National Library of Energy BETA

Sample records for gan films grown

  1. Spectroscopic and magnetic properties of Mn doped GaN epitaxial films grown by plasma assisted molecular beam epitaxy

    SciTech Connect

    Vidyasagar, R.; Lin, Y.-T.; Tu, L.-W.

    2012-12-15

    Graphical abstract: We report here that micro-Raman scattering spectrum for Mn doped GaN thin film has displayed a new peak manifested at 578 cm{sup −1}, by which it is attributed to interior LVM originated by the incorporation of Mn ions in place of Ga sites. Mn doped GaN thin film also showed the typical negative magnetoresistance up to ∼50 K, revealing that the film showed magnetic ordering of spins below 50 K. Display Omitted Highlights: ► GaN and Mn doped GaN single phase wurtzite structures grown by PAMBE. ► The phase purity of the epilayers investigated by HRXRD, HRSEM and EDX. ► The red shift in near band edge emission has been observed using micro-PL. ► A new peak related LVM at 578 cm{sup −1} in micro-Raman scattering measurements confirmed Mn doped into GaN. ► Negative-magnetoresistance investigations have showed that the film has T{sub c} < 50 K. -- Abstract: Spectroscopic and magnetic properties of Mn doped GaN, and GaN epitaxial films have been investigated by employing micro-photoluminescence, micro-Raman, and temperature dependent magneto-resistance measurements. The HR-XRD profiles have shown that the epitaxial films are in hexagonal wurtzite structures. Morphology and composition of the films have been examined by field emission scanning electron microscopy, and energy-dispersive X-ray analysis. Micro-photoluminescence spectrum displayed a dominant near band edge emission at 362 nm, which is assigned to near band edge transition within the hexagonal structure of GaN. Raman scattering profiles showed a new vibrational mode at 578 cm{sup −1}, which is attributed to the vacancy-related local vibrational mode of Mn occupying the Ga site. Temperature dependent negative magnetoresistance measurements provide a direct evidence of magnetic ordering below 50 K for the Mn doped GaN thin film.

  2. Highly c-axis oriented GaN films grown on free-standing diamond substrates for high-power devices

    SciTech Connect

    Zhang, D. [School of Physics and Optoelectronic Technology, Dalian University of Technology, Dalian 116024 (China) [School of Physics and Optoelectronic Technology, Dalian University of Technology, Dalian 116024 (China); Key Laboratory of Materials Modification by Laser, Ion and Electron Beams, Ministry of Education, Dalian University of Technology, Dalian 116024 (China); Bian, J.M., E-mail: jmbian@dlut.edu.cn [School of Physics and Optoelectronic Technology, Dalian University of Technology, Dalian 116024 (China); Qin, F.W.; Wang, J.; Pan, L. [School of Physics and Optoelectronic Technology, Dalian University of Technology, Dalian 116024 (China) [School of Physics and Optoelectronic Technology, Dalian University of Technology, Dalian 116024 (China); Key Laboratory of Materials Modification by Laser, Ion and Electron Beams, Ministry of Education, Dalian University of Technology, Dalian 116024 (China); Zhao, J.M. [School of Physics and Optoelectronic Technology, Dalian University of Technology, Dalian 116024 (China)] [School of Physics and Optoelectronic Technology, Dalian University of Technology, Dalian 116024 (China); Zhao, Y.; Bai, Y.Z. [School of Physics and Optoelectronic Technology, Dalian University of Technology, Dalian 116024 (China) [School of Physics and Optoelectronic Technology, Dalian University of Technology, Dalian 116024 (China); Key Laboratory of Materials Modification by Laser, Ion and Electron Beams, Ministry of Education, Dalian University of Technology, Dalian 116024 (China); Du, G.T. [School of Physics and Optoelectronic Technology, Dalian University of Technology, Dalian 116024 (China)] [School of Physics and Optoelectronic Technology, Dalian University of Technology, Dalian 116024 (China)

    2011-10-15

    Highlights: {yields} GaN films are deposited on diamond substrates by ECR-PEMOCVD. {yields} Influence of deposition temperature on the properties of samples is investigated. {yields} Properties of GaN films are dependent on the deposition temperature. -- Abstract: GaN films with highly c-axis preferred orientation are deposited on free-standing thick diamond films by low temperature electron cyclotron resonance plasma enhanced metal organic chemical vapor deposition (ECR-PEMOCVD). The TMGa and N{sub 2} are applied as precursors of Ga and N, respectively. The quality of as-grown GaN films are systematically investigated as a function of deposition temperature by means of X-ray diffraction (XRD) analysis, Hall Effect measurement (HL), room temperature photoluminescence (PL) and atomic force microscopy (AFM). The results show that the dense and uniformed GaN films with highly c-axis preferred orientation are successfully achieved on free-standing diamond substrates under optimized deposition temperature of 400 {sup o}C, and the room temperature PL spectra of the optimized GaN film show a intense ultraviolet near band edge emission and a weak yellow luminescence. The obtained GaN/diamond structure has great potential for the development of high-power semiconductor devices due to its excellent heat dissipation nature.

  3. Microstructures of GaN and In{sub x}Ga{sub 1-x}N films grown by MOCVD on free-standing GaN templates

    SciTech Connect

    Jasinski, J.; Liliental-Weber, Z.; Huang, D.; Reshchikov, M.A.; Yun, F.; Morkoc, H.; Sone, C.; Park, S.S.; Lee, K.Y.

    2002-04-30

    We summarize structural properties of thick HVPE GaN templates from the point of view of their application as substrates for growth of nitride layers. This is followed by the results of optical and structural studies, mostly transmission electron microscopy, of nitride layers grown by MOCVD on top of the HVPE substrates. The results indicate high structural quality of these layers with a low density of threading dislocations (in the range of 10{sup 6} cm{sup -2}). Convergent beam electron diffraction studies showed that the MOCVD GaN films have Ga-polarity, the same polarity as the HVPE GaN substrates. Structural studies of an InGaN layer grown on top of the MOCVD GaN film showed the presence of two layers, which differed in lattice parameter and composition. The upper layer, on the top of the structure had a c-lattice parameter about 2% larger than that of GaN and contained 10.3 {+-} 0.8% of In. Values measured for the thinner, intermediate layer adjacent to the GaN layer were about 2 .5 times lower.

  4. Effects of substrate temperature, substrate orientation, and energetic atomic collisions on the structure of GaN films grown by reactive sputtering

    SciTech Connect

    Schiaber, Ziani S.; Lisboa-Filho, Paulo N.; Silva, Jos H. D. da; Leite, Douglas M. G.; Bortoleto, Jos R. R.

    2013-11-14

    The combined effects of substrate temperature, substrate orientation, and energetic particle impingement on the structure of GaN films grown by reactive radio-frequency magnetron sputtering are investigated. Monte-Carlo based simulations are employed to analyze the energies of the species generated in the plasma and colliding with the growing surface. Polycrystalline films grown at temperatures ranging from 500 to 1000 C clearly showed a dependence of orientation texture and surface morphology on substrate orientation (c- and a-plane sapphire) in which the (0001) GaN planes were parallel to the substrate surface. A large increase in interplanar spacing associated with the increase in both a- and c-parameters of the hexagonal lattice and a redshift of the optical bandgap were observed at substrate temperatures higher than 600 C. The results showed that the tensile stresses produced during the film's growth in high-temperature deposition ranges were much larger than the expected compressive stresses caused by the difference in the thermal expansion coefficients of the film and substrate in the cool-down process after the film growth. The best films were deposited at 500 C, 30 W and 600 C, 45 W, which corresponds to conditions where the out diffusion from the film is low. Under these conditions the benefits of the temperature increase because of the decrease in defect density are greater than the problems caused by the strongly strained lattice that occurr at higher temperatures. The results are useful to the analysis of the growth conditions of GaN films by reactive sputtering.

  5. 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

    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.

  6. Low temperature thin film transistors with hollow cathode plasma-assisted atomic layer deposition based GaN channels

    SciTech Connect

    Bolat, S. E-mail: aokyay@ee.bilkent.edu.tr; Tekcan, B.; Ozgit-Akgun, C.; Biyikli, N.; Okyay, A. K. E-mail: aokyay@ee.bilkent.edu.tr

    2014-06-16

    We report GaN thin film transistors (TFT) with a thermal budget below 250?C. GaN thin films are grown at 200?C by hollow cathode plasma-assisted atomic layer deposition (HCPA-ALD). HCPA-ALD-based GaN thin films are found to have a polycrystalline wurtzite structure with an average crystallite size of 9.3?nm. TFTs with bottom gate configuration are fabricated with HCPA-ALD grown GaN channel layers. Fabricated TFTs exhibit n-type field effect characteristics. N-channel GaN TFTs demonstrated on-to-off ratios (I{sub ON}/I{sub OFF}) of 10{sup 3} and sub-threshold swing of 3.3?V/decade. The entire TFT device fabrication process temperature is below 250?C, which is the lowest process temperature reported for GaN based transistors, so far.

  7. Electrical and optical properties of carbon-doped GaN grown by MBE on MOCVD GaN templates using a CCl4 dopant source

    SciTech Connect

    Armitage, Rob; Yang, Qing; Feick, Henning; Park, Yeonjoon; Weber, Eicke R.

    2002-04-15

    Carbon-doped GaN was grown by plasma-assisted molecular-beam epitaxy using carbon tetrachloride vapor as the dopant source. For moderate doping mainly acceptors were formed, yielding semi-insulating GaN. However at higher concentrations p-type conductivity was not observed, and heavily doped films (>5 x 10{sup 20} cm{sup -3}) were actually n-type rather than semi-insulating. Photoluminescence measurements showed two broad luminescence bands centered at 2.2 and 2.9 eV. The intensity of both bands increased with carbon content, but the 2.2 eV band dominated in n-type samples. Intense, narrow ({approx}6 meV) donor-bound exciton peaks were observed in the semi-insulating samples.

  8. Evolution of deep centers in GaN grown by hydride vapor phaseepitaxy

    SciTech Connect

    Fang, Z.-Q.; Look, D.C.; Jasinski, J.; Benamara, M.; Liliental-Weber, Z.; Molnar, R.J.

    2001-04-18

    Deep centers and dislocation densities in undoped n GaN, grown by hydride vapor phase epitaxy (HVPE), were characterized as a function of the layer thickness by deep level transient spectroscopy and transmission electron microscopy, respectively. As the layer thickness decreases, the variety and concentration of deep centers increase, in conjunction with the increase of dislocation density. Based on comparison with electron irradiation induced centers, some dominant centers in HVPE GaN are identified as possible point defects.

  9. Enhanced UV detection by non-polar epitaxial GaN films

    SciTech Connect

    Mukundan, Shruti; Chandan, Greeshma; Mohan, Lokesh; Krupanidhi, S. B.; Roul, Basanta; Shetty, Arjun

    2015-12-15

    Nonpolar a-GaN (11-20) epilayers were grown on r-plane (1-102) sapphire substrates using plasma assisted molecular beam epitaxy. High resolution x-ray diffractometer confirmed the orientation of the grown film. Effect of the Ga/N ratio on the morphology and strain of a-GaN epilayers was compared and the best condition was obtained for the nitrogen flow of 1 sccm. Atomic force microscopy was used to analyze the surface morphology while the strain in the film was quantitatively measured using Raman spectroscopy and qualitatively analyzed by reciprocal space mapping technique. UV photo response of a-GaN film was measured after fabricating a metal-semiconductor-metal structure over the film with gold metal. The external quantum efficiency of the photodetectors fabricated in the (0002) polar and (11-20) nonpolar growth directions were compared in terms of responsivity and nonpolar GaN showed the best sensitivity at the cost of comparatively slow response time.

  10. Surfactant assisted growth of MgO films on GaN

    SciTech Connect

    Paisley, E. A.; Shelton, T. C.; Collazo, R.; Sitar, Z.; Maria, J.-P.; Christen, H. M.; Biegalski, M. D.; Mita, S.

    2012-08-27

    Thin epitaxial films of <111> oriented MgO on [0001]-oriented GaN were grown by molecular beam epitaxy and pulsed laser deposition using the assistance of a vapor phase surfactant. In both cases, surfactant incorporation enabled layer-by-layer growth and a smooth terminal surface by stabilizing the {l_brace}111{r_brace} rocksalt facet. Metal-insulator-semiconductor capacitor structures were fabricated on n-type GaN. A comparison of leakage current density for conventional and surfactant-assisted growth reveals a nearly 100 Multiplication-Sign reduction in leakage current density for the surfactant-assisted samples. These data verify numerous predictions regarding the role of H-termination in regulating the habit of rocksalt crystals.

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

    SciTech Connect

    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.

  12. Catalyst and its diameter dependent growth kinetics of CVD grown GaN nanowires

    SciTech Connect

    Samanta, Chandan [Department of Physics, Indian Institute of Technology Kanpur (India)] [Department of Physics, Indian Institute of Technology Kanpur (India); Chander, D. Sathish [Department of Physics, Indian Institute of Technology Kanpur (India) [Department of Physics, Indian Institute of Technology Kanpur (India); Department of Mechanical Engineering, Indian Institute of Technology Kanpur (India); Ramkumar, J. [Department of Mechanical Engineering, Indian Institute of Technology Kanpur (India)] [Department of Mechanical Engineering, Indian Institute of Technology Kanpur (India); Dhamodaran, S., E-mail: kdams2003@gmail.com [Department of Physics, Indian Institute of Technology Kanpur (India)

    2012-04-15

    Graphical abstract: GaN nanowires with controlled diameter and aspect ratio has been grown using a simple CVD technique. The growth kinetics of CVD grown nanowires investigated in detail for different catalysts and their diameters. A critical diameter important to distinguish the growth regimes has been discussed in detail. The results are important which demonstrates the growth of diameter and aspect ratio controlled GaN nanowires and also understand their growth kinetics. Highlights: Black-Right-Pointing-Pointer Controlled diameter and aspect ratio of GaN nanowires achieved in simple CVD reactor. Black-Right-Pointing-Pointer Nanowire growth kinetics for different catalyst and its diameters were understood. Black-Right-Pointing-Pointer Adatoms vapor pressure inside reactor plays a crucial role in growth kinetics. Black-Right-Pointing-Pointer Diffusion along nanowire sidewalls dominate for gold and nickel catalysts. Black-Right-Pointing-Pointer Gibbs-Thomson effect dominates for palladium catalyst. -- Abstract: GaN nanowires were grown using chemical vapor deposition with controlled aspect ratio. The catalyst and catalyst-diameter dependent growth kinetics is investigated in detail. We first discuss gold catalyst diameter dependent growth kinetics and subsequently compare with nickel and palladium catalyst. For different diameters of gold catalyst there was hardly any variation in the length of the nanowires but for other catalysts with different diameter a strong length variation of the nanowires was observed. We calculated the critical diameter dependence on adatoms pressure inside the reactor and inside the catalytic particle. This gives an increasing trend in critical diameter as per the order gold, nickel and palladium for the current set of experimental conditions. Based on the critical diameter, with gold and nickel catalyst the nanowire growth was understood to be governed by limited surface diffusion of adatoms and by Gibbs-Thomson effect for the palladium

  13. Surfactant assisted growth of MgO films on GaN

    SciTech Connect

    Paisley, Elisibeth A.; Shelton, T C; Mita, S; Gaddy, Brian E.; Irving, D L; Christen, Hans M; Sitar, Z; Biegalski, Michael D; Maria, Jon Paul

    2012-01-01

    Thin epitaxial films of <111> oriented MgO on [0001]-oriented GaN were grown by molecular beam epitaxy (MBE) and pulsed laser deposition (PLD) using the assistance of a vapor phase surfactant. In both cases, surfactant incorporation enabled layer-by-layer growth and a smooth terminal surface due to stabilizing the {111} rocksalt facet. MBE growth of MgO in water terminates after several monolayers, and is attributed to saturation of surface active sites needed to facilitate the Mg oxidation reaction. MgO films prepared by PLD grow continuously, this occurs due to the presence of excited oxidizing species in the laser plasma eliminate the need for catalytic surface sites. Metal-insulator-semiconductor capacitor structures were fabricated on n-type GaN. A comparison of leakage current density for conventional and surfactant-assisted growth reveals a nearly two order of magnitude reduction in leakage current density for the smoother surfactant-assisted samples. Collectively, these data verify numerous predictions and calculations regarding the role of H-termination in regulating the habit of MgO crystals.

  14. Electronic and optical device applications of hollow cathode plasma assisted atomic layer deposition based GaN thin films

    SciTech Connect

    Bolat, Sami Tekcan, Burak; Ozgit-Akgun, Cagla; Biyikli, Necmi; Okyay, Ali Kemal

    2015-01-15

    Electronic and optoelectronic devices, namely, thin film transistors (TFTs) and metalsemiconductormetal (MSM) photodetectors, based on GaN films grown by hollow cathode plasma-assisted atomic layer deposition (PA-ALD) are demonstrated. Resistivity of GaN thin films and metal-GaN contact resistance are investigated as a function of annealing temperature. Effect of the plasma gas and postmetallization annealing on the performances of the TFTs as well as the effect of the annealing on the performance of MSM photodetectors are studied. Dark current to voltage and responsivity behavior of MSM devices are investigated as well. TFTs with the N{sub 2}/H{sub 2} PA-ALD based GaN channels are observed to have improved stability and transfer characteristics with respect to NH{sub 3} PA-ALD based transistors. Dark current of the MSM photodetectors is suppressed strongly after high-temperature annealing in N{sub 2}:H{sub 2} ambient.

  15. TEM studies of laterally overgrown GaN layers grown on non-polarsubstrates

    SciTech Connect

    Liliental-Weber, Z.; Ni, X.; Morkoc, H.

    2006-01-05

    Transmission electron microscopy (TEM) was used to study pendeo-epitaxial GaN layers grown on polar and non-polar 4H SiC substrates. The structural quality of the overgrown layers was evaluated using a number of TEM methods. Growth of pendeo-epitaxial layers on polar substrates leads to better structural quality of the overgrown areas, however edge-on dislocations are found at the meeting fronts of two wings. Some misorientation between the 'seed' area and wing area was detected by Convergent Beam Electron Diffraction. Growth of pendeo-epitaxial layers on non-polar substrates is more difficult. Two wings on the opposite site of the seed area grow in two different polar directions with different growth rates. Most dislocations in a wing grown with Ga polarity are 10 times wider than wings grown with N-polarity making coalescence of these layers difficult. Most dislocations in a wing grown with Ga polarity bend in a direction parallel to the substrate, but some of them also propagate to the sample surface. Stacking faults formed on the c-plane and prismatic plane occasionally were found. Some misorientation between the wings and seed was detected using Large Angle Convergent Beam Diffraction.

  16. Ferroelectric PLZT thick films grown by poly(1-vinylpyrrolidone...

    U.S. Department of Energy (DOE) - all webpages (Extended Search)

    PLZT thick films grown by poly(1-vinylpyrrolidone-co-vinyl acetate) (PVPVA)-modified sol-gel process Title Ferroelectric PLZT thick films grown by poly(1-vinylpyrrolidone-co-vi...

  17. Radiation-induced defects in GaN bulk grown by halide vapor phase epitaxy

    SciTech Connect

    Duc, Tran Thien; Pozina, Galia; Son, Nguyen Tien; Janzén, Erik; Hemmingsson, Carl; Ohshima, Takeshi

    2014-09-08

    Defects induced by electron irradiation in thick free-standing GaN layers grown by halide vapor phase epitaxy were studied by deep level transient spectroscopy. In as-grown materials, six electron traps, labeled D2 (E{sub C}–0.24 eV), D3 (E{sub C}–0.60 eV), D4 (E{sub C}–0.69 eV), D5 (E{sub C}–0.96 eV), D7 (E{sub C}–1.19 eV), and D8, were observed. After 2 MeV electron irradiation at a fluence of 1 × 10{sup 14 }cm{sup −2}, three deep electron traps, labeled D1 (E{sub C}–0.12 eV), D5I (E{sub C}–0.89 eV), and D6 (E{sub C}–1.14 eV), were detected. The trap D1 has previously been reported and considered as being related to the nitrogen vacancy. From the annealing behavior and a high introduction rate, the D5I and D6 centers are suggested to be related to primary intrinsic defects.

  18. Refractive index of erbium doped GaN thin films

    SciTech Connect

    Alajlouni, S.; Sun, Z. Y.; Li, J.; Lin, J. Y.; Jiang, H. X.; Zavada, J. M.

    2014-08-25

    GaN is an excellent host for erbium (Er) to provide optical emission in the technologically important as well as eye-safe 1540 nm wavelength window. Er doped GaN (GaN:Er) epilayers were synthesized on c-plane sapphire substrates using metal organic chemical vapor deposition. By employing a pulsed growth scheme, the crystalline quality of GaN:Er epilayers was significantly improved over those obtained by conventional growth method of continuous flow of reaction precursors. X-ray diffraction rocking curve linewidths of less than 300 arc sec were achieved for the GaN (0002) diffraction peak, which is comparable to the typical results of undoped high quality GaN epilayers and represents a major improvement over previously reported results for GaN:Er. Spectroscopic ellipsometry was used to determine the refractive index of the GaN:Er epilayers in the 1540 nm wavelength window and a linear dependence on Er concentration was found. The observed refractive index increase with Er incorporation and the improved crystalline quality of the GaN:Er epilayers indicate that low loss GaN:Er optical waveguiding structures are feasible.

  19. Effect of ZnO seed layer on the morphology and optical properties of ZnO nanorods grown on GaN buffer layers

    SciTech Connect

    Nandi, R. Mohan, S. Major, S. S.; Srinivasa, R. S.

    2014-04-24

    ZnO nanorods were grown by chemical bath deposition on sputtered, polycrystalline GaN buffer layers with and without ZnO seed layer. Scanning electron microscopy and X-ray diffraction show that the ZnO nanorods on GaN buffer layers are not vertically well aligned. Photoluminescence spectrum of ZnO nanorods grown on GaN buffer layer, however exhibits a much stronger near-band-edge emission and negligible defect emission, compared to the nanorods grown on ZnO buffer layer. These features are attributed to gallium incorporation at the ZnO-GaN interface. The introduction of a thin (25 nm) ZnO seed layer on GaN buffer layer significantly improves the morphology and vertical alignment of ZnO-NRs without sacrificing the high optical quality of ZnO nanorods on GaN buffer layer. The presence of a thick (200 nm) ZnO seed layer completely masks the effect of the underlying GaN buffer layer on the morphology and optical properties of nanorods.

  20. Ultraviolet light-emitting diodes grown by plasma-assisted molecular beam epitaxy on semipolar GaN (2021) substrates

    SciTech Connect

    Sawicka, M.; Grzanka, S.; Skierbiszewski, C.; Turski, H.; Muziol, G.; Krysko, M.; Grzanka, E.; Sochacki, T.; Siekacz, M.; Kucharski, R.

    2013-03-18

    Multi-quantum well (MQW) structures and light emitting diodes (LEDs) were grown on semipolar (2021) and polar (0001) GaN substrates by plasma-assisted molecular beam epitaxy. The In incorporation efficiency was found to be significantly lower for the semipolar plane as compared to the polar one. The semipolar MQWs exhibit a smooth surface morphology, abrupt interfaces, and a high photoluminescence intensity. The electroluminescence of semipolar (2021) and polar (0001) LEDs fabricated in the same growth run peaks at 387 and 462 nm, respectively. Semipolar LEDs with additional (Al,Ga)N cladding layers exhibit a higher optical output power but simultaneously a higher turn-on voltage.

  1. Group III-nitride thin films grown using MBE and bismuth

    DOEpatents

    Kisielowski, Christian K.; Rubin, Michael

    2002-01-01

    The present invention comprises growing gallium nitride films in the presence of bismuth using MBE at temperatures of about 1000 K or less. The present invention further comprises the gallium nitride films fabricated using the inventive fabrication method. The inventive films may be doped with magnesium or other dopants. The gallium nitride films were grown on sapphire substrates using a hollow anode Constricted Glow Discharge nitrogen plasma source. When bismuth was used as a surfactant, two-dimensional gallium nitride crystal sizes ranging between 10 .mu.m and 20 .mu.m were observed. This is 20 to 40 times larger than crystal sizes observed when GaN films were grown under similar circumstances but without bismuth. It is thought that the observed increase in crystal size is due bismuth inducing an increased surface diffusion coefficient for gallium. The calculated value of 4.7.times.10.sup.-7 cm.sup.2 /sec. reveals a virtual substrate temperature of 1258 K which is 260 degrees higher than the actual one.

  2. Group III-nitride thin films grown using MBE and bismuth

    DOEpatents

    Kisielowski, Christian K.; Rubin, Michael

    2000-01-01

    The present invention comprises growing gallium nitride films in the presence of bismuth using MBE at temperatures of about 1000 K or less. The present invention further comprises the gallium nitride films fabricated using the inventive fabrication method. The inventive films may be doped with magnesium or other dopants. The gallium nitride films were grown on sapphire substrates using a hollow anode Constricted Glow Discharge nitrogen plasma source. When bismuth was used as a surfactant, two-dimensional gallium nitride crystal sizes ranging between 10 .mu.m and 20 .mu.m were observed. This is 20 to 40 times larger than crystal sizes observed when GaN films were grown under similar circumstances but without bismuth. It is thought that the observed increase in crystal size is due bismuth inducing an increased surface diffusion coefficient for gallium. The calculated value of 4.7.times.10.sup.-7 cm.sup.2 /sec. reveals a virtual substrate temperature of 1258 K which is 260 degrees higher than the actual one.

  3. Properties of radio-frequency-sputter-deposited GaN films in a nitrogen/hydrogen mixed gas

    SciTech Connect

    Miyazaki, Takayuki; Takada, Kouhei; Adachi, Sadao; Ohtsuka, Kohji

    2005-05-01

    GaN films have been deposited by reactive sputtering in nitrogen gas at pressures from 0.08 to 2.70 Pa with and without the addition of hydrogen gas. X-ray diffraction (XRD), Fourier transform infrared (FTIR), optical absorption, and photoluminescence (PL) spectroscopy have been used to characterize the sputter-deposited GaN films. The XRD pattern reveals that the GaN films deposited in nitrogen gas at pressures lower than 0.53 Pa are polycrystals with the (0001) texture ({alpha}-GaN), while those deposited at or above 1.07 Pa display mixed crystalline orientations or an amorphous-like nature. The GaN:H films deposited in nitrogen/hydrogen mixed gas, on the other hand, show an amorphous or amorphous-like nature. The FTIR spectra indicate that the GaN:H films show peaks arising from hydrogen-related bonds at {approx}1000 and {approx}3200 cm{sup -1}, in addition to the GaN absorption band at {approx}555 cm{sup -1}. The optical absorption spectra at 300 K indicate the fundamental absorption edges at {approx}3.38 and {approx}3.7 eV for the highly oriented {alpha}-GaN and amorphous GaN:H films, respectively. PL emission has been observed from sputter-deposited {alpha}-GaN films at temperatures below 100 K. The GaN:H films also show strong band-edge and donor-acceptor pair emissions. The PL emission in the GaN:H film may arise from crystalline GaN particles embedded in the amorphous GaN matrix.

  4. Characterization of GaN nanowires grown on PSi, PZnO and PGaN on Si (111) substrates by thermal evaporation

    SciTech Connect

    Shekari, Leila; Hassan, Haslan Abu; Thahab, Sabah M.; Hassan, Zainuriah

    2012-06-20

    In this research, we used an easy and inexpensive method to synthesize highly crystalline GaN nanowires (NWs); on different substrates such as porous silicon (PSi), porous zinc oxide (PZnO) and porous gallium nitride (PGaN) on Si (111) wafer by thermal evaporation using commercial GaN powder without any catalyst. Micro structural studies by scanning electron microscopy and transmission electron microscope measurements reveal the role of different substrates in the morphology, nucleation and alignment of the GaN nanowires. The degree of alignment of the synthesized nanowires does not depend on the lattice mismatch between wires and their substrates. Further structural and optical characterizations were performed using high resolution X-ray diffraction and energy-dispersive X-ray spectroscopy. Results indicate that the nanowires are of single-crystal hexagonal GaN. The quality and density of grown GaN nanowires for different substrates are highly dependent on the lattice mismatch between the nanowires and their substrates and also on the size of the porosity of the substrates. Nanowires grown on PGaN have the best quality and highest density as compared to nanowires on other substrates. By using three kinds of porous substrates, we are able to study the increase in the alignment and density of the nanowires.

  5. Electroreflectance study of the effect of {gamma} radiation on the optical properties of epitaxial GaN films

    SciTech Connect

    Belyaev, A. E.; Klyui, N. I. Konakova, R. V.; Lukyanov, A. N.; Danilchenko, B. A.; Sveshnikov, J. N.; Klyui, A. N.

    2012-03-15

    Experimental data on the electroreflectance spectra of {gamma}-irradiated epitaxial GaN films on sapphire are reported. The irradiation doses are 10{sup 5}-2 Multiplication-Sign 10{sup 6} rad. The theoretical electroreflectance spectra calculated on the basis of a model of three types of transitions are in agreement with experimental data with reasonable accuracy. The energies and broadenings of the transitions derived in the context of the model give grounds to infer that, in the GaN films, there are internal stresses dependent on the {gamma}-irradiation dose.

  6. Morphology in electrochemically grown conducting polymer films

    DOEpatents

    Rubinstein, Israel; Gottesfeld, Shimshon; Sabatani, Eyal

    1992-01-01

    A conducting polymer film with an improved space filling is formed on a metal electrode surface. A self-assembling monolayer is formed directly on the metal surface where the monolayer has a first functional group that binds to the metal surface and a second chemical group that forms a chemical bonding site for molecules forming the conducting polymer. The conducting polymer is then conventioonally deposited by electrochemical deposition. In one example, a conducting film of polyaniline is formed on a gold electrode surface with an intermediate monolayer of p-aminothiophenol.

  7. Morphology in electrochemically grown conducting polymer films

    DOEpatents

    Rubinstein, I.; Gottesfeld, S.; Sabatani, E.

    1992-04-28

    A conducting polymer film with an improved space filling is formed on a metal electrode surface. A self-assembling monolayer is formed directly on the metal surface where the monolayer has a first functional group that binds to the metal surface and a second chemical group that forms a chemical bonding site for molecules forming the conducting polymer. The conducting polymer is then conventionally deposited by electrochemical deposition. In one example, a conducting film of polyaniline is formed on a gold electrode surface with an intermediate monolayer of p-aminothiophenol. 2 figs.

  8. Method of growing GaN films with a low density of structural defects using an interlayer

    DOEpatents

    Bourret-Courchesne, Edith D.

    2003-01-01

    A dramatic reduction of the dislocation density in GaN was obtained by insertion of a single thin interlayer grown at an intermediate temperature (IT-IL) after the growth of an initial grown at high temperature. A description of the growth process is presented with characterization results aimed at understanding the mechanisms of reduction in dislocation density. A large percentage of the threading dislocations present in the first GaN epilayer are found to bend near the interlayer and do not propagate into the top layer which grows at higher temperature in a lateral growth mode. TEM studies show that the mechanisms of dislocation reduction are similar to those described for the epitaxial lateral overgrowth process, however a notable difference is the absence of coalescence boundaries.

  9. Structural anisotropic properties of a-plane GaN epilayers grown on r-plane sapphire by molecular beam epitaxy

    SciTech Connect

    Lotsari, A.; Kehagias, Th.; Katsikini, M.; Arvanitidis, J.; Ves, S.; Komninou, Ph.; Dimitrakopulos, G. P.; Tsiakatouras, G.; Tsagaraki, K.; Georgakilas, A.; Christofilos, D.

    2014-06-07

    Heteroepitaxial non-polar III-Nitride layers may exhibit extensive anisotropy in the surface morphology and the epilayer microstructure along distinct in-plane directions. The structural anisotropy, evidenced by the M-shape dependence of the (112{sup }0) x-ray rocking curve widths on the beam azimuth angle, was studied by combining transmission electron microscopy observations, Raman spectroscopy, high resolution x-ray diffraction, and atomic force microscopy in a-plane GaN epilayers grown on r-plane sapphire substrates by plasma-assisted molecular beam epitaxy (PAMBE). The structural anisotropic behavior was attributed quantitatively to the high dislocation densities, particularly the Frank-Shockley partial dislocations that delimit the I{sub 1} intrinsic basal stacking faults, and to the concomitant plastic strain relaxation. On the other hand, isotropic samples exhibited lower dislocation densities and a biaxial residual stress state. For PAMBE growth, the anisotropy was correlated to N-rich (or Ga-poor) conditions on the surface during growth, that result in formation of asymmetric a-plane GaN grains elongated along the c-axis. Such conditions enhance the anisotropy of gallium diffusion on the surface and reduce the GaN nucleation rate.

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

    SciTech Connect

    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. Method of fabricating low-dislocation-density epitaxially-grown films with textured surfaces

    DOEpatents

    Li, Qiming; Wang, George T

    2015-01-13

    A method for forming a surface-textured single-crystal film layer by growing the film atop a layer of microparticles on a substrate and subsequently selectively etching away the microparticles to release the surface-textured single-crystal film layer from the substrate. This method is applicable to a very wide variety of substrates and films. In some embodiments, the film is an epitaxial film that has been grown in crystallographic alignment with respect to a crystalline substrate.

  12. Polarity characterization by anomalous x-ray dispersion of ZnO films and GaN lateral polar structures

    SciTech Connect

    Shelton, Christopher T.; Sachet, Edward; Paisley, Elizabeth A.; Hoffmann, Marc P.; Rajan, Joseph; Collazo, Ramn; Sitar, Zlatko; Maria, Jon-Paul

    2014-01-28

    We demonstrate the use of anomalous x-ray scattering of constituent cations at their absorption edge, in a conventional Bragg-Brentano diffractometer, to measure absolutely and quantitatively the polar orientation and polarity fraction of unipolar and mixed polar wurtzitic crystals. In one set of experiments, the gradual transition between c+ and c? polarity of epitaxial ZnO films on sapphire as a function of MgO buffer layer thickness is monitored quantitatively, while in a second experiment, we map the polarity of a lateral polar homojunction in GaN. The dispersion measurements are compared with piezoforce microscopy images, and we demonstrate how x-ray dispersion and scanning probe methods can provide complementary information that can discriminate between polarity fractions at a material surface and polarity fractions averaged over the film bulk.

  13. Hydride vapor phase GaN films with reduced density of residual electrons and deep traps

    SciTech Connect

    Polyakov, A. Y.; Smirnov, N. B.; Govorkov, A. V.; Yugova, T. G.; Cox, H.; Helava, H.; Makarov, Yu.; Usikov, A. S.

    2014-05-14

    Electrical properties and deep electron and hole traps spectra are compared for undoped n-GaN films grown by hydride vapor phase epitaxy (HVPE) in the regular process (standard HVPE samples) and in HVPE process optimized for decreasing the concentration of residual donor impurities (improved HVPE samples). It is shown that the residual donor density can be reduced by optimization from ?10{sup 17}?cm{sup ?3} to (25)??10{sup 14}?cm{sup ?3}. The density of deep hole traps and deep electron traps decreases with decreased donor density, so that the concentration of deep hole traps in the improved samples is reduced to ?5??10{sup 13}?cm{sup ?3} versus 2.9??10{sup 16}?cm{sup ?3} in the standard samples, with a similar decrease in the electron traps concentration.

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

    SciTech Connect

    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.

  15. Ar{sup +}-irradiation-induced damage in hydride vapor-phase epitaxy GaN films

    SciTech Connect

    Nakano, Yoshitaka Ogawa, Daisuke; Nakamura, Keiji; Kawakami, Retsuo; Niibe, Masahito

    2015-07-15

    The authors have investigated the electrical characteristics of hydride vapor-phase epitaxy GaN films exposed to Ar{sup +} irradiation, employing Schottky barrier diodes. The Ar{sup +} irradiation tends to largely increase the effective carrier concentration in the near surface region of GaN up to ∼25 nm, due to the generation of donor-type N vacancy defects, compared to the original value before the irradiation. More interestingly, acceptor-type deep-level defects are found to be formed at ∼2.1, ∼2.9, and ∼3.2 eV below the conduction band in the subsequently deeper region, in which Ga vacancies introduced by the Ar{sup +} irradiation are considered to be in-diffused and immediately combined with hydrogen. These N vacancies and hydrogenated Ga vacancies formed are dominantly responsible for changing the depth profiles of the effective carrier concentration via the carrier generation, the carrier trapping, and/or carrier compensation.

  16. Influence of growth temperature and temperature ramps on deep level defect incorporation in m-plane GaN

    SciTech Connect

    Armstrong, A. M.; Kelchner, K.; Nakamura, S.; DenBaars, S. P.; Materials Department, University of California, Santa Barbara, California 93106 ; Speck, J. S.

    2013-12-02

    The dependence of deep level defect incorporation in m-plane GaN films grown by metal-organic chemical vapor deposition on bulk m-plane GaN substrates as a function of growth temperature (T{sub g}) and T{sub g} ramping method was investigated using deep level optical spectroscopy. Understanding the influence of T{sub g} on GaN deep level incorporation is important for InGaN/GaN multi-quantum well (MQW) light emitting diodes (LEDs) and laser diodes (LDs) because GaN quantum barrier (QB) layers are grown much colder than thin film GaN to accommodate InGaN QW growth. Deep level spectra of low T{sub g} (800?C) GaN films grown under QB conditions were compared to deep level spectra of high T{sub g} (1150?C) GaN. Reducing T{sub g}, increased the defect density significantly (>50) through introduction of emergent deep level defects at 2.09?eV and 2.9?eV below the conduction band minimum. However, optimizing growth conditions during the temperature ramp when transitioning from high to low T{sub g} substantially reduced the density of these emergent deep levels by approximately 40%. The results suggest that it is important to consider the potential for non-radiative recombination in QBs of LED or LD active regions, and tailoring the transition from high T{sub g} GaN growth to active layer growth can mitigate such non-radiative channels.

  17. Multicycle rapid thermal annealing optimization of Mg-implanted GaN: Evolution of surface, optical, and structural properties

    SciTech Connect

    Greenlee, Jordan D.; Feigelson, Boris N.; Anderson, Travis J.; Hite, Jennifer K.; Mastro, Michael A.; Eddy, Charles R.; Hobart, Karl D.; Kub, Francis J.; Tadjer, Marko J.

    2014-08-14

    The first step of a multi-cycle rapid thermal annealing process was systematically studied. The surface, structure, and optical properties of Mg implanted GaN thin films annealed at temperatures ranging from 900 to 1200?C were investigated by Raman spectroscopy, photoluminescence, UV-visible spectroscopy, atomic force microscopy, and Nomarski microscopy. The GaN thin films are capped with two layers of in-situ metal organic chemical vapor deposition -grown AlN and annealed in 24 bar of N{sub 2} overpressure to avoid GaN decomposition. The crystal quality of the GaN improves with increasing annealing temperature as confirmed by UV-visible spectroscopy and the full widths at half maximums of the E{sub 2} and A{sub 1} (LO) Raman modes. The crystal quality of films annealed above 1100?C exceeds the quality of the as-grown films. At 1200?C, Mg is optically activated, which is determined by photoluminescence measurements. However, at 1200?C, the GaN begins to decompose as evidenced by pit formation on the surface of the samples. Therefore, it was determined that the optimal temperature for the first step in a multi-cycle rapid thermal anneal process should be conducted at 1150?C due to crystal quality and surface morphology considerations.

  18. Temperature threshold for nanorod structuring of metal and oxide films grown by glancing angle deposition

    SciTech Connect

    Deniz, Derya; Lad, Robert J.

    2011-01-15

    Thin films of tin (Sn), aluminum (Al), gold (Au), ruthenium (Ru), tungsten (W), ruthenium dioxide (RuO{sub 2}), tin dioxide (SnO{sub 2}), and tungsten trioxide (WO{sub 3}) were grown by glancing angle deposition (GLAD) to determine the nanostructuring temperature threshold, {Theta}{sub T}, above which adatom surface diffusion becomes large enough such that nanorod morphology is no longer formed during growth. The threshold was found to be lower in metals compared to oxides. Films were grown using both dc and pulsed dc magnetron sputtering with continuous substrate rotation over the temperature range from 291 to 866 K. Film morphologies, structures, and compositions were characterized by high resolution scanning electron microscopy, x-ray diffraction, and x-ray photoelectron spectroscopy. Films were also grown in a conventional configuration for comparison. For elemental metals, nanorod structuring occurs for films with melting points higher than that of Al (933 K) when grown at room temperature with a rotation rate of {approx}5 rpm, corresponding to a value of {Theta}{sub T}{approx_equal}0.33{+-}0.01. For the oxide films, a value of {Theta}{sub T}{approx_equal}0.5 was found, above which GLAD nanorod structuring does not occur. The existence of a nanostructuring temperature threshold in both metal and oxide GLAD films can be attributed to greater adatom mobilities as temperature is increased resulting in nonkinetically limited film nucleation and growth processes.

  19. Increased p-type conductivity through use of an indium surfactant in the growth of Mg-doped GaN

    SciTech Connect

    Kyle, Erin C. H. Kaun, Stephen W.; Young, Erin C.; Speck, James S.

    2015-06-01

    We have examined the effect of an indium surfactant on the growth of p-type GaN by ammonia-based molecular beam epitaxy. p-type GaN was grown at temperatures ranging from 700 to 780 °C with and without an indium surfactant. The Mg concentration in all films in this study was 4.5–6 × 10{sup 19} cm{sup −3} as measured by secondary ion mass spectroscopy. All p-type GaN films grown with an indium surfactant had higher p-type conductivities and higher hole concentrations than similar films grown without an indium surfactant. The lowest p-type GaN room temperature resistivity was 0.59 Ω-cm, and the highest room temperature carrier concentration was 1.6 × 10{sup 18} cm{sup −3}. Fits of the temperature-dependent carrier concentration data showed a one to two order of magnitude lower unintentional compensating defect concentration in samples grown with the indium surfactant. Samples grown at higher temperature had a lower active acceptor concentration. Improvements in band-edge luminescence were seen by cathodoluminescence for samples grown with the indium surfactant, confirming the trends seen in the Hall data.

  20. Optical and mechanical properties of nanocrystalline ZrC thin films grown by pulsed laser deposition.

    DOE PAGES [OSTI]

    Craciun, D.; Socol, G.; Lambers, E.; McCumiskey, E. J.; Taylor, C. R.; Martin, C.; Argibay, Nicolas; Craciun, V.; Tanner, D. B.

    2015-01-17

    Thin ZrC films (<500 nm) were grown on (100) Si substrates at a substrate temperature of 500 °C by the pulsed laser deposition (PLD) technique using a KrF excimer laser under different CH4 pressures. Glancing incidence X-ray diffraction showed that films were nanocrystalline, while X-ray reflectivity studies found out films were very dense and exhibited a smooth surface morphology. Optical spectroscopy data shows that the films have high reflectivity (>90%) in the infrared region, characteristic of metallic behavior. Nanoindentation results indicated that films deposited under lower CH4 pressures exhibited slightly higher nanohardness and Young modulus values than films deposited undermore » higher pressures. As a result, tribological characterization revealed that these films exhibited relatively high wear resistance and steady-state friction coefficients on the order of μ = 0.4.« less

  1. Optical and mechanical properties of nanocrystalline ZrC thin films grown by pulsed laser deposition.

    SciTech Connect

    Craciun, D.; Socol, G.; Lambers, E.; McCumiskey, E. J.; Taylor, C. R.; Martin, C.; Argibay, Nicolas; Craciun, V.; Tanner, D. B.

    2015-01-17

    Thin ZrC films (<500 nm) were grown on (100) Si substrates at a substrate temperature of 500 °C by the pulsed laser deposition (PLD) technique using a KrF excimer laser under different CH4 pressures. Glancing incidence X-ray diffraction showed that films were nanocrystalline, while X-ray reflectivity studies found out films were very dense and exhibited a smooth surface morphology. Optical spectroscopy data shows that the films have high reflectivity (>90%) in the infrared region, characteristic of metallic behavior. Nanoindentation results indicated that films deposited under lower CH4 pressures exhibited slightly higher nanohardness and Young modulus values than films deposited under higher pressures. As a result, tribological characterization revealed that these films exhibited relatively high wear resistance and steady-state friction coefficients on the order of μ = 0.4.

  2. Metallic impurities in gallium nitride grown by molecular beam epitaxy

    SciTech Connect

    McHugo, S.A.; Krueger, J.; Kisielowski, C.

    1997-04-01

    Transition metals are often encountered in trace amounts in semiconductors. They have been extensively studied in most elemental and compound systems, since they form deep donor and/or acceptor levels which usually degrade the electronic and optical material properties. Only very little is known about transition metals in recent III-V semiconducting materials, such as GaN, AlN and InN. These few studies have been done exclusively on Metal-Organic Chemical Vapor Deposition (MOCVD) or Hybrid Vapor Phase Epitaxy HVPE-grown GaN. Preliminary x-ray fluorescence studies at the Advanced Light Source, beamline 10.3.1, Lawrence Berkeley National Laboratory have revealed that GaN materials grown by Molecular Beam Epitaxy (MBE) have Fe, Ni and Cr as the dominant transition metal contaminants. This finding is commensurate with the extremely high concentrations of hydrogen, carbon and oxygen (up to 10{sup 20} cm{sup {minus}3}) measured by Secondary Ion Mass Spectroscopy (SIMS). Preliminary work using the mapping capabilities of the x-ray fluorescence microprobe revealed the metal impurities were inhomogeneously distributed over the film. Future work of this collaboration will be to find a correlation between the existence of transition metals in MBE films, as revealed by x-ray fluorescence, and Photoluminescence (PL) spectra taken in the infrared region. Also, the authors will make use of the 1 {mu}m spatial resolution of x-ray microprobe to locate the contaminants in relation to structural defects in the GaN films. Because of the large strain caused by the lattice mismatch between the GaN films and the substrates, the films grow in a columnar order with high densities of grain boundaries and dislocations. These structural defects offer preferential sites for metal precipitation or agglomeration which could degrade the optical properties of this material more so than if the impurities were left dissolved in the GaN.

  3. Epitaxial single-crystal thin films of MnxTi1-xO2-δ grown on...

    Office of Scientific and Technical Information (OSTI)

    Epitaxial single-crystal thin films of MnxTi1-xO2- grown on (rutile)TiO2 substrates with ... Title: Epitaxial single-crystal thin films of MnxTi1-xO2- grown on (rutile)TiO2 ...

  4. Hafnium nitride buffer layers for growth of GaN on silicon

    DOEpatents

    Armitage, Robert D.; Weber, Eicke R.

    2005-08-16

    Gallium nitride is grown by plasma-assisted molecular-beam epitaxy on (111) and (001) silicon substrates using hafnium nitride buffer layers. Wurtzite GaN epitaxial layers are obtained on both the (111) and (001) HfN/Si surfaces, with crack-free thickness up to 1.2 {character pullout}m. However, growth on the (001) surface results in nearly stress-free films, suggesting that much thicker crack-free layers could be obtained.

  5. Structural characterization of InSb thin films grown by electrodeposition

    SciTech Connect

    Singh, Joginder Rajaram, P.

    2015-06-24

    In the present work we have grown InSb thin films on brass substrates, using the electrodeposition technique. The electrochemical baths used in the growth were made up of aqueous solutions of InCl{sub 3} and SbCl{sub 3} mixed together in various proportions. The films grown were characterized by X-Ray diffraction (XRD), Scanning Electron Microscopy (SEM), and Energy Dispersive Analysis of X-rays (EDAX). Compositional studies show that stoichiometric InSb films can be prepared from a bath containing 0.05M InCl{sub 3} and 0.04M SbCl{sub 3}. XRD studies reveal that the films grown are polycrystalline having the zinc blende structure with (111) orientation. Crystallite size, dislocation density and strain were calculated using the XRD results. Optical transmission spectra were recorded using an FTIR spectrophotometer. The value of direct band gap was found to be around 0.20 eV for the thin films having the best stoichiometry.

  6. High active nitrogen flux growth of GaN by plasma assisted molecular beam epitaxy

    SciTech Connect

    McSkimming, Brian M. Speck, James S.; Chaix, Catherine

    2015-09-15

    In the present study, the authors report on a modified Riber radio frequency (RF) nitrogen plasma source that provides active nitrogen fluxes more than 30 times higher than those commonly used for plasma assisted molecular beam epitaxy (PAMBE) growth of gallium nitride (GaN) and thus a significantly higher growth rate than has been previously reported. GaN films were grown using N{sub 2} gas flow rates between 5 and 25 sccm while varying the plasma source's RF forward power from 200 to 600 W. The highest growth rate, and therefore the highest active nitrogen flux, achieved was ∼7.6 μm/h. For optimized growth conditions, the surfaces displayed a clear step-terrace structure with an average RMS roughness (3 × 3 μm) on the order of 1 nm. Secondary ion mass spectroscopy impurity analysis demonstrates oxygen and hydrogen incorporation of 1 × 10{sup 16} and ∼5 × 10{sup 17}, respectively. In addition, the authors have achieved PAMBE growth of GaN at a substrate temperature more than 150 °C greater than our standard Ga rich GaN growth regime and ∼100 °C greater than any previously reported PAMBE growth of GaN. This growth temperature corresponds to GaN decomposition in vacuum of more than 20 nm/min; a regime previously unattainable with conventional nitrogen plasma sources. Arrhenius analysis of the decomposition rate shows that samples with a flux ratio below stoichiometry have an activation energy greater than decomposition of GaN in vacuum while samples grown at or above stoichiometry have decreased activation energy. The activation energy of decomposition for GaN in vacuum was previously determined to be ∼3.1 eV. For a Ga/N flux ratio of ∼1.5, this activation energy was found to be ∼2.8 eV, while for a Ga/N flux ratio of ∼0.5, it was found to be ∼7.9 eV.

  7. Dysprosium oxide and dysprosium-oxide-doped titanium oxide thin films grown by atomic layer deposition

    SciTech Connect

    Tamm, Aile Kozlova, Jekaterina; Aarik, Lauri; Aarik, Jaan; Kukli, Kaupo; Link, Joosep; Stern, Raivo

    2015-01-15

    Dysprosium oxide and dysprosium-oxide-doped titanium oxide thin films were grown by atomic layer deposition on silicon substrates. For depositing dysprosium and titanium oxides Dy(thd){sub 3}-O{sub 3} and TiCl{sub 4}-O{sub 3} were used as precursors combinations. Appropriate parameters for Dy(thd){sub 3}-O{sub 3} growth process were obtained by using a quartz crystal microbalance system. The Dy{sub 2}O{sub 3} films were deposited on planar substrates and on three-dimensional substrates with aspect ratio 1:20. The Dy/Ti ratio of Dy{sub 2}O{sub 3}-doped TiO{sub 2} films deposited on a planar silicon substrate ranged from 0.04 to 0.06. Magnetometry studies revealed that saturation of magnetization could not be observed in planar Dy{sub 2}O{sub 3} films, but it was observable in Dy{sub 2}O{sub 3} films on 3D substrates and in doped TiO{sub 2} films with a Dy/Ti atomic ratio of 0.06. The latter films exhibited saturation magnetization 10{sup −6} A cm{sup 2} and coercivity 11 kA/m at room temperature.

  8. Photoinduced Br Desorption from CsBr Thin Films Grown on Cu(100)

    SciTech Connect

    Halliday, Matthew T.; Joly, Alan G.; Hess, Wayne P.; Shluger, AL

    2015-10-22

    Thin films of CsBr deposited onto metals such as copper are potential photocathode materials for light sources and other applications. We investigate desorption dynamics of Br atoms from CsBr films grown on insulator (KBr, LiF) and metal (Cu) substrates induced by sub-bandgap 6.4 eV laser pulses. The experimental results demonstrate that the peak kinetic energy of Br atoms desorbed from CsBr/Cu films is much lower than that for the hyperthermal desorption from CsBr/LiF films. Kelvin probe measurements indicate negative charge at the surface following Br desorption from CsBr/Cu films. Our ab initio calculations of excitons at CsBr surfaces demonstrate that this behavior can be explained by an exciton model of desorption including electron trapping at the CsBr surface. Trapped negative charges reduce the energy of surface excitons available for Br desorption. We examine the electron-trapping characteristics of low-coordinated sites at the surface, in particular, divacancies and kink sites. We also provide a model of cation desorption caused by Franck-Hertz excitation of F centers at the surface in the course of irradiation of CsBr/Cu films. These results provide new insights into the mechanisms of photoinduced structural evolution of alkali halide films on metal substrates and activation of metal photocathodes coated with CsBr.

  9. Elastic properties of B-C-N films grown by N{sub 2}-reactive sputtering from boron carbide targets

    SciTech Connect

    Salas, E.; Jimnez Riobo, R. J.; Jimnez-Villacorta, F.; Prieto, C.; Snchez-Marcos, J.; Dept. Qumica-Fsica Aplicada, Universidad Autnoma de Madrid, Cantoblanco, 28049 Madrid ; Muoz-Martn, A.; Prieto, J. E.; Joco, V.

    2013-12-07

    Boron-carbon-nitrogen films were grown by RF reactive sputtering from a B{sub 4}C target and N{sub 2} as reactive gas. The films present phase segregation and are mechanically softer than boron carbide films (a factor of more than 2 in Young's modulus). This fact can turn out as an advantage in order to select buffer layers to better anchor boron carbide films on substrates eliminating thermally induced mechanical tensions.

  10. Zinc blende GaAs films grown on wurtzite GaN/sapphire templates

    SciTech Connect

    Chaldyshev, V.V.; Nielsen, B.; Mendez, E.E.; Musikhin, Yu.G.; Bert, N.A.; Ma, Zh.; Holden, Todd

    2005-03-28

    1-{mu}m-thick zinc-blende GaAs (111) films were grown by molecular-beam epitaxy on wurtzite GaN/sapphire (0001) templates. In spite of a {approx}20% lattice mismatch, epitaxial growth was realized, so that the GaAs films showed good adhesion and their surface had a larger mirror-like area with an average surface roughness of 10 nm. Transmission electron microscopy revealed a flat and abrupt epitaxial GaAs/GaN interface with some nanocavities and a large number of dislocations. Reasonably good crystalline quality of the GaAs films was confirmed by Raman characterization. Spectroscopic ellipsometry showed sharp interference fringes and characteristic parameters in the range of 0.75-5.3 eV. Photoluminescence study revealed extended band tails and dominance of non-radiative carrier recombination.

  11. Nanostructural engineering of nitride nucleation layers for GaN substrate dislocation reduction.

    SciTech Connect

    Koleske, Daniel David; Lee, Stephen Roger; Lemp, Thomas Kerr; Coltrin, Michael Elliott; Cross, Karen Charlene; Thaler, Gerald

    2009-07-01

    With no lattice matched substrate available, sapphire continues as the substrate of choice for GaN growth, because of its reasonable cost and the extensive prior experience using it as a substrate for GaN. Surprisingly, the high dislocation density does not appear to limit UV and blue LED light intensity. However, dislocations may limit green LED light intensity and LED lifetime, especially as LEDs are pushed to higher current density for high end solid state lighting sources. To improve the performance for these higher current density LEDs, simple growth-enabled reductions in dislocation density would be highly prized. GaN nucleation layers (NLs) are not commonly thought of as an application of nano-structural engineering; yet, these layers evolve during the growth process to produce self-assembled, nanometer-scale structures. Continued growth on these nuclei ultimately leads to a fully coalesced film, and we show in this research program that their initial density is correlated to the GaN dislocation density. In this 18 month program, we developed MOCVD growth methods to reduce GaN dislocation densities on sapphire from 5 x 10{sup 8} cm{sup -2} using our standard delay recovery growth technique to 1 x 10{sup 8} cm{sup -2} using an ultra-low nucleation density technique. For this research, we firmly established a correlation between the GaN nucleation thickness, the resulting nucleation density after annealing, and dislocation density of full GaN films grown on these nucleation layers. We developed methods to reduce the nuclei density while still maintaining the ability to fully coalesce the GaN films. Ways were sought to improve the GaN nuclei orientation by improving the sapphire surface smoothness by annealing prior to the NL growth. Methods to eliminate the formation of additional nuclei once the majority of GaN nuclei were developed using a silicon nitride treatment prior to the deposition of the nucleation layer. Nucleation layer thickness was determined

  12. Heteroepitaxial film silicon solar cell grown on Ni-W foils

    SciTech Connect

    Wee, Sung Hun; Cantoni, Claudia; Fanning, Thomas; Teplin, Charles; Bogorin, Daniela Florentina; Bornstein, Jon; Bowers, Karen; Schroeter,; Hasoon, Falah; Branz, Howard; Paranthaman, Mariappan Parans; Goyal, Amit

    2013-01-01

    Today, silicon-wafer-based technology dominates the photovoltaic (PV) industry because it enables high efficiency, is produced from abundant, non-toxic materials and is proven in the PV marketplace.[1] However, costs associated with the wafer itself limit ultimate cost reductions.[1,2] PV based on absorber layers of crystalline Si with only 2 to 10 m thickness are a promising route to reduce these costs, while maintaining efficiencies above 15%.[3-5] With the goal of fabricating low-cost film crystalline Si (c-Si), recent research has explored wafer peeling,[6,7] crystallization of amorphous silicon films on glass,[4,8-10] and seed and epitaxy approaches.[3,5,11] In this third approach, one initially forms a seed layer that establishes the grain size and crystalline order. The Si layer is then grown heteroepitaxially on the seed layer, so that it replicates the seed crystal structure. In all of these film c-Si approaches, the critical challenge is to grow c-Si with adequate material quality: specifically, the diffusion length (LD) must be at least three times the film thickness.[12] In polycrystalline Si films, grain boundaries (GBs) are recombination-active and significantly reduce LD. This adverse effects of GBs motivates research into growth of large grained c-Si [13,14] (for a low density of GBs) and biaxially-textured c-Si [11] (for low-angle GBs).

  13. Transparent conductive Al-doped ZnO thin films grown at room temperature

    SciTech Connect

    Wang Yuping; Lu Jianguo; Bie Xun; Gong Li; Li Xiang; Song Da; Zhao Xuyang; Ye Wenyi; Ye Zhizhen

    2011-05-15

    Aluminum-doped ZnO (ZnO:Al, AZO) thin films were prepared on glass substrates by dc reactive magnetron sputtering from a Zn-Al alloy target at room temperature. The effects of the Ar-to-O{sub 2} partial pressure ratios on the structural, electrical, and optical properties of AZO films were studied in detail. AZO films grown using 100:4 to 100:8 Ar-to-O{sub 2} ratio result in acceptable quality films with c-axis orientated crystals, uniform grains, 10{sup -3} {Omega} cm resistivity, greater than 10{sup 20} cm{sup -3} electron concentration, and high transmittance, 90%, in the visible region. The lowest resistivity of 4.11x10{sup -3} {Omega} cm was obtained under the Ar-to-O{sub 2} partial pressure ratio of 100:4. A relatively strong UV emission at {approx}3.26 eV was observed in the room-temperature photoluminescence spectrum. X-ray photoelectron spectroscopy analysis confirmed that Al was introduced into ZnO and substitutes for Zn and doped the film n-type.

  14. Growth modes of InN(000-1) on GaN buffer layers on sapphire

    SciTech Connect

    Liu, Bing; Kitajima, Takeshi; Chen, Dongxue; Leone, Stephen R.

    2005-01-24

    In this work, using atomic force microscopy and scanning tunneling microscopy, we study the surface morphologies of epitaxial InN films grown by plasma-assisted molecular beam epitaxy with intervening GaN buffer layers on sapphire substrates. On smooth GaN buffer layers, nucleation and evolution of three-dimensional InN islands at various coverages and growth temperatures are investigated. The shapes of the InN islands are observed to be predominantly mesa-like with large flat (000-1) tops, which suggests a possible role of indium as a surfactant. Rough GaN buffer layers composed of dense small GaN islands are found to significantly improve uniform InN wetting of the substrates, on which atomically smooth InN films are obtained that show the characteristics of step-flow growth. Scanning tunneling microscopy imaging reveals the defect-mediated surface morphology of smooth InN films, including surface terminations of screw dislocations and a high density of shallow surface pits with depths less than 0.3 nm. The mechanisms of the three-dimensional island size and shape evolution and formation of defects on smooth surfaces are considered.

  15. Temperature dependence of mechanical stiffness and dissipation in ultrananocrystalline diamond films grown by the HFCVD techinque.

    SciTech Connect

    Adiga, V. P.; Sumant, A. V.; Suresh, S.; Gudeman, C.; Auciello, O.; Carlisle, J. A.; Carpick, R. W.; Materials Science Division; Univ. of Pennsylvania; Innovative Micro Tech.; Advanced Diamond Tech.

    2009-06-01

    We have characterized mechanical properties of ultrananocrystalline diamond (UNCD) thin films grown using the hot filament chemical vapor deposition (HFCVD) technique at 680 C, significantly lower than the conventional growth temperature of -800 C. The films have -4.3% sp{sup 2} content in the near-surface region as revealed by near edge x-ray absorption fine structure spectroscopy. The films, -1 {micro}m thick, exhibit a net residual compressive stress of 370 {+-} 1 MPa averaged over the entire 150 mm wafer. UNCD microcantilever resonator structures and overhanging ledges were fabricated using lithography, dry etching, and wet release techniques. Overhanging ledges of the films released from the substrate exhibited periodic undulations due to stress relaxation. This was used to determine a biaxial modulus of 838 {+-} 2 GPa. Resonant excitation and ring-down measurements in the kHz frequency range of the microcantilevers were conducted under ultrahigh vacuum (UHV) conditions in a customized UHV atomic force microscope system to determine Young's modulus as well as mechanical dissipation of cantilever structures at room temperature. Young's modulus is found to be 790 {+-} 30 GPa. Based on these measurements, Poisson's ratio is estimated to be 0.057 {+-} 0.038. The quality factors (Q) of these resonators ranged from 5000 to 16000. These Q values are lower than theoretically expected from the intrinsic properties of diamond. The results indicate that surface and bulk defects are the main contributors to the observed dissipation in UNCD resonators.

  16. Orientation epitaxy of Ge1–xSnx films grown on single crystal CaF2 substrates

    DOE PAGES [OSTI]

    A. J. Littlejohn; Zhang, L. H.; Lu, T. -M.; Kisslinger, K.; and Wang, G. -C.

    2016-03-15

    Ge1–xSnx films were grown via physical vapor deposition below the crystallization temperature of Ge on single crystal (111) and (100) CaF2 substrates to assess the role of Sn alloying in Ge crystallization. By studying samples grown at several growth temperatures ranging from 250 °C to 400 °C we report temperature-dependent trends in several of the films' properties. X-ray diffraction theta vs. two-theta (θ/2θ) scans indicate single orientation Ge1–xSnx(111) films are grown on CaF2(111) substrates at each temperature, while a temperature-dependent superposition of (111) and (100) orientations are exhibited in films grown on CaF2(100) above 250 °C. This is the firstmore » report of (111) oriented Ge1–xSnx grown on a (100) oriented CaF2 substrate, which is successfully predicted by a superlattice area matching model. These results are confirmed by X-ray diffraction pole figure analysis. θ/2θ results indicate substitutional Sn alloying in each film of about 5%, corroborated by energy dispersive spectroscopy. In addition, morphological and electrical properties are measured by scanning electron microscopy, atomic force microscopy and Hall mobility measurements and are also shown to be dependent upon growth temperature.« less

  17. Defect study in molecular beam epitaxy-grown HgCdTe films with activated and unactivated arsenic

    SciTech Connect

    Izhnin, I. I.; Dvoretsky, S. A.; Mikhailov, N. N.; Varavin, V. S.; Mynbaev, K. D.; Fitsych, O. I.; Pociask-Bialy, M.; Sheregii, E.; Voitsekhovskii, A. V.

