National Library of Energy BETA

Sample records for al ga fl

  1. Degradation mechanisms of 2 MeV proton irradiated AlGaN/GaN HEMTs...

    Office of Scientific and Technical Information (OSTI)

    irradiated AlGaNGaN HEMTs This content will become publicly available on August 26, 2016 Title: Degradation mechanisms of 2 MeV proton irradiated AlGaNGaN HEMTs Authors: ...

  2. Reactive codoping of GaAlInP compound semiconductors

    DOE Patents [OSTI]

    Hanna, Mark Cooper; Reedy, Robert

    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.

  3. Graphene induced remote surface scattering in graphene/AlGaN/GaN heterostructures

    SciTech Connect (OSTI)

    Liu, Xiwen; Li, Dan; Wang, Bobo; Liu, Bin; Chen, Famin; Jin, Guangri; Lu, Yanwu

    2014-10-20

    The mobilities of single-layer graphene combined with AlGaN/GaN heterostructures on two-dimensional electron gases in graphene/AlGaN/GaN double heterojunction are calculated. The impact of electron density in single-layer graphene is also studied. Remote surface roughness (RSR) and remote interfacial charge (RIC) scatterings are introduced into this heterostructure. The mobilities limited by RSR and RIC are an order of magnitude higher than that of interface roughness and misfit dislocation. This study contributes to designing structures for generation of higher electron mobility in graphene/AlGaN/GaN double heterojunction.

  4. 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}.

  5. AlGaAsSb/GaSb Distributed Bragg Reflectors Grown by Organometallic Vapor Phase Epitaxy

    SciTech Connect (OSTI)

    C.A. Wang; C.J. Vineis; D.R. Calawa

    2002-02-13

    The first AlGaAsSb/GaSb quarter-wave distributed Bragg reflectors grown by metallic vapor phase epitaxy are reported. The peak reflectance is 96% for a 10-period structure.

  6. Alloy inhomogeneity and carrier localization in AlGaN sections and AlGaN/AlN nanodisks in nanowires with 240350?nm emission

    SciTech Connect (OSTI)

    Himwas, C.; Hertog, M. den; Dang, Le Si; Songmuang, R.; Monroy, E.

    2014-12-15

    We present structural and optical studies of AlGaN sections and AlGaN/AlN nanodisks (NDs) in nanowires grown by plasma-assisted molecular beam epitaxy. The Al-Ga intermixing at Al(Ga)N/GaN interfaces and the chemical inhomogeneity in AlGaN NDs evidenced by scanning transmission electron microscopy are attributed to the strain relaxation process. This interpretation is supported by the three-dimensional strain distribution calculated by minimizing the elastic energy in the structure. The alloy inhomogeneity increases with the Al content, leading to enhanced carrier localization signatures in the luminescence characteristics, i.e., red shift of the emission, s-shaped temperature dependence, and linewidth broadening. Despite these effects, the emission energy of AlGaN/AlN NDs can be tuned in the 240350?nm range with internal quantum efficiencies around 30%.

  7. Synthesis, morphology and optical properties of GaN and AlGaN semiconductor nanostructures

    SciTech Connect (OSTI)

    Kuppulingam, B. Singh, Shubra Baskar, K.

    2014-04-24

    Hexagonal Gallium Nitride (GaN) and Aluminum Gallium Nitride (AlGaN) nanoparticles were synthesized by sol-gel method using Ethylene Diamine Tetra Acetic acid (EDTA) complex route. Powder X-ray diffraction (PXRD) analysis confirms the hexagonal wurtzite structure of GaN and Al{sub 0.25}Ga{sub 0.75}N nanoparticles. Surface morphology and elemental analysis were carried out by Scanning Electron Microscope (SEM) and Energy Dispersive X-ray spectroscopy (EDX). The room temperature Photoluminescence (PL) study shows the near band edge emission for GaN at 3.35 eV and at 3.59 eV for AlGaN nanoparticles. The Aluminum (Al) composition of 20% has been obtained from PL emission around 345 nm.

  8. Simplified 2DEG carrier concentration model for composite barrier AlGaN/GaN HEMT

    SciTech Connect (OSTI)

    Das, Palash Biswas, Dhrubes

    2014-04-24

    The self consistent solution of Schrodinger and Poisson equations is used along with the total charge depletion model and applied with a novel approach of composite AlGaN barrier based HEMT heterostructure. The solution leaded to a completely new analytical model for Fermi energy level vs. 2DEG carrier concentration. This was eventually used to demonstrate a new analytical model for the temperature dependent 2DEG carrier concentration in AlGaN/GaN HEMT.

  9. Reactive codoping of GaAlInP compound semiconductors (Patent...

    Office of Scientific and Technical Information (OSTI)

    Patent: Reactive codoping of GaAlInP compound semiconductors Citation Details In-Document Search Title: Reactive codoping of GaAlInP compound semiconductors A GaAlInP compound ...

  10. AlGaN/GaN heterostructure prepared on a Si (110) substrate via pulsed sputtering

    SciTech Connect (OSTI)

    Watanabe, T.; Ohta, J.; Kondo, T.; Ohashi, M.; Ueno, K.; Kobayashi, A.; Fujioka, H.

    2014-05-05

    GaN films were grown on Si (110) substrates using a low-temperature growth technique based on pulsed sputtering. Reduction of the growth temperature suppressed the strain in the GaN films, leading to an increase in the critical thickness for crack formation. In addition, an AlGaN/GaN heterostructure with a flat heterointerface was prepared using this technique. Furthermore, the existence of a two dimensional electron gas at the heterointerface with a mobility of 1360 cm{sup 2}/Vs and a sheet carrier density of 1.3??10{sup 13}?cm{sup ?2} was confirmed. Finally, the use of the AlGaN/GaN heterostructure in a high electron mobility transistor was demonstrated. These results indicate that low-temperature growth via pulsed sputtering is quite promising for the fabrication of GaN-based electronic devices.

  11. Magnetic coupling in ferromagnetic semiconductor (Ga,Mn)As/(Al,Ga,Mn)As bilayers

    SciTech Connect (OSTI)

    Wang, M.; Wadley, P.; Campion, R. P.; Rushforth, A. W.; Edmonds, K. W.; Gallagher, B. L.; Charlton, T. R.; Kinane, C. J.; Langridge, S.

    2015-08-07

    We report on a study of ferromagnetic semiconductor (Ga,Mn)As/(Al,Ga,Mn)As bilayers using magnetometry and polarized neutron reflectivity (PNR). From depth-resolved characterization of the magnetic structure obtained by PNR, we concluded that the (Ga,Mn)As and (Al,Ga,Mn)As layers have in-plane and perpendicular-to-plane magnetic easy axes, respectively, with weak interlayer coupling. Therefore, the layer magnetizations align perpendicular to each other under low magnetic fields and parallel at high fields.

  12. AlGaAs/GaAs photovoltaic converters for high power narrowband radiation

    SciTech Connect (OSTI)

    Khvostikov, Vladimir; Kalyuzhnyy, Nikolay; Mintairov, Sergey; Potapovich, Nataliia; Shvarts, Maxim; Sorokina, Svetlana; Andreev, Viacheslav; Luque, Antonio

    2014-09-26

    AlGaAs/GaAs-based laser power PV converters intended for operation with high-power (up to 100 W/cm{sup 2}) radiation were fabricated by LPE and MOCVD techniques. Monochromatic (? = 809 nm) conversion efficiency up to 60% was measured at cells with back surface field and low (x = 0.2) Al concentration 'window'. Modules with a voltage of 4 V and the efficiency of 56% were designed and fabricated.

  13. Sheet resistance under Ohmic contacts to AlGaN/GaN heterostructures

    SciTech Connect (OSTI)

    Hajłasz, M.; Donkers, J. J. T. M.; Sque, S. J.; Heil, S. B. S.; Gravesteijn, D. J.; Rietveld, F. J. R.; Schmitz, J.

    2014-06-16

    For the determination of specific contact resistance in semiconductor devices, it is usually assumed that the sheet resistance under the contact is identical to that between the contacts. This generally does not hold for contacts to AlGaN/GaN structures, where an effective doping under the contact is thought to come from reactions between the contact metals and the AlGaN/GaN. As a consequence, conventional extraction of the specific contact resistance and transfer length leads to erroneous results. In this Letter, the sheet resistance under gold-free Ti/Al-based Ohmic contacts to AlGaN/GaN heterostructures on Si substrates has been investigated by means of electrical measurements, transmission electron microscopy, and technology computer-aided design simulations. It was found to be significantly lower than that outside of the contact area; temperature-dependent electrical characterization showed that it exhibits semiconductor-like behavior. The increase in conduction is attributed to n-type activity of nitrogen vacancies in the AlGaN. They are thought to form during rapid thermal annealing of the metal stack when Ti extracts nitrogen from the underlying semiconductor. The high n-type doping in the region between the metal and the 2-dimensional electron gas pulls the conduction band towards the Fermi level and enhances horizontal electron transport in the AlGaN. Using this improved understanding of the properties of the material underneath the contact, accurate values of transfer length and specific contact resistance have been extracted.

  14. Mismatch relaxation by stacking fault formation of AlN islands in AlGaN/GaN structures on m-plane GaN substrates

    SciTech Connect (OSTI)

    Smalc-Koziorowska, Julita; Sawicka, Marta; Skierbiszewski, Czeslaw; Grzegory, Izabella

    2011-08-08

    We study the mismatch relaxation of 2-5 nm thin elongated AlN islands formed during growth of AlGaN on bulk m-plane GaN by molecular beam epitaxy. The relaxation of these m-plane AlN layers is anisotropic and occurs through the introduction of stacking faults in [0001] planes during island coalescence, while no relaxation is observed along the perpendicular [1120] direction. This anisotropy in the mismatch relaxation and the formation of stacking faults in the AlN islands are explained by the growth mode of the AlN platelets and their coalescence along the [0001] direction.

  15. Structure and magnetic properties of Ce₃(Ni/Al/Ga)₁₁-A...

    Office of Scientific and Technical Information (OSTI)

    ...AlGa)-A new phase with the LaAl structure type Prev Next Title: Structure and magnetic properties of Ce(NiAlGa)-A new phase with the ...

  16. Composition profiling of GaAs/AlGaAs quantum dots grown by droplet epitaxy

    SciTech Connect (OSTI)

    Bocquel, J.; Koenraad, P. M.; Giddings, A. D.; Prosa, T. J.; Larson, D. J.; Mano, T.

    2014-10-13

    Droplet epitaxy (DE) is a growth method which can create III-V quantum dots (QDs) whose optoelectronic properties can be accurately controlled through the crystallisation conditions. In this work, GaAs/AlGaAs DE-QDs have been analyzed with the complimentary techniques of cross-sectional scanning tunneling microscopy and atom probe tomography. Structural details and a quantitative chemical analysis of QDs of different sizes are obtained. Most QDs were found to be pure GaAs, while a small proportion exhibited high intermixing caused by a local etching process. Large QDs with a high aspect ratio were observed to have an Al-rich crown above the GaAs QD. This structure is attributed to differences in mobility of the cations during the capping phase of the DE growth.

  17. AlGaAs diode pumped tunable chromium lasers

    DOE Patents [OSTI]

    Krupke, William F.; Payne, Stephen A.

    1992-01-01

    An all-solid-state laser system is disclosed wherein the laser is pumped in the longwave wing of the pump absorption band. By utilizing a laser material that will accept unusually high dopant concentrations without deleterious effects on the crystal lattice one is able to compensate for the decreased cross section in the wing of the absorption band, and the number of pump sources which can be used with such a material increases correspondingly. In a particular embodiment a chromium doped colquiriite-structure crystal such as Cr:LiSrAlF.sub.6 is the laser material. The invention avoids the problems associated with using AlGaInP diodes by doping the Cr:LiSrAlF.sub.6 heavily to enable efficient pumping in the longwave wing of the absorption band with more practical AlGaAs diodes.

  18. 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.

  19. Degradation mechanisms of Ti/Al/Ni/Au-based Ohmic contacts on AlGaN/GaN HEMTs

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

    Hwang, Ya-Hsi; Ahn, Shihyun; Dong, Chen; Zhu, Weidi; Kim, Byung-Jae; Le, Lingcong; Ren, Fan; Lind, Aaron G.; Dahl, James; Jones, Kevin S.; et al

    2015-04-27

    We investigated the degradation mechanism of Ti/Al/Ni/Au-based Ohmic metallization on AlGaN/GaN high electron mobility transistors upon exposure to buffer oxide etchant (BOE). The major effect of BOE on the Ohmic metal was an increase of sheet resistance from 2.89 to 3.69 Ω/ₜafter 3 min BOE treatment. The alloyed Ohmic metallization consisted 3–5 μm Ni-Al alloy islands surrounded by Au-Al alloy-rings. The morphology of both the islands and ring areas became flatter after BOE etching. Lastly, we used energy dispersive x-ray analysis and Auger electron microscopy to analyze the compositions and metal distributions in the metal alloys prior to and aftermore » BOE exposure.« less

  20. Enhanced thermoelectric transport in modulation-doped GaN/AlGaN core/shell nanowires

    SciTech Connect (OSTI)

    Song, Erdong; Li, Qiming; Swartzentruber, Brian; Pan, Wei; Wang, George T.; Martinez, Julio A.

    2015-11-25

    The thermoelectric properties of unintentionally n-doped core GaN/AlGaN core/shell N-face nanowires are reported. We found that the temperature dependence of the electrical conductivity is consistent with thermally activated carriers with two distinctive donor energies. The Seebeck coefficient of GaN/AlGaN nanowires is more than twice as large as that for the GaN nanowires alone. However, an outer layer of GaN deposited onto the GaN/AlGaN core/shell nanowires decreases the Seebeck coefficient at room temperature, while the temperature dependence of the electrical conductivity remains the same. We attribute these observations to the formation of an electron gas channel within the heavily-doped GaN core of the GaN/AlGaN nanowires. The room-temperature thermoelectric power factor for the GaN/AlGaN nanowires can be four times higher than the GaN nanowires. As a result, selective doping in bandgap engineered core/shell nanowires is proposed for enhancing the thermoelectric power.

  1. Enhanced thermoelectric transport in modulation-doped GaN/AlGaN core/shell nanowires

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

    Song, Erdong; Li, Qiming; Swartzentruber, Brian; Pan, Wei; Wang, George T.; Martinez, Julio A.

    2015-11-25

    The thermoelectric properties of unintentionally n-doped core GaN/AlGaN core/shell N-face nanowires are reported. We found that the temperature dependence of the electrical conductivity is consistent with thermally activated carriers with two distinctive donor energies. The Seebeck coefficient of GaN/AlGaN nanowires is more than twice as large as that for the GaN nanowires alone. However, an outer layer of GaN deposited onto the GaN/AlGaN core/shell nanowires decreases the Seebeck coefficient at room temperature, while the temperature dependence of the electrical conductivity remains the same. We attribute these observations to the formation of an electron gas channel within the heavily-doped GaN coremore » of the GaN/AlGaN nanowires. The room-temperature thermoelectric power factor for the GaN/AlGaN nanowires can be four times higher than the GaN nanowires. As a result, selective doping in bandgap engineered core/shell nanowires is proposed for enhancing the thermoelectric power.« less

  2. Electron tunneling spectroscopy study of electrically active traps in AlGaN/GaN high electron mobility transistors

    SciTech Connect (OSTI)

    Yang, Jie Cui, Sharon; Ma, T. P.; Hung, Ting-Hsiang; Nath, Digbijoy; Krishnamoorthy, Sriram; Rajan, Siddharth

    2013-11-25

    We investigate the energy levels of electron traps in AlGaN/GaN high electron mobility transistors by the use of electron tunneling spectroscopy. Detailed analysis of a typical spectrum, obtained in a wide gate bias range and with both bias polarities, suggests the existence of electron traps both in the bulk of AlGaN and at the AlGaN/GaN interface. The energy levels of the electron traps have been determined to lie within a 0.5?eV band below the conduction band minimum of AlGaN, and there is strong evidence suggesting that these traps contribute to Frenkel-Poole conduction through the AlGaN barrier.

  3. High-field quasi-ballistic transport in AlGaN/GaN heterostructures

    SciTech Connect (OSTI)

    Danilchenko, B. A.; Tripachko, N. A.; Belyaev, A. E.; Vitusevich, S. A. Hardtdegen, H.; Lth, H.

    2014-02-17

    Mechanisms of electron transport formation in 2D conducting channels of AlGaN/GaN heterostructures in extremely high electric fields at 4.2?K have been studied. Devices with a narrow constriction for the current flow demonstrate high-speed electron transport with an electron velocity of 6.8??10{sup 7}?cm/s. Such a velocity is more than two times higher than values reported for conventional semiconductors and about 15% smaller than the limit value predicted for GaN. Superior velocity is attained in the channel with considerable carrier reduction. The effect is related to a carrier runaway phenomenon. The results are in good agreement with theoretical predictions for GaN-based materials.

  4. Enhanced sheet carrier densities in polarization controlled AlInN/AlN/GaN/InGaN field-effect transistor on Si (111)

    SciTech Connect (OSTI)

    Hennig, J. Dadgar, A.; Witte, H.; Bläsing, J.; Lesnik, A.; Strittmatter, A.; Krost, A.

    2015-07-15

    We report on GaN based field-effect transistor (FET) structures exhibiting sheet carrier densities of n = 2.9 10{sup 13} cm{sup −2} for high-power transistor applications. By grading the indium-content of InGaN layers grown prior to a conventional GaN/AlN/AlInN FET structure control of the channel width at the GaN/AlN interface is obtained. The composition of the InGaN layer was graded from nominally x{sub In} = 30 % to pure GaN just below the AlN/AlInN interface. Simulations reveal the impact of the additional InGaN layer on the potential well width which controls the sheet carrier density within the channel region of the devices. Benchmarking the In{sub x}Ga{sub 1−x}N/GaN/AlN/Al{sub 0.87}In{sub 0.13}N based FETs against GaN/AlN/AlInN FET reference structures we found increased maximum current densities of I{sub SD} = 1300 mA/mm (560 mA/mm). In addition, the InGaN layer helps to achieve broader transconductance profiles as well as reduced leakage currents.

  5. Reactive codoping of GaAlInP compound semiconductors (Patent...

    Office of Scientific and Technical Information (OSTI)

    This site is a product of DOE's Office of Scientific and Technical Information (OSTI) and ... A GaAlInP compound semiconductor and a method of producing a GaAlInP compound ...

  6. AlGaAs/InGaAlP tunnel junctions for multijunction solar cells

    SciTech Connect (OSTI)

    SHARPS,P.R.; LI,N.Y.; HILLS,J.S.; HOU,H.; CHANG,PING-CHIH; BACA,ALBERT G.

    2000-05-16

    Optimization of GaInP{sub 2}/GaAs dual and GaInP{sub 2}/GaAs/Ge triple junction cells, and development of future generation monolithic multi-junction cells will involve the development of suitable high bandgap tunnel junctions. There are three criteria that a tunnel junction must meet. First, the resistance of the junction must be kept low enough so that the series resistance of the overall device is not increased. For AMO, 1 sun operation, the tunnel junction resistance should be below 5 x 10{sup {minus}2} {Omega}-cm. Secondly, the peak current density for the tunnel junction must also be larger than the J{sub sc} of the cell so that the tunnel junction I-V curve does not have a deleterious effect on the I-V curve of the multi-junction device. Finally, the tunnel junction must be optically transparent, i.e., there must be a minimum of optical absorption of photons that will be collected by the underlying subcells. The paper reports the investigation of four high bandgap tunnel junctions grown by metal-organic chemical vapor deposition.

  7. Lateral and Vertical Transistors Using the AlGaN/GaN Heterostructure

    SciTech Connect (OSTI)

    Chowdhury, S; Mishra, UK

    2013-10-01

    Power conversion losses are endemic in all areas of electricity consumption, including motion control, lighting, air conditioning, and information technology. Si, the workhorse of the industry, has reached its material limits. Increasingly, the lateral AlGaN/GaN HEMT based on gallium nitride (GaN-on-Si) is becoming the device of choice for medium power electronics as it enables high-power conversion efficiency and reduced form factor at attractive pricing for wide market penetration. The reduced form factor enabled by high-efficiency operation at high frequency further enables significant system price reduction because of savings in bulky extensive passive elements and heat sink costs. The high-power market, however, still remains unaddressed by lateral GaN devices. The current and voltage demand for high power conversion application makes the chip area in a lateral topology so large that it becomes more difficult to manufacture. Vertical GaN devices would play a big role alongside of silicon carbide (SiC) to address the high power conversion needs. In this paper, the development, performance, and status of lateral and vertical GaN devices are discussed.

  8. Strain dependence on polarization properties of AlGaN and AlGaN-based ultraviolet lasers grown on AlN substrates

    SciTech Connect (OSTI)

    Bryan, Zachary Bryan, Isaac; Sitar, Zlatko; Collazo, Ramn; Mita, Seiji; Tweedie, James

    2015-06-08

    Since the band ordering in AlGaN has a profound effect on the performance of UVC light emitting diodes (LEDs) and even determines the feasibility of surface emitting lasers, the polarization properties of emitted light from c-oriented AlGaN and AlGaN-based laser structures were studied over the whole composition range, as well as various strain states, quantum confinements, and carrier densities. A quantitative relationship between the theoretical valence band separation, determined using kp theory, and the experimentally measured degree of polarization is presented. Next to composition, strain was found to have the largest influence on the degree of polarization while all other factors were practically insignificant. The lowest crossover point from the transverse electric to transverse magnetic polarized emission of 245?nm was found for structures pseudomorphically grown on AlN substrates. This finding has significant implications toward the efficiency and feasibility of surface emitting devices below this wavelength.

  9. Integrating AlGaN/GaN high electron mobility transistor with Si: A comparative study of integration schemes

    SciTech Connect (OSTI)

    Mohan, Nagaboopathy; Raghavan, Srinivasan; Manikant,; Soman, Rohith

    2015-10-07

    AlGaN/GaN high electron mobility transistor stacks deposited on a single growth platform are used to compare the most common transition, AlN to GaN, schemes used for integrating GaN with Si. The efficiency of these transitions based on linearly graded, step graded, interlayer, and superlattice schemes on dislocation density reduction, stress management, surface roughness, and eventually mobility of the 2D-gas are evaluated. In a 500 nm GaN probe layer deposited, all of these transitions result in total transmission electron microscopy measured dislocations densities of 1 to 3 × 10{sup 9}/cm{sup 2} and <1 nm surface roughness. The 2-D electron gas channels formed at an AlGaN-1 nm AlN/GaN interface deposited on this GaN probe layer all have mobilities of 1600–1900 cm{sup 2}/V s at a carrier concentration of 0.7–0.9 × 10{sup 13}/cm{sup 2}. Compressive stress and changes in composition in GaN rich regions of the AlN-GaN transition are the most effective at reducing dislocation density. Amongst all the transitions studied the step graded transition is the one that helps to implement this feature of GaN integration in the simplest and most consistent manner.

  10. Chemical beam epitaxy growth of AlGaAs/GaAs tunnel junctions using trimethyl aluminium for multijunction solar cells

    SciTech Connect (OSTI)

    Paquette, B.; DeVita, M.; Turala, A.; Kolhatkar, G.; Boucherif, A.; Jaouad, A.; Aimez, V.; Ars, R.; Wilkins, M.; Wheeldon, J. F.; Walker, A. W.; Hinzer, K.; Fafard, S.

    2013-09-27

    AlGaAs/GaAs tunnel junctions for use in high concentration multijunction solar cells were designed and grown by chemical beam epitaxy (CBE) using trimethyl aluminium (TMA) as the p-dopant source for the AlGaAs active layer. Controlled hole concentration up to 4?10{sup 20} cm{sup ?3} was achieved through variation in growth parameters. Fabricated tunnel junctions have a peak tunneling current up to 6140 A/cm{sup 2}. These are suitable for high concentration use and outperform GaAs/GaAs tunnel junctions.

  11. Metal-interconnection-free integration of InGaN/GaN light emitting diodes with AlGaN/GaN high electron mobility transistors

    SciTech Connect (OSTI)

    Liu, Chao; Cai, Yuefei; Liu, Zhaojun; Ma, Jun; Lau, Kei May

    2015-05-04

    We report a metal-interconnection-free integration scheme for InGaN/GaN light emitting diodes (LEDs) and AlGaN/GaN high electron mobility transistors (HEMTs) by combining selective epi removal (SER) and selective epitaxial growth (SEG) techniques. SER of HEMT epi was carried out first to expose the bottom unintentionally doped GaN buffer and the sidewall GaN channel. A LED structure was regrown in the SER region with the bottom n-type GaN layer (n-electrode of the LED) connected to the HEMTs laterally, enabling monolithic integration of the HEMTs and LEDs (HEMT-LED) without metal-interconnection. In addition to saving substrate real estate, minimal interface resistance between the regrown n-type GaN and the HEMT channel is a significant improvement over metal-interconnection. Furthermore, excellent off-state leakage characteristics of the driving transistor can also be guaranteed in such an integration scheme.

  12. Strain-compensated (Ga,In)N/(Al,Ga)N/GaN multiple quantum wells for improved yellow/amber light emission

    SciTech Connect (OSTI)

    Lekhal, K.; Damilano, B. De Mierry, P.; Venngus, P.; Ngo, H. T.; Rosales, D.; Gil, B.; Hussain, S.

    2015-04-06

    Yellow/amber (570600?nm) emitting In{sub x}Ga{sub 1?x}N/Al{sub y}Ga{sub 1?y}N/GaN multiple quantum wells (QWs) have been grown by metal organic chemical vapor deposition on GaN-on- sapphire templates. When the (Al,Ga)N thickness of the barrier increases, the room temperature photoluminescence is red-shifted while its yield increases. This is attributed to an increase of the QW internal electric field and an improvement of the material quality due to the compensation of the compressive strain of the In{sub x}Ga{sub 1?x}N QWs by the Al{sub y}Ga{sub 1?y}N layers, respectively.

  13. Linear and nonlinear optical properties of GaAs/Al{sub x}Ga{sub 1?x}As/GaAs/Al{sub y}Ga{sub 1?y}As multi-shell spherical quantum dot

    SciTech Connect (OSTI)

    Emre Kavruk, Ahmet E-mail: aekavruk@gmail.com; Koc, Fatih; Sahin, Mehmet E-mail: mehsahin@gmail.com

    2013-11-14

    In this work, the optical properties of GaAs/Al{sub x}Ga{sub 1?x}As/GaAs/Al{sub y}Ga{sub 1?y}As multi-shell quantum dot heterostructure have been studied as a function of Al doping concentrations for cases with and without a hydrogenic donor atom. It has been observed that the absorption coefficient strength and/or resonant absorption wavelength can be adjusted by changing the Al content of inner-barrier and/or outer-barrier regions. Besides, it has been shown that the donor atom has an important effect on the control of the electronic and optical properties of the structure. The results have been presented as a function of the Al contents of the inner-barrier x and outer-barrier y regions and probable physical reasons have been discussed.

  14. Theoretical model of the polarization Coulomb field scattering in strained AlGaN/AlN/GaN heterostructure field-effect transistors

    SciTech Connect (OSTI)

    Luan, Chongbiao; Lin, Zhaojun Zhao, Jingtao; Wang, Yutang; Lv, Yuanjie; Chen, Hong; Wang, Zhanguo

    2014-07-28

    The theoretical model of the polarization Coulomb field scattering (PCF) caused by the polarization charge density variation at the AlGaN/AlN interface in strained AlGaN/AlN/GaN heterostructure field-effect transistors has been developed. And the theoretical values for the electron drift mobility, which were calculated using the Matthiessen's rule that includes PCF, piezoelectric scattering, polar optical-phonon scattering, and interface roughness scattering, are in good agreement with our experimental values. Therefore, the theoretical model for PCF has been confirmed.

  15. Room temperature spin transport in undoped (110) GaAs/AlGaAs quantum wells

    SciTech Connect (OSTI)

    Yokota, Nobuhide Aoshima, Yohei; Ikeda, Kazuhiro; Kawaguchi, Hitoshi

    2014-02-17

    We are reporting on our first observation of a micrometer-order electron spin transport in a (110) GaAs/AlGaAs multiple quantum well (QW) at room temperature using a space- and time-resolved Kerr rotation technique. A 37-μm transport was observed within an electron spin lifetime of 1.2 ns at room temperature when using an in-plane electric field of 1.75 kV/cm. The spatio-temporal profiles of electron spins were well reproduced by the spin drift-diffusion equations coupled with the Poisson equation, supporting the validity of the measurement. The results suggest that (110) QWs are useful as a spin transport layer for semiconductor spintronic devices operating at room temperature.

  16. Large linear magnetoresistance in a GaAs/AlGaAs heterostructure

    SciTech Connect (OSTI)

    Aamir, Mohammed Ali Goswami, Srijit Ghosh, Arindam; Baenninger, Matthias; Farrer, Ian; Ritchie, David A.; Tripathi, Vikram; Pepper, Michael

    2013-12-04

    We report non-saturating linear magnetoresistance (MR) in a two-dimensional electron system (2DES) at a GaAs/AlGaAs heterointerface in the strongly insulating regime. We achieve this by driving the gate voltage below the pinch-off point of the device and operating it in the non-equilibrium regime with high source-drain bias. Remarkably, the magnitude of MR is as large as 500% per Tesla with respect to resistance at zero magnetic field, thus dwarfing most non-magnetic materials which exhibit this linearity. Its primary advantage over most other materials is that both linearity and the enormous magnitude are retained over a broad temperature range (0.3 K to 10 K), thus making it an attractive candidate for cryogenic sensor applications.

  17. 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.

  18. Effect of Al-mole fraction in Al{sub x}Ga{sub 1−x}N grown by MOCVD

    SciTech Connect (OSTI)

    Jayasakthi, M. Ramesh, R. Prabakaran, K. Loganathan, R. Kuppulingam, B. Balaji, M. Arivazhagan, P. Sankaranarayanan, S. Singh, Shubra Baskar, K.

    2014-04-24

    AlGaN/AlN layers were grown by metalorganic chemical vapor deposition (MOCVD) on sapphire substrates. The Al{sub x}Ga{sub 1−x}N layer composition was varied from 15% to 25%. The crystalline quality, thickness and aluminum (Al) composition of AlGaN were determined using high resolution X-ray diffraction (HRXRD). The growth rate decreases on increasing Al composition. Reciprocal space mapping (RSM) was used to estimate the strain and relaxation between AlGaN and AlN. The optical properties of AlGaN layers were investigated by room temperature Photoluminescence (PL). The AlGaN peak shifts towards lower wavelength with Al composition. The surface morphology of AlGaN was studied by atomic force microscopy (AFM). Root mean square (RMS) roughness values were found to be increased in AlGaN layers with composition.

