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Sample records for ga metal buffer

  1. Effects of buffered HF cleaning on metal-oxide-semiconductor interface properties of Al2O3/InAs/GaSb structures

    NASA Astrophysics Data System (ADS)

    Nishi, Koichi; Yokoyama, Masafumi; Yokoyama, Haruki; Hoshi, Takuya; Sugiyama, Hiroki; Takenaka, Mitsuru; Takagi, Shinichi

    2015-06-01

    We studied the impact of buffered HF (BHF) cleaning on the interface properties of Al2O3/InAs/GaSb metal-oxide-semiconductor (MOS) structures fabricated by the ex-situ surface cleaning process. The Al2O3/InAs/GaSb MOS structures fabricated with BHF cleaning exhibited lower Dit values than those fabricated with sulfur passivation. In addition, the Al2O3/InAs/GaSb MOS structures fabricated with BHF cleaning were robust with respect to the MOS field-effect transistor fabrication process by using W gate metal with PMA in the 250-300 °C range.

  2. Control of metamorphic buffer structure and device performance of In(x)Ga(1-x)As epitaxial layers fabricated by metal organic chemical vapor deposition.

    PubMed

    Nguyen, H Q; Yu, H W; Luc, Q H; Tang, Y Z; Phan, V T H; Hsu, C H; Chang, E Y; Tseng, Y C

    2014-12-05

    Using a step-graded (SG) buffer structure via metal-organic chemical vapor deposition, we demonstrate a high suitability of In0.5Ga0.5As epitaxial layers on a GaAs substrate for electronic device application. Taking advantage of the technique's precise control, we were able to increase the number of SG layers to achieve a fairly low dislocation density (∼10(6) cm(-2)), while keeping each individual SG layer slightly exceeding the critical thickness (∼80 nm) for strain relaxation. This met the demanded but contradictory requirements, and even offered excellent scalability by lowering the whole buffer structure down to 2.3 μm. This scalability overwhelmingly excels the forefront studies. The effects of the SG misfit strain on the crystal quality and surface morphology of In0.5Ga0.5As epitaxial layers were carefully investigated, and were correlated to threading dislocation (TD) blocking mechanisms. From microstructural analyses, TDs can be blocked effectively through self-annihilation reactions, or hindered randomly by misfit dislocation mechanisms. Growth conditions for avoiding phase separation were also explored and identified. The buffer-improved, high-quality In0.5Ga0.5As epitaxial layers enabled a high-performance, metal-oxide-semiconductor capacitor on a GaAs substrate. The devices displayed remarkable capacitance-voltage responses with small frequency dispersion. A promising interface trap density of 3 × 10(12) eV(-1) cm(-2) in a conductance test was also obtained. These electrical performances are competitive to those using lattice-coherent but pricey InGaAs/InP systems.

  3. Control of metamorphic buffer structure and device performance of InxGa1-xAs epitaxial layers fabricated by metal organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Nguyen, H. Q.; Yu, H. W.; Luc, Q. H.; Tang, Y. Z.; Phan, V. T. H.; Hsu, C. H.; Chang, E. Y.; Tseng, Y. C.

    2014-12-01

    Using a step-graded (SG) buffer structure via metal-organic chemical vapor deposition, we demonstrate a high suitability of In0.5Ga0.5As epitaxial layers on a GaAs substrate for electronic device application. Taking advantage of the technique’s precise control, we were able to increase the number of SG layers to achieve a fairly low dislocation density (˜106 cm-2), while keeping each individual SG layer slightly exceeding the critical thickness (˜80 nm) for strain relaxation. This met the demanded but contradictory requirements, and even offered excellent scalability by lowering the whole buffer structure down to 2.3 μm. This scalability overwhelmingly excels the forefront studies. The effects of the SG misfit strain on the crystal quality and surface morphology of In0.5Ga0.5As epitaxial layers were carefully investigated, and were correlated to threading dislocation (TD) blocking mechanisms. From microstructural analyses, TDs can be blocked effectively through self-annihilation reactions, or hindered randomly by misfit dislocation mechanisms. Growth conditions for avoiding phase separation were also explored and identified. The buffer-improved, high-quality In0.5Ga0.5As epitaxial layers enabled a high-performance, metal-oxide-semiconductor capacitor on a GaAs substrate. The devices displayed remarkable capacitance-voltage responses with small frequency dispersion. A promising interface trap density of 3 × 1012 eV-1 cm-2 in a conductance test was also obtained. These electrical performances are competitive to those using lattice-coherent but pricey InGaAs/InP systems.

  4. GaN Epitaxial Layer Grown with Conductive Al(x)Ga(1-x)N Buffer Layer on SiC Substrate Using Metal Organic Chemical Vapor Deposition.

    PubMed

    So, Byeongchan; Lee, Kyungbae; Lee, Kyungjae; Heo, Cheon; Pyeon, Jaedo; Ko, Kwangse; Jang, Jongjin; Nam, Okhyun

    2016-05-01

    This study investigated GaN epitaxial layer growth with a conductive Al(x)Ga(1-x)N buffer layer on n-type 4H-SiC by high-temperature metalorganic chemical vapor deposition (HT-MOCVD). The Al composition of the Al(x)Ga(1-x)N buffer was varied from 0% to 100%. In terms of the crystal quality of the GaN layer, 79% Al was the optimal composition of the Al(x)Ga(1-x)N buffer layer in our experiment. A vertical conductive structure was fabricated to measure the current voltage (I-V) characteristics as a function of Al composition, and the I-V curves showed that the resistance increased with increasing Al concentration of the Al(x)Ga(1-x)N buffer layer.

  5. 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 that—with respect to the basic GaN/oxide/Si system without DBR—the 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.

  6. New buffer layers for GaN on sapphire by atomic layer and molecular stream epitaxy

    SciTech Connect

    Piner, E.L.; He, Y.W.; Boutros, K.S.; McIntosh, F.G.; Roberts, J.C.; Bedair, S.M.; El-Masry, N.A.

    1996-11-01

    The current approach of depositing a low temperature then annealed AlN or GaN buffer for the growth of GaN on sapphire results in a high dislocation density. These dislocations thread through the GaN layer to the surface. Reducing their density either by growing thicker films or using a strained layer superlattice is ineffective. Two new approaches for AlN/GaN buffer layer growth for GaN on sapphire have been employed: Atomic Layer Epitaxy (ALE) and molecular Stream Epitaxy (MSE). ALE is distinguished by organo-metallic/ammonia separation while MSE is distinguished by cyclic annealing of the growing film. Both ALE and MSE enhance two dimensional growth of single crystal GaN on sapphire. The structural quality of epitaxial GaN grown on these buffer layers was studied by transmission electron microscopy (TEM) and x-ray diffraction (XRD). The initial result for the ALE buffer shows an improved quality GaN film with lower defect densities. The MSE grown buffer layer closely resembles that of conventionally grown MOCVD buffer layers observed by others, with dislocations threading through the GaN epilayer. The effects of these buffer layers on the structural and optical properties of GaN grown on sapphire will be presented.

  7. Effect of buffer structures on AlGaN/GaN high electron mobility transistor reliability

    SciTech Connect

    Liu, L.; Xi, Y. Y.; Ren, F.; Pearton, S. J.; Laboutin, O.; Cao, Yu; Johnson, Wayne J.; Kravchenko, Ivan I

    2012-01-01

    AlGaN/GaN high electron mobility transistors (HEMTs) with three different types of buffer layers, including a GaN/AlGaN composite layer, or 1 or 2 lm GaN thick layers, were fabricated and their reliability compared. The HEMTs with the thick GaN buffer layer showed the lowest critical voltage (Vcri) during off-state drain step-stress, but this was increased by around 50% and 100% for devices with the composite AlGaN/GaN buffer layers or thinner GaN buffers, respectively. The Voff - state for HEMTs with thin GaN and composite buffers were 100 V, however, this degraded to 50 60V for devices with thick GaN buffers due to the difference in peak electric field near the gate edge. A similar trend was observed in the isolation breakdown voltage measurements, with the highest Viso achieved based on thin GaN or composite buffer designs (600 700 V), while a much smaller Viso of 200V was measured on HEMTs with the thick GaN buffer layers. These results demonstrate the strong influence of buffer structure and defect density on AlGaN/GaN HEMT performance and reliability.

  8. Growth of InSb on GaAs Using InAlSb Buffer Layers

    SciTech Connect

    BIEFELD, ROBERT M.; PHILLIPS, JAMIE D.

    1999-09-20

    We report the growth of InSb on GaAs using InAlSb buffers of high interest for magnetic field sensors. We have grown samples by metal-organic chemical vapor deposition consisting of {approximately} 0.55 {micro}m thick InSb layers with resistive InAlSb buffers on GaAs substrates with measured electron nobilities of {approximately}40,000 cm{sup 2}/V.s. We have investigated the In{sub 1{minus}x}Al{sub x}Sb buffers for compositions x{le}0.22 and have found that the best results are obtained near x=0.12 due to the tradeoff of buffer layer bandgap and lattice mismatch.

  9. Reduction in leakage current in AlGaN/GaN HEMT with three Al-containing step-graded AlGaN buffer layers on silicon

    NASA Astrophysics Data System (ADS)

    Yu, Xinxin; Ni, Jinyu; Li, Zhonghui; Zhou, Jianjun; Kong, Cen

    2014-05-01

    AlGaN/GaN high-electron-mobility transistor (HEMT) structures with two and three Al-containing step-graded AlGaN buffer layers (BLs) were grown on silicon (111) substrates by metal organic chemical vapor deposition. Considerable tensile stress was observed in the GaN grown with only two 0.8 µm AlGaN BLs, while a large in-plane compression in GaN grown with three 2.3 µm AlGaN BLs. The reverse gate leakage current in the HEMT with three AlGaN BLs was approximately 0.1 µA/mm, which was more than one order of magnitude smaller than that for the HEMT with two AlGaN BLs. A three-terminal off-state breakdown voltage of 265 V and a vertical gate-to-substrate breakdown voltage of 510 V were obtained in the HEMT with three AlGaN BLs. Detailed analysis was performed on the basis of the structural properties of AlGaN/GaN heterostructures.

  10. Buffer layers on biaxially textured metal substrates

    DOEpatents

    Shoup, Shara S.; Paranthamam, Mariappan; Beach, David B.; Kroeger, Donald M.; Goyal, Amit

    2001-01-01

    A method is disclosed for forming a biaxially textured buffer layer on a biaxially oriented metal substrate by using a sol-gel coating technique followed by pyrolyzing/annealing in a reducing atmosphere. This method is advantageous for providing substrates for depositing electronically active materials thereon.

  11. Leakage effects in n-GaAs MESFET with n-GaAs buffer layer

    NASA Technical Reports Server (NTRS)

    Wang, Y. C.; Bahrami, M.

    1983-01-01

    Whereas improvement of the interface between the active layer and the buffer layer has been demonstrated, the leakage effects can be important if the buffer layer resistivity is not sufficiently high and/or the buffer layer thickness is not sufficiently small. It was found that two buffer leakage currents exist from the channel under the gate to the source and from drain to the channel in addition to the buffer leakage resistance between drain and source. It is shown that for a 1 micron gate-length n-GaAs MESFET, if the buffer layer resistivity is 12 OHM-CM and the buffer layer thickness h is 2 microns, the performance of the device degrades drastically. It is suggested that h should be below 2 microns.

  12. Leakage effects in n-GaAs MESFET with n-GaAs buffer layer

    NASA Technical Reports Server (NTRS)

    Wang, Y. C.; Bahrami, M.

    1983-01-01

    Whereas improvement of the interface between the active layer and the buffer layer has been demonstrated, the leakage effects can be important if the buffer layer resistivity is not sufficiently high and/or the buffer layer thickness is not sufficiently small. It was found that two buffer leakage currents exist from the channel under the gate to the source and from drain to the channel in addition to the buffer leakage resistance between drain and source. It is shown that for a 1 micron gate-length n-GaAs MESFET, if the buffer layer resistivity is 12 OHM-CM and the buffer layer thickness h is 2 microns, the performance of the device degrades drastically. It is suggested that h should be below 2 microns.

  13. GaN on Silicon Substrate with AlN Buffer Layer for UV Photodiode

    NASA Astrophysics Data System (ADS)

    Chuah, L. S.; Thahab, S. M.; Hassan, Z.

    Nitrogen plasma-assisted molecular beam epitaxy (PAMBE) deposited GaN thin films on (111) n-type silicon substrate with different thickness AlN buffer layers are investigated and distinguished by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM) and Raman scattering. The thickness of AlN buffer layer ranged from 200 nm to 300 nm. Besides that, the electrical characteristics of the GaN thin film for ultraviolet detecting utilizations are studied by calculating the photo current/dark current ratio on a metal-semiconductor-metal (MSM) photodiode with and without the illumination of Hg-lamp source. The devices have been tested over room temperature (RT). The photocurrent analysis, together with the study of Schottky barrier height (SBH) development, ascertain that the principal mechanism of photo transport is thermionic emission. The photocurrent value is rigorously dependent on Schottky barrier height. The GaN/AlN(200 nm)/n-Si MSM photodiode produces the highest photo/dark current ratio for the lowest strain that consists of the GaN film grown on the AlN (200 nm) buffer layer.

  14. Long wavelength emitting GaInN quantum wells on metamorphic GaInN buffer layers with enlarged in-plane lattice parameter

    SciTech Connect

    Däubler, J. Passow, T.; Aidam, R.; Köhler, K.; Kirste, L.; Kunzer, M.; Wagner, J.

    2014-09-15

    Metamorphic (i.e., linear composition graded) GaInN buffer layers with an increased in-plane lattice parameter, grown by plasma-assisted molecular beam epitaxy, were used as templates for metal organic vapor phase epitaxy (MOVPE) grown GaInN/GaInN quantum wells (QWs), emitting in the green to red spectral region. A composition pulling effect was observed allowing considerable higher growth temperatures for the QWs for a given In composition. The internal quantum efficiency (IQE) of the QWs was determined by temperature and excitation power density dependent photoluminescence (PL) spectroscopy. An increase in IQE by a factor of two was found for green emitting QWs grown on metamorphic GaInN buffer compared to reference samples grown on standard GaN buffer layers. The ratio of room temperature to low temperature intensity PL of the red emitting QWs were found to be comparable to the PL efficiency of green emitting QWs, both grown on metamorphic GaInN buffers. The excitation density and well width dependence of the IQE indicate a reduction of the quantum confined Stark effect upon growth on GaInN buffer layers with increased in-plane lattice parameter.

  15. Study of strain boundary conditions and GaAs buffer sizes in InGaAs quantum dots

    NASA Technical Reports Server (NTRS)

    Oyafuso, F.; Klimeck, G.; Boykin, T. B.; Bowen, R. C.; Allmen, P. von

    2003-01-01

    NEMO 3-D has been developed for the simulation of electronic structure in self-assembled InGaAs quantum dots on GaAs substrates. Typical self-assembled quantum dots in that material system contain about 0.5 to 1 million atoms. Effects of strain by the surrounding GaAs buffer modify the electronic structure inside the quantum dot significantly and a large GaAs buffer must be included in the strain and electronic structure.

  16. Study of strain boundary conditions and GaAs buffer sizes in InGaAs quantum dots

    NASA Technical Reports Server (NTRS)

    Oyafuso, F.; Klimeck, G.; Boykin, T. B.; Bowen, R. C.; Allmen, P. von

    2003-01-01

    NEMO 3-D has been developed for the simulation of electronic structure in self-assembled InGaAs quantum dots on GaAs substrates. Typical self-assembled quantum dots in that material system contain about 0.5 to 1 million atoms. Effects of strain by the surrounding GaAs buffer modify the electronic structure inside the quantum dot significantly and a large GaAs buffer must be included in the strain and electronic structure.

  17. Single Junction InGaP/GaAs Solar Cells Grown on Si Substrates using SiGe Buffer Layers

    NASA Technical Reports Server (NTRS)

    Ringel, S. A.; Carlin, J. A.; Andre, C. L.; Hudait, M. K.; Gonzalez, M.; Wilt, D. M.; Clark, E. B.; Jenkins, P.; Scheiman, D.; Allerman, A.

    2002-01-01

    Single junction InGaP/GaAs solar cells displaying high efficiency and record high open circuit voltage values have been grown by metalorganic chemical vapor deposition on Ge/graded SiGe/Si substrates. Open circuit voltages as high as 980 mV under AM0 conditions have been verified to result from a single GaAs junction, with no evidence of Ge-related sub-cell photoresponse. Current AM0 efficiencies of close to 16% have been measured for a large number of small area cells, whose performance is limited by non-fundamental current losses due to significant surface reflection resulting from greater than 10% front surface metal coverage and wafer handling during the growth sequence for these prototype cells. It is shown that at the material quality currently achieved for GaAs grown on Ge/SiGe/Si substrates, namely a 10 nanosecond minority carrier lifetime that results from complete elimination of anti-phase domains and maintaining a threading dislocation density of approximately 8 x 10(exp 5) per square centimeter, 19-20% AM0 single junction GaAs cells are imminent. Experiments show that the high performance is not degraded for larger area cells, with identical open circuit voltages and higher short circuit current (due to reduced front metal coverage) values being demonstrated, indicating that large area scaling is possible in the near term. Comparison to a simple model indicates that the voltage output of these GaAs on Si cells follows ideal behavior expected for lattice mismatched devices, demonstrating that unaccounted for defects and issues that have plagued other methods to epitaxially integrate III-V cells with Si are resolved using SiGe buffers and proper GaAs nucleation methods. These early results already show the enormous and realistic potential of the virtual SiGe substrate approach for generating high efficiency, lightweight and strong III-V solar cells.

  18. Threading dislocations in GaAs epitaxial layers on various thickness Ge buffers on 300 mm Si substrates

    NASA Astrophysics Data System (ADS)

    Bogumilowicz, Y.; Hartmann, J. M.; Rochat, N.; Salaun, A.; Martin, M.; Bassani, F.; Baron, T.; David, S.; Bao, X.-Y.; Sanchez, E.

    2016-11-01

    We have grown GaAs epitaxial layers on Ge buffers, themselves on Si (001) substrates, using an Applied Materials 300 mm metal organic chemical vapor deposition tool. We varied the Ge buffer thickness between 0.36 and 1.38 μm and studied the properties of a 0.27 μm thick GaAs layer on top. We found that increasing the Ge buffer thickness yielded smoother GaAs films with an rms surface roughness as low as 0.5 nm obtained on a 5×5 μm2 area. The bow of the substrate increased following a linear law with the epitaxial stack thickness up to 240 μm for a 1.65 μm stack. We have also characterized the threading dislocations present in the GaAs layers using X-ray diffraction and cathodoluminescence. Increasing the Ge buffer thickness resulted in lower threading dislocation densities, enabling us to obtain anti-phase boundary - free GaAs films with a threading dislocation density as low as 3×107 cm-2. In addition, atomic force microscopy surface topology measurements showed the presence of pits in the GaAs layers whose density agreed well with other threading dislocation density assessments. It thus seems that threading dislocations can in certain cases induce some growth rate variations, making them visible in as-grown GaAs films. Using thicker Ge buffers results in smoother films with less threading dislocations, with the side effect of increasing the bow on the wafer. If bow is not an issue, this is a practical approach to improve the GaAs (on Ge buffer) on silicon quality.

  19. Probing temperature gradients within the GaN buffer layer of AlGaN/GaN high electron mobility transistors with Raman thermography

    SciTech Connect

    Hodges, C. Pomeroy, J.; Kuball, M.

    2014-02-14

    We demonstrate the ability of confocal Raman thermography using a spatial filter and azimuthal polarization to probe vertical temperature gradients within the GaN buffer layer of operating AlGaN/GaN high electron mobility transistors. Temperature gradients in the GaN layer are measured by using offset focal planes to minimize the contribution from different regions of the GaN buffer. The measured temperature gradient is in good agreement with a thermal simulation treating the GaN thermal conductivity as homogeneous throughout the layer and including a low thermal conductivity nucleation layer to model the heat flow between the buffer and substrate.

  20. New MBE buffer for micron- and quarter-micron-gateGaAs MESFETs

    NASA Technical Reports Server (NTRS)

    1988-01-01

    A new buffer layer has been developed that eliminates backgating in GaAs MESFETs and substantially reduces short-channel effects in GaAs MESFETs with 0.27-micron-long gates. The new buffer is grown by molecular beam epitaxy (MBE) at a substrate temperature of 200 C using Ga and As sub 4 beam fluxes. The buffer is crystalline, highly resistive, optically inactive, and can be overgrown with high quality GaAs. GaAs MESFETs with a gate length of 0.27 microns that incorporate the new buffer show improved dc and RF properties in comparison with a similar MESFET with a thin undoped GaAs buffer. To demonstrate the backgating performance improvement afforded by the new buffer, MESFETs were fabricated using a number of different buffer layers and structures. A schematic cross section of the MESFET structure used in this study is shown. The measured gate length, gate width, and source-drain spacing of this device are 2,98, and 5.5 microns, respectively. An ohmic contact, isolated from the MESFET by mesa etching, served as the sidegate. The MESFETs were fabricated in MBE n-GaAs layers grown on the new buffer and also in MBE n-GaAs layers grown on buffer layers of undoped GaAs, AlGaAs, and GaAs/AlGaAs superlattices. All the buffer layers were grown by MBE and are 2 microns thick. The active layer is doped to approximately 2 x 10 to the 17th/cu cm with silicon and is 0.3 microns thick.

  1. New MBE buffer for micron- and quarter-micron-gateGaAs MESFETs

    NASA Technical Reports Server (NTRS)

    1988-01-01

    A new buffer layer has been developed that eliminates backgating in GaAs MESFETs and substantially reduces short-channel effects in GaAs MESFETs with 0.27-micron-long gates. The new buffer is grown by molecular beam epitaxy (MBE) at a substrate temperature of 200 C using Ga and As sub 4 beam fluxes. The buffer is crystalline, highly resistive, optically inactive, and can be overgrown with high quality GaAs. GaAs MESFETs with a gate length of 0.27 microns that incorporate the new buffer show improved dc and RF properties in comparison with a similar MESFET with a thin undoped GaAs buffer. To demonstrate the backgating performance improvement afforded by the new buffer, MESFETs were fabricated using a number of different buffer layers and structures. A schematic cross section of the MESFET structure used in this study is shown. The measured gate length, gate width, and source-drain spacing of this device are 2,98, and 5.5 microns, respectively. An ohmic contact, isolated from the MESFET by mesa etching, served as the sidegate. The MESFETs were fabricated in MBE n-GaAs layers grown on the new buffer and also in MBE n-GaAs layers grown on buffer layers of undoped GaAs, AlGaAs, and GaAs/AlGaAs superlattices. All the buffer layers were grown by MBE and are 2 microns thick. The active layer is doped to approximately 2 x 10 to the 17th/cu cm with silicon and is 0.3 microns thick.

  2. Dislocation annihilation in regrown GaN on nanoporous GaN template with optimization of buffer layer growth

    NASA Astrophysics Data System (ADS)

    Soh, C. B.; Hartono, H.; Chow, S. Y.; Chua, S. J.; Fitzgerald, E. A.

    2007-01-01

    Nanoporous GaN template has been fabricated by electrochemical etching to give hexagonal pits with nanoscale pores of size 20-50nm in the underlying grains. The effect of GaN buffer layer grown at various temperatures from 650to1015°C on these as-fabricated nanopores templates is investigated by transmission electron microscopy. The buffer layer grown at the optimized temperature of 850°C partially fill up the pores and voids with annihilation of threading dislocations, serving as an excellent template for high-quality GaN growth. This phenomenon is, however, not observed for the samples grown with other temperature buffer layers. Micro-Raman measurements show significant strain relaxation and improvement in the crystal quality of the overgrown GaN layer on nanoporous GaN template as compared to overgrown on conventional GaN template.

  3. Optimization of InGaP metamorphic buffers grown by MOVPE

    NASA Astrophysics Data System (ADS)

    Ebert, C.; Pulwin, Z.; Reynolds, C. L.; Ramos Sn., F.; Li, Y.; Farrell, S.

    2015-03-01

    Inverted metamorphic multijunction solar cells have shown high solar conversion efficiencies and utilized InGaP based metamorphic (MM) buffers to change the lattice constant using compositional graded buffer layers while minimizing dislocation density in the final material layers. In this study, optimization of InGaP metamorphic buffers was done by systematically exploring key metalorganic vapor phase epitaxy (MOVPE) growth conditions and the MM buffer epitaxial stack structure. To optimize MOVPE growth parameters, growth temperature and V/III ratio were varied during the growth of a standard MM buffer test structure and the final InGaP buffer layer was characterized by photoluminescence, X-ray reciprocal space maps, atomic force microscope, cathodoluminesence, and ex situ bow measurements. The in situ measurement of wafer curvature was also monitored during MM buffer layer growth. Evaluation of material characterization data provided optimized growth conditions for the InGaP based MM buffer. The second part of this study evaluated the actual layer thickness and number of compositional graded steps in a MM buffer. Our results showed that in situ deflectometer measurements of the wafer curvature of the MM buffer layer can be correlated to ex situ determined strain relaxation of the final buffer layer of the MM buffer. Process optimization tests showed a growth temperature of 580 °C with a V/III ratio of 37 provided for the best surface roughness, highest PL intensity and also allowed for low dislocation defect density of the final buffer layer. Using the optimized growth conditions, further optimization of the step grade layers showed that a 350 nm thick grade layer for a six step layer MM buffer for a final buffer composition targeted for In0.8Ga0.2P provided the best surface roughness and 100% final buffer relaxation.

  4. Structure optimization of high indium content InGaAs/InP heterostructure for the growth of In0.82Ga0.18As buffer layer

    NASA Astrophysics Data System (ADS)

    Wei, Qiu-lin; Guo, Zuo-xing; Zhao, Lei; Zhao, Liang; Yuan, De-zeng; Miao, Guo-qing; Xia, Mao-sheng

    2016-11-01

    Microstructure and misfit dislocation behavior in In x Ga1- x As/InP heteroepitaxial materials grown by low pressure metal organic chemical vapor deposition (LP-MOCVD) were analyzed by high resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), atomic force microscopy (AFM), Raman spectroscopy and Hall effect measurements. To optimize the structure of In0.82Ga0.18As/InP heterostructure, the In x Ga1- x As buffer layer was grown. The residual strain of the In0.82Ga0.18As epitaxial layer was calculated. Further, the periodic growth pattern of the misfit dislocation at the interface was discovered and verified. Then the effects of misfit dislocation on the surface morphology and microstructure of the material were studied. It is found that the misfit dislocation of high indium (In) content In0.82Ga0.82As epitaxial layer has significant influence on the carrier concentration.

  5. Metamorphic GaAsP buffers for growth of wide-bandgap InGaP solar cells

    NASA Astrophysics Data System (ADS)

    Simon, J.; Tomasulo, S.; Simmonds, P. J.; Romero, M.; Lee, M. L.

    2011-01-01

    GaAsxP1-x graded buffers were grown via solid source molecular beam epitaxy (MBE) to enable the fabrication of wide-bandgap InyGa1-yP solar cells. Tensile-strained GaAsxP1-x buffers grown on GaAs using unoptimized conditions exhibited asymmetric strain relaxation along with formation of faceted trenches, 100-300 nm deep, running parallel to the [01¯1] direction. We engineered a 6 μm thick grading structure to minimize the faceted trench density and achieve symmetric strain relaxation while maintaining a threading dislocation density of ≤106 cm-2. In comparison, compressively-strained graded GaAsxP1-x buffers on GaP showed nearly-complete strain relaxation of the top layers and no evidence of trenches but possessed threading dislocation densities that were one order of magnitude higher. We subsequently grew and fabricated wide-bandgap InyGa1-yP solar cells on our GaAsxP1-x buffers. Transmission electron microscopy measurements gave no indication of CuPt ordering. We obtained open circuit voltage as high as 1.42 V for In0.39Ga0.61P with a bandgap of 2.0 eV. Our results indicate MBE-grown InyGa1-yP is a promising material for the top junction of a future multijunction solar cell.

  6. Electron channel mobility in silicon-doped Ga2O3 MOSFETs with a resistive buffer layer

    NASA Astrophysics Data System (ADS)

    Wong, Man Hoi; Sasaki, Kohei; Kuramata, Akito; Yamakoshi, Shigenobu; Higashiwaki, Masataka

    2016-12-01

    The electron mobility in depletion-mode lateral β-Ga2O3(010) metal-oxide-semiconductor field-effect transistors (MOSFETs) with an n-channel formed by Si-ion (Si+) implantation doping was extracted using low-field electrical measurements on FET structures. An undoped Ga2O3 buffer layer protected the channel against charge compensation by suppressing outdiffusion of deep Fe acceptors from the semi-insulating substrate. The molecular beam epitaxy growth temperature was identified as a key process parameter for eliminating parasitic conduction at the buffer/substrate growth interface. Devices with a resistive buffer showed room temperature channel mobilities of 90-100 cm2 V-1 s-1 at carrier concentrations of low- to mid-1017 cm-3, with small in-plane mobility anisotropy of 10-15% ascribable to anisotropic carrier scattering.

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

    DOE PAGES

    Ahn, Shihyun; Zhu, Weidi; Dong, Chen; ...

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

    SciTech Connect

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

    2013-06-15

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

  10. Effect of buffer layer and external stress on magnetic properties of flexible FeGa films

    NASA Astrophysics Data System (ADS)

    Zhang, Xiaoshan; Zhan, Qingfeng; Dai, Guohong; Liu, Yiwei; Zuo, Zhenghu; Yang, Huali; Chen, Bin; Li, Run-Wei

    2013-05-01

    We systematically investigated the effect of a Ta buffer layer and external stress on the magnetic properties of magnetostrictive Fe81Ga19 films deposited on flexible polyethylene terephthalate (PET) substrates. The Ta buffer layers could effectively smoothen the rough surface of PET. As a result, the FeGa films grown on Ta buffer layers exhibit a weaker uniaxial magnetic anisotropy and lower coercivity, as compared to those films directly grown on PET substrates. By inward and outward bending the FeGa/Ta/PET samples, external in-plane compressive and tensile stresses were applied to the magnetic films. Due to the inverse magnetostrictive effect of FeGa, both the coercivity and squareness of hysteresis loops for FeGa/Ta films could be well tuned under various strains.

  11. EXAMINATION OF DISLOCATIONS IN LATTICE-MISMATCHED GaInAs/BUFFER LAYER/GaAs FOR III-V PHOTOVOLTAICS

    SciTech Connect

    Levander, A.; Geisz, J.

    2007-01-01

    Dislocations act as sites for nonradiative electron/hole pair recombination, which reduces the effi ciency of photovoltaics. Lattice-matched materials can be grown on top of one another without forming a high density of dislocations. However, when the growth of lattice-mismatched (LMM) materials is attempted, many dislocations result from the relaxation of strain in the crystal structure. In an attempt to reduce the number of dislocations that propagate into a solar device when using LMM materials, a compositionally step-graded buffer is placed between the two LMM materials. In order to confi ne the dislocations to the buffer layer and therefore increase material quality and device effi ciency, the growth temperature and thickness of the buffer layer were varied. A GaInP compositionally graded buffer and GaInAs p-n junction were grown on a GaAs substrate in a metal-organic chemical vapor deposition (MOCVD) system. A multibeam optical stress sensor (MOSS) and X-ray diffraction (XRD) were used to characterize the strain in the epilayers. Electrical and optoelectronic properties were measured using a probe station and multimeter setup, solar simulator, and a quantum effi ciency instrument. It was determined that device functionality was highly dependent on the growth temperature of the graded buffer. As growth temperature increased, so did the dislocation density in the device despite an increase in the dislocation velocity, which should have increased the dislocation annihilation rate and the diffusion of dislocations to the edge of the crystal. The thickness of the graded buffer also affected device effi ciency with thinner samples performing poorly. The thinner graded buffer layers had high internal resistances from reduced carrier concentrations. In terms of effi ciency, the empirically derived recipe developed by the scientists at the National Renewable Energy Laboratory (NREL) produced the highest quality cells.

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

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

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

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

    SciTech Connect

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

    2015-05-04

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

  14. The effects of the porous buffer layer and doping with dysprosium on internal stresses in the GaInP:Dy/por-GaAs/GaAs(100) heterostructures

    SciTech Connect

    Seredin, P. V.; Gordienko, N. N.; Glotov, A. V.; Zhurbina, I. A.; Domashevskaya, E. P.; Arsent'ev, I. N. Shishkov, M. V.

    2009-08-15

    In structures with a porous buffer layer, residual internal stresses caused by a mismatch between the crystal-lattice parameters of the epitaxial GaInP alloy and the GaAs substrate are redistributed to the porous layer that acts as a buffer and is conducive to disappearance of internal stresses. Doping of the epitaxial layer with dysprosium exerts a similar effect on the internal stresses in the film-substrate structure.

  15. The impact of substrate nitridation temperature and buffer design and synthesis on the polarity of GaN epitaxial films

    NASA Astrophysics Data System (ADS)

    Namkoong, Gon; Alan Doolittle, W.; Brown, April S.; Losurdo, Maria; Giangregorio, Maria M.; Bruno, Giovanni

    2003-05-01

    The polarity of GaN epitaxial layers grown on GaN and AlN buffer layers was investigated and found to be dependent on nitridation temperature over the range of 200-700°C. When low temperature (LT), 500°C, GaN buffer layers are used, GaN epitaxial layers grown on 200°C nitrided sapphire have a higher density of N-polar inversion domains. However, a high density of dislocation pits was observed on GaN epitaxial layers based on AFM morphology when GaN epitaxial layers were grown on LT GaN buffer of 700°C nitrided sapphire substrate. With high temperature (HT), 850°C, AlN buffer layers, the density of N-polar inversion domains in GaN epitaxial layers depends on the thickness of AlN buffer layer. The structural quality of Ga-polar GaN epitaxial layer is dramatically improved when LT GaN and HT AlN buffer layers are combined with an optimized annealing time. The measured full-widths at half-maximum of (0 0 0 2) symmetric and (1 0 .4) asymmetric reflections are 68 and 246 arcsec, respectively, for 1.0 μm GaN epitaxial layers. The results presented here can be implemented to produce low dislocation density, single Ga-polar GaN epitaxial layers.

  16. Growth of InGaN/GaN quantum wells with graded InGaN buffer for green-to-yellow light emitters

    NASA Astrophysics Data System (ADS)

    Hu, Chia-Hsuan; Lo, Ikai; Hsu, Yu-Chi; Shih, Cheng-Hung; Pang, Wen-Yuan; Wang, Ying-Chieh; Lin, Yu-Chiao; Yang, Chen-Chi; Tsai, Cheng-Da; Hsu, Gary Z. L.

    2016-08-01

    We have studied the growth of high-indium-content In x Ga1- x N/GaN double quantum wells (QWs) for yellow and green light emitters by plasma-assisted molecular beam epitaxy at a low substrate temperature (570 °C). By introducing a graded In y Ga1- y N buffer layer, the PL intensity of QWs can be increased sixfold compared with that of the original structure. In addition, the indium content in InGaN QWs was increased owing the prolonged growth time of the graded In y Ga1- y N buffer layer. After adjusting to optimal growth conditions, we achieved In x Ga1- x N/GaN QWs with x = 0.32. Photoluminescence measurements showed that the emission wavelength from In x Ga1- x N/GaN QWs was 560 nm (2.20 eV). The optimal condition for the gradient In y Ga1- y N buffer layer was obtained for light emission from green to yellow.

  17. Selective area growth of In(Ga)N/GaN nanocolumns by molecular beam epitaxy on GaN-buffered Si(111): from ultraviolet to infrared emission.

    PubMed

    Albert, S; Bengoechea-Encabo, A; Sánchez-García, M A; Kong, X; Trampert, A; Calleja, E

    2013-05-03

    Selective area growth of In(Ga)N/GaN nanocolumns was performed on GaN-buffered Si(111) substrates by plasma-assisted molecular beam epitaxy. Undoped and Si-doped GaN buffer layers were first grown on Si(111) substrates, showing photoluminescence excitonic emission without traces of other low energy contributions, in particular, the yellow band. The GaN buffer surface roughness (between 10 and 14 nm, the rms value in a 10 × 10 μm(2) area) was low enough to allow the fabrication of a thin (7 nm thick) well defined Ti nanohole mask, for the selective area growth. Ordered In(Ga)N/GaN nanocolumns emitting from the ultraviolet (3.2 eV) to the infrared (0.78 eV) were obtained. The morphology and the emission efficiency of the In(Ga)N/GaN nanocolumns emitting at a given wavelength could be substantially improved by tuning the In/Ga and total III/N ratios. An estimated internal quantum efficiency of 36% was derived from photoluminescence data for green emitting nanocolumns.

  18. Microstructure of GaN epitaxy on SiC using AlN buffer layers

    SciTech Connect

    Ponce, F.A.; Krusor, B.S.; Major, J.S. Jr.; Plano, W.E.; Welch, D.F.

    1995-07-17

    The crystalline structure of GaN epilayers on (0001) SiC substrates has been studied using x-ray diffraction and transmission microscopy. The films were grown by metalorganic chemical vapor deposition, using AlN buffer layers. X-ray diffraction measurements show negligible strain in the epilayer, and a long-range variation in orientation. Transmission electron lattice images show that the AlN buffer layer consists of small crystallites. The nature of the buffer layer and its interfaces with the substrate and the GaN film is discussed. The defect structure of the GaN film away from the substrate consists mostly of threading dislocations with a density of {similar_to}10{sup 9} cm{sup {minus}2}. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.

  19. Mg-compensation effect in GaN buffer layer for AlGaN/GaN high-electron-mobility transistors grown on 4H-SiC substrate

    NASA Astrophysics Data System (ADS)

    Ko, Kwangse; Lee, Kyeongjae; So, Byeongchan; Heo, Cheon; Lee, Kyungbae; Kwak, Taemyung; Han, Sang-Woo; Cha, Ho-Young; Nam, Okhyun

    2017-01-01

    The present study investigated the Mg doping effect in the gallium nitride (GaN) buffer layers (BLs) of AlGaN/GaN high-electron-mobility transistor (HEMT) structures grown on semi-insulating 4H-SiC substrates by metal organic chemical vapor deposition. When the Mg concentration was increased from 3 × 1017 to 8 × 1018 cm-3, the crystal quality slightly deteriorated, whereas electrical properties were significantly changed. The buffer leakage increased approximately 50 times from 0.77 to 39.2 nA at -50 V with the Mg doping concentration. The Mg-compensation effect and electron trapping effect were observed at Mg concentration of 3 × 1017 and 8 × 1018 cm-3, respectively, which were confirmed by an isolation leakage current test and low-temperature photoluminescence. When the BL was compensated, the two-dimensional electron gas (2DEG) mobility and sheet carrier concentration of the HEMTs were 1560 cm2 V-1 s-1 and 5.06 × 1012 cm-2, respectively. As a result, Mg-doped GaN BLs were demonstrated as a candidates of semi-insulating BLs for AlGaN/GaN HEMT.

  20. Rare earth zirconium oxide buffer layers on metal substrates

    DOEpatents

    Williams, Robert K.; Paranthaman, Mariappan; Chirayil, Thomas G.; Lee, Dominic F.; Goyal, Amit; Feenstra, Roeland

    2001-01-01

    A laminate article comprises a substrate and a biaxially textured (RE.sub.x A.sub.(1-x)).sub.2 O.sub.2-(x/2) buffer layer over the substrate, wherein 0buffer layer can be deposited using sol-gel or metal-organic decomposition. The laminate article can include a layer of YBCO over the (RE.sub.x A.sub.(1-x)).sub.2 O.sub.2-(x/2) buffer layer. A layer of CeO.sub.2 between the YBCO layer and the (RE.sub.x A.sub.(1-x)).sub.2 O.sub.2-(x/2) buffer layer can also be include. Further included can be a layer of YSZ between the CeO.sub.2 layer and the (RE.sub.x A.sub.(1-x)).sub.2 O.sub.2-(x/2) buffer layer. The substrate can be a biaxially textured metal, such as nickel. A method of forming the laminate article is also disclosed.

  1. Method of depositing buffer layers on biaxially textured metal substrates

    DOEpatents

    Beach, David B.; Morrell, Jonathan S.; Paranthaman, Mariappan; Chirayil, Thomas; Specht, Eliot D.; Goyal, Amit

    2002-08-27

    A laminate article comprises a substrate and a biaxially textured (RE.sup.1.sub.x RE.sup.2.sub.(1-x)).sub.2 O.sub.3 buffer layer over the substrate, wherein 0buffer layer can be deposited using sol-gel or metal-organic decomposition. The laminate article can include a layer of YBCO over the (RE.sup.1.sub.x RE.sup.2.sub.(1-x)).sub.2 O.sub.3 buffer layer. A layer of CeO.sub.2 between the YBCO layer and the (RE.sup.1.sub.x RE.sup.2.sub.(1-x)).sub.2 O.sub.3 buffer can also be include. Further included can be a layer of YSZ between the CeO.sub.2 layer and the (RE.sup.1.sub.x RE.sup.2.sub.(1-x)).sub.2 O.sub.3 buffer layer. The substrate can be a biaxially textured metal, such as nickel. A method of forming the laminate article is also disclosed.

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

    SciTech Connect

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

    2014-02-24

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

  3. Demonstrating antiphase domain boundary-free GaAs buffer layer on zero off-cut Si (0 0 1) substrate for interfacial misfit dislocation GaSb film by metalorganic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Ha, Minh Thien Huu; Hoang Huynh, Sa; Binh Do, Huy; Nguyen, Tuan Anh; Luc, Quang Ho; Chang, Edward Yi

    2017-08-01

    High quality 40 nm GaSb thin film was grown on the zero off-cut Si (0 0 1)-oriented substrate using metalorganic chemical vapor deposition with the temperature-graded GaAs buffer layer. The growth time of the GaAs nucleation layer, which was deposited at a low temperature of 490 °C, is systematically investigated in this paper. Cross-sections of the high resolution transmission electron microscopy images indicate that the GaAs compound formed 3D-islands first before to quasi-2D islands, and finally formed uniform GaAs layer. The optimum thickness of the 490 °C-GaAs layer was found to be 10 nm to suppress the formation of antiphase domain boundaries (APDs). The thin GaAs nucleation layer had a root-mean-square surface roughness of 0.483 nm. This allows the continued high temperature GaAs buffer layer to be achieved with low threading dislocation density of around 7.1  ×  106 cm-2 and almost invisible APDs. Finally, a fully relaxed GaSb film was grown on the top of the GaAs/Si heterostructure using interfacial misfit dislocation growth mode. These results indicate that the GaSb epitaxial layer can be grown on Si substrate with GaAs buffer layer for future p-channel metal-oxide-semiconductor field effect transistors (MOSFETs) applications.

  4. Improved mobility of AlGaN channel heterojunction material using an AlGaN/GaN composite buffer layer

    NASA Astrophysics Data System (ADS)

    Wen, Hui-Juan; Zhang, Jin-Cheng; Lu, Xiao-Li; Wang, Zhi-Zhe; Ha, Wei; Ge, Sha-Sha; Cao, Rong-Tao; Hao, Yue

    2014-03-01

    The quality of an AlGaN channel heterojunction on a sapphire substrate is massively improved by using an AlGaN/GaN composite buffer layer. We demonstrate an Al0.4Ga0.5N/Al0.18Ga0.82N heterojunction with a state-of-the-art mobility of 815 cm2/(V·s) and a sheet resistance of 890 Ω/□ under room temperature. The crystalline quality and the electrical properties of the AlGaN heterojunction material are analyzed by atomic force microscopy, high-resolution X-ray diffraction, and van der Pauw Hall and capacitance—voltage (C—V) measurements. The results indicate that the improved electrical properties should derive from the reduced surface roughness and low dislocation density.

  5. Ultraviolet light emitting diodes by ammonia molecular beam epitaxy on metamorphic (20 2 bar 1) AlGaN/GaN buffer layers

    NASA Astrophysics Data System (ADS)

    Young, Erin C.; Yonkee, Benjamin P.; Wu, Feng; Saifaddin, Burhan K.; Cohen, Daniel A.; DenBaars, Steve P.; Nakamura, Shuji; Speck, James S.

    2015-09-01

    In this paper we demonstrate ultraviolet (UV) light emitting diodes (LEDs) grown on metamorphic AlGaN buffers on freestanding GaN (20 2 bar 1) substrates by ammonia assisted molecular beam epitaxy (MBE). Misfit and related threading dislocations were confined to the stress relaxed, compositionally graded buffer layers, and single quantum well devices emitting at 355, 310 and 274 nm were grown on top of the graded buffers. The devices showed excellent structural and electrical (I-V) characteristics.