    2014-04-28

    A defect study was performed on molecular beam epitaxy-grown HgCdTe films in situ doped with arsenic. Doping was performed from either effusion cell or cracker cell, and studied were both as-grown samples and samples subjected to arsenic activation annealing. Electrical properties of the films were investigated with the use of ion milling as a means of stirring defects in the material. As a result of the study, it was confirmed that the most efficient incorporation of electrically active arsenic occurs at the cracking zone temperature of 700?C. Interaction between arsenic and tellurium during the growth was observed and is discussed in the paper.

  18. Structural defects in GaN revealed by Transmission Electron Microscopy

    DOE PAGES [OSTI]

    Liliental-Weber, Zuzanna

    2014-09-08

    This paper reviews the various types of structural defects observed by Transmission Electron Microscopy in GaN heteroepitaxial layers grown on foreign substrates and homoepitaxial layers grown on bulk GaN substrates. The structural perfection of these layers is compared to the platelet self-standing crystals grown by High Nitrogen Pressure Solution. Defects in undoped and Mg doped GaN are discussed. Lastly, some models explaining the formation of inversion domains in heavily Mg doped layers that are possible defects responsible for the difficulties of p-doping in GaN are also reviewed.

  19. Structural defects in GaN revealed by Transmission Electron Microscopy

    SciTech Connect

    Liliental-Weber, Zuzanna

    2014-04-18

    This paper reviews the various types of structural defects observed by Transmission Electron Microscopy in GaN heteroepitaxial layers grown on foreign substrates and homoepitaxial layers grown on bulk GaN substrates. The structural perfection of these layers is compared to the platelet self-standing crystals grown by High Nitrogen Pressure Solution. Defects in undoped and Mg doped GaN are discussed. Some models explaining the formation of inversion domains in heavily Mg doped layers that are possible defects responsible for the difficulties of p-doping in GaN are also reviewed.

  20. Reversible Change in Electrical and Optical Properties in Epitaxially Grown Al-Doped ZnO Thin Films

    SciTech Connect

    Noh, J. H.; Jung, H. S.; Lee, J. K.; Kim, J. Y; Cho, C. M.; An, J.; Hong, K. S.

    2008-01-01

    Aluminum-doped ZnO (AZO) films were epitaxially grown on sapphire (0001) substrates using pulsed laser deposition. As-deposited AZO films had a low resistivity of 8.01 x 10{sup -4} {Omega} cm. However, after annealing at 450 C in air, the electrical resistivity of the AZO films increased to 1.97 x 10{sup -1} {Omega} cm because of a decrease in the carrier concentration. Subsequent annealing of the air-annealed AZO films in H{sub 2} recovered the electrical conductivity of the AZO films. In addition, the conductivity change was reversible upon repeated air and H{sub 2} annealing. A photoluminescence study showed that oxygen interstitial (O{sub i}) is a critical material parameter allowing for the reversible control of the electrical conducting properties of AZO films.

  1. Composition and Bonding in Amorphous Carbon Films Grown by Ion Beam Assisted Deposition: Influence of the Assistance Voltage

    SciTech Connect

    Albella, J.M.; Banks, J.C.; Climent-Font, A.; Doyle, B.L.; Gago, R.; Jimenez, I.; Terminello, L.J.

    1998-11-12

    Amorphous carbon films have been grown by evaporation of graphite with concurrent Ar+ ions bombardment assistance. The ion energy has been varied between 0-800 V while keeping a constant ion to carbon atom arrival ratio. Film composition and density were determined by ion scattering techniques (RBS and ERDA), indicating a negligible hydrogen content and a density dependence with the assistance voltage. The bonding structure of the films has been studied by Raman and X-ray Absorption Near-Edge (XANES) spectroscopy. Different qualitative effects have been found depending on the ion energy range. For ion energies below 300 eV, there is a densification of the carbon layer due to the increase in the sp3 content. For ion energies above 300 eV sputtering phenomena dominate over densification, and thinner films are found with increasing assistance voltage until no film is grown over 600 V. The films with the highest SP3 content are grown with intermediate energies between 200-300 V.

  2. Characterization of Epitaxial Film Silicon Solar Cells Grown on Seeded Display Glass: Preprint

    SciTech Connect

    Young, D. L.; Grover, S.; Teplin, C.; Stradins, P.; LaSalvia, V.; Chuang, T. K.; Couillard, J. G.; Branz, H. M.

    2012-06-01

    We report characterizations of epitaxial film crystal silicon (c-Si) solar cells with open-circuit voltages (Voc) above 560 mV. The 2-um absorber cells are grown by low-temperature (<750 degrees C) hot-wire CVD (HWCVD) on Corning EAGLE XG display glass coated with a layer-transferred (LT) Si seed. The high Voc is a result of low-defect epitaxial Si (epi-Si) growth and effective hydrogen passivation of defects. The quality of HWCVD epitaxial growth on seeded glass substrates depends on the crystallographic quality of the seed and the morphology of the epitaxial growth surface. Heterojunction devices consist of glass/c-Si LT seed/ epi n+ Si:P/epi n- Si:P/intrinsic a-Si:H/p+ a-Si:H/ITO. Similar devices grown on electronically 'dead' n+ wafers have given Voc {approx}630 mV and {approx}8% efficiency with no light trapping features. Here we study the effects of the seed surface polish on epi-Si quality, how hydrogenation influences the device character, and the dominant junction transport physics.

  3. Nucleation and growth dynamics of MBE-grown topological insulator Bi{sub 2}Te{sub 3} films on Si (111)

    SciTech Connect

    Borisova, Svetlana; Krumrain, Julian; Mussler, Gregor; Grützmacher, Detlev; Luysberg, Martina

    2013-12-04

    Topological insulator Bi{sub 2}Te{sub 3} films have been grown by molecular beam epitaxy on Si (111) substrates. The structural properties of the ultra-thin films and their evolution in morphology during the growth have been investigated. The growth starts by a nucleation of separate islands and subsequently turns into a layer-by-layer growth mode. Despite this, the grown film is found to be single crystalline and fully relaxed from the first atomic layer.

  4. Surface structure determinations of crystalline ionic thin films grown on transition metal single crystal surfaces by low energy electron diffraction

    SciTech Connect

    Roberts, J.G.

    2000-05-01

    The surface structures of NaCl(100), LiF(100) and alpha-MgCl2(0001) adsorbed on various metal single crystals have been determined by low energy electron diffraction (LEED). Thin films of these salts were grown on metal substrates by exposing the heated metal surface to a molecular flux of salt emitted from a Knudsen cell. This method of investigating thin films of insulators (ionic salts) on a conducting substrate (metal) circumvents surface charging problems that plagued bulk studies, thereby allowing the use of electron-based techniques to characterize the surface.

  5. Room temperature ferromagnetism in epitaxial Cr{sub 2}O{sub 3} thin films grown on r-sapphire

    SciTech Connect

    Punugupati, Sandhyarani Narayan, Jagdish; Hunte, Frank

    2015-05-21

    We report on the epitaxial growth and magnetic properties of Cr{sub 2}O{sub 3} thin films grown on r-sapphire substrate using pulsed laser deposition. The X-ray diffraction (XRD) (2θ and Φ) and TEM characterization confirm that the films are grown epitaxially. The r-plane (011{sup ¯}2) of Cr{sub 2}O{sub 3} grows on r-plane of sapphire. The epitaxial relations can be written as [011{sup ¯}2] Cr{sub 2}O{sub 3} ‖ [011{sup ¯}2] Al{sub 2}O{sub 3} (out-of-plane) and [1{sup ¯}1{sup ¯}20] Cr{sub 2}O{sub 3} ‖ [1{sup ¯}1{sup ¯}20] Al{sub 2}O{sub 3} (in-plane). The as-deposited films showed ferromagnetic behavior up to 400 K but ferromagnetism almost vanishes with oxygen annealing. The Raman spectroscopy data together with strain measurements using high resolution XRD indicate that ferromagnetism in r-Cr{sub 2}O{sub 3} thin films is due to the strain caused by defects, such as oxygen vacancies.

  6. Engineering the Mechanical Properties of Ultrabarrier Films Grown by Atomic Layer Deposition for the Encapsulation of Printed Electronics

    SciTech Connect

    Bulusu, Anuradha; Singh, Ankit K.; Wang, Cheng-Yin; Dindar, Amir; Fuentes-Hernandez, Canek; Kim, Hyungchul; Cullen, David A.; Kippelen, Bernard; Graham, Samuel

    2015-08-28

    Direct deposition of barrier films by atomic layer deposition (ALD) onto printed electronics presents a promising method for packaging devices. Films made by ALD have been shown to possess desired ultrabarrier properties, but face challenges when directly grown onto surfaces with varying composition and topography. Challenges include differing nucleation and growth rates across the surface, stress concentrations from topography and coefficient of thermal expansion (CTE) mismatch, elastic mismatch, and particle contamination that may impact the performance of the ALD barrier. In such cases, a polymer smoothing layer may be needed to coat the surface prior to ALD barrier film deposition. We present the impact of architecture on the performance of aluminum oxide (Al2O3)/hafnium oxide (HfO2) ALD nanolaminate barrier films deposited on fluorinated polymer layer using an optical calcium (Ca) test under damp heat. It is found that with increasing polymer thickness, the barrier films with residual tensile stress are prone to cracking resulting in rapid failure of the Ca sensor at 50{degree sign}C/85% RH. Inserting a SiNx layer with residual compressive stress between the polymer and ALD layers is found to prevent cracking over a range of polymer thicknesses with more than 95% of the Ca sensor remaining after 500 h of testing. These results suggest that controlling mechanical properties and film architecture play an important role in the performance of direct deposited ALD barriers.

  7. Engineering the mechanical properties of ultrabarrier films grown by atomic layer deposition for the encapsulation of printed electronics

    SciTech Connect

    Bulusu, A.; Singh, A.; Kim, H.; Wang, C. Y.; Dindar, A.; Fuentes-Hernandez, C.; Kippelen, B.; Cullen, D.; Graham, S.

    2015-08-28

    Direct deposition of barrier films by atomic layer deposition (ALD) onto printed electronics presents a promising method for packaging devices. Films made by ALD have been shown to possess desired ultrabarrier properties, but face challenges when directly grown onto surfaces with varying composition and topography. Challenges include differing nucleation and growth rates across the surface, stress concentrations from topography and coefficient of thermal expansion mismatch, elastic constant mismatch, and particle contamination that may impact the performance of the ALD barrier. In such cases, a polymer smoothing layer may be needed to coat the surface prior to ALD barrier film deposition. We present the impact of architecture on the performance of aluminum oxide (Al{sub 2}O{sub 3})/hafnium oxide (HfO{sub 2}) ALD nanolaminate barrier films deposited on fluorinated polymer layer using an optical calcium (Ca) test under damp heat. It is found that with increasing polymer thickness, the barrier films with residual tensile stress are prone to cracking resulting in rapid failure of the Ca sensor at 50 °C/85% relative humidity. Inserting a SiN{sub x} layer with residual compressive stress between the polymer and ALD layers is found to prevent cracking over a range of polymer thicknesses with more than 95% of the Ca sensor remaining after 500 h of testing. These results suggest that controlling mechanical properties and film architecture play an important role in the performance of direct deposited ALD barriers.

  8. Engineering the Mechanical Properties of Ultrabarrier Films Grown by Atomic Layer Deposition for the Encapsulation of Printed Electronics

    DOE PAGES [OSTI]

    Bulusu, Anuradha; Singh, Ankit K.; Wang, Cheng-Yin; Dindar, Amir; Fuentes-Hernandez, Canek; Kim, Hyungchul; Cullen, David A.; Kippelen, Bernard; Graham, Samuel

    2015-08-28

    Direct deposition of barrier films by atomic layer deposition (ALD) onto printed electronics presents a promising method for packaging devices. Films made by ALD have been shown to possess desired ultrabarrier properties, but face challenges when directly grown onto surfaces with varying composition and topography. Challenges include differing nucleation and growth rates across the surface, stress concentrations from topography and coefficient of thermal expansion (CTE) mismatch, elastic mismatch, and particle contamination that may impact the performance of the ALD barrier. In such cases, a polymer smoothing layer may be needed to coat the surface prior to ALD barrier film deposition.more » We present the impact of architecture on the performance of aluminum oxide (Al2O3)/hafnium oxide (HfO2) ALD nanolaminate barrier films deposited on fluorinated polymer layer using an optical calcium (Ca) test under damp heat. It is found that with increasing polymer thickness, the barrier films with residual tensile stress are prone to cracking resulting in rapid failure of the Ca sensor at 50{degree sign}C/85% RH. Inserting a SiNx layer with residual compressive stress between the polymer and ALD layers is found to prevent cracking over a range of polymer thicknesses with more than 95% of the Ca sensor remaining after 500 h of testing. These results suggest that controlling mechanical properties and film architecture play an important role in the performance of direct deposited ALD barriers.« less

  9. Structure disorder degree of polysilicon thin films grown by different processing: Constant C from Raman spectroscopy

    SciTech Connect

    Wang, Quan; Zhang, Yanmin; Hu, Ran; Ren, Naifei; Ge, Daohan

    2013-11-14

    Flat, low-stress, boron-doped polysilicon thin films were prepared on single crystalline silicon substrates by low pressure chemical vapor deposition. It was found that the polysilicon films with different deposition processing have different microstructure properties. The confinement effect, tensile stresses, defects, and the Fano effect all have a great influence on the line shape of Raman scattering peak. But the effect results are different. The microstructure and the surface layer are two important mechanisms dominating the internal stress in three types of polysilicon thin films. For low-stress polysilicon thin film, the tensile stresses are mainly due to the change of microstructure after thermal annealing. But the tensile stresses in flat polysilicon thin film are induced by the silicon carbide layer at surface. After the thin film doped with boron atoms, the phenomenon of the tensile stresses increasing can be explained by the change of microstructure and the increase in the content of silicon carbide. We also investigated the disorder degree states for three polysilicon thin films by analyzing a constant C. It was found that the disorder degree of low-stress polysilicon thin film larger than that of flat and boron-doped polysilicon thin films due to the phase transformation after annealing. After the flat polysilicon thin film doped with boron atoms, there is no obvious change in the disorder degree and the disorder degree in some regions even decreases.

  10. Nanostructured and wide bandgap CdS:O thin films grown by reactive RF sputtering

    SciTech Connect

    Islam, M. A.; Rahman, K. S.; Haque, F.; Rashid, M. J.; Akhtaruzzaman, M.; Sopian, K.; Sulaiman, Y.; Amin, N.

    2015-05-15

    In this study, CdS:O thin films were prepared from a 99.999% CdS target by reactive sputtering in a Ar:O{sub 2} (99:1) ambient with different RF power at room temperature. The deposited films were studied by means of XRD, SEM, EDX, Hall Effect and UV-Vis spectrometry. The incorporations of O{sub 2} into the films were observed to increase with the decrease of deposition power. The cryatallinity of the films were reduced, whereas the band gaps of the films were increased by the increase of O{sub 2} content on the films. The films were found in nano-structured grains with a compact surface. It has been seen that the highest carrier density is observed in the film with O{sub 2} at.% 21.10, while the values decreased with the further increase or decrease of O{sub 2} content on the films; indicating that specific amount of donor like O{sub 2} atoms substitute to the S atoms can improve the carrier density of the CdS:O thin film.

  11. ECR Nb Films Grown on Amorphous and Crystalline Cu Substrates: Influence of Ion Energy

    SciTech Connect

    Valente, Anne-Marie; Eremeev, Grigory V.; Spradlin, Joshua K.; Phillips, H. Lawrence; Reece, Charles E.; Cao, C.; Proslier, Thomas; Tao, T.

    2014-02-01

    In the pursuit of niobium (Nb) films with similar performance with the commonly used bulk Nb surfaces for Superconducting RF (SRF) applications, significant progress has been made with the development of energetic condensation deposition techniques. Using energetic condensation of ions extracted from plasma generated by Electron Cyclotron Resonance, it has been demonstrated that Nb films with good structural properties and RRR comparable to bulk values can be produced on metallic substrates. The controlled incoming ion energy enables a number of processes such as desorption of adsorbed species, enhanced mobility of surface atoms and sub-implantation of impinging ions, thus producing improved film structures at lower process temperatures. Particular attention is given to the nucleation conditions to create a favourable template for growing the final surface exposed to SRF fields. The influence of the deposition energy on film growth on copper substrates is investigated with the characterization of the film surface, structure, superconducting properties and RF performance.

  12. Elevated temperature dependence of energy band gap of ZnO thin films grown by e-beam deposition

    SciTech Connect

    Rai, R. C.; Guminiak, M.; Wilser, S.; Cai, B.; Nakarmi, M. L.

    2012-04-01

    We report the surface, structural, electronic, and optical properties of the epitaxial ZnO thin films grown on (0001) sapphire substrate at 600 deg. C by an electron-beam deposition technique. ZnO thin films have been deposited in an oxygen environment and post-deposition annealed to improve the stoichiometry and the crystal quality. In order to investigate the free exciton binding energy and the temperature dependence of the energy bandgap, we carried out variable temperature (78-450 K) transmittance measurements on ZnO thin films. The absorption data below the energy bandgap have been modeled with the Urbach tail and a free exciton, while the data above the gap have been modeled with the charge transfer excitations. The exciton binding energy is measured to be E{sub 0}= 64 {+-} 7 meV, and the energy band gaps of the ZnO film are measured to be E{sub g}-tilde 3.51 and 3.48 eV at 78 and 300 K, respectively. The temperature dependence of the energy gap has been fitted with the Varshni model to extract the fitting parameters {alpha}= 0.00020 {+-} 0.00002 eV/K, {beta}= 325 {+-} 20 K, and E{sub g} (T = 0 K) = 3.516 {+-} 0.0002 eV.

  13. Critical thickness and strain relaxation in molecular beam epitaxy-grown SrTiO{sub 3} films

    SciTech Connect

    Wang, Tianqi; Ganguly, Koustav; Marshall, Patrick; Xu, Peng; Jalan, Bharat

    2013-11-18

    We report on the study of the critical thickness and the strain relaxation in epitaxial SrTiO{sub 3} film grown on (La{sub 0.3}Sr{sub 0.7})(Al{sub 0.65}Ta{sub 0.35})O{sub 3} (001) (LSAT) substrate using the hybrid molecular beam epitaxy approach. No change in the film's lattice parameter (both the in-plane and the out-of-plane) was observed up to a film thickness of 180 nm, which is in sharp contrast to the theoretical critical thickness of ∼12 nm calculated using the equilibrium theory of strain relaxation. For film thicknesses greater than 180 nm, the out-of-plane lattice parameter was found to decrease hyperbolically in an excellent agreement with the relaxation via forming misfit dislocations. Possible mechanisms are discussed by which the elastic strain energy can be accommodated prior to forming misfit dislocations leading to such anomalously large critical thickness.

  14. Characterization of ZnO thin films grown on different p-Si substrate elaborated by solgel spin-coating method

    SciTech Connect

    Chebil, W.; Fouzri, A.; Fargi, A.; Azeza, B.; Zaaboub, Z.; and others

    2015-10-15

    Highlights: • High quality ZnO thin films grown on different p-Si substrates were successful obtained by sol–gel process. • PL measurement revealed that ZnO thin film grown on porous Si has the better optical quality. • I–V characteristics for all heterojunctions exhibit successful diode formation. • The diode ZnO/PSi shows a better photovoltaic effect under illumination with a maximum {sub Voc} of 0.2 V. - Abstract: In this study, ZnO thin films are deposited by sol–gel technique on p-type crystalline silicon (Si) with [100] orientation, etched silicon and porous silicon. The structural analyses showed that the obtained thin films were polycrystalline with a hexagonal wurtzite structure and preferentially oriented along the c-axis direction. Morphological study revealed the presence of rounded and facetted grains irregularly distributed on the surface of all samples. PL spectra at room temperature revealed that ZnO thin film grown on porous Si has a strong UV emission with low defects in the visible region comparing with ZnO grown on plat Si and etched Si surface. The heterojunction parameters were evaluated from the (I–V) under dark and illumination at room temperature. The ideality factor, barrier height and series resistance of heterojunction grown on different p-Si substrates are determined by using different methods. Best electrical properties are obtained for ZnO layer deposited on porous silicon.

  15. High electron mobility thin-film transistors based on Ga{sub 2}O{sub 3} grown by atmospheric ultrasonic spray pyrolysis at low temperatures

    SciTech Connect

    Thomas, Stuart R. E-mail: thomas.anthopoulos@imperial.ac.uk; Lin, Yen-Hung; Faber, Hendrik; Anthopoulos, Thomas D. E-mail: thomas.anthopoulos@imperial.ac.uk; Adamopoulos, George; Sygellou, Labrini; Stratakis, Emmanuel; Pliatsikas, Nikos; Patsalas, Panos A.

    2014-09-01

    We report on thin-film transistors based on Ga{sub 2}O{sub 3} films grown by ultrasonic spray pyrolysis in ambient atmosphere at 400450?C. The elemental, electronic, optical, morphological, structural, and electrical properties of the films and devices were investigated using a range of complementary characterisation techniques, whilst the effects of post deposition annealing at higher temperature (700?C) were also investigated. Both as-grown and post-deposition annealed Ga{sub 2}O{sub 3} films are found to be slightly oxygen deficient, exceptionally smooth and exhibit a wide energy bandgap of ?4.9?eV. Transistors based on as-deposited Ga{sub 2}O{sub 3} films show n-type conductivity with the maximum electron mobility of ?2?cm{sup 2}/V s.

  16. Field emission from bias-grown diamond thin films in a microwave plasma

    DOEpatents

    Gruen, Dieter M.; Krauss, Alan R.; Ding, Ming Q.; Auciello, Orlando

    2002-01-01

    A method of producing diamond or diamond like films in which a negative bias is established on a substrate with an electrically conductive surface in a microwave plasma chemical vapor deposition system. The atmosphere that is subjected to microwave energy includes a source of carbon, nitrogen and hydrogen. The negative bias is maintained on the substrate through both the nucleation and growth phase of the film until the film is continuous. Biases between -100V and -200 are preferred. Carbon sources may be one or more of CH.sub.4, C.sub.2 H.sub.2 other hydrocarbons and fullerenes.

  17. Zero lattice mismatch and twin-free single crystalline ScN buffer layers for GaN growth on silicon

    SciTech Connect

    Lupina, L.; Zoellner, M. H.; Dietrich, B.; Capellini, G.; Niermann, T.; Lehmann, M.; Thapa, S. B.; Haeberlen, M.; Storck, P.; Schroeder, T.

    2015-11-16

    We report the growth of thin ScN layers deposited by plasma-assisted molecular beam epitaxy on Sc{sub 2}O{sub 3}/Y{sub 2}O{sub 3}/Si(111) substrates. Using x-ray diffraction, Raman spectroscopy, and transmission electron microscopy, we find that ScN films grown at 600 °C are single crystalline, twin-free with rock-salt crystal structure, and exhibit a direct optical band gap of 2.2 eV. A high degree of crystalline perfection and a very good lattice matching between ScN and GaN (misfit < 0.1%) makes the ScN/Sc{sub 2}O{sub 3}/Y{sub 2}O{sub 3} buffer system a very promising template for the growth of high quality GaN layers on silicon.

  18. Pseudo capacitive performance of copper oxide thin films grown by RF sputtering

    SciTech Connect

    Reddy, B. Purusottam; Ganesh, K. Sivajee; Hussain, O. M.

    2015-06-24

    Thin films of Copper Oxide were prepared by radio frequency magnetron sputtering on steel substrates maintained at 250°C under different RF powers ranging from 150W to 250W by keeping the sputtering pressure at 5.7×10{sup −3} mbar and O{sub 2}:Ar ratio of 1:7. The influence of RF power on the pseudo capacitive performance of thin films was studied. The X-ray diffraction studies and Raman studies indicates that all the thin films exhibits CuO phase. The electrochemical studies was done by using three electrode configuration with platinum as reference electrode. From the cyclic voltammetry studies a high rate pseudocapacitance of 227 mFcm{sup −2} at 0.5 mVs{sup −1} and 77% of capacity retention after 1000 cycles was obtained for the CuO thin films prepared at an RF power of 220W.

  19. Flexible cadmium telluride thin films grown on electron-beam-irradiated graphene/thin glass substrates

    SciTech Connect

    Seo, Won-Oh; Kim, Jihyun; Koo, Yong Hwan; Kim, Byungnam; Lee, Byung Cheol; Kim, Donghwan

    2014-08-25

    We demonstrate the close-spaced sublimation growth of polycrystalline cadmium telluride (CdTe) thin films on a flexible graphene electrode/thin glass substrate structure. Prior to the growth of CdTe films, chemical-vapor-deposited graphene was transferred onto a flexible glass substrate and subjected to electron-beam irradiation at an energy of 0.2 MeV in order to intentionally introduce the defects into it in a controlled manner. Micro-Raman spectroscopy and sheet resistance measurements were employed to monitor the damage and disorder in the electron-beam irradiated graphene layers. The morphology and optical properties of the CdTe thin films deposited on a graphene/flexible glass substrate were systematically characterized. The integration of the defective graphene layers with a flexible glass substrate can be a useful platform to grow various thin-film structures for flexible electronic and optoelectronic devices.

  20. Enhanced photocatalytic performance in atomic layer deposition grown TiO{sub 2} thin films via hydrogen plasma treatment

    SciTech Connect

    Sasinska, Alexander; Singh, Trilok; Wang, Shuangzhou; Mathur, Sanjay; Kraehnert, Ralph

    2015-01-15

    The authors report the effect of hydrogen plasma treatment on TiO{sub 2} thin films grown by atomic layer deposition as an effective approach for modifying the photoanode materials in order to enhance their photoelectrochemical performance. Hydrogen plasma treated TiO{sub 2} thin films showed an improved absorption in the visible spectrum probably due to surface reduction. XPS analysis confirmed the formation of Ti{sup 3+} states upon plasma treatment. Hydrogen plasma treatment of TiO{sub 2} films enhanced the measured photocurrent densities by a factor of 8 (1 mA/cm{sup 2} at 0.8 V versus normal hydrogen electrode) when compared to untreated TiO{sub 2} (0.12 mA/cm{sup 2}). The enhancement in photocurrent is attributed to the formation of localized electronic states in mid band-gap region, which facilitate efficient separation and transportation of photo excited charge carriers in the UV region of electromagnetic spectrum.

  1. Characterization of ZnO film grown on polycarbonate by atomic layer deposition at low temperature

    SciTech Connect

    Lee, Gyeong Beom; Han, Gwon Deok; Shim, Joon Hyung; Choi, Byoung-Ho

    2015-01-15

    ZnO is an attractive material for use in various technological products such as phosphors, gas sensors, and transparent conductors. Recently, aluminum-doped zinc oxide has received attention as a potential replacement for indium tin oxide, which is one of the transparent conductive oxides used in flat panel displays, organic light-emitting diodes, and organic solar cells. In this study, the characteristics of ZnO films deposited on polycarbonate (PC) substrates by atomic layer deposition (ALD) are investigated for various process temperatures. The growth mechanism of these films was investigated at low process temperatures using x-ray diffraction (XRD) and x-ray photoelectron spectroscopy (XPS). XRD and XPS were used to determine the preferred orientation and chemical composition of the films, respectively. Furthermore, the difference of the deposition mechanisms on an amorphous organic material, i.e., PC substrate and an inorganic material such as silicon was discussed from the viewpoint of the diffusion and deposition of precursors. The structure of the films was also investigated by chemical analysis in order to determine the effect of growth temperature on the films deposited by ALD.

  2. Elimination of surface band bending on N-polar InN with thin GaN capping

    SciTech Connect

    Kuzmík, J. Haščík, Š.; Kučera, M.; Kúdela, R.; Dobročka, E.; Adikimenakis, A.; Mičušík, M.; Gregor, M.; Plecenik, A.; Georgakilas, A.

    2015-11-09

    0.5–1 μm thick InN (0001) films grown by molecular-beam epitaxy with N- or In-polarity are investigated for the presence of native oxide, surface energy band bending, and effects introduced by 2 to 4 monolayers of GaN capping. Ex situ angle-resolved x-ray photo-electron spectroscopy is used to construct near-surface (GaN)/InN energy profiles, which is combined with deconvolution of In3d signal to trace the presence of InN native oxide for different types of polarity and capping. Downwards surface energy band bending was observed on bare samples with native oxide, regardless of the polarity. It was found that the In-polar InN surface is most readily oxidized, however, with only slightly less band bending if compared with the N-polar sample. On the other hand, InN surface oxidation was effectively mitigated by GaN capping. Still, as confirmed by ultra-violet photo-electron spectroscopy and by energy band diagram calculations, thin GaN cap layer may provide negative piezoelectric polarization charge at the GaN/InN hetero-interface of the N-polar sample, in addition to the passivation effect. These effects raised the band diagram up by about 0.65 eV, reaching a flat-band profile.

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

    SciTech Connect

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

    1999-02-23

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

  4. Synthesis of nanocrystalline Cu{sub 2}ZnSnS{sub 4} thin films grown by the spray-pyrolysis technique

    SciTech Connect

    Chandel, Tarun Singh, Joginder; Rajaram, P.

    2015-08-28

    Spray pyrolysis was used to deposit Cu{sub 2}ZnSnS{sub 4} (CZTS) thin films on soda lime glass substrates at 300 °C. Aqueous solutions of copper chloride, zinc chloride, stannous chloride and thiourea were mixed together to form the spray liquid. The sprayed films were annealed under vacuum at 350 °C, 400 °C and 450 °C. Structural and optical characterization was performed on the CZTS films using X-ray diffraction (XRD) and UV-VIS spectrophotometry. XRD results indicate that the films are single phase nanocrystalline CZTS. Optical studies show that the optical gap values are 1.44 eV for the as-grown film and 1.46 eV, 1.48 eV and 1.49 eV for the films annealed at 350 °C, 400 °C and 450 °C, respectively.

  5. Grain size dependent mechanical properties of nanocrystalline diamond films grown by hot-filament CVD

    SciTech Connect

    Wiora, M; Bruehne, K; Floeter, A; Gluche, P; Willey, T M; Kucheyev, S O; Van Buuren, A W; Hamza, A V; Biener, J; Fecht, H

    2008-08-01

    Nanocrystalline diamond (NCD) films with a thickness of {approx}6 {micro}m and with average grain sizes ranging from 60 to 9 nm were deposited on silicon wafers using a hot-filament chemical vapor deposition (HFCVD) process. These samples were then characterized with the goal to identify correlations between grain size, chemical composition and mechanical properties. The characterization reveals that our films are phase pure and exhibit a relatively smooth surface morphology. The levels of sp{sup 2}-bonded carbon and hydrogen impurities are low, and showed a systematic variation with the grain size. The hydrogen content increases with decreasing grain size, whereas the sp{sup 2} carbon content decreases with decreasing grain size. The material is weaker than single crystalline diamond, and both stiffness and hardness decrease with decreasing grain size. These trends suggest gradual changes of the nature of the grain boundaries, from graphitic in the case of the 60 nm grain size material to hydrogen terminated sp{sup 3} carbon for the 9 nm grain size material. The films exhibit low levels of internal stress and freestanding structures with a length of several centimeters could be fabricated without noticeable bending.

  6. Superexchange and iron valence control by off-stoichiometry in yttrium iron garnet thin films grown by pulsed laser deposition

    SciTech Connect

    Dumont, Y.; Keller, N.; Popova, E.; Schmool, D.S.; Bhattacharya, S.; Stahl, B.; Tessier, M.; Guyot, M.

    2005-05-15

    Controlled off-stoichiometric single phase polycrystalline yttrium iron garnet (YIG) thin films have been grown by pulsed laser deposition, adjusting the oxygen partial pressure P{sub O2} between 5 and 400 mTorr. Atomic stoichiometry by RBS shows an oxygen deficiency for P{sub O2}P{sub stoich}. P{sub stoich}=30 mTorr refers to films showing magnetic and structural properties of the bulk stoichiometric YIG. Curie temperature T{sub c} and saturation magnetization 4{pi}Ms decreased for P{sub O2}P{sub stoich}: Increase of Tc (up to +10%) and of 4{pi}Ms (up to +20%) and lattice parameter compression. Microscopic interpretation is given in terms of superexchange interaction and creation and site selectivity of iron vacancies.

  7. Reactor design for uniform chemical vapor deposition-grown films without substrate rotation

    DOEpatents

    Wanlass, Mark

    1987-01-01

    A quartz reactor vessel for growth of uniform semiconductor films includes a vertical, cylindrical reaction chamber in which a substrate-supporting pedestal provides a horizontal substrate-supporting surface spaced on its perimeter from the chamber wall. A cylindrical confinement chamber of smaller diameter is disposed coaxially above the reaction chamber and receives reaction gas injected at a tangent to the inside chamber wall, forming a helical gas stream that descends into the reaction chamber. In the reaction chamber, the edge of the substrate-supporting pedestal is a separation point for the helical flow, diverting part of the flow over the horizontal surface of the substrate in an inwardly spiraling vortex.

  8. Reactor design for uniform chemical vapor deposition-grown films without substrate rotation

    DOEpatents

    Wanlass, M.

    1985-02-19

    A quartz reactor vessel for growth of uniform semiconductor films includes a vertical, cylindrical reaction chamber in which a substrate-supporting pedestal provides a horizontal substrate-supporting surface spaced on its perimeter from the chamber wall. A cylindrical confinement chamber of smaller diameter is disposed coaxially above the reaction chamber and receives reaction gas injected at a tangent to the inside chamber wall, forming a helical gas stream that descends into the reaction chamber. In the reaction chamber, the edge of the substrate-supporting pedestal is a separation point for the helical flow, diverting part of the flow over the horizontal surface of the substrate in an inwardly spiraling vortex.

  9. Influence of growth temperature on electrical, optical, and plasmonic properties of aluminum:zinc oxide films grown by radio frequency magnetron sputtering

    SciTech Connect

    Dondapati, Hareesh; Santiago, Kevin; Pradhan, A. K.

    2013-10-14

    We have investigated the responsible mechanism for the observation of metallic conductivity at room temperature and metal-semiconductor transition (MST) at lower temperatures for aluminum-doped zinc oxide (AZO) films. AZO films were grown on glass substrates by radio-frequency magnetron sputtering with varying substrate temperatures (T{sub s}). The films were found to be crystalline with the electrical resistivity close to 1.1 × 10{sup −3} Ω cm and transmittance more than 85% in the visible region. The saturated optical band gap of 3.76 eV was observed for the sample grown at T{sub s} of 400 °C, however, a slight decrease in the bandgap was noticed above 400 °C, which can be explained by Burstein–Moss effect. Temperature dependent resistivity measurements of these highly conducting and transparent films showed a MST at ∼110 K. The observed metal-like and metal-semiconductor transitions are explained by taking into account the Mott phase transition and localization effects due to defects. All AZO films demonstrate crossover in permittivity from positive to negative and low loss in the near-infrared region, illustrating its applications for plasmonic metamaterials, including waveguides for near infrared telecommunication region. Based on the results presented in this study, the low electrical resistivity and high optical transmittance of AZO films suggested a possibility for the application in the flexible electronic devices, such as transparent conducting oxide film on LEDs, solar cells, and touch panels.

  10. Ultraviolet GaN photodetectors on Si via oxide buffer heterostructures with integrated short period oxide-based distributed Bragg reflectors and leakage suppressing metal-oxide-semiconductor contacts

    SciTech Connect

    Szyszka, A. E-mail: adam.szyszka@pwr.wroc.pl; Haeberlen, M.; Storck, P.; Thapa, S. B.; Schroeder, T.

    2014-08-28

    Based on a novel double step oxide buffer heterostructure approach for GaN integration on Si, we present an optimized Metal-Semiconductor-Metal (MSM)-based Ultraviolet (UV) GaN photodetector system with integrated short-period (oxide/Si) Distributed Bragg Reflector (DBR) and leakage suppressing Metal-Oxide-Semiconductor (MOS) electrode contacts. In terms of structural properties, it is demonstrated by in-situ reflection high energy electron diffraction and transmission electron microscopy-energy dispersive x-ray studies that the DBR heterostructure layers grow with high thickness homogeneity and sharp interface structures sufficient for UV applications; only minor Si diffusion into the Y{sub 2}O{sub 3} films is detected under the applied thermal growth budget. As revealed by comparative high resolution x-ray diffraction studies on GaN/oxide buffer/Si systems with and without DBR systems, the final GaN layer structure quality is not significantly influenced by the growth of the integrated DBR heterostructure. In terms of optoelectronic properties, it is demonstrated thatwith respect to the basic GaN/oxide/Si system without DBRthe insertion of (a) the DBR heterostructures and (b) dark current suppressing MOS contacts enhances the photoresponsivity below the GaN band-gap related UV cut-off energy by almost up to two orders of magnitude. Given the in-situ oxide passivation capability of grown GaN surfaces and the one order of magnitude lower number of superlattice layers in case of higher refractive index contrast (oxide/Si) systems with respect to classical III-N DBR superlattices, virtual GaN substrates on Si via functional oxide buffer systems are thus a promising robust approach for future GaN-based UV detector technologies.

  11. Ferromagnetism in undoped One-dimensional GaN Nanowires

    SciTech Connect

    Jeganathan, K. E-mail: jagan@physics.bdu.ac.in; Purushothaman, V.; Debnath, R.; Arumugam, S.

    2014-05-15

    We report an intrinsic ferromagnetism in vertical aligned GaN nanowires (NW) fabricated by molecular beam epitaxy without any external catalyst. The magnetization saturates at ?0.75 emu/gm with the applied field of 3000 Oe for the NWs grown under the low-Gallium flux of 2.4 10{sup ?8} mbar. Despite a drop in saturation magnetization, narrow hysteresis loop remains intact regardless of Gallium flux. Magnetization in vertical standing GaN NWs is consistent with the spectral analysis of low-temperature photoluminescence pertaining to Ga-vacancies associated structural defects at the nanoscale.

  12. Spectral behavior of the optical constants in the visible/near infrared of GeSbSe chalcogenide thin films grown at glancing angle

    SciTech Connect

    Martin-Palma, R. J.; Ryan, Joseph V.; Pantano, C. G.

    2007-04-23

    GeSbSe chalcogenide thin films were deposited using glancing angle deposition onto transparent glass substrates for the determination of the spectral behavior of the optical constants (index of refraction n and extinction coefficient k) in the visible and near infrared ranges (400-2500 nm) as a function of the deposition angle. Computational simulations based on the matrix method were employed to determine the values of the optical constants of the different films from the experimental reflectance and transmittance spectra. A significant dependence of the overall optical behavior on the deposition angle is found. Furthermore, the band gap of the GeSbSe thin films was calculated. The accurate determination of the optical constants of films grown at glancing angle will enable the development of sculptured thin film fiber-optic chemical sensors and biosensors.

  13. GaN: Defect and Device Issues

    SciTech Connect

    Pearton, S.J.; Ren, F.; Shul, R.J.; Zolper, J.C.

    1998-11-09

    The role of extended and point defects, and key impurities such as C, O and H, on the electrical and optical properties of GaN is reviewed. Recent progress in the development of high reliability contacts, thermal processing, dry and wet etching techniques, implantation doping and isolation and gate insulator technology is detailed. Finally, the performance of GaN-based electronic and photonic devices such as field effect transistors, UV detectors, laser diodes and light-emitting diodes is covered, along with the influence of process-induced or grown-in defects and impurities on the device physics.

  14. p-type conduction from Sb-doped ZnO thin films grown by dual ion beam sputtering in the absence of oxygen ambient

    SciTech Connect

    Kumar Pandey, Sushil; Kumar Pandey, Saurabh; Awasthi, Vishnu; Kumar, Ashish; Mukherjee, Shaibal; Deshpande, Uday P.; Gupta, Mukul

    2013-10-28

    Sb-doped ZnO (SZO) thin films were deposited on c-plane sapphire substrates by dual ion beam sputtering deposition system in the absence of oxygen ambient. The electrical, structural, morphological, and elemental properties of SZO thin films were studied for films grown at different substrate temperatures ranging from 200 °C to 600 °C and then annealed in situ at 800 °C under vacuum (pressure ∼5 × 10{sup −8} mbar). Films grown for temperature range of 200–500 °C showed p-type conduction with hole concentration of 1.374 × 10{sup 16} to 5.538 × 10{sup 16} cm{sup −3}, resistivity of 66.733–12.758 Ω cm, and carrier mobility of 4.964–8.846 cm{sup 2} V{sup −1} s{sup −1} at room temperature. However, the film grown at 600 °C showed n-type behavior. Additionally, current-voltage (I–V) characteristic of p-ZnO/n-Si heterojunction showed a diode-like behavior, and that further confirmed the p-type conduction in ZnO by Sb doping. X-ray diffraction measurements showed that all SZO films had (002) preferred crystal orientation. X-ray photoelectron spectroscopy analysis confirmed the formation of Sb{sub Zn}–2V{sub Zn} complex caused acceptor-like behavior in SZO films.

  15. Design of step composition gradient thin film transistor channel layers grown by atomic layer deposition

    SciTech Connect

    Ahn, Cheol Hyoun; Hee Kim, So; Gu Yun, Myeong; Koun Cho, Hyung

    2014-12-01

    In this study, we proposed the artificially designed channel structure in oxide thin-film transistors (TFTs) called a “step-composition gradient channel.” We demonstrated Al step-composition gradient Al-Zn-O (AZO) channel structures consisting of three AZO layers with different Al contents. The effects of stacking sequence in the step-composition gradient channel on performance and electrical stability of bottom-gate TFT devices were investigated with two channels of inverse stacking order (ascending/descending step-composition). The TFT with ascending step-composition channel structure (5 → 10 → 14 at. % Al composition) showed relatively negative threshold voltage (−3.7 V) and good instability characteristics with a reduced threshold voltage shift (Δ 1.4 V), which was related to the alignment of the conduction band off-set within the channel layer depending on the Al contents. Finally, the reduced Al composition in the initial layer of ascending step-composition channel resulted in the best field effect mobility of 4.5 cm{sup 2}/V s. We presented a unique active layer of the “step-composition gradient channel” in the oxide TFTs and explained the mechanism of adequate channel design.

  16. Co{sub 2}FeAl Heusler thin films grown on Si and MgO substrates: Annealing temperature effect

    SciTech Connect

    Belmeguenai, M. Tuzcuoglu, H.; Zighem, F.; Chérif, S. M.; Moch, P.; Gabor, M. S. Petrisor, T.; Tiusan, C.

    2014-01-28

    10 nm and 50 nm Co{sub 2}FeAl (CFA) thin films have been deposited on MgO(001) and Si(001) substrates by magnetron sputtering and annealed at different temperatures. X-rays diffraction revealed polycrystalline or epitaxial growth (according to CFA(001)[110]//MgO(001)[100] epitaxial relation) for CFA films grown on a Si and on a MgO substrate, respectively. For these later, the chemical order varies from the A2 phase to the B2 phase when increasing the annealing temperature (T{sub a}), while only the A2 disorder type has been observed for CFA grown on Si. Microstrip ferromagnetic resonance (MS-FMR) measurements revealed that the in-plane anisotropy results from the superposition of a uniaxial and a fourfold symmetry term for CFA grown on MgO substrates. This fourfold anisotropy, which disappears completely for samples grown on Si, is in accord with the crystal structure of the samples. The fourfold anisotropy field decreases when increasing T{sub a}, while the uniaxial anisotropy field is nearly unaffected by T{sub a} within the investigated range. The MS-FMR data also allow for concluding that the gyromagnetic factor remains constant and that the exchange stiffness constant increases with T{sub a}. Finally, the FMR linewidth decreases when increasing T{sub a}, due to the enhancement of the chemical order. We derive a very low intrinsic damping parameter (1.1×10{sup −3} and 1.3×10{sup −3} for films of 50 nm thickness annealed at 615 °C grown on MgO and on Si, respectively)

  17. Thermal stability of Al- and Zr-doped HfO{sub 2} thin films grown by direct current magnetron sputtering

    SciTech Connect

    Hong, Yeong-Eui; Kim, Yong-Seok; Do, Kihoon; Lee, Dongwon; Ko, Dae-Hong; Ku, Ja-Hum; Kim, Hyoungsub

    2005-09-15

    Ultrathin HfO{sub 2} dielectric films doped with Al and Zr were grown on p-type Si(100) substrates by dc magnetron sputtering, and their microstructural and electrical properties were examined. Compositions and chemical states of the dielectric films were analyzed by Rutherford backscattering spectrometry and x-ray photoelectron spectroscopy. The HfO{sub 2} films doped with Zr were crystallized even from the as-deposited state, however, the crystallization temperature of the HfO{sub 2} film doped with 16% Al{sub 2}O{sub 3} was delayed up to 900 deg. C. As the annealing temperature increases, high-resolution transmission electron microscopy analyses of all doped HfO{sub 2} films showed an increase of the interfacial layer thickness due to the diffusion of small partial pressure of oxygen in annealing ambient. Our results also showed that the addition of Al{sub 2}O{sub 3} to 14% is not useful for blocking the oxygen diffusion through the (HfO{sub 2}){sub 0.86}(Al{sub 2}O{sub 3}){sub 0.14} film. From the capacitance-voltage measurements, the dielectric constants of the Al- and Zr-doped HfO{sub 2} thin films were measured to be 18.7 and 7.6, respectively.

  18. Preparation and characterization of one-dimensional GaN nanorods with Tb intermediate layer

    SciTech Connect

    Shi, Feng; Xue, Chengshan

    2012-12-15

    Graphical abstract: Display Omitted Highlights: ► GaN nanorods have been prepared on Si substrates by magnetron sputtering. ► GaN nanorods are single crystal with hexagonal wurtzite structure. ► GaN nanorods are high-quality crystalline after ammoniating at 950 °C for 15 min. ► Ammoniating temperatures and times affect the growth of GaN nanorods significantly. -- Abstract: GaN nanorods have been successfully prepared on Si(1 1 1) substrates by magnetron sputtering through ammoniating Ga{sub 2}O{sub 3}/Tb thin films. X-ray diffraction (XRD), X-ray photoelectron spectroscope (XPS), FT-IR spectrophotometer, scanning electron microscope (SEM), high-resolution transmission electron microscope (HRTEM), and photoluminescence (PL) spectroscopy were used to characterize the microstructures, morphologies compositions and optical properties of the GaN samples. The results demonstrate that the nanorods are single crystal GaN with hexagonal wurtzite structure and high-quality crystalline after ammoniating at 950 °C for 15 min, which have the size of 100–150 nm in diameter. Ammoniating temperatures and times affect the growth of GaN nanorods significantly. The growth procedure mainly follows the Tb catalyst-assisted VLS mechanism.

  19. Growth temperature effect on the structural and magnetic properties of Fe{sub 3}O{sub 4} films grown by the self-template method

    SciTech Connect

    Takahashi, R. Misumi, H.; Lippmaa, M.

    2014-07-21

    We have investigated the effect of growth temperature on the structure, surface morphology, and magnetic properties of Fe{sub 3}O{sub 4} thin films grown on SrTiO{sub 3}(001) substrates by a self-template method. To eliminate the intermixing of (001) and (111) orientations that usually occurs in spinel films grown on perovskite substrates, a thin self-template layer of (001)-oriented Fe{sub 3}O{sub 4} was deposited on a SrTiO{sub 3}(001) substrate at 400 °C prior to the main film growth at temperatures of up to 1100 °C. Increasing the growth temperature from 400 °C to 1100 °C resulted in greatly improved crystallinity of the Fe{sub 3}O{sub 4} thin films, with the rocking curve width dropping from 1.41° to 0.28°. Surface analysis by atomic force microscopy showed that raising the growth temperature increased the grain size and the surface roughness, ultimately leading to the formation of regular nanopyramid arrays at 1100 °C. The surface roughening and pyramid formation are caused by the dominance of the lowest surface energy spinel (111) crystal facet. The nanopyramids were fully relaxed but still perfectly (001)-oriented in the out-of-plane direction. The largest pyramids had the lowest coercivity due to a reduction of the demagnetization effect.

  20. Structural properties of InN films grown on O-face ZnO(0001) by plasma-assisted molecular beam epitaxy

    SciTech Connect

    Cho, Yong Jin; Brandt, Oliver; Kaganer, Vladimir M.; Ramsteiner, Manfred; Riechert, Henning; Korytov, Maxim; Albrecht, Martin

    2012-04-09

    We study the impact of substrate temperature and layer thickness on the morphological and structural properties of InN films directly grown on O-face ZnO(0001) substrates by plasma-assisted molecular beam epitaxy. With increasing substrate temperature, an interfacial reaction between InN and ZnO takes place that eventually results in the formation of cubic In{sub 2}O{sub 3} and voids. The properties of the InN films, however, are found to be unaffected by this reaction for substrate temperatures less than 550 deg. C. In fact, both the morphological and the structural quality of InN improve with increasing substrate temperature in the range from 350 to 500 deg. C. High quality films with low threading dislocation densities are demonstrated.

  1. Domain formation due to surface steps in topological insulator Bi{sub 2}Te{sub 3} thin films grown on Si (111) by molecular beam epitaxy

    SciTech Connect

    Borisova, S.; Kampmeier, J.; Mussler, G.; Grützmacher, D.; Jülich Aachen Research Alliance, Fundamentals of Future Information Technologies, Jülich 52425 ; Luysberg, M.

    2013-08-19

    The atomic structure of topological insulators Bi{sub 2}Te{sub 3} thin films on Si (111) substrates grown in van der Waals mode by molecular beam epitaxy has been investigated by in situ scanning tunneling microscopy and scanning transmission electron microscopy. Besides single and multiple quintuple layer (QL) steps, which are typical for the step-flow mode of growth, a number of 0.4 QL steps is observed. We determine that these steps originate from single steps at the substrate surface causing domain boundaries in the Bi{sub 2}Te{sub 3} film. Due to the peculiar structure of these domain boundaries the domains are stable and penetrate throughout the entire film.

  2. Properties of molecular beam epitaxy grown Eu{sub x}(transition metal){sub y} films (transition metals: Mn, Cr)

    SciTech Connect

    Balin, K.; Nowak, A.; Gibaud, A.; Szade, J.; Celinski, Z.

    2011-04-01

    The electronic and crystallographic structures, as well as the magnetic properties, of Eu{sub x}(transition metal){sub y} (transition metals: Mn, Cr) thin films grown by molecular beam epitaxy were studied. Relative changes of the Eu/Mn and Eu/Cr ratios derived from the XPS lines, as well as x-ray reflectivity, indicate mixing of the Eu/Mn and Eu/Cr layers. Valency transitions from Eu{sup 2+} to Eu{sup 3+} were observed in both systems for most studied stoichiometries. A transition to a magnetically ordered phase was observed at 15 K, 40 K, and 62 K for selected films in the Eu-Mn system, and at 50 K for the film with a Eu/Cr ratio of 0.5.

  3. Structural characterization of metastable hcp-Ni thin films epitaxially grown on Au(100) single-crystal underlayers

    SciTech Connect

    Ohtake, Mitsuru; Tanaka, Takahiro; Futamoto, Masaaki; Kirino, Fumiyoshi

    2010-05-15

    Ni(1120) epitaxial thin films with hcp structure were prepared on Au(100) single-crystal underlayers at 100 deg. C by ultra high vacuum molecular beam epitaxy. The detailed film structure is studied by in situ reflection high energy electron diffraction, x-ray diffraction, and transmission electron microscopy. The hcp-Ni film consists of two types of variants whose c-axes are rotated around the film normal by 90 deg. each other. An atomically sharp boundary is recognized between the film and the underlayer, where misfit dislocations are introduced. Presence of such dislocations seems to relieve the strain caused by the lattice mismatch between the film and the underlayer.

  4. Room temperature photoluminescence from In{sub x}Al{sub (1?x)}N films deposited by plasma-assisted molecular beam epitaxy

    SciTech Connect

    Kong, W. Jiao, W. Y.; Kim, T. H.; Brown, A. S.; Mohanta, A.; Roberts, A. T.; Fournelle, J.; Losurdo, M.; Everitt, H. O.

    2014-09-29

    InAlN films deposited by plasma-assisted molecular beam epitaxy exhibited a lateral composition modulation characterized by 1012?nm diameter, honeycomb-shaped, columnar domains with Al-rich cores and In-rich boundaries. To ascertain the effect of this microstructure on its optical properties, room temperature absorption and photoluminescence characteristics of In{sub x}Al{sub (1?x)}N were comparatively investigated for indium compositions ranging from x?=?0.092 to 0.235, including x?=?0.166 lattice matched to GaN. The Stokes shift of the emission was significantly greater than reported for films grown by metalorganic chemical vapor deposition, possibly due to the phase separation in these nanocolumnar domains. The room temperature photoluminescence also provided evidence of carrier transfer from the InAlN film to the GaN template.

  5. Properties of H, O and C in GaN

    SciTech Connect

    Pearton, S.J.; Abernathy, C.R.; Lee, J.W.

    1996-04-01

    The electrical properties of the light ion impurities H, O and C in GaN have been examined in both as-grown and implanted material. H is found to efficiently passivate acceptors such as Mg, Ca and C. Reactivation occurs at {ge} 450 C and is enhanced by minority carrier injection. The hydrogen does not leave the GaN crystal until > 800 C, and its diffusivity is relatively high ({approximately} 10{sup {minus}11} cm{sup 2}/s) even at low temperatures (< 200 C) during injection by wet etching, boiling in water or plasma exposure. Oxygen shows a low donor activation efficiency when implanted into GaN, with an ionization level of 30--40 meV. It is essentially immobile up to 1,100 C. Carbon can produce low p-type levels (3 {times} 10{sup 17} cm{sup {minus}3}) in GaN during MOMBE, although there is some evidence it may also create n-type conduction in other nitrides.

  6. Nano-indentation of single-layer optical oxide thin films grown by electron-beam deposition

    SciTech Connect

    Mehrotra, K.; Oliver, J. B.; Lambropoulos, J. C.

    2015-01-01

    Mechanical characterization of optical oxide thin films is performed using nano-indentation, and the results are explained based on the deposition conditions used. These oxide films are generally deposited to have a porous microstructure that optimizes laser induced damage thresholds, but changes in deposition conditions lead to varying degrees of porosity, density, and possibly the microstructure of the thin film. This can directly explain the differences in the mechanical properties of the film studied here and those reported in literature. Of the four single-layer thin films tested, alumina was observed to demonstrate the highest values of nano-indentation hardness and elastic modulus. This is likely a result of the dense microstructure of the thin film arising from the particular deposition conditions used.

  7. AnGa{sub 2}O{sub 4} Thin-Film Phosphors Grown by Pulsed Laser Ablation

    SciTech Connect

    Lee, Y.E.; Rouleau, C.M.; Park, C.; Norton, D.P.

    1999-04-05

    The growth and properties of undoped and Mn-doped ZnGa{sub 2}O{sub 4} thin-film phosphors on (100) MgO and glass substrates using pulsed laser ablation were investigated. Blue-white and green emission were observed for as-deposited undoped and Mn-doped films, respectively. Luminescent properties as well as crystallinity were considerably affected by processing conditions and film stoichiometry. Films with enhanced luminescent characteristics were obtained on single crystal substrates without post-annealing.

  8. Enlarged Mn 3s splitting and room-temperature ferromagnetism in epitaxially grown oxygen doped Mn{sub 2}N{sub 0.86} films

    SciTech Connect

    Meng, M.; Wu, S. X. Ren, L. Z.; Zhou, W. Q.; Wang, Y. J.; Wang, G. L.; Li, S. W.

    2014-11-07

    Single-phase and oxygen doped Mn{sub 2}N{sub 0.86} thin films have been grown on MgO (111) by plasma-assisted molecular beam epitaxy. The films grow under tensile strain and, remarkably, they show ferromagnetic-like interactions at low temperature and ferromagnetic ordering agreed well with the Bloch-law T{sup 3/2} at room-temperature. We further demonstrate the enlarged Mn 3s splitting (6.46 eV) and its possible relation to the observed ferromagnetism. Our study not only provide a strategy for further theoretical work on oxygen doped manganese nitrides, but also shed promising light on utilizing its room-temperature FM property to fabricate spintronic devices.

  9. Microstructure of Co/X (X=Cu,Ag,Au) epitaxial thin films grown on Al{sub 2}O{sub 3}(0001) substrates

    SciTech Connect

    Ohtake, Mitsuru; Akita, Yuta; Futamoto, Masaaki; Kirino, Fumiyoshi

    2007-05-01

    Epitaxial thin films of Co/X (X=Cu,Ag,Au) were prepared on Al{sub 2}O{sub 3}(0001) substrates at substrate temperatures of 100 and 300 degree sign C by UHV molecular beam epitaxy. A complicated microstructure was realized for the epitaxial thin films. In-situ reflection high-energy electron diffraction observation has shown that X atoms of the buffer layer segregated to the surface during Co layer deposition, and it yielded a unique epitaxial granular structure. The structure consists of small Co grains buried in the X buffer layer, where both the magnetic small Co grains and the nonmagnetic X layer are epitaxially grown on the single crystal substrate. The structure varied depending on the X element and the substrate temperature. The crystal structure of Co grains is influenced by the buffer layer material and determined to be hcp and fcc structures for the buffer layer materials of Au and Cu, respectively.

  10. Element-specific study of epitaxial NiO/Ag/CoO/Fe films grown on vicinal Ag(001) using photoemission electron microscopy

    SciTech Connect

    Meng, Y.; Li, J.; Tan, A.; Jin, E.; Son, J.; Park, J. S.; Doran, A.; Young, A. T.; Scholl, A.; Arenholz, E.; Wu, J.; Hwang, C.; Zhao, H. W.; Qiu, Z. Q.

    2011-01-10

    NiO/Ag/CoO/Fe single crystalline films are grown epitaxially on a vicinal Ag(001) substrate using molecular beam epitaxy and investigated by photoemission electron microscopy. We find that after zero-field cooling, the in-plane Fe magnetization switches from parallel to perpendicular direction of the atomic steps of the vicinal surface at thinner CoO thickness but remains in its original direction parallel to the steps at thicker CoO thickness. CoO and NiO domain imaging result shows that both CoO/Fe and NiO/CoO spins are perpendicularly coupled, suggesting that the Fe magnetization switching may be associated with the rotatable-frozen spin transition of the CoO film.

  11. Microstructure of (110)-Oriented Epitaxial SrRuO3 Thin Films Grown on Off-Cut Single Crystal YSZ(100) Substrates

    SciTech Connect

    Zhu, Xinhua; Lee, Sung Kyun; Lee, Ho Nyung; Hesse, Dietrich

    2005-01-01

    The microstructure of (1 1 0){sup pc}-oriented epitaxial SrRuO{sub 3} (SRO) thin films grown by pulsed laser deposition on (1 0 0)YSZ (YSZ: yttria-stabilized zirconia) single crystal substrates with a miscut angle of 5{sup o} has been investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The films grow epitaxially with their pseudocubic (1 1 0) plane parallel to the (1 0 0) surface of the YSZ single crystal substrate, and with an in-plane orientation relationship of [{ovr 1} 1 1]{sub SRO}//[0 1 1]{sub YSZ}. Cross-sectional TEM investigations show that the films have a rough, facetted surface. Generally, four different azimuthal domains are present in (1 1 0)SRO films on (1 0 0)YSZ. Their number can be significantly reduced using annealed offcut YSZ substrates before SRO deposition, and this reduction effect is shown to be much stronger on [0 1 1]-miscut (1 0 0)YSZ than on [0 0 1]-miscut ones. Size and morphology of the azimuthal pseudocubic domains and their domain boundaries, as well as of anti-phase domains and their domain boundaries are studied by plan-view and cross-section TEM.

  12. Microstructure and magnetic properties of FeCo epitaxial thin films grown on MgO single-crystal substrates

    SciTech Connect

    Shikada, Kouhei; Ohtake, Mitsuru; Futamoto, Masaaki; Kirino, Fumiyoshi

    2009-04-01

    FeCo epitaxial films were prepared on MgO(100), MgO(110), and MgO(111) substrates by ultrahigh vacuum molecular beam epitaxy. FeCo thin films with (100), (211), and (110) planes parallel to the substrate surface grow on respective MgO substrates. FeCo/MgO interface structures are studied by high-resolution cross-sectional transmission electron microscopy and the epitaxial growth mechanism is discussed. Atomically sharp boundaries are recognized between the FeCo thin films and the MgO substrates where misfit dislocations are introduced in the FeCo thin films presumably to decrease the lattice misfits. Misfit dislocations are observed approximately every 9 and 1.4 nm in FeCo thin film at the FeCo/MgO(100) and the FeCo/MgO(110) interfaces, respectively. X-ray diffraction analysis indicates that the lattice spacing measured parallel to the single-crystal substrate surfaces are in agreement within 0.1% with those of the respective bulk values of Fe{sub 50}Co{sub 50} alloy crystal, showing that the FeCo film strain is very small. The magnetic anisotropies of these epitaxial films basically reflect the magnetocrystalline anisotropy of bulk FeCo alloy crystal.

  13. Effects of substrate temperature on properties of NbNx films grown on Nb by pulsed laser deposition

    SciTech Connect

    Ashraf Hassan Farha, Ali Oguz Er, Yüksel Ufuktepe, Ganapati Myneni, Hani E. Elsayed-Ali

    2011-12-01

    NbN{sub x} films were deposited on Nb substrate using pulsed laser deposition. The effects of substrate deposition temperature, from room temperature to 950 C, on the preferred orientation, phase, and surface properties of NbN{sub x} films were studied by X-ray diffraction, atomic force microscopy, and electron probe micro analyzer. We find that the substrate temperature is a critical factor in determining the phase of the NbN{sub x} films. For a substrate temperature up to 450 C the film showed poor crystalline quality. With temperature increase the film became textured and for a substrate temperature of 650-850 C, mix of cubic {delta}-NbN and hexagonal phases ({beta}-Nb{sub 2}N + {delta}'-NbN) were formed. Films with a mainly {beta}-Nb{sub 2}N hexagonal phase were obtained at deposition temperature above 850 C. The c/a ratio of {beta}-Nb{sub 2}N hexagonal shows an increase with increased nitrogen content. The surface roughness of the NbN{sub x} films increased as the temperature was raised from 450 to 850 C.