  19. Influence of strain induced by AlN nucleation layer on the electrical properties of AlGaN/GaN heterostructures on Si(111) substrate

    SciTech Connect (OSTI)

    Christy, Dennis; Watanabe, Arata; Egawa, Takashi

    2014-10-15

    The crack-free metal-organic chemical vapor deposition (MOCVD) grown AlGaN/GaN heterostructures on Si substrate with modified growth conditions of AlN nucleation layer (NL) and its influence on the electrical and structural properties of conductive GaN layer are presented. From the Hall electrical measurements, a gradual decrease of two-dimensional electron gas (2DEG) concentration near heterointerface as the function of NL thickness is observed possibly due to the reduction in difference of piezoelectric polarization charge densities between AlGaN and GaN layers. It also indicates that the minimum tensile stress and a relatively less total dislocation density for high pressure grown NL can ensure a 20 % increment in mobility at room temperature irrespective of the interface roughness. The thickness and pressure variations in NL and the subsequent changes in growth mode of AlN contributing to the post growth residual tensile stress are investigated using X-ray diffraction and Raman scattering experiments, respectively. The post growth intrinsic residual stress in top layers of heterostructures arises from lattice mismatches, NL parameters and defect densities in GaN. Hence, efforts to reduce the intrinsic residual stress in current conducting GaN layer give an opportunity to further improve the electrical characteristics of AlGaN/GaN device structures on Si.

  20. Influence of Growth Temperature on AlGaN Multi-Quantum Well Point...

    Office of Scientific and Technical Information (OSTI)

    Influence of Growth Temperature on AlGaN Multi-Quantum Well Point Defect Incorporation and Photoluminescence Efficiency. Citation Details In-Document Search Title: Influence of ...

  1. Relaxation of compressively strained AlGaN by inclined threading...

    Office of Scientific and Technical Information (OSTI)

    Journal Article: Relaxation of compressively strained AlGaN by inclined threading dislocations. Citation Details ... Publication Date: 2005-06-01 OSTI Identifier: 973648 Report ...

  2. Study of the effects of GaN buffer layer quality on the dc characteristics of AlGaN/GaN high electron mobility transistors

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

    Ahn, Shihyun; Zhu, Weidi; Dong, Chen; Le, Lingcong; Hwang, Ya-Hsi; Kim, Byung-Jae; Ren, Fan; Pearton, Stephen J.; Lind, Aaron G.; Jones, Kevin S.; et al

    2015-04-21

    Here we studied the effect of buffer layer quality on dc characteristics of AlGaN/GaN high electron mobility (HEMTs). AlGaN/GaN HEMT structures with 2 and 5 μm GaN buffer layers on sapphire substrates from two different vendors with the same Al concentration of AlGaN were used. The defect densities of HEMT structures with 2 and 5 μm GaN buffer layer were 7 × 109 and 5 × 108 cm₋2, respectively, as measured by transmission electron microscopy. There was little difference in drain saturation current or in transfer characteristics in HEMTs on these two types of buffer. However, there was no dispersionmore » observed on the nonpassivated HEMTs with 5 μm GaN buffer layer for gate-lag pulsed measurement at 100 kHz, which was in sharp contrast to the 71% drain current reduction for the HEMT with 2 μm GaN buffer layer.« less

  3. Effects of high-temperature AIN buffer on the microstructure of AlGaN/GaN HEMTs

    SciTech Connect (OSTI)

    Coerekci, S.; Oeztuerk, M. K.; Yu, Hongbo; Cakmak, M.; Oezcelik, S.; Oezbay, E.

    2013-06-15

    Effects on AlGaN/GaN high-electron-mobility transistor structure of a high-temperature AlN buffer on sapphire substrate have been studied by high-resolution x-ray diffraction and atomic force microscopy techniques. The buffer improves the microstructural quality of GaN epilayer and reduces approximately one order of magnitude the edge-type threading dislocation density. As expected, the buffer also leads an atomically flat surface with a low root-mean-square of 0.25 nm and a step termination density in the range of 10{sup 8} cm{sup -2}. Due to the high-temperature buffer layer, no change on the strain character of the GaN and AlGaN epitaxial layers has been observed. Both epilayers exhibit compressive strain in parallel to the growth direction and tensile strain in perpendicular to the growth direction. However, an high-temperature AlN buffer layer on sapphire substrate in the HEMT structure reduces the tensile stress in the AlGaN layer.

  4. Enhanced optical property in quaternary GaInAsSb/AlGaAsSb quantum wells

    SciTech Connect (OSTI)

    Lin, Chien-Hung Lee, Chien-Ping

    2014-10-21

    High quality GaInAsSb/AlGaAsSb quantum wells (QWs) have been grown by molecular beam epitaxy using proper interface treatments. By controlling the group-V elements at interfaces, we obtained excellent optical quality QWs, which were free from undesired localized trap states, which may otherwise severely affect the exciton recombination. Strong and highly efficient exciton emissions up to room temperature with a wavelength of 2.2 μm were observed. A comprehensive investigation on the QW quality was carried out using temperature dependent and power dependent photoluminescence (PL) measurements. The PL emission intensity remains nearly constant at low temperatures and is free from the PL quenching from the defect induced localized states. The temperature dependent emission energy had a bulk-like behavior, indicating high quality well/barrier interfaces. Because of the uniformity of the QWs and smooth interfaces, the low temperature limit of inhomogeneous line width broadening is as small as 5 meV.

  5. High Quantum Efficiency AlGaN/InGaN Photodetectors

    SciTech Connect (OSTI)

    Buckley, James H; Leopold, Daniel

    2009-11-24

    High efficiency photon counting detectors in use today for high energy particle detection applications have a significant spectral mismatch with typical sources and have a number of practical problems compared with conventional bialkali photomultiplier tubes. Numerous high energy physics experiments that employ scintillation light detectors or Cherenkov detectors would benefit greatly from photomultipliers with higher quantum efficiencies. The need for extending the sensitivity of photon detectors to the blue and UV wavebands comes from the fact that both Cherenkov light and some scintillators have an emission spectrum which is peaked at short wavelengths. This research involves the development of high quantum efficiency, high gain, UV/blue photon counting detectors based on AlGaN/InGaN photocathode heterostructures grown by molecular beam epitaxy (MBE). The work could eventually lead to nearly ideal light detectors with a number of distinct advantages over existing technologies for numerous applications in high-energy physics and particle astrophysics. Potential advantages include much lower noise detection, better stability and radiation resistance than other cathode structures, very low radioactive background levels for deep underground experiments and high detection efficiency of individual UV-visible photons. We are also working on the development of photocathodes with intrinsic gain, initially improving the detection efficiency of hybrid semiconductor-vacuum tube devices, and eventually leading to an all-solid-state photomultiplier device.

  6. Effects of light illumination on electron velocity of AlGaN/GaN heterostructures under high electric field

    SciTech Connect (OSTI)

    Guo, Lei; Yang, Xuelin Cheng, Jianpeng; Sang, Ling; Xu, Fujun; Tang, Ning; Feng, Zhihong; Lv, Yuanjie; Wang, Xinqiang; Shen, B.; Ge, Weikun

    2014-12-15

    We have investigated the variation of electron velocity in AlGaN/GaN heterostructures depending on illuminating light intensity and wavelength. It is shown that the electron velocity at high electric field increases under above-band light illumination. This electron velocity enhancement is found to be related to the photo-generated cold holes which interact with hot electrons and thus accelerate the energy relaxation at high electric field. The results suggest an alternative way to improve the electron energy relaxation rate and hence the electron velocity in GaN based heterostructures.

  7. Electron density and currents of AlN/GaN high electron mobility transistors with thin GaN/AlN buffer layer

    SciTech Connect (OSTI)

    Bairamis, A.; Zervos, Ch.; Georgakilas, A.; Adikimenakis, A.; Kostopoulos, A.; Kayambaki, M.; Tsagaraki, K.; Konstantinidis, G.

    2014-09-15

    AlN/GaN high electron mobility transistor (HEMT) structures with thin GaN/AlN buffer layer have been analyzed theoretically and experimentally, and the effects of the AlN barrier and GaN buffer layer thicknesses on two-dimensional electron gas (2DEG) density and transport properties have been evaluated. HEMT structures consisting of [300?nm GaN/ 200?nm AlN] buffer layer on sapphire were grown by plasma-assisted molecular beam epitaxy and exhibited a remarkable agreement with the theoretical calculations, suggesting a negligible influence of the crystalline defects that increase near the heteroepitaxial interface. The 2DEG density varied from 6.8??10{sup 12} to 2.1 10{sup 13} cm{sup ?2} as the AlN barrier thickness increased from 2.2 to 4.5?nm, while a 4.5?nm AlN barrier would result to 3.1??10{sup 13} cm{sup ?2} on a GaN buffer layer. The 3.0?nm AlN barrier structure exhibited the highest 2DEG mobility of 900?cm{sup 2}/Vs for a density of 1.3??10{sup 13} cm{sup ?2}. The results were also confirmed by the performance of 1??m gate-length transistors. The scaling of AlN barrier thickness from 1.5?nm to 4.5?nm could modify the drain-source saturation current, for zero gate-source voltage, from zero (normally off condition) to 0.63?A/mm. The maximum drain-source current was 1.1?A/mm for AlN barrier thickness of 3.0?nm and 3.7?nm, and the maximum extrinsic transconductance was 320 mS/mm for 3.0?nm AlN barrier.

  8. Stimulated emission and optical gain in AlGaN heterostructures grown on bulk AlN substrates

    SciTech Connect (OSTI)

    Guo, Wei Bryan, Zachary; Kirste, Ronny; Bryan, Isaac; Hussey, Lindsay; Bobea, Milena; Haidet, Brian; Collazo, Ramn; Sitar, Zlatko; Xie, Jinqiao; Mita, Seiji; Gerhold, Michael

    2014-03-14

    Optical gain spectra for ?250?nm stimulated emission were compared in three different AlGaN-based structures grown on single crystalline AlN substrates: a single AlGaN film, a double heterostructure (DH), and a Multiple Quantum Well (MQW) structure; respective threshold pumping power densities of 700, 250, and 150?kW/cm{sup 2} were observed. Above threshold, the emission was transverse-electric polarized and as narrow as 1.8?nm without a cavity. The DH and MQW structures showed gain values of 5060?cm{sup ?1} when pumped at 1?MW/cm{sup 2}. The results demonstrated the excellent optical quality of the AlGaN-based heterostructures grown on AlN substrates and their potential for realizing electrically pumped sub-280?nm laser diodes.

  9. High internal quantum efficiency in AlGaN multiple quantum wells grown on bulk AlN substrates

    SciTech Connect (OSTI)

    Bryan, Zachary Bryan, Isaac; Sitar, Zlatko; Collazo, Ramn; Xie, Jinqiao; Mita, Seiji

    2015-04-06

    The internal quantum efficiency (IQE) of Al{sub 0.55}Ga{sub 0.45}N/AlN and Al{sub 0.55}Ga{sub 0.45}N/Al{sub 0.85}Ga{sub 0.15}N UVC MQW structures was analyzed. The use of bulk AlN substrates enabled us to undoubtedly distinguish the effect of growth conditions, such as V/III ratio, on the optical quality of AlGaN based MQWs from the influence of dislocations. At a high V/III ratio, a record high IQE of ?80% at a carrier density of 10{sup 18?}cm{sup ?3} was achieved at ?258?nm. The high IQE was correlated with the decrease of the non-radiative coefficient A and a reduction of midgap defect luminescence, all suggesting that, in addition to dislocations, point defects are another major factor that strongly influences optical quality of AlGaN MQW structures.

  10. Degradation mechanisms of 2 MeV proton irradiated AlGaN/GaN HEMTs

    SciTech Connect (OSTI)

    Greenlee, Jordan D. Anderson, Travis J.; Koehler, Andrew D.; Weaver, Bradley D.; Kub, Francis J.; Hobart, Karl D.; Specht, Petra; Dubon, Oscar D.; Luysberg, Martina; Weatherford, Todd R.

    2015-08-24

    Proton-induced damage in AlGaN/GaN HEMTs was investigated using energy-dispersive X-ray spectroscopy (EDS) and transmission electron microscopy (TEM), and simulated using a Monte Carlo technique. The results were correlated to electrical degradation using Hall measurements. It was determined by EDS that the interface between GaN and AlGaN in the irradiated HEMT was broadened by 2.2 nm, as estimated by the width of the Al EDS signal compared to the as-grown interface. The simulation results show a similar Al broadening effect. The extent of interfacial roughening was examined using high resolution TEM. At a 2 MeV proton fluence of 6 × 10{sup 14} H{sup +}/cm{sup 2}, the electrical effects associated with the Al broadening and surface roughening include a degradation of the ON-resistance and a decrease in the electron mobility and 2DEG sheet carrier density by 28.9% and 12.1%, respectively.

  11. Epitaxial growth of aluminum nitride on AlGaN by reactive sputtering at low temperature

    SciTech Connect (OSTI)

    Duquenne, C.; Djouadi, M. A.; Tessier, P. Y.; Jouan, P. Y.; Besland, M. P.; Brylinski, C.; Aubry, R.; Delage, S.

    2008-08-04

    We report the synthesis of 1 {mu}m thick single crystalline aluminum nitride films by dc magnetron sputtering on AlGaN/GaN layer grown on sapphire substrate at low temperature (substrate temperature <250 deg. C). The microstructure of c-axis oriented AlN films deposited on Si (100) and AlGaN <0001> substrates was studied by x-ray diffraction, selected area electron diffraction, and transmission electron microscopy. The optimization of process parameters, involving low energetic ion bombardment on film surface (20-30 eV) during the growth, leads to an increase in the surface mobility and thus promotes AlN epitaxial growth on AlGaN substrate at 250 deg. C.

  12. An electrically injected AlGaN nanowire laser operating in the ultraviolet-C band

    SciTech Connect (OSTI)

    Zhao, S.; Liu, X.; Kang, J.; Mi, Z.; Woo, S. Y.; Botton, G. A.

    2015-07-27

    We have investigated the molecular beam epitaxial growth and characterization of nearly defect-free AlGaN nanowire heterostructures grown directly on Si substrate. By exploiting the Anderson localization of light, we have demonstrated electrically injected AlGaN nanowire lasers that can operate at 262.1 nm. The threshold current density is 200 A/cm{sup 2} at 77 K. The relatively low threshold current is attributed to the high Q-factor of the random cavity and the three-dimensional quantum confinement offered by the atomic-scale composition modulation in self-organized AlGaN nanowires.

  13. AlGaAs converters and arrays for laser power beaming

    SciTech Connect (OSTI)

    Khvostikov, Vladimir Sorokina, Svetlana; Potapovich, Nataliia; Khvostikova, Olga; Shvarts, Maxim; Timoshina, Nailya; Andreev, Viacheslav

    2015-09-28

    This study reports on the development of AlGaAs/GaAs-based laser power photovoltaic (PV) converters fabricated by LPE. The monochromatic (λ = 809 nm) conversion efficiency up to 58% is measured for cells with p-n junction in Al{sub 0.07}Ga{sub 0.93}As and low (x = 0.25-0.3) Al concentration ‘window’. Modules, which have converters of low and high power laser radiation and the voltage of 4V, have been designed and fabricated. Comparison of output parameters measured at two different conditions (i.e., under flash lamp and laser beam) has been performed.

  14. Reliability of AlGaN/GaN high electron mobility transistors on low dislocation density bulk GaN substrate: Implications of surface step edges

    SciTech Connect (OSTI)

    Killat, N. E-mail: Martin.Kuball@bristol.ac.uk; Montes Bajo, M.; Kuball, M. E-mail: Martin.Kuball@bristol.ac.uk; Paskova, T.; Materials Science and Engineering Department, North Carolina State University, Raleigh, North Carolina 27695 ; Evans, K. R.; Leach, J.; Electrical and Computer Engineering Department, Virginia Commonwealth University, Richmond, Virginia 23284 ; Li, X.; Özgür, Ü.; Morkoç, H.; Chabak, K. D.; Crespo, A.; Gillespie, J. K.; Fitch, R.; Kossler, M.; Walker, D. E.; Trejo, M.; Via, G. D.; Blevins, J. D.

    2013-11-04

    To enable gaining insight into degradation mechanisms of AlGaN/GaN high electron mobility transistors, devices grown on a low-dislocation-density bulk-GaN substrate were studied. Gate leakage current and electroluminescence (EL) monitoring revealed a progressive appearance of EL spots during off-state stress which signify the generation of gate current leakage paths. Atomic force microscopy evidenced the formation of semiconductor surface pits at the failure location, which corresponds to the interaction region of the gate contact edge and the edges of surface steps.

  15. Terahertz intersubband absorption in non-polar m-plane AlGaN/GaN quantum wells

    SciTech Connect (OSTI)

    Edmunds, C.; Malis, O.; Shao, J.; Shirazi-HD, M.; Manfra, M. J.

    2014-07-14

    We demonstrate THz intersubband absorption (15.6–26.1 meV) in m-plane AlGaN/GaN quantum wells. We find a trend of decreasing peak energy with increasing quantum well width, in agreement with theoretical expectations. However, a blue-shift of the transition energy of up to 14 meV was observed relative to the calculated values. This blue-shift is shown to decrease with decreasing charge density and is, therefore, attributed to many-body effects. Furthermore, a ∼40% reduction in the linewidth (from roughly 8 to 5 meV) was obtained by reducing the total sheet density and inserting undoped AlGaN layers that separate the wavefunctions from the ionized impurities in the barriers.

  16. Microstructure of V-based ohmic contacts to AlGaN/GaN heterostructures at a reduced annealing temperature

    SciTech Connect (OSTI)

    Schmid, A. Schroeter, Ch.; Otto, R.; Heitmann, J.; Schuster, M.; Klemm, V.; Rafaja, D.

    2015-02-02

    Ohmic contacts with V/Al/Ni/Au and V/Ni/Au metalization schemes were deposited on AlGaN/GaN heterostructures. The dependence of the specific contact resistance on the annealing conditions and the V:Al thickness ratio was shown. For an optimized electrode stack, a low specific contact resistance of 8.9??10{sup ?6} ? cm{sup 2} was achieved at an annealing temperature of 650?C. Compared to the conventional Ti/Al/Ni/Au contact, this is a reduction of 150?K. The microstructure and contact formation at the AlGaN/metal interface were investigated by transmission electron microscopy including high-resolution micrographs and energy dispersive X-ray analysis. It was shown that for low-resistive contacts, the resistivity of the metalization has to be taken into account. The V:Al thickness ratio has an impact on the formation of different intermetallic phases and thus is crucial for establishing ohmic contacts at reduced annealing temperatures.

  17. Effect of proton irradiation energy on AlGaN/GaN metal-oxide semiconductor high electron mobility transistors

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

    Ahn, S.; Dong, C.; Zhu, W.; Kim, B. -j.; Hwang, Ya-Hsi; Ren, F.; Pearton, S. J.; Yang, Gwangseok; Kim, J.; Patrick, Erin; et al

    2015-08-18

    The effects of proton irradiation energy on dc characteristics of AlGaN/GaN metal-oxide semiconductor high electron mobility transistors (MOSHEMTs) using Al2O3 as the gate dielectric were studied. Al2O3/AlGaN/GaN MOSHEMTs were irradiated with a fixed proton dose of 5 × 1015 cm-2 at different energies of 5, 10, or 15 MeV. More degradation of the device dc characteristics was observed for lower irradiation energy due to the larger amount of nonionizing energy loss in the active region of the MOSHEMTs under these conditions. The reductions in saturation current were 95.3%, 68.3%, and 59.8% and reductions in maximum transconductance were 88%, 54.4%, andmore » 40.7% after 5, 10, and 15 MeV proton irradiation, respectively. Both forward and reverse gate leakage current were reduced more than one order of magnitude after irradiation. The carrier removal rates for the irradiation energies employed in this study were in the range of 127–289 cm-1. These are similar to the values reported for conventional metal-gate high-electron mobility transistors under the same conditions and show that the gate dielectric does not affect the response to proton irradiation for these energies.« less

  18. The Band Gap of AlGaN Alloys (Journal Article) | SciTech Connect

    Office of Scientific and Technical Information (OSTI)

    Journal Article: The Band Gap of AlGaN Alloys Citation Details In-Document Search Title: The Band ... Publication Date: 1999-01-29 OSTI Identifier: 3336 Report Number(s): ...

  19. Demonstration of isotype GaN/AlN/GaN heterobarrier diodes by NH{sub 3}-molecular beam epitaxy

    SciTech Connect (OSTI)

    Fireman, Micha N.; Browne, David A.; Mazumder, Baishakhi; Speck, James S.; Mishra, Umesh K.

    2015-05-18

    The results of vertical transport through nitride heterobarrier structures grown by ammonia molecular beam epitaxy are presented. Structures are designed with binary layers to avoid the effects of random alloy fluctuations in ternary nitride barriers. The unintentional incorporation of Ga in the AlN growth is investigated by atom probe tomography and is shown to be strongly dependent on both the NH{sub 3} flowrate and substrate temperature growth parameters. Once nominally pure AlN layer growth conditions are achieved, structures consisting of unintentionally doped (UID) GaN spacer layers adjacent to a nominally pure AlN are grown between two layers of n+ GaN, from which isotype diodes are fabricated. Varying the design parameters of AlN layer thickness, UID spacer layer thickness, and threading dislocation density show marked effects on the vertical transport characteristics of these structures. The lack of significant temperature dependence, coupled with Fowler-Nordheim and/or Milliken-Lauritsen analysis, point to a prevalently tunneling field emission mechanism through the AlN barrier. Once flatband conditions in the UID layer are achieved, electrons leave the barrier with significant energy. This transport mechanism is of great interest for applications in hot electron structures.

  20. Quaternary AlInGaN/InGaN quantum well on vicinal c-plane substrate for high emission intensity of green wavelengths

    SciTech Connect (OSTI)

    Park, Seoung-Hwan; Pak, Y. Eugene; Park, Chang Young; Mishra, Dhaneshwar; Yoo, Seung-Hyun; Cho, Yong-Hee Shim, Mun-Bo; Kim, Sungjin

    2015-05-14

    Electronic and optical properties of non-trivial semipolar AlInGaN/InGaN quantum well (QW) structures are investigated by using the multiband effective-mass theory and non-Markovian optical model. On vicinal c-plane GaN substrate miscut by a small angle (??AlInGaN/InGaN system is shown to have ?3 times larger spontaneous emission peak intensity than the conventional InGaN/GaN system at green wavelength. It is attributed to much larger optical matrix element of the quaternary AlInGaN/InGaN system, derived from the reduction of internal electric field induced by polarizations. This effect exceeds the performance-degrading factor of smaller quasi-Fermi-level separation for the quaternary AlInGaN/InGaN system than that for the conventional InGaN/GaN system. Results indicate that the use of quaternary III-nitride QWs on vicinal substrates may be beneficial in improving the performance of optical devices emitting green light.

  1. Current transient spectroscopy for trapping analysis on Au-free AlGaN/GaN Schottky barrier diode

    SciTech Connect (OSTI)

    Hu, J. Groeseneken, G.; Stoffels, S.; Lenci, S.; Venegas, R.; Decoutere, S.; Bakeroot, B.

    2015-02-23

    This paper presents a combined technique of high voltage off-state stress and current transient measurements to investigate the trapping/de-trapping characteristics of Au-free AlGaN/GaN Schottky barrier diodes. The device features a symmetric three-terminal structure with a central anode contact surrounded by two separate cathodes. Under the diode off-state stress conditions, the two separate cathodes were electrically shorted. The de-trapping dynamics was studied by monitoring the recovery of the two-dimensional electron gas (2DEG) current at different temperatures by applying 0.5?V at cathode 2 while grounding cathode 1. During the recovery, the anode contact acts as a sensor of changes in diode leakage current. This leakage variation was found to be mainly due to the barrier height variation. With this method, the energy level and capture cross section of different traps in the AlGaN/GaN Schottky barrier diode can be extracted. Furthermore, the physical location of different trapping phenomena is indicated by studying the variation of the diode leakage current during the recovery. We have identified two distinct trapping mechanisms: (i) electron trapping at the AlGaN surface in the vicinity of the Schottky contact which results in the leakage reduction (barrier height ?{sub B} increase) together with R{sub ON} degradation; (ii) the electron trapping in the GaN channel layer which partially depletes the 2DEG. The physical origin of the two different traps is discussed in the text.

  2. Strain relaxation in GaN/Al{sub x}Ga{sub 1-x}N superlattices grown by plasma-assisted molecular-beam epitaxy

    SciTech Connect (OSTI)

    Kotsar, Y.; Bellet-Amalric, E.; Das, A.; Monroy, E.; Sarigiannidou, E.

    2011-08-01

    We have investigated the misfit relaxation process in GaN/Al{sub x}Ga{sub 1-x}N (x = 0.1, 0.3, 0.44) superlattices (SL) deposited by plasma-assisted molecular beam epitaxy. The SLs under consideration were designed to achieve intersubband absorption in the mid-infrared spectral range. We have considered the case of growth on GaN (tensile stress) and on AlGaN (compressive stress) buffer layers, both deposited on GaN-on-sapphire templates. Using GaN buffer layers, the SL remains almost pseudomorphic for x = 0.1, 0.3, with edge-type threading dislocation densities below 9 x 10{sup 8} cm{sup -2} to 2 x 10{sup 9} cm{sup -2}. Increasing the Al mole fraction to 0.44, we observe an enhancement of misfit relaxation resulting in dislocation densities above 10{sup 10} cm{sup -2}. In the case of growth on AlGaN, strain relaxation is systematically stronger, with the corresponding increase in the dislocation density. In addition to the average relaxation trend of the SL, in situ measurements indicate a periodic fluctuation of the in-plane lattice parameter, which is explained by the different elastic response of the GaN and AlGaN surfaces to the Ga excess at the growth front. The results are compared with GaN/AlN SLs designed for near-infrared intersubband absorption.

  3. On the redox origin of surface trapping in AlGaN/GaN high electron mobility transistors

    SciTech Connect (OSTI)

    Gao, Feng; Chen, Di; Tuller, Harry L.; Thompson, Carl V.; Palacios, Toms

    2014-03-28

    Water-related redox couples in ambient air are identified as an important source of the surface trapping states, dynamic on-resistance, and drain current collapse in AlGaN/GaN high electron mobility transistors (HEMTs). Through in-situ X-ray photoelectron spectroscopy (XPS), direct signature of the water-related specieshydroxyl groups (OH) was found at the AlGaN surface at room temperature. It was also found that these species, as well as the current collapse, can be thermally removed above 200?C in vacuum conditions. An electron trapping mechanism based on the H{sub 2}O/H{sub 2} and H{sub 2}O/O{sub 2} redox couples is proposed to explain the 0.5?eV energy level commonly attributed to the surface trapping states. Finally, the role of silicon nitride passivation in successfully removing current collapse in these devices is explained by blocking the water molecules away from the AlGaN surface.

  4. OMVPE Growth of Quaternary (Al,Ga,In)N for UV Optoelectronics (title change from A)

    SciTech Connect (OSTI)

    HAN,JUNG; FIGIEL,JEFFREY J.; PETERSEN,GARY A.; MYERS JR.,SAMUEL M.; CRAWFORD,MARY H.; BANAS,MICHAEL ANTHONY; HEARNE,SEAN JOSEPH

    2000-01-18

    We report the growth and characterization of quaternary AlGaInN. A combination of photoluminescence (PL), high-resolution x-ray diffraction (XRD), and Rutherford backscattering spectrometry (RBS) characterizations enables us to explore the contours of constant PL peak energy and lattice parameter as functions of the quaternary compositions. The observation of room temperature PL emission at 351nm (with 20% Al and 5% In) renders initial evidence that the quaternary could be used to provide confinement for GaInN (and possibly GaN). AlGaInN/GrdnN MQW heterostructures have been grown; both XRD and PL measurements suggest the possibility of incorporating this quaternary into optoelectronic devices.

  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. Plasmonic terahertz detectors based on a high-electron mobility GaAs/AlGaAs heterostructure

    SciTech Connect (OSTI)

    Bia?ek, M. Witowski, A. M.; Grynberg, M.; ?usakowski, J.; Orlita, M.; Potemski, M.; Czapkiewicz, M.; Umansky, V.

    2014-06-07

    In order to characterize magnetic field (B) tunable THz plasmonic detectors, spectroscopy experiments were carried out at liquid helium temperatures and high magnetic fields on devices fabricated on a high electron mobility GaAs/AlGaAs heterostructure. The samples were either gated (the gate of a meander shape) or ungated. Spectra of a photovoltage generated by THz radiation were obtained as a function of B at a fixed THz excitation from a THz laser or as a function of THz photon frequency at a fixed B with a Fourier spectrometer. In the first type of measurements, the wave vector of magnetoplasmons excited was defined by geometrical features of samples. It was also found that the magnetoplasmon spectrum depended on the gate geometry which gives an additional parameter to control plasma excitations in THz detectors. Fourier spectra showed a strong dependence of the magnetoplasmon resonance amplitude on the conduction-band electron filling factor which was explained within a model of the electron gas heating with THz radiation. The study allows to define both the advantages and limitations of plasmonic devices based on high-mobility GaAs/AlGaAs heterostructures for THz detection at low temperatures and high magnetic fields.

  7. Compositionally graded relaxed AlGaN buffers on semipolar GaN for mid-ultraviolet emission

    SciTech Connect (OSTI)

    Young, Erin C.; Wu Feng; Haeger, Daniel A.; Nakamura, Shuji; Denbaars, Steven P.; Cohen, Daniel A.; Speck, James S.; Romanov, Alexey E.

    2012-10-01

    In this Letter, we report on the growth and properties of relaxed, compositionally graded Al{sub x}Ga{sub 1-x}N buffer layers on freestanding semipolar (2021) GaN substrates. Continuous and step compositional grades with Al concentrations up to x = 0.61 have been achieved, with emission wavelengths in the mid-ultraviolet region as low as 265 nm. Coherency stresses were relaxed progressively throughout the grades by misfit dislocation generation via primary (basal) slip and secondary (non-basal) slip systems. Threading dislocation densities in the final layers of the grades were less than 10{sup 6}/cm{sup 2} as confirmed by plan-view transmission electron microscopy and cathodoluminescence studies.

  8. Comparison of the degradation characteristics of AlON/InGaAs and Al{sub 2}O{sub 3}/InGaAs stacks

    SciTech Connect (OSTI)

    Palumbo, F. Krylov, I.; Eizenberg, M.

    2015-03-14

    In this paper, the degradation characteristics of MOS (Metal-Oxide-Semiconductor) stacks with Al{sub 2}O{sub 3}/AlON or Al{sub 2}O{sub 3} only as dielectric layers on InGaAs were studied. The dielectric nitrides are proposed as possible passivation layers to prevent InGaAs oxidation. At negative bias, it has been found out that the main contribution to the overall degradation of the gate oxide is dominated by the generation of positive charge in the gate oxide. This effect is pronounced in MOS stacks with Al{sub 2}O{sub 3}/AlON as dielectric, where we think the positive charge is mainly generated in the AlON interlayer. At positive bias, the degradation is dominated by buildup of negative charge due to electron trapping in pre-existing or stress-induced traps. For stress biases where the leakage currents are low, the changes in the electrical characteristics are dominated by electron-trapping into traps located in energy levels in the upper part of the semiconductor gap. For stress biases with higher leakage current levels, the electron trapping occurs in stress-induced traps increasing the shift of V{sub FB} towards positive bias. The overall results clearly show that the improvement of the high-k dielectric/InGaAs interface by introducing N into the Al-oxide does not necessarily mean an increase in the reliability of the MOS stack.

