Diode Spectroscopy for Monitoring Gases in Geothermal Plants

    SciTech Connect (OSTI)

    J. K. Partin

    2006-08-01

    The results of an investigation directed at the development of instrument-tation for the real-time monitoring of gases, such as hydrogen sulfide (H2S) and chloride (HCl), in geothermal process streams is described. The geothermal power industry has an interest in the development of new low maintenance techniques since improved capabilities could lead to considerable cost savings through the optimization of various gas abatement processes. Tunable diode laser spectroscopy was identified as a candidate tech-nology for this application and a commercial instrument was specified and procured for testing. The measurement principle involved the use of solid state diode lasers and frequency modulation techniques. The gallium arsenide diode lasers employed emit light in the 0.7 to 2.0 micron region of the electromagnetic spectrum. This region contains the overtone and combination absorption bands of a number of species of industrial interest, including H2S and HCl. A particular device can be tuned over a small range to match the absorption line by changing its applied temperature and current. The diode current can also be sinusoidally modulated in frequency as it is tuned across the line. This modulation allows measurements to be conducted at frequencies where the laser intensity noise is minimal; and therefore, very high signal-to-noise measurements are possible. The feasibility of using this technology in various types of geothermal process streams has been explored. The results of laboratory and field studies are presented along with new advances in laser technology that could allow more sensitive and selective measurements to be performed.

  15. Mineral-Surfactant Interactions for Minimum Reagents Precipitation and Adsorption for Improved Oil Recovery

    SciTech Connect (OSTI)

    P. Somasundaran

    2008-09-20

    Chemical EOR can be an effective method for increasing oil recovery and reducing the amount of produced water; however, reservoir fluids are chemically complex and may react adversely to the polymers and surfactants injected into the reservoir. While a major goal is to alter rock wettability and interfacial tension between oil and water, rock-fluid and fluid-fluid interactions must be understood and controlled to minimize reagent loss, maximize recovery and mitigate costly failures. The overall objective of this project was to elucidate the mechanisms of interactions between polymers/surfactants and the mineral surfaces responsible for determining the chemical loss due to adsorption and precipitation in EOR processes. The role of dissolved inorganic species that are dependent on the mineralogy is investigated with respect to their effects on adsorption. Adsorption, wettability and interfacial tension are studied with the aim to control chemical losses, the ultimate goal being to devise schemes to develop guidelines for surfactant and polymer selection in EOR. The adsorption behavior of mixed polymer/surfactant and surfactant/surfactant systems on typical reservoir minerals (quartz, alumina, calcite, dolomite, kaolinite, gypsum, pyrite, etc.) was correlated to their molecular structures, intermolecular interactions and the solution conditions such as pH and/or salinity. Predictive models as well as general guidelines for the use of polymer/surfactant surfactant/surfactant system in EOR have been developed The following tasks have been completed under the scope of the project: (1) Mineral characterization, in terms of SEM, BET, size, surface charge, and point zero charge. (2) Study of the interactions among typical reservoir minerals (quartz, alumina, calcite, dolomite, kaolinite, gypsum, pyrite, etc.) and surfactants and/or polymers in terms of adsorption properties that include both macroscopic (adsorption density, wettability) and microscopic (orientation/conformation of the adsorbed layers), as well as precipitation/abstraction characteristics. (3) Investigation of the role of dissolved species, especially multivalent ions, on interactions between reservoir minerals and surfactants and/or polymers leading to surfactant precipitation or activated adsorption. (4) Solution behavior tests--surface tension, interaction, ultra filtration, and other tests. (5) Surfactant-mineral interactions relative to adsorption, wettability, and electrophoresis. (6) Work on the effects of multivalent ions, pH, temperature, salinity, and mixing ratio on the adsorption. Developments of adsorption models to explain interactions between surfactants/polymers/minerals. (7) General guidelines for the use of certain surfactants, polymers and their mixtures in micelle flooding processes.

  16. A fast coherent synchrotron radiation monitor for the bunch length of the short CEBAF bunches

    SciTech Connect (OSTI)

    Wang, D.X.; Krafft, G.A.; Price, E.; Wood, P.; Porterfield, D.; Crowe, T.

    1996-04-01

    A novel bunch length monitor for short (down to subpicosecond) electron bunches has been developed in a collaboration between CEBAF and the University of Virginia (UVA), using coherent synchrotron radiation (CSR) detection techniques. The monitor employs a state of the art {open_quote}{open_quote}narrowband{close_quote}{close_quote} GaAs Schottky whisker diode developed by the UVA group, and has the following features: it is non-invasive, compact, and low cost, it has fast rise time, low noise, high sensitivity, and it operates at room temperature. In this paper, the design parameters and performance of the monitor and selected measurement results will be presented. {copyright} {ital 1996 American Institute of Physics.}

  17. Proceedings of the 12th Space Photovoltaic Research and Technology Conference (SPRAT 12)

    SciTech Connect (OSTI)

    1993-05-01

    The Twelfth Space Photovoltaic Research and Technology conference was held at the NASA Lewis Research Center from 20 to 22 Oct. 1992. The papers and workshops presented in this volume report substantial progress in a variety of areas in space photovoltaics. Topics covered include: high efficiency GaAs and InP solar cells, GaAs/Ge cells as commercial items, flexible amorphous and thin film solar cells (in the early stages of pilot production), high efficiency multiple bandgap cells, laser power converters, solar cell and array technology, heteroepitaxial cells, betavoltaic energy conversion, and space radiation effects in InP cells. Space flight data on a variety of cells were also presented. Separate abstracts have been prepared for articles from this report.

  18. Lattice constant grading in the Al.sub.y Ga.sub.1-y As.sub.1-x Sb.sub.x alloy system

    DOE Patents [OSTI]

    Moon, Ronald L. (Palo Alto, CA)

    1980-01-01

    Liquid phase epitaxy is employed to grow a lattice matched layer of GaAsSb on GaAs substrates through the compositional intermediary of the III-V alloy system AlGaAsSb which acts as a grading layer. The Al constituent reaches a peak atomic concentration of about 6% within the first 2.5 .mu.m of the transition layer, then decreases smoothly to about 1% to obtain a lattice constant of 5.74 A. In the same interval the equilibrium concentration of Sb smoothly increases from 0 to about 9 atomic percent to form a surface on which a GaAsSb layer having the desired energy bandgap of 1.1 ev for one junction of an optimized dual junction photolvoltaic device. The liquid phase epitaxy is accomplished with a step cooling procedure whereby dislocation defects are more uniformly distributed over the surface of growing layer.

  19. Lattice constant grading in the Al.sub.y Ca.sub.1-y As.sub.1-x Sb.sub.x alloy system

    DOE Patents [OSTI]

    Moon, Ronald L. (Palo Alto, CA)

    1981-01-01

    Liquid phase epitaxy is employed to grow a lattice matched layer of GaAsSb on GaAs substrates through the compositional intermediary of the III-V alloy system AlGaAsSb which acts as a grading layer. The Al constituent reaches a peak atomic concentration of about 6% within the first 2.5.mu.m of the transition layer, then decreases smoothly to about 1% to obtain a lattice constant of 5.74 A. In the same interval the equilibrium concentration of Sb smoothly increases from 0 to about 9 atomic percent to form a surface on which a GaAsSb layer having the desired energy bandgap of 1.1 ev for one junction of an optimized dual junction photovoltaic device. The liquid phase epitaxy is accomplished with a step cooling procedure whereby dislocation defects are more uniformly distributed over the surface of the growing layer.

  20. Pocked surface neutron detector

    DOE Patents [OSTI]

    McGregor, Douglas; Klann, Raymond

    2003-04-08

    The detection efficiency, or sensitivity, of a neutron detector material such as of Si, SiC, amorphous Si, GaAs, or diamond is substantially increased by forming one or more cavities, or holes, in its surface. A neutron reactive material such as of elemental, or any compound of, .sup.10 B, .sup.6 Li, .sup.6 LiF, U, or Gd is deposited on the surface of the detector material so as to be disposed within the cavities therein. The portions of the neutron reactive material extending into the detector material substantially increase the probability of an energetic neutron reaction product in the form of a charged particle being directed into and detected by the neutron detector material.

  1. Charge noise, spin-orbit coupling, and dephasing of single-spin qubits

    SciTech Connect (OSTI)

    Bermeister, Adam; Keith, Daniel; Culcer, Dimitrie

    2014-11-10

    Quantum dot quantum computing architectures rely on systems in which inversion symmetry is broken, and spin-orbit coupling is present, causing even single-spin qubits to be susceptible to charge noise. We derive an effective Hamiltonian for the combined action of noise and spin-orbit coupling on a single-spin qubit, identify the mechanisms behind dephasing, and estimate the free induction decay dephasing times T{sub 2}{sup *} for common materials such as Si and GaAs. Dephasing is driven by noise matrix elements that cause relative fluctuations between orbital levels, which are dominated by screened whole charge defects and unscreened dipole defects in the substrate. Dephasing times T{sub 2}{sup *} differ markedly between materials and can be enhanced by increasing gate fields, choosing materials with weak spin-orbit, making dots narrower, or using accumulation dots.

  2. Native defects in MBE-grown CdTe

    SciTech Connect (OSTI)

    Olender, Karolina; Wosinski, Tadeusz; Makosa, Andrzej; Tkaczyk, Zbigniew; Kolkovsky, Valery; Karczewski, Grzegorz

    2013-12-04

    Deep-level traps in both n- and p-type CdTe layers, grown by molecular-beam epitaxy on GaAs substrates, have been investigated by means of deep-level transient spectroscopy (DLTS). Four of the traps revealed in the DLTS spectra, which displayed exponential kinetics for capture of charge carriers into the trap states, have been assigned to native point defects: Cd interstitial, Cd vacancy, Te antisite defect and a complex formed of the Te antisite and Cd vacancy. Three further traps, displaying logarithmic capture kinetics, have been ascribed to electron states of treading dislocations generated at the mismatched interface with the substrate and propagated through the CdTe layer.

  3. Photocapacitance study of type-II GaSb/GaAs quantum ring solar cells

    SciTech Connect (OSTI)

    Wagener, M. C.; Botha, J. R.; Carrington, P. J.; Krier, A.

    2014-01-07

    In this study, the density of states associated with the localization of holes in GaSb/GaAs quantum rings are determined by the energy selective charging of the quantum ring distribution. The authors show, using conventional photocapacitance measurements, that the excess charge accumulated within the type-II nanostructures increases with increasing excitation energies for photon energies above 0.9?eV. Optical excitation between the localized hole states and the conduction band is therefore not limited to the ?(k?=?0) point, with pseudo-monochromatic light charging all states lying within the photon energy selected. The energy distribution of the quantum ring states could consequently be accurately related from the excitation dependence of the integrated photocapacitance. The resulting band of localized hole states is shown to be well described by a narrow distribution centered 407?meV above the GaAs valence band maximum.

  4. Electric field induced spin-polarized current

    DOE Patents [OSTI]

    Murakami, Shuichi; Nagaosa, Naoto; Zhang, Shoucheng

    2006-05-02

    A device and a method for generating an electric-field-induced spin current are disclosed. A highly spin-polarized electric current is generated using a semiconductor structure and an applied electric field across the semiconductor structure. The semiconductor structure can be a hole-doped semiconductor having finite or zero bandgap or an undoped semiconductor of zero bandgap. In one embodiment, a device for injecting spin-polarized current into a current output terminal includes a semiconductor structure including first and second electrodes, along a first axis, receiving an applied electric field and a third electrode, along a direction perpendicular to the first axis, providing the spin-polarized current. The semiconductor structure includes a semiconductor material whose spin orbit coupling energy is greater than room temperature (300 Kelvin) times the Boltzmann constant. In one embodiment, the semiconductor structure is a hole-doped semiconductor structure, such as a p-type GaAs semiconductor layer.

  5. Fabrication and Characterization of a Single Hole Transistor in p-type GaAs/AlGaAs Heterostructures

    SciTech Connect (OSTI)

    Tracy, Lisa A; Reno, John L.; Hargett, Terry W.

    2015-09-01

    Most spin qubit research to date has focused on manipulating single electron spins in quantum dots. However, hole spins are predicted to have some advantages over electron spins, such as reduced coupling to host semiconductor nuclear spins and the ability to control hole spins electrically using the large spin-orbit interaction. Building on recent advances in fabricating high-mobility 2D hole systems in GaAs/AlGaAs heterostructures at Sandia, we fabricate and characterize single hole transistors in GaAs. We demonstrate p-type double quantum dot devices with few-hole occupation, which could be used to study the physics of individual hole spins and control over coupling between hole spins, looking towards eventual applications in quantum computing. Intentionally left blank

  6. Phonon Spectrum Engineering in Rolled-up Micro- and Nano-Architectures

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Fomin, Vladimir M.; Balandin, Alexander A.

    2015-10-10

    We report on a possibility of efficient engineering of the acoustic phonon energy spectrum in multishell tubular structures produced by a novel high-tech method of self-organization of micro- and nano-architectures. The strain-driven roll-up procedure paved the way for novel classes of metamaterials such as single semiconductor radial micro- and nano-crystals and multi-layer spiral micro- and nano-superlattices. The acoustic phonon dispersion is determined by solving the equations of elastodynamics for InAs and GaAs material systems. It is shown that the number of shells is an important control parameter of the phonon dispersion together with the structure dimensions and acoustic impedance mismatchmore » between the superlattice layers. The obtained results suggest that rolled up nano-architectures are promising for thermoelectric applications owing to a possibility of significant reduction of the thermal conductivity without degradation of the electronic transport.« less

  7. Reactive codoping of GaAlInP compound semiconductors

    DOE Patents [OSTI]

    Hanna, Mark Cooper (Boulder, CO); Reedy, Robert (Golden, CO)

    2008-02-12

    A GaAlInP compound semiconductor and a method of producing a GaAlInP compound semiconductor are provided. The apparatus and method comprises a GaAs crystal substrate in a metal organic vapor deposition reactor. Al, Ga, In vapors are prepared by thermally decomposing organometallic compounds. P vapors are prepared by thermally decomposing phospine gas, group II vapors are prepared by thermally decomposing an organometallic group IIA or IIB compound. Group VIB vapors are prepared by thermally decomposing a gaseous compound of group VIB. The Al, Ga, In, P, group II, and group VIB vapors grow a GaAlInP crystal doped with group IIA or IIB and group VIB elements on the substrate wherein the group IIA or IIB and a group VIB vapors produced a codoped GaAlInP compound semiconductor with a group IIA or IIB element serving as a p-type dopant having low group II atomic diffusion.

  8. Bond order potential module for LAMMPS

    Energy Science and Technology Software Center (OSTI)

    2012-09-11

    pair_bop is a module for performing energy calculations using the Bond Order Potential (BOP) for use in the parallel molecular dynamics code LAMMPS. The bop pair style computes BOP based upon quantum mechanical incorporating both sigma and pi bondings. By analytically deriving the BOP pair bop from quantum mechanical theory its transferability to different phases can approach that of quantum mechanical methods. This potential is extremely effective at modeling 111-V and II-VI compounds such asmore » GaAs and CdTe. This potential is similar to the original BOP developed by Pettifor and later updated by Murdock et al. and Ward et al.« less

  9. Cathode performance during two beam operation of the high current high polarization electron gun for eRHIC

    SciTech Connect (OSTI)

    Rahman, O.; Ben-Zvi, I.; Degen, C.; Gassner, D. M.; Lambiase, R.; Meng, W.; Pikin, A.; Rao, T.; Sheehy, B.; Skaritka, J.; Wang, E.; Pietz, J.; Ackeret, M.; Yeckel, C.; Miller, R.; Dobrin, E.; Thompson, K.

    2015-05-03

    Two electron beams from two activated bulk GaAs photocathodes were successfully combined during the recent beam test of the High Current High Polarization Electron gun for eRHIC. The beam test took place in Stangenes Industries in Palo Alto, CA, where the cathodes were placed in diagonally opposite locations inside the high voltage shroud. No significant cross talking between the cathodes was found for the pertinent vacuum and low average current operation, which is very promising towards combining multiple beams for higher average current. This paper describes the cathode preparation, transport and cathode performance in the gun for the combining test, including the QE and lifetimes of the photocathodes at various steps of the experiment.

  10. Single InAs quantum dot coupled to different 'environments' in one wafer for quantum photonics

    SciTech Connect (OSTI)

    Yu, Ying; Shang, Xiang-Jun; Li, Mi-Feng; Zha, Guo-Wei; Xu, Jian-Xing; Wang, Li-Juan; Wang, Guo-Wei; Ni, Hai-Qiao; Dou, Xiuming; Sun, Baoquan; Niu, Zhi-Chuan

    2013-05-20

    Self assembled small InAs quantum dots (SQDs) were formed in various densities and environments using gradient InAs deposition on a non-rotating GaAs substrate. Two SQD environments (SQD I and SQD II) were characterized. SQD I featured SQDs surrounded by large QDs, and SQD II featured individual SQDs in the wetting layer (WL). Micro-photoluminescence of single QDs embedded in a cavity under various excitation powers and electric fields gave insight into carrier transport processes. Potential fluctuations of the WL in SQD II, induced by charge redistribution, show promise for charge-tunable QD devices; SQD I shows higher luminescence intensity as a single-photon source.

  11. High voltage photovoltaic power converter

    DOE Patents [OSTI]

    Haigh, Ronald E. (Arvada, CO); Wojtczuk, Steve (Cambridge, MA); Jacobson, Gerard F. (Livermore, CA); Hagans, Karla G. (Livermore, CA)

    2001-01-01

    An array of independently connected photovoltaic cells on a semi-insulating substrate contains reflective coatings between the cells to enhance efficiency. A uniform, flat top laser beam profile is illuminated upon the array to produce electrical current having high voltage. An essentially wireless system includes a laser energy source being fed through optic fiber and cast upon the photovoltaic cell array to prevent stray electrical signals prior to use of the current from the array. Direct bandgap, single crystal semiconductor materials, such as GaAs, are commonly used in the array. Useful applications of the system include locations where high voltages are provided to confined spaces such as in explosive detonation, accelerators, photo cathodes and medical appliances.

  12. Improved efficiency of photoconductive THz emitters by increasing the effective contact length of electrodes

    SciTech Connect (OSTI)

    Singh, Abhishek; Surdi, Harshad; Nikesh, V. V.; Prabhu, S. S.; Döhler, G. H.

    2013-12-15

    We study the effect of a surface modification at the interface between metallic electrodes and semiconducting substrate in Semi-Insulating GaAs (SI-GaAs) based photoconductive emitters (PCE) on the emission of Tera-Hertz (THz) radiation. We partially etch out a 500 nm thick layer of SI-GaAs in grating like pattern with various periods before the contact deposition. By depositing the electrodes on the patterned surface, the electrodes follow the contour of the grating period. This increases the effective contact length of the electrodes per unit area of the active regions on the PCE. The maxima of the electric field amplitude of the THz pulses emitted from the patterned surface are enhanced by up to more than a factor 2 as compared to an un-patterned surface. We attribute this increase to the increase of the effective contact length of the electrode due to surface patterning.

  13. Optical data latch

    DOE Patents [OSTI]

    Vawter, G. Allen

    2010-08-31

    An optical data latch is formed on a substrate from a pair of optical logic gates in a cross-coupled arrangement in which optical waveguides are used to couple an output of each gate to an photodetector input of the other gate. This provides an optical bi-stability which can be used to store a bit of optical information in the latch. Each optical logic gate, which can be an optical NOT gate (i.e. an optical inverter) or an optical NOR gate, includes a waveguide photodetector electrically connected in series with a waveguide electroabsorption modulator. The optical data latch can be formed on a III-V compound semiconductor substrate (e.g. an InP or GaAs substrate) from III-V compound semiconductor layers. A number of optical data latches can be cascaded to form a clocked optical data shift register.

  14. The Pd/Fe Interface in the Epitaxial System Pd/Fe/GaAs(001)- 4 x 6

    SciTech Connect (OSTI)

    Budnik, P.S.; Gordon, R.A.; Crozier, E.D.