  14. Influence of dosing sequence and film thickness on structure and resistivity of Al-ZnO films grown by atomic layer deposition

    SciTech Connect

    Pollock, Evan B. Lad, Robert J.

    2014-07-01

    Aluminum-doped zinc oxide (AZO) films were deposited onto amorphous silica substrates using an atomic layer deposition process with diethyl zinc (DEZ), trimethyl aluminum (TMA), and deionized water at 200 °C. Three different Al doping sequences were used at a ZnO:Al ratio of 11:1 within the films. A minimum film resistivity of 1.6 × 10{sup −3} Ω cm was produced using sequential dosing of DEZ, TMA, DEZ, followed by H{sub 2}O for the Al doping step. This “ZAZW” sequence yielded an AZO film resistivity that is independent of film thickness, crystallographic texture, and grain size, as determined by high resolution x-ray diffraction (XRD). A pseudo-Voigt analysis method yields values for grain sizes that are smaller than those calculated using other XRD methods. Anisotropic grain sizes or variations in crystallographic texture have minimal influence on film resistivity, which suggests that factors other than film texture, such as intragrain scattering, may be important in influencing film resistivity.

  15. Potential variation around grain boundaries in BaSi{sub 2} films grown on multicrystalline silicon evaluated using Kelvin probe force microscopy

    SciTech Connect

    Baba, Masakazu; Tsukahara, Daichi; Toko, Kaoru; Hara, Kosuke O.; Usami, Noritaka; Sekiguchi, Takashi; Suemasu, Takashi

    2014-12-21

    Potential variations across the grain boundaries (GBs) in a 100?nm thick undoped n-BaSi{sub 2} film on a cast-grown multicrystalline Si (mc-Si) substrate are evaluated using Kelvin probe force microscopy (KFM). The ?-2? X-ray diffraction pattern reveals diffraction peaks, such as (201), (301), (410), and (411) of BaSi{sub 2}. Local-area electron backscatter diffraction reveals that the a-axis of BaSi{sub 2} is tilted slightly from the surface normal, depending on the local crystal plane of the mc-Si. KFM measurements show that the potentials are not significantly disordered in the grown BaSi{sub 2}, even around the GBs of mc-Si. The potentials are higher at GBs of BaSi{sub 2} around Si GBs that are formed by grains with a Si(111) face and those with faces that deviate slightly from Si(111). Thus, downward band bending occurs at these BaSi{sub 2} GBs. Minority carriers (holes) undergo a repelling force near the GBs, which may suppress recombination as in the case of undoped n-BaSi{sub 2} epitaxial films on a single crystal Si(111) substrate. The barrier height for hole transport across the GBs varies in the range from 10 to 55?meV. The potentials are also higher at the BaSi{sub 2} GBs grown around Si GBs composed of grains with Si(001) and Si(111) faces. The barrier height for hole transport ranges from 5 to 55?meV. These results indicate that BaSi{sub 2} GBs formed on (111)-dominant Si surfaces do not have a negative influence on the minority-carrier properties, and thus BaSi{sub 2} formed on underlayers, such as (111)-oriented Si or Ge and on (111)-oriented mc-Si, can be utilized as a solar cell active layer.

  16. Preparation and structure characterization of SmCo{sub 5}(0001) epitaxial thin films grown on Cu(111) underlayers

    SciTech Connect

    Ohtake, Mitsuru; Nukaga, Yuri; Futamoto, Masaaki; Kirino, Fumiyoshi

    2009-04-01

    SmCo{sub 5}(0001) epitaxial films were prepared on Cu(111) single-crystal underlayers formed on Al{sub 2}O{sub 3}(0001) substrates at 500 deg. C. The nucleation and growth mechanism of (0001)-oriented SmCo{sub 5} crystal on Cu(111) underlayer is investigated and a method to control the nucleation is proposed. The SmCo{sub 5} epitaxial thin film formed directly on Cu underlayer consists of two types of domains whose orientations are rotated around the film normal by 30 deg. each other. By introducing a thin Co seed layer on the Cu underlayer, a SmCo{sub 5}(0001) single-crystal thin film is successfully obtained. Nucleation of SmCo{sub 5} crystal on Cu underlayer seems controllable by varying the interaction between the Cu underlayer and the SmCo{sub 5} layer.

  17. Effect of Ag addition to L1{sub 0} FePt and L1{sub 0} FePd films grown by molecular beam epitaxy

    SciTech Connect

    Tokuoka, Y.; Seto, Y.; Kato, T.; Iwata, S.

    2014-05-07

    L1{sub 0} ordered FePt-Ag (5?nm) and FePd-Ag (5?nm) films were grown on MgO (001) substrate at temperatures of 250400?C by using molecular beam epitaxy method, and their crystal and surface structures, perpendicular magnetic anisotropies and Curie temperatures were investigated. In the case of FePt-Ag, Ag addition with the amount of 1020 at.?% was effective to promote L1{sub 0} ordering and granular growth, resulting in the increase of the perpendicular magnetic anisotropy and coercivity of the FePt-Ag films. On the other hand, in the case of FePd-Ag, Ag addition changed the surface morphology from island to continuous film associated with the reductions of its coercivity and perpendicular anisotropy. The variations of lattice constants and Curie temperature with Ag addition were significantly different between FePt-Ag and FePd-Ag. For FePd-Ag, the c and a axes lattice spacings and Curie temperature gradually changed with increasing Ag content, while they unchanged for FePt-Ag. These results suggest the possibility of the formation of FePdAg alloy in FePd-Ag, while Ag segregation in FePt-Ag.

  18. Enhanced off-resonance magnetoelectric response in laser annealed PZT thick film grown on magnetostrictive amorphous metal substrate

    SciTech Connect

    Palneedi, Haribabu; Maurya, Deepam; Priya, Shashank; Kim, Gi-Yeop; Choi, Si-Young; Kang, Suk-Joong L.; Kim, Kwang-Ho; Ryu, Jungho

    2015-07-06

    A highly dense, 4 μm-thick Pb(Zr,Ti)O{sub 3} (PZT) film is deposited on amorphous magnetostrictive Metglas foil (FeBSi) by granule spray in vacuum process at room temperature, followed by its localized annealing with a continuous-wave 560 nm ytterbium fiber laser radiation. This longer-wavelength laser radiation is able to anneal the whole of thick PZT film layer without any deteriorative effects, such as chemical reaction and/or atomic diffusion, at the interface and crystallization of amorphous Metglas substrate. Greatly enhanced dielectric and ferroelectric properties of the annealed PZT are attributed to its better crystallinity and grain growth induced by laser irradiation. As a result, a colossal off-resonance magnetoelectric (ME) voltage coefficient that is two orders of magnitude larger than previously reported output from PZT/Metglas film-composites is achieved. The present work addresses the problems involved in the fabrication of PZT/Metglas film-composites and opens up emerging possibilities in employing piezoelectric materials with low thermal budget substrates (suitable for integrated electronics) and designing laminate composites for ME based devices.

  19. Structural controlled magnetic anisotropy in Heusler L1{sub 0}-MnGa epitaxial thin films

    SciTech Connect

    Wang Kangkang; Lu Erdong; Smith, Arthur R.; Knepper, Jacob W.; Yang Fengyuan

    2011-04-18

    Ferromagnetic L1{sub 0}-MnGa thin films have been epitaxially grown on GaN, sapphire, and MgO substrates using molecular beam epitaxy. Using diffraction techniques, the epitaxial relationships are determined. It is found that the crystalline orientation of the films differ due to the influence of the substrate. By comparing the magnetic anisotropy to the structural properties, a clear correlation could be established indicating that the in-plane and out-of-plane anisotropy is directly determined by the crystal orientation of the film and could be controlled via selection of the substrates. This result could be helpful in tailoring magnetic anisotropy in thin films for spintronic applications.

  20. Atomic layer deposition grown MO{sub x} thin films for solar water splitting: Prospects and challenges

    SciTech Connect

    Singh, Trilok; Lehnen, Thomas; Leuning, Tessa; Mathur, Sanjay

    2015-01-15

    The magnitude of energy challenge not only calls for efficient devices but also for abundant, inexpensive, and stable photoactive materials that can enable efficient light harvesting, charge separation and collection, as well as chemical transformations. Photoelectrochemical systems based on semiconductor materials have the possibility to transform solar energy directly into chemical energy the so-called “solar hydrogen.” The current challenge lies in the harvesting of a larger fraction of electromagnetic spectrum by enhancing the absorbance of electrode materials. In this context, atomically precise thin films of metal oxide semiconductors and their multilayered junctions are promising candidates to integrate high surface areas with well-defined electrode–substrate interface. Given its self-limited growth mechanism, the atomic layer deposition (ALD) technique offers a wide range of capabilities to deposit and modify materials at the nanoscale. In addition, it opens new frontiers for developing precursor chemistry that is inevitable to design new processes. Herein, the authors review the properties and potential of metal oxide thin films deposited by ALD for their application in photoelectrochemical water splitting application. The first part of the review covers the basics of ALD processes followed by a brief discussion on the electrochemistry of water splitting reaction. The second part focuses on different MO{sub x} films deposited by atomic layer deposition for water splitting applications; in this section, The authors discuss the most explored MO{sub x} semiconductors, namely, Fe{sub 2}O{sub 3}, TiO{sub 2}, WO{sub 3}, and ZnO, as active materials and refer to their application as protective coatings, conductive scaffolds, or in heterojunctions. The third part deals with the current challenges and future prospects of ALD processed MO{sub x} thin films for water splitting reactions.

  1. X-ray magnetic circular dichroism for Co{sub x}Fe{sub 4?x}N (x?=?0, 3, 4) films grown by molecular beam epitaxy

    SciTech Connect

    Ito, Keita; Sanai, Tatsunori; Yasutomi, Yoko; Toko, Kaoru; Suemasu, Takashi; Zhu, Siyuan; Kimura, Akio; Takeda, Yukiharu; Saitoh, Yuji

    2014-05-07

    We evaluated orbital (m{sub orb}) and spin magnetic moments (m{sub spin}) of Co{sub x}Fe{sub 4?x}N (x?=?0, 3, 4) epitaxial thin films grown by molecular beam epitaxy using x-ray magnetic circular dichroism, and discussed the dependence of these values on x. Site-averaged m{sub spin} value of Fe atoms was deduced to be 1.91??{sub B} per atom, and that of Co atoms to be 1.47??{sub B} per atom in Co{sub 3}FeN at 300?K. These values are close to 1.87??{sub B} per Fe atom in Fe{sub 4}N and 1.43??{sub B} per Co atom in Co{sub 4}N, respectively. This result implies that the Fe and Co atoms in the Co{sub 3}FeN films were located both at corner and face-centered sites in the anti-perovskite lattice. Spin magnetic moments per unit cell were decreased linearly with increasing x in Co{sub x}Fe{sub 4?x}N. This tendency is in good agreement with theory predicted by the first-principle calculation.

  2. Precise calibration of Mg concentration in Mg{sub x}Zn{sub 1-x}O thin films grown on ZnO substrates

    SciTech Connect

    Kozuka, Y.; Falson, J.; Tsukazaki, A.; Segawa, Y.; Makino, T.; Kawasaki, M.

    2012-08-15

    The growth techniques for Mg{sub x}Zn{sub 1-x}O thin films have advanced at a rapid pace in recent years, enabling the application of this material to a wide range of optical and electrical applications. In designing structures and optimizing device performances, it is crucial that the Mg content of the alloy be controllable and precisely determined. In this study, we have established laboratory-based methods to determine the Mg content of Mg{sub x}Zn{sub 1-x}O thin films grown on ZnO substrates, ranging from the solubility limit of x {approx} 0.4 to the dilute limit of x < 0.01. For the absolute determination of Mg content, Rutherford backscattering spectroscopy is used for the high Mg region above x = 0.14, while secondary ion mass spectroscopy is employed to quantify low Mg content. As a lab-based method to determine the Mg content, c-axis length is measured by x-ray diffraction and is well associated with Mg content. The interpolation enables the determination of Mg content to x = 0.023, where the peak from the ZnO substrate overlaps the Mg{sub x}Zn{sub 1-x}O peak in standard laboratory equipment, and thus limits quantitative determination. At dilute Mg contents below x = 0.023, the localized exciton peak energy of the Mg{sub x}Zn{sub 1-x}O films as measured by photoluminescence is found to show a linear Mg content dependence, which is well resolved from the free exciton peak of ZnO substrate down to x = 0.0043. Our results demonstrate that x-ray diffraction and photoluminescence in combination are appropriate methods to determine Mg content in a wide Mg range from x = 0.004 to 0.40 in a laboratory environment.

  3. Appearance of large crystalline domains in VO{sub 2} films grown on sapphire (001) and their phase transition characteristics

    SciTech Connect

    Azhan, Nurul Hanis; Su, Kui; Okimura, Kunio; Zaghrioui, Mustapha; Sakai, Joe

    2015-06-28

    We report the first observation of large crystalline domains of several μm-size in VO{sub 2} films deposited on Al{sub 2}O{sub 3} (001) substrates by rf-biased reactive sputtering technique. The large crystalline domains, dominated with random in-plane oriented growth of (011){sub M1}-orientation, appear only under adequate substrate biasing, such as 10 W, while most biasing conditions result in conventional nanosized grains of highly oriented (010){sub M1}-orientation. Two temperature-controlled analyses, x-ray diffraction and micro-Raman spectroscopy, have revealed that some parts of large crystalline domains undergo intermediate monoclinic (M2) phase during the thermally-induced structural phase transition from monoclinic (M1) to rutile-tetragonal (R) phase. As an effect of the appearance of large crystalline domains, the film showed in-plane tensile stress, resulting in high T{sub IMT} of 69 °C due to the elongation of the V-V distance in its low-temperature monoclinic phase.

  4. The effects of oxygen pressure on disordering and magneto-transport properties of Ba{sub 2}FeMoO{sub 6} thin films grown via pulsed laser deposition

    SciTech Connect

    Kim, Kyeong-Won; Mhin, Sungwook; Jones, Jacob L.; Norton, David P.; Ghosh, Siddhartha Buvaev, Sanal; Hebard, Arthur F.

    2015-07-21

    Epitaxial Ba{sub 2}FeMoO{sub 6} thin films were grown via pulsed laser deposition under low oxygen pressure and their structural, chemical, and magnetic properties were examined, focusing on the effects of oxygen pressure. The chemical disorder, off-stoichiometry in B site cations (Fe and Mo) increased with increasing oxygen pressure and thus magnetic properties were degraded. Interestingly, in contrast, negative magneto-resistance, which is the characteristics of this double perovskite material, was enhanced with increasing oxygen pressure. It is believed that phase segregation of highly disordered thin films is responsible for the increased magneto-resistance of thin films grown at high oxygen pressure. The anomalous Hall effect, which behaves hole-like, was also observed due to spin-polarized itinerant electrons under low magnetic field below 1 T and the ordinary electron-like Hall effect was dominant at higher magnetic fields.

  5. Dislocation core structures in Si-doped GaN

    SciTech Connect

    Rhode, S. L. Fu, W. Y.; Sahonta, S.-L.; Kappers, M. J.; Humphreys, C. J.; Horton, M. K.; Pennycook, T. J.; Dusane, R. O.; Moram, M. A.

    2015-12-14

    Aberration-corrected scanning transmission electron microscopy was used to investigate the core structures of threading dislocations in plan-view geometry of GaN films with a range of Si-doping levels and dislocation densities ranging between (5 ± 1) × 10{sup 8} and (10 ± 1) × 10{sup 9} cm{sup −2}. All a-type (edge) dislocation core structures in all samples formed 5/7-atom ring core structures, whereas all (a + c)-type (mixed) dislocations formed either double 5/6-atom, dissociated 7/4/8/4/9-atom, or dissociated 7/4/8/4/8/4/9-atom core structures. This shows that Si-doping does not affect threading dislocation core structures in GaN. However, electron beam damage at 300 keV produces 4-atom ring structures for (a + c)-type cores in Si-doped GaN.

  6. Solution-grown small-molecule organic semiconductor with enhanced crystal alignment and areal coverage for organic thin film transistors

    DOE PAGES [OSTI]

    Bi, Sheng; He, Zhengran; Chen, Jihua; Li, Dawen

    2015-07-24

    Drop casting of small-molecule organic semiconductors typically forms crystals with random orientation and poor areal coverage, which leads to significant performance variations of organic thin-film transistors (OTFTs). In this study, we utilize the controlled evaporative self-assembly (CESA) method combined with binary solvent system to control the crystal growth. A small-molecule organic semiconductor,2,5-Di-(2-ethylhexyl)-3,6-bis(5"-n-hexyl-2,2',5',2"]terthiophen-5-yl)-pyrrolo[3,4-c]pyrrole-1,4-dione (SMDPPEH), is used as an example to demonstrate the effectiveness of our approach. By optimizing the double solvent ratios, well-aligned SMDPPEH crystals with significantly improved areal coverage were achieved. As a result, the SMDPPEH based OTFTs exhibit a mobility of 1.6 × 10-2 cm2/V s, which is themore » highest mobility from SMDPPEH ever reported.« less

  7. Solution-grown small-molecule organic semiconductor with enhanced crystal alignment and areal coverage for organic thin film transistors

    SciTech Connect

    Bi, Sheng; He, Zhengran; Chen, Jihua; Li, Dawen

    2015-07-24

    Drop casting of small-molecule organic semiconductors typically forms crystals with random orientation and poor areal coverage, which leads to significant performance variations of organic thin-film transistors (OTFTs). In this study, we utilize the controlled evaporative self-assembly (CESA) method combined with binary solvent system to control the crystal growth. A small-molecule organic semiconductor,2,5-Di-(2-ethylhexyl)-3,6-bis(5"-n-hexyl-2,2',5',2"]terthiophen-5-yl)-pyrrolo[3,4-c]pyrrole-1,4-dione (SMDPPEH), is used as an example to demonstrate the effectiveness of our approach. By optimizing the double solvent ratios, well-aligned SMDPPEH crystals with significantly improved areal coverage were achieved. As a result, the SMDPPEH based OTFTs exhibit a mobility of 1.6 × 10-2 cm2/V s, which is the highest mobility from SMDPPEH ever reported.

  8. Epitaxial single-crystal thin films of MnxTi1-xO2-? grown on (rutile)TiO2 substrates with pulsed laser deposition: Experiment and theory

    SciTech Connect

    Ilton, Eugene S.; Droubay, Timothy C.; Chaka, Anne M.; Kovarik, Libor; Varga, Tamas; Arey, Bruce W.; Kerisit, Sebastien N.

    2015-02-01

    Epitaxial rutile-structured single-crystal MnxTi1-xO2-? films were synthesized on rutile- (110) and -(001) substrates using pulsed laser deposition. The films were characterized by reflection high-energy electron diffraction (RHEED), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and aberration-corrected transmission electron microscopy (ACTEM). Under the present conditions, 400oC and PO2 = 20 mTorr, single crystal epitaxial thin films were grown for x = 0.13, where x is the nominal average mole fraction of Mn. In fact, arbitrarily thick films could be grown with near invariant Mn/Ti concentration profiles from the substrate/film interface to the film surface. In contrast, at x = 0.25, Mn became enriched towards the surface and a secondary nano-scale phase formed which appeared to maintain the basic rutile structure but with enhanced z-contrast in the tunnels, or tetrahedral interstitial sites. Ab initio thermodynamic calculations provided quantitative estimates for the destabilizing effect of expanding the ?-MnO2 lattice parameters to those of TiO2-rutile, the stabilizing effect of diluting Mn with increasing Ti concentration, and competing reaction pathways.

  9. Development of an IR-transparent, inverted-grown, thin-film, Al[sub 0. 34]Ga[sub 0. 66]As/GaAs cascade solar cell

    SciTech Connect

    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.

  10. Localized tip enhanced Raman spectroscopic study of impurity incorporated single GaN nanowire in the sub-diffraction limit

    SciTech Connect

    Patsha, Avinash E-mail: dhara@igcar.gov.in; Dhara, Sandip; Tyagi, A. K.

    2015-09-21

    The localized effect of impurities in single GaN nanowires in the sub-diffraction limit is reported using the study of lattice vibrational modes in the evanescent field of Au nanoparticle assisted tip enhanced Raman spectroscopy (TERS). GaN nanowires with the O impurity and the Mg dopants were grown by the chemical vapor deposition technique in the catalyst assisted vapor-liquid-solid process. Symmetry allowed Raman modes of wurtzite GaN are observed for undoped and doped nanowires. Unusually very strong intensity of the non-zone center zone boundary mode is observed for the TERS studies of both the undoped and the Mg doped GaN single nanowires. Surface optical mode of A{sub 1} symmetry is also observed for both the undoped and the Mg doped GaN samples. A strong coupling of longitudinal optical (LO) phonons with free electrons, however, is reported only in the O rich single nanowires with the asymmetric A{sub 1}(LO) mode. Study of the local vibration mode shows the presence of Mg as dopant in the single GaN nanowires.

  11. Effects of N{sub 2}O gas addition on the properties of ZnO films grown by catalytic reaction-assisted chemical vapor deposition

    SciTech Connect

    Yasui, Kanji Morioka, Makoto; Kanauchi, Shingo; Ohashi, Yuki; Kato, Takahiro; Tamayama, Yasuhiro

    2015-11-15

    The influence of N{sub 2}O gas addition on the properties of zinc oxide (ZnO) films grown on a-plane (11–20) sapphire (a-Al{sub 2}O{sub 3}) substrates was investigated, using a chemical vapor deposition method based on the reaction between dimethylzinc and high-temperature H{sub 2}O produced by a catalytic H{sub 2}-O{sub 2} reaction on platinum (Pt) nanoparticles. The addition of N{sub 2}O was found to increase the size of the crystalline facets and to improve the crystal orientation along the c-axis. The electron mobility at 290 K was also increased to 234 cm{sup 2}/Vs following the addition of N{sub 2}O gas at a pressure of 3.2 × 10{sup −3 }Pa. In addition, the minimum full width at half maximum of the most intense photoluminescence peak derived from neutral donor bound excitons at 10 K decreased to 0.6 meV by the addition of N{sub 2}O gas at a pressure of 3.1 × 10{sup −2 }Pa.

  12. Converse magnetoelectric coupling in NiFe/Pb(Mg{sub 1/3}Nb{sub 2/3})O{sub 3}PbTiO{sub 3} nanocomposite thin films grown on Si substrates

    SciTech Connect

    Feng, Ming; Key Laboratory of Functional Materials Physics and Chemistry of the Ministry of Education, Jilin Normal University, Siping 136000 ; Hu, Jiamian; Wang, Jianjun; Li, Zheng; Shu, Li; Nan, C. W.

    2013-11-04

    Multiferroic NiFe (?30 nm)/Pb(Mg{sub 1/3}Nb{sub 2/3})O{sub 3}PbTiO{sub 3}(PMNPT, ?220 nm) bilayered thin films were grown on common Pt/Ti/SiO{sub 2}/Si substrates by a combination of off-axis magnetron sputtering and sol-gel spin-coating technique. By using AC-mode magneto-optical Kerr effect technique, the change in the Kerr signal (magnetization) of the NiFe upon applying a low-frequency AC voltage to the PMNPT film was in situ acquired at zero magnetic field. The obtained Kerr signal versus voltage loop essentially tracks the electromechanical strain curve of the PMNPT thin film, clearly demonstrating a strain-mediated converse magnetoelectric coupling, i.e., voltage-modulated magnetization, in the NiFe/PMNPT nanocomposite thin films.

  13. Ultra High p-doping Material Research for GaN Based Light Emitters

    SciTech Connect

    Vladimir Dmitriev

    2007-06-30

    The main goal of the Project is to investigate doping mechanisms in p-type GaN and AlGaN and controllably fabricate ultra high doped p-GaN materials and epitaxial structures. Highly doped p-type GaN-based materials with low electrical resistivity and abrupt doping profiles are of great importance for efficient light emitters for solid state lighting (SSL) applications. Cost-effective hydride vapor phase epitaxial (HVPE) technology was proposed to investigate and develop p-GaN materials for SSL. High p-type doping is required to improve (i) carrier injection efficiency in light emitting p-n junctions that will result in increasing of light emitting efficiency, (ii) current spreading in light emitting structures that will improve external quantum efficiency, and (iii) parameters of Ohmic contacts to reduce operating voltage and tolerate higher forward currents needed for the high output power operation of light emitters. Highly doped p-type GaN layers and AlGaN/GaN heterostructures with low electrical resistivity will lead to novel device and contact metallization designs for high-power high efficiency GaN-based light emitters. Overall, highly doped p-GaN is a key element to develop light emitting devices for the DOE SSL program. The project was focused on material research for highly doped p-type GaN materials and device structures for applications in high performance light emitters for general illumination P-GaN and p-AlGaN layers and multi-layer structures were grown by HVPE and investigated in terms of surface morphology and structure, doping concentrations and profiles, optical, electrical, and structural properties. Tasks of the project were successfully accomplished. Highly doped GaN materials with p-type conductivity were fabricated. As-grown GaN layers had concentration N{sub a}-N{sub d} as high as 3 x 10{sup 19} cm{sup -3}. Mechanisms of doping were investigated and results of material studies were reported at several International conferences providing

  14. ARM - AMIE Gan Island - Data Plots

    U.S. Department of Energy (DOE) - all webpages (Extended Search)

    Gan Related Links amie.png 34h AMIE Home cindy.png 50h CINDY2011 dynamo.png 34h DYNAMO ARM Data Discovery Browse Data Outreach News & Press Blog Backgrounder (PDF, 1.2MB) Education Flyer (PDF, 2.0MB) Images ARM flickr site Official AMIE Logo AMIE Gear Experiment Planning Steering Committee AMIE-MANUS Proposal Abstract AMIE-GAN Proposal Abstract Meetings Cloud Life Cycle Working Group Deployment Operations Science Plan - TWP Manus Site (PDF, 2.1 MB) Science Plan - Gan Island Site (PDF, 2.0

  15. Tellurium n-type doping of highly mismatched amorphous GaN1-xAsx alloys in plasma-assisted molecular beam epitaxy

    DOE PAGES [OSTI]

    Novikov, S. V.; Ting, M.; Yu, K. M.; Sarney, W. L.; Martin, R. W.; Svensson, S. P.; Walukiewicz, W.; Foxon, C. T.

    2014-10-01

    In this paper we report our study on n-type Te doping of amorphous GaN1-xAsx layers grown by plasma-assisted molecular beam epitaxy. We have used a low temperature PbTe source as a source of tellurium. Reproducible and uniform tellurium incorporation in amorphous GaN1-xAsx layers has been successfully achieved with a maximum Te concentration of 9×10²⁰ cm⁻³. Tellurium incorporation resulted in n-doping of GaN1-xAsx layers with Hall carrier concentrations up to 3×10¹⁹ cm⁻³ and mobilities of ~1 cm²/V s. The optimal growth temperature window for efficient Te doping of the amorphous GaN1-xAsx layers has been determined.

  16. Tunnel-injection GaN quantum dot ultraviolet light-emitting diodes

    SciTech Connect

    Verma, Jai; Kandaswamy, Prem Kumar; Protasenko, Vladimir; Verma, Amit; Grace Xing, Huili; Jena, Debdeep

    2013-01-28

    We demonstrate a GaN quantum dot ultraviolet light-emitting diode that uses tunnel injection of carriers through AlN barriers into the active region. The quantum dot heterostructure is grown by molecular beam epitaxy on AlN templates. The large lattice mismatch between GaN and AlN favors the formation of GaN quantum dots in the Stranski-Krastanov growth mode. Carrier injection by tunneling can mitigate losses incurred in hot-carrier injection in light emitting heterostructures. To achieve tunnel injection, relatively low composition AlGaN is used for n- and p-type layers to simultaneously take advantage of effective band alignment and efficient doping. The small height of the quantum dots results in short-wavelength emission and are simultaneously an effective tool to fight the reduction of oscillator strength from quantum-confined Stark effect due to polarization fields. The strong quantum confinement results in room-temperature electroluminescence peaks at 261 and 340 nm, well above the 365 nm bandgap of bulk GaN. The demonstration opens the doorway to exploit many varied features of quantum dot physics to realize high-efficiency short-wavelength light sources.

  17. Isotope analysis of diamond-surface passivation effect of high-temperature H{sub 2}O-grown atomic layer deposition-Al{sub 2}O{sub 3} films

    SciTech Connect

    Hiraiwa, Atsushi E-mail: qs4a-hriw@asahi-net.or.jp; Saito, Tatsuya; Matsumura, Daisuke; Kawarada, Hiroshi

    2015-06-07

    The Al{sub 2}O{sub 3} film formed using an atomic layer deposition (ALD) method with trimethylaluminum as Al precursor and H{sub 2}O as oxidant at a high temperature (450?C) effectively passivates the p-type surface conduction (SC) layer specific to a hydrogen-terminated diamond surface, leading to a successful operation of diamond SC field-effect transistors at 400?C. In order to investigate this excellent passivation effect, we carried out an isotope analysis using D{sub 2}O instead of H{sub 2}O in the ALD and found that the Al{sub 2}O{sub 3} film formed at a conventional temperature (100?C) incorporates 50 times more CH{sub 3} groups than the high-temperature film. This CH{sub 3} is supposed to dissociate from the film when heated afterwards at a higher temperature (550?C) and causes peeling patterns on the H-terminated surface. The high-temperature film is free from this problem and has the largest mass density and dielectric constant among those investigated in this study. The isotope analysis also unveiled a relatively active H-exchange reaction between the diamond H-termination and H{sub 2}O oxidant during the high-temperature ALD, the SC still being kept intact. This dynamic and yet steady H termination is realized by the suppressed oxidation due to the endothermic reaction with H{sub 2}O. Additionally, we not only observed the kinetic isotope effect in the form of reduced growth rate of D{sub 2}O-oxidant ALD but found that the mass density and dielectric constant of D{sub 2}O-grown Al{sub 2}O{sub 3} films are smaller than those of H{sub 2}O-grown films. This is a new type of isotope effect, which is not caused by the presence of isotopes in the films unlike the traditional isotope effects that originate from the presence of isotopes itself. Hence, the high-temperature ALD is very effective in forming Al{sub 2}O{sub 3} films as a passivation and/or gate-insulation layer of high-temperature-operation diamond SC devices, and the knowledge of the

  18. Structure and electronic properties of mixed (a + c) dislocation cores in GaN

    SciTech Connect

    Horton, M. K.; Rhode, S. L.; Moram, M. A.

    2014-08-14

    Classical atomistic models and atomic-resolution scanning transmission electron microscopy studies of GaN films reveal that mixed (a + c)-type dislocations have multiple different core structures, including a dissociated structure consisting of a planar fault on one of the (12{sup ¯}10) planes terminated by two different partial dislocations. Density functional theory calculations show that all cores introduce localized states into the band gap, which affects device performance.

  19. Analysis of the carbon-related 'blue' luminescence in GaN

    SciTech Connect

    Armitage, R.; Yang, Q.; Weber, E.R.

    2004-09-24

    The properties of a broad 2.86 eV photoluminescence band in carbon-doped GaN were studied as a function of C-doping level, temperature, and excitation density. The results are consistent with a C{sub Ga}-C{sub N} deep donor-deep acceptor recombination mechanism as proposed by Seager et al. For GaN:C grown by molecular-beam epitaxy (MBE) the 2.86 eV band is observed in Si co-doped layers exhibiting high n-type conductivity as well as in semi-insulating material. For low excitation density (4 W/cm{sup 2}) the 2.86 eV band intensity decreases as a function of cw-laser exposure time over a period of many minutes. The transient behavior is consistent with a model based on carrier diffusion and charge trapping-induced Coulomb barriers. The temperature dependence of the blue luminescence below 150 K was different for carbon-contaminated GaN grown by metalorganic vapor phase epitaxy (MOVPE) compared to C-doped MBE GaN.

  20. Order parameters and magnetocrystalline anisotropy of off-stoichiometric D0{sub 22} Mn{sub 2.36}Ga epitaxial films grown on MgO (001) and SrTiO{sub 3} (001)

    SciTech Connect

    Lee, Hwachol; Sukegawa, Hiroaki Mitani, Seiji; Hono, Kazuhiro

    2015-07-21

    We study the relationship between long range order parameters and the magnetocrystalline anisotropy of off-stoichiometric D0{sub 22} Mn{sub 2.36}Ga (MnGa) epitaxial films grown on MgO (001) and SrTiO{sub 3} (STO) (001) single crystalline substrates. MnGa films deposited on MgO (001) show rather large irregular variation in magnetization with increasing substrate temperature in spite of the improved long range order of total atomic sites. The specific site long range order of Mn-I site characterized in the [101] orientation revealed the fluctuation of the occupation fraction of two Mn atomic sites with elevated substrate temperature, which appears more relevant to the observed magnetization change than the long range order of the total atomic sites. In case of MnGa films grown on the lattice-matched STO (001), high long range order of the total atomic sites in spite of the existence of secondary phase represents that the lattice mismatch plays a crucial role in determining the atomic arrangement of Mn and Ga atoms in the off-stoichiometric compositional case of MnGa.

  1. Mechanisms of the micro-crack generation in an ultra-thin AlN/GaN superlattice structure grown on Si(110) substrates by metalorganic chemical vapor deposition

    SciTech Connect

    Shen, X. Q. Takahashi, T.; Ide, T.; Shimizu, M.

    2015-09-28

    We investigate the generation mechanisms of micro-cracks (MCs) in an ultra-thin AlN/GaN superlattice (SL) structure grown on Si(110) substrates by metalorganic chemical vapor deposition. The SL is intended to be used as an interlayer (IL) for relaxing tensile stress and obtaining high-quality crack-free GaN grown on Si substrates. It is found that the MCs can be generated by two different mechanisms, where large mismatches of the lattice constant (LC) and the coefficient of thermal expansion (CTE) play key roles in the issue. Different MC configurations (low-density and high-density MCs) are observed, which are considered to be formed during the different growth stages (SL growth and cooling down processes) due to the LC and the CTE effects. In-situ and ex-situ experimental results support the mechanism interpretations of the MCs generation. The mechanism understanding makes it possible to optimize the SL IL structure for growing high-quality crack-free GaN films on Si substrates for optical and electronic device applications.

  2. Structural and dielectric properties of Ba{sub 0.7}Sr{sub 0.3}TiO{sub 3} thin films grown by PLD

    SciTech Connect

    James, K. K.; Satish, B.; Jayaraj, M. K.

    2014-01-28

    Ferroelectric thin films of Ba{sub 0.7}Sr{sub 0.3}TiO{sub 3} (BST) were deposited on Si/SiO{sub 2}/TiO{sub 2}/Pt (PtSi) substrate by pulsed laser deposition (PLD). Crystalline films with perovskite structure were obtained without post-deposition annealing. Phase purity of the deposited films was confirmed by x-ray diffraction. The lowest value of FWHM obtained for the film deposited at oxygen pressure 5.410{sup ?4} mbar and substrate temperature 600C, indicates the high crystallinity of the film. The room temperature dielectric constant at 100 kHz was 85. Butterfly loop, which is the characteristic of ferroelectric materials, was obtained in the regime of ?4 to +4V. The leakage current density was nearly 910{sup ?13} Acm{sup ?2}.

  3. Perpendicularly magnetized (001)-textured D0{sub 22} MnGa films grown on an (Mg{sub 0.2}Ti{sub 0.8})O buffer with thermally oxidized Si substrates

    SciTech Connect

    Lee, Hwachol; Sukegawa, Hiroaki; Liu, Jun; Mitani, Seiji; Hono, Kazuhiro

    2015-10-28

    We report the growth of (001)-textured polycrystalline D0{sub 22} MnGa films with perpendicular magnetic anisotropy (PMA) on thermally oxidized Si substrates using an (Mg{sub 0.2}Ti{sub 0.8})O (MTO) buffer layer. The ordered D0{sub 22} MnGa film grown at the optimum substrate temperature of 530 °C on the MTO buffer layer shows PMA with magnetization of 80 kA/m, PMA energy density of 0.28 MJ/m{sup 3}, and coercivity of 2.3 T. The scanning transmission electron microscope analysis confirms the formation of a highly (001)-textured structure and the elementally sharp interfaces between the MTO layer and the MnGa layer. The achieved D0{sub 22} MnGa PMA films on an amorphous substrate will provide the possible pathway of integration of a Mn-based PMA film into Si-based substrates.

  4. Strain-dependence Of The Structure And Ferroic Properties Of Epitaxial Ni-1 (-) Ti-x(1) (-) O-y(3) Thin Films Grown On Sapphire Substrates

    SciTech Connect

    Varga, Tamas; Droubay, Timothy C.; Bowden, Mark E.; Stephens, Sean A.; Manandhar, Sandeep; Shutthanandan, V.; Colby, Robert J.; Hu, Dehong; Shelton, William A.; Chambers, Scott A.

    2015-03-01

    Polarization-induced weak ferromagnetism has been predicted a few years back in perovskite MTiO3 (M = Fe, Mn, Ni) [Fennie, Phys. Rev. Lett. 100, 167203 (2008)]. We set out to stabilize this metastable perovskite structure by growing NiTiO3 epitaxially on sapphire Al2O3 (001) substrate, and to control the polar and magnetic properties via strain. Epitaxial Ni1-xTi1-yO3 films of different Ni/Ti ratios and thicknesses were deposited on Al2O3 substrates by pulsed laser deposition at different temperatures, and characterized using several techniques. The effect of film thickness, deposition temperature, and film stoichiometry on lattice strain, film structure, and physical properties was investigated. Our structural data from x-ray diffraction, electron microscopy, and x-ray absorption spectroscopy shows that substrate-induced strain has a marked effect on the structure and crystalline quality of the films. Physical property measurements reveal a dependence of the Nel transition and lattice polarization on strain, and highlight our ability to control the ferroic properties in NiTiO3 thin films by film stoichiometry and thickness.

  5. ARM - News from the Gan Island Deployment

    U.S. Department of Energy (DOE) - all webpages (Extended Search)

    News from the Gan Island Deployment Related Links amie.png 34h AMIE Home cindy.png 50h CINDY2011 dynamo.png 34h DYNAMO ARM Data Discovery Browse Data Outreach News & Press Blog Backgrounder (PDF, 1.2MB) Education Flyer (PDF, 2.0MB) Images ARM flickr site Official AMIE Logo AMIE Gear Experiment Planning Steering Committee AMIE-MANUS Proposal Abstract AMIE-GAN Proposal Abstract Meetings Cloud Life Cycle Working Group Deployment Operations Science Plan - TWP Manus Site (PDF, 2.1 MB) Science

  6. Direct spontaneous growth and interfacial structural properties of inclined GaN nanopillars on r-plane sapphire

    SciTech Connect

    Adikimenakis, A.; Aretouli, K. E.; Tsagaraki, K.; Androulidaki, M.; Georgakilas, A.; Lotsari, A.; Dimitrakopulos, G. P. Kehagias, Th.; Komninou, Ph.

    2015-06-28

    The spontaneous growth of GaN nanopillars (NPs) by direct plasma-assisted molecular beam epitaxy on nitridated r-plane sapphire substrates has been studied. The emanation of metal-polarity NPs from inside an a-plane nonpolar GaN film was found to depend on both the substrate nitridation and the growth conditions. The density of NPs increased with increasing the duration of the nitridation process and the power applied on the radio-frequency plasma source, as well as the III/V flux ratio, while variation of the first two parameters enhanced the roughness of the substrate's surface. Transmission electron microscopy (TEM) techniques were employed to reveal the structural characteristics of the NPs and their nucleation mechanism from steps on the sapphire surface and/or interfacial semipolar GaN nanocrystals. Lattice strain measurements showed a possible Al enrichment of the first 5–6 monolayers of the NPs. By combining cross-sectional and plan-view TEM observations, the three-dimensional model of the NPs was constructed. The orientation relationship and interfacial accommodation between the NPs and the nonpolar a-plane GaN film were also elucidated. The NPs exhibited strong and narrow excitonic emission, suggesting an excellent structural quality.

  7. Nanostructured light-absorbing crystalline CuIn{sub (1x)}Ga{sub x}Se{sub 2} thin films grown through high flux, low energy ion irradiation

    SciTech Connect

    Hall, Allen J.; Hebert, Damon; Rockett, Angus A.; Shah, Amish B.; Bettge, Martin

    2013-10-21

    A hybrid effusion/sputtering vacuum system was modified with an inductively coupled plasma (ICP) coil enabling ion assisted physical vapor deposition of CuIn{sub 1?x}Ga{sub x}Se{sub 2} thin films on GaAs single crystals and stainless steel foils. With <80 W rf power to the ICP coil at 620740 C, film morphologies were unchanged compared to those grown without the ICP. At low temperature (600670 C) and high rf power (80400 W), a light absorbing nanostructured highly anisotropic platelet morphology was produced with surface planes dominated by (112){sub T} facets. At 80400 W rf power and 640740 C, both interconnected void and small platelet morphologies were observed while at >270 W and above >715 C nanostructured pillars with large inter-pillar voids were produced. The latter appeared black and exhibited a strong (112){sub T} texture with interpillar twist angles of 8. Application of a negative dc bias of 050 V to the film during growth was not found to alter the film morphology or stoichiometry. The results are interpreted as resulting from the plasma causing strong etching favoring formation of (112){sub T} planes and preferential nucleation of new grains, balanced against conventional thermal diffusion and normal growth mechanisms at higher temperatures. The absence of effects due to applied substrate bias suggests that physical sputtering or ion bombardment effects were minimal. The nanostructured platelet and pillar films were found to exhibit less than one percent reflectivity at angles up to 75 from the surface normal.

  8. Atomic structure of defects in GaN:Mg grown with Ga polarity

    SciTech Connect

    Liliental-Weber, Z.; Tomaszewicz, T.; Zakharov, D.; Jasinski, J.; O'Keefe, M.A.; Hautakangas, S.; Laakso, A.; Saarinen, K.

    2003-11-25

    Electron microscope phase images, produced by direct reconstruction of the scattered electron wave from a focal series of high-resolution images, were used to determine the nature of defects formed in GaN:Mg crystals. We studied bulk crystals grown from dilute solutions of atomic nitrogen in liquid gallium at high pressure and thin films grown by the MOCVD method. All the crystals were grown with Ga-polarity. In both types of samples the majority of defects were three dimensional Mg-rich hexagonal pyramids with bases on the (0001) plane and six walls on {l_brace}11{und 2}3{r_brace} planes seen in cross-section as triangulars. Some other defects appear in cross-section as trapezoidal (rectangular) defects as a result of presence of truncated pyramids. Both type of defects have hollow centers. They are decorated by Mg on all six side walls and a base. The GaN which grows inside on the defect walls shows polarity inversion. It is shown that change of polarity starts from the defect tip and propagates to the base, and that the stacking sequence changes from ab in the matrix to bc inside the defect. Exchange of the Ga sublattice with the N sublattice within the defect leads to 0.6 {+-} 0.2{angstrom} displacement between Ga sublattices outside and inside the defects. It is proposed that lateral overgrowth of the cavities formed within the defect takes place to restore matrix polarity on the defect base.

  9. Transport properties of ultra-thin VO{sub 2} films on (001) TiO{sub 2} grown by reactive molecular-beam epitaxy

    SciTech Connect

    Paik, Hanjong; Tashman, Joshua W.; Moyer, Jarrett A.; Schiffer, Peter; Spila, Timothy; Mundy, Julia A.; Freeman, Eugene; Shukla, Nikhil; Datta, Suman; Lapano, Jason M.; Engel-Herbert, Roman; Zander, Willi; Schubert, Jürgen; Muller, David A.; Schlom, Darrell G.

    2015-10-19

    We report the growth of (001)-oriented VO{sub 2} films as thin as 1.5 nm with abrupt and reproducible metal-insulator transitions (MIT) without a capping layer. Limitations to the growth of thinner films with sharp MITs are discussed, including the Volmer-Weber type growth mode due to the high energy of the (001) VO{sub 2} surface. Another key limitation is interdiffusion with the (001) TiO{sub 2} substrate, which we quantify using low angle annular dark field scanning transmission electron microscopy in conjunction with electron energy loss spectroscopy. We find that controlling island coalescence on the (001) surface and minimization of cation interdiffusion by using a low growth temperature followed by a brief anneal at higher temperature are crucial for realizing ultrathin VO{sub 2} films with abrupt MIT behavior.

  10. Fundamental Bulk/Surface Structure Photoactivity Relationships of Supported (Rh2-yCryO3)/GaN Photocatalysts

    SciTech Connect

    Phivilay, Somphonh; Roberts, Charles; Puretzky, Alexander A; Domen, Kazunari Domen; Wachs, Israel

    2013-01-01

    ABSTRACT. The supported (Rh2-yCryO3)/GaN photocatalyst was examined as a model nitride photocatalyst system to assist in the development of fundamental structure photoactivity relationships for UV activated water splitting. Surface characterization of the outermost surface layers by High Sensitivity-LEIS and High Resolution-XPS revealed for the first time that the GaN support consists of a GaOx outermost surface layer and a thin film of GaOxNy in the surface region. HR-XPS also demonstrates that the supported (Rh2-yCryO3) mixed oxide nanoparticles (NPs) exclusively consist of Cr+3 and Rh+3 cations and are surface enriched for the supported (Rh2-yCryO3)/GaN photocatalyst. Bulk analysis by Raman and UV-vis spectroscopy show that the bulk molecular and electronic structures, respectively, of the GaN support are not perturbed by the deposition of the (Rh2-yCryO3) mixed oxide NPs. The function of the GaN bulk lattice is to generate photoexcited electrons/holes, with the electrons harnessed by the surface Rh+3 sites for evolution of H2 and the holes trapped at the Ga oxide/oxynitride surface sites for splitting of water and evolving O2. These new structure-photoactivity relationships for supported (Rh2-yCryO3)/GaN also extend to the best performing visible light activated supported (Rh2-yCryO3)/(Ga1-xZnx)(N1-xOx) photocatalyst.

  11. Performance enhancement of GaN metalsemiconductormetal ultraviolet photodetectors by insertion of ultrathin interfacial HfO{sub 2} layer

    SciTech Connect

    Kumar, Manoj E-mail: aokyay@ee.bilkent.edu.tr; Tekcan, Burak; Okyay, Ali Kemal E-mail: aokyay@ee.bilkent.edu.tr

    2015-03-15

    The authors demonstrate improved device performance of GaN metalsemiconductormetal ultraviolet (UV) photodetectors (PDs) by ultrathin HfO{sub 2} (UT-HfO{sub 2}) layer on GaN. The UT-HfO{sub 2} interfacial layer is grown by atomic layer deposition. The dark current of the PDs with UT-HfO{sub 2} is significantly reduced by more than two orders of magnitude compared to those without HfO{sub 2} insertion. The photoresponsivity at 360?nm is as high as 1.42 A/W biased at 5 V. An excellent improvement in the performance of the devices is ascribed to allowed electron injection through UT-HfO{sub 2} on GaN interface under UV illumination, resulting in the photocurrent gain with fast response time.

  12. Strain-Dependence of the Structure and Ferroic Properties of Epitaxial NiTiO 3 Thin Films Grown on Different Substrates

    DOE PAGES [OSTI]

    Varga, Tamas; Droubay, Timothy C.; Bowden, Mark E.; Kovarik, Libor; Hu, Dehong; Chambers, Scott A.

    2015-01-01

    Polarization-induced weak ferromagnetism has been predicted a few years back in perovskite MTiO 3 (M = Fe, Mn, and Ni). We set out to stabilize this metastable perovskite structure by growing NiTiO 3 epitaxially on different substrates and to investigate the dependence of polar and magnetic properties on strain. Epitaxial NiTiO 3 films were deposited on Al 2 O 3 , Fe 2 O 3 , and LiNbO 3 substrates by pulsed laser deposition and characterized using several techniques. The effect of substrate choice on lattice strain, film structure, and physical properties was investigated. Our structural data from X-raymore » diffraction and electron microscopy shows that substrate-induced strain has a marked effect on the structure and crystalline quality of the films. Physical property measurements reveal a dependence of the weak ferromagnetism and lattice polarization on strain and highlight our ability to control the ferroic properties in NiTiO 3 thin films by the choice of substrate. Our results are also consistent with the theoretical prediction that the ferromagnetism in acentric NiTiO 3 is polarization induced. From the substrates studied here, the perovskite substrate LiNbO 3 proved to be the most promising one for strong multiferroism.« less

  13. Strain-dependence Of The Structure And Ferroic Properties Of Epitaxial NiTiO3 Thin Films Grown On Different Substrates

    SciTech Connect

    Varga, Tamas; Droubay, Timothy C.; Bowden, Mark E.; Kovarik, Libor; Hu, Dehong; Chambers, Scott A.

    2015-08-14

    Polarization-induced weak ferromagnetism has been predicted a few years back in perovskite MTiO3 (M = Fe, Mn, Ni) [Fennie, Phys. Rev. Lett. 100, 167203 (2008)]. We set out to stabilize this metastable perovskite structure by growing NiTiO3 epitaxially on different substrates, and to investigate the dependence of polar and magnetic properties on strain. Epitaxial NiTiO3 films were deposited on Al2O3, Fe2O3, and LiNbO3 substrates by pulsed laser deposition, and characterized using several techniques. The effect of substrate choice on lattice strain, film structure, and physical properties was investigated. Our structural data from x-ray diffraction and electron microscopy shows that substrate-induced strain has a marked effect on the structure and crystalline quality of the films. Physical property measurements reveal a dependence of the weak ferromagnetism and lattice polarization on strain, and highlight our ability to control the ferroic properties in NiTiO3 thin films by the choice of substrate. Our results are also consistent with the theoretical prediction that the ferromagnetism in acentric NiTiO3 is polarization-induced. From the substrates studied here, the perovskite substrate LiNbO3 proved to be the most promising one for strong multiferroism.

  14. Photovoltaic properties of Aurivillius phase Bi{sub 5}FeTi{sub 3}O{sub 15} thin films grown by pulsed laser deposition

    SciTech Connect

    Kooriyattil, Sudheendran; Katiyar, Rajesh K.; Pavunny, Shojan P. E-mail: shojanpp@gmail.com; Morell, Gerardo; Katiyar, Ram S. E-mail: shojanpp@gmail.com

    2014-08-18

    We report a remarkable photovoltaic effect in pulsed laser deposited multiferroic aurivillius phase Bi{sub 5}FeTi{sub 3}O{sub 15} (BFTO) thin films sandwiched between ZnO:Al transparent conductive oxide top electrode and SrRuO{sub 3} bottom electrode fabricated on amorphous fused silica substrates. The structural and micro structural properties of these films were analysed by X-ray diffraction and atomic force microscopy techniques. The films were showing a photo sensitive ferroelectric behaviour with a notable apparent polarization in the range of 1015??C/cm{sup 2}. These films also exhibited a switchable photo-response and this parameter was observed to be sensitive to polarisation field and the polarization direction. The device shows a large ON/OFF photo current ratio with an open circuit voltage of 0.14?V. The photo response at zero bias of this BFTO based heterostructures showed rapid increase to a saturation value of 6??A at zero bias.

  15. X-ray magnetic spectroscopy of MBE-grown Mn-doped Bi{sub 2}Se{sub 3} thin films

    SciTech Connect

    Collins-McIntyre, L. J.; Watson, M. D.; Zhang, S. L.; Coldea, A. I.; Hesjedal, T.; Baker, A. A.; Harrison, S. E.; Pushp, A.; Kellock, A. J.; Parkin, S. S. P.; Laan, G. van der

    2014-12-15

    We report the growth of Mn-doped Bi{sub 2}Se{sub 3} thin films by molecular beam epitaxy (MBE), investigated by x-ray diffraction (XRD), atomic force microscopy (AFM), SQUID magnetometry and x-ray magnetic circular dichroism (XMCD). Epitaxial films were deposited on c-plane sapphire substrates by co-evaporation. The films exhibit a spiral growth mechanism typical of this material class, as revealed by AFM. The XRD measurements demonstrate a good crystalline structure which is retained upon doping up to ?7.5 atomic-% Mn, determined by Rutherford backscattering spectrometry (RBS), and show no evidence of the formation of parasitic phases. However an increasing interstitial incorporation of Mn is observed with increasing doping concentration. A magnetic moment of 5.1 ?{sub B}/Mn is obtained from bulk-sensitive SQUID measurements, and a much lower moment of 1.6 ?{sub B}/Mn from surface-sensitive XMCD. At ?2.5 K, XMCD at the Mn L{sub 2,3} edge, reveals short-range magnetic order in the films and indicates ferromagnetic order below 1.5 K.

  16. Strain-Dependence of the Structure and Ferroic Properties of Epitaxial NiTiO3Thin Films Grown on Different Substrates

    DOE PAGES [OSTI]

    Varga, Tamas; Droubay, Timothy C.; Bowden, Mark E.; Kovarik, Libor; Hu, Dehong; Chambers, Scott A.

    2015-01-01

    Polarization-induced weak ferromagnetism has been predicted a few years back in perovskite MTiO3(M = Fe, Mn, and Ni). We set out to stabilize this metastable perovskite structure by growing NiTiO3epitaxially on different substrates and to investigate the dependence of polar and magnetic properties on strain. Epitaxial NiTiO3films were deposited on Al2O3, Fe2O3, and LiNbO3substrates by pulsed laser deposition and characterized using several techniques. The effect of substrate choice on lattice strain, film structure, and physical properties was investigated. Our structural data from X-ray diffraction and electron microscopy shows that substrate-induced strain has a marked effect on the structure and crystallinemorequality of the films. Physical property measurements reveal a dependence of the weak ferromagnetism and lattice polarization on strain and highlight our ability to control the ferroic properties in NiTiO3thin films by the choice of substrate. Our results are also consistent with the theoretical prediction that the ferromagnetism in acentric NiTiO3is polarization induced. From the substrates studied here, the perovskite substrate LiNbO3proved to be the most promising one for strong multiferroism.less

  17. Photo-induced valence change of the sulfur atom in an L-cysteine thin film grown on a silver metal substrate in a saliva-emulated aqueous solution

    SciTech Connect

    Tsujibayashi, Toru; Azuma, Junpei; Yamamoto, Isamu; Takahashi, Kazutoshi; Kamada, Masao

    2015-04-27

    A thin film of L-cysteine (HSCH{sub 2}CH(NH{sub 2})COOH) is grown on a silver substrate in saliva-emulated aqueous solution. X-ray photoemission spectroscopic measurements have revealed that the sulfur atom shows valence change under IR laser irradiation at 825?nm. The valence change maintains for about a minute at room temperature and more than an hour between 110 and 250?K after stopping the laser irradiation. It is not observed at all at temperatures lower than 110?K. This temperature-dependent behavior indicates that the photo-excited electronic change should be accompanied by a conformational change in the L-cysteine molecule. It is strongly suggested that the reversible valence change of the sulfur atom is applicable to a memory used around room temperature.

  18. Two-dimensional weak anti-localization in Bi{sub 2}Te{sub 3} thin film grown on Si(111)-(7 Multiplication-Sign 7) surface by molecular beam epitaxy

    SciTech Connect

    Roy, Anupam; Guchhait, Samaresh; Sonde, Sushant; Dey, Rik; Pramanik, Tanmoy; Rai, Amritesh; Movva, Hema C. P.; Banerjee, Sanjay K. [Microelectronics Research Center, The University of Texas at Austin, Austin, Texas 78758 (United States)] [Microelectronics Research Center, The University of Texas at Austin, Austin, Texas 78758 (United States); Colombo, Luigi [Texas Instruments, 12500 TI Boulevard, Dallas, Texas 75266 (United States)] [Texas Instruments, 12500 TI Boulevard, Dallas, Texas 75266 (United States)

    2013-04-22

    We report on low temperature transport studies of Bi{sub 2}Te{sub 3} topological insulator thin films grown on Si(111)-(7 Multiplication-Sign 7) surface by molecular beam epitaxy. A sharp increase in the magnetoresistance with magnetic field at low temperature indicates the existence of weak anti-localization. The measured weak anti-localization effect agrees well with the Hikami-Larkin-Nagaoka model, and the extracted phase coherence length shows a power-law dependence with temperature indicating the existence of a two-dimensional system. An insulating ground state has also been observed at low temperature showing a logarithmic divergence of the resistance that appears to be the influence of electron-electron interaction in a two-dimensional system.

  19. Ferromagnetism and magneto-transport properties of Mn{sub 0.92}Ca{sub 0.08}As thin film grown on Al{sub 2}O{sub 3}(0001) substrate

    SciTech Connect

    Dung, Dang Duc; Van Thiet, Duong; Anh Tuan, Duong; Cho, Sunglae; Feng, Wuwei

    2014-05-07

    The epitaxial Mn{sub 0.92}Ca{sub 0.08}As thin film was grown on Al{sub 2}O{sub 3}(0001) substrate by molecular beam epitaxy. The Curie temperature (T{sub C}) around 340 K was enhanced with the addition of Ca, compared to that of bulk MnAs (T{sub C} ∼ 318 K). The maxima magnetoresistance, ∼2.08% at 0.7 T, was observed near the critical magnetic transition temperature. Moreover, the giant magnetocaloric effect was found with the maximum magnetic entropy change, ∼200 J/kgK, around 330 K at 5 T.

  20. Effects of laser energy fluence on the onset and growth of the Rayleigh-Taylor instabilities and its influence on the topography of the Fe thin film grown in pulsed laser deposition facility

    SciTech Connect

    Mahmood, S. [National Institute of Education, Nanyang Technological University, 1 Nanyang Walk, Singapore 637616 (Singapore); Department of Physics, University of Karachi, Karachi 75270 (Pakistan); Rawat, R. S.; Wang, Y.; Lee, S.; Tan, T. L.; Springham, S. V.; Lee, P. [National Institute of Education, Nanyang Technological University, 1 Nanyang Walk, Singapore 637616 (Singapore); Zakaullah, M. [Department of Physics, Quaid-i-Azam University, 45320 Islamabad (Pakistan)

    2012-10-15

    The effect of laser energy fluence on the onset and growth of Rayleigh-Taylor (RT) instabilities in laser induced Fe plasma is investigated using time-resolved fast gated imaging. The snow plow and shock wave models are fitted to the experimental results and used to estimate the ablation parameters and the density of gas atoms that interact with the ablated species. It is observed that RT instability develops during the interface deceleration stage and grows for a considerable time for higher laser energy fluence. The effects of RT instabilities formation on the surface topography of the Fe thin films grown in pulsed laser deposition system are investigated (i) using different laser energy fluences for the same wavelength of laser radiation and (ii) using different laser wavelengths keeping the energy fluence fixed. It is concluded that the deposition achieved under turbulent condition leads to less smooth deposition surfaces with bigger sized particle agglomerates or network.

  1. On the crystalline structure, stoichiometry and band gap of InN thin films

    SciTech Connect

    Yu, K.M.; Liliental-Weber, Z.; Walukiewicz, W.; Li, S.X.; Jones, R.E.; Shan, W.; Ager III, J.W.; Haller, E.E.; Lu, Hai; Schaff, William J.

    2004-09-23

    Detailed transmission electron microscopy (TEM), x-ray diffraction (XRD), and optical characterization of a variety of InN thin films grown by molecular beam epitaxy under both optimized and non-optimized conditions is reported. Optical characterization by absorption and photoluminescence confirms that the band gap of single crystalline and polycrystalline wurtzite InN is 0.70 {+-} 0.05 eV. Films grown under optimized conditions with a AlN nucleation layer and a GaN buffer layer are stoichiometric, single crystalline wurtzite structure with dislocation densities not exceeding mid-10{sup 10} cm{sup -2}. Non-optimal films can be poly-crystalline and display an XRD diffraction feature at 2{theta} {approx} 33{sup o}; this feature has been attributed by others to the presence of metallic In clusters. Careful indexing of wide angle XRD scans and selected area diffraction patterns shows that this peak is in fact due to the presence of polycrystalline InN grains; no evidence of metallic In clusters was found in any of the studied samples.

  2. Low-temperature grown quaternary Heusler-compound Co{sub 2}Mn{sub 1-x}Fe{sub x}Si films on Ge(111)

    SciTech Connect

    Yamada, S.; Murakami, T.; Hamaya, K.; Varaprasad, B.; Rajanikanth, A.; Hono, K.; Takahashi, Y. K.; Miyao, M.

    2011-04-01

    Highly ordered quaternary Co{sub 2}Mn{sub 1-x}Fe{sub x}Si films on Ge(111) are explored for spintronic device applications on Si-large-scale integrated circuit (LSI) platform. By using low-temperature molecular beam epitaxy techniques, relatively large magnetic moments are demonstrated for x between 0.50 and 1.0 despite extremely low temperature growth of 130 deg. C. Also, L2{sub 1}-ordered crystal structures can be realized even on a group-IV semiconductor substrate, Ge, compatible with Si-LSI technologies. By the point contact Andreev reflection method, the spin polarization of Co{sub 2}Mn{sub 0.5}Fe{sub 0.5}Si films is estimated to be P= 0.58 {+-} 0.02. We believe that this study will be a first step for integration of high-performance spintronic applications with next ultra LSI.

  3. Structural, magnetic, and electronic properties of GdTiO{sub 3} Mott insulator thin films grown by pulsed laser deposition

    SciTech Connect

    Grisolia, M. N.; Bruno, F. Y.; Sando, D.; Jacquet, E.; Barthlmy, A.; Bibes, M.; Zhao, H. J.; Chen, X. M.; Bellaiche, L.

    2014-10-27

    We report on the optimization process to synthesize epitaxial thin films of GdTiO{sub 3} on SrLaGaO{sub 4} substrates by pulsed laser deposition. Optimized films are free of impurity phases and are fully strained. They possess a magnetic Curie temperature T{sub C}?=?31.8?K with a saturation magnetization of 4.2??{sub B} per formula unit at 10?K. Transport measurements reveal an insulating response, as expected. Optical spectroscopy indicates a band gap of ?0.7?eV, comparable to the bulk value. Our work adds ferrimagnetic orthotitanates to the palette of perovskite materials for the design of emergent strongly correlated states at oxide interfaces using a versatile growth technique such as pulsed laser deposition.

  4. Electronic excitations and structure of Li{sub 2}IrO{sub 3} thin films grown on ZrO{sub 2}:Y (001) substrates

    SciTech Connect

    Jenderka, Marcus Schmidt-Grund, Rüdiger; Grundmann, Marius; Lorenz, Michael

    2015-01-14

    Thin films are a prerequisite for application of the emergent exotic ground states in iridates that result from the interplay of strong spin-orbit coupling and electronic correlations. We report on pulsed laser deposition of Li{sub 2}IrO{sub 3} films on ZrO{sub 2}:Y (001) single crystalline substrates. X-ray diffraction confirms preferential (001) and (10-1) out-of-plane crystalline orientations with well defined in-plane orientation. Resistivity between 35 and 300 K is dominated by a three-dimensional variable range hopping mechanism. The dielectric function is determined by means of spectroscopic ellipsometry and, complemented by Fourier transform infrared transmission spectroscopy, reveals a small optical gap of ≈300 meV, a splitting of the 5d-t{sub 2g} manifold, and several in-gap excitations attributed to phonons and possibly magnons.