  6. Study on electrical properties of metal/GaSb junctions using metal-GaSb alloys

    SciTech Connect

    Nishi, Koichi Yokoyama, Masafumi; Kim, Sanghyeon; Takenaka, Mitsuru; Takagi, Shinichi; Yokoyama, Haruki

    2014-01-21

    We study the metal-GaSb alloy formation, the structural properties and the electrical characteristics of the metal-alloy/GaSb diodes by employing metal materials such as Ni, Pd, Co, Ti, Al, and Ta, in order to clarify metals suitable for GaSb p-channel metal-oxide-semiconductor field-effect transistors (pMOSFETs) as metal-GaSb alloy source/drain (S/D). It is found that Ni, Pd, Co, and Ti can form alloy with GaSb by rapid thermal annealing at 250, 250, 350, and 450 °C, respectively. The Ni-GaSb and Pd-GaSb alloy formation temperature of 250 °C is lower than the conventional dopant activation annealing for ion implantation, which enable us to lower the process temperature. The alloy layers show lower sheet resistance (R{sub Sheet}) than that of p{sup +}-GaSb layer formed by ion implantation and activation annealing. We also study the electrical characteristics of the metal-alloy/GaSb junctions. The alloy/n-GaSb contact has large Schottky barrier height (ϕ{sub B}) for electrons, ∼0.6 eV, and low ϕ{sub B} for holes, ∼0.2 eV, which enable us to realize high on/off ratio in pMOSFETs. We have found that the Ni-GaSb/GaSb Schottky junction shows the best electrical characteristics with ideal factor (n) of 1.1 and on-current/off-current ratio (I{sub on}/I{sub off}) of ∼10{sup 4} among the metal-GaSb alloy/GaSb junctions evaluated in the present study. These electrical properties are also superior to those of a p{sup +}-n diode fabricated by Be ion implantation with activation annealing at 350 °C. As a result, the Ni-GaSb alloy can be regarded as one of the best materials to realize metal S/D in GaSb pMOSFETs.

  7. Buffer transport mechanisms in intentionally carbon doped GaN heterojunction field effect transistors

    SciTech Connect

    Uren, Michael J.; Cäsar, Markus; Kuball, Martin; Gajda, Mark A.

    2014-06-30

    Temperature dependent pulsed and ramped substrate bias measurements are used to develop a detailed understanding of the vertical carrier transport in the buffer layers in a carbon doped GaN power heterojunction field effect transistor. Carbon doped GaN and multiple layers of AlGaN alloy are used in these devices to deliver an insulating and strain relieved buffer with high breakdown voltage capability. However, understanding of the detailed physical mechanism for its operation is still lacking. At the lowest electric fields (<10 MV/m), charge redistribution within the C doped layer is shown to occur by hole conduction in the valence band with activation energy 0.86 eV. At higher fields, leakage between the two-dimensional electron gas and the buffer dominates occurring by a Poole-Frenkel mechanism with activation energy ∼0.65 eV, presumably along threading dislocations. At higher fields still, the strain relief buffer starts to conduct by a field dependent process. Balancing the onset of these leakage mechanisms is essential to allow the build-up of positive rather than negative space charge, and thus minimize bulk-related current-collapse in these devices.

  8. Heteroepitaxial growth of In0.30Ga0.70As high-electron mobility transistor on 200 mm silicon substrate using metamorphic graded buffer

    NASA Astrophysics Data System (ADS)

    Kohen, David; Nguyen, Xuan Sang; Yadav, Sachin; Kumar, Annie; Made, Riko I.; Heidelberger, Christopher; Gong, Xiao; Lee, Kwang Hong; Lee, Kenneth Eng Kian; Yeo, Yee Chia; Yoon, Soon Fatt; Fitzgerald, Eugene A.

    2016-08-01

    We report on the growth of an In0.30Ga0.70As channel high-electron mobility transistor (HEMT) on a 200 mm silicon wafer by metal organic vapor phase epitaxy. By using a 3 μm thick buffer comprising a Ge layer, a GaAs layer and an InAlAs compositionally graded strain relaxing buffer, we achieve threading dislocation density of (1.0 ± 0.3) × 107 cm-2 with a surface roughness of 10 nm RMS. No phase separation was observed during the InAlAs compositionally graded buffer layer growth. 1.4 μm long channel length transistors are fabricated from the wafer with IDS of 70 μA/μm and gm of above 60 μS/μm, demonstrating the high quality of the grown materials.

  9. GaN membrane metal-semiconductor-metal ultraviolet photodetector.

    PubMed

    Müller, A; Konstantinidis, G; Dragoman, M; Neculoiu, D; Kostopoulos, A; Androulidaki, M; Kayambaki, M; Vasilache, D

    2008-04-01

    GaN is a wide-bandgap semiconductor with still unexplored capabilities for ultraviolet detection. To exploit GaN properties better for ultraviolet detection, a metal-semiconductor-metal-type photodetector structure was designed and manufactured on a 2.2 microm thin GaN membrane fabricated by micromachining techniques. As a result, a very low dark current (30 pA at 3 V) and a maximum responsivity of 14 mA/W at a wavelength of 370 nm were obtained.

  10. Alternative buffer layer development in Cu(In,Ga)Se2 thin film solar cells

    NASA Astrophysics Data System (ADS)

    Xin, Peipei

    Cu(In,Ga)Se2-based thin film solar cells are considered to be one of the most promising photovoltaic technologies. Cu(In,Ga)Se2 (CIGS) solar devices have the potential advantage of low-cost, fast fabrication by using semiconductor layers of only a few micrometers thick and high efficiency photovoltaics have been reported at both the cell and the module levels. CdS via chemical bath deposition (CBD) has been the most widely used buffer option to form the critical junction in CIGS-based thin film photovoltaic devices. However, the disadvantages of CdS can’t be ignored - regulations on cadmium usage are getting stricter primarily due to its toxicity and environmental impacts, and the proper handling of the large amount of toxic chemical bath waste is a massive and expensive task. This dissertation is devoted to the development of Cd-free alternative buffer layers in CIGS-based thin film solar cells. Based on the considerations of buffer layer selection criteria and extensive literature review, Zn-compound buffer materials are chosen as the primary investigation candidates. Radio frequency magnetron sputtering is the preferred buffer deposition approach since it’s a clean and more controllable technique compared to CBD, and is readily scaled to large area manufacturing. First, a comprehensive study of the ZnSe1-xOx compound prepared by reactive sputtering was completed. As the oxygen content in the reactive sputtering gas increased, ZnSe1-xOx crystallinity and bandgap decreased. It’s observed that oxygen miscibility in ZnSe was low and a secondary phase formed when the O2 / (O2 + Ar) ratio in the sputtering gas exceeded 2%. Two approaches were proposed to optimize the band alignment between the CIGS and buffer layer. One method focused on the bandgap engineering of the absorber, the other focused on the band structure modification of the buffer. As a result, improved current of the solar cell was achieved although a carrier transport barrier at the junction

  11. Crack-free thick (∼5 µm) α-Ga2O3 films on sapphire substrates with α-(Al,Ga)2O3 buffer layers

    NASA Astrophysics Data System (ADS)

    Oda, Masaya; Kaneko, Kentaro; Fujita, Shizuo; Hitora, Toshimi

    2016-12-01

    To obtain crack-free thick α-Ga2O3 films on sapphire substrates, effects and behaviors of buffer layers have been investigated. With the growth of an α-Ga2O3 layer, there appeared an unintentionally formed layer in the sample, which was associated with stress accumulation and could be the seed for crack generation. We obtained a thick (∼5 µm) α-Ga2O3 layer on a sapphire substrate with the insertion of α-(Al0.12Ga0.88)2O3/α-(Al0.02Ga0.98)2O3 buffer layers, and for this sample, we did not observe the intermediate layer, suggesting that the buffer layers were effective for eliminating the stress accumulation at the α-Ga2O3/sapphire interface region.

  12. 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.

  13. Study on GaN buffer leakage current in AlGaN/GaN high electron mobility transistor structures grown by ammonia-molecular beam epitaxy on 100-mm Si(111)

    SciTech Connect

    Ravikiran, L.; Radhakrishnan, K. Ng, G. I.; Munawar Basha, S.; Dharmarasu, N.; Agrawal, M.; Manoj kumar, C. M.; Arulkumaran, S.

    2015-06-28

    The effect of carbon doping on the structural and electrical properties of GaN buffer layer of AlGaN/GaN high electron mobility transistor (HEMT) structures has been studied. In the undoped HEMT structures, oxygen was identified as the dominant impurity using secondary ion mass spectroscopy and photoluminescence (PL) measurements. In addition, a notable parallel conduction channel was identified in the GaN buffer at the interface. The AlGaN/GaN HEMT structures with carbon doped GaN buffer using a CBr{sub 4} beam equivalent pressure of 1.86 × 10{sup −7} mTorr showed a reduction in the buffer leakage current by two orders of magnitude. Carbon doped GaN buffers also exhibited a slight increase in the crystalline tilt with some pits on the growth surface. PL and Raman measurements indicated only a partial compensation of donor states with carbon acceptors. However, AlGaN/GaN HEMT structures with carbon doped GaN buffer with 200 nm thick undoped GaN near the channel exhibited good 2DEG characteristics.

  14. Abrupt GaP/Si hetero-interface using bistepped Si buffer

    SciTech Connect

    Ping Wang, Y. Kuyyalil, J.; Nguyen Thanh, T.; Almosni, S.; Bernard, R.; Tremblay, R.; Da Silva, M.; Létoublon, A.; Rohel, T.; Tavernier, K.; Le Corre, A.; Cornet, C.; Durand, O.; Stodolna, J.; Ponchet, A.; Bahri, M.; Largeau, L.; Patriarche, G.; Magen, C.

    2015-11-09

    We evidence the influence of the quality of the starting Si surface on the III-V/Si interface abruptness and on the formation of defects during the growth of III-V/Si heterogeneous crystal, using high resolution transmission electron microscopy and scanning transmission electron microscopy. GaP layers were grown by molecular beam epitaxy on vicinal Si (001). The strong effect of the Si substrate chemical preparation is first demonstrated by studying structural properties of both Si homoepitaxial layer and GaP/Si heterostructure. It is then shown that choosing adequate chemical preparation conditions and subsequent III-V regrowth conditions enables the quasi-suppression of micro-twins in the epilayer. Finally, the abruptness of GaP/Si interface is found to be very sensitive to the Si chemical preparation and is improved by the use of a bistepped Si buffer prior to III-V overgrowth.

  15. Lattice-matched HfN buffer layers for epitaxy of GaN on Si

    SciTech Connect

    Armitage, Robert; Yang, Qing; Feick, Henning; Gebauer, Joerg; Weber, Eicke R.; Shinkai, Satoko; Sasaki, Katsutaka

    2002-05-08

    Gallium nitride is grown by plasma-assisted molecular-beam epitaxy on (111) and (001) silicon substrates using sputter-deposited 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 (mu)m. Initial results for GaN grown on the (111) surface show a photoluminescence peak width of 17 meV at 11 K, and an asymmetric x-ray rocking curve width of 20 arcmin. Wurtzite GaN on HfN/Si(001) shows reduced structural quality and peculiar low-temperature luminescence features. However, growth on the (001) surface results in nearly stress-free films, suggesting that much thicker crack-free layers could be obtained.

  16. Spacer-thickness dependence of interlayer exchange coupling in GaMnAs/InGaAs/GaMnAs trilayers grown on ZnCdSe buffers

    NASA Astrophysics Data System (ADS)

    Tivakornsasithorn, Kritsanu; Yoo, Taehee; Lee, Hakjoon; Choi, Seonghoon; Lee, Sanghoon; Liu, Xinyu; Dobrowolska, M.; Furdyna, Jacek K.

    2017-03-01

    Interlayer exchange coupling (IEC) between GaMnAs layers in GaMnAs/InGaAs/GaMnAs tri-layers was studied by magnetization measurements. Minor hysteresis loops are observed to shift in a direction indicating the presence of ferromagnetic (FM) IEC in the structures. The strength of the FM IEC clearly exhibits an exponential decrease with respect to nonmagnetic InGaAs spacer thickness. The fitting of the spacer thickness dependence of the FM IEC to an exponential decay function provides a decay length of 3.3±0.3 nm, which is relatively large compared to metallic multilayers, indicating a long ranged IEC in systems based on GaMnAs.

  17. 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.

  18. Buffer Layer Effects on Tandem InGaAs TPV Devices

    NASA Technical Reports Server (NTRS)

    Wilt, David M.; Wehrer, Rebecca J.; Maurer, William F.

    2004-01-01

    Single junction indium gallium arsenide (InGaAs) based TPV devices have demonstrated efficiencies in excess of 20% at radiator temperatures of 1058 C. Modeling suggests that efficiency improvements in single bandgap devices should continue although they will eventually plateau. One approach for extending efficiencies beyond the single bandgap limit is to follow the technique taken in the solar cell field, namely tandem TPV cells. Tandem photovoltaic devices are traditionally composed of cells of decreasing bandgap, connected electrically and optically in series. The incident light impinges upon the highest bandgap first. This device acts as a sieve, absorbing the high-energy photons, while allowing the remainder to pass through to the underlying cell(s), and so on. Tandem devices reduce the energy lost to overexcitation as well as reducing the current density (Jsc). Reduced Jsc results in lower resistive losses and enables the use of thinner and lower doped lateral current conducting layers as well as a higher pitch grid design. Fabricating TPV tandem devices utilizing InGaAs for all of the component cells in a two cell tandem necessitates the inclusion of a buffer layer in-between the high bandgap device (In0.53 Ga0.47As - 0.74eV) and the low bandgap device (In0.66Ga0.34As - 0.63eV) to accommodate the approximately 1% lattice strain generated due to the change in InGaAs composition. To incorporate only a single buffer layer structure, we have investigated the use of the indium phosphide (InP) substrate as a superstrate. Thus the high-bandgap, lattice- matched device is deposited first, followed by the buffer structure and the low-bandgap cell. The near perfect transparency of the high bandgap (1.35eV) iron-doped InP permits the device to be oriented such that the light enters through the substrate. In this paper we examine the impact of the buffer layer on the underlying lattice-matched InGaAs device. 0.74eV InGaAs devices were produced in a variety of

  19. Buffer Layer Effects on Tandem InGaAs TPV Devices

    NASA Technical Reports Server (NTRS)

    Wilt, David M.; Wehrer, Rebecca J.; Maurer, William F.

    2004-01-01

    Single junction indium gallium arsenide (InGaAs) based TPV devices have demonstrated efficiencies in excess of 20% at radiator temperatures of 1058 C. Modeling suggests that efficiency improvements in single bandgap devices should continue although they will eventually plateau. One approach for extending efficiencies beyond the single bandgap limit is to follow the technique taken in the solar cell field, namely tandem TPV cells. Tandem photovoltaic devices are traditionally composed of cells of decreasing bandgap, connected electrically and optically in series. The incident light impinges upon the highest bandgap first. This device acts as a sieve, absorbing the high-energy photons, while allowing the remainder to pass through to the underlying cell(s), and so on. Tandem devices reduce the energy lost to overexcitation as well as reducing the current density (Jsc). Reduced Jsc results in lower resistive losses and enables the use of thinner and lower doped lateral current conducting layers as well as a higher pitch grid design. Fabricating TPV tandem devices utilizing InGaAs for all of the component cells in a two cell tandem necessitates the inclusion of a buffer layer in-between the high bandgap device (In0.53 Ga0.47As - 0.74eV) and the low bandgap device (In0.66Ga0.34As - 0.63eV) to accommodate the approximately 1% lattice strain generated due to the change in InGaAs composition. To incorporate only a single buffer layer structure, we have investigated the use of the indium phosphide (InP) substrate as a superstrate. Thus the high-bandgap, lattice- matched device is deposited first, followed by the buffer structure and the low-bandgap cell. The near perfect transparency of the high bandgap (1.35eV) iron-doped InP permits the device to be oriented such that the light enters through the substrate. In this paper we examine the impact of the buffer layer on the underlying lattice-matched InGaAs device. 0.74eV InGaAs devices were produced in a variety of

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

    SciTech Connect

    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 buffer 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.

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

    SciTech Connect

    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 buffer 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.

  2. GaN metal-semiconductor-metal UV sensor with multi-layer graphene as Schottky electrodes

    NASA Astrophysics Data System (ADS)

    Lee, Chang-Ju; Kang, Sang-Bum; Cha, Hyeon-Gu; Won, Chul-Ho; Hong, Seul-Ki; Cho, Byung-Jin; Park, Hongsik; Lee, Jung-Hee; Hahm, Sung-Ho

    2015-06-01

    We fabricated a GaN-based metal-semiconductor-metal (MSM)-type UV sensor using a multilayer graphene as transparent Schottky electrodes. The fabricated GaN MSM UV sensor showed a high photo-to-dark current contrast ratio of 3.9 × 105 and a UV-to-visible rejection ratio of 1.8 × 103 at 7 V. The as-fabricated GaN MSM UV sensor with graphene electrodes has a low bias dependence of maximum photoresponsivity and a noise-like response at a visible wavelength in the 500 nm region. These problems were successfully solved by treatment with a buffered oxide etcher (BOE), and the photoresponse characteristics of the fabricated GaN MSM UV sensor after the treatment were better than those before the treatment.

  3. Metalorganic vapor phase epitaxy of GaAs on Si using II a-flouride buffer layers

    NASA Astrophysics Data System (ADS)

    Tiwari, A. N.; Freundlich, A.; Beaumont, B.; Blunier, S.; Zogg, H.; Teodoropol, S.; Vèrié, C.

    1992-11-01

    Metalorganic vapor phase epitaxy has been used for the first time to grow epitaxial GaAs layers on (111) and (100) oriented Si either using CaF 2 or stacked (Ca,Sr)F 2/CaF 2 as a buffer. The GaAs layers show sharp and well resolved electron channeling patterns. The Rutherford backscattering (RBS) ion channeling minimum yield is 5% for (111) orientation and 6% for (100) orientation. The GaAs(111) layers are untwinned. The strain in the GaAs layer has been measured with RBS and X-ray diffraction and it is found that the thermal mismatch-induced strain in the GaAs layer is considerably lower than in similar GaAs films grown without flouride buffer.

  4. Surface electronic structure of ZrB2 buffer layers for GaN growth on Si wafers

    NASA Astrophysics Data System (ADS)

    Yamada-Takamura, Yukiko; Bussolotti, Fabio; Fleurence, Antoine; Bera, Sambhunath; Friedlein, Rainer

    2010-08-01

    The electronic structure of epitaxial, predominantly single-crystalline thin films of zirconium diboride (ZrB2), a lattice-matching, conductive ceramic to GaN, grown on Si(111) was studied using angle-resolved ultraviolet photoelectron spectroscopy. The existence of Zr-derived surface states dispersing along the Γ¯-M¯ direction indicates a metallic character provided by a two-dimensional Zr-layer at the surface. Together with the measured work function, the results demonstrate that the surface electronic properties of such thin ZrB2(0001) buffer layers are comparable to those of the single crystals promising excellent conduction between nitride layers and the substrate in vertical light-emitting diodes on economic substrates.

  5. Investigation of AlGaN/GaN high electron mobility transistor structures on 200-mm silicon (111) substrates employing different buffer layer configurations

    PubMed Central

    Lee, H.-P.; Perozek, J.; Rosario, L. D.; Bayram, C.

    2016-01-01

    AlGaN/GaN high electron mobility transistor (HEMT) structures are grown on 200-mm diameter Si(111) substrates by using three different buffer layer configurations: (a) Thick-GaN/3 × {AlxGa1−xN}/AlN, (b) Thin-GaN/3 × {AlxGa1−xN}/AlN, and (c) Thin-GaN/AlN, so as to have crack-free and low-bow (<50 μm) wafer. Scanning electron microscopy, energy-dispersive X-ray spectroscopy, high resolution-cross section transmission electron microscopy, optical microscopy, atomic-force microscopy, cathodoluminescence, Raman spectroscopy, X-ray diffraction (ω/2θ scan and symmetric/asymmetric ω scan (rocking curve scan), reciprocal space mapping) and Hall effect measurements are employed to study the structural, optical, and electrical properties of these AlGaN/GaN HEMT structures. The effects of buffer layer stacks (i.e. thickness and content) on defectivity, stress, and two-dimensional electron gas (2DEG) mobility and 2DEG concentration are reported. It is shown that 2DEG characteristics are heavily affected by the employed buffer layers between AlGaN/GaN HEMT structures and Si(111) substrates. Particularly, we report that in-plane stress in the GaN layer affects the 2DEG mobility and 2DEG carrier concentration significantly. Buffer layer engineering is shown to be essential for achieving high 2DEG mobility (>1800 cm2/V∙s) and 2DEG carrier concentration (>1.0 × 1013 cm−2) on Si(111) substrates. PMID:27869222

  6. Investigation of AlGaN/GaN high electron mobility transistor structures on 200-mm silicon (111) substrates employing different buffer layer configurations

    NASA Astrophysics Data System (ADS)

    Lee, H.-P.; Perozek, J.; Rosario, L. D.; Bayram, C.

    2016-11-01

    AlGaN/GaN high electron mobility transistor (HEMT) structures are grown on 200-mm diameter Si(111) substrates by using three different buffer layer configurations: (a) Thick-GaN/3 × {AlxGa1‑xN}/AlN, (b) Thin-GaN/3 × {AlxGa1‑xN}/AlN, and (c) Thin-GaN/AlN, so as to have crack-free and low-bow (<50 μm) wafer. Scanning electron microscopy, energy-dispersive X-ray spectroscopy, high resolution-cross section transmission electron microscopy, optical microscopy, atomic-force microscopy, cathodoluminescence, Raman spectroscopy, X-ray diffraction (ω/2θ scan and symmetric/asymmetric ω scan (rocking curve scan), reciprocal space mapping) and Hall effect measurements are employed to study the structural, optical, and electrical properties of these AlGaN/GaN HEMT structures. The effects of buffer layer stacks (i.e. thickness and content) on defectivity, stress, and two-dimensional electron gas (2DEG) mobility and 2DEG concentration are reported. It is shown that 2DEG characteristics are heavily affected by the employed buffer layers between AlGaN/GaN HEMT structures and Si(111) substrates. Particularly, we report that in-plane stress in the GaN layer affects the 2DEG mobility and 2DEG carrier concentration significantly. Buffer layer engineering is shown to be essential for achieving high 2DEG mobility (>1800 cm2/V•s) and 2DEG carrier concentration (>1.0 × 1013 cm‑2) on Si(111) substrates.

  7. InGaN/InGaN multiple-quantum-well grown on InGaN/GaN semi-bulk buffer for blue to cyan emission with improved optical emission and efficiency droop

    NASA Astrophysics Data System (ADS)

    Alam, Saiful; Sundaram, Suresh; Elouneg-Jamroz, Miryam; Li, Xin; El Gmili, Youssef; Robin, Ivan Christophe; Voss, Paul L.; Salvestrini, Jean-Paul; Ougazzaden, Abdallah

    2017-04-01

    In0.16Ga0.84N/In0.05Ga0.95N Multiple Quantum Well (MQW) structure grown on a 70 nm thick high quality semi-bulk InGaN buffer layer is reported. Temperature dependent photoluminescence (PL) reveals 67.5% of room temperature Internal Quantum Efficiency (IQE) at an emission peak of ∼455 nm with FWHM of 20 nm. Low temperature PL study shows clear improvement in emission intensity when conventional GaN buffer and GaN barrier are replaced by semi-bulk InGaN buffer in addition with InGaN barrier. Simulation confirms improved IQE and reduced efficiency droop when using semi-bulk as buffer which is attributed to the improved overlapping of electron-hole wave functions due to the reduced internal electric field from counteraction by surface polarization field. This efficiency improvement is very beneficial for high In content green LEDs where the efficiency is limited by polarization induced Quantum Confined Stark Effect (QCSE) for excess indium content.

  8. TEM study of dislocations structure in In0.82Ga0.18As/InP heterostructure with InGaAs as buffer layer

    NASA Astrophysics Data System (ADS)

    Zhao, Liang; Guo, Zuo-xing; Yuan, De-zeng; Wei, Qiu-lin; Zhao, Lei

    2016-05-01

    In order to improve the quality of detector, In x Ga1- x As ( x=0.82) buffer layer has been introduced in In0.82Ga0.18As/InP heterostructure. Dislocation behavior of the multilayer is analyzed through plane and cross section [110] by transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM). The dislocations are effectively suppressed in In x Ga1- x As ( x=0.82) buffer layer, and the density of dislocations in epilayer is reduced obviously. No lattice mismatch between buffer layer and epilayer results in no misfit dislocation (MD). The threading dislocations (TDs) are directly related to the multiplication of the MDs in buffer layer.

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

    DOE PAGES

    Ren, Fan; Pearton, Stephen J.; Ahn, Shihyun; ...

    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

  10. Improvement of luminescence properties of GaN buffer layer for fast nitride scintillator structures

    NASA Astrophysics Data System (ADS)

    Hubáček, T.; Hospodková, A.; Oswald, J.; Kuldová, K.; Pangrác, J.

    2017-04-01

    We have optimized technology of GaN buffer layer growth with respect to the application in fast scintillation structures. The deep defect luminescence so called yellow band (YB) with decay time up to tens of microseconds is undesired for these applications and should be suppressed or at least the ratio of intensities of excitonic to YB maximum has to be considerably increased. The required photoluminescence properties were achieved by optimization of growth parameters of nucleation and coalescence layer on sapphire substrate. We have shown that decrease of NH3 flow, decrease of coalescence temperature, increase of nucleation time and nucleation pressure lead to improvement of the structure and luminescence properties of the buffer layer. Results indicate a significant increased ratio of excitonic/YB luminescence intensity.

  11. Lattice-engineered Si1-xGex-buffer on Si(001) for GaP integration

    NASA Astrophysics Data System (ADS)

    Skibitzki, Oliver; Paszuk, Agnieszka; Hatami, Fariba; Zaumseil, Peter; Yamamoto, Yuji; Andreas Schubert, Markus; Trampert, Achim; Tillack, Bernd; Ted Masselink, W.; Hannappel, Thomas; Schroeder, Thomas

    2014-03-01

    We report a detailed structure and defect characterization study on gallium phosphide (GaP) layers integrated on silicon (Si) (001) via silicon-germanium (SiGe) buffer layers. The presented approach uses an almost fully relaxed SiGe buffer heterostructure of only 400 nm thickness whose in-plane lattice constant is matched to GaP—not at room but at GaP deposition temperature. Single crystalline, pseudomorphic 270 nm thick GaP is successfully grown by metalorganic chemical vapour deposition on a 400 nm Si0.85Ge0.15/Si(001) heterosystem, but carries a 0.08% tensile strain after cooling down to room temperature due to the bigger thermal expansion coefficient of GaP with respect to Si. Transmission electron microscopy (TEM) studies confirm the absence of misfit dislocations in the pseudomorphic GaP film but growth defects (e.g., stacking faults, microtwins, etc.) especially at the GaP/SiGe interface region are detected. We interpret these growth defects as a residue of the initial 3D island coalescence phase of the GaP film on the SiGe buffer. TEM-energy-dispersive x-ray spectroscopy studies reveal that these defects are often correlated with stoichiometric inhomogeneities in the GaP film. Time-of-flight Secondary ion mass spectrometry detects sharp heterointerfaces between GaP and SiGe films with a minor level of Ga diffusion into the SiGe buffer.

  12. Ultralow threading dislocation density in GaN epilayer on near-strain-free GaN compliant buffer layer and its applications in hetero-epitaxial LEDs

    PubMed Central

    Shih, Huan-Yu; Shiojiri, Makoto; Chen, Ching-Hsiang; Yu, Sheng-Fu; Ko, Chung-Ting; Yang, Jer-Ren; Lin, Ray-Ming; Chen, Miin-Jang

    2015-01-01

    High threading dislocation (TD) density in GaN-based devices is a long unresolved problem because of the large lattice mismatch between GaN and the substrate, which causes a major obstacle for the further improvement of next-generation high-efficiency solid-state lighting and high-power electronics. Here, we report InGaN/GaN LEDs with ultralow TD density and improved efficiency on a sapphire substrate, on which a near strain-free GaN compliant buffer layer was grown by remote plasma atomic layer deposition. This “compliant” buffer layer is capable of relaxing strain due to the absorption of misfit dislocations in a region within ~10 nm from the interface, leading to a high-quality overlying GaN epilayer with an unusual TD density as low as 2.2 × 105 cm−2. In addition, this GaN compliant buffer layer exhibits excellent uniformity up to a 6” wafer, revealing a promising means to realize large-area GaN hetero-epitaxy for efficient LEDs and high-power transistors. PMID:26329829

  13. Ultralow threading dislocation density in GaN epilayer on near-strain-free GaN compliant buffer layer and its applications in hetero-epitaxial LEDs.

    PubMed

    Shih, Huan-Yu; Shiojiri, Makoto; Chen, Ching-Hsiang; Yu, Sheng-Fu; Ko, Chung-Ting; Yang, Jer-Ren; Lin, Ray-Ming; Chen, Miin-Jang

    2015-09-02

    High threading dislocation (TD) density in GaN-based devices is a long unresolved problem because of the large lattice mismatch between GaN and the substrate, which causes a major obstacle for the further improvement of next-generation high-efficiency solid-state lighting and high-power electronics. Here, we report InGaN/GaN LEDs with ultralow TD density and improved efficiency on a sapphire substrate, on which a near strain-free GaN compliant buffer layer was grown by remote plasma atomic layer deposition. This "compliant" buffer layer is capable of relaxing strain due to the absorption of misfit dislocations in a region within ~10 nm from the interface, leading to a high-quality overlying GaN epilayer with an unusual TD density as low as 2.2 × 10(5) cm(-2). In addition, this GaN compliant buffer layer exhibits excellent uniformity up to a 6" wafer, revealing a promising means to realize large-area GaN hetero-epitaxy for efficient LEDs and high-power transistors.

  14. Growth of thicker zinc-blende CrSb layers by using (In,Ga)As buffer layers

    NASA Astrophysics Data System (ADS)

    Deng, J. J.; Zhao, J. H.; Bi, J. F.; Niu, Z. C.; Yang, F. H.; Wu, X. G.; Zheng, H. Z.

    2006-05-01

    Zinc-blende CrSb (zb-CrSb) layers with room-temperature ferromagnetism have been grown on (In,Ga)As buffer layers epitaxially prepared on (001) GaAs substrates by molecular-beam epitaxy. Compared with the typical thickness [2-3 ML (ML denotes monolayers)] of zb-CrSb grown directly on GaAs, the thickness of zb-CrSb grown on (In,Ga)As has been increased largely; the maximum can be up to ~9 ML. High-resolution cross sectional transmission electron microscopy images show that the zb-CrSb layer is combined with (In,Ga)As buffer layer without any dislocations at the interface.

  15. Growth of thicker zinc-blende CrSb layers by using (In,Ga)As buffer layers

    SciTech Connect

    Deng, J.J.; Zhao, J.H.; Bi, J.F.; Niu, Z.C.; Yang, F.H.; Wu, X.G.; Zheng, H.Z.

    2006-05-01

    Zinc-blende CrSb (zb-CrSb) layers with room-temperature ferromagnetism have been grown on (In,Ga)As buffer layers epitaxially prepared on (001) GaAs substrates by molecular-beam epitaxy. Compared with the typical thickness [2-3 ML (ML denotes monolayers)] of zb-CrSb grown directly on GaAs, the thickness of zb-CrSb grown on (In,Ga)As has been increased largely; the maximum can be up to {approx}9 ML. High-resolution cross sectional transmission electron microscopy images show that the zb-CrSb layer is combined with (In,Ga)As buffer layer without any dislocations at the interface.

  16. Metal contacts to n-GaN

    NASA Astrophysics Data System (ADS)

    Dobos, L.; Pécz, B.; Tóth, L.; Horváth, Zs. J.; Horváth, Z. E.; Tóth, A.; Horváth, E.; Beaumont, B.; Bougrioua, Z.

    2006-11-01

    Al, Au, Ti/Al and Ti/Au contacts were prepared on n-GaN and annealed up to 900 °C. The structure, phase and morphology were studied by cross-sectional transmission and scanning electron microscopy as well as by X-ray diffraction (XRD), the electrical behaviour by current-voltage measurements. It was obtained that annealing resulted in interdiffusion, lateral diffusion along the surface, alloying and bowling up of the metal layers. The current-voltage characteristics of as-deposited Al and Ti/Al contacts were linear, while the Au and Ti/Au contacts exhibited rectifying behaviour. Except the Ti/Au contact which became linear, the contacts degraded during heat treatment at 900 °C. The surface of Au and Ti/Au contacts annealed at 900 °C have shown fractal-like structures revealed by scanning electron microscopy. Transmission electron microscopy and XRD investigations of the Ti/Au contact revealed that Au diffused into the n-GaN layer at 900 °C. X-ray diffraction examinations showed, that new Ti 2N, Au 2Ga and Ga 3Ti 2 interface phases formed in Ti/Au contact at 900 °C, new Ti 2N phase formed in Ti/Al contact at 700 and 900 °C, as well as new AlN interface phase developed in Ti/Al contact at 900 °C.

  17. AlGaN/GaN high electron mobility transistors with intentionally doped GaN buffer using propane as carbon precursor

    NASA Astrophysics Data System (ADS)

    Bergsten, Johan; Li, Xun; Nilsson, Daniel; Danielsson, Örjan; Pedersen, Henrik; Janzén, Erik; Forsberg, Urban; Rorsman, Niklas

    2016-05-01

    AlGaN/GaN high electron mobility transistors (HEMTs) fabricated on a heterostructure grown by metalorganic chemical vapor deposition using an alternative method of carbon (C) doping the buffer are characterized. C-doping is achieved by using propane as precursor, as compared to tuning the growth process parameters to control C-incorporation from the gallium precursor. This approach allows for optimization of the GaN growth conditions without compromising material quality to achieve semi-insulating properties. The HEMTs are evaluated in terms of isolation and dispersion. Good isolation with OFF-state currents of 2 × 10-6 A/mm, breakdown fields of 70 V/µm, and low drain induced barrier lowering of 0.13 mV/V are found. Dispersive effects are examined using pulsed current-voltage measurements. Current collapse and knee walkout effects limit the maximum output power to 1.3 W/mm. With further optimization of the C-doping profile and GaN material quality this method should offer a versatile approach to decrease dispersive effects in GaN HEMTs.

  18. High Quality GaAs Growth by MBE on Si Using GeSi Buffers and Prospects for Space Photovoltaics

    NASA Technical Reports Server (NTRS)

    Carlin, J. A.; Ringel, S. A.; Fitzgerald, E. A.; Bulsara, M.

    2005-01-01

    III-V solar cells on Si substrates are of interest for space photovoltaics since this would combine high performance space cells with a strong, lightweight and inexpensive substrate. However, the primary obstacles blocking III-V/Si cells from achieving high performance to date have been fundamental materials incompatabilities, namely the 4% lattice mismatch between GaAs and Si, and the large mismatch in thermal expansion coefficient. In this paper, we report on the molecular beam epitaxial (MBE) growth and properties of GaAs layers and single junction GaAs cells on Si wafers which utilize compositionally graded GeSi Intermediate buffers grown by ultra-high vacuum chemical vapor deposition (UHVCVD) to mitigate the large lattice mismatch between GaAs and Si. Ga As cell structures were found to incorporate a threading dislocation density of 0.9-1.5 x 10 (exp 6) per square centimeter, identical to the underlying relaxed Ge cap of the graded buffer, via a combination of transmission electron microscopy, electron beam induced current, and etch pit density measurements. AlGaAs/GaAs double heterostructures wre grown on the GeSi/Si substrates for time-resolved photoluminescence measurements, which revealed a bulk GaAs minority carrier lifetime in excess of 10 ns, the highest lifetime ever reported for GaAs on Si. A series of growth were performed to ass3ss the impact of a GaAs buffer to a thickness of only 0.1 micrometer. Secondary ion mass spectroscopy studies revealed that there is negligible cross diffusion of Ga, As and Ge at he III-V/Ge interface, identical to our earlier findings for GaAs grown on Ge wafers using MBE. This indicates that there is no need for a buffer to "bury" regions of high autodopjing,a nd that either pn or np configuration cells are easily accomodated by these substrates. Preliminary diodes and single junction Al Ga As heteroface cells were grown and fabricated on the Ge/GeSi/Si substrates for the first time. Diodes fabricated on GaAs, Ge and Ge

  19. Characteristics of GaN-based light emitting diodes with different thicknesses of buffer layer grown by HVPE and MOCVD

    NASA Astrophysics Data System (ADS)

    Tian, Pengfei; Edwards, Paul R.; Wallace, Michael J.; Martin, Robert W.; McKendry, Jonathan J. D.; Gu, Erdan; Dawson, Martin D.; Qiu, Zhi-Jun; Jia, Chuanyu; Chen, Zhizhong; Zhang, Guoyi; Zheng, Lirong; Liu, Ran

    2017-02-01

    GaN-based light emitting diodes (LEDs) have been fabricated on sapphire substrates with different thicknesses of GaN buffer layer grown by a combination of hydride vapor phase epitaxy and metalorganic chemical vapor deposition. We analyzed the LED efficiency and modulation characteristics with buffer thicknesses of 12 μm and 30 μm. With the buffer thickness increase, cathodoluminescence hyperspectral imaging shows that the dislocation density in the buffer layer decreases from  ∼1.3  ×  108 cm‑2 to  ∼1.0  ×  108 cm‑2, and Raman spectra suggest that the compressive stress in the quantum wells is partly relaxed, which leads to a large blue shift in the peak emission wavelength of the photoluminescence and electroluminescent spectra. The combined effects of the low dislocation density and stress relaxation lead to improvements in the efficiency of LEDs with the 30 μm GaN buffer, but the electrical-to-optical modulation bandwidth is higher for the LEDs with the 12 μm GaN buffer. A rate equation analysis suggests that defect-related nonradiative recombination can help increase the modulation bandwidth but reduce the LED efficiency at low currents, suggesting that a compromise should be made in the choice of defect density.

  20. Single-photon emission at 1.55 μm from MOVPE-grown InAs quantum dots on InGaAs/GaAs metamorphic buffers

    NASA Astrophysics Data System (ADS)

    Paul, Matthias; Olbrich, Fabian; Höschele, Jonatan; Schreier, Susanne; Kettler, Jan; Portalupi, Simone Luca; Jetter, Michael; Michler, Peter

    2017-07-01

    By metal-organic vapor-phase epitaxy, we have fabricated InAs quantum dots (QDs) on InGaAs/GaAs metamorphic buffer layers on a GaAs substrate with area densities that allow addressing single quantum dots. The photoluminescence emission from the quantum dots is shifted to the telecom C-band at 1.55 μm with a high yield due to the reduced stress in the quantum dots. The lowered residual strain at the surface of the metamorphic buffer layer results in a reduced lattice mismatch between the quantum dot material and growth surface. The quantum dots exhibit resolution-limited linewidths (mean value: 59 μeV) and low fine-structure splittings. Furthermore, we demonstrate single-photon emission ( g ( 2 ) ( 0 ) = 0.003 ) at 1.55 μm and decay times on the order of 1.4 ns comparable to InAs QDs directly deposited on GaAs substrates. Our results suggest that these quantum dots can not only compete with their counterparts deposited on InP substrates but also constitute an InAs/GaAs-only approach for the development of non-classical light sources in the telecom C-band.

  1. Investigation of buffer traps in AlGaN/GaN-on-Si devices by thermally stimulated current spectroscopy and back-gating measurement

    SciTech Connect

    Yang, Shu; Zhou, Chunhua; Jiang, Qimeng; Chen, Kevin J.; Lu, Jianbiao; Huang, Baoling

    2014-01-06

    Thermally stimulated current (TSC) spectroscopy and high-voltage back-gating measurement are utilized to study GaN buffer traps specific to AlGaN/GaN lateral heterojunction structures grown on a low-resistivity Si substrate. Three dominating deep-level traps in GaN buffer with activation energies of ΔE{sub T1} ∼ 0.54 eV, ΔE{sub T2} ∼ 0.65 eV, and ΔE{sub T3} ∼ 0.75 eV are extracted from TSC spectroscopy in a vertical GaN-on-Si structure. High back-gate bias applied to the Si substrate could influence the drain current in an AlGaN/GaN-on-Si high-electron-mobility transistor in a way that cannot be explained with a simple field-effect model. By correlating the trap states identified in TSC with the back-gating measurement results, it is proposed that the ionization/deionization of both donor and acceptor traps are responsible for the generation of buffer space charges, which impose additional modulation to the 2DEG channel.

  2. Effects of grazing management and buffer strips on metal runoff from pastures fertilized with poultry litter

    USDA-ARS?s Scientific Manuscript database

    Metal runoff from fields fertilized with poultry litter may pose a threat to aquatic systems. Buffer strips have been added to fields to reduce nutrients and solids runoff. However, scant information exists on the effects of buffer strips combined with grazing management strategies on metal runoff f...

  3. Dataset representing the effect of indirect band gap region of Cd-free AlGaAs buffer layer in Cu(In,Ga)Se photovoltaic cell.

    PubMed

    Shachi, Sadia Islam; Bahar, Ali Newaz

    2017-10-01

    The dataset of physical properties for the proposed CIGS solar cell with Cd-free AlGaAs buffer layer has been depicted in this data article. The cell performance outcome due to different AlGaAs buffer layer band gap is reported along with optimum solar cell performance parameters for instance, open circuit voltage [Formula: see text], short circuit current density ([Formula: see text], fill factor [Formula: see text], efficiency [Formula: see text], as well as collection efficiency [Formula: see text].

  4. Nearly 4-Inch-Diameter Free-Standing GaN Wafer Fabricated by Hydride Vapor Phase Epitaxy with Pit-Inducing Buffer Layer

    NASA Astrophysics Data System (ADS)

    Sato, Tadashige; Okano, Shinya; Goto, Takenari; Yao, Takafumi; Seto, Ritsu; Sato, Akira; Goto, Hideki

    2013-08-01

    A free-standing GaN wafer was fabricated by depositing a GaN buffer that induced the formation of pits (hereafter, pit-inducing GaN buffer) on a low-temperature-grown GaN buffer on the sapphire substrate. A high-temperature-grown GaN layer was grown on the pit-inducing GaN buffer that induced the formation of pits on the high-temperature-grown GaN layer. The pit-inducing buffer suppresses crack formation in the thick GaN film thereby releasing growth stress. Thermal stress in GaN on a sapphire system is also discussed on the basis of calculations utilizing a bilayer model. We have succeeded in the fabrication of a nearly 4-in.-diameter free-standing GaN thick wafer with a pit-inducing GaN buffer by one-stop hydride vapor phase epitaxy, which will lead to a low-cost fabrication of free-standing GaN wafers.

  5. Growth and Magnetic Properties of Zincblende CrSb Epilayers on Relaxed and Strained (In, Ga)As Buffers

    NASA Astrophysics Data System (ADS)

    Deng, Jia-Jun; Zhao, Jian-Hua; Bi, Jing-Feng; Zheng, Yu-Hong; Jia, Quan-Jie; Niu, Zhi-Chuan; Wu, Xiao-Guang; Zheng, Hou-Zhi

    2006-02-01

    Zincblende CrSb (zb-CrSb) layers with room-temperature ferromagnetism have been grown on relaxed and strained (In,Ga)As buffer layers epitaxially prepared on (001) GaAs substrates by molecular-beam epitaxy. The structural characterizations of CrSb layers fabricated under the two cases are studied by using synchrotron grazing incidence x-ray diffraction (GID). The results of GID experiments indicate that no sign of second phase exists in all the zb-CrSb layers. Superconducting quantum interference device measurements demonstrate that the thickness of zb-CrSb layers grown on both relaxed and strained (In,Ga)As buffer layers can be increased to ~12 monolayers (~3.6 nm), compared to ~3 monolayers (~1 nm) on GaAs directly.