    2007-01-18

    Magnetic properties of thin magnetic films are strongly affected by the nature of the interface between magnetic and non-magnetic layers. In spintronic devices the extent to which spins are scattered at an interface depends upon interfacial roughness, alloying, and impurities. We present a polarization-dependent XAFS study of a 1Pd/9Fe/GaAs(001)-(4 x 6) structure grown in situ in the MBE facility at the PNC/XOR, APS. To increase the interfacial roughness, the 1ML Pd was grown on the 9 ML Fe without first sputtering and annealing the Fe. An estimate of interfacial roughness, evidence for formation of Pd islands, their height, and the amount of As floating to the Pd surface from the GaAs are given.

  15. Tandem Microwire Solar Cells for Flexible High Efficiency Low Cost Photovoltaics

    SciTech Connect (OSTI)

    Atwater, Harry A.

    2015-03-10

    This project has developed components of a waferless, flexible, low-cost tandem multijunction III-V/Si microwire array solar cell technology which combines the efficiency of wafered III-V photovoltaic technologies with the process designed to meet the Sunshot object. The project focused on design of lattice-matched GaAsP/SiGe two junction cell design and lattice-mismatched GaInP/Si tandem cell design. Combined electromagnetic simulation/device physics models using realistic microwire tandem structures were developed that predict >22% conversion efficiency for known material parameters, such as tunnel junction structure, window layer structure, absorber lifetimes and optical absorption and these model indicate a clear path to 30% efficiency for high quality III-V heterostructures. SiGe microwire arrays were synthesized via Cu-catalyzed vapor-liquid-solid (VLS) growth with inexpensive chlorosilane and chlorogermance precursors in an atmospheric pressure reactor. SiGe alloy composition in microwires was found to be limited to a maximum of 12% Ge incorporation during chlorogermane growth, due to the melting of the alloy near the solidus composition. Lattice mismatched InGaP double heterostructures were grown by selective epitaxy with a thermal oxide mask on Si microwire substrates using metallorganic vapor phase epitaxy. Transmission electron microscopy (TEM) analysis confirms the growth of individual step graded layers and a high density of defects near the wire/III-V interface. Selective epitaxy was initiated with a low temperature nucleation scheme under “atomic layer epitaxy” or “flow mediated epitaxy” conditions whereby the Ga and P containing precursors are alternately introduced into the reactor to promote layer-bylayer growth. In parallel to our efforts on conformal GaInP heteroepitaxy on selectively masked Si microwires, we explored direct, axial growth of GaAs on Si wire arrays as another route to a tandem junction architecture. We proposed axial, lattice-mismatched growth of a GaAs segment that extrude out of a Si wire via a self-aligned SiO2 hollow cylindrical mask. With this growth strategy, misfit dislocations that would normally form at the GaAs/Si interface during thin film epitaxy may bend over to and thus terminate at the sidewall of the SiO2 tube. A reactive-ion etching technique was employed 1) to remove Si to form a hollow, self-aligned SiO2 cylindrical tube as a growth template for GaAs epitaxy using a vertical, showerhead, low-pressure metal-organic chemical-vapor deposition reactor that was operated at 0.1 atm. Successful epitaxy of axial GaAs wires on non-polar, <111>-oriented Si wire substrates was found at temperatures of ~850C. This and the other III-V/Si heterojunction wire synthesis strategies described here are promising approaches to realize future III-V/Si tandem solar cell designs.

  16. Highly tunable quantum Hall far-infrared photodetector by use of GaAs/Al{sub x}Ga{sub 1?x}As-graphene composite material

    SciTech Connect (OSTI)

    Tang, Chiu-Chun [Department of Physics, National Tsing Hua University, Hsinchu 30013, Taiwan (China); Ling, D. C. [Department of Physics, Tamkang University, Tamsui Dist., New Taipei City 25137, Taiwan (China); Chi, C. C.; Chen, Jeng-Chung [Department of Physics, National Tsing Hua University, Hsinchu 30013, Taiwan (China); Frontier Research Center on Fundamental and Applied Sciences of Matters, National Tsing Hua University, Hsinchu 30013, Taiwan (China)

    2014-11-03

    We have developed a highly tunable, narrow band far-infrared (FIR) photodetector which utilizes the characteristic merits of graphene and two-dimensional electron gas (2DEG) in GaAs/Al{sub x}Ga{sub 1?x}As heterostructure in the Quantum Hall states (QHS). The heterostructure surface is covered with chemical vapor-deposited graphene, which functions as a transparent top-gate to vary the electron density of the 2DEG. FIR response observed in the vicinity of integer QH regime can be effectively tuned in a wide range of 27102?cm{sup ?1} with a bias voltage less than ?1?V. In addition, we have found that the presence of graphene can genuinely modulate the photoresponse. Our results demonstrate a promising direction for realizing a tunable long-wavelength FIR detector using QHS in GaAs 2DEG/ graphene composite material.

  17. Experimental demonstration of hot-carrier photo-current in an InGaAs quantum well solar cell

    SciTech Connect (OSTI)

    Hirst, L. C.; Walters, R. J.; Fhrer, M. F.; Ekins-Daukes, N. J.

    2014-06-09

    An unambiguous observation of hot-carrier photocurrent from an InGaAs single quantum well solar cell is reported. Simultaneous photo-current and photoluminescence measurements were performed for incident power density 0.043?kW cm{sup ?2}, lattice temperature 10?K, and forward bias 1.2?V. An order of magnitude photocurrent increase was observed for non-equilibrium hot-carrier temperatures >35?K. This photocurrent activation temperature is consistent with that of equilibrium carriers in a lattice at elevated temperature. The observed hot-carrier photo-current is extracted from the well over an energy selective GaAs barrier, thus integrating two essential components of a hot-carrier solar cell: a hot-carrier absorber and an energy selective contact.

  18. Characteristics of GaAsSb single quantum well lasers emitting near 1.3 {micro}m

    SciTech Connect (OSTI)

    SPAHN,OLGA B.; KLEM,JOHN F.

    2000-02-17

    The authors report data on GaAsSb single quantum well lasers grown on GaAs substrates. Room temperature pulsed emission at 1.275 {micro}m in a 1,250 {micro}m-long device has been observed. Minimum threshold current densities of 535 A/cm{sup 2} were measured in 2000 {micro}m long lasers. The authors also measured internal losses of 2--5 cm{sup {minus}1}, internal quantum efficiencies of 30-38% and characteristic temperature T{sub 0} of 67--77 C. From these parameters a gain constant G{sub 0} of 1,660 cm{sup {minus}1} and a transparency current density J{sub tr} of 134 A/cm{sup 2} were calculated. The results indicate the potential for fabricating 1.3 {micro}m VCSELs from these materials.

  19. Seeding of InP islands on InAs quantum dot templates

    SciTech Connect (OSTI)

    Medeiros-Ribeiro, G.; Maltez, R. L.; Bernussi, A. A.; Ugarte, D.; de Carvalho, W.

    2001-06-01

    The ability of stacking layers of islands and their corresponding alignment have prompted a number of studies. The main focus so far has been on stacking self-assembled quantum dot (QD) layers of the same material and composition. Our goal is to create systems of coupled QDs of different electronic properties, aiming at hybridization of their different electronic levels. In this work, we investigate the early stages of the coupling of alternate InAs{endash}InP QD layers through a GaAs spacer layer. We have found that by using an InAs layer containing QDs as seeds, we can control the size, shape and density of InP islands by varying the spacer thickness. We have observed a significant improvement of the InP island size uniformity, as well as an induced size reduction, thus providing an extra degree of tunability previously available only through growth kinetics. {copyright} 2001 American Institute of Physics.

  20. Room temperature continuous wave InGaAsN quantum well vertical cavity lasers emitting at 1.3 um

    SciTech Connect (OSTI)

    CHOQUETTE,KENT D.; KLEM,JOHN F.; FISCHER,ARTHUR J.; SPAHN,OLGA B.; ALLERMAN,ANDREW A.; FRITZ,IAN J.; KURTZ,STEVEN R.; BREILAND,WILLIAM G.; SIEG,ROBERT M.; GEIB,KENT M.; SCOTT,J.W.; NAONE,R.L.

    2000-06-05

    Selectively oxidized vertical cavity lasers emitting at 1294 nm using InGaAsN quantum wells are reported for the first time which operate continuous wave at and above room temperature. The lasers employ two n-type Al{sub 0.94}Ga{sub 0.06}As/GaAs distributed Bragg reflectors each with a selectively oxidized current aperture adjacent to the optical cavity, and the top output mirror contains a tunnel junction to inject holes into the active region. Continuous wave single mode lasing is observed up to 55 C. These lasers exhibit the longest wavelength reported to date for vertical cavity surface emitting lasers grown on GaAs substrates.

  1. Strain-compensated infrared photodetector and photodetector array

    DOE Patents [OSTI]

    Kim, Jin K; Hawkins, Samuel D; Klem, John F; Cich, Michael J

    2013-05-28

    A photodetector is disclosed for the detection of infrared light with a long cutoff wavelength in the range of about 4.5-10 microns. The photodetector, which can be formed on a semiconductor substrate as an nBn device, has a light absorbing region which includes InAsSb light-absorbing layers and tensile-strained layers interspersed between the InAsSb light-absorbing layers. The tensile-strained layers can be formed from GaAs, InAs, InGaAs or a combination of these III-V compound semiconductor materials. A barrier layer in the photodetector can be formed from AlAsSb or AlGaAsSb; and a contact layer in the photodetector can be formed from InAs, GaSb or InAsSb. The photodetector is useful as an individual device, or to form a focal plane array.

  2. Ion bombardment in RF photoguns

    SciTech Connect (OSTI)

    Pozdeyev,E.; Kayran, D.; Litvinenko, V. N.

    2009-05-04

    A linac-ring eRHIC design requires a high-intensity CW source of polarized electrons. An SRF gun is viable option that can deliver the required beam. Numerical simulations presented elsewhere have shown that ion bombardment can occur in an RF gun, possibly limiting lifetime of a NEA GaAs cathode. In this paper, we analytically solve the equations of motion of ions in an RF gun using the ponderomotive potential of the Rf field. We apply the method to the BNL 1/2-cell SRF photogun and demonstrate that a significant portion of ions produced in the gun can reach the cathode if no special precautions are taken. Also, the paper discusses possible mitigation techniques that can reduce the rate of ion bombardment.

  3. Two-band lasing in epitaxially stacked tunnel-junction semiconductor lasers

    SciTech Connect (OSTI)

    Vinokurov, D. A.; Ladugin, M. A.; Lyutetskii, A. V.; Marmalyuk, A. A.; Petrunov, A. N.; Pikhtin, N. A.; Slipchenko, S. O. Sokolova, Z. N.; Stankevich, A. L.; Fetisova, N. V.; Shashkin, I. S.; Averkiev, N. S.; Tarasov, I. S.

    2010-06-15

    Epitaxially stacked tunnel-junction laser hetero structures were grown by hydride metalorganic vapor-phase epitaxy in the system of AlGaAs/GaAs/In GaAs alloys. Based on such structures, mesa stripe lasers with an aperture of 150 s- 7 m were fabricated. The possibility of controlling the lasing wavelength by varying the active region thickness in each tunnel-junction laser structure was demonstrated. Independent two-band lasing at wavelengths of 914 and 925 nm (the difference frequency is 2.3 THz) was achieved at a maximum optical radiation power of 20 W in each band of the epitaxially stacked tunnel-junction semiconductor laser.

  4. Development of a High Volume Capable Process to Manufacture High Performance Photovoltaic Cells: Cooperative Research and Development Final Report, CRADA Number CRD-08-322

    SciTech Connect (OSTI)

    Geisz, J. F.

    2012-11-01

    The intent of the work is for RFMD and NREL to cooperate in the development of a commercially viable and high volume capable process to manufacture high performance photovoltaic cells, based on inverted metamorphic (IMM) GaAs technology. The successful execution of the agreement will result in the production of a PV cell using technology that is capable of conversion efficiency at par with the market at the time of release (reference 2009: 37-38%), using RFMD's production facilities. The CRADA work has been divided into three phases: (1) a foundation phase where the teams will demonstrate the manufacturing of a basic PV cell at RFMD's production facilities; (2) a technology demonstration phase where the teams will demonstrate the manufacturing of prototype PV cells using IMM technology at RFMD's production facilities, and; (3) a production readiness phase where the teams will demonstrate the capability to manufacture PV cells using IMM technology with high yields, high reliability, high reproducibility and low cost.

  5. Using Measurements of Fill Factor at High Irradiance to Deduce Heterobarrier Band Offsets: Preprint

    SciTech Connect (OSTI)

    Olson, J. M.; Steiner, M. A.; Kanevce, A.

    2011-07-01

    Using a 2D device simulation tool, we examine the high irradiance behavior of a single junction, GaAs concentrator cell as a function of the doping in the back surface confinement layer. The confinement layer is designed to be a barrier for both holes and electrons in the base of the solar cell. For a p-type base we show that the FF of the cell at high concentrations is a strong function of both the magnitude of the valence band offset and the doping level in the barrier. In short, for a given valence band offset (VBO), there is a critical barrier doping, below which the FF drops rapidly with lower doping. This behavior is confirmed experimentally for a GaInP/GaAs double heterostructure solar cell where the critical doping concentration (at 500 suns) in the back surface confinement layer is ~1e18 cm-3 for a VBO of 300 meV.

  6. Carrier localization and in-situ annealing effect on quaternary Ga{sub 1-x}In{sub x}As{sub y}Sb{sub 1-y}/GaAs quantum wells grown by Sb pre-deposition

    SciTech Connect (OSTI)

    Thoma, Jiri; Huyet, Guillaume; Tyndall National Institute, UCC, Lee Maltings, Cork ; Liang, Baolai; Huffaker, Diana L.; Lewis, Liam; Hegarty, Stephen P.

    2013-03-18

    Using temperature-dependent photoluminescence spectroscopy, we have investigated and compared intrinsic InGaAs, intrinsic GaInAsSb, and p-i-n junction GaInAsSb quantum wells (QWs) embedded in GaAs barriers. Strong carrier localization inside the intrinsic GaInAsSb/GaAs QW has been observed together with its decrease inside the p-i-n sample. This is attributed to the effect of an in-situ annealing during the top p-doped AlGaAs layer growth at an elevated temperature of 580 Degree-Sign C, leading to Sb-atom diffusion and even atomic redistribution. High-resolution X-ray diffraction measurements and the decrease of both maximum localization energy and full delocalization temperature in the p-i-n QW sample further corroborated this conclusion.

  7. Thin-layer black phosphorous/GaAs heterojunction p-n diodes

    SciTech Connect (OSTI)

    Gehring, Pascal; Urcuyo, Roberto; Duong, Dinh Loc; Burghard, Marko; Kern, Klaus

    2015-06-08

    Owing to its high carrier mobility and thickness-tunable direct band gap, black phosphorous emerges as a promising component of optoelectronic devices. Here, we evaluate the device characteristics of p-n heterojunction diodes wherein thin black phosphorous layers are interfaced with an underlying, highly n-doped GaAs substrate. The p-n heterojunctions exhibit close-to-ideal diode behavior at low bias, while under illumination they display a photoresponse that is evenly distributed over the entire junction area, with an external quantum efficiency of up to 10% at zero bias. Moreover, the observed maximum open circuit voltage of 0.6 V is consistent with the band gap estimated for a black phosphorous sheet with a thickness on the order of 10?nm. Further analysis reveals that the device performance is limited by the structural quality of the black phosphorous surface.

  8. Hot-carrier solar cells using low-dimensional quantum structures

    SciTech Connect (OSTI)

    Watanabe, Daiki; Kasamatsu, Naofumi; Harada, Yukihiro; Kita, Takashi

    2014-10-27

    We propose a high-conversion-efficiency solar cell (SC) utilizing the hot carrier (HC) population in an intermediate-band (IB) of a quantum dot superlattice (QDSL) structure. The bandgap of the host semiconductor in this device plays an important role as an energy-selective barrier for HCs in the QDSLs. According to theoretical calculation using the detailed balance model with an air mass 1.5 spectrum, the optimum IB energy is determined by a trade-off relation between the number of HCs with energy exceeding the conduction-band edge and the number of photons absorbed by the valence band?IB transition. Utilizing experimental data of HC temperature in InAs/GaAs QDSLs, the maximum conversion efficiency under maximum concentration (45?900 suns) has been demonstrated to increase by 12.6% as compared with that for a single-junction GaAs SC.

  9. Lasing modes in polycrystalline and amorphous photonic structures

    SciTech Connect (OSTI)

    Yang, Jin-Kyu; Noh, Heeso; Liew, Seng Fatt; Rooks, Michael J.; Solomon, Glenn S.; Cao Hui

    2011-09-15

    We systematically studied the lasing characteristics in photonic polycrystalline and amorphous structures. 2D arrays of air holes were fabricated in a GaAs membrane. InAs quantum dots embedded in the membrane provide gain for lasing under optical pumping. The lasing modes are spatially localized, and blue shift as the structural order becomes short ranged. Our three-dimensional numerical simulations reveal that the out-of-plane leakage of the lasing mode dominates over the in-plane leakage. The lasing modes in a photonic polycrystalline move away from the center frequency of the photonic band gap to reduce the out-of-plane leakage. In a photonic amorphous structure, the short-range order improves optical confinement and enhances the quality factor of resonances. Understanding the behavior of photonic polycrystalline laser and amorphous laser opens the possibility of controlling lasing characteristic by varying the degree of structural order.

  10. Gamma ray measurements with photoconductive detectors using a dense plasma focus

    SciTech Connect (OSTI)

    May, M. J. Brown, G. V.; Halvorson, C.; Schmidt, A.; Bower, D.; Tran, B.; Lewis, P.; Hagen, C.

    2014-11-15

    Photons in the MeV range emitted from the dense plasma focus (DPF) at the NSTec North Las Vegas Facility have been measured with both neutron-damaged GaAs and natural diamond photoconductive detectors (PCDs). The DPF creates or pinches plasmas of various gases (e.g., H{sub 2}, D{sub 2}, Ne, Ar., etc.) that have enough energy to create MeV photons from either bremsstrahlung and/or (n,n{sup ?}) reactions if D{sub 2} gas is used. The high bandwidth of the PCDs enabled the first ever measurement of the fast micro-pinches present in DPF plasmas. Comparisons between a slower more conventional scintillator/photomultiplier tube based nuclear physics detectors were made to validate the response of the PCDs to fast intense MeV photon signals. Significant discrepancies in the diamond PCD responses were evident.

  11. Radiation resistance of GaAs-GaAlAs vertical cavity surface emitting lasers

    SciTech Connect (OSTI)

    Jabbour, J.; Zazoui, M.; Sun, G.C.; Bourgoin, J.C.; Gilard, O.

    2005-02-15

    The variations of the optical and electrical characteristics of a vertical cavity surface emitting laser based on GaAs quantum wells have been monitored versus irradiation with 1 MeV electrons. The results are understood by the introduction of nonradiative recombination centers in the wells whose characteristics, capture cross section for minority carriers times their introduction rate, can be determined. A similar study performed for proton irradiation shows that the results can be explained in the same way when the introduction rate of the defects is replaced by the proton energy loss into atomic collisions. These results allow us to deduce the equivalence between electron and proton irradiations: A flux of 1 proton cm{sup -2} which loses an energy E{sub nl} (eV) into atomic collisions is equivalent to a fluence of about 9x10{sup -2} E{sub nl} cm{sup -2}, 1 MeV electrons.

  12. Semiconductor switch geometry with electric field shaping

    DOE Patents [OSTI]

    Booth, R.; Pocha, M.D.