  9. Structure and scintillation yield of Ce-doped AlGa substituted yttrium garnet

    SciTech Connect (OSTI)

    Sidletskiy, Oleg; Kononets, Valerii; Lebbou, Kheirreddine; Neicheva, Svetlana; Voloshina, Olesya; Bondar, Valerii; Baumer, Vyacheslav; Belikov, Konstantin; Gektin, Alexander; Grinyov, Boris; Joubert, Marie-France

    2012-11-15

    Highlights: ? Range of Y{sub 3}(Al{sub 1?x}Ga{sub x}){sub 5}O{sub 12}:Ce solid solution crystals are grown from melt by the Czochralski method. ? Light yield of mixed crystals reaches 130% of the YAG:Ce value at x ? 0.4. ? ?1% of antisite defects is formed in YGG:Ce, but no evidence of this is obtained for the rest of crystals. -- Abstract: Structure and scintillation yield of Y{sub 3}(Al{sub 1?x}Ga{sub x}){sub 5}O{sub 12}:Ce solid solution crystals are studied. Crystals are grown from melt by the Czochralski method. Distribution of host cations in crystal lattice is determined. Quantity of antisite defects in crystals is evaluated using XRD and atomic emission spectroscopy data. Trend of light output at Al/Ga substitution in Y{sub 3}(Al{sub 1?x}Ga{sub x}){sub 5}O{sub 12}:Ce is determined for the first time. Light output in mixed crystals reaches 130% comparative to Ce-doped yttriumaluminum garnet. Luminescence properties at Al/Ga substitution are evaluated.

  10. Ultrasensitive detection of Hg{sup 2+} using oligonucleotide-functionalized AlGaN/GaN high electron mobility transistor

    SciTech Connect (OSTI)

    Cheng, Junjie; Li, Jiadong; Miao, Bin; Wu, Dongmin; Wang, Jine; Pei, Renjun; Wu, Zhengyan

    2014-08-25

    An oligonucleotide-functionalized ion sensitive AlGaN/GaN high electron mobility transistor (HEMT) was fabricated to detect trace amounts of Hg{sup 2+}. The advantages of ion sensitive AlGaN/GaN HEMT and highly specific binding interaction between Hg{sup 2+} and thymines were combined. The current response of this Hg{sup 2+} ultrasensitive transistor was characterized. The current increased due to the accumulation of Hg{sup 2+} ions on the surface by the highly specific thymine-Hg{sup 2+}-thymine recognition. The dynamic linear range for Hg{sup 2+} detection has been determined in the concentrations from 10{sup −14} to 10{sup −8} M and a detection limit below 10{sup −14} M level was estimated, which is the best result of AlGaN/GaN HEMT biosensors for Hg{sup 2+} detection till now.

  11. Electron heating due to microwave photoexcitation in the high mobility GaAs/AlGaAs two dimensional electron system

    SciTech Connect (OSTI)

    Ramanayaka, A. N.; Mani, R. G.; Wegscheider, W.

    2013-12-04

    We extract the electron temperature in the microwave photo-excited high mobility GaAs/AlGaAs two dimensional electron system (2DES) by studying the influence of microwave radiation on the amplitude of Shubnikov-de Haas oscillations (SdHOs) in a regime where the cyclotron frequency, ?{sub c}, and the microwave angular frequency, ?, satisfy 2? ? ?{sub c} ? 3.5? The results indicate that increasing the incident microwave power has a weak effect on the amplitude of the SdHOs and therefore the electron temperature, in comparison to the influence of modest temperature changes on the dark-specimen SdH effect. The results indicate negligible electron heating under modest microwave photo-excitation, in good agreement with theoretical predictions.

  12. 1.9 kV AlGaN/GaN Lateral Schottky Barrier Diodes on Silicon

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

    Zhu, Mingda; Song, Bo; Qi, Meng; Hu, Zongyang; Nomoto, Kazuki; Yan, Xiaodong; Cao, Yu; Johnson, Wayne; Kohn, Erhard; Jena, Debdeep; et al

    2015-02-16

    In this letter, we present AlGaN/GaN lateral Schottky barrier diodes on silicon with recessed anodes and dual field plates. A low specific on-resistance RON,SP (5.12 mΩ · cm2), a low turn-on voltage (<0.7 V) and a high reverse breakdown voltage BV (>1.9 kV), were simultaneously achieved in devices with a 25 μm anode/cathode separation, resulting in a power figure-of-merit (FOM) BV2/RON,SP of 727 MW·cm2. The record high breakdown voltage of 1.9 kV is attributed to the dual field plate structure.

  13. Study of the one dimensional electron gas arrays confined by steps in vicinal GaN/AlGaN heterointerfaces

    SciTech Connect (OSTI)

    Li, Huijie E-mail: sh-yyang@semi.ac.cn; Zhao, Guijuan; Liu, Guipeng; Wei, Hongyuan; Jiao, Chunmei; Yang, Shaoyan E-mail: sh-yyang@semi.ac.cn; Wang, Lianshan; Zhu, Qinsheng

    2014-05-21

    One dimensional electron gas (1DEG) arrays in vicinal GaN/AlGaN heterostructures have been studied. The steps at the interface would lead to the lateral barriers and limit the electron movement perpendicular to such steps. Through a self-consistent Schrdinger-Poisson approach, the electron energy levels and wave functions were calculated. It was found that when the total electron density was increased, the lateral barriers were lowered due to the screening effects by the electrons, and the electron gas became more two-dimension like. The calculated 1DEG densities were compared to the experimental values and good agreements were found. Moreover, we found that a higher doping density is more beneficial to form 1-D like electron gas arrays.

  14. 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.

  15. Al00.3Ga0.7N PN diode with breakdown voltage >1600 V

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

    Allerman, A. A.; Armstrong, A. M.; Fischer, A. J.; Dickerson, J. R.; Crawford, M. H.; King, M. P.; Moseley, M. W.; Wierer, J. J.; Kaplar, R. J.

    2016-07-21

    Demonstration of Al00.3Ga0.7N PN diodes grown with breakdown voltages in excess of 1600 V is reported. The total epilayer thickness is 9.1 μm and was grown by metal-organic vapour-phase epitaxy on 1.3-mm-thick sapphire in order to achieve crack-free structures. A junction termination edge structure was employed to control the lateral electric fields. A current density of 3.5 kA/cm2 was achieved under DC forward bias and a reverse leakage current <3 nA was measured for voltages <1200 V. The differential on-resistance of 16 mΩ cm2 is limited by the lateral conductivity of the n-type contact layer required by the front-surface contactmore » geometry of the device. An effective critical electric field of 5.9 MV/cm was determined from the epilayer properties and the reverse current–voltage characteristics. To our knowledge, this is the first aluminium gallium nitride (AlGaN)-based PN diode exhibiting a breakdown voltage in excess of 1 kV. Finally, we note that a Baliga figure of merit (Vbr2/Rspec,on) of 150 MW/cm2 found is the highest reported for an AlGaN PN diode and illustrates the potential of larger-bandgap AlGaN alloys for high-voltage devices.« less

  16. 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.

  17. Growth mechanisms of GaSb heteroepitaxial films on Si with an AlSb buffer layer

    SciTech Connect (OSTI)

    Vajargah, S. Hosseini; Botton, G. A.; Brockhouse Institute for Materials Research, McMaster University, Hamilton, Ontario L8S 4M1; Canadian Centre for Electron Microscopy, McMaster University, Hamilton, Ontario L8S 4M1 ; Ghanad-Tavakoli, S.; Preston, J. S.; Kleiman, R. N.; Centre for Emerging Device Technologies, McMaster University, Hamilton, Ontario L8S 4L7; Department of Engineering Physics, McMaster University, Hamilton, Ontario L8S 4L7

    2013-09-21

    The initial growth stages of GaSb epilayers on Si substrates and the role of the AlSb buffer layer were studied by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). Heteroepitaxy of GaSb and AlSb on Si both occur by Volmer-Weber (i.e., island mode) growth. However, the AlSb and GaSb islands have distinctly different characteristics as revealed through an atomic-resolution structural study using Z-contrast of HAADF-STEM imaging. While GaSb islands are sparse and three dimensional, AlSb islands are numerous and flattened. The introduction of 3D island-forming AlSb buffer layer facilitates the nucleation of GaSb islands. The AlSb islands-assisted nucleation of GaSb islands results in the formation of drastically higher quality planar film at a significantly smaller thickness of films. The interface of the AlSb and GaSb epilayers with the Si substrate was further investigated with energy dispersive X-ray spectrometry to elucidate the key role of the AlSb buffer layer in the growth of GaSb epilayers on Si substrates.

  18. Relaxation and critical strain for maximum In incorporation in AlInGaN on GaN grown by metal organic vapour phase epitaxy

    SciTech Connect (OSTI)

    Reuters, Benjamin; Finken, M.; Wille, A.; Kalisch, H.; Vescan, A.; Hollaender, B.; Heuken, M.

    2012-11-01

    Quaternary AlInGaN layers were grown on conventional GaN buffer layers on sapphire by metal organic vapour phase epitaxy at different surface temperatures and different reactor pressures with constant precursor flow conditions. A wide range in compositions within 30-62% Al, 5-29% In, and 23-53% Ga was covered, which leads to different strain states from high tensile to high compressive. From high-resolution x-ray diffraction and Rutherford backscattering spectrometry, we determined the compositions, strain states, and crystal quality of the AlInGaN layers. Atomic force microscopy measurements were performed to characterize the surface morphology. A critical strain value for maximum In incorporation near the AlInGaN/GaN interface is presented. For compressively strained layers, In incorporation is limited at the interface as residual strain cannot exceed an empirical critical value of about 1.1%. Relaxation occurs at about 15 nm thickness accompanied by strong In pulling. Tensile strained layers can be grown pseudomorphically up to 70 nm at a strain state of 0.96%. A model for relaxation in compressively strained AlInGaN with virtual discrete sub-layers, which illustrates the gradually changing lattice constant during stress reduction is presented.

  19. X-ray diffraction study of short-period AlN/GaN superlattices

    SciTech Connect (OSTI)

    Kyutt, R. N. Shcheglov, M. P.; Ratnikov, V. V.; Yagovkina, M. A.; Davydov, V. Yu.; Smirnov, A. N.; Rozhavskaya, M. M.; Zavarin, E. E.; Lundin, V. V.

    2013-12-15

    The structure of short-period hexagonal GaN/AlN superlattices (SLs) has been investigated by X-ray diffraction. The samples have been grown by metalorganic vapor-phase epitaxy (MOVPE) in a horizontal reactor at a temperature of 1050°C on (0001)Al{sub 2}O{sub 3} substrates using GaN and AlN buffer layers. The SL period changes from 2 to 6 nm, and the thickness of the structure varies in a range from 0.3 to 1 μm. The complex of X-ray diffraction techniques includes a measurement of θ-2θ rocking curves of symmetric Bragg reflection, the construction of intensity maps for asymmetric reflections, a measurement and analysis of peak broadenings in different diffraction geometries, a precise measurement of lattice parameters, and the determination of radii of curvature. The thickness and strain of separate SL layers are determined by measuring the θ-2θ rocking curves subsequent simulation. It is shown that most SL samples are completely relaxed as a whole. At the same time, relaxation is absent between sublayers, which is why strains in the AlN and GaN sublayers (on the order of 1.2 × 10{sup −2}) have different signs. An analysis of diffraction peak half-widths allows us to determine the densities of individual sets of dislocations and observe their change from buffer layers to SLs.

  20. ALD TiO2-Al2O3 Stack: An Improved Gate Dielectrics on Ga-polar GaN MOSCAPs

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

    Wei, Daming; Edgar, James H.; Briggs, Dayrl P.; Srijanto, Bernadeta R.; Retterer, Scott T.; Meyer, III, Harry M.

    2014-10-15

    This research focuses on the benefits and properties of TiO2-Al2O3 nano-stack thin films deposited on Ga2O3/GaN by plasma-assisted atomic layer deposition (PA-ALD) for gate dielectric development. This combination of materials achieved a high dielectric constant, a low leakage current, and a low interface trap density. Correlations were sought between the films’ structure, composition, and electrical properties. The gate dielectrics were approximately 15 nm thick and contained 5.1 nm TiO2, 7.1 nm Al2O3 and 2 nm Ga2O3 as determined by spectroscopic ellipsometry. The interface carbon concentration, as measured by x-ray photoelectron spectroscopy (XPS) depth profile, was negligible for GaN pretreated bymore » thermal oxidation in O2 for 30 minutes at 850°C. The RMS roughness slightly increased after thermal oxidation and remained the same after ALD of the nano-stack, as determined by atomic force microscopy. The dielectric constant of TiO2-Al2O3 on Ga2O3/GaN was increased to 12.5 compared to that of pure Al2O3 (8~9) on GaN. In addition, the nano-stack's capacitance-voltage (C-V) hysteresis was small, with a total trap density of 8.74 × 1011 cm-2. The gate leakage current density (J=2.81× 10-8 A/cm2) was low at +1 V gate bias. These results demonstrate the promising potential of plasma ALD deposited TiO2/Al2O3 for serving as the gate oxide on Ga2O3/GaN based MOS devices.« less

  1. Sulfuric acid and hydrogen peroxide surface passivation effects on AlGaN/GaN high electron mobility transistors

    SciTech Connect (OSTI)

    Zaidi, Z. H. Lee, K. B.; Qian, H.; Jiang, S.; Houston, P. A.; Guiney, I.; Wallis, D. J.; Humphreys, C. J.

    2014-12-28

    In this work, we have compared SiN{sub x} passivation, hydrogen peroxide, and sulfuric acid treatment on AlGaN/GaN HEMTs surface after full device fabrication on Si substrate. Both the chemical treatments resulted in the suppression of device pinch-off gate leakage current below 1??A/mm, which is much lower than that for SiN{sub x} passivation. The greatest suppression over the range of devices is observed with the sulfuric acid treatment. The device on/off current ratio is improved (from 10{sup 4}10{sup 5} to 10{sup 7}) and a reduction in the device sub-threshold (S.S.) slope (from ?215 to 90?mV/decade) is achieved. The sulfuric acid is believed to work by oxidizing the surface which has a strong passivating effect on the gate leakage current. The interface trap charge density (D{sub it}) is reduced (from 4.86 to 0.90??10{sup 12?}cm{sup ?2} eV{sup ?1}), calculated from the change in the device S.S. The gate surface leakage current mechanism is explained by combined Mott hopping conduction and Poole Frenkel models for both untreated and sulfuric acid treated devices. Combining the sulfuric acid treatment underneath the gate with the SiN{sub x} passivation after full device fabrication results in the reduction of D{sub it} and improves the surface related current collapse.

  2. Optical reflection and contactless electroreflection from GaAlAs layers with periodically arranged GaAs quantum wells

    SciTech Connect (OSTI)

    Chaldyshev, V. V. Shkol'nik, A. S.; Evtikhiev, V. P.; Holden, T.

    2006-12-15

    Optical reflection and electroreflection for the AlGaAs layers containing the periodically arranged GaAs quantum wells of different thickness are studied at photon energies ranging from 1 to 2 eV. It is established that the spectral dependence of the reflectance involves three different contributions made by (i) the reflection from the medium-air interface; (ii) the interference reflection due to the periodically modulated refractive index, since the materials of the wells and barriers have different refractive indices; and (iii) the reflection produced by the interaction of electromagnetic waves with the excition states in the quantum wells. Analysis of the reflection spectra shows that these contributions are characterized by different behavior with variations in temperature, angle of incidence of light, and polarization; however, quantitative separation of the spectra into individual contributions presents a rather difficult problem. To separate the contribution originating from the interaction of light with the exciton states from the optical spectra, a special approach based on contactless measurements of the optical electroreflectance over a certain spectral region is developed. It is shown that this method provides a means for determining the parameters of the exciton states in the quantum wells.

  3. Improving p-type doping efficiency in Al{sub 0.83}Ga{sub 0.17}N alloy substituted by nanoscale (AlN){sub 5}/(GaN){sub 1} superlattice with Mg{sub Ga}-O{sub N} δ-codoping: Role of O-atom in GaN monolayer

    SciTech Connect (OSTI)

    Zhong, Hong-xia; Shi, Jun-jie Jiang, Xin-he; Huang, Pu; Ding, Yi-min; Zhang, Min

    2015-01-15

    We calculate Mg-acceptor activation energy E{sub A} and investigate the influence of O-atom, occupied the Mg nearest-neighbor, on E{sub A} in nanoscale (AlN){sub 5}/(GaN){sub 1} superlattice (SL), a substitution for Al{sub 0.83}Ga{sub 0.17}N disorder alloy, using first-principles calculations. We find that the N-atom bonded with Ga-atom is more easily substituted by O-atom and nMg{sub Ga}-O{sub N} (n = 1-3) complexes are favorable and stable in the SL. The O-atom plays a dominant role in reducing E{sub A}. The shorter the Mg-O bond is, the smaller the E{sub A} is. The Mg-acceptor activation energy can be reduced significantly by nMg{sub Ga}-O{sub N} δ-codoping. Our calculated E{sub A} for 2Mg{sub Ga}-O{sub N} is 0.21 eV, and can be further reduced to 0.13 eV for 3Mg{sub Ga}-O{sub N}, which results in a high hole concentration in the order of 10{sup 20} cm{sup −3} at room temperature in (AlN){sub 5}/(GaN){sub 1} SL. Our results prove that nMg{sub Ga}-O{sub N} (n = 2,3) δ-codoping in AlN/GaN SL with ultrathin GaN-layer is an effective way to improve p-type doping efficiency in Al-rich AlGaN.

  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. 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.

  6. Properties of Cu(In,Ga,Al)Se{sub 2} thin films fabricated by magnetron sputtering

    SciTech Connect (OSTI)

    Hameed, Talaat A.; Cao, Wei; Mansour, Bahiga A.; Elzawaway, Inas K.; Abdelrazek, El-Metwally M.; Elsayed-Ali, Hani E.

    2015-05-15

    Cu(In,Ga,Al)Se{sub 2} (CIGAS) thin films were studied as an alternative absorber layer material to Cu(In{sub x}Ga{sub 1?x})Se{sub 2}. CIGAS thin films with varying Al content were prepared by magnetron sputtering on Si(100) and soda-lime glass substrates at 350?C, followed by postdeposition annealing at 520?C for 5 h in vacuum. The film composition was measured by an electron probe microanalyzer while the elemental depth profiles were determined by secondary ion mass spectrometry. X-ray diffraction studies indicated that CIGAS films are single phase with chalcopyrite structure and that the (112) peak clearly shifts to higher 2? values with increasing Al content. Scanning electron microscopy images revealed dense and well-defined grains, as well as sharp CIGAS/Si(100) interfaces for all films. Atomic force microscopy analysis indicated that the roughness of CIGAS films decreases with increasing Al content. The bandgap of CIGAS films was determined from the optical transmittance and reflectance spectra and was found to increase as Al content increased.

  7. Enhanced internal quantum efficiency and light extraction efficiency from textured GaN/AlGaN quantum wells grown by molecular beam epitaxy

    SciTech Connect (OSTI)

    Cabalu, J.S.; Thomidis, C.; Moustakas, T.D.; Riyopoulos, S.; Zhou Lin; Smith, David J.

    2006-03-15

    GaN/Al{sub 0.2}Ga{sub 0.8}N multiple quantum wells (MQWs) were grown by molecular beam epitaxy on randomly textured and atomically smooth (0001) GaN templates. Smooth and textured GaN templates were deposited on (0001) sapphire substrates by varying the III/V ratio and the substrate temperature during growth by the hydride vapor-phase epitaxy method. We find that the MQWs replicate the texture of the GaN template, which was found to have a Gaussian distribution. The peak photoluminescence intensity from the textured MQWs is always higher than from the smooth MQWs and for GaN (7 nm)/Al{sub 0.2}Ga{sub 0.8}N (8 nm) MQWs, it is 700 times higher than that from similarly produced MQWs on smooth GaN templates. This result is attributed partly to the enhancement in light extraction efficiency and partly to the enhancement in internal quantum efficiency. The origin of the increase in internal quantum efficiency is partly due to the reduction of the quantum-confined Stark effect, since the polarization vector intersects the quantum well (QW) planes at angles smaller than 90 deg. , and partly due to the charge redistribution in the QWs caused by the polarization component parallel to the planes of the QWs.

  8. FL J. Smith, Jr.

    Office of Legacy Management (LM)

    ct. B. Duillap (THPJJs L. Kassel) FL J. Smith, Jr. c c Kelley from R. 1. Cook, Kslley from R. 1. Cook, J J cit cit In accordawe with Secret memorandum dated October , 1951 ta IA. ...

  9. Thermal stability of the deep ultraviolet emission from AlGaN/AlN Stranski-Krastanov quantum dots

    SciTech Connect (OSTI)

    Himwas, C.; Songmuang, R.; Le Si Dang; Bleuse, J.; Monroy, E.; Rapenne, L.; Sarigiannidou, E.

    2012-12-10

    We report on the structural and optical properties of AlGaN/AlN quantum dot (QD) superlattices synthesized by plasma-assisted molecular-beam epitaxy. Modifying the composition and geometry of the QDs, the peak emission wavelength can be shifted from 320 nm to 235 nm while keeping the internal quantum efficiency larger than 30%. The efficient carrier confinement is confirmed by the stability of the photoluminescence (PL) intensity and decay time, from low temperature up to 100 K. Above this threshold, the PL intensity decreases and the radiative lifetime increases due to carrier thermalization. We also identified the intraband electronic transition between the ground level of the conduction band and the first excited state confined along the growth axis (s-p{sub z}).

  10. Aluminum nitride transitional layer for reducing dislocation density and cracking of AlGaN epitaxial films

    DOE Patents [OSTI]

    Allerman, Andrew A.; Crawford, Mary H.; Lee, Stephen R.

    2013-01-08

    A denticulated Group III nitride structure that is useful for growing Al.sub.xGa.sub.1-xN to greater thicknesses without cracking and with a greatly reduced threading dislocation (TD) density.

  11. Laser diodes with 353 nm wavelength enabled by reduced-dislocation-density AlGaN templates

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

    Crawford, Mary H.; Allerman, Andrew A.; Armstrong, Andrew M.; Smith, Michael L.; Cross, Karen C.

    2015-10-30

    We fabricated optically pumped and electrically injected ultraviolet (UV) lasers on reduced-threading-dislocation-density (reduced-TDD) AlGaN templates. The overgrowth of sub-micron-wide mesas in the Al0.32Ga0.68N templates enabled a tenfold reduction in TDD, to (2–3) × 108 cm–2. Optical pumping of AlGaN hetero-structures grown on the reduced-TDD templates yielded a low lasing threshold of 34 kW/cm2 at 346 nm. Room-temperature pulsed operation of laser diodes at 353 nm was demonstrated, with a threshold of 22.5 kA/cm2. Furthermore, reduced-TDD templates have been developed across the entire range of AlGaN compositions, presenting a promising approach for extending laser diodes into the deep UV.

  12. Laser diodes with 353 nm wavelength enabled by reduced-dislocation-density AlGaN templates

    SciTech Connect (OSTI)

    Crawford, Mary H.; Allerman, Andrew A.; Armstrong, Andrew M.; Smith, Michael L.; Cross, Karen C.

    2015-10-30

    We fabricated optically pumped and electrically injected ultraviolet (UV) lasers on reduced-threading-dislocation-density (reduced-TDD) AlGaN templates. The overgrowth of sub-micron-wide mesas in the Al0.32Ga0.68N templates enabled a tenfold reduction in TDD, to (2–3) × 108 cm–2. Optical pumping of AlGaN hetero-structures grown on the reduced-TDD templates yielded a low lasing threshold of 34 kW/cm2 at 346 nm. Room-temperature pulsed operation of laser diodes at 353 nm was demonstrated, with a threshold of 22.5 kA/cm2. Furthermore, reduced-TDD templates have been developed across the entire range of AlGaN compositions, presenting a promising approach for extending laser diodes into the deep UV.

  13. Material-dependent amorphization and epitaxial crystallization in ion-implanted AlAs/GaAs layer structures

    SciTech Connect (OSTI)

    Cullis, A.G.; Chew, N.G.; Whitehouse, C.R. ); Jacobson, D.C.; Poate, J.M.; Pearton, S.J.

    1989-09-18

    When AlAs/GaAs layer samples are subjected to Ar{sup +} ion bombardment at liquid-nitrogen temperature, it is shown that very different damage structures are produced in the two materials. While the GaAs is relatively easily amorphized, the AlAs is quite resistant to damage accumulation and remains crystalline for the ion doses employed in these investigations. Epitaxial regrowth of buried amorphous GaAs layers of thicknesses up to 150 nm can be induced by rapid thermal annealing. It is demonstrated that differences in the initial damage state have a strong influence upon the nature of lattice defects produced by annealing.

  14. Screening of the quantum-confined Stark effect in AlN/GaN nanowire superlattices by germanium doping

    SciTech Connect (OSTI)

    Hille, P. Mener, J.; Becker, P.; Teubert, J.; Schrmann, J.; Eickhoff, M.; Mata, M. de la; Rosemann, N.; Chatterjee, S.; Magn, C.; Arbiol, J.; Institucio Catalana de Recerca i Estudis Avanats , 08010 Barcelona, CAT

    2014-03-10

    We report on electrostatic screening of polarization-induced internal electric fields in AlN/GaN nanowire heterostructures with germanium-doped GaN nanodiscs embedded between AlN barriers. The incorporation of germanium at concentrations above 10{sup 20}?cm{sup 3} shifts the photoluminescence emission energy of GaN nanodiscs to higher energies accompanied by a decrease of the photoluminescence decay time. At the same time, the thickness-dependent shift in emission energy is significantly reduced. In spite of the high donor concentration, a degradation of the photoluminescence properties is not observed.

  15. Comparison of single junction AlGaInP and GaInP solar cells grown by molecular beam epitaxy

    SciTech Connect (OSTI)

    Masuda, Taizo Tomasulo, Stephanie; Lang, Jordan R.; Lee, Minjoo Larry

    2015-03-07

    We have investigated ∼2.0 eV (Al{sub x}Ga{sub 1−x}){sub 0.51}In{sub 0.49}P and ∼1.9 eV Ga{sub 0.51}In{sub 0.49}P single junction solar cells grown on both on-axis and misoriented GaAs substrates by molecular beam epitaxy (MBE). Although lattice-matched (Al{sub x}Ga{sub 1−x}){sub 0.51}In{sub 0.49}P solar cells are highly attractive for space and concentrator photovoltaics, there have been few reports on the MBE growth of such cells. In this work, we demonstrate open circuit voltages (V{sub oc}) ranging from 1.29 to 1.30 V for Ga{sub 0.51}In{sub 0.49}P cells, and 1.35–1.37 V for (Al{sub x}Ga{sub 1−x}){sub 0.51}In{sub 0.49}P cells. Growth on misoriented substrates enabled the bandgap-voltage offset (W{sub oc} = E{sub g}/q − V{sub oc}) of Ga{sub 0.51}In{sub 0.49}P cells to decrease from ∼575 mV to ∼565 mV, while that of (Al{sub x}Ga{sub 1−x}){sub 0.51}In{sub 0.49}P cells remained nearly constant at 620 mV. The constant W{sub oc} as a function of substrate offcut for (Al{sub x}Ga{sub 1−x}){sub 0.51}In{sub 0.49}P implies greater losses from non-radiative recombination compared with the Ga{sub 0.51}In{sub 0.49}P devices. In addition to larger W{sub oc} values, the (Al{sub x}Ga{sub 1−x}){sub 0.51}In{sub 0.49}P cells exhibited significantly lower internal quantum efficiency (IQE) values than Ga{sub 0.51}In{sub 0.49}P cells due to recombination at the emitter/window layer interface. A thin emitter design is experimentally shown to be highly effective in improving IQE, particularly at short wavelengths. Our work shows that with further optimization of both cell structure and growth conditions, MBE-grown (Al{sub x}Ga{sub 1−x}){sub 0.51}In{sub 0.49}P will be a promising wide-bandgap candidate material for high-efficiency, lattice-matched multi-junction solar cells.

  16. A polarity-driven nanometric luminescence asymmetry in AlN/GaN heterostructures

    SciTech Connect (OSTI)

    Tizei, L. H. G. Meuret, S.; March, K.; Kociak, M.; Hestroffer, K.; Auzelle, T.; Daudin, B.

    2014-10-06

    Group III Nitrides nanowires are well suited materials for the design of light emitting devices. The internal electric field created by spontaneaous and piezoelectric polarizations in these materials poses some difficulties, but also possible solutions, towards this goal. Here, we report on the high spatial asymmetry of the cathodoluminescence intensity across a GaN quantum well embedded in an AlN nanowire, when a 60 keV, 1 nm wide electron beam is scanned over this heterostructure. This asymmetry is remarkable between positions at different sides of the quantum well. We interpret this asymmetry as originating from the different drift directions of carriers due to the internal electric field. This interpretation is corroborated by the direct determination of the polarity with convergent beam electron diffraction. A precise knowledge of hole mobility and diffusion coefficients would allow an estimate of the electric field in the AlN segment of the nanowire.

  17. 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.

  18. Influence of composition and heat treatment on damping and magnetostrictive properties of Fe18%(Ga+Al) alloys

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

    Golovin, I. S.; Palacheva, V. V.; Zadorozhnyy, V. Yu.; Zhu, J.; Jiang, H.; Cifre, J.; Lograsso, T. A.