  6. Selectively Enhanced UV-A Photoresponsivity of a GaN MSM UV Photodetector with a Step-Graded AlxGa1−xN Buffer Layer

    PubMed Central

    Lee, Chang-Ju; Won, Chul-Ho; Lee, Jung-Hee; Hahm, Sung-Ho; Park, Hongsik

    2017-01-01

    The UV-to-visible rejection ratio is one of the important figure of merits of GaN-based UV photodetectors. For cost-effectiveness and large-scale fabrication of GaN devices, we tried to grow a GaN epitaxial layer on silicon substrate with complicated buffer layers for a stress-release. It is known that the structure of the buffer layers affects the performance of devices fabricated on the GaN epitaxial layers. In this study, we show that the design of a buffer layer structure can make effect on the UV-to-visible rejection ratio of GaN UV photodetectors. The GaN photodetector fabricated on GaN-on-silicon substrate with a step-graded AlxGa−xN buffer layer has a highly-selective photoresponse at 365-nm wavelength. The UV-to-visible rejection ratio of the GaN UV photodetector with the step-graded AlxGa1−xN buffer layer was an order-of-magnitude higher than that of a photodetector with a conventional GaN/AlN multi buffer layer. The maximum photoresponsivity was as high as 5 × 10−2 A/W. This result implies that the design of buffer layer is important for photoresponse characteristics of GaN UV photodetectors as well as the crystal quality of the GaN epitaxial layers. PMID:28753989

  7. High-quality III-nitride films on conductive, transparent (2̅01)-oriented β-Ga2O3 using a GaN buffer layer.

    PubMed

    Muhammed, M M; Roldan, M A; Yamashita, Y; Sahonta, S-L; Ajia, I A; Iizuka, K; Kuramata, A; Humphreys, C J; Roqan, I S

    2016-07-14

    We demonstrate the high structural and optical properties of InxGa1-xN epilayers (0 ≤ x ≤ 23) grown on conductive and transparent (01)-oriented β-Ga2O3 substrates using a low-temperature GaN buffer layer rather than AlN buffer layer, which enhances the quality and stability of the crystals compared to those grown on (100)-oriented β-Ga2O3. Raman maps show that the 2″ wafer is relaxed and uniform. Transmission electron microscopy (TEM) reveals that the dislocation density reduces considerably (~4.8 × 10(7) cm(-2)) at the grain centers. High-resolution TEM analysis demonstrates that most dislocations emerge at an angle with respect to the c-axis, whereas dislocations of the opposite phase form a loop and annihilate each other. The dislocation behavior is due to irregular (01) β-Ga2O3 surface at the interface and distorted buffer layer, followed by relaxed GaN epilayer. Photoluminescence results confirm high optical quality and time-resolved spectroscopy shows that the recombination is governed by bound excitons. We find that a low root-mean-square average (≤1.5 nm) of InxGa1-xN epilayers can be achieved with high optical quality of InxGa1-xN epilayers. We reveal that (01)-oriented β-Ga2O3 substrate has a strong potential for use in large-scale high-quality vertical light emitting device design.

  8. High-quality III-nitride films on conductive, transparent (2̅01)-oriented β-Ga2O3 using a GaN buffer layer

    PubMed Central

    Muhammed, M. M.; Roldan, M. A.; Yamashita, Y.; Sahonta, S.-L.; Ajia, I. A.; Iizuka, K.; Kuramata, A.; Humphreys, C. J.; Roqan, I. S.

    2016-01-01

    We demonstrate the high structural and optical properties of InxGa1−xN epilayers (0 ≤ x ≤ 23) grown on conductive and transparent (01)-oriented β-Ga2O3 substrates using a low-temperature GaN buffer layer rather than AlN buffer layer, which enhances the quality and stability of the crystals compared to those grown on (100)-oriented β-Ga2O3. Raman maps show that the 2″ wafer is relaxed and uniform. Transmission electron microscopy (TEM) reveals that the dislocation density reduces considerably (~4.8 × 107 cm−2) at the grain centers. High-resolution TEM analysis demonstrates that most dislocations emerge at an angle with respect to the c-axis, whereas dislocations of the opposite phase form a loop and annihilate each other. The dislocation behavior is due to irregular (01) β-Ga2O3 surface at the interface and distorted buffer layer, followed by relaxed GaN epilayer. Photoluminescence results confirm high optical quality and time-resolved spectroscopy shows that the recombination is governed by bound excitons. We find that a low root-mean-square average (≤1.5 nm) of InxGa1−xN epilayers can be achieved with high optical quality of InxGa1−xN epilayers. We reveal that (01)-oriented β-Ga2O3 substrate has a strong potential for use in large-scale high-quality vertical light emitting device design. PMID:27412372

  9. High-quality III-nitride films on conductive, transparent (2̅01)-oriented β-Ga2O3 using a GaN buffer layer

    NASA Astrophysics Data System (ADS)

    Muhammed, M. M.; Roldan, M. A.; Yamashita, Y.; Sahonta, S.-L.; Ajia, I. A.; Iizuka, K.; Kuramata, A.; Humphreys, C. J.; Roqan, I. S.

    2016-07-01

    We demonstrate the high structural and optical properties of InxGa1‑xN epilayers (0 ≤ x ≤ 23) grown on conductive and transparent (01)-oriented β-Ga2O3 substrates using a low-temperature GaN buffer layer rather than AlN buffer layer, which enhances the quality and stability of the crystals compared to those grown on (100)-oriented β-Ga2O3. Raman maps show that the 2″ wafer is relaxed and uniform. Transmission electron microscopy (TEM) reveals that the dislocation density reduces considerably (~4.8 × 107 cm‑2) at the grain centers. High-resolution TEM analysis demonstrates that most dislocations emerge at an angle with respect to the c-axis, whereas dislocations of the opposite phase form a loop and annihilate each other. The dislocation behavior is due to irregular (01) β-Ga2O3 surface at the interface and distorted buffer layer, followed by relaxed GaN epilayer. Photoluminescence results confirm high optical quality and time-resolved spectroscopy shows that the recombination is governed by bound excitons. We find that a low root-mean-square average (≤1.5 nm) of InxGa1‑xN epilayers can be achieved with high optical quality of InxGa1‑xN epilayers. We reveal that (01)-oriented β-Ga2O3 substrate has a strong potential for use in large-scale high-quality vertical light emitting device design.

  10. Growing GaN LEDs on amorphous SiC buffer with variable C/Si compositions.

    PubMed

    Cheng, Chih-Hsien; Tzou, An-Jye; Chang, Jung-Hung; Chi, Yu-Chieh; Lin, Yung-Hsiang; Shih, Min-Hsiung; Lee, Chao-Kuei; Wu, Chih-I; Kuo, Hao-Chung; Chang, Chun-Yen; Lin, Gong-Ru

    2016-01-22

    The epitaxy of high-power gallium nitride (GaN) light-emitting diode (LED) on amorphous silicon carbide (a-SixC(1-x)) buffer is demonstrated. The a-SixC(1-x) buffers with different nonstoichiometric C/Si composition ratios are synthesized on SiO2/Si substrate by using a low-temperature plasma enhanced chemical vapor deposition. The GaN LEDs on different SixC(1-x) buffers exhibit different EL and C-V characteristics because of the extended strain induced interfacial defects. The EL power decays when increasing the Si content of SixC(1-x) buffer. The C-rich SixC(1-x) favors the GaN epitaxy and enables the strain relaxation to suppress the probability of Auger recombination. When the SixC(1-x) buffer changes from Si-rich to C-rich condition, the EL peak wavelengh shifts from 446 nm to 450 nm. Moreover, the uniform distribution contour of EL intensity spreads between the anode and the cathode because the traping density of the interfacial defect gradually reduces. In comparison with the GaN LED grown on Si-rich SixC(1-x) buffer, the device deposited on C-rich SixC(1-x) buffer shows a lower turn-on voltage, a higher output power, an external quantum efficiency, and an efficiency droop of 2.48 V, 106 mW, 42.3%, and 7%, respectively.

  11. Growing GaN LEDs on amorphous SiC buffer with variable C/Si compositions

    PubMed Central

    Cheng, Chih-Hsien; Tzou, An-Jye; Chang, Jung-Hung; Chi, Yu-Chieh; Lin, Yung-Hsiang; Shih, Min-Hsiung; Lee, Chao-Kuei; Wu, Chih-I; Kuo, Hao-Chung; Chang, Chun-Yen; Lin, Gong-Ru

    2016-01-01

    The epitaxy of high-power gallium nitride (GaN) light-emitting diode (LED) on amorphous silicon carbide (a-SixC1−x) buffer is demonstrated. The a-SixC1−x buffers with different nonstoichiometric C/Si composition ratios are synthesized on SiO2/Si substrate by using a low-temperature plasma enhanced chemical vapor deposition. The GaN LEDs on different SixC1−x buffers exhibit different EL and C-V characteristics because of the extended strain induced interfacial defects. The EL power decays when increasing the Si content of SixC1−x buffer. The C-rich SixC1−x favors the GaN epitaxy and enables the strain relaxation to suppress the probability of Auger recombination. When the SixC1−x buffer changes from Si-rich to C-rich condition, the EL peak wavelengh shifts from 446 nm to 450 nm. Moreover, the uniform distribution contour of EL intensity spreads between the anode and the cathode because the traping density of the interfacial defect gradually reduces. In comparison with the GaN LED grown on Si-rich SixC1−x buffer, the device deposited on C-rich SixC1−x buffer shows a lower turn-on voltage, a higher output power, an external quantum efficiency, and an efficiency droop of 2.48 V, 106 mW, 42.3%, and 7%, respectively. PMID:26794268

  12. Growing GaN LEDs on amorphous SiC buffer with variable C/Si compositions

    NASA Astrophysics Data System (ADS)

    Cheng, Chih-Hsien; Tzou, An-Jye; Chang, Jung-Hung; Chi, Yu-Chieh; Lin, Yung-Hsiang; Shih, Min-Hsiung; Lee, Chao-Kuei; Wu, Chih-I.; Kuo, Hao-Chung; Chang, Chun-Yen; Lin, Gong-Ru

    2016-01-01

    The epitaxy of high-power gallium nitride (GaN) light-emitting diode (LED) on amorphous silicon carbide (a-SixC1‑x) buffer is demonstrated. The a-SixC1‑x buffers with different nonstoichiometric C/Si composition ratios are synthesized on SiO2/Si substrate by using a low-temperature plasma enhanced chemical vapor deposition. The GaN LEDs on different SixC1‑x buffers exhibit different EL and C-V characteristics because of the extended strain induced interfacial defects. The EL power decays when increasing the Si content of SixC1‑x buffer. The C-rich SixC1‑x favors the GaN epitaxy and enables the strain relaxation to suppress the probability of Auger recombination. When the SixC1‑x buffer changes from Si-rich to C-rich condition, the EL peak wavelengh shifts from 446 nm to 450 nm. Moreover, the uniform distribution contour of EL intensity spreads between the anode and the cathode because the traping density of the interfacial defect gradually reduces. In comparison with the GaN LED grown on Si-rich SixC1‑x buffer, the device deposited on C-rich SixC1‑x buffer shows a lower turn-on voltage, a higher output power, an external quantum efficiency, and an efficiency droop of 2.48 V, 106 mW, 42.3%, and 7%, respectively.

  13. Opportunities and challenges in GaN metal organic chemical vapor deposition for electron devices

    NASA Astrophysics Data System (ADS)

    Matsumoto, Koh; Yamaoka, Yuya; Ubukata, Akinori; Arimura, Tadanobu; Piao, Guanxi; Yano, Yoshiki; Tokunaga, Hiroki; Tabuchi, Toshiya

    2016-05-01

    The current situation and next challenge in GaN metal organic chemical vapor deposition (MOCVD) for electron devices of both GaN on Si and GaN on GaN are presented. We have examined the possibility of increasing the growth rate of GaN on 200-mm-diameter Si by using a multiwafer production MOCVD machine, in which the vapor phase parasitic reaction is well controlled. The impact of a high-growth-rate strained-layer-superlattice (SLS) buffer layer is presented in terms of material properties. An SLS growth rate of as high as 3.46 µm/h, which was 73% higher than the current optimum, was demonstrated. As a result, comparable material properties were obtained. Next, a typical result of GaN doped with Si of 1 × 1016 cm-3 grown at the growth rate of 3.7 µm/h is shown. For high-voltage application, we need a thick high-purity GaN drift layer with a low carbon concentration, of less than 1016 cm-3. It is shown that achieving a high growth rate by precise control of the vapor phase reaction is still challenge in GaN MOCVD.

  14. Reducing interface recombination for Cu(In,Ga)Se{sub 2} by atomic layer deposited buffer layers

    SciTech Connect

    Hultqvist, Adam; Bent, Stacey F.; Li, Jian V.; Kuciauskas, Darius; Dippo, Patricia; Contreras, Miguel A.; Levi, Dean H.

    2015-07-20

    Partial CuInGaSe{sub 2} (CIGS) solar cell stacks with different atomic layer deposited buffer layers and pretreatments were analyzed by photoluminescence (PL) and capacitance voltage (CV) measurements to investigate the buffer layer/CIGS interface. Atomic layer deposited ZnS, ZnO, and SnO{sub x} buffer layers were compared with chemical bath deposited CdS buffer layers. Band bending, charge density, and interface state density were extracted from the CV measurement using an analysis technique new to CIGS. The surface recombination velocity calculated from the density of interface traps for a ZnS/CIGS stack shows a remarkably low value of 810 cm/s, approaching the range of single crystalline II–VI systems. Both the PL spectra and its lifetime depend on the buffer layer; thus, these measurements are not only sensitive to the absorber but also to the absorber/buffer layer system. Pretreatment of the CIGS prior to the buffer layer deposition plays a significant role on the electrical properties for the same buffer layer/CIGS stack, further illuminating the importance of good interface formation. Finally, ZnS is found to be the best performing buffer layer in this study, especially if the CIGS surface is pretreated with potassium cyanide.

  15. Reducing interface recombination for Cu(In,Ga)Se 2 by atomic layer deposited buffer layers

    SciTech Connect

    Hultqvist, Adam; Li, Jian V.; Kuciauskas, Darius; Dippo, Patricia; Contreras, Miguel A.; Levi, Dean H.; Bent, Stacey F.

    2015-07-20

    Partial CuInGaSe2 (CIGS) solar cell stacks with different atomic layer deposited buffer layers and pretreatments were analyzed by photoluminescence (PL) and capacitance voltage (CV) measurements to investigate the buffer layer/CIGS interface. Atomic layer deposited ZnS, ZnO, and SnOx buffer layers were compared with chemical bath deposited CdS buffer layers. Band bending, charge density, and interface state density were extracted from the CV measurement using an analysis technique new to CIGS. The surface recombination velocity calculated from the density of interface traps for a ZnS/CIGS stack shows a remarkably low value of 810 cm/s, approaching the range of single crystalline II-VI systems. Both the PL spectra and its lifetime depend on the buffer layer; thus, these measurements are not only sensitive to the absorber but also to the absorber/buffer layer system. Pretreatment of the CIGS prior to the buffer layer deposition plays a significant role on the electrical properties for the same buffer layer/CIGS stack, further illuminating the importance of good interface formation. Finally, ZnS is found to be the best performing buffer layer in this study, especially if the CIGS surface is pretreated with potassium cyanide.

  16. Orientation-controlled epitaxial lateral overgrowth of semipolar GaN on Si(001) with a directionally sputtered AlN buffer layer

    NASA Astrophysics Data System (ADS)

    Lee, Ho-Jun; Bae, Si-Young; Lekhal, Kaddour; Tamura, Akira; Suzuki, Takafumi; Kushimoto, Maki; Honda, Yoshio; Amano, Hiroshi

    2017-06-01

    We successfully grew semipolar (10 1 ̅ 3) and (10 1 ̅ 5) GaN films on Si(001) substrates employing metal-organic chemical vapor deposition (MOCVD) by inserting a directionally sputtered AlN (DS-AlN) buffer layer. To improve the crystal quality of the orientation-controlled semipolar (10 1 ̅ 3) and (10 1 ̅ 5) GaN films, a two-step epitaxial lateral overgrowth (ELO) process was performed with a striped mask. According to low-temperature cathodoluminescence (LT-CL) characterization, the ELO results in a coalesced morphology and a low defect density of <2.72×108 cm-2 for both semipolar (10 1 ̅ 3) and (10 1 ̅ 5) GaN films. For comparing the properties of planar and ELO semipolar GaN, a rocking curve of x-ray diffraction (XRD) and low-temperature photoluminescence (LT-PL) spectra was measured. The crystal orientation of semipolar GaN films was confirmed using electron backscatter diffraction (EBSD).

  17. Spectroscopic, radiochemical, and theoretical studies of the Ga3+-N-2-hydroxyethyl piperazine-N'-2-ethanesulfonic acid (HEPES buffer) system: evidence for the formation of Ga3+ - HEPES complexes in (68) Ga labeling reactions.

    PubMed

    Martins, André F; Prata, M I M; Rodrigues, S P J; Geraldes, Carlos F G C; Riss, P J; Amor-Coarasa, A; Burchardt, C; Kroll, C; Roesch, F

    2013-01-01

    Recent reports have claimed a superior performance of HEPES buffer in comparison to alternative buffer systems for (67/68) Ga labeling in aqueous media. In this paper we report spectroscopic ((1) H and (71) Ga NMR), radiochemical, mass spectrometry and theoretical modeling studies on the Ga(3+)/HEPES system (HEPES = N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid) performed with the aim of elucidating a potential contribution of HEPES in the (68/67) Ga radiolabeling process. Our results demonstrate that HEPES acts as a weakly but competitive chelator of Ga(3+) and that this interaction depends on the relative Ga(3+): HEPES concentration. A by-product formed in the labeling mixture has been identified as a [(68) Ga]Ga(HEPES) complex via chromatographic comparison with the nonradioactive analog. The formation of this complex was verified to compete with [(68) Ga]Ga(NOTA) complexation at low NOTA concentration. Putative chelation of Ga(3+) by the hydroxyl and adjacent ring nitrogen of HEPES is proposed on the basis of (1)H NMR shifts induced by Ga(3+) and theoretical modeling studies.

  18. Nitrogen-Polar (0001¯) GaN Grown on c-Plane Sapphire with a High-Temperature AlN Buffer

    PubMed Central

    Song, Jie; Han, Jung

    2017-01-01

    We demonstrate growing nitrogen-polar (N-polar) GaN epilayer on c-plane sapphire using a thin AlN buffer layer by metalorganic chemical vapor deposition. We have studied the influence of the AlN buffer layer on the polarity, crystalline quality, and surface morphology of the GaN epilayer and found that the growth temperature of the AlN buffer layer played a critical role in the growth of the GaN epilayer. The low growth temperature of the AlN buffer results in gallium-polar GaN. Even a nitridation process has been conducted. High growth temperature for an AlN buffer layer is required to achieve pure N-polarity, high crystalline quality, and smooth surface morphology for a GaN epilayer. PMID:28772612

  19. Metamorphic InAlAs/InGaAs/InAlAs/GaAs HEMT heterostructures containing strained superlattices and inverse steps in the metamorphic buffer

    NASA Astrophysics Data System (ADS)

    Galiev, G. B.; Vasil'evskii, I. S.; Pushkarev, S. S.; Klimov, Е. А.; Imamov, R. M.; Buffat, P. A.; Dwir, B.; Suvorova, Е. I.

    2013-03-01

    Metamorphic InхAl1-хAs buffer design features influence on electrophysical and structural properties of the heterostructures was investigated. Two types of MHEMT heterostructures In0.70Al0.30As/In0.76Ga0.24As with novel design contained inverse steps or strained superlattices were grown by MBE on GaAs substrates. Electrophysical properties of the heterostructures were characterized by Hall measurements, while the structural features were described with the help of different transmission electron microscopy techniques. The metamorphic HEMT with strained superlattices inserted in the metamorphic buffer had the smoother surface and more defect-free crystal structure, as well as a higher Hall mobility, than metamorphic HEMT with inverse steps within the metamorphic buffer.

  20. The effect of the carbon nanotube buffer layer on the performance of a Li metal battery.

    PubMed

    Zhang, Ding; Zhou, Yi; Liu, Changhong; Fan, Shoushan

    2016-06-07

    Lithium (Li) metal is one of the most promising candidates as an anode for the next-generation energy storage systems because of its high specific capacity and lowest negative electrochemical potential. But the growth of Li dendrites limits the application of the Li metal battery. In this work, a type of modified Li metal battery with a carbon nanotube (CNT) buffer layer inserted between the separator and the Li metal electrode was reported. The electrochemical results show that the modified batteries have a much better rate capability and cycling performance than the conventional Li metal batteries. The mechanism study by electrochemical impedance spectroscopy reveals that the modified battery has a smaller charge transfer resistance and larger Li ion diffusion coefficient during the deposition process on the Li electrode than the conventional Li metal batteries. Symmetric battery tests show that the interfacial behavior of the Li metal electrode with the buffer layer is more stable than the naked Li metal electrode. The morphological characterization of the CNT buffer layer and Li metal lamina reveals that the CNT buffer layer has restrained the growth of Li dendrites. The CNT buffer layer has great potential to solve the safety problem of the Li metal battery.

  1. Conduction band offset engineering in wide-bandgap Ag(In,Ga)Se2 solar cells by hybrid buffer layer

    NASA Astrophysics Data System (ADS)

    Umehara, Takeshi; Zulkifly, Faris Akira Bin Mohd; Nakada, Kazuyoshi; Yamada, Akira

    2017-08-01

    Ag(In,Ga)Se2 (AIGS) is one of the promising candidates for the top cell absorber in the tandem structure. However, the conversion efficiency of AIGS solar cells is still lower than that required for the top cell. In this study, to improve the conversion efficiency of AIGS solar cells, we controlled the conduction band offset (CBO) at the buffer layer/ZnO and buffer layer/AIGS interfaces. The reduction in interface recombination at the CdS buffer layer/AIGS interface was achieved by introducing a ZnS(O,OH) buffer layer instead of a CdS buffer layer, although the fill factor (FF) decreased markedly because the CBO at the ZnS(O,OH)/ZnO interface prevented the electron flow under a forward bias. We found that the introduction of a CdS/ZnS(O,OH) hybrid buffer layer is efficient in controlling the CBO at both the buffer layer/AIGS and buffer layer/ZnO interfaces and improving the solar cell conversion efficiency.

  2. Crystallographic tilt and in-plane anisotropies of an a-plane InGaN/GaN layered structure grown by MOCVD on r-plane sapphire using a ZnO buffer

    NASA Astrophysics Data System (ADS)

    Liu, H. F.; Liu, W.; Guo, S.; Chi, D. Z.

    2016-03-01

    High-resolution x-ray diffraction (HRXRD) was used to investigate the crystallographic tilts and structural anisotropies in epitaxial nonpolar a-plane InGaN/GaN grown by metal-organic chemical vapor deposition on r-plane sapphire using a ZnO buffer. The substrate had an unintentional miscut of 0.14° towards its [-4 2 2 3] axis. However, HRXRD revealed a tilt of 0.26° (0.20°) between the ZnO (GaN) (11-20) and the Al2O3 (1-102) atomic planes, with the (11-20) axis of ZnO (GaN) tilted towards its c-axis, which has a difference of 163° in azimuth from that of the substrate’s miscut. Excess broadenings in the GaN/ZnO (11-20) rocking curves (RCs) were observed along its c-axis. Specific analyses revealed that partial dislocations and anisotropic in-plane strains, rather than surface-related effects, wafer curvature or stacking faults, are the dominant factors for the structural anisotropy. The orientation of the partial dislocations is most likely affected by the miscut of the substrate, e.g. via tilting of the misfit dislocation gliding planes created during island coalescences. Their Burgers vector components in the growth direction, in turn, gave rise to crystallographic tilts in the same direction as that of the excess RC-broadenings.

  3. Buffer layers on metal alloy substrates for superconducting tapes

    DOEpatents

    Jia, Quanxi; Foltyn, Stephen R.; Arendt, Paul N.; Groves, James R.

    2004-10-05

    An article including a substrate, at least one intermediate layer upon the surface of the substrate, a layer of an oriented cubic oxide material having a rock-salt-like structure upon the at least one intermediate layer, and a layer of a SrRuO.sub.3 buffer material upon the oriented cubic oxide material layer is provided together with additional layers such as a HTS top-layer of YBCO directly upon the layer of a SrRuO.sub.3 buffer material layer. With a HTS top-layer of YBCO upon at least one layer of the SrRuO.sub.3 buffer material in such an article, J.sub.c 's of up to 1.3.times.10.sup.6 A/cm.sup.2 have been demonstrated with projected I.sub.c 's of over 200 Amperes across a sample 1 cm wide.

  4. MOCVD of BN and GaN thin films on silicon: new attempt of GaN growth with BN buffer layer

    NASA Astrophysics Data System (ADS)

    Boo, Jin-Hyo; Rohr, Carsten; Ho, Wilson

    1998-06-01

    Highly oriented polycrystalline h-BN thin films were deposited on silicon substrates in the temperature range of 600-900°C from the single molecular precursor of borane-triethylamine complex, (C 2H 5) 3N : BH 3, by supersonic jet assisted chemical vapor deposition. Hydrogen was used as carrier gas, and additional nitrogen was supplied by either ammonia through a nozzle or nitrogen via a remote microwave plasma. Hexagonal GaN films were also grown on Si(1 0 0) with h-BN buffer layers at temperatures between 550 and 750°C with dual supersonic molecular beam sources. Triethylgallium, (C 2H 5) 3Ga, and ammonia, NH 3, were used as precursors. Hydrogen was used as seeding gas for the precursors, providing a wide range of possible kinetic energies for the supersonic beams. The h-BN buffer layers and the GaN films were characterized in situ by Auger electron spectroscopy (AES), and ex situ by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and optical transmission. This is the first report of growing the h-BN films on silicon substrates from the single source precursor of borane-triethylamine complex and new attempts of GaN film growth on silicon with BN buffer layer.

  5. Heteroepitaxial growth of In{sub 0.30}Ga{sub 0.70}As high-electron mobility transistor on 200 mm silicon substrate using metamorphic graded buffer

    SciTech Connect

    Kohen, David Nguyen, Xuan Sang; Made, Riko I; Lee, Kwang Hong; Lee, Kenneth Eng Kian; Yadav, Sachin; Kumar, Annie; Gong, Xiao; Yeo, Yee Chia; Heidelberger, Christopher; Yoon, Soon Fatt; Fitzgerald, Eugene A.

    2016-08-15

    We report on the growth of an In{sub 0.30}Ga{sub 0.70}As channel high-electron mobility transistor (HEMT) on a 200 mm silicon wafer by metal organic vapor phase epitaxy. By using a 3 μm thick buffer comprising a Ge layer, a GaAs layer and an InAlAs compositionally graded strain relaxing buffer, we achieve threading dislocation density of (1.0 ± 0.3) × 10{sup 7} cm{sup −2} with a surface roughness of 10 nm RMS. No phase separation was observed during the InAlAs compositionally graded buffer layer growth. 1.4 μm long channel length transistors are fabricated from the wafer with I{sub DS} of 70 μA/μm and g{sub m} of above 60 μS/μm, demonstrating the high quality of the grown materials.

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

    NASA Astrophysics Data System (ADS)

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

    2005-03-01

    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 mesalike 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.

  7. 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.

  8. Carbon doped GaN buffer layer using propane for high electron mobility transistor applications: Growth and device results

    NASA Astrophysics Data System (ADS)

    Li, X.; Bergsten, J.; Nilsson, D.; Danielsson, Ö.; Pedersen, H.; Rorsman, N.; Janzén, E.; Forsberg, U.

    2015-12-01

    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 × 1018 cm-3) epitaxial layer closest to the substrate and a lower doped layer (3 × 1016 cm-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 × 1018 cm-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.

  9. High-resistivity GaN buffer templates and their optimization for GaN-based HFETs

    NASA Astrophysics Data System (ADS)

    Hubbard, S. M.; Zhao, G.; Pavlidis, D.; Sutton, W.; Cho, E.

    2005-11-01

    High-resistance (HR) GaN templates for AlGaN/GaN heterojunction field effect transistor (HFET) applications were grown using organometallic vapor phase epitaxy. The GaN sheet resistance was tuned using final nucleation layer (NL) annealing temperature and NL thickness. Using an annealing temperature of 1033 °C and NL thickness of 26 nm, GaN with sheet resistance of 10 10 Ω/sq was achieved, comparable to that of Fe-doped GaN. Material characterization results show that the high-resistance GaN is achieved due to compensating acceptor levels that may be introduced through edge-type threading dislocations. Optimization of annealing temperature and NL thickness provided a means to maximize GaN sheet resistance without significantly degrading material quality. In situ laser reflectance was used to correlate the NL properties to sheet resistance and material quality, providing a figure of merit for expected sheet resistance. AlGaN/GaN HFET layers grown using HR GaN templates with R of 10 10 Ω/sq gave surface and interface roughness of 14 and 7 Å, respectively. The 2DEG Hall mobility and sheet charge of HFETs grown using HR GaN templates was comparable to similar layers grown using unintentionally doped (UID) GaN templates.

  10. 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.

  11. Buffer layers on metal alloy substrates for superconducting tapes

    DOEpatents

    Jia, Quanxi; Foltyn, Stephen R.; Arendt, Paul N.; Groves, James R.

    2004-06-29

    An article including a substrate, a layer of an inert oxide material upon the surface of the substrate, a layer of an amorphous oxide or oxynitride material upon the inert oxide material layer, a layer of an oriented cubic oxide material having a rock-salt-like structure upon the amorphous oxide material layer, and a layer of a SrRuO.sub.3 buffer material upon the oriented cubic oxide material layer is provided together with additional layers such as a HTS top-layer of YBCO directly upon the layer of a SrRuO.sub.3 buffer material layer. With a HTS top-layer of YBCO upon at least one layer of the SrRuO.sub.3 buffer material in such an article, J.sub.c 's of up to 1.3.times.10.sup.6 A/cm.sup.2 have been demonstrated with projected IC's of over 200 Amperes across a sample 1 cm wide.

  12. Investigations into alterntive substrate, absorber, and buffer layer processing for Cu(In,Ga)Se{sub 2}-based solar cells

    SciTech Connect

    Tuttle, J.R.; Berens, T.A.; Keane, J.

    1996-05-01

    High-performance Cu(In,Ga)Se{sub 2}(CIGS)-based solar cells are presently fabricated within a narrow range of processing options. In this contribution, alternative substrate, absorber, and buffer layer processing is considered. Cell performance varies considerably when alternative substrates are employed. These variations are narrowed with the addition of Na via a Na{sub 2}S compound. Sputtered and electrodeposited CIGS precursors and completed absorbers show promise as alternatives to evaporation. A recrystallization process is required to improve their quality. (In,Ga){sub y}Se buffer layers contribute to cell performance above 10. Further improvements in these alternatives will lead to combined cell performance greater than 10% in the near term.

  13. Liquid metal/metal oxide frameworks with incorporated Ga2O3 for photocatalysis.

    PubMed

    Zhang, Wei; Naidu, Boddu S; Ou, Jian Zhen; O'Mullane, Anthony P; Chrimes, Adam F; Carey, Benjamin J; Wang, Yichao; Tang, Shi-Yang; Sivan, Vijay; Mitchell, Arnan; Bhargava, Suresh K; Kalantar-Zadeh, Kourosh

    2015-01-28

    Solvothermally synthesized Ga2O3 nanoparticles are incorporated into liquid metal/metal oxide (LM/MO) frameworks in order to form enhanced photocatalytic systems. The LM/MO frameworks, both with and without incorporated Ga2O3 nanoparticles, show photocatalytic activity due to a plasmonic effect where performance is related to the loading of Ga2O3 nanoparticles. Optimum photocatalytic efficiency is obtained with 1 wt % incorporation of Ga2O3 nanoparticles. This can be attributed to the sub-bandgap states of LM/MO frameworks, contributing to pseudo-ohmic contacts which reduce the free carrier injection barrier to Ga2O3.

  14. Proximity Effects of Beryllium-Doped GaN Buffer Layers on the Electronic Properties of Epitaxial AlGaN/GaN Heterostructures

    DTIC Science & Technology

    2010-05-17

    rf - plasma assisted MBE - grown homoepitaxial GaN has shown that oxygen, a shallow donor in GaN , is present at...properties of Al- GaN / GaN HEMTs grown by rf - MBE on native GaN substrates . 2. Experimental Seven AlGaN/ GaN heterostructures were grown by rf - plasma assisted... GaN /Be:GaN heterostructures have been grown by rf - plasma molecular beam epitaxy on free- standing semi-insulating

  15. Peculiarities of strain relaxation in linearly graded InxGa1-xAs/GaAs(001) metamorphic buffer layers grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Sorokin, S. V.; Klimko, G. V.; Sedova, I. V.; Sitnikova, A. A.; Kirilenko, D. A.; Baidakova, M. V.; Yagovkina, M. A.; Komissarova, T. A.; Belyaev, K. G.; Ivanov, S. V.

    2016-12-01

    This paper presents a comprehensive study of structural, optical and electrical properties of heterostructures with linearly graded InxGa1-xAs metamorphic buffer layers (MBLs) grown by molecular beam epitaxy on GaAs (001) substrates. The low density of threading dislocations (well below 106 cm-2) in 1-μm-thick In0.3Ga0.7As layers grown atop of the linearly graded InxGa1-xAs/GaAs MBLs has been confirmed by using transmission electron microscopy (TEM). X-ray diffraction (XRD) data demonstrate good agreement between the experimentally measured In step-back and its calculations in the frames of existing models. Combining the XRD reciprocal space maps (RSM) of the structures and the spatially-resolved selective area electron diffraction measurements by cross-sectional TEM in depth-profiled RSM diagrams allowed direct visualization of the strain relaxation dynamics during the MBL growth. Strong effect of the azimuth angle and the value of an unintentional initial miscut of nominally (001) oriented GaAs substrate on the strain relaxation dynamics was observed.

  16. Coaxial metal-oxide-semiconductor (MOS) Au/Ga2O3/GaN nanowires.

    PubMed

    Hsieh, Chin-Hua; Chang, Mu-Tung; Chien, Yu-Jen; Chou, Li-Jen; Chen, Lih-Juann; Chen, Chii-Dong

    2008-10-01

    Coaxial metal-oxide-semiconductor (MOS) Au-Ga2O3-GaN heterostructure nanowires were successfully fabricated by an in situ two-step process. The Au-Ga2O3 core-shell nanowires were first synthesized by the reaction of Ga powder, a mediated Au thin layer, and a SiO2 substrate at 800 degrees C. Subsequently, these core-shell nanowires were nitridized in ambient ammonia to form a GaN coating layer at 600 degrees C. The GaN shell is a single crystal, an atomic flat interface between the oxide and semiconductor that ensures that the high quality of the MOS device is achieved. These novel 1D nitride-based MOS nanowires may have promise as building blocks to the future nitride-based vertical nanodevices.

  17. Electrical properties of n-type GaSb substrates and p-type GaSb buffer layers for InAs/InGaSb superlattice infrared detectors

    SciTech Connect

    Mitchel, W. C. Haugan, H. J.; Mou, Shin; Brown, G. J.; Elhamri, S.; Berney, R.

    2015-09-15

    Lightly doped n-type GaSb substrates with p-type GaSb buffer layers are the preferred templates for growth of InAs/InGaSb superlattices used in infrared detector applications because of relatively high infrared transmission and a close lattice match to the superlattices. We report here temperature dependent resistivity and Hall effect measurements of bare substrates and substrate-p-type buffer layer structures grown by molecular beam epitaxy. Multicarrier analysis of the resistivity and Hall coefficient data demonstrate that high temperature transport in the substrates is due to conduction in both the high mobility zone center Γ band and the low mobility off-center L band. High overall mobility values indicate the absence of close compensation and that improved infrared and transport properties were achieved by a reduction in intrinsic acceptor concentration. Standard transport measurements of the undoped buffer layers show p-type conduction up to 300 K indicating electrical isolation of the buffer layer from the lightly n-type GaSb substrate. However, the highest temperature data indicate the early stages of the expected p to n type conversion which leads to apparent anomalously high carrier concentrations and lower than expected mobilities. Data at 77 K indicate very high quality buffer layers.

  18. Investigation of CdZnS Buffer Layers on the Performance of CuInGaSe2 and CuGaSe2 Solar Cells

    SciTech Connect

    Song, J.; Li, S. S.; Chen, L.; Noufi, R.; Anderson, T. J.; Crisalle, O. D.

    2006-01-01

    Cu(In,Ga)Se{sub 2} (CIGS) and CuGaSe{sub 2} (CGS) solar cells were fabricated using Cd{sub 1-x}Zn{sub x}S (CdZnS) buffer layers prepared by chemical bath deposition (CBD) with relative Zn compositions in the CBD bath values of X{sub bath} = 0 (i.e., pure CdS), 0.1, 0.2, 0.3, 0.4, and 0.5. The cell performance parameters of CIGS and CGS films treated with a KCN solution were investigated and compared to cells without KCN treatment. It was found that absorber films treated with KCN etching prior to the buffer CBD step show an improved cell performance for both the CIGS and CGS cells deposited with either CdS or CdZnS buffer layer. A CIGS cell with CdZnS buffer layer of X{sub bath} = 0.2 produced a 13% AM1.5G conversion efficiency with higher V{sub oc}, J{sub sc}, and FF values as compared to the CdZnS/CIGS cells with different Zn contents. Results of photo- J-V and quantum efficiency (QE) measurements reveal that the CGS cell with CdZnS buffer layer of X{sub bath} = 0.3 performed better than the CGS cell deposited with a pure CdS buffer layer. This result is suggested as a result of an increased photocurrent at shorter wavelengths and a more favorable conduction band-offset at the CdZnS/CGS junction.

  19. Structural and morphological properties of GaN buffer layers grown by ammonia molecular beam epitaxy on SiC substrates for AlGaN/GaN high electron mobility transistors

    SciTech Connect

    Corrion, A. L.; Poblenz, C.; Wu, F.; Speck, J. S.

    2008-05-01

    The impact of growth conditions on the surface morphology and structural properties of ammonia molecular beam epitaxy GaN buffers layers on SiC substrates was investigated. The threading dislocation (TD) density was found to decrease with decreasing NH{sub 3}:Ga flux ratio, which corresponded to an increase in surface roughness and reduction in residual compressive lattice mismatch stress. Furthermore, the dislocation density and compressive stress decreased for increasing buffer thickness. TD inclination was proposed to account for these observations. Optimized surface morphologies were realized at high NH{sub 3}:Ga flux ratios and were characterized by monolayer-high steps, spiral hillocks, and pyramidal mounds, with rms roughness of {approx}1.0 nm over 2x2 {mu}m{sup 2} atomic force microscopy images. Smooth surface morphologies were realized over a large range of growth temperatures and fluxes, and growth rates of up to 1 {mu}m/h were achieved. TD densities in the buffers as low as 3x10{sup 9} cm{sup -2} were demonstrated. These buffers were highly insulating and were used in recently reported AlGaN/GaN HEMTs with power densities of >11 W/mm at 4 and 10 GHz.

  20. Theoretical and experimental study of highly textured GaAs on silicon using a graphene buffer layer

    SciTech Connect

    Alaskar, Yazeed; Arafin, Shamsul; Lin, Qiyin; Wickramaratne, Darshana; McKay, Jeff; Norman, Andrew G.; Zhang, Zhi; Yao, Luchi; Ding, Feng; Zou, Jin; Goorsky, Mark S.; Lake, Roger K.; Zurbuchen, Mark A.; Wang, Kang L.

    2015-09-01

    A novel heteroepitaxial growth technique, quasi-van der Waals epitaxy, promises the ability to deposit three-dimensional GaAs materials on silicon using two-dimensional graphene as a buffer layer by overcoming the lattice and thermal expansion mismatch. In this study, density functional theory (DFT) simulations were performed to understand the interactions at the GaAs/graphene hetero-interface as well as the growth orientations of GaAs on graphene. To develop a better understanding of the molecular beam epitaxy-grown GaAs films on graphene, samples were characterized by x-ray diffraction (..theta..-2..theta.. scan, ..omega..-scan, grazing incidence XRD and pole figure measurement) and transmission electron microscopy. The realizations of smooth GaAs films with a strong (111) oriented fiber-texture on graphene/silicon using this deposition technique are a milestone towards an eventual demonstration of the epitaxial growth of GaAs on silicon, which is necessary for integrated photonics application.

  1. Microstructures of GaN Buffer Layers Grown on Si(111) Using Rapic Thermal Process Low-Pressure Metalorganic Chemical Vapor Deposition

    NASA Astrophysics Data System (ADS)

    Peng, Chen; Bo, Shen; Jian-Min, Zhu; Zhi-Zhong, Chen; Yu-Gang, Zhou; Shi-Yong, Xie; Rong, Zhang; Ping, Han; Shu-Lin, Gu; You-Dou, Zheng; Shu-Sheng, Jiang; Duan, Feng; Z, Huang C.

    2000-03-01

    Microstructures of GaN buffer layers grown on Si (111) substrates using rapid thermal process low-pressure metalorganic chemical vapor deposition are investigated by an atomic force microscope (AFM) and a high-resolution transmission electron microscope (HRTEM). AFM images show that the islands appear in the GaN buffer layer after annealing at high temperature. Cross-sectional HRTEM micrographs of the buffer region of these samples indicate that there are bunched steps on the surface of the Si substrate and a lot of domains in GaN misorienting each other with small angles. The boundaries of those domains locate near the bunched steps, and the regions of the film on a terrace between steps have the same crystal orientation. An amorphous-like layer, about 3 nm thick, can also be observed between the GaN buffer layer and the Si substrate.

  2. 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.

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

    SciTech Connect

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

    2014-09-15

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

  4. Electrodeposition of Metal on GaAs Nanowires

    NASA Astrophysics Data System (ADS)

    Liu, Chao; Einabad, Omid; Watkins, Simon; Kavanagh, Karen

    2010-10-01

    Copper (Cu) electrical contacts to freestanding gallium arsenide (GaAs) nanowires have been fabricated via electrodeposition. The nanowires are zincblende (111) oriented grown epitaxially on n-type Si-doped GaAs (111)B substrates by gold-catalyzed Vapor Liquid Solid (VLS) growth in a metal organic vapour phase epitaxy (MOVPE) reactor. The epitaxial electrodeposition process, based on previous work with bulk GaAs substrates, consists of a substrate oxide pre-etch in dilute ammonium-hydroxide carried out prior to galvanostatic electrodeposition in a pure Cu sulphate aqueous electrolyte at 20-60^oC. For GaAs nanowires, we find that Cu or Fe has a preference for growth on the gold catalyst avoiding the sidewalls. After removing gold, both metals still prefer to grow only on top of the nanowire, which has the largest potential field.

  5. Interface roughness of double buffer layer of GaN film grown on Si(1 1 1) substrate using GIXR analysis

    NASA Astrophysics Data System (ADS)

    Yamamoto, Y.; Yamabe, N.; Ohachi, T.

    2011-03-01

    A double buffer layer (DBL), interface reaction epitaxy (IRE) AlN/β-Si3N4/Si, grown by an IRE of β-Si3N4 and AlN films on Si, was fabricated to improve the crystalline quality of successively grown 30 nm GaN on a 30 nm AlN buffer layer using plasma-assisted molecular beam epitaxy (PA-MBE). The DBL was first prepared by surface nitridation of Si and successively prepared by IRE between the deposited Al and N atoms in β-Si3N4. Both the AlN buffer layer on the DBL and GaN film on the AlN buffer layer were grown by activity-modulation migration enhanced epitaxy (AM-MEE). Hetero epitaxial grown films of GaN(30 nm)/AlN buffer(30 nm)/DBL/Si(1 1 1) were prepared for analysis using a three layer model of grazing incidence-angle X-ray reflectivity (GIXR), which consisted of three layers of GaN, AlN buffer and Si and of the three interfaces of the GaN surface, GaN/AlN buffer and AlN buffer/DBL/Si. The nitridation temperature dependence of the interface roughness of the DBL was measured to be 0.5 and 0.6 nm, for nitridation temperatures of 780 and 830 °C, respectively. The full width at half maximum (FWHM) of rocking curve GaN(0 0 0 2) measured by X-ray diffraction (XRD) for nitridation temperatures of 780 and 830 °C were 58.2 and 55.2 arcmin, respectively.

  6. Effects of Grazing Management and Buffer Strips on Metal Runoff from Pastures Fertilized with Poultry Litter.

    PubMed

    Pilon, C; Moore, P A; Pote, D H; Martin, J W; DeLaune, P B

    2017-03-01

    Metal runoff from fields fertilized with poultry litter may pose a threat to aquatic systems. Buffer strips located adjacent to fields may reduce nutrients and solids in runoff. However, scant information exists on the long-term effects of buffer strips combined with grazing management on metal runoff from pastures. The objective of this study was to assess the 12-yr impact of grazing management and buffer strips on metal runoff from pastures receiving poultry litter. The research was conducted using 15 watersheds (25 m wide and 57 m long) with five treatments: hayed (H), continuously grazed (CG), rotationally grazed (R), rotationally grazed with a buffer strip (RB), and rotationally grazed with a fenced riparian buffer strip (RBR). Poultry litter was applied annually in spring at 5.6 Mg ha. Runoff samples were collected after every rainfall event. Aluminum (Al) and iron (Fe) concentrations were strongly and positively correlated with total suspended solids, indicating soil erosion was the primary source. Soluble Al and Fe were not related to total Al and Fe. However, there was a strong positive correlation between soluble and total copper (Cu) concentrations. The majority of total Cu and zinc was in water-soluble form. The CG treatment had the highest metal concentrations and loads of all treatments. The RBR and H treatments resulted in lower concentrations of total Al, Cu, Fe, potassium, manganese, and total organic carbon in the runoff. Rotational grazing with a fenced riparian buffer and converting pastures to hayfields appear to be effective management systems for decreasing concentrations and loads of metals in surface runoff from pastures fertilized with poultry litter. Copyright © by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc.