  5. GaN nanowires with pentagon shape cross-section by ammonia-source molecular beam epitaxy

    DOE PAGES [OSTI]

    Lin, Yong; Leung, Benjamin; Li, Qiming; Figiel, Jeffrey J.; Wang, George T.

    2015-07-14

    In this study, ammonia-based molecular beam epitaxy (NH3-MBE) was used to grow catalyst-assisted GaN nanowires on (11¯02) r-plane sapphire substrates. Dislocation free [112¯0] oriented nanowires are formed with pentagon shape cross-section, instead of the usual triangular shape facet configuration. Specifically, the cross-section is the result of the additional two nonpolar {101¯0} side facets, which appear due to a decrease in relative growth rate of the {101¯0} facets to the {101¯1} and {101¯1} facets under the growth regime in NH3-MBE. Compared to GaN nanowires grown by Ni-catalyzed metal–organic chemical vapor deposition, the NH3-MBE grown GaN nanowires show more than an ordermore » of magnitude increase in band-edge to yellow luminescence intensity ratio, as measured by cathodoluminescence, indicating improved microstructural and optical properties.« less

  6. GaN nanowires with pentagon shape cross-section by ammonia-source molecular beam epitaxy

    SciTech Connect

    Lin, Yong; Leung, Benjamin; Li, Qiming; Figiel, Jeffrey J.; Wang, George T.

    2015-07-14

    In this study, ammonia-based molecular beam epitaxy (NH3-MBE) was used to grow catalyst-assisted GaN nanowires on (11¯02) r-plane sapphire substrates. Dislocation free [112¯0] oriented nanowires are formed with pentagon shape cross-section, instead of the usual triangular shape facet configuration. Specifically, the cross-section is the result of the additional two nonpolar {101¯0} side facets, which appear due to a decrease in relative growth rate of the {101¯0} facets to the {101¯1} and {101¯1} facets under the growth regime in NH3-MBE. Compared to GaN nanowires grown by Ni-catalyzed metal–organic chemical vapor deposition, the NH3-MBE grown GaN nanowires show more than an order of magnitude increase in band-edge to yellow luminescence intensity ratio, as measured by cathodoluminescence, indicating improved microstructural and optical properties.

  7. High oxidation state at the epitaxial interface of {gamma}-Al{sub 2}O{sub 3} thin films grown on Si(111) and Si(001)

    SciTech Connect

    El Kazzi, M.; Silly, M.; Sirotti, F.; Merckling, C.; Saint-Girons, G.; Grenet, G.; Hollinger, G.

    2010-10-11

    High resolution synchrotron radiation x-ray photoelectron spectroscopy allowed us to identify the chemical bonding at the interface between epitaxial {gamma}-Al{sub 2}O{sub 3} and Si substrate. The experiments were performed on 1 nm thick epitaxial {gamma}-Al{sub 2}O{sub 3} layers grown on both Si(111) and Si(001) substrates. In both cases, the Si 2p core level decomposition recorded at photon energy of 160 eV provided evidence for the absence of Si{sup 2+} and Si{sup 3+} species and the presence of two different Si{sup 4+} species. A microscopic model is proposed for the interface obtained with two incomplete SiO{sub 2} planes based on the Si 2p{sub 3/2} line shape.

  8. Development of very high Jc in Ba(Fe1-xCox)2As2 thin films grown on CaF2

    DOE PAGES [OSTI]

    Tarantini, C.; Kametani, F.; Lee, S.; Jiang, J.; Weiss, J. D.; Jaroszynski, J.; Hellstrom, E. E.; Eom, C. B.; Larbalestier, D. C.

    2014-12-03

    Ba(Fe1-xCox)2As2 is the most tunable of the Fe-based superconductors (FBS) in terms of acceptance of high densities of self-assembled and artificially introduced pinning centres which are effective in significantly increasing the critical current density, Jc. Moreover, FBS are very sensitive to strain, which induces an important enhancement in critical temperature,Tc, of the material. In this study we demonstrate that strain induced by the substrate can further improve Jc of both single and multilayer films by more than that expected simply due to the increase in Tc. The multilayer deposition of Ba(Fe1-xCox)2As2 on CaF2 increases the pinning force density (Fp=Jc xmore » μ₀H) by more than 60% compared to a single layer film, reaching a maximum of 84 GN/m3 at 22.5 T and 4.2 K, the highest value ever reported in any 122 phase.« less

  9. Perpendicular uniaxial magnetic anisotropy of Fe{sub 16}N{sub 2}(001) single crystal films grown by molecular beam epitaxy

    SciTech Connect

    Takahashi, H.; Igarashi, M.; Kaneko, A.; Miyajima, H.; Sugita, Y.

    1999-09-01

    The uniaxial magnetic anisotropies by torque measurement have been measured for Fe{sub 16}N{sub 2}(001) films exhibits perpendicular uniaxial anisotropy which makes the easy axis along the [001] direction, and those anisotropy constants K{sub U1} and K{sub U2} for Fe{sub 16}N{sub 2} were 1.6 x 10{sup 7} and 0.4 x 10{sup 7} erg/cm{sup 3}, respectively. Those K{sub U1} and K{sub U2} for Fe{sub 16}N{sub 2} were constant in the thickness range from 34 to 83 nm. The ferromagnetic resonance of Fe{sub 16}N{sub 2}(001) single crystal films have been measured. The saturation magnetic flux densities, 4{pi}M{sub s} for Fe{sub 16}N{sub 2} measured by the magnetic torques and resonance fields agreed well with the values measured with a vibrating sample magnetometer (VSM).

  10. Impact of defects on the electrical transport, optical properties and failure mechanisms of GaN nanowires.

    SciTech Connect

    Armstrong, Andrew M.; Aubry, Sylvie; Shaner, Eric Arthur; Siegal, Michael P.; Li, Qiming; Jones, Reese E.; Westover, Tyler; Wang, George T.; Zhou, Xiao Wang; Talin, Albert Alec; Bogart, Katherine Huderle Andersen; Harris, C. Thomas; Huang, Jian Yu

    2010-09-01

    We present the results of a three year LDRD project that focused on understanding the impact of defects on the electrical, optical and thermal properties of GaN-based nanowires (NWs). We describe the development and application of a host of experimental techniques to quantify and understand the physics of defects and thermal transport in GaN NWs. We also present the development of analytical models and computational studies of thermal conductivity in GaN NWs. Finally, we present an atomistic model for GaN NW electrical breakdown supported with experimental evidence. GaN-based nanowires are attractive for applications requiring compact, high-current density devices such as ultraviolet laser arrays. Understanding GaN nanowire failure at high-current density is crucial to developing nanowire (NW) devices. Nanowire device failure is likely more complex than thin film due to the prominence of surface effects and enhanced interaction among point defects. Understanding the impact of surfaces and point defects on nanowire thermal and electrical transport is the first step toward rational control and mitigation of device failure mechanisms. However, investigating defects in GaN NWs is extremely challenging because conventional defect spectroscopy techniques are unsuitable for wide-bandgap nanostructures. To understand NW breakdown, the influence of pre-existing and emergent defects during high current stress on NW properties will be investigated. Acute sensitivity of NW thermal conductivity to point-defect density is expected due to the lack of threading dislocation (TD) gettering sites, and enhanced phonon-surface scattering further inhibits thermal transport. Excess defect creation during Joule heating could further degrade thermal conductivity, producing a viscous cycle culminating in catastrophic breakdown. To investigate these issues, a unique combination of electron microscopy, scanning luminescence and photoconductivity implemented at the nanoscale will be used in

  11. Microstructure and dielectric properties of Ba{sub 1-x}Sr{sub x}TiO{sub 3} films grown on LaAlO{sub 3} substrates

    SciTech Connect

    Gim, Y.; Hudson, T.; Fan, Y.; Kwon, C.; Findikoglu, A. T.; Gibbons, B. J.; Park, B. H.; Jia, Q. X.

    2000-08-21

    We report a systematic study of the microstructure and dielectric properties of barium strontium titanate, Ba{sub 1-x}Sr{sub x}TiO{sub 3}, films grown by laser ablation on LaAlO{sub 3} substrates, where x=0.1-0.9 at an interval of 0.1. X-ray diffraction analysis shows that when x<0.4, the longest unit-cell axis is parallel to the plane of the substrate but perpendicular as x approaches 1. Dielectric constant versus temperature measurements show that the relative dielectric constant has a maximum value and that the peak temperatures corresponding to the maximum relative dielectric constant are about 70 degree sign C higher when x{<=}0.4 but similar when x>0.4, compared with the peak temperatures of the bulk Ba{sub 1-x}Sr{sub x}TiO{sub 3}. At room temperature, the dielectric constant and tunability are relatively high when x{<=}0.4 but start to decrease rapidly as x increases. (c) 2000 American Institute of Physics.

  12. Excitation mechanisms of Er optical centers in GaN epilayers

    SciTech Connect

    George, D. K.; Hawkins, M. D.; McLaren, M.; Vinh, N. Q.; Jiang, H. X.; Lin, J. Y.; Zavada, J. M.

    2015-10-26

    We report direct evidence of two mechanisms responsible for the excitation of optically active Er{sup 3+} ions in GaN epilayers grown by metal-organic chemical vapor deposition. These mechanisms, resonant excitation via the higher-lying inner 4f shell transitions and band-to-band excitation of the semiconductor host, lead to narrow emission lines from isolated and the defect-related Er optical centers. However, these centers have different photoluminescence spectra, local defect environments, decay dynamics, and excitation cross sections. The photoluminescence at 1.54 μm from the isolated Er optical center which can be excited by either mechanism has the same decay dynamics, but possesses a much higher excitation cross-section under band-to-band excitation. In contrast, the photoluminescence at 1.54 μm from the defect-related Er optical center can only be observed through band-to-band excitation but has the largest excitation cross-section. These results explain the difficulty in achieving gain in Er doped GaN and indicate approaches for realization of optical amplification, and possibly lasing, at room temperature.

  13. ARM - Field Campaign - AMIE-Gan Ancillary Disdrometer

    U.S. Department of Energy (DOE) - all webpages (Extended Search)

    would love to hear from you Send us a note below or call us at 1-888-ARM-DATA. Send Campaign : AMIE-Gan Ancillary Disdrometer 2012.01.01 - 2012.02.10 Lead Scientist : Mariko Oue...

  14. AMIE Gan Island Ancillary Disdrometer Field Campaign Report (Program

    Office of Scientific and Technical Information (OSTI)

    Document) | SciTech Connect AMIE Gan Island Ancillary Disdrometer Field Campaign Report Citation Details In-Document Search Title: AMIE Gan Island Ancillary Disdrometer Field Campaign Report As part of the U.S. Department of Energy (DOE)'s Atmospheric Radiation Measurement Climate Research Facility (ARM) Madden-Julian Oscillation (MJO) Investigation Experiment (AMIE), in January 2012 a disdrometer observation took place with the second ARM Mobile Facility (AMF2), the Scanning ARM Cloud Radar

  15. Temperature dependent dielectric function and the E{sub 0} critical points of hexagonal GaN from 30 to 690 K

    SciTech Connect

    Kim, Tae Jung Hwang, Soon Yong; Byun, Jun Seok; Barange, Nilesh S.; Park, Han Gyeol; Dong Kim, Young

    2014-02-15

    The complex dielectric function ? and the E{sub 0} excitonic and band-edge critical-point structures of hexagonal GaN are reported for temperatures from 30 to 690 K and energies from 0.74 to 6.42 eV, obtained by rotating-compensator spectroscopic ellipsometry on a 1.9 ?m thick GaN film deposited on a c-plane (0001) sapphire substrate by molecular beam epitaxy. Direct inversion and B-splines in a multilayer-structure calculation were used to extract the optical properties of the film from the measured pseudodielectric function ???. At low temperature sharp E{sub 0} excitonic and critical-point interband transitions are separately observed. Their temperature dependences were determined by fitting the data to the empirical Varshni relation and the phenomenological expression that contains the Bose-Einstein statistical factor.

  16. Demonstration of forward inter-band tunneling in GaN by polarization engineering

    SciTech Connect

    Krishnamoorthy, Sriram; Park, Pil Sung; Rajan, Siddharth

    2011-12-05

    We report on the design, fabrication, and characterization of GaN interband tunnel junction showing forward tunneling characteristics. We have achieved very high forward tunneling currents (153 mA/cm{sup 2} at 10 mV, and 17.7 A/cm{sup 2} peak current) in polarization-engineered GaN/InGaN/GaN heterojunction diodes grown by plasma assisted molecular beam epitaxy. We also report the observation of repeatable negative differential resistance in interband III-Nitride tunnel junctions, with peak-valley current ratio of 4 at room temperature. The forward current density achieved in this work meets the typical current drive requirements of a multi-junction solar cell.

  17. Monolithic single GaN nanowire laser with photonic crystal microcavity on silicon

    SciTech Connect

    Heo, Junseok; Guo Wei; Bhattacharya, Pallab

    2011-01-10

    Optically pumped lasing at room temperature in a silicon based monolithic single GaN nanowire with a two-dimensional photonic crystal microcavity is demonstrated. Catalyst-free nanowires with low density ({approx}10{sup 8} cm{sup -2}) are grown on Si by plasma-assisted molecular beam epitaxy. High resolution transmission electron microscopy images reveal that the nanowires are of wurtzite structure and they have no observable defects. A single nanowire laser fabricated on Si is characterized by a lasing transition at {lambda}=371.3 nm with a linewidth of 0.55 nm. The threshold is observed at a pump power density of {approx}120 kW/cm{sup 2} and the spontaneous emission factor {beta} is estimated to be 0.08.

  18. ARM MJO Investigation Experiment on Gan Island (AMIE-Gan) Science Plan

    SciTech Connect

    Long, CL; Del Genio, A; Deng, M; Fu, X; Gustafson, W; Houze, R; Jakob, C; Jensen, M; Johnson, R; Liu, X; Luke, E; May, P; McFarlane, S; Minnis, P; Schumacher, C; Vogelmann, A; Wang, Y; Webster, P; Xie, S; Zhang, C

    2011-04-11

    The overarching campaign, which includes the ARM Mobile Facility 2 (AMF2) deployment in conjunction with the Dynamics of the Madden-Julian Oscillation (DYNAMO) and the Cooperative Indian Ocean experiment on intraseasonal variability in the Year 2011 (CINDY2011) campaigns, is designed to test several current hypotheses regarding the mechanisms responsible for Madden-Julian Oscillation (MJO) initiation and propagation in the Indian Ocean area. The synergy between the proposed AMF2 deployment with DYNAMO/CINDY2011, and the corresponding funded experiment on Manus, combine for an overarching ARM MJO Investigation Experiment (AMIE) with two components: AMF2 on Gan Island in the Indian Ocean (AMIE-Gan), where the MJO initiates and starts its eastward propagation; and the ARM Manus site (AMIE-Manus), which is in the general area where the MJO usually starts to weaken in climate models. AMIE-Gan will provide measurements of particular interest to Atmospheric System Research (ASR) researchers relevant to improving the representation of MJO initiation in climate models. The framework of DYNAMO/CINDY2011 includes two proposed island-based sites and two ship-based locations forming a square pattern with sonde profiles and scanning precipitation and cloud radars at both island and ship sites. These data will be used to produce a Variational Analysis data set coinciding with the one produced for AMIE-Manus. The synergy between AMIE-Manus and AMIE-Gan will allow studies of the initiation, propagation, and evolution of the convective cloud population within the framework of the MJO. As with AMIE-Manus, AMIE-Gan/DYNAMO also includes a significant modeling component geared toward improving the representation of MJO initiation and propagation in climate and forecast models. This campaign involves the deployment of the second, marine-capable, AMF; all of the included measurement systems; and especially the scanning and vertically pointing radars. The campaign will include sonde

  19. Ge doped GaN with controllable high carrier concentration for...

    Office of Scientific and Technical Information (OSTI)

    Ge doped GaN with controllable high carrier concentration for plasmonic applications Citation Details In-Document Search Title: Ge doped GaN with controllable high carrier...

  20. High Voltage GaN Schottky Rectifiers

    SciTech Connect

    CAO,X.A.; CHO,H.; CHU,S.N.G.; CHUO,C.-C.; CHYI,J.-I.; DANG,G.T.; HAN,JUNG; LEE,C.-M.; PEARTON,S.J.; REN,F.; WILSON,R.G.; ZHANG,A.P.

    1999-10-25

    Mesa and planar GaN Schottky diode rectifiers with reverse breakdown voltages (V{sub RB}) up to 550V and >2000V, respectively, have been fabricated. The on-state resistance, R{sub ON}, was 6m{Omega}{center_dot} cm{sup 2} and 0.8{Omega}cm{sup 2}, respectively, producing figure-of-merit values for (V{sub RB}){sup 2}/R{sub ON} in the range 5-48 MW{center_dot}cm{sup -2}. At low biases the reverse leakage current was proportional to the size of the rectifying contact perimeter, while at high biases the current was proportional to the area of this contact. These results suggest that at low reverse biases, the leakage is dominated by the surface component, while at higher biases the bulk component dominates. On-state voltages were 3.5V for the 550V diodes and {ge}15 for the 2kV diodes. Reverse recovery times were <0.2{micro}sec for devices switched from a forward current density of {approx}500A{center_dot}cm{sup -2} to a reverse bias of 100V.

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

    DOE PAGES [OSTI]

    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

  2. Conductivity based on selective etch for GaN devices and applications thereof

    SciTech Connect

    Zhang, Yu; Sun, Qian; Han, Jung

    2015-12-08

    This invention relates to methods of generating NP gallium nitride (GaN) across large areas (>1 cm.sup.2) with controlled pore diameters, pore density, and porosity. Also disclosed are methods of generating novel optoelectronic devices based on porous GaN. Additionally a layer transfer scheme to separate and create free-standing crystalline GaN thin layers is disclosed that enables a new device manufacturing paradigm involving substrate recycling. Other disclosed embodiments of this invention relate to fabrication of GaN based nanocrystals and the use of NP GaN electrodes for electrolysis, water splitting, or photosynthetic process applications.

  3. Magnetic anisotropy and order structure of L1{sub 0}-FePt(001) single-crystal films grown epitaxially on (001) planes of MgO, SrTiO{sub 3}, and MgAl{sub 2}O{sub 4} substrates

    SciTech Connect

    Hotta, A. Hatayama, M.; Tsumura, K.; Ono, T.; Kikuchi, N.; Okamoto, S.; Kitakami, O.; Shimatsu, T.

    2014-05-07

    L1{sub 0}–FePt(001) single-crystal films were grown epitaxially on SrTiO{sub 3}(001), MgAl{sub 2}O{sub 4}(001), and MgO(001) substrates. Their uniaxial magnetic anisotropy K{sub u} and the order structure were examined for the film thickness t range of 2–14 nm. All series of films show large K{sub u} of 4 × 10{sup 7} erg/cm{sup 3} in the thickness range higher than 10 nm, with order parameter S of 0.8 and saturation magnetization M{sub s} of 1120 emu/cm{sup 3}. K{sub u} decreased gradually as t decreased. The K{sub u} reduction was considerable when t decreased from 4 nm to 2 nm. No marked difference in the thickness dependence of K{sub u} was found in any series of films, although the lattice mismatch between FePt and the substrates was markedly different. K{sub u} reduction showed good agreement with the reduction of S for the films on MgAl{sub 2}O{sub 4} and MgO. The K{sub u} ∼ S{sup 2} plot showed an almost linear relation, which is in good agreement with theoretical predictions. Transmission electron microscopy images for a FePt film on MgO substrate revealed that the lattice mismatch between FePt(001) and MgO(001) was relaxed in the initial 1 or 2 layers of FePt(001) lattices, which is likely to be true also for two other series of films.

  4. Highly transparent ammonothermal bulk GaN substrates

    SciTech Connect

    Jiang, WK; Ehrentraut, D; Downey, BC; Kamber, DS; Pakalapati, RT; Do Yoo, H; D'Evelyn, MP

    2014-10-01

    A novel apparatus has been employed to grow ammonothermal (0001) gallium nitride (GaN) with diameters up to 2 in The crystals have been characterized by x-ray diffraction rocking-curve (XRC) analysis, optical and scanning electron microscopy (SEM), cathodoluminescence (CL), and optical spectroscopy. High crystallinity GaN with FWHM values about 20-50 arcsec and dislocation densities below 1 x 10(5) cm(-2) have been obtained. High optical transmission was achieved with an optical absorption coefficient below 1 cm(-1) at a wavelength of 450 nm. (C) 2014 Elsevier B.V. All rights reserved.

  5. InGaN/GaN tunnel junctions for hole injection in GaN light emitting diodes

    SciTech Connect

    Krishnamoorthy, Sriram E-mail: rajan@ece.osu.edu; Akyol, Fatih; Rajan, Siddharth E-mail: rajan@ece.osu.edu

    2014-10-06

    InGaN/GaN tunnel junction contacts were grown using plasma assisted molecular beam epitaxy (MBE) on top of a metal-organic chemical vapor deposition (MOCVD)-grown InGaN/GaN blue (450 nm) light emitting diode. A voltage drop of 5.3 V at 100 mA, forward resistance of 2 × 10{sup −2} Ω cm{sup 2}, and a higher light output power compared to the reference light emitting diodes (LED) with semi-transparent p-contacts were measured in the tunnel junction LED (TJLED). A forward resistance of 5 × 10{sup −4} Ω cm{sup 2} was measured in a GaN PN junction with the identical tunnel junction contact as the TJLED, grown completely by MBE. The depletion region due to the impurities at the regrowth interface between the MBE tunnel junction and the MOCVD-grown LED was hence found to limit the forward resistance measured in the TJLED.

  6. Evaluation of AlGaN/GaN high electron mobility transistors grown on ZrTi buffer layers with sapphire substrates

    DOE PAGES [OSTI]

    Ren, Fan; Pearton, Stephen J.; Ahn, Shihyun; Lin, Yi -Hsuan; Machuca, Francisco; Weiss, Robert; Welsh, Alex; McCartney, Martha R.; Smith, David J.; Kravchenko, Ivan I.

    2016-09-21

    Here, AlGaN/GaN high electron mobility transistors (HEMTs) have been grown on sapphire substrates, using ZrTi buffer layers to provide in-plane lattice-matching to hexagonal GaN. X-ray diffraction (XRD) as well as cross-section transmission electron microscopy (TEM) were used to assess the quality of the HEMT structure. The XRD 2θ scans showed full-width-at-half-maximum values of 0.16°, 0.07°, and 0.08° for ZrTi alloy, GaN buffer layer, and the entire HEMT structure, respectively. TEM studies of the GaN buffer layer and the AlN/ZrTi/AlN stack showed the importance of growing thin AlN buffer layers on the ZrTi layer prior to growth of the GaN buffermore » layer. The density of threading dislocations in the GaN channel layer of the HEMT structure was estimated to be in the 108 cm–2 range. The HEMT device exhibited a saturation drain current density of 820 mA/mm, and the channel of the fabricated HEMTs could be well modulated. A cutoff frequency (fT) of 8.9 GHz and a maximum frequency of oscillation (fmax) of 17.3 GHz were achieved for HEMTs with gate dimensions of 1 × 200 μm.« less

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

    SciTech Connect

    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. Strong geometrical effects in submillimeter selective area growth and light extraction of GaN light emitting diodes on sapphire

    DOE PAGES [OSTI]

    Tanaka, Atsunori; Chen, Renjie; Jungjohann, Katherine L.; Dayeh, Shadi A.

    2015-11-27

    Advanced semiconductor devices often utilize structural and geometrical effects to tailor their characteristics and improve their performance. Our detailed understanding of such geometrical effects in the epitaxial selective area growth of GaN on sapphire substrates is reported here, and we utilize them to enhance light extraction from GaN light emitting diodes. Systematic size and spacing effects were performed side-by-side on a single 2” sapphire substrate to minimize experimental sampling errors for a set of 144 pattern arrays with circular mask opening windows in SiO2. We show that the mask opening diameter leads to as much as 4 times increase inmore » the thickness of the grown layers for 20 μm spacings and that spacing effects can lead to as much as 3 times increase in thickness for a 350 μm dot diameter. We also observed that the facet evolution in comparison with extracted Ga adatom diffusion lengths directly influences the vertical and lateral overgrowth rates and can be controlled with pattern geometry. Lastly, such control over the facet development led to 2.5 times stronger electroluminescence characteristics from well-faceted GaN/InGaN multiple quantum well LEDs compared to non-faceted structures.« less

  9. Strong geometrical effects in submillimeter selective area growth and light extraction of GaN light emitting diodes on sapphire

    SciTech Connect

    Tanaka, Atsunori; Chen, Renjie; Jungjohann, Katherine L.; Dayeh, Shadi A.

    2015-11-27

    Advanced semiconductor devices often utilize structural and geometrical effects to tailor their characteristics and improve their performance. Our detailed understanding of such geometrical effects in the epitaxial selective area growth of GaN on sapphire substrates is reported here, and we utilize them to enhance light extraction from GaN light emitting diodes. Systematic size and spacing effects were performed side-by-side on a single 2” sapphire substrate to minimize experimental sampling errors for a set of 144 pattern arrays with circular mask opening windows in SiO2. We show that the mask opening diameter leads to as much as 4 times increase in the thickness of the grown layers for 20 μm spacings and that spacing effects can lead to as much as 3 times increase in thickness for a 350 μm dot diameter. We also observed that the facet evolution in comparison with extracted Ga adatom diffusion lengths directly influences the vertical and lateral overgrowth rates and can be controlled with pattern geometry. Lastly, such control over the facet development led to 2.5 times stronger electroluminescence characteristics from well-faceted GaN/InGaN multiple quantum well LEDs compared to non-faceted structures.

  10. Effect of postdeposition annealing on the electrical properties of ?-Ga{sub 2}O{sub 3} thin films grown on p-Si by plasma-enhanced atomic layer deposition

    SciTech Connect

    Altuntas, Halit; Donmez, Inci; Ozgit-Akgun, Cagla; Biyikli, Necmi

    2014-07-01

    Ga{sub 2}O{sub 3} dielectric thin films were deposited on (111)-oriented p-type silicon wafers by plasma-enhanced atomic layer deposition using trimethylgallium and oxygen plasma. Structural analysis of the Ga{sub 2}O{sub 3} thin films was carried out using grazing-incidence x-ray diffraction. As-deposited films were amorphous. Upon postdeposition annealing at 700, 800, and 900?C for 30?min under N{sub 2} ambient, films crystallized into ?-form monoclinic structure. Electrical properties of the ?-Ga{sub 2}O{sub 3} thin films were then investigated by fabricating and characterizing Al/?-Ga{sub 2}O{sub 3}/p-Si metaloxide-semiconductor capacitors. The effect of postdeposition annealing on the leakage current densities, leakage current conduction mechanisms, dielectric constants, flat-band voltages, reverse breakdown voltages, threshold voltages, and effective oxide charges of the capacitors were presented. The effective oxide charges (Q{sub eff}) were calculated from the capacitancevoltage (C-V) curves using the flat-band voltage shift and were found as 2.6??10{sup 12}, 1.9??10{sup 12}, and 2.5??10{sup 12} cm{sup ?2} for samples annealed at 700, 800, and 900?C, respectively. Effective dielectric constants of the films decreased with increasing annealing temperature. This situation was attributed to the formation of an interfacial SiO{sub 2} layer during annealing process. Leakage mechanisms in the regions where current increases gradually with voltage were well fitted by the Schottky emission model for films annealed at 700 and 900?C, and by the FrenkelPoole emission model for film annealed at 800?C. Leakage current density was found to improve with annealing temperature. ?-Ga{sub 2}O{sub 3} thin film annealed at 800?C exhibited the highest reverse breakdown field value.

  11. Highly mismatched crystalline and amorphous GaN(1-x)As(x) alloys in the whole composition range

    SciTech Connect

    Yu, K. M.; Novikov, S. V.; Broesler, R.; Demchenko, I. N.; Denlinger, J. D.; Liliental-Weber, Z.; Luckert, F.; Martin, R. W.; Walukiewicz, W.; Foxon, C. T.

    2009-08-29

    Alloying is a commonly accepted method to tailor properties of semiconductor materials for specific applications. Only a limited number of semiconductor alloys can be easily synthesized in the full composition range. Such alloys are, in general, formed of component elements that are well matched in terms of ionicity, atom size, and electronegativity. In contrast there is a broad class of potential semiconductor alloys formed of component materials with distinctly different properties. In most instances these mismatched alloys are immiscible under standard growth conditions. Here we report on the properties of GaN1-xAsx, a highly mismatched, immiscible alloy system that was successfully synthesized in the whole composition range using a nonequilibrium low temperature molecular beam epitaxy technique. The alloys are amorphous in the composition range of 0.17films have smooth morphology, homogeneous composition, and sharp, well defined optical absorption edges. The band gap energy varies in a broad energy range from ~;;3.4 eV in GaN to ~;;0.8 eV at x~;;0.85. The reduction in the band gap can be attributed primarily to the downward movement of the conduction band for alloys with x>0.2, and to the upward movement of the valence band for alloys with x<0.2. The unique features of the band structure offer an opportunity of using GaN1-xAsx alloys for various types of solar power conversion devices.

  12. Formation of GaN quantum dots by molecular beam epitaxy using NH{sub 3} as nitrogen source

    SciTech Connect

    Damilano, B. Brault, J.; Massies, J.

    2015-07-14

    Self-assembled GaN quantum dots (QDs) in Al{sub x}Ga{sub 1−x}N (0.3 ≤ x ≤ 1) were grown on c-plane sapphire and Si (111) substrates by molecular beam epitaxy using ammonia as nitrogen source. The QD formation temperature was varied from 650 °C to 800 °C. Surprisingly, the density and size of QDs formed in this temperature range are very similar. This has been explained by considering together experimental results obtained from reflection high-energy electron diffraction, atomic force microscopy, and photoluminescence to discuss the interplay between thermodynamics and kinetics in the QD formation mechanisms. Finally, possible ways to better control the QD optical properties are proposed.

  13. Counting molecular-beam grown graphene layers

    SciTech Connect

    Plaut, Annette S.; Wurstbauer, Ulrich; Pinczuk, Aron; Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York 10027 ; Garcia, Jorge M.; Pfeiffer, Loren N.

    2013-06-17

    We have used the ratio of the integrated intensity of graphene's Raman G peak to that of the silicon substrate's first-order optical phonon peak, accurately to determine the number of graphene layers across our molecular-beam (MB) grown graphene films. We find that these results agree well both, with those from our own exfoliated single and few-layer graphene flakes, and with the results of Koh et al.[ACS Nano 5, 269 (2011)]. We hence distinguish regions of single-, bi-, tri-, four-layer, etc., graphene, consecutively, as we scan coarsely across our MB-grown graphene. This is the first, but crucial, step to being able to grow, by such molecular-beam-techniques, a specified number of large-area graphene layers, to order.

  14. Determination of crystallographic orientation of lead-free piezoelectric (K,Na)NbO{sub 3} epitaxial thin films grown on SrTiO{sub 3} (100) surfaces

    SciTech Connect

    Yu, Qi; Zhu, Fang-Yuan; Cheng, Li-Qian; Wang, Ke; Li, Jing-Feng

    2014-03-10

    Crystallographic structure of sol-gel-processed lead-free (K,Na)NbO{sub 3} (KNN) epitaxial films on [100]-cut SrTiO{sub 3} single-crystalline substrates was investigated for a deeper understanding of its piezoelectric response. Lattice parameter measurement by high-resolution X-ray diffraction and transmission electron microscopy revealed that the orthorhombic KNN films on SrTiO{sub 3} (100) surfaces are [010] oriented (b-axis-oriented) rather than commonly identified c-axis orientation. Based on the crystallographic orientation and corresponding ferroelectric domain structure investigated by piezoresponse force microscopy, the superior piezoelectric property along b-axis of epitaxial KNN films than other orientations can be explained.

  15. Structural and optical properties of InGaN--GaN nanowire heterostructures grown by molecular beam epitaxy

    SciTech Connect

    Limbach, F.; Gotschke, T.; Stoica, T.; Calarco, R.; Sutter, E.; Ciston, J.; Cusco, R.; Artus, L.; Kremling, S.; Hofling, S.; Worschech, L.; Grutzmacher, D.

    2011-01-01

    InGaN/GaN nanowire (NW) heterostructures grown by plasma assisted molecular beam epitaxy were studied in comparison to their GaN and InGaN counterparts. The InGaN/GaN heterostructure NWs are composed of a GaN NW, a thin InGaN shell, and a multifaceted InGaN cap wrapping the top part of the GaN NW. High-resolution transmission electron microscopy (HRTEM) images taken from different parts of a InGaN/GaN NW show a wurtzite structure of the GaN core and the epitaxial InGaN shell around it, while additional crystallographic domains are observed whithin the InGaN cap region. Large changes in the lattice parameter along the wire, from pure GaN to higher In concentration demonstrate the successful growth of a complex InGaN/GaN NW heterostructure. Photoluminescence (PL) spectra of these heterostructure NW ensembles show rather broad and intense emission peak at 2.1 eV. However, μ-PL spectra measured on single NWs reveal a reduced broadening of the visible luminescence. The analysis of the longitudinal optical phonon Raman peak position and its shape reveal a variation in the In content between 20% and 30%, in agreement with the values estimated by PL and HRTEM investigations. The reported studies are important for understanding of the growth and properties of NW heterostructures suitable for applications in optoelectronics and photovoltaics.

  16. (11-22) semipolar InGaN emitters from green to amber on overgrown GaN on micro-rod templates

    SciTech Connect

    Bai, J. Xu, B.; Guzman, F. G.; Xing, K.; Gong, Y.; Hou, Y.; Wang, T.

    2015-12-28

    We demonstrate semipolar InGaN single-quantum-well light emitting diodes (LEDs) in the green, yellow-green, yellow and amber spectral region. The LEDs are grown on our overgrown semipolar (11-22) GaN on micro-rod array templates, which are fabricated on (11-22) GaN grown on m-plane sapphire. Electroluminescence measurements on the (11-22) green LED show a reduced blue-shift in the emission wavelength with increasing driving current, compared to a reference commercial c-plane LED. The blue-shifts for the yellow-green and yellow LEDs are also significantly reduced. All these suggest an effective suppression in quantum confined Stark effect in our (11-22) LEDs. On-wafer measurements yield a linear increase in the light output with the current, and external quantum efficiency demonstrates a significant improvement in the efficiency-droop compared to a commercial c-plane LED. Electro-luminescence polarization measurements show a polarization ratio of about 25% in our semipolar LEDs.

  17. Yellow luminescence and related deep states in undoped GaN

    SciTech Connect

    Calleja, E.; Sanchez, F.J.; Basak, D.; Sanchez-Garcia, M.A.; Munoz, E.; Izpura, I.; Calle, F.; Tijero, J.M.; Sanchez-Rojas, J.L.; Beaumont, B.; Lorenzini, P.; Gibart, P.

    1997-02-01

    Photocapacitance spectra in undoped, metal-organic vapor-phase-epitaxy-grown GaN layers, in a range of photon energies from 0.6 to 3.5 eV, reveal two main persistent features: a broad increase of the capacitance from 2.0 to 2.5 eV, and a steep {ital decrease} at 1 eV, only observed after a previous light exposure to photon energies above 2.5 eV. A deep trap (E{sub v}+1 eV) that captures photoelectrons from the valence band, after being emptied with photons above 2.5 eV, is proposed as the origin of these features. Optical-current deep-level transient spectroscopy results also show the presence of a trap at 0.94 eV {ital above} the valence band, {ital only} detected after light excitation with photon energies above 2.5 eV. A correlation is found between the {open_quotes}yellow band{close_quotes} luminescence intensity at 2.2 eV and the amplitude of the photocapacitance decrease at 1 eV, pointing to a deep trap at 1 eV {ital above} the valence band as the recombination path for the yellow band. The detection of the yellow band with below-the-gap photoluminescence excitation supports the proposed model. {copyright} {ital 1997} {ital The American Physical Society}

  18. Polycrystalline MBE-grown GaAs for solar cells

    SciTech Connect

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

    1997-02-01

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

  19. Polycrystalline MBE-grown GaAs for solar cells

    SciTech Connect

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

    1997-02-15

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

  20. Development of very high Jc in Ba(Fe1-xCox)2As2 thin films grown on CaF2

    SciTech Connect

    Tarantini, C.; Kametani, F.; Lee, S.; Jiang, J.; Weiss, J. D.; Jaroszynski, J.; Hellstrom, E. E.; Eom, C. B.; Larbalestier, D. C.

    2014-12-03

    Ba(Fe1-xCox)2As2 is the most tunable of the Fe-based superconductors (FBS) in terms of acceptance of high densities of self-assembled and artificially introduced pinning centres which are effective in significantly increasing the critical current density, Jc. Moreover, FBS are very sensitive to strain, which induces an important enhancement in critical temperature,Tc, of the material. In this study we demonstrate that strain induced by the substrate can further improve Jc of both single and multilayer films by more than that expected simply due to the increase in Tc. The multilayer deposition of Ba(Fe1-xCox)2As2 on CaF2 increases the pinning force density (Fp=Jc x μ₀H) by more than 60% compared to a single layer film, reaching a maximum of 84 GN/m3 at 22.5 T and 4.2 K, the highest value ever reported in any 122 phase.

  1. Biaxially oriented film on flexible polymeric substrate

    DOEpatents

    Finkikoglu, Alp T.; Matias, Vladimir

    2009-10-13

    A flexible polymer-based template having a biaxially oriented film grown on the surface of a polymeric substrate. The template having the biaxially oriented film can be used for further epitaxial growth of films of interest for applications such as photovoltaic cells, light emitting diodes, and the like. Methods of forming such a flexible template and providing the polymeric substrate with a biaxially oriented film deposited thereon are also described.

  2. This invention relates to methods of generating NP gallium nitride (GaN) across large areas (>1 cm.sup.2) with controlled pore diameters, pore density, and porosity. Also disclosed are methods of generating novel optoelectronic devices based on porous GaN. Additionally a layer transfer scheme to separate and create free-standing crystalline GaN thin layers is disclosed that enables a new device manufacturing paradigm involving substrate recycling. Other disclosed embodiments of this invention relate to fabrication of GaN based nanocrystals and the use of NP GaN electrodes for electrolysis, water splitting, or photosynthetic process applications.

    DOEpatents

    Zhang, Yu; Sun, Qian; Han, Jung

    2015-12-08

    This invention relates to methods of generating NP gallium nitride (GaN) across large areas (>1 cm.sup.2) with controlled pore diameters, pore density, and porosity. Also disclosed are methods of generating novel optoelectronic devices based on porous GaN. Additionally a layer transfer scheme to separate and create free-standing crystalline GaN thin layers is disclosed that enables a new device manufacturing paradigm involving substrate recycling. Other disclosed embodiments of this invention relate to fabrication of GaN based nanocrystals and the use of NP GaN electrodes for electrolysis, water splitting, or photosynthetic process applications.

  3. Structural and optical properties of InGaN--GaN nanowire heterostructures grown by molecular beam epitaxy

    DOE PAGES [OSTI]

    Limbach, F.; Gotschke, T.; Stoica, T.; Calarco, R.; Sutter, E.; Ciston, J.; Cusco, R.; Artus, L.; Kremling, S.; Hofling, S.; et al

    2011-01-01

    InGaN/GaN nanowire (NW) heterostructures grown by plasma assisted molecular beam epitaxy were studied in comparison to their GaN and InGaN counterparts. The InGaN/GaN heterostructure NWs are composed of a GaN NW, a thin InGaN shell, and a multifaceted InGaN cap wrapping the top part of the GaN NW. High-resolution transmission electron microscopy (HRTEM) images taken from different parts of a InGaN/GaN NW show a wurtzite structure of the GaN core and the epitaxial InGaN shell around it, while additional crystallographic domains are observed whithin the InGaN cap region. Large changes in the lattice parameter along the wire, from pure GaNmore » to higher In concentration demonstrate the successful growth of a complex InGaN/GaN NW heterostructure. Photoluminescence (PL) spectra of these heterostructure NW ensembles show rather broad and intense emission peak at 2.1 eV. However, μ-PL spectra measured on single NWs reveal a reduced broadening of the visible luminescence. The analysis of the longitudinal optical phonon Raman peak position and its shape reveal a variation in the In content between 20% and 30%, in agreement with the values estimated by PL and HRTEM investigations. The reported studies are important for understanding of the growth and properties of NW heterostructures suitable for applications in optoelectronics and photovoltaics.« less

  4. Structural and optical properties of InGaNGaN nanowire heterostructures grown by molecular beam epitaxy

    DOE PAGES [OSTI]

    Limbach, F.; Gotschke, T.; Stoica, T.; Calarco, R.; Sutter, E.; Ciston, J.; Cusco, R.; Artus, L.; Kremling, S.; Ho?fling, S.; et al

    2011-01-01

    InGaN/GaN nanowire (NW) heterostructures grown by plasma assisted molecular beam epitaxy were studied in comparison to their GaN and InGaN counterparts. The InGaN/GaN heterostructure NWs are composed of a GaN NW, a thin InGaN shell, and a multifaceted InGaN cap wrapping the top part of the GaN NW. High-resolution transmission electron microscopy (HRTEM) images taken from different parts of a InGaN/GaN NW show a wurtzite structure of the GaN core and the epitaxial InGaN shell around it, while additional crystallographic domains are observed whithin the InGaN cap region. Large changes in the lattice parameter along the wire, from pure GaNmoreto higher In concentration demonstrate the successful growth of a complex InGaN/GaN NW heterostructure. Photoluminescence (PL) spectra of these heterostructure NW ensembles show rather broad and intense emission peak at 2.1 eV. However, ?-PL spectra measured on single NWs reveal a reduced broadening of the visible luminescence. The analysis of the longitudinal optical phonon Raman peak position and its shape reveal a variation in the In content between 20% and 30%, in agreement with the values estimated by PL and HRTEM investigations. The reported studies are important for understanding of the growth and properties of NW heterostructures suitable for applications in optoelectronics and photovoltaics.less

  5. Photo-induced wettability of TiO{sub 2} film with Au buffer layer

    SciTech Connect

    Purkayastha, Debarun Dhar; Sangani, L. D. Varma; Krishna, M. Ghanashyam; Madhurima, V.

    2014-04-24

    The effect of thickness of Au buffer layer (15-25 nm) between TiO{sub 2} film and substrate on the wettability of TiO{sub 2} films is reported. TiO{sub 2} films grown on Au buffer layer have a higher contact angle of 96-;100 as compared to 47.6o for the film grown without buffer layer. The transition from hydrophobicity to hydrophilicity under UV irradiation occurs within 10 min. for the buffer layered films whereas it is almost 30 min. for the film grown without buffer layer. The enhanced photo induced hydrophilicity is shown to be surface energy driven.

  6. Dislocation confinement in the growth of Na flux GaN on metalorganic...

    Office of Scientific and Technical Information (OSTI)

    Dislocation confinement in the growth of Na flux GaN on metalorganic chemical vapor deposition-GaN Citation Details In-Document Search Title: Dislocation confinement in the growth ...

  7. Growth and Band Offsets of Epitaxial Lanthanide Oxides on GaN...

    Office of Scientific and Technical Information (OSTI)

    M.T.T., 60 (6) (2012) 3 Jon Ihlefeld, Sandia National Laboratories Electronic Materials ... Undoped GaN Undoped AlGaN Doped AlGaN 2D Electron Gas Enhancement Mode (nominally ...

  8. Continuous and Dynamic Lasing Tuning of Single GaN Nanowires with

    Office of Scientific and Technical Information (OSTI)

    sub-nanometer resolution using Hydrostatic Pressure. (Conference) | SciTech Connect Continuous and Dynamic Lasing Tuning of Single GaN Nanowires with sub-nanometer resolution using Hydrostatic Pressure. Citation Details In-Document Search Title: Continuous and Dynamic Lasing Tuning of Single GaN Nanowires with sub-nanometer resolution using Hydrostatic Pressure. Abstract not provided. Authors: Liu, Sheng ; Brener, Igal ; Wang, George T. ; Li, Changyi ; Brueck, Steven R. J. Publication Date:

  9. Hybrid device based on GaN nanoneedles and MEH-PPV/PEDOT:PSS polymer

    SciTech Connect

    Shin, Min Jeong; Gwon, Dong-Oh; Lee, Chan-Mi; Lee, Gang Seok; Jeon, In-Jun; Ahn, Hyung Soo; Yi, Sam Nyung; Ha, Dong Han

    2015-08-15

    Highlights: • A hybrid device was demonstrated by using MEH-PPV, PEDOT:PSS, and GaN nanoneedles. • I–V curve of the hybrid device showed its rectification behaviour, similar to a diode. • EL peak originated by the different potential barriers at MEH-PPV and GaN interface. - Abstract: A hybrid device that combines the properties of organic and inorganic semiconductors was fabricated and studied. It incorporated poly[2-methoxy-5-(2-ethylhexyloxy)- 1,4-phenylenevinylene] (MEH-PPV) and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as organic polymers and GaN nanoneedles as an inorganic semiconductor. Layers of the two polymers were spin coated on to the GaN nanoneedles. The one peak in the electroluminescence spectrum originated from the MEH-PPV layer owing to the different potential barriers of electrons and holes at its interface with the GaN nanoneedles. However, the photoluminescence spectrum showed peaks due to both GaN nanoneedles and MEH-PPV. Such hybrid structures, suitably developed, might be able to improve the efficiency of optoelectronic devices.

  10. Intrinsic polarization control in rectangular GaN nanowire lasers

    DOE PAGES [OSTI]

    Li, Changyi; Liu, Sheng; Luk, Ting S.; Figiel, Jeffrey J.; Brener, Igal; Brueck, S. R. J.; Wang, George T.

    2016-02-01

    In this study, we demonstrate intrinsic, linearly polarized lasing from single GaN nanowires using cross-sectional shape control. A two-step top-down fabrication approach was employed to create straight nanowires with controllable rectangular cross-sections. A clear lasing threshold of 444kW/cm2 and a narrow spectral line width of 0.16 nm were observed under optical pumping at room temperature, indicating the onset of lasing. The polarization was along the short dimension (y-direction) of the nanowire due to the higher transverse confinement factors for y-polarized transverse modes resulting from the rectangular nanowire cross-section. The results show that cross-sectioned shape control can enable inherent control overmore » the polarization of nanowire lasers without additional environment requirements, such as placement onto lossy substrates.« less

  11. Size dictated thermal conductivity of GaN

    DOE PAGES [OSTI]

    Thomas Edwin Beechem; McDonald, Anthony E.; Fuller, Elliot James; Talin, Albert Alec; Rost, Christina M.; Maria, Jon -Paul; Gaskins, John T.; Hopkins, Patrick E.; Allerman, Andrew A.

    2016-04-01

    The thermal conductivity on n- and p-type doped gallium nitride (GaN) epilayers having thickness of 3-4 μm was investigated using time domain thermoreflectance (TDTR). Despite possessing carrier concentrations ranging across 3 decades (1015 – 1018 cm–3), n-type layers exhibit a nearly constant thermal conductivity of 180 W/mK. The thermal conductivity of p-type epilayers, in contrast, reduces from 160 to 110 W/mK with increased doping. These trends–and their overall reduction relative to bulk–are explained leveraging established scattering models where it is shown that size effects play a primary role in limiting thermal conductivity for layers even tens of microns thick. GaNmore » device layers, even of pristine quality, will therefore exhibit thermal conductivities less than the bulk value of 240 W/mK owing to their finite thickness.« less

  12. Structural and morphological evolution of gallium nitride nanorods grown by chemical beam epitaxy

    SciTech Connect

    Kuo, Shou-Yi; Lai, Fang-I; Chen, Wei-Chun; Hsiao, Chien-Nan; Lin, Woei-Tyng

    2009-07-15

    The morphological and structural evolution is presented for GaN nanorods grown by chemical beam epitaxy on (0001) Al{sub 2}O{sub 3} substrates. Their structural and optical properties are investigated by x-ray diffraction, scanning and transmission electron microscopy, and temperature-dependent photoluminescence measurements. While increasing the growth temperature and the flow rate of radio-frequency nitrogen radical, the three-dimensional growth mode will be enhanced to form one-dimensional nanostructures. The high density of well-aligned nanorods with a diameter of 30-50 nm formed uniformly over the entire sapphire substrate. The x-ray diffraction patterns and transmission electron microscopic images indicate that the self-assembled GaN nanorods are a pure single crystal and preferentially oriented in the c-axis direction. Particularly, the ''S-shape'' behavior with localization of {approx}10 meV observed in the temperature-dependent photoluminescence might be ascribed to the fluctuation in crystallographic defects and composition.

  13. Investigation of the optical properties of MoS{sub 2} thin films...

    Office of Scientific and Technical Information (OSTI)

    ellipsometry Spectroscopic ellipsometry (SE) characterization of layered transition metal dichalcogenide (TMD) thin films grown by vapor phase sulfurization is reported. By...

  14. GaN Initiative for Grid Applications (GIGA)

    SciTech Connect

    Turner, George

    2015-07-03

    For nearly 4 ½ years, MIT Lincoln Laboratory (MIT/LL) led a very successful, DoE-funded team effort to develop GaN-on-Si materials and devices, targeting high-voltage (>1 kV), high-power, cost-effective electronics for grid applications. This effort, called the GaN Initiative for Grid Applications (GIGA) program, was initially made up of MIT/LL, the MIT campus group of Prof. Tomas Palacios (MIT), and the industrial partner M/A Com Technology Solutions (MTS). Later in the program a 4th team member was added (IQE MA) to provide commercial-scale GaN-on-Si epitaxial materials. A basic premise of the GIGA program was that power electronics, for ubiquitous utilization -even for grid applications - should be closer in cost structure to more conventional Si-based power electronics. For a number of reasons, more established GaN-on-SiC or even SiC-based power electronics are not likely to reach theses cost structures, even in higher manufacturing volumes. An additional premise of the GIGA program was that the technical focus would be on materials and devices suitable for operating at voltages > 1 kV, even though there is also significant commercial interest in developing lower voltage (< 1 kV), cost effective GaN-on-Si devices for higher volume applications, like consumer products. Remarkable technical progress was made during the course of this program. Advances in materials included the growth of high-quality, crack-free epitaxial GaN layers on large-diameter Si substrates with thicknesses up to ~5 μm, overcoming significant challenges in lattice mismatch and thermal expansion differences between Si and GaN in the actual epitaxial growth process. Such thick epilayers are crucial for high voltage operation of lateral geometry devices such as Schottky barrier (SB) diodes and high electron mobility transistors (HEMTs). New “Normally-Off” device architectures were demonstrated – for safe operation of power electronics circuits. The trade-offs between lateral and

  15. Nitrogen doped zinc oxide thin film

    SciTech Connect

    Li, Sonny X.

    2003-12-15

    To summarize, polycrystalline ZnO thin films were grown by reactive sputtering. Nitrogen was introduced into the films by reactive sputtering in an NO{sub 2} plasma or by N{sup +} implantation. All ZnO films grown show n-type conductivity. In unintentionally doped ZnO films, the n-type conductivities are attributed to Zn{sub i}, a native shallow donor. In NO{sub 2}-grown ZnO films, the n-type conductivity is attributed to (N{sub 2}){sub O}, a shallow double donor. In NO{sub 2}-grown ZnO films, 0.3 atomic % nitrogen was found to exist in the form of N{sub 2}O and N{sub 2}. Upon annealing, N{sub 2}O decomposes into N{sub 2} and O{sub 2}. In furnace-annealed samples N{sub 2} redistributes diffusively and forms gaseous N{sub 2} bubbles in the films. Unintentionally doped ZnO films were grown at different oxygen partial pressures. Zni was found to form even at oxygen-rich condition and led to n-type conductivity. N{sup +} implantation into unintentionally doped ZnO film deteriorates the crystallinity and optical properties and leads to higher electron concentration. The free electrons in the implanted films are attributed to the defects introduced by implantation and formation of (N{sub 2}){sub O} and Zni. Although today there is still no reliable means to produce good quality, stable p-type ZnO material, ZnO remains an attractive material with potential for high performance short wavelength optoelectronic devices. One may argue that gallium nitride was in a similar situation a decade ago. Although we did not obtain any p-type conductivity, we hope our research will provide a valuable reference to the literature.

  16. Epitaxial growth of high quality WO3 thin films

    DOE PAGES [OSTI]

    Leng, X.; Pereiro, J.; Strle, J.; Bollinger, A. T.; Bozovic, I.

    2015-09-09

    We have grown epitaxial WO3 films on various single-crystal substrates using radio-frequency (RF) magnetron sputtering. While pronounced surface roughness is observed in films grown on LaSrAlO4 substrates, films grown on YAlO3 substrates show atomically flat surfaces, as demonstrated by atomic force microscopy (AFM) and X-ray diffraction (XRD) measurements. The crystalline structure has been confirmed to be monoclinic by symmetric and skew-symmetric XRD. Furthermore, the dependence of the growth modes and the surface morphology on the lattice mismatch is discussed.

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

    SciTech Connect

    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.

  18. High Quality, Low Cost Bulk Gallium Nitride Substrates Grown...

    Office of Energy Efficiency and Renewable Energy (EERE) (indexed site)

    of crystalline GaN growth in ESG Results and Accomplishments HRXRD vs reference SEM surface view 0 20 40 60 80 100 120 140 160 180 200 0 10 20 30 40 50 Deposition rate ...

  19. Comparative study of polar and semipolar (112?2) InGaN layers grown by metalorganic vapour phase epitaxy

    SciTech Connect

    Dinh, Duc V. E-mail: peter.parbrook@tyndall.ie; Zubialevich, V. Z.; Oehler, F.; Kappers, M. J.; Humphreys, C. J.; Alam, S. N.; Parbrook, P. J. E-mail: peter.parbrook@tyndall.ie; Caliebe, M.; Scholtz, F.

    2014-10-21

    InGaN layers were grown simultaneously on (112?2) GaN and (0001) GaN templates by metalorganic vapour phase epitaxy. At higher growth temperature (?750C), the indium content (<15%) of the (112?2) and (0001) InGaN layers was similar. However, for temperatures less than 750C, the indium content of the (112?2) InGaN layers (15%26%) were generally lower than those with (0001) orientation (15%32%). The compositional deviation was attributed to the different strain relaxations between the (112?2) and (0001) InGaN layers. Room temperature photoluminescence measurements of the (112?2) InGaN layers showed an emission wavelength that shifts gradually from 380 nm to 580 nm with decreasing growth temperature (or increasing indium composition). The peak emission wavelength of the (112?2) InGaN layers with an indium content of more than 10% blue-shifted a constant value of ?(5060) nm when using higher excitation power densities. This blue-shift was attributed to band filling effects in the layers.

  20. Optical and structural properties of sputtered CdS films for thin film solar cell applications

    SciTech Connect

    Kim, Donguk; Park, Young; Kim, Minha; Choi, Youngkwan; Park, Yong Seob; Lee, Jaehyoeng

    2015-09-15

    Graphical abstract: Photo current–voltage curves (a) and the quantum efficiency (QE) (b) for the solar cell with CdS film grown at 300 °C. - Highlights: • CdS thin films were grown by a RF magnetron sputtering method. • Influence of growth temperature on the properties of CdS films was investigated. • At higher T{sub g}, the crystallinity of the films improved and the grains enlarged. • CdS/CdTe solar cells with efficiencies of 9.41% were prepared at 300 °C. - Abstract: CdS thin films were prepared by radio frequency magnetron sputtering at various temperatures. The effects of growth temperature on crystallinity, surface morphology and optical properties of the films were characterized with X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Raman spectra, UV–visible spectrophotometry, and photoluminescence (PL) spectra. As the growth temperature was increased, the crystallinity of the sputtered CdS films was improved and the grains were enlarged. The characteristics of CdS/CdTe thin film solar cell appeared to be significantly influenced by the growth temperature of the CdS films. Thin film CdS/CdTe solar cells with efficiencies of 9.41% were prepared at a growth temperature of 300 °C.

  1. 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

    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 (λ = 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 (2.33–1.92), 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

  2. Nanocomposite films

    DOEpatents

    Mitlin, David; , Ophus, Colin; Evoy, Stephane; Radmilovic, Velimir; Mohammadi, Reza; Westra, Ken; Nelson-Fitzpatrick, Nathaniel; Lee, Zonghoon

    2010-07-20

    A thin-film composition of nanocrystal molybdenum in an amorphous metallic matrix may be formed by co-sputtering Mo with aluminum or nickel. NEMS cantilevers may be formed from the film. The films exhibit high nanoindentation hardness and a reduction in roughness and intrinsic stress, while maintaining resistivity in the metallic range.

  3. Performance and breakdown characteristics of irradiated vertical power GaN P-i-N diodes

    DOE PAGES [OSTI]

    King, M. P.; Armstrong, A. M.; Dickerson, J. R.; Vizkelethy, G.; Fleming, R. M.; Campbell, J.; Wampler, W. R.; Kizilyalli, I. C.; Bour, D. P.; Aktas, O.; et al

    2015-10-29

    Electrical performance and defect characterization of vertical GaN P-i-N diodes before and after irradiation with 2.5 MeV protons and neutrons is investigated. Devices exhibit increase in specific on-resistance following irradiation with protons and neutrons, indicating displacement damage introduces defects into the p-GaN and n- drift regions of the device that impact on-state device performance. The breakdown voltage of these devices, initially above 1700 V, is observed to decrease only slightly for particle fluence <; 1013 cm-2. Furthermore, the unipolar figure of merit for power devices indicates that while the on-resistance and breakdown voltage degrade with irradiation, vertical GaN P-i-Ns remainmore » superior to the performance of the best available, unirradiated silicon devices and on-par with unirradiated modern SiC-based power devices.« less

  4. Anisotropy of two-photon absorption and free-carrier effect in nonpolar GaN

    SciTech Connect

    Fang, Yu; Zhou, Feng; Yang, Junyi; Wu, Xingzhi; Xiao, Zhengguo; Li, Zhongguo; Song, Yinglin

    2015-03-30

    We reported a systematic study about the anisotropic optical nonlinearities in bulk m-plane and a-plane GaN crystals by Z-scan and pump-probe with phase object methods under picosecond at 532 nm. The two-photon absorption coefficient, which was measured as a function of polarization angle, exhibited oscillation curves with a period of π/2, indicating a highly polarized optical third-order nonlinearity in both nonpolar GaN samples. Furthermore, free-carrier absorption revealed stronger hole-related absorption for E⊥c than for E//c probe polarization. In contrast, free-carrier refraction was found almost isotropic due to electron-related refraction in the isotropic conduction bands.

  5. High voltage and high current density vertical GaN power diodes

    SciTech Connect

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

    2016-01-01

    We report on the realization of a GaN high voltage vertical p-n diode operating at > 3.9 kV breakdown with a specific on-resistance < 0.9 mΩ.cm2. Diodes achieved a forward current of 1 A for on-wafer, DC measurements, corresponding to a current density > 1.4 kA/cm2. An effective critical electric field of 3.9 MV/cm was estimated for the devices from analysis of the forward and reverse current-voltage characteristics. Furthermore this suggests that the fundamental limit to the GaN critical electric field is significantly greater than previously believed.

  6. High voltage and high current density vertical GaN power diodes

    DOE PAGES [OSTI]

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

    2016-01-01

    We report on the realization of a GaN high voltage vertical p-n diode operating at > 3.9 kV breakdown with a specific on-resistance < 0.9 mΩ.cm2. Diodes achieved a forward current of 1 A for on-wafer, DC measurements, corresponding to a current density > 1.4 kA/cm2. An effective critical electric field of 3.9 MV/cm was estimated for the devices from analysis of the forward and reverse current-voltage characteristics. Furthermore this suggests that the fundamental limit to the GaN critical electric field is significantly greater than previously believed.

  7. HIGH-QUALITY, LOW-COST BULK GALLIUM NITRIDE SUBSTRATES GROWN BY THE ELECTROCHEMICAL SOLUTION GROWTH METHOD

    Energy.gov [DOE]

    To develop ESG into a viable bulk growth process for GaN that is more scalable to large-area wafer manufacturing and able to produce cost-effective, high-quality bulk GaN substrates.

  8. Space-and-time-resolved spectroscopy of single GaN nanowires

    SciTech Connect

    Upadhya, Prashanth C.; Martinez, Julio A.; Li, Qiming; Wang, George T.; Swartzentruber, Brian S.; Taylor, Antoinette J.; Prasankumar, Rohit P.

    2015-06-29

    Gallium nitride nanowires have garnered much attention in recent years due to their attractive optical and electrical properties. An understanding of carrier transport, relaxation, and recombination in these quasi-one-dimensional nanosystems is therefore important in optimizing them for various applications. Here, we present ultrafast optical microscopic measurements on single GaN nanowires. Our experiments, performed while varying the light polarization, excitation fluence, and position, give insight into the mechanisms governing carrier dynamics in these nanosystems.

  9. Vertical GaN power diodes with a bilayer edge termination

    SciTech Connect

    Dickerson, Jeramy R.; Allerman, Andrew A.; Bryant, Benjamin N.; Fischer, Arthur J.; King, Michael P.; Moseley, Michael W.; Armstrong, Andrew M.; Kaplar, Robert J.; Kizilyalli, Isik C.; Aktas, Ozgur; Wierer, Jr., Jonathan J.

    2015-12-07

    Vertical GaN power diodes with a bilayer edge termination (ET) are demonstrated. The GaN p-n junction is formed on a low threading dislocation defect density (104 - 105 cm-2) GaN substrate, and has a 15-μm-thick n-type drift layer with a free carrier concentration of 5 × 1015 cm-3. The ET structure is formed by N implantation into the p+-GaN epilayer just outside the p-type contact to create compensating defects. The implant defect profile may be approximated by a bilayer structure consisting of a fully compensated layer near the surface, followed by a 90% compensated (p) layer near the n-type drift region. These devices exhibit avalanche breakdown as high as 2.6 kV at room temperature. In addition simulations show that the ET created by implantation is an effective way to laterally distribute the electric field over a large area. This increases the voltage at which impact ionization occurs and leads to the observed higher breakdown voltages.

  10. Vertical GaN power diodes with a bilayer edge termination

    DOE PAGES [OSTI]

    Dickerson, Jeramy R.; Allerman, Andrew A.; Bryant, Benjamin N.; Fischer, Arthur J.; King, Michael P.; Moseley, Michael W.; Armstrong, Andrew M.; Kaplar, Robert J.; Kizilyalli, Isik C.; Aktas, Ozgur; et al

    2015-12-07

    Vertical GaN power diodes with a bilayer edge termination (ET) are demonstrated. The GaN p-n junction is formed on a low threading dislocation defect density (104 - 105 cm-2) GaN substrate, and has a 15-μm-thick n-type drift layer with a free carrier concentration of 5 × 1015 cm-3. The ET structure is formed by N implantation into the p+-GaN epilayer just outside the p-type contact to create compensating defects. The implant defect profile may be approximated by a bilayer structure consisting of a fully compensated layer near the surface, followed by a 90% compensated (p) layer near the n-type driftmore » region. These devices exhibit avalanche breakdown as high as 2.6 kV at room temperature. In addition simulations show that the ET created by implantation is an effective way to laterally distribute the electric field over a large area. This increases the voltage at which impact ionization occurs and leads to the observed higher breakdown voltages.« less

  11. Formation of manganese {delta}-doped atomic layer in wurtzite GaN

    SciTech Connect

    Shi Meng; Chinchore, Abhijit; Wang Kangkang; Mandru, Andrada-Oana; Liu Yinghao; Smith, Arthur R.