    2014-07-16

    The structure, magnetostriction and damping properties of Fe82Ga(18x)Alx (x = 0, 5, 8, 12) alloys were analyzed. The anelastic response of Fe18(Ga + Al) alloys was studied as a function of temperature (from 0 to 600 C), frequency (from 0.01 to 200 Hz) and amplitude (from 0.0004% to 0.2%) of forced vibrations. The origin of the relatively high damping capacity of FeGaAl alloy at room temperature was determined by applying a magnetic field and different heat treatment regimes. The substitution of Ga by Al in Fe18% Ga alloys was found to decrease magnetostriction and damping. The heat treatment of alloysmoreinfluences the damping capacity of alloys more than variations of their chemical compositions. Thermally activated frequency and temperature-dependent anelastic effects in FeGaAl alloys were analyzed and the corresponding activation parameters for relaxation processes were evaluated. Internal friction effects caused by structural transformations were recorded and were found to be consistent with the A2 ? D03 ? L12 reaction. Thus, the physical mechanisms for all anelastic effects are discussed.less

  19. Growth and electrical characterization of Al{sub 0.24}Ga{sub 0.76}As/Al{sub x}Ga{sub 1-x}As/Al{sub 0.24}Ga{sub 0.76}As modulation-doped quantum wells with extremely low x

    SciTech Connect (OSTI)

    Gardner, Geoffrey C.; School of Materials Engineering, Purdue University, West Lafayette, Indiana 47907 ; Watson, John D.; Mondal, Sumit; Department of Physics, Purdue University, West Lafayette, Indiana 47907 ; Deng, Nianpei; Csathy, Gabor A.; Manfra, Michael J.; School of Materials Engineering, Purdue University, West Lafayette, Indiana 47907; Department of Physics, Purdue University, West Lafayette, Indiana 47907; School of Electrical and Computer Engineering, Purdue University, West Lafayette, Indiana 47907

    2013-06-24

    We report on the growth and electrical characterization of modulation-doped Al{sub 0.24}Ga{sub 0.76}As/Al{sub x}Ga{sub 1-x}As/Al{sub 0.24}Ga{sub 0.76}As quantum wells with mole fractions as low as x = 0.00057. Such structures will permit detailed studies of the impact of alloy disorder in the fractional quantum Hall regime. At zero magnetic field, we extract an alloy scattering rate of 24 ns{sup -1} per%Al. Additionally, we find that for x as low as 0.00057 in the quantum well, alloy scattering becomes the dominant mobility-limiting scattering mechanism in ultra-high purity two-dimensional electron gases typically used to study the fragile {nu} = 5/2 and {nu} = 12/5 fractional quantum Hall states.

  20. Effects of Mg-doped AlN/AlGaN superlattices on properties of p-GaN contact layer and performance of deep ultraviolet light emitting diodes

    SciTech Connect (OSTI)

    Al tahtamouni, T. M.; Lin, J. Y.; Jiang, H. X.

    2014-04-15

    Mg-doped AlN/AlGaN superlattice (Mg-SL) and Mg-doped AlGaN epilayers have been investigated in the 284 nm deep ultraviolet (DUV) light emitting diodes (LEDs) as electron blocking layers. It was found that the use of Mg-SL improved the material quality of the p-GaN contact layer, as evidenced in the decreased density of surface pits and improved surface morphology and crystalline quality. The performance of the DUV LEDs fabricated using Mg-SL was significantly improved, as manifested by enhanced light intensity and output power, and reduced turn-on voltage. The improved performance is attributed to the enhanced blocking of electron overflow, and enhanced hole injection.

  1. Impacts of SiN passivation on the degradation modes of AlGaN/GaN high electron mobility transistors under reverse-bias stress

    SciTech Connect (OSTI)

    Chen, Wei-Wei; Ma, Xiao-Hua E-mail: yhao@xidian.edu.cn; Hou, Bin; Zhu, Jie-Jie; Chen, Yong-He; Zheng, Xue-Feng; Zhang, Jin-Cheng; Hao, Yue E-mail: yhao@xidian.edu.cn

    2014-10-27

    Impacts of SiN passivation on the degradation modes of AlGaN/GaN high electron mobility transistors are investigated. The gate leakage current decreases significantly upon removing the SiN layer and no clear critical voltage for the sudden degradation of the gate leakage current can be observed in the reverse-bias step-stress experiments. Gate-lag measurements reveal the decrease of the fast-state surface traps and the increase of slow-state traps after the passivation layer removal. It is postulated that consistent surface charging relieves the electric field peak on the gate edge, thus the inverse piezoelectric effect is shielded.

  2. Dual optical marker Raman characterization of strained GaN-channels on AlN using AlN/GaN/AlN quantum wells and {sup 15}N isotopes

    SciTech Connect (OSTI)

    Qi, Meng; Li, Guowang; Protasenko, Vladimir; Zhao, Pei; Verma, Jai; Song, Bo; Ganguly, Satyaki; Zhu, Mingda; Hu, Zongyang; Yan, Xiaodong; Xing, Huili Grace; Jena, Debdeep; Mintairov, Alexander

    2015-01-26

    This work shows that the combination of ultrathin highly strained GaN quantum wells embedded in an AlN matrix, with controlled isotopic concentrations of Nitrogen enables a dual marker method for Raman spectroscopy. By combining these techniques, we demonstrate the effectiveness in studying strain in the vertical direction. This technique will enable the precise probing of properties of buried active layers in heterostructures, and can be extended in the future to vertical devices such as those used for optical emitters and for power electronics.

  3. Mechanisms of lighting enhancement of Al nanoclusters-embedded Al-doped ZnO film in GaN-based light-emitting diodes

    SciTech Connect (OSTI)

    Lee, Hsin-Ying; Chou, Ying-Hung; Lee, Ching-Ting

    2010-01-15

    Aluminum (Al)-doped ZnO (AZO) films with embedded Al nanoclusters were proposed and utilized to enhance the light output power and maximum operation current of GaN-based light-emitting diodes (LEDs). The AZO films were sputtered using ZnO and Al targets in a magnetron cosputtering system. With Al dc power of 7 W and ZnO 100 W ac power, the electron concentration of 4.1x10{sup 20} cm{sup -3}, electron mobility of 16.2 cm{sup 2}/V s, and resistivity of 7.2x10{sup -4} {Omega} cm were obtained for the deposited AZO film annealed at 600 deg. C for 1 min in a N{sub 2} ambient. As verified by a high resolution transmission electron microscopy, the deposited AZO films with embedded Al nanoclusters were clearly observed. A 35% increase in light output power of the GaN-based LEDs with Al nanoclusters-embedded AZO films was realized compared with the conventional LEDs operated at 500 mA. It was verified experimentally that the various characteristics of GaN-based LEDs including the antireflection, light scattering, current spreading, and the light extraction efficiency in light emission could be significantly enhanced with the use of Al nanoclusters-embedded AZO films.

  4. Thermal conduction in lattice–matched superlattices of InGaAs/InAlAs

    SciTech Connect (OSTI)

    Sood, Aditya; Rowlette, Jeremy A.; Caneau, Catherine G.; Bozorg-Grayeli, Elah; Asheghi, Mehdi; Goodson, Kenneth E.

    2014-08-04

    Understanding the relative importance of interface scattering and phonon-phonon interactions on thermal transport in superlattices (SLs) is essential for the simulation of practical devices, such as quantum cascade lasers (QCLs). While several studies have looked at the dependence of the thermal conductivity of SLs on period thickness, few have systematically examined the effect of varying material thickness ratio. Here, we study through-plane thermal conduction in lattice-matched In{sub 0.53}Ga{sub 0.47}As/In{sub 0.52}Al{sub 0.48}As SLs grown by metalorganic chemical vapor deposition as a function of SL period thickness (4.2 to 8.4 nm) and layer thickness ratio (1:3 to 3:1). Conductivities are measured using time-domain thermoreflectance and vary between 1.21 and 2.31 W m{sup −1} K{sup −1}. By studying the trends of the thermal conductivities for large SL periods, we estimate the bulk conductivities of In{sub 0.53}Ga{sub 0.47}As and In{sub 0.52}Al{sub 0.48}As to be approximately 5 W m{sup −1} K{sup −1} and 1 W m{sup −1} K{sup −1}, respectively, the latter being an order of magnitude lower than theoretical estimates. Furthermore, we find that the Kapitza resistance between alloy layers has an upper bound of ≈0.1 m{sup 2} K GW{sup −1}, and is negligible compared to the intrinsic alloy resistances, even for 2 nm thick layers. A phonon Boltzmann transport model yields good agreement with the data when the alloy interfaces are modeled using a specular boundary condition, pointing towards the high-quality of interfaces. We discuss the potential impact of these results on the design and operation of high-power QCLs comprised of In{sub 1−x}Ga{sub x}As/In{sub 1−y}Al{sub y}As SL cores.

  5. Demonstration of solar-blind Al{sub x}Ga{sub 1−x}N-based heterojunction phototransistors

    SciTech Connect (OSTI)

    Zhang, Lingxia; Tang, Shaoji; Liu, Changshan; Li, Bin; Wu, Hualong; Wang, Hailong; Wu, Zhisheng; Jiang, Hao

    2015-12-07

    Al{sub 0.4}Ga{sub 0.6}N/Al{sub 0.65}Ga{sub 0.35}N heterojunction phototransistors have been fabricated from the epi-structure grown by low-pressure metal organic chemical vapor deposition on c-plane sapphire substrates. P-type conductivity of the AlGaN base layer was realized by using indium surfactant-assisted Mg-delta doping method. Regrowth technique was used to suppress the Mg memory effect on the n-type emitter. The fabricated devices with a 150-μm-diameter active area exhibited a bandpass spectral response between 235 and 285 nm. Dark current was measured to be less than 10 pA for bias voltages below 2.0 V. A high optical gain of 1.9 × 10{sup 3} was obtained at 6 V bias.

  6. Development of a 2.0 eV AlGaInP Solar Cell Grown by OMVPE

    SciTech Connect (OSTI)

    Perl, Emmett E.; Simon, John; Geisz, John F.; Olavarria, Waldo; Young, Michelle; Duda, Anna; Dippo, Pat; Friedman, Daniel J.; Steiner, Myles A.

    2015-06-14

    AlGaInP solar cells with a bandgap (Eg) of ~2.0 eV are developed for use in next-generation multijunction photovoltaic devices. This material system is of great interest for both space and concentrator photovoltaics due to its high bandgap, which enables the development of high-efficiency five-junction and six-junction devices and is also useful for solar cells operated at elevated temperatures. In this work, we explore the conditions for the Organometallic Vapor Phase Epitaxy (OMVPE) growth of AlGaInP and study their effects on cell performance. A ~2.0 eV AlGaInP solar cell is demonstrated with an open circuit voltage (VOC) of 1.59V, a bandgap-voltage offset (WOC) of 420mV, a fill factor (FF) of 88.0%, and an efficiency of 14.8%. These AlGaInP cells have attained a similar FF, WOC and internal quantum efficiency (IQE) to the best upright GaInP cells grown in our lab to date.

  7. Emission mechanisms in Al-rich AlGaN/AlN quantum wells assessed by excitation power dependent photoluminescence spectroscopy

    SciTech Connect (OSTI)

    Iwata, Yoshiya; Banal, Ryan G.; Ichikawa, Shuhei; Funato, Mitsuru; Kawakami, Yoichi

    2015-02-21

    The optical properties of Al-rich AlGaN/AlN quantum wells are assessed by excitation-power-dependent time-integrated (TI) and time-resolved (TR) photoluminescence (PL) measurements. Two excitation sources, an optical parametric oscillator and the 4th harmonics of a Ti:sapphire laser, realize a wide range of excited carrier densities between 10{sup 12} and 10{sup 21 }cm{sup −3}. The emission mechanisms change from an exciton to an electron-hole plasma as the excitation power increases. Accordingly, the PL decay time is drastically reduced, and the integrated PL intensities increase in the following order: linearly, super-linearly, linearly again, and sub-linearly. The observed results are well accounted for by rate equations that consider the saturation effect of non-radiative recombination processes. Using both TIPL and TRPL measurements allows the density of non-radiative recombination centers, the internal quantum efficiency, and the radiative recombination coefficient to be reliably extracted.

  8. Mid-infrared electro-luminescence and absorption from AlGaN/GaN-based multi-quantum well inter-subband structures

    SciTech Connect (OSTI)

    Hofstetter, Daniel; Bour, David P.; Kirste, Lutz

    2014-06-16

    We present electro-modulated absorption and electro-luminescence measurements on chirped AlGaN/GaN-based multi-quantum well inter-subband structures grown by metal-organic vapour phase epitaxy. The absorption signal is a TM-polarized, 70?meV wide feature centred at 230?meV. At medium injection current, a 58?meV wide luminescence peak corresponding to an inter-subband transition at 1450?cm{sup ?1} (180?meV) is observed. Under high injection current, we measured a 4?meV wide structure peaking at 92.5?meV in the luminescence spectrum. The energy location of this peak is exactly at the longitudinal optical phonon of GaN.

  9. 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.

  10. Magneto-photoluminescence of InAs/InGaAs/InAlAs quantum well structures

    SciTech Connect (OSTI)

    Terent'ev, Ya. V.; Danilov, S. N.; Loher, J.; Schuh, D.; Bougeard, D.; Weiss, D.; Ganichev, S. D.; Durnev, M. V.; Tarasenko, S. A.; Mukhin, M. S.; Ivanov, S. V.

    2014-03-10

    Photoluminescence (PL) and highly circularly polarized magneto-PL (up to 50% at 6 T) from two-step bandgap InAs/InGaAs/InAlAs quantum wells (QWs) are studied. Bright PL is observed up to room temperature, indicating a high quantum efficiency of the radiative recombination in these QWs. The sign of the circular polarization indicates that it stems from the spin polarization of heavy holes caused by the Zeeman effect. Although in magnetic field the PL lines are strongly circularly polarized, no energy shift between the counter-polarized PL lines was observed. The results suggest the electron and the hole g-factor to be of the same sign and close magnitudes.

  11. Birefringence in the transparency region of GaAs/AlAs multiple quantum wells

    SciTech Connect (OSTI)

    Sirenko, A.A.; Etchegoin, P.; Fainstein, A.; Eberl, K.; Cardona, M.

    1999-09-01

    Birefringence measurements for in-plane propagation of light below the absorption edge in GaAs/AlAs multiple quantum wells (MQW{close_quote}s) are reported for different well/barrier widths. A remarkable drop in the low-frequency limit of the birefringence has been observed for MQW structures with small periods and ascribed to the presence of local fields. The temperature dependence of the birefringence is also studied and complementary results in InP quantum dot structures are also presented. The latter exhibit a strong resonant birefringence, which can be explained by the reduced dimensionality in the joint density of states for optical transitions in the dots. {copyright} {ital 1999} {ital The American Physical Society}

  12. Deep ultraviolet distributed Bragg reflectors based on graded composition AlGaN alloys

    SciTech Connect (OSTI)

    Brummer, Gordie; Nothern, Denis; Nikiforov, A. Yu.; Moustakas, T. D.

    2015-06-01

    Distributed Bragg reflectors (DBRs) with peak reflectivity at approximately 280 nm, based on compositionally graded Al{sub x}Ga{sub 1−x}N alloys, were grown on 6H-SiC substrates by plasma-assisted molecular beam epitaxy. DBRs with square, sinusoidal, triangular, and sawtooth composition profiles were designed with the transfer matrix method. The crystal structure of these DBRs was studied with high-resolution x-ray diffraction of the (1{sup ¯}015) reciprocal lattice point. The periodicity of the DBR profiles was confirmed with cross-sectional Z-contrast scanning transmission electron microscopy. The peak reflectance of these DBRs with 15.5 periods varies from 77% to 56% with corresponding full width at half maximum of 17–14 nm. Coupled mode analysis was used to explain the dependence of the reflectivity characteristics on the profile of the graded composition.

  13. 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.

  14. Capacitance-voltage characteristics of (Al/Ti)/Al{sub 2}O{sub 3}/n-GaN MIS structures

    SciTech Connect (OSTI)

    Ivanov, P. A. Potapov, A. S.; Nikolaev, A. E.; Lundin, V. V.; Sakharov, A. V.; Tsatsulnikov, A. F.; Afanas’ev, A. V.; Romanov, A. A.; Osachev, E. V.

    2015-08-15

    The capacitance-voltage characteristics of (Al/Ti)/Al{sub 2}O{sub 3}/n-GaN metal—insulator-semiconductor (MIS) structures are measured and analyzed. n-Type GaN films are grown on sapphire (0001) substrates by the metal-organic chemical vapor deposition method. An aluminum-oxide layer with a thickness of 60 nm is deposited onto the surface of GaN by the method of atomic-layer deposition from the gas phase. Metallic contacts are deposited by the electron-beam evaporation of titanium and aluminum in vacuum. According to the measurement results, the breakdown-field strength of the oxide, its dielectric constant, and the integrated electron density of states at the oxide-semiconductor interface are 5 × 10{sup 6} V/cm, 7.5, and 3 × 10{sup 12} cm{sup −2}, respectively.

  15. Mid-infrared pump-related electric-field domains in GaAs/(Al,Ga)As quantum-cascade structures for terahertz lasing without population inversion

    SciTech Connect (OSTI)

    Giehler, M.; Wienold, M.; Schrottke, L.; Hey, R.; Grahn, H. T.; Pavlov, S. G.; Huebers, H.-W.; Winnerl, S.; Schneider, H.

    2011-11-15

    We investigate the effect of mid-infrared (MIR) pumping on the transport properties of GaAs/(Al,Ga)As terahertz (THz) quantum lasers (TQLs), which rely on quantum coherence effects of intersubband transitions. Aiming at THz lasing at elevated temperatures, we extend the concept of THz gain with and without population inversion of a single, MIR-pumped, electrically driven THz stage proposed by Waldmueller et al.[Phys. Rev. Lett. 99, 117401 (2007)] to an entire TQL. However, experiments using a CO{sub 2} as well as a free-electron laser and numerical simulations show that this resonant MIR pumping causes a negative differential conductivity (NDC) in addition to the NDC caused by sequential tunneling. Lasing of these TQLs is prevented by the formation of electric-field domains below the resonance field strength for gain of each single THz stage.

  16. Influence of composition and heat treatment on damping and magnetostrictive properties of Fe–18%(Ga + Al) alloys

    SciTech Connect (OSTI)

    Golovin, I. S.; Palacheva, V. V.; Zadorozhnyy, V. Yu.; Zhu, J.; Jiang, H.; Cifre, J.; Lograsso, T. A.

    2014-07-16

    The structure, magnetostriction and damping properties of Fe82Ga(18–x)Alx (x = 0, 5, 8, 12) alloys were analyzed. The anelastic response of Fe–18(Ga + Al) alloys was studied as a function of temperature (from 0 to 600 °C), frequency (from 0.01 to 200 Hz) and amplitude (from 0.0004% to 0.2%) of forced vibrations. The origin of the relatively high damping capacity of Fe–Ga–Al alloy at room temperature was determined by applying a magnetic field and different heat treatment regimes. The substitution of Ga by Al in Fe–18% Ga alloys was found to decrease magnetostriction and damping. The heat treatment of alloys influences the damping capacity of alloys more than variations of their chemical compositions. Thermally activated frequency and temperature-dependent anelastic effects in Fe–Ga–Al alloys were analyzed and the corresponding activation parameters for relaxation processes were evaluated. Internal friction effects caused by structural transformations were recorded and were found to be consistent with the A2 → D03 → L12 reaction. Thus, the physical mechanisms for all anelastic effects are discussed.

  17. Al{sub x}Ga{sub 1−x}As/GaAs(100) hetermostructures with anomalously high carrier mobility

    SciTech Connect (OSTI)

    Seredin, P. V. Goloshchapov, D. L.; Lenshin, A. S.; Ternovaya, V. E.; Arsentyev, I. N. Nikolaev, D. N.; Tarasov, I. S.; Shamakhov, V. V.; Popov, A. V.

    2015-08-15

    Structural and spectroscopic methods are used to study the epitaxial layers of n-type Al{sub x}Ga{sub 1−x}As solid solutions produced by the metal-organic chemical vapor deposition method. It is shown that, when Al{sub x}Ga{sub 1−x}As solid solutions are doped with carbon to a level of (1.2–6.7) × 10{sup 17} cm{sup −3}, the electron mobility is anomalously high for the given impurity concentration and twice exceeds the calculated value. It is assumed that the ordered arrangement of carbon in the metal sublattice of the solid solution leads to a change in the average distance between impurity ions, i.e., to an increase in the mean free path of the carriers and, consequently, in the carrier mobility. The observed effect has immediate practical importance in the search for various technological ways of increasing the operating speed of functional elements of modern optoelectronic devices. The effect of the anomalously high carrier mobility in the epitaxial layer of a heteropair opens up new opportunities for the development of new structures on the basis of Al{sub x}Ga{sub 1−x}As compounds.

  18. Metalorganic chemical vapor deposition and characterization of (Al,Si)O dielectrics for GaN–based devices

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

    Chan, Silvia; Mishra, Umesh K.; Tahhan, Maher; Liu, Xiang; Bisi, David; Gupta, Chirag; Koksaldi, Onur; Li, Haoran; Mates, Tom; DenBaars, Steven P.; et al

    2016-01-20

    In this study, we report on the growth and electrical characterization of (Al,Si)O dielectrics grown by metalorganic chemical vapor deposition (MOCVD) using trimethylaluminum, oxygen, and silane as precursors. The growth rates, refractive indices, and composition of (Al,Si)O films grown on Si(001) were determined from ellipsometry and XPS measurements. Crystallinity and electrical properties of (Al,Si)O films grown in situ on c-plane GaN were characterized using grazing incidence X-ray diffraction and capacitance–voltage with current–voltage measurements, respectively. Si concentration in the films was found to be tunable by varying the trimethylaluminum and/or oxygen precursor flows. The Si incorporation suppressed the formation of crystallinemore » domains, leading to amorphous films that resulted in reduced interfacial trap density, low gate leakage and ultra-low hysteresis in (Al,Si)O/n-GaN MOS-capacitors.« less

  19. Physics of gate leakage current in N-polar InAlN/GaN heterojunction field effect transistors

    SciTech Connect (OSTI)

    Goswami, Arunesh; Trew, Robert J.; Bilbro, Griff L.

    2014-10-28

    A physics based model of the gate leakage current in N-polar InAlN/GaN heterojunction field effect transistors is demonstrated. The model is based on the space charge limited current flow dominated by the effects of deep traps in the InAlN surface layer. The model predicts accurately the gate-leakage measurement data of the N-polar InAlN/GaN device with InAlN cap layer. In the pinch-off state, the gate leakage current conduction through the surface of the device in the drain access region dominates the current flow through the two dimensional electron gas channel. One deep trap level and two levels of shallow traps are extracted by fitting the model results with measurement data.

  20. Hysteresis phenomena of the two dimensional electron gas density in lattice-matched InAlN/GaN heterostructures

    SciTech Connect (OSTI)

    Sang, Ling; Yang, Xuelin Cheng, Jianpeng; Guo, Lei; Hu, Anqi; Xiang, Yong; Yu, Tongjun; Xu, Fujun; Tang, Ning; Jia, Lifang; He, Zhi; Wang, Maojun; Wang, Xinqiang; Shen, Bo; Ge, Weikun

    2015-08-03

    High-temperature transport properties in high-mobility lattice-matched InAlN/GaN heterostructures have been investigated. An interesting hysteresis phenomenon of the two dimensional electron gas (2DEG) density is observed in the temperature-dependent Hall measurements. After high-temperature thermal cycles treatment, the reduction of the 2DEG density is observed, which is more serious in thinner InAlN barrier samples. This reduction can then be recovered by light illumination. We attribute these behaviors to the shallow trap states with energy level above the Fermi level in the GaN buffer layer. The electrons in the 2DEG are thermal-excited when temperature is increased and then trapped by these shallow trap states in the buffer layer, resulting in the reduction and hysteresis phenomenon of their density. Three trap states are observed in the GaN buffer layer and C{sub Ga} may be one of the candidates responsible for the observed behaviors. Our results provide an alternative approach to assess the quality of InAlN/GaN heterostructures for applications in high-temperature electronic devices.

  1. Selective layer disordering in intersubband Al0.028Ga0.972 N/AlN superlattices with silicon nitride capping layer

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

    Wierer, Jonathan J.; Allerman, Andrew A.; Skogen, Erik J.; Tauke-Pedretti, Anna; Vawter, Gregory A.; Montaño, Ines

    2015-06-01

    We demonstrate the selective layer disordering in intersubband Al0.028Ga0.972 N/AlN superlattices using a silicon nitride (SiNx) capping layer. The (SiNx) capped superlattice exhibits suppressed layer disordering under high-temperature annealing. In addition, the rate of layer disordering is reduced with increased SiNx thickness. The layer disordering is caused by Si diffusion, and the SiNx layer inhibits vacancy formation at the crystal surface and ultimately, the movement of Al and Ga atoms across the heterointerfaces. In conclusion, patterning of the SiNx layer results in selective layer disordering, an attractive method to integrate active and passive III–nitride-based intersubband devices.

  2. Influence of composition and heat treatment on damping and magnetostrictive properties of Fe–18%(Ga + Al) alloys

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

    Golovin, I. S.; Palacheva, V. V.; Zadorozhnyy, V. Yu.; Zhu, J.; Jiang, H.; Cifre, J.; Lograsso, T. A.

    2014-07-16

    The structure, magnetostriction and damping properties of Fe82Ga(18–x)Alx (x = 0, 5, 8, 12) alloys were analyzed. The anelastic response of Fe–18(Ga + Al) alloys was studied as a function of temperature (from 0 to 600 °C), frequency (from 0.01 to 200 Hz) and amplitude (from 0.0004% to 0.2%) of forced vibrations. The origin of the relatively high damping capacity of Fe–Ga–Al alloy at room temperature was determined by applying a magnetic field and different heat treatment regimes. The substitution of Ga by Al in Fe–18% Ga alloys was found to decrease magnetostriction and damping. The heat treatment of alloysmore » influences the damping capacity of alloys more than variations of their chemical compositions. Thermally activated frequency and temperature-dependent anelastic effects in Fe–Ga–Al alloys were analyzed and the corresponding activation parameters for relaxation processes were evaluated. Internal friction effects caused by structural transformations were recorded and were found to be consistent with the A2 → D03 → L12 reaction. Thus, the physical mechanisms for all anelastic effects are discussed.« less

  3. Radiation damage resistance of AlGaN detectors for applications in the extreme-ultraviolet spectral range

    SciTech Connect (OSTI)

    Barkusky, Frank; Peth, Christian; Bayer, Armin; Mann, Klaus; John, Joachim; Malinowski, Pawel E.

    2009-09-15

    We report on the fabrication of aluminum gallium nitride (AlGaN) Schottky-photodiode-based detectors. AlGaN layers were grown using metal-organic chemical vapor deposition (MOCVD) on Si(111) wafers. The diodes were characterized at a wavelength of 13.5 nm using a table-top extreme-ultraviolet (EUV) radiation source, consisting of a laser-produced xenon plasma and a Schwarzschild objective. The responsivity of the diodes was tested between EUV energies ranging from 320 nJ down to several picojoules. For low fluences, a linear responsivity of 7.14 mAs/J could be determined. Saturation starts at approximately 1 nJ, merging into a linear response of 0.113 mAs/J, which could be attributed to the photoeffect on the Au electrodes on top of the diode. Furthermore, degradation tests were performed up to an absolute dose of 3.3x10{sup 19} photons/cm{sup 2}. AlGaN photodiodes were compared to commercially available silicon-based photodetectors. For AlGaN diodes, responsivity does not change even for the highest EUV dose, whereas the response of the Si diode decreases linearly to {approx}93% after 2x10{sup 19} photons/cm{sup 2}.

  4. High performance TiN gate contact on AlGaN/GaN transistor using a mechanically strain induced P-doping

    SciTech Connect (OSTI)

    Soltani, A. Rousseau, M.; Gerbedoen, J.-C.; Bourzgui, N.; Mattalah, M.; Bonanno, P. L.; Ougazzaden, A.; Telia, A.; Patriarche, G.; BenMoussa, A.

    2014-06-09

    High performance titanium nitride sub-100 nm rectifying contact, deposited by sputtering on AlGaN/GaN high electron mobility transistors, shows a reverse leakage current as low as 38 pA/mm at V{sub GS} = −40 V and a Schottky barrier height of 0.95 eV. Based on structural characterization and 3D simulations, it is found that the polarization gradient induced by the gate metallization forms a P-type pseudo-doping region under the gate between the tensile surface and the compressively strained bulk AlGaN barrier layer. The strain induced by the gate metallization can compensate for the piezoelectric component. As a result, the gate contact can operate at temperatures as high as 700 °C and can withstand a large reverse bias of up to −100 V, which is interesting for high-performance transistors dedicated to power applications.

  5. Effect of proton irradiation dose on InAlN/GaN metal-oxide semiconductor high electron mobility transistors with Al2O3 gate oxide

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

    Ahn, Shihyun; Kim, Byung -Jae; Lin, Yi -Hsuan; Ren, Fan; Pearton, Stephen J.; Yang, Gwangseok; Kim, Jihyun; Kravchenko, Ivan I.

    2016-07-26

    The effects of proton irradiation on the dc performance of InAlN/GaN metal-oxide-semiconductor high electron mobility transistors (MOSHEMTs) with Al2O3 as the gate oxide were investigated. The InAlN/GaN MOSHEMTs were irradiated with doses ranging from 1×1013 to 1×1015cm–2 at a fixed energy of 5MeV. There was minimal damage induced in the two dimensional electron gas at the lowest irradiation dose with no measurable increase in sheet resistance, whereas a 9.7% increase of the sheet resistance was observed at the highest irradiation dose. By sharp contrast, all irradiation doses created more severe degradation in the Ohmic metal contacts, with increases of specificmore » contact resistance from 54% to 114% over the range of doses investigated. These resulted in source-drain current–voltage decreases ranging from 96 to 242 mA/mm over this dose range. The trap density determined from temperature dependent drain current subthreshold swing measurements increased from 1.6 × 1013 cm–2 V–1 for the reference MOSHEMTs to 6.7 × 1013 cm–2 V–1 for devices irradiated with the highest dose. In conclusion, the carrier removal rate was 1287 ± 64 cm–1, higher than the authors previously observed in AlGaN/GaN MOSHEMTs for the same proton energy and consistent with the lower average bond energy of the InAlN.« less

  6. 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.

  7. Effect of AlN buffer layer properties on the morphology and polarity of GaN nanowires grown by molecular beam epitaxy

    SciTech Connect (OSTI)

    Brubaker, Matt D.; Rourke, Devin M.; Sanford, Norman A.; Bertness, Kris A.; Bright, Victor M.

    2011-09-01

    Low-temperature AlN buffer layers grown via plasma-assisted molecular beam epitaxy on Si (111) were found to significantly affect the subsequent growth morphology of GaN nanowires. The AlN buffer layers exhibited nanowire-like columnar protrusions, with their size, shape, and tilt determined by the AlN V/III flux ratio. GaN nanowires were frequently observed to adopt the structural characteristics of the underlying AlN columns, including the size and the degree of tilt. Piezoresponse force microscopy and polarity-sensitive etching indicate that the AlN films and the protruding columns have a mixed crystallographic polarity. Convergent beam electron diffraction indicates that GaN nanowires are Ga-polar, suggesting that Al-polar columns are nanowire nucleation sites for Ga-polar nanowires. GaN nanowires of low density could be grown on AlN buffers that were predominantly N-polar with isolated Al-polar columns, indicating a high growth rate for Ga-polar nanowires and suppressed growth of N-polar nanowires under typical growth conditions. AlN buffer layers grown under slightly N-rich conditions (V/III flux ratio = 1.0 to 1.3) were found to provide a favorable growth surface for low-density, coalescence-free nanowires.