  7. Stabilization of metastable ɛ-Fe2O3 thin films using a GaFeO3 buffer

    NASA Astrophysics Data System (ADS)

    Thai, Trang Minh Nguyen; Nguyen, Dong Tri; Lee, Nam-Suk; Rhyee, Jong-Soo; Song, Jonghyun; Kim, Heon-Jung

    2016-11-01

    This paper reports a simple and robust route to stabilize metastable ɛ-Fe2O3 as an epitaxial thin film using a GaFeO3 (GFO) buffer in pulsed laser deposition. The use of an isostructural GFO buffer widens the range of film growth, allowing for stabilization on a range of substrates even with different surface symmetries, such as Al2O3 (0001), SrTiO3 (111), and Y:ZrO2 (100). All films grown on these substrates were c-axis oriented with the characteristic in-plane domain structures. Magnetization of these buffered thin films showed considerable magnetic anisotropy at 350 K. In particular, in-plane magnetization was found to be relatively larger in the films grown on the Y:ZrO2 (100) compared to the other cases. Heterostructuring ɛ-Fe2O3 on GFO is promising in the applications of ɛ-Fe2O3 for magnetic and multiferroic devices in that it provides a larger growth window and an effective means to optimize the film properties beyond the simple substitution of Fe with Ga.

  8. Leaching with Penicillium simplicissimum: Influence of metals and buffers on proton extrusion and citric acid production

    SciTech Connect

    Franz, A.; Burgstaller, W.; Schinner, F. )

    1991-03-01

    In the presence of insoluble metal oxides (industrial filter dust, zinc oxide, synthetic mixture of metal oxides), Penicillium simplicissimum developed the ability to excrete considerable amounts of citric acid (>100 mM). Parallel with the increase of citric acid concentration in the culture broth, zinc was solubilized from zinc oxide. The adsorption of filter dust onto the mycelium (the pellets formed were less than 1 mm in diameter) was required for not only the citric acid excretion but also the leaching of zinc. When the filter dust was replaced with a synthetic mixture of metal oxides or with zinc oxide in combination with trace elements, levels of adsorption and citric acid production were observed to be similar to those in experiments where industrial filter dust was used. The two most important properties of the filter dust were its heavy-metal content and its buffering capacity. These properties were simulated by adding heavy metals in soluble form (as chlorides, sulfates, or nitrates) or soluble buffers to the medium. Both heavy metals and buffers were not able to induce a citric acid efflux. As with citric acid production by Aspergillus niger, the addition of manganese lowered citric acid excretion (by 40% with metal oxide-induced citric acid efflux and by 100% with urea-induced citric acid efflux). Copper antagonized the effect of manganese. The mechanism for the bulk of citric acid excretion by P. simplicissimum, however, seemed to be different from that described for citric acid accumulation by A. niger. Because of the inefficiency of metals in solubilized form and of soluble buffers to induce a strong citric acid efflux, adsorption of an insoluble metal compound (zinc oxide) turned out to be essential.

  9. Formation of metallic In in InGaN /GaN multiquantum wells

    NASA Astrophysics Data System (ADS)

    Daele, B. Van; Tendeloo, G. Van; Jacobs, K.; Moerman, I.; Leys, M. R.

    2004-11-01

    InxGa1-xN/GaN light-emitting diode structures with a high In concentration may lose all optical output after capping the active region with a p-type GaN layer. Transmission electron microscopy has been applied to determine the microstructural changes that occur in the quantum-well (QW) region during this capping process. The loss of the optical output is related to a clustering of In into metallic In platelets in the QW region. The properties of these In platelets are described and a formation model is proposed.

  10. Bending stability of GaN grown on a metallic flexible substrate by plasma-assisted molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Rodríguez, A. G.; Chávez-Veloz, S. G.; Compeán-García, V. D.; López-Luna, E.; Vidal, M. A.

    2017-08-01

    GaN thin films were grown on flexible metallic substrates by molecular beam epitaxy. MgO buffer layers were deposited by spin coating on Ni-Mo-Cr (Hastelloy C-276) alloy tapes that were used as substrates. The structural characterization of the GaN/MgO/hastelloy samples was performed by x-ray diffraction and Raman spectroscopy. The obtained nanometric films have the stable hexagonal phase (α-GaN) with an average crystallite size of 18 nm. The long and short range order of GaN decrease when the structure is bent. The most significant variations in the structural properties occur between 100 and 250 bending cycles.

  11. Sol-gel deposition of buffer layers on biaxially textured metal substances

    SciTech Connect

    Shoup, S.S.; Paranthamam, M.; Beach, D.B.; Kroeger, D.M.; Goyal, A.

    2000-06-20

    A method is disclosed for forming a biaxially textured buffer layer on a biaxially oriented metal substrate by using a sol-gel coating technique followed by pyrolyzing/annealing in a reducing atmosphere. This method is advantageous for providing substrates for depositing electronically active materials thereon.

  12. Sol-gel deposition of buffer layers on biaxially textured metal substances

    DOEpatents

    Shoup, Shara S.; Paranthamam, Mariappan; Beach, David B.; Kroeger, Donald M.; Goyal, Amit

    2000-01-01

    A method is disclosed for forming a biaxially textured buffer layer on a biaxially oriented metal substrate by using a sol-gel coating technique followed by pyrolyzing/annealing in a reducing atmosphere. This method is advantageous for providing substrates for depositing electronically active materials thereon.

  13. 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.

  14. Lattice-engineered Si{sub 1-x}Ge{sub x}-buffer on Si(001) for GaP integration

    SciTech Connect

    Skibitzki, Oliver Zaumseil, Peter; Yamamoto, Yuji; Andreas Schubert, Markus; Paszuk, Agnieszka; Hannappel, Thomas; Hatami, Fariba; Ted Masselink, W.; Trampert, Achim; Tillack, Bernd; Schroeder, Thomas

    2014-03-14

    We report a detailed structure and defect characterization study on gallium phosphide (GaP) layers integrated on silicon (Si) (001) via silicon-germanium (SiGe) buffer layers. The presented approach uses an almost fully relaxed SiGe buffer heterostructure of only 400 nm thickness whose in-plane lattice constant is matched to GaP—not at room but at GaP deposition temperature. Single crystalline, pseudomorphic 270 nm thick GaP is successfully grown by metalorganic chemical vapour deposition on a 400 nm Si{sub 0.85}Ge{sub 0.15}/Si(001) heterosystem, but carries a 0.08% tensile strain after cooling down to room temperature due to the bigger thermal expansion coefficient of GaP with respect to Si. Transmission electron microscopy (TEM) studies confirm the absence of misfit dislocations in the pseudomorphic GaP film but growth defects (e.g., stacking faults, microtwins, etc.) especially at the GaP/SiGe interface region are detected. We interpret these growth defects as a residue of the initial 3D island coalescence phase of the GaP film on the SiGe buffer. TEM-energy-dispersive x-ray spectroscopy studies reveal that these defects are often correlated with stoichiometric inhomogeneities in the GaP film. Time-of-flight Secondary ion mass spectrometry detects sharp heterointerfaces between GaP and SiGe films with a minor level of Ga diffusion into the SiGe buffer.

  15. Y-Ba-Cu-O film deposition by metal organic chemical vapor deposition on buffered metal substrates.

    SciTech Connect

    Selvamanickam, V.; Galinski, G.; DeFrank, J.; Trautwein, C.; Haldar, P.; Balachandran, U.; Lanagan, M.; Chudzik, M.

    1999-10-12

    YBa{sub 2}Cu{sub 3}O{sub 2} (YBCO) films have been deposited on buffered metal substrates by Metal Organic Chemical Vapor Deposition (MOCVD). Cube-textured nickel substrates were fabricated by a thermomechanical process. Epitaxial CeO{sub 2}films were deposited on these substrates by thermal evaporation. Nickel alloy substrates with biaxially-textured Yttria-Stabilized Zirconia (YSZ) buffer layers deposited by Ion Beam Assisted Deposition were also prepared. Highly biaxially-textured YBCO films were deposited by MOCVD on both types of metal substrates. A critical current density greater than 10{sup 5} A/cm{sup 2} at 77 K has been achieved in YBCO films on metal substrates.

  16. Impact of residual carbon impurities and gallium vacancies on trapping effects in AlGaN/GaN metal insulator semiconductor high electron mobility transistors

    SciTech Connect

    Huber, Martin; Silvestri, Marco; Knuuttila, Lauri; Pozzovivo, Gianmauro; Andreev, Andrei; Lundskog, Anders; Kadashchuk, Andrey; Bonanni, Alberta

    2015-07-20

    Effects of residual C impurities and Ga vacancies on the dynamic instabilities of AlN/AlGaN/GaN metal insulator semiconductor high electron mobility transistors are investigated. Secondary ion mass spectroscopy, positron annihilation spectroscopy, and steady state and time-resolved photoluminescence (PL) measurements have been performed in conjunction with electrical characterization and current transient analyses. The correlation between yellow luminescence (YL), C- and Ga vacancy concentrations is investigated. Time-resolved PL indicating the C{sub N} O{sub N} complex as the main source of the YL, while Ga vacancies or related complexes with C seem not to play a major role. The device dynamic performance is found to be significantly dependent on the C concentration close to the channel of the transistor. Additionally, the magnitude of the YL is found to be in agreement with the threshold voltage shift and with the on-resistance degradation. Trap analysis of the GaN buffer shows an apparent activation energy of ∼0.8 eV for all samples, pointing to a common dominating trapping process and that the growth parameters affect solely the density of trap centres. It is inferred that the trapping process is likely to be directly related to C based defects.

  17. Dislocation analysis of InGaN/GaN quantum dots grown by metal organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Yang, Di; Wang, Lai; Hao, Zhi-Biao; Luo, Yi; Sun, Changzheng; Han, Yanjun; Xiong, Bing; Wang, Jian; Li, Hongtao

    2016-11-01

    The dislocations in InGaN/GaN quantum dots grown by metal organic chemical vapor deposition were studied by high-resolution transmission electron microscopy combining the Fourier filtering process. The misfit dislocations were observed in uncapped InGaN/GaN quantum dots. However, for the capped InGaN/GaN quantum dots, the GaN capping layer was found to suppress the generation of misfit dislocations and hence hindered the strain relaxation. Therefore, an overgrowth InGaN layer was used to relieve the strain in InGaN quantum dots and misfit dislocations were correspondingly found in these samples. In addition, defects were observed in low temperature GaN layers which suggested the existence of stacking faults.

  18. Metal contacts on ZnSe and GaN

    SciTech Connect

    Duxstad, Kristin Joy

    1997-05-01

    Recently, considerable interest has been focused on the development of blue light emitting materials and devices. The focus has been on GaN and ZnSe, direct band gap semiconductors with bands gaps of 3.4 and 2.6 eV, respectively. To have efficient, reliable devices it is necessary to have thermally and electrically stable Ohmic contacts. This requires knowledge of the metal-semiconductor reaction behavior. To date few studies have investigated this behavior. Much information has accumulated over the years on the behavior of metals on Si and GaAs. This thesis provides new knowledge for the more ionic wide band gap semiconductors. The initial reaction temperatures, first phases formed, and phase stability of Pt, Pd, and Ni on both semiconductors were investigated. The reactions of these metals on ZnSe and GaN are discussed in detail and correlated with predicted behavior. In addition, comparisons are made between these highly ionic semiconductors and Si and GaAs. The trends observed here should also be applicable to other II-VI and III-Nitride semiconductor systems, while the information on phase formation and stability should be useful in the development of contacts for ZnSe and GaN devices.

  19. Metallic versus covalent bonding: Ga nanoparticles as a case study.

    PubMed

    Ghigna, Paolo; Spinolo, Giorgio; Parravicini, Giovanni Battista; Stella, Angiolino; Migliori, Andrea; Kofman, Richard

    2007-06-27

    A systematic X-ray absorption spectroscopy investigation of the local coordination in gallium nanostructures has been performed as a function of temperature and particle size. It is shown that the nanostructure strongly affects the polymorphism of solid gallium and the (meta)stability range of the liquid phase (in agreement with previous works) and that the surface tension acts in the same direction as hydrostatic pressure in stabilizing the Ga solid phases. The effect of surface free energy is first to favor the metallic arrangement of the delta phase and then to stabilize a liquid-like phase based on dimeric molecules even at 90 K. The Ga-Ga distance in the dimers is lower in the liquid phase than in the alpha solid. The experimental results are discussed in comparison with molecular dynamic calculations to assess the presence of covalent character of the dimeric Ga2 units in liquid nanostructured gallium.

  20. Effect of Temperature on GaGdO/GaN Metal Oxide Semiconductor Field Effect Transistors

    SciTech Connect

    Abernathy, C.R.; Baca, A.; Chu, S.N.G.; Hong, M.; Lothian, J.R.; Marcus, M.A.; Pearton, S.J.; Ren, F.; Schurman, M.J.

    1998-10-14

    GaGdO was deposited on GaN for use as a gate dielectric in order to fabricate a depletion metal oxide semiconductor field effect transistor (MOSFET). This is the fmt demonstration of such a device in the III-Nitride system. Analysis of the effect of temperature on the device shows that gate leakage is significantly reduced at elevated temperature relative to a conventional metal semiconductor field effeet transistor (MESFET) fabricated on the same GaN layer. MOSFET device operation in fact improved upon heating to 400 C. Modeling of the effeet of temperature on contact resistance suggests that the improvement is due to a reduction in the parasitic resistances present in the device.

  1. A new strategy to stabilize oxytocin in aqueous solutions: I. The effects of divalent metal ions and citrate buffer.

    PubMed

    Avanti, Christina; Amorij, Jean-Pierre; Setyaningsih, Dewi; Hawe, Andrea; Jiskoot, Wim; Visser, Jan; Kedrov, Alexej; Driessen, Arnold J M; Hinrichs, Wouter L J; Frijlink, Henderik W

    2011-06-01

    In the current study, the effect of metal ions in combination with buffers (citrate, acetate, pH 4.5) on the stability of aqueous solutions of oxytocin was investigated. Both monovalent metal ions (Na(+) and K(+)) and divalent metal ions (Ca(2+), Mg(2+), and Zn(2+)) were tested all as chloride salts. The effect of combinations of buffers and metal ions on the stability of aqueous oxytocin solutions was determined by RP-HPLC and HP-SEC after 4 weeks of storage at either 4°C or 55°C. Addition of sodium or potassium ions to acetate- or citrate-buffered solutions did not increase stability, nor did the addition of divalent metal ions to acetate buffer. However, the stability of aqueous oxytocin in aqueous formulations was improved in the presence of 5 and 10 mM citrate buffer in combination with at least 2 mM CaCl(2), MgCl(2), or ZnCl(2) and depended on the divalent metal ion concentration. Isothermal titration calorimetric measurements were predictive for the stabilization effects observed during the stability study. Formulations in citrate buffer that had an improved stability displayed a strong interaction between oxytocin and Ca(2+), Mg(2+), or Zn(2+), while formulations in acetate buffer did not. In conclusion, our study shows that divalent metal ions in combination with citrate buffer strongly improved the stability of oxytocin in aqueous solutions.

  2. Charge movement in a GaN-based hetero-structure field effect transistor structure with carbon doped buffer under applied substrate bias

    SciTech Connect

    Pooth, Alexander; Uren, Michael J.; Cäsar, Markus; Kuball, Martin; Martin, Trevor

    2015-12-07

    Charge trapping and transport in the carbon doped GaN buffer of a GaN-based hetero-structure field effect transistor (HFET) has been investigated under both positive and negative substrate bias. Clear evidence of redistribution of charges in the carbon doped region by thermally generated holes is seen, with electron injection and capture observed during positive bias. Excellent agreement is found with simulations. It is shown that these effects are intrinsic to the carbon doped GaN and need to be controlled to provide reliable and efficient GaN-based power HFETs.

  3. Influence of annealed ohmic contact metals on electron mobility of strained AlGaN/GaN heterostructures

    NASA Astrophysics Data System (ADS)

    Jianzhi, Zhao; Zhaojun, Lin; D, Corrigan T.; Yu, Zhang; Huijun, Li; Zhanguo, Wang

    2009-10-01

    The influence of annealed ohmic contact metals on the electron mobility of a two dimensional electron gas (2DEG) is investigated on ungated AlGaN/GaN heterostructures and AlGaN/GaN heterostructure field effect transistors (AlGaN/GaN HFETs). Current-voltage (I-V) characteristics for ungated AlGaN/GaN heterostructures and capacitance-voltage (C-V) characteristics for AlGaN/GaN HFETs are obtained, and the electron mobility for the ungated AlGaN/GaN heterostructure is calculated. It is found that the electron mobility of the 2DEG for the ungated AlGaN/GaN heterostructure is decreased by more than 50% compared with the electron mobility of Hall measurements. We propose that defects are introduced into the AlGaN barrier layer and the strain of the AlGaN barrier layer is changed during the annealing process of the source and drain, causing the decrease in the electron mobility.

  4. Heteroepitaxial growth of GaN on atomically flat LiTaO 3 (0 0 0 1) using low-temperature AIN buffer layers

    NASA Astrophysics Data System (ADS)

    Tsuchiya, Y.; Kobayashi, A.; Ohta, J.; Fujioka, H.; Oshima, M.

    2006-07-01

    We have grown GaN films on atomically-flat LiTaO 3 substrates by using pulsed laser deposition (PLD), and we then investigated the effect of the use of low-temperature AlN (LT-AlN) buffer layers on the structural properties of GaN. The full-width at half-maximum (FWHM) values for the crystal orientation distribution of the GaN films in the tilt directions were reduced from 0.48° to 0.17°, and those in the twist directions were reduced from 0.40° to 0.17° by the incorporation of AlN buffer layers grown at 580 °C. The surface morphology of GaN has also been improved by the insertion of LT-AlN buffer layers. X-ray reflectivity measurements have revealed that the interfacial layer thickness between LT-AlN and LiTaO 3 is as thin as 1.7 nm, and that the increase in the interfacial layer thickness caused by annealing at up to 700 °C is quite small. These results indicate that the PLD growth of GaN on atomically flat substrates using LT-AlN buffer layers is quite promising for achieving GaN on LiTaO 3.

  5. Anisotropic structural and optical properties of semi-polar (11–22) GaN grown on m-plane sapphire using double AlN buffer layers

    PubMed Central

    Zhao, Guijuan; Wang, Lianshan; Yang, Shaoyan; Li, Huijie; Wei, Hongyuan; Han, Dongyue; Wang, Zhanguo

    2016-01-01

    We report the anisotropic structural and optical properties of semi-polar (11–22) GaN grown on m-plane sapphire using a three-step growth method which consisted of a low temperature AlN buffer layer, followed by a high temperature AlN buffer layer and GaN growth. By introducing double AlN buffer layers, we substantially improve the crystal and optical qualities of semi-polar (11–22) GaN, and significantly reduce the density of stacking faults and dislocations. The high resolution x-ray diffraction measurement revealed that the in-plane anisotropic structural characteristics of GaN layer are azimuthal dependent. Transmission electron microscopy analysis showed that the majority of dislocations in the GaN epitaxial layer grown on m-sapphire are the mixed-type and the orientation of GaN layer was rotated 58.4° against the substrate. The room temperature photoluminescence (PL) spectra showed the PL intensity and wavelength have polarization dependence along parallel and perpendicular to the [1–100] axis (polarization degrees ~ 0.63). The realization of a high polarization semi-polar GaN would be useful to achieve III-nitride based lighting emission device for displays and backlighting. PMID:26861595

  6. ZnO buffer layer for metal films on silicon substrates

    SciTech Connect

    Ihlefeld, Jon

    2014-09-16

    Dramatic improvements in metallization integrity and electroceramic thin film performance can be achieved by the use of the ZnO buffer layer to minimize interfacial energy between metallization and adhesion layers. In particular, the invention provides a substrate metallization method utilizing a ZnO adhesion layer that has a high work of adhesion, which in turn enables processing under thermal budgets typically reserved for more exotic ceramic, single-crystal, or metal foil substrates. Embodiments of the present invention can be used in a broad range of applications beyond ferroelectric capacitors, including microelectromechanical systems, micro-printed heaters and sensors, and electrochemical energy storage, where integrity of metallized silicon to high temperatures is necessary.

  7. Gate metal dependent electrical characteristics of AlGaN/GaN HEMTs

    SciTech Connect

    Koo, Sang-Mo Kang, Min-Seok

    2014-10-15

    Highlights: • We investigated transfer characteristics of AlGaN/GaN high electron mobility transistors. • We demonstrate the effect of the barrier height of Schottky gate metals. • The conduction mechanisms examine by comparing the experimental results with numerical simulations. • 2-DEG concentration depends on the barrier height of Schottky gate metals. - Abstract: We investigated transfer characteristics of AlGaN/GaN high electron mobility transistors (HEMTs) and the effect of the barrier height of Schottky gate metals. It is found that the threshold voltage of the HEMT structures with the Ni Schottky contact shows a positive shift compared to that of the Ti Schottky contacts (ΔV{sub th} = 2.9 V). The maximum saturation current of the HEMT structures with the Ti Schottky contact (∼1.4 × 10{sup 7} A/cm{sup 2}) is found to be ∼2.5 times higher than that of the Ni Schottky contact (2.9 × 10{sup 7} A/cm{sup 2}). The conduction mechanisms have been examined by comparing the experimental results with numerical simulations, which confirm that the increased barrier height is mainly attributed to the reduction of 2-DEG concentration.

  8. RF-MBE growth of cubic AlN on MgO (001) substrates via 2-step c-GaN buffer layer

    NASA Astrophysics Data System (ADS)

    Kakuda, M.; Morikawa, S.; Kuboya, S.; Katayama, R.; Yaguchi, H.; Onabe, K.

    2013-09-01

    We fabricated cubic AlN (c-AlN) films on MgO (001) substrates via 2-step c-GaN buffer layer by radio-frequency-plasma-assisted molecular beam epitaxy (RF-MBE). The effect of low temperature c-GaN buffer layer on the surface flatness and crystal quality of c-AlN was investigated by AFM and XRD reciprocal space mapping analysis. We examined optical properties of the c-AlN film by spectroscopic ellipsometry. The absorption edge by the direct transition of the c-AlN film was 5.95 eV caused by the hexagonal phase incorporation.

  9. Quality-enhanced In{sub 0.3}Ga{sub 0.7}As film grown on GaAs substrate with an ultrathin amorphous In{sub 0.6}Ga{sub 0.4}As buffer layer

    SciTech Connect

    Gao, Fangliang; Li, Guoqiang

    2014-01-27

    Using low-temperature molecular beam epitaxy, amorphous In{sub 0.6}Ga{sub 0.4}As layers have been grown on GaAs substrates to act as buffer layers for the subsequent epitaxial growth of In{sub 0.3}Ga{sub 0.7}As films. It is revealed that the crystallinity of as-grown In{sub 0.3}Ga{sub 0.7}As films is strongly affected by the thickness of the large-mismatched amorphous In{sub 0.6}Ga{sub 0.4}As buffer layer. Given an optimized thickness of 2 nm, this amorphous In{sub 0.6}Ga{sub 0.4}As buffer layer can efficiently release the misfit strain between the In{sub 0.3}Ga{sub 0.7}As epi-layer and the GaAs substrate, trap the threading and misfit dislocations from propagating to the following In{sub 0.3}Ga{sub 0.7}As epi-layer, and reduce the surface fluctuation of the as-grown In{sub 0.3}Ga{sub 0.7}As, leading to a high-quality In{sub 0.3}Ga{sub 0.7}As film with competitive crystallinity to that grown on GaAs substrate using compositionally graded In{sub x}Ga{sub 1-x}As metamorphic buffer layers. Considering the complexity of the application of the conventional In{sub x}Ga{sub 1-x}As graded buffer layers, this work demonstrates a much simpler approach to achieve high-quality In{sub 0.3}Ga{sub 0.7}As film on GaAs substrate and, therefore, is of huge potential for the InGaAs-based high-efficiency photovoltaic industry.

  10. Direct charge carrier injection into Ga2O3 thin films using an In2O3 cathode buffer layer: their optical, electrical and surface state properties

    NASA Astrophysics Data System (ADS)

    Cui, W.; Zhao, X. L.; An, Y. H.; Guo, D. Y.; Qing, X. Y.; Wu, Z. P.; Li, P. G.; Li, L. H.; Cui, C.; Tang, W. H.

    2017-04-01

    Conductive Ga2O3 thin films with an In2O3 buffer layer have been prepared on c-plane sapphire substrates using a laser molecular beam epitaxy technique. The effects of the In2O3 buffer layer on the structure and optical, electrical and surface state properties of the Ga2O3 films have been studied. The change in conductivity of the thin films is attributed to different thicknesses of the In2O3 buffer layer, which determine the concentration of charge carriers injected into the upper Ga2O3 layer from the interface of the bilayer thin films. In addition, the increase in flat band voltage shift and capacitance values as the In2O3 buffer layer thickens are attributed to the increase in surface state density, which also contributes to the rapid shrinkage of the optical band gap of the Ga2O3. With transparency to visible light, high n-type conduction and the ability to tune the optical band gap and surface state density, we propose that Ga2O3/In2O3 bilayer thin film is an ideal n-type semiconductor for fabrication of transparent power devices, solar cell electrodes and gas sensors.

  11. Performance of metal dihalide dissociation lasers by changed buffer gas composition

    SciTech Connect

    Celto, J.E.; Schimitschek, E.J.

    1981-04-14

    A pulsed laser emits laser energy by dissociative excitation of metal dihalide and cyclic recombination. A metal dihalide selected from subgroup ii-b of the periodic table of elements is contained within an elongate sealed enclosure. Two elongate electrodes having external terminals are supported in parallel relationship within the enclosure, forming a gap parallel to the principal axis of the enclosure. A source of pulsed electric power is connected to the terminals of the two electrodes, producing repetitive transverse electric discharges across the gap. An inert buffer gas is included within the enclosure for aiding electric discharge uniformity, to provide vibrational relaxation of the lasing medium in its electronic states and to participate in the dissociative excitation process. The buffer gas is one of several mixtures of discrete percentages of neon and nitrogen. The gas/vapor mixture, consisting of the chosen buffer gases and the chosen metal dihalide vapor is ionized by ; the total economic market potential is 64.4% of the technical potential, or 2072.4 MW, equivalent to 83,621 BPDE; and the lack of an operating history-detailing system reliability, safety, and operating costs-iment and test components; technology testing; analytmperature fatigue stren obtained.

  12. Impact of varying buffer thickness generated strain and threading dislocations on the formation of plasma assisted MBE grown ultra-thin AlGaN/GaN heterostructure on silicon

    SciTech Connect

    Chowdhury, Subhra; Biswas, Dhrubes

    2015-05-15

    Plasma-assisted molecular beam epitaxy (PAMBE) growth of ultra-thin Al{sub 0.2}Ga{sub 0.8}N/GaN heterostructures on Si(111) substrate with three buffer thickness (600 nm/400 nm/200 nm) have been reported. An unique growth process has been developed that supports lower temperature epitaxy of GaN buffer which minimizes thermally generated tensile strain through appropriate nitridation and AlN initiated epitaxy for achieving high quality GaN buffer which supports such ultra-thin heterostructures in the range of 10-15Å. It is followed by investigations of role of buffer thickness on formation of ultra-thin Al{sub 0.2}Ga{sub 0.8}N/GaN heterostructure, in terms of stress-strain and threading dislocation (TD). Structural characterization were performed by High-Resolution X-Ray Diffraction (HRXRD), room-temperature Photoluminescence (RT-PL), High Resolution Transmission Electron Microscopy (HRTEM) and Atomic Force Microscopy (AFM). Analysis revealed increasing biaxial tensile stress of 0.6918 ± 0.04, 1.1084, 1.1814 GPa in heterostructures with decreasing buffer thickness of 600, 400, 200 nm respectively which are summed up with residual tensile strain causing red-shift in RT-PL peak. Also, increasing buffer thickness drastically reduced TD density from the order 10{sup 10} cm{sup −2} to 10{sup 8} cm{sup −2}. Surface morphology through AFM leads to decrease of pits and root mean square value with increasing buffer thickness which are resulted due to reduction of combined effect of strain and TDs.

  13. Tailoring Photoelectrochemical Performance and Stability of Cu(In,Ga)Se2 Photocathode via TiO2-Coupled Buffer Layers.

    PubMed

    Koo, Bonhyeong; Nam, Sung-Wook; Haight, Richard; Kim, Suncheul; Oh, Seungtaeg; Cho, Minhyung; Oh, Jihun; Lee, Jeong Yong; Ahn, Byung Tae; Shin, Byungha

    2017-02-15

    We report on the photoelectrochemical (PEC) performance and stability of Cu(In,Ga)Se2 (CIGS)-based photocathodes for photocatalytic hydrogen evolution from water. Various functional overlayers, such as CdS, TiO2, ZnxSnyOz, and a combination of the aforementioned, were applied on the CIGS to improve the performance and stability. We identified that the insertion of TiO2 overlayer on p-CIGS/n-buffer layers significantly improves the PEC performance. A multilayered photocathode consisting of CIGS/CdS/TiO2/Pt exhibited the best current-potential characteristics among the tested photocathodes, which demonstrates a power-saved efficiency of 2.63%. However, repeated linear sweep voltammetry resulted in degradation of performance. In this regard, we focused on the PEC durability issues through in-depth chemical characterization that revealed the degradation was attributed to atomic redistribution of elements constituting the photocathode, namely, in-diffusion of Pt catalysts, out-diffusion of elements from the CIGS, and removal of the metal-oxide layers; the best-performing CIGS/CdS/TiO2/Pt photocathode retained its initial performance until the TiO2 overlayer was removed. It was also found that the durability of CIGS photocathodes with a TiO2-coated metal-oxide buffer layer such as ZnxSnyOz was better than those with a TiO2-coated CdS, and the degradation mechanism was different, suggesting that the stability of a CIGS-based photocathode can be improved by careful design of the structure.

  14. The W-W02 Oxygen Fugacity Buffer at High Pressures and Temperatures: Implications for f02 Buffering and Metal-silicate Partitioning

    NASA Technical Reports Server (NTRS)

    Shofner, G. A.; Campbell, A. J.; Danielson, L.; Righter, K.

    2013-01-01

    Oxygen fugacity (fO2) controls multivalent phase equilibria and partitioning of redox-sensitive elements, and it is important to understand this thermodynamic parameter in experimental and natural systems. The coexistence of a metal and its oxide at equilibrium constitutes an oxygen buffer which can be used to control or calculate fO2 in high pressure experiments. Application of 1-bar buffers to high pressure conditions can lead to inaccuracies in fO2 calculations because of unconstrained pressure dependencies. Extending fO2 buffers to pressures and temperatures corresponding to the Earth's deep interior requires precise determinations of the difference in volume (Delta) V) between the buffer phases. Synchrotron x-ray diffraction data were obtained using diamond anvil cells (DAC) and a multi anvil press (MAP) to measure unit cell volumes of W and WO2 at pressures and temperatures up to 70 GPa and 2300 K. These data were fitted to Birch-Murnaghan 3rd-order thermal equations of state using a thermal pressure approach; parameters for W are KT = 306 GPa, KT' = 4.06, and aKT = 0.00417 GPa K-1. Two structural phase transitions were observed for WO2 at 4 and 32 GPa with structures in P21/c, Pnma and C2/c space groups. Equations of state were fitted for these phases over their respective pressure ranges yielding the parameters KT = 190, 213, 300 GPa, KT' = 4.24, 5.17, 4 (fixed), and aKT = 0.00506, 0.00419, 0.00467 GPa K-1 for the P21/c, Pnma and C2/c phases, respectively. The W-WO2 buffer (WWO) was extended to high pressure by inverting the W and WO2 equations of state to obtain phase volumes at discrete pressures (1-bar to 100 GPa, 1 GPa increments) along isotherms (300 to 3000K, 100 K increments). The slope of the absolute fO2 of the WWO buffer is positive with increasing temperature up to approximately 70 GPa and is negative above this pressure. The slope is positive along isotherms from 1000 to 3000K with increasing pressure up to at least 100 GPa. The WWO buffer is at

  15. Magnetic anisotropy of crystalline Fe films grown on (001) GaAs substrates using Ge buffer layers

    NASA Astrophysics Data System (ADS)

    Bac, Seul-Ki; Lee, Hakjoon; Lee, Sangyeop; Choi, Seonghoon; Yoo, Taehee; Lee, Sanghoon; Liu, X.; Furdyna, J. K.

    2016-05-01

    Magnetic anisotropy of Fe films grown on (001) GaAs substrates using Ge buffer layers were investigated by planar Hall effect measurements. In addition to phenomena arising from dominant cubic symmetry of the Fe specimen, the study of angular dependence of magnetization reversal revealed breaking of this symmetry in the form of systematic asymmetric shifts of magnetic hysteresis loops around the <110 > crystallographic directions. We ascribe such symmetry breaking to an admixture of uniaxial anisotropy associated with the [100] direction in the Fe film. To determine the parameters associated with this uniaxial anisotropy, we quantitatively analyze the asymmetric shifts of the hysteresis loop centers from the <110 > directions. Even though the value of these parameters turns out to be relatively small compared to that of the cubic anisotropy (by about two orders of magnitude), they survive up to room temperature.

  16. Preparation of GaN Nanostructures by Laser Ablation of ga Metal

    NASA Astrophysics Data System (ADS)

    El Nadi, Lotfia; Omar, Magdy M.; Mehena, Galila A.; Moniem, Hussien M. A.

    2011-06-01

    In the present study, GaN nanodots (0D) and nanowires (1D) nanostructures were prepared on stainless steal substrates applying laser ablation technique. The target of Ga metal mixed with NaNO2 was introduced in a central bore of a graphite rod of a confined geometry set up. The laser beam was normally focused onto the central bore and the ablated plume of Ga metal was deposited on stainless steal substrate lying below the graphite rod in an atmosphere of slow flow of nitrogen gas with or without ammonia vapor. The pulsed N2 laser beam having a wavelength of 337± 2 nm, pulse duration 15±1 ns and energy per pulse of 15±1 m J, could be focused on the central bore by a cylindrical quartz lens to a spot of dimensions 500 × 700 μm2 t providing target irradiance of 0.2-0.3 GW/cm2 per pulse. The ablated plum was collected after several thousand laser shots. The morphology and structure of the formed nanostructures were investigated by Scanning electron microscope and Energy Dispersive X-Ray Spectroscopy. The growth mechanism is most likely by Solid-Liquid-Vapor phase during the laser ablation processes. The role of the carbon, the NaNO2 and the flowing gas on the growth of Nanostructures of GaN are discussed.

  17. Improved interface properties of GaN-based metal-oxide-semiconductor devices with thin Ga-oxide interlayers

    NASA Astrophysics Data System (ADS)

    Yamada, Takahiro; Ito, Joyo; Asahara, Ryohei; Watanabe, Kenta; Nozaki, Mikito; Hosoi, Takuji; Shimura, Takayoshi; Watanabe, Heiji

    2017-06-01

    The impact of thin Ga-oxide (GaOx) interlayers on the electrical properties of GaN-based metal-oxide-semiconductor (MOS) devices was systematically investigated. Thin thermal oxides formed at around 900 °C were found to be beneficial for improving the electrical properties of insulator/GaN interfaces, despite the fact that thermal oxidation of GaN surfaces at high temperatures proceeds by means of grain growth. Consequently, well-behaved capacitance-voltage characteristics of SiO2/GaOx/n-GaN stacked MOS capacitors with an interface state density (Dit) as low as 1.7 × 1011 cm-2 eV-1 were demonstrated. Moreover, the Dit value was further reduced for the SiO2/GaOx/GaN capacitor with a 2-nm-thick sputter-deposited GaOx interlayer. These results clearly indicate the intrinsically superior nature of the oxide/GaN interfaces and provide plausible guiding principles for fabricating high-performance GaN-MOS devices with thin GaOx interlayers.

  18. [Acid buffer capacity of sewage sludge barrier for immobilization of heavy metals].

    PubMed

    Zhang, Hu-Yuan; Ju, Yuan-Yuan; Fan, Zhi-Ming; Wang, Bao

    2010-12-01

    Employing the anaerobic activities of microorganisms, sewage sludge can be used as a barrier to immobilize the heavy metals leached from tailings. Due to the interactions between sewage sludge barrier and acid mine drainage (AMD), it is possible that the heavy metals that have been immobilized previously might be released out. The acid buffering capacity (ABC) of sewage sludge suspensions with various anaerobic incubation time and the effect of ABC on the mobility of heavy metals were investigated by acid titration tests. Test results showed that ABC of sewage sludge suspensions was increased with the solid-liquid ratio of the suspensions and the anaerobic incubation time, and that carbonate and organics play an important role in acid buffer of sewage sludge suspensions. During the acid titration test, Zn, Pb and Cu were released out obviously following the order of Zn > Cu > Pb as pH was decreased less than 6.2. A mathematical model was established to predict the ABC consumption of the sewage sludge barrier under AMD penetration condition. The simulation results showed that a sewage sludge barrier with 2.0 m thickness, even undergoing 666-years acidification by AMD under 10.0 m water head, can maintain a condition of pH > or = 6.2 and, therefore, keep immobilize the heavy metals of AMD in the barrier.

  19. Direct label-free electrical immunodetection of transplant rejection protein biomarker in physiological buffer using floating gate AlGaN/GaN high electron mobility transistors.

    PubMed

    Tulip, Fahmida S; Eteshola, Edward; Desai, Suchita; Mostafa, Salwa; Roopa, Subramanian; Evans, Boyd; Islam, Syed Kamrul

    2014-06-01

    Monokine induced by interferon gamma (MIG/CXCL9) is used as an immune biomarker for early monitoring of transplant or allograft rejection. This paper demonstrates a direct electrical, label-free detection method of recombinant human MIG with anti-MIG IgG molecules in physiologically relevant buffer environment. The sensor platform used is a biologically modified GaN-based high electron mobility transistor (HEMT) device. Biomolecular recognition capability was provided by using high affinity anti-MIG monoclonal antibody to form molecular affinity interface receptors on short N-hydroxysuccinimide-ester functionalized disulphide (DSP) self-assembled monolayers (SAMs) on the gold sensing gate of the HEMT device. A floating gate configuration has been adopted to eliminate the influences of external gate voltage. Preliminary test results with the proposed chemically treated GaN HEMT biosensor show that MIG can be detected for a wide range of concentration varying from 5 ng/mL to 500 ng/mL.

  20. Investigation of Surface Defects in AlInSb Metamorphic Buffer (MB) Grown on GaSb

    NASA Astrophysics Data System (ADS)

    Addamane, Sadhvikas; Shima, Darryl; Soudachanh, Amy Lili; Hains, Christopher; Dawson, Ralph; Balakrishnan, Ganesh

    2016-12-01

    We have conducted an investigation of the different surface defects observed on InAlSb metamorphic buffers grown on GaSb. There are two different defect modes found in this system: crystallographic surface features and surface cross-hatching. We have characterized both defect modes using optical microscopy, scanning electron microscopy, and plan-view and cross-sectional transmission electron microscopy. It is found that particulates from polishing slurry or incomplete oxide desorption on the substrate before the growth are the root of the crystallographic defects. Surface crosshatching is shown to be caused by the coalescence of strained islands formed at the onset of buffer layer growth. Despite the presence of these defects, we have shown that substantial areas of the surface are defect-free and can be effectively used for realizing devices on this platform. Threading dislocation and crystallographic defect densities are found to be ˜1 × 107/cm2 and ˜5 × 104/cm2, respectively.

  1. Self-organization of dislocation-free, high-density, vertically aligned GaN nanocolumns involving InGaN quantum wells on graphene/SiO2 covered with a thin AlN buffer layer.

    PubMed

    Hayashi, Hiroaki; Konno, Yuta; Kishino, Katsumi

    2016-02-05

    We demonstrated the self-organization of high-density GaN nanocolumns on multilayer graphene (MLG)/SiO2 covered with a thin AlN buffer layer by RF-plasma-assisted molecular beam epitaxy. MLG/SiO2 substrates were prepared by the transfer of CVD graphene onto thermally oxidized SiO2/Si [100] substrates. Employing the MLG with an AlN buffer layer enabled the self-organization of high-density and vertically aligned nanocolumns. Transmission electron microscopy observation revealed that no threading dislocations, stacking faults, or twinning defects were included in the self-organized nanocolumns. The photoluminescence (PL) peak intensities of the self-organized GaN nanocolumns were 2.0-2.6 times higher than those of a GaN substrate grown by hydride vapor phase epitaxy. Moreover, no yellow luminescence or ZB-phase GaN emission was observed from the nanocolumns. An InGaN/GaN MQW and p-type GaN were integrated into GaN nanocolumns grown on MLG, displaying a single-peak PL emission at a wavelength of 533 nm. Thus, high-density nitride p-i-n nanocolumns were fabricated on SiO2/Si using the transferred MLG interlayer, indicating the possibility of developing visible nanocolumn LEDs on graphene/SiO2.

  2. GaN nanowire arrays by a patterned metal-assisted chemical etching

    NASA Astrophysics Data System (ADS)

    Wang, K. C.; Yuan, G. D.; Wu, R. W.; Lu, H. X.; Liu, Z. Q.; Wei, T. B.; Wang, J. X.; Li, J. M.; Zhang, W. J.

    2016-04-01

    We developed an one-step and two-step metal-assisted chemical etching method to produce self-organized GaN nanowire arrays. In one-step approach, GaN nanowire arrays are synthesized uniformly on GaN thin film surface. However, in a two-step etching processes, GaN nanowires are formed only in metal uncovered regions, and GaN regions with metal-covering show nano-porous sidewalls. We propose that nanowires and porous nanostructures are tuned by sufficient and limited etch rate, respectively. PL spectra shows a red-shift of band edge emission in GaN nanostructures. The formation mechanism of nanowires was illustrated by two separated electrochemical reactions occur simultaneously. The function of metals and UV light was illustrated by the scheme of potential relationship between energy bands in Si, GaN and standard hydrogen electrode potential of solution and metals.

  3. Study towards integration of In0.53Ga0.47As on 300 mm Si for CMOS sub-7 nm node: Development of thin graded InxGa1-xAs buffers on GaAs

    NASA Astrophysics Data System (ADS)

    Mols, Y.; Kunert, B.; Gaudin, G.; Langer, R.; Caymax, M.

    2016-10-01

    High-quality InxGa1-xAs layers with indium composition between 0.46 and 0.50 have been grown in a 300 mm industrial MOVPE reactor using ≤1 μm thin InxGa1-xAs buffers on 2″ GaAs substrates. Aggressive grading of 3.7 to 3.8% misfit/μm, fast growth rates in the range of 0.2-2.2 nm/s and low growth temperatures of 530 °C and 450 °C were used. AFM reveals a significant difference in root mean square surface roughness of 3.6 nm (530 °C) versus 15.5 nm (450 °C). Cross-section TEM analysis shows that for both temperatures threading dislocations are effectively confined to the buffer region. However, at 450 °C phase separation is observed in the upper part of the structure. From plan-view TEM threading dislocation densities as low as 1×105 cm-2 and 4.5×105 cm-2 are estimated for growth at 530 °C and 450 °C, respectively.

  4. High Cubic-Phase Purity InN on MgO (001) Using Cubic-Phase GaN as a Buffer Layer

    SciTech Connect

    Sanorpim, S.; Kuntharin, S.; Parinyataramas, J.; Yaguchi, H.; Iwahashi, Y.; Orihara, M.; Hijikata, Y.; Yoshida, S.

    2011-12-23

    High cubic-phase purity InN films were grown on MgO (001) substrates by molecular beam epitaxy with a cubic-phase GaN buffer layer. The cubic phase purity of the InN grown layers has been analyzed by high resolution X-ray diffraction, {mu}-Raman scattering and transmission electron microscopy. It is evidenced that the hexagonal-phase content in the InN overlayer much depends on hexagonal-phase content in the cubic-phase GaN buffer layer and increases with increasing the hexagonal-phase GaN content. From Raman scattering measurements, in addition, the InN layer with lowest hexagonal component (6%), only Raman characteristics of cubic TO{sub InN} and LO{sub InN} modes were observed, indicating a formation of a small amount of stacking faults, which does not affect on vibrational property.

  5. The role of AlGaN buffers and channel thickness in the electronic transport properties of Al x In1- x N/AlN/GaN heterostructures

    NASA Astrophysics Data System (ADS)

    Amirabbasi, M.

    2016-01-01

    We try to theoretically analyze the reported experimental data of the Al x In1- x N/AlN/GaN heterostructures grown by MOCVD and quantitatively investigate the effects of AlGaN buffers and the GaNchannel thickness on the electrical transport properties of these systems. Also, we obtain the most important effective parameters of the temperature-dependent mobility in the range 35-300 K. Our results show that inserting a 1.1 μm thick Al0.04Ga0.96N buffer enhances electron mobility by decreasing the effect of phonons, the interface roughness, and dislocation and crystal defect scattering mechanisms. Also, as the channel thickness increases from 20 nm to 40 nm, the electron mobility increases from 2200 to 2540 cm2/(V s) and from 870 to 1000 cm2/(V s) at 35 and 300 K respectively, which is attributed to the reduction in the dislocation density and the strain-induced field. Finally, the reported experimental data show that inserting a 450 nm graded AlGaN layer before an Al0.04Ga0.96N buffer causes a decrease in the electron mobility, which is attributed to the enhancement of the lateral size of roughness, the dislocation density, and the strain-induced field in this sample.