    1994-08-23

    An optoelectric switch is disclosed that utilizes a cylindrically shaped and contoured GaAs medium or other optically active semiconductor medium to couple two cylindrically shaped metal conductors with flat and flared termination points each having an ovoid prominence centrally extending there from. Coupling the truncated ovoid prominence of each conductor with the cylindrically shaped optically active semiconductor causes the semiconductor to cylindrically taper to a triple junction circular line at the base of each prominence where the metal conductor conjoins with the semiconductor and a third medium such as epoxy or air. Tapering the semiconductor at the triple junction inhibits carrier formation and injection at the triple junction and thereby enables greater current carrying capacity through and greater sensitivity of the bulk area of the optically active medium. 10 figs.

  13. Semiconductor switch geometry with electric field shaping

    DOE Patents [OSTI]

    Booth, Rex (Livermore, CA); Pocha, Michael D. (Livermore, CA)

    1994-01-01

    An optoelectric switch is disclosed that utilizes a cylindrically shaped and contoured GaAs medium or other optically active semiconductor medium to couple two cylindrically shaped metal conductors with flat and flared termination points each having an ovoid prominence centrally extending there from. Coupling the truncated ovoid prominence of each conductor with the cylindrically shaped optically active semiconductor causes the semiconductor to cylindrically taper to a triple junction circular line at the base of each prominence where the metal conductor conjoins with the semiconductor and a third medium such as epoxy or air. Tapering the semiconductor at the triple junction inhibits carrier formation and injection at the triple junction and thereby enables greater current carrying capacity through and greater sensitivity of the bulk area of the optically active medium.

  14. Progress toward technology transition of GaInP{sub 2}/GaAs/Ge multijunction solar cells

    SciTech Connect (OSTI)

    Keener, D.N.; Marvin, D.C.; Brinker, D.J.; Curtis, H.B.; Price, P.M.

    1997-12-31

    The objective of the joint WL/PL/NASA Multijunction Solar Cell Manufacturing Technology (ManTech) Program is to scale up high efficiency GaInP{sub 2}/GaAs/Ge multijunction solar cells to production size, quantity, and yield while limiting the production cost/Watt ($/W) to 15% over GaAs cells. Progress made by the program contractors, Spectrolab and TECSTAR, include, respectively, best cell efficiencies of 25.76% and 24.7% and establishment of 24.2% and 23.8% lot average efficiency baseline designs. The paper also presents side-by-side testing results collected by Phillips Laboratory and NASA Lewis on Phase 1 deliverable cells, which shows compliance with program objectives. Cell performance, pre- and post-radiation, and temperature coefficient results on initial production GaInP{sub 2}/GaAs/Ge solar cells will be presented.

  15. Optical set-reset latch

    DOE Patents [OSTI]

    Skogen, Erik J.

    2013-01-29

    An optical set-reset (SR) latch is formed from a first electroabsorption modulator (EAM), a second EAM and a waveguide photodetector (PD) which are arranged in an optical and electrical feedback loop which controls the transmission of light through the first EAM to latch the first EAM in a light-transmissive state in response to a Set light input. A second waveguide PD controls the transmission of light through the second EAM and is used to switch the first EAM to a light-absorptive state in response to a Reset light input provided to the second waveguide PD. The optical SR latch, which may be formed on a III-V compound semiconductor substrate (e.g. an InP or a GaAs substrate) as a photonic integrated circuit (PIC), stores a bit of optical information and has an optical output for the logic state of that bit of information.

  16. 100 mm Engineered InP-on-Si Laminate Substrates for InP-based Multijunction Solar Cells

    SciTech Connect (OSTI)

    Atwater, Harry

    2012-06-25

    The project focused on fabrication of InP/Si laminate substrates as templates for growth of InGaAsP/InGaAs and InAlAs/InGaAsP/InGaAs multijunction solar cells. InP/Si template substrates were developed and used as templates for InGaAs solar growth. A novel feature of the program was development of the virtual substrate template, which enables a substrate to be formed with a lattice constant intermediate between those of GaAs and InP. Large-area virtual substrate templates were formed by transfer and bonding of dislocation free InGaAs films wafer onto silicon substrates.

  17. III-V-N materials for super high-efficiency multijunction solar cells

    SciTech Connect (OSTI)

    Yamaguchi, Masafumi; Bouzazi, Boussairi; Suzuki, Hidetoshi; Ikeda, Kazuma; Kojima, Nobuaki; Ohshita, Yoshio

    2012-10-06

    We have been studying concentrator multi-junction solar cells under Japanese Innovative Photovoltaic R and D program since FY2008. InGaAsN is one of appropriate materials for 4-or 5-junction solar cell configuration because this material can be lattice-matched to GaAs and Ge substrates. However, present InGaAsN single-junction solar cells have been inefficient because of low minority-carrier lifetime due to N-related recombination centers and low carrier mobility due to alloy scattering and non-homogeneity of N. This paper presents our major results in the understanding of majority and minority carrier traps in GaAsN grown by chemical beam epitaxy and their relationships with the poor electrical properties of the materials.

  18. GaInNAs Structures Grown by MBE for High-Efficiency Solar Cells: Final Report; 25 June 1999--24 August 2002

    SciTech Connect (OSTI)

    Tu, C. W.

    2003-08-01

    The focus of this work is to improve the quality of GaInNAs by advanced thin-film growth techniques, such as digital-alloy growth techniques and migration-enhanced epitaxy (MEE). The other focus is to further investigate the properties of such materials, which are potentially beneficial for high-efficiency, multijunction solar cells. 400-nm-thick strain-compensated Ga0.92In0.08As/GaN0.03As0.97 short-period superlattices (SPSLs) are grown lattice-matched to GaAs substrates. The photoluminescence (PL) intensity of digital alloys is 3 times higher than that of random alloys at room temperature, and the improvement is even greater at low temperature, by a factor of about 12. The room-temperature PL intensity of the GaInNAs quantum well grown by the strained InAs/GaN0.023As SPSL growth mode is higher by a factor 5 as compare to the continuous growth mode. The SPSL growth method allows for independent adjustment of the In-to-Ga ratio without group III competition. MEE reduces the low-energy tail of PL, and PL peaks become more intense and sharper. The twin peaks photoluminescence of GaNAs grown on GaAs was observed at room temperature. The peaks splitting increase with increase in nitrogen alloy content. The strain-induced splitting of light-hole and heavy-hole bands of tensile-strained GaNAs is proposed as an explanation of such behavior.

  19. Carrier Multiplication in Semiconductor Nanocrystals: Theoretical Screening of Candidate Materials Based on Band-Structure Effects

    SciTech Connect (OSTI)

    Luo, J. W.; Franceschetti, A.; Zunger, A.

    2008-01-01

    Direct carrier multiplication (DCM) occurs when a highly excited electron-hole pair decays by transferring its excess energy to the electrons rather than to the lattice, possibly exciting additional electron-hole pairs. Atomistic electronic structure calculations have shown that DCM can be induced by electron-hole Coulomb interactions, in an impact-ionization-like process whose rate is proportional to the density of biexciton states {rho}{sub XX}. Here we introduce a DCM 'figure of merit' R{sub 2}(E) which is proportional to the ratio between the biexciton density of states {rho}{sub XX} and the single-exciton density of states {rho}{sub x}, restricted to single-exciton and biexciton states that are coupled by Coulomb interactions. Using R{sub 2}(E), we consider GaAs, InAs, InP, GaSb, InSb, CdSe, Ge, Si, and PbSe nanocrystals of different sizes. Although DCM can be affected by both quantum-confinement effects (reflecting the underly electronic structure of the confined dot-interior states) and surface effects, here we are interested to isolate the former. To this end the nanocrystal energy levels are obtained from the corresponding bulk band structure via the truncated crystal approximation. We find that PbSe, Si, GaAs, CdSe, and InP nanocrystals have larger DCM figure of merit than the other nanocrystals. Our calculations suggest that high DCM efficiency requires high degeneracy of the corresponding bulk band-edge states. Interestingly, by considering band structure effects we find that as the dot size increases the DCM critical energy E{sub 0} (the energy at which R{sub 2}(E) becomes {ge}1) is reduced, suggesting improved DCM. However, whether the normalized E{sub 0}/{var_epsilon}{sub g} increases or decreases as the dot size increases depends on dot material.

  20. InGaAs/GaAs (110) quantum dot formation via step meandering

    SciTech Connect (OSTI)

    Diez-Merino, Laura; Tejedor, Paloma

    2011-07-01

    InGaAs (110) semiconductor quantum dots (QDs) offer very promising prospects as a material base for a new generation of high-speed spintronic devices, such as single electron transistors for quantum computing. However, the spontaneous formation of InGaAs QDs is prevented by two-dimensional (2D) layer-by-layer growth on singular GaAs (110) substrates. In this work we have studied, by using atomic force microscopy and photoluminescence spectroscopy (PL), the growth of InGaAs/GaAs QDs on GaAs (110) stepped substrates by molecular beam epitaxy (MBE), and the modification of the adatom incorporation kinetics to surface steps in the presence of chemisorbed atomic hydrogen. The as-grown QDs exhibit lateral dimensions below 100 nm and emission peaks in the 1.35-1.37 eV range. It has been found that a step meandering instability derived from the preferential attachment of In adatoms to [110]-step edges relative to [11n]-type steps plays a key role in the destabilization of 2D growth that leads to 3D mound formation on both conventional and H-terminated vicinal substrates. In the latter case, the driving force for 3D growth via step meandering is enhanced by H-induced upward mass transport in addition to the lower energy cost associated with island formation on H-terminated substrates, which results in a high density array of InGaAs/GaAs dots selectively nucleated on the terrace apices with reduced lateral dimensions and improved PL efficiency relative to those of conventional MBE-grown samples.

  1. National Coal Quality Inventory (NACQI)

    SciTech Connect (OSTI)

    Robert Finkelman

    2005-09-30

    The U.S. Geological Survey (USGS) conducted the National Coal Quality Inventory (NaCQI) between 1999 and 2005 to address a need for quality information on coals that will be mined during the next 20-30 years. Collaboration between the USGS, State geological surveys, universities, coal burning utilities, and the coal mining industry plus funding support from the Electric Power Research Institute (EPRI) and the U.S. Department of Energy (DOE) permitted collection and submittal of coal samples for analysis. The chemical data (proximate and ultimate analyses; major, minor and trace element concentrations) for 729 samples of raw or prepared coal, coal associated shale, and coal combustion products (fly ash, hopper ash, bottom ash and gypsum) from nine coal producing States are included. In addition, the project identified a new coal reference analytical standard, to be designated CWE-1 (West Elk Mine, Gunnison County, Colorado) that is a high-volatile-B or high-volatile-A bituminous coal with low contents of ash yield and sulfur, and very low, but detectable contents of chlorine, mercury and other trace elements.

  2. Risk Reduction and Soil Ecosystem Restoration in an Active Oil Producing Area in an Ecologically Sensitive Setting

    SciTech Connect (OSTI)

    Kerry L. Sublette; Greg Thoma; Kathleen Duncan

    2006-01-01

    The empowerment of small independent oil and gas producers to solve their own remediation problems will result in greater environmental compliance and more effective protection of the environment as well as making small producers more self-reliant. In Chapter 1 we report on the effectiveness of a low-cost method of remediation of a combined spill of crude oil and brine in the Tallgrass Prairie Preserve in Osage County, OK. Specifically, we have used hay and fertilizer as amendments for remediation of both the oil and the brine. No gypsum was used. Three spills of crude oil plus produced water brine were treated with combinations of ripping, fertilizers and hay, and a downslope interception trench in an effort to demonstrate an inexpensive, easily implemented, and effective remediation plan. There was no statistically significant effect of treatment on the biodegradation of crude oil. However, TPH reduction clearly proceeded in the presence of brine contamination. The average TPH half-life considering all impacted sites was 267 days. The combination of hay addition, ripping, and a downslope interception trench was superior to hay addition with ripping, or ripping plus an interception trench in terms of rates of sodium and chloride leaching from the impacted sites. Reductions in salt inventories (36 months) were 73% in the site with hay addition, ripping and an interception trench, 40% in the site with hay addition and ripping only, and < 3% in the site with ripping and an interception trench.

  3. Value-Added Products from FGD Sulfite-Rich Scrubber Materials

    SciTech Connect (OSTI)

    Vivak Malhotra

    2010-01-31

    According to the American Coal Ash Association, about 29.25 million tons of flue gas desulfurization (FGD) byproducts were produced in the USA in 2003. Out of 29.25 million tons, 17.35 million tons were sulfite-rich scrubber materials. At present, unlike its cousin FGD gypsum, the prospect for effective utilization of sulfite-rich scrubber materials is not bright. In fact, almost 16.9 million tons are leftover every year. In our pursuit to mitigate the liability of sulfite-rich FGD scrubber materials' disposal, we are attempting to develop value-added products that can commercially compete. More specifically, for this Innovative Concept Phase I project, we have the following objectives: to characterize the sulfite-rich scrubber material for toxic metals; to optimize the co-blending and processing of scrubber material and natural byproducts; to formulate and develop structural composites from sulfite-rich scrubber material; and to evaluate the composites' mechanical properties and compare them with current products on the market. After successfully demonstrating the viability of our research, a more comprehensive approach will be proposed to take these value-added materials to fruition.

  4. Applications of high-temperature solar heat to the production of selected fuels and chemicals

    SciTech Connect (OSTI)

    Beall, S.E. Jr.; Bamberger, C.E.; Goeller, H.A.

    1981-07-01

    An attempt is made to judge whether solar heat in the 500 K to 2500 K temperature range might be economical for some important fuel- and chemical-production processes. Previous work in related areas is reviewed and the chemicals aluminum oxide (and bauxite), calcium sulfate (and gypsum), and calcium oxide (lime) chosen for detailed study. In addition to reviewing the energy needs of the more common bulk chemicals, several innovative processes requiring heat in the 1500 to 2500 K range were investigated. Hydrogen production by several thermochemical means, carbon monoxide production by thermochemical and direct thermal dissociation, and nitrogen fixation by direct thermal reaction of nitrogen and oxygen in air were considered. The engineering feasibility of the processes is discussed. The problem of matching the conventional and innovative processes to a high-temperature solar supply is studied. Some solar-thermal power plants of current designs are examined and several advanced concepts of highly concentrating systems are considered for very high-temperature applications. Conclusions and recommendations are presented.

  5. Relation between facies, diagenesis, and reservoir quality of Rotliegende reservoirs in north Germany

    SciTech Connect (OSTI)

    David, F.; Gast, R.; Kraft, T. (BEB Erdgas Erdol GmbH, Hannover (Germany))

    1993-09-01

    In north Germany, the majority of Rotliegende gas fields is confined to an approximately 50 km-wide east-west-orientated belt, which is situated on the gently north-dipping flank of the southern Permian basin. Approximately 400 billion m[sup 3] of natural gas has been found in Rotliegende reservoir sandstones with average porosities of depths ranging from 3500 to 5000 m. Rotliegende deposition was controlled by the Autunian paleo-relief, and arid climate and cyclic transgressions of the desert lake. In general, wadis and large dunefields occur in the hinterland, sebkhas with small isolate dunes and shorelines define the coastal area, and a desert lake occurs to the north. The sandstones deposited in large dunefields contain only minor amounts of illite, anhydrite, and calcite and form good reservoirs. In contrast, the small dunes formed in the sebkha areas were affected by fluctuations of the desert lake groundwaters, causing the infiltration of detrital clay and precipitation of gypsum and calcite. These cements were transformed to illite, anhydrite, and calcite-II during later diagenesis, leading to a significant reduction of the reservoir quality. The best reservoirs occur in the shoreline sandstones because porosity and permeability were preserved by early magnesium-chlorite diagenesis. Since facies controls diagenesis and consequently reservoir quality, mapping of facies also indicates the distribution of reservoir and nonreservoir rocks. This information is used to identify play area and to interpret and calibrate three-dimensional seismic data.

  6. FGD Additives to Segregate and Sequester Mercury in Solid Byproducts - Final Report

    SciTech Connect (OSTI)

    Searcy, K; Bltyhe, G M; Steen, W A

    2012-02-28

    Many mercury control strategies for U.S. coal-fired power generating plants involve co-benefit capture of oxidized mercury from flue gases treated by wet flue gas desulfurization (FGD) systems. For these processes to be effective at overall mercury control, the captured mercury must not be re-emitted to the atmosphere or into surface or ground water. The project sought to identify scrubber additives and FGD operating conditions under which mercury re-emissions would decrease and mercury would remain in the liquor and be blown down from the system in the chloride purge stream. After exiting the FGD system, mercury would react with precipitating agents to form stable solid byproducts and would be removed in a dewatering step. The FGD gypsum solids, free of most of the mercury, could then be disposed or processed for reuse as wallboard or in other beneficial reuse. The project comprised extensive bench-scale FGD scrubber tests in Phases I and II. During Phase II, the approaches developed at the bench scale were tested at the pilot scale. Laboratory wastewater treatment tests measured the performance of precipitating agents in removing mercury from the chloride purge stream. Finally, the economic viability of the approaches tested was evaluated.

  7. Coal combustion products: trash or treasure?

    SciTech Connect (OSTI)

    Hansen, T.

    2006-07-15

    Coal combustion by-products can be a valuable resource to various industries. The American Coal Ash Association (ACAA) collects data on production and uses of coal combustion products (CCPs). 122.5 million tons of CCPs were produced in 2004. The article discusses the results of the ACCA's 2004 survey. Fly ash is predominantly used as a substitute for Portland cement; bottom ash for structural fill, embankments and paved road cases. Synthetic gypsum from the FGD process is commonly used in wallboard. Plant owners are only likely to have a buyer for a portion of their CCPs. Although sale of hot water (from Antelope Valley Station) from condensers for use in a fish farm to raise tilapia proved unviable, the Great Plains Synfuels Plant which manufactures natural gas from lignite produces a wide range of products including anhydrous ammonia, phenol, krypton, carbon dioxide (for enhanced oil recovery), tar oils and liquid nitrogen. ACCA's goal is to educate people about CCPs and how to make them into useful products, and market them, in order to reduce waste disposal and enhance revenue. The article lists members of the ACCA. 2 photos., 1 tab.

  8. Diagenetic features of Trenton Limestone in northern Indiana: petrographic evidence for Late (Mesogenetic) Dolostone

    SciTech Connect (OSTI)

    Fara, D.R.

    1986-08-01

    Three conventional cores of the entire Trenton section were examined in detail by in-depth visual description, analysis of more than 250 thin sections, scanning electron microscopy, and x-ray diffraction. The cores are located in the northern half of Indiana where they span the major dolostone pinch-out that is the trap for the prolific Trenton oil and gas field. The Trenton Limestone is completely dolomitized in northern Indiana. Dolostone abundance decreases to the south where the dolostone is restricted to the upper few feet of the formation. Two major types of dolostone are recognized. The top 5-20 ft of the Trenton cores consists of medium crystalline nonporous xenotopic ferroan dolostone. Mesogenetic dewatering of the overlying Maquoketa shale is the proposed dolomitizing mechanisms for this ferroan dolostone cap. Below the ferroan dolostone cap in northern Indiana is coarsely crystalline dolostone, which consists of thin intercalated subfacies of porous idiotopic and nonporous xenotopic dolostone. This is the dominant dolostone type and is the reservoir in the Trenton field. The coarsely crystalline dolostone postdates the ferroan dolostone cap, chert nodule formation, and initial pressure solution. Therefore, this dolostone is considered to have formed relatively late in the diagenetic history of the Trenton under mesogenetic conditions. In the northernmost core, nearly all of the secondary dolomitic porosity is plugged by poikilotopic gypsum and minor amounts of calcite and celestite. Other diagenetic features observed in Trenton are also discussed, including silicification, ferroan calcite cement, upper Trenton contact formation, hardgrounds, and pressure solution.

  9. Ground-water geochemistry and radionuclide activity in the Cambrian-Ordovician aquifer of Dodge and Fond du Lac counties, Wisconsin. Technical report

    SciTech Connect (OSTI)

    Weaver, T.R.; Bahr, J.M.; Anderson, M.P.