  8. Recovery in dc and rf performance of off-state step-stressed AlGaN/GaN high electron mobility transistors with thermal annealing

    SciTech Connect (OSTI)

    Kim, Byung-Jae; Hwang, Ya-Hsi; Ahn, Shihyun; Zhu, Weidi; Dong, Chen; Lu, Liu; Ren, Fan; Holzworth, M. R.; Jones, Kevin S.; Pearton, Stephen J.; Smith, David J.; Kim, Jihyun; Zhang, Ming-Lan

    2015-04-13

    The recovery effects of thermal annealing on dc and rf performance of off-state step-stressed AlGaN/GaN high electron mobility transistors were investigated. After stress, reverse gate leakage current and sub-threshold swing increased and drain current on-off ratio decreased. However, these degradations were completely recovered after thermal annealing at 450?C for 10 mins for devices stressed either once or twice. The trap densities, which were estimated by temperature-dependent drain-current sub-threshold swing measurements, increased after off-state step-stress and were reduced after subsequent thermal annealing. In addition, the small signal rf characteristics of stressed devices were completely recovered after thermal annealing.

  9. Frequency up-conversion in nonpolar a-plane GaN/AlGaN based multiple quantum wells optimized for applications with silicon solar cells

    SciTech Connect (OSTI)

    Radosavljevi?, S.; Radovanovi?, J. Milanovi?, V.; Tomi?, S.

    2014-07-21

    We have described a method for structural parameters optimization of GaN/AlGaN multiple quantum well based up-converter for silicon solar cells. It involves a systematic tuning of individual step quantum wells by use of the genetic algorithm for global optimization. In quantum well structures, the up-conversion process can be achieved by utilizing nonlinear optical effects based on intersubband transitions. Both single and double step quantum wells have been tested in order to maximize the second order susceptibility derived from the density matrix formalism. The results obtained for single step wells proved slightly better and have been further pursued to obtain a more complex design, optimized for conversion of an entire range of incident photon energies.

  10. Current collapse imaging of Schottky gate AlGaN/GaN high electron mobility transistors by electric field-induced optical second-harmonic generation measurement

    SciTech Connect (OSTI)

    Katsuno, Takashi Ishikawa, Tsuyoshi; Ueda, Hiroyuki; Uesugi, Tsutomu; Manaka, Takaaki; Iwamoto, Mitsumasa

    2014-06-23

    Two-dimensional current collapse imaging of a Schottky gate AlGaN/GaN high electron mobility transistor device was achieved by optical electric field-induced second-harmonic generation (EFISHG) measurements. EFISHG measurements can detect the electric field produced by carriers trapped in the on-state of the device, which leads to current collapse. Immediately after (e.g., 1, 100, or 800 μs) the completion of drain-stress voltage (200 V) in the off-state, the second-harmonic (SH) signals appeared within 2 μm from the gate edge on the drain electrode. The SH signal intensity became weak with time, which suggests that the trapped carriers are emitted from the trap sites. The SH signal location supports the well-known virtual gate model for current collapse.

  11. Spin depolarization under low electric fields at low temperatures in undoped InGaAs/AlGaAs multiple quantum well

    SciTech Connect (OSTI)

    Zhu, Laipan; Liu, Yu; Jiang, Chongyun; Yu, Jinling; Gao, Hansong; Ma, Hui; Qin, Xudong; Li, Yuan; Wu, Qing; Chen, Yonghai

    2014-10-13

    The spin polarization under low electric fields (≤300 V/cm) at low temperatures has been studied in undoped InGaAs/AlGaAs multiple quantum well. The spin polarization was created by optical spin orientation using circularly polarized light and the inverse spin-Hall effect was employed to measure the spin polarization current. We observed an obvious spin depolarization especially at lower temperatures (80–120 K). We ascribed the spin depolarization of the photoinduced electrons to the heating effect from the low electric fields (the low field regime 50–300 V/cm). This spin depolarization due to the heating effect is sensitive to temperature and electric field, suggesting a wide range of potential applications and devices.

  12. Single photon emission of a charge-tunable GaAs/Al{sub 0.25}Ga{sub 0.75}As droplet quantum dot device

    SciTech Connect (OSTI)

    Langer, Fabian Plischke, David; Kamp, Martin; Hfling, Sven

    2014-08-25

    In this work, we report the fabrication of a charge-tunable GaAs/Al{sub 0.25}Ga{sub 0.75}As quantum dot (QD) device containing QDs deposited by modified droplet epitaxy producing almost strain and composition gradient free QDs. We obtained a QD density in the low 10{sup 9?}cm{sup ?2} range that enables us to perform spectroscopy on single droplet QDs showing linewidths as narrow as 40??eV. The integration of the QDs into a Schottky diode allows us to controllably charge a single QD with up to four electrons, while non-classical photoluminescence is proven by photon auto-correlation measurements showing photon-antibunching (g{sup (2)}(0)?=?0.05).

  13. In situ study of atomic layer deposition Al{sub 2}O{sub 3} on GaP (100)

    SciTech Connect (OSTI)

    Dong, H.; Brennan, B.; Qin, X.; Hinkle, C. L.; Kim, J.; Wallace, R. M.; Zhernokletov, D. M.

    2013-09-16

    The interfacial chemistry of atomic layer deposition (ALD) of Al{sub 2}O{sub 3} on chemically treated GaP (100) has been studied using in situ X-ray photoelectron spectroscopy. A “self-cleaning” effect for Ga-oxide upon exposure to trimethylaluminum is seen to be efficient on the native oxide and chemically treated surfaces. The phosphorus oxide chemical states are seen to change during the ALD process, but the total concentration of P-oxides is seen to remain constant throughout the ALD process.

  14. High-temperature luminescence in an n-GaSb/n-InGaAsSb/p-AlGaAsSb light-emitting heterostructure with a high potential barrier

    SciTech Connect (OSTI)

    Petukhov, A. A., E-mail: andrey-rus29@rambler.ru; Zhurtanov, B. E.; Kalinina, K. V.; Stoyanov, N. D.; Salikhov, H. M.; Mikhailova, M. P.; Yakovlev, Yu. P. [Russian Academy of Sciences, Ioffe Physical-Technical Institute (Russian Federation)] [Russian Academy of Sciences, Ioffe Physical-Technical Institute (Russian Federation)

    2013-09-15

    The electroluminescent properties of an n-GaSb/n-InGaAsSb/p-AlGaAsSb heterostructure with a high potential barrier in the conduction band (large conduction-band offset) at the n-GaSb/n-InGaAsSb type-II heterointerface ({Delta}E{sub c} = 0.79 eV) are studied. Two bands with peaks at 0.28 and 0.64 eV at 300 K, associated with radiative recombination in n-InGaAsSb and n-GaSb, respectively, are observed in the electroluminescence (EL) spectrum. In the entire temperature range under study, T = 290-480 K, additional electron-hole pairs are formed in the n-InGaAsSb active region by impact ionization with hot electrons heated as a result of the conduction-band offset. These pairs contribute to radiative recombination, which leads to a nonlinear increase in the EL intensity and output optical power with increasing pump current. A superlinear increase in the emission power of the long-wavelength band is observed upon heating in the temperature range T = 290-345 K, and a linear increase is observed at T > 345 K. This work for the first time reports an increase in the emission power of a light-emitting diode structure with increasing temperature. It is shown that this rise is caused by a decrease in the threshold energy of the impact ionization due to narrowing of the band gap of the active region.

  15. KOH based selective wet chemical etching of AlN, AlxGa1-xN, and GaN crystals: A way towards substrate removal in deep ultraviolet-light emitting diode

    SciTech Connect (OSTI)

    Guo, W; Kirste, R; Bryan, I; Bryan, Z; Hussey, L; Reddy, P; Tweedie, J; Collazo, R; Sitar, Z

    2015-02-23

    A controllable and smooth potassium hydroxide-based wet etching technique was developed for the AlGaN system. High selectivity between AlN and AlxGa1-xN (up to 12 x) was found to be critical in achieving effective substrate thinning or removal for AlGaN-based deep ultraviolet light emitting diodes, thus increasing light extraction efficiency. The mechanism of high selectivity of AlGaN as a function of Al composition can be explained as related to the formation and dissolution of oxide/hydroxide on top of N-polar surface. Cross-sectional transmission electron microscopic analysis served as ultimate proof that these hillocks were not related to underlying threading dislocations. (C) 2015 AIP Publishing LLC.

  16. Vision FL LLC | Open Energy Information

    Open Energy Info (EERE)

    FL LLC Jump to: navigation, search Name: VisionFL, LLC Place: Florida Sector: Biomass Product: Florida-based biomass project developer. References: VisionFL, LLC1 This article...

  17. Border trap reduction in Al{sub 2}O{sub 3}/InGaAs gate stacks

    SciTech Connect (OSTI)

    Tang, Kechao; McIntyre, Paul C.; Winter, Roy; Eizenberg, Moshe; Zhang, Liangliang; Droopad, Ravi

    2015-11-16

    The effect of Al{sub 2}O{sub 3} atomic layer deposition (ALD) temperature on the border trap density (N{sub bt}) of Al{sub 2}O{sub 3}/InGaAs gate stacks is investigated quantitatively, and we demonstrate that lowering the trimethylaluminum (TMA)/water vapor ALD temperature from 270 °C to 120 °C significantly reduces N{sub bt}. The reduction of N{sub bt} coincides with increased hydrogen incorporation in low temperature ALD-grown Al{sub 2}O{sub 3} films during post-gate metal forming gas annealing. It is also found that large-dose (∼6000 L) exposure of the In{sub 0.53}Ga{sub 0.47}As (100) surface to TMA immediately after thermal desorption of a protective As{sub 2} capping layer is an important step to guarantee the uniformity and reproducibility of high quality Al{sub 2}O{sub 3}/InGaAs samples made at low ALD temperatures.

  18. Studies of scattering mechanisms in gate tunable InAs/(Al,Ga)Sb two dimensional electron gases

    SciTech Connect (OSTI)

    Shojaei, B.; McFadden, A.; Schultz, B. D.; Shabani, J.; Palmstrøm, C. J.

    2015-06-01

    A study of scattering mechanisms in gate tunable two dimensional electron gases confined to InAs/(Al,Ga)Sb heterostructures with varying interface roughness and dislocation density is presented. By integrating an insulated gate structure the evolution of the low temperature electron mobility and single-particle lifetime was determined for a previously unexplored density regime, 10{sup 11}–10{sup 12 }cm{sup −2}, in this system. Existing theoretical models were used to analyze the density dependence of the electron mobility and single particle lifetime in InAs quantum wells. Scattering was found to be dominated by charged dislocations and interface roughness. It was demonstrated that the growth of InAs quantum wells on nearly lattice matched GaSb substrate results in fewer dislocations, lower interface roughness, and improved low temperature transport properties compared to growth on lattice mismatched GaAs substrates.

  19. Electronic structure of Al- and Ga-doped ZnO films studied by hard X-ray photoelectron spectroscopy

    SciTech Connect (OSTI)

    Gabás, M.; Ramos Barrado, José R.; Torelli, P.; Barrett, N. T.

    2014-01-01

    Al- and Ga-doped sputtered ZnO films (AZO, GZO) are semiconducting and metallic, respectively, despite the same electronic valence structure of the dopants. Using hard X-ray photoelectron spectroscopy we observe that both dopants induce a band in the electronic structure near the Fermi level, accompanied by a narrowing of the Zn 3d/O 2p gap in the valence band and, in the case of GZO, a substantial shift in the Zn 3d. Ga occupies substitutional sites, whereas Al dopants are in both substitutional and interstitial sites. The latter could induce O and Zn defects, which act as acceptors explaining the semiconducting character of AZO and the lack of variation in the optical gap. By contrast, mainly substitutional doping is consistent with the metallic-like behavior of GZO.

  20. Anti-site disorder and improved functionality of Mn?NiX (X = Al, Ga, In, Sn) inverse Heusler alloys

    SciTech Connect (OSTI)

    Paul, Souvik; Kundu, Ashis; Ghosh, Subhradip; Sanyal, Biplab

    2014-10-07

    Recent first-principles calculations have predicted Mn?NiX (X = Al, Ga, In, Sn) alloys to be magnetic shape memory alloys. Moreover, experiments on Mn?NiGa and Mn?NiSn suggest that the alloys deviate from the perfect inverse Heusler arrangement and that there is chemical disorder at the sublattices with tetrahedral symmetry. In this work, we investigate the effects of such chemical disorder on phase stabilities and magnetic properties using first-principles electronic structure methods. We find that except Mn?NiAl, all other alloys show signatures of martensitic transformations in presence of anti-site disorder at the sublattices with tetrahedral symmetry. This improves the possibilities of realizing martensitic transformations at relatively low fields and the possibilities of obtaining significantly large inverse magneto-caloric effects, in comparison to perfect inverse Heusler arrangement of atoms. We analyze the origin of such improvements in functional properties by investigating electronic structures and magnetic exchange interactions.

  1. 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

  2. Depth-resolved ultra-violet spectroscopic photo current-voltage measurements for the analysis of AlGaN/GaN high electron mobility transistor epilayer deposited on Si

    SciTech Connect (OSTI)

    Ozden, Burcu; Yang, Chungman; Tong, Fei; Khanal, Min P.; Mirkhani, Vahid; Sk, Mobbassar Hassan; Ahyi, Ayayi Claude; Park, Minseo

    2014-10-27

    We have demonstrated that the depth-dependent defect distribution of the deep level traps in the AlGaN/GaN high electron mobility transistor (HEMT) epi-structures can be analyzed by using the depth-resolved ultra-violet (UV) spectroscopic photo current-voltage (IV) (DR-UV-SPIV). It is of great importance to analyze deep level defects in the AlGaN/GaN HEMT structure, since it is recognized that deep level defects are the main source for causing current collapse phenomena leading to reduced device reliability. The AlGaN/GaN HEMT epi-layers were grown on a 6 in. Si wafer by metal-organic chemical vapor deposition. The DR-UV-SPIV measurement was performed using a monochromatized UV light illumination from a Xe lamp. The key strength of the DR-UV-SPIV is its ability to provide information on the depth-dependent electrically active defect distribution along the epi-layer growth direction. The DR-UV-SPIV data showed variations in the depth-dependent defect distribution across the wafer. As a result, rapid feedback on the depth-dependent electrical homogeneity of the electrically active defect distribution in the AlGaN/GaN HEMT epi-structure grown on a Si wafer with minimal sample preparation can be elucidated from the DR-UV-SPIV in combination with our previously demonstrated spectroscopic photo-IV measurement with the sub-bandgap excitation.

  3. Development of high-bandgap AlGaInP solar cells grown by organometallic vapor-phase epitaxy

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

    Perl, Emmett E.; Simon, John; Geisz, John F.; Olavarria, Waldo; Young, Michelle; Duda, Anna; Friedman, Daniel J.; Steiner, Myles A.

    2016-03-29

    AlGaInP solar cells with bandgaps between 1.9 and 2.2 eV are investigated for use in next-generation multijunction photovoltaic devices. This quaternary alloy is of great importance to the development of III-V solar cells with five or more junctions and for cells optimized for operation at elevated temperatures because of the high bandgaps required in these designs. In this work, we explore the conditions for the organometallic vapor-phase epitaxy growth of AlGaInP and study their effects on cell performance. Initial efforts focused on developing ~2.0-eV AlGaInP solar cells with a nominal aluminum composition of 12%. Under the direct spectrum at 1000more » W/m2 (AM1.5D), the best of these samples had an open-circuit voltage of 1.59 V, a bandgap-voltage offset of 440 mV, a fill factor of 88.0%, and an efficiency of 14.8%. We then varied the aluminum composition of the alloy from 0% to 24% and were able to tune the bandgap of the AlGaInP layers from ~1.9 to ~2.2 eV. Furthermore, while the samples with a higher aluminum composition exhibited a reduced quantum efficiency and increased bandgap-voltage offset, the bandgap-voltage offset remained at 500 mV or less, up to a bandgap of ~2.1 eV.« less

  4. Strongly transverse-electric-polarized emission from deep ultraviolet AlGaN quantum well light emitting diodes

    SciTech Connect (OSTI)

    Reich, Christoph Guttmann, Martin; Wernicke, Tim; Mehnke, Frank; Kuhn, Christian; Feneberg, Martin; Goldhahn, Rüdiger; Rass, Jens; Kneissl, Michael; Lapeyrade, Mickael; Einfeldt, Sven; Knauer, Arne; Kueller, Viola; Weyers, Markus

    2015-10-05

    The optical polarization of emission from ultraviolet (UV) light emitting diodes (LEDs) based on (0001)-oriented Al{sub x}Ga{sub 1−x}N multiple quantum wells (MQWs) has been studied by simulations and electroluminescence measurements. With increasing aluminum mole fraction in the quantum well x, the in-plane intensity of transverse-electric (TE) polarized light decreases relative to that of the transverse-magnetic polarized light, attributed to a reordering of the valence bands in Al{sub x}Ga{sub 1−x}N. Using k ⋅ p theoretical model calculations, the AlGaN MQW active region design has been optimized, yielding increased TE polarization and thus higher extraction efficiency for bottom-emitting LEDs in the deep UV spectral range. Using (i) narrow quantum wells, (ii) barriers with high aluminum mole fractions, and (iii) compressive growth on patterned aluminum nitride sapphire templates, strongly TE-polarized emission was observed at wavelengths as short as 239 nm.

  5. Inductively coupled plasmareactive ion etching of c- and a-plane AlGaN over the entire Al composition range: Effect of BCl{sub 3} pretreatment in Cl{sub 2}/Ar plasma chemistry

    SciTech Connect (OSTI)

    Shah, Amit P.; Laskar, Masihhur R.; Azizur Rahman, A.; Gokhale, Maheshwar R.; Bhattacharya, Arnab

    2013-11-15

    Inductively coupled plasma (ICP)reactive ion etching (RIE) patterning is a standard processing step for UV and optical photonic devices based on III-nitride materials. There is little research on ICP-RIE of high Al-content AlGaN alloys and for nonpolar nitride orientations. The authors present a comprehensive study of the ICP-RIE of c- and a-plane AlGaN in Cl{sub 2}/Ar plasma over the entire Al composition range. The authors find that the etch rate decreases in general with increasing Al content, with different behavior for c- and a-plane AlGaN. They also study the effect of BCl{sub 3} deoxidizing plasma pretreatment. An ICP deoxidizing BCl{sub 3} plasma with the addition of argon is more efficient in removal of surface oxides from Al{sub x}Ga{sub 1?x}N than RIE alone. These experiments show that Al{sub x}Ga{sub 1?x}N etching is affected by the higher binding energy of AlN and the higher affinity of oxygen to aluminum compared to gallium, with oxides on a-plane AlGaN more difficult to etch as compared to oxides on c-plane AlGaN, specifically for high Al composition materials. The authors achieve reasonably high etch rate (?350 nm/min) for high Al-content materials with a smooth surface morphology at a low DC bias of ??45 VDC.

  6. Optical characteristics of nanocrystalline Al{sub x}Ga{sub 1?x}N thin films deposited by hollow cathode plasma-assisted atomic layer deposition

    SciTech Connect (OSTI)

    Goldenberg, Eda; Ozgit-Akgun, Cagla; Biyikli, Necmi; Kemal Okyay, Ali

    2014-05-15

    Gallium nitride (GaN), aluminum nitride (AlN), and Al{sub x}Ga{sub 1?x}N films have been deposited by hollow cathode plasma-assisted atomic layer deposition at 200?C on c-plane sapphire and Si substrates. The dependence of film structure, absorption edge, and refractive index on postdeposition annealing were examined by x-ray diffraction, spectrophotometry, and spectroscopic ellipsometry measurements, respectively. Well-adhered, uniform, and polycrystalline wurtzite (hexagonal) GaN, AlN, and Al{sub x}Ga{sub 1?x}N films were prepared at low deposition temperature. As revealed by the x-ray diffraction analyses, crystallite sizes of the films were between 11.7 and 25.2?nm. The crystallite size of as-deposited GaN film increased from 11.7 to 12.1 and 14.4?nm when the annealing duration increased from 30?min to 2?h (800?C). For all films, the average optical transmission was ?85% in the visible (VIS) and near infrared spectrum. The refractive indices of AlN and Al{sub x}Ga{sub 1?x}N were lower compared to GaN thin films. The refractive index of as-deposited films decreased from 2.33 to 2.02 (??=?550?nm) with the increased Al content x (0???x???1), while the extinction coefficients (k) were approximately zero in the VIS spectrum (>400?nm). Postdeposition annealing at 900?C for 2?h considerably lowered the refractive index value of GaN films (2.331.92), indicating a significant phase change. The optical bandgap of as-deposited GaN film was found to be 3.95?eV, and it decreased to 3.90?eV for films annealed at 800?C for 30?min and 2?h. On the other hand, this value increased to 4.1?eV for GaN films annealed at 900?C for 2?h. This might be caused by Ga{sub 2}O{sub 3} formation and following phase change. The optical bandgap value of as-deposited Al{sub x}Ga{sub 1?x}N films decreased from 5.75 to 5.25?eV when the x values decreased from 1 to 0.68. Furthermore, postdeposition annealing did not affect the bandgap of Al-rich films.

  7. Investigation of the negative differential resistance reproducibility in AlN/GaN double-barrier resonant tunnelling diodes

    SciTech Connect (OSTI)

    Boucherit, M.; Soltani, A.; Rousseau, M.; Deresmes, D.; Berthe, M.; Durand, C.; De Jaeger, J.-C.

    2011-10-31

    AlN/GaN double-barrier resonant tunnelling diodes were grown by molecular beam epitaxy on GaN/sapphire template and processed into mesa diameters from 2 {mu}m to 4 {mu}m. The current-voltage characteristics were carried out in direct current operation and under-high vacuum. A sharp negative differential resistance (NDR) was detected in the forward bias at 120 K. The NDR was observed for the mesa size of 2 {mu}m at 4 V with a peak-to-valley current ratio of 3.5. The measurement conditions were chosen to make NDR reproducible more than 50 times and apparent in both scan voltage directions after electrical treatment.

  8. 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.

  9. Correlation of interface states/border traps and threshold voltage shift on AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistors

    SciTech Connect (OSTI)

    Wu, Tian-Li Groeseneken, Guido; Marcon, Denis; De Jaeger, Brice; Lin, H. C.; Franco, Jacopo; Stoffels, Steve; Van Hove, Marleen; Decoutere, Stefaan; Bakeroot, Benoit; Roelofs, Robin

    2015-08-31

    In this paper, three electrical techniques (frequency dependent conductance analysis, AC transconductance (AC-g{sub m}), and positive gate bias stress) were used to evaluate three different gate dielectrics (Plasma-Enhanced Atomic Layer Deposition Si{sub 3}N{sub 4}, Rapid Thermal Chemical Vapor Deposition Si{sub 3}N{sub 4}, and Atomic Layer Deposition (ALD) Al{sub 2}O{sub 3}) for AlGaN/GaN Metal-Insulator-Semiconductor High-Electron-Mobility Transistors. From these measurements, the interface state density (D{sub it}), the amount of border traps, and the threshold voltage (V{sub TH}) shift during a positive gate bias stress can be obtained. The results show that the V{sub TH} shift during a positive gate bias stress is highly correlated to not only interface states but also border traps in the dielectric. A physical model is proposed describing that electrons can be trapped by both interface states and border traps. Therefore, in order to minimize the V{sub TH} shift during a positive gate bias stress, the gate dielectric needs to have a lower interface state density and less border traps. However, the results also show that the commonly used frequency dependent conductance analysis technique to extract D{sub it} needs to be cautiously used since the resulting value might be influenced by the border traps and, vice versa, i.e., the g{sub m} dispersion commonly attributed to border traps might be influenced by interface states.

  10. Recombination luminescence and trap levels in undoped and Al-doped ZnO thin films on quartz and GaSe (0 0 0 1) substrates

    SciTech Connect (OSTI)

    Evtodiev, I.; Caraman, I.; Leontie, L.; Rusu, D.-I.; Dafinei, A.; Nedeff, V.; Lazar, G.

    2012-03-15

    Highlights: Black-Right-Pointing-Pointer ZnO films on GaSe create electron trapping states and PL recombination levels. Black-Right-Pointing-Pointer Zn and Al diffusion in GaSe produces low-energy widening of its PL emission. Black-Right-Pointing-Pointer ZnO:Al films on GaSe lamellas are suitable for gas-discharge lamp applications. -- Abstract: Photoluminescence spectra of ZnO and ZnO:Al (1.00, 2.00 and 5.00 at.%) films on GaSe (0 0 0 1) lamellas and amorphous quartz substrates, obtained by annealing, at 700 K, of undoped and Al-doped metal films, are investigated. For all samples, the nonequilibrium charge carriers recombine by radiative band-to-band transitions with energy of 3.27 eV, via recombination levels created by the monoionized oxygen atoms, forming the impurity band laying in the region 2.00 - 2.70 eV. Al doping induces an additional recombination level at 1.13 eV above the top of the valence band of ZnO films on GaSe substrates. As a result of thermal diffusion of Zn and Al into the GaSe interface layer from ZnO:Al/GaSe heterojunction, electron trap levels located at 0.22 eV and 0.26 eV below the conduction band edge of GaSe, as well as a deep recombination level, responsible for the luminescent emission in the region 1.10 - 1.40 eV, are created.

  11. Impact of N{sub 2} and forming gas plasma exposure on the growth and interfacial characteristics of Al{sub 2}O{sub 3} on AlGaN

    SciTech Connect (OSTI)

    Qin, Xiaoye; Dong, Hong; Brennan, Barry; Azacatl, Angelica; Kim, Jiyoung; Wallace, Robert M.

    2013-11-25

    The interface and atomic layer deposition (ALD) of Al{sub 2}O{sub 3} on the annealed, N{sub 2} plasma and forming gas (N{sub 2}:H{sub 2}) exposed Al{sub 0.25}Ga{sub 0.75}N surface was studied using in situ X-ray photoelectron spectroscopy and low energy ion scattering spectroscopy. Exposure of the Al{sub 0.25}Ga{sub 0.75}N surface to the plasma treatments is able to remove spurious carbon, and readily facilitate uniform ALD Al{sub 2}O{sub 3} nucleation.

  12. Magnetic field effect on the terahertz emission from nanometer InGaAs/AlInAs high electron mobility transistors

    SciTech Connect (OSTI)

    Dyakonova, N.; Teppe, F.; Lusakowski, J.; Knap, W.; Levinshtein, M.; Dmitriev, A.P.; Shur, M.S.; Bollaert, S.; Cappy, A.

    2005-06-01

    The influence of the magnetic field on the excitation of plasma waves in InGaAs/AlInAs lattice matched high electron mobility transistors is reported. The threshold source-drain voltage of the excitation of the terahertz emission shifts to higher values under a magnetic field increasing from 0 to 6 T. We show that the main change of the emission threshold in relatively low magnetic fields (smaller than approximately 4 T) is due to the magnetoresistance of the ungated parts of the channel. In higher magnetic fields, the effect of the magnetic field on the gated region of the device becomes important.

  13. Role of an ultra-thin AlN/GaN superlattice interlayer on the strain engineering of GaN films grown on Si(110) and Si(111) substrates by plasma-assisted molecular beam epitaxy

    SciTech Connect (OSTI)

    Shen, X. Q.; Takahashi, T.; Matsuhata, H.; Ide, T.; Shimizu, M.; Rong, X.; Chen, G.; Wang, X. Q.; Shen, B.

    2013-12-02

    We investigate the role of an ultra-thin AlN/GaN superlattice interlayer (SL-IL) on the strain engineering of the GaN films grown on Si(110) and Si(111) substrates by plasma-assisted molecular beam epitaxy. It is found that micro-cracks limitted only at the SL-IL position are naturally generated. These micro-cracks play an important role in relaxing the tensile strain caused by the difference of the coefficient of thermal expansion between GaN and Si and keeping the residual strain in the crack-free GaN epilayers resulted from the SL-IL during the growth. The mechanism understanding of the strain modulation by the SL-IL in the GaN epilayers grown on Si substrates makes it possible to design new heterostructures of III-nitrides for optic and electronic device applications.

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

    SciTech Connect (OSTI)

    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., 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.

  15. Optically confined polarized resonance Raman studies in identifying crystalline orientation of sub-diffraction limited AlGaN nanostructure

    SciTech Connect (OSTI)

    Sivadasan, A. K. Patsha, Avinash; Dhara, Sandip

    2015-04-27

    An optical characterization tool of Raman spectroscopy with extremely weak scattering cross section tool is not popular to analyze scattered signal from a single nanostructure in the sub-diffraction regime. In this regard, plasmonic assisted characterization tools are only relevant in spectroscopic studies of nanoscale object in the sub-diffraction limit. We have reported polarized resonance Raman spectroscopic (RRS) studies with strong electron-phonon coupling to understand the crystalline orientation of a single AlGaN nanowire of diameter ∼100 nm. AlGaN nanowire is grown by chemical vapor deposition technique using the catalyst assisted vapor-liquid-solid process. The results are compared with the high resolution transmission electron microscopic analysis. As a matter of fact, optical confinement effect due to the dielectric contrast of nanowire with respect to that of surrounding media assisted with electron-phonon coupling of RRS is useful for the spectroscopic analysis in the sub-diffraction limit of 325 nm (λ/2N.A.) using an excitation wavelength (λ) of 325 nm and near ultraviolet 40× far field objective with a numerical aperture (N.A.) value of 0.50.

  16. Role of Ce4+ in the scintillation mechanism of codoped Gd3Ga3Al2O12:Ce

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

    Wu, Yuntao; Meng, Fang; Li, Qi; Koschan, Merry; Melcher, Charles L.

    2014-10-17

    To control the time-response performance of widely used cerium-activated scintillators in cutting-edge medical-imaging devices, such as time-of-flight positron-emission tomography, a comprehensive understanding of the role of Ce valence states, especially stable Ce4+, in the scintillation mechanism is essential. However, despite some progress made recently, an understanding of the physical processes involving Ce4+ is still lacking. The aim of this work is to clarify the role of Ce4+ in scintillators by studying Ca2+ codoped Gd3Ga3Al2O12∶Ce (GGAG∶Ce). By using a combination of optical absorption spectra and x-ray absorption near-edge spectroscopies, the correlation between Ca2+codoping content and the Ce4+ fraction is seen. The energy-levelmore »diagrams of Ce3+ and Ce4+ in the Gd3Ga3Al2O12 host are established by using theoretical and experimental methods, which indicate a higher position of the 5d1 state of Ce4+ in the forbidden gap in comparison to that of Ce3+. Underlying reasons for the decay-time acceleration resulting from Ca2+ codoping are revealed, and the physical processes of the Ce4+-emission model are proposed and further demonstrated by temperature-dependent radioluminescence spectra under x-ray excitation.« less

  17. Role of Ce4+ in the scintillation mechanism of codoped Gd3Ga3Al2O12:Ce

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

    Wu, Yuntao; Meng, Fang; Li, Qi; Koschan, Merry; Melcher, Charles L.