  6. The role of AlGaN buffers and channel thickness in the electronic transport properties of Al{sub x}In{sub 1–x}N/AlN/GaN heterostructures

    SciTech Connect

    Amirabbasi, M.

    2016-01-15

    We try to theoretically analyze the reported experimental data of the Al{sub x}In{sub 1–x}N/AlN/GaN heterostructures grown by MOCVD and quantitatively investigate the effects of AlGaN buffers and the GaNchannel thickness on the electrical transport properties of these systems. Also, we obtain the most important effective parameters of the temperature-dependent mobility in the range 35–300 K. Our results show that inserting a 1.1 μm thick Al{sub 0.04}Ga{sub 0.96}N buffer enhances electron mobility by decreasing the effect of phonons, the interface roughness, and dislocation and crystal defect scattering mechanisms. Also, as the channel thickness increases from 20 nm to 40 nm, the electron mobility increases from 2200 to 2540 cm{sup 2}/(V s) and from 870 to 1000 cm{sup 2}/(V s) at 35 and 300 K respectively, which is attributed to the reduction in the dislocation density and the strain-induced field. Finally, the reported experimental data show that inserting a 450 nm graded AlGaN layer before an Al{sub 0.04}Ga{sub 0.96}N buffer causes a decrease in the electron mobility, which is attributed to the enhancement of the lateral size of roughness, the dislocation density, and the strain-induced field in this sample.

  7. Ab initio study of Ga-GaN system: Transition from adsorbed metal atoms to a metal–semiconductor junction

    SciTech Connect

    Witczak, Przemysław; Kempisty, Pawel; Strak, Pawel

    2015-11-15

    Ab initio studies of a GaN(0001)-Ga system with various thicknesses of a metallic Ga layer were undertaken. The studied systems extend from a GaN(0001) surface with a fractional coverage of gallium atoms to a Ga-GaN metal–semiconductor (m–s) contact. Electronic properties of the system are simulated using density functional theory calculations for different doping of the bulk semiconductor. It is shown that during transition from a bare GaN(0001) surface to a m–s heterostructure, the Fermi level stays pinned at a Ga-broken bond highly dispersive surface state to Ga–Ga states at the m–s interface. Adsorption of gallium leads to an energy gain of about 4 eV for a clean GaN(0001) surface and the energy decreases to 3.2 eV for a thickly Ga-covered surface. The transition to the m–s interface is observed. For a thick Ga overlayer such interface corresponds to a Schottky contact with a barrier equal to 0.9 and 0.6 eV for n- and p-type, respectively. Bond polarization-related dipole layer occurring due to an electron transfer to the metal leads to a potential energy jump of 1.5 eV, independent on the semiconductor doping. Additionally high electron density in the Ga–Ga bond region leads to an energy barrier about 1.2 eV high and 4 Å wide. This feature may adversely affect the conductivity of the n-type m–s system.

  8. Output power enhancement in AlGaN/GaN heterostructure field-effect transistors with multilevel metallization

    NASA Astrophysics Data System (ADS)

    Oh, Seung Kyu; Jang, Taehoon; Pouladi, Sara; Jo, Young Je; Ko, Hwa-Young; Ryou, Jae-Hyun; Kwak, Joon Seop

    2017-01-01

    To improve wafer utilization efficiency and heat dissipation performance, this paper proposes multilevel metallization-structured, lateral-type AlGaN/GaN heterostructure field-effect transistors (HFETs) on a 150 mm Si substrate using photosensitive polyimide (PSPI) as the intermetal dielectric layer. The maximum drain current of the HFETs is 46.3 A, which is 240% higher than that of conventional AlGaN/GaN HFETs with the same die size. Furthermore, the drain current drop of the HFETs under high-bias operation is reduced from 14.07 to 8.09%, as compared to that of conventional HFETs.

  9. Microstructures of YBa2Cu3Oy Layers Deposited on Conductive Layer-Buffered Metal Tapes

    NASA Astrophysics Data System (ADS)

    Ichinose, Ataru; Hashimoto, Masayuki; Horii, Shigeru; Doi, Toshiya

    REBa2Cu3Oy (REBCO; RE: rare-earth elements)-coated conductors (CCs) have high potential for use in superconducting devices. In particular, REBCO CCs are useful for superconducting devices working at relatively high temperatures near 77 K. The important issues in their applications are high performance, reliability and low cost. To date, sufficient performance for some applications has almost been achieved by considerable efforts. The establishment of the reliability of superconducting devices is under way at present. The issue of low cost must be resolved to realize the application of superconducting devices in the near future. Therefore, we have attempted several ways to reduce the cost of REBCO CCs. The coated conductors using a Nb-doped SrTiO3 buffer layer and Ni-plated Cu and stainless steel laminate metal tapes have recently been developed to eliminate the use of electric stabilization layers of Cu and Ag, which are expected to reduce the material cost. Good superconducting properties are obtained at 77 K. The critical current density (JC) at 77 K under a magnetic self-field is determined to be more than 2x106 A/cm2. The microstructures of the CCs are analyzed by transmission electron microscopy to obtain a much higher quality. By microscopic structure analysis, an overgrowth of the buffer layer is observed at a grain boundary of the metal substrate, which is one of the reasons for the high JC.

  10. Step buffer layer of Al0.25Ga0.75N/Al0.08Ga0.92N on P-InAlN gate normally-off high electron mobility transistors

    NASA Astrophysics Data System (ADS)

    Shrestha, Niraj M.; Li, Yiming; Chang, E. Y.

    2016-07-01

    Normally-off AlGaN/GaN high electron mobility transistors (HEMTs) are indispensable devices for power electronics as they can greatly simplify circuit designs in a cost-effective way. In this work, the electrical characteristics of p-type InAlN gate normally-off AlGaN/GaN HEMTs with a step buffer layer of Al0.25Ga0.75N/Al0.1Ga0.9N is studied numerically. Our device simulation shows that a p-InAlN gate with a step buffer layer allows the transistor to possess normally-off behavior with high drain current and high breakdown voltage simultaneously. The gate modulation by the p-InAlN gate and the induced holes appearing beneath the gate at the GaN/Al0.25Ga0.75N interface is because a hole appearing in the p-InAlN layer can effectively vary the threshold voltage positively. The estimated threshold voltage of the normally-off HEMTs explored is 2.5 V at a drain bias of 25 V, which is 220% higher than the conventional p-AlGaN normally-off AlGaN/GaN gate injection transistor (GIT). Concurrently, the maximum current density of the explored HEMT at a drain bias of 10 V slightly decreases by about 7% (from 240 to 223 mA mm-1). At a drain bias of 15 V, the current density reached 263 mA mm-1. The explored structure is promising owing to tunable positive threshold voltage and the maintenance of similar current density; notably, its breakdown voltage significantly increases by 36% (from 800 V, GIT, to 1086 V). The engineering findings of this study indicate that novel p-InAlN for both the gate and the step buffer layer can feature a high threshold voltage, large current density and high operating voltage for advanced AlGaN/GaN HEMT devices.

  11. Growth of ZnO(0001) on GaN(0001)/4H-SiC buffer layers by plasma-assisted hybrid molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Adolph, David; Tingberg, Tobias; Ive, Tommy

    2015-09-01

    Plasma-assisted molecular beam epitaxy was used to grow ZnO(0001) layers on GaN(0001)/4H-SiC buffer layers deposited in the same growth chamber equipped with both N- and O-plasma sources. The GaN buffer layers were grown immediately before initiating the growth of ZnO. Using a substrate temperature of 445 °C and an O2 flow rate of 2.5 standard cubic centimeters per minute, we obtained ZnO layers with statistically smooth surfaces having a root-mean-square roughness of 0.3 nm and a peak-to-valley distance of 3 nm as revealed by atomic force microscopy. The full-width-at-half-maximum for x-ray rocking curves obtained across the ZnO(0002) and ZnO(10 1 bar 5) reflections was 198 and 948 arcsec, respectively. These values indicated that the mosaicity of the ZnO layer was comparable to the corresponding values of the underlying GaN buffer layer. Reciprocal space maps showed that the in-plane relaxation of the GaN and ZnO layers was 82% and 73%, respectively, and that the relaxation occurred abruptly during the growth. Room-temperature Hall-effect measurements revealed that the layers were inherently n-type and had an electron concentration of 1×1019 cm-3 and a Hall mobility of 51 cm2/V s.

  12. Direct Growth of a-Plane GaN on r-Plane Sapphire by Metal Organic Chemical Vapor Deposition

    NASA Astrophysics Data System (ADS)

    Hsu, Hsiao-Chiu; Su, Yan-Kuin; Huang, Shyh-Jer; Wang, Yu-Jen; Wu, Chun-Ying; Chou, Ming-Chieh

    2010-04-01

    In this study, we had demonstrated the direct growth of nonpolar a-plane GaN on an r-plane sapphire by metal organic chemical vapor deposition (MOCVD) without any buffer layer. First, in this experiment, we had determined the optimum temperature for two-step growth, including obtaining three-dimensional (3D) GaN islands in the nucleation layer and coalescing with a further two-dimensional (2D) growth mode. The result shows that the nucleation layer grown under high temperature (1150 °C) leads to large islands with few grain boundaries. Under the same temperature, the effect of the V/III ratio on the growth of the overlaying GaN layer to obtain a flat and void free a-plane GaN layer is also studied. The result indicates one can directly grow a smooth epitaxial layer on an r-plane sapphire by changing the V/III ratio. The rms roughness decreases from 13.61 to 2.02 nm. The GaN crystal quality is verified using a mixed acid to etch the film surface. The etch pit density (EPD) is 3.16 ×107 cm-2.

  13. Thin, high quality GaInP compositionally graded buffer layers grown at high growth rates for metamorphic III-V solar cell applications

    NASA Astrophysics Data System (ADS)

    Garcia, I.; France, R. M.; Geisz, J. F.; Simon, J.

    2014-05-01

    The metamorphic growth of lattice-mismatched materials has allowed optimizing the bandgap combination in multijunction solar cells for the solar spectrum under consideration. Buffer structures are used to accommodate the lattice-mismatch by introducing dislocations and relaxing the material in a controlled way. However, the metamorphic buffers typically involve significant growth time and material usage, which increases the cost of these solar cells. In this work, the thinning of buffer structures with continuously, linearly graded misfit is addressed with the goal of increasing the cost-effectiveness of metamorphic multijunction solar cells. The relaxation dynamics and quality of the buffer layers analyzed were assessed by in-situ stress measurements and ex-situ measurements of residual strain, threading dislocation density and surface roughness. Their ultimate quality has been tested using these buffers as templates for the growth of 1 eV Ga0.73In0.27As solar cells. The deleterious effect of thinning the grade layer of these buffer structures from 2 to 1 μm was investigated. It is shown that prompting the relaxation of the buffer by using a stepwise misfit jump at the beginning of the grade layer improves the quality of the thinned buffer structure. The residual threading dislocation density of the optimized thin buffers, grown at a high growth rate of 7 μm/h, is 3×106 cm-2, and solar cells on these buffers exhibit near-ideal carrier collection efficiency and a Voc of 0.62 V at 1-sun direct terrestrial spectrum.

  14. The GaN/noble metal interface: metal induced gap states and Schottky barrier heights

    NASA Astrophysics Data System (ADS)

    Picozzi, Silvia; Continenza, Alessandra; Satta, Guido; Massidda, Sandro; Freeman, Arthur J.

    2000-03-01

    We present ab-initio FLAPW (E. Wimmer, H. Krakauer, M. Weinert and A.J. Freeman, Phys. Rev. B 24), 864 (1981) calculations on N-terminated [001] ordered GaN/Ag and GaN/Au interfaces. Our results show that the density of gap states is appreciable in the interface semiconductor layer; however, the gap states are efficiently screened and become negligible already in the sub-interface layer. The gap states' decay length in the semiconductor side is about 2.0 ± 0.1 Å\\: and seems to be independent of the deposited metal, therefore being, to a good approximation, a bulk GaN property. Our estimated Schottky barrier heights for the GaN/noble-metal interfaces are both smaller than that of the GaN/Al barrier, showing a large dispersion in the values - which seems to exclude the possibility of a Fermi level pinning within the gap. Finally, we investigate the role of atomic positions and of different chemical species at the interface region in determining the final value of the potential line-up.

  15. Characterization of Zn(O,S) Buffer Layers for Cu(In,Ga)Se2 Solar Cells.

    PubMed

    Choi, Ji Hyun; Jung, Sung Hee; Chung, Chee Won

    2016-05-01

    Zn(O,S) thin films were deposited using a ZnS target under Ar/O2 gases by radio-frequency magnetron sputtering. As the O2 concentration increased, the deposition rates of the Zn(O,S) films decreased due to increase of O-. The crystalline structure of Zn(O,S) was maintained at up to 0.6% O2, while the films became unstable at the condition exceeding 0.8% O2. This was attributed to incomplete nucleation and film growth on the substrate at the room temperature. Additionally, optical emission spectroscopy analysis indicated that an increased O- intensity at high O2 concentration was responsible for the slow deposition rate and increased oxygen concentration of the films. X-ray diffraction and scanning electron microscopy revealed the formation of a Zn(O,S) crystal structure with partial substitution of O for S and uniform and dense grains of the films. X-ray photoelectron spectroscopy showed that the Zn(O,S) films have a uniform composition of each element and consisted of a mixed crystal structure of Zn(O,S) with Zn-O bonding. Overall, the results of this study confirmed that Zn(O,S) films deposited by radio-frequency sputtering using Ar/O2 gas at room temperature can be applied to Cu(In,Ga)Se2 solar cells as a buffer layer.

  16. Theoretical Study of the Effect of an AlGaAs Double Heterostructure on Metal-Semiconductor-Metal Photodetector Performance

    NASA Technical Reports Server (NTRS)

    Salem, Ali F.; Smith, Arlynn W.; Brennan, Kevin F.

    1994-01-01

    The impulse and square-wave input response of different GaAs metal-semiconductor-metal photodetector (MSM) designs are theoretically examined using a two dimensional drift- diffusion numerical calculation with a thermionic-field emission boundary condition model for the heterojunctions. The rise time and the fall time of the output signal current are calculated for a simple GaAs, epitaxially grown, MSM device as well as for various double-heterostructure barrier devices. The double heterostructure devices consist of an AlGaAs layer sandwiched between the top GaAs active, absorption layer and the bottom GaAs substrate. The effect of the depth of the AlGaAs layer on the speed and responsivity of the MSM devices is examined. It is found that there is an optimal depth, at fixed applied bias, of the AlGaAs layer within the structure that provides maximum responsivity at minimal compromise in speed.

  17. Low defect InGaAs quantum well selectively grown by metal organic chemical vapor deposition on Si(100) 300 mm wafers for next generation non planar devices

    NASA Astrophysics Data System (ADS)

    Cipro, R.; Baron, T.; Martin, M.; Moeyaert, J.; David, S.; Gorbenko, V.; Bassani, F.; Bogumilowicz, Y.; Barnes, J. P.; Rochat, N.; Loup, V.; Vizioz, C.; Allouti, N.; Chauvin, N.; Bao, X. Y.; Ye, Z.; Pin, J. B.; Sanchez, E.

    2014-06-01

    Metal organic chemical vapor deposition of GaAs, InGaAs, and AlGaAs on nominal 300 mm Si(100) at temperatures below 550 °C was studied using the selective aspect ratio trapping method. We clearly show that growing directly GaAs on a flat Si surface in a SiO2 cavity with an aspect ratio as low as 1.3 is efficient to completely annihilate the anti-phase boundary domains. InGaAs quantum wells were grown on a GaAs buffer and exhibit room temperature micro-photoluminescence. Cathodoluminescence reveals the presence of dark spots which could be associated with the presence of emerging dislocation in a direction parallel to the cavity. The InGaAs layers obtained with no antiphase boundaries are perfect candidates for being integrated as channels in n-type metal oxide semiconductor field effect transistor (MOSFET), while the low temperatures used allow the co-integration of p-type MOSFET.

  18. Strain states of AlN/GaN-stress mitigating layer and their effect on GaN buffer layer grown by ammonia molecular beam epitaxy on 100-mm Si(111)

    SciTech Connect

    Ravikiran, L.; Radhakrishnan, K.; Agrawal, M.; Dharmarasu, N.; Munawar Basha, S.

    2013-09-28

    The effect of strain states of AlN/GaN-stress mitigating layer (SML) on buried crack density and its subsequent influence on the residual stresses in GaN buffer layers grown using ammonia-molecular beam epitaxy on 100-mm Si(111) substrate has been investigated. Different stages involved in the formation of buried cracks, which are crack initialization, growth of relaxed AlN layer, and subsequent lateral over growth, are identified using in-situ curvature measurements. While the increase of GaN thickness in AlN/GaN-SML enhanced its compressive strain relaxation and resulted in reduced buried crack spacing, the variation of AlN thickness did not show any effect on the crack spacing. Moreover, the decrease in the crack spacing (or increase in the buried crack density) was found to reduce the residual compression in 1st and 2nd GaN layers of AlN/GaN-SML structure. The higher buried crack density relaxed the compressive strain in 1st GaN layer, which further reduced its ability to compensate the tensile stress generated during substrate cool down, and hence resulted in lower residual compressive stress in 2nd GaN layer.

  19. Strain states of AlN/GaN-stress mitigating layer and their effect on GaN buffer layer grown by ammonia molecular beam epitaxy on 100-mm Si(111)

    NASA Astrophysics Data System (ADS)

    Ravikiran, L.; Radhakrishnan, K.; Dharmarasu, N.; Agrawal, M.; Munawar Basha, S.

    2013-09-01

    The effect of strain states of AlN/GaN-stress mitigating layer (SML) on buried crack density and its subsequent influence on the residual stresses in GaN buffer layers grown using ammonia-molecular beam epitaxy on 100-mm Si(111) substrate has been investigated. Different stages involved in the formation of buried cracks, which are crack initialization, growth of relaxed AlN layer, and subsequent lateral over growth, are identified using in-situ curvature measurements. While the increase of GaN thickness in AlN/GaN-SML enhanced its compressive strain relaxation and resulted in reduced buried crack spacing, the variation of AlN thickness did not show any effect on the crack spacing. Moreover, the decrease in the crack spacing (or increase in the buried crack density) was found to reduce the residual compression in 1st and 2nd GaN layers of AlN/GaN-SML structure. The higher buried crack density relaxed the compressive strain in 1st GaN layer, which further reduced its ability to compensate the tensile stress generated during substrate cool down, and hence resulted in lower residual compressive stress in 2nd GaN layer.

  20. AlGaN/GaN metal-insulator-semiconductor high electron mobility transistors with reduced leakage current and enhanced breakdown voltage using aluminum ion implantation

    SciTech Connect

    Sun, Shichuang; Fu, Kai E-mail: cqchen@mail.hust.edu.cn; Yu, Guohao; Zhang, Zhili; Song, Liang; Deng, Xuguang; Li, Shuiming; Sun, Qian; Cai, Yong; Zhang, Baoshun; Qi, Zhiqiang; Dai, Jiangnan; Chen, Changqing E-mail: cqchen@mail.hust.edu.cn

    2016-01-04

    This letter has studied the performance of AlGaN/GaN metal-insulator-semiconductor high electron mobility transistors on silicon substrate with GaN buffer treated by aluminum ion implantation for insulating followed by a channel regrown by metal–organic chemical vapor deposition. For samples with Al ion implantation of multiple energies of 140 keV (dose: 1.4 × 10{sup 14} cm{sup −2}) and 90 keV (dose: 1 × 10{sup 14} cm{sup −2}), the OFF-state leakage current is decreased by more than 3 orders and the breakdown voltage is enhanced by nearly 6 times compared to the samples without Al ion implantation. Besides, little degradation of electrical properties of the 2D electron gas channel is observed where the maximum drain current I{sub DSmax} at a gate voltage of 3 V was 701 mA/mm and the maximum transconductance g{sub mmax} was 83 mS/mm.

  1. Buffer layers on metal surfaces having biaxial texture as superconductor substrates

    DOEpatents

    Paranthaman, Mariappan; Lee, Dominic F.; Kroeger, Donald M.; Goyal, Amit

    2000-01-01

    Buffer layer architectures are epitaxially deposited on biaxially-textured rolled substrates of nickel and/or copper and their alloys for high current conductors, and more particularly buffer layer architectures such as Y.sub.2 O.sub.3 /Ni, YSZ/Y.sub.2 O.sub.3 /Ni, RE.sub.2 O.sub.3 /Ni, (RE=Rare Earth), RE.sub.2 O.sub.3 /Y.sub.2 O.sub.3 /Ni, RE.sub.2 O.sub.3 /CeO.sub.2 /Ni, and RE.sub.2 O.sub.3 /YSZ/CeO.sub.2 /Ni, Y.sub.2 O.sub.3 /Cu, YSZ/Y.sub.2 O.sub.3 /Cu, RE.sub.2 O.sub.3 /Cu, RE.sub.2 O.sub.3 /Y.sub.2 O.sub.3 /Cu, RE.sub.2 O.sub.3 /CeO.sub.2 /Cu, and RE.sub.2 O.sub.3 /YSZ/CeO.sub.2 /Cu. Deposition methods include physical vapor deposition techniques which include electron-beam evaporation, rf magnetron sputtering, pulsed laser deposition, thermal evaporation, and solution precursor approaches, which include chemical vapor deposition, combustion CVD, metal-organic decomposition, sol-gel processing, and plasma spray.

  2. Compatibility of the selective area growth of GaN nanowires on AlN-buffered Si substrates with the operation of light emitting diodes.

    PubMed

    Musolino, M; Tahraoui, A; Fernández-Garrido, S; Brandt, O; Trampert, A; Geelhaar, L; Riechert, H

    2015-02-27

    AlN layers with thicknesses between 2 and 14 nm were grown on Si(111) substrates by molecular beam epitaxy. The effect of the AlN layer thickness on the morphology and nucleation time of spontaneously formed GaN nanowires (NWs) was investigated by scanning electron microscopy and line-of-sight quadrupole mass spectrometry, respectively. We observed that the alignment of the NWs grown on these layers improves with increasing layer thickness while their nucleation time decreases. Our results show that 4 nm is the smallest thickness of the AlN layer that allows the growth of well-aligned NWs with short nucleation time. Such an AlN buffer layer was successfully employed, together with a patterned SiOx mask, for the selective-area growth (SAG) of vertical GaN NWs. In addition, we fabricated light-emitting diodes (LEDs) from NW ensembles that were grown by means of self-organization phenomena on bare and on AlN-buffered Si substrates. A careful characterization of the optoelectronic properties of the two devices showed that the performance of NW-LEDs on bare and AlN-buffered Si is similar. Electrical conduction across the AlN buffer is facilitated by a high number of grain boundaries that were revealed by transmission electron microscopy. These results demonstrate that grainy AlN buffer layers on Si are compatible both with the SAG of GaN NWs and LED operation. Therefore, this study is a first step towards the fabrication of LEDs on Si substrates based on homogeneous NW ensembles.

  3. A nanoporous AlN layer patterned by anodic aluminum oxide and its application as a buffer layer in a GaN-based light-emitting diode.

    PubMed

    Chen, Lung-Chien; Wang, Chih-Kai; Huang, Jenn-Bin; Hong, Lu-Sheng

    2009-02-25

    This work investigates a nanoporous aluminum nitride (AlN) layer prepared using an anodic aluminum oxide (AAO) process and its application as a buffer layer for a GaN-based light-emitting diode (LED) fabricated on sapphire substrate. Following this AAO process, the average pore spacing and pore diameter of the nanoporous AlN layer were in the ranges 180-200 nm and 100-150 nm, respectively. The light output power of the GaN-based LED with a nanoporous AlN layer was about 53% higher than that of a GaN-based LED without a nanoporous AlN layer at an injection current of 20 mA. At an injection current of 80 mA, the light output power was increased by about 34%.

  4. Crystallization kinetics of Ga metallic nano-droplets under As flux.

    PubMed

    Bietti, S; Somaschini, C; Sanguinetti, S

    2013-05-24

    We present an experimental investigation of the crystallization dynamics of Ga nano-droplets under As flux. The transformation of the metallic Ga contained in the droplets into a GaAs nano-island proceeds by increasing the size of a tiny ring of GaAs which is formed just after the Ga deposition at the rim of a droplet. The GaAs crystallization rate depends linearly on the liquid-solid interface area. The maximum growth rate is set by the As flux impinging on the droplet, thus showing an efficient As incorporation and transport despite the predicted low solubility of the As in metallic Ga at the crystallization temperatures.

  5. Modified dislocation filter method: toward growth of GaAs on Si by metal organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Hu, Haiyang; Wang, Jun; He, Yunrui; Liu, Kai; Liu, Yuanyuan; Wang, Qi; Duan, Xiaofeng; Huang, Yongqing; Ren, Xiaomin

    2016-06-01

    In this paper, metamorphic growth of GaAs on (001) oriented Si substrate, with a combination method of applying dislocation filter layer (DFL) and three-step growth process, was conducted by metal organic chemical vapor deposition. The effectiveness of the multiple InAs/GaAs self-organized quantum dot (QD) layers acting as a dislocation filter was researched in detail. And the growth conditions of the InAs QDs were optimized by theoretical calculations and experiments. A 2-μm-thick buffer layer was grown on the Si substrate with the three-step growth method according to the optimized growth conditions. Then, a 114-nm-thick DFL and a 1-μm-thick GaAs epilayer were grown. The results we obtained demonstrated that the DFL can effectively bend dislocation direction via the strain field around the QDs. The optimal structure of the DFL is composed of three-layer InAs QDs with a growth time of 55 s. The method could reduce the etch pit density from about 3 × 106 cm-2 to 9 × 105 cm-2 and improve the crystalline quality of the GaAs epilayers on Si.

  6. Epitaxial Growth and Electro-Optical Properties of Metal GaAs Superlattices.

    DTIC Science & Technology

    1991-05-31

    34Phase sta- bility versus the lattice mismatch of (100)Col-.Ga. thin films on (100)GaAs," J. Vac. Sci. Technol. (in press). T. C. Kuo and K. L. Wang...and annealing of Co-,Ga, thin films on (100)GaAs," J. Mats. Res. (submitted to). (b.) Published Papers in Referred Journals R. A. Fiscer, H. D. Kaesz...and Y. K. Kim: "Deposition of transition-metal and mixed- metal thin films from organometallic precursors," New J. Chem. 14, 527-534 (1990). Y. K

  7. Effect of rear-surface buffer layer on performance of lift-off Cu(In,Ga)Se2 solar cells

    NASA Astrophysics Data System (ADS)

    Aoyagi, Kenta; Tamura, Akihiro; Takakura, Hideyuki; Minemoto, Takashi

    2014-01-01

    The effect of an Au and MoOx rear-surface buffer layer inserted between Cu(In,Ga)Se2 (CIGS) and ZnO:Al on solar cell performances was examined. The lift-off CIGS solar cell without a rear-surface buffer layer showed particular characteristics of two series-connected diodes in the reverse direction, and its short-circuit current density was almost zero. In contrast, the Au or MoOx rear-surface buffer layer improved these characteristics. Although the lift-off CIGS solar cell with the Au rear-surface buffer layer showed shunt characteristics and low efficiency, the efficiency of the lift-off CIGS solar cell with the MoOx rear-surface buffer layer was approximately 50% of that of substrate-type CIGS solar cells. Diode parameters of lift-off CIGS solar cells were determined by fitting analysis of current density-voltage curves using a proposed new equivalent circuit model for lift-off CIGS solar cells.

  8. Optimization of the ZnS Buffer Layer by Chemical Bath Deposition for Cu(In,Ga)Se2 Solar Cells.

    PubMed

    Jeon, Dong-Hwan; Hwang, Dae-Kue; Kim, Dae-Hwan; Kang, Jin-Kyu; Lee, Chang-Seop

    2016-05-01

    We evaluated a ZnS buffer layer prepared using a chemical bath deposition (CBD) process for application in cadmium-free Cu(In,Ga)Se2 (CIGS) solar cells. The ZnS buffer layer showed good transmittance (above 90%) in the spectral range from 300 to 800 nm and was non-toxic compared with the CdS buffer layers normally used in CIGS solar cells. The CBD process was affected by several deposition conditions. The deposition rate was dependent on the ammonia concentration (complexing agent). When the ammonia concentration was either too high or low, a decrease in the deposition rate was observed. In addition, post heat treatments at high temperatures had detrimental influences on the ZnS buffer layers because portions of the ZnS thin films were transformed into ZnO. With optimized deposition conditions, a CIGS solar cell with a ZnS buffer layer showed an efficiency of 14.18% with a 0.23 cm2 active area under 100 mW/cm2 illumination.

  9. Heterogeneous Integration of Epitaxial Ge on Si using AlAs/GaAs Buffer Architecture: Suitability for Low-power Fin Field-Effect Transistors

    PubMed Central

    Hudait, Mantu K.; Clavel, Michael; Goley, Patrick; Jain, Nikhil; Zhu, Yan

    2014-01-01

    Germanium-based materials and device architectures have recently appeared as exciting material systems for future low-power nanoscale transistors and photonic devices. Heterogeneous integration of germanium (Ge)-based materials on silicon (Si) using large bandgap buffer architectures could enable the monolithic integration of electronics and photonics. In this paper, we report on the heterogeneous integration of device-quality epitaxial Ge on Si using composite AlAs/GaAs large bandgap buffer, grown by molecular beam epitaxy that is suitable for fabricating low-power fin field-effect transistors required for continuing transistor miniaturization. The superior structural quality of the integrated Ge on Si using AlAs/GaAs was demonstrated using high-resolution x-ray diffraction analysis. High-resolution transmission electron microscopy confirmed relaxed Ge with high crystalline quality and a sharp Ge/AlAs heterointerface. X-ray photoelectron spectroscopy demonstrated a large valence band offset at the Ge/AlAs interface, as compared to Ge/GaAs heterostructure, which is a prerequisite for superior carrier confinement. The temperature-dependent electrical transport properties of the n-type Ge layer demonstrated a Hall mobility of 370 cm2/Vs at 290 K and 457 cm2/Vs at 90 K, which suggests epitaxial Ge grown on Si using an AlAs/GaAs buffer architecture would be a promising candidate for next-generation high-performance and energy-efficient fin field-effect transistor applications. PMID:25376723

  10. Heterogeneous integration of epitaxial Ge on Si using AlAs/GaAs buffer architecture: suitability for low-power fin field-effect transistors.

    PubMed

    Hudait, Mantu K; Clavel, Michael; Goley, Patrick; Jain, Nikhil; Zhu, Yan

    2014-11-07

    Germanium-based materials and device architectures have recently appeared as exciting material systems for future low-power nanoscale transistors and photonic devices. Heterogeneous integration of germanium (Ge)-based materials on silicon (Si) using large bandgap buffer architectures could enable the monolithic integration of electronics and photonics. In this paper, we report on the heterogeneous integration of device-quality epitaxial Ge on Si using composite AlAs/GaAs large bandgap buffer, grown by molecular beam epitaxy that is suitable for fabricating low-power fin field-effect transistors required for continuing transistor miniaturization. The superior structural quality of the integrated Ge on Si using AlAs/GaAs was demonstrated using high-resolution x-ray diffraction analysis. High-resolution transmission electron microscopy confirmed relaxed Ge with high crystalline quality and a sharp Ge/AlAs heterointerface. X-ray photoelectron spectroscopy demonstrated a large valence band offset at the Ge/AlAs interface, as compared to Ge/GaAs heterostructure, which is a prerequisite for superior carrier confinement. The temperature-dependent electrical transport properties of the n-type Ge layer demonstrated a Hall mobility of 370 cm(2)/Vs at 290 K and 457 cm(2)/Vs at 90 K, which suggests epitaxial Ge grown on Si using an AlAs/GaAs buffer architecture would be a promising candidate for next-generation high-performance and energy-efficient fin field-effect transistor applications.

  11. Concentration of 68Ga via solvent extraction.

    PubMed

    Bokhari, Tanveer Hussain; Mushtaq, A; Khan, Islam Ullah

    2009-01-01

    The metallic cation, (68)Ga (III) is suitable for complexation with chelators either naked or conjugated with biological macromolecules, however, such labeling procedure requires high chemical purity and concentrated solutions of (68)Ga (III), which cannot be sufficiently fulfilled by the presently available (68)Ge/(68)Ga generator eluate. A method to increase the concentration and purity of (68)Ga obtained from a commercial (68)Ge/(68)Ga generator has been developed. The (68)Ga eluate (1M HCl) is extracted in methyl ethyl ketone, which is evaporated and taken in a small volume of buffer.

  12. Strain modulating half-metallicity of semifluorinated GaN nanosheets

    NASA Astrophysics Data System (ADS)

    Xiao, Meixia; Ao, Zhimin; Xu, Tianhan; He, Cheng; Song, Haiyang; Wang, Lei

    2016-06-01

    Strain-dependent half-metallicity of two-bilayer GaN nanosheets (NSs) with fluorinated Ga atoms is studied using density-functional theory. Our results demonstrate that the band gaps in spin-up states and half-metallic gaps vary with biaxial strain and uniaxial compressive strain along the zigzag direction, while the metallic behaviors in spin-down states remain regardless of strain. However, biaxial strain has a better effect on the half-metallicity. Semifluorinated GaN NSs may undergo a structural phase transition from wurtzite to graphite-like phase at high biaxial tension. Therefore, biaxial strain tuning half-metallicity efficiently could provide a viable route to GaN-based spintronic nanodevices.

  13. Reduced dislocation density in GaxIn1–xP compositionally graded buffer layers through engineered glide plane switch

    SciTech Connect

    Schulte, Kevin L.; France, Ryan M.; McMahon, William E.; Norman, Andrew G.; Guthrey, Harvey L.; Geisz, John F.

    2016-11-17

    In this work we develop control over dislocation glide dynamics in GaxIn1-xP compositionally graded buffer layers (CGBs) through control of CuPt ordering on the group-III sublattice. The ordered structure is metastable in the bulk, so any glissile dislocation that disrupts the ordered pattern will release stored energy, and experience an increased glide force. Here we show how this connection between atomic ordering and dislocation glide force can be exploited to control the threading dislocation density (TDD) in GaxIn1-xP CGBs. When ordered GaxIn1-xP is graded from the GaAs lattice constant to InP, the order parameter ..eta.. decreases as x decreases, and dislocation glide switches from one set of glide planes to the other. This glide plane switch (GPS) is accompanied by the nucleation of dislocations on the new glide plane, which typically leads to increased TDD. We develop control of the GPS position within a GaxIn1-xP CGB through manipulation of deposition temperature, surfactant concentration, and strain-grading rate. We demonstrate a two-stage GaxIn1-xP CGB from GaAs to InP with sufficiently low TDD for high performance devices, such as the 4-junction inverted metamorphic multi-junction solar cell, achieved through careful control the GPS position. Here, experimental results are analyzed within the context of a model that considers the force balance on dislocations on the two competing glide planes as a function of the degree of ordering.

  14. Design of optimal buffer layers for CuInGaSe2 thin-film solar cells(Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Lordi, Vincenzo; Varley, Joel B.; He, Xiaoqing; Rockett, Angus A.; Bailey, Jeff; Zapalac, Geordie H.; Mackie, Neil; Poplavskyy, Dmitry; Bayman, Atiye

    2016-09-01

    Optimizing the buffer layer in manufactured thin-film PV is essential to maximize device efficiency. Here, we describe a combined synthesis, characterization, and theory effort to design optimal buffers based on the (Cd,Zn)(O,S) alloy system for CIGS devices. Optimization of buffer composition and absorber/buffer interface properties in light of several competing requirements for maximum device efficiency were performed, along with process variations to control the film and interface quality. The most relevant buffer properties controlling performance include band gap, conduction band offset with absorber, dopability, interface quality, and film crystallinity. Control of an all-PVD deposition process enabled variation of buffer composition, crystallinity, doping, and quality of the absorber/buffer interface. Analytical electron microscopy was used to characterize the film composition and morphology, while hybrid density functional theory was used to predict optimal compositions and growth parameters based on computed material properties. Process variations were developed to produce layers with controlled crystallinity, varying from amorphous to fully epitaxial, depending primarily on oxygen content. Elemental intermixing between buffer and absorber, particularly involving Cd and Cu, also is controlled and significantly affects device performance. Secondary phase formation at the interface is observed for some conditions and may be detrimental depending on the morphology. Theoretical calculations suggest optimal composition ranges for the buffer based on a suite of computed properties and drive process optimizations connected with observed film properties. Prepared by LLNL under Contract DE-AC52-07NA27344.

  15. Nanoselective area growth and characterization of dislocation-free InGaN nanopyramids on AlN buffered Si(111) templates

    SciTech Connect

    Sundaram, S.; El Gmili, Y.; Puybaret, R.; Li, X.; Bonanno, P. L.; Voss, P. L.; Ougazzaden, A.; Pantzas, K.; Patriarche, G.; Salvestrini, J. P.

    2015-09-14

    We report the metal organic chemical vapor deposition growth of dislocation-free 100 nm thick hexagonal InGaN nanopyramid arrays with up to 33% of indium content by nano-selective area growth on patterned AlN/Si (111) substrates. InGaN grown on SiO{sub 2} patterned templates exhibit high selectivity. Their single crystal structure is confirmed by scanning transmission electron microscope combined with an energy dispersive X-ray analysis, which also reveals the absence of threading dislocations in the InGaN nanopyramids due to elastic strain relaxation mechanisms. Cathodoluminescence measurements on a single InGaN nanopyramid clearly show an improvement of the optical properties when compared to planar InGaN grown under the same conditions. The good structural, morphological, and optical quality of the InGaN nanostructures grown on AlN/Si indicates that the nano-selective area growth technology is attractive for the realization of site-controlled indium-rich InGaN nanostructure-based devices and can also be transferred to other highly mismatched substrates.

  16. Metal oxide, Group V-VI chalcogenides and GaN/AlGaN photodetectors

    NASA Astrophysics Data System (ADS)

    Hasan, Md. Rezaul

    In this work, a simple, low-cost and catalyst free one-step solution processing of onedimensional Sb2S3 nanostructures on polyimide substrates was done. This structure demonstrated its potential application as a photoconductor in the UV and visible regime. Using-field emission scanning electron microscopy (SEM), grazing incidence X-Ray diffraction, Raman spectra and transmission electron microscopy measurements, it was shown that the Sb 2S3 films have high crystallinity, uniform morphology and nearstoichiometric composition. Further, using tauc plot, it was found that the films have a direct bandgap of 1.67 eV. MSM photodetectors, fabricated using these films showed a clear photo response in both UV as well as visible wavelength. These devices showed UV on/off ratio as high as 160 under the light intensity of 30 mW/cm2 and a small rise time and fall time of 44 ms 28 ms respectively. The effect of geometry of metal pad and bonding wire orientation of a multi-channel FET on the coupling of THz radiation was studied. The spatial variation images were taken by raster scan with the resolution of 0.07 mm steps in both x and y directions. An effective gate bias, where the effect of noise is minimum and photoresponse is maximum, was used for imaging. By applying VGS =-2.8V and VDS =380mV, the images were taken for all different combinations of activated bonding wires and metal pads. It was observed that, effect of bonding wire orientation is negligible for the large source pad as the radiation is coupled basically between drain and gate pad. Effect of drain bonding wire on coupling depends on the maximum width or diameter of metal pad and the incoming wavelength. In this work, Position of activated Drain pad and orientation of respective bonding wire defined the image tilting angle. Voltage drop across the shorting metal between drain pads, also played a role in increasing the asymmetry by selectively exciting a certain portion of FET Channels more than the other portion

  17. How is (68)Ga labeling of macrocyclic chelators influenced by metal ion contaminants in (68)Ge/(68)Ga generator eluates?

    PubMed

    Šimeček, Jakub; Hermann, Petr; Wester, Hans-Jürgen; Notni, Johannes

    2013-01-01

    To assess the influence of Zn(2+) , Cu(2+) , Fe(3+) , Al(3+) , Ti(IV) , and Sn(IV) on incorporation of (68) Ga(3+) into pendant-arm macrocyclic chelators, the (68) Ga labeling of 1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA), 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA), 1,4,7-triazacyclononane-1,4,7-tris[methyl(2-carboxyethyl)phosphinic acid]) (TRAP), and 1,4,7-triazacyclononane-1-[methyl(2-carboxyethyl)phosphinic acid]-4,7-bis[methyl(2-hydroxymethyl)phosphinic acid] (NOPO), as well as their peptide conjugates, was investigated in the presence of varying concentrations of these metal ions. The (68) Ga labeling yield for carboxylate-type chelators NOTA and DOTA is decreased at lower metal ion contaminant concentrations compared with phosphinate-type chelators TRAP and NOPO. The latter are able to rapidly exchange coordinated Zn(II) with (68) Ga(3+) , as confirmed by mass spectrometry and (31) P NMR spectroscopy. (68) Ga labeling of Zn(II) complexes of TRAP and NOPO proceeds as efficient as labeling of neat NOTA; this applies also to the corresponding peptide conjugates of these chelators. This behavior results in substantially improved selectivity for Ga(3+) and, therefore, in more robust and reliable (68) Ga labeling procedures. In addition, none of the investigated chelators binds (68) Ge, rendering post-labeling purification protocols, for example, solid-phase extraction, a reliable means of removal of (68) Ge contamination from (68) Ga radiopharmaceuticals. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  18. Surface-bound iron: a metal ion buffer in the marine brown alga Ectocarpus siliculosus?

    PubMed

    Miller, Eric P; Böttger, Lars H; Weerasinghe, Aruna J; Crumbliss, Alvin L; Matzanke, Berthold F; Meyer-Klaucke, Wolfram; Küpper, Frithjof C; Carrano, Carl J

    2014-02-01

    Although the iron uptake and storage mechanisms of terrestrial/higher plants have been well studied, the corresponding systems in marine algae have received far less attention. Studies have shown that while some species of unicellular algae utilize unique mechanisms of iron uptake, many acquire iron through the same general mechanisms as higher plants. In contrast, the iron acquisition strategies of the multicellular macroalgae remain largely unknown. This is especially surprising since many of these organisms represent important ecological and evolutionary niches in the coastal marine environment. It has been well established in both laboratory and environmentally derived samples, that a large amount of iron can be 'non-specifically' adsorbed to the surface of marine algae. While this phenomenon is widely recognized and has prompted the development of experimental protocols to eliminate its contribution to iron uptake studies, its potential biological significance as a concentrated iron source for marine algae is only now being recognized. This study used an interdisciplinary array of techniques to explore the nature of the extensive and powerful iron binding on the surface of both laboratory and environmental samples of the marine brown alga Ectocarpus siliculosus and shows that some of this surface-bound iron is eventually internalized. It is proposed that the surface-binding properties of E. siliculosus allow it to function as a quasibiological metal ion 'buffer', allowing iron uptake under the widely varying external iron concentrations found in coastal marine environments.

  19. Comprehensive strain and band gap analysis of PA-MBE grown AlGaN/GaN heterostructures on sapphire with ultra thin buffer

    SciTech Connect

    Mahata, Mihir Kumar; Ghosh, Saptarsi; Jana, Sanjay Kumar; Bag, Ankush; Kumar, Rahul; Chakraborty, Apurba; Biswas, Dhrubes; Mukhopadhyay, Partha

    2014-11-15

    In this work, cluster tool (CT) Plasma Assisted Molecular Beam Epitaxy (PA-MBE) grown AlGaN/GaN heterostructure on c-plane (0 0 0 1) sapphire (Al{sub 2}O{sub 3}) were investigated by High Resolution X-ray Diffraction (HRXRD), Room Temperature Raman Spectroscopy (RTRS), and Room Temperature Photoluminescence (RTPL). The effects of strain and doping on GaN and AlGaN layers were investigated thoroughly. The out-of-plane (‘c’) and in-plane (‘a’) lattice parameters were measured from RTRS analysis and as well as reciprocal space mapping (RSM) from HRXRD scan of (002) and (105) plane. The in-plane (out-of plane) strain of the samples were found to be −2.5 × 10{sup −3}(1 × 10{sup −3}), and −1.7 × 10{sup −3}(2 × 10{sup −3}) in GaN layer and 5.1 × 10{sup −3} (−3.3 × 10{sup −3}), and 8.8 × 10{sup −3}(−1.3 × 10{sup −3}) in AlGaN layer, respectively. In addition, the band structures of AlGaN/GaN interface were estimated by both theoretical (based on elastic theory) and experimental observations of the RTPL spectrum.