    2012-09-01

    We describe the formation of a {delta}-doped manganese layer embedded within c-plane wurtzite gallium nitride using a special molecular beam epitaxy growth process. Manganese is first deposited on the gallium-poor GaN (0001) surface, forming a {radical}(3) Multiplication-Sign {radical}(3)-R30 Degree-Sign reconstructed phase. This well-defined surface reconstruction is then nitrided using plasma nitridation, and gallium nitride is overgrown. The manganese content of the {radical}(3) Multiplication-Sign {radical}(3)-R30 Degree-Sign phase, namely one Mn per each {radical}(3) Multiplication-Sign {radical}(3)-R30 Degree-Sign unit cell, implies that the MnGaN alloy layer has a Mn concentration of up to 33%. The structure and chemical content of the surface are monitored beginning from the initial growth stage up through the overgrowth of 20 additional monolayers (MLs) of GaN. An exponential-like drop-off of the Mn signal with increasing GaN monolayers, as measured by Auger electron spectroscopy, indicates that the highly concentrated Mn layer remains at the {delta}-doped interface. A model of the resultant {delta}-doped structure is formulated based on the experimental data, and implications for possible spintronic applications are discussed.

  12. Theoretical and experimental study of dynamics of photoexcited carriers in GaN

    SciTech Connect

    Shishehchi, Sara; Bellotti, Enrico; Rudin, Sergey; Garrett, Gregory A.; Wraback, Michael

    2013-12-21

    We present a theoretical and experimental study of the sub-picosecond dynamics of photo-excited carriers in GaN. In the theoretical model, interaction with an external ultrafast laser pulse is treated coherently and to account for the scattering mechanisms and dephasing processes, a generalized Monte-Carlo simulation is used. The scattering mechanisms included are carrier interactions with polar optical phonons and acoustic phonons, and carrier-carrier Coulomb interactions. We study the effect of different scattering mechanisms on the carrier densities. In the case that the excitation energy satisfies the threshold for polar optical scattering, phonon contribution is the dominant process in relaxing the system, otherwise, carrier-carrier mechanism is dominant. Furthermore, we present the temperature and pulse power dependent normalized luminescence intensity. The results are presented over a range of temperatures, electric field, and excitation energy of the laser pulse. For comparison, we also report the experimental time-resolved photoluminescence studies on GaN samples. There is a good agreement between the simulation and experiment in normalized luminescence intensity results. Therefore, we show that we can explain the dynamics of the photo-excited carriers in GaN by including only carrier-carrier and carrier-phonon interactions and a relatively simple two-band electronic structure model.

  13. Low-energy electro- and photo-emission spectroscopy of GaN materials and devices

    SciTech Connect

    Piccardo, Marco; Weisbuch, Claude; Iveland, Justin; Nakamura, Shuji; Speck, James S.; Martinelli, Lucio Peretti, Jacques; Choi, Joo Won

    2015-03-21

    In hot-electron semiconductor devices, carrier transport extends over a wide range of conduction states, which often includes multiple satellite valleys. Electrical measurements can hardly give access to the transport processes over such a wide range without resorting to models and simulations. An alternative experimental approach however exists which is based on low-energy electron spectroscopy and provides, in a number of cases, very direct and selective information on hot-electron transport mechanisms. Recent results obtained in GaN crystals and devices by electron emission spectroscopy are discussed. Using near-band-gap photoemission, the energy position of the first satellite valley in wurtzite GaN is directly determined. By electro-emission spectroscopy, we show that the measurement of the electron spectrum emitted from a GaN p-n junction and InGaN/GaN light-emitting diodes (LEDs) under electrical injection of carriers provides a direct observation of transport processes in these devices. In particular, at high injected current density, high-energy features appear in the electro-emission spectrum of the LEDs showing that Auger electrons are being generated in the active region. These measurements allow us identifying the microscopic mechanism responsible for droop which represents a major hurdle for widespread adoption of solid-state lighting.

  14. Epitaxial growth of high quality WO3 thin films

    SciTech Connect

    Leng, X.; Pereiro, J.; Strle, J.; Bollinger, A. T.; Bozovic, I.

    2015-09-09

    We have grown epitaxial WO3 films on various single-crystal substrates using radio-frequency (RF) magnetron sputtering. While pronounced surface roughness is observed in films grown on LaSrAlO4 substrates, films grown on YAlO3 substrates show atomically flat surfaces, as demonstrated by atomic force microscopy (AFM) and X-ray diffraction (XRD) measurements. The crystalline structure has been confirmed to be monoclinic by symmetric and skew-symmetric XRD. Furthermore, the dependence of the growth modes and the surface morphology on the lattice mismatch is discussed.

  15. Growth process for gallium nitride porous nanorods

    DOEpatents

    Wildeson, Isaac Harshman; Sands, Timothy David

    2015-03-24

    A GaN nanorod and formation method. Formation includes providing a substrate having a GaN film, depositing SiN.sub.x on the GaN film, etching a growth opening through the SiN.sub.x and into the GaN film, growing a GaN nanorod through the growth opening, the nanorod having a nanopore running substantially through its centerline. Focused ion beam etching can be used. The growing can be done using organometallic vapor phase epitaxy. The nanopore diameter can be controlled using the growth opening diameter or the growing step duration. The GaN nanorods can be removed from the substrate. The SiN.sub.x layer can be removed after the growing step. A SiO.sub.x template can be formed on the GaN film and the GaN can be grown to cover the SiO.sub.x template before depositing SiN.sub.x on the GaN film. The SiO.sub.x template can be removed after growing the nanorods.

  16. Origins of low energy-transfer efficiency between patterned GaN quantum well and CdSe quantum dots

    SciTech Connect

    Xu, Xingsheng

    2015-03-02

    For hybrid light emitting devices (LEDs) consisting of GaN quantum wells and colloidal quantum dots, it is necessary to explore the physical mechanisms causing decreases in the quantum efficiencies and the energy transfer efficiency between a GaN quantum well and CdSe quantum dots. This study investigated the electro-luminescence for a hybrid LED consisting of colloidal quantum dots and a GaN quantum well patterned with photonic crystals. It was found that both the quantum efficiency of colloidal quantum dots on a GaN quantum well and the energy transfer efficiency between the patterned GaN quantum well and the colloidal quantum dots decreased with increases in the driving voltage or the driving time. Under high driving voltages, the decreases in the quantum efficiency of the colloidal quantum dots and the energy transfer efficiency can be attributed to Auger recombination, while those decreases under long driving time are due to photo-bleaching and Auger recombination.

  17. Utilization of native oxygen in Eu(RE)-doped GaN for enabling device compatibility in optoelectronic applications

    DOE PAGES [OSTI]

    Mitchell, Brandon; Timmerman, D.; Poplawsky, Jonathan D.; Zhu, W.; Lee, D.; Wakamatsu, R.; Takatsu, J.; Matsuda, M.; Guo, Wei; Lorenz, K.; et al

    2016-01-04

    The detrimental influence of oxygen on the performance and reliability of V/III nitride based devices is well known. However, the influence of oxygen on the nature of the incorporation of other co-dopants, such as rare earth ions, has been largely overlooked in GaN. Here, we report the first comprehensive study of the critical role that oxygen has on Eu in GaN, as well as atomic scale observation of diffusion and local concentration of both atoms in the crystal lattice. We find that oxygen plays an integral role in the location, stability, and local defect structure around the Eu ions thatmore » were doped into the GaN host. Although the availability of oxygen is essential for these properties, it renders the material incompatible with GaN-based devices. However, the utilization of the normally occurring oxygen in GaN is promoted through structural manipulation, reducing its concentration by 2 orders of magnitude, while maintaining both the material quality and the favorable optical properties of the Eu ions. Furthermore, these findings open the way for full integration of RE dopants for optoelectronic functionalities in the existing GaN platform.« less

  18. Film Vault

    U.S. Department of Energy (DOE) - all webpages (Extended Search)

    Volume One Film Collection Volume Two 75th Anniversary Hydropower in the Northwest Woody Guthrie Videos Strategic Direction Branding & Logos Power of the River History Book...

  19. Ab initio study on noncompensated CrO codoping of GaN for enhanced solar energy conversion

    SciTech Connect

    Pan, Hui; Gu, Baohua; Eres, Gyula; Zhang, Zhenyu

    2010-03-01

    We describe a novel photocatalyst obtained by codoping GaN with CrO, according to a new "noncompensated" codoping concept based on first-principles calculations. The approach enables controllable narrowing of the GaN band gap with significantly enhanced carrier mobility and photocatalytic activity in the visible light region and thus offers immense potential for application in solar energy conversion, water splitting, and a variety of solar-assisted photocatalysis. Our calculations indicate that the formation energy for the cation doping is greatly reduced by noncompensated codoping with an anion. Although Cr doping alone can split the band gap with the formation of an intermediate band, the mobility is low due to carrier trapping by the localized states. The first-principles calculations also demonstrate that CrO codoping of GaN shifts the Fermi level into the conduction band resulting in high carrier density and mobility.

  20. Dispersion and absorption of longitudinal electro-kinetic wave in ion-implanted GaN semiconductor plasmas

    SciTech Connect

    Soni, Dilip; Sharma, Giriraj; Saxena, Ajay; Jadhav, Akhilesh

    2015-07-31

    An analytical study on propagation characteristics of longitudinal electro-kinetic (LEK) waves is presented. Based on multi-fluid model of plasma, we have derived a dispersion relation for LEK waves in colloid laden GaN semiconductor plasmas. It is assumed that ions are implanted to form colloids in the GaN sample. The colloids are continuously bombarded by the plasma particles and stick on them, but they acquire a net negative charge due to relatively higher mobility of electrons. It is found from the dispersion relation that the presence of charged colloids not only modifies the existing modes but also supports new novel modes of LEKWs. It is hoped that the study would enhance understanding on dispersion and absorption of LEKWs and help in singling out the appropriate configurations in which GaN crystal would be better suited for fabrication of microwave devices.

  1. Q-factor of (In,Ga)N containing III-nitride microcavity grown by multiple deposition techniques

    SciTech Connect

    Gačević, Ž. Calleja, E.; Réveret, F.

    2013-12-21

    A 3λ/2 (In,Ga)N/GaN resonant cavity, designed for ∼415 nm operation, is grown by molecular beam epitaxy and is sandwiched between a 39.5-period (In,Al)N/GaN distributed Bragg reflector (DBR), grown on c-plane GaN-on-sapphire pseudo-substrate by metal-organic vapor phase epitaxy and an 8-period SiO{sub 2}/ZrO{sub 2} DBR, deposited by electron beam evaporation. Optical characterization reveals an improvement in the cavity emission spectral purity of approximately one order of magnitude due to resonance effects. The combination of spectrophotometric and micro-reflectivity measurements confirms the strong quality (Q)-factor dependence on the excitation spot size. We derive simple analytical formulas to estimate leak and residual absorption losses and propose a simple approach to model the Q-factor and to give a quantitative estimation of the weight of cavity disorder. The model is in good agreement with both transfer-matrix simulation and the experimental findings. We point out that the realization of high Q-factor (In,Ga)N containing microcavities on GaN pseudo-substrates is likely to be limited by the cavity disorder.

  2. Evidence of martensitic phase transitions in magnetic Ni-Mn-In thin films

    SciTech Connect

    Sokolov, A.; Zhang, Le; Dubenko, I.; Samanta, T.; Ali, N.; Stadler, S.

    2013-02-18

    Ni{sub 50}Mn{sub 35}In{sub 15} Heusler alloy thin films (with thicknesses of about 10 nm) have been grown on single crystal MgO and SrTiO{sub 3} (STO) (100) substrates using a laser-assisted molecular beam epitaxy method. Films of mixed austenitic and martensitic phases and of pure martensitic phase have been detected for those grown on MgO and STO substrates, respectively. Thermomagnetic curves were measured using a SQUID magnetometer and are consistent with those of off-stoichiometric In-based bulk Heusler alloys, including a martensitic transition at T = 315 K for films grown on MgO. The differences in the properties of the films grown on MgO and STO are discussed.

  3. Nanoscale size dependence parameters on lattice thermal conductivity of Wurtzite GaN nanowires

    SciTech Connect

    Mamand, S.M.; Omar, M.S.; Muhammad, A.J.

    2012-05-15

    Graphical abstract: Temperature dependence of calculated lattice thermal conductivity of Wurtzite GaN nanowires. Highlights: Black-Right-Pointing-Pointer A modified Callaway model is used to calculate lattice thermal conductivity of Wurtzite GaN nanowires. Black-Right-Pointing-Pointer A direct method is used to calculate phonon group velocity for these nanowires. Black-Right-Pointing-Pointer 3-Gruneisen parameter, surface roughness, and dislocations are successfully investigated. Black-Right-Pointing-Pointer Dislocation densities are decreases with the decrease of wires diameter. -- Abstract: A detailed calculation of lattice thermal conductivity of freestanding Wurtzite GaN nanowires with diameter ranging from 97 to 160 nm in the temperature range 2-300 K, was performed using a modified Callaway model. Both longitudinal and transverse modes are taken into account explicitly in the model. A method is used to calculate the Debye and phonon group velocities for different nanowire diameters from their related melting points. Effect of Gruneisen parameter, surface roughness, and dislocations as structure dependent parameters are successfully used to correlate the calculated values of lattice thermal conductivity to that of the experimentally measured curves. It was observed that Gruneisen parameter will decrease with decreasing nanowire diameters. Scattering of phonons is assumed to be by nanowire boundaries, imperfections, dislocations, electrons, and other phonons via both normal and Umklapp processes. Phonon confinement and size effects as well as the role of dislocation in limiting thermal conductivity are investigated. At high temperatures and for dislocation densities greater than 10{sup 14} m{sup -2} the lattice thermal conductivity would be limited by dislocation density, but for dislocation densities less than 10{sup 14} m{sup -2}, lattice thermal conductivity would be independent of that.

  4. Impact of the GaN nanowire polarity on energy harvesting

    SciTech Connect

    Gogneau, Noelle Galopin, Elisabeth; Guilet, Stephane; Travers, Laurent; Harmand, Jean-Christophe; Chrétien, Pascal; Houzé, Frédéric

    2014-05-26

    We investigate the piezoelectric generation properties of GaN nanowires (NWs) by atomic force microscopy equipped with a Resiscope module for electrical measurements. By correlating the topography profile of the NWs with the recorded voltage peaks generated by these nanostructures in response to their deformation, we demonstrate the influence of their polarity on the rectifying behavior of the Schottky diode formed between the NWs and the electrode of measurement. These results establish that the piezo-generation mechanism crucially depends on the structural characteristics of the NWs.

  5. Mechanism of the GaN LED efficiency falloff with increasing current

    SciTech Connect

    Bochkareva, N. I.; Voronenkov, V. V.; Gorbunov, R. I.; Zubrilov, A. S.; Lelikov, Y. S.; Latyshev, F. E.; Rebane, Y. T.; Tsyuk, A. I.; Shreter, Y. G.

    2010-06-15

    The quantum efficiency of GaN LED structures has been studied at various temperatures and biases. It was found that an efficiency falloff is observed with increasing current density and, simultaneously, the tunnel component of the current through the LED grows and the quasi-Fermi levels reach the mobility edge in the InGaN active layer. It is shown that the internal quantum efficiency falloff with increasing current density is due to the carrier leakage from the quantum well as a result of tunnel transitions from its band-tail states to local defect-related energy levels within the energy gaps of the barrier layers.

  6. Modifications of the cell wall of yeasts grown on hexadecane...

    U.S. Department of Energy (DOE) - all webpages (Extended Search)

    Modifications of the cell wall of yeasts grown on hexadecane and under starvation conditions Title Modifications of the cell wall of yeasts grown on hexadecane and under starvation...

  7. Texture evolution in nanocrystalline iron films deposited using biased magnetron sputtering

    SciTech Connect

    Vetterick, G.; Taheri, M. L.; Baldwin, J. K.; Misra, A.

    2014-12-21

    Fe thin films were deposited on sodium chloride (NaCl) substrates using magnetron sputtering to investigate means of texture control in free standing metal films. The Fe thin films were studied using transmission electron microscopy equipped with automated crystallographic orientation microscopy. Using this technique, the microstructure of each film was characterized in order to elucidate the effects of altering deposition parameters. The natural tendency for Fe films grown on (100) NaCl is to form a randomly oriented nanocrystalline microstructure. By careful selection of substrate and deposition conditions, it is possible to drive the texture of the film toward a single (100) orientation while retaining the nanocrystalline microstructure.

  8. Near-field microwave microscopy of high-? oxides grown on graphene with an organic seeding layer

    SciTech Connect

    Tselev, Alexander Kalinin, Sergei V.; Sangwan, Vinod K.; Jariwala, Deep; Lauhon, Lincoln J.; Marks, Tobin J.; Hersam, Mark C.; Department of Chemistry, Northwestern University, Evanston, Illinois 60208

    2013-12-09

    Near-field scanning microwave microscopy (SMM) is used for non-destructive nanoscale characterization of Al{sub 2}O{sub 3} and HfO{sub 2} films grown on epitaxial graphene on SiC by atomic layer deposition using a self-assembled perylene-3,4,9,10-tetracarboxylic dianhydride seeding layer. SMM allows imaging of buried inhomogeneities in the dielectric layer with a spatial resolution close to 100?nm. The results indicate that, while topographic features on the substrate surface cannot be eliminated as possible sites of defect nucleation, the use of a vertically heterogeneous Al{sub 2}O{sub 3}/HfO{sub 2} stack suppresses formation of large outgrowth defects in the oxide film, ultimately improving lateral uniformity of the dielectric film.

  9. High-mobility BaSnO{sub 3} grown by oxide molecular beam epitaxy

    SciTech Connect

    Raghavan, Santosh; Schumann, Timo; Kim, Honggyu; Zhang, Jack Y.; Cain, Tyler A.; Stemmer, Susanne

    2016-01-01

    High-mobility perovskite BaSnO{sub 3} films are of significant interest as new wide bandgap semiconductors for power electronics, transparent conductors, and as high mobility channels for epitaxial integration with functional perovskites. Despite promising results for single crystals, high-mobility BaSnO{sub 3} films have been challenging to grow. Here, we demonstrate a modified oxide molecular beam epitaxy (MBE) approach, which supplies pre-oxidized SnO{sub x}. This technique addresses issues in the MBE of ternary stannates related to volatile SnO formation and enables growth of epitaxial, stoichiometric BaSnO{sub 3}. We demonstrate room temperature electron mobilities of 150 cm{sup 2} V{sup −1} s{sup −1} in films grown on PrScO{sub 3}. The results open up a wide range of opportunities for future electronic devices.

  10. Ferromagnetic properties of fcc Gd thin films

    SciTech Connect

    Bertelli, T. P. Passamani, E. C.; Larica, C.; Nascimento, V. P.; Takeuchi, A. Y.

    2015-05-28

    Magnetic properties of sputtered Gd thin films grown on Si (100) substrates kept at two different temperatures were investigated using X-ray diffraction, ac magnetic susceptibility, and dc magnetization measurements. The obtained Gd thin films have a mixture of hcp and fcc structures, but with their fractions depending on the substrate temperature T{sub S} and film thickness x. Gd fcc samples were obtained when T{sub S} = 763 K and x = 10 nm, while the hcp structure was stabilized for lower T{sub S} (300 K) and thicker film (20 nm). The fcc structure is formed on the Ta buffer layer, while the hcp phase grows on the fcc Gd layer as a consequence of the lattice relaxation process. Spin reorientation phenomenon, commonly found in bulk Gd species, was also observed in the hcp Gd thin film. This phenomenon is assumed to cause the magnetization anomalous increase observed below 50 K in stressed Gd films. Magnetic properties of fcc Gd thin films are: Curie temperature above 300 K, saturation magnetization value of about 175 emu/cm{sup 3}, and coercive field of about 100 Oe at 300 K; features that allow us to classify Gd thin films, with fcc structure, as a soft ferromagnetic material.

  11. Ultrashort pulse laser deposition of thin films

    DOEpatents

    Perry, Michael D.; Banks, Paul S.; Stuart, Brent C.

    2002-01-01

    Short pulse PLD is a viable technique of producing high quality films with properties very close to that of crystalline diamond. The plasma generated using femtosecond lasers is composed of single atom ions with no clusters producing films with high Sp.sup.3 /Sp.sup.2 ratios. Using a high average power femtosecond laser system, the present invention dramatically increases deposition rates to up to 25 .mu.m/hr (which exceeds many CVD processes) while growing particulate-free films. In the present invention, deposition rates is a function of laser wavelength, laser fluence, laser spot size, and target/substrate separation. The relevant laser parameters are shown to ensure particulate-free growth, and characterizations of the films grown are made using several diagnostic techniques including electron energy loss spectroscopy (EELS) and Raman spectroscopy.

  12. The effect of N-polar GaN domains as Ohmic contacts

    SciTech Connect

    Xie, J.; Mita, S.; Collazo, R.; Rice, A.; Tweedie, J.; Sitar, Z.

    2010-09-20

    Transfer line method measurements revealed that if the Ohmic contact regions were replaced by N-polar GaN, the contact resistance could be reduced from 0.71 {Omega} mm (or {rho}{sub c}=4x10{sup -6} {Omega} cm{sup 2}) to 0.24 {Omega} mm for a {approx}200 nm thick Si-doped GaN layer. The reduction in contact resistance was largely due to the {approx}10{sup 19} cm{sup -3} free carriers in N-polar source/drain regions as measured by Hall effect. Secondary ion mass spectroscopy confirmed that oxygen doping in the N-polar region was more than three orders of magnitude greater than that in the Ga-polar region that was explained by the large difference in the adsorption energy for oxygen ({approx}1.3 eV/atom) between the N- and Ga-polar surfaces during the metalorganic chemical vapor deposition.

  13. Voltage controlled biaxial strain in VO{sub 2} films grown on 0.72Pb(Mg{sub 1∕3}Nb{sub 2∕3})-0.28PbTiO{sub 3} crystals and its effect on the transition temperature

    SciTech Connect

    Petraru, A. Soni, R.; Kohlstedt, H.

    2014-09-01

    Vanadium oxide thin films (VO{sub 2}) were deposited on 0.72Pb(Mg{sub 1∕3}Nb{sub 2∕3})-0.28PbTiO{sub 3} (PMN-PT) crystalline substrates using pulsed laser deposition method. Due to their huge piezoelectric coefficients in the order of 2500 pm/V, the PMN-PT substrates are used to impose additional amount of biaxial strain to the VO{sub 2} films by applying an external bias to the substrates. The influence of the biaxial strain on the transition temperature and on the conductive properties of the VO{sub 2} films is investigated in this work. Thus, a change in the biaxial strain of −0.8 × 10{sup −3} applied in the (110) plane of the rutile cell of the VO{sub 2} lowered the metal-to-insulator transition temperature by 1.35 °C.

  14. Polymer films

    DOEpatents

    Granick, Steve; Sukhishvili, Svetlana A.

    2008-12-30

    A film contains a first polymer having a plurality of hydrogen bond donating moieties, and a second polymer having a plurality of hydrogen bond accepting moieties. The second polymer is hydrogen bonded to the first polymer.

  15. Polymer films

    DOEpatents

    Granick, Steve; Sukhishvili, Svetlana A.

    2004-05-25

    A film contains a first polymer having a plurality of hydrogen bond donating moieties, and a second polymer having a plurality of hydrogen bond accepting moieties. The second polymer is hydrogen bonded to the first polymer.

  16. Tunable electrical and optical properties of hafnium nitride thin films

    SciTech Connect

    Farrell, I. L.; Reeves, R. J.; Preston, A. R. H.; Ludbrook, B. M.; Ruck, B. J.; Downes, J. E.; Durbin, S. M.

    2010-02-15

    We report structural and electronic properties of epitaxial hafnium nitride films grown on MgO by plasma-assisted pulsed laser deposition. The electronic structure measured using soft x-ray absorption and emission spectroscopy is in excellent agreement with the results of a band structure calculation. We show that by varying the growth conditions we can extend the films' reflectance further toward the UV, and we relate this observation to the electronic structure.

  17. Effects of GaN interlayer on the transport properties of lattice-matched AlInN/AlN/GaN heterostructures

    SciTech Connect

    Wu, F.; Gao, K. H. Li, Z. Q.; Lin, T.; Zhou, W. Z.

    2015-04-21

    We study the effects of GaN interlayer on the transport properties of two-dimensional electron gases confined in lattice-matched AlInN/AlN/GaN heterostructures. It is found that the Hall mobility is evidently enhanced when an additional ultrathin GaN interlayer is introduced between AlInN and AlN layers. The enhancement of the Hall mobility is especially remarkable at low temperature. The high Hall mobility results in a low sheet resistance of 23 Ω/◻ at 2 K. Meanwhile, Shubnikov-de Haas oscillations (SdH) are also remarkably enhanced due to the existence of GaN interlayer. The enhancement of the SdH oscillations is related to the larger quantum mobility μ{sub q} owing to the suppression of the interface roughness, alloy disorder, and ionized impurity scatterings by the GaN interlayer.

  18. Effect of hydrogen passivation on charge storage in silicon quantum dots embedded in silicon nitride film

    SciTech Connect

    Cho, Chang-Hee; Kim, Baek-Hyun; Kim, Tae-Wook; Park, Seong-Ju; Park, Nae-Man; Sung, Gun-Yong

    2005-04-04

    The effect of hydrogen passivation on the charge storage characteristics of two types of silicon nitride films containing silicon quantum dots (Si QDs) grown by SiH{sub 4}+N{sub 2} and SiH{sub 4}+NH{sub 3} plasma was investigated. The transmission electron microscope analysis and the capacitance-voltage measurement showed that the silicon nitride film grown by SiH{sub 4}+NH{sub 3} plasma has a lower interface trap density and a higher density of Si QDs compared to that grown by SiH{sub 4}+N{sub 2} plasma. It was also found that the charge retention characteristics in the Si QDs were greatly enhanced in the samples grown by means of SiH{sub 4}+NH{sub 3} plasma, due to the hydrogen passivation of the defects in the silicon nitride films by NH{sub 3} during the growth of the Si QDs.

  19. The possibly important role played by Ga{sub 2}O{sub 3} during the activation of GaN photocathode

    SciTech Connect

    Fu, Xiaoqian E-mail: 214808748@qq.com; Wang, Honggang; Zhang, Junju; Li, Zhiming; Cui, Shiyao; Zhang, Lejuan

    2015-08-14

    Three different chemical solutions are used to remove the possible contamination on GaN surface, while Ga{sub 2}O{sub 3} is still found at the surface. After thermal annealing at 710 °C in the ultrahigh vacuum (UHV) chamber and activated with Cs/O, all the GaN samples are successfully activated to the effective negative electron affinity (NEA) photocathodes. Among all samples, the GaN sample with the highest content of Ga{sub 2}O{sub 3} after chemical cleaning obtains the highest quantum efficiency. By analyzing the property of Ga{sub 2}O{sub 3}, the surface processing results, and electron affinity variations during Cs and Cs/O{sub 2} deposition on GaN of other groups, it is suggested that before the adsorption of Cs, Ga{sub 2}O{sub 3} is not completely removed from GaN surface in our samples, which will combine with Cs and lead to a large decrease in electron affinity. Furthermore, the effective NEA is formed for GaN photocathode, along with the surface downward band bending. Based on this assumption, a new dipole model Ga{sub 2}O{sub 3}-Cs is suggested, and the experimental effects are explained and discussed.

  20. Influence of the adatom diffusion on selective growth of GaN nanowire regular arrays

    SciTech Connect

    Gotschke, T.; Schumann, T.; Limbach, F.; Calarco, R.; Stoica, T.

    2011-03-07

    Molecular beam epitaxy (MBE) on patterned Si/AlN/Si(111) substrates was used to obtain regular arrays of uniform-size GaN nanowires (NWs). The silicon top layer has been patterned with e-beam lithography, resulting in uniform arrays of holes with different diameters (d{sub h}) and periods (P). While the NW length is almost insensitive to the array parameters, the diameter increases significantly with d{sub h} and P till it saturates at P values higher than 800 nm. A diffusion induced model was used to explain the experimental results with an effective diffusion length of the adatoms on the Si, estimated to be about 400 nm.

  1. Resonant energy transfer between Eu luminescent sites and their local geometry in GaN

    SciTech Connect

    Timmerman, Dolf; Wakamatsu, Ryuta; Tanaka, Kazuteru; Lee, Dong-gun; Koizumi, Atsushi; Fujiwara, Yasufumi

    2015-10-12

    Eu-doped GaN is a solid state material with promising features for quantum manipulation. In this study, we investigate the population dynamics of Eu in ions in this system by resonant excitation. From differences in the emission related to transitions between the {sup 5}D{sub 0} and {sup 7}F{sub 2} manifold in the Eu ions, we can distinguish different luminescence sites and observe that a resonant energy transfer takes place between two of these sites which are in proximity of each other. The time constants related to this energy transfer are on the order of 100 μs. By using different substrates, the energy transfer efficiency could be strongly altered, and it is demonstrated that the coupling between ions has an out-of-plane character. Based on these results, a microscopic model of this combined center is presented.

  2. Ion-assisted physical vapor deposition for enhanced film properties on nonflat surfaces

    SciTech Connect

    Alami, J.; Persson, P.O.A.; Music, D.; Gudmundsson, J. T.; Bohlmark, J.; Helmersson, U.

    2005-03-01

    We have synthesized Ta thin films on Si substrates placed along a wall of a 2-cm-deep and 1-cm-wide trench, using both a mostly neutral Ta flux by conventional dc magnetron sputtering (dcMS) and a mostly ionized Ta flux by high-power pulsed magnetron sputtering (HPPMS). Structure of the grown films was evaluated by scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. The Ta thin film grown by HPPMS has a smooth surface and a dense crystalline structure with grains oriented perpendicular to the substrate surface, whereas the film grown by dcMS exhibits a rough surface, pores between the grains, and an inclined columnar structure. The improved homogeneity achieved by HPPMS is a direct consequence of the high ion fraction of sputtered species.

  3. High carrier concentration p-type transparent conducting oxide films

    DOEpatents

    Yan, Yanfa; Zhang, Shengbai

    2005-06-21

    A p-type transparent conducting oxide film is provided which is consisting essentially of, the transparent conducting oxide and a molecular doping source, the oxide and doping source grown under conditions sufficient to deliver the doping source intact onto the oxide.

  4. Comparison of topotactic fluorination methods for complex oxide films

    SciTech Connect

    Moon, E. J. Choquette, A. K.; Huon, A.; Kulesa, S. Z.; May, S. J.; Barbash, D.

    2015-06-01

    We have investigated the synthesis of SrFeO{sub 3??}F{sub ?} (? and ? ? 1) perovskite films using topotactic fluorination reactions utilizing poly(vinylidene fluoride) as a fluorine source. Two different fluorination methods, a spin-coating and a vapor transport approach, were performed on as-grown SrFeO{sub 2.5} films. We highlight differences in the structural, compositional, and optical properties of the oxyfluoride films obtained via the two methods, providing insight into how fluorination reactions can be used to modify electronic and optical behavior in complex oxide heterostructures.

  5. Magnetic anisotropy in ultrathin Fe films on GaAs, ZnSe, and Ge (001) substrates

    SciTech Connect

    Tivakornsasithorn, K.; Liu, X.; Li, X.; Dobrowolska, M.; Furdyna, J. K.

    2014-07-28

    We discuss magnetic anisotropy parameters of ferromagnetic body-centered cubic (bcc) Fe films grown by molecular beam epitaxy (MBE) on (001) substrates of face-centered cubic (fcc) GaAs, ZnSe, and Ge. High-quality MBE growth of these metal/semiconductor combinations is made possible by the fortuitous atomic relationship between the bcc Fe and the underlying fcc semiconductor surfaces, resulting in excellent lattice match. Magnetization measurements by superconducting quantum interference device (SQUID) indicate that the Fe films grown on (001) GaAs surfaces are characterized by a very strong uniaxial in-plane anisotropy; those grown on (001) Ge surfaces have a fully cubic anisotropy; and Fe films grown on ZnSe represent an intermediate case between the preceding two combinations. Ferromagnetic resonance measurements carried out on these three systems provide a strikingly clear quantitative picture of the anisotropy parameters, in excellent agreement with the SQUID results. Based on these results, we propose that the observed anisotropy of cubic Fe films grown in this way results from the surface reconstruction of the specific semiconductor substrate on which the Fe film is deposited. These results suggest that, by controlling surface reconstruction of the substrate during the MBE growth, one may be able to engineer the magnetic anisotropy in Fe, and possibly also in other MBE-grown ferromagnetic films.

  6. Growth evolution of AlN films on silicon (111) substrates by pulsed laser deposition

    SciTech Connect

    Wang, Haiyan; Wang, Wenliang; Yang, Weijia; Zhou, Shizhong; Lin, Zhiting; Li, Guoqiang

    2015-05-14

    AlN films with various thicknesses have been grown on Si(111) substrates by pulsed laser deposition (PLD). The surface morphology and structural property of the as-grown AlN films have been investigated carefully to comprehensively explore the epitaxial behavior. The ∼2 nm-thick AlN film initially grown on Si substrate exhibits an atomically flat surface with a root-mean-square surface roughness of 0.23 nm. As the thickness increases, AlN grains gradually grow larger, causing a relatively rough surface. The surface morphology of ∼120 nm-thick AlN film indicates that AlN islands coalesce together and eventually form AlN layers. The decreasing growth rate from 240 to 180 nm/h is a direct evidence that the growth mode of AlN films grown on Si substrates by PLD changes from the islands growth to the layer growth. The evolution of AlN films throughout the growth is studied deeply, and its corresponding growth mechanism is hence proposed. These results are instructional for the growth of high-quality nitride films on Si substrates by PLD, and of great interest for the fabrication of AlN-based devices.

  7. Performance and breakdown characteristics of irradiated vertical power GaN P-i-N diodes

    SciTech Connect

    King, M. P.; Armstrong, A. M.; Dickerson, J. R.; Vizkelethy, G.; Fleming, R. M.; Campbell, J.; Wampler, W. R.; Kizilyalli, I. C.; Bour, D. P.; Aktas, O.; Nie, H.; Disney, D.; Wierer, Jr., J.; Allerman, A. A.; Moseley, M. W.; Kaplar, R. J.

    2015-10-29

    Electrical performance and defect characterization of vertical GaN P-i-N diodes before and after irradiation with 2.5 MeV protons and neutrons is investigated. Devices exhibit increase in specific on-resistance following irradiation with protons and neutrons, indicating displacement damage introduces defects into the p-GaN and n- drift regions of the device that impact on-state device performance. The breakdown voltage of these devices, initially above 1700 V, is observed to decrease only slightly for particle fluence <; 1013 cm-2. Furthermore, the unipolar figure of merit for power devices indicates that while the on-resistance and breakdown voltage degrade with irradiation, vertical GaN P-i-Ns remain superior to the performance of the best available, unirradiated silicon devices and on-par with unirradiated modern SiC-based power devices.

  8. Efficient Switches for Solar Power Conversion: Four Quadrant GaN Switch Enabled Three Phase Grid-Tied Microinverters

    SciTech Connect

    2012-02-13

    Solar ADEPT Project: Transphorm is developing power switches for new types of inverters that improve the efficiency and reliability of converting energy from solar panels into useable electricity for the grid. Transistors act as fast switches and control the electrical energy that flows in an electrical circuit. Turning a transistor off opens the circuit and stops the flow of electrical current; turning it on closes the circuit and allows electrical current to flow. In this way a transistor can be used to convert DC from a solar panel into AC for use in a home. Transphorm’s transistors will enable a single semiconductor device to switch electrical currents at high-voltage in both directions—making the inverter more compact and reliable. Transphorm is using Gallium Nitride (GaN) as a semiconductor material in its transistors instead of silicon, which is used in most conventional transistors, because GaN transistors have lower losses at higher voltages and switching frequencies.

  9. Propagation of electro-kinetic waves in magnetized GaN semiconductor with nano-sized ion colloids

    SciTech Connect

    Saxena, Ajay; Sharma, Giriraj; Jat, K. L.; Rishi, M. P.

    2015-07-31

    Based on hydrodynamic model of multi-component plasma, an analytical study on propagation of longitudinal electro-kinetic (LEK) waves in wurtzite and zincblende structures of GaN is carried out. Nano-sized ion colloids (NICs) are embedded in the sample by the technique of ion-implantation. The implanted NICs are considered massive by an order as compared to the host lattice points and do not participate in Based LEK perturbations. Though, the NICs are continuously bombarded by the electrons as well as the holes yet, the former acquires a net negative charge owing to relatively higher mobility of electrons and consequently results into depletion of electron density in the medium. It i s found that the presence of charged NICs significantly modifies the dispersion and amplification characteristics of LEK waves in magnetized GaN semiconductor plasma and their role becomes increasingly effective as the fraction of charge on them increases.

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

    SciTech Connect

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

    2012-12-15

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

  11. HIGH-QUALITY, LOW-COST BULK GALLIUM NITRIDE SUBSTRATES GROWN...

    Office of Energy Efficiency and Renewable Energy (EERE) (indexed site)

    Efficient manufacturing of gallium nitride (GaN) could reduce the cost of and improve the output for light-emitting diodes, solid-state lighting, laser displays, and other power ...

  12. Low hydrogen content, high quality hydrogenated amorphous silicon grown by hot-wire CVD

    SciTech Connect

    Nelson, B.P.; Crandall, R.S.; Iwaniczko, E.; Mahan, A.H.; Wang, Q.; Xu, Y.; Gao, W.

    1999-07-01

    The authors grow hydrogenated amorphous silicon (a-Si:H) by Hot-Wire Chemical Vapor Deposition (HWCVD). The early work with this technique has shown that they can grow a-Si:H that is different from typical a-Si:H materials. Specifically, they demonstrated the ability to grow a-Si:H of exceptional quality with very low hydrogen (H) contents (0.01 to 4 at.%). The deposition chambers in which this early work was done have two limitations; they hold only small-area substrates and they are incompatible with a load-lock. In the efforts to scale up to larger area chambers--that have load-lock compatibility--they encountered difficulty in growing high-quality films that also have a low H content. Substrate temperature has a direct effect on the H content of HWCVD grown a-Si:H. They found that making dramatic changes to the other deposition process parameters--at fixed substrate temperature and filament-to-substrate spacing--did not have much effect on the H content of the resulting films in the new chambers. However, these changes did have profound effects on film quality. They can grow high-quality a-Si:H in the new larger area chambers at 4 at. % H. For example, the lowest known stabilized defect density of a-Si:H is approximately 2 x 10{sup 16} cm{sup {minus}3}, which they have grown in the new chamber at 18 {angstrom}/s. Making changes to the original chamber--making it more like the new reactor--did not increase the hydrogen content at a fixed substrate temperature and filament-to-substrate spacing. They continued to grow high quality films with low H content in spite of these changes. An interesting, and very useful, result of these experiments is that the orientation of the filament with respect to silane flow direction had no influence on film quality or the H content of the films. The condition of the filament is much more important to growing quality films than the geometry of the chamber due to tungsten-silicide formation on the filament.

  13. Transistors for Electric Motor Drives: High-Performance GaN HEMT Modules for Agile Power Electronics

    SciTech Connect

    2010-09-01

    ADEPT Project: Transphorm is developing transistors with gallium nitride (GaN) semiconductors that could be used to make cost-effective, high-performance power converters for a variety of applications, including electric motor drives which transmit power to a motor. A transistor acts like a switch, controlling the electrical energy that flows around an electrical circuit. Most transistors today use low-cost silicon semiconductors to conduct electrical energy, but silicon transistors don’t operate efficiently at high speeds and voltage levels. Transphorm is using GaN as a semiconductor material in its transistors because GaN performs better at higher voltages and frequencies, and it is more energy efficient than straight silicon. However, Transphorm is using inexpensive silicon as a base to help keep costs low. The company is also packaging its transistors with other electrical components that can operate quickly and efficiently at high power levels—increasing the overall efficiency of both the transistor and the entire motor drive.

  14. Characterization of transparent zinc oxide films prepared by electrochemical reaction

    SciTech Connect

    Izaki, Masanobu; Omi, Takashi

    1997-06-01

    Transparent zinc oxide (ZnO) films have been grown by galvanostatic cathodic deposition onto conductive glasses from a simple aqueous zinc nitrate electrolyte maintained at 335 K. The as-deposited ZnO films were characterized with Fourier transform infrared absorption spectroscopy, x-ray diffraction, scanning electron microscopy, optical transmission and absorption studies, and measurement of sheet resistivity as a function of cathodic current density. The ZnO films prepared had a wurtzite structure and exhibited an optical bandgap energy of 3.3 eV which is characteristic of ZnO. At a low cathodic current density of 0.05 mA/cm{sup 2}, ZnO films with excellent electrical characteristics have been obtained. A 2 {micro}m thick ZnO film with an optical transmittance of 72% was deposited by electrolysis for approximately 20 min at a cathodic current density of 10 mA/cm{sup 2}.

  15. Suppression of metastable-phase inclusion in N-polar (0001{sup }) InGaN/GaN multiple quantum wells grown by metalorganic vapor phase epitaxy

    SciTech Connect

    Shojiki, Kanako Iwabuchi, Takuya; Kuboya, Shigeyuki; Choi, Jung-Hun; Tanikawa, Tomoyuki; Hanada, Takashi; Katayama, Ryuji; Matsuoka, Takashi; Usami, Noritaka

    2015-06-01

    The metastable zincblende (ZB) phase in N-polar (0001{sup }) (?c-plane) InGaN/GaN multiple quantum wells (MQWs) grown by metalorganic vapor phase epitaxy is elucidated by the electron backscatter diffraction measurements. From the comparison between the ?c-plane and Ga-polar (0001) (+c-plane), the ?c-plane MQWs were found to be suffered from the severe ZB-phase inclusion, while ZB-inclusion is negligible in the +c-plane MQWs grown under the same growth conditions. The ZB-phase inclusion is a hurdle for fabricating the ?c-plane light-emitting diodes because the islands with a triangular shape appeared on a surface in the ZB-phase domains. To improve the purity of stable wurtzite (WZ)-phase, the optimum conditions were investigated. The ZB-phase is dramatically eliminated with decreasing the V/III ratio and increasing the growth temperature. To obtain much-higher-quality MQWs, the thinner InGaN wells and the hydrogen introduction during GaN barriers growth were tried. Consequently, MQWs with almost pure WZ phase and with atomically smooth surface have been demonstrated.

  16. Electrical transport properties of Ti-doped Fe2O3(0001) epitaxial films

    SciTech Connect

    Zhao, Bo; Kaspar, Tiffany C.; Droubay, Timothy C.; McCloy, John S.; Bowden, Mark E.; Shutthanandan, V.; Heald, Steve M.; Chambers, Scott A.

    2011-12-30

    The electrical transport properties for compositionally and structurally well-defined epitaxial ?-(TixFe1?x)2O3(0001) films have been investigated for x ? 0.09. All films were grown by oxygen plasma-assisted molecular beam epitaxy using two different growth rates: 0.050.06 /s and 0.220.24 /s. Despite no detectable difference in cation valence and structural properties, films grown at the lower rate were highly resistive whereas those grown at the higher rate were semiconducting (? = ?1 ???cm at 25?C). Hall effect measurements reveal carrier concentrations between 1019 and 1020 cm?3 at room temperature and mobilities in the range of 0.1 to 0.6 cm2/V??s for films grown at the higher rate. The conduction mechanism transitions from small-polaron hopping at higher temperatures to variable-range hopping at a transition temperature between 180 and 140 K. The absence of conductivity in the slow-grown films is attributed to donor electron compensation by cation vacancies, which may form to a greater extent at the lower rate because of higher oxygen fugacity at the growth front.

  17. Ferromagnetism of manganese-doped indium tin oxide films deposited on polyethylene naphthalate substrates

    SciTech Connect

    Nakamura, Toshihiro; Isozaki, Shinichi; Tanabe, Kohei; Tachibana, Kunihide

    2009-04-01

    Mn-doped indium tin oxide (ITO) films were deposited on polyethylene naphthalate (PEN) substrates using radio-frequency magnetron sputtering. The magnetic, electrical, and optical properties of the films deposited on PEN substrates were investigated by comparing with the properties of films grown on glass substrates at the same growth conditions. Thin films on PEN substrates exhibited low electrical resistivity of the order of 10{sup -4} {omega} cm and high optical transmittance between 75% and 90% in the visible region. Ferromagnetic hysteresis loops were observed at room temperature for the samples grown on PEN substrates. Mn-doped ITO films can be one of the most promising candidates of transparent ferromagnetic materials for flexible spintronic devices.

  18. Tungsten oxide (WO{sub 3}) thin films for application in advanced energy systems

    SciTech Connect

    Gullapalli, S. K.; Vemuri, R. S.; Manciu, F. S.; Enriquez, J. L.; Ramana, C. V.

    2010-07-15

    Inherent processes in coal gasification plants produce hazardous hydrogen sulfide (H{sub 2}S), which must be continuously and efficiently detected and removed before the fuel is used for power generation. An attempt has been made in this work to fabricate tungsten oxide (WO{sub 3}) thin films by radio-frequency reactive magnetron-sputter deposition. The impetus being the use of WO{sub 3} films for H{sub 2}S sensors in coal gasification plants. The effect of growth temperature, which is varied in the range of 30-500 deg. C, on the growth and microstructure of WO{sub 3} thin films is investigated. Characterizations made using scanning electron microscopy (SEM) and x-ray diffraction (XRD) indicate that the effect of temperature is significant on the microstructure of WO{sub 3} films. XRD and SEM results indicate that the WO{sub 3} films grown at room temperature are amorphous, whereas films grown at higher temperatures are nanocrystalline. The average grain-size increases with increasing temperature. WO{sub 3} films exhibit smooth morphology at growth temperatures {<=}300 deg. C while relatively rough at >300 deg. C. The analyses indicate that the nanocrystalline WO{sub 3} films grown at 100-300 deg. C could be the potential candidates for H{sub 2}S sensor development for application in coal gasification systems.

  19. Recycling process for recovery of gallium from GaN an e-waste of LED industry through ball milling, annealing and leaching

    SciTech Connect

    Swain, Basudev Mishra, Chinmayee; Kang, Leeseung; Park, Kyung-Soo Lee, Chan Gi; Hong, Hyun Seon

    2015-04-15

    Waste dust generated during manufacturing of LED contains significant amounts of gallium and indium, needs suitable treatment and can be an important resource for recovery. The LED industry waste dust contains primarily gallium as GaN. Leaching followed by purification technology is the green and clean technology. To develop treatment and recycling technology of these GaN bearing e-waste, leaching is the primary stage. In our current investigation possible process for treatment and quantitative leaching of gallium and indium from the GaN bearing e-waste or waste of LED industry dust has been developed. To recycle the waste and quantitative leaching of gallium, two different process flow sheets have been proposed. In one, process first the GaN of the waste the LED industry dust was leached at the optimum condition. Subsequently, the leach residue was mixed with Na{sub 2}CO{sub 3}, ball milled followed by annealing, again leached to recover gallium. In the second process, the waste LED industry dust was mixed with Na{sub 2}CO{sub 3}, after ball milling and annealing, followed acidic leaching. Without pretreatment, the gallium leaching was only 4.91 w/w % using 4 M HCl, 100 °C and pulp density of 20 g/L. After mechano-chemical processing, both these processes achieved 73.68 w/w % of gallium leaching at their optimum condition. The developed process can treat and recycle any e-waste containing GaN through ball milling, annealing and leaching. - Highlights: • Simplest process for treatment of GaN an LED industry waste developed. • The process developed recovers gallium from waste LED waste dust. • Thermal analysis and phase properties of GaN to Ga{sub 2}O{sub 3} and GaN to NaGaO{sub 2} revealed. • Solid-state chemistry involved in this process reported. • Quantitative leaching of the GaN was achieved.

  20. Ferroelectric ultrathin perovskite films

    DOEpatents

    Rappe, Andrew M; Kolpak, Alexie Michelle

    2013-12-10

    Disclosed herein are perovskite ferroelectric thin-film. Also disclosed are methods of controlling the properties of ferroelectric thin films. These films can be used in a variety materials and devices, such as catalysts and storage media, respectively.

  1. Magnetization dynamics of cobalt grown on graphene

    SciTech Connect

    Berger, A. J.; White, S. P.; Adur, R.; Pu, Y.; Hammel, P. C.; Amamou, W.; Kawakami, R. K.

    2014-05-07

    Ferromagnetic resonance (FMR) spin pumping is a rapidly growing field which has demonstrated promising results in a variety of material systems. This technique utilizes the resonant precession of magnetization in a ferromagnet to inject spin into an adjacent non-magnetic material. Spin pumping into graphene is attractive on account of its exceptional spin transport properties. This article reports on FMR characterization of cobalt grown on chemical vapor deposition graphene and examines the validity of linewidth broadening as an indicator of spin pumping. In comparison to cobalt samples without graphene, direct contact cobalt-on-graphene exhibits increased FMR linewidthan often used signature of spin pumping. Similar results are obtained in Co/MgO/graphene structures, where a 1?nm MgO layer acts as a tunnel barrier. However, magnetometry, magnetic force microscopy, and Kerr microscopy measurements demonstrate increased magnetic disorder in cobalt grown on graphene, perhaps due to changes in the growth process and an increase in defects. This magnetic disorder may account for the observed linewidth enhancement due to effects such as two-magnon scattering or mosaicity. As such, it is not possible to conclude successful spin injection into graphene from FMR linewidth measurements alone.

  2. Carrier and photon dynamics in a topological insulator Bi{sub 2}Te{sub 3}/GaN type II staggered heterostructure

    SciTech Connect

    Chaturvedi, P.; Chouksey, S.; Banerjee, D.; Ganguly, S.; Saha, D.

    2015-11-09

    We have demonstrated a type-II band-aligned heterostructure between pulsed laser deposited topological insulator bismuth telluride and metal organic-chemical-vapour deposited GaN on a sapphire substrate. The heterostructure shows a large valence band-offset of 3.27 eV as determined from x-ray photoelectron spectroscopy, which is close to the bandgap of GaN (3.4 eV). Further investigation using x-ray diffraction, Raman spectroscopy, and energy-dispersive x-ray spectrum reveals the stoichiometric and material properties of bismuth telluride on GaN. Steady state photon emission from GaN is found to be modulated by the charge transfer process due to diffusion across the junction. The time constant involved with the charge transfer process is found to be 0.6 ns by transient absorption spectroscopy. The heterostructure can be used for designing devices with different functionalities and improving the performance of the existing devices on GaN.

  3. Comparative study of field-dependent carrier dynamics and emission kinetics of InGaN/GaN light-emitting diodes grown on (112{sup }2) semipolar versus (0001) polar planes

    SciTech Connect

    Ji, Yun; Liu, Wei; Chen, Rui; Tiam Tan, Swee; Zhang, Zi-Hui; Ju, Zhengang; Zhang, Xueliang; Sun, Handong; Wei Sun, Xiao; Erdem, Talha; Zhao, Yuji; DenBaars, Steven P. E-mail: volkan@stanfordalumni.org; Nakamura, Shuji; Volkan Demir, Hilmi E-mail: volkan@stanfordalumni.org

    2014-04-07

    The characteristics of electroluminescence (EL) and photoluminescence (PL) emission from GaN light-emitting diodes (LEDs) grown on (112{sup }2) semipolar plane and (0001) polar plane have been comparatively investigated. Through different bias-dependent shifting trends observed from the PL and time-resolved PL spectra (TRPL) for the two types of LEDs, the carrier dynamics within the multiple quantum wells (MQWs) region is systematically analyzed and the distinct field-dependent emission kinetics are revealed. Moreover, the polarization induced internal electric field has been deduced for each of the LEDs. The relatively stable emission behavior observed in the semipolar LED is attributed to the smaller polarization induced internal electric field. The study provides meaningful insight for the design of quantum well (QW) structures with high radiative recombination rates.

  4. Electrochemical removal of hydrogen atoms in Mg-doped GaN epitaxial layers

    SciTech Connect

    Lee, June Key E-mail: hskim7@jbnu.ac.kr; Hyeon, Gil Yong; Tawfik, Wael Z.; Choi, Hee Seok; Ryu, Sang-Wan; Jeong, Tak; Jung, Eunjin; Kim, Hyunsoo E-mail: hskim7@jbnu.ac.kr

    2015-05-14

    Hydrogen atoms inside of an Mg-doped GaN epitaxial layer were effectively removed by the electrochemical potentiostatic activation (EPA) method. The role of hydrogen was investigated in terms of the device performance of light-emitting diodes (LEDs). The effect of the main process parameters for EPA such as solution type, voltage, and time was studied and optimized for application to LED fabrication. In optimized conditions, the light output of 385-nm LEDs was improved by about 26% at 30 mA, which was caused by the reduction of the hydrogen concentration by ∼35%. Further removal of hydrogen seems to be involved in the breaking of Ga-H bonds that passivate the nitrogen vacancies. An EPA process with high voltage breaks not only Mg-H bonds that generate hole carriers but also Ga-H bonds that generate electron carriers, thus causing compensation that impedes the practical increase of hole concentration, regardless of the drastic removal of hydrogen atoms. A decrease in hydrogen concentration affects the current-voltage characteristics, reducing the reverse current by about one order and altering the forward current behavior in the low voltage region.

  5. Enhanced stability of Eu in GaN nanoparticles: Effects of Si co-doping

    SciTech Connect

    Kaur, Prabhsharan; Sekhon, S. S.; Zavada, J. M.; Kumar, Vijay

    2015-06-14

    Ab initio calculations on Eu doped (GaN){sub n} (n = 12, 13, and 32) nanoparticles show that Eu doping in nanoparticles is favorable compared with bulk GaN as a large fraction of atoms lie on the surface where strain can be released compared with bulk where often Eu doping is associated with a N vacancy. Co-doping of Si further facilitates Eu doping as strain from an oversized Eu atom and an undersized Si atom is compensated. These results along with low symmetry sites in nanoparticles make them attractive for developing strongly luminescent nanomaterials. The atomic and electronic structures are discussed using generalized gradient approximation (GGA) for the exchange-correlation energy as well as GGA + U formalism. In all cases of Eu (Eu + Si) doping, the magnetic moments are localized on the Eu site with a large value of 6μ{sub B} (7μ{sub B}). Our results suggest that co-doping can be a very useful way to achieve rare-earth doping in different hosts for optoelectronic materials.

  6. Wet chemical synthesis of quantum confined nanostructured tin oxide thin films by successive ionic layer adsorption and reaction technique

    SciTech Connect

    Murali, K.V., E-mail: kvmuralikv@gmail.com [School of Pure and Applied Physics, Department of Physics, Kannur University, Kerala 670327 (India); Department of Physics, Nehru Arts and Science College, Kanhangad, Kerala 671314 (India); Ragina, A.J. [School of Pure and Applied Physics, Department of Physics, Kannur University, Kerala 670327 (India); Department of Physics, Nehru Arts and Science College, Kanhangad, Kerala 671314 (India); Preetha, K.C. [School of Pure and Applied Physics, Department of Physics, Kannur University, Kerala 670327 (India); Department of Physics, Sree Narayana College, Kannur, Kerala 670007 (India); Deepa, K.; Remadevi, T.L. [School of Pure and Applied Physics, Department of Physics, Kannur University, Kerala 670327 (India); Department of Physics, Pazhassi Raja N.S.S. College, Mattannur, Kerala 670702 (India)

    2013-09-01

    Graphical abstract: - Highlights: Quantum confined SnO{sub 2} thin films were synthesized at 80 C by SILAR technique. Film formation mechanism is discussed. Films with snow like crystallite morphology offer high specific surface area. The blue-shifted value of band gap confirmed the quantum confinement effect. Present synthesis has advantages low cost, low temperature and green friendly. - Abstract: Quantum confined nanostructured SnO{sub 2} thin films were synthesized at 353 K using ammonium chloride (NH{sub 4}Cl) and other chemicals by successive ionic layer adsorption and reaction technique. Film formation mechanism is discussed. Structural, morphological, optical and electrical properties were investigated and compared with the as-grown and annealed films fabricated without NH{sub 4}Cl solution. SnO{sub 2} films were polycrystalline with crystallites of tetragonal structure with grain sizes lie in the 58 nm range. Films with snow like crystallite morphology offer high specific surface area. The blue-shifted value of band gap of as-grown films confirmed the quantum confinement effect of grains. Refractive index of the films lies in the 2.12.3 range. Films prepared with NH{sub 4}Cl exhibit relatively lower resistivity of the order of 10{sup 0}10{sup ?1} ? cm. The present synthesis has advantages such as low cost, low temperature and green friendly, which yields small particle size, large surfacevolume ratio, and high crystallinity SnO{sub 2} films.

  7. Hot filament CVD of boron nitride films

    DOEpatents

    Rye, Robert R.

    1992-01-01

    Using a hot filament (.apprxeq.1400.degree. C.) to activate borazine (B.sub.3 N.sub.3 H.sub.6) molecules for subsequent reaction with a direct line-of-sight substrate, transparent boron ntiride films as thick as 25,000 angstroms are grown for a substrate temperature as low as 100.degree. C. The minimum temperature is determined by radiative heating from the adjacent hot filament. The low temperature BN films show no indication of crystallinity with X-ray diffraction (XRD). X-ray photoelectron spectra (XPS) show the films to have a B:N ratio of 0.97:1 with no other XPS detectable impurities above the 0.5% level. Both Raman and infrared (IR) spectroscopy are characteristic of h-BN with small amounts of hydrogen detected as N-H and B-H bands in the IR spectrum. An important feature of this method is the separation and localization of the thermal activation step at the hot filament from the surface reaction and film growth steps at the substrate surface. This allows both higher temperature thermal activation and lower temperature film growth.

  8. Tunable giant magnetic anisotropy in amorphous SmCo thin films

    SciTech Connect

    Magnus, F.; Moubah, R.; Roos, A. H.; Kapaklis, V.; Hjoervarsson, B.; Andersson, G.; Kruk, A.; Hase, T.

    2013-04-22

    SmCo thin films have been grown by magnetron sputtering at room temperature with a composition of 2-35 at. % Sm. Films with 5 at. % or higher Sm are amorphous and smooth. A giant tunable uniaxial in-plane magnetic anisotropy is induced in the films which peaks in the composition range 11-22 at. % Sm. This cross-over behavior is not due to changes in the atomic moments but rather the local configuration changes. The excellent layer perfection combined with highly tunable magnetic properties make these films important for spintronics applications.

  9. High-power blue laser diodes with indium tin oxide cladding on semipolar (202{sup }1{sup }) GaN substrates

    SciTech Connect

    Pourhashemi, A. Farrell, R. M.; Cohen, D. A.; Speck, J. S.; DenBaars, S. P.; Nakamura, S.

    2015-03-16

    We demonstrate a high power blue laser diode (LD) using indium tin oxide as a cladding layer on semipolar oriented GaN. These devices show peak output powers and external quantum efficiencies comparable to state-of-the-art commercial c-plane devices. Ridge waveguide LDs were fabricated on (202{sup }1{sup }) oriented GaN substrates using InGaN waveguiding layers and GaN cladding layers. At a lasing wavelength of 451?nm at room temperature, an output power of 2.52?W and an external quantum efficiency of 39% were measured from a single facet under a pulsed injection current of 2.34?A. The measured differential quantum efficiency was 50%.

  10. Photochemical Properties, Composition, and Structure in Molecular Beam Epitaxy Grown Fe Doped and (Fe,N) Codoped Rutile TiO2(110)

    SciTech Connect

    Mangham, Andrew N.; Govind, Niranjan; Bowden, Mark E.; Shutthanandan, V.; Joly, Alan G.; Henderson, Michael A.; Chambers, Scott A.

    2011-08-11

    We have investigated the surface photochemical properties of Fe "doped" and (Fe,N) co-doped homoepitaxial rutile TiO2 (110) films grown by plasma assisted molecular beam epitaxy. Fe does not incorporate as an electronic dopant in the rutile lattice, but rather segregates to the film surface. However, co-deposition of Fe with N enhances the solubility of Fe, and DFT calculations suggest that co-dopant complex formation is the driving force behind the enhanced solubility. The co-doped films, in which a few atomic percent of Ti (O) are replaced with Fe (N), exhibit significant disorder compared to undoped films grown under the same conditions, presumably due to dopant-induced strain. Co-doping redshifts the rutile bandgap into the visible. However, the film surfaces are photochemically inert with respect to hole-mediated decomposition of adsorbed trimethyl acetate. The absence of photochemical activity may result from dopant-induced trap and/or recombination sites within the film. This study indicates that enhanced visible light absorptivity in TiO2 does not necessarily result in visible light initiated surface photochemistry.

  11. Liquid-phase exfoliation of chemical vapor deposition-grown single layer graphene and its application in solution-processed transparent electrodes for flexible organic light-emitting devices

    SciTech Connect

    Wu, Chaoxing; Li, Fushan E-mail: gtl-fzu@hotmail.com; Wu, Wei; Chen, Wei; Guo, Tailiang E-mail: gtl-fzu@hotmail.com

    2014-12-15

    Efficient and low-cost methods for obtaining high performance flexible transparent electrodes based on chemical vapor deposition (CVD)-grown graphene are highly desirable. In this work, the graphene grown on copper foil was exfoliated into micron-size sheets through controllable ultrasonication. We developed a clean technique by blending the exfoliated single layer graphene sheets with conducting polymer to form graphene-based composite solution, which can be spin-coated on flexible substrate, forming flexible transparent conducting film with high conductivity (?8 ?/?), high transmittance (?81% at 550?nm), and excellent mechanical robustness. In addition, CVD-grown-graphene-based polymer light emitting diodes with excellent bendable performances were demonstrated.

  12. Laser Focus World highlights Kaminski's home-grown ARPES spectroscopy...

    U.S. Department of Energy (DOE) - all webpages (Extended Search)

    Laser Focus World highlights Kaminski's home-grown ARPES spectroscopy system Laser Focus World senior editor Gail Overton wrote a story on angled-resolved photo-emission...

  13. Structural and Morphological Difference Between Ti/TiN/TiCN Coatings Grown in Multilayer and Graded Form

    SciTech Connect

    Restrepo, E.; Baena, A.; Agudelo, C.; Castillo, H.; Devia, A.; Marino, A.