    2014-10-17

    To control the time-response performance of widely used cerium-activated scintillators in cutting-edge medical-imaging devices, such as time-of-flight positron-emission tomography, a comprehensive understanding of the role of Ce valence states, especially stable Ce4+, in the scintillation mechanism is essential. However, despite some progress made recently, an understanding of the physical processes involving Ce4+ is still lacking. The aim of this work is to clarify the role of Ce4+ in scintillators by studying Ca2+ codoped Gd3Ga3Al2O12∶Ce (GGAG∶Ce). By using a combination of optical absorption spectra and x-ray absorption near-edge spectroscopies, the correlation between Ca2+codoping content and the Ce4+ fraction is seen. The energy-levelmore » diagrams of Ce3+ and Ce4+ in the Gd3Ga3Al2O12 host are established by using theoretical and experimental methods, which indicate a higher position of the 5d1 state of Ce4+ in the forbidden gap in comparison to that of Ce3+. Underlying reasons for the decay-time acceleration resulting from Ca2+ codoping are revealed, and the physical processes of the Ce4+-emission model are proposed and further demonstrated by temperature-dependent radioluminescence spectra under x-ray excitation.« less

  18. US SoAtl FL Site Consumption

    U.S. Energy Information Administration (EIA) Indexed Site

    FL Site Consumption kilowatthours 0 500 1,000 1,500 2,000 US SoAtl FL Expenditures dollars ELECTRICITY ONLY ... CONSUMPTION BY END USE More than a quarter (27%) of the ...

  19. Category:Miami, FL | Open Energy Information

    Open Energy Info (EERE)

    are in this category, out of 16 total. SVFullServiceRestaurant Miami FL Florida Power & Light Co..png SVFullServiceRestauran... 77 KB SVHospital Miami FL Florida Power & Light...

  20. Category:Tampa, FL | Open Energy Information

    Open Energy Info (EERE)

    are in this category, out of 16 total. SVFullServiceRestaurant Tampa FL Florida Power & Light Co..png SVFullServiceRestauran... 77 KB SVHospital Tampa FL Florida Power & Light...

  1. Structure and magnetic properties of Ce?(Ni/Al/Ga)??-A...

    Office of Scientific and Technical Information (OSTI)

    Z 2) with a 436.38(14), b 1004.5(3) and c 1293.4(4) pm. This is a standardized unit cell of the previously published LaAl structure type. Wavelength dispersive...

  2. 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.

    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.

  3. US SoAtl FL Site Consumption

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

    FL Site Consumption million Btu 0 500 1,000 1,500 2,000 2,500 US SoAtl FL ... 8,000 12,000 16,000 US SoAtl FL Site Consumption kilowatthours 0 500 1,000 1,500 ...

  4. Electron effective mass in Al{sub 0.72}Ga{sub 0.28}N alloys determined by mid-infrared optical Hall effect

    SciTech Connect (OSTI)

    Schöche, S. Kühne, P.; Hofmann, T.; Schubert, M.; Nilsson, D.; Kakanakova-Georgieva, A.; Janzén, E.; Darakchieva, V.

    2013-11-18

    The effective electron mass parameter in Si-doped Al{sub 0.72}Ga{sub 0.28}N is determined to be m{sup ∗}=(0.336±0.020) m{sub 0} from mid-infrared optical Hall effect measurements. No significant anisotropy of the effective electron mass parameter is found supporting theoretical predictions. Assuming a linear change of the effective electron mass with the Al content in AlGaN alloys and m{sup ∗}=0.232 m{sub 0} for GaN, an average effective electron mass of m{sup ∗}=0.376 m{sub 0} can be extrapolated for AlN. The analysis of mid-infrared spectroscopic ellipsometry measurements further confirms the two phonon mode behavior of the E{sub 1}(TO) and one phonon mode behavior of the A{sub 1}(LO) phonon mode in high-Al-content AlGaN alloys as seen in previous Raman scattering studies.

  5. 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.

  6. Indium out-diffusion in Al{sub 2}O{sub 3}/InGaAs stacks during anneal at different ambient conditions

    SciTech Connect (OSTI)

    Krylov, Igor; Winter, Roy; Ritter, Dan; Eizenberg, Moshe

    2014-06-16

    Indium out-diffusion during anneal enhances leakage currents in metal/dielectric/InGaAs gate stacks. In this work, we study the influence of ambient conditions during anneal on indium out-diffusion in Al{sub 2}O{sub 3}/InGaAs structures, prior to the gate metal deposition. Using X-ray photoemission spectroscopy and time of flight secondary ions mass spectrometry, we observed much lower indium concentrations in the Al{sub 2}O{sub 3} layer following vacuum and O{sub 2} anneals compared to forming gas or nitrogen anneals. The electrical characteristics of the Ni/Al{sub 2}O{sub 3}/InGaAs gate stack following these pre-metallization anneals as well as after subsequent post metallization anneals are presented. Possible explanations for the role of the annealing ambient conditions on indium out-diffusion are presented.

  7. CuAl{sub x}Ga{sub 1?x}Se{sub 2} thin films for photovoltaic applications: Optical and compositional analysis

    SciTech Connect (OSTI)

    Lpez-Garca, J.; Maffiotte, C.; Guilln, C.; Herrero, J.

    2013-03-15

    Highlights: ? Wide band gap CAGS thin films have been obtained by selenization of evaporated metallic precursors. ? Direct nonlinear dependence of the band gap energy with the Al/(Al + Ga) ratio is found. ? The bowing parameter decreases when the CAGS film thickness increases. ? The Cu at% remains constant in depth, together with some Al, Ga and Se gradients. ? Surface is strongly oxidized but the oxidation is relatively low in bulk. - Abstract: Wide-band gap chalcopyrite semiconductors have a great interest due to their potential application in multi-junction thin film solar cells or as window layers. Polycrystalline CuAl{sub x}Ga{sub 1?x}Se{sub 2} (CAGS) thin films have been prepared by selenization of evaporated metallic precursor layers on bare and Mo-coated soda lime glass substrates. The optical properties of CAGS films of 2 thicknesses have been analyzed by spectrophotometry in the visible-infrared (VIS-IR) and the compositional characteristics have been studied by energy dispersive analysis of X-rays (EDAX) and X-ray photoelectron spectroscopy (XPS). The optical transmission increases and the band gap energy shifts toward higher values as the Al content increases, which indicates the partial substitution of Ga by Al. The dependence of the band gap with the composition has resulted to be nonlinear and a bowing parameter of b = 0.62 and b = 0.54 for 0.6 ?m and 1.1 ?m-CAGS samples, respectively, has been obtained. XPS data have shown an Al, Ga and Se composition gradient in depth and a surface strongly oxidized. However, XPS reveals that the Cu composition remains constant in depth and the oxidation is relatively low in bulk increasing slightly in the interface with Mo/SLG. Moreover, samples with high Al content reveal a higher contribution of CuO in depth.

  8. Thermodynamics of CoAl{sub 2}O{sub 4}-CoGa{sub 2}O{sub 4} solid solutions

    SciTech Connect (OSTI)

    Lilova, Kristina I.; Navrotsky, Alexandra; Melot, Brent C.; Seshadri, Ram

    2010-06-15

    CoAl{sub 2}O{sub 4}, CoGa{sub 2}O{sub 4}, and their solid solution Co(Ga{sub z}Al{sub 1-z}){sub 2}O{sub 4} have been studied using high temperature oxide melt solution calorimetry in molten 2PbO.B{sub 2}O{sub 3} at 973 K. There is an approximately linear correlation between lattice parameters, enthalpy of formation from oxides, and the Ga content. The experimental enthalpy of mixing is zero within experimental error. The cation distribution parameters are calculated using the O'Neill and Navrotsky thermodynamic model. The enthalpies of mixing calculated from these parameters are small and consistent with the calorimetric data. The entropies of mixing are calculated from site occupancies and compared to those for a random mixture of Ga and Al ions on octahedral site with all Co tetrahedral and for a completely random mixture of all cations on both sites. Despite a zero heat of mixing, the solid solution is not ideal in that activities do not obey Raoult's Law because of the more complex entropy of mixing. - Graphical abstract: Measured enthalpies of mixing of CoAl{sub 2}O{sub 4}-CoGa{sub 2}O{sub 4} solid solutions are close to zero but entropies of mixing reflect the complex cation distribution, so the system is not an ideal solution.

  9. Radio-frequency measurements of UNiX compounds (X= Al, Ga, Ge) in high magnetic fields

    SciTech Connect (OSTI)

    Mielke, Charles H; Mcdonald, David R; Zapf, Vivien; Altarawneh, Moaz M; Lacerda, Alex H; Adak, Sourav; Karunakar, Kothapalli; Nakotte, Heinrich; Chang, S; Alsmadi, A M; Alyones, S

    2009-01-01

    We performed radio-frequency (RF) skin-depth measurements of antiferromagnetic UNiX compounds (X=Al, Ga, Ge) in magnetic fields up to 60 T and at temperatures between 1.4 to {approx}60 K. Magnetic fields are applied along different crystallographic directions and RF penetration-depth was measured using a tunnel-diode oscillator (TDO) circuit. The sample is coupled to the inductive element of a TDO resonant tank circuit, and the shift in the resonant frequency {Delta}f of the circuit is measured. The UNiX compounds exhibit field-induced magnetic transitions at low temperatures, and those transitions are accompanied by a drastic change in {Delta}f. The results of our skin-depth measurements were compared with previously published B-T phase diagrams for these three compounds.

  10. Luminescence and superradiance in electron-beam-excited Al{sub x}Ga{1-sub x}N

    SciTech Connect (OSTI)

    Bokhan, P. A.; Gugin, P. P.; Zakrevsky, Dm. E.; Malin, T. V.; Zhuravlev, K. S.; Osinnykh, I. V.; Solomonov, V. I.; Spirina, A. V.

    2014-09-21

    Luminescence and superradiance characteristics of 0.51.2-?m thick Al{sub x}Ga{sub 1-x}N films grown by molecular-beam epitaxy on sapphire substrates were studied under excitation of the films with low-energy (<20 keV) and high-energy (170 keV) electron beams. In both cases, the luminescence spectra looked quite similarly; they exhibited a band-edge luminescence with x-dependent wavelength ranging from 365 nm to 310 nm and a broadband emission taking over the whole visible spectral region. Superradiance within the broad band was obtained by pumping the samples with powerful an electron beam in the form of an open-discharge-generated filament.

  11. Electronic properties of binary and mixed [RMNH]{sub n} (R=H,CH{sub 3}, M=Al,Ga,In) oligomers

    SciTech Connect (OSTI)

    Oranskaya, A. A. Pomogaeva, A. V. Timoshkin, A. Y.

    2015-03-30

    Theoretical investigation of structural and electronic properties is presented for the rod-like oligomers R{sub 3}-[MRNH]{sub 3n}-H{sub 3} and [RMNH]{sub n+1} (M=Ga,Al,In R=H,CH{sub 3}) of different lengths. Electronic structures of the oligomers with and without substitutions of Ga atoms with Al or In were studied at DFT level of theory. Clusters up to 8 nm of length were considered. A type of terminal groups of the oligomers is found to have a dominant influence on their electronic properties.

  12. Investigation of high hole mobility In{sub 0.41}Ga{sub 0.59}Sb/Al{sub 0.91}Ga{sub 0.09}Sb quantum well structures grown by molecular beam epitaxy

    SciTech Connect (OSTI)

    Wang, Juan; Xing, Jun-Liang; Xiang, Wei; Wang, Guo-Wei; Xu, Ying-Qiang; Ren, Zheng-Wei; Niu, Zhi-Chuan

    2014-02-03

    Modulation-doped In{sub 0.41}Ga{sub 0.59}Sb/Al{sub 0.91}Ga{sub 0.09}Sb quantum-well (QW) structures were grown by molecular beam epitaxy. Cross-sectional transmission electron microscopy and atomic force microscopy studies show high crystalline quality and smooth surface morphology. X-ray diffraction investigations confirm 1.94% compressive strain within In{sub 0.41}Ga{sub 0.59}Sb channel. High room temperature hole mobility with high sheet density of 1000 cm{sup 2}/Vs, 0.877??10{sup 12}/cm{sup 2}, and 965 cm{sup 2}/Vs, 1.112??10{sup 12}/cm{sup 2} were obtained with different doping concentrations. Temperature dependent Hall measurements show different scattering mechanisms on hole mobility at different temperature range. The sheet hole density keeps almost constantly from 300?K to 77?K. This study shows great potential of In{sub 0.41}Ga{sub 0.59}Sb/Al{sub 0.91}Ga{sub 0.09}Sb QW for high-hole-mobility device applications.

  13. Investigations on the electronic, structural, magnetic properties related to shape-memory behavior in Ti{sub 2}CoX (X=Al, Ga, In)

    SciTech Connect (OSTI)

    Wei, Xiao-Ping; Chu, Yan-Dong; Sun, Xiao-Wei; E, Yan; Deng, Jian-Bo; Xing, Yong-Zhong

    2015-02-15

    Highlights: • The analysis of phase stability trend is studied for Ti{sub 2}CoX(X = Al, Ga, In). • Ti{sub 2}CoGa is more suitable as shape memory alloy. • Total magnetic moments disappear with a increase of c/a ratio for all systems. • Density of states at the Fermi level are also shown. - Abstract: Using the full-potential local orbital minimum-basis method, we have performed a systematic investigations on the electronic, structural, and magnetic properties related to shape memory applications for Ti{sub 2}CoX (X=Al, Ga, In) alloys. Our results confirm that these alloys are half-metallic ferromagnets with total magnetic moment of 2μ{sub B} per formula unit in austenite phase, and undergo a martensitic transformation at low temperatures. The relative stabilities of the martensitic phases differ considerably between Ti{sub 2}CoX (X=Al, Ga, In). Details of the electronic structures suggest that the differences in hybridizations between the magnetic components are responsible for trends of phase. Quantitative estimates for the energetics and the magnetizations indicate that Ti{sub 2}CoGa is a promising candidate for shape memory applications.

  14. Comparison of single junction AlGaInP and GaInP solar cells grown by molecular beam epitaxy

    SciTech Connect (OSTI)

    Masuda, T; Tomasulo, S; Lang, JR; Lee, ML

    2015-03-07

    We have investigated similar to 2.0 eV (AlxGa1-x)(0.51)In0.49P and similar to 1.9 eV Ga0.51In0.49P single junction solar cells grown on both on-axis and misoriented GaAs substrates by molecular beam epitaxy (MBE). Although lattice-matched (AlxGa1-x)(0.51)In0.49P solar cells are highly attractive for space and concentrator photovoltaics, there have been few reports on the MBE growth of such cells. In this work, we demonstrate open circuit voltages (V-oc) ranging from 1.29 to 1.30 V for Ga0.51In0.49P cells, and 1.35-1.37 V for (AlxGa1-x)(0.51)In0.49P cells. Growth on misoriented substrates enabled the bandgap-voltage offset (W-oc = E-g/q - V-oc) of Ga0.51In0.49P cells to decrease from similar to 575 mV to similar to 565 mV, while that of (AlxGa1-x)(0.51)In0.49P cells remained nearly constant at 620 mV. The constant Woc as a function of substrate offcut for (AlxGa1-x)(0.51)In0.49P implies greater losses from non-radiative recombination compared with the Ga0.51In0.49P devices. In addition to larger Woc values, the (AlxGa1-x)(0.51)In0.49P cells exhibited significantly lower internal quantum efficiency (IQE) values than Ga0.51In0.49P cells due to recombination at the emitter/window layer interface. A thin emitter design is experimentally shown to be highly effective in improving IQE, particularly at short wavelengths. Our work shows that with further optimization of both cell structure and growth conditions, MBE-grown (AlxGa1-x)(0.51)In0.49P will be a promising wide-bandgap candidate material for high-efficiency, lattice-matched multi-junction solar cells. (C) 2015 AIP Publishing LLC.

  15. InGaN/GaN multi-quantum well and LED growth on wafer-bonded sapphire-on-polycrystalline AlN substrates by metalorganic chemical vapor deposition.

    SciTech Connect (OSTI)

    Crawford, Mary Hagerott; Olson, S. M.; Banas, M.; Park, Y. -B.; Ladous, C.; Russell, Michael J.; Thaler, Gerald; Zahler, J. M.; Pinnington, T.; Koleske, Daniel David; Atwater, Harry A.

    2008-06-01

    We report growth of InGaN/GaN multi-quantum well (MQW) and LED structures on a novel composite substrate designed to eliminate the coefficient of thermal expansion (CTE) mismatch problems which impact GaN growth on bulk sapphire. To form the composite substrate, a thin sapphire layer is wafer-bonded to a polycrystalline aluminum nitride (P-AlN) support substrate. The sapphire layer provides the epitaxial template for the growth; however, the thermo-mechanical properties of the composite substrate are determined by the P-AlN. Using these substrates, thermal stresses associated with temperature changes during growth should be reduced an order of magnitude compared to films grown on bulk sapphire, based on published CTE data. In order to test the suitability of the substrates for GaN LED growth, test structures were grown by metalorganic chemical vapor deposition (MOCVD) using standard process conditions for GaN growth on sapphire. Bulk sapphire substrates were included as control samples in all growth runs. In situ reflectance monitoring was used to compare the growth dynamics for the different substrates. The material quality of the films as judged by X-ray diffraction (XRD), photoluminescence and transmission electron microscopy (TEM) was similar for the composite substrate and the sapphire control samples. Electroluminescence was obtained from the LED structure grown on a P-AlN composite substrate, with a similar peak wavelength and peak width to the control samples. XRD and Raman spectroscopy results confirm that the residual strain in GaN films grown on the composite substrates is dramatically reduced compared to growth on bulk sapphire substrates.

  16. Measuring the depth profiles of strain/composition in AlGaN-graded layer by high-resolution x-ray diffraction

    SciTech Connect (OSTI)

    Kuchuk, A. V.; Stanchu, H. V.; Kladko, V. P.; Belyaev, A. E.; Li, Chen; Ware, M. E.; Mazur, Yu. I.; Salamo, G. J.

    2014-12-14

    Here, we demonstrate X-ray fitting through kinematical simulations of the intensity profiles of symmetric reflections for epitaxial compositionally graded layers of AlGaN grown by molecular beam epitaxy pseudomorphically on [0001]-oriented GaN substrates. These detailed simulations depict obvious differences between changes in thickness, maximum concentration, and concentration profile of the graded layers. Through comparison of these simulations with as-grown samples, we can reliably determine these parameters, most important of which are the profiles of the concentration and strain which determine much of the electrical properties of the film. In addition to learning about these parameters for the characterization of thin film properties, these fitting techniques create opportunities to calibrate growth rates and control composition profiles of AlGaN layers with a single growth rather than multiple growths as has been done traditionally.

  17. AlGaN UV LED and Photodiodes Radiation Hardness and Space Qualifications and Their Applications in Space Science and High Energy Density Physics

    SciTech Connect (OSTI)

    Sun, K. X.

    2011-05-31

    This presentation provides an overview of robust, radiation hard AlGaN optoelectronic devices and their applications in space exploration & high energy density physics. Particularly, deep UV LED and deep UV photodiodes are discussed with regard to their applications, radiation hardness and space qualification. AC charge management of UV LED satellite payload instruments, which were to be launched in late 2012, is covered.

  18. Correlation between Ga-O signature and midgap states at the Al{sub 2}O{sub 3}/In{sub 0.53}Ga{sub 0.47}As interface

    SciTech Connect (OSTI)

    Krylov, Igor; Gavrilov, Arkady; Eizenberg, Moshe; Ritter, Dan

    2012-08-06

    Al{sub 2}O{sub 3}/In{sub 0.53}Ga{sub 0.47}As gate stacks were fabricated using different concentrations of NH{sub 4}OH as a pre-deposition treatment. Increased NH{sub 4}OH concentrations significantly reduced the C-V weak inversion hump and the measured near midgap interface states density (D{sub it}). X-ray photoelectron spectroscopy (XPS) studies revealed that these changes in the electrical properties were accompanied by a reduction in the amount of the Ga-O bonding while As-As dimers as well as other XPS detected InGaAs surface species did not correlate with the observed D{sub it} trend. Possible explanations for these findings are suggested.

  19. Raman scattering as a tool for the evaluation of strain in GaN/AlN quantum dots: The effect of capping

    SciTech Connect (OSTI)

    Cros, A.; Cantarero, A.; Garro, N.; Coraux, J.; Daudin, B.

    2007-10-15

    The strain state of GaN/AlN quantum dots grown on 6H-SiC has been investigated as a function of AlN capping thickness by three different techniques. On the one hand, resonant Raman scattering allowed the detection of the A{sub 1}(LO) quasiconfined mode. It was found that its frequency increases with AlN deposition, while its linewidth did not evolve significantly. Available experiments of multiwavelength anomalous diffraction and diffraction anomalous fine structure on the same samples provided the determination of the wurtzite lattice parameters a and c of the quantum dots. A very good agreement is found between resonant Raman scattering and x-ray measurements, especially concerning the in-plane strain state. The results demonstrate the adequacy of Raman scattering, in combination with the deformation potential and biaxial approximations, to determine quantitatively values of strain in GaN quantum dot layers.

  20. Tuning of in-plane optical anisotropy by inserting ultra-thin InAs layer at interfaces in (001)-grown GaAs/AlGaAs quantum wells

    SciTech Connect (OSTI)

    Yu, J. L.; Cheng, S. Y.; Lai, Y. F.; Zheng, Q.

    2015-01-07

    The in-plane optical anisotropy (IPOA) in (001)-grown GaAs/AlGaAs quantum wells (QWs) with different well widths varying from 2?nm to 8?nm has been studied by reflectance difference spectroscopy. Ultra-thin InAs layers with thickness ranging from 0.5 monolayer (ML) to 1.5 ML have been inserted at GaAs/AlGaAs interfaces to tune the asymmetry in the QWs. It is demonstrated that the IPOA can be accurately tailored by the thickness of the inserted ultra-thin InAs layer at the interfaces. Strain-induced IPOA has also been extracted by using a stress apparatus. We find that the intensity of the strain-induced IPOA decreases with the thickness of the inserted InAs layer, while that of the interface-induced IPOA increases with the thickness of the InAs layer. Theoretical calculations based on 6 band k ? p theory have been carried out, and good agreements with experimental results are obtained. Our results demonstrate that, the IPOA of the QWs can be greatly and effectively tuned by inserting an ultra-thin InAs layer with different thicknesses at the interfaces of QWs, which does not significantly influence the transition energies and the transition probability of QWs.

  1. Structure and magnetic properties of Ce₃(Ni/Al/Ga)₁₁—A new phase with the La₃Al₁₁ structure type

    SciTech Connect (OSTI)

    Janka, Oliver; Shang, Tian; Baumbach, Ryan E.; Bauer, Eric D.; Thompson, Joe D.; Kauzlarich, Susan M.

    2015-03-01

    Single crystals of Ce₃(Ni/Al/Ga)₁₁ were obtained from an Al flux reaction. Single crystals of the title compound crystallizing in the orthorhombic space group Immm (No. 71, Z = 2) with a = 436.38(14), b = 1004.5(3) and c = 1293.4(4) pm. This is a standardized unit cell of the previously published La₃Al₁₁ structure type. Wavelength dispersive microprobe provides the composition of Ce₃.₁₁₍₁₎Ni₀.₀₃₍₁₎Al₈.₉₅₍₁₎Ga₁.₉₀₍₁₎. Single crystal refinement provides the composition Ce₃Ni₀.₀₈Al₉.₁₃Ga₁.₇₈ with substitution of the Ni and Ga on the Al1 and Al4 sites with the Al2 and Al3 solely occupied by Al. Magnetic susceptibility measurements reveal antiferromagnetic ordering with TN = 4.8 K and there is no evidence for a ferromagnetic ordering that has been reported for Ce₃Al₁₁. The effective magnetic moment was found to be μeff = 1.9μB/Ce, which is lower than the expected value for trivalent Ce (2.54μB/Ce).

  2. Structure and magnetic properties of Ce₃(Ni/Al/Ga)₁₁—A new phase with the La₃Al₁₁ structure type

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

    Janka, Oliver; Shang, Tian; Baumbach, Ryan E.; Bauer, Eric D.; Thompson, Joe D.; Kauzlarich, Susan M.

    2015-03-01

    Single crystals of Ce₃(Ni/Al/Ga)₁₁ were obtained from an Al flux reaction. Single crystals of the title compound crystallizing in the orthorhombic space group Immm (No. 71, Z = 2) with a = 436.38(14), b = 1004.5(3) and c = 1293.4(4) pm. This is a standardized unit cell of the previously published La₃Al₁₁ structure type. Wavelength dispersive microprobe provides the composition of Ce₃.₁₁₍₁₎Ni₀.₀₃₍₁₎Al₈.₉₅₍₁₎Ga₁.₉₀₍₁₎. Single crystal refinement provides the composition Ce₃Ni₀.₀₈Al₉.₁₃Ga₁.₇₈ with substitution of the Ni and Ga on the Al1 and Al4 sites with the Al2 and Al3 solely occupied by Al. Magnetic susceptibility measurements reveal antiferromagnetic ordering with TN =more » 4.8 K and there is no evidence for a ferromagnetic ordering that has been reported for Ce₃Al₁₁. The effective magnetic moment was found to be μeff = 1.9μB/Ce, which is lower than the expected value for trivalent Ce (2.54μB/Ce).« less

  3. Systematic investigation of effects of exciton–acoustic-phonon scattering on photoluminescence rise times of free excitons in GaAs/Al{sub 0.3}Ga{sub 0.7}As single quantum wells

    SciTech Connect (OSTI)

    Nakayama, Masaaki Ohno, Tatsuya; Furukawa, Yoshiaki

    2015-04-07

    We have systematically investigated the photoluminescence (PL) dynamics of free excitons in GaAs/Al{sub 0.3}Ga{sub 0.7}As single quantum wells, focusing on the energy relaxation process due to exciton–acoustic-phonon scattering under non-resonant and weak excitation conditions as a function of GaAs-layer thickness from 3.6 to 12.0 nm and temperature from 30 to 50 K. The free exciton characteristics were confirmed by observation that the PL decay time has a linear dependence with temperature. We found that the free exciton PL rise rate, which is the reciprocal of the rise time, is inversely linear with the GaAs-layer thickness and linear with temperature. This is consistent with a reported theoretical study of the exciton–acoustic-phonon scattering rate in the energy relaxation process in quantum wells. Consequently, it is conclusively verified that the PL rise rate is dominated by the exciton–acoustic-phonon scattering rate. In addition, from quantitative analysis of the GaAs-layer thickness and temperature dependences, we suggest that the PL rise rate reflects the number of exciton–acoustic-phonon scattering events.

  4. 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.

  5. Degradation of (InAlGa)N-based UV-B light emitting diodes stressed by current and temperature

    SciTech Connect (OSTI)

    Glaab, Johannes Ploch, Christian; Kelz, Rico; Stölmacker, Christoph; Lapeyrade, Mickael; Ploch, Neysha Lobo; Rass, Jens; Kolbe, Tim; Einfeldt, Sven; Weyers, Markus; Mehnke, Frank; Kuhn, Christian; Wernicke, Tim; Kneissl, Michael

    2015-09-07

    The degradation of the electrical and optical properties of (InAlGa)N-based multiple quantum well light emitting diodes (LEDs) emitting near 308 nm under different stress conditions has been studied. LEDs with different emission areas were operated at room temperature and at constant current densities of 75 A/cm{sup 2}, 150 A/cm{sup 2}, and 225 A/cm{sup 2}. In addition, the heat sink temperature was varied between 15 °C and 80 °C. Two main modes for the reduction of the optical power were found, which dominate at different times of operation: (1) Within the first 100 h, a fast drop of the optical power is observed scaling exponentially with the temperature and having an activation energy of about 0.13 eV. The drop in optical power is accompanied by changes of the current-voltage (I-V) characteristic. (2) For operation times beyond 100 h, the optical power decreases slowly which can be reasonably described by a square root time dependence. Here, the degradation rate depends on the current density, rather than the current. Again, the rate of optical power reduction of the second mode depends exponentially on the temperature with an activation energy of about 0.21 eV. The drop in the optical power is accompanied by an increased reverse-bias leakage current.

  6. Deep-level defects introduced by 1 MeV electron radiation in AlInGaP for multijunction space solar cells

    SciTech Connect (OSTI)

    Lee, H.S.; Yamaguchi, M.; Ekins-Daukes, N. J.; Khan, A.; Takamoto, T.; Agui, T.; Kamimura, K.; Kaneiwa, M.; Imaizumi, M.; Ohshima, T.; Itoh, H.

    2005-11-01

    Presented in this paper are 1 MeV electron irradiation effects on wide-band-gap (1.97 eV) (Al{sub 0.08}Ga{sub 0.92}){sub 0.52}In{sub 0.48}P diodes and solar cells. The carrier removal rate estimated in p-AlInGaP with electron fluence is about 1 cm{sup -1}, which is lower than that in InP and GaAs. From high-temperature deep-level transient spectroscopy measurements, a deep-level defect center such as majority-carrier (hole) trap H2 (E{sub {nu}}+0.90{+-}0.05 eV) was observed. The changes in carrier concentrations ({delta}p) and trap densities as a function of electron fluence were compared, and as a result the total introduction rate, 0.39 cm{sup -1}, of majority-carrier trap centers (H1 and H2) is different from the carrier removal rate, 1 cm{sup -1}, in p-AlInGaP. From the minority-carrier injection annealing (100 mA/cm{sup 2}), the annealing activation energy of H2 defect is {delta}E=0.60 eV, which is likely to be associated with a vacancy-phosphorus Frenkel pair (V{sub p}-P{sub i}). The recovery of defect concentration and carrier concentration in the irradiated p-AlInGaP by injection relates that a deep-level defect H2 acts as a recombination center as well as compensator center.

  7. Selective layer disordering in intersubband Al0.028Ga0.972 N/AlN superlattices with silicon nitride capping layer

    SciTech Connect (OSTI)

    Wierer, Jonathan J.; Allerman, Andrew A.; Skogen, Erik J.; Tauke-Pedretti, Anna; Vawter, Gregory A.; Montaño, Ines

    2015-06-01

    We demonstrate the selective layer disordering in intersubband Al0.028Ga0.972 N/AlN superlattices using a silicon nitride (SiNx) capping layer. The (SiNx) capped superlattice exhibits suppressed layer disordering under high-temperature annealing. In addition, the rate of layer disordering is reduced with increased SiNx thickness. The layer disordering is caused by Si diffusion, and the SiNx layer inhibits vacancy formation at the crystal surface and ultimately, the movement of Al and Ga atoms across the heterointerfaces. In conclusion, patterning of the SiNx layer results in selective layer disordering, an attractive method to integrate active and passive III–nitride-based intersubband devices.