    1990-01-01

    Analyses of groundwater from wells in the Cambrian-Ordovician aquifer of eastern Wisconsin indicate that regions of the aquifer contain elevated concentrations of dissolved solids, chloride and sulfate. Groundwater from several wells in the area also approach or exceed the current drinking water standard for combined radium activity. Significant changes in groundwater chemistry occur where the aquifer becomes confined by the Maquoketa shale. Concentrations of Cl(-), SO4(2-) and Na(+) increase in the confined region, and the highest combined radium activities are typically observed in the area. Geochemical modeling implies that the observed changes in major ion groundwater chemistry occur in response to the presence of the confining unit which may act as a source of SO4(2-), through gypsum dissolution, and Na(+), through cation exchange. A finite difference groundwater flow model was linked to a particle tracking routine to determine groundwater flow paths and residence times in the aquifer near the boundary between unconfined and confined conditions. Results suggest that the presence of the confining unit produces a vertically stratified flow regime in the confined region.

  10. Small-Chamber Measurements of Chemical-Specific Emission Factors for Drywall

    SciTech Connect (OSTI)

    Maddalena, Randy; Russell, Marion; Apte, Michael G.

    2010-06-01

    Imported drywall installed in U.S. homes is suspected of being a source of odorous and potentially corrosive indoor pollutants. To support an investigation of those building materials by the Consumer Products Safety Commission (CPSC), Lawrence Berkeley National Laboratory (LBNL) measured chemical-specific emission factors for 30 samples of drywall materials. Emission factors are reported for 75 chemicals and 30 different drywall samples encompassing both domestic and imported stock and incorporating natural, synthetic, or mixed gypsum core material. CPSC supplied all drywall materials. First the drywall samples were isolated and conditioned in dedicated chambers, then they were transferred to small chambers where emission testing was performed. Four sampling and analysis methods were utilized to assess (1) volatile organic compounds, (2) low molecular weight carbonyls, (3) volatile sulfur compounds, and (4) reactive sulfur gases. LBNL developed a new method that combines the use of solid phase microextraction (SPME) with small emission chambers to measure the reactive sulfur gases, then extended that technique to measure the full suite of volatile sulfur compounds. The testing procedure and analysis methods are described in detail herein. Emission factors were measured under a single set of controlled environmental conditions. The results are compared graphically for each method and in detailed tables for use in estimating indoor exposure concentrations.

  11. Effects of weathering on coal and its sulfur constituents in refuse piles

    SciTech Connect (OSTI)

    Khan, L.A.; Berggren, D.J.; Hughes, R.E.

    1984-12-01

    The rejects from coal mining and processing operations are intensively weathered in refuse piles. The effects of weathering on coal and and its associated sulfur-containing compounds are economically and environmentally significant. Chemical and x-ray diffraction analyses of material from abandoned mined lands, collected for a study of historic long-wall mines in Illinois, showed that most pyrite in weathered samples is converted to gypsum, jarosite, and minor alunite. There were only small reductions in the trace element concentrations of these samples. Coal readily takes up oxygen from air. Coal-oxygen complexes produced by oxygen adsorption or peroxide formation are very unstable, and the oxygen can be removed as oxygen gas, CO/sub 2/, or H/sub 2/O upon heating and evacuation. Heating coal under partial vacuum decreases its surface charge. The decrease in surface charge increases with heating time and temperature. This suggests that the adverse effect of exposure to air may be partially reversed, with a corresponding gain in the efficiency of the coal recovery processes.

  12. High-volume, high-value usage of Flue Gas Desulfurization (FGD) by-products in underground mines Phase 1: Laboratory investigations. Quarterly report, July 1994--September 1994

    SciTech Connect (OSTI)

    1994-12-01

    During the quarter a second series of samples were collected and partially characterized chemically and mineralogically. The samples were collected at the disposal site operated by Freeman United Coal Co. The second collection was necessary because of deterioration due to hydration of the original samples. A study of the hydration characteristics was completed during the quarter. Important reactions included the immediate formation of ettringite and portlandite. The hydration and transformation was found to be a slow process. A second phase of gypsum formation from ettringite deterioration was identified. The slow hydration of anhydrite with its resultant swell is a potential problem which will be addressed further. Geotechnical characterization, during the quarter included completion of the preliminary characterization, analysis of the findings, experimentation with sample preparation for the final characterization/mix design, and design of the final experimental program. The analysis of the coals collected during the core drilling and hydrologic planning were completed. Also during the quarter a meeting was held with representatives of the shotcrete industry to discuss transport systems for emplacement. The pros and cons of pneumatic and hydraulic systems were discussed and plans formulated for further investigations.

  13. BUILDING MATERIALS MADE FROM FLUE GAS DESULFURIZATION BY-PRODUCTS

    SciTech Connect (OSTI)

    Michael W. Grutzeck; Maria DiCola; Paul Brenner

    2006-03-30

    Flue gas desulphurization (FGD) materials are produced in abundant quantities by coal burning utilities. Due to environmental restrains, flue gases must be ''cleaned'' prior to release to the atmosphere. They are two general methods to ''scrub'' flue gas: wet and dry. The choice of scrubbing material is often defined by the type of coal being burned, i.e. its composition. Scrubbing is traditionally carried out using a slurry of calcium containing material (slaked lime or calcium carbonate) that is made to contact exiting flue gas as either a spay injected into the gas or in a bubble tower. The calcium combined with the SO{sub 2} in the gas to form insoluble precipitates. Some plants have been using dry injection of these same materials or their own Class C fly ash to scrub. In either case the end product contains primarily hannebachite (CaSO{sub 3} {center_dot} 1/2H{sub 2}O) with smaller amounts of gypsum (CaSO{sub 4} {center_dot} 2H{sub 2}O). These materials have little commercial use. Experiments were carried out that were meant to explore the feasibility of using blends of hannebachite and fly ash mixed with concentrated sodium hydroxide to make masonry products. The results suggest that some of these mixtures could be used in place of conventional Portland cement based products such as retaining wall bricks and pavers.

  14. The fate of mercury in coal utilization byproducts

    SciTech Connect (OSTI)

    William Aljoe; Thomas Feeley; James Murphy; Lynn Brickett [US Department of Energy's National Energy Technology Laboratory (DOE/NETL), Pittsburgh, PA (US)

    2005-05-01

    The US Department of Energy National Energy Technology Laboratory's (DOE/NETL's) research has helped to further scientific understanding of the environmental characteristics of coal-utilization by-products (CUBs) in both disposal and beneficial utilization applications. The following general observations can be drawn from results of the research that has been carried out to date: There appears to be only minimal mercury release to the environment in typical disposal or utilization applications for CUBs generated using activated carbon injection (ACI) control technologies; There appears to be only minimal mercury release to the environment in typical disposal and utilization applications for CUBs generated using wet FGD control technologies. The potential release of mercury from wet FGD gypsum during the manufacture of wallboard is still under evaluation; The amount of mercury leached from CUB samples tested by DOE/NETL is significantly lower than the federal drinking water standards and water quality criteria for the protection of aquatic life; in many cases, leachate concentrations were below the standard test method detection limits. DOE/NETL will continue to partner with industry and other key stakeholders in carrying out research to better understand the fate of mercury and other trace elements in the byproducts from coal combustion. 16 refs., 6 tabs.

  15. Mineralogy of the hardpan formation processes in the interface between sulfide-rich sludge and fly ash: Applications for acid mine drainage mitigation

    SciTech Connect (OSTI)

    Perez-Lopez, R.; Nieto, J.M.; Alvarez-Valero, A.M.; De Almodovar, G.R.

    2007-11-15

    In the present study, experiments in non-saturated leaching columns were conducted to characterize the neoformed phases that precipitate at the interface between two waste residues having different chemical characteristics: an acid mine drainage producer residue (i.e., pyritic sludge) and an acidity neutralizer residue (i.e., coal combustion fly ash). A heating source was placed on top of one of the columns to accelerate oxidation and precipitation of newly formed phases, and thus, to observe longer-scale processes. When both residues are deposited together, the resulting leachates are characterized by alkaline pH, and low sulfate and metal concentrations. Two mechanisms help to improve the quality of the leachates. Over short-time scales, the leaching of pyrite at high pH (as a consequence of fly ash addition) favors the precipitation of ferrihydrite, encapsulating the pyrite grains and attenuating the oxidation process. Over longer time scales, a hardpan is promoted at the interface between both residues due to the precipitation of ferrihydrite, jarosite, and a Ca phase-gypsum or aragonite, depending on carbonate ion activity. Geochemical modeling of leachates using PHREEQC software predicted supersaturation in the observed minerals. The development of a relatively rigid crust at the interface favors the isolation of the mining waste from weathering processes, helped by the cementation of fly ash owing to aragonite precipitation, which ensures total isolation and neutralization of the mine residues.

  16. Milliken Clean Coal Technology Demonstration Project. Environmental monitoring report, July--September 1996

    SciTech Connect (OSTI)

    1998-05-01

    New York State Electric and Gas Corporation (NYSEG) has installed and is presently operating a high-efficiency flue gas desulfurization (FGD) system to demonstrate innovative emissions control technology and comply with the Clean Air Act Amendments of 1990. The host facility for this demonstration project is NYSEG`s Milliken Station, in the Town of Lansing, New York. The primary objective of this project is to demonstrate a retrofit of energy-efficient SO{sub 2} and NO{sub x} control systems with minimal impact on overall plant efficiency. The demonstration project has added a forced oxidation, formic acid-enhanced wet limestone FGD system, which is expected to reduce SO{sub 2} emissions by at least 90 percent. NYSEG also made combustion modifications to each boiler and plans to demonstrate selective non-catalytic reduction (SNCR) technology on unit 1, which will reduce NO{sub x} emissions. Goals of the proposed demonstration include up to 98 percent SO{sub 2} removal efficiency while burning high-sulfur coal, 30 percent NO{sub x} reductions through combustion modifications, additional NO{sub x} reductions using SNCR technology, production of marketable commercial-grade gypsum and calcium chloride by-products to minimize solid waste disposal, and zero wastewater discharge.

  17. Combined experimental and numerical evaluation of a prototype nano-PCM enhanced wallboard

    SciTech Connect (OSTI)

    Biswas, Kaushik; LuPh.D., Jue; Soroushian, Parviz; Shrestha, Som S

    2014-01-01

    In the United States, forty-eight (48) percent of the residential end-use energy consumption is spent on space heating and air conditioning. Reducing envelope-generated heating and cooling loads through application of phase change material (PCM)-enhanced building envelopes can facilitate maximizing the energy efficiency of buildings. Combined experimental testing and numerical modeling of PCM-enhanced envelope components are two important aspects of the evaluation of their energy benefits. An innovative phase change material (nano-PCM) was developed with PCM encapsulated with expanded graphite (interconnected) nanosheets, which is highly conductive for enhanced thermal storage and energy distribution, and is shape-stable for convenient incorporation into lightweight building components. A wall with cellulose cavity insulation and prototype PCM-enhanced interior wallboards was built and tested in a natural exposure test (NET) facility in a hot-humid climate location. The test wall contained PCM wallboards and regular gypsum wallboard, for a side-by-side annual comparison study. Further, numerical modeling of the walls containing the nano-PCM wallboard was performed to determine its actual impact on wall-generated heating and cooling loads. The model was first validated using experimental data, and then used for annual simulations using Typical Meteorological Year (TMY3) weather data. This article presents the measured performance and numerical analysis evaluating the energy-saving potential of the nano-PCM-enhanced wallboard.

  18. Technology Solutions Case Study: Investigating Solutions to Wind Washing Issues in Two-Story Florida Homes: Phase 2, Southeastern United States

    SciTech Connect (OSTI)

    2015-05-01

    In many two-story homes, there are attic spaces above the first-floor of the home that border portions of the second-story conditioned space. These spaces have breaches of the air and thermal boundaries, creating a phenomenon known as wind washing. This can cause attic air above the first-floor space to be driven into the cavity between the first and second floors by wind, thermal buoyancy forces, or mechanical driving forces as well as circulation of hot attic air against the wallboard because of gaps between insulation batts installed on knee walls and the gypsum wallboard. In this project, the U.S. Department of Energy team Building America Partnership for Improved Residential Construction (BA-PIRC) investigated wind washing in 56 homes. The goals were to identify the failure mechanisms that lead to wind washing, characterize the pathways for air and heat to enter the house, and evaluate the seasonal energy savings and peak demand reduction that can result from repairing these wind washing problems. Based on this research, the team developed recommendations for cost-effective retrofit solutions and information that can help avoid these problems in new construction.

  19. Identification of concrete deteriorating minerals by polarizing and scanning electron microscopy

    SciTech Connect (OSTI)

    Gregerova, Miroslava; Vsiansky, Dalibor

    2009-07-15

    The deterioration of concrete represents one of the most serious problems of civil engineering worldwide. Besides other processes, deterioration of concrete consists of sulfate attack and carbonation. Sulfate attack results in the formation of gypsum, ettringite and thaumasite in hardened concrete. Products of sulfate attack may cause a loss of material strength and a risk of collapse of the concrete constructions. The authors focused especially on the microscopical research of sulfate attack. Concrete samples were taken from the Charles Bridge in Prague, Czech Republic. A succession of degrading mineral formation was suggested. Microscope methods represent a new approach to solving the deterioration problems. They enable evaluation of the state of concrete constructions and in cooperation with hydro-geochemistry, mathematics and statistics permit prediction of the durability of a structure. Considering the number of concrete constructions and their age, research of concrete deterioration has an increasing importance. The results obtained can also be useful for future construction, because they identify the risk factors associated with formation of minerals known to degrade structures.

  20. Zero Liquid Discharge (ZLD) System for Flue-Gas Derived Water From Oxy-Combustion Process

    SciTech Connect (OSTI)

    Sivaram Harendra; Danylo Oryshchyn; Thomas Ochs; Stephen J. Gerdemann; John Clark

    2011-10-16

    Researchers at the National Energy Technology Laboratory (NETL) located in Albany, Oregon, have patented a process - Integrated Pollutant Removal (IPR) that uses off-the-shelf technology to produce a sequestration ready CO{sub 2} stream from an oxy-combustion power plant. Capturing CO{sub 2} from fossil-fuel combustion generates a significant water product which can be tapped for use in the power plant and its peripherals. Water condensed in the IPR{reg_sign} process may contain fly ash particles, sodium (from pH control), and sulfur species, as well as heavy metals, cations and anions. NETL is developing a treatment approach for zero liquid discharge while maximizing available heat from IPR. Current treatment-process steps being studied are flocculation/coagulation, for removal of cations and fine particles, and reverse osmosis, for anion removal as well as for scavenging the remaining cations. After reverse osmosis process steps, thermal evaporation and crystallization steps will be carried out in order to build the whole zero liquid discharge (ZLD) system for flue-gas condensed wastewater. Gypsum is the major product from crystallization process. Fast, in-line treatment of water for re-use in IPR seems to be one practical step for minimizing water treatment requirements for CO{sub 2} capture. The results obtained from above experiments are being used to build water treatment models.

  1. Oral Mucositis Prevention By Low-Level Laser Therapy in Head-and-Neck Cancer Patients Undergoing Concurrent Chemoradiotherapy: A Phase III Randomized Study

    SciTech Connect (OSTI)

    Gouvea de Lima, Aline; Villar, Rosangela Correa; Castro, Gilberto de; Antequera, Reynaldo; Gil, Erlon; Rosalmeida, Mauro Cabral; Federico, Miriam Hatsue Honda; Snitcovsky, Igor Moises Longo

    2012-01-01

    Purpose: Oral mucositis is a major complication of concurrent chemoradiotherapy (CRT) in head-and-neck cancer patients. Low-level laser (LLL) therapy is a promising preventive therapy. We aimed to evaluate the efficacy of LLL therapy to decrease severe oral mucositis and its effect on RT interruptions. Methods and Materials: In the present randomized, double-blind, Phase III study, patients received either gallium-aluminum-arsenide LLL therapy 2.5 J/cm{sup 2} or placebo laser, before each radiation fraction. Eligible patients had to have been diagnosed with squamous cell carcinoma or undifferentiated carcinoma of the oral cavity, pharynx, larynx, or metastases to the neck with an unknown primary site. They were treated with adjuvant or definitive CRT, consisting of conventional RT 60-70 Gy (range, 1.8-2.0 Gy/d, 5 times/wk) and concurrent cisplatin. The primary endpoints were the oral mucositis severity in Weeks 2, 4, and 6 and the number of RT interruptions because of mucositis. The secondary endpoints included patient-reported pain scores. To detect a decrease in the incidence of Grade 3 or 4 oral mucositis from 80% to 50%, we planned to enroll 74 patients. Results: A total of 75 patients were included, and 37 patients received preventive LLL therapy. The mean delivered radiation dose was greater in the patients treated with LLL (69.4 vs. 67.9 Gy, p = .03). During CRT, the number of patients diagnosed with Grade 3 or 4 oral mucositis treated with LLL vs. placebo was 4 vs. 5 (Week 2, p = 1.0), 4 vs. 12 (Week 4, p = .08), and 8 vs. 9 (Week 6, p = 1.0), respectively. More of the patients treated with placebo had RT interruptions because of mucositis (6 vs. 0, p = .02). No difference was detected between the treatment arms in the incidence of severe pain. Conclusions: LLL therapy was not effective in reducing severe oral mucositis, although a marginal benefit could not be excluded. It reduced RT interruptions in these head-and-neck cancer patients, which might translate into improved CRT efficacy.

  2. Electrical Breakdown Physics in Photoconductive Semiconductor Switches (PCSS).

    SciTech Connect (OSTI)

    Mar, Alan; Zutavern, Fred J.; Vawter, Gregory A.; Hjalmarson, Harold P.; Gallegos, Richard Joseph; Bigman, Verle Howard

    2016-01-01

    Advanced switching devices with long lifetime will be critical components for Linear Transformer Drivers (LTDs) in next-generation accelerators. LTD designs employ high switch counts. With current gas switch technology at %7E10e3 shot life, a potential game-changer would be the development of a reliable low-impedance (%3C35nh) optically-triggered compact solid-state switch capable of switching 200kV and 50kA with 10e5 shotlife or better. Other applications of this technology, are pulse shaping programmable systems for dynamic material studies (Z-next, Genesis), efficient pulsed power systems for biofuel feedstock, short pulse (10 ns) accelerator designs for the Defense Threat Reduction Agency (DTRA), and sprytron replacements in NW firing sets. This LDRD project has succeeded in developing new optically-triggered photoconductive semiconductor switch (PCSS) designs that show great promise for scaling to modules capable of 200kV (DC) and 5kA current that can be stacked in parallel to achieve 100's of kA with 10e5 shot lifetime. . Executive Summary Advanced switching devices with long lifetime will be critical components for Linear Transformer Drivers (LTDs) in next-generation accelerators. LTD designs employ high switch counts. With current gas switch technology at %7E10e3 shot life, a potential game-changer would be the development of a reliable low-impedance (%3C35nh) optically-triggered compact solid-state switch capable of switching 200kV and 50kA with 10e5 shotlife or better. Other applications of this technology, are pulse shaping programmable systems for dynamic material studies (Z-next, Genesis), efficient pulsed power systems for biofuel feedstock, short pulse (10 ns) accelerator designs for the Defense Threat Reduction Agency (DTRA), and sprytron replacements in NW firing sets. This LDRD project has succeeded in developing new optically-triggered photoconductive semiconductor switch (PCSS) designs that show great promise for scaling to modules capable of 200kV (DC) and 5kA current that can be stacked in parallel to achieve 100's of kA with 10e5 shot lifetime. The new vertical switch design configuration generates parallel filaments in the bulk GaAs (as opposed to just beneath the surface as in previous designs) to achieve breakdown fields close to the maximum for the bulk GaAs while operating in air, and with 2-D scalability of the number of current-sharing filaments. This design also may be highly compatible with 2-D VCSEL arrays for optical triggering. The demonstration of this design in this LDRD utilized standard thickness wafers to trigger 0.4kA at 35kV/cm (limited by 0.6mm wafer thickness), tested to 1e5 shots with no detectable degradation of switch performance. Higher fields, total current, and switching voltages would be achievable with thicker GaAs wafers. Another important application pursued in this LDRD is the use of PCSS for trigger generator applications. Conventional in-plane PCSS have achieved triggering of a 100kV sparkgap (Kinetech-type) switch of the type similar to switches being considered for accelerator upgrades. The trigger is also being developed for pulsed power for HPM applications that require miniaturization and robust performance in noisy compact environments. This has spawned new programs for developing this technology, including an STTR for VCSEL trigger laser integration, also pursuing other follow-on applications.