    2006-12-04

    Thin films can be grown in super-lattice, multilayers and graded form, having each one advantages and disadvantages. The difference between multilayer and graded coatings is the interface. In multilayers the interface is abrupt and in graded coatings it is diffuse. The interface influences many chemical and physical properties of the materials, and its choice depends on the application. Graded coatings have the advantage of having gradual properties such as thermal expansion coefficient and lattice parameter, avoiding adherence problems due to good match between their component materials. In this work the comparison between some properties of coatings grown as multilayer and graded is performed. The materials are produced using the sputtering DC technique because of its facility to control the deposition parameters and generate a slow growth. The target is a disc of titanium and the samples are made of stainless steel 304. The working gases are argon, nitrogen and methane, which are mixed according to the material to be produced, i.e. Ti layer is grown with argon, the TiN film is produced with a mixture of argon and nitrogen, and the TiCN material is obtained mixing argon, nitrogen and methane. These materials are characterized with AFM in order to determine grain size and with XPS studying the chemical composition and performing depth profiles.

  14. X-ray absorption and reflection as probes of the GaN conduction bands: Theory and experiments

    SciTech Connect

    Lambrecht, W.R.L.; Rashkeev, S.N.; Segall, B.

    1997-04-01

    X-ray absorption measurements are a well-known probe of the unoccupied states in a material. The same information can be obtained by using glancing angle X-ray reflectivity. In spite of several existing band structure calculations of the group III nitrides and previous optical studies in UV range, a direct probe of their conduction band densities of states is of interest. The authors performed a joint experimental and theoretical investigation using both of these experimental techniques for wurtzite GaN.

  15. (001) Oriented piezoelectric films prepared by chemical solution deposition on Ni foils

    SciTech Connect

    Yeo, Hong Goo Trolier-McKinstry, Susan

    2014-07-07

    Flexible metal foil substrates are useful in some microelectromechanical systems applications including wearable piezoelectric sensors or energy harvesters based on Pb(Zr,Ti)O₃ (PZT) thin films. Full utilization of the potential of piezoelectrics on metal foils requires control of the film crystallographic texture. In this study, (001) oriented PZT thin films were grown by chemical solution deposition (CSD) on Ni foil and Si substrates. Ni foils were passivated using HfO₂ grown by atomic layer deposition in order to suppress substrate oxidation during subsequent thermal treatment. To obtain the desired orientation of PZT film, strongly (100) oriented LaNiO₃ films were integrated by CSD on the HfO₂ coated substrates. A high level of (001) LaNiO₃ and PZT film orientation were confirmed by X-ray diffraction patterns. Before poling, the low field dielectric permittivity and loss tangents of (001) oriented PZT films on Ni are near 780 and 0.04 at 1 kHz; the permittivity drops significantly on poling due to in-plane to out-of-plane domain switching. (001) oriented PZT film on Ni displayed a well-saturated hysteresis loop with a large remanent polarization ~36 μC/cm², while (100) oriented PZT on Si showed slanted P-E hysteresis loops with much lower remanent polarizations. The |e{sub 31,f}| piezoelectric coefficient was around 10.6 C/m² for hot-poled (001) oriented PZT film on Ni.

  16. Modifying magnetic properties of ultra-thin magnetite films by growth on Fe pre-covered MgO(001)

    SciTech Connect

    Schemme, T. Krampf, A.; Kuepper, K.; Wollschläger, J.; Bertram, F.; Kuschel, T.

    2015-09-21

    Iron oxide films were reactively grown on iron buffer films, which were deposited before on MgO(001) substrates to analyze the influence of the initial iron buffer layers on the magnetic properties of the magnetite films. X-ray photoelectron spectroscopy and low energy electron diffraction showed that magnetite films of high crystalline quality in the surface near region were formed by this two-step deposition procedure. The underlying iron film, however, was completely oxidized as proved by x-ray reflectometry and diffraction. The structural bulk quality of the iron oxide film is poor compared to magnetite films directly grown on MgO(001). Although the iron film was completely oxidized, we found drastically modified magnetic properties for these films using the magnetooptic Kerr effect. The magnetite films had strongly increased coercive fields, and their magnetic in-plane anisotropy is in-plane rotated by 45∘ compared to magnetite films formed directly by one step reactive growth on MgO(001)

  17. TEM characterization of nanodiamond thin films.

    SciTech Connect

    Qin, L.-C.; Zhou, D.; Krauss, A. R.; Gruen, D. M.; Chemistry

    1998-05-01

    The microstructure of thin films grown by microwave plasma-enhanced chemical vapor deposition (MPCVD) from fullerene C{sub 60} precursors has been characterized by scanning electron microscopy (SEM), selected-area electron diffraction (SAED), bright-field electron microscopy, high-resolution electron microscopy (HREM), and parallel electron energy loss spectroscopy (PEELS). The films are composed of nanosize crystallites of diamond, and no graphitic or amorphous phases were observed. The diamond crystallite size measured from lattice images shows that most grains range between 3-5 nm, reflecting a gamma distribution. SAED gave no evidence of either sp2-bonded glassy carbon or sp3-bonded diamondlike amorphous carbon. The sp2-bonded configuration found in PEELS was attributed to grain boundary carbon atoms, which constitute 5-10% of the total. Occasionally observed larger diamond grains tend to be highly faulted.

  18. DOE - NNSA/NFO -- Films

    U.S. Department of Energy (DOE) - all webpages (Extended Search)

    Films NNSANFO Language Options U.S. DOENNSA - Nevada Field Office Nevada Field Office Current Film Library A large number of films depicting historical as well as current ...

  19. Size-effects on the optical properties of zirconium oxide thin films

    SciTech Connect

    Ramana, C. V.; Vemuri, R. S.; Fernandez, I.; Campbell, A. L.

    2009-12-07

    Zirconium oxide (ZrO{sub 2}) thin films with an average crystallite-size (L) ranging from 5 to 25 nm were grown by sputter deposition onto optical grade quartz substrates. The optical properties of grown ZrO{sub 2} films were evaluated using optical transmission and reflectance spectroscopic measurements. The size-effects were significant on the optical characteristics of ZrO{sub 2} films. The bandgap energy (E{sub g}) was found to increase from 5.78 to 6.07 eV with decreasing L values from 20 to 7 nm. A direct, linear inverse L-E{sub g} relationship found for ZrO{sub 2} films suggest that tuning optical properties for desired applications can be achieved by controlling the size.

  20. Process for forming silicon carbide films and microcomponents

    DOEpatents

    Hamza, A.V.; Balooch, M.; Moalem, M.

    1999-01-19

    Silicon carbide films and microcomponents are grown on silicon substrates at surface temperatures between 900 K and 1700 K via C{sub 60} precursors in a hydrogen-free environment. Selective crystalline silicon carbide growth can be achieved on patterned silicon-silicon oxide samples. Patterned SiC films are produced by making use of the high reaction probability of C{sub 60} with silicon at surface temperatures greater than 900 K and the negligible reaction probability for C{sub 60} on silicon dioxide at surface temperatures less than 1250 K. 5 figs.

  1. Process for forming silicon carbide films and microcomponents

    DOEpatents

    Hamza, Alex V.; Balooch, Mehdi; Moalem, Mehran

    1999-01-01

    Silicon carbide films and microcomponents are grown on silicon substrates at surface temperatures between 900 K and 1700 K via C.sub.60 precursors in a hydrogen-free environment. Selective crystalline silicon carbide growth can be achieved on patterned silicon-silicon oxide samples. Patterned SiC films are produced by making use of the high reaction probability of C.sub.60 with silicon at surface temperatures greater than 900 K and the negligible reaction probability for C.sub.60 on silicon dioxide at surface temperatures less than 1250 K.

  2. Investigation to the deep center related properties of low temperature grown InPBi with Hall and photoluminescence

    SciTech Connect

    Wang, Peng; Pan, Wenwu; Wu, Xiaoyan; Wang, Kai; Yue, Li; Gong, Qian; Wang, Shumin

    2015-12-15

    InP{sub 1-x}Bi{sub x} epilayers with bismuth (Bi) concentration x= 1.0% were grown on InP by gas source molecular beam epitaxy (GS-MBE) at low temperature (LT). Bi incorporation decreased the intrinsic free electron concentration of low temperature grown InP indicated by hall analysis. It is concluded that deep level center was introduced by Bi. Influence of Si doping on the InP{sub 1-x}Bi{sub x} films Photoluminescence (PL) was investigated. N-type doping in the InP{sub 1-x}Bi{sub x} epilayers was found to be effective at PL enhancement. Blue shift of InPBi PL emission wavelength was observed as the Si doping concentration increasing. Two independent peaks were fitted and their temperature dependence behavior was observed to be distinct obviously. Two individual radiative recombination processes were expected to be involved.

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

    SciTech Connect

    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.

  4. Effect of Fe-doping on nonlinear optical responses and carrier trapping dynamics in GaN single crystals

    SciTech Connect

    Fang, Yu; Yang, Junyi; Yang, Yong; Zhou, Feng; Wu, Xingzhi; Xiao, Zhengguo; Song, Yinglin

    2015-08-03

    We presented a quantitative study on the Fe-doping concentration dependence of optical nonlinearities and ultrafast carrier dynamics in Fe-doped GaN (GaN:Fe) single crystals using picosecond Z-scan and femtosecond pump-probe with phase object techniques under two-photon excitation. In contrast to the two-photon absorption that was found to be independent on the Fe-doping, the nonlinear refraction decreased with the Fe concentration due to the fast carrier trapping effect of Fe{sup 3+}/Fe{sup 2+} deep acceptors, which simultaneously acted as an efficient non-radiative recombination channels for excess carriers. Remarkably, compared to that of Si-doped GaN bulk crystal, the free-carrier refraction effect in GaN:Fe crystals was found to be enhanced considerably since Fe-doping and the effective carrier lifetime (∼10 ps) could be tuned over three orders of magnitude at high Fe-doping level of 1 × 10{sup 19 }cm{sup −3}.

  5. Growth of crystalline ZnO films on the nitridated (0001) sapphire surface

    SciTech Connect

    Butashin, A. V.; Kanevsky, V. M.; Muslimov, A. E. Prosekov, P. A.; Kondratev, O. A.; Blagov, A. E.; Vasil’ev, A. L.; Rakova, E. V.; Babaev, V. A.; Ismailov, A. M.; Vovk, E. A.; Nizhankovsky, S. V.

    2015-07-15

    The surface morphology and structure of (0001) sapphire substrates subjected to thermochemical nitridation in a mixture of N{sub 2}, CO, and H{sub 2} gases are investigated by electron and probe microscopy and X-ray and electron diffraction. It is shown that an aluminum nitride layer is formed on the substrate surface and heteroepitaxial ZnO films deposited onto such substrates by magnetron sputtering have a higher quality when compared with films grown on sapphire.

  6. Magneto-optical characterizations of FeTe???Se??? thin films with critical current density over 1 MA/cm

    SciTech Connect

    Sun, Yue; Li, Qiang; Tsuchiya, Yuji; Pyon, Sunseng; Tamegai, Tsuyoshi; Zhang, Cheng; Ozaki, Toshinori

    2015-01-01

    We performed magneto-optical (MO) measurements on FeTe???Se??? thin films grown on LaAlO? (LAO) and Yttria-stabilized zirconia (YSZ) single-crystalline substrates. These thin films show superconducting transition temperature Tc ~19 K, 4 K higher than the bulk sample. Typical roof-top patterns can be observed in the MO images of thin films grown on LAO and YSZ, from which a large and homogeneous critical current density Jc ~ 3 - 4 x 10? A/cm at 5 K was obtained. Magnetic flux penetration measurement reveals that the current is almost isotropically distributed in the two thin films. Compared with bulk crystals, FeTe???Se??? thin film demonstrates not only higher Tc, but also much larger Jc, which is attractive for applications.

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

    DOE PAGES [OSTI]

    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

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

    SciTech Connect

    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.; Kravchenko, I. I.; Zhang, Ming-Lan

    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 dispersion 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.

  9. Density dependence of the room temperature thermal conductivity of atomic layer deposition-grown amorphous alumina (Al{sub 2}O{sub 3})

    SciTech Connect

    Gorham, Caroline S.; Gaskins, John T.; Hopkins, Patrick E.; Parsons, Gregory N.; Losego, Mark D.

    2014-06-23

    We report on the thermal conductivity of atomic layer deposition-grown amorphous alumina thin films as a function of atomic density. Using time domain thermoreflectance, we measure the thermal conductivity of the thin alumina films at room temperature. The thermal conductivities vary ?35% for a nearly 15% change in atomic density and are substrate independent. No density dependence of the longitudinal sound speeds is observed with picosecond acoustics. The density dependence of the thermal conductivity agrees well with a minimum limit to thermal conductivity model that is modified with a differential effective-medium approximation.

  10. Martensite transformation of epitaxial Ni-Ti films

    SciTech Connect

    Buschbeck, J.; Kozhanov, A.; Kawasaki, J. K.; James, R. D.; Palmstroem, C. J.

    2011-05-09

    The structure and phase transformations of thin Ni-Ti shape memory alloy films grown by molecular beam epitaxy are investigated for compositions from 43 to 56 at. % Ti. Despite the substrate constraint, temperature dependent x-ray diffraction and resistivity measurements reveal reversible, martensitic phase transformations. The results suggest that these occur by an in-plane shear which does not disturb the lattice coherence at interfaces.

  11. Indium Phosphide Polycrystalline Films on Metal Foil for PV Applications -

    U.S. Department of Energy (DOE) - all webpages (Extended Search)

    Energy Innovation Portal Indium Phosphide Polycrystalline Films on Metal Foil for PV Applications Lawrence Berkeley National Laboratory Contact LBL About This Technology Publications: PDF Document Publication Zheng, M., Yu, Z., Seok, T.J., Chen, Y-Z., Kapadia, R., Takei, K., Aloni, S., Ager, J.W., Wu, M., Chueh, Y-L., Javey, A. "High optical quality polycrystalline indium phosphide grown on metal substrates by metalorganic chemical vapor deposition," Journal of Applied Physics 111,

  12. Observation of second spin reorientation transition within ultrathin region in Fe films on Ag(001) surface

    SciTech Connect

    Khim, T.-Y.; Shin, M.; Lee, H. E-mail: jhp@postech.ac.kr; Park, B.-G.; Park, J.-H. E-mail: jhp@postech.ac.kr

    2014-06-21

    We acquired direct measurements for in-plane and perpendicular-to-plane magnetic moments of Fe films using an x-ray magnetic circular dichroism technique with increase of the Fe thickness (up to 40 Å) on the Ag(001) surface. Epitaxial Fe/Ag(001) films were grown in situ with the thickness varying from 2 Å to 40 Å, and the magnetic anisotropy was carefully investigated as a function of the film thickness. We found re-entrance of the in-plane magnetic anisotropy of the Fe film in ultrathin region. The results manifest that the epitaxial Fe/Ag(001) film undergoes two distinct spin reorientation transitions from in-plane to out-of-plane at the film thickness t ≈ 9 Å and back to in-plane at t ≈ 18 Å as t increases.

  13. High sensitive formaldehyde graphene gas sensor modified by atomic layer deposition zinc oxide films

    SciTech Connect

    Mu, Haichuan; Zhang, Zhiqiang; Wang, Keke; Xie, Haifen, E-mail: hfxie@ecust.edu.cn [Department of Physics, School of Science, East China University of Science and Technology, 130 Meilong Road, Shanghai 200237 (China); Zhao, Xiaojing; Liu, Feng [Department of Physics, Shanghai Normal University, 100 Guilin Road, Shanghai 200234 (China)

    2014-07-21

    Zinc oxide (ZnO) thin films with various thicknesses were fabricated by Atomic Layer Deposition on Chemical Vapor Deposition grown graphene films and their response to formaldehyde has been investigated. It was found that 0.5?nm ZnO films modified graphene sensors showed high response to formaldehyde with the resistance change up to 52% at the concentration of 9 parts-per-million (ppm) at room temperature. Meanwhile, the detection limit could reach 180 parts-per-billion (ppb) and fast response of 36?s was also obtained. The high sensitivity could be attributed to the combining effect from the highly reactive, top mounted ZnO thin films, and high conductive graphene base network. The dependence of ZnO films surface morphology and its sensitivity on the ZnO films thickness was also investigated.

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

    SciTech Connect

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

    1999-04-26

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

  15. Study of non-linear Hall effect in nitrogen-grown ZnO microstructure and the effect of H{sup +}-implantation

    SciTech Connect

    Kumar, Yogesh Bern, Francis; Barzola-Quiquia, Jose; Lorite, Israel; Esquinazi, Pablo

    2015-07-13

    We report magnetotransport studies on microstructured ZnO film grown by pulsed laser deposition in N{sub 2} atmosphere on a-plane Al{sub 2}O{sub 3} substrates and the effect of low energy H{sup +}-implantation. Non-linearity has been found in the magnetic field dependent Hall resistance, which decreases with temperature. We explain this effect with a two-band model assuming the conduction through two different parallel channels having different types of charge carriers. Reduced non-linearity after H{sup +}-implantation in the grown film is due to the shallow-donor effect of hydrogen giving rise to an increment in the electron density, reducing the effect of the other channel.

  16. Self-modulated nanostructures in super-large-period Bi{sub 11}(Fe{sub 5}CoTi{sub 3}){sub 10/9}O{sub 33} epitaxial thin films

    SciTech Connect

    Meng, Dechao; Huang, Haoliang; Yun, Yu; Huang, Yan; Zhai, Xiaofang; Ma, Chao; Fu, Zhengping; Peng, Ranran; Mao, Xiangyu; Chen, Xiaobing; Brown, Gail; and others

    2015-05-25

    Super-large-period Aurivillius thin films with a pseudo-period of ten were grown on (0 0 1) SrTiO{sub 3} substrates using the pulsed laser deposition method. The as-grown films are found to be coherently strained to the substrate and atomically smooth. X-ray diffraction indicates an average periodicity of ten, while analysis with the high resolution scanning transmission electron microscopy reveals a self-modulated nanostructure in which the periodicity changes as the film thickness increases. Finally, we discuss the magnetic and possible ferroelectric properties of the self-modulated large period Aurivillius films at the room temperature.

  17. Influence of nanostructure on charge transport in RuO{sub 2} thin films

    SciTech Connect

    Steeves, M. M.; Lad, R. J.

    2010-07-15

    Polycrystalline thin films of RuO{sub 2} were grown on fused-quartz substrates and a parametric study was carried out to probe the influence of film nanostructure on the four-point Van der Pauw resistivity and Hall coefficient. The films were grown via reactive rf magnetron sputtering of a Ru target in an Ar/O{sub 2} plasma using deposition rates from 0.27 to 3.5 A/s and substrate temperatures from 16 to 500 deg. C Room-temperature resistivities of the RuO{sub 2} films ranged from 58 to 360 {mu}{Omega} cm. Upon first heating following deposition, some films showed decreasing resistivity with increasing temperature, but the resistivities also decreased upon subsequent cooling suggesting that the annealing treatment reduces the film defect density. The temperature coefficient of resistance was found to be small (<0.001 K{sup -1}) in agreement with previous investigations. Hall coefficient measurements of the polycrystalline thin films demonstrated that either n-type or p-type majority carriers can be present depending on deposition conditions and the resulting nanostructure, in contrast to single-crystal RuO{sub 2}, which is an n-type metal. Grain size and homogeneous strain within the films were measured by x-ray diffraction and are correlated to the majority carrier type.

  18. Microstructure investigations of hcp phase CoPt thin films with high coercivity

    SciTech Connect

    Yang, Y.; Varghese, B.; Tan, H. K.; Wong, S. K.; Piramanayagam, S. N.

    2014-02-28

    CoPt films have been grown in the past with a high anisotropy in L1{sub 1} or L1{sub 0} phase, and a high coercivity is observed only in L1{sub 0} CoPt films. Recently, we have grown CoPt films which exhibited a high coercivity without exhibiting an ordered phase. In this study, high resolution transmission electron microscopy (HRTEM) investigations have been carried out to understand the strong thickness and deposition pressure dependent magnetic properties. HRTEM studies revealed the formation of an initial growth layer in a metastable hexagonal (hcp) CoPt with high anisotropy. This phase is believed to be aided by the heteroepitaxial growth on Ru as well as the formation of Ru-doped CoPt phase. As the films grew thicker, transformation from hcp phase to an energetically favourable face-centered cubic (fcc) phase was observed. Stacking faults were found predominantly at the hcp-fcc transformation region of the CoPt film. The higher coercivity of thinner CoPt film is attributed to relatively less fcc fraction, less stacking faults, and to the isolated grain structure of these films compared to the thicker films.

  19. Iso-oriented monolayer α-MoO3(010) films epitaxially grown on...

    Office of Scientific and Technical Information (OSTI)

    the splitting of streaks in reflection high-energy electron diffraction (RHEED) patterns. ... in thickness, which is explained by a balance between deposition and thermal desorption ...

  20. Peculiarly strong room-temperature ferromagnetism from low Mn-doping in ZnO grown by molecular beam epitaxy

    SciTech Connect

    Zuo Zheng; Morshed, Muhammad; Liu Jianlin; Beyermann, W. P.; Zheng Jianguo; Xin Yan

    2013-03-15

    Strong room-temperature ferromagnetism is demonstrated in single crystalline Mn-doped ZnO thin films grown by molecular beam epitaxy. Very low Mn doping concentration is investigated, and the measured magnetic moment is much larger than what is expected for an isolated ion based on Hund's rules. The ferromagnetic behavior evolves with Mn concentration. Both magnetic anisotropy and anomalous Hall effect confirm the intrinsic nature of ferromagnetism. While the Mn dopant plays a crucial role, another entity in the system is needed to explain the observed large magnetic moments.

  1. Thickness-dependent blue shift in the excitonic peak of conformally grown ZnO:Al on ion-beam fabricated self-organized Si ripples

    SciTech Connect

    Basu, T.; Kumar, M.; Som, T.; Nandy, S.; Satpati, B.; Saini, C. P.; Kanjilal, A.

    2015-09-14

    Al-doped ZnO (AZO) thin films of thicknesses 5,10, 15, 20, and 30 nm were deposited on 500 eV argon ion-beam fabricated nanoscale self-organized rippled-Si substrates at room temperature and are compared with similar films deposited on pristine-Si substrates (without ripples). It is observed that morphology of self-organized AZO films is driven by the underlying substrate morphology. For instance, for pristine-Si substrates, a granular morphology evolves for all AZO films. On the other hand, for rippled-Si substrates, morphologies having chain-like arrangement (anisotropic in nature) are observed up to a thickness of 20 nm, while a granular morphology evolves (isotropic in nature) for 30 nm-thick film. Photoluminescence studies reveal that excitonic peaks corresponding to 5–15 nm-thick AZO films, grown on rippled-Si templates, show a blue shift of 8 nm and 3 nm, respectively, whereas the peak shift is negligible for 20-nm thick film (with respect to their pristine counter parts). The observed blue shifts are substantiated by diffuse reflectance study and attributed to quantum confinement effect, associated with the size of the AZO grains and their spatial arrangements driven by the anisotropic morphology of underlying rippled-Si templates. The present findings will be useful for making tunable AZO-based light-emitting devices.

  2. Growth of epitaxial (Sr,Ba){sub n+1}Ru{sub n}O{sub 3n+1} films

    SciTech Connect

    Schlom, D.G.; Knapp, S.B.; Wozniak, S. [Pennsylvania State Univ., University Park, PA (United States). Dept. of Materials Science and Engineering] [and others

    1997-12-01

    We have grown epitaxial (Sr,Ba) (n+1)Ru(n)O(3n+1) films, n = 1, 2, and infinity, by pulsed laser deposition (PLD) and controlled their orientation by choosing appropriate substrates. The growth conditions yielding phase pure films have been mapped out. Resistivity versus temperature measurements show that both a and c axis films of Sr2RuO4 are metallic, but not superconducting. The latter is probably due to the presence of low-level impurities that are difficult to avoid given the target preparation process involved in growing these films by PLD.

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

    SciTech Connect

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

    2013-09-27

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

  4. Vehicle Technologies Office Merit Review 2014: Advanced Low-Cost SiC and GaN Wide Bandgap Inverters for Under-the-Hood Electric Vehicle Traction Drives

    Energy.gov [DOE]

    Presentation given by APEI Inc. at 2014 DOE Hydrogen and Fuel Cells Program and Vehicle Technologies Office Annual Merit Review and Peer Evaluation Meeting about Advanced low-cost SIC and GaN wide...

  5. Vehicle Technologies Office Merit Review 2015: Advanced Low-Cost SiC and GaN Wide Bandgap Inverters for Under-the-Hood Electric Vehicle Traction Drives

    Energy.gov [DOE]

    Presentation given by APEI Inc. at 2015 DOE Hydrogen and Fuel Cells Program and Vehicle Technologies Office Annual Merit Review and Peer Evaluation Meeting about advanced low-cost SiC and GaN wide...

  6. Nanotransfer and nanoreplication using deterministically grown sacrificial nanotemplates

    DOEpatents

    Melechko, Anatoli V.; McKnight, Timothy E.; Guillorn, Michael A.; Ilic, Bojan; Merkulov, Vladimir I.; Doktycz, Mitchel J.; Lowndes, Douglas H.; Simpson, Michael L.

    2011-08-23

    Methods, manufactures, machines and compositions are described for nanotransfer and nanoreplication using deterministically grown sacrificial nanotemplates. An apparatus, includes a substrate and a nanoreplicant structure coupled to a surface of the substrate.

  7. Tuning thermoelectricity in a Bi2Se3 topological insulator via varied film thickness

    DOE PAGES [OSTI]

    Guo, Minghua; Wang, Zhenyu; Xu, Yong; Huang, Huaqing; Zang, Yunyi; Liu, Chang; Duan, Wenhui; Gan, Zhongxue; Zhang, Shou-Cheng; He, Ke; et al

    2016-01-12

    We report thermoelectric transport studies on Bi2Se3 topological insulator thin films with varied thickness grown by molecular beam epitaxy. We find that the Seebeck coefficient and thermoelectric power factor decrease systematically with the reduction of film thickness. These experimental observations can be explained quantitatively by theoretical calculations based on realistic electronic band structure of the Bi2Se3 thin films. Lastly, this work illustrates the crucial role played by the topological surface states on the thermoelectric transport of topological insulators, and sheds new light on further improvement of their thermoelectric performance.

  8. Strain-induced optical band gap variation of SnO2 films (Journal Article) |

    Office of Scientific and Technical Information (OSTI)

    SciTech Connect Strain-induced optical band gap variation of SnO2 films Citation Details In-Document Search This content will become publicly available on June 29, 2017 Title: Strain-induced optical band gap variation of SnO2 films In this paper, thickness dependent strain relaxation effects are utilized to study the impact of crystal anisotropy on the optical band gap of epitaxial SnO2 films grown by pulsed laser deposition on (0001)-oriented sapphire substrates. An X-ray diffraction

  9. Atomic layer deposition of superparamagnetic and ferrimagnetic magnetite thin films

    SciTech Connect

    Zhang, Yijun; Liu, Ming E-mail: wren@mail.xjtu.edu.cn Ren, Wei E-mail: wren@mail.xjtu.edu.cn; Zhang, Yuepeng; Chen, Xing; Ye, Zuo-Guang E-mail: wren@mail.xjtu.edu.cn

    2015-05-07

    One of the key challenges in realizing superparamagnetism in magnetic thin films lies in finding a low-energy growth way to create sufficiently small grains and magnetic domains which allow the magnetization to randomly and rapidly reverse. In this work, well-defined superparamagnetic and ferrimagnetic Fe{sub 3}O{sub 4} thin films are successfully prepared using atomic layer deposition technique by finely controlling the growth condition and post-annealing process. As-grown Fe{sub 3}O{sub 4} thin films exhibit a conformal surface and poly-crystalline nature with an average grain size of 7 nm, resulting in a superparamagnetic behavior with a blocking temperature of 210 K. After post-annealing in H{sub 2}/Ar at 400 °C, the as-grown α−Fe{sub 2}O{sub 3} sample is reduced to Fe{sub 3}O{sub 4} phase, exhibiting a ferrimagnetic ordering and distinct magnetic shape anisotropy. Atomic layer deposition of magnetite thin films with well-controlled morphology and magnetic properties provides great opportunities for integrating with other order parameters to realize magnetic nano-devices with potential applications in spintronics, electronics, and bio-applications.

  10. Process for growing a film epitaxially upon a MgO surface

    DOEpatents

    McKee, Rodney Allen; Walker, Frederick Joseph

    1997-01-01

    A process and structure wherein optical quality perovskites, such as BaTiO.sub.3 or SrTiO.sub.3, are grown upon a single crystal MgO substrate involves the epitaxial build up of alternating planes of TiO.sub.2 and metal oxide wherein the first plane grown upon the MgO substrate is a plane of TiO.sub.2. The layering sequence involved in the film build up reduces problems which would otherwise result from the interfacial electrostatics at the first atomic layers, and these oxides can be stabilized as commensurate thin films at a unit cell thickness or grown with high crystal quality to thicknesses of 0.5-0.7 .mu.m for optical device applications.

  11. Process for growing a film epitaxially upon a MGO surface and structures formed with the process

    DOEpatents

    McKee, Rodney Allen; Walker, Frederick Joseph

    1998-01-01

    A process and structure wherein optical quality perovskites, such as BaTiO.sub.3 or SrTiO.sub.3, are grown upon a single crystal MgO substrate involves the epitaxial build up of alternating planes of TiO.sub.2 and metal oxide wherein the first plane grown upon the MgO substrate is a plane of TiO.sub.2. The layering sequence involved in the film build up reduces problems which would otherwise result from the interfacial electrostatics at the first atomic layers, and these oxides can be stabilized as commensurate thin films at a unit cell thickness or grown with high crystal quality to thicknesses of 0.5-0.7 .mu.m for optical device applications.

  12. Growth of CdTe thin films on graphene by close-spaced sublimation method

    SciTech Connect

    Jung, Younghun; Yang, Gwangseok; Kim, Jihyun, E-mail: hyunhyun7@korea.ac.kr [Department of Chemical and Biological Engineering, Korea University, Seoul 136-701 (Korea, Republic of)] [Department of Chemical and Biological Engineering, Korea University, Seoul 136-701 (Korea, Republic of); Chun, Seungju; Kim, Donghwan [Department of Materials Science and Engineering, Korea University, Seoul 136-701 (Korea, Republic of)] [Department of Materials Science and Engineering, Korea University, Seoul 136-701 (Korea, Republic of)

    2013-12-02

    CdTe thin films grown on bi-layer graphene were demonstrated by using the close-spaced sublimation method, where CdTe was selectively grown on the graphene. The density of the CdTe domains was increased with increasing the number of the defective sites in the graphene, which was controlled by the duration of UV exposure. The CdTe growth rate on the bi-layer graphene electrodes was 400?nm/min with a bandgap energy of 1.451.49?eV. Scanning electron microscopy, micro-Raman spectroscopy, micro-photoluminescence, and X-ray diffraction technique were used to confirm the high quality of the CdTe thin films grown on the graphene electrodes.

  13. Phase-field simulations of GaN growth by selective area epitaxy from complex mask geometries

    SciTech Connect

    Aagesen, Larry K.; Thornton, Katsuyo; Coltrin, Michael E.; Han, Jung

    2015-05-21

    Three-dimensional phase-field simulations of GaN growth by selective area epitaxy were performed. The model includes a crystallographic-orientation-dependent deposition rate and arbitrarily complex mask geometries. The orientation-dependent deposition rate can be determined from experimental measurements of the relative growth rates of low-index crystallographic facets. Growth on various complex mask geometries was simulated on both c-plane and a-plane template layers. Agreement was observed between simulations and experiment, including complex phenomena occurring at the intersections between facets. The sources of the discrepancies between simulated and experimental morphologies were also investigated. The model provides a route to optimize masks and processing conditions during materials synthesis for solar cells, light-emitting diodes, and other electronic and opto-electronic applications.

  14. Phase-field simulations of GaN growth by selective area epitaxy on complex mask geometries

    DOE PAGES [OSTI]

    Aagesen, Larry K.; Coltrin, Michael Elliott; Han, Jung; Thornton, Katsuyo

    2015-05-15

    Three-dimensional phase-field simulations of GaN growth by selective area epitaxy were performed. Furthermore, this model includes a crystallographic-orientation-dependent deposition rate and arbitrarily complex mask geometries. The orientation-dependent deposition rate can be determined from experimental measurements of the relative growth rates of low-index crystallographic facets. Growth on various complex mask geometries was simulated on both c-plane and a-plane template layers. Agreement was observed between simulations and experiment, including complex phenomena occurring at the intersections between facets. The sources of the discrepancies between simulated and experimental morphologies were also investigated. We found that the model provides a route to optimize masks andmore » processing conditions during materials synthesis for solar cells, light-emitting diodes, and other electronic and opto-electronic applications.« less

  15. Phase-field simulations of GaN growth by selective area epitaxy on complex mask geometries

    SciTech Connect

    Aagesen, Larry K.; Coltrin, Michael Elliott; Han, Jung; Thornton, Katsuyo

    2015-05-15

    Three-dimensional phase-field simulations of GaN growth by selective area epitaxy were performed. Furthermore, this model includes a crystallographic-orientation-dependent deposition rate and arbitrarily complex mask geometries. The orientation-dependent deposition rate can be determined from experimental measurements of the relative growth rates of low-index crystallographic facets. Growth on various complex mask geometries was simulated on both c-plane and a-plane template layers. Agreement was observed between simulations and experiment, including complex phenomena occurring at the intersections between facets. The sources of the discrepancies between simulated and experimental morphologies were also investigated. We found that the model provides a route to optimize masks and processing conditions during materials synthesis for solar cells, light-emitting diodes, and other electronic and opto-electronic applications.

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

    SciTech Connect

    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.

  17. Influence of defects on the structural and magnetic properties of multifunctional La2NiMnO6 thin films

    SciTech Connect

    Guo, HZ; Burgess, J; Ada, E; Street, S; Gupta, A.; Iliev, M N; Kellock, A J; Magen Dominguez, Cesar; Varela del Arco, Maria; Pennycook, Stephen J

    2008-01-01

    Thin films of the double perovskite La2NiMnO6 (LNMO) have been grown on various lattice-matched substrates (SrTiO3, LaAlO3, NdGaO3 and MgO) by pulsed laser deposition under varying oxygen background pressure (25 - 800 mTorr). The out-of-plane lattice constant of the LNMO film initially decreases with increasing pressure, likely caused by a reduction in the defect concentration and improved structural ordering, before leveling off at higher pressures. Scanning transmission electron microscopy results show that the films are epitaxial, and the interface is sharp and coherent. While very few defects are observed by STEM in a film grown at high oxygen pressure (800 mTorr), a film grown at a lower pressure (100 mTorr) shows the formation of defects that extend throughout the thickness except for a very thin layer near the interface. The Raman spectra of the films are dominated by two broad peaks at around 540 cm-1 and 685 cm-1, which are assigned to the antisymmetric stretching (AS) and symmetric stretching (S) modes of MnO6 and NiO6 octahedra, respectively. The Raman peaks of the LNMO thin films grown in 800 mTorr background O2 are blue shifted in comparison to those of LNMO bulk, and the shift increases with decreasing film thickness, indicating the increased influence of strain. The critical thickness for strain relaxation as determined from the Raman spectra is between 40 - 80 nm. The strain is observed to have a negligible influence on the magnetic properties for films grown at high oxygen pressures. However, films grown at low pressures exhibit degraded magnetic properties, which can be attributed to a combination of B-site cation disorder and an increase in the concentration of Mn3+ and Ni3+ Jahn-Teller ions caused by oxygen defects. With increasing oxygen pressure during growth, the paramagnetic-ferromagnetic transition temperature (~280 K) gets sharper and the saturation magnetization at low temperatures is enhanced. Based on electron energy loss spectroscopy

  18. Carbon doped GaN buffer layer using propane for high electron mobility transistor applications: Growth and device results

    SciTech Connect

    Li, X.; Nilsson, D.; Danielsson, Ö.; Pedersen, H.; Janzén, E.; Forsberg, U.; Bergsten, J.; Rorsman, N.

    2015-12-28

    The creation of a semi insulating (SI) buffer layer in AlGaN/GaN High Electron Mobility Transistor (HEMT) devices is crucial for preventing a current path beneath the two-dimensional electron gas (2DEG). In this investigation, we evaluate the use of a gaseous carbon gas precursor, propane, for creating a SI GaN buffer layer in a HEMT structure. The carbon doped profile, using propane gas, is a two stepped profile with a high carbon doping (1.5 × 10{sup 18 }cm{sup −3}) epitaxial layer closest to the substrate and a lower doped layer (3 × 10{sup 16 }cm{sup −3}) closest to the 2DEG channel. Secondary Ion Mass Spectrometry measurement shows a uniform incorporation versus depth, and no memory effect from carbon doping can be seen. The high carbon doping (1.5 × 10{sup 18 }cm{sup −3}) does not influence the surface morphology, and a roughness root-mean-square value of 0.43 nm is obtained from Atomic Force Microscopy. High resolution X-ray diffraction measurements show very sharp peaks and no structural degradation can be seen related to the heavy carbon doped layer. HEMTs are fabricated and show an extremely low drain induced barrier lowering value of 0.1 mV/V, demonstrating an excellent buffer isolation. The carbon doped GaN buffer layer using propane gas is compared to samples using carbon from the trimethylgallium molecule, showing equally low leakage currents, demonstrating the capability of growing highly resistive buffer layers using a gaseous carbon source.

  19. Characterization of Thin Films by XAFS: Application to Spintronics Materials

    SciTech Connect

    Heald, Steve M.; Kaspar, Tiffany C.; Droubay, Timothy C.; Chambers, Scott A.

    2009-10-25

    X-ray absorption fine structure (XAFS) has proven very valuable in characterizing thin films. This is illustrated with some examples from the area of diluted magnetic semiconductor (DMS) materials for spintronics applications. A promising route to DMS materials is doping of oxides such as TiO2 and ZnO with magnetic atoms such as Co. These can be grown as epitaxial thin films on various substrates. XAFS is especially valuable for characterizing the dopant atoms. The near edge region is sensitive to the symmetry of the bonding and valence of the dopants, and the extended XAFS can determine the details of the lattice site. XAFS is also valuable for detecting metallic nanoparticles. These can be difficult to detect by other methods, and can give a spurious magnetic signal. The power of XAFS is illustrated by examples from studies on Co doped ZnO films.

  20. Helium release and microstructural changes in Er(D,T)2-x3Hex films).

    SciTech Connect

    Gelles, D. S.; Browning, James Frederick; Snow, Clark Sheldon; Banks, James Clifford; Mangan, Michael A.; Rodriguez, Mark Andrew; Brewer, Luke N.; Kotula, Paul Gabriel

    2007-12-01

    Er(D,T){sub 2-x} {sup 3}He{sub x}, erbium di-tritide, films of thicknesses 500 nm, 400 nm, 300 nm, 200 nm, and 100 nm were grown and analyzed by Transmission Electron Microscopy, X-Ray Diffraction, and Ion Beam Analysis to determine variations in film microstructure as a function of film thickness and age, due to the time-dependent build-up of {sup 3}He in the film from the radioactive decay of tritium. Several interesting features were observed: One, the amount of helium released as a function of film thickness is relatively constant. This suggests that the helium is being released only from the near surface region and that the helium is not diffusing to the surface from the bulk of the film. Two, lenticular helium bubbles are observed as a result of the radioactive decay of tritium into {sup 3}He. These bubbles grow along the [111] crystallographic direction. Three, a helium bubble free zone, or 'denuded zone' is observed near the surface. The size of this region is independent of film thickness. Four, an analysis of secondary diffraction spots in the Transmission Electron Microscopy study indicate that small erbium oxide precipitates, 5-10 nm in size, exist throughout the film. Further, all of the films had large erbium oxide inclusions, in many cases these inclusions span the depth of the film.

  1. Correlation between surface chemistry, density and band gap in nanocrystalline WO3 thin films

    SciTech Connect

    Vemuri, Venkata Rama Ses; Engelhard, Mark H.; Ramana, C.V.

    2012-03-01

    Nanocrystalline WO3 thin films were produced by sputter-deposition by varying the ratio of argon to oxygen in the reactive gas mixture during deposition. The surface chemistry, physical characteristics, and optical properties of nanocrystalline WO3 films were evaluated using X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray reflectivity (XRR), and spectrophotometric measurements. The effect of ultra-microstructure was significant on the optical properties of WO3 films. The XPS analyses indicate the formation of stoichiometric WO3 with tungsten existing in fully oxidized valence state (W6+). However, WO3 films grown at high oxygen concentration (>60%) in the sputtering gas mixture were over stoichiometric with excess oxygen. XRR simulations, which are based on isotropic WO3 film - SiO2 interface - Si substrate model, indicate that the density of WO3 films is sensitive to the oxygen content in the sputtering gas. The spectral transmission of the films increased with the increasing oxygen. The band gap of these films increases from 2.78 eV to 3.25 eV with increasing oxygen. A direct correlation between the film-density and band gap in nanocrystalline WO3 films is established based on the observed results.

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

    DOE PAGES [OSTI]

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

    2014-12-05

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

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

    SciTech Connect

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

    2014-12-07

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

  4. Effect of InGaAs interlayer on the properties of GaAs grown on Si (111) substrate by molecular beam epitaxy

    SciTech Connect

    Wen, Lei; Gao, Fangliang; Li, Jingling; Guan, Yunfang; Wang, Wenliang; Zhou, Shizhong; Lin, Zhiting; Zhang, Xiaona; Zhang, Shuguang E-mail: mssgzhang@scut.edu.cn; Li, Guoqiang E-mail: mssgzhang@scut.edu.cn

    2014-11-21

    High-quality GaAs films have been epitaxially grown on Si (111) substrates by inserting an In{sub x}Ga{sub 1−x}As interlayer with proper In composition by molecular beam epitaxy (MBE). The effect of In{sub x}Ga{sub 1−x}As (0 < x < 0.2) interlayers on the properties of GaAs films grown on Si (111) substrates by MBE has been studied in detailed. Due to the high compressive strain between InGaAs and Si, InGaAs undergoes partial strain relaxation. Unstrained InGaAs has a larger lattice constant than GaAs. Therefore, a thin InGaAs layer with proper In composition may adopt a close lattice constant with that of GaAs, which is beneficial to the growth of high-quality GaAs epilayer on top. It is found that the proper In composition in In{sub x}Ga{sub 1−x}As interlayer of 10% is beneficial to obtaining high-quality GaAs films, which, on the one hand, greatly compensates the misfit stress between GaAs film and Si substrate, and on the other hand, suppresses the formation of multiple twin during the heteroepitaxial growth of GaAs film. However, when the In composition does not reach the proper value (∼10%), the In{sub x}Ga{sub 1−x}As adopts a lower strain relaxation and undergoes a lattice constant smaller than unstrained GaAs, and therefore introduces compressive stress to GaAs grown on top. When In composition exceeds the proper value, the In{sub x}Ga{sub 1−x}As will adopt a higher strain relaxation and undergoes a lattice constant larger than unstrained GaAs, and therefore introduces tensile stress to GaAs grown on top. As a result, In{sub x}Ga{sub 1−x}As interlayers with improper In composition introduces enlarged misfit stress to GaAs epilayers grown on top, and deteriorates the quality of GaAs epilayers. This work demonstrates a simple but effective method to grow high-quality GaAs epilayers and brings up a broad prospect for the application of GaAs-based optoelectronic devices on Si substrates.

  5. Epitaxial growth, structure, and intermixing at the LaAlO{sub 3}/SrTiO{sub 3} interface as the film stoichiometry is varied

    SciTech Connect

    Qiao, L.; Droubay, T. C.; Kaspar, T. C.; Chambers, S. A.; Varga, T.; Bowden, M. E.; Shutthanandan, V.; Zhu, Z.

    2011-02-15

    LaAlO{sub 3} epitaxial films with La:Al cation ratios ranging from 0.9 to 1.2 were grown on TiO{sub 2}-terminated SrTiO{sub 3} (001) substrates by off-axis pulsed laser deposition. Although all films are epitaxial, rocking curve measurements show that the crystallographic quality degrades with increasing La:Al ratio. Films with La:Al ratios of 0.9, 1.0, and 1.1 were coherently strained to the substrate. However, the out-of-plane lattice parameter increases over this range, revealing a decrease in film tetragonality. Although all film surfaces exhibit hydroxylation, the extent of hydroxylation is greater for the La-rich films. Rutherford backscattering spectrometry reveals that La from the film diffuses deeply into the SrTiO{sub 3} substrate and secondary-ion-mass spectroscopy shows unambiguous Sr outdiffusion into the films.

  6. Modified Magnetic Ground State in Nimn (2) O (4) Thin Films

    SciTech Connect

    Nelson-Cheeseman, B.B.; Chopdekar, R.V.; Iwata, J.M.; Toney, M.F.; Arenholz, E.; Suzuki, Y.; /SLAC

    2012-08-23

    The authors demonstrate the stabilization of a magnetic ground state in epitaxial NiMn{sub 2}O{sub 4} (NMO) thin films not observed in their bulk counterpart. Bulk NMO exhibits a magnetic transition from a paramagnetic phase to a collinear ferrimagnetic moment configuration below 110 K and to a canted moment configuration below 70 K. By contrast, as-grown NMO films exhibit a single magnetic transition at 60 K and annealed films exhibit the magnetic behavior found in bulk. Cation inversion and epitaxial strain are ruled out as possible causes for the new magnetic ground state in the as-grown films. However, a decrease in the octahedral Mn{sup 4+}:Mn{sup 3+} concentration is observed and likely disrupts the double exchange that produces the magnetic state at intermediate temperatures. X-ray magnetic circular dichroism and bulk magnetometry indicate a canted ferrimagnetic state in all samples at low T. Together these results suggest that the collinear ferrimagnetic state observed in bulk NMO at intermediate temperatures is suppressed in the as grown NMO thin films due to a decrease in octahedral Mn{sup 4+}, while the canted moment ferrimagnetic ordering is preserved below 60 K.

  7. Epitaxial Crystal Silicon Absorber Layers and Solar Cells Grown at 1.8 Microns per Minute: Preprint

    SciTech Connect

    Bobela, D. C.; Teplin, C. W.; Young, D. L.; Branz, H. M.; Stradins, P.

    2011-07-01

    We have grown device-quality epitaxial silicon thin films at growth rates up to 1.8 ?m/min, using hot-wire chemical vapor deposition from silane at substrate temperatures below 750 degrees C. At these rates, which are more than 30 times faster than those used by the amorphous and nanocrystalline Si industry, capital costs for large-scale solar cell production would be dramatically reduced, even for cell absorber layers up to 10 ?m thick. We achieved high growth rates by optimizing the three key parameters: silane flow, depletion, and filament geometry, based on our model developed earlier. Hydrogen coverage of the filament surface likely limits silane decomposition and growth rate at high system pressures. No considerable deterioration in PV device performance is observed when grown at high rate, provided that the epitaxial growth is initiated at low rate. A simple mesa device structure (wafer/epi Si/a-Si(i)/a-Si:H(p)/ITO) with a 2.3 um epitaxial silicon absorber layer was grown at 700 nm/min. The finished device had an open-circuit voltage of 0.424 V without hydrogenation treatment.

  8. Electric field-induced magnetic switching in Mn:ZnO film

    SciTech Connect

    Ren, S. X.; Sun, G. W.; Zhao, J.; Dong, J. Y.; Zhao, X.; Chen, W.; Wei, Y.; Ma, Z. C.

    2014-06-09

    A large magnetic modulation, accompanied by stable bipolar resistive switching (RS) behavior, was observed in a Mn:ZnO film by applying a reversible electric field. A significant enhancement of the ferromagnetism of the film, to about five times larger than that in the initial (as-grown) state (IS), was obtained by switching the film into the low resistance state. X-ray photoelectron spectroscopy demonstrated the existence of abundant oxygen vacancies in the IS of the film. We suggest that this electric field-induced magnetic switching effect originates with the migration and redistribution of oxygen vacancies during RS. Our work indicates that electric switching is an effective and simple method to increase the ferromagnetism of diluted magnetic oxide films. This provides a promising direction for research in spintronic devices.

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

    SciTech Connect

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

    1997-12-31

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

  10. Graphene layer growth on silicon substrates with nickel film by pulse arc plasma deposition

    SciTech Connect

    Fujita, K.; Banno, K.; Aryal, H. R.; Egawa, T.

    2012-10-15

    Carbon layer has been grown on a Ni/SiO{sub 2}/Si(111) substrate under high vacuum pressure by pulse arc plasma deposition. From the results of Raman spectroscopy for the sample, it is found that graphene was formed by ex-situ annealing of sample grown at room temperature. Furthermore, for the sample grown at high temperature, graphene formation was shown and optimum temperature was around 1000 Degree-Sign C. Transmission electron microscopy observation of the sample suggests that the graphene was grown from step site caused by grain of Ni film. The results show that the pulse arc plasma technique has the possibility for acquiring homogenous graphene layer with controlled layer thickness.

  11. Lattice accommodation of epitaxial Bi(111) films on Si(001) studied with SPA-LEED and AFM

    SciTech Connect

    Jnawali, G.; Hattab, H.; Krenzer, B.; Horn von Hoegen, M.

    2006-11-15

    The growth of Bi on a Si(001) surface is studied in situ by spot profile analyzing low-energy electron diffraction and ex situ by atomic force microscopy. A continuous epitaxial Bi(111) film with a thickness of 6 nm is grown at 150 K in a bilayer growth mode. During annealing to 450 K the lattice mismatch between Si(001) and Bi(111) is accommodated by a periodic interfacial misfit dislocation array. On this relaxed template, Bi(111) films can be grown to any desired thickness. Such films are composed of twinned and 90 deg. rotated micrometer sized Bi(111) crystallites with a roughness of less than 0.6 nm for a 30 nm thick film.

  12. Metallic transport and large anomalous Hall effect at room temperature in ferrimagnetic Mn{sub 4}N epitaxial thin film

    SciTech Connect

    Shen, Xi; Shigematsu, Kei; Chikamatsu, Akira Fukumura, Tomoteru; Hirose, Yasushi; Hasegawa, Tetsuya

    2014-08-18

    We report the electrical transport properties of ferrimagnetic Mn{sub 4}N (001) epitaxial thin films grown by pulsed laser deposition on MgO (001) substrates. The Mn{sub 4}N thin films were tetragonally distorted with a ratio of out-of-plane to in-plane lattice constants of 0.987 and showed perpendicular magnetic anisotropy with an effective magnetic anisotropy constant of 0.16 MJ/m{sup 3}, which is comparable with that of a recently reported molecular-beam-epitaxy-grown film. The thin films exhibited metallic transport with a room temperature resistivity of 125 μΩ cm in addition to a large anomalous Hall effect with a Hall angle tangent of 0.023.

  13. Film Collection Volume One

    U.S. Department of Energy (DOE) - all webpages (Extended Search)

    Volume One Film Collection Volume Two 75th Anniversary Hydropower in the Northwest Woody Guthrie Videos Strategic Direction Branding & Logos Power of the River History Book...

  14. BPA Historical Films Promo

    U.S. Department of Energy (DOE) - all webpages (Extended Search)

    Volume One Film Collection Volume Two 75th Anniversary Hydropower in the Northwest Woody Guthrie Videos Strategic Direction Branding & Logos Power of the River History Book...

  15. Porous thin films

    DOEpatents

    Xu, Ting

    2015-11-17

    Compositions of porous thin films and methods of making are provided. The methods involve self-assembly of a cyclic peptide in the presence of a block copolymer.

  16. Film Collection Volume Two

    U.S. Department of Energy (DOE) - all webpages (Extended Search)

    sag it for the best transmission of high-voltage electricity. It features wonderful animation and tower models. The next film, "The World Behind Your Light Switch" (1966),...

  17. Amorphous diamond films

    DOEpatents

    Falabella, Steven

    1998-01-01

    Amorphous diamond films having a significant reduction in intrinsic stress are prepared by biasing a substrate to be coated and depositing carbon ions thereon under controlled temperature conditions.

  18. Magneto-optical characterizations of FeTe₀̣₅Se₀̣₅ thin films with critical current density over 1 MA/cm²

    DOE PAGES [OSTI]

    Sun, Yue; Li, Qiang; Tsuchiya, Yuji; Pyon, Sunseng; Tamegai, Tsuyoshi; Zhang, Cheng; Ozaki, Toshinori

    2014-12-03

    We performed magneto-optical (MO) measurements on FeTe₀̣₅Se₀̣₅ thin films grown on LaAlO₃ (LAO) and Yttria-stabilized zirconia (YSZ) single-crystalline substrates. These thin films show superconducting transition temperature Tc ~19 K, 4 K higher than the bulk sample. Typical roof-top patterns can be observed in the MO images of thin films grown on LAO and YSZ, from which a large and homogeneous critical current density Jc ~ 3 - 4 x 10⁶ A/cm² at 5 K was obtained. In this study, magnetic flux penetration measurement reveals that the current is almost isotropically distributed in the two thin films. Compared with bulk crystals,more » FeTe₀̣₅Se₀̣₅ thin film demonstrates not only higher Tc, but also much larger Jc, which is attractive for applications.« less

  19. Obtaining strong ferromagnetism in diluted Gd-doped ZnO thin films through controlled Gd-defect complexes

    SciTech Connect

    Roqan, I. S. Venkatesh, S.; Zhang, Z.; Hussain, S.; Bantounas, I.; Flemban, T. H.; Schwingenschlogl, U.; Franklin, J. B.; Zou, B.; Petrov, P. K.; Ryan, M. P.; Alford, N. M.; Lee, J.-S.

    2015-02-21

    We demonstrate the fabrication of reproducible long-range ferromagnetism (FM) in highly crystalline Gd{sub x}Zn{sub 1−x}O thin films by controlling the defects. Films are grown on lattice-matched substrates by pulsed laser deposition at low oxygen pressures (≤25 mTorr) and low Gd concentrations (x ≤ 0.009). These films feature strong FM (10 μ{sub B} per Gd atom) at room temperature. While films deposited at higher oxygen pressure do not exhibit FM, FM is recovered by post-annealing these films under vacuum. These findings reveal the contribution of oxygen deficiency defects to the long-range FM. We demonstrate the possible FM mechanisms, which are confirmed by density functional theory study, and show that Gd dopants are essential for establishing FM that is induced by intrinsic defects in these films.

  20. Shock initiation experiments on ratchet grown PBX 9502

    SciTech Connect

    Gustavsen, Richard L; Thompson, Darla G; Olinger, Barton W; Deluca, Racci; Bartram, Brian D; Pierce, Timothy H; Sanchez, Nathaniel J

    2010-01-01

    This study compares the shock initiation behavior of PBX 9502 pressed to less than nominal density (nominal density is 1.890 {+-} 0.005 g/cm{sup 3}) with PBX 9502 pressed to nominal density and then ''ratchet grown'' to low density. PBX 9502 is an insensitive plastic bonded explosive consisting of 95 weight % dry-aminated tri-amino-tri-nitro-benzene (TATB) and 5 weight % Kel-F 800 plastic binder. ''Ratchet growth'' - an irreversible increase in specific volume - occurs when an explosive based on TATB is temperature cycled. The design of our study is as follows: PBX 9502, all from the same lot, received the following four treatments. Samples in the first group were pressed to less than nominal density. These were not ratchet grown and used as a baseline. Samples in the second group were pressed to nominal density and then ratchet grown by temperature cycling 30 times between -54 C and +80 C. Samples in the final group were pressed to nominal density and cut into 100 mm by 25.4 mm diameter cylinders. During thermal cycling the cylinders were axially constrained by a 100 psi load. Samples for shock initiation experiments were cut perpendicular (disks) and parallel (slabs) to the axial load. The four sample groups can be summarized with the terms pressed low, ratchet grown/no load, axial load/disks, and axial load/slabs. All samples were shock initiated with nearly identical inputs in plate impact experiments carried out on a gas gun. Wave profiles were measured after propagation through 3, 4, 5, and 6 mm of explosive. Side by side comparison of wave profiles from different samples is used as a measure of relative sensitivity. All reduced density samples were more shock sensitive than nominal density PBX 9502. Differences in shock sensitivity between ratchet grown and pressed to low density PBX 9502 were small, but the low density pressings are slightly more sensitive than the ratchet grown samples.

  1. Dual acceptor doping and aging effect of p-ZnO:(Na, N) nanorod thin films by spray pyrolysis

    SciTech Connect

    Swapna, R. E-mail: santhoshmc@nitt.edu; Amiruddin, R. E-mail: santhoshmc@nitt.edu; Santhosh Kumar, M. C. E-mail: santhoshmc@nitt.edu

    2014-01-28

    An attempt has been made to realize p-type ZnO by dual acceptor doping (Na-N) into ZnO thin films. Na and N doped ZnO thin films of different concentrations (0 to 8 at.%) have been grown by spray pyrolysis at 623 K. The grown films on glass substrate have been characterized by X-ray diffraction (XRD), Hall measurement, UV-Vis spectrophotometer, Photoluminescence (PL) and Energy dispersive spectroscopy (EDS) to validate the p-type conduction. The surface morphology and roughness of the ZnO:(Na, N) films are studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM), respectively. Hall measurement shows that all the films exhibit p-type conductivity except for 0 at.% Na-N doped ZnO film. The obtained resistivity (5.60×10{sup −2} Ω cm) and hole concentration (3.15×10{sup 18} cm{sup −3}) for the best dual acceptor doped film is 6 at.%. It has been predicted that (Na{sub Zn}−N{sub O}) acceptor complex is responsible for the p-type conduction. The p-type conductivity of the ZnO:(Na, N) films is stable even after 6 months. The crystallinity of the films has been studied by XRD. Energy dispersive spectroscopy (EDS) confirms the presence of Na and N in 6 at.% ZnO:(Na, N) film. Photoluminescence (PL) spectra of ZnO:(Na, N) films show NBE and deep level emissions in the UV and visible regions, respectively. The ZnO:(Na, N) films exhibit a high transmittance about 90% in the visible region.

  2. Shading, Films and Window Attachments

    Office of Energy Efficiency and Renewable Energy (EERE) (indexed site)

    ... Interior Louvered Shutter ("Venetian" Blind) 3 31 Roller Shade 4 55 Applied Film (standard solar control) 6 80 Applied Film (advanced or spectrally-selective) 10 125 ...

  3. Protolytic carbon film technology

    SciTech Connect

    Renschler, C.L.; White, C.A.

    1996-04-01

    This paper presents a technique for the deposition of polyacrylonitrile (PAN) on virtually any surface allowing carbon film formation with only the caveat that the substrate must withstand carbonization temperatures of at least 600 degrees centigrade. The influence of processing conditions upon the structure and properties of the carbonized film is discussed. Electrical conductivity, microstructure, and morphology control are also described.

  4. Thick film hydrogen sensor

    DOEpatents

    Hoffheins, B.S.; Lauf, R.J.

    1995-09-19

    A thick film hydrogen sensor element includes an essentially inert, electrically-insulating substrate having deposited thereon a thick film metallization forming at least two resistors. The metallization is a sintered composition of Pd and a sinterable binder such as glass frit. An essentially inert, electrically insulating, hydrogen impermeable passivation layer covers at least one of the resistors. 8 figs.

  5. Thick film hydrogen sensor

    DOEpatents

    Hoffheins, Barbara S. (Knoxville, TN); Lauf, Robert J. (Oak Ridge, TN)

    1995-01-01

    A thick film hydrogen sensor element includes an essentially inert, electrically-insulating substrate having deposited thereon a thick film metallization forming at least two resistors. The metallization is a sintered composition of Pd and a sinterable binder such as glass frit. An essentially inert, electrically insulating, hydrogen impermeable passivation layer covers at least one of the resistors.

  6. Stabilized chromium oxide film

    DOEpatents

    Garwin, Edward L.; Nyaiesh, Ali R.

    1988-01-01

    Stabilized air-oxidized chromium films deposited on high-power klystron ceramic windows and sleeves having a thickness between 20 and 150.ANG. are useful in lowering secondary electron emission yield and in avoiding multipactoring and window failure due to overheating. The ceramic substrate for the film is chosen from alumina, sapphire or beryllium oxide.

  7. Stabilized chromium oxide film

    DOEpatents

    Nyaiesh, A.R.; Garwin, E.L.

    1986-08-04

    Stabilized air-oxidized chromium films deposited on high-power klystron ceramic windows and sleeves having a thickness between 20 and 150A are useful in lowering secondary electron emission yield and in avoiding multipactoring and window failure due to overheating. The ceramic substrate for the film is chosen from alumina, sapphire or beryllium oxide.

  8. Thermal Conductivity Measurement of Xe-Implanted Uranium Dioxide Thick Films using Multilayer Laser Flash Analysis

    SciTech Connect

    Nelson, Andrew T.

    2012-08-30

    The Fuel Cycle Research and Development program's Advanced Fuels campaign is currently pursuing use of ion beam assisted deposition to produce uranium dioxide thick films containing xenon in various morphologies. To date, this technique has provided materials of interest for validation of predictive fuel performance codes and to provide insight into the behavior of xenon and other fission gasses under extreme conditions. In addition to the structural data provided by such thick films, it may be possible to couple these materials with multilayer laser flash analysis in order to measure the impact of xenon on thermal transport in uranium dioxide. A number of substrate materials (single crystal silicon carbide, molybdenum, and quartz) containing uranium dioxide films ranging from one to eight microns in thickness were evaluated using multilayer laser flash analysis in order to provide recommendations on the most promising substrates and geometries for further investigation. In general, the uranium dioxide films grown to date using ion beam assisted deposition were all found too thin for accurate measurement. Of the substrates tested, molybdenum performed the best and looks to be the best candidate for further development. Results obtained within this study suggest that the technique does possess the necessary resolution for measurement of uranium dioxide thick films, provided the films are grown in excess of fifty microns. This requirement is congruent with the material needs when viewed from a fundamental standpoint, as this length scale of material is required to adequately sample grain boundaries and possible second phases present in ceramic nuclear fuel.

  9. Valorization of GaN based metal-organic chemical vapor deposition dust a semiconductor power device industry waste through mechanochemical oxidation and leaching: A sustainable green process

    SciTech Connect

    Swain, Basudev; Mishra, Chinmayee; Lee, Chan Gi; Park, Kyung-Soo; Lee, Kun-Jae

    2015-07-15

    Dust generated during metal organic vapor deposition (MOCVD) process of GaN based semiconductor power device industry contains significant amounts of gallium and indium. These semiconductor power device industry wastes contain gallium as GaN and Ga{sub 0.97}N{sub 0.9}O{sub 0.09} is a concern for the environment which can add value through recycling. In the present study, this waste is recycled through mechanochemical oxidation and leaching. For quantitative recovery of gallium, two different mechanochemical oxidation leaching process flow sheets are proposed. In one process, first the Ga{sub 0.97}N{sub 0.9}O{sub 0.09} of the MOCVD dust is leached at the optimum condition. Subsequently, the leach residue is mechanochemically treated, followed by oxidative annealing and finally re-leached. In the second process, the MOCVD waste dust is mechanochemically treated, followed by oxidative annealing and finally leached. Both of these treatment processes are competitive with each other, appropriate for gallium leaching and treatment of the waste MOCVD dust. Without mechanochemical oxidation, 40.11 and 1.86 w/w% of gallium and Indium are leached using 4 M HCl, 100 °C and pulp density of 100 kg/m{sup 3,} respectively. After mechanochemical oxidation, both these processes achieved 90 w/w% of gallium and 1.86 w/w% of indium leaching at their optimum condition. - Highlights: • Waste MOCVD dust is treated through mechanochemical leaching. • GaN is hardly leached, and converted to NaGaO{sub 2} through ball milling and annealing. • Process for gallium recovery from waste MOCVD dust has been developed. • Thermal analysis and phase properties of GaN to Ga{sub 2}O{sub 3} and GaN to NaGaO{sub 2} is revealed. • Solid-state chemistry involved in this process is reported.