  8. Band alignment and electrical properties of Al{sub 2}O{sub 3}/?-Ga{sub 2}O{sub 3} heterojunctions

    SciTech Connect (OSTI)

    Kamimura, Takafumi Hoi Wong, Man; Krishnamurthy, Daivasigamani; Higashiwaki, Masataka; Sasaki, Kohei; Kuramata, Akito; Yamakoshi, Shigenobu; Masui, Takekazu

    2014-05-12

    The band alignment of Al{sub 2}O{sub 3}/n-Ga{sub 2}O{sub 3} was investigated by x-ray photoelectron spectroscopy (XPS). With a band gap of 6.8??0.2?eV measured for Al{sub 2}O{sub 3}, the conduction and valence band offsets at the interface were estimated to be 1.5??0.2?eV and 0.7??0.2?eV, respectively. The conduction band offset was also obtained from tunneling current in Al{sub 2}O{sub 3}/n-Ga{sub 2}O{sub 3} (2{sup }01) metal-oxide-semiconductor (MOS) diodes using the Fowler-Nordheim model. The electrically extracted value was in good agreement with the XPS data. Furthermore, the MOS diodes exhibited small capacitance-voltage hysteresis loops, indicating the successful engineering of a high-quality Al{sub 2}O{sub 3}/Ga{sub 2}O{sub 3} interface.

  9. Two dimensional electron transport in modulation-doped In{sub 0.53}Ga{sub 0.47}As/AlAs{sub 0.56}Sb{sub 0.44} ultrathin quantum wells

    SciTech Connect (OSTI)

    Huang, Cheng-Ying Law, Jeremy J. M.; Rodwell, Mark J. W.; Lu, Hong; Gossard, Arthur C.; Jena, Debdeep

    2014-03-28

    We have investigated the growth and electron transport in In{sub 0.53}Ga{sub 0.47}As/AlAs{sub 0.56}Sb{sub 0.44} two dimensional electron gases (2DEG) and compared their properties with In{sub 0.53}Ga{sub 0.47}As/In{sub 0.52}Al{sub 0.48}As 2DEGs. For 10?nm thick InGaAs wells, the electron mobility of InGaAs/AlAsSb 2DEGs is comparable to that of InGaAs/InAlAs 2DEGs. Upon thinning the wells to 3?nm, the 2DEG mobility is degraded quickly and stronger interface roughness scattering is observed for InGaAs/AlAsSb heterointerfaces than for InGaAs/InAlAs heterointerfaces. Changing the group-V exposure between As and Sb during growth interruptions at the InGaAs/AlAsSb interfaces did not significantly change the 2DEG mobility. With the insertion of a two monolayer InAlAs at the InGaAs/AlAsSb interfaces, the interface roughness scattering is reduced and the mobility greatly increased. The room temperature 2DEG mobility shows 66% improvement from 1.63??10{sup 3} cm{sup 2}/Vs to 2.71??10{sup 3}?cm{sup 2}/Vs for a 3?nm InGaAs well.

  10. Poole-Frenkel effect on electrical characterization of Al-doped ZnO films deposited on p-type GaN

    SciTech Connect (OSTI)

    Huang, Bohr-Ran; Liao, Chung-Chi; Ke, Wen-Cheng Chang, Yuan-Ching; Huang, Hao-Ping; Chen, Nai-Chuan

    2014-03-21

    This paper presents the electrical properties of Al-doped ZnO (AZO) films directly grown on two types of p-type GaN thin films. The low-pressure p-GaN thin films (LP-p-GaN) exhibited structural properties of high-density edge-type threading dislocations (TDs) and compensated defects (i.e., nitrogen vacancy). Compared with high-pressure p-GaN thin films (HP-p-GaN), X-ray photoemission spectroscopy of Ga 3d core levels indicated that the surface Fermi-level shifted toward the higher binding-energy side by approximately 0.7 eV. The high-density edge-type TDs and compensated defects enabled surface Fermi-level shifting above the intrinsic Fermi-level, causing the surface of LP-p-GaN thin films to invert to n-type semiconductor. A highly nonlinear increase in leakage current regarding reverse-bias voltage was observed for AZO/LP-p-GaN. The theoretical fits for the reverse-bias voltage region indicated that the field-assisted thermal ionization of carriers from defect associated traps, which is known as the Poole-Frenkel effect, dominated the I-V behavior of AZO/LP-p-GaN. The fitting result estimated the trap energy level at 0.62 eV below the conduction band edge. In addition, the optical band gap increased from 3.50 eV for as-deposited AZO films to 3.62 eV for 300 °C annealed AZO films because of the increased carrier concentration. The increasing Fermi-level of the 300 °C annealed AZO films enabled the carrier transport to move across the interface into the LP-p-GaN thin films without any thermal activated energy. Thus, the Ohmic behavior of AZO contact can be achieved directly on the low-pressure p-GaN films at room temperature.

  11. Synchrotron radiation based cross-sectional scanning photoelectron microscopy and spectroscopy of n-ZnO:Al/p-GaN:Mg heterojunction

    SciTech Connect (OSTI)

    Lee, Kai-Hsuan; Chen, Chia-Hao; Chang, Ping-Chuan; Chen, Tse-Pu; Chang, Sheng-Po; Chang, Shoou-Jinn; Department of Physics, National Tsing Hua University, Kuang-Fu Rd. 101, 30013 Hsinchu, Taiwan

    2013-02-18

    Al-doped ZnO (AZO) deposited by radio frequency co-sputtering is formed on epitaxial Mg-doped GaN template at room temperature to achieve n-AZO/p-GaN heterojunction. Alignment of AZO and GaN bands is investigated using synchrotron radiation based cross-sectional scanning photoelectron microscopy and spectroscopy on the nonpolar side-facet of a vertically c-axis aligned heterostructure. It shows type-II band configuration with valence band offset of 1.63 {+-} 0.1 eV and conduction band offset of 1.61 {+-} 0.1 eV, respectively. Rectification behavior is clearly observed, with a ratio of forward-to-reverse current up to six orders of magnitude when the bias is applied across the p-n junction.

  12. DOE - Office of Legacy Management -- University of Florida - FL 09

    Office of Legacy Management (LM)

    Florida - FL 09 FUSRAP Considered Sites Site: UNIVERSITY OF FLORIDA (FL.09) Eliminated from consideration under FUSRAP - Referred to NRC Designated Name: Not Designated Alternate Name: None Location: Gainesville , Florida FL.09-1 Evaluation Year: 1995 FL.09-1 Site Operations: Research and development using test quantities of radioactive metal. FL.09-2 Site Disposition: Eliminated - No Authority - NRC licensed FL.09-1 Radioactive Materials Handled: Yes Primary Radioactive Materials Handled: Test

  13. Effects of rapid thermal annealing on properties of Ga-doped Mg{sub x}Zn{sub 1−x}O films and Ga-doped Mg{sub x}Zn{sub 1−x}O/AlGaN heterojunction diodes

    SciTech Connect (OSTI)

    Hsueh, Kuang-Po E-mail: kphsueh@mail.vnu.edu.tw; Cheng, Po-Wei

    2014-08-14

    This study investigated the thermal annealing effects of Ga-doped Mg{sub x}Zn{sub 1−x}O (GMZO) films and GMZO/AlGaN heterojunction diodes. GMZO films were deposited using a radio-frequency magnetron sputtering system with a 4-in. ZnO/MgO/Ga{sub 2}O{sub 3} target. In addition, the Hall results, X-ray diffraction, transparent performance, and X-ray photoelectron spectroscopy (XPS) spectra were measured. The as-grown GMZO film deposited in this study exhibited a high transparency with transmittances over 95% in the visible region (360–700 nm) and a sharp absorption edge in the UV region (275–350 nm). The phenomenon of phase separation in the GMZO films was investigated based on the XPS spectra, revealing that an increase in the O-Zn signal accompanied a decline in the O-Ga signal after the thermal annealing. Moreover, the current-voltage (I-V) characteristics of the GMZO/AlGaN n-p junction diodes were examined at different annealing temperatures. The light emission derived from the forward-biased junction and near-ultraviolet (near-UV) light emission was evident at all p-n junctions. The n-GMZO/p-AlGaN diode annealed at 800 °C exhibited a brighter near-UV emission compared with the other diodes. In addition, the spectrum of diode annealed at 800 °C exhibited a broad peak at 474 nm (2.62 eV) and a tail of the emission spectrum extending to 850 nm. Based on these findings, the GMZO films are suitable for forming transparent contact layers in optoelectronic devices, and the n-GMZO/p-AlGaN junction diode is a feasible alternative in near-UV light emission devices.

  14. DOE - Office of Legacy Management -- Humphreys Gold Co - FL 08

    Office of Legacy Management (LM)

    Humphreys Gold Co - FL 08 FUSRAP Considered Sites Site: Humphreys Gold Co. (FL.08 ) Eliminated from consideration under FUSRAP Designated Name: Not Designated Alternate Name: None Location: Jacksonville , Florida FL.08-1 Evaluation Year: 1987 FL.08-2 FL.08-3 Site Operations: Processed monazite ore in the 1950s. FL.08-3 Site Disposition: Eliminated - No Authority - No AEC involvement at the site FL.08-2 Radioactive Materials Handled: Yes Primary Radioactive Materials Handled: Thorium FL.08-1

  15. Fermi level pinning in metal/Al{sub 2}O{sub 3}/InGaAs gate stack after post metallization annealing

    SciTech Connect (OSTI)

    Winter, R.; Krylov, I.; Cytermann, C.; Eizenberg, M.; Tang, K.; Ahn, J.; McIntyre, P. C.

    2015-08-07

    The effect of post metal deposition annealing on the effective work function in metal/Al{sub 2}O{sub 3}/InGaAs gate stacks was investigated. The effective work functions of different metal gates (Al, Au, and Pt) were measured. Flat band voltage shifts for these and other metals studied suggest that their Fermi levels become pinned after the post-metallization vacuum annealing. Moreover, there is a difference between the measured effective work functions of Al and Pt, and the reported vacuum work function of these metals after annealing. We propose that this phenomenon is caused by charging of indium and gallium induced traps at the annealed metal/Al{sub 2}O{sub 3} interface.

  16. Electrical Current Leakage and Open-Core Threading Dislocations in AlGaN-Based Deep Ultraviolet Light-Emitting Diodes.

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

    Moseley, Michael William; Allerman, Andrew A.; Crawford, Mary H.; Wierer, Jonathan; Smith, Michael L.; Biedermann, Laura

    2014-08-04

    Electrical current transport through leakage paths in AlGaN-based deep ultraviolet (DUV) lightemitting diodes (LEDs) and their effect on LED performance are investigated. Open-core threading dislocations, or nanopipes, are found to conduct current through nominally insulating Al0.7Ga0.3N layers and limit the performance of DUV-LEDs. A defect-sensitive phosphoric acid etch reveals these opencore threading dislocations in the form of large, micron-scale hexagonal etch pits visible with optical microscopy, while closed-core screw-, edge-, and mixed-type threading dislocations are represented by smaller and more numerous nanometer-scale pits visible by atomic-force microscopy. The electrical and optical performances of DUV-LEDs fabricated on similar Si-doped Al0.7Ga0.3N templatesmore » are found to have a strong correlation to the density of these nanopipes, despite their small fraction (<0.1% in this study) of the total density of threading dislocations.« less

  17. Electrical current leakage and open-core threading dislocations in AlGaN-based deep ultraviolet light-emitting diodes

    SciTech Connect (OSTI)

    Moseley, Michael Allerman, Andrew; Crawford, Mary; Wierer, Jonathan J.; Smith, Michael; Biedermann, Laura

    2014-08-07

    Electrical current transport through leakage paths in AlGaN-based deep ultraviolet (DUV) light-emitting diodes (LEDs) and their effect on LED performance are investigated. Open-core threading dislocations, or nanopipes, are found to conduct current through nominally insulating Al{sub 0.7}Ga{sub 0.3}N layers and limit the performance of DUV-LEDs. A defect-sensitive phosphoric acid etch reveals these open-core threading dislocations in the form of large, micron-scale hexagonal etch pits visible with optical microscopy, while closed-core screw-, edge-, and mixed-type threading dislocations are represented by smaller and more numerous nanometer-scale pits visible by atomic-force microscopy. The electrical and optical performances of DUV-LEDs fabricated on similar Si-doped Al{sub 0.7}Ga{sub 0.3}N templates are found to have a strong correlation to the density of these nanopipes, despite their small fraction (<0.1% in this study) of the total density of threading dislocations.

  18. Al

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

    on the way to the drip line .... 31 Al 28 Mg 32 Si 12 B + 18 O 30 Al* (-pn) 28 Mg 15 C + 18 O 33 Si* (-pn) 31 Al 16 N + 18 O 34 P* (-pn) 32 Si 15 C 10 7 s...

  19. FL V1.3

    Energy Science and Technology Software Center (OSTI)

    2009-08-03

    A library of utility classes for computer vision. Contains implementations of various well-known image processing techniques, such as interest point operators and region descriptors. Includes interfaces to various libraries for image and video I/O, as well as an interface to LAPACK/BLAS. FL was developed at the University of Illinois, Urbana-Champaign (UIUC) and released under an open source license. Version 1.2 was a maintenance release provided by SNL under the LGPL license. Version 1.3 is amore » maintenance release, containing the following changes: - Improved image format handling. Now handles strided and planar memory layouts and a wider range of pixel formats. - Improved image file I/O, including better support for metadata, a wider range of stored pixel types, and a couple of new file formats. - Improvements to DOG and SIFT, and efficiency improvements in low-level convolution. - Improvements to networking, including a generic TCP listener. - Various improvements to numerical processing. The HISTORY file included in the distribution contains a more detailed description of the changes.« less

  20. Interband emission energy in wurtzite GaN/Ga{sub 0.8}Al{sub 0.2}N and ZnO/ Zn{sub 0.607}Mg{sub 0.393}O strained quantum dots

    SciTech Connect (OSTI)

    Minimala, N. S.; Peter, A. John

    2014-04-24

    The effects of geometrical confinement on the exciton binding energies and thereby the interband emission energy are investigated in wurtzite /Ga{sub 0.8}Al{sub 0.2}N and ZnO/ Zn{sub 0.607}Mg{sub 0.393}O quantum dots taking into account the geometrical confinement. The calculations are performed with the same barrier height of both the materials. The effects of strain and the internal electric field, induced by spontaneous and piezoelectric polarization, are taken into consideration in all the calculations.

  1. X ray photoelectron analysis of oxide-semiconductor interface after breakdown in Al{sub 2}O{sub 3}/InGaAs stacks

    SciTech Connect (OSTI)

    Shekhter, P.; Palumbo, F.; Cohen Weinfeld, K.; Eizenberg, M.

    2014-09-08

    In this work, the post-breakdown characteristics of metal gate/Al{sub 2}O{sub 3}/InGaAs structures were studied using surface analysis by x ray photoelectron spectroscopy. The results show that for dielectric breakdown under positive bias, localized filaments consisting of oxidized substrate atoms (In, Ga and As) were formed, while following breakdown under negative bias, a decrease of oxidized substrate atoms was observed. Such differences in the microstructure at the oxide-semiconductor interface after breakdown for positive and negative voltages are explained by atomic diffusion of the contact atoms into the gate dielectric in the region of the breakdown spot by the current induced electro-migration effect. These findings show a major difference between Al{sub 2}O{sub 3}/InGaAs and SiO{sub 2}/Si interfaces, opening the way to a better understanding of the breakdown characteristics of III-V complementary-metal-oxide-semiconductor technology.

  2. Characterization of heavy masses of two-dimensional conduction subband in InGaAs/InAlAs MQW structures by pulsed cyclotron resonance technology

    SciTech Connect (OSTI)

    Kotera, N.; Tanaka, K. [Kyushu Inst. of Technology, Iizuka, Fukuoka (Japan); Arimoto, H.; Miura, N. [Univ. of Tokyo, Roppongi, Tokyo (Japan). Inst. of Solid State Physics; Jones, E.D. [Sandia National Labs., Albuquerque, NM (United States); Mishima, T. [Hitachi Ltd., Kokubunji, Tokyo (Japan). Central Research Lab.; Washima, M. [Hitachi Cable, Ltd., Tsukuba, Ibaraki (Japan). Advanced Research Center

    1998-05-01

    Conduction-band effective masses in a direction parallel to the quantum well plane were investigated in n-type-modulation-doped InGaAs/InAlAs multiquantum well system. Thicknesses of well and barrier were 5 and 10 nm. Three highly-doped specimens having about 1 {times} 10{sup 12} cm{sup {minus}2} per one quantum well were prepared by MBE. Double-crystal X-ray diffraction was used to check the crystal quality. Heavy electron effective masses, almost 50% bigger than the band edge mass of 0.041m{sub 0}, were measured by far-infrared and infrared cyclotron resonances under pulse high magnetic fields up to 100 T. Nonparabolicity of this subband was less than 12% by comparing the two cyclotron resonances. Observed two-dimensional subband structure was quite different from conduction-band effective mass in a direction perpendicular to the same quantum well and from GaAs/GaAlAs quantum well system.

  3. Analysis of different tunneling mechanisms of In{sub x}Ga{sub 1?x}As/AlGaAs tunnel junction light-emitting transistors

    SciTech Connect (OSTI)

    Wu, Cheng-Han; Wu, Chao-Hsin

    2014-10-27

    The electrical and optical characteristics of tunnel junction light-emitting transistors (TJLETs) with different indium mole fractions (x?=?5% and 2.5%) of the In{sub x}Ga{sub 1?x}As base-collector tunnel junctions have been investigated. Two electron tunneling mechanisms (photon-assisted or direct tunneling) provide additional currents to electrical output and resupply holes back to the base region, resulting in the upward slope of I-V curves and enhanced optical output under forward-active operation. The larger direct tunneling probability and stronger Franz-Keldysh absorption for 5% TJLET lead to higher collector current slope and less optical intensity enhancement when base-collector junction is under reverse-biased.

  4. Ultraviolet band-pass Schottky barrier photodetectors formed by Al-doped ZnO contacts to n-GaN

    SciTech Connect (OSTI)

    Sheu, J.K.; Lee, M.L.; Tun, C.J.; Lin, S.W.

    2006-01-23

    This work prepared Al-doped ZnO(AZO) films using dc sputtering to form Schottky contacts onto GaN films with low-temperature-grown GaN cap layer. Application of ultraviolet photodetector showed that spectral responsivity exhibits a narrow bandpass characteristic ranging from 345 to 375 nm. Moreover, unbiased peak responsivity was estimated to be around 0.12 A/W at 365 nm, which corresponds to a quantum efficiency of around 40%. In our study, relatively low responsivity can be explained by the marked absorption of the AZO contact layer. When the reverse biases were below 5 V, the study revealed that dark currents were well below 5x10{sup -12} A even though the samples were annealed at increased temperatures.

  5. DOE - Office of Legacy Management -- Gardinier Inc - FL 05

    Office of Legacy Management (LM)

    Gardinier Inc - FL 05 FUSRAP Considered Sites Site: GARDINIER, INC. ( FL.05 ) Eliminated from consideration under FUSRAP - Referred to EPA and State of Florida Designated Name: Not Designated Alternate Name: U. S. Phosphoric Products FL.05-1 Location: Tampa , Florida FL.05-2 Evaluation Year: 1984 FL.05-3 Site Operations: U. S. Phosphoric Products constructed and operated a small scale pilot plant for uranium recovery; and Gardinier investigated a process for the recovery of by-product uranium

  6. Demonstration of transverse-magnetic deep-ultraviolet stimulated emission from AlGaN multiple-quantum-well lasers grown on a sapphire substrate

    SciTech Connect (OSTI)

    Li, Xiao-Hang E-mail: dupuis@gatech.edu; Kao, Tsung-Ting; Satter, Md. Mahbub; Shen, Shyh-Chiang; Yoder, P. Douglas; Detchprohm, Theeradetch; Dupuis, Russell D. E-mail: dupuis@gatech.edu; Wei, Yong O.; Wang, Shuo; Xie, Hongen; Fischer, Alec M.; Ponce, Fernando A.

    2015-01-26

    We demonstrate transverse-magnetic (TM) dominant deep-ultraviolet (DUV) stimulated emission from photo-pumped AlGaN multiple-quantum-well lasers grown pseudomorphically on an AlN/sapphire template by means of photoluminescence at room temperature. The TM-dominant stimulated emission was observed at wavelengths of 239, 242, and 243 nm with low thresholds of 280, 250, and 290 kW/cm{sup 2}, respectively. In particular, the lasing wavelength of 239 nm is shorter compared to other reports for AlGaN lasers grown on foreign substrates including sapphire and SiC. The peak wavelength difference between the transverse-electric (TE)-polarized emission and TM-polarized emission was approximately zero for the lasers in this study, indicating the crossover of crystal-field split-off hole and heavy-hole valence bands. The rapid variation of polarization between TE- and TM-dominance versus the change in lasing wavelength from 243 to 249 nm can be attributed to a dramatic change in the TE-to-TM gain coefficient ratio for the sapphire-based DUV lasers in the vicinity of TE-TM switch.

  7. Spectroscopic determination of the bandgap crossover composition in MBE-grown AlxGa1-xAs

    SciTech Connect (OSTI)

    Fluegel, Brian; Alberi, Kirstin; Reno, John; Mascarenhas, Angelo

    2015-03-12

    The aluminum concentration dependence of the energies of the direct and indirect bandgaps arising from the Γ and X conduction bands are measured at 1.7 K in the semiconductor alloy AlxGa1-xAs. The composition at which the bands cross is determined from photoluminescence of molecular-beam epitaxy samples grown very close to crossover. The use of resonant laser excitation and the improved sample linewidth allows precise determination of the bound exciton transition energies. Moreover, photoluminescence excitation spectroscopy is used to measure the binding energies of the donor-bound excitons and the Γ free exciton binding energy.

  8. Spectroscopic determination of the bandgap crossover composition in MBE-grown AlxGa1-xAs

    SciTech Connect (OSTI)

    Fluegel, Brian; Alberi, Kirstin; Reno, John; Mascarenhas, Angelo

    2015-03-12

    The aluminum concentration dependence of the energies of the direct and indirect bandgaps arising from the ? and X conduction bands are measured at 1.7 K in the semiconductor alloy AlxGa1-xAs. The composition at which the bands cross is determined from photoluminescence of molecular-beam epitaxy samples grown very close to crossover. The use of resonant laser excitation and the improved sample linewidth allows precise determination of the bound exciton transition energies. Moreover, photoluminescence excitation spectroscopy is used to measure the binding energies of the donor-bound excitons and the ? free exciton binding energy.

  9. Impact of La{sub 2}O{sub 3} interfacial layers on InGaAs metal-oxide-semiconductor interface properties in Al{sub 2}O{sub 3}/La{sub 2}O{sub 3}/InGaAs gate stacks deposited by atomic-layer-deposition

    SciTech Connect (OSTI)

    Chang, C.-Y. Takenaka, M.; Takagi, S.; Ichikawa, O.; Osada, T.; Hata, M.; Yamada, H.

    2015-08-28

    We examine the electrical properties of atomic layer deposition (ALD) La{sub 2}O{sub 3}/InGaAs and Al{sub 2}O{sub 3}/La{sub 2}O{sub 3}/InGaAs metal-oxide-semiconductor (MOS) capacitors. It is found that the thick ALD La{sub 2}O{sub 3}/InGaAs interface provides low interface state density (D{sub it}) with the minimum value of ∼3 × 10{sup 11} cm{sup −2} eV{sup −1}, which is attributable to the excellent La{sub 2}O{sub 3} passivation effect for InGaAs surfaces. It is observed, on the other hand, that there are a large amount of slow traps and border traps in La{sub 2}O{sub 3}. In order to simultaneously satisfy low D{sub it} and small hysteresis, the effectiveness of Al{sub 2}O{sub 3}/La{sub 2}O{sub 3}/InGaAs gate stacks with ultrathin La{sub 2}O{sub 3} interfacial layers is in addition evaluated. The reduction of the La{sub 2}O{sub 3} thickness to 0.4 nm in Al{sub 2}O{sub 3}/La{sub 2}O{sub 3}/InGaAs gate stacks leads to the decrease in hysteresis. On the other hand, D{sub it} of the Al{sub 2}O{sub 3}/La{sub 2}O{sub 3}/InGaAs interfaces becomes higher than that of the La{sub 2}O{sub 3}/InGaAs ones, attributable to the diffusion of Al{sub 2}O{sub 3} through La{sub 2}O{sub 3} into InGaAs and resulting modification of the La{sub 2}O{sub 3}/InGaAs interface structure. As a result of the effective passivation effect of La{sub 2}O{sub 3} on InGaAs, however, the Al{sub 2}O{sub 3}/10 cycle (0.4 nm) La{sub 2}O{sub 3}/InGaAs gate stacks can realize still lower D{sub it} with maintaining small hysteresis and low leakage current than the conventional Al{sub 2}O{sub 3}/InGaAs MOS interfaces.

  10. A detailed investigation on the impact of post-growth annealing on the materials and device characteristics of 35-layer In{sub 0.50}Ga{sub 0.50}As/GaAs quantum dot infrared photodetector with quaternary In{sub 0.21}Al{sub 0.21}Ga{sub 0.58}As capping

    SciTech Connect (OSTI)

    Adhikary, Sourav; Chakrabarti, Subhananda

    2012-11-15

    Highlights: ? We investigated the effect of ex situ annealing on InGaAs/GaAs QDIP with InAlGaAs layer. ? As-grown defect was removed by using post-growth annealing treatment. ? Increase in the compressive strain due to annealing is calculated from XRD curve. ? Three-fold enhancement in responsivity is observed in the QDIPs annealed at 650 C. ? Two-fold enhancement in D* is observed sample annealed at 650 C compared to as grown. -- Abstract: The effect of post-growth rapid thermal annealing on 35-layer In{sub 0.50}Ga{sub 0.50}As/GaAs quantum dot infrared photodetector (QDIP) with quaternary In{sub 0.21}Al{sub 0.21}Ga{sub 0.58}As capping has been investigated. Transmission electron microscopy showed some as-grown defects were removed by post growth annealing treatment. An increase in the compressive strain in the heterostructure due to annealing was identified from X-ray diffraction curve. A two-color photoresponse in the long-wave region (8.5 and 10.2 ?m) was observed in both as-grown device and those annealed at 650 C temperature. A three-fold enhancement in peak responsivity was observed in the QDIPs annealed at 650 C (1.19 A/W) compared to that in the as-grown (0.34 A/W). Detectivity also increased by two fold from as-grown to 650 C annealed device. The changes are attributed to the removal of as-grown defects and dislocations during epitaxial growth. These removals changed the confinement potential profile, which resulted in an improvement in the detectivity and responsivity of the annealed sample.

  11. Analysis of natural gases, AL, AR, FL, GA, IL, IN, IA, KY, LA, MD, MI, MS, MO, NJ, NY, NC, OH, PA, TN, VA, and WV; 1951-1991 (for microcomputers). Data file

    SciTech Connect (OSTI)

    Not Available

    1991-01-01

    The U.S. Bureau of Mines diskette contains analysis and related source data for 2,357 natural gas samples collected from miscellaneous states, which include the following states: Alabama, Arkansas (except Arkoma Basin), Florida, Georgia, Illinois, Indiana, Iowa, Kentucky, Louisiana, Maryland, Michigan, Mississippi, Missouri, New Jersey, New York, North Carolina, Ohio, Pennsylvania, Tennessee, Virginia, and West Virginia. All samples were obtained and analyzed as part of the Bureau's investigations of occurrences of helium in natural gases of countries with free market economies. The survey has been conducted since 1917. The analysis contained on the diskette contain the full range of component analysis data. Five files are on the diskette: READ.ME, MISC.TXT, MISC.DBF, USHEANAL.DBF, and BASINCDE.TXT.

  12. 230 s room-temperature storage time and 1.14 eV hole localization energy in In{sub 0.5}Ga{sub 0.5}As quantum dots on a GaAs interlayer in GaP with an AlP barrier

    SciTech Connect (OSTI)

    Bonato, Leo Sala, Elisa M.; Stracke, Gernot; Nowozin, Tobias; Strittmatter, André; Ajour, Mohammed Nasser; Daqrouq, Khaled; Bimberg, Dieter

    2015-01-26

    A GaP n{sup +}p-diode containing In{sub 0.5}Ga{sub 0.5}As quantum dots (QDs) and an AlP barrier is characterized electrically, together with two reference samples: a simple n{sup +}p-diode and an n{sup +}p-diode with AlP barrier. Localization energy, capture cross-section, and storage time for holes in the QDs are determined using deep-level transient spectroscopy. The localization energy is 1.14(±0.04) eV, yielding a storage time at room temperature of 230(±60) s, which marks an improvement of 2 orders of magnitude compared to the former record value in QDs. Alternative material systems are proposed for still higher localization energies and longer storage times.

  13. 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.

  14. Thickness Effect of Al-Doped ZnO Window Layer on Damp Heat Stability of CuInGaSe2 Solar Cells: Preprint

    SciTech Connect (OSTI)

    Pern, F. J.; Mansfield, L.; DeHart, C.; Glick, S. H.; Yan, F.; Noufi, R.

    2011-07-01

    We investigated the damp heat (DH) stability of CuInGaSe2 (CIGS) solar cells as a function of thickness of the Al-doped ZnO (AZO) window layer from the 'standard' 0.12 μm to a modest 0.50 μm over an underlying 0.10-μm intrinsic ZnO buffer layer. The CIGS cells were prepared with external electrical contact using fine Au wire to the tiny 'standard' Ni/Al (0.05 μm/3 μm) metal grid contact pads. Bare cell coupons and sample sets encapsulated in a specially designed, Al-frame test structure with an opening for moisture ingress control using a TPT backsheet were exposed to DH at 85oC and 85% relative humidity, and characterized by current-voltage (I-V), quantum efficiency (QE), and (electrochemical) impedance spectroscopy (ECIS). The results show that bare cells exhibited rapid degradation within 50-100 h, accompanied by film wrinkling and delamination and corrosion of Mo and AlNi grid, regardless of AZO thickness. In contrast, the encapsulated cells did not show film wrinkling, delamination, and Mo corrosion after 168 h DH exposure; but the trend of efficiency degradation rate showed a weak correlation to the AZO thickness.

  15. Thickness Effect of Al-Doped ZnO Window Layer on Damp-Heat Stability of CuInGaSe2 Solar Cells

    SciTech Connect (OSTI)

    Pern, F. J.; Mansfield, L.; DeHart, C.; Glick, S. H.; Yan, F.; Noufi, R.