  3. Combustion Byproducts Recycling Consortium

    SciTech Connect (OSTI)

    Paul Ziemkiewicz; Tamara Vandivort; Debra Pflughoeft-Hassett; Y. Paul Chugh; James Hower

    2008-08-31

    The Combustion Byproducts Recycling Consortium (CBRC) program was developed as a focused program to remove and/or minimize the barriers for effective management of over 123 million tons of coal combustion byproducts (CCBs) annually generated in the USA. At the time of launching the CBRC in 1998, about 25% of CCBs were beneficially utilized while the remaining was disposed in on-site or off-site landfills. During the ten (10) year tenure of CBRC (1998-2008), after a critical review, 52 projects were funded nationwide. By region, the East, Midwest, and West had 21, 18, and 13 projects funded, respectively. Almost all projects were cooperative projects involving industry, government, and academia. The CBRC projects, to a large extent, successfully addressed the problems of large-scale utilization of CCBs. A few projects, such as the two Eastern Region projects that addressed the use of fly ash in foundry applications, might be thought of as a somewhat smaller application in comparison to construction and agricultural uses, but as a novel niche use, they set the stage to draw interest that fly ash substitution for Portland cement might not attract. With consideration of the large increase in flue gas desulfurization (FGD) gypsum in response to EPA regulations, agricultural uses of FGD gypsum hold promise for large-scale uses of a product currently directed to the (currently stagnant) home construction market. Outstanding achievements of the program are: (1) The CBRC successfully enhanced professional expertise in the area of CCBs throughout the nation. The enhanced capacity continues to provide technology and information transfer expertise to industry and regulatory agencies. (2) Several technologies were developed that can be used immediately. These include: (a) Use of CCBs for road base and sub-base applications; (b) full-depth, in situ stabilization of gravel roads or highway/pavement construction recycled materials; and (c) fired bricks containing up to 30%-40% F-fly ash. Some developed technologies have similar potential in the longer term. (3) Laboratory studies have been completed that indicate that much higher amounts of fly ash could be added in cement-concrete applications under some circumstances. This could significantly increase use of fly ash in cement-concrete applications. (4) A study of the long-term environmental effects of structural fills in a surface mine in Indiana was completed. This study has provided much sought after data for permitting large-volume management options in both beneficial as well as non-beneficial use settings. (5) The impact of CBRC on CCBs utilization trends is difficult to quantify. However it is fair to say that the CBRC program had a significant positive impact on increased utilization of CCBs in every region of the USA. Today, the overall utilization of CCBs is over 43%. (6) CBRC-developed knowledge base led to a large number of other projects completed with support from other sources of funding. (7) CBRC research has also had a large impact on CCBs management across the globe. Information transfer activities and visitors from leading coal producing countries such as South Africa, Australia, England, India, China, Poland, Czech Republic and Japan are truly noteworthy. (8) Overall, the CBRC has been a truly successful, cooperative research program. It has brought together researchers, industry, government, and regulators to deal with a major problem facing the USA and other coal producing countries in the world.

  4. Modeling of coupled heat transfer and reactive transport processesin porous media: Application to seepage studies at Yucca Mountain, Nevada

    SciTech Connect (OSTI)

    Mukhopadhyay, Sumit; Sonnenthal, Eric L.; Spycher, Nicolas

    2007-01-15

    When hot radioactive waste is placed in subsurface tunnels, a series of complex changes occurs in the surrounding medium. The water in the pore space of the medium undergoes vaporization and boiling. Subsequently, vapor migrates out of the matrix pore space, moving away from the tunnel through the permeable fracture network. This migration is propelled by buoyancy, by the increased vapor pressure caused by heating and boiling, and through local convection. In cooler regions, the vapor condenses on fracture walls, where it drains through the fracture network. Slow imbibition of water thereafter leads to gradual rewetting of the rock matrix. These thermal and hydrological processes also bring about chemical changes in the medium. Amorphous silica precipitates from boiling and evaporation, and calcite from heating and CO2 volatilization. The precipitation of amorphous silica, and to a much lesser extent calcite, results in long-term permeability reduction. Evaporative concentration also results in the precipitation of gypsum (or anhydrite), halite, fluorite and other salts. These evaporative minerals eventually redissolve after the boiling period is over, however, their precipitation results in a significant temporary decrease in permeability. Reduction of permeability is also associated with changes in fracture capillary characteristics. In short, the coupled thermal-hydrological-chemical (THC) processes dynamically alter the hydrological properties of the rock. A model based on the TOUGHREACT reactive transport software is presented here to investigate the impact of THC processes on flow near an emplacement tunnel at Yucca Mountain, Nevada. We show how transient changes in hydrological properties caused by THC processes often lead to local flow channeling and saturation increases above the tunnel. For models that include only permeability changes to fractures, such local flow channeling may lead to seepage relative to models where THC effects are ignored. However, coupled THC seepage models that include both permeability and capillary changes to fractures may not show this additional seepage.

  5. Management of by-products from fossil-fired power plants

    SciTech Connect (OSTI)

    Kofod, J.

    1998-07-01

    The world production of by-products from power plants is in excess of 500 Mt/year. Most of it consists of coal fly ash and bottom ash, but an increasing share is made up of by-products from flue gas desulfurization processes. In some countries less than 10% of the by-products are utilized, whereas the utilization ratio is as high as 90% in others. In the EU about half of the by-products is utilized, but according to the EU's policy the degree of utilization should be increased. Coal fly ash can be used in concrete pursuant to the provisions of the European standard EN 450, Fly Ash for Concrete. In addition quality fly ash can be used in the production of cement and gas concrete and in the building industry. Road construction and soil amendment can also make use of this material. Gypsum produced as a result of the flue gas desulfurization process can be used as wall boards, in the building industry and in the production of cement. Also other by-products from the flue gas desulfurization processes can be used for industrial purposes. By-products where utilization is no option will be disposed of. According to the EU's environmental legislation most of the by-products from the power plants are categorized as non-hazardous waste. This papers discusses how to design a landfill deposit for power plant residues in accordance with applicable EU-directives. However, as can be seen from the conclusion it will become increasingly difficult in the future to deposit these residues. This will urge power producers to cooperate with relevant industries to ensure utilization of a larger part of the by-products and to create solutions that will be profitable to both parties.

  6. Evapotranspiration And Geochemical Controls On Groundwater Plumes At Arid Sites: Toward Innovative Alternate End-States For Uranium Processing And Tailings Facilities

    SciTech Connect (OSTI)

    Looney, Brian B.; Denham, Miles E.; Eddy-Dilek, Carol A.; Millings, Margaret R.; Kautsky, Mark

    2014-01-08

    Management of legacy tailings/waste and groundwater contamination are ongoing at the former uranium milling site in Tuba City AZ. The tailings have been consolidated and effectively isolated using an engineered cover system. For the existing groundwater plume, a system of recovery wells extracts contaminated groundwater for treatment using an advanced distillation process. The ten years of pump and treat (P&T) operations have had minimal impact on the contaminant plume primarily due to geochemical and hydrological limits. A flow net analysis demonstrates that groundwater contamination beneath the former processing site flows in the uppermost portion of the aquifer and exits the groundwater as the plume transits into and beneath a lower terrace in the landscape. The evaluation indicates that contaminated water will not reach Moenkopi Wash, a locally important stream. Instead, shallow groundwater in arid settings such as Tuba City is transferred into the vadose zone and atmosphere via evaporation, transpiration and diffuse seepage. The dissolved constituents are projected to precipitate and accumulate as minerals such as calcite and gypsum in the deep vadose zone (near the capillary fringe), around the roots of phreatophyte plants, and near seeps. The natural hydrologic and geochemical controls common in arid environments such as Tuba City work together to limit the size of the groundwater plume, to naturally attenuate and detoxify groundwater contaminants, and to reduce risks to humans, livestock and the environment. The technical evaluation supports an alternative beneficial reuse (brownfield) scenario for Tuba City. This alternative approach would have low risks, similar to the current P&T scenario, but would eliminate the energy and expense associated with the active treatment and convert the former uranium processing site into a resource for future employment of local citizens and ongoing benefit to the Native American Nations.

  7. Permitting and solid waste management issues for the Bailly Station wet limestone Advanced Flue Gas Desulfurization (AFGD) system

    SciTech Connect (OSTI)

    Bolinsky, F.T. (Pure Air, Allentown, PA (United States)); Ross, J. (Northern Indiana Public Service Co., Hammond, IN (United States)); Dennis, D.S. (United Engineers and Constructors, Inc., Denver, CO (United States). Stearns-Roger Div.); Huston, J.S. (Environmental Alternatives, Inc., Warren NJ (USA))

    1991-01-01

    Pure Air (a general partnership between Air Products and Chemicals, Inc., and Mitsubishi Heavy Industries America, Inc.). is constructing a wet limestone co-current advanced flue gas desulfurization (AFGD) system that has technological and commercial advantages over conventional FGD systems in the United States. The AFGD system is being installed at the Northern Indiana Public Service Company's Bailly Generating Station near Gary, Indiana. The AFGD system is scheduled to be operational by the Summer, 1992. The AFGD system will remove at least 90 percent of the sulfur dioxide (SO{sub 2}) in the flue gas from Boilers 7 and 8 at the Station while burning 3.2 percent sulfur coal. Also as part of testing the AFGD system, 95 percent removal of SO{sub 2} will be demonstrated on coals containing up to 4.5 percent sulfur. At the same time that SO{sub 2} is removed from the flue gas, a gypsum by-product will be produced which will be used for wallboard manufacturing. Since the AFGD system is a pollution control device, one would expect its installation to be received favorably by the public and regulatory agencies. Although the project was well received by regulatory agencies, on public group (Save the Dunes Council) was initially concerned since the project is located adjacent to the Indiana Dunes National Lakeshore. The purpose of this paper is to describe the project team's experiences in obtaining permits/approvals from regulatory agencies and in dealing with the public. 1 ref., 1 fig., 2 tabs.

  8. Waste systems progress report, March 1983 through February 1984

    SciTech Connect (OSTI)

    Hickle, G.L.

    1984-10-01

    Preliminary design engineering for a Beryllum Electrorefining Demonstration Process has been completed and final engineering for fabrication of the process will be completed by the fourth quarter of FY-84. A remotely operated Advanced Size Reduction Facility (ASRF) is under construction and, when completed, will be used for sectioning plutonium-contaminated gloveboxes for disposal. Modification and additions were made to the 82 kg/hr Fluidized Bed Incinerator (FBI) in preparation for turning the unit over to Production. Several types of cementation processes are being developed to treat various TRU and low-level waste streams to reduce the dispersibility of the wastes. Portland cement and Envirostone gypsum cement were investigated as immobilization media for wet precipitation sludges and organic liquid wastes. Transuranic contaminated waste is being retrieved from storage at the Idaho National Engineering Laboratory for examination at Rocky Flats Plant for compliance with the Waste Isolation Pilot Plant-Waste Acceptance Criteria. The removal of unreacted calcium metal from the waste salt formed during the direct oxide reduction of plutonium oxide to plutonium metal is necessary in order to comply with regulations regarding the transportation and storage of waste material containing flammable substances. Chemical methods of denitrification of simulated low-level nitrate wastes were investigated on a laboratory scale. Methods of inserting the carbon composite filters into presently stored and currently generated radioactive waste drums have been investigated and their sealing efficiencies determined. Analyses of carbon tetrachloride (CCl/sub 4/) recovered from spent lathe coolant revealed contamination levels above usable limits. A handbook covering techniques and processes that have been successfully demonstrated to minimize generation of new transuranic waste is being prepared.

  9. Investigation of techniques to improve continuous air monitors under conditions of high dust loading in environmental setting. 1998 annual progress report

    SciTech Connect (OSTI)

    Schery, S.D.; Wasiolek, P.T. [New Mexico Inst. of Mining and Technology, Socorro, NM (US); Rodgers, J. [Los Alamos National Lab., NM (US)

    1998-06-01

    'Improvement in understanding of the deposition of ambient dust particles on ECAM (Environmental Continuous Air Monitor) filters, reduction of the alpha-particle interference of radon progeny and other radioactive aerosols in different particle size ranges on filters, and development of ECAM''s with increased sensitivity under dusty outdoor conditions. As of May 1, 1998 (1/2 year into the project) the research-prototype 30-cm pulsed ionization chamber (PIC) is assembled and operational with an alpha particle energy resolution of better than 45 keV for 5-MeV alpha particles. Measurements of spectral resolution for alpha particles from radon decay products have been made as a function of filter type and dust loading conditions. So far, a study of ten filter types has found that the best combination of resolution and throughput is obtained with 3.0 \\265m Millipore fluoropore and 1.0 \\265m Corning FNMB filters. Experiments with gypsum and Portland cement dust in the size range 1 to 20 \\265m indicate significant degradation in alpha particle resolution for dust loading above about 0.5 mg cm{sup -2}. Study of metalized films for possible use as a PIC window indicate a minimum broadening of 5-MeV alpha particle peaks from 43 (no film) to 301 keV (with film) for AVR film type B8 (0.20 mg cm{sup -2} polycarbonate). A modified ECAM sampling head, equipped with an optical microscopy system feeding data to a high resolution video data capture and logging instrument, was constructed. This system will enable time-lapse study of dust build-up on ECAM filters and formation of dendrite structures that can reduce alpha-particle resolution.'

  10. Waste systems. Progress report, January 1982-February 1983

    SciTech Connect (OSTI)

    Hickle, G.L.

    1983-10-24

    A laboratory-scale beryllium electrorefining cell has been placed in operation and metallic beryllium with a purity greater than 99.95% has been produced. Methods of uranium chip disposal have been evaluated by performing bench- and pilot-scale testing and by surveying present chip disposal methods. A design criteria has been completed for a new production uranium chip disposal facility. Two types of cementation immobilization processes are being developed to treat several Rocky Flats wastes which do not currently meet repository acceptance criteria. The nitrate salts, as now shipped, are an extremely fine powder, composed chiefly of sodium and potassium nitrate. Nitrates are an oxidizer, and their behavior in a possible fire would be of concern. Accident caused fires involving a cargo of boxed nitrate salts were modeled and the burning characteristics noted. In addition, gypsum cement was tested as an immobilization matrix to reduce dispersibility. A program is in process to construct a facility to remotely size reduce gloveboxes and miscellaneous equipment contaminated with plutonium and other radioactive nuclides. The Title II engineering package is completed and the construction of the facility has been initiated. Modification and additions to the 82 kg/h Fluidized Bed Incinerator were made in preparation for turning the unit over to Production. A program was initiated to identify, characterize, and evaluate for recycle all the spent oil and solvent streams which are immobilized and disposed as Transuranic (TRU) waste. Three technologies were evaluted for denitrification method was studied at Rocky Flats while a thermal decomposition process and a molten salt chemical conversion technique were investigated on a subcontract basis with Thagard Research Corporation and Rockwell International, Energy Systems Group, respectively.

  11. Simulation of integrated pollutant removal (IPR) water-treatment system using ASPEN Plus

    SciTech Connect (OSTI)

    Harendra, Sivaram; Oryshcyhn, Danylo [U.S. DOE Ochs, Thomas [U.S. DOE Gerdemann, Stephen; Clark, John

    2013-01-01

    Capturing CO2 from fossil fuel combustion provides an opportunity for tapping a significant water source which can be used as service water for a capture-ready power plant and its peripherals. Researchers at the National Energy Technology Laboratory (NETL) have patented a processIntegrated Pollutant Removal (IPR)that uses off-the-shelf technology to produce a sequestration ready CO2 stream from an oxy-combustion power plant. Water condensed from oxy-combustion flue gas via the IPR system has been analyzed for composition and an approach for its treatmentfor in-process reuse and for releasehas been outlined. A computer simulation model in ASPEN Plus has been developed to simulate water treatment of flue gas derived wastewater from IPR systems. At the field installation, water condensed in the IPR process contains fly ash particles, sodium (largely from spray-tower buffering) and sulfur species as well as heavy metals, cations, and anions. An IPR wastewater treatment system was modeled using unit operations such as equalization, coagulation and flocculation, reverse osmosis, lime softening, crystallization, and pH correction. According to the model results, 70% (by mass) of the inlet stream can be treated as pure water, the other 20% yields as saleable products such as gypsum (CaSO4) and salt (NaCl) and the remaining portion is the waste. More than 99% of fly ash particles are removed in the coagulation and flocculation unit and these solids can be used as filler materials in various applications with further treatment. Results discussed relate to a slipstream IPR installation and are verified experimentally in the coagulation/flocculation step.

  12. Partitioning of mercury, arsenic, selenium, boron, and chloride in a full-scale coal combustion process equipped with selective catalytic reduction, electrostatic precipitation, and flue gas desulfurization systems

    SciTech Connect (OSTI)

    Chin-Min Cheng; Pauline Hack; Paul Chu; Yung-Nan Chang; Ting-Yu Lin; Chih-Sheng Ko; Po-Han Chiang; Cheng-Chun He; Yuan-Min Lai; Wei-Ping Pan

    2009-09-15

    A full-scale field study was carried out at a 795 MWe coal-fired power plant equipped with selective catalytic reduction (SCR), an electrostatic precipitator (ESP), and wet flue gas desulfurization (FGD) systems to investigate the distribution of selected trace elements (i.e., mercury, arsenic, selenium, boron, and chloride) from coal, FGD reagent slurry, makeup water to flue gas, solid byproduct, and wastewater streams. Flue gases were collected from the SCR outlet, ESP inlet, FGD inlet, and stack. Concurrent with flue gas sampling, coal, bottom ash, economizer ash, and samples from the FGD process were also collected for elemental analysis. By combining plant operation parameters, the overall material balances of selected elements were established. The removal efficiencies of As, Se, Hg, and B by the ESP unit were 88, 56, 17, and 8%, respectively. Only about 2.5% of Cl was condensed and removed from flue gas by fly ash. The FGD process removed over 90% of Cl, 77% of B, 76% of Hg, 30% of Se, and 5% of As. About 90% and 99% of the FGD-removed Hg and Se were associated with gypsum. For B and Cl, over 99% were discharged from the coal combustion process with the wastewater. Mineral trona (trisodium hydrogendicarbonate dehydrate, Na{sub 3}H(CO{sub 3}){sub 2}.2H{sub 2}O) was injected before the ESP unit to control the emission of sulfur trioxide (SO{sub 3}). By comparing the trace elements compositions in the fly ash samples collected from the locations before and after the trona injection, the injection of trona did not show an observable effect on the partitioning behaviors of selenium and arsenic, but it significantly increased the adsorption of mercury onto fly ash. The stack emissions of mercury, boron, selenium, and chloride were for the most part in the gas phase. 47 refs., 3 figs., 11 tabs.

  13. Measurement of in-situ strength using projectile penetration: Tests of a new launching system

    SciTech Connect (OSTI)

    Hearst, J.R.; Newmark, R.L.; Charest, J.A.; Lynch, C.S.