  10. Formation of calcium carbonate films on chitosan substrates in the presence of polyacrylic acid

    SciTech Connect

    He, Linghao; Xue, Rui; Song, Rui

    2009-05-15

    In this investigation, chitosan membranes with different surface average degrees of deacetylation (DA) are prepared and then are employed as the support matrix to culture calcium carbonate (CaCO{sub 3}). In the presence of high concentration of polyacrylic acid (PAA), the CaCO{sub 3} films obtained on the surface of all chitosan films mainly consisted of vaterite, which suggests the presence of bulk PAA plays an overwhelming part in stabilizing the vaterite. As a comparison, the influences of active groups indicate that only in case of low concentration PAA the thin CaCO{sub 3} films grown on chitosan with 8% DA mainly consisted of vaterite owing to the strong nucleation ability of -NH{sub 2} group, whereas, for those grown on chitosan with 80% DA the CaCO{sub 3} films mainly consisted of aragonite. A more complex scenario revealed that in the case of intermediate concentration of PAA the formed polymorphs behave as mixtures of vaterite and aragonite. - Graphical abstract: Chitosan membranes with different degrees of deacetylation (DA) are employed as support to culture calcium carbonate (CaCO{sub 3}). In high concentration of polyacrylic acid (PAA), the CaCO{sub 3} films obtained consisted of vaterite. However, the CaCO{sub 3} film grown on chitosan with 8% DA mainly consisted of vaterite as opposed to aragonite for chitosan with 8% DA. The schematic presentation of the formation of calcium carbonate on chitosan films with different degrees of acetylation in the presence of PAA with low-, mid- and high concentrations.

  11. Ferromagnetic response of multiferroic TbMnO{sub 3} films mediated by epitaxial strain and chemical pressure

    SciTech Connect

    Izquierdo, J.; Morán, O.; Astudillo, A.; Bolaños, G.; Arnache, O.

    2014-05-07

    High quality Tb{sub 1−x}Al{sub x}MnO{sub 3} (x = 0, 0.3) films have been grown under different values of compressive/tensile strain using (001)-oriented SrTiO{sub 3} and MgO substrates. The films were grown by means of rf sputtering at substrate temperature of 800  °C. X-ray diffraction analysis shows that films are single phase, preferentially oriented in the (111) and (122) directions for films deposited on SrTiO{sub 3} and MgO substrates, respectively. Although the TbMnO{sub 3} target shows antiferromagnetic order, the films deposited on both substrates show weak ferromagnetic phase at low temperature coexisting with the antiferromagnetic phase. The introduction of Al in the films clearly enhances their ferromagnetic behavior, improving the magnetic performance of this material. Indeed, M(H) measurements at 5 K show a well-defined hysteresis for films grown on both substrates. However, a stronger magnetic signal (larger values of remanence and coercive field) is observed for films deposited on MgO substrates. The chemical pressure generated by Al doping together with the substrate-induced strain seem to modify the subtle competition between magnetic interactions in the system. It is speculated that such modification could lead to a non-collinear magnetic state that may be tuned by strain modifications. This may be performed by varying the thickness of the films and/or considering other substrate materials.

  12. Non-vacuum growth of graphene films using solid carbon source

    SciTech Connect

    Nguyen, Ba-Son; Lin, Jen-Fin E-mail: dcperng@ee.ncku.edu.tw

    2015-06-01

    This study demonstrates that air annealing can grow high-quality graphene films on the surface of polycrystalline nickel film with the help of an effective SiO{sub 2} capping layer. The number of graphene layers can be modulated by the amount of carbon embedded in the Ni film before annealing. Raman analysis results, transmission electron microscopy images, and electron diffraction patterns of the samples confirm that graphene films can be grown in air with an oxygen blocking layer and a 10 °C/s cooling rate in an open-vented rapid thermal annealing chamber or an open tube furnace. The high-quality low-defect air-annealing grown graphene is comparable to commercially available graphene grown via chemical vapor deposition. The proposed graphene growth using air annealing technique is simple and low-cost, making it highly attractive for mass production. It is transfer-free to a silicon substrate and can speed up graphene development, opening up new applications.

  13. Investigation of deep level defects in CdTe thin films

    SciTech Connect

    Shankar, H.; Castaldini, A.; Dauksta, E.; Medvid, A.; Cavallini, A.

    2014-02-21

    In the past few years, a large body of work has been dedicated to CdTe thin film semiconductors, as the electronic and optical properties of CdTe nanostructures make them desirable for photovoltaic applications. The performance of semiconductor devices is greatly influenced by the deep levels. Knowledge of parameters of deep levels present in as-grown materials and the identification of their origin is the key factor in the development of photovoltaic device performance. Photo Induced Current Transient Spectroscopy technique (PICTS) has proven to be a very powerful method for the study of deep levels enabling us to identify the type of traps, their activation energy and apparent capture cross section. In the present work, we report the effect of growth parameters and LASER irradiation intensity on the photo-electric and transport properties of CdTe thin films prepared by Close-Space Sublimation method using SiC electrical heating element. CdTe thin films were grown at three different source temperatures (630, 650 and 700 C). The grown films were irradiated with Nd:YAG LASER and characterized by Photo-Induced Current Transient Spectroscopy, Photocurrent measurementand Current Voltage measurements. The defect levels are found to be significantly influenced by the growth temperature.

  14. Tailoring the index of refraction of nanocrystalline hafnium oxide thin films

    SciTech Connect

    Vargas, Mirella; Murphy, N. R.; Ramana, C. V.

    2014-03-10

    Hafnium oxide (HfO{sub 2}) films were grown by sputter-deposition by varying the growth temperature (T{sub s} = 25–700 °C). HfO{sub 2} films grown at T{sub s} < 200 °C were amorphous, while those grown at T{sub s} ≥ 200 °C were monoclinic, nanocrystalline with (1{sup ¯}11) texturing. X-ray reflectivity (XRR) analyses indicate that the film-density (ρ) increases with increasing T{sub s}. The index of refraction (n) profiles derived from spectroscopic ellipsometry analyses follow the Cauchy dispersion relation. Lorentz-Lorenz analysis (n{sub (λ)} = 550 nm) and optical-model adopted agree well with the XRR data/analyses. A direct T{sub s}-ρ-n relationship suggests that tailoring the optical quality is possible by tuning T{sub s} and the microstructure of HfO{sub 2} films.

  15. Adsorption of iso-/n-butane on an Anatase Thin Film: A Molecular Beam Scattering and TDS Study

    SciTech Connect

    Goering, J.; Kadossov, E.; Burghaus, Uwe; Yu, Zhongqing; Thevuthasan, Suntharampillai; Saraf, Laxmikant V.

    2007-07-01

    Binding energies and adsorption probabilities have been determined for n/iso-butane adsorption on an anatase thin film grown on SrTiO3(001) by means of thermal desorption spectroscopy (TDS) and molecular beam scattering. The sample has been characterized by x-ray diffraction (XRD) and Auger electrons spectroscopy (AES).

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

    DOE PAGES [OSTI]

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

    2014-09-01

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

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

    SciTech Connect

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

    2014-09-01

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

  18. The Effect of Roll Waves on the Hydrodynamics of Falling Films Observed in Vertical Column Absorbers

    SciTech Connect

    Miller, W.A.

    2001-06-28

    A thin falling film is well suited to simultaneous heat and mass transfer because of the small thermal resistance through the film and because of the large contact surface achievable at low flow rates. The film enters as a smooth laminar flow and quickly transitions into small-amplitude wavy flow. The waves grown in length and amplitude and are identified as roll waves. This flow regime is termed wavy-laminar flow, and modern heat and mass transfer equipment operate in this complicated transition regime. Research published in open literature has shown the mass flow rate in the rollwaves to be about 10 to 20 times greater than that in the laminar substrate. As the film fully develops, the waves grow in mass and the film substrate thins because fluid is swept from the substrate by the secondary flows of the roll wave. Many studies have been conducted to measure and correlate the film thickness of wavy-laminar flows. Literature data show that Nusselt's theory for smooth laminar flow can over predict the film thickness by as much as 20% for certain wavy-laminar flow conditions. The hydrodynamics of falling films were therefore studied to measure the film thickness of a free-surface falling film and to better understand the parameters that affect the variations of the film thickness. A flow loop was set up for measuring the thickness, wave amplitude,and frequency of a film during hydrodynamic flow. Decreasing the pipe diameter caused the amplitude of the wavy flow to diminish. Measurements monitored from stations along the falling film showed a thinning of film thickness. Fully developed flow required large starting lengths of about 0.5 m. The film thickness increases as the Reynolds number (Re) increases. Increasing the Kapitza number (Ka) causes a decrease in the film thickness. Regression analysis showed that the Re and Ka numbers described the data trends in wavy-laminar flow. Rather than correlating the Re number in discrete ranges of the Ka number as earlier

  19. Flexible indium zinc oxide/Ag/indium zinc oxide multilayer electrode grown on polyethersulfone substrate by cost-efficient roll-to-roll sputtering for flexible organic photovoltaics

    SciTech Connect

    Park, Yong-Seok; Kim, Han-Ki

    2010-01-15

    The authors describe the preparation and characteristics of flexible indium zinc oxide (IZO)-Ag-IZO multilayer electrodes grown on flexible polyethersulfone (PES) substrates using a roll-to-roll sputtering system for use in flexible organic photovoltaics. By the continuous roll-to-roll sputtering of the bottom IZO, Ag, and top IZO layers at room temperature, they were able to fabricate a high quality IZO-Ag-IZO multilayer electrode with a sheet resistance of 6.15 {epsilon}/square, optical transmittance of 87.4%, and figure of merit value of 42.03x10{sup -3} {Omega}{sup -1} on the PES substrate. In addition, the IZO-Ag-IZO multilayer electrode exhibited superior flexibility to the roll-to-roll sputter grown single ITO electrode due to the existence of a ductile Ag layer between the IZO layers and stable amorphous structure of the IZO film. Furthermore, the flexible organic solar cells (OSCs) fabricated on the roll-to-roll sputter grown IZO-Ag-IZO electrode showed higher power efficiency (3.51%) than the OSCs fabricated on the roll-to-roll sputter grown single ITO electrode (2.67%).

  20. Deposition of hetero-epitaxial In{sub 2}O{sub 3} thin films by molecular beam epitaxy

    SciTech Connect

    Taga, N.; Maekawa, M.; Shigesato, Y.; Yasui, I.; Haynes, T.E.

    1996-05-01

    Highly oriented thin film In{sub 2}O{sub 3} was heteroepitaxially grown on optically polished (100) plane of single crystalline yttria stabilized zirconia (YSZ) substrate using Molecular Beam Epitaxy (MBE). Full-width at half-maximum (FWHM) of X-ray rocking-curve showed 0.08{degree} for In{sub 2}O{sub 3} 200 nm thick layers indicating that excellent uniformity orientation compared with the heteroepitaxially-grown In{sub 2}O{sub 3} epitaxially deposited by the conventional methods such as electron-beam (e-beam) evaporation or sputtering method. The minimum yield ({chi}{sub min}) of the MBE grown in In{sub 2}O{sub 3} film of Rutherford Backscattering Spectrometry (RBS) was also extremely small value 3.1%, implying the very high crystallinity.

  1. Measurement of the hot electron mean free path and the momentum relaxation rate in GaN

    SciTech Connect

    Suntrup, Donald J.; Gupta, Geetak; Li, Haoran; Keller, Stacia; Mishra, Umesh K.

    2014-12-29

    We present a method for measuring the mean free path and extracting the momentum relaxation time of hot electrons in GaN using the hot electron transistor (HET). In this device, electrons are injected over a high energy emitter barrier into the base where they experience quasi-ballistic transport well above the conduction band edge. After traversing the base, high energy electrons either surmount the base-collector barrier and become collector current or reflect off the barrier and become base current. We fabricate HETs with various base thicknesses and measure the common emitter transfer ratio (α) for each device. The mean free path is extracted by fitting α to a decaying exponential as a function of base width and the relaxation time is computed using a suitable injection velocity. For devices with an injection energy of ∼1 eV, we measure a hot electron mean free path of 14 nm and calculate a momentum relaxation time of 16 fs. These values are in agreement with theoretical calculations where longitudinal optical phonon scattering is the dominant momentum relaxation mechanism.

  2. Design, fabrication, and performance analysis of GaN vertical electron transistors with a buried p/n junction

    SciTech Connect

    Yeluri, Ramya Lu, Jing; Keller, Stacia; Mishra, Umesh K.; Hurni, Christophe A.; Browne, David A.; Speck, James S.; Chowdhury, Srabanti

    2015-05-04

    The Current Aperture Vertical Electron Transistor (CAVET) combines the high conductivity of the two dimensional electron gas channel at the AlGaN/GaN heterojunction with better field distribution offered by a vertical design. In this work, CAVETs with buried, conductive p-GaN layers as the current blocking layer are reported. The p-GaN layer was regrown by metalorganic chemical vapor deposition and the subsequent channel regrowth was done by ammonia molecular beam epitaxy to maintain the p-GaN conductivity. Transistors with high ON current (10.9?kA/cm{sup 2}) and low ON-resistance (0.4 m? cm{sup 2}) are demonstrated. Non-planar selective area regrowth is identified as the limiting factor to transistor breakdown, using planar and non-planar n/p/n structures. Planar n/p/n structures recorded an estimated electric field of 3.1 MV/cm, while non-planar structures showed a much lower breakdown voltage. Lowering the p-GaN regrowth temperature improved breakdown in the non-planar n/p/n structure. Combining high breakdown voltage with high current will enable GaN vertical transistors with high power densities.

  3. Thin film hydrogen sensor

    DOEpatents

    Cheng, Y.T.; Poli, A.A.; Meltser, M.A.

    1999-03-23

    A thin film hydrogen sensor includes a substantially flat ceramic substrate with first and second planar sides and a first substrate end opposite a second substrate end; a thin film temperature responsive resistor on the first planar side of the substrate proximate to the first substrate end; a thin film hydrogen responsive metal resistor on the first planar side of the substrate proximate to the fist substrate end and proximate to the temperature responsive resistor; and a heater on the second planar side of the substrate proximate to the first end. 5 figs.

  4. Thin film hydrogen sensor

    DOEpatents

    Cheng, Yang-Tse; Poli, Andrea A.; Meltser, Mark Alexander

    1999-01-01

    A thin film hydrogen sensor, includes: a substantially flat ceramic substrate with first and second planar sides and a first substrate end opposite a second substrate end; a thin film temperature responsive resistor on the first planar side of the substrate proximate to the first substrate end; a thin film hydrogen responsive metal resistor on the first planar side of the substrate proximate to the fist substrate end and proximate to the temperature responsive resistor; and a heater on the second planar side of the substrate proximate to the first end.

  5. Characteristics of conductive SrRuO{sub 3} thin films with different microstructures

    SciTech Connect

    Jia, Q.X.; Chu, F.; Adams, C.D.; Wu, X.D.; Hawley, M.; Cho, J.H.; Findikoglu, A.T.; Foltyn, S.R.; Smith, J.L.; Mitchell, T.E.

    1996-09-01

    Conductive SrRuO{sub 3} thin films were epitaxially grown on (100) LaAlO{sub 3} substrates by pulsed laser deposition over a temperature range from 650{degree}C to 825{degree}C. Well-textured films exhibiting a strong orientation relationship to the underlying substrate could be obtained at a deposition temperature as low as 450{degree}C. The degree of crystallinity of the films improved with increasing deposition temperature as confirmed by x-ray diffraction, transmission electron microscopy, and scanning tunneling microscopy. Scanning electron microscopy revealed no particulates on the film surface. The resistivity of the SrRuO{sub 3} thin films was found to be a strong function of the crystallinity of the film and hence the substrate temperature during film deposition. A residual resistivity ratio (RRR={rho}{sub 300K}/{rho}{sub 4.2K}) of more than 8 was obtained for the SrRuO{sub 3} thin films deposited under optimized processing conditions. {copyright} {ital 1996 Materials Research Society.}

  6. In-situ surface composition measurements of CuGaSe{sub 2} thin films

    SciTech Connect

    Fons, P.; Yamada, A.; Niki, S.; Oyanagi, H.

    1998-12-31

    Two CuGaSe{sub 2} films were grown by molecular beam epitaxy onto GaAs (001) substrates with varying Cu/Ga flux ratios under Se overpressure conditions. Growth was interrupted at predetermined times and the surface composition was measured using Auger electron spectroscopy after which growth was continued. After growth, the film composition was analyzed using voltage dependent electron microprobe spectroscopy. Film structure and morphology were also analyzed using x-ray diffraction and atomic force microscopy. The film with a Cu/Ga ratio larger than unity showed evidence of surface segregation of a second Cu-rich phase with a Cu/Se composition ratio slightly greater than unity. A second CuGaSe{sub 2} film with a Cu/Ga ratio of less than unity showed no change in surface composition with time and was also consistent with bulk composition measurements. Diffraction measurements indicated a high concentration of twins as well as the presence of domains with mixed c and a axes in the Ga-rich film. The Cu-rich films by contrast were single domain and had a narrower mosaics. High sensitivity scans along the [001] reciprocal axis did not exhibit any new peaks not attributable to either the substrate or the CuGaSe{sub 2} thin film.

  7. Ferromagnetic and paramagnetic magnetization of implanted GaN:Ho,Tb,Sm,Tm films

    SciTech Connect

    Maryško, M. Hejtmánek, J.; Laguta, V.; Sofer, Z.; Sedmidubský, D.; Šimek, P.; Veselý, M.; Mikulics, M.; Buchal, C.; Macková, A.; Malínský, P.; Wilhelm, R. A.

    2015-05-07

    The SQUID magnetic measurements were performed on the GaN films prepared by metal-organic vapour phase epitaxy and implanted by Tb{sup 3+}, Tm{sup 3+}, Sm{sup 3+}, and Ho{sup 3+} ions. The sapphire substrate was checked by the electron paramagnetic resonance method which showed a content of Cr{sup 3+} and Fe{sup 3+} impurities. The samples 5 × 5 mm{sup 2} were positioned in the classical straws and within an estimated accuracy of 10{sup −6 }emu, no ferromagnetic moment was detected in the temperature region of 2–300 K. The paramagnetic magnetization was studied for parallel and perpendicular orientation. In the case of GaN:Tb sample, at T = 2 K, a pronounced anisotropy with the easy axis perpendicular to the film was observed which can be explained by the lowest quasi-doublet state of the non-Kramers Tb{sup 3+} ion. The Weiss temperature deduced from the susceptibility data using the Curie-Weiss (C-W) law was found to depend substantially on the magnetic field.

  8. Inversion by metalorganic chemical vapor deposition from N- to Ga-polar gallium nitride and its application to multiple quantum well light-emitting diodes

    SciTech Connect

    Hosalli, A. M.; Van Den Broeck, D. M.; Bedair, S. M. [Department of Electrical and Computer Engineering, NCSU, Raleigh, North Carolina 27695 (United States)] [Department of Electrical and Computer Engineering, NCSU, Raleigh, North Carolina 27695 (United States); Bharrat, D.; El-Masry, N. A. [Department of Material Science and Engineering, NCSU, Raleigh, North Carolina 27695 (United States)] [Department of Material Science and Engineering, NCSU, Raleigh, North Carolina 27695 (United States)

    2013-12-02

    We demonstrate a metalorganic chemical vapor deposition growth approach for inverting N-polar to Ga-polar GaN by using a thin inversion layer grown with high Mg flux. The introduction of this inversion layer allowed us to grow p-GaN films on N-polar GaN thin film. We have studied the dependence of hole concentration, surface morphology, and degree of polarity inversion for the inverted Ga-polar surface on the thickness of the inversion layer. We then use this approach to grow a light emitting diode structure which has the MQW active region grown on the advantageous N-polar surface and the p-layer grown on the inverted Ga-polar surface.

  9. Healing of graphene on single crystalline Ni(111) films

    SciTech Connect

    Zeller, Patrick; Wintterlin, Joost; Speck, Florian; Ostler, Markus; Weinl, Michael; Schreck, Matthias; Seyller, Thomas

    2014-11-10

    The annealing of graphene layers grown on 150?nm thick single crystal Ni(111) films was investigated in situ by low energy electron microscopy and photoemission electron microscopy. After growth, by means of chemical vapor deposition of ethylene, the graphene layers consist of several domains showing different orientations with respect to the underlying Ni surface and also of small bilayer areas. It is shown that, in a controlled process, the rotated domains can be transformed into lattice-aligned graphene, and the bilayer areas can be selectively dissolved, so that exclusively the aligned monolayer graphene is obtained. The ordering mechanism involves transport of C atoms across the surface and solution in the bulk.

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

    SciTech Connect

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

    2014-12-05

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

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

    SciTech Connect

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

    2014-12-05

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

  12. Low-temperature electrical transport in B-doped ultrananocrystalline diamond film

    SciTech Connect

    Li, Lin; Zhao, Jing; Hu, Zhaosheng; Quan, Baogang; Li, Junjie Gu, Changzhi

    2014-05-05

    B-doped ultrananocrystalline diamond (UNCD) films are grown using hot-filament chemical vapor deposition method, and their electrical transport properties varying with temperature are investigated. When the B-doped concentration of UNCD film is low, a step-like increase feature of the resistance is observed with decreasing temperature, reflecting at least three temperature-modified electronic state densities at the Fermi level according to three-dimensional Mott's variable range hopping transport mechanism, which is very different from that of reported B-doped nanodiamond. With increasing B-doped concentration, a superconductive transformation occurs in the UNCD film and the highest transformation temperature of 5.3?K is observed, which is higher than that reported for superconducting nanodiamond films. In addition, the superconducting coherence length is about 0.63?nm, which breaks a reported theoretical and experimental prediction about ultra-nanoscale diamond's superconductivity.

  13. Transparent and conductive indium doped cadmium oxide thin films prepared by pulsed filtered cathodic arc deposition

    SciTech Connect

    Zhu, Yuankun; Mendelsberg, Rueben J.; Zhu, Jiaqi; Han, Jiecai; Anders, Andr

    2012-11-26

    Indium doped cadmium oxide (CdO:In) films with different In concentrations were prepared on low-cost glass substrates by pulsed filtered cathodic arc deposition (PFCAD). In this study, it is shown that polycrystalline CdO:In films with smooth surface and dense structure are obtained. In-doping introduces extra electrons leading to remarkable improvements of electron mobility and conductivity, as well as improvement in the optical transmittance due to the Burstein Moss effect. CdO:In films on glass substrates with thickness near 230 nm show low resistivity of 7.23 x 10-5 ?cm, high electron mobility of 142 cm2/Vs, and mean transmittance over 80% from 500-1250 nm (including the glass substrate). These high quality pulsed arc-grown CdO:In films are potentially suitable for high efficiency multi-junction solar cells that harvest a broad range of the solar spectrum.

  14. Superconducting thin films of (100) and (111) oriented indium doped topological crystalline insulator SnTe

    DOE PAGES [OSTI]

    Si, W.; Zhang, C.; Wu, L.; Ozaki, T.; Gu, G.; Li, Q.

    2015-09-01

    Recent discovery of the topological crystalline insulator SnTe has triggered a search for topological superconductors, which have potential application to topological quantum computing. The present work reports on the superconducting properties of indium doped SnTe thin films. The (100) and (111) oriented thin films were epitaxially grown by pulsed-laser deposition on (100) and (111) BaF2 crystalline substrates respectively. The onset superconducting transition temperatures are about 3.8 K for (100) and 3.6 K for (111) orientations, slightly lower than that of the bulk. Magneto-resistive measurements indicate that these thin films may have upper critical fields higher than that of the bulk.more » With large surface-to-bulk ratio, superconducting indium doped SnTe thin films provide a rich platform for the study of topological superconductivity and potential device applications based on topological superconductors.« less

  15. Epitaxial growth of iridate pyrochlore Nd2Ir2O7 films

    DOE PAGES [OSTI]

    Gallagher, J. C.; Esser, B. D.; Morrow, R.; Dunsiger, S. R.; Williams, R. E. A.; Woodward, P. M.; McComb, D. W.; Yang, F. Y.

    2016-02-29

    Epitaxial films of the pyrochlore Nd2Ir2O7 have been grown on (111)-oriented yttria-stabilized zirconia (YSZ) substrates by off-axis sputtering followed by post-growth annealing. X-ray diffraction (XRD) results demonstrate phase-pure epitaxial growth of the pyrochlore films on YSZ. Scanning transmission electron microscopy (STEM) investigation of an Nd2Ir2O7 film with a short post-annealing provides insight into the mechanism for crystallization of Nd2Ir2O7 during the post-annealing process. STEM images reveal clear pyrochlore ordering of Nd and Ir in the films. As a result, the epitaxial relationship between the YSZ and Nd2Ir2O7 is observed clearly while some interfacial regions show a thin region with polycrystallinemore » Ir nanocrystals.« less

  16. Superconducting thin films of (100) and (111) oriented indium doped topological crystalline insulator SnTe

    SciTech Connect

    Si, W.; Zhang, C.; Wu, L.; Ozaki, T.; Gu, G.; Li, Q.

    2015-09-01

    Recent discovery of the topological crystalline insulator SnTe has triggered a search for topological superconductors, which have potential application to topological quantum computing. The present work reports on the superconducting properties of indium doped SnTe thin films. The (100) and (111) oriented thin films were epitaxially grown by pulsed-laser deposition on (100) and (111) BaF2 crystalline substrates respectively. The onset superconducting transition temperatures are about 3.8 K for (100) and 3.6 K for (111) orientations, slightly lower than that of the bulk. Magneto-resistive measurements indicate that these thin films may have upper critical fields higher than that of the bulk. With large surface-to-bulk ratio, superconducting indium doped SnTe thin films provide a rich platform for the study of topological superconductivity and potential device applications based on topological superconductors.

  17. Sharp semiconductor-to-metal transition of VO{sub 2} thin films on glass substrates

    SciTech Connect

    Jian, Jie; Chen, Aiping; Zhang, Wenrui; Wang, Haiyan

    2013-12-28

    Outstanding phase transition properties of vanadium dioxide (VO{sub 2}) thin films on amorphous glass were achieved and compared with the ones grown on c-cut sapphire and Si (111) substrates, all by pulsed laser deposition. The films on glass substrate exhibit a sharp semiconductor-to-metal transition (∼4.3 °C) at a near bulk transition temperature of ∼68.4 °C with an electrical resistance change as high as 3.2 × 10{sup 3} times. The excellent phase transition properties of the films on glass substrate are correlated with the large grain size and low defects density achieved. The phase transition properties of VO{sub 2} films on c-cut sapphire and Si (111) substrates were found to be limited by the high defect density.

  18. Effects of catalyst film thickness on plasma-enhanced carbon nanotube growth

    SciTech Connect

    Hofmann, S.; Cantoro, M.; Kleinsorge, B.; Casiraghi, C.; Parvez, A.; Robertson, J.; Ducati, C.

    2005-08-01

    A systematic study is presented of the influence of catalyst film thickness on carbon nanostructures grown by plasma-enhanced chemical-vapor deposition from acetylene and ammonia mixtures. We show that reducing the Fe/Co catalyst film thickness below 3 nm causes a transition from larger diameter (>40 nm), bamboolike carbon nanofibers to small diameter ({approx}5 nm) multiwalled nanotubes with two to five walls. This is accompanied by a more than 50 times faster growth rate and a faster catalyst poisoning. Thin Ni catalyst films only trigger such a growth transition when pretreated with an ammonia plasma. We observe a limited correlation between this growth transition and the coarsening of the catalyst film before deposition. For a growth temperature of {<=}550 deg. C, all catalysts showed mainly a tip growth regime and a similar activity on untreated silicon, oxidized silicon, and silicon nitride support.

  19. Nanostructured thermoplastic polyimide films

    DOEpatents

    Aglan, Heshmat

    2015-05-19

    Structured films containing multi-walled carbon nanotubes ("MWCNTs") have enhanced mechanical performance in terms of strength, fracture resistance, and creep recovery of polyimide ("PI") films. Preferably, the loadings of MWCNTs can be in the range of 0.1 wt % to 0.5 wt %. The strength of the new PI films dried at 60.degree. C. increased by 55% and 72% for 0.1 wt % MWCNT and 0.5 wt % MWCNT loadings, respectively, while the fracture resistance increased by 23% for the 0.1 wt % MWCNTs and then decreases at a loading of 0.5 wt % MWCNTs. The films can be advantageously be created by managing a corresponding shift in the annealing temperature at which the maximum strength occurs as the MWCNT loadings increase.

  20. Quantitative film radiography

    SciTech Connect

    Devine, G.; Dobie, D.; Fugina, J.; Hernandez, J.; Logan, C.; Mohr, P.; Moss, R.; Schumacher, B.; Updike, E.; Weirup, D.

    1991-02-26

    We have developed a system of quantitative radiography in order to produce quantitative images displaying homogeneity of parts. The materials that we characterize are synthetic composites and may contain important subtle density variations not discernible by examining a raw film x-radiograph. In order to quantitatively interpret film radiographs, it is necessary to digitize, interpret, and display the images. Our integrated system of quantitative radiography displays accurate, high-resolution pseudo-color images in units of density. We characterize approximately 10,000 parts per year in hundreds of different configurations and compositions with this system. This report discusses: the method; film processor monitoring and control; verifying film and processor performance; and correction of scatter effects.

  1. Magnetron sputtered boron films

    DOEpatents

    Makowiecki, Daniel M.; Jankowski, Alan F.

    1998-01-01

    A method is described for the production of thin boron and titanium/boron films by magnetron sputter deposition. The amorphous boron films contain no morphological growth features, unlike those found when thin films are prepared by various physical vapor deposition processes. Magnetron sputter deposition method requires the use of a high density crystalline boron sputter target which is prepared by hot isostatic pressing. Thin boron films prepared by this method are useful for producing hardened surfaces, surfacing machine tools, etc. and for ultra-thin band pass filters as well as the low Z element in low Z/high Z optical components, such as mirrors which enhance reflectivity from grazing to normal incidence.

  2. Magnetron sputtered boron films

    DOEpatents

    Makowiecki, D.M.; Jankowski, A.F.

    1998-06-16

    A method is described for the production of thin boron and titanium/boron films by magnetron sputter deposition. The amorphous boron films contain no morphological growth features, unlike those found when thin films are prepared by various physical vapor deposition processes. Magnetron sputter deposition method requires the use of a high density crystalline boron sputter target which is prepared by hot isostatic pressing. Thin boron films prepared by this method are useful for producing hardened surfaces, surfacing machine tools, etc. and for ultra-thin band pass filters as well as the low Z element in low Z/high Z optical components, such as mirrors which enhance reflectivity from grazing to normal incidence. 8 figs.

  3. TAMPERPROOF FILM BADGE

    DOEpatents

    Kocher, L.F.

    1958-10-01

    A persornel dosimeter film badge made of plastic, with provision for a picture of the wearer and an internal slide containing photographic film that is sensitive to various radiations, is described. Four windows made of differing material selectively attenuate alpha, beta, gamma rays, and neutrons so as to distinguish the particular type of radiation the wearer was subjected to. In addition, a lead shield has the identification number of the wearer perforated thereon so as to identify the film after processing. An internal magnetically actuated latch securely locks the slide within the body, and may be withdrawn only upon the external application of two strong magnetic forces in order to insure that the wearer or other curious persons will not accidentally expose the film to visual light.

  4. Amorphous diamond films

    DOEpatents

    Falabella, S.

    1998-06-09

    Amorphous diamond films having a significant reduction in intrinsic stress are prepared by biasing a substrate to be coated and depositing carbon ions thereon under controlled temperature conditions. 1 fig.

  5. Multifunctional thin film surface

    DOEpatents

    Brozik, Susan M.; Harper, Jason C.; Polsky, Ronen; Wheeler, David R.; Arango, Dulce C.; Dirk, Shawn M.

    2015-10-13

    A thin film with multiple binding functionality can be prepared on an electrode surface via consecutive electroreduction of two or more aryl-onium salts with different functional groups. This versatile and simple method for forming multifunctional surfaces provides an effective means for immobilization of diverse molecules at close proximities. The multifunctional thin film has applications in bioelectronics, molecular electronics, clinical diagnostics, and chemical and biological sensing.

  6. Thin film tritium dosimetry

    DOEpatents

    Moran, Paul R.

    1976-01-01

    The present invention provides a method for tritium dosimetry. A dosimeter comprising a thin film of a material having relatively sensitive RITAC-RITAP dosimetry properties is exposed to radiation from tritium, and after the dosimeter has been removed from the source of the radiation, the low energy electron dose deposited in the thin film is determined by radiation-induced, thermally-activated polarization dosimetry techniques.

  7. Magnetoresistance of Au films

    DOE PAGES [OSTI]

    Zhang, D. L.; Song, X. H.; Zhang, X.; Zhang, Xiaoguang

    2014-12-10

    Measurement of the magnetoresistance (MR) of Au films as a function of temperature and film thickness reveals a strong dependence on grain size distribution and clear violation of the Kohler s rule. Using a model of random resistor network, we show that this result can be explained if the MR arises entirely from inhomogeneity due to grain boundary scattering and thermal activation of grain boundary atoms.

  8. Polymer film composite transducer

    DOEpatents

    Owen, Thomas E.

    2005-09-20

    A composite piezoelectric transducer, whose piezoeletric element is a "ribbon wound" film of piezolectric material. As the film is excited, it expands and contracts, which results in expansion and contraction of the diameter of the entire ribbon winding. This is accompanied by expansion and contraction of the thickness of the ribbon winding, such that the sound radiating plate may be placed on the side of the winding.

  9. Magnetic x-ray dichroism in ultrathin epitaxial films

    SciTech Connect

    Tobin, J.G.; Goodman, K.W.; Cummins, T.R.

    1997-04-01

    The authors have used Magnetic X-ray Linear Dichroism (MXLD) and Magnetic X-ray Circular Dichroism (MXCD) to study the magnetic properties of epitaxial overlayers in an elementally specific fashion. Both MXLD and MXCD Photoelectron Spectroscopy were performed in a high resolution mode at the Spectromicroscopy Facility of the ALS. Circular Polarization was obtained via the utilization of a novel phase retarder (soft x-ray quarter wave plate) based upon transmission through a multilayer film. The samples were low temperature Fe overlayers, magnetic alloy films of NiFe and CoNi, and Gd grown on Y. The authors results include a direct comparison of high resolution angle resolved Photoelectron Spectroscopy performed in MXLD and MXCD modes as well as structural studies with photoelectron diffraction.

  10. Characterization of few-layered graphene grown by carbon implantation

    SciTech Connect

    Lee, Kin Kiong; McCallum, Jeffrey C.; Jamieson, David N.

    2014-02-21

    Graphene is considered to be a very promising material for applications in nanotechnology. The properties of graphene are strongly dependent on defects that occur during growth and processing. These defects can be either detrimental or beneficial to device performance depending on defect type, location and device application. Here we present experimental results on formation of few-layered graphene by carbon ion implantation into nickel films and characteristics of graphene devices formed by graphene transfer and lithographic patterning. Micro-Raman spectroscopy was used to determine the number of graphene layers formed and identify defects arising from the device processing. The graphene films were cleaned by annealing in vacuum. Transport properties of cleaned graphene films were investigated by fabrication of back-gated field-effect transistors, which exhibited high hole and electron mobility of 1935 and 1905 cm2/Vs, respectively.

  11. Defect reduction in epitaxial GaSb grown on nanopatterned GaAs substrates using full wafer block copolymer lithography

    SciTech Connect

    Jha, Smita; Liu, C.-C.; Nealey, P. F.; Kuech, T. F.; Kuan, T. S.; Babcock, S. E.; Park, J. H.; Mawst, L. J.

    2009-08-10

    Defect reduction in the large lattice mismatched system of GaSb on GaAs, {approx}7%, was accomplished using full wafer block copolymer (BCP) lithography. A self-assembled BCP mask layer was used to generate a hexagonal pattern of {approx}20 nm holes on {approx}40 nm centers in a 20 nm SiO{sub 2} layer. GaSb growth initially takes place selectively within these holes leading to a dense array of small, strain-relaxed epitaxial GaSb islands. The GaSb grown on the patterned SiO{sub 2} layer exhibits a reduction in the x-ray linewidth attributed to a decrease in the threading dislocation density when compared to blanket pseudomorphic film growth.

  12. Nano transfer and nanoreplication using deterministically grown sacrificial nanotemplates

    DOEpatents

    Melechko, Anatoli V.; McKnight, Timothy E.; Guillorn, Michael A.; Ilic, Bojan; Merkulov, Vladimir I.; Doktycz, Mitchel J.; Lowndes, Douglas H.; Simpson, Michael L.

    2012-03-27

    Methods, manufactures, machines and compositions are described for nanotransfer and nanoreplication using deterministically grown sacrificial nanotemplates. An apparatus, includes a substrate and a nanoconduit material coupled to a surface of the substrate. The substrate defines an aperture and the nanoconduit material defines a nanoconduit that is i) contiguous with the aperture and ii) aligned substantially non-parallel to a plane defined by the surface of the substrate.

  13. Correlation Between Optical Properties And Chemical Composition Of Sputter-deposited Germanium Cxide (GeOx) Films

    SciTech Connect

    Murphy, Neil R.; Grant, J. T.; Sun, L.; Jones, J. G.; Jakubiak, R.; Shutthanandan, V.; Ramana, Chintalapalle V.

    2014-03-18

    Germanium oxide (GeOx) films were grown on (1 0 0) Si substrates by reactive Direct-Current (DC) magnetron sputter-deposition using an elemental Ge target. The effects of oxygen gas fraction, Г = O2/(Ar + O2), on the deposition rate, structure, chemical composition and optical properties of GeOx films have been investigated. The chemistry of the films exhibits an evolution from pure Ge to mixed Ge + GeO + GeO2 and then finally to GeO2 upon increasing Г from 0.00 to 1.00. Grazing incidence X-ray analysis indicates that the GeOx films grown were amorphous. The optical properties probed by spectroscopic ellipsometry indicate that the effect of Г is significant on the optical constants of the GeOx films. The measured index of refraction (n) at a wavelength (λ) of 550 nm is 4.67 for films grown without any oxygen, indicating behavior characteristic of semiconducting Ge. The transition from germanium to mixed Ge + GeO + GeO2 composition is associated with a characteristic decrease in n (λ = 550 nm) to 2.62 and occurs at Г = 0.25. Finally n drops to 1.60 for Г = 0.50–1.00, where the films become GeO2. A detailed correlation between Г, n, k and stoichiometry in DC sputtered GeOx films is presented and discussed.

  14. DOE - NNSA/NFO -- Test Films

    U.S. Department of Energy (DOE) - all webpages (Extended Search)

    Historical Test Films > Film Page NNSANFO Language Options U.S. DOENNSA - Nevada Field Office Historical Test Film Instructions: Click the Windows Media or MPG Movie link below ...

  15. DOE - NNSA/NFO -- Historical Test Films

    U.S. Department of Energy (DOE) - all webpages (Extended Search)

    Films > Historical Test Films NNSANFO Language Options U.S. DOENNSA - Nevada Field Office Historical Test Films Instructions: Click the document Title or Thumbnail to view the ...

  16. Negligible substrate clamping effect on piezoelectric response in (111)-epitaxial tetragonal Pb(Zr, Ti)O{sub 3} films

    SciTech Connect

    Yamada, Tomoaki; Yasumoto, Jun; Ito, Daisuke; Yoshino, Masahito; Nagasaki, Takanori; Sakata, Osami; Imai, Yasuhiko; Kiguchi, Takanori; Shiraishi, Takahisa; Shimizu, Takao; Funakubo, Hiroshi

    2015-08-21

    The converse piezoelectric responses of (111)- and (001)-epitaxial tetragonal Pb(Zr{sub 0.35}Ti{sub 0.65})O{sub 3} [PZT] films were compared to investigate the orientation dependence of the substrate clamping effect. Synchrotron X-ray diffraction (XRD) and piezoelectric force microscopy revealed that the as-grown (111)-PZT film has a polydomain structure with normal twin boundaries that are changed by the poling process to inclined boundaries, as predicted by Romanov et al. [Phys. Status Solidi A 172, 225 (1999)]. Time-resolved synchrotron XRD under bias voltage showed the negligible impact of substrate clamping on the piezoelectric response in the (111)-PZT film, unlike the case for (001)-PZT film. The origin of the negligible clamping effect in the (111)-PZT film is discussed from the viewpoint of the elastic properties and the compensation of lattice distortion between neighboring domains.

  17. Strong room-temperature ferromagnetism of high-quality lightly Mn-doped ZnO grown by molecular beam epitaxy

    SciTech Connect

    Zuo Zheng; Zhou Huimei; Olmedo, Mario J.; Kong Jieying; Liu Jianlin; Beyermann, Ward P.; Zheng Jianguo; Xin Yan

    2012-09-01

    Strong room-temperature ferromagnetism is demonstrated in single crystalline Mn-doped ZnO grown by molecular beam epitaxy. With a low Mn concentration of 2 Multiplication-Sign 10{sup 19} cm{sup -3}, Mn-doped ZnO films exhibited room-temperature ferromagnetism with a coercivity field larger than 200 Oe, a large saturation moment of 6 {mu}{sub B}/ion, and a large residue moment that is {approx}70% of the saturation magnetization. Isolated ions with long range carrier mediated spin-spin coupling may be responsible for the intrinsic ferromagnetism.

  18. Accumulation of heavy metals by vegetables grown in mine wastes

    SciTech Connect

    Cobb, G.P.; Sands, K.; Waters, M.; Wixson, B.G.; Dorward-King, E.

    2000-03-01

    Lead, cadmium, arsenic, and zinc were quantified in mine wastes and in soils mixed with mine wastes. Metal concentrations were found to be heterogeneous in the wastes. Iceberg lettuce, Cherry Belle radishes, Roma bush beans, and Better Boy tomatoes were cultivated in mine wastes and in waste-amended soils. Lettuce and radishes had 100% survival in the 100% mine waste treatments compared to 0% and 25% survival for tomatoes and beans, respectively. Metal concentrations were determined in plant tissues to determine uptake and distribution of metals in the edible plant parts. Individual soil samples were collected beneath each plant to assess metal content in the immediate plant environment. This analysis verified heterogeneous metal content of the mine wastes. The four plant species effectively accumulated and translocated lead, cadmium, arsenic, and zinc. Tomato and bean plants contained the four metals mainly in the roots and little was translocated to the fruits. Radish roots accumulated less metals compared to the leaves, whereas lettuce roots and leaves accumulated similar concentrations of the four metals. Lettuce leaves and radish roots accumulated significantly more metals than bean and tomato fruits. This accumulation pattern suggests that consumption of lettuce leaves or radish roots from plants grown in mine wastes would pose greater risks to humans and wildlife than would consumption of beans or tomatoes grown in the same area. The potential risk may be mitigated somewhat in humans, as vegetables grown in mine wastes exhibited stunted growth and chlorosis.

  19. Mechanical and Electrical Performance of Thermally Stable Au-ZnO films

    DOE PAGES [OSTI]

    Schoeppner, Rachel L.; Goeke, Ronald S.; Moody, Neville R.; Bahr, David F.

    2015-03-28

    The mechanical properties, thermal stability, and electrical performance of Au–ZnO composite thin films are determined in this work. The co-deposition of ZnO with Au via physical vapor deposition leads to grain refinement over that of pure Au; the addition of 0.1 vol.% ZnO reduces the as-grown grain size by over 30%. The hardness of the as-grown films doubles with 2% ZnO, from 1.8 to 3.6 GPa as measured by nanoindentation. Films with ZnO additions greater than 0.5% show no significant grain growth after annealing at 350 °C, while pure gold and smaller additions do exhibit grain growth and subsequent mechanicalmore » softening. Films with 1% and 2% ZnO show a decrease of approximately 50% in electrical resistivity and no change in hardness after annealing. A model accounting for both changes in the interface structure between dispersed ZnO particles and the Au matrix captures the changes in mechanical and electrical resistivity. Furthermore, the addition of 1–2% ZnO co-deposited with Au provides a method to create mechanically hard and thermally stable films with a resistivity less than 80 nΩ-m. Our results complement previous studies of other alloying systems, suggesting oxide dispersion strengthened (ODS) gold shows a desirable hardness–resistivity relationship that is relatively independent of the particular ODS chemistry.« less

  20. Mechanical and Electrical Performance of Thermally Stable Au-ZnO films

    SciTech Connect

    Schoeppner, Rachel L.; Goeke, Ronald S.; Moody, Neville R.; Bahr, David F.

    2015-03-28

    The mechanical properties, thermal stability, and electrical performance of AuZnO composite thin films are determined in this work. The co-deposition of ZnO with Au via physical vapor deposition leads to grain refinement over that of pure Au; the addition of 0.1 vol.% ZnO reduces the as-grown grain size by over 30%. The hardness of the as-grown films doubles with 2% ZnO, from 1.8 to 3.6 GPa as measured by nanoindentation. Films with ZnO additions greater than 0.5% show no significant grain growth after annealing at 350 C, while pure gold and smaller additions do exhibit grain growth and subsequent mechanical softening. Films with 1% and 2% ZnO show a decrease of approximately 50% in electrical resistivity and no change in hardness after annealing. A model accounting for both changes in the interface structure between dispersed ZnO particles and the Au matrix captures the changes in mechanical and electrical resistivity. Furthermore, the addition of 12% ZnO co-deposited with Au provides a method to create mechanically hard and thermally stable films with a resistivity less than 80 n?-m. Our results complement previous studies of other alloying systems, suggesting oxide dispersion strengthened (ODS) gold shows a desirable hardnessresistivity relationship that is relatively independent of the particular ODS chemistry.

  1. Mechanical and Electrical Performance of Thermally Stable Au-ZnO films

    SciTech Connect

    Schoeppner, Rachel L.; Goeke, Ronald S.; Moody, Neville R.; Bahr, David F.

    2015-03-28

    The mechanical properties, thermal stability, and electrical performance of Au–ZnO composite thin films are determined in this work. The co-deposition of ZnO with Au via physical vapor deposition leads to grain refinement over that of pure Au; the addition of 0.1 vol.% ZnO reduces the as-grown grain size by over 30%. The hardness of the as-grown films doubles with 2% ZnO, from 1.8 to 3.6 GPa as measured by nanoindentation. Films with ZnO additions greater than 0.5% show no significant grain growth after annealing at 350 °C, while pure gold and smaller additions do exhibit grain growth and subsequent mechanical softening. Films with 1% and 2% ZnO show a decrease of approximately 50% in electrical resistivity and no change in hardness after annealing. A model accounting for both changes in the interface structure between dispersed ZnO particles and the Au matrix captures the changes in mechanical and electrical resistivity. Furthermore, the addition of 1–2% ZnO co-deposited with Au provides a method to create mechanically hard and thermally stable films with a resistivity less than 80 nΩ-m. Our results complement previous studies of other alloying systems, suggesting oxide dispersion strengthened (ODS) gold shows a desirable hardness–resistivity relationship that is relatively independent of the particular ODS chemistry.

  2. Photo-induced water oxidation at the aqueous GaN (1010) interface: Deprotonation kinetics of the first proton-coupled electron-transfer step

    SciTech Connect

    Ertem, Mehmed Z.; Kharche, Neerav; Batista, Victor S.; Hybertsen, Mark S.; Tully, John C.; Muckerman, James T.

    2015-03-12

    Photoeclectrochemical water splitting plays a key role in a promising path to the carbon-neutral generation of solar fuels. Wurzite GaN and its alloys (e.g., GaN/ZnO and InGaN) are demonstrated photocatalysts for water oxidation, and they can drive the overall water splitting reaction when coupled with co-catalysts for proton reduction. In the present work, we investigate the water oxidation mechanism on the prototypical GaN (1010) surface using a combined ab initio molecular dynamics and molecular cluster model approach taking into account the role of water dissociation and hydrogen bonding within the first solvation shell of the hydroxylated surface. The investigation of free-energy changes for the four proton-coupled electron-transfer (PCET) steps of the water oxidation mechanism shows that the first PCET step for the conversion of Ga-OH to Ga-O?? requires the highest energy input. We further examine the sequential PCETs, with the proton transfer (PT) following the electron transfer (ET), and find that photo-generated holes localize on surface NH sites is thermodynamically more favorable than OH sites. However, proton transfer from OH sites with subsequent localization of holes on oxygen atoms is kinetically favored owing to hydrogen bonding interactions at the GaN (1010)water interface. We find that the deprotonation of surface OH sites is the limiting factor for the generation of reactive oxyl radical ion intermediates and consequently for water oxidation.

  3. Photo-induced water oxidation at the aqueous GaN (101¯0) interface: Deprotonation kinetics of the first proton-coupled electron-transfer step

    DOE PAGES [OSTI]

    Ertem, Mehmed Z.; Kharche, Neerav; Batista, Victor S.; Hybertsen, Mark S.; Tully, John C.; Muckerman, James T.

    2015-03-12

    Photoeclectrochemical water splitting plays a key role in a promising path to the carbon-neutral generation of solar fuels. Wurzite GaN and its alloys (e.g., GaN/ZnO and InGaN) are demonstrated photocatalysts for water oxidation, and they can drive the overall water splitting reaction when coupled with co-catalysts for proton reduction. In the present work, we investigate the water oxidation mechanism on the prototypical GaN (101¯0) surface using a combined ab initio molecular dynamics and molecular cluster model approach taking into account the role of water dissociation and hydrogen bonding within the first solvation shell of the hydroxylated surface. The investigation ofmore » free-energy changes for the four proton-coupled electron-transfer (PCET) steps of the water oxidation mechanism shows that the first PCET step for the conversion of –Ga-OH to –Ga-O˙⁻ requires the highest energy input. We further examine the sequential PCETs, with the proton transfer (PT) following the electron transfer (ET), and find that photo-generated holes localize on surface –NH sites is thermodynamically more favorable than –OH sites. However, proton transfer from –OH sites with subsequent localization of holes on oxygen atoms is kinetically favored owing to hydrogen bonding interactions at the GaN (101¯0)–water interface. We find that the deprotonation of surface –OH sites is the limiting factor for the generation of reactive oxyl radical ion intermediates and consequently for water oxidation.« less

  4. Surface excitons on a ZnO (000-1) thin film

    SciTech Connect

    Kuehn, S. Friede, S.; Elsaesser, T.; Sadofev, S.; Blumstengel, S.; Henneberger, F.

    2013-11-04

    Elementary excitations at the polar (000-1) surface of a 20 nm pseudomorphically grown ZnO thin film are examined by steady state and time-resolved photoluminescence spectroscopy at low temperature. We control the density of emission centers through the deposition of prototypical organic molecules with a carboxylic acid anchor group by the Langmuir-Blodgett technique. Knowledge of the precise film thickness, defect concentrations and number density of deposited molecules leads us to associate the surface exciton emission to defect-related localization centers that are generated through a photochemical process.

  5. Microwave properties of RF- sputtered ZnFe{sub 2}O{sub 4} thin films

    SciTech Connect

    Garg, T. Kulkarni, A. R.; Venkataramani, N.; Sahu, B. N.; Prasad, Shiva

    2014-04-24

    In this work, RF- magnetron sputtering technique has been employed to deposit nanocrystalline ZnFe{sub 2}O{sub 4} thin films at room temperature. The as grown films were ex-situ annealed in air for 2 h at temperatures from 150C to 650C. X-ray diffraction, vibrating sample magnetometer and ferromagnetic resonance were used to analyze the phase formation, magnetic properties and microwave properties respectively. From the hysteresis loops and ferromagnetic resonance spectra taken at room temperature, a systematic study on the effect of O{sub 2} plasma on microwave properties with respect to processing temperature has been carried out.

  6. Proposed Route to Thin Film Crystal Si Using Biaxially Textured Foreign Template Layers

    SciTech Connect

    Teplin, C. W.; Ginley, D. S.; van Hest, M.F.A.M.; Perkins, J. D.; Young, D. L.; Stradins, P.; Wang, Q.; Al-Jassim, M.; Iwaniczko, E.; Leenheer, A.; Jones, K. M.; Branz, H. M.

    2005-11-01

    We have developed a new approach to growing photovoltaic-quality crystal silicon (c-Si) films on glass. Other approaches to film c-Si focus on increasing grain size in order to reduce the deleterious effects of grain boundaries. Instead, we have developed an approach to align the silicon grains biaxially (both in and out of plane) so that 1) grain boundaries are "low-angle" and have less effect on the electronic properties of the material and 2) subsequent epitaxial thickening is simplified. They key to our approach is the use of a foreign template layer that can be grown with biaxial texture directly on glass.

  7. Group I-III-VI.sub.2 semiconductor films for solar cell application

    DOEpatents

    Basol, Bulent M.; Kapur, Vijay K.

    1991-01-01

    This invention relates to an improved thin film solar cell with excellent electrical and mechanical integrity. The device comprises a substrate, a Group I-III-VI.sub.2 semiconductor absorber layer and a transparent window layer. The mechanical bond between the substrate and the Group I-III-VI.sub.2 semiconductor layer is enhanced by an intermediate layer between the substrate and the Group I-III-VI.sub.2 semiconductor film being grown. The intermediate layer contains tellurium or substitutes therefor, such as Se, Sn, or Pb. The intermediate layer improves the morphology and electrical characteristics of the Group I-III-VI.sub.2 semiconductor layer.

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

    SciTech Connect

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

    2013-09-30

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

  9. Influence of aluminium doping on thermoelectric performance of atomic layer deposited ZnO thin films

    SciTech Connect

    Ruoho, Mikko Pale, Ville; Erdmanis, Mikhail; Tittonen, Ilkka

    2013-11-11

    We study the effect of Al doping on thermoelectric power factor of ZnO films grown using atomic layer deposition method. The overall doping level is tuned by either varying the precursor pulsing sequence or by varying the number of precursor pulses while keeping the sequence unchanged. We observe that commonly utilized doping approach when periodic dopant layers are densely packed results in reduced power factor. At the same time, we find that thermoelectric performance can be improved by clustering the dopants. In addition, the clustering was found to tune the preferred crystal orientation of the polycrystalline film.

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

    Office of Scientific and Technical Information (OSTI)

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

  11. Luminescent properties of solution-grown ZnO nanorods. (Journal...

    Office of Scientific and Technical Information (OSTI)

    Luminescent properties of solution-grown ZnO nanorods. Citation Details In-Document Search Title: Luminescent properties of solution-grown ZnO nanorods. The optical properties of ...

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

    SciTech Connect

    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.

  13. Saturated defect densities of hydrogenated amorphous silicon grown by hot-wire chemical vapor deposition at rates up to 150 {angstrom}/s

    SciTech Connect

    Mahan, A. H.; Xu, Y.; Nelson, B. P.; Crandall, R. S.; Cohen, J. D.; Palinginis, K. C.; Gallagher, A. C.

    2001-06-11

    Hydrogenated amorphous-silicon (a-Si:H) is grown by hot-wire chemical vapor deposition (HWCVD) at deposition rates (R{sub d}) exceeding 140 {angstrom}/s ({approx}0.8 {mu}m/min). These high rates are achieved by using multiple filaments and deposition conditions different than those used to produce our standard 20 {angstrom}/s material. With proper deposition parameter optimization, an AM1.5 photo-to-dark-conductivity ratio of 10{sup 5} is maintained at an R{sub d} up to 130 {angstrom}/s, beyond which it decreases. In addition, the first saturated defect densities of high R{sub d} a-Si:H films are presented. These saturated defected densities are similar to those of the best HWCVD films deposited at 5--8 {angstrom}/s, and are invariant with R{sub d} up to 130 {angstrom}/s.

  14. Resistive switching characteristics of polycrystalline SrTiO{sub 3} films

    SciTech Connect

    Jong Choi, Hyung; Won Park, Suk; Deok Han, Gwon; Hyung Shim, Joon; Na, Junhong; Kim, Gyu-Tae

    2014-06-16

    Strontium titanate (STO) thin films 90?nm in thickness were grown on a Pt substrate through atomic layer deposition (ALD). The as-deposited ALD STO grown with an ALD cycle ratio of 1:1 (Sr:Ti) was in an amorphous phase, and annealing at 800?C in air crystallized the films into the perovskite phase. This phase change was confirmed by x-ray diffraction and transmission electron microscopy. The as-deposited ALD STO exhibited no discernible switching mechanism, whereas unipolar switching behavior was reproducibly observed with a high resistance ratio (10{sup 8}10{sup 9}) and strict separation of the set/reset voltages and currents in the annealed ALD STO. Mechanisms for charge transport in both the low- and high-resistance states and for resistive switching in the annealed ALD STO are also proposed.

  15. Surface control of epitaxial manganite films via oxygen pressure

    DOE PAGES [OSTI]

    Tselev, Alexander; Vasudevan, Rama K.; Gianfrancesco, Anthony G.; Qiao, Liang; Ganesh, Panchapakesan; Meyer, Tricia L.; Lee, Ho Nyung; Biegalski, Michael D.; Baddorf, Arthur P.; Kalinin, Sergei

    2015-03-11

    The trend to reduce device dimensions demands increasing attention to atomic-scale details of structure of thin films as well as to pathways to control it. We found that this is of special importance in the systems with multiple competing interactions. We have used in situ scanning tunneling microscopy to image surfaces of La5/8Ca3/8MnO3 films grown by pulsed laser deposition. The atomically resolved imaging was combined with in situ angle-resolved X-ray photoelectron spectroscopy. We find a strong effect of the background oxygen pressure during deposition on structural and chemical features of the film surface. Deposition at 50 mTorr of O2 leadsmore » to mixed-terminated film surfaces, with B-site (MnO2) termination being structurally imperfect at the atomic scale. Moreover, a relatively small reduction of the oxygen pressure to 20 mTorr results in a dramatic change of the surface structure leading to a nearly perfectly ordered B-site terminated surface with only a small fraction of A-site (La,Ca)O termination. This is accompanied, however, by surface roughening at a mesoscopic length scale. The results suggest that oxygen has a strong link to the adatom mobility during growth. The effect of the oxygen pressure on dopant surface segregation is also pronounced: Ca surface segregation is decreased with oxygen pressure reduction.« less

  16. Surface control of epitaxial manganite films via oxygen pressure

    SciTech Connect

    Tselev, Alexander; Vasudevan, Rama K.; Gianfrancesco, Anthony G.; Qiao, Liang; Ganesh, Panchapakesan; Meyer, Tricia L.; Lee, Ho Nyung; Biegalski, Michael D.; Baddorf, Arthur P.; Kalinin, Sergei

    2015-03-11

    The trend to reduce device dimensions demands increasing attention to atomic-scale details of structure of thin films as well as to pathways to control it. We found that this is of special importance in the systems with multiple competing interactions. We have used in situ scanning tunneling microscopy to image surfaces of La5/8Ca3/8MnO3 films grown by pulsed laser deposition. The atomically resolved imaging was combined with in situ angle-resolved X-ray photoelectron spectroscopy. We find a strong effect of the background oxygen pressure during deposition on structural and chemical features of the film surface. Deposition at 50 mTorr of O2 leads to mixed-terminated film surfaces, with B-site (MnO2) termination being structurally imperfect at the atomic scale. Moreover, a relatively small reduction of the oxygen pressure to 20 mTorr results in a dramatic change of the surface structure leading to a nearly perfectly ordered B-site terminated surface with only a small fraction of A-site (La,Ca)O termination. This is accompanied, however, by surface roughening at a mesoscopic length scale. The results suggest that oxygen has a strong link to the adatom mobility during growth. The effect of the oxygen pressure on dopant surface segregation is also pronounced: Ca surface segregation is decreased with oxygen pressure reduction.

  17. Thermal stability of deep level defects induced by high energy proton irradiation in n-type GaN

    SciTech Connect

    Zhang, Z.; Farzana, E.; Sun, W. Y.; Arehart, A. R.; Ringel, S. A.; Chen, J.; Zhang, E. X.; Fleetwood, D. M.; Schrimpf, R. D.; McSkimming, B.; Kyle, E. C. H.; Speck, J. S.

    2015-10-21

    The impact of annealing of proton irradiation-induced defects in n-type GaN devices has been systematically investigated using deep level transient and optical spectroscopies. Moderate temperature annealing (>200–250 °C) causes significant reduction in the concentration of nearly all irradiation-induced traps. While the decreased concentration of previously identified N and Ga vacancy related levels at E{sub C} − 0.13 eV, 0.16 eV, and 2.50 eV generally followed a first-order reaction model with activation energies matching theoretical values for N{sub I} and V{sub Ga} diffusion, irradiation-induced traps at E{sub C} − 0.72 eV, 1.25 eV, and 3.28 eV all decrease in concentration in a gradual manner, suggesting a more complex reduction mechanism. Slight increases in concentration are observed for the N-vacancy related levels at E{sub C} − 0.20 eV and 0.25 eV, which may be due to the reconfiguration of other N-vacancy related defects. Finally, the observed reduction in concentrations of the states at E{sub C} − 1.25 and E{sub C} − 3.28 eV as a function of annealing temperature closely tracks the detailed recovery behavior of the background carrier concentration as a function of annealing temperature. As a result, it is suggested that these two levels are likely to be responsible for the underlying carrier compensation effect that causes the observation of carrier removal in proton-irradiated n-GaN.

  18. Nanocrystalline zinc ferrite films studied by magneto-optical spectroscopy

    SciTech Connect

    Likov-Jakubisov, E. Vi?ovsk, .; irok, P.; Hrabovsk, D.; Pitora, J.; Sahoo, Subasa C.; Prasad, Shiva; Venkataramani, N.; Bohra, Murtaza; Krishnan, R.

    2015-05-07

    Ferrimagnetic Zn-ferrite (ZnFe{sub 2}O{sub 4}) films can be grown with the ferromagnetic resonance linewidth of 40?Oe at 9.5?GHz without going through a high temperature processing. This presents interest for applications. The work deals with laser ablated ZnFe{sub 2}O{sub 4} films deposited at O{sub 2} pressure of 0.16?mbar onto fused quartz substrates. The films about 120?nm thick are nanocrystalline and their spontaneous magnetization, 4?M{sub s}, depends on the nanograin size, which is controlled by the substrate temperature (T{sub s}). At T{sub s}???350?C, where the grain distribution peaks around ?2030?nm, the room temperature 4?M{sub s} reaches a maximum of ?2.3?kG. The films were studied by magnetooptical polar Kerr effect (MOKE) spectroscopy at photon energies between 1 and 5?eV. The complementary characteristics were provided by spectral ellipsometry (SE). Both the SE and MOKE spectra confirmed ferrimagnetic ordering. The structural details correspond to those observed in MgFe{sub 2}O{sub 4} and Li{sub 0.5}Fe{sub 2.5}O{sub 4} spinels. SE experiments confirm the insulator behavior. The films display MOKE amplitudes somewhat reduced with respect to those in Li{sub 0.5}Fe{sub 2.5}O{sub 4} and MgFe{sub 2}O{sub 4} due to a lower degree of spinel inversion and nanocrystalline structure. The results indicate that the films are free of oxygen vacancies and Fe{sup 3+}-Fe{sup 2+} exchange.