  20. Deep-level transient spectroscopy of interfacial states in ``buffer-free'' p-i-n GaSb/GaAs devices

    NASA Astrophysics Data System (ADS)

    Aziz, Mohsin; Ferrandis, Philippe; Mesli, Abdelmadjid; Hussain Mari, Riaz; Francisco Felix, Jorlandio; Sellai, Azzouz; Jameel, Dler; Al Saqri, Noor; Khatab, Almontaser; Taylor, David; Henini, Mohamed

    2013-10-01

    A systematic study was carried out on defect states in Interfacial Misfit (IMF) unpassivated and Te-passivated IMF in p-i-n GaSb/GaAs devices using Deep Level Transient Spectroscopy (DLTS) and Laplace DLTS. Additionally, Current-Voltage (I-V) measurements were performed, which showed that the turn-on voltage (Von) of passivated samples is lower than that for unpassivated samples; an effect which can be explained by the introduction of new defects states near to the interface of GaSb/GaAs, where Te was incorporated to passivate the IMF. The Capacitance-Voltage (C-V) analysis demonstrates that these new states are the consequence of adding Te at the misfit of GaSb/GaAs. Furthermore, DLTS measurements reveal a distribution of states including a main midgap energy level, namely the well documented EL2 trap, with some peculiar behaviour. Most of these levels are related to interface states that are generated by the mismatch between GaAs and GaSb. Originally, the addition of Te atoms was thought to passivate these interface states. On the contrary, this paper, which attempts at correlating the current-voltage and capacitance-voltage characteristics to the DLTS results, shows clearly that Te atoms increase the density of interface states.

  1. The growth and characterization of GaInAsSb and AlGaAsSb on GaSb by metal-organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Biefeld, R. M.; Cederberg, J. G.; Peake, G. M.; Kurtz, S. R.

    2001-05-01

    The growth conditions for GaInAsSb and AlGaAsSb using metal-organic chemical vapor deposition in an high speed rotating disk reactor are described. Trimethylindium, triethylgallium, arsine, and trimethylantimony were used as precursors for the growth of GaInAsSb. Triethylgallium, ethyldimethylamine alane, triethylantimony, and arsine were the precursors used for the growth of AlGaAsSb. These materials were doped both n- and p-type using a mixture of diethyltellurium and diethylzinc as sources. An optimum growth temperature of 520°C was determined for the growth of GaInAsSb. Growth at this temperature yielded a root-mean-square (rms) surface roughness of 0.142 nm. AlGaAsSb could be grown over the range of 500-600°C with somewhat rougher surfaces (rms>0.7 nm). The photoluminescence was found to correlate with surface roughness, increasing with smoother surfaces. AlGaAsSb mesa isolated diodes were prepared and characterized. These diodes showed good current-voltage characteristics with breakdown voltages greater than -6 V.

  2. 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.

  3. Current transport mechanism in a metal-GaN nanowire Schottky diode.

    PubMed

    Lee, Seung-Yong; Lee, Sang-Kwon

    2007-12-12

    We investigated nano-Schottky diodes of gallium nitride nanowires with three Schottky metals (Cr, Ti, and Au) using current-voltage characteristics. All of the GaN nano-Schottky diodes showed a rectifying behavior. The abnormal electrical characteristics of a single GaN nanowire Schottky diode can be explained by a thermionic-field emission and an enhancement of the tunneling effects owing to both the relatively high concentration of the GaN nanowire itself and the nanoscale junction size of the GaN nanowire Schottky diodes.

  4. Reaction and barrier formation at metal-GaP(110) interfaces

    NASA Astrophysics Data System (ADS)

    Miyano, K. E.; Cao, R.; Kendelewicz, T.; Wahi, A. K.; Lindau, I.; Spicer, W. E.

    1990-01-01

    The interfacial chemistry of Cu, Ag, Au, Ni, Pd, Al, Ga, In, Sn, and Bi deposited on cleaved GaP(110) surfaces has been studied using soft-x-ray photoemission spectroscopy. Of the noble metals, Cu and Au tend to disassociate the GaP, whereas the Ag shows little sign of reactivity with the substrate. The transition metals Ni and Pd react strongly with the GaP to form phosphides in which Ga is segregated. Of the column-III overlayers, Ga and In display strong clustering and little reactivity with the substrate, but the interface with Al shows a cation replacement reaction similar to that seen at Al/GaAs(110). Sn and Bi exhibit Stranski-Krastanov growth, with the establishment of metallic islands on a laminar first monolayer. Despite the differences in reactivity, the barrier heights for all the metals but In are observed to stabilize in the range of 1.14 to 1.46 eV. Hence the n-type GaP barrier height shows a much weaker dependence on the overlayer work function than reported previously. As with GaAs(110) this Fermi-level stabilization position is in the range of both the defect levels as created by irradiation, and the theoretical charge neutrality level toward which metal-induced gap states should move the surface Fermi level. The influence of overlayer reactivity, morphology, and metallicity on the barrier development is discussed in relation to these two potential sources of interface states.

  5. Method of deforming a biaxially textured buffer layer on a textured metallic substrate and articles therefrom

    DOEpatents

    Lee, Dominic F.; Kroeger, Donald M.; Goyal, Amit

    2000-01-01

    The present invention provides methods and biaxially textured articles having a deformed epitaxial layer formed therefrom for use with high temperature superconductors, photovoltaic, ferroelectric, or optical devices. A buffer layer is epitaxially deposited onto biaxially-textured substrates and then mechanically deformed. The deformation process minimizes or eliminates grooves, or other irregularities, formed on the buffer layer while maintaining the biaxial texture of the buffer layer. Advantageously, the biaxial texture of the buffer layer is not altered during subsequent heat treatments of the deformed buffer. The present invention provides mechanical densification procedures which can be incorporated into the processing of superconducting films through the powder deposit or precursor approaches without incurring unfavorable high-angle grain boundaries.

  6. Zn (O,S) buffer layers by atomic layer deposition in Cu (In,Ga)Se2 based thin film solar cells: Band alignment and sulfur gradient

    NASA Astrophysics Data System (ADS)

    Platzer-Björkman, C.; Törndahl, T.; Abou-Ras, D.; Malmström, J.; Kessler, J.; Stolt, L.

    2006-08-01

    Thin film solar cells with the structure sodalimeglass /Mo/Cu(In,Ga)Se2/Zn(O,S)/ZnO/ZnO:Al are studied for varying thickness and sulfur content of the Zn (O,S) buffer layer. These Zn (O,S) layers were deposited by atomic layer deposition (ALD) at 120°C. Devices with no or small concentrations of sulfur in the buffer layer show low open-circuit voltages. This is explained by the cliff, or negative conduction-band offset (CBO), of -0.2eV measured by photoelectron spectroscopy (PES) and optical methods for the Cu (In,Ga)Se2 (CIGS)/ZnO interface. Devices with ZnS buffer layers exhibit very low photocurrent. This is expected from the large positive CBO (spike) of 1.2eV measured for the CIGS /ZnS interface. For devices with Zn (O,S) buffer layers, two different deposition recipes were found to yield devices with efficiencies equal to or above reference devices in which standard CdS buffer layers were used; ultrathin Zn (O,S) layers with S /Zn ratios of 0.8-0.9, and Zn (O,S) layers of around 30nm with average S /Zn ratios of 0.3. The sulfur concentration increases towards the CIGS interface as revealed by transmission electron microscopy and in vacuo PES measurements. The occurrence of this sulfur gradient in ALD-Zn (O,S) is explained by longer incubation time for ZnO growth compared to ZnS growth. For the Zn (O,S) film with high sulfur content, the CBO is large which causes blocking of the photocurrent unless the film is ultrathin. For the Zn (O,S) film with lower sulfur content, a CBO of 0.2eV is obtained which is close to ideal, according to simulations. Efficiencies of up to 16.4% are obtained for devices with this buffer layer.

  7. Physical-Chemical Treatment of Metals and Radionuclides in the Saturated Zone Using Colloidal Buffers - 12515

    SciTech Connect

    Lai, Yenjung; Borden, Robert C.; Alperin, Ed

    2012-07-01

    There are numerous acidic plumes throughout the DOE complex and the nation as a whole. Low aquifer pH is a major concern since many important radionuclides (Pu, Ra, Sr, Tc) and metals (Cd, Co, Cs, Mn, Ni, Pb, Zn) strongly sorb to iron hydroxides and aluminosilicates under neutral to alkaline conditions, but are mobile in acidic plumes. To effectively use natural and enhanced attenuation (NEA) for management of these contaminants, we must be able to raise aquifer pH and maintain it at background levels until the external acid loading to the aquifer has dissipated. Geochemical modeling showed that a permeable reactive barrier (PRB) formed by injection of colloidal Mg(OH){sub 2} would last much longer than colloidal Ca(OH){sub 2} due to the much lower solubility of Mg(OH){sub 2}. Assuming a 1,000 meq/L suspension of colloidal Mg(OH)2 could be effectively distributed, the PRB could last over twenty years before rejuvenation was required. Preliminary bench-scale treatability studies were conducted to demonstrate the efficacy of increasing the aquifer pH using a colloidal pH buffer. Laboratory studies demonstrated that three different colloidal Mg(OH){sub 2} suspensions (concentration varied from 1,000 to 1,250 meq/L) could be transported through the columns packed with aquifer sand without significant permeability loss. The time before suspension breakthrough into the column effluent varied with surface treatment, indicating the Mg(OH)2 retention and PRB longevity could be controlled by varying the suspension surface treatment. (authors)

  8. Improved emission efficiency of a-plane GaN light emitting diodes with silica nano-spheres integrated into a-plane GaN buffer layer

    NASA Astrophysics Data System (ADS)

    Park, S. H.; Park, J.; You, D.-J.; Joo, K.; Moon, D.; Jang, J.; Kim, D.-U.; Chang, H.; Moon, S.; Song, Y.-K.; Lee, G.-D.; Jeon, H.; Xu, J.; Nanishi, Y.; Yoon, E.

    2012-05-01

    A simple and inexpensive technique to improve the emission efficiency of nonpolar a-plane light emitting diodes (LEDs) is proposed. The 3-dimensional growth nature of a-plane GaN was utilized to form the regrowth template of a-plane GaN. Subsequently, the controlled integration of silica nano-spheres (CIS) into the regrowth template is performed to improve the crystal quality of a-plane GaN by epitaxial lateral overgrowth method. In addition, the CIS improves light extraction by the scattering process. The light output power from the CIS a-plane GaN LEDs showed 130%-150% increase compared to that of LED without silica nano-spheres.

  9. Buffering the buffer

    Treesearch

    Leslie M. Reid; Sue Hilton

    1998-01-01

    Riparian buffer strips are a widely accepted tool for helping to sustain aquatic ecosystems and to protect downstream resources and values in forested areas, but controversy persists over how wide a buffer strip is necessary. The physical integrity of stream channels is expected to be sustained if the characteristics and rates of tree fall along buffered reaches are...

  10. Ohmic contact formation between metal and AlGaN/GaN heterostructure via graphene insertion

    NASA Astrophysics Data System (ADS)

    Sung Park, Pil; Reddy, Kongara M.; Nath, Digbijoy N.; Yang, Zhichao; Padture, Nitin P.; Rajan, Siddharth

    2013-04-01

    A simple method for the creation of Ohmic contact to 2D electron gas in AlGaN/GaN high electron-mobility transistors using Cr/graphene layer is demonstrated. A weak temperature dependence of this Ohmic contact observed in the range 77 to 300 K precludes thermionic emission or trap-assisted hopping as possible carrier-transport mechanisms. It is suggested that the Cr/graphene combination acts akin to a doped n-type semiconductor in contact with AlGaN/GaN heterostructure, and promotes carrier transport along percolating Al-lean paths through the AlGaN layer. This use of graphene offers a simple method for making Ohmic contacts to AlGaN/GaN heterostructures, circumventing complex additional processing steps involving high temperatures. These results could have important implications for the fabrication and manufacturing of AlGaN/GaN-based microelectronic and optoelectronic devices/sensors of the future.

  11. Photovoltaic Performance and Interface Behaviors of Cu(In,Ga)Se2 Solar Cells with a Sputtered-Zn(O,S) Buffer Layer by High-Temperature Annealing.

    PubMed

    Wi, Jae-Hyung; Kim, Tae Gun; Kim, Jeong Won; Lee, Woo-Jung; Cho, Dae-Hyung; Han, Won Seok; Chung, Yong-Duck

    2015-08-12

    We selected a sputtered-Zn(O,S) film as a buffer material and fabricated a Cu(In,Ga)Se2 (CIGS) solar cell for use in monolithic tandem solar cells. A thermally stable buffer layer was required because it should withstand heat treatment during processing of top cell. Postannealing treatment was performed on a CIGS solar cell in vacuum at temperatures from 300-500 °C to examine its thermal stability. Serious device degradation particularly in VOC was observed, which was due to the diffusion of thermally activated constituent elements. The elements In and Ga tend to out-diffuse to the top surface of the CIGS, while Zn diffuses into the interface of Zn(O,S)/CIGS. Such rearrangement of atomic fractions modifies the local energy band gap and band alignment at the interface. The notch-shape induced at the interface after postannealing could function as an electrical trap during electron transport, which would result in the reduction of solar cell efficiency.

  12. Photoelectric characteristics of metal-Ga{sub 2}O{sub 3}-GaAs structures

    SciTech Connect

    Kalygina, V. M. Vishnikina, V. V.; Petrova, Yu. S.; Prudaev, I. A.; Yaskevich, T. M.

    2015-03-15

    We investigate the effect of thermal annealing in argon and of oxygen plasma processing on the photoelectric properties of GaAs-Ga{sub 2}O{sub 3}-Me structures. Gallium-oxide films are fabricated by photostimulated electrochemical oxidation of epitaxial gallium-arsenide layers with n-type conductivity. The as-deposited films were amorphous, but their processing in oxygen plasma led to the nucleation of β-Ga{sub 2}O{sub 3} crystallites. The unannealed films are nontransparent in the visible and ultraviolet (UV) ranges and there is no photocurrent in structures based on them. After annealing at 900°C for 30 min, the gallium-oxide films contain only β-Ga{sub 2}O{sub 3} crystallites and become transparent. Under illumination of the Ga{sub 2}O{sub 3}-GaAs structures with visible light, the photocurrent appears. This effect can be attributed to radiation absorption in GaAs. The photocurrent and its voltage dependence are determined by the time of exposure to the oxygen plasma. In the UV range, the sensitivity of the structures increases with decreasing radiation wavelength, starting at λ ≤ 230 nm. This is due to absorption in the Ga{sub 2}O{sub 3} film. Reduction in the structure sensitivity with an increase in the time of exposure to oxygen plasma can be caused by the incorporation of defects both at the Ga{sub 2}O{sub 3}-GaAs interface and in the Ga{sub 2}O{sub 3} film.

  13. Screening of isolates and strains of Rhizobium leguminosarum biovar trifolii for heavy metal resistance using buffered media

    SciTech Connect

    Chaudri, A.M.; McGrath, S.P. . Soil Science Dept.); Giller, K.E. . Wye College, Dept. of Biochemistry and Biological Sciences); Angle, J.S. . Dept. of Agronomy); Chaney, R.L. )

    1993-09-01

    The computer program GEOCHEM-PC was used to calculate the metal ion activities of Cu, Zn, Cd, and Ni in defined media amended with various metal ion buffers at pH 6.6 or 6.0 so that the lowest-observed-effect concentrations (LOECs) of these metals to isolates and strains of Rhizobium leguminosarum biovar trifolii could be determined. Strains from the U.S. Department of Agriculture (USDA) Beltsville (MD) Rhizobium culture collection were generally more tolerant of the metals than any of the isolates from the sludge-treated soil (S-isolates) and those from farm-yard manure-treated soil (F-isolates), although the S- were more metal resistant than the F-isolates. All isolates and strains, however, tolerated much larger concentrations in the buffered systems than those found in the solutions of soils from which they originated. Copper toxicity, using iminodiacetate (IDA), occurred for the F- and S-isolates and USDA strains at concentrations of 16, 47, and 430 [mu]g mL[sup [minus]1], respectively, corresponding to predicted ion activities of 0.002, 0.006, and 0.06 [mu]g ml[sup [minus]1], respectively. The Zn LOECs for the F- and S-isolates, without a buffer, occurred at concentrations of 47 and 207 [mu]g ml[sup [minus]1], respectively, corresponding to predicted ion activities of 37 and 157 [mu]g ml[sup [minus]1], respectively. No toxicity occurred when nitrilotriacetate was used for Cd up to concentrations of 356 [mu]g ml[sup [minus]1]. Nickel concentrations up to 0.6 [mu]g ml[sup [minus]1] had no effect with ethylene-bis(oxyethylenenitrilo)tetraacetate and up to 186 [mu]g ml[sup [minus]1] with IDA.

  14. Electric field modulated half-metallicity of semichlorinated GaN nanosheets

    NASA Astrophysics Data System (ADS)

    Xiao, M. X.; Song, H. Y.; Ao, Z. M.; Xu, T. H.; Wang, L. L.

    2016-11-01

    Through density-functional theory calculations, we investigated the half-metallic properties of semichlorinated gallium nitride (Cl-GaN) nanosheets (NSs) under an electric field F. The results show that the electric field can modulate Cl-GaN NSs efficiently from ferromagnetic metals to half-metals. More interestingly, under a broad range of electric field intensity (-0.10~-1.30 V/Å), Cl-GaN NSs have the excellently half-metallic properties with the band gaps (3.71-0.96 eV) and maximal half-metallic gaps with 0.30 eV in spin-up states and metallic behaviors in spin-down states. Moreover, the total magnetic moment decreases (increases) depending on the negative (positive) F, mainly induced by the unpaired N atoms. Our studies demonstrate that the electronic and magnetic properties of GaN NSs can be delicately tuned by the combined surface modification and electric field, indicating the potential of GaN NSs for developing high-performance spintronic nanodevices.

  15. Second harmonic generation from patterned GaAs inside a subwavelength metallic hole array

    NASA Astrophysics Data System (ADS)

    Fan, Wenjun; Zhang, Shuang; Malloy, K. J.; Brueck, S. R. J.; Panoiu, N. C.; Osgood, R. M.

    2006-10-01

    By extending GaAs dielectric posts with a large second-order nonlinear susceptibility through the holes of a subwavelength metallic hole array coupled to the metal surface-plasma wave, strong second harmonic (SH) signal is observed. The SH signal is strengthened as a result of the enhanced electromagnetic fields inside the hole apertures.

  16. AlN/GaN Metal Insulator Semiconductor Field Effect Transistor on Sapphire Substrate

    NASA Astrophysics Data System (ADS)

    Seo, Sanghyun; Ghose, Kaustav; Zhao, Guang Yuan; Pavlidis, Dimitris

    AlN/GaN Metal Insulator Semiconductor Field Effect Transistors (MISFETs) were designed, simulated and fabricated. DC, S-parameter and power measurements were also performed. Drift-diffusion simulations using DESSIS compared AlN/GaN MISFETs and Al32Ga68N/GaN Heterostructure FETs (HFETs) with the same geometries. The simulation results show the advantages of AlN/GaN MISFETs in terms of higher saturation current, lower gate leakage and higher transconductance than AlGaN/GaN HFETs. First results from fabricated AlN/GaN devices with 1μm gate length and 200μm gate width showed a maximum drain current density of ˜380mA/mm and a peak extrinsic transconductance of 85mS/mm. S-parameter measurements showed that currentgain cutoff frequency (fT) and maximum oscillation frequency (fmax) were 5.85GHz and 10.57GHz, respectively. Power characteristics were measured at 2GHz and showed output power density of 850mW/mm with 23.8% PAE at VDS=15V. To the authors knowledge this is the first report of a systematic study of AlN/GaN MISFETs addressing their physical modeling and experimental high-frequency characteristics including the power performance.

  17. Solar blind metal-semiconductor-metal ultraviolet photodetectors using quasi-alloy of BGaN/GaN superlattices

    NASA Astrophysics Data System (ADS)

    Srour, H.; Salvestrini, J. P.; Ahaitouf, A.; Gautier, S.; Moudakir, T.; Assouar, B.; Abarkan, M.; Hamady, S.; Ougazzaden, A.

    2011-11-01

    Large internal gains that can be obtained in wide band gap semiconductors-based (GaN and ZnO types) Schottky and/or metal-semiconductor-metal photodetectors are generally accompanied by large dark current and time response. We show that, using quasi-alloy of BGaN/GaN superlattices as the active layer, the dark current can be lowered while maintaining high internal gain (up to 3 × 104) for optical power in the nW range and low time response (few tens of ns) for optical power in the W range. Furthermore, the boron incorporation allows the tuning of the cutoff wavelength.

  18. Assessment of spatial distribution of soil heavy metals using ANN-GA, MSLR and satellite imagery.

    PubMed

    Naderi, Arman; Delavar, Mohammad Amir; Kaboudin, Babak; Askari, Mohammad Sadegh

    2017-05-01

    This study aims to assess and compare heavy metal distribution models developed using stepwise multiple linear regression (MSLR) and neural network-genetic algorithm model (ANN-GA) based on satellite imagery. The source identification of heavy metals was also explored using local Moran index. Soil samples (n = 300) were collected based on a grid and pH, organic matter, clay, iron oxide contents cadmium (Cd), lead (Pb) and zinc (Zn) concentrations were determined for each sample. Visible/near-infrared reflectance (VNIR) within the electromagnetic ranges of satellite imagery was applied to estimate heavy metal concentrations in the soil using MSLR and ANN-GA models. The models were evaluated and ANN-GA model demonstrated higher accuracy, and the autocorrelation results showed higher significant clusters of heavy metals around the industrial zone. The higher concentration of Cd, Pb and Zn was noted under industrial lands and irrigation farming in comparison to barren and dryland farming. Accumulation of industrial wastes in roads and streams was identified as main sources of pollution, and the concentration of soil heavy metals was reduced by increasing the distance from these sources. In comparison to MLSR, ANN-GA provided a more accurate indirect assessment of heavy metal concentrations in highly polluted soils. The clustering analysis provided reliable information about the spatial distribution of soil heavy metals and their sources.

  19. Laser spectroscopy with nanometric cells containing atomic vapor of metal: influence of buffer gas

    NASA Astrophysics Data System (ADS)

    Sarkisyan, D.; Hakhumyan, G.; Sargsyan, A.; Mirzoyan, R.; Leroy, C.; Pashayan-Leroy, Y.

    2010-10-01

    Comparison of absorption and fluorescence in a nano-cell containing Rb vapor with other Rb nano-cells with addition of neon gas is presented. It is shown that the effect of collapse and revival of Dicke-type narrowing occurs for Rb nanocells containing N2 as buffer gas under 6 and 20 Torr pressure for the thickness L = λ /2 and L = where λ is the resonant λ, laser wavelength 794 nm (D1 line). Particularly for 6 Torr the line-width of the transmission spectrum for the thickness L =λ/2 is 2 times narrower than that for L = λ. For an ordinary Rb cell with L = 0.1 - 10 cm with addition of buffer gas, the velocity selective optical pumping/saturation (VSOP) resonances in saturated absorption spectra are fully suppressed when the buffer gas pressure > 0.5 Torr. A spectacular difference is that for L = λ, VSOP resonances located at the atomic transitions are still observable even when Ne pressure is >= 6 Torr. Narrowband fluorescence spectra of a nano-cell with L = λ/2 can be used as a convenient tool for online buffer gas pressure monitoring for the conditions when ordinary pressure gauges are unusable. Comparison of electromagnetically induced transparency (EIT) effect in a nano-cell filled with pure (without a buffer gas) Rb with another nano-cell, where buffer gas nitrogen is added, is presented. The use of N2 gas inside Rb nano-cells strongly extends the range of coupling laser detunings in which it is still possible to form EIT resonance.

  20. Impact of Ni/Ge/Au/Ti/Au and Ti/Pt/Au collector metal on GaInP/GaAs HBT characteristics

    NASA Astrophysics Data System (ADS)

    Park, Jae-Woo; Mohammadi, Saeed; Pavlidis, Dimitris

    2000-10-01

    The collector-emitter offset voltage of GaInP/GaAs HBTs grown by chemical-beam epitaxy with reduced toxicity precursors is investigated for Ni/Ge/Au/Ti/Au and Ti/Pt/Au collector contact metals. The offset voltage for HBTs with Ti/Pt/Au collector metal is increased by 0.26 V compared to Ni/Ge/Au/Ti/Au due to the 0.26 eV barrier existing between the n-GaAs subcollector and the Ti/Pt/Au contact metal. Other parameters affected by the collector contact barrier and impacting transistor performance include DC gain, microwave and power performance.

  1. GaN Stress Evolution During Metal-Organic Chemical Vapor Deposition

    SciTech Connect

    Amano, H.; Chason, E.; Figiel, J.; Floro, J.A.; Han, J.; Hearne, S.; Hunter, J.; Tsong, I.

    1998-10-14

    The evolution of stress in gallium nitride films on sapphire has been measured in real- time during metal organic chemical vapor deposition. In spite of the 161%0 compressive lattice mismatch of GaN to sapphire, we find that GaN consistently grows in tension at 1050"C. Furthermore, in-situ stress monitoring indicates that there is no measurable relaxation of the tensile growth stress during annealing or thermal cycling.

  2. Role of electrode metallization in performance of semi-insulating GaAs radiation detectors

    NASA Astrophysics Data System (ADS)

    Dubecký, František; Boháček, Pavol; Sekáčová, Mária; Zaťko, Bohumír; Lalinský, Tibor; Linhart, Vladimír; Šagátová-Perd'ochová, Andrea; Mudroň, Ján; Pospíšil, Stanislav

    2007-06-01

    In the present work, a comparative study of semi-insulating (SI) GaAs radiation detectors with different blocking (Schottky) and ohmic contact metallization is presented. The detectors fabricated from "detector-grade" bulk SI GaAs are characterized by current-voltage measurements and their detection performance is evaluated from pulse-height spectra of 241Am and 57Co γ-sources. Observed results are evaluated and discussed. Importance of the optimized electrodes technology of SI GaAs detector with good performance is demonstrated.

  3. Magneto-optical properties of Nd0.5Bi2.5Fe4GaO12 thin films on glass substrates with various thicknesses prepared using metal-organic decomposition

    NASA Astrophysics Data System (ADS)

    Lou, Gengjian; Yoshida, Tomohiko; Ishibashi, Takayuki

    2015-05-01

    Nd0.5Bi2.5Fe4GaO12 (Bi2.5:NIGG) thin films with thicknesses of d = 200-1200 nm are prepared on Nd2BiFe4GaO12 (Bi1:NIGG) buffer layers on glass substrates using metal-organic decomposition. The shapes of the Faraday rotation spectra and hysteresis did not change with an increasing film thickness. The Faraday rotation angles increased in proportion with the film thickness, indicating that Bi2.5:NIGG grew without any deterioration for thicknesses up to 1200 nm.

  4. An evaporated aluminum metallization for high efficiency GaAs solar cells

    NASA Astrophysics Data System (ADS)

    Ladle Ristow, M.; Kuryla, M. S.; MacMillan, H. F.; Kaminar, N. R.; Virshup, G. F.

    A thick aluminum grid metallization for p-n GaAs solar cells which can be deposited completely by evaporation has been developed. The contacts are weldable, have low specific contact resistance (5 x 10 to the -6th Ohm-sq cm) to p-GaAs, and are compatible with the subsequent processing steps used on a GaAs solar cell pilot line. The total metallization is approximately 4-micron thick with nearly vertical sidewalls, and height-to-width aspect ratios greater than one can be achieved. This cross-sectional geometry provides sufficient current-carrying capacity with minimum obscuration. Large-area (4-sq cm) devices have been fabricated with this aluminum metal scheme, resulting in a median efficiency of 20.52 percent (one-sun, AM0). Fabrication details, test results for large-area cells, and applications for high-temperature stability and concentrator cells are discussed.

  5. Low defect InGaAs quantum well selectively grown by metal organic chemical vapor deposition on Si(100) 300 mm wafers for next generation non planar devices

    SciTech Connect

    Cipro, R.; Gorbenko, V.; Baron, T. Martin, M.; Moeyaert, J.; David, S.; Bassani, F.; Bogumilowicz, Y.; Barnes, J. P.; Rochat, N.; Loup, V.; Vizioz, C.; Allouti, N.; Chauvin, N.; Bao, X. Y.; Ye, Z.; Pin, J. B.; Sanchez, E.

    2014-06-30

    Metal organic chemical vapor deposition of GaAs, InGaAs, and AlGaAs on nominal 300 mm Si(100) at temperatures below 550 °C was studied using the selective aspect ratio trapping method. We clearly show that growing directly GaAs on a flat Si surface in a SiO{sub 2} cavity with an aspect ratio as low as 1.3 is efficient to completely annihilate the anti-phase boundary domains. InGaAs quantum wells were grown on a GaAs buffer and exhibit room temperature micro-photoluminescence. Cathodoluminescence reveals the presence of dark spots which could be associated with the presence of emerging dislocation in a direction parallel to the cavity. The InGaAs layers obtained with no antiphase boundaries are perfect candidates for being integrated as channels in n-type metal oxide semiconductor field effect transistor (MOSFET), while the low temperatures used allow the co-integration of p-type MOSFET.

  6. Spatially correlated distributions of local metallic properties in bulk and nanocrystalline GaN

    NASA Astrophysics Data System (ADS)

    Yesinowski, James P.; Berkson, Zachariah J.; Cadars, Sylvian; Purdy, Andrew P.; Chmelka, Bradley F.

    2017-06-01

    We compare local electronic structure at different atom types of a metallic semiconductor in bulk and nanocrystalline form. Multinuclear magic-angle-spinning nuclear magnetic resonance (MAS NMR) establishes that GaN synthesized as an intentionally doped bulk powder or as annealed nanocrystalline particles exhibits metallic behavior and a wide distribution of differing electronic environments in both forms. Bulk polycrystalline wurtzite GaN doped with 0.13% Ge as a shallow donor exhibits a temperature-independent distribution of 71Ga Knight shifts over the temperature range 123-473 K. Each Knight shift frequency in the inhomogeneously broadened spectrum is characterized by a 71Ga spin-lattice relaxation time T1 that is in good agreement with the value predicted by the Knight-Korringa relation across the broad range of temperatures. The 14N spectrum shows a slightly smaller Knight shift distribution with spin-lattice relaxation time T1 values at 295 K across the distribution also in good agreement with the Knight-Korringa relation. Similarly, annealed nanocrystalline wurtzite GaN (50-100 nm, and without Ge) exhibits a 71Ga Knight shift distribution and T1 values (at 295 K) that follow the same Knight-Korringa behavior. Thus, both bulk and nanocrystalline forms of GaN are n type and well above the metal-insulator transition (MIT), the nanocrystals most likely as a result of incorporation of shallow donor oxygen atoms during synthesis. Carriers in both forms of samples exhibit the near-ideal characteristics of a degenerate Fermi gas of noninteracting spins. The observation of NMR signals from both atom types, Ga and N, allows for the direct spatial correlation of the local electronic structure at the two sites in the lattice, specifically the s -orbital character of the electronic wave function of conduction band electrons at the Fermi edge. The relative values of these carrier wave-function probabilities (nearly twice as great for the N atom as for the Ga) are in line

  7. High-efficiency cadmium-free Cu(In,Ga)Se{sub 2} thin-film solar cells with chemically deposited ZnS buffer layers

    SciTech Connect

    Nakada, Tokio; Furumi, Keisuke; Kunioka, Akio

    1999-10-01

    Cadmium-free Cu(In,Ga)Se{sub 2} (CIGS) thin-film solar cells with a MgF{sub 2}/ZnO:Al/CBD-ZnS/CIGS/Mo/SLG structure have been fabricated using chemical bath deposition (CBD)-ZnS buffer layers and high-quality CIGS absorber layers grown using molecular beam epitaxy (MBE) system. The use of CBD-ZnS, which is a wider band gap material than CBD-CdS, improved the quantum efficiency of fabricated cells at short wavelengths, leading to an increase in the short-circuit current. The best cell at present yielded an active area efficiency of 16.9% which is the highest value reported previously for Cd-free CIGS thin-film solar cells. The as-fabricated solar cells exhibited a reversible light-soaking effect under AM 1.5, 100 mW/cm{sup 2} illumination. This paper also presents a discussion of the issues relating to the use of the CBD-ZnS buffer material for improving device performance.

  8. Effect of impurities in the CdS buffer layer on the performance of the Cu(In, Ga)Se2 thin film solar cell

    NASA Astrophysics Data System (ADS)

    Kylner, A.

    1999-05-01

    The highest efficiencies of Cu(In, Ga)Se2 (CIGS) thin film solar cells have been achieved when incorporating a thin CdS buffer layer grown by chemical bath deposition (CBD). The reason for this success has recently been discussed in terms of a pure Cd-doping effect in the CIGS layer. Such a model suggests that the bulk properties of the CBD-CdS buffer layer would be of minor importance. In this work, CBD-CdS layers having different bulk properties (i.e., concentrations of incorporated impurities) were employed in a number of CIGS solar cells. To further explore the bulk versus interface properties, half of these CIGS devices were subjected to a pre-deposition of an additional intermediate ultrathin layer. Moreover, CIGS devices made with CBD-CdS layers of different thickness were fabricated. Both standard and temperature dependent current-voltage (I-V) measurements were performed. The results indicate that the bulk properties of the CBD-CdS buffer layer indeed play an important role in the formation of the CdS/CIGS heterojunction. By increasing the impurity concentration or the thickness of the CBD-CdS layer, the open-circuit voltage Voc was observed to substantially increase. This favorable effect was counteracted by the appearance of a crossover effect in the I-V characteristics for devices with the highest impurity concentration or thickness of the CBD-CdS layer. The pre-deposition of an ultrathin layer did not affect these results. The presence of the crossover effect was strongly correlated to the appearance of trap-assisted tunneling in addition to the thermally assisted tunneling. The observed crossover effect was suggested to originate from too high a number of impurities (defect states) in the bulk of the CdS layer.

  9. Large-roll growth of 25-inch hexagonal BN monolayer film for self-release buffer layer of free-standing GaN wafer

    NASA Astrophysics Data System (ADS)

    Wu, Chenping; Soomro, Abdul Majid; Sun, Feipeng; Wang, Huachun; Huang, Youyang; Wu, Jiejun; Liu, Chuan; Yang, Xiaodong; Gao, Na; Chen, Xiaohong; Kang, Junyong; Cai, Duanjun

    2016-10-01

    Hexagonal boron nitride (h-BN) is known as promising 2D material with a wide band-gap (~6 eV). However, the growth size of h-BN film is strongly limited by the size of reaction chamber. Here, we demonstrate the large-roll synthesis of monolayer and controllable sub-monolayer h-BN film on wound Cu foil by low pressure chemical vapor deposition (LPCVD) method. By winding the Cu foil substrate into mainspring shape supported by a multi-prong quartz fork, the reactor size limit could be overcome by extending the substrate area to a continuous 2D curl of plane inward. An extremely large-size monolayer h-BN film has been achieved over 25 inches in a 1.2” tube. The optical band gap of h-BN monolayer was determined to be 6.0 eV. The h-BN film was uniformly transferred onto 2” GaN or 4” Si wafer surfaces as a release buffer layer. By HVPE method, overgrowth of thick GaN wafer over 200 μm has been achieved free of residual strain, which could provide high quality homo-epitaxial substrate.

  10. Large-roll growth of 25-inch hexagonal BN monolayer film for self-release buffer layer of free-standing GaN wafer.

    PubMed

    Wu, Chenping; Soomro, Abdul Majid; Sun, Feipeng; Wang, Huachun; Huang, Youyang; Wu, Jiejun; Liu, Chuan; Yang, Xiaodong; Gao, Na; Chen, Xiaohong; Kang, Junyong; Cai, Duanjun

    2016-10-19

    Hexagonal boron nitride (h-BN) is known as promising 2D material with a wide band-gap (~6 eV). However, the growth size of h-BN film is strongly limited by the size of reaction chamber. Here, we demonstrate the large-roll synthesis of monolayer and controllable sub-monolayer h-BN film on wound Cu foil by low pressure chemical vapor deposition (LPCVD) method. By winding the Cu foil substrate into mainspring shape supported by a multi-prong quartz fork, the reactor size limit could be overcome by extending the substrate area to a continuous 2D curl of plane inward. An extremely large-size monolayer h-BN film has been achieved over 25 inches in a 1.2" tube. The optical band gap of h-BN monolayer was determined to be 6.0 eV. The h-BN film was uniformly transferred onto 2" GaN or 4" Si wafer surfaces as a release buffer layer. By HVPE method, overgrowth of thick GaN wafer over 200 μm has been achieved free of residual strain, which could provide high quality homo-epitaxial substrate.

  11. Large-roll growth of 25-inch hexagonal BN monolayer film for self-release buffer layer of free-standing GaN wafer

    PubMed Central

    Wu, Chenping; Soomro, Abdul Majid; Sun, Feipeng; Wang, Huachun; Huang, Youyang; Wu, Jiejun; Liu, Chuan; Yang, Xiaodong; Gao, Na; Chen, Xiaohong; Kang, Junyong; Cai, Duanjun

    2016-01-01

    Hexagonal boron nitride (h-BN) is known as promising 2D material with a wide band-gap (~6 eV). However, the growth size of h-BN film is strongly limited by the size of reaction chamber. Here, we demonstrate the large-roll synthesis of monolayer and controllable sub-monolayer h-BN film on wound Cu foil by low pressure chemical vapor deposition (LPCVD) method. By winding the Cu foil substrate into mainspring shape supported by a multi-prong quartz fork, the reactor size limit could be overcome by extending the substrate area to a continuous 2D curl of plane inward. An extremely large-size monolayer h-BN film has been achieved over 25 inches in a 1.2” tube. The optical band gap of h-BN monolayer was determined to be 6.0 eV. The h-BN film was uniformly transferred onto 2” GaN or 4” Si wafer surfaces as a release buffer layer. By HVPE method, overgrowth of thick GaN wafer over 200 μm has been achieved free of residual strain, which could provide high quality homo-epitaxial substrate. PMID:27756906

  12. A buffer-free method for growth of InAsSb films on GaAs (001) substrates using MOCVD

    NASA Astrophysics Data System (ADS)

    Ni, Pei-Nan; Tong, Jin-Chao; Tobing, Landobasa Y. M.; Xu, Zheng-Ji; Qiu, Shupeng; Tang, Xiao-Hong; Zhang, Dao-Hua

    2017-06-01

    We report a simple thermal treatment method for direct growth of InAsSb films on GaAs (001) substrates for the first time. The properties of the grown InAsSb films are systematically characterized by scanning electron microscopy, atomic force microscopy, X-ray diffraction, photo-luminescence and Hall measurement. It is found that the grown InAsSb films by this method have high quality with very smooth, mirror-like morphology, good electrical and optical properties. In particular, strong photoluminescence peak at around 3660 nm can be observed even at room temperature, which demonstrates the capabilities of the grown InAsSb films for room temperature MIR optoelectronic application. The mechanism for this growth method is discussed in details. We believe that this work provides a simple and feasible buffer-free strategy for the growth of high quality InAsSb films directly on GaAs substrate and it may also benefit other heteroepitaxial growth.

  13. Ln₃FeGaQ₇: A new series of transition-metal rare-earth chalcogenides

    SciTech Connect

    Yin, Wenlong; Wang, Wendong; Kang, Lei; Lin, Zheshuai; Feng, Kai; Shi, Youguo; and others

    2013-06-01

    A new series of transition-metal rare-earth chalcogenides, Ln₃FeGaQ₇ (Ln=Nd, Sm, Gd, Dy, Q=S; Ln=Nd, Gd, Dy, Q=Se), have been synthesized by solid state reactions. They are isostructural and crystallize in the space group P6₃. They adopt a three-dimensional framework composed of LnQ₇ monocapped trigonal prisms with the interesting 1[FeS₃]⁴⁻ chains and isolated GaQ₄ tetrahedra lying in two sets of channels in the framework. Magnetic susceptibility measurements on Ln₃FeGaQ₇ (Ln=Gd, Dy; Q=S, Se) indicate that they are paramagnetic and obey the Curie–Weiss law. Based on the diffuse reflectance spectra, Ln₃FeGaQ₇ (Ln=Gd, Dy; Q=S, Se) should have band gaps smaller than 0.5 eV. Electronic conductivity measurement on Dy₃FeGaSe₇ demonstrates semiconducting behavior with σ₃₀₀=0.124 S/cm. The first-principles calculations were also performed to study the electronic structures of these compounds. - Graphical abstract: Ln₃FeGaQ₇ adopt a three-dimensional framework composed of LnQ₇ monocapped trigonal prisms with interesting 1[FeS₃]⁴⁻ chains and isolated GaQ₄ tetrahedra lying in two sets of channels in the framework. Highlights: • New compounds, Ln₃FeGaQ₇ (Ln=Nd, Sm, Gd, Dy, Q=S, Se), were synthesized. • They are isostructural and crystallize in the noncentrosymmetric space group P6₃. • They adopt a three-dimensional framework built by LnQ₇ monocapped trigonal prisms. • Ln₃FeGaQ₇ (Ln=Gd, Dy; Q=S, Se) are paramagnetic and obey the Curie–Weiss law. • Electronic conductivity of Dy₃FeGaSe₇ shows semiconducting behavior.

  14. Layered transition metal dichalcogenides: promising near-lattice-matched substrates for GaN growth

    PubMed Central

    Gupta, Priti; Rahman, A. A.; Subramanian, Shruti; Gupta, Shalini; Thamizhavel, Arumugam; Orlova, Tatyana; Rouvimov, Sergei; Vishwanath, Suresh; Protasenko, Vladimir; Laskar, Masihhur R.; Xing, Huili Grace; Jena, Debdeep; Bhattacharya, Arnab

    2016-01-01

    Most III-nitride semiconductors are grown on non-lattice-matched substrates like sapphire or silicon due to the extreme difficulty of obtaining a native GaN substrate. We show that several layered transition-metal dichalcogenides are closely lattice-matched to GaN and report the growth of GaN on a range of such layered materials. We report detailed studies of the growth of GaN on mechanically-exfoliated flakes WS2 and MoS2 by metalorganic vapour phase epitaxy. Structural and optical characterization show that strain-free, single-crystal islands of GaN are obtained on the underlying chalcogenide flakes. We obtain strong near-band-edge emission from these layers, and analyse their temperature-dependent photoluminescence properties. We also report a proof-of-concept demonstration of large-area growth of GaN on CVD MoS2. Our results show that the transition-metal dichalcogenides can serve as novel near-lattice-matched substrates for nitride growth. PMID:27025461

  15. Effects of the buffering capacity of the soil on the mobilization of heavy metals. Equilibrium and kinetics.

    PubMed

    Villen-Guzman, Maria; Paz-Garcia, Juan M; Amaya-Santos, Gema; Rodriguez-Maroto, Jose M; Vereda-Alonso, Carlos; Gomez-Lahoz, Cesar

    2015-07-01

    Understanding the possible pH-buffering processes is of maximum importance for risk assessment and remediation feasibility studies of heavy-metal contaminated soils. This paper presents the results about the effect of the buffering capacity of a polluted soil, rich in carbonates, on the pH and on the leaching evolution of its main contaminant (lead) when a weak acid (acetic acid) or a strong one (nitric acid) are slowly added. In both cases, the behavior of lead dissolution could be predicted using available (scientifically verified freeware) models assuming equilibrium between the solid and the aqueous phase. However, the experimental results indicate that the dissolution of calcium and magnesium carbonates is kinetically controlled. These kinetic limitations affect the overall behavior, and should be considered to understand also the response of the metals under local equilibrium. The well-known BCR sequential extraction procedure was used before- and after-treatment, to fractionate the lead concentration in the soil according to its mobility. The BCR results were also in agreement with the predictions of the equilibrium model. This agreement allows new insights about the information that could be derived from the BCR fractionation analysis. Copyright © 2015 Elsevier Ltd. All rights reserved.

  16. Nanostructured europium oxide thin films deposited by pulsed laser ablation of a metallic target in a He buffer atmosphere

    SciTech Connect

    Luna, H.; Franceschini, D. F.; Prioli, R.; Guimaraes, R. B.; Sanchez, C. M.; Canal, G. P.; Barbosa, M. D. L.; Galvao, R. M. O.

    2010-09-15

    Nanostrucured europium oxide and hydroxide films were obtained by pulsed Nd:YAG (532 nm) laser ablation of a europium metallic target, in the presence of a 1 mbar helium buffer atmosphere. Both the produced film and the ambient plasma were characterized. The plasma was monitored by an electrostatic probe, for plume expansion in vacuum or in the presence of the buffer atmosphere. The time evolution of the ion saturation current was obtained for several probe to substrate distances. The results show the splitting of the plume into two velocity groups, being the lower velocity profile associated with metal cluster formation within the plume. The films were obtained in the presence of helium atmosphere, for several target-to-substrate distances. They were analyzed by Rutherford backscattering spectrometry, x-ray diffraction, and atomic force microscopy, for as-deposited and 600 deg. C treated-in-air samples. The results show that the as-deposited samples are amorphous and have chemical composition compatible with europium hydroxide. The thermally treated samples show x-ray diffraction peaks of Eu{sub 2}O{sub 3}, with chemical composition showing excess oxygen. Film nanostructuring was shown to be strongly correlated with cluster formation, as shown by velocity splitting in probe current versus time plots.