    1987-10-01

    The Lawrence Livermore National Laboratory has a continuing need to measure rock strength in situ, both for simple prediction of cavity size, and as input to computational models. In a previous report we compared two methods for measuring formation strength in situ: projectile penetration and a cone penetrometer. We determined that the projectile method was more promising for application to our large-diameter (2-4-m) hole environment. A major practical problem has been the development of a launcher and an apparatus for measuring depth of penetration that would be suitable for use in large-diameter holes. We are developing a gas-gun launcher system that will be capable of measuring both depth of penetration and deceleration of a reusable projectile. The current version of the launcher is trailer-mounted for testing at our Nevada Test Site (NTS) in tunnels and outcrops, but its design is such that it can be readily adapted for emplacement hole use. We test the current launcher on 60-cm cubes of gypsum cement, mixed to provie a range of densities (1.64 to 2.0 g/cc) and strengths (3 to 17 MPa). We compared depth of penetration of a 84-g projectile from a ''Betsy'' seismic gun - traveling on the order of 500 m/s - with the depth of penetration of a 13-kg projectile from the gas gun - traveling on the order of 30 m/s. For projectiles with the same nose size and shape, impacting targets of approximately constant strength, penetration depth was proportional to projectile kinetic energy. The ratio of kinetic energy to penetration depth was approximately proportional to target strength. Tests in tuffs with a wide range of strengths at NTS gave a similar linear relationship between the ratio of kinetic energy to penetration and target strength, and also a linear relationship between deceleration and strength. It appears that penetration can indeed be used as a semiquantitative measure of strength.

  14. DUSEL Facility Cooling Water Scaling Issues

    SciTech Connect (OSTI)

    Daily, W D

    2011-04-05

    Precipitation (crystal growth) in supersaturated solutions is governed by both kenetic and thermodynamic processes. This is an important and evolving field of research, especially for the petroleum industry. There are several types of precipitates including sulfate compounds (ie. barium sulfate) and calcium compounds (ie. calcium carbonate). The chemical makeup of the mine water has relatively large concentrations of sulfate as compared to calcium, so we may expect that sulfate type reactions. The kinetics of calcium sulfate dihydrate (CaSO4 {center_dot} 2H20, gypsum) scale formation on heat exchanger surfaces from aqueous solutions has been studied by a highly reproducible technique. It has been found that gypsum scale formation takes place directly on the surface of the heat exchanger without any bulk or spontaneous precipitation in the reaction cell. The kinetic data also indicate that the rate of scale formation is a function of surface area and the metallurgy of the heat exchanger. As we don't have detailed information about the heat exchanger, we can only infer that this will be an issue for us. Supersaturations of various compounds are affected differently by temperature, pressure and pH. Pressure has only a slight affect on the solubility, whereas temperature is a much more sensitive parameter (Figure 1). The affect of temperature is reversed for calcium carbonate and barium sulfate solubilities. As temperature increases, barium sulfate solubility concentrations increase and scaling decreases. For calcium carbonate, the scaling tendencies increase with increasing temperature. This is all relative, as the temperatures and pressures of the referenced experiments range from 122 to 356 F. Their pressures range from 200 to 4000 psi. Because the cooling water system isn't likely to see pressures above 200 psi, it's unclear if this pressure/scaling relationship will be significant or even apparent. The most common scale minerals found in the oilfield include calcium carbonates (CaCO3, mainly calcite) and alkaline-earth metal sulfates (barite BaSO4, celestite SrSO4, anhydrite CaSO4, hemihydrate CaSO4 1/2H2O, and gypsum CaSO4 2H2O or calcium sulfate). The cause of scaling can be difficult to identify in real oil and gas wells. However, pressure and temperature changes during the flow of fluids are primary reasons for the formation of carbonate scales, because the escape of CO2 and/or H2S gases out of the brine solution, as pressure is lowered, tends to elevate the pH of the brine and result in super-saturation with respect to carbonates. Concerning sulfate scales, the common cause is commingling of different sources of brines either due to breakthrough of injected incompatible waters or mixing of two different brines from different zones of the reservoir formation. A decrease in temperature tends to cause barite to precipitate, opposite of calcite. In addition, pressure drops tend to cause all scale minerals to precipitate due to the pressure dependence of the solubility product. And we can expect that there will be a pressure drop across the heat exchanger. Weather or not this will be offset by the rise in pressure remains to be seen. It's typically left to field testing to prove out. Progress has been made toward the control and treatment of the scale deposits, although most of the reaction mechanisms are still not well understood. Often the most efficient and economic treatment for scale formation is to apply threshold chemical inhibitors. Threshold scale inhibitors are like catalysts and have inhibition efficiency at very low concentrations (commonly less than a few mg/L), far below the stoichiometric concentrations of the crystal lattice ions in solution. There are many chemical classes of inhibitors and even more brands on the market. Based on the water chemistry it is anticipated that there is a high likelihood for sulfate compound precipitation and scaling. This may be dependent on the temperature and pressure, which vary throughout the system. Therefore, various types and amounts of scaling may occur at different

  15. Photovoltaic self-assembly.

    SciTech Connect (OSTI)

    Lavin, Judith; Kemp, Richard Alan; Stewart, Constantine A.

    2010-10-01

    This late-start LDRD was focused on the application of chemical principles of self-assembly on the ordering and placement of photovoltaic cells in a module. The drive for this chemical-based self-assembly stems from the escalating prices in the 'pick-and-place' technology currently used in the MEMS industries as the size of chips decreases. The chemical self-assembly principles are well-known on a molecular scale in other material science systems but to date had not been applied to the assembly of cells in a photovoltaic array or module. We explored several types of chemical-based self-assembly techniques, including gold-thiol interactions, liquid polymer binding, and hydrophobic-hydrophilic interactions designed to array both Si and GaAs PV chips onto a substrate. Additional research was focused on the modification of PV cells in an effort to gain control over the facial directionality of the cells in a solvent-based environment. Despite being a small footprint research project worked on for only a short time, the technical results and scientific accomplishments were significant and could prove to be enabling technology in the disruptive advancement of the microelectronic photovoltaics industry.

  16. Properties of Wide-Gap Chalcopyrite Semiconductors for Photovoltaic Applications: Final Report, 8 July 1998 -- 17 October 2001

    SciTech Connect (OSTI)

    Rockett, A.

    2003-07-01

    The objectives of this project were to obtain a fundamental understanding of wide-gap chalcopyrite semiconductors and photovoltaic devices. Information to be gathered included significant new fundamental materials data necessary for accurate modeling of single- and tandem-junction devices, basic materials science of wider-gap chalcopyrite semiconductors to be used in next-generation devices, and practical information on the operation of devices incorporating these materials. Deposition used a hybrid sputtering and evaporation method shown previously to produce high-quality epitaxial layers of Cu(In,Ga)Se2 (CIGS). Materials analysis was also provided to assist members of the National CIS Team, of which, through this contract, we were a member. Solar cells produced from resulting single-crystal epitaxial layers in collaboration with various members of the CIS Team were used to determine the factors limiting performance of the devices based on analysis of the results. Because epitaxial growth allows us to determine the surface orientation of our films specifically by choice of the substrate surface on which the film is grown, a major focus of the project concerned the nature of (110)-oriented CIGS films and the performance of solar cells produced from these films. We begin this summary with a description of the results for growth on (110) GaAs, which formed a basis for much of the work ultimately conducted under the program.

  17. In-situ surface composition measurements of CuGaSe{sub 2} thin films

    SciTech Connect (OSTI)

    Fons, P.; Yamada, A.; Niki, S.; Oyanagi, H.

    1998-12-31

    Two CuGaSe{sub 2} films were grown by molecular beam epitaxy onto GaAs (001) substrates with varying Cu/Ga flux ratios under Se overpressure conditions. Growth was interrupted at predetermined times and the surface composition was measured using Auger electron spectroscopy after which growth was continued. After growth, the film composition was analyzed using voltage dependent electron microprobe spectroscopy. Film structure and morphology were also analyzed using x-ray diffraction and atomic force microscopy. The film with a Cu/Ga ratio larger than unity showed evidence of surface segregation of a second Cu-rich phase with a Cu/Se composition ratio slightly greater than unity. A second CuGaSe{sub 2} film with a Cu/Ga ratio of less than unity showed no change in surface composition with time and was also consistent with bulk composition measurements. Diffraction measurements indicated a high concentration of twins as well as the presence of domains with mixed c and a axes in the Ga-rich film. The Cu-rich films by contrast were single domain and had a narrower mosaics. High sensitivity scans along the [001] reciprocal axis did not exhibit any new peaks not attributable to either the substrate or the CuGaSe{sub 2} thin film.

  18. Light sources based on semiconductor current filaments

    DOE Patents [OSTI]

    Zutavern, Fred J.; Loubriel, Guillermo M.; Buttram, Malcolm T.; Mar, Alan; Helgeson, Wesley D.; O'Malley, Martin W.; Hjalmarson, Harold P.; Baca, Albert G.; Chow, Weng W.; Vawter, G. Allen

    2003-01-01

    The present invention provides a new type of semiconductor light source that can produce a high peak power output and is not injection, e-beam, or optically pumped. The present invention is capable of producing high quality coherent or incoherent optical emission. The present invention is based on current filaments, unlike conventional semiconductor lasers that are based on p-n junctions. The present invention provides a light source formed by an electron-hole plasma inside a current filament. The electron-hole plasma can be several hundred microns in diameter and several centimeters long. A current filament can be initiated optically or with an e-beam, but can be pumped electrically across a large insulating region. A current filament can be produced in high gain photoconductive semiconductor switches. The light source provided by the present invention has a potentially large volume and therefore a potentially large energy per pulse or peak power available from a single (coherent) semiconductor laser. Like other semiconductor lasers, these light sources will emit radiation at the wavelength near the bandgap energy (for GaAs 875 nm or near infra red). Immediate potential applications of the present invention include high energy, short pulse, compact, low cost lasers and other incoherent light sources.

  19. Development of a high average current polarized electron source with long cathode operational lifetime

    SciTech Connect (OSTI)

    C. K. Sinclair; P. A. Adderley; B. M. Dunham; J. C. Hansknecht; P. Hartmann; M. Poelker; J. S. Price; P. M. Rutt; W. J. Schneider; M. Steigerwald

    2007-02-01

    Substantially more than half of the electromagnetic nuclear physics experiments conducted at the Continuous Electron Beam Accelerator Facility of the Thomas Jefferson National Accelerator Facility (Jefferson Laboratory) require highly polarized electron beams, often at high average current. Spin-polarized electrons are produced by photoemission from various GaAs-based semiconductor photocathodes, using circularly polarized laser light with photon energy slightly larger than the semiconductor band gap. The photocathodes are prepared by activation of the clean semiconductor surface to negative electron affinity using cesium and oxidation. Historically, in many laboratories worldwide, these photocathodes have had short operational lifetimes at high average current, and have often deteriorated fairly quickly in ultrahigh vacuum even without electron beam delivery. At Jefferson Lab, we have developed a polarized electron source in which the photocathodes degrade exceptionally slowly without electron emission, and in which ion back bombardment is the predominant mechanism limiting the operational lifetime of the cathodes during electron emission. We have reproducibly obtained cathode 1/e dark lifetimes over two years, and 1/e charge density and charge lifetimes during electron beam delivery of over 2?105???C/cm2 and 200 C, respectively. This source is able to support uninterrupted high average current polarized beam delivery to three experimental halls simultaneously for many months at a time. Many of the techniques we report here are directly applicable to the development of GaAs photoemission electron guns to deliver high average current, high brightness unpolarized beams.

  20. Radiation response analysis of wide-gap p-AlInGaP for superhigh-efficiency space photovoltaics

    SciTech Connect (OSTI)

    Khan, Aurangzeb; Marupaduga, S.; Anandakrishnan, S.S.; Alam, M.; Ekins-Daukes, N.J.; Lee, H.S.; Sasaki, T.; Yamaguchi, M.; Takamoto, T.; Agui, T.; Kamimura, K.; Kaneiwa, M.; Imazumi, M.

    2004-11-29

    We present here the direct observation of the majority and minority carrier defects generation from wide-band-gap (2.04 eV) and thick (2 {mu}m) p-AlInGaP diodes and solar cells structures before and after 1 MeV electron irradiation by deep level transient spectroscopy (DLTS). One dominant hole-emitting trap H1 (E{sub V}+0.37{+-}0.05 eV) and two electron-emitting traps, E1 (E{sub C}-0.22{+-}0.04 eV) and E3 (E{sub C}-0.78{+-}0.05 eV) have been observed in the temperature range, which we could scan by DLTS. Detailed analysis of the minority carrier injection annealing experiment reveals that the H1 center has shown the same annealing characteristics, which has been previously observed in all phosphide-based materials such as InP, InGaP, and InGaAsP. The annealing property of the radiation-induced defects in p-AlInGaP reveals that multijunction solar cells and other optoelectronic devices such as light-emitting diodes based on this material could be considerably better to Si and GaAs in a radiation environment.

  1. Improvement of the quality of graphene-capped InAs/GaAs quantum dots

    SciTech Connect (OSTI)

    Othmen, Riadh Rezgui, Kamel; Ajlani, Hosni; Oueslati, Meherzi; Cavanna, Antonella; Madouri, Ali

    2014-06-07

    In this paper, we study the transfer of graphene onto InAs/GaAs quantum dots (QDs). The graphene is first grown on Cu foils by chemical vapor deposition and then polymer Polymethyl Methacrylate (PMMA) is deposited on the top of graphene/Cu. High quality graphene sheet has been obtained by lowering the dissolving rate of PMMA using vapor processing. Uncapped as well as capped graphene InAs/GaAs QDs have been studied using optical microscopy, scanning electron microscopy, and Raman spectroscopy. We gather from this that the average shifts ?? of QDs Raman peaks are reduced compared to those previously observed in graphene and GaAs capped QDs. The encapsulation by graphene makes the indium atomic concentration intact in the QDs by the reduction of the strain effect of graphene on QDs and the migration of In atoms towards the surface. This gives us a new hetero-structure grapheneInAs/GaAs QDs wherein the graphene plays a key role as a cap layer.

  2. Enhancing photovoltaic output power by 3-band spectrum-splitting and concentration using a diffractive micro-optic

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Mohammad, Nabil; Wang, Peng; Friedman, Daniel J.; Menon, Rajesh

    2014-09-17

    We report the enhancement of photovoltaic output power by separating the incident spectrum into 3 bands, and concentrating these bands onto 3 different photovoltaic cells. The spectrum-splitting and concentration is achieved via a thin, planar micro-optical element that demonstrates high optical efficiency over the entire spectrum of interest. The optic (which we call a polychromat) was designed using a modified version of the direct-binary-search algorithm. The polychromat was fabricated using grayscale lithography. Rigorous optical characterization demonstrates excellent agreement with simulation results. Electrical characterization of the solar cells made from GaInP, GaAs and Si indicate increase in the peak output powermore » density of 43.63%, 30.84% and 30.86%, respectively when compared to normal operation without the polychromat. This represents an overall increase of 35.52% in output power density. As a result, the potential for cost-effective large-area manufacturing and for high system efficiencies makes our approach a strong candidate for low cost solar power.« less

  3. Blending Cr2O3 into a NiO-Ni electrocatalyst for sustained water splitting

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Gong, Ming; Zhou, Wu; Kenney, Michael James; Kapusta, Rich; Cowley, Sam; Wu, Yingpeng; Lu, Bingan; Lin, Meng -Chang; Wang, Di -Yan; Yang, Jiang; et al

    2015-08-24

    The rising H2 economy demands active and durable electrocatalysts based on low-cost, earth-abundant materials for water electrolysis/photolysis. Here we report nanoscale Ni metal cores over-coated by a Cr2O3-blended NiO layer synthesized on metallic foam substrates. The Ni@NiO/Cr2O3 triphase material exhibits superior activity and stability similar to Pt for the hydrogen-evolution reaction in basic solutions. The chemically stable Cr2O3 is crucial for preventing oxidation of the Ni core, maintaining abundant NiO/Ni interfaces as catalytically active sites in the heterostructure and thus imparting high stability to the hydrogen-evolution catalyst. The highly active and stable electrocatalyst enables an alkaline electrolyzer operating at 20more » mA cm–2 at a voltage lower than 1.5 V, lasting longer than 3 weeks without decay. Thus, the non-precious metal catalysts afford a high efficiency of about 15 % for light-driven water splitting using GaAs solar cells.« less

  4. Ion beam nanopatterning of III-V semiconductors: Consistency of experimental and simulation trends within a chemistry-driven theory

    SciTech Connect (OSTI)

    El-Atwani, O.; Norris, S. A.; Ludwig, K.; Gonderman, S.; Allain, J. P.

    2015-12-16

    In this study, several proposed mechanisms and theoretical models exist concerning nanostructure evolution on III-V semiconductors (particularly GaSb) via ion beam irradiation. However, making quantitative contact between experiment on the one hand and model-parameter dependent predictions from different theories on the other is usually difficult. In this study, we take a different approach and provide an experimental investigation with a range of targets (GaSb, GaAs, GaP) and ion species (Ne, Ar, Kr, Xe) to determine new parametric trends regarding nanostructure evolution. Concurrently, atomistic simulations using binary collision approximation over the same ion/target combinations were performed to determine parametric trends on several quantities related to existing model. A comparison of experimental and numerical trends reveals that the two are broadly consistent under the assumption that instabilities are driven by chemical instability based on phase separation. Furthermore, the atomistic simulations and a survey of material thermodynamic properties suggest that a plausible microscopic mechanism for this process is an ion-enhanced mobility associated with energy deposition by collision cascades.

  5. Photodetector with absorbing region having resonant periodic absorption between reflectors

    DOE Patents [OSTI]

    Bryan, R.P.; Olbright, G.R.; Brennan, T.M.; Tsao, J.Y.

    1995-02-14

    A photodetector is disclosed that is responsive to a wavelength or wavelengths of interest which have heretofore been unrealized. The photodetector includes a resonant cavity structure bounded by first and second reflectors, the resonant cavity structure being resonant at the wavelength or wavelengths of interest for containing a plurality of standing waves therein. The photodetector further includes a radiation absorbing region disposed within the resonant cavity structure, the radiation absorbing region including a plurality of radiation absorbing layers spaced apart from one another by a distance substantially equal to a distance between antinodes of adjacent ones of the standing waves. Each of radiation absorbing layers is spatially positioned at a location of one of the antinodes of one of the standing waves such that radiation absorption is enhanced. The radiation absorbing layers may be either bulk layers or quantum wells includes a plurality of layers, each of which is comprised of a strained layer of InGaAs. Individual ones of the InGaAs layers are spaced apart from one another by a GaAs barrier layer. 11 figs.

  6. Blending Cr2O3 into a NiO-Ni electrocatalyst for sustained water splitting

    SciTech Connect (OSTI)

    Gong, Ming; Zhou, Wu; Kenney, Michael James; Kapusta, Rich; Cowley, Sam; Wu, Yingpeng; Lu, Bingan; Lin, Meng -Chang; Wang, Di -Yan; Yang, Jiang; Hwang, Bing -Joe; Dai, Hongjie

    2015-08-24

    The rising H2 economy demands active and durable electrocatalysts based on low-cost, earth-abundant materials for water electrolysis/photolysis. Here we report nanoscale Ni metal cores over-coated by a Cr2O3-blended NiO layer synthesized on metallic foam substrates. The Ni@NiO/Cr2O3 triphase material exhibits superior activity and stability similar to Pt for the hydrogen-evolution reaction in basic solutions. The chemically stable Cr2O3 is crucial for preventing oxidation of the Ni core, maintaining abundant NiO/Ni interfaces as catalytically active sites in the heterostructure and thus imparting high stability to the hydrogen-evolution catalyst. The highly active and stable electrocatalyst enables an alkaline electrolyzer operating at 20 mA cm2 at a voltage lower than 1.5 V, lasting longer than 3 weeks without decay. Thus, the non-precious metal catalysts afford a high efficiency of about 15 % for light-driven water splitting using GaAs solar cells.

  7. Robust activation method for negative electron affinity photocathodes

    DOE Patents [OSTI]

    Mulhollan, Gregory A. (Dripping Springs, TX); Bierman, John C. (Austin, TX)

    2011-09-13

    A method by which photocathodes(201), single crystal, amorphous, or otherwise ordered, can be surface modified to a robust state of lowered and in best cases negative, electron affinity has been discovered. Conventional methods employ the use of Cs(203) and an oxidizing agent(207), typically carried by diatomic oxygen or by more complex molecules, for example nitrogen trifluoride, to achieve a lowered electron affinity(404). In the improved activation method, a second alkali, other than Cs(205), is introduced onto the surface during the activation process, either by co-deposition, yo-yo, or sporadic or intermittent application. Best effect for GaAs photocathodes has been found through the use of Li(402) as the second alkali, though nearly the same effect can be found by employing Na(406). Suitable photocathodes are those which are grown, cut from boules, implanted, rolled, deposited or otherwise fabricated in a fashion and shape desired for test or manufacture independently supported or atop a support structure or within a framework or otherwise affixed or suspended in the place and position required for use.