    2011-01-01

    We investigated the damp heat (DH) stability of CuInGaSe{sub 2} (CIGS) solar cells as a function of thickness of the Al-doped ZnO (AZO) window layer from the 'standard' 0.12 {micro}m to a modest 0.50 {micro}m over an underlying 0.10-{micro}m intrinsic ZnO buffer layer. The CIGS cells were prepared with external electrical contact using fine Au wire to the tiny 'standard' Ni/Al (0.05 {micro}m/3 {micro}m) metal grid contact pads. Bare cell coupons and sample sets encapsulated in a specially designed, Al-frame test structure with an opening for moisture ingress control using a TPT backsheet were exposed to DH at 85 C and 85% relative humidity, and characterized by current-voltage (I-V), quantum efficiency (QE), and (electrochemical) impedance spectroscopy (ECIS). The results show that bare cells exhibited rapid degradation within 50-100 h, accompanied by film wrinkling and delamination and corrosion of Mo and AlNi grid, regardless of AZO thickness. In contrast, the encapsulated cells did not show film wrinkling, delamination, and Mo corrosion after 168 h DH exposure; but the trend of efficiency degradation rate showed a weak correlation to the AZO thickness.

  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. 0.15 {mu}m InGaAs/AlGaAs/GaAs HEMT production process for high performance and high yield v-band power MMICs

    SciTech Connect (OSTI)

    Lai, R.; Biedenbender, M.; Lee, J.

    1995-12-31

    The authors present a unique high yield, high performance 0.15 {mu}m HEMT production process which supports fabrication of MMW power MMICs up to 70 GHz. This process has been transferred successfully from an R&D process to TRW`s GaAs production line. This paper reports the on-wafer test results of more than 1300 V-band MMIC PA circuits measured over 24 wafers. The best 2-stage V-band power MMICs have demonstrated state-of-the-art performance with 9 dB power gain, 20% PAE and 330 mW output power. An excellent RF yield of 60% was achieved with an 8 dB power gain and 250 mW output power specification.

  18. A combined capacitance-voltage and hard x-ray photoelectron spectroscopy characterisation of metal/Al{sub 2}O{sub 3}/In{sub 0.53}Ga{sub 0.47}As capacitor structures

    SciTech Connect (OSTI)

    Lin, Jun; Povey, Ian M.; Hurley, Paul K.; Walsh, Lee; Hughes, Greg; Woicik, Joseph C.; O'Regan, Terrance P.

    2014-07-14

    Capacitance-Voltage (C-V) characterization and hard x-ray photoelectron spectroscopy (HAXPES) measurements have been used to study metal/Al{sub 2}O{sub 3}/In{sub 0.53}Ga{sub 0.47}As capacitor structures with high (Ni) and low (Al) work function metals. The HAXPES measurements observe a band bending occurring prior to metal deposition, which is attributed to a combination of fixed oxide charges and interface states of donor-type. Following metal deposition, the Fermi level positions at the Al{sub 2}O{sub 3}/In{sub 0.53}Ga{sub 0.47}As interface move towards the expected direction as observed from HAXPES measurements. The In{sub 0.53}Ga{sub 0.47}As surface Fermi level positions determined from both the C-V analysis at zero gate bias and HAXPES measurements are in reasonable agreement. The results are consistent with the presence of electrically active interface states at the Al{sub 2}O{sub 3}/In{sub 0.53}Ga{sub 0.47}As interface and suggest an interface state density increasing towards the In{sub 0.53}Ga{sub 0.47}As valence band edge.

  19. Characteristics of the dynamics of breakdown filaments in Al{sub 2}O{sub 3}/InGaAs stacks

    SciTech Connect (OSTI)

    Palumbo, F.; Shekhter, P.; Eizenberg, M.; Cohen Weinfeld, K.

    2015-09-21

    In this paper, the Al{sub 2}O{sub 3}/InGaAs interface was studied by X-ray photoelectron spectroscopy (XPS) after a breakdown (BD) event at positive bias applied to the gate contact. The dynamics of the BD event were studied by comparable XPS measurements with different current compliance levels during the BD event. The overall results show that indium atoms from the substrate move towards the oxide by an electro-migration process and oxidize upon arrival following a power law dependence on the current compliance of the BD event. Such a result reveals the physical feature of the breakdown characteristics of III-V based metal-oxide-semiconductor devices.

  20. Magnetooptical study of Zeeman effect in Mn modulation-doped InAs/InGaAs/InAlAs quantum well structures

    SciTech Connect (OSTI)

    Terent'ev, Ya. V.; Danilov, S. N.; Plank, H.; Loher, J.; Schuh, D.; Bougeard, D.; Weiss, D.; Ganichev, S. D.; Durnev, M. V.; Ivanov, S. V.; Tarasenko, S. A.; Rozhansky, I. V.; Yakovlev, D. R.

    2015-09-21

    We report on a magneto-photoluminescence (PL) study of Zeeman effect in Mn modulation-doped InAs/InGaAs/InAlAs quantum wells (QW). Two PL lines corresponding to the radiative recombination of photoelectrons with free and bound-on-Mn holes have been observed. In the presence of a magnetic field applied in the Faraday geometry, both lines split into two circularly polarized components. While temperature and magnetic field dependence of the splitting are well described by the Brillouin function, providing an evidence for exchange interaction with spin polarized manganese ions, the value of the splitting exceeds by two orders of magnitude the value of the giant Zeeman splitting estimated for the average Mn density in QW obtained by the secondary ion mass spectroscopy.

  1. Fermi level control of compensating point defects during metalorganic chemical vapor deposition growth of Si-doped AlGaN

    SciTech Connect (OSTI)

    Bryan, Z; Bryan, I; Gaddy, BE; Reddy, P; Hussey, L; Bobea, M; Guo, W; Hoffmann, M; Kirste, R; Tweedie, J; Gerhold, M; Irving, DL; Sitar, Z; Collazo, R

    2014-12-01

    A Fermi-level control scheme for point defect management using above-bandgap UV illumination during growth is presented. We propose an extension to the analogy between the Fermi level and the electrochemical potential such that the electrochemical potential of a charged defect in a material with steady-state populations of free charge carriers may be expressed in terms of the quasi-Fermi levels. A series of highly Si-doped Al0.65Ga0.35N films grown by metalorganic chemical vapor deposition with and without UV illumination showed that samples grown under UV illumination had increased free carrier concentration, free carrier mobility, and reduced midgap photoluminescence all indicating a reduction in compensating point defects. (c) 2014 AIP Publishing LLC.

  2. Bias current dependence of the spin lifetime in insulating Al{sub 0.3}Ga{sub 0.7}As

    SciTech Connect (OSTI)

    Misuraca, Jennifer Kim, Joon-Il; Xiong, Peng; Molnár, Stephan von; Lu, Jun; Meng, Kangkang; Chen, Lin; Yu, Xuezhe; Zhao, Jianhua

    2014-02-24

    The spin lifetime and Hanle signal amplitude dependence on bias current has been investigated in insulating Al{sub 0.3}Ga{sub 0.7}As:Si using a three-terminal Hanle effect geometry. The amplitudes of the Hanle signals are much larger for forward bias than for reverse bias, although the spin lifetimes found are statistically equivalent. The spin resistance-area product shows a strong increase with bias current for reverse bias and small forward bias until 150 μA, beyond which a weak dependence is observed. The spin lifetimes diminish substantially with increasing bias current. The dependence of the spin accumulation and lifetime diminish only moderately with temperature from 5 K to 30 K.

  3. Real space pseudopotential calculations for size trends in Ga- and Al-doped zinc oxide nanocrystals with wurtzite and zincblende structures

    SciTech Connect (OSTI)

    Bobbitt, N. Scott; Kim, Minjung; Sai, Na; Marom, Noa; Chelikowsky, James R.

    2014-09-07

    Zinc oxide is often used as a popular inexpensive transparent conducting oxide. Here, we employ density functional theory and local density approximation to examine the effects of quantum confinement in doped nanocrystals of this material. Specifically, we examine the addition of Ga and Al dopants to ZnO nanocrystals on the order of 1.0 nm. We find that the inclusion of these dopants is energetically less favorable in smaller particles and that the electron binding energy, which is associated with the dopant activation, decreases with the nanocrystal size. We find that the introduction of impurities does not alter significantly the Kohn-Sham eigenspectrum for small nanocrystals of ZnO. The added electron occupies the lowest existing state, i.e., no new bound state is introduced in the gap. We verify this assertion with hybrid functional calculations.

  4. Exciton and biexciton dynamics in single self-assembled InAs/InGaAlAs/InP quantum dash emitting near 1.55??m

    SciTech Connect (OSTI)

    Dusanowski, ?.; Syperek, M. Rudno-Rudzi?ski, W.; Mrowi?ski, P.; Sek, G.; Misiewicz, J.; Somers, A.; Reithmaier, J. P.; Hfling, S.; Forchel, A.

    2013-12-16

    Exciton and biexciton dynamics in a single self-assembled InAs/In{sub 0.53}Ga{sub 0.23}Al{sub 0.24}As/InP(001) quantum dash emitting near 1.55??m has been investigated by micro-photoluminescence and time-resolved micro-photoluminescence at T?=?4.2?K. The exciton and biexciton fine structure splitting of ?60??eV, the biexciton binding energy of ?3.5?meV, and the characteristic exciton and biexciton decay times of 2.0??0.1?ns and 1.1??0.1?ns, respectively, have been determined. The measurement of the biexciton and exciton cross-correlation statistics of the photon emission confirmed the cascaded relaxation process. The exciton-to-biexciton decay time ratio and a small fine structure splitting suggest carrier localization within the investigated quantum dash.

  5. S M Stoller Quarterly Sampling, STAR Center, Largo, FL

    Office of Legacy Management (LM)

    Quarterly Sampling, STAR Center, Largo, FL 7030-226 Accutest Job Number: F27229 Sampling Date: 10/07/04 Report to: S M Stoller Cathy.Kelleher@gjo.doe.gov ATTN: Cathy Kelleher Total number of pages in report: Certifications: FL (DOH E83510), NC (573), NJ (FL002), MA (FL946), IA (366), LA (03051), KS (E-10327), SC, AK This report shall not be reproduced, except in its entirety, without the written approval of Accutest Laboratories. Southeast * 4405 Vineland Road * Suite C-15 * Orlando, FL 32811 *

  6. Investigation of arsenic and antimony capping layers, and half cycle reactions during atomic layer deposition of Al{sub 2}O{sub 3} on GaSb(100)

    SciTech Connect (OSTI)

    Zhernokletov, Dmitry M.; Dong, Hong; Brennan, Barry; Kim, Jiyoung; Wallace, Robert M.; Yakimov, Michael; Tokranov, Vadim; Oktyabrsky, Serge

    2013-11-15

    In-situ monochromatic x-ray photoelectron spectroscopy, low energy electron diffraction, ion scattering spectroscopy, and transmission electron microscopy are used to examine the GaSb(100) surfaces grown by molecular beam epitaxy after thermal desorption of a protective As or Sb layer and subsequent atomic layer deposition (ALD) of Al{sub 2}O{sub 3}. An antimony protective layer is found to be more favorable compared to an arsenic capping layer as it prevents As alloys from forming with the GaSb substrate. The evolution of oxide free GaSb/Al{sub 2}O{sub 3} interface is investigated by “half-cycle” ALD reactions of trimethyl aluminum and deionized water.

  7. Influence of buffer-layer construction and substrate orientation on the electron mobilities in metamorphic In{sup 0.70}Al{sup 0.30}As/In{sup 0.76}Ga{sup 0.24}As/In{sup 0.70}Al{sup 0.30}As structures on GaAs substrates

    SciTech Connect (OSTI)

    Kulbachinskii, V. A.; Oveshnikov, L. N.; Lunin, R. A.; Yuzeeva, N. A.; Galiev, G. B.; Klimov, E. A.; Pushkarev, S. S.; Maltsev, P. P.

    2015-07-15

    The influence of construction of the buffer layer and misorientation of the substrate on the electrical properties of In{sup 0.70}Al{sup 0.30}As/In{sup 0.76}Ga{sup 0.24}As/In{sup 0.70}Al{sup 0.30}As quantum wells on a GaAs substrate is studied. The temperature dependences (in the temperature range of 4.2 K < T < 300 K) and field dependences (in magnetic fields as high as 6 T) of the sample resistances are measured. Anisotropy of the resistances in different crystallographic directions is detected; this anisotropy depends on the substrate orientation and construction of the metamorphic buffer layer. In addition, the Hall effect and the Shubnikov–de Haas effect are studied. The Shubnikov–de Haas effect is used to determine the mobilities of electrons separately in several occupied dimensionally quantized subbands in different crystallographic directions. The calculated anisotropy of mobilities is in agreement with experimental data on the anisotropy of the resistances.

  8. S M Stoller Quarterly Sampling, STAR Center, Largo, FL

    Office of Legacy Management (LM)

    0/06 Technical Report for S M Stoller Quarterly Sampling, STAR Center, Largo, FL 110406202 Accutest Job Number: F39137 Sampling Dates: 03/08/06 - 03/09/06 Report to: S M Stoller Cathy.Kelleher@gjo.doe.gov ATTN: Cathy Kelleher Total number of pages in report: Certifications: FL (DOH E83510), NC (573), NJ (FL002), MA (FL946), IA (366), LA (03051), KS (E-10327), SC, AK This report shall not be reproduced, except in its entirety, without the written approval of Accutest Laboratories. Southeast *

  9. S M Stoller Quarterly Sampling, STAR Center, Largo, FL

    Office of Legacy Management (LM)

    531 Sampling Date: 04/16/04 Report to: S M Stoller Cathy.Kelleher@gjo.doe.gov ATTN: Cathy Kelleher Total number of pages in report: Certifications: FL (DOH E83510), NC (573), NJ (FL002), MA (FL946), IA (366), LA (03051), KS (E-10327), SC, AK This report shall not be reproduced, except in its entirety, without the written approval of Accutest Laboratories. Southeast * 4405 Vineland Road * Suite C-15 * Orlando, FL 32811 * tel: 407-425-6700 * fax: 407-425-0707 * http://www.accutest.com Test results

  10. S M Stoller Quarterly Sampling, STAR Center, Largo, FL

    Office of Legacy Management (LM)

    2/04 Technical Report for S M Stoller Quarterly Sampling, STAR Center, Largo, FL 110406202 Accutest Job Number: F25409 Sampling Dates: 07/13/04 - 07/14/04 Report to: S M Stoller Cathy.Kelleher@gjo.doe.gov ATTN: Cathy Kelleher Total number of pages in report: Certifications: FL (DOH E83510), NC (573), NJ (FL002), MA (FL946), IA (366), LA (03051), KS (E-10327), SC, AK This report shall not be reproduced, except in its entirety, without the written approval of Accutest Laboratories. Southeast *

  11. S M Stoller Quarterly Sampling, STAR Center, Largo, FL

    Office of Legacy Management (LM)

    Quarterly Sampling, STAR Center, Largo, FL 110406202 Accutest Job Number: F33211 Sampling Dates: 07/13/05 - 07/14/05 Report to: S M Stoller Cathy.Kelleher@gjo.doe.gov ATTN: Cathy Kelleher Total number of pages in report: Certifications: FL (DOH E83510), NC (573), NJ (FL002), MA (FL946), IA (366), LA (03051), KS (E-10327), SC, AK This report shall not be reproduced, except in its entirety, without the written approval of Accutest Laboratories. Southeast * 4405 Vineland Road * Suite C-15 *

  12. S M Stoller Star Center-WWNA Monthly; Largo, FL

    Office of Legacy Management (LM)

    7170 Sampling Date: 10/05/04 Report to: S M Stoller Cathy.Kelleher@gjo.doe.gov ATTN: Cathy Kelleher Total number of pages in report: Certifications: FL (DOH E83510), NC (573), NJ (FL002), MA (FL946), IA (366), LA (03051), KS (E-10327), SC, AK This report shall not be reproduced, except in its entirety, without the written approval of Accutest Laboratories. Southeast * 4405 Vineland Road * Suite C-15 * Orlando, FL 32811 * tel: 407-425-6700 * fax: 407-425-0707 * http://www.accutest.com Test

  13. S M Stoller Star Center-WWNA Monthly; Largo, FL

    Office of Legacy Management (LM)

    6/04 Technical Report for S M Stoller Star Center-WWNA Monthly; Largo, FL 110406202 Accutest Job Number: F25242 Sampling Date: 07/06/04 Report to: S M Stoller Cathy.Kelleher@gjo.doe.gov ATTN: Cathy Kelleher Total number of pages in report: Certifications: FL (DOH E83510), NC (573), NJ (FL002), MA (FL946), IA (366), LA (03051), KS (E-10327), SC, AK This report shall not be reproduced, except in its entirety, without the written approval of Accutest Laboratories. Southeast * 4405 Vineland Road *

  14. S M Stoller Monthly Sampling, STAR Center, Largo, FL

    Office of Legacy Management (LM)

    Sampling, STAR Center, Largo, FL 110406202 Accutest Job Number: F23261 Sampling Date: 04... Test results contained within this data package meet the requirements of the National ...

  15. S M Stoller Quarterly Sampling, STAR Center, Largo, FL

    Office of Legacy Management (LM)

    ... Technical Report for S M Stoller Quarterly Sampling, STAR Center, Largo, FL 110406202 Accutest Job Number: F23505 Sampling Dates: 041504 - 041604 Report to: S M Stoller ...

  16. Quantifying Fl Value of Hydro in Transmission Grid | Department...

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

    Quantifying Fl Value of Hydro in Transmission Grid 72hydrogridserviceseprikey.ppt (3.96 MB) More Documents & Publications Enviro effects of hydrokinetic turbines on fish ...

  17. Distribution of cations in wurtzitic InxGa1-xN and InxAl1-xN alloys: Consequences for energetics and quasiparticle electronic structures

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

    de Carvalho, Luiz Cláudio; Schleife, André; Furthmüller, Jürgen; Bechstedt, Friedhelm

    2012-03-27

    The ternary, isostructural, wurtzite-derived group-III mononitride alloys InxGa1-xN andInxAl1-xN are reexamined within a cluster expansion approach. Using density functional theory together with the AM05 exchange-correlation functional, the total energies and the optimized atomic geometries of all 22 clusters classes of the cluster expansion for each material system are calculated. The computationally demanding calculation of the corresponding quasiparticle electronic structures is achieved for all cluster classes by means of a recently developed scheme to approximately solve the quasiparticle equation based on the HSE06 hybrid functional and the G₀W₀ approach. Using two different alloy statistics, the configurational averages for the lattice parameters,more » the mixing enthalpies, and the bulk moduli are calculated. The composition-dependent electronic structures of the alloys are discussed based on configurationally averaged electronic states, band gaps, and densities of states. Ordered cluster arrangements are found to be energetically rather unfavorable, however, they possess the smallest energy gaps and, hence, contribute to light emission. The influence of the alloy statistics on the composition dependencies and the corresponding bowing parameters of the band gaps is found to be significant and should, hence, lead to different signatures in the optical-absorption or -emission spectra.« less

  18. Lattice parameters and Raman-active phonon modes of β-(Al{sub x}Ga{sub 1−x}){sub 2}O{sub 3}

    SciTech Connect (OSTI)

    Kranert, Christian Jenderka, Marcus; Lenzner, Jörg; Lorenz, Michael; Wenckstern, Holger von; Schmidt-Grund, Rüdiger; Grundmann, Marius

    2015-03-28

    We present X-ray diffraction and Raman spectroscopy investigations of a (100)-oriented (Al{sub x}Ga{sub 1–x}){sub 2}O{sub 3} thin film on MgO (100) and bulk-like ceramics in dependence on their composition. The thin film grown by pulsed laser deposition has a continuous lateral composition spread allowing to determine precisely the dependence of the phonon mode properties and lattice parameters on the chemical composition. For x < 0.4, we observe the single-phase β-modification. Its lattice parameters and phonon energies depend linearly on the composition. We determined the slopes of these dependencies for the individual lattice parameters and for nine Raman lines, respectively. While the lattice parameters of the ceramics follow Vegard's rule, deviations are observed for the thin film. This deviation has only a small effect on the phonon energies, which show a reasonably good agreement between thin film and ceramics.

  19. Effect of tunnel injection through the Schottky gate on the static and noise behavior of GaInAs/AlInAs high electron mobility transistor

    SciTech Connect (OSTI)

    Moro-Melgar, Diego; Mateos, Javier Gonzlez, Toms Vasallo, Beatriz G.

    2014-12-21

    By using a Monte Carlo simulator, the influence of the tunnel injection through the Schottky contact at the gate electrode of a GaInAs/AlInAs High Electron Mobility Transistor (HEMT) has been studied in terms of the static and noise performance. The method used to characterize the quantum tunnel current has been the Wentzel-Kramers-Brillouin (WKB) approach. The possibility of taking into account the influence of the image charge effect in the potential barrier height has been included as well. Regarding the static behavior, tunnel injection leads to a decrease in the drain current I{sub D} due to an enhancement of the potential barrier controlling the carrier transport through the channel. However, the pinch-off is degraded due to the tunneling current. Regarding the noise behavior, since the fluctuations in the potential barrier height caused by the tunnel-injected electrons are strongly coupled with the drain current fluctuations, a significant increase in the drain-current noise takes place, even when the tunnel effect is hardly noticeable in the static I-V characteristics, fact that must be taken into account when designing scaled HEMT for low-noise applications. In addition, tunnel injection leads to the appearance of full shot noise in the gate current.

  20. Comparison of the properties of AlGaInN light-emitting diode chips of vertical and flip-chip design using silicon as the a submount

    SciTech Connect (OSTI)

    Markov, L. K., E-mail: l.markov@mail.ioffe.ru; Smirnova, I. P.; Pavlyuchenko, A. S. [Russian Academy of Sciences, Ioffe Physical-Technical Institute (Russian Federation); Kukushkin, M. V.; Vasil'eva, E. D. [ZAO Innovation 'Tetis' (Russian Federation); Chernyakov, A. E. [Russian Academy of Sciences, Science-and-Technology Microelectronics Center (Russian Federation); Usikov, A. S. [De Core Nanosemiconductors Ltd. (India)

    2013-03-15

    Vertical and flip-chip light-emitting diode (LED) chips are compared from the viewpoint of the behavior of current spreading in the active region and the distribution of local temperatures and thermal resistances of chips. AlGaInN LED chips of vertical design are fabricated using Si as a submount and LED flipchips were fabricated with the removal of a sapphire substrate. The latter are also mounted on a Si submount. The active regions of both chips are identical and are about 1 mm{sup 2} in size. It is shown that both the emittance of the crystal surface in the visible range and the distribution of local temperatures estimated from radiation in the infrared region are more uniform in crystals of vertical design. Heat removal from flip-chips is insufficient in regions of the n contact, which do not possess good thermal contact with the submount. As a result, the total thermal resistances between the p-n junction and the submount both for the vertical chips and for flip-chips are approximately 1 K/W. The total area of the flip-chips exceeds that of the vertical design chips by a factor of 1.4.

  1. First principles study of the structural, elastic, electronic and phonon properties of CdX{sub 2}O{sub 4} (X=Al, Ga, In) spinel-type oxides

    SciTech Connect (OSTI)

    Candan, Abdullah; U?ur, Gkay

    2014-10-06

    We have performed ab-initio calculations of the structural, electronic, elastic and dynamical properties for the spinel compounds CdX{sub 2}O{sub 4} (X=Al, Ga, In) using the plane wave pseudo-potential method within the generalized gradient approximation (GGA). The calculated lattice parameters, elastic constants for these compounds are in good agreement with the previous calculated values. The computed direct band gaps of CdAl{sub 2}O{sub 4}, CdGa{sub 2}O{sub 4} and CdIn{sub 2}O{sub 4} are 2.90 eV, 1.92 eV and 1.16 eV, respectively. The lattice vibrations were calculated by direct method. The calculated phonon dispersion curves show that all compounds are dynamically stable in the spinel structure.

  2. Thermoelectric power generator module of 16x16 Bi{sub 2}Te{sub 3} and 0.6%ErAs:(InGaAs){sub 1-x}(InAlAs){sub x} segmented elements

    SciTech Connect (OSTI)

    Zeng Gehong; Bahk, Je-Hyeong; Bowers, John E.; Lu Hong; Gossard, Arthur C.; Singer, Suzanne L.; Majumdar, Arun; Bian, Zhixi; Zebarjadi, Mona; Shakouri, Ali

    2009-08-24

    We report the fabrication and characterization of thermoelectric power generator modules of 16x16 segmented elements consisting of 0.8 mm thick Bi{sub 2}Te{sub 3} and 50 {mu}m thick ErAs:(InGaAs){sub 1-x}(InAlAs){sub x} with 0.6% ErAs by volume. An output power up to 6.3 W was measured when the heat source temperature was at 610 K. The thermoelectric properties of (InGaAs){sub 1-x}(InAlAs){sub x} were characterized from 300 up to 830 K. The finite element modeling shows that the performance of the generator modules can further be enhanced by improving the thermoelectric properties of the element materials, and reducing the electrical and thermal parasitic losses.

  3. First-principles study on stability, energy gaps, optical phonon and related parameters of In{sub 1-x-y}Al{sub x}Ga{sub y}As alloys

    SciTech Connect (OSTI)

    Ghebouli, M.A.; Choutri, H.; Bouarissa, N.; Ghebouli, B.

    2012-08-15

    Based on the density functional theory as implemented in the Abinit code under the virtual crystal approximation, the lattice constant, bulk modulus, elastic constants, gap energies, electron effective mass, the dielectric constants and born effective charge in In{sub 1-x-y}Al{sub x}Ga{sub y}As have been calculated with both GGA and LDA in the range 0{<=}y{<=}0.9801. The optical and acoustical phonon frequencies, Froehlich coupling parameter, deformation energy and polaron effective mass are calculated and their dependence on the Ga content is examined. For AlAs, our results are in reasonable agreement with the known data in the literature; while for other contents our treatments are predictions. Highlights: Black-Right-Pointing-Pointer We predict phonon frequencies, Froehlich coupling and polaron parameters. Black-Right-Pointing-Pointer Elastic constants, gap energies, the dielectric constants and born effective charge are prediction.

  4. DOE - Office of Legacy Management -- University of Miami - FL 0-01

    Office of Legacy Management (LM)

    Miami - FL 0-01 FUSRAP Considered Sites Site: UNIVERSITY OF MIAMI (FL.0-01 ) Eliminated from consideration under FUSRAP Designated Name: Not Designated Alternate Name: None Location: Miami , Florida FL.0-01-1 Evaluation Year: 1987 FL.0-01-1 Site Operations: Research. FL.0-01-1 Site Disposition: Eliminated - Potential for contamination considered remote based on nature of the operations FL.0-01-1 Radioactive Materials Handled: None Indicated Primary Radioactive Materials Handled: None Indicated

  5. GaSb molecular beam epitaxial growth on p-InP(001) and passivation with in situ deposited Al{sub 2}O{sub 3} gate oxide

    SciTech Connect (OSTI)

    Merckling, C.; Brammertz, G.; Hoffmann, T. Y.; Caymax, M.; Dekoster, J.; Sun, X.; Alian, A.; Heyns, M.; Afanas'ev, V. V.

    2011-04-01

    The integration of high carrier mobility materials into future CMOS generations is presently being studied in order to increase drive current capability and to decrease power consumption in future generation CMOS devices. If III-V materials are the candidates of choice for n-type channel devices, antimonide-based semiconductors present high hole mobility and could be used for p-type channel devices. In this work we first demonstrate the heteroepitaxy of fully relaxed GaSb epilayers on InP(001) substrates. In a second part, the properties of the Al{sub 2}O{sub 3}/GaSb interface have been studied by in situ deposition of an Al{sub 2}O{sub 3} high-{kappa} gate dielectric. The interface is abrupt without any substantial interfacial layer, and is characterized by high conduction and valence band offsets. Finally, MOS capacitors show well-behaved C-V with relatively low D{sub it} along the bandgap, these results point out an efficient electrical passivation of the Al{sub 2}O{sub 3}/GaSb interface.

  6. Growth of large-domain YBa{sub 2}Cu{sub 3}O{sub x} with new seeding crystals of CaNdAlO{sub 4} and SrLaGaO{sub 4}.

    SciTech Connect (OSTI)

    Shi, D.; Hull, J. R.; LeBlanc, D.; LeBlanc, M. A. R.; Dabkowski, A.; Chang, Y.; Jiang, Y.; Zhang, Z.; Fan, H.; Energy Technology; Univ. of Cincinnati; Univ. of Ottawa; McMaster Univ.; Chinese Academy of Sciences

    1995-05-10

    Single crystals of CaNdAlO{sub 4} and SrLaGaO{sub 4} were used as seeds to grow large domains of YBa{sub 2}Cu{sub 3}O{sub x} for levitation applications. These crystals have high melting temperatures (> 1500 C) and similar lattice structures to that of YBa{sub 2}Cu{sub 3}O{sub x}. In a seeded melt-texturing method developed previously, the single crystals of CaNdAlO{sub 4}, SrLaGaO{sub 4}, and NdBa{sub 2}Cu{sub 3}O{sub x} were used as seeds for comparison. After melt processing, scanning electron microscopy analysis did not reveal any major differences in all these seeded melt-textured samples. However, the levitation forces in the samples seeded with single crystals of CaNdAlO{sub 4} and SrLaGaO{sub 4} increased considerably compared to that of the sample seeded with NdBa{sub 2}Cu{sub 3}O{sub x}. A model is proposed to describe the domain growth mechanism during seeded melt processing.

  7. Electrical and physical characterization of the Al{sub 2}O{sub 3}/p-GaSb interface for 1%, 5%, 10%, and 22% (NH{sub 4}){sub 2}S surface treatments

    SciTech Connect (OSTI)

    Peralagu, Uthayasankaran Thayne, Iain G.; Povey, Ian M.; Carolan, Patrick; Lin, Jun; Hurley, Paul K.; Contreras-Guerrero, Rocio; Droopad, Ravi

    2014-10-20

    In this work, the impact of ammonium sulfide ((NH{sub 4}){sub 2}S) surface treatment on the electrical passivation of the Al{sub 2}O{sub 3}/p-GaSb interface is studied for varying sulfide concentrations. Prior to atomic layer deposition of Al{sub 2}O{sub 3}, GaSb surfaces were treated in 1%, 5%, 10%, and 22% (NH{sub 4}){sub 2}S solutions for 10 min at 295 K. The smallest stretch-out and flatband voltage shifts coupled with the largest capacitance swing, as indicated by capacitance-voltage (CV) measurements, were obtained for the 1% treatment. The resulting interface defect trap density (D{sub it}) distribution showed a minimum value of 4 × 10{sup 12 }cm{sup −2}eV{sup −1} at E{sub v} + 0.27 eV. Transmission electron microscopy and atomic force microscopy examination revealed the formation of interfacial layers and increased roughness at the Al{sub 2}O{sub 3}/p-GaSb interface of samples treated with 10% and 22% (NH{sub 4}){sub 2}S. In combination, these effects degrade the interface quality as reflected in the CV characteristics.

  8. 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.

  9. S M Stoller Star Center-WWNA Monthly; Largo, FL

    Office of Legacy Management (LM)

    ... F25982 4 4.1 102504 Technical Report for S M Stoller Star Center-WWNA Monthly; Largo, FL 110406202 Accutest Job Number: F26616 Sampling Date: 090904 Report to: S M Stoller ...

  10. 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.