  17. Theoretical confirmation of Ga-stabilized anti-ferromagnetism in plutonium metal

    NASA Astrophysics Data System (ADS)

    Söderlind, Per; Landa, Alex

    2014-05-01

    Density functional theory (DFT) for plutonium metal is shown to be consistent with recent magnetic measurements that suggest anti-ferromagnetism in Pu-Ga alloys at low temperatures. The theoretical model predicts a stabilization of the face-centered-cubic (fcc, δ) form of plutonium in an anti-ferromagnetic configuration when alloyed with gallium. The ordered magnetic phase occurs because Ga removes the mechanical instability that exists for unalloyed δ-Pu. The cause of the Ga-induced stabilization is a combination of a lowering of the band (kinetic) and electrostatic (Coulomb) energies for the cubic relative to the tetragonal phase. Similarly, gallium plays an important role in stabilizing anti-ferromagnetism in the tetragonal P4/mmm Pu3Ga compound.

  18. Metal-oxide-semiconductor capacitors on GaAs with germanium nitride passivation layer

    NASA Astrophysics Data System (ADS)

    Zhao, Han; Kim, Hyoung-Sub; Zhu, Feng; Zhang, Manhong; OK, Injo; Park, Sung Il; Yum, Jung Hwan; Lee, Jack C.

    2007-10-01

    We present gallium arsenide (GaAs) metal-oxide-semiconductor capacitors (MOSCAPs) with a thin HfO2 gate dielectric and a thin germanium nitride (GexNy) interfacial passivation layer (IPL). TaN /HfO2/GexNy/GaAs MOSCAPs show a low interface state density and a thin equivalent oxide thickness (1.6nm). Compared to GaAs MOSCAPs with germanium (Ge) IPL, the GexNy IPL has a smaller slow trap density, which is confirmed by improved C-V characteristics without humps near the flatband voltage. The lower rate of flatband voltage shift and gate leakage decreasing under constant gate voltage stress were also demonstrated in GaAs MOSCAPs with GexNy IPL than the Ge IPL.

  19. Metallic behavior of GaAs/BaTiO3 heterostructure

    NASA Astrophysics Data System (ADS)

    Yuan, Mengqi; Wang, Jianli; Pu, Long; Tang, Gang; Guo, Sandong

    2016-07-01

    The integration of III-V semiconductors on functional perovskite-oxide can lead to new material properties and new device applications by combining the rich properties of perovskite-oxides together with the superior optical and electronic properties of III-V semiconductors. The structural and electronic properties of the surface and interface of the GaAs/BaTiO3 are studied using first-principles calculations. We point out the energetically favorable GaAs/BaTiO3 interfaces according to the GaAs initial adsorption on the BaTiO3(001) substrate. Our calculations predict the existence of the metallic behavior at the GaAs/BaTiO3 interfaces.

  20. Generation of continuous wave terahertz frequency radiation from metal-organic chemical vapour deposition grown Fe-doped InGaAs and InGaAsP

    SciTech Connect

    Mohandas, Reshma A.; Freeman, Joshua R. Rosamond, Mark C.; Chowdhury, Siddhant; Cunningham, John E.; Davies, A. Giles; Linfield, Edmund H.; Dean, Paul; Hatem, Osama; Ponnampalam, Lalitha; Fice, Martyn; Seeds, Alwyn J.; Cannard, Paul J.; Robertson, Michael J.; Moodie, David G.

    2016-04-21

    We demonstrate the generation of continuous wave terahertz (THz) frequency radiation from photomixers fabricated on both Fe-doped InGaAs and Fe-doped InGaAsP, grown by metal-organic chemical vapor deposition. The photomixers were excited using a pair of distributed Bragg reflector lasers with emission around 1550 nm, and THz radiation was emitted over a bandwidth of greater than 2.4 THz. Two InGaAs and four InGaAsP wafers with different Fe doping concentrations were investigated, with the InGaAs material found to outperform the InGaAsP in terms of emitted THz power. The dependencies of the emitted power on the photomixer applied bias, incident laser power, and material doping level were also studied.

  1. InGaAs heterostructure formation in catalyst-free GaAs nanopillars by selective-area metal-organic vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    Shapiro, J. N.; Lin, A.; Wong, P. S.; Scofield, A. C.; Tu, C.; Senanayake, P. N.; Mariani, G.; Liang, B. L.; Huffaker, D. L.

    2010-12-01

    We investigate axial GaAs/InGaAs/GaAs heterostructures embedded in GaAs nanopillars via catalyst-free selective-area metal-organic chemical vapor deposition. Structural characterization by transmission electron microscopy with energy dispersive x-ray spectroscopy (EDS) indicates formation of axial InxGa1-xAs (x˜0.20) inserts with thicknesses from 36 to 220 nm with ±10% variation and graded Ga:In transitions controlled by In segregation. Using the heterointerfaces as markers, the vertical growth rate is determined to increase linearly during growth. Photoluminescence from 77 to 290 K and EDS suggest the presence of strain in the shortest inserts. This capability to control the formation of axial nanopillar heterostructures is crucial for optimized device integration.

  2. Intermixing at the absorber-buffer layer interface in thin-film solar cells: The electronic effects of point defects in Cu(In,Ga)(Se,S)2 and Cu2ZnSn(Se,S)4 devices

    NASA Astrophysics Data System (ADS)

    Varley, J. B.; Lordi, V.

    2014-08-01

    We investigate point defects in the buffer layers CdS and ZnS that may arise from intermixing with Cu(In,Ga)(S,Se)2 (CIGS) or Cu2ZnSn(S,Se)4 (CZTS) absorber layers in thin-film photovoltaics. Using hybrid functional calculations, we characterize the electrical and optical behavior of Cu, In, Ga, Se, Sn, Zn, Na, and K impurities in the buffer. We find that In and Ga substituted on the cation site act as shallow donors in CdS and tend to enhance the prevailing n-type conductivity at the interface facilitated by Cd incorporation in CIGS, whereas they are deep donors in ZnS and will be less effective dopants. Substitutional In and Ga can favorably form complexes with cation vacancies (A-centers) which may contribute to the "red kink" effect observed in some CIGS-based devices. For CZTS absorbers, we find that Zn and Sn defects substituting on the buffer cation site are electrically inactive in n-type buffers and will not supplement the donor doping at the interface as in CIGS/CdS or ZnS devices. Sn may also preferentially incorporate on the S site as a deep acceptor in n-type ZnS, which suggests possible concerns with absorber-related interfacial compensation in CZTS devices with ZnS-derived buffers. Cu, Na, and K impurities are found to all have the same qualitative behavior, most favorably acting as compensating acceptors when substituting on the cation site. Our results suggest one beneficial role of K and Na incorporation in CIGS or CZTS devices is the partial passivation of vacancy-related centers in CdS and ZnS buffers, rendering them less effective interfacial hole traps and recombination centers.

  3. Self-Organized InGaAs/GaAs Quantum Wire Nanostructures Grown by Metal-Organic Vapor Phase Epitaxy

    DTIC Science & Technology

    1999-06-18

    quantum wells with x = 0.9 and the thickness equal to 2 and 3 monolayers (0.6 and 0.9 nm) respectively on the basis of comparing the calculated...GaAs quantum wire nanostructures grown by metal-organic vapor phase epitaxy I. A. Karpovicht, B. N. Zvonkov§, N. V. Baidus§, D. 0. Filatov.t, Yu. Yu...Organic Vapor Phase Epitaxy. Atomic Force Microscopy (AFM) studies show presence of a homogeneous system of well ordered shaped rectangular nanoislands

  4. Plasma assisted molecular beam epitaxy growth and effect of varying buffer thickness on the formation of ultra-thin In{sub 0.17}Al{sub 0.83}N/GaN heterostructure on Si(111)

    SciTech Connect

    Chowdhury, Subhra; Biswas, Dhrubes

    2015-02-23

    This work reports on the detailed plasma-assisted molecular beam epitaxy (PAMBE) growth of ultra-thin In{sub 0.17}Al{sub 0.83}N/GaN heterostructures on Si(111) substrate with three different buffer thickness (600 nm, 400 nm, and 200 nm). Growth through critical optimization of growth conditions is followed by the investigation of impact of varying buffer thickness on the formation of ultra-thin 1.5 nm, In{sub 0.17}Al{sub 0.83}N–1.25 nm, GaN–1.5 nm, In{sub 0.17}Al{sub 0.83}N heterostructure, in terms of threading dislocation (TD) density. Analysis reveals a drastic reduction of TD density from the order 10{sup 10 }cm{sup −2} to 10{sup 8 }cm{sup −2} with increasing buffer thickness resulting smooth ultra-thin active region for thick buffer structure. Increasing strain with decreasing buffer thickness is studied through reciprocal space mapping analysis. Surface morphology through atomic force microscopy analysis also supports our study by observing an increase of pits and root mean square value (0.89 nm, 1.2 nm, and 1.45 nm) with decreasing buffer thickness which are resulted due to the internal strain and TDs.

  5. Epitaxial growth of YBCO films on metallic substrates buffered with yttria-stabilized zirconia

    NASA Astrophysics Data System (ADS)

    Ma, B.; Li, M.; Fisher, B. L.; Koritala, R. E.; Balachandran, U.

    2002-05-01

    Biaxially textured yttria-stabilized zirconia (YSZ) films were grown on polished Hastelloy C (HC) substrates by ion-beam-assisted deposition (IBAD) and electron-beam evaporation. A water-cooled sample stage was used to dissipate heat generated by the Kaufman ion source and to maintain the substrate temperature below 100 °C during deposition. X-ray pole figures were used for texture analysis. In-plane texture measured from the YSZ (111) φ-scan full-width-at-half-maximum (FWHM) was 13.2° and out-of-plane texture from the YSZ (002) ω-scan FWHM was 7.7°. In-plane texture improved with lowered substrate temperature during IBAD deposition. RMS surface roughness of 3.3 nm was measured by atomic force microscopy. A thin CeO2 buffer layer (≈10 nm) was deposited to improve the lattice match between the YSZ and YBCO films and to enhance the biaxial alignment of YBCO films. YBCO films were epitaxially grown on IBAD-YSZ buffered HC substrates with and without CeO2 buffer layers by pulsed laser deposition (PLD). In-plane texture FWHMs of 12° and 9° were observed for CeO2 (111) and YBCO (103), respectively. Tc=90 K, with sharp transition, and Jc values of ≈2×106 A/cm2 at 77 K in zero field were observed on 0.5-μm-thick, 5-mm-wide, and 1-cm-long samples.

  6. Determination of the nitrogen vacancy as a shallow compensating center in GaN doped with divalent metals.

    PubMed

    Buckeridge, J; Catlow, C R A; Scanlon, D O; Keal, T W; Sherwood, P; Miskufova, M; Walsh, A; Woodley, S M; Sokol, A A

    2015-01-09

    We report accurate energetics of defects introduced in GaN on doping with divalent metals, focusing on the technologically important case of Mg doping, using a model that takes into consideration both the effect of hole localization and dipolar polarization of the host material, and includes a well-defined reference level. Defect formation and ionization energies show that divalent dopants are counterbalanced in GaN by nitrogen vacancies and not by holes, which explains both the difficulty in achieving p-type conductivity in GaN and the associated major spectroscopic features, including the ubiquitous 3.46 eV photoluminescence line, a characteristic of all lightly divalent-metal-doped GaN materials that has also been shown to occur in pure GaN samples. Our results give a comprehensive explanation for the observed behavior of GaN doped with low concentrations of divalent metals in good agreement with relevant experiment.

  7. Spin dependent transport properties of Mn-Ga/MgO/Mn-Ga magnetic tunnel junctions with metal(Mg, Co, Cr) insertion layer

    SciTech Connect

    Liang, S. H.; Tao, L. L.; Liu, D. P. Han, X. F.; Lu, Y.

    2014-04-07

    We report a first principles theoretical investigation of spin polarized quantum transport in Mn{sub 2}Ga/MgO/Mn{sub 2}Ga and Mn{sub 3}Ga/MgO/Mn{sub 3}Ga magnetic tunneling junctions (MTJs) with the consideration of metal(Mg, Co, Cr) insertion layer effect. By changing the concentration of Mn, our calculation shows a considerable disparity in transport properties: A tunneling magnetoresistance (TMR) ratio of 852% was obtained for Mn{sub 2}Ga-based MTJs, however, only a 5% TMR ratio for Mn{sub 3}Ga-based MTJs. In addition, the influence of insertion layer has been considered in our calculation. We found the Co insertion layer can increase the TMR of Mn{sub 2}Ga-based MTJ to 904%; however, the Cr insertion layer can decrease the TMR by 668%; A negative TMR ratio can be obtained with Mg insertion layer. Our work gives a comprehensive understanding of the influence of different insertion layer in Mn-Ga based MTJs. It is proved that, due to the transmission can be modulated by the interfacial electronic structure of insertion, the magnetoresistance ratio of Mn{sub 2}Ga/MgO/Mn{sub 2}Ga MTJ can be improved by inserting Co layer.

  8. Impact of eigenvalues on the pseudopotential calculation of superconducting parameters of metals Ga, Cd and In

    NASA Astrophysics Data System (ADS)

    Yadav, Jayprakash; Rafique, S. M.; Kumari, Shanti

    2009-10-01

    In the present paper some superconducting (SC) state parameters of metals Ga, Cd and In have been studied through Harrison's First Principle [HFP] pseudopotential technique using McMillan's formalism. The impact of choosing two different sets of core energy eigenvalues viz. Herman-Skillman and Clementi (or Experimental) has been studied.

  9. X-ray induced, substrate-carrier mediated deposition of metal on GaAs

    SciTech Connect

    Ma Qing; Divan, R.; Mancini, D. C.; Rosenberg, R. A.; Quintana, J. P.; Keane, D. T.

    2006-08-21

    A wet metal deposition process on GaAs surfaces is described. The process is induced by high energy x-ray photons and is mediated by photon-generated carriers through the photoelectrochemical mechanism similar to that for light-induced wet etching. The micrometer to submicrometer feature fabrication using this process is demonstrated.

  10. GaBi alloy liquid metal ion source for microelectronics research.

    PubMed

    Bischoff, L; Pilz, W; Ganetsos, Th; Forbes, R G; Akhmadaliev, Ch

    2007-09-01

    A GaBi alloy liquid metal ion source has been studied. From an analysis of the source mass spectra as a function of emission current, a mechanism is suggested for the production of single- and double-charged ions. There is good agreement with the results of Swanson's investigations of a pure Bi source.

  11. Reflection Properties of Metallic Gratings on ZnO Films over GaAs Substrates

    NASA Technical Reports Server (NTRS)

    Hickernell, Fred S.; Kim, Yoonkee; Hunt, William D.

    1994-01-01

    A potential application for piezoelectric film deposited on GaAs substrates is the monolithic integration of surface acoustic wave (SAW) devices with GaAs electronics. Metallic gratings are basic elements required for the construction of such devices, and analyzing the reflectivity and the velocity change due to metallic gratings is often a critical design parameter. In this article, Datta and Hunsinger technique is extended to the case of a multilayered structure, and the developed technique is applied to analyze shorted and open gratings on ZnO films sputtered over (001)-cut (110)-propagating GaAs substrates. The analysis shows that zero reflectivity of shorted gratings can be obtained by a combination of the ZnO film and the metal thickness and the metalization ratio of the grating. Experiments are performed on shorted and an open gratings (with the center frequency of about 180 MHz) for three different metal thicknesses over ZnO films which are 0.8 and 2.6 micrometers thick. From the experiments, zero reflectivity at the resonant frequency of the grating is observed for a reasonable thickness (h/Alpha = 0.5%) of aluminum metalization. The velocity shift between the shorted and the open grating is also measured to be 0.18 MHz and 0.25 MHz for 0.8 and 1.6 micrometers respectively. The measured data show relatively good agreement with theoretical predictions.

  12. High efficiency Cu(In,Ga)Se{sub 2} thin film solar cells without intermediate buffer layers

    SciTech Connect

    Ramanathan, K.; Wiesner, H.; Asher, S.; Niles, D.; Bhattacharya, R.N.; Keane, J.; Contreras, M.A.; Noufi, R.

    1998-09-01

    The nature of the interface between CuInGaSe{sub 2} (CIGS) and the chemical bath deposited CdS layer has been investigated. The authors show that heat-treating the absorbers in Cd- or Zn-containing solutions in the presence of ammonium hydroxide sets up an interfacial reaction with the possibility of an ion exchange occurring between Cd and Cu. The characteristics of devices made in this manner suggest that the reaction generates a thin, n-doped region in the absorber. The authors suggest that this aspect might be more important than the CdS layer in the formation of the junction. It is quite possible that the CdS/CuInSe{sub 2} device is a buried, shallow junction with a CdS window layer, rather than a heterojunction between CdS and CIGS. The authors use these ideas to develop methods for fabricating diodes without CdS or Cd.

  13. Development of buffer layers on 30 mm wide textured metal substrates for REBCO coated conductors

    NASA Astrophysics Data System (ADS)

    Yamaguchi, T.; Ota, H.; Ohki, K.; Konishi, M.; Ohmatsu, K.

    2010-11-01

    We have been studying REBa2Cu3Ox (RE: rare earth elements) coated conductors on clad-type substrates. We developed coated conductors on the 10 mm wide clad-type tape, and succeeded in obtaining the maximum critical current of 380 A/cm with the 2.0 μm thick GdBa2Cu3Ox superconducting film. At present, we are trying to widen the tape width from 10 mm to 30 mm in order to increase production throughput. We report our recent progress on scaling-up of the buffer layers and their properties. The buffer layers consisted of three layers; CeO2 as the seed layer, yttrium-stabilized zirconia (YSZ) as the diffusion barrier layer and CeO2 as the lattice matching layer. They were grown by the RF-sputtering method and the electron beam evaporation technique (EB). EB deposition has possibility of higher throughput compared with the RF-sputtering. The intensity ratio of (2 0 0) to (2 0 0) + (1 1 1) for the lattice matching layer showed as high as 98%. The uniform properties of 40 m long and 30 mm wide substrates were successfully produced by all sputtering method. Additionally, the tape travel speed of the seed layer can be increased from 7 m/h (RF-sputtering deposition) to 10 m/h (EB deposition) on short sample (0.3 m long).

  14. Optical, structural, and chemical properties of flash evaporated In{sub 2}S{sub 3} buffer layer for Cu(In,Ga)Se{sub 2} solar cells

    SciTech Connect

    Verma, Rajneesh; Chirila, Adrian; Guettler, Dominik; Perrenoud, Julian; Pianezzi, Fabian; Tiwari, Ayodhya N.; Datta, Debjit; Kumar, Satyendra; Mueller, Ulrich

    2010-10-15

    In{sub 2}S{sub 3} layers were deposited by flash evaporation technique with varying flash rates. The optical constants of layers based on Tauc-Lorentz model dielectric function were extracted from spectroscopic ellipsometry measurements. X-ray photoelectron spectroscopic investigation revealed the presence of oxygen impurity in as-deposited and air-annealed layers with traces of Na inclusion in the layer grown at high flash rate. The enhancement in crystalline arrangement of as-deposited layer after air annealing was confirmed by Raman spectroscopy. Rutherford backscattering measurements revealed the growth of off-stoichiometric layers at all flash rates. An analytical layer growth model has been proposed supporting the results obtained by various layer characterization techniques. The solar cells were prepared with flash evaporated In{sub 2}S{sub 3} buffer layers and their performances were compared with CdS reference solar cell. A significant gain in short-circuit current was obtained after air annealing of the complete device at 200 deg. C for 20 min. A maximum conversion efficiency of 12.6% was delivered by a high flash rate In{sub 2}S{sub 3} buffered cell with open-circuit voltage close to that of CdS reference cell. The improvement in device performance after air annealing treatment is explained by thermally enhanced Cu and oxygen diffusion from Cu(In,Ga)Se{sub 2} and i-ZnO to In{sub 2}S{sub 3} layer, respectively.

  15. Improved high temperature integration of Al{sub 2}O{sub 3} on MoS{sub 2} by using a metal oxide buffer layer

    SciTech Connect

    Son, Seokki; Choi, Moonseok; Kim, Dohyung; Choi, Changhwan; Yu, Sunmoon

    2015-01-12

    We deposited a metal oxide buffer layer before atomic layer deposition (ALD) of Al{sub 2}O{sub 3} onto exfoliated molybdenum disulfide (MoS{sub 2}) in order to accomplish enhanced integration. We demonstrate that even at a high temperature, functionalization of MoS{sub 2} by means of a metal oxide buffer layer can effectively provide nucleation sites for ALD precursors, enabling much better surface coverage of Al{sub 2}O{sub 3}. It is shown that using a metal oxide buffer layer not only allows high temperature ALD process, resulting in highly improved quality of Al{sub 2}O{sub 3}/MoS{sub 2} interface, but also leaves MoS{sub 2} intact.

  16. Adhesion studies of GaAs-based ohmic contact and bond pad metallization

    SciTech Connect

    Seigal, P.K.; Briggs, R.D.; Rieger, D.J.; Baca, A.G.; Howard, A.J.

    1996-03-01

    Adhesion strength and surface morphology of commonly used n- and p-type ohmic contacts and pad metallization schemes for GaAs were investigated. GeNiAu, GePdAu, BeAu, and TiPtAu (being studied as potential ohmic contacts for internal optoelectronic devices) had quantitiative measurements made using wire bond pull testing to determine adhesion. Bond pad metals deposited as evaporated TiAu, TiPtAu, and 2-5 micron thick electroplated Au deposited on both semi-insulating GaAs and on Si{sub 3}N{sub 4}/GaAs were evaluated independently from the ohmic contact metals. In all samples was observed a strong correlation between surface treatment, surface morphology, wire bondability, and bond strength. Very high bond strengths (pull test average values above 6.5 grams force with 25 micron dia Au wire) wereobtained for n-type, p-type, and bond pad metals. Average values of 8.0 gram force were achieved with two-step GeAu/NiAu/TiPtAu metallization, while one-step deposition yielded poorer values. Adhesion was also monitored after aging at 250 C in air for four different times up to 60 hr by wire bond pull testing, with little degradation occurring.

  17. Novel recycle technology for recovering rare metals (Ga, In) from waste light-emitting diodes.

    PubMed

    Zhan, Lu; Xia, Fafa; Ye, Qiuyu; Xiang, Xishu; Xie, Bing

    2015-12-15

    This work develops a novel process of recycling rare metals (Ga, In) from waste light-emitting diodes using the combination of pyrolysis, physical disaggregation methods and vacuum metallurgy separation. Firstly, the pure chips containing InGaN/GaN are adopted to study the vacuum separation behavior of rare metals, which aims to provide the theoretical foundation for recycling gallium and indium from waste light-emitting diodes. In order to extract the rare-metal-rich particles from waste light-emitting diodes, pyrolysis and physical disaggregation methods (crushing, screening, grinding and secondly screening) are studied respectively, and the operating parameters are optimized. With low boiling points and high saturation vapor pressures under vacuum, gallium and indium are separated from rare-metal-rich particles by the process of evaporation and condensation. By reference to the separating parameters of pure chips, gallium and indium in waste light-emitting diodes are recycled with the recovery efficiencies of 93.48% and 95.67% under the conditions as follows: heating temperature of 1373 K, vacuum pressure of 0.01-0.1 Pa, and holding time of 60 min. There are no secondary hazardous materials generated in the whole processes. This work provides an efficient and environmentally friendly process for recycling rare metals from waste light-emitting diodes.

  18. First principles calculations of point defect diffusion in CdS buffer layers: Implications for Cu(In,Ga)(Se,S)2 and Cu2ZnSn(Se,S)4-based thin-film photovoltaics

    NASA Astrophysics Data System (ADS)

    Varley, J. B.; Lordi, V.; He, X.; Rockett, A.

    2016-01-01

    We investigate point defects in CdS buffer layers that may arise from intermixing with Cu(In,Ga)Se2 (CIGSe) or Cu2ZnSn(S,Se)4 (CZTSSe) absorber layers in thin-film photovoltaics (PV). Using hybrid functional calculations, we characterize the migration barriers of Cu, In, Ga, Se, Sn, Zn, Na, and K impurities and assess the activation energies necessary for their diffusion into the bulk of the buffer. We find that Cu, In, and Ga are the most mobile defects in CIGS-derived impurities, with diffusion expected to proceed into the buffer via interstitial-hopping and cadmium vacancy-assisted mechanisms at temperatures ˜400 °C. Cu is predicted to strongly favor migration paths within the basal plane of the wurtzite CdS lattice, which may facilitate defect clustering and ultimately the formation of Cu-rich interfacial phases as observed by energy dispersive x-ray spectroscopic elemental maps in real PV devices. Se, Zn, and Sn defects are found to exhibit much larger activation energies and are not expected to diffuse within the CdS bulk at temperatures compatible with typical PV processing temperatures. Lastly, we find that Na interstitials are expected to exhibit slightly lower activation energies than K interstitials despite having a larger migration barrier. Still, we find both alkali species are expected to diffuse via an interstitially mediated mechanism at slightly higher temperatures than enable In, Ga, and Cu diffusion in the bulk. Our results indicate that processing temperatures in excess of ˜400 °C will lead to more interfacial intermixing with CdS buffer layers in CIGSe devices, and less so for CZTSSe absorbers where only Cu is expected to significantly diffuse into the buffer.

  19. First principles calculations of point defect diffusion in CdS buffer layers: Implications for Cu(In,Ga)(Se,S){sub 2} and Cu{sub 2}ZnSn(Se,S){sub 4}-based thin-film photovoltaics

    SciTech Connect

    Varley, J. B.; Lordi, V.; He, X.; Rockett, A.

    2016-01-14

    We investigate point defects in CdS buffer layers that may arise from intermixing with Cu(In,Ga)Se{sub 2} (CIGSe) or Cu{sub 2}ZnSn(S,Se){sub 4} (CZTSSe) absorber layers in thin-film photovoltaics (PV). Using hybrid functional calculations, we characterize the migration barriers of Cu, In, Ga, Se, Sn, Zn, Na, and K impurities and assess the activation energies necessary for their diffusion into the bulk of the buffer. We find that Cu, In, and Ga are the most mobile defects in CIGS-derived impurities, with diffusion expected to proceed into the buffer via interstitial-hopping and cadmium vacancy-assisted mechanisms at temperatures ∼400 °C. Cu is predicted to strongly favor migration paths within the basal plane of the wurtzite CdS lattice, which may facilitate defect clustering and ultimately the formation of Cu-rich interfacial phases as observed by energy dispersive x-ray spectroscopic elemental maps in real PV devices. Se, Zn, and Sn defects are found to exhibit much larger activation energies and are not expected to diffuse within the CdS bulk at temperatures compatible with typical PV processing temperatures. Lastly, we find that Na interstitials are expected to exhibit slightly lower activation energies than K interstitials despite having a larger migration barrier. Still, we find both alkali species are expected to diffuse via an interstitially mediated mechanism at slightly higher temperatures than enable In, Ga, and Cu diffusion in the bulk. Our results indicate that processing temperatures in excess of ∼400 °C will lead to more interfacial intermixing with CdS buffer layers in CIGSe devices, and less so for CZTSSe absorbers where only Cu is expected to significantly diffuse into the buffer.

  20. AlGaN/GaN Metal-Oxide-Semiconductor High-Electron-Mobility Transistor with Polarized P(VDF-TrFE) Ferroelectric Polymer Gating.

    PubMed

    Liu, Xinke; Lu, Youming; Yu, Wenjie; Wu, Jing; He, Jiazhu; Tang, Dan; Liu, Zhihong; Somasuntharam, Pannirselvam; Zhu, Deliang; Liu, Wenjun; Cao, Peijiang; Han, Sun; Chen, Shaojun; Tan, Leng Seow

    2015-09-14

    Effect of a polarized P(VDF-TrFE) ferroelectric polymer gating on AlGaN/GaN metal-oxide-semiconductor high-electron-mobility transistors (MOS-HEMTs) was investigated. The P(VDF-TrFE) gating in the source/drain access regions of AlGaN/GaN MOS-HEMTs was positively polarized (i.e., partially positively charged hydrogen were aligned to the AlGaN surface) by an applied electric field, resulting in a shift-down of the conduction band at the AlGaN/GaN interface. This increases the 2-dimensional electron gas (2-DEG) density in the source/drain access region of the AlGaN/GaN heterostructure, and thereby reduces the source/drain series resistance. Detailed material characterization of the P(VDF-TrFE) ferroelectric film was also carried out using the atomic force microscopy (AFM), X-ray Diffraction (XRD), and ferroelectric hysteresis loop measurement.

  1. AlGaN/GaN Metal-Oxide-Semiconductor High-Electron-Mobility Transistor with Polarized P(VDF-TrFE) Ferroelectric Polymer Gating

    PubMed Central

    Liu, Xinke; Lu, Youming; Yu, Wenjie; Wu, Jing; He, Jiazhu; Tang, Dan; Liu, Zhihong; Somasuntharam, Pannirselvam; Zhu, Deliang; Liu, Wenjun; Cao, Peijiang; Han, Sun; Chen, Shaojun; Seow Tan, Leng

    2015-01-01

    Effect of a polarized P(VDF-TrFE) ferroelectric polymer gating on AlGaN/GaN metal-oxide-semiconductor high-electron-mobility transistors (MOS-HEMTs) was investigated. The P(VDF-TrFE) gating in the source/drain access regions of AlGaN/GaN MOS-HEMTs was positively polarized (i.e., partially positively charged hydrogen were aligned to the AlGaN surface) by an applied electric field, resulting in a shift-down of the conduction band at the AlGaN/GaN interface. This increases the 2-dimensional electron gas (2-DEG) density in the source/drain access region of the AlGaN/GaN heterostructure, and thereby reduces the source/drain series resistance. Detailed material characterization of the P(VDF-TrFE) ferroelectric film was also carried out using the atomic force microscopy (AFM), X-ray Diffraction (XRD), and ferroelectric hysteresis loop measurement. PMID:26364872

  2. Studies of Electron Beam Evaporated SiO2/AlGaN/GaN Metal-Oxide-Semiconductor High-Electron-Mobility Transistors

    NASA Astrophysics Data System (ADS)

    Arulkumaran, Subramaniam; Egawa, Takashi; Ishikawa, Hiroyasu

    2005-06-01

    The metal-oxide-semiconductor high-electron-mobility transistors (MOSHEMTs) have been demonstrated and its dc characteristics were examined and compared with the conventional AlGaN/GaN HEMTs. The electron beam (EB) evaporated SiO2 layers were used as a gate-insulator. Capacitance-voltage plot of MOS contacts revealed the existence of injection type complete accumulation up to +4.0 V. The fabricated MOSHEMTs have exhibited better dc characteristics when compared with the conventional AlGaN/GaN HEMTs. The MOSHEMTs could operate at positive gate-biases as high as +4.0 V. The 2.0-μm-gate-length EB-SiO2 MOSHEMTs exhibited higher drain current density and extrinsic transconductance of 856 mA/mm and 145 mS/mm when compared to the conventional AlGaN/GaN HEMTs. The gate leakage current (IgLeak) was three orders of magnitude lower than that of the conventional AlGaN/GaN HEMTs. The stable device operations at high operating voltages with low IgLeak and high gmmax values leads to the occurrence of low trap density at EB-SiO2/AlGaN interface.

  3. High responsivity A-plane GaN-based metal-semiconductor-metal photodetectors for polarization-sensitive applications

    SciTech Connect

    Navarro, A.; Rivera, C.; Pereiro, J.; Munoz, E.; Imer, B.; DenBaars, S. P.; Speck, J. S.

    2009-05-25

    The fabrication and characterization of metal-semiconductor-metal polarization-sensitive photodetectors based on A-plane GaN grown on R-plane sapphire substrates is reported. These photodetectors take advantage of the in-plane crystal anisotropy, which results in linear dichroism near the band gap energy. The high resistivity of the A-plane GaN material leads to extremely low dark currents. For an optimized finger spacing of 1 {mu}m, dark current density and responsivity at 30 V are 0.3 nA/mm{sup 2} and 2 A/W, respectively. A maximum polarization sensitivity ratio of 1.8 was determined. In a differential configuration, the full width at half maximum of the polarization-sensitive region is 8.5 nm.

  4. Improvement of Surge Protection by Using an AlGaN/GaN-Based Metal-Semiconductor-Metal Two-Dimensional Electron Gas Varactor

    NASA Astrophysics Data System (ADS)

    Ferng, Yi-Cherng; Chang, Liann-Be; Das, Atanu; Lin, Ching-Chi; Cheng, Chun-Yu; Kuei, Ping-Yu; Chow, Lee

    2012-12-01

    In this paper, a varactor with metal-semiconductor-metal diodes on top of the (NH4)2S/P2S5-treated AlGaN/GaN two-dimensional electron gas epitaxial structure (MSM-2DEG) is proposed to the surge protection for the first time. The sulfur-treated MSM-2DEG varactor properties, including current-voltage (I-V), capacitance-voltage (C-V), and frequency response of the proposed surge protection circuit, are presented. To verify its capability of surge protection, we replace the metal oxide varistor (MOV) and resistor (R) in a state-of-the-art surge protection circuit with the sulfur-treated MSM-2DEG varactor under the application conditions of system-level surge tests. The measured results show that the proposed surge protection circuit, consisted of a gas discharge arrester (GDA) and a sulfur-treated MSM-2DEG varactor, can suppress an electromagnetic pulse (EMP) voltage of 4000 to 360 V, a reduction of 91%, whereas suppression is to 1780 V, a reduction of 55%, when using only a GDA.

  5. Interface reactions and Kirkendall voids in metal organic vapor-phase epitaxy grown Cu(In ,Ga)Se2 thin films on GaAs

    NASA Astrophysics Data System (ADS)

    Lei, C. H.; Rockett, A. A.; Robertson, I. M.; Papathanasiou, N.; Siebentritt, S.

    2006-12-01

    Cu(In1-xGax)Se2 (CIGS) films were grown on (001) GaAs at 570 or 500°C by means of metal organic vapor-phase epitaxy. All films were Cu-rich [Cu /(In+Ga)>1] with pseudomorphic Cu2Se second phase particles found only on the growth surface. During growth, diffusion of Ga from the substrate and vacancies generated by the formation of CIGS from Cu2Se at the surface occurred. The diffusion processes lead to the formation of Kirkendall voids at the GaAs/CIGS interface. Transmission electron microscopy and nanoprobe energy dispersive spectroscopy were used to analyze the diffusion and void formation processes. The diffusivity of Ga in CIGS was found to be relatively low. This is postulated to be due to a comparatively low concentration of point defects in the epitaxial films. A reaction model explaining the observed profiles and voids is proposed.

  6. Growth of ultrathin GaSb layer on GaAs using metal-organic chemical vapor deposition with Sb interfacial treatment

    NASA Astrophysics Data System (ADS)

    Hsiao, Chih-Jen; Ha, Minh-Thien-Huu; Hsu, Ching-Yi; Lin, Yueh-Chin; Chang, Sheng-Po; Chang, Shoou-Jinn; Chang, Edward Yi

    2016-09-01

    GaSb epitaxial layers were directly grown on GaAs substrates by metal-organic chemical vapor deposition involving Sb interfacial treatment with optimized growth temperature and V/III ratio. The interfacial treatment effectively reduces the surface energy and strain energy difference, resulting in a quasi-2D growth mode. When the GaSb layer was grown at 520 °C, the strain induced by lattice mismatch was accommodated by 90° dislocations with a period of 5.67 nm. By optimizing the V/III ratio, the surface roughness of the ultrathin GaSb/GaAs heterostructure was reduced, resulting in a reduced carrier scattering and improved electronic properties.

  7. Effect of nitrogen incorporation into Al-based gate insulators in AlON/AlGaN/GaN metal-oxide-semiconductor structures

    NASA Astrophysics Data System (ADS)

    Asahara, Ryohei; Nozaki, Mikito; Yamada, Takahiro; Ito, Joyo; Nakazawa, Satoshi; Ishida, Masahiro; Ueda, Tetsuzo; Yoshigoe, Akitaka; Hosoi, Takuji; Shimura, Takayoshi; Watanabe, Heiji

    2016-10-01

    The superior physical and electrical properties of aluminum oxynitride (AlON) gate dielectrics on AlGaN/GaN substrates in terms of thermal stability, reliability, and interface quality were demonstrated by direct AlON deposition and subsequent annealing. Nitrogen incorporation into alumina was proven to be beneficial both for suppressing intermixing at the insulator/AlGaN interface and reducing the number of electrical defects in Al2O3 films. Consequently, we achieved high-quality AlON/AlGaN/GaN metal-oxide-semiconductor capacitors with improved stability against charge injection and a reduced interface state density as low as 1.2 × 1011 cm-2 eV-1. The impact of nitrogen incorporation into the insulator will be discussed on the basis of experimental findings.

  8. Study of the Nucleation and Growth of YBCO on Oxide Buffered Metallic Tapes

    SciTech Connect

    Solovyov, Vyacheslav

    2009-04-10

    The CRADA collaboration concentrated on developing the scientific understanding of the factors necessary for commercialization of high temperature superconductors (HTS) based on the YBCO coated conductor technology for electric power applications. The project pursued the following objectives: 1. Establish the correlations between the YBCO nuclei density and the properties of the CeO{sub 2} layer of the RABiTS{trademark} template; 2. Compare the nucleation and growth of e-beam and MOD based precursors on the buffered RABiTS{trademark} templates and clarify the materials science behind the difference; and 3. Explore routes for the optimization of the nucleation and growth of thick film MOD precursors in order to achieve high critical current densities in thick films. The CRADA work proceeded in two steps: 1. Detailed characterization of epitaxial ceria layers on “model” substrates, such as (001) YSZ and on RABiTS tapes; and 2. Study of YBCO nucleation on well-defined substrates and on long-length RABiTS.

  9. Characterization of metallic adatoms on GaAs

    NASA Astrophysics Data System (ADS)

    Gohlke, David; Gupta, Jay

    2012-04-01

    As semiconductor nanostructures become smaller, defects play an ever-increasing role in systems of interest. Scanning tunneling microscopy (STM) can be used to probe and manipulate systems on the atomic scale. For exceptionally clean systems, we study our samples at low-temperature (5K) and ultra-high vacuum (UHV). Here we examine the properties of charged atoms on the surface of the semiconductor gallium arsenide (GaAs). We determine the binding site and charge of these adatoms, and use this information to tune the energy levels of electron acceptors in the surface. Funding for this research was provided by the Center for Emergent Materials at the Ohio State University, an NSF MRSEC (Award Number DMR-0820414). http://www.physics.ohio-state.edu/˜jgupta/

  10. New sulphide precursors for Zn(O,S) buffer layers in Cu(In,Ga)Se2 solar cells for faster reaction kinetics

    NASA Astrophysics Data System (ADS)

    Löckinger, Johannes; Nishiwaki, Shiro; Fuchs, Peter; Buecheler, Stephan; Romanyuk, Yaroslav E.; Tiwari, Ayodhya N.

    2016-08-01

    The development of a novel chemistry for the chemical bath deposition of Zn(O,S) buffer layers for Cu(In,Ga)Se2 (CIGS) solar cells is desired for a higher growth rate, hence reduced deposition time, while reducing simultaneously the required concentration of reactants. State-of-the-art recipes are based on thiourea as sulphide precursor requiring a high molarity of reactants and relatively long deposition times due to the slow decomposition rate of thiourea. In this contribution thioamide based sulphide precursors were investigated for their decomposition and growth behaviour. A co-solvent approach in an ethanolic/aqueous ammonia medium was evaluated omitting the need for additional complexants. By replacing thiourea with the investigated thioamides, homogeneous dense layers of around 30 nm were grown with a greatly decreased deposition time of 8 min compared to 25 min for thiourea. Likewise, the concentration of the sulphide precursor was 40-fold reduced. The photovoltaic performance as characterized by external quantum efficiency and current-voltage measurements, showed conversion efficiencies of 15% comparable to the thiourea based process.

  11. Effects of Photowashing Treatment on Gate Leakage Current of GaAs Metal-Semiconductor Field-Effect Transistors

    NASA Astrophysics Data System (ADS)

    Choi, Kyoung Jin; Moon, Jae Kyoung; Park, Min; Kim, Haechon; Lee, Jong-Lam

    2002-05-01

    Effects of photowashing treatment on gate leakage current (IGD) of a GaAs metal-semiconductor field-effect transistor were studied by observing changes in atomic composition and band bending at the surface of GaAs through X-ray photoemission spectroscopy. The photowashing treatment produces Ga2O3 on the surface of GaAs, leaving acceptor-type Ga antisites behind under the oxide. The Ga antisites played a role in reducing the maximum electric field at the drain edge of the gate, leading to the decrease of IGD. The longer photowashing time produced thicker oxide on the surface of GaAs, acting as a conducting pass for electrons, leading to the increase of IGD.

  12. Reflective metal/semiconductor tunnel junctions for hole injection in AlGaN UV LEDs

    NASA Astrophysics Data System (ADS)

    Zhang, Yuewei; Krishnamoorthy, Sriram; Akyol, Fatih; Johnson, Jared M.; Allerman, Andrew A.; Moseley, Michael W.; Armstrong, Andrew M.; Hwang, Jinwoo; Rajan, Siddharth

    2017-07-01

    In this work, we investigate the use of nanoscale polarization engineering to achieve efficient hole injection from metals to ultra-wide bandgap AlGaN, and we show that UV-reflective aluminum (Al) layers can be used for hole injection into p-AlGaN. The dependence of tunneling on the work function of the metal was investigated, and it was found that highly reflective Al metal layers can enable efficient hole injection into p-AlGaN, despite the relatively low work function of Al. Efficient tunneling hole injection was confirmed by light emission at 326 nm with an on-wafer peak external quantum efficiency and a wall-plug efficiency of 2.43% and 1.33%, respectively. A high power density of 79.0 W/cm2 was measured at 1200 A/cm2. The metal/semiconductor tunnel junction structure demonstrated here could provide significant advantages for efficient and manufacturable device topologies for high power UV emitters.

  13. Electronic properties of embedded MnAs nano-clusters in a GaAs matrix and (Ga,Mn)As films: Evidence of distinct metallic character

    NASA Astrophysics Data System (ADS)

    Rache Salles, B.; Girard, J. C.; David, C.; Offi, F.; Borgatti, F.; Eddrief, M.; Etgens, V. H.; Simonelli, L.; Marangolo, M.; Panaccione, G.

    2012-05-01

    We investigated the electronic properties of MnAs nano-clusters embedded in GaAs by bulk sensitive photoemission spectroscopy and cross-sectional scanning tunneling microscopy/spectroscopy. We report experimental evidences that the clusters are metallic MnAs, in close resemblance to MnAs thin films, and display a sharp interface with the surrounding GaAs. These results are supported by the comparison with GaMnAs and MnAs film in the same experimental condition. Furthermore, we observe a clear Coulomb blockade effect, as due to confinement and their nanometric size.

  14. Design and control of interface reaction between Al-based dielectrics and AlGaN layer in AlGaN/GaN metal-oxide-semiconductor structures

    NASA Astrophysics Data System (ADS)

    Watanabe, Kenta; Nozaki, Mikito; Yamada, Takahiro; Nakazawa, Satoshi; Anda, Yoshiharu; Ishida, Masahiro; Ueda, Tetsuzo; Yoshigoe, Akitaka; Hosoi, Takuji; Shimura, Takayoshi; Watanabe, Heiji

    2017-07-01

    Important clues for achieving well-behaved AlGaN/GaN metal-oxide-semiconductor (MOS) devices with Al-based gate dielectrics were systematically investigated on the basis of electrical and physical characterizations. We found that low-temperature deposition of alumina insulators on AlGaN surfaces is crucial to improve the interface quality, thermal stability, and variability of MOS devices by suppressing Ga diffusion into the gate oxides. Moreover, aluminum oxynitride grown in a reactive nitric atmosphere was proven to expand the optimal process window that would improve the interface quality and to enhance immunity against charge injection into the gate dielectrics. The results constitute common guidelines for achieving high-performance and reliable AlGaN/GaN MOS devices.

  15. Irradiation effects of graphene-enhanced gallium nitride (GaN) metal-semiconductor-metal (MSM) ultraviolet photodetectors

    NASA Astrophysics Data System (ADS)

    Chiamori, Heather C.; Miller, Ruth; Suria, Ateeq; Broad, Nicholas; Senesky, Debbie G.