  8. Method for manufacturing compound semiconductor field-effect transistors with improved DC and high frequency performance

    DOE Patents [OSTI]

    Zolper, John C.; Sherwin, Marc E.; Baca, Albert G.

    2000-01-01

    A method for making compound semiconductor devices including the use of a p-type dopant is disclosed wherein the dopant is co-implanted with an n-type donor species at the time the n-channel is formed and a single anneal at moderate temperature is then performed. Also disclosed are devices manufactured using the method. In the preferred embodiment n-MESFETs and other similar field effect transistor devices are manufactured using C ions co-implanted with Si atoms in GaAs to form an n-channel. C exhibits a unique characteristic in the context of the invention in that it exhibits a low activation efficiency (typically, 50% or less) as a p-type dopant, and consequently, it acts to sharpen the Si n-channel by compensating Si donors in the region of the Si-channel tail, but does not contribute substantially to the acceptor concentration in the buried p region. As a result, the invention provides for improved field effect semiconductor and related devices with enhancement of both DC and high-frequency performance.

  9. New approaches for high-efficiency solar cells. Final report

    SciTech Connect (OSTI)

    Bedair, S.M.; El-Masry, N.A.

    1997-12-01

    This report summarizes the activities carried out in this subcontract. These activities cover, first the atomic layer epitaxy (ALE) growth of GaAs, AlGaAs and InGaP at fairly low growth temperatures. This was followed by using ALE to achieve high levels of doping both n-type and p-type required for tunnel junctions (Tj) in the cascade solar cell structures. Then the authors studied the properties of AlGaAs/InGaP and AlGaAs/GaAs tunnel junctions and their performances at different growth conditions. This is followed by the use of these tunnel junctions in stacked solar cell structures. The effect of these tunnel junctions on the performance of stacked solar cells was studied at different temperatures and different solar fluences. Finally, the authors studied the effect of different types of black surface fields (BSF), both p/n and n/p GaInP solar cell structures, and their potential for window layer applications. Parts of these activities were carried in close cooperation with Dr. Mike Timmons of the Research Triangle Institute.

  10. Stability of S and Se induced reconstructions on GaP(001)(21) surface

    SciTech Connect (OSTI)

    Li , D. F.; Guo, Zhi C.; Xiao, Hai Yan; Zu, Xiaotao T.; Gao, Fei

    2010-10-15

    The structural and electronic properties of S- and Se- passivated GaP(001)(21) surfaces were studied using first-principles simulations. Our calculations showed that the most stable structure consists of a single chalcogen atom (S or Se) in the first crystal layer, which is bonded to two Ga atoms of the second layer, and the third P layer replaced by chalcogen atoms, similar to the passivation of GaAs(001)(21) surface by chalcogen atoms. The structural parameters were determined and the surface band characters and the local density of states were also analyzed. The results showed that the preferable structure has no surface states in the bulk band gap, but the energy band gaps of the S- and Se-adsorbed GaP(001) surfaces are 1.83eV and 1.63eV, respectively. The passivation effects for the S- and Se-adsorbed surfaces are similar to each other.

  11. Final Report for PV Incubator Subcontract No. NAT-0-99013-01: June 14, 2010 - March 2, 2012

    SciTech Connect (OSTI)

    Ghosal, K.

    2012-04-01

    The goal of the subcontract is to scale up Semprius' novel micro-cell based modules to an annualized rate of 500 kW of receivers and 10 kW of modules, in support of the DOE 2020 Sunshot Initiative goals. The statement of work (SOW) was broken up into two Phases. Phase I was directed towards process development efforts towards addressing fundamental manufacturing metrics such as yield, die per wafer, automation and throughput. Phase II objectives are to scale to an annualized production rate of 500 kW of receivers and 10 kW of modules, while improving cell efficiency, module efficiency and transfer yield. Semprius has met all the technical milestones and deliverables for the contract. All subtasks were completed earlier than expected and the results exceeded the technical targets. In particular, 3J cell efficiency of 41.2% exceeded the target of 38%, module efficiency of 28.3% exceeded the target of 28% and transfer yield of 96.4% exceeds the target of 95%, with all tasks completed well ahead of schedule. Also, devices fabricated from 1st use GaAs substrates and substrates with two re-uses have been shown to be identical.

  12. Bent crystal spectrometer for both frequency and wavenumber resolved x-ray scattering at a seeded free-electron laser

    SciTech Connect (OSTI)

    Zastrau, Ulf; Fletcher, Luke B.; Galtier, Eric Ch.; Gamboa, Eliseo; Glenzer, Siegfried H.; Heimann, Philipp; Nagler, Bob; Schropp, Andreas; Lee, Hae Ja; Frster, Eckhart; Marschner, Heike; Wehrhan, Ortrud

    2014-09-15

    We present a cylindrically curved GaAs x-ray spectrometer with energy resolution ?E/E = 1.1 ?10{sup ?4} and wave-number resolution of ?k/k = 3 ?10{sup ?3}, allowing plasmon scattering at the resolution limits of the Linac Coherent Light Source (LCLS) x-ray free-electron laser. It spans scattering wavenumbers of 3.6 to 5.2/ in 100 separate bins, with only 0.34% wavenumber blurring. The dispersion of 0.418 eV/13.5??m agrees with predictions within 1.3%. The reflection homogeneity over the entire wavenumber range was measured and used to normalize the amplitude of scattering spectra. The proposed spectrometer is superior to a mosaic highly annealed pyrolytic graphite spectrometer when the energy resolution needs to be comparable to the LCLS seeded bandwidth of 1 eV and a significant range of wavenumbers must be covered in one exposure.

  13. First-principles studies on molecular beam epitaxy growth of GaAs1-xBix

    SciTech Connect (OSTI)

    Luo, Guangfu; Yang, Shujiang; Li, Jincheng; Arjmand, Mehrdad; Szlufarska, Izabela; Brown, April S.; Kuech, Thomas F.; Morgan, Dane

    2015-07-14

    We investigate the molecular beam epitaxy (MBE) growth of GaAs1-xBix film using density functional theory with spin-orbit coupling to understand the growth of this film, especially the mechanisms of Bi incorporation. We study the stable adsorption structures and kinetics of the incident molecules (As? molecule, Ga atom, Bi atom, and Bi? molecule) on the (2 x 1)-Gasub||Bi surface and a proposed q(1 x 1)-Gasub||AsAs surface has a quasi-(1 x 1) As layer above the Ga-terminated GaAs substrate and a randomly oriented As dimer layer on top. We obtain the desorption and diffusion barriers of the adsorbed molecules and also the reaction barriers of three key processes related to Bi evolution, namely, Bi incorporation, As/Bi exchange, and Bi clustering. The results help explain the experimentally observed dependence of Bi incorporation on the As/Ga ratio and growth temperature. Furthermore, we find that As? exchange with Bi of the (2 x 1)-Gasub||Bi surface is a key step controlling the kinetics of the Bi incorporation. Finally, we explore two possible methods to enhance the Bi incorporation, namely, replacing the MBE growth mode from codeposition of all fluxes with a sequential deposition of fluxes and applying asymmetric in-plane strain to the substrate.

  14. Spontaneous formation of nanostructures by surface spinodal decomposition in GaAs{sub 1?x}Bi{sub x} epilayers

    SciTech Connect (OSTI)

    Luna, E. Wu, M.; Trampert, A.; Puustinen, J.; Guina, M.

    2015-05-14

    We report on the spontaneous formation of lateral composition modulations (LCMs) in Ga(As,Bi) epilayers grown by low-temperature (<300?C) molecular beam epitaxy (MBE) on GaAs(001). Both cross-section and plan-view transmission electron microscopy techniques are used to investigate the nature of the LCMs, consisting of Bi-rich cylinder-like nanostructures lying along the [001] growth direction. The observed LCMs are the consequence of a two-dimensional phase separation process occurring at the surface of the growing epilayers, and their columnar nature is consistent with a surface-directed spinodal decomposition process. Although LCMs are thermodynamically driven, we show how they can be kinetically controlled, in particular, through the As/Ga flux ratio and the substrate temperature. This is a result of LCMs developing from surface atomic diffusion processes, since the atomic dimer configurations on the surface alter adatom diffusivity. The significant role of the surface reconstructions is also discussed.

  15. Formation of self-organized quantum dot structures and quasi-perfect CuPt-type ordering by gas-source MBE growth of (GaP){sub n}(InP){sub n} superlattices

    SciTech Connect (OSTI)

    Kim, S.J.; Asahi, H.; Takemoto, M.; Asami, K.; Takeuchi, M.; Gonda, S.

    1996-12-31

    (GaP){sub n}(InP){sub n} short period superlattices (SLs) are grown on GaAs(N11) substrates by gas-source MBE. Transmission electron microscopy observations show that the SLs grown on GaAs(311)A and (411)A have dot structures with a size of about 10--20nm. Photoluminescence (PL) peak energies are greatly dependent on substrate orientation and monolayer number n. On the other hand, the (GaP){sub 1}(InP){sub 1} SLs grown on (111) have no composition modulation and have quasi-perfect CuPt-type ordering along the [111] growth direction. The PL peak energy is 321 meV lower than that of disordered InGaP alloy. Self-organized (GaP){sub n}(InP){sub m} SL(dot/barrier)/In{sub 0.49}Ga{sub 0.51}P(barrier) quantum dot structures exhibit strong 77K PL with a full width at half maximum of about 70 meV.

  16. Photopumped red-emitting InP/In{sub 0.5}Al{sub 0.3}Ga{sub 0.2}P self-assembled quantum dot heterostructure lasers grown by metalorganic chemical vapor deposition

    SciTech Connect (OSTI)

    Ryou, J. H.; Dupuis, R. D.; Walter, G.; Kellogg, D. A.; Holonyak, N.; Mathes, D. T.; Hull, R.; Reddy, C. V.; Narayanamurti, V.

    2001-06-25

    We report the 300 K operation of optically pumped red-emitting lasers fabricated from InP self-assembled quantum dots embedded in In{sub 0.5}Al{sub 0.3}Ga{sub 0.2}P layers on GaAs (100) substrates grown by metalorganic chemical vapor deposition. Quantum dots grown at 650{degree}C on In{sub 0.5}Al{sub 0.3}Ga{sub 0.2}P layers have a high density on the order of 10{sup 10} cm{sup {minus}2} and the dominant size of individual quantum dots ranges from {similar_to}5 to {similar_to}10 nm for 7.5 monolayer {open_quotes}equivalent growth.{close_quotes} These InP/In{sub 0.5}Al{sub 0.3}Ga{sub 0.2}P quantum dot heterostructures are characterized by atomic force microscopy, high-resolution transmission electron microscopy, and photoluminescence. Laser structures are prepared from wafers having two vertically stacked InP quantum dot active layers within a 100-nm-thick In{sub 0.5}Al{sub 0.3}Ga{sub 0.2}P waveguide and upper and lower 600 nm InAlP cladding layers. We observe lasing at {lambda}{similar_to}680 nm at room temperature in optically pumped samples. {copyright} 2001 American Institute of Physics.

  17. Excitonic exchange splitting in bulk semiconductors

    SciTech Connect (OSTI)

    Fu, H.; Wang, L.; Zunger, A.

    1999-02-01

    We present an approach to calculate the excitonic fine-structure splittings due to electron-hole short-range exchange interactions using the local-density approximation pseudopotential method, and apply it to bulk semiconductors CdSe, InP, GaAs, and InAs. Comparing with previous theoretical results, the current calculated splittings agree well with experiments. Furthermore, we provide an approximate relationship between the short-range exchange splitting and the exciton Bohr radius, which can be used to estimate the exchange splitting for other materials. The current calculation indicates that a commonly used formula for exchange splitting in quantum dot is not valid. Finally, we find a very large pressure dependence of the exchange splitting: a factor of 4.5 increase as the lattice constant changes by 3.5{percent}. This increase is mainly due to the decrease of the Bohr radius via the change of electron effective mass. {copyright} {ital 1999} {ital The American Physical Society}

  18. Growth and Characterization of MBE Parametric Variations Upon Polarization Independent Strained Films

    SciTech Connect (OSTI)

    Theda Daniels-Race

    2003-04-30

    This project was designed to comprehensively investigate the effects of molecular beam epitaxy (MBE) growth variations upon tensile-strained films. Using two dimensional (2-D) structures, such as quantum wells of variable configurations, we worked to observe the electro-optical response of polarization independence. The latter had been studied for compressively strained systems. However, the proof of principle for the feasibility of tensile-strained single and double quantum wells, particularly in the GaAs as opposed to the InP material system, had been much less investigated by comparison. The significance of this project, from a Basic Energy Sciences perspective, has been in its contribution to the understanding of how MBE parameters and sample design effect the physics of strained materials which themselves have been tailored to react with polarization insensitivity. Fundamental issues of materials structure control, growth parameter modifications, and characterization methods were investigated. Both single and double quantum well systems were used with both symmetric and asymmetric well widths for the latter. In this work, we essentially investigated both the growth of and potential applications for quantum based structures that use tensile strain to induce polarization independence.

  19. Synthesis, optical properties, and microstructure of semiconductor nanocrystals formed by ion implantation

    SciTech Connect (OSTI)

    Budai, J.D.; White, C.W.; Withrow, S.P.; Zuhr, R.A.; Zhu, J.G.

    1996-12-01

    High-dose ion implantation, followed by annealing, has been shown to provide a versatile technique for creating semiconductor nanocrystals encapsulated in the surface region of a substrate material. The authors have successfully formed nanocrystalline precipitates from groups IV (Si, Ge, SiGe), III-V (GaAs, InAs, GaP, InP, GaN), and II-VI (CdS, CdSe, CdS{sub x}Se{sub 1{minus}x}, CdTe, ZnS, ZnSe) in fused silica, Al{sub 2}O{sub 3} and Si substrates. Representative examples will be presented in order to illustrate the synthesis, microstructure, and optical properties of the nanostructured composite systems. The optical spectra reveal blue-shifts in good agreement with theoretical estimates of size-dependent quantum-confinement energies of electrons and holes. When formed in crystalline substrates, the nanocrystal lattice structure and orientation can be reproducibly controlled by adjusting the implantation conditions.

  20. Formation of linear InAs quantum dot arrays on InGaAsP/InP (100) by self-organized anisotropic strain engineering and their optical properties

    SciTech Connect (OSTI)

    Sritirawisarn, N.; Otten, F. W. M. van; Eijkemans, T. J.; Noetzel, R.

    2007-09-01

    The formation of linear InAs quantum dot (QD) arrays based on self-organized anisotropic strain engineering of an InGaAsP/InP (100) superlattice (SL) template in chemical beam epitaxy is demonstrated, and the optimized growth window is determined. InAs QD formation, thin InGaAsP capping, annealing, InGaAsP overgrowth, and stacking in SL template formation produce wirelike InAs structures along [001] due to anisotropic surface migration and lateral and vertical strain correlations. InAs QD ordering is governed by the corresponding lateral strain field modulation on the SL template surface. Careful optimization of InGaAsP cap layer thickness, annealing temperature, InAs amount and growth rate, and number of SL periods results in straight and well-separated InAs QD arrays. The InAs QD arrays exhibit excellent photoluminescence (PL) emission up to room temperature which is tuned into the 1.55 {mu}m telecommunications wavelength region through the insertion of ultrathin GaAs interlayers. Temperature dependent PL measurements and the linear polarization behavior indicate lateral electronic coupling of the QDs in the arrays.

  1. Design of Semiconducting Tetrahedral Mn 1 ₋ x Zn x O Alloys and Their Application to Solar Water Splitting

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Peng, Haowei; Ndione, Paul F.; Ginley, David S.; Zakutayev, Andriy; Lany, Stephan

    2015-05-18

    Transition metal oxides play important roles as contact and electrode materials, but their use as active layers in solar energy conversion requires achieving semiconducting properties akin to those of conventional semiconductors like Si or GaAs. In particular, efficient bipolar carrier transport is a challenge in these materials. Based on the prediction that a tetrahedral polymorph of MnO should have such desirable semiconducting properties, and the possibility to overcome thermodynamic solubility limits by nonequilibrium thin-film growth, we exploit both structure-property and composition-structure relationships to design and realize novel wurtzite-structure Mn₁₋xZnxO alloys. At Zn compositions above x ≈ 0.3, thin films ofmore » these alloys assume the tetrahedral wurtzite structure instead of the octahedral rocksalt structure of MnO, thereby enabling semiconductor properties that are unique among transition metal oxides, i.e., a band gap within the visible spectrum, a band-transport mechanism for both electron and hole carriers, electron doping, and a band lineup suitable for solar hydrogen generation. A proof of principle is provided by initial photo-electrocatalytic device measurements, corroborating, in particular, the predicted favorable hole-transport properties of these alloys.« less

  2. Method for reducing or eliminating interface defects in mismatched semiconductor epilayers

    DOE Patents [OSTI]

    Fitzgerald, E.A. Jr.; Ast, D.G.

    1992-10-20

    The present invention and process relates to crystal lattice mismatched semiconductor composite having a first semiconductor layer and a second semiconductor growth layer deposited thereon to form an interface wherein the growth layer can be deposited at thicknesses in excess of the critical thickness, even up to about 10[times] critical thickness. Such composite has an interface which is substantially free of interface defects. For example, the size of the growth areas in a mismatched In[sub 0.05]Ga[sub 0.95]As/(001)GaAs interface was controlled by fabricating 2-[mu]m high pillars of various lateral geometries and lateral dimensions before the epitaxial deposition of 3500 [angstrom] of In[sub 0.05]Ga[sub 0.95]As. The linear dislocation density at the interface was reduced from >5000 dislocations/cm to about zero for 25-[mu]m lateral dimensions and to less than 800 dislocations/cm for lateral dimensions as large as 100 [mu]m. The fabricated pillars control the lateral dimensions of the growth layer and block the glide of misfit dislocations with the resultant decrease in dislocation density. 7 figs.

  3. Method and apparatus for rapidly growing films on substrates using pulsed supersonic jets

    DOE Patents [OSTI]

    Eres, Diula (Knoxville, TN); Lowndes, Douglas H. (Oak Ridge, TN)

    1992-01-01

    A method and apparatus for the rapid and economical deposition of uniform and high quality films upon a substrate for subsequent use in producing electronic devices, for example. The resultant films are either epitaxial (crystalline) or amorphous depending upon the incidence rate and the temperature and structure of the substrate. The deposition is carried out in a chamber maintained at about 10.sup.-6 Torr. A gaseous source of the material for forming the deposit is injected into the deposition chamber in the form of a pulsed supersonic jet so as to obtain a high incidence rate. The supersonic jet is produced by a pulsed valve between a relatively high presure reservoir, containing the source gaseous molecules, and the deposition chamber; the valve has a small nozzle orifice (e.g., 0.1-1.0 mm diameter). The type of deposit (crystalline amorphous) is then dependent upon the temperature and structure of the substrate. Very high deposition rates are achieved, and the deposit is very smooth and of uniform thickness. Typically the deposition rate is about 100 times that of much more expensive conventional molecular beam methods for deposition, and comparable to certain expensive plasma-assisted CVD methods of the art. The high growth rate of this method results in a reduced contamination of the deposit from other elements in the environment. The method is illustrated by the deposition of epitaxial and amorphour germanium films upon GaAs substrates.