  19. Oxygen vacancy-driven evolution of structural and electrical properties in SrFeO3₋δ thin films and a method of stabilization

    DOE PAGES [OSTI]

    Enriquez, Erik M.; Chen, Aiping; Harrell, Zachary John; Lu, Xujie; Dowden, Paul Charles; Koskelo, Nicholas Aaron; Janoschek, Marc; Chen, Chonglin; Jia, Quanxi

    2016-10-06

    Epitaxial SrFeO3-δ (SFO) thin films have been grown on various substrates by pulsed laser deposition. The structural and electrical properties of SFO thin films are monitored with time in different atmospheres at room temperature, showing time-dependent crystal structure and electrical conductivity. The increased out-of-plane lattice parameter and resistivity over time are associated with the increased oxygen vacancies density in SFO thin films. The epitaxial strain plays an important role in determining the initial resistivity, and the sample environment determines the trend of resistivity change over time. An amorphous Al2O3 passivation layer has been found to be effective in stabilizing themore » structure and electrical properties of SFO thin films. Lastly, this work explores time dependent structure and properties variation in oxide films and provides a way to stabilize thin film materials that are sensitive to oxygen vacancies.« less

  20. Epitaxial thin films

    DOEpatents

    Hunt, Andrew Tye; Deshpande, Girish; Lin, Wen-Yi; Jan, Tzyy-Jiuan

    2006-04-25

    Epitatial thin films for use as buffer layers for high temperature superconductors, electrolytes in solid oxide fuel cells (SOFC), gas separation membranes or dielectric material in electronic devices, are disclosed. By using CCVD, CACVD or any other suitable deposition process, epitaxial films having pore-free, ideal grain boundaries, and dense structure can be formed. Several different types of materials are disclosed for use as buffer layers in high temperature superconductors. In addition, the use of epitaxial thin films for electrolytes and electrode formation in SOFCs results in densification for pore-free and ideal gain boundary/interface microstructure. Gas separation membranes for the production of oxygen and hydrogen are also disclosed. These semipermeable membranes are formed by high-quality, dense, gas-tight, pinhole free sub-micro scale layers of mixed-conducting oxides on porous ceramic substrates. Epitaxial thin films as dielectric material in capacitors are also taught herein. Capacitors are utilized according to their capacitance values which are dependent on their physical structure and dielectric permittivity. The epitaxial thin films of the current invention form low-loss dielectric layers with extremely high permittivity. This high permittivity allows for the formation of capacitors that can have their capacitance adjusted by applying a DC bias between their electrodes.

  1. High-quality EuO thin films the easy way via topotactic transformation

    SciTech Connect

    Mairoser, Thomas; Mundy, Julia A.; Melville, Alexander; Hodash, Daniel; Cueva, Paul; Held, Rainer; Glavic, Artur; Schubert, Jürgen; Muller, David A.; Schlom, Darrell G.; Schmehl, Andreas

    2015-07-16

    Epitaxy is widely employed to create highly oriented crystalline films. A less appreciated, but nonetheless powerful means of creating such films is via topotactic transformation, in which a chemical reaction transforms a single crystal of one phase into a single crystal of a different phase, which inherits its orientation from the original crystal. Topotactic reactions may be applied to epitactic films to substitute, add or remove ions to yield epitactic films of different phases. Here we exploit a topotactic reduction reaction to provide a non-ultra-high vacuum (UHV) means of growing highly oriented single crystalline thin films of the easily over-oxidized half-metallic semiconductor europium monoxide (EuO) with a perfection rivalling that of the best films of the same material grown by molecular-beam epitaxy or UHV pulsed-laser deposition. Lastly, as the technique only requires high-vacuum deposition equipment, it has the potential to drastically improve the accessibility of high-quality single crystalline films of EuO as well as other difficult-to-synthesize compounds.

  2. High-quality EuO thin films the easy way via topotactic transformation

    DOE PAGES [OSTI]

    Mairoser, Thomas; Mundy, Julia A.; Melville, Alexander; Hodash, Daniel; Cueva, Paul; Held, Rainer; Glavic, Artur; Schubert, Jürgen; Muller, David A.; Schlom, Darrell G.; et al

    2015-07-16

    Epitaxy is widely employed to create highly oriented crystalline films. A less appreciated, but nonetheless powerful means of creating such films is via topotactic transformation, in which a chemical reaction transforms a single crystal of one phase into a single crystal of a different phase, which inherits its orientation from the original crystal. Topotactic reactions may be applied to epitactic films to substitute, add or remove ions to yield epitactic films of different phases. Here we exploit a topotactic reduction reaction to provide a non-ultra-high vacuum (UHV) means of growing highly oriented single crystalline thin films of the easily over-oxidizedmore » half-metallic semiconductor europium monoxide (EuO) with a perfection rivalling that of the best films of the same material grown by molecular-beam epitaxy or UHV pulsed-laser deposition. Lastly, as the technique only requires high-vacuum deposition equipment, it has the potential to drastically improve the accessibility of high-quality single crystalline films of EuO as well as other difficult-to-synthesize compounds.« less

  3. Electron-beam-evaporated thin films of hafnium dioxide for fabricating electronic devices

    SciTech Connect

    Xiao, Zhigang; Kisslinger, Kim

    2015-06-17

    Thin films of hafnium dioxide (HfO2) are widely used as the gate oxide in fabricating integrated circuits because of their high dielectric constants. In this paper, the authors report the growth of thin films of HfO2 using e-beam evaporation, and the fabrication of complementary metal-oxide semiconductor (CMOS) integrated circuits using this HfO2 thin film as the gate oxide. The authors analyzed the thin films using high-resolution transmission electron microscopy and electron diffraction, thereby demonstrating that the e-beam-evaporation-grown HfO2 film has a polycrystalline structure and forms an excellent interface with silicon. Accordingly, we fabricated 31-stage CMOS ring oscillator to test the quality of the HfO2 thin film as the gate oxide, and obtained excellent rail-to-rail oscillation waveforms from it, denoting that the HfO2 thin film functioned very well as the gate oxide.

  4. Electron-beam-evaporated thin films of hafnium dioxide for fabricating electronic devices

    DOE PAGES [OSTI]

    Xiao, Zhigang; Kisslinger, Kim

    2015-06-17

    Thin films of hafnium dioxide (HfO2) are widely used as the gate oxide in fabricating integrated circuits because of their high dielectric constants. In this paper, the authors report the growth of thin films of HfO2 using e-beam evaporation, and the fabrication of complementary metal-oxide semiconductor (CMOS) integrated circuits using this HfO2 thin film as the gate oxide. The authors analyzed the thin films using high-resolution transmission electron microscopy and electron diffraction, thereby demonstrating that the e-beam-evaporation-grown HfO2 film has a polycrystalline structure and forms an excellent interface with silicon. Accordingly, we fabricated 31-stage CMOS ring oscillator to test themore » quality of the HfO2 thin film as the gate oxide, and obtained excellent rail-to-rail oscillation waveforms from it, denoting that the HfO2 thin film functioned very well as the gate oxide.« less

  5. Multi-jump magnetic switching in ion-beam sputtered amorphous Co{sub 20}Fe{sub 60}B{sub 20} thin films

    SciTech Connect

    Raju, M.; Chaudhary, Sujeet; Pandya, D. K.

    2013-08-07

    Unconventional multi-jump magnetization reversal and significant in-plane uniaxial magnetic anisotropy (UMA) in the ion-beam sputtered amorphous Co{sub 20}Fe{sub 60}B{sub 20}(5–75 nm) thin films grown on Si/amorphous SiO{sub 2} are reported. While such multi-jump behavior is observed in CoFeB(10 nm) film when the magnetic field is applied at 10°–20° away from the easy-axis, the same is observed in CoFeB(12.5 nm) film when the magnetic field is 45°–55° away from easy-axis. Unlike the previous reports of multi-jump switching in epitaxial films, their observance in the present case of amorphous CoFeB is remarkable. This multi-jump switching is found to disappear when the films are crystallized by annealing at 420 °C. The deposition geometry and the energy of the sputtered species appear to intrinsically induce a kind of bond orientation anisotropy in the films, which leads to the UMA in the as-grown amorphous CoFeB films. Exploitation of such multi-jump switching in amorphous CoFeB thin films could be of technological significance because of their applications in spintronic devices.

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

    SciTech Connect

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

    2013-04-29

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

  7. Thin films and uses

    DOEpatents

    Baskaran, Suresh; Graff, Gordon L.; Song, Lin

    1998-01-01

    The invention provides a method for synthesizing a titanium oxide-containing film comprising the following steps: (a) preparing an aqueous solution of a titanium chelate with a titanium molarity in the range of 0.01M to 0.6M. (b) immersing a substrate in the prepared solution, (c) decomposing the titanium chelate to deposit a film on the substrate. The titanium chelate maybe decomposed acid, base, temperature or other means. A preferred method provides for the deposit of adherent titanium oxide films from C2 to C5 hydroxy carboxylic acids. In another aspect the invention is a novel article of manufacture having a titanium coating which protects the substrate against ultraviolet damage. In another aspect the invention provides novel semipermeable gas separation membranes, and a method for producing them.

  8. Ga-doped ZnO grown by pulsed laser deposition in H2: the roles of Ga and H

    SciTech Connect

    Look, David; Droubay, Timothy C.; McCloy, John S.; Zhu, Zihua; Chambers, Scott A.

    2011-01-11

    Highly conductive thin films of ZnO doped with Ga were grown by pulsed-laser deposition (PLD) with 10 mTorr of H2 in the growth chamber. Compared with a more conventional method of producing conductive films of ZnO, i.e., growth in O2 followed by annealing in forming gas (5% H2 in Ar), the H2 method requires no post-growth anneal and also produces higher carrier concentrations and lower resistivities with better depth uniformity. As an example, a 65-nm-thick sample had a room-temperature mobility of 32 cm2/V-s, a concentration of 6.8 x 1020 cm-3, and a resistivity of 2.9 x 10^-4 ohm-cm. From a scattering model, the donor and acceptor concentrations were calculated as 8.9 x 1020 and 2.1 x 10^20 cm-3, respectively, as compared to the Ga and H concentrations of 11 x 10^20 and 1 x 10^20 cm-3. Thus, H does not play a significant role as a donor in this type of ZnO

  9. Crossover of electron-electron interaction effect in Sn-doped indium oxide films

    SciTech Connect

    Zhang, Yu-Jie; Gao, Kuang-Hong; Li, Zhi-Qing

    2015-03-09

    We systematically study the structures and electrical transport properties of a series of Sn-doped indium oxide (ITO) films with thickness t ranging from ∼5 to ∼53 nm. Scanning electron microscopy and x-ray diffraction results indicate that the t ≲ 16.8 nm films are polycrystalline, while those t ≳ 26.7 nm films are epitaxially grown along [100] direction. For the epitaxial films, the Altshuler and Aronov electron-electron interaction (EEI) effect governs the temperature behaviors of the sheet conductance σ{sub □} at low temperatures, and the ratios of relative change of Hall coefficient ΔR{sub H}/R{sub H} to relative change of sheet resistance ΔR{sub □}/R{sub □} are ≈2, which is quantitatively consistent with Altshuler and Aronov EEI theory and seldom observed in other systems. For those polycrystalline films, both the sheet conductance and Hall coefficient vary linearly with logarithm of temperature below several tens Kelvin, which can be well described by the current EEI theories in granular metals. We extract the intergranular tunneling conductance of each film by comparing the σ{sub □}(T) data with the predication of EEI theories in granular metals. It is found that when the tunneling conductance is less than the conductance of a single indium tin oxide (ITO) grain, the ITO film reveals granular metal characteristics in transport properties; conversely, the film shows transport properties of homogeneous disordered conductors. Our results indicate that electrical transport measurement can not only reveal the underlying charge transport properties of the film but also be a powerful tool to detect the subtle homogeneity of the film.

  10. Homoepitaxy of ZnO and MgZnO Films at 90 C

    SciTech Connect

    Ehrentraut, Dirk; Goh, Gregory K.L.; Fujii, Katsushi; Ooi, Chin Chun; Quang, Le Hong; Fukuda, Tsuguo; Kano, Masataka; Zhang, Yuantao; Matsuoka, Takashi

    2014-06-01

    The aqueous synthesis of uniform single crystalline homoepitaxial zinc oxide, ZnO, and magnesium zinc oxide, Mg{sub x}Zn{sub 1?x}O, films under very low temperature conditions at T=90 C and ambient pressure has been explored. A maximum Mg content of 1 mol% was recorded by energy dispersive spectroscopy. The growth on the polar (0 0 0 1) and (0 0 0 1) faces resulted in films that are strongly different in their structural and optical quality as evidenced by high-resolution X-ray diffraction, secondary electron microscopy, and photoluminescence. This is a result of the chemistry and temperature of the solution dictating the stability range of growth-governing metastable species. The use of trisodium citrate, Na{sub 3}C{sub 6}H{sub 5}O{sub 7}, yielded coalesced, mirror-like homoepitaxial films whereas adding magnesium nitrate hexahydrate, Mg(NO{sub 3}){sub 2}6H{sub 2}O, favors the growth of films with pronounced faceting. - Graphical abstract: Homoepitaxial ZnO films grown from aqueous solution below boiling point of water on a ZnO substrate with off-orientation reveal parallel grooves that are characterized by (1 0 1{sup } 1) facets. Adding trisodium citrate yields closed, single-crystalline ZnO films, which can further be functionalized. Alloying with MgO yields MgZnO films with low Mg content only. - Highlights: A simple method to synthesize uniform single crystalline homoepitaxial ZnO and MgZnO films. ZnO growth on (0 0 0 1) and (0 0 0 1{sup }) face resulted in films that are strongly different in their structural and optical quality. Single crystalline MgZnO film was fabricated under mild conditions (90 C and ambient pressure). Mg incorporation of nearly 1 mol% was obtained while maintaining single phase wurtzite structure.

  11. Thickness-dependent coherent phonon frequency in ultrathin FeSe/SrTiO3 films

    SciTech Connect

    Yang, Shuolong; Sobota, Jonathan A.; Leuenberger, Dominik; Kemper, Alexander F.; Lee, James J.; Schmitt, Felix T.; Li, Wei; Moore, Rob G.; Kirchmann, Patrick S.; Shen, Zhi -Xun

    2015-06-01

    Ultrathin FeSe films grown on SrTiO3 substrates are a recent milestone in atomic material engineering due to their important role in understanding unconventional superconductivity in Fe-based materials. By using femtosecond time- and angle-resolved photoelectron spectroscopy, we study phonon frequencies in ultrathin FeSe/SrTiO3 films grown by molecular beam epitaxy. After optical excitation, we observe periodic modulations of the photoelectron spectrum as a function of pump–probe delay for 1-unit-cell, 3-unit-cell, and 60-unit-cell thick FeSe films. The frequencies of the coherent intensity oscillations increase from 5.00 ± 0.02 to 5.25 ± 0.02 THz with increasing film thickness. By comparing with previous works, we attribute this mode to the Se A1g phonon. The dominant mechanism for the phonon softening in 1-unit-cell thick FeSe films is a substrate-induced lattice strain. Results demonstrate an abrupt phonon renormalization due to a lattice mismatch between the ultrathin film and the substrate.

  12. Nanotransfer and nanoreplication using deterministically grown sacrificial nanotemplates

    DOEpatents

    Melechko, Anatoli V.; McKnight, Timothy E. , Guillorn, Michael A.; Ilic, Bojan; Merkulov, Vladimir I.; Doktycz, Mitchel J.; Lowndes, Douglas H.; Simpson, Michael L.

    2011-05-17

    Methods, manufactures, machines and compositions are described for nanotransfer and nanoreplication using deterministically grown sacrificial nanotemplates. A method includes depositing a catalyst particle on a surface of a substrate to define a deterministically located position; growing an aligned elongated nanostructure on the substrate, an end of the aligned elongated nanostructure coupled to the substrate at the deterministically located position; coating the aligned elongated nanostructure with a conduit material; removing a portion of the conduit material to expose the catalyst particle; removing the catalyst particle; and removing the elongated nanostructure to define a nanoconduit.

  13. Unusual thermopower of inhomogeneous graphene grown by chemical vapor deposition

    SciTech Connect

    Nam, Youngwoo, E-mail: youngwoo.nam@chalmers.se [Department of Physics and Astronomy, Seoul National University, Seoul 151-747 (Korea, Republic of); Department of Microtechnology and Nanoscience, Chalmers University of Technology, SE-412 96 Gothenburg (Sweden); Sun, Jie; Lindvall, Niclas; Yurgens, August [Department of Microtechnology and Nanoscience, Chalmers University of Technology, SE-412 96 Gothenburg (Sweden); Jae Yang, Seung; Rae Park, Chong [Department of Materials Science and Engineering, Seoul National University, Seoul 151-747 (Korea, Republic of); Woo Park, Yung [Department of Physics and Astronomy, Seoul National University, Seoul 151-747 (Korea, Republic of)

    2014-01-13

    We report on thermopower (TEP) and resistance measurements of inhomogeneous graphene grown by chemical vapor deposition (CVD). Unlike the conventional resistance of pristine graphene, the gate-dependent TEP shows a large electron-hole asymmetry. This can be accounted for by inhomogeneity of the CVD-graphene where individual graphene regions contribute with different TEPs. At the high magnetic field and low temperature, the TEP has large fluctuations near the Dirac point associated with the disorder in the CVD-graphene. TEP measurements reveal additional characteristics of CVD-graphene, which are difficult to obtain from the measurement of resistance alone.

  14. Trap states in enhancement-mode double heterostructures AlGaN/GaN high electron mobility transistors with different GaN channel layer thicknesses

    SciTech Connect

    He, Yunlong; Wang, Chong Li, Xiangdong; Zhao, Shenglei; Mi, Minhan; Pei, Jiuqing; Zhang, Jincheng; Hao, Yue; Li, Peixian; Ma, Xiaohua

    2015-08-10

    This is the report on trap states in enhancement-mode AlGaN/GaN/AlGaN double heterostructures high electron mobility transistors by fluorine plasma treatment with different GaN channel layer thicknesses. Compared with the thick GaN channel layer sample, the thin one has smaller 2DEG concentration, lower electron mobility, lower saturation current, and lower peak transconductance, but it has a higher threshold voltage of 1.2 V. Deep level transient spectroscopy measurements are used to obtain the accurate capture cross section of trap states. By frequency dependent capacitance and conductance measurements, the trap state density of (1.98–2.56) × 10{sup 12 }cm{sup −2} eV{sup −1} is located at E{sub T} in a range of (0.37–0.44) eV in the thin sample, while the trap state density of (2.3–2.92) × 10{sup 12 }cm{sup −2} eV{sup −1} is located at E{sub T} in a range of (0.33–0.38) eV in the thick one. It indicates that the trap states in the thin sample are deeper than those in the thick one.

  15. Thin film photovoltaic device

    DOEpatents

    Catalano, Anthony W.; Bhushan, Manjul

    1982-01-01

    A thin film photovoltaic solar cell which utilizes a zinc phosphide semiconductor is of the homojunction type comprising an n-type conductivity region forming an electrical junction with a p-type region, both regions consisting essentially of the same semiconductor material. The n-type region is formed by treating zinc phosphide with an extrinsic dopant such as magnesium. The semiconductor is formed on a multilayer substrate which acts as an opaque contact. Various transparent contacts may be used, including a thin metal film of the same chemical composition as the n-type dopant or conductive oxides or metal grids.

  16. Thin film photovoltaic device

    DOEpatents

    Catalano, A.W.; Bhushan, M.

    1982-08-03

    A thin film photovoltaic solar cell which utilizes a zinc phosphide semiconductor is of the homojunction type comprising an n-type conductivity region forming an electrical junction with a p-type region, both regions consisting essentially of the same semiconductor material. The n-type region is formed by treating zinc phosphide with an extrinsic dopant such as magnesium. The semiconductor is formed on a multilayer substrate which acts as an opaque contact. Various transparent contacts may be used, including a thin metal film of the same chemical composition as the n-type dopant or conductive oxides or metal grids. 5 figs.

  17. Structure-property correlation in epitaxial (2 0 0) rutile films on sapphire substrates

    SciTech Connect

    Bayati, M.R.; Joshi, Sh.; Molaei, R.; Narayan, R.J.; Narayan, J.

    2012-03-15

    We have investigated the influence of the deposition variables on photocatalytic properties of epitaxial rutile films. Despite a large lattice misfit of rutile with sapphire substrate, (2 0 0) epitaxial layers were grown on (0 0 0 1)sapphire by domain matching epitaxy paradigm. Using {phi}-scan XRD and cross section TEM, the epitaxial relationship was determined to be rutile(1 0 0)||sapphire(0 0 0 1), rutile(0 0 1)||sapphire(1 0 -1 0), and rutile(0 1 0)||sapphire(1 -2 1 0). Based on the XRD patterns, increasing the repetition rate introduced tensile stress along the film normal direction, which may arise as a result of trapped defects. Formation of such defects was studied by UV-VIS, PL, and XPS techniques. AFM studies showed that the film roughness increases with the repetition rate. Finally, photocatalytic performance of the layers was investigated through measuring decomposition rate of 4-chlorophenol on the films surface. The films grown at higher frequencies revealed higher photocatalytic efficiency. This behavior was mainly related to formation of point defects which enhance the charge separation. - Graphical abstract: In this report, epitaxial rutile TiO{sub 2} thin films were deposited by PLD process under various deposition rates (frequencies) and their physical and chemical properties, especially photocatalytic performance, were investigated. It was found that photocatalytic efficiency improves when frequency increases. This behavior was mainly related to formation of point defects which enhance the charge separation. Highlights: Black-Right-Pointing-Pointer Rutile epitaxial thin films were deposited via PLD process under different frequencies. Black-Right-Pointing-Pointer Defect characteristic was studied. Black-Right-Pointing-Pointer Photocatalytic performance of the layers was investigated.

  18. NMR characterization of thin films

    DOEpatents

    Gerald II, Rex E.; Klingler, Robert J.; Rathke, Jerome W.; Diaz, Rocio; Vukovic, Lela

    2010-06-15

    A method, apparatus, and system for characterizing thin film materials. The method, apparatus, and system includes a container for receiving a starting material, applying a gravitational force, a magnetic force, and an electric force or combinations thereof to at least the starting material, forming a thin film material, sensing an NMR signal from the thin film material and analyzing the NMR signal to characterize the thin film of material.

  19. NMR characterization of thin films

    DOEpatents

    Gerald, II, Rex E.; Klingler, Robert J.; Rathke, Jerome W.; Diaz, Rocio; Vukovic, Lela

    2008-11-25

    A method, apparatus, and system for characterizing thin film materials. The method, apparatus, and system includes a container for receiving a starting material, applying a gravitational force, a magnetic force, and an electric force or combinations thereof to at least the starting material, forming a thin film material, sensing an NMR signal from the thin film material and analyzing the NMR signal to characterize the thin film of material.

  20. Methods for producing complex films, and films produced thereby

    SciTech Connect

    Duty, Chad E.; Bennett, Charlee J. C.; Moon, Ji -Won; Phelps, Tommy J.; Blue, Craig A.; Dai, Quanqin; Hu, Michael Z.; Ivanov, Ilia N.; Jellison, Jr., Gerald E.; Love, Lonnie J.; Ott, Ronald D.; Parish, Chad M.; Walker, Steven

    2015-11-24

    A method for producing a film, the method comprising melting a layer of precursor particles on a substrate until at least a portion of the melted particles are planarized and merged to produce the film. The invention is also directed to a method for producing a photovoltaic film, the method comprising depositing particles having a photovoltaic or other property onto a substrate, and affixing the particles to the substrate, wherein the particles may or may not be subsequently melted. Also described herein are films produced by these methods, methods for producing a patterned film on a substrate, and methods for producing a multilayer structure.

  1. Status review of the science and technology of Ultrananoscrystalline Diamond (UNCD (sup {trademark}) films and application to multifunctional devices.

    SciTech Connect

    Auciello, O.; Sumant, A. V.

    2010-07-01

    This review focuses on a status report on the science and technology of ultrananocrystalline diamond (UNCD) films developed and patented at Argonne National Laboratory. The UNCD material has been developed in thin film form and exhibit multifunctionalities applicable to a broad range of macro to nanoscale multifunctional devices. UNCD thin films are grown by microwave plasma chemical vapor deposition (MPCVD) or hot filament chemical vapor deposition (HFCVD) using new patented Ar-rich/CH4 or H2/CH4 plasma chemistries. UNCD films exhibit a unique nanostructure with 2-5 nm grain size (thus the trade name UNCD) and grain boundaries of 0.4-0.6 nm for plain films, and grain sizes of 7-10 nm and grain boundaries of 2-4 nm when grown with nitrogen introduced in the Ar-rich/CH4 chemistry, to produce UNCD films incorporated with nitrogen, which exhibit electrical conductivity up to semi-metallic level. This review provides a status report on the synthesis of UNCD films via MPCVD and integration with dissimilar materials like oxides for piezoactuated MEMS/NEMS, metal films for contacts, and biological matter for a new generation of biomedical devices and biosensors. A broad range of applications from macro to nanoscale multifunctional devices is reviewed, such as coatings for mechanical pumps seals, field-emission cold cathodes, RF MEMS/NEMS resonators and switches for wireless communications and radar systems, NEMS devices, biomedical devices, biosensors, and UNCD as a platform for developmental biology, involving biological cells growth on the surface. Comparisons with nanocrystalline diamond films and technology are made when appropriate.

  2. Chemical and microstructural characterization of thermally grown alumina scales

    SciTech Connect

    Natesan, K.; Richier, C.; Veal, B.W.

    1995-09-01

    An experimental program has been initiated to evaluate the chemical, microstructural, and mechanical integrity of thermally grown oxide scales to establish requirements for improved corrosion performance in terms of composition, structure, and properties. Iron aluminides of several compositions were selected for the study. Oxidation studies were conducted in air and oxygen environments at 1000{degrees}C. The results showed that the scaling kinetics followed a parabolic rate law but that the rates in early stages of oxidation were significantly greater than in later stages; the difference could be attributed to the presence of fast-growing transient iron oxides in the layer during the early stages. Further, scale failure occurred via gross spallation, scale cracking, and nodule formation and was influenced by alloy composition. Auger electron spectroscopy of Ar-exposed specimens of ternary Fe-Cr-Al alloy showed sulfur on the gas/scale side of the interface; the sulfur decreased as the exposure time increased. Raman spectroscopy and ruby fluorescence were used to examine the scale development as a function of oxidation temperature. Ruby-line shift is used to examine phase transformations in alumina and to calculate compressive strains in thermally grown scales.

  3. Thin film photovoltaic cell

    DOEpatents

    Meakin, John D.; Bragagnolo, Julio

    1982-01-01

    A thin film photovoltaic cell having a transparent electrical contact and an opaque electrical contact with a pair of semiconductors therebetween includes utilizing one of the electrical contacts as a substrate and wherein the inner surface thereof is modified by microroughening while being macro-planar.

  4. Diamond films: Historical perspective

    SciTech Connect

    Messier, R.

    1993-01-01

    This section is a compilation of notes and published international articles about the development of methods of depositing diamond films. Vapor deposition articles are included from American, Russian, and Japanese publications. The international competition to develop new deposition methodologies is stressed. The current status of chemical vapor deposition of diamond is assessed.

  5. Dynamics of helium films

    SciTech Connect

    Clements, B.E.; Epstein, J.L.; Krotscheck, E.; Tymczak, C.J.; Saarela, M.

    1992-11-01

    The authors present quantitative calculations for the static structure and the dynamics of quantum liquid films on a translationally invariant substrate. The excitation spectrum is calculated by solving the equations of motion for time-dependent one- and two-body densities. They find significant corrections to the Feynman spectrum for the phonon-like collective excitations. 8 refs., 2 figs.

  6. Light-trapped, interconnected, silicon-film {trademark} modules. Annual subcontract report, 18 November 1994--18 November 1995

    SciTech Connect

    Hall, R.B.; Rand, J.A.; Cotter, J.E.; Ford, D.H.

    1996-03-01

    This report describes the first year of work performed by AstroPower, Inc., of Newark, Delaware, under the Thin-Film PV Partnership Program. The work led to the development of a new barrier-coated substrate that has enabled high-quality thin-layer polycrystalline silicon to be grown on a low-cost substrate. High diffusion lengths were measured after external phosphorous gettering. This led to a confirmed efficiency for a 0.57cm{sup 2}, thin-layer solar cell grown on a low-cost substrate.

  7. Physical properties of epitaxial ZrN/MgO(001) layers grown by reactive magnetron sputtering

    SciTech Connect

    Mei, A. B.; Zhang, C.; Sardela, M.; Eckstein, J. N.; Rockett, A.; Howe, B. M.; Hultman, L.; Petrov, I.; Greene, J. E.

    2013-11-15

    Single-crystal ZrN films, 830 nm thick, are grown on MgO(001) at 450 °C by magnetically unbalanced reactive magnetron sputtering. The combination of high-resolution x-ray diffraction reciprocal lattice maps, high-resolution cross-sectional transmission electron microscopy, and selected-area electron diffraction shows that ZrN grows epitaxially on MgO(001) with a cube-on-cube orientational relationship, (001){sub ZrN}‖(001){sub MgO} and [100]{sub ZrN}‖[100]{sub MgO}. The layers are essentially fully relaxed with a lattice parameter of 0.4575 nm, in good agreement with reported results for bulk ZrN crystals. X-ray reflectivity results reveal that the films are completely dense with smooth surfaces (roughness = 1.3 nm, consistent with atomic-force microscopy analyses). Based on temperature-dependent electronic transport measurements, epitaxial ZrN/MgO(001) layers have a room-temperature resistivity ρ{sub 300K} of 12.0 μΩ-cm, a temperature coefficient of resistivity between 100 and 300 K of 5.6 × 10{sup −8}Ω-cm K{sup −1}, a residual resistivity ρ{sub o} below 30 K of 0.78 μΩ-cm (corresponding to a residual resistivity ratio ρ{sub 300Κ}/ρ{sub 15K} = 15), and the layers exhibit a superconducting transition temperature of 10.4 K. The relatively high residual resistivity ratio, combined with long in-plane and out-of-plane x-ray coherence lengths, ξ{sub ‖} = 18 nm and ξ{sub ⊥} = 161 nm, indicates high crystalline quality with low mosaicity. The reflectance of ZrN(001), as determined by variable-angle spectroscopic ellipsometry, decreases slowly from 95% at 1 eV to 90% at 2 eV with a reflectance edge at 3.04 eV. Interband transitions dominate the dielectric response above 2 eV. The ZrN(001) nanoindentation hardness and modulus are 22.7 ± 1.7 and 450 ± 25 GPa.

  8. Orientation filtering for crystalline films

    DOEpatents

    Smith, H.I.; Atwater, H.A.; Thompson, C.V.; Geis, M.W.

    1986-12-30

    A substrate is coated with a film to be recrystallized. A pattern of crystallization barriers is created in the film, for example, by etching voids in the film. An encapsulation layer is generally applied to protect the film, fill the voids and otherwise enhance a recrystallization process. Recrystallization is carried out such that certain orientations pass preferentially through the barrier, generally as a result of growth-velocity anisotropy. The result is a film of a specific predetermined crystallographic orientation, a range of orientations or a set of discrete orientations. 7 figs.

  9. Thin-film optical initiator

    DOEpatents

    Erickson, Kenneth L.

    2001-01-01

    A thin-film optical initiator having an inert, transparent substrate, a reactive thin film, which can be either an explosive or a pyrotechnic, and a reflective thin film. The resultant thin-film optical initiator system also comprises a fiber-optic cable connected to a low-energy laser source, an output charge, and an initiator housing. The reactive thin film, which may contain very thin embedded layers or be a co-deposit of a light-absorbing material such as carbon, absorbs the incident laser light, is volumetrically heated, and explodes against the output charge, imparting about 5 to 20 times more energy than in the incident laser pulse.

  10. Process to form mesostructured films

    DOEpatents

    Brinker, C. Jeffrey; Anderson, Mark T.; Ganguli, Rahul; Lu, Yunfeng

    1999-01-01

    This invention comprises a method to form a family of supported films film with pore size in the approximate range 0.8-20 nm exhibiting highly ordered microstructures and porosity derived from an ordered micellar or liquid-crystalline organic-inorganic precursor structure that forms during film deposition. Optically transparent, 100-500-nm thick films exhibiting a unique range of microstructures and uni-modal pore sizes are formed in seconds in a continuous coating operation. Applications of these films include sensors, membranes, low dielectric constant interlayers, anti-reflective coatings, and optical hosts.

  11. Orientation filtering for crystalline films

    DOEpatents

    Smith, Henry I.; Atwater, Harry A.; Thompson, Carl V.; Geis, Michael W.

    1986-12-30

    A substrate is coated with a film to be recrystallized. A pattern of crystallization barriers is created in the film, for example, by etching voids in the film. An encapsulation layer is generally applied to protect the film, fill the voids and otherwise enhance a recrystallization process. Recrystallization is carried out such that certain orientations pass preferentially through the barrier, generally as a result of growth-velocity anisotropy. The result is a film of a specific predetermined crystallographic orientation, a range of orientations or a set of discrete orientations.

  12. Strain-relaxation and critical thickness of epitaxial La1.85Sr0.15CuO4 films

    DOE PAGES [OSTI]

    Meyer, Tricia L; Jiang, Lu; Park, Sungkyun; Egami, Takeshi; Lee, Ho Nyung

    2015-12-08

    We report the thickness-dependent strain-relaxation behavior and the associated impacts upon the superconductivity in epitaxial La1.85Sr0.15CuO4 films grown on different substrates, which provide a range of strain. We have found that the critical thickness for the onset of superconductivity in La1.85Sr0.15CuO4 films is associated with the finite thickness effect and epitaxial strain. In particular, thin films with tensile strain greater than ~0.25% revealed no superconductivity. We attribute this phenomenon to the inherent formation of oxygen vacancies that can be minimized via strain relaxation.

  13. Direct growth of nanocrystalline hexagonal boron nitride films on dielectric substrates

    SciTech Connect

    Tay, Roland Yingjie; Tsang, Siu Hon; Loeblein, Manuela; Chow, Wai Leong; Loh, Guan Chee; Toh, Joo Wah; Ang, Soon Loong; Teo, Edwin Hang Tong

    2015-03-09

    Atomically thin hexagonal-boron nitride (h-BN) films are primarily synthesized through chemical vapor deposition (CVD) on various catalytic transition metal substrates. In this work, a single-step metal-catalyst-free approach to obtain few- to multi-layer nanocrystalline h-BN (NCBN) directly on amorphous SiO{sub 2}/Si and quartz substrates is demonstrated. The as-grown thin films are continuous and smooth with no observable pinholes or wrinkles across the entire deposited substrate as inspected using optical and atomic force microscopy. The starting layers of NCBN orient itself parallel to the substrate, initiating the growth of the textured thin film. Formation of NCBN is due to the random and uncontrolled nucleation of h-BN on the dielectric substrate surface with no epitaxial relation, unlike on metal surfaces. The crystallite size is ?25?nm as determined by Raman spectroscopy. Transmission electron microscopy shows that the NCBN formed sheets of multi-stacked layers with controllable thickness from ?2 to 25?nm. The absence of transfer process in this technique avoids any additional degradation, such as wrinkles, tears or folding and residues on the film which are detrimental to device performance. This work provides a wider perspective of CVD-grown h-BN and presents a viable route towards large-scale manufacturing of h-BN substrates and for coating applications.

  14. Growth of polycrystalline Cu(In,Ga)Se{sub 2} thin films using a radio frequency-cracked Se-radical beam source and application for photovoltaic devices

    SciTech Connect

    Ishizuka, Shogo; Shibata, Hajime; Yamada, Akimasa; Fons, Paul; Sakurai, Keiichiro; Matsubara, Koji; Niki, Shigeru

    2007-07-23

    Cu(In,Ga)Se{sub 2} (CIGS) thin films were grown using a rf-cracked Se-radical beam source. A unique combination of film properties, a highly dense and smooth surface with large grain size, is shown. These features seem to have no significant influence on the photovoltaic performance. Defect control in bulk CIGS leading to corresponding variations in the electrical and photoluminescence properties was found to be possible by regulating the Se-radical source parameters. A competitive energy conversion efficiency of 17.5%, comparable to that of a Se-evaporative source grown CIGS device, has been demonstrated from a solar cell fabricated using a Se-radical source grown CIGS absorber.

  15. Method for making carbon films

    DOEpatents

    Tan, Ming X.

    1999-01-01

    A method for treating an organic polymer material, preferably a vinylidene chloride/vinyl chloride copolymer (Saran) to produce a flat sheet of carbon film material having a high surface area (.apprxeq.1000 m.sup.2 /g) suitable as an electrode material for super capacitor applications. The method comprises heating a vinylidene chloride/vinyl chloride copolymer film disposed between two spaced apart graphite or ceramic plates to a first temperature of about 160.degree. C. for about 14 hours to form a stabilized vinylidene chloride/vinyl chloride polymer film, thereafter heating the stabilized film to a second temperature of about 750.degree. C. in an inert atmosphere for about one hour to form a carbon film; and finally activating the carbon film to increase the surface area by heating the carbon film in an oxidizing atmosphere to a temperature of at least 750-850.degree. C. for between 1-6 hours.

  16. Method for making carbon films

    DOEpatents

    Tan, M.X.

    1999-07-29

    A method for treating an organic polymer material, preferably a vinylidene chloride/vinyl chloride copolymer (Saran) to produce a flat sheet of carbon film material having a high surface area ([approx equal]1000 m[sup 2] /g) suitable as an electrode material for super capacitor applications. The method comprises heating a vinylidene chloride/vinyl chloride copolymer film disposed between two spaced apart graphite or ceramic plates to a first temperature of about 160 C for about 14 hours to form a stabilized vinylidene chloride/vinyl chloride polymer film, thereafter heating the stabilized film to a second temperature of about 750 C in an inert atmosphere for about one hour to form a carbon film; and finally activating the carbon film to increase the surface area by heating the carbon film in an oxidizing atmosphere to a temperature of at least 750--850 C for between 1--6 hours. 2 figs.

  17. Thin film superconductor magnetic bearings

    DOEpatents

    Weinberger, Bernard R.

    1995-12-26

    A superconductor magnetic bearing includes a shaft (10) that is subject to a load (L) and rotatable around an axis of rotation, a magnet (12) mounted to the shaft, and a stator (14) in proximity to the shaft. The stator (14) has a superconductor thin film assembly (16) positioned to interact with the magnet (12) to produce a levitation force on the shaft (10) that supports the load (L). The thin film assembly (16) includes at least two superconductor thin films (18) and at least one substrate (20). Each thin film (18) is positioned on a substrate (20) and all the thin films are positioned such that an applied magnetic field from the magnet (12) passes through all the thin films. A similar bearing in which the thin film assembly (16) is mounted on the shaft (10) and the magnet (12) is part of the stator (14) also can be constructed.

  18. Room-temperature ferroelectricity of SrTiO{sub 3} films modulated by cation concentration

    SciTech Connect

    Yang, Fang; Zhang, Qinghua; Yang, Zhenzhong; Gu, Junxing; Liang, Yan; Li, Wentao; Wang, Weihua; Jin, Kuijuan; Gu, Lin; Guo, Jiandong

    2015-08-24

    The room-temperature ferroelectricity of SrTiO{sub 3} is promising for oxide electronic devices controlled by multiple fields. An effective way to control the ferroelectricity is highly demanded. Here, we show that the off-centered antisite-like defects in SrTiO{sub 3} films epitaxially grown on Si (001) play the determinative role in the emergence of room-temperature ferroelectricity. The density of these defects changes with the film cation concentration sensitively, resulting in a varied coercive field of the ferroelectric behavior. Consequently, the room-temperature ferroelectricity of SrTiO{sub 3} films can be effectively modulated by tuning the temperature of metal sources during the molecular beam epitaxy growth. Such an easy and reliable modulation of the ferroelectricity enables the flexible engineering of multifunctional oxide electronic devices.

  19. Control method and system for use when growing thin-films on semiconductor-based materials

    DOEpatents

    McKee, Rodney A.; Walker, Frederick J.

    2001-01-01

    A process and system for use during the growth of a thin film upon the surface of a substrate by exposing the substrate surface to vaporized material in a high vacuum (HV) facility involves the directing of an electron beam generally toward the surface of the substrate as the substrate is exposed to vaporized material so that electrons are diffracted from the substrate surface by the beam and the monitoring of the pattern of electrons diffracted from the substrate surface as vaporized material settles upon the substrate surface. When the monitored pattern achieves a condition indicative of the desired condition of the thin film being grown upon the substrate, the exposure of the substrate to the vaporized materials is shut off or otherwise adjusted. To facilitate the adjustment of the crystallographic orientation of the film relative to the electron beam, the system includes a mechanism for altering the orientation of the surface of the substrate relative to the electron beam.

  20. Microstructure, optical property, and electronic band structure of cuprous oxide thin films

    SciTech Connect

    Park, Jun-Woo; Jang, Hyungkeun; Kim, Sung; Choi, Suk-Ho; Lee, Hosun; Kang, Joongoo; Wei, Su-Huai

    2011-11-15

    Cuprous oxide (Cu{sub 2}O) thin films were grown via radio frequency sputtering deposition at various temperatures. The dielectric functions and luminescence properties of the Cu{sub 2}O thin films were measured using spectroscopic ellipsometry and photoluminescence, respectively. High-energy peaks were observed in the photoluminescence spectra. Several critical points (CPs) were found using second derivative spectra of the dielectric functions and the standard critical point model. The electronic band structure and the dielectric functions were calculated using density functional theory, and the CP energies were estimated to compare with the experimental data. We identified the high-energy photoluminescence peaks to quasi-direct transitions which arose from the granular structures of the Cu{sub 2}O thin films.

  1. Role of thermal processes in dewetting of epitaxial Ag(111) film on Si(111)

    DOE PAGES [OSTI]

    Sanders, Charlotte E.; Zhang, Chendong D.; Kellogg, Gary L.; Shih, Chih-Kang

    2014-08-01

    Epitaxially grown silver (Ag) film on silicon (Si) is an optimal plasmonic device platform, but its technological utility has been limited by its tendency to dewet rapidly under ambient conditions (standard temperature and pressure). The mechanisms driving this dewetting have not heretofore been determined. In our study, scanning probe microscopy and low-energy electron microscopy are used to compare the morphological evolution of epitaxial Ag(111)/Si(111) under ambient conditions with that of similarly prepared films heated under ultra-high vacuum (UHV) conditions. Furthermore, dewetting is seen to be initiated with the formation of pinholes, which might function to relieve strain in the film.more » We find that in the UHV environment, dewetting is determined by thermal processes, and while under ambient conditions, thermal processes are not required. Finally, we conclude that dewetting in ambient conditions is triggered by some chemical process, most likely oxidation.« less

  2. Highly conducting SrMoO{sub 3} thin films for microwave applications

    SciTech Connect

    Radetinac, Aldin Mani, Arzhang; Ziegler, Jürgen; Alff, Lambert; Komissinskiy, Philipp; Melnyk, Sergiy; Nikfalazar, Mohammad; Zheng, Yuliang; Jakoby, Rolf

    2014-09-15

    We have measured the microwave resistance of highly conducting perovskite oxide SrMoO{sub 3} thin film coplanar waveguides. The epitaxial SrMoO{sub 3} thin films were grown by pulsed laser deposition and showed low mosaicity and smooth surfaces with a root mean square roughness below 0.3 nm. Layer-by-layer growth could be achieved for film thicknesses up to 400 nm as monitored by reflection high-energy electron diffraction and confirmed by X-ray diffraction. We obtained a constant microwave resistivity of 29 μΩ·cm between 0.1 and 20 GHz by refining the frequency dependence of the transmission coefficients. Our result shows that SrMoO{sub 3} is a viable candidate as a highly conducting electrode material for all-oxide microwave electronic devices.

  3. Impact of strain on electronic defects in (Mg,Zn)O thin films

    SciTech Connect

    Schmidt, Florian Müller, Stefan; Wenckstern, Holger von; Benndorf, Gabriele; Pickenhain, Rainer; Grundmann, Marius

    2014-09-14

    We have investigated the impact of strain on the incorporation and the properties of extended and point defects in (Mg,Zn)O thin films by means of photoluminescence, X-ray diffraction, deep-level transient spectroscopy (DLTS), and deep-level optical spectroscopy. The recombination line Y₂, previously detected in ZnO thin films grown on an Al-doped ZnO buffer layer and attributed to tensile strain, was exclusively found in (Mg,Zn)O samples being under tensile strain and is absent in relaxed or compressively strained thin films. Furthermore a structural defect E3´ can be detected via DLTS measurements and is only incorporated in tensile strained samples. Finally it is shown that the omnipresent deep-level E3 in ZnO can only be optically recharged in relaxed ZnO samples.

  4. Resistance switching in epitaxial SrCoO{sub x} thin films

    SciTech Connect

    Tambunan, Octolia T.; Parwanta, Kadek J.; Acharya, Susant K.; Lee, Bo Wha; Jung, Chang Uk; Kim, Yeon Soo; Park, Bae Ho; Jeong, Huiseong; Park, Ji-Yong; Cho, Myung Rae; Park, Yun Daniel; Choi, Woo Seok; Kim, Dong-Wook; Jin, Hyunwoo; Lee, Suyoun; Song, Seul Ji; Kang, Sung-Jin; Kim, Miyoung; Hwang, Cheol Seong

    2014-08-11

    We observed bipolar switching behavior from an epitaxial strontium cobaltite film grown on a SrTiO{sub 3} (001) substrate. The crystal structure of strontium cobaltite has been known to undergo topotactic phase transformation between two distinct phases: insulating brownmillerite (SrCoO{sub 2.5}) and conducting perovskite (SrCoO{sub 3−δ}) depending on the oxygen content. The current–voltage characteristics of the strontium cobaltite film showed that it could have a reversible insulator-to-metal transition triggered by electrical bias voltage. We propose that the resistance switching in the SrCoO{sub x} thin film could be related to the topotactic phase transformation and the peculiar structure of SrCoO{sub 2.5}.

  5. Magnetic x-ray linear dichroism of ultrathin Fe-Ni alloy films

    SciTech Connect

    Schumann, F.O.; Willis, R.F.; Goodman, K.W.

    1997-04-01

    The authors have studied the magnetic structure of ultrathin Fe-Ni alloy films as a function of Fe concentration by measuring the linear dichroism of the 3p-core levels in angle-resolved photoemission spectroscopy. The alloy films, grown by molecular-beam epitaxy on Cu(001) surfaces, were fcc and approximately four monolayers thick. The intensity of the Fe dichroism varied with Fe concentration, with larger dichroisms at lower Fe concentrations. The implication of these results to an ultrathin film analogue of the bulk Invar effect in Fe-Ni alloys will be discussed. These measurements were performed at the Spectromicroscopy Facility (Beamline 7.0.1) of the Advanced Light Source.

  6. Method for continuous control of composition and doping of pulsed laser deposited films by pressure control

    DOEpatents

    Lowndes, Douglas H.; McCamy, James W.

    1996-01-01

    A method for growing a deposit upon a substrate of semiconductor material involves the utilization of pulsed laser deposition techniques within a low-pressure gas environment. The substrate and a target of a first material are positioned within a deposition chamber and a low-pressure gas atmosphere is developed within the chamber. The substrate is then heated, and the target is irradiated, so that atoms of the target material are ablated from the remainder of the target, while atoms of the gas simultaneously are adsorbed on the substrate/film surface. The ablated atoms build up upon the substrate, together with the adsorbed gas atoms to form the thin-film deposit on the substrate. By controlling the pressure of the gas of the chamber atmosphere, the composition of the formed deposit can be controlled, and films of continuously variable composition or doping can be grown from a single target of fixed composition.

  7. Method for continuous control of composition and doping of pulsed laser deposited films

    DOEpatents

    Lowndes, Douglas H.; McCamy, James W.

    1995-01-01

    A method for growing a deposit upon a substrate of semiconductor material involves the utilization of pulsed laser deposition techniques within a low-pressure gas environment. The substrate and a target of a first material are positioned within a deposition chamber and a low-pressure gas atmosphere is developed within the chamber. The substrate is then heated, and the target is irradiated, so that atoms of the target material are ablated from the remainder of the target, while atoms of the gas simultaneously are adsorbed on the substrate/film surface. The ablated atoms build up upon the substrate, together with the adsorbed gas atoms to form the thin-film deposit on the substrate. By controlling the pressure of the gas of the chamber atmosphere, the composition of the formed deposit can be controlled, and films of continuously variable composition or doping can be grown from a single target of fixed composition.

  8. Role of thermal processes in dewetting of epitaxial Ag(111) film on Si(111)

    SciTech Connect

    Sanders, Charlotte E.; Zhang, Chendong D.; Kellogg, Gary L.; Shih, Chih-Kang

    2014-08-01

    Epitaxially grown silver (Ag) film on silicon (Si) is an optimal plasmonic device platform, but its technological utility has been limited by its tendency to dewet rapidly under ambient conditions (standard temperature and pressure). The mechanisms driving this dewetting have not heretofore been determined. In our study, scanning probe microscopy and low-energy electron microscopy are used to compare the morphological evolution of epitaxial Ag(111)/Si(111) under ambient conditions with that of similarly prepared films heated under ultra-high vacuum (UHV) conditions. Furthermore, dewetting is seen to be initiated with the formation of pinholes, which might function to relieve strain in the film. We find that in the UHV environment, dewetting is determined by thermal processes, and while under ambient conditions, thermal processes are not required. Finally, we conclude that dewetting in ambient conditions is triggered by some chemical process, most likely oxidation.

  9. Process for growing a film epitaxially upon an oxide surface and structures formed with the process

    DOEpatents

    McKee, Rodney Allen; Walker, Frederick Joseph

    1998-01-01

    A process and structure wherein a film comprised of a perovskite or a spinel is built epitaxially upon a surface, such as an alkaline earth oxide surface, involves the epitaxial build up of alternating constituent metal oxide planes of the perovskite or spinel. The first layer of metal oxide built upon the surface includes a metal element which provides a small cation in the crystalline structure of the perovskite or spinel, and the second layer of metal oxide built upon the surface includes a metal element which provides a large cation in the crystalline structure of the perovskite or spinel. The layering sequence involved in the film build up reduces problems which would otherwise result from the interfacial electrostatics at the first atomic layers, and these oxides can be stabilized as commensurate thin films at a unit cell thickness or grown with high crystal quality to thicknesses of 0.5-0.7 .mu.m for optical device applications.

  10. Process for growing a film epitaxially upon an oxide surface and structures formed with the process

    DOEpatents

    McKee, Rodney A.; Walker, Frederick J.

    1995-01-01

    A process and structure wherein a film comprised of a perovskite or a spinel is built epitaxially upon a surface, such as an alkaline earth oxide surface, involves the epitaxial build up of alternating constituent metal oxide planes of the perovskite or spinel. The first layer of metal oxide built upon the surface includes a metal element which provides a small cation in the crystalline structure of the perovskite or spinel, and the second layer of metal oxide built upon the surface includes a metal element which provides a large cation in the crystalline structure of the perovskite or spinel. The layering sequence involved in the film build up reduces problems which would otherwise result from the interfacial electrostatics at the first atomic layers, and these oxides can be stabilized as commensurate thin films at a unit cell thickness or grown with high crystal quality to thicknesses of 0.5-0.7 .mu.m for optical device applications.

  11. The structural, electrical, and optical properties of hydrogenated chromium-doped CdO films

    SciTech Connect

    Dakhel, A.A.; Hamad, H.

    2013-12-15

    Cadmium oxide thin films doped with different amounts of chromium and annealed in hydrogen atmosphere have been grown on glass substrates by means of physical vapour deposition (PVD) method. The structural, electrical, and optical properties of the prepared Cr-doped CdO (CdO:Cr–H) films were systematically studied. The structural investigations show that the incorporated Cr ions mainly occupied locations in interstitial positions of CdO lattice. The bandgap engineer by Cr incorporation and hydrogenation were studied. The variations of the electrical parameters of CdO:Cr–H films with Cr incorporation and hydrogenation were investigated. It was established that among the investigated samples, the largest mobility and conductivity were measured with 1.5%:Cr–H film. Therefore, hydrogenated CdO:Cr films can be effectively used in different applications of near infrared-transparent-conducting-oxide (NIR-TCO). - Graphical abstract: Optoelectronic properties of synthesised chromium-doped CdO thin films. It was established that the largest mobility (53.4 cm{sup 2}/V.s) and conductivity (2136.8 S/cm) were measured in 1.5%:Cr–H doped CdO film. Therefore, such films can be effectively used in near infrared-transparent-conducting-oxide (NIR-TCO). - Highlights: • The properties of CdO films annealed in H{sub 2} gas were systematically studied. • Cr{sup 3+} ions most likely occupied interstitial locations in CdO lattice and as donors. • Improvement of conductivity parameters with Cr doping and H annealing. • Bandgap narrowing observed with Cd-doping.

  12. Epitaxial Cu{sub 2}ZnSnS{sub 4} thin film on Si (111) 4° substrate

    SciTech Connect

    Song, Ning; Liu, Fangyang; Huang, Yidan; Hao, Xiaojing E-mail: xj.hao@unsw.edu.au; Green, Martin A.; Young, Matthew; Erslev, Pete; Harvey, Steven P.; Teeter, Glenn E-mail: xj.hao@unsw.edu.au; Wilson, Samual

    2015-06-22

    To explore the possibility of Cu{sub 2}ZnSnS{sub 4} (CZTS)/Si based tandem solar cells, the heteroepitaxy of tetragonal Cu{sub 2}ZnSnS{sub 4} thin films on single crystalline cubic Si (111) wafers with 4° miscut is obtained by molecular beam epitaxy. The X-ray θ-2θ scan and selected area diffraction patterns of the CZTS thin films and Si substrates, and the high resolution transmission electron microscopy image of the CZTS/Si interface region demonstrate that the CZTS thin films are epitaxially grown on the Si substrates. A CZTS/Si P-N junction is formed and shows photovoltaic responses, indicating the promising application of epitaxial CZTS thin films on Si.

  13. Heteroepitaxial growth of highly conductive metal oxide RuO{sub 2} thin films by pulsed laser deposition

    SciTech Connect

    Jia, Q.X.; Wu, X.D.; Foltyn, S.R.; Findikoglu, A.T.; Tiwari, P.; Zheng, J.P.; Jow, T.R.

    1995-09-18

    Highly conductive ruthenium oxide (RuO{sub 2}) has been epitaxially grown on LaAlO{sub 3} substrates by pulsed laser deposition. The RuO{sub 2} film is ({ital h}00) oriented normal to the substrate surface. The heteroepitaxial growth of RuO{sub 2} on LaAlO{sub 3} is demonstrated by the strong in-plane orientation of thin films with respect to the major axes of the substrate. High crystallinity of RuO{sub 2} thin films is also determined from Rutherford backscattering channeling measurements. Electrical measurements on the RuO{sub 2} thin films demonstrate a quite low room-temperature resistivity of 35{plus_minus}2 {mu}{Omega} cm at deposition temperatures of above 500 {degree}C. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.

  14. Preparation and characterization of Chitosan/Konjac glucomannan/CdS nanocomposite film with low infrared emissivity

    SciTech Connect

    Zhang, Feng-Ying; Zhou, Yu-Ming; Sun, Yan-qing; Chen, Jing; Ye, Xiao-yun; Huang, Jing-yi

    2010-07-15

    Novel organic-inorganic nanocomposite films were prepared with Chitosan (CS), Konjac glucomannan (KGM) and CdS by one-step synthesis. As-prepared films were characterized by IR spectra, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and infrared emissometer (IR). The results indicated that grown CdS dendrites were formed with reaction time of 12 h for Cd{sup 2+} and CS/KGM, and were well dispersed in CS/KGM with an average diameter of 40 nm. The CS/KGM/CdS nanocomposite films had significantly low infrared emissivity. When the mole ratio of CdS to summation of CS and KGM construction units was 1.0 with CdS size of 10-20 nm, the film got the lowest infrared emissivity value of 0.011, which could be attributed to the strong synergism effect existing between CS/KGM and CdS dendrites.

  15. High quality ZnO:Al transparent conducting oxide films synthesized by pulsed filtered cathodic arc deposition

    SciTech Connect

    Anders, Andre; Lim, Sunnie H.N.; Yu, Kin Man; Andersson, Joakim; Rosen, Johanna; McFarland, Mike; Brown, Jeff

    2009-04-24

    Aluminum-doped zinc oxide, ZnO:Al or AZO, is a well-known n-type transparent conducting oxide with great potential in a number of applications currently dominated by indium tin oxide (ITO). In this study, the optical and electrical properties of AZO thin films deposited on glass and silicon by pulsed filtered cathodic arc deposition are systematically studied. In contrast to magnetron sputtering, this technique does not produce energetic negative ions, and therefore ion damage can be minimized. The quality of the AZO films strongly depends on the growth temperature while only marginal improvements are obtained with post-deposition annealing. The best films, grown at a temperature of about 200?C, have resistivities in the low to mid 10-4 Omega cm range with a transmittance better than 85percent in the visible part of the spectrum. It is remarkable that relatively good films of small thickness (60 nm) can be fabricated using this method.

  16. Photocatalytic and magnetic behaviors of BiFeO{sub 3} thin films deposited on different substrates

    SciTech Connect

    Xu, Hao-Min; Wang, Huan-Chun; Shen, Yang; Lin, Yuan-Hua Nan, Ce-Wen

    2014-11-07

    Single phase polycrystalline BiFeO{sub 3} thin films were grown on three different substrates via chemical solution deposition. Our results indicate that the band gap of as-prepared BiFeO{sub 3} films can be tuned (2.02–2.67 eV) by the grain size effects caused by the substrates. These BiFeO{sub 3} films show good photocatalytic properties by the degradation of Congo red solution under visible-light irradiation (λ{sub  }> 400 nm). Additionally, weak ferromagnetic behaviors can be observed at room temperature in all the films, which should be correlated to the destruction of the incommensurate cycloid spin structure of BiFeO{sub 3} phase and the coexistence of Fe{sup 3+} and Fe{sup 2+} as confirmed by X-ray photoelectron spectroscopy.

  17. Native defects in MBE-grown CdTe

    SciTech Connect

    Olender, Karolina; Wosinski, Tadeusz; Makosa, Andrzej; Tkaczyk, Zbigniew; Kolkovsky, Valery; Karczewski, Grzegorz

    2013-12-04

    Deep-level traps in both n- and p-type CdTe layers, grown by molecular-beam epitaxy on GaAs substrates, have been investigated by means of deep-level transient spectroscopy (DLTS). Four of the traps revealed in the DLTS spectra, which displayed exponential kinetics for capture of charge carriers into the trap states, have been assigned to native point defects: Cd interstitial, Cd vacancy, Te antisite defect and a complex formed of the Te antisite and Cd vacancy. Three further traps, displaying logarithmic capture kinetics, have been ascribed to electron states of treading dislocations generated at the mismatched interface with the substrate and propagated through the CdTe layer.

  18. Carbon nanotubes grown on bulk materials and methods for fabrication

    DOEpatents

    Menchhofer, Paul A.; Montgomery, Frederick C.; Baker, Frederick S.

    2011-11-08

    Disclosed are structures formed as bulk support media having carbon nanotubes formed therewith. The bulk support media may comprise fibers or particles and the fibers or particles may be formed from such materials as quartz, carbon, or activated carbon. Metal catalyst species are formed adjacent the surfaces of the bulk support material, and carbon nanotubes are grown adjacent the surfaces of the metal catalyst species. Methods employ metal salt solutions that may comprise iron salts such as iron chloride, aluminum salts such as aluminum chloride, or nickel salts such as nickel chloride. Carbon nanotubes may be separated from the carbon-based bulk support media and the metal catalyst species by using concentrated acids to oxidize the carbon-based bulk support media and the metal catalyst species.

  19. Optical spectroscopy of sputtered nanometer-thick yttrium iron garnet films

    SciTech Connect

    Jakubisova-Liskova, Eva Visnovsky, Stefan; Chang, Houchen; Wu, Mingzhong

    2015-05-07

    Nanometer (nm)-thick yttrium iron garnet (Y{sub 3}Fe{sub 5}O{sub 12}, YIG) films present interest for spintronics. This work employs spectral ellipsometry and magneto-optic Kerr effect (MOKE) spectra to characterize nm-thick YIG films grown on single-crystal Gd{sub 3}Ga{sub 5}O{sub 12} substrates by magnetron sputtering. The thickness (t) of the films ranges between 10 nm and 40 nm. Independent on t, the polar MOKE hysteresis loops saturate in the field of about 1.8 kOe, consistent with the saturation magnetization in bulk YIG (4πM{sub s} ≈ 1.75 kG). The MOKE spectrum measured at photon energies between 1.3 eV and 4.5 eV on the 38-nm-thick film agrees with that measured on single-crystal YIG bulk materials. The MOKE spectrum of the 12-nm-thick film still preserves the structure of the bulk YIG but its amplitude at lower photon energies is modified due to the fact that the radiation penetration depth exceeds 20 nm. The t dependence of the MOKE amplitude is consistent with MOKE calculations. The results indicate that the films are stoichiometric, strain free, without Fe{sup 2+}, and preserve bulk YIG properties down to t ≈ 10 nm.

  20. Effects of sputtering power on properties of copper oxides thin films deposited on glass substrates

    SciTech Connect

    Ooi, P. K.; Ng, S. S.; Abdullah, M. J.

    2015-04-24

    Copper oxides are deposited by radio frequency sputtering using copper target in the mixture of argon and oxygen gasses. The structural and optical properties of the copper oxides deposited at different sputtering powers have been investigated. All the films are single phase polycrystalline. At low RF power (100 W), the film is monoclinic structure of cupric oxide (CuO). Meanwhile, the films are cubic structure of cuprous oxide (Cu2O) at higher RF power. Field emission scanning electron microscopy images show the films have different morphologies with small grain size and consist of a lot of voids. The analysis of energy dispersive X-ray spectroscopy shows that the ratio of Cu to O is increased as the RF power increased. From the ultraviolet–visible spectroscopy, the films have a broad absorption edge in the range of 300–500 nm. The band gap of the films grown at RF power of 100 W, and 120 W and above, were 1.18 eV and 2.16 eV, respectively.