  4. Method for reducing or eliminating interface defects in mismatched semiconductor epilayers

    DOE Patents [OSTI]

    Fitzgerald, Jr., Eugene A. (Ithaca, NY); Ast, Dieter G. (Ithaca, NY)

    1992-01-01

    The present invention and process relates to crystal lattice mismatched semiconductor composite having a first semiconductor layer and a second semiconductor growth layer deposited thereon to form an interface wherein the growth layer can be deposited at thicknesses in excess of the critical thickness, even up to about 10.times. critical thickness. Such composite has an interface which is substantially free of interface defects. For example, the size of the growth areas in a mismatched In.sub.0.05 Ga.sub.0.95 As/(001)GaAs interface was controlled by fabricating 2-.mu.m high pillars of various lateral geometries and lateral dimensions before the epitaxial deposition of 3500.ANG. of In.sub.0.05 Ga.sub.0.95 As. The linear dislocation density at the interface was reduced from >5000 dislocations/cm to about zero for 25-.mu.m lateral dimensions and to less than 800 dislocations/cm for lateral dimensions as large as 100 .mu.m. The fabricated pillars control the lateral dimensions of the growth layer and block the glide of misfit dislocations with the resultant decrease in dislocation density.

  5. Method for reducing or eliminating interface defects in mismatched semiconductor eiplayers

    DOE Patents [OSTI]

    Fitzgerald, Jr., Eugene A. (Ithaca, NY); Ast, Dieter G. (Ithaca, NY)

    1991-01-01

    The present invention and process relates to crystal lattice mismatched semiconductor composite having a first semiconductor layer and a second semiconductor growth layer deposited thereon to form an interface wherein the growth layer can be deposited at thicknesses in excess of the critical thickness, even up to about 10x critical thickness. Such composite has an interface which is substantially free of interface defects. For example, the size of the growth areas in a mismatched In.sub.0.05 Ga.sub.0.95 As/(001)GaAs interface was controlled by fabricating 2-.mu.m high pillars of various lateral geometries and lateral dimensions before the epitaxial deposition of 3500.ANG. of In.sub.0.05 Ga.sub.0.95 As. The linear dislocation density at the interface was reduced from >5000 dislocations/cm to about zero for 25-.mu.m lateral dimensions and to less than 800 dislocations/cm for lateral dimensions as large as 100 .mu.m. The fabricated pillars control the lateral dimensions of the growth layer and block the glide of misfit dislocations with the resultant decrease in dislocation density.

  6. Characterization of an SRF gun: a 3D full wave simulation

    SciTech Connect (OSTI)

    Wang, E.; Ben-Zvi, I.; Wang, J.

    2011-03-28

    We characterized a BNL 1.3GHz half-cell SRF gun is tested for GaAs photocathode. The gun already was simulated several years ago via two-dimensional (2D) numerical codes (i.e., Superfish and Parmela) with and without the beam. In this paper, we discuss our investigation of its characteristics using a three dimensional (3D) full-wave code (CST STUDIO SUITE{trademark}).The input/pickup couplers are sited symmetrically on the same side of the gun at an angle of 180{sup o}. In particular, the inner conductor of the pickup coupler is considerably shorter than that of the input coupler. We evaluated the cross-talk between the beam (trajectory) and the signal on the input coupler compared our findings with published results based on analytical models. The CST STUDIO SUITE{trademark} also was used to predict the field within the cavity; particularly, a combination of transient/eigenmode solvers was employed to accurately construct the RF field for the particles, which also includes the effects of the couplers. Finally, we explored the beam's dynamics with a particle in cell (PIC) simulation, validated the results and compare them with 2D code result.

  7. Photorefractive Interferometers for Ultrasonic Measurements on Paper

    SciTech Connect (OSTI)

    Lafond, E. F.; Brodeur, P. H.; Gerhardstein, J. P.; Habeger, C. C.; Telschow, Kenneth Louis

    2002-12-01

    Photorefractive interferometers have been employed for the detection of ultrasound in metals and composites since 1991 [14]. Instances of laser-generated ultrasound and laser-based detection in paper were reported in 1996 [5]. More recently, bismuth silicon oxide (BSO) photorefractive interferometers were adapted to detect ultrasound in paper [6]. In this article we discuss BSO and GaAs photorefractive detection of ultrasound on different paper grades and present the resulting waveforms. Compared to contact piezoelectric transducer methods, laser interferometry offers signifcant advantages. One of these is that it is a noncontact technique. This is especially important for on-line application to lightweight papers which could be marked or damaged by contact transducers. Broadband ultrasonic laser generation matched with the broadband sensitivity of laser interferometers is another beneft. This is important for obtaining narrow pulses in nondispersive time-of-fight determinations and for measuring the phase velocity of dispersive modes over a wide frequency band. Also, laser ultrasonic techniques provide a measure of bending stiffness through the analysis of low frequency A0 waves.

  8. Alternative fabrication techniques for high-efficiency CuInSe{sub 2} and CuInSe{sub 2}-alloy films and cells. Final subcontract report, 1 March 1990--31 August 1992

    SciTech Connect (OSTI)

    Rockett, A.; Yang, L.C.; Kenshole, G.; Banda, E.; Feen, A.

    1994-07-01

    Work performed during the course of this subcontract has led to improved CuInSe{sub 2} (CIS) processing techniques and materials resulting in improved solar cell performance (up to 10% active area efficiency) based on a thick conductive evaporated CdS window layer and an indium-tin-oxide transparent conductor. Modeling of the device performance has indicated that an optimal CdS thickness should exist if pinholes occur in the CIS layer (for example, due to adhesion failures) leading to shunts between the CdS and the back contact. Pinholes in the CIS layer have been dramatically reduced by the use of a Cu-Mo two-phase back contact metallization resulting from significant increases in adhesion between the CIS and the back contact. Controlled leaching of the Cu from the back contact apparently contributes to this improvement without degradation of the solar cells. Finally, CIS has been grown epitaxially on GaAs. Preliminary results suggest explanations for the morphology and defect structures of polycrystalline layers used in devices as well as indicating the general mechanism for growth of CIS by vapor phase methods.

  9. Period-doubling reconstructions of semiconductor partial dislocations

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Park, Ji -Sang; Huang, Bing; Wei, Su -Huai; Kang, Joongoo; McMahon, William E.

    2015-09-18

    Atomic-scale understanding and control of dislocation cores is of great technological importance, because they act as recombination centers for charge carriers in optoelectronic devices. Using hybrid density-functional calculations, we present period-doubling reconstructions of a 90° partial dislocation in GaAs, for which the periodicity of like-atom dimers along the dislocation line varies from one to two, to four dimers. The electronic properties of a dislocation change drastically with each period doubling. The dimers in the single-period dislocation are able to interact, to form a dispersive one-dimensional band with deep-gap states. However, the inter-dimer interaction for the double-period dislocation becomes significantly reduced;more » hence, it is free of mid-gap states. The Ga core undergoes a further period-doubling transition to a quadruple-period reconstruction induced by the formation of small hole polarons. Lastly, the competition between these dislocation phases suggests a new passivation strategy via population manipulation of the detrimental single-period phase.« less

  10. Ion beam nanopatterning of III-V semiconductors: Consistency of experimental and simulation trends within a chemistry-driven theory

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    El-Atwani, O.; Norris, S. A.; Ludwig, K.; Gonderman, S.; Allain, J. P.

    2015-12-16

    In this study, several proposed mechanisms and theoretical models exist concerning nanostructure evolution on III-V semiconductors (particularly GaSb) via ion beam irradiation. However, making quantitative contact between experiment on the one hand and model-parameter dependent predictions from different theories on the other is usually difficult. In this study, we take a different approach and provide an experimental investigation with a range of targets (GaSb, GaAs, GaP) and ion species (Ne, Ar, Kr, Xe) to determine new parametric trends regarding nanostructure evolution. Concurrently, atomistic simulations using binary collision approximation over the same ion/target combinations were performed to determine parametric trends onmore » several quantities related to existing model. A comparison of experimental and numerical trends reveals that the two are broadly consistent under the assumption that instabilities are driven by chemical instability based on phase separation. Furthermore, the atomistic simulations and a survey of material thermodynamic properties suggest that a plausible microscopic mechanism for this process is an ion-enhanced mobility associated with energy deposition by collision cascades.« less

  11. Electron and hole gas in modulation-doped GaAs/Al{sub 1-x}Ga{sub x}As radial heterojunctions

    SciTech Connect (OSTI)

    Bertoni, Andrea; Royo, Miquel; Mahawish, Farah; Goldoni, Guido

    2011-11-15

    We perform self-consistent Schroedinger-Poisson calculations with exchange and correlation corrections to determine the electron and hole gas in a radial heterojunction formed in a GaAs/AlGaAs core-multi-shell nanowire, which is either n- or p-doped. We show that the electron and hole gases can be tuned to different localizations and symmetries inside the core as a function of the doping density/gate potential. Contrary to planar heterojunctions, conduction electrons do not form a uniform 2D electron gas (2DEG) localized at the GaAs/AlGaAs interface, but rather show a transition between an isotropic, cylindrical distribution deep in the GaAs core (low doping) and a set of six tunnel-coupled quasi-1D channels at the edges of the interface (high doping). Holes, on the other hand, are much more localized at the GaAs/AlGaAs interface. At low doping, they present an additional localization pattern with six separated 2DEGs strips. The field generated by a back-gate may easily deform the electron or hole gas, breaking the sixfold symmetry. Single 2DEGs at one interface or multiple quasi-1D channels are shown to form as a function of voltage intensity, polarity, and carrier type.

  12. Measurement of the transmission magnetic circular dichroism of Ga{sub 1?x}Mn{sub x}As epilayers using a built-in p-i-n photodiode

    SciTech Connect (OSTI)

    He, Z. X.; Zheng, H. Z. Wang, H. L.; Zhao, J. H.

    2014-02-28

    By constructing a GaMnAs epilayer/semi-insulating In{sub 0.2}Ga{sub 0.8}As/(001) n{sup +}-GaAs substrate layer structure as a built-in p-i-n photodiode, we developed a scheme for on-chip measurements of transmission magnetic circular dichroism (T-MCD). Both the hysteresis loops in the magnetic field sweeps and the wavelength scans at saturated magnetic fields measured using the new T-MCD scheme, illustrated the same features as those previously measured on the freestanding GaMnAs thin films by conventional T-MCD. Because a large group of epitaxially grown magnetic film/semiconductor heterostructures, such as Fe, NiFe, CoFeAl, and MnGa films on semiconductor substrates, are becoming important new building blocks for semiconductor-based spin field-effect transistor, perpendicular magnetic tunnel junction (p-MTJ) and lateral MTJ devices, the new T-MCD scheme can be applied to tests of their magnetic properties by forming either p-i-n or Schottky photodiodes.

  13. Ordering ferromagnetic In{sub 1?x}Mn{sub x}As quantum dots

    SciTech Connect (OSTI)

    Ferri, Fabio A.; Marega Jr, Euclydes; Kunets, Vasyl P.; Salamo, Gregory J.

    2013-12-04

    In this work, we present a method to order low temperature (LT) self-assembled ferromagnetic In{sub 1?x}Mn{sub x}As quantum dots (QDs) grown by molecular beam epitaxy (MBE). The ordered In{sub 1?x}Mn{sub x}As QDs were grown on top of a non-magnetic In{sub 0.4}Ga{sub 0.6}As/GaAs(100) QDs multi-layered structure. The modulation of the chemical potential, due to the stacking, provides a nucleation center for the LT In{sub 1?x}Mn{sub x}As QDs. For particular conditions, such as surface morphology and growth conditions, the In{sub 1?x}Mn{sub x}As QDs align along lines like chains. For comparison purposes, we also report the study of QDs grown on plain GaAs(100) substrates. Ferromagnetic behavior was observed for all structures at 2 K.

  14. Anisotropic emission and photon-recycling in strain-balanced quantum well solar cells

    SciTech Connect (OSTI)

    Cabrera, C. I.; Enciso, A.; Contreras-Solorio, D. A.; Hernandez, L.; Connolly, J. P.

    2014-04-28

    Strain-balanced quantum well solar cells (SB-QWSCs) extend the photon absorption edge beyond that of bulk GaAs by incorporation of quantum wells in the i-region of a pin device. Anisotropy arises from a splitting of the valence band due to compressive strain in the quantum wells, suppressing a transition which contributes to emission from the edge of the quantum wells. We have studied both the emission light polarized in the plane perpendicular (TM) to the quantum well which couples exclusively to the light hole transition and the emission polarized in the plane of the quantum wells (TE) which couples mainly to the heavy hole transition. It was found that the spontaneous emission rates TM and TE increase when the quantum wells are deeper. The addition of a distributed Bragg reflector can substantially increase the photocurrent while decreasing the radiative recombination current. We have examined the impact of the photon recycling effect on SB-QWSC performance. We have optimized SB-QWSC design to achieve single junction efficiencies above 30%.

  15. Low-cost, compact, robust laser-based ultrasound sensors using photo-EMF detection

    SciTech Connect (OSTI)

    Pepper, D.M.; Dunning, G.J.; Chiao, M.P.; O`Meara, T.R.; Mitchell, P.V.

    1996-12-31

    There is a great need in the manufacturing, aerospace, commercial, energy, automotive, microelectronics and DoD communities for diagnostic systems that can improve the efficiency, yield and performance of various materials processes--while reducing cost, labor, scrap, and machine downtime. Laser-based ultrasound (LBU) represents a noncontact, reconfigurable, high-bandwidth ultrasonic inspection and process control technology. LBU enables remote ultrasonic sensing by replacing conventional PZT transducers, squirters, and immersion systems with laser beams. One laser beam generates the ultrasound in an opaque workpiece, while a second laser beam probes the sample to sense minute surface displacements, induced by the ultrasound or via other acoustic emission mechanisms. LBU systems have yet to be fielded commercially, owing primarily to the cost, size, and complexity of the system components. The authors have developed a low-cost, compact sensor which can potentially enable LBU systems to become a reality. The sensor employs a semiconductor crystal (GaAs) using a mechanism called nonsteady-state photo-induced emf. When combined with a laser diode as an optical source, the result is a very compact, low-cost robust sensor, which can function under in-factory conditions, including inspection of rough-cut workpieces which undergo rapid platform motion, such as high-speed, scanning laser welders. Experimental results will be discussed, including the potential for optical fiber delivery.

  16. A self-consistent model of the lateral behavior of a twin-stripe injection laser

    SciTech Connect (OSTI)

    Kumar, T.; Ormondroyd, R.F.; Rozzi, T.E.

    1986-10-01

    A fully self-consistent computer model of the steady-state behavior of the zero-order lateral optical field of a GaAs twin-stripe injection laser is presented which takes into account current spreading in the p-type confining layer, the effect of lateral diffusion of carriers in the active layer, and bimolecular and stimulated radiative recombination. The results predict the lateral movement of the near field of the optical signal under asymmetric drive conditions, as observed in practice. Also calculated are the corresponding carrier and current density distributions. It is shown that the near-field zero order lateral optical field can be beam steered across the facet by only 2 ..mu..m, typically. However, the initial position of the beam can be controlled by the two-stripe currents and also the geometry of the device. For the case where I/sub s1/ approx. = I/sub s2/ the beam movement is seen to be proportional to either I/sub s1/ or I/sub s2/. The results show that beam steering is not accompanied by a negative slope to the I-L characteristics. The effect of geometry and diffusion coefficient on the value of maximum current allowed before modal instability occurs is also given.

  17. Evaluation of stacking faults and associated partial dislocations in AlSb/GaAs (001) interface by aberration-corrected high-resolution transmission electron microscopy

    SciTech Connect (OSTI)

    Wen, C.; Ge, B. H.; Cui, Y. X.; Li, F. H.; Zhu, J.; Yu, R.; Cheng, Z. Y.

    2014-11-15

    The stacking faults (SFs) in an AlSb/GaAs (001) interface were investigated using a 300 kV spherical aberration-corrected high-resolution transmission electron microscope (HRTEM). The structure and strain distribution of the single and intersecting (V-shaped) SFs associated with partial dislocations (PDs) were characterized by the [110] HRTEM images and geometric phase analysis, respectively. In the biaxial strain maps ?{sub xx} and ?{sub yy}, a SF can be divided into several sections under different strain states (positive or negative strain values). Furthermore, the strain state for the same section of a SF is in contrast to each other in ?{sub xx} and ?{sub yy} strain maps. The modification in the strain states was attributed to the variation in the local atomic displacements for the SF in the AlSb film on the GaAs substrate recorded in the lattice image. Finally, the single SF was found to be bounded by two 30 PDs. A pair of 30 PDs near the heteroepitaxial interface reacted to form a Lomer-Cottrell sessile dislocation located at the vertices of V-shaped SFs with opposite screw components. The roles of misfit dislocations, such as the PDs, in strain relaxation were also discussed.

  18. Multiple-hydrogen complexes in dilute nitride alloys

    SciTech Connect (OSTI)

    Amore Bonapasta, A.; Filippone, F.; Mattioli, G.

    2007-04-10

    Complexes formed by H and the isoelectronic impurity N in GaAs1-yNy alloys have been widely investigated to explain the significant effects of N on the host material properties and their passivation by H. However, available results still present a quite puzzling picture, none of the models proposed by theory for the N-H complexes being able to account for all of the experimental findings. An N-H{sub 2}* complex first proposed by theory was challenged by infrared results. A following C2{nu} complex has been challenged by a recent high resolution x-ray diffraction and photoluminescence spectroscopy study questioning the structural effects of this complex. In the present study, we show that a peculiar character of the H interaction with an isoelectronic impurity can induce the formation of novel, multiple-H complexes. In turn, one of this complexes can account for the H structural effects recently observed, thus reconciling theory and experiment.

  19. Mutual passivation of group IV donors and isovalent nitrogen in diluted GaN{sub x}As{sub 1-x} alloys

    SciTech Connect (OSTI)

    Yu, K.M.; Wu, J.; Walukiewicz, W.; Shan, W.; Beeman, J.; Mars, D.E.; Chamberlin, D.R.; Scarpulla, M.A.; Dubon, O.D.; Ridgway, M.C.; Geisz, J.F.

    2003-07-23

    We demonstrate the mutual passivation of electrically active group IV donors and isovalent N atoms in the GaN{sub x}As{sub 1-x} alloy system. This phenomenon occurs through the formation of a donor-nitrogen bond in the nearest neighbor IV{sub Ga}-N{sub As} pairs. In Si doped GaInN{sub 0.017}As{sub 0.983} the electron concentration starts to decrease rapidly at an annealing temperature of 700 C from {approx} 3 x 10{sup 19}cm{sup -3} in the as-grown state to less than 10{sup 16}cm{sup -3} after an annealing at 900 C for 10 s. At the same time annealing of this sample at 950 C increases the gap by about 35 meV, corresponding to a reduction of the concentration of the active N atoms by an amount very close to the total Si concentration. We also show that the formation of Si{sub Ga}-N{sub As} pairs is controlled by the diffusion of Si via Ga vacancies to the nearest N{sub As} site. The general nature of this mutual passivation effect is confirmed by our study of Ge doped GaN{sub x}As{sub 1-x} layers formed by N and Ge co-implantation in GaAs followed by pulsed laser melting.

  20. TJ Solar Cell

    SciTech Connect (OSTI)

    Friedman, Daniel

    2009-04-17

    This talk will discuss recent developments in III-V multijunction photovoltaic technology which have led to the highest-efficiency solar cells ever demonstrated. The relationship between the materials science of III-V semiconductors and the achievement of record solar cell efficiencies will be emphasized. For instance, epitaxially-grown GAInP has been found to form a spontaneously-ordered GaP/InP (111) superlattice. This ordering affects the band gap of the material, which in turn affects the design of solar cells which incorporate GaInP. For the next generation of ultrahigh-efficiency III-V solar cells, we need a new semiconductor which is lattice-matched to GaAs, has a band gap of 1 eV, and has long minority-carrier diffusion lengths. Out of a number of candidate materials, the recently-discovered alloy GaInNAs appears to have the greatest promise. This material satisfies the first two criteria, but has to date shown very low diffusion lengths, a problem which is our current focus in the development of these next-generation cells.