    2015-05-01

    Ultraviolet (UV) photodetectors are used for applications such as flame detection, space navigation, biomedical and environmental monitoring. Robust operation within large ranges of temperatures, radiation, salinity and/or corrosive chemicals require sensor materials with the ability to withstand and function reliably within these extreme harsh environments. For example, spacecraft can utilize a sun sensor (light-based sensor) to assist with determination of orientation and may be exposed to both ionizing radiation and extreme temperature swings during operation. Gallium nitride (GaN), a wide bandgap semiconductor material, has material properties enabling visible-blindness, tunable cutoff wavelength selection based on ternary alloy mole fraction, high current density, thermal/chemical stability and high radiation tolerance due to the strength of the chemical bond. Graphene, with outstanding electrical, optical and mechanical properties and a flat absorption spectrum from 300 to 2,500 nm, has potential use as a transparent conductor for GaN-based metal-semiconductor-metal (MSM) photodetectors. Here, graphene-enhanced MSM UV photodetectors are fabricated with transparent and conductive graphene interdigitated electrodes on thin film GaN-on-sapphire substrates serving as back-to-back Schottky contacts. We report on the irradiation response of graphene/GaN-based MSM UV photodetectors up to 750 krad total ionizing dose (TID) then tested under dark and UV light (365 nm) conditions. In addition, based on current-voltage measurements from 75 krad to 750 krad TID, calculated photodetector responsivity values change slightly by 25% and 11% at -5 V and -2 V, respectively. These initial findings suggest that graphene/GaN MSM UV photodetectors could potentially be engineered to reliably operate within radiation environments.

  16. Investigations of AlGaN/GaN HFETs utilizing post-metallization etching by nitric acid treatment

    NASA Astrophysics Data System (ADS)

    Chou, Bo-Yi; Hsu, Wei-Chou; Lee, Ching-Sung; Liu, Han-Yin; Tsai, Chih-Ming; Ho, Chiu-Sheng

    2013-07-01

    This work investigates AlGaN/GaN heterostructure field-effect transistors (HFETs) processed by using a simple post-metallization etching (PME) treatment. Decreased gate length (LG) can be achieved by using nitric acid (HNO3) PME treatment owing to the high etching selectivity of HNO3 of Ni against the Au and GaN layer. Influences on LG, etched gate profiles and device characteristics with respect to different PME processing parameters by HNO3 treatment are systematically investigated. Optimum device performance is obtained as LG was reduced to 0.5 µm by using a 1 µm long gate mask by immersing the device into a 45% diluted HNO3 solution for 35 s. Improved device performances, including maximum drain-source current density (IDS, max: 657.6 mA mm-1 → 898.5 mA mm-1), drain-source saturation current density at zero gate bias (IDSS0: 448.3 mA mm-1 → 653.4 mA mm-1), maximum extrinsic transconductance (gm, max: 158.3 mS mm-1 → 219.2 mS mm-1), unity-gain cut-off frequency (fT: 12.35 GHz → 22.05 GHz), maximum oscillation frequency (fmax: 17.55 GHz → 29.4 GHz) and power-added efficiency (P.A.E.: 26.3% → 34.5%) compared to the untreated reference device, have been successfully achieved.

  17. Effects of substrate nitridation and buffer layer on the crystalline improvements of semi-polar InN(101¯3) crystal on GaAs(110) by MOVPE

    NASA Astrophysics Data System (ADS)

    Cho, H. C.; Togashi, R.; Murakami, H.; Kumagai, Y.; Koukitu, A.

    2013-03-01

    In this report, effects of ammonia nitridation and low temperature InN buffer growth were investigated to improve the crystalline quality of InN(101¯3) grown on GaAs(110) by metalorganic vapor phase epitaxy (MOVPE). InN(101¯3) single crystal including less than 0.1% of differently oriented domains was successfully grown by inserting low temperature InN buffer layer. The full width at half maximum (FWHM) values of InN(101¯3) epitaxial layer were drastically decreased from 89 arcmin to 55 arcmin after processing ammonia nitridation of GaAs(110) substrate surface. Furthermore, the FWHM value was decreased to 38 arcmin by increasing growth time, and the mechanism of dislocation annihilation happened during epitaxial growth was discussed.

  18. Transition metal doping of GaSe implemented with low temperature liquid phase growth

    NASA Astrophysics Data System (ADS)

    Lei, Nuo; Sato, Youhei; Tanabe, Tadao; Maeda, Kensaku; Oyama, Yutaka

    2017-02-01

    Our group works on improving the conversion efficiencies of terahertz (THz) wave generation using GaSe crystals. The operating principle is based on difference frequency generation (DFG) which has the advantages such as high output power, a single tunable frequency, and room temperature operation. In this study, GaSe crystals were grown by the temperature difference method under controlled vapor pressure (TDM-CVP). It is a liquid phase growth method with temperature 300 °C lower than that of the Bridgman method. Using this method, the point defects concentration is decreased and the polytype can be controlled. The transition metal Ti was used to dope the GaSe in order to suppress free carrier absorption in the low frequency THz region. As a result, a deep acceptor level of 38 meV was confirmed as being formed in GaSe with 1.4 at% Ti doping. Compared with undoped GaSe, a decrease in carrier concentration ( 1014 cm-3) at room temperature was also confirmed. THz wave transmittance measurements reveal the tendency for the absorption coefficient to increase as the amount of dopant is increased. It is expected that there is an optimum amount of dopant.

  19. Growth behavior of GaSb by metal organic vapor-phase epitaxy

    NASA Astrophysics Data System (ADS)

    Rathi, Manish K.; Hawkins, Brian E.; Kuech, Thomas F.

    2006-11-01

    The growth mechanisms of GaSb in a metal-organic vapor-phase epitaxy (MOVPE) system were studied for both trimethyl gallium (TMG)/trimethyl antimony (TMSb) and triethyl gallium (TEG)/TMSb growth chemistries. The effect of growth temperature and precursor mole fractions on GaSb growth rate was determined experimentally. Numerical analysis of the reactor and growth process was described in a combined chemical-thermal-fluid flow model. A Langmuir-Hinshelwood-type mechanism involving a surface reaction between adsorbed monomethyl gallium (MMG) and adsorbed monomethyl antimony (MMSb) or adsorbed Ga and adsorbed MMSb was proposed for the growth of GaSb by MOVPE using TMG or TEG and TMSb chemistries, respectively. The chemical model for TMG/TMSb chemistry included bounds on the surface chemistry derived for the range of V/III precursor ratio which were observed to lead to a second phase, i.e., elemental Ga or Sb, formation. Two growth regimes were observed for TMG/TMSb chemistry: above 575 °C the growth rate was mass transfer controlled whereas for lower temperatures it is kinetically limited. No such temperature dependence has been found for the TEG/TMSb chemistry over all experimental employed ranges of growth parameters.

  20. Electrical properties of hybrid (ferromagnetic metal)-(layered semiconductor) Ni/p-GaSe structures

    SciTech Connect

    Bakhtinov, A. P. Vodopyanov, V. N.; Kovalyuk, Z. D.; Netyaga, V. V.; Lytvyn, O. S.

    2010-02-15

    Two-barrier Ni/n-Ga2Se3/p-GaSe structures with nanoscale Ni-alloy grains caused by reactions at the 'metal-layered semiconductor' interface were formed after growing Ni layers on the p-GaSe (0001) surface. Current-voltage and capacitance-voltage characteristics of hybrid structures were studied in the temperature range of 220-350 K. The dependence of the impedance spectra on the bias voltage was studied at various temperatures. The frequency dependences of the impedance at high frequencies (f = 10{sup 6} Hz) are discussed in terms of the phenomena of spin injection and extraction in structures with an ultrathin spin-selective Ni/n-Ga{sub 2}Se{sub 3} barrier and the effects of spin diffusion and relaxation in the semiconductor substrate. The room-temperature phenomena of the Coulomb blockade and negative differential capacitance were detected. These phenomena are explained based on an analysis of transport processes in a narrow region near the 'ferromagnetic metal-semiconductor' interface, where nanoscale grains are arranged.

  1. White light emission from GaN stack layers doped by different rare-earth metals

    NASA Astrophysics Data System (ADS)

    Zhang, Lei; Liu, Chang

    2015-02-01

    Experimental progress of electroluminescence devices (ELDs) employing GaN doped with rare-earth metals had been significantly made targeting RGB displays. However, reports on the theoretical models to design the devices and the applications were limited. Our previous paper proposed a device model using the quantum collision theory and Judd-Ofelt approximation to design the ELDs for white light illumination. In the present study, the model is modified by considering the light extraction efficiency and optical loss during propagating in the films. To improve the luminous efficiency, an ELD with three stack layers of GaN:Tm/GaN:Er/GaN:Eu is proposed and designed. The model predicts that the color of the integrated light can be controlled by applied voltage, thickness of each doping layer and doping concentrations of the rare earth metals. The luminous efficacy of white light emission at a bias of -100 V is calculated to be 274 lm/W, which is much higher than that of fluorescent lumps. The proposed ELD will open a door to efficient solid-state lighting.

  2. Robust half-metallic properties in inverse Heusler alloys composed of 4d transition metal elements: Zr2RhZ (Z=Al, Ga, In)

    NASA Astrophysics Data System (ADS)

    Wang, X. T.; Lin, T. T.; Rozale, H.; Dai, X. F.; Liu, G. D.

    2016-03-01

    A first-principles approach is used to study the electronic and magnetic properties of Zr2RhZ (Z=Al, Ga, In) alloys in the Hg2CuTi-type structure. The Zr2RhZ (Z=Al, Ga, In) alloys are found to be half-metallic ferrimagnets. The half-metallicity is quite robust against hydrostatic strain and tetragonal deformation in Zr2RhZ (Z=Al, Ga, In) alloys. The magnetization of Zr2RhZ (Z=Al, Ga, In) alloys mainly originates from the 4d electrons of Zr atoms and follows the rule: Mt=Zt-18. Zr2Rh-based alloys do not contain any 3d transition metal element, which implies a wider field to search for new half-metallic materials.

  3. Impact of GaN cap on charges in Al₂O₃/(GaN/)AlGaN/GaN metal-oxide-semiconductor heterostructures analyzed by means of capacitance measurements and simulations

    SciTech Connect

    Ťapajna, M. Jurkovič, M.; Válik, L.; Haščík, Š.; Gregušová, D.; Kuzmík, J.; Brunner, F.; Cho, E.-M.; Hashizume, T.

    2014-09-14

    Oxide/semiconductor interface trap density (D{sub it}) and net charge of Al₂O₃/(GaN)/AlGaN/GaN metal-oxide-semiconductor high-electron mobility transistor (MOS-HEMT) structures with and without GaN cap were comparatively analyzed using comprehensive capacitance measurements and simulations. D{sub it} distribution was determined in full band gap of the barrier using combination of three complementary capacitance techniques. A remarkably higher D{sub it} (∼5–8 × 10¹²eV⁻¹ cm⁻²) was found at trap energies ranging from EC-0.5 to 1 eV for structure with GaN cap compared to that (D{sub it} ∼ 2–3 × 10¹²eV⁻¹ cm⁻²) where the GaN cap was selectively etched away. D{sub it} distributions were then used for simulation of capacitance-voltage characteristics. A good agreement between experimental and simulated capacitance-voltage characteristics affected by interface traps suggests (i) that very high D{sub it} (>10¹³eV⁻¹ cm⁻²) close to the barrier conduction band edge hampers accumulation of free electron in the barrier layer and (ii) the higher D{sub it} centered about EC-0.6 eV can solely account for the increased C-V hysteresis observed for MOS-HEMT structure with GaN cap. Analysis of the threshold voltage dependence on Al₂O₃ thickness for both MOS-HEMT structures suggests that (i) positive charge, which compensates the surface polarization, is not necessarily formed during the growth of III-N heterostructure, and (ii) its density is similar to the total surface polarization charge of the GaN/AlGaN barrier, rather than surface polarization of the top GaN layer only. Some constraints for the positive surface compensating charge are discussed.

  4. High yield fabrication of low threshold single-mode GaAs/AlGaAs semiconductor ring lasers using metallic etch masks.

    PubMed

    Dutta, Neilanjan; Murakowski, Janusz A; Shi, Shouyuan; Prather, Dennis W

    2010-05-24

    We demonstrate a novel high yield fabrication process for single-mode ridge-waveguide GaAs/AlGaAs ring lasers with significantly lower threshold currents than previously reported for similar devices. In this fabrication process, the ridge waveguide structure is patterned using a metallic etch mask, which survives ensuing fabrication steps to form a continuous metallic cover over the entire resonator structure. This metallic cover improves the uniformity of electrical contact between the resonator structure and the metallic biasing layer deposited at the conclusion of the fabrication process. This leads to optimum electrical pumping of the fabricated devices. This fabrication process also allows for the passivation of the ridge-waveguide device sidewalls and separation of the metallic biasing layer from the optical mode.

  5. Growth of thick (112xAF0) GaN using a metal interlayer

    NASA Astrophysics Data System (ADS)

    Tavernier, P. R.; Imer, B.; DenBaars, S. P.; Clarke, D. R.

    2004-11-01

    Thick films of (112¯0)-oriented GaN have been grown on Ti-coated metal organic chemical vapor deposition templates using hydride vapor phase epitaxy. Significant reductions in crack density were observed enabling 240μm thick films to be grown on sapphire. The use of Ti interlayers was shown to generate significant fractions of voids at the interlayer regrowth interface facilitating void-assisted separation on cooling. Ti metal layers annealed under optimal conditions were found to produce a TiN nanomask suitable for lateral overgrowth during HVPE. An estimate of the void size required to allow spontaneous delamination of the substrate at the TiN-GaN interface is discussed with reference to growth conditions.

  6. Magnetometory of AlGaN/GaN heterostructure wafers

    NASA Astrophysics Data System (ADS)

    Tsubaki, K.; Maeda, N.; Saitoh, T.; Kobayashi, N.

    2005-06-01

    AlGaN/GaN heterostructure wafers are becoming a key technology for next generation cellar-phone telecommunication system because of their potential for high-performance microwave applications. Therefore, the electronic properties of a 2DEG in AlGaN/GaN heterostructures have recently been discussed. In this paper, we performed the extraordinary Hall effect measurement and the SQUID magnetometory of AlGaN/GaN heterostructure wafer at low temperature. The AlGaN/GaN heterostructures were grown by low-pressure metal-organic chemical vapour phase epitaxy on (0001) SiC substrate using AlN buffers. The electron mobility and electron concentration at 4.2 K are 9,540cm2/V s and 6.6 × 1012cm-2, respectively. In the extraordinary Hall effect measurement of AlGaN/GaN heterostructures, the hysteresis of Hall resistance appeared below 4.5 K and disappeared above 4.5 K. On the other hand, the hysteresis of magnetometric data obtained by SQUID magnetometory appears near zero magnetic field when the temperature is lower than 4.5 K. At the temperature larger than 4.5 K, the hysteresis of magnetometric data disappears. And the slopes of magnetometric data with respect to magnetic field become lower as obeying Currie-Weiss law and the Curie temperature TC is 4.5 K. Agreement of TC measured by the extraordinary Hall effect and the SQUID magnetometory implies the ferromagnetism at the AlGaN/GaN heterojunction. However, the conformation of the ferromagnetism of AlGaN/GaN heterostructure is still difficult and the detailed physical mechanism is still unclear.

  7. Wafer-scale controlled exfoliation of metal organic vapor phase epitaxy grown InGaN/GaN multi quantum well structures using low-tack two-dimensional layered h-BN

    NASA Astrophysics Data System (ADS)

    Ayari, Taha; Sundaram, Suresh; Li, Xin; El Gmili, Youssef; Voss, Paul L.; Salvestrini, Jean Paul; Ougazzaden, Abdallah

    2016-04-01

    Recent advances in epitaxial growth have led to the growth of III-nitride devices on 2D layered h-BN. This advance has the potential for wafer-scale transfer to arbitrary substrates, which could improve the thermal management and would allow III-N devices to be used more flexibly in a broader range of applications. We report wafer scale exfoliation of a metal organic vapor phase epitaxy grown InGaN/GaN Multi Quantum Well (MQW) structure from a 5 nm thick h-BN layer that was grown on a 2-inch sapphire substrate. The weak van der Waals bonds between h-BN atomic layers break easily, allowing the MQW structure to be mechanically lifted off from the sapphire substrate using a commercial adhesive tape. This results in the surface roughness of only 1.14 nm on the separated surface. Structural characterizations performed before and after the lift-off confirm the conservation of structural properties after lift-off. Cathodoluminescence at 454 nm was present before lift-off and 458 nm was present after. Electroluminescence near 450 nm from the lifted-off structure has also been observed. These results show that the high crystalline quality ultrathin h-BN serves as an effective sacrificial layer—it maintains performance, while also reducing the GaN buffer thickness and temperature ramps as compared to a conventional two-step growth method. These results support the use of h-BN as a low-tack sacrificial underlying layer for GaN-based device structures and demonstrate the feasibility of large area lift-off and transfer to any template, which is important for industrial scale production.

  8. Wafer-scale controlled exfoliation of metal organic vapor phase epitaxy grown InGaN/GaN multi quantum well structures using low-tack two-dimensional layered h-BN

    SciTech Connect

    Ayari, Taha; Li, Xin; Voss, Paul L.; Ougazzaden, Abdallah; Sundaram, Suresh; El Gmili, Youssef; Salvestrini, Jean Paul

    2016-04-25

    Recent advances in epitaxial growth have led to the growth of III-nitride devices on 2D layered h-BN. This advance has the potential for wafer-scale transfer to arbitrary substrates, which could improve the thermal management and would allow III-N devices to be used more flexibly in a broader range of applications. We report wafer scale exfoliation of a metal organic vapor phase epitaxy grown InGaN/GaN Multi Quantum Well (MQW) structure from a 5 nm thick h-BN layer that was grown on a 2-inch sapphire substrate. The weak van der Waals bonds between h-BN atomic layers break easily, allowing the MQW structure to be mechanically lifted off from the sapphire substrate using a commercial adhesive tape. This results in the surface roughness of only 1.14 nm on the separated surface. Structural characterizations performed before and after the lift-off confirm the conservation of structural properties after lift-off. Cathodoluminescence at 454 nm was present before lift-off and 458 nm was present after. Electroluminescence near 450 nm from the lifted-off structure has also been observed. These results show that the high crystalline quality ultrathin h-BN serves as an effective sacrificial layer—it maintains performance, while also reducing the GaN buffer thickness and temperature ramps as compared to a conventional two-step growth method. These results support the use of h-BN as a low-tack sacrificial underlying layer for GaN-based device structures and demonstrate the feasibility of large area lift-off and transfer to any template, which is important for industrial scale production.

  9. Micro-Reactions on Metal Contacts on Various Types of GaAs Surfaces.

    DTIC Science & Technology

    1986-02-01

    GaAs surfaces as generally employed for the manufacture of MeSFETs and their IC’s, particularly _- . - in view of device-life-time optimization...electrodes (points A(v) and (vii) of Section C-I, Award Dec.); in particular here the formation of ._ narrow, short circuiting metal filaments by field... MeSFETs has beco . -’.. a field of wide current interest particularly from the device aging point of view /9/. : - . -. . p. . Here, we describe the

  10. Selective metal-organic chemical vapor deposition growth of high quality GaAs on Si(001)

    SciTech Connect

    Guo, W. Pena, V.; Merckling, C.; Waldron, N.; Collaert, N.; Caymax, M.; Vancoille, E.; Barla, K.; Thean, A.; Eyben, P.; Date, L.; Bao, X.; Sanchez, E.; Vandervorst, W.

    2014-08-11

    High quality GaAs is selectively grown in 40 nm width Shallow Trench Isolation patterned structures. The patterned wafers have a V-shape Si (111) surface obtained by Tetramethylammonium hydroxide etching. By employing a SiCoNi™ pre-epi clean and two-step growth procedure (low temperature buffer and high temperature main layer), defects are effectively confined at the trench bottom, leaving a dislocation-free GaAs layer at the upper part. The high crystal quality is confirmed by transmission electron microscopy. Scanning spreading resistance microscopy indicates a high resistance of GaAs. The process conditions and GaAs material quality are highly compatible with Si technology platform.

  11. Selective metal-organic chemical vapor deposition growth of high quality GaAs on Si(001)

    NASA Astrophysics Data System (ADS)

    Guo, W.; Date, L.; Pena, V.; Bao, X.; Merckling, C.; Waldron, N.; Collaert, N.; Caymax, M.; Sanchez, E.; Vancoille, E.; Barla, K.; Thean, A.; Eyben, P.; Vandervorst, W.

    2014-08-01

    High quality GaAs is selectively grown in 40 nm width Shallow Trench Isolation patterned structures. The patterned wafers have a V-shape Si (111) surface obtained by Tetramethylammonium hydroxide etching. By employing a SiCoNi™ pre-epi clean and two-step growth procedure (low temperature buffer and high temperature main layer), defects are effectively confined at the trench bottom, leaving a dislocation-free GaAs layer at the upper part. The high crystal quality is confirmed by transmission electron microscopy. Scanning spreading resistance microscopy indicates a high resistance of GaAs. The process conditions and GaAs material quality are highly compatible with Si technology platform.

  12. Metal diffusion barriers for GaAs solar cells.

    PubMed

    van Leest, R H; Mulder, P; Bauhuis, G J; Cheun, H; Lee, H; Yoon, W; van der Heijden, R; Bongers, E; Vlieg, E; Schermer, J J

    2017-03-15

    In this study accelerated ageing testing (AAT), J-V characterization and TEM imaging in combination with phase diagram data from literature are used to assess the potential of Ti, Ni, Pd and Pt as diffusion barriers for Au/Cu-based metallization of III-V solar cells. Ni barriers show the largest potential as at an AAT temperature of 250 °C both cells with 10 and 100 nm thick Ni barriers show significantly better performance compared to Au/Cu cells, with the cells with 10 nm Ni barriers even showing virtually no degradation after 7.5 days at 250 °C (equivalent to 10 years at 100 °C at an Ea of 0.70 eV). Detailed investigation shows that Ni does not act as a barrier in the classical sense, i.e. preventing diffusion of Cu and Au across the barrier. Instead Ni modifies or slows down the interactions taking place during device degradation and thus effectively acts as an 'interaction' barrier. Different interactions occur at temperatures below and above 250 °C and for thin (10 nm) and thick (100 nm) barriers. The results of this study indicate that 10-100 nm thick Ni intermediate layers in the Cu/Au based metallization of III-V solar cells may be beneficial to improve the device stability upon exposure to elevated temperatures.

  13. Tetrahedral Clusters of GaMo 4S 8-Type Compounds: A Metal Bonding Analysis

    NASA Astrophysics Data System (ADS)

    Le Beuze, A.; Loirat, H.; Zerrouki, M. C.; Lissillour, R.

    1995-11-01

    Extended Hückel tight binding calculations have been performed on ligated as well as on ligand-free Mo4 and Mo6 extended frames, in order to analyze the metal-metal bonding within the clusters and particularly the appreciable changes of the metal-metal bond lengths through the M4 tetrahedral units contained in GaM4X8 (M = Mo, Nb, V, Ta; X = S, Se, Te), Mo4S4Y4 (Y = Cl, Br, I). A comparison with the M6 octahedral units of the M Mo6X8 (M = Pb, Ag, La; X = S, Se) series is made. By means of DOS, COOP curves, and overlap populations, results clearly display the strong reorganization of the electronic structure of the bare metal clusters network while the ligand interactions occur, inducing a strong reduction of the strength of the metal-metal bonds. We outline the relationship between the metal-metal bond lengths and various parameters such as the valence electron count (VEC) per cluster and the nature of the ligands. Our results indicate that the two series M4 and M6 differ: M-M bond lengths are unaffected by the VEC in the regular M4 cluster, whereas some M-M bond lengths undergo a significant change when the VEC increases in the distorded M6 clusters. Likewise, it is worthy to note that metal d orbitals have a more significant effect in M4 cluster series. In contrast, the metal-ligand covalency induces similar elongations of metal-metal bonds in the two series.

  14. 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.

  15. Metal ferroelectric insulator Si devices using HfTaO buffer layers

    NASA Astrophysics Data System (ADS)

    Lu, Xu-bing; Maruyama, Kenji; Ishiwara, Hiroshi

    2008-04-01

    Metal-ferroelectric-insulator-Si (MFIS) diodes and transistors using Pt/Sr0.8Bi2.2Ta2O9 (SBT)/HfTaO/Si gate structures were fabricated. HfTaO films were deposited at room temperature by electron beam evaporation under a background vacuum of ~1.5 × 10-9 Torr. By process optimization of post-deposition annealing, a small effective oxide thickness of 1.6 nm, a small leakage current of 2.4 × 10-4 A cm-2 at a voltage shifted from the flat band voltage by 1 V and a negligible hysteresis loop were obtained for Al/HfTaO (4 nm)/Si diodes. The MFIS diodes were fabricated by the deposition of SBT films on the HfTaO (4 nm)/Si substrate using chemical solution deposition. A memory window of 0.62 V was obtained for Pt/SBT (300 nm)/HfTaO (4 nm)/Si diodes for a voltage sweep between +4 V and -4 V. P-channel ferroelectric-gate transistors were fabricated using the same gate structure, which showed a memory window of 0.6 V and good long-term retention characteristics. A drain current ON/OFF ratio as high as 103 was attained at a fixed reading voltage of -0.7 V even after over 104 s has elapsed.

  16. Surface-bound iron: a metal ion buffer in the marine brown alga Ectocarpus siliculosus?

    PubMed Central

    Carrano, Carl J.

    2014-01-01

    Although the iron uptake and storage mechanisms of terrestrial/higher plants have been well studied, the corresponding systems in marine algae have received far less attention. Studies have shown that while some species of unicellular algae utilize unique mechanisms of iron uptake, many acquire iron through the same general mechanisms as higher plants. In contrast, the iron acquisition strategies of the multicellular macroalgae remain largely unknown. This is especially surprising since many of these organisms represent important ecological and evolutionary niches in the coastal marine environment. It has been well established in both laboratory and environmentally derived samples, that a large amount of iron can be ‘non-specifically’ adsorbed to the surface of marine algae. While this phenomenon is widely recognized and has prompted the development of experimental protocols to eliminate its contribution to iron uptake studies, its potential biological significance as a concentrated iron source for marine algae is only now being recognized. This study used an interdisciplinary array of techniques to explore the nature of the extensive and powerful iron binding on the surface of both laboratory and environmental samples of the marine brown alga Ectocarpus siliculosus and shows that some of this surface-bound iron is eventually internalized. It is proposed that the surface-binding properties of E. siliculosus allow it to function as a quasibiological metal ion ‘buffer’, allowing iron uptake under the widely varying external iron concentrations found in coastal marine environments. PMID:24368501

  17. Buffer Loading for Counteracting Metal Salt-Induced Signal Suppression in Electrospray Ionization

    PubMed Central

    Iavarone, Anthony T.; Udekwu, Osita A.; Williams, Evan R.

    2005-01-01

    The decrease in the sensitivity of electrospray ionization mass spectrometry caused by the presence of metal salts, such as sodium chloride, in the sample matrix is well known and is particularly problematic for biological samples. We report here that addition of high levels of ammonium acetate can improve analyte signal in aqueous electrospray solutions and counteracts the signal suppression caused by sodium chloride. A ~3-fold improvement in S/N is obtained by adding 8 M ammonium acetate to aqueous solutions of cytochrome c without added sodium chloride. No organic solvents or acids are added into the electrospray solutions. The signal-to-noise ratios of cytochrome c and ubiquitin (10−5 M) ions formed from aqueous solutions containing 2.0 × 10−2 M sodium chloride are improved by factors of ~7 and 11, respectively, by adding 7 M ammonium acetate to the solution. We propose that this effect is a result of the precipitation of Na+ and Cl− from solution within the evaporating electrospray droplets prior to the formation of gas-phase protein ions. This method is potentially useful for improving the abundance of protein ions formed from solutions in which the molecules have a nativelike conformation and is particularly advantageous for such solutions that have high levels of sodium. PMID:15253628

  18. Heteroepitaxial VO2 thin films on GaN: Structure and metal-insulator transition characteristics

    NASA Astrophysics Data System (ADS)

    Zhou, You; Ramanathan, Shriram

    2012-10-01

    Monolithic integration of correlated oxide and nitride semiconductors may open up new opportunities in solid-state electronics and opto-electronics that combine desirable functional properties of both classes of materials. Here, we report on epitaxial growth and phase transition-related electrical properties of vanadium dioxide (VO2) thin films on GaN epitaxial layers on c-sapphire. The epitaxial relation is determined to be (010)vo2‖(0001)GaN‖(0001)A12O3 and [100]vo2‖[1¯21¯0]A12O3 from x-ray diffraction. VO2 heteroepitaxial growth and lattice mismatch are analyzed by comparing the GaN basal plane (0001) with the almost close packed corrugated oxygen plane in vanadium dioxide and an experimental stereographic projection describing the orientation relationship is established. X-ray photoelectron spectroscopy suggests a slightly oxygen rich composition at the surface, while Raman scattering measurements suggests that the quality of GaN layer is not significantly degraded by the high-temperature deposition of VO2. Electrical characterization of VO2 films on GaN indicates that the resistance changes by about four orders of magnitude upon heating, similar to epitaxial VO2 films grown directly on c-sapphire. It is shown that the metal-insulator transition could also be voltage-triggered at room temperature and the transition threshold voltage scaling variation with temperature is analyzed in the framework of a current-driven Joule heating model. The ability to synthesize high quality correlated oxide films on GaN with sharp phase transition could enable new directions in semiconductor-photonic integrated devices.

  19. High-performance GaN metal-insulator-semiconductor ultraviolet photodetectors using gallium oxide as gate layer.

    PubMed

    Lee, Ming-Lun; Mue, T S; Huang, F W; Yang, J H; Sheu, J K

    2011-06-20

    In this study, gallium nitride (GaN)-based metal-insulator-semiconductor (MIS) ultraviolet (UV) photodetectors (PDs) with a gallium oxide (GaO(x)) gate layer formed by alternating current bias-assisted photoelectrochemical oxidation of n-GaN are presented. By introducing the GaO(x) gate layer to the GaN MIS UV PDs, the leakage current is reduced and a much larger UV-to-visible rejection ratio (R(UV/vis)) of spectral responsivity is achieved. In addition, a bias-dependent spectral response results in marked increase of the R(UV/vis) with bias voltage up to ~10(5). The bias-dependent responsivity suggests the possible existence of internal gain in of the GaN MIS PDs.

  20. Surface kinetics study of metal-organic vapor phase epitaxy of GaAs1-yBiy on offcut and mesa-patterned GaAs substrates

    NASA Astrophysics Data System (ADS)

    Guan, Yingxin; Forghani, Kamran; Kim, Honghyuk; Babcock, Susan E.; Mawst, Luke J.; Kuech, Thomas F.

    2017-04-01

    The influence of the surface step termination on the metal-organic vapor phase epitaxy of GaAs1-yBiy was explored by examining the epitaxial layer growth rate, composition, and morphology characteristics on the offcut and mesa-patterned (001) GaAs substrates. Vicinal surfaces offcut to (111)B with a high density of As-terminated steps ('B-steps') increased the GaAs1-yBiy layer growth rate as well as possessed the fastest lateral growth rate on mesa-patterned substrates at a growth temperature of 420 °C, indicating that B-steps enhanced the Ga incorporation. With Bi accumulation on the surface, the Ga incorporation rate was reduced by the Bi preferential presence at B-steps blocking the Ga incorporation. Vicinal surfaces offcut to (111)A, which generated Ga-terminated steps ('A-steps') enhanced the Bi incorporation rate during growth at 380 °C. This work reveals that the surface step termination plays an important role in the growth of the metastable alloy. Appropriate choices of both the substrate surface-step structure and other growth parameters could lead to an enhanced Bi incorporation.

  1. P-Channel InGaN/GaN heterostructure metal-oxide-semiconductor field effect transistor based on polarization-induced two-dimensional hole gas.

    PubMed

    Zhang, Kexiong; Sumiya, Masatomo; Liao, Meiyong; Koide, Yasuo; Sang, Liwen

    2016-03-29

    The concept of p-channel InGaN/GaN heterostructure field effect transistor (FET) using a two-dimensional hole gas (2DHG) induced by polarization effect is demonstrated. The existence of 2DHG near the lower interface of InGaN/GaN heterostructure is verified by theoretical simulation and capacitance-voltage profiling. The metal-oxide-semiconductor FET (MOSFET) with Al2O3 gate dielectric shows a drain-source current density of 0.51 mA/mm at the gate voltage of -2 V and drain bias of -15 V, an ON/OFF ratio of two orders of magnitude and effective hole mobility of 10 cm(2)/Vs at room temperature. The normal operation of MOSFET without freeze-out at 8 K further proves that the p-channel behavior is originated from the polarization-induced 2DHG.

  2. Normally-off AlGaN/GaN-on-Si metal-insulator-semiconductor heterojunction field-effect transistor with nitrogen-incorporated silicon oxide gate insulator

    NASA Astrophysics Data System (ADS)

    Roh, Seung-Hyun; Eom, Su-Keun; Choi, Gwang-Ho; Kang, Myoung-Jin; Kim, Dong-Hwan; Hwang, Il-Hwan; Seo, Kwang-Seok; Lee, Jae-Gil; Byun, Young-Chul; Cha, Ho-Young

    2017-08-01

    We have developed a nitrogen-incorporated silicon oxide (SiOxNy) deposition process using plasma enhanced atomic layer deposition (PEALD) for the gate insulator of recessed-gate Al-GaN/GaN metal-insulator-semiconductor heterojunction field-effect transistors. The SiOxNy film deposited on a recessed GaN surface exhibited a breakdown field of 13.2 MV/cm and a conduction band offset of 3.37 eV, which are the highest values reported for GaN MIS structures to the best of our knowledge. The fabricated normally-off transistor exhibited very promising characteristics such as a threshold voltage of 2.2 V, a maximum drain current density of 428 mA/mm, and a breakdown voltage of 928 V.

  3. Interface states in Al2O3/AlGaN/GaN metal-oxide-semiconductor structure by frequency dependent conductance technique

    NASA Astrophysics Data System (ADS)

    Liao, Xue-Yang; Zhang, Kai; Zeng, Chang; Zheng, Xue-Feng; En, Yun-Fei; Lai, Ping; Hao, Yue

    2014-05-01

    Frequency dependent conductance measurements are implemented to investigate the interface states in Al2O3/AlGaN/GaN metal-oxide-semiconductor (MOS) structures. Two types of device structures, namely, the recessed gate structure (RGS) and the normal gate structure (NGS), are studied in the experiment. Interface trap parameters including trap density Dit, trap time constant τit, and trap state energy ET in both devices have been determined. Furthermore, the obtained results demonstrate that the gate recess process can induce extra traps with shallower energy levels at the Al2O3/AlGaN interface due to the damage on the surface of the AlGaN barrier layer resulting from reactive ion etching (RIE).

  4. Evaluation of a gate-first process for AlGaN/GaN metal-oxide-semiconductor heterostructure field-effect transistors with low ohmic annealing temperature

    NASA Astrophysics Data System (ADS)

    Liuan, Li; Jiaqi, Zhang; Yang, Liu; Jin-Ping, Ao

    2016-03-01

    In this paper, TiN/AlOx gated AlGaN/GaN metal-oxide-semiconductor heterostructure field-effect transistors (MOS-HFETs) were fabricated for gate-first process evaluation. By employing a low temperature ohmic process, ohmic contact can be obtained by annealing at 600 °C with the contact resistance approximately 1.6 Ω·mm. The ohmic annealing process also acts as a post-deposition annealing on the oxide film, resulting in good device performance. Those results demonstrated that the TiN/AlOx gated MOS-HFETs with low temperature ohmic process can be applied for self-aligned gate AlGaN/GaN MOS-HFETs. Project supported by the International Science and Technology Collaboration Program of China (Grant No. 2012DFG52260).

  5. InGaP/GaAs heterojunction phototransistors transferred to a Si substrate by metal wafer bonding combined with epitaxial lift-off.

    PubMed

    Park, Min-Su; Geum, Dae-Myeong; Kyhm, Ji Hoon; Song, Jin Dong; Kim, SangHyeon; Choi, Won Jun

    2015-10-19

    We report fabrication and optical characteristics of an InGaP/GaAs heterojunction phototransistor (HPT) transferred to a Si substrate by a metal wafer bonding (MWB) and epitaxial lift-off (ELO) process at room temperature. An intermediate Pt/Au double layer between the HPT layer and Si provided a very smooth surface by which to achieve the MWB, and excellent durability against the acid solution during the ELO process. These processes were observed using scanning electron microscope (SEM) and atomic force microscopy (AFM). While the results on a low temperature photoluminescence (LTPL) signal and high resolution x-ray diffraction (HRXRD) rocking curve of the bonded device film implied a defect-free bonding, a very low collector dark current of the fabricated HPT was observed. The optical performance of a bonded InGaP/GaAs HPT on Si, operating at 635 nm wavelength is also investigated.

  6. Transistor sizing in the design of high-speed CMOS (complementary-symmetry metal-oxide-semiconductor) super buffers. Master's thesis

    SciTech Connect

    Steele, G.R.

    1988-03-01

    An algorithm for sizing transistors for static Complementary-symmetry Metal-Oxide-Semiconductor (CMOS) integrated-circuit logic design using silicon-gate enhancement-mode Field-Effect Transistors (FET) is derived and implemented in software. The algorithm is applied to the mask-level hardware design of a three-micron-minimum feature-size p-well high-speed super buffer. A software representation of the super buffer can be used for the automated design of custom Very-Large-Scale Integrated (VLSI) circuits.

  7. Gain mechanism and carrier transport in high responsivity AlGaN-based solar blind metal semiconductor metal photodetectors

    NASA Astrophysics Data System (ADS)

    Rathkanthiwar, Shashwat; Kalra, Anisha; Solanke, Swanand V.; Mohta, Neha; Muralidharan, Rangarajan; Raghavan, Srinivasan; Nath, Digbijoy N.

    2017-04-01

    We report on the highest responsivity for III-nitride Metal Semiconductor Metal solar-blind photodetectors on sapphire. Devices on unintentionally doped AlGaN epilayers grown by Metal Organic Chemical Vapor Deposition exhibited sharp absorption cut-off in the range of 245-290 nm. Very high responsivity >5 A/W at 10 V bias was achieved with visible rejection exceeding three orders of magnitude for front illumination. Compared to the responsivity values reported in the literature for state-of-the-art solar-blind photodetectors, this work presents the highest values of responsivity at a given bias and up to sub-250 nm detection threshold. The high responsivity is attributed to an internal gain mechanism operating on these devices. The reverse-bias leakage current across these samples was found to be dominated by thermionic field emission at low biases and Poole-Frenkel emission from a deep trap level (0.7 eV from the conduction band-edge for Al0.50Ga0.50 N) at high biases.

  8. Low Al-composition p-GaN/Mg-doped Al0.25Ga0.75N/n+-GaN polarization-induced backward tunneling junction grown by metal-organic chemical vapor deposition on sapphire substrate

    PubMed Central

    Zhang, Kexiong; Liang, Hongwei; Liu, Yang; Shen, Rensheng; Guo, Wenping; Wang, Dongsheng; Xia, Xiaochuan; Tao, Pengcheng; Yang, Chao; Luo, Yingmin; Du, Guotong

    2014-01-01

    Low Al-composition p-GaN/Mg-doped Al0.25Ga0.75N/n+-GaN polarization-induced backward tunneling junction (PIBTJ) was grown by metal-organic chemical vapor deposition on sapphire substrate. A self-consistent solution of Poisson-Schrödinger equations combined with polarization-induced theory was used to model PIBTJ structure, energy band diagrams and free carrier concentrations distribution. The PIBTJ displays reliable and reproducible backward tunneling with a current density of 3 A/cm2 at the reverse bias of −1 V. The absence of negative differential resistance behavior of PIBTJ at forward bias can mainly be attributed to the hole compensation centers, including C, H and O impurities, accumulated at the p-GaN/Mg-doped AlGaN heterointerface. PMID:25205042

  9. Spatially correlated two-dimensional arrays of semiconductor and metal quantum dots in GaAs-based heterostructures

    SciTech Connect

    Nevedomskiy, V. N. Bert, N. A.; Chaldyshev, V. V.; Preobrazhernskiy, V. V.; Putyato, M. A.; Semyagin, B. R.

    2015-12-15

    A single molecular-beam epitaxy process is used to produce GaAs-based heterostructures containing two-dimensional arrays of InAs semiconductor quantum dots and AsSb metal quantum dots. The twodimensional array of AsSb metal quantum dots is formed by low-temperature epitaxy which provides a large excess of arsenic in the epitaxial GaAs layer. During the growth of subsequent layers at a higher temperature, excess arsenic forms nanoinclusions, i.e., metal quantum dots in the GaAs matrix. The two-dimensional array of such metal quantum dots is created by the δ doping of a low-temperature GaAs layer with antimony which serves as a precursor for the heterogeneous nucleation of metal quantum dots and accumulates in them with the formation of AsSb metal alloy. The two-dimensional array of InAs semiconductor quantum dots is formed via the Stranski–Krastanov mechanism at the GaAs surface. Between the arrays of metal and semiconductor quantum dots, a 3-nm-thick AlAs barrier layer is grown. The total spacing between the arrays of metal and semiconductor quantum dots is 10 nm. Electron microscopy of the structure shows that the arrangement of metal quantum dots and semiconductor quantum dots in the two-dimensional arrays is spatially correlated. The spatial correlation is apparently caused by elastic strain and stress fields produced by both AsSb metal and InAs semiconductor quantum dots in the GaAs matrix.

  10. Bi-modal nanoheteroepitaxy of GaAs on Si by metal organic vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    Prieto, Ivan; Kozak, Roksolana; Skibitzki, Oliver; Rossell, Marta D.; Zaumseil, Peter; Capellini, Giovanni; Gini, Emilio; Kunze, Karsten; Arroyo Rojas Dasilva, Yadira; Erni, Rolf; Schroeder, Thomas; von Känel, Hans

    2017-03-01

    Nano-heteroepitaxial growth of GaAs on Si(001) by metal organic vapor phase epitaxy was investigated to study emerging materials phenomena on the nano-scale of III-V/Si interaction. Arrays of Si nano-tips (NTs) embedded in a SiO2 matrix were used as substrates. The NTs had top Si openings of 50-90 nm serving as seeds for the selective growth of GaAs nano-crystals (NCs). The structural and morphological properties were investigated by high resolution scanning electron microscopy, atomic force microscopy, electron backscatter diffraction, x-ray diffraction, and high resolution scanning transmission electron microscopy. The GaAs growth led to epitaxial NCs featuring a bi-modal distribution of size and morphology. NCs of small size exhibited high structural quality and well-defined {111}-{100} faceting. Larger clusters had less regular shapes and contained twins. The present work shows that the growth of high quality GaAs NCs on Si NTs is feasible and can provide an alternate way to the integration of compound semiconductors with Si micro- and opto-electronics technology.

  11. Bi-modal nanoheteroepitaxy of GaAs on Si by metal organic vapor phase epitaxy.

    PubMed

    Prieto, Ivan; Kozak, Roksolana; Skibitzki, Oliver; Rossell, Marta D; Zaumseil, Peter; Capellini, Giovanni; Gini, Emilio; Kunze, Karsten; Rojas Dasilva, Yadira Arroyo; Erni, Rolf; Schroeder, Thomas; Känel, Hans von

    2017-03-01

    Nano-heteroepitaxial growth of GaAs on Si(001) by metal organic vapor phase epitaxy was investigated to study emerging materials phenomena on the nano-scale of III-V/Si interaction. Arrays of Si nano-tips (NTs) embedded in a SiO2 matrix were used as substrates. The NTs had top Si openings of 50-90 nm serving as seeds for the selective growth of GaAs nano-crystals (NCs). The structural and morphological properties were investigated by high resolution scanning electron microscopy, atomic force microscopy, electron backscatter diffraction, x-ray diffraction, and high resolution scanning transmission electron microscopy. The GaAs growth led to epitaxial NCs featuring a bi-modal distribution of size and morphology. NCs of small size exhibited high structural quality and well-defined {111}-{100} faceting. Larger clusters had less regular shapes and contained twins. The present work shows that the growth of high quality GaAs NCs on Si NTs is feasible and can provide an alternate way to the integration of compound semiconductors with Si micro- and opto-electronics technology.

  12. Reproducible increased Mg incorporation and large hole concentration in GaN using metal modulated epitaxy

    SciTech Connect

    Burnham, Shawn D.; Doolittle, W. Alan; Namkoong, Gon; Look, David C.; Clafin, Bruce

    2008-07-15

    The metal modulated epitaxy (MME) growth technique is reported as a reliable approach to obtain reproducible large hole concentrations in Mg-doped GaN grown by plasma-assisted molecular-beam epitaxy on c-plane sapphire substrates. An extremely Ga-rich flux was used, and modulated with the Mg source according to the MME growth technique. The shutter modulation approach of the MME technique allows optimal Mg surface coverage to build between MME cycles and Mg to incorporate at efficient levels in GaN films. The maximum sustained concentration of Mg obtained in GaN films using the MME technique was above 7x10{sup 20} cm{sup -3}, leading to a hole concentration as high as 4.5x10{sup 18} cm{sup -3} at room temperature, with a mobility of 1.1 cm{sup 2} V{sup -1} s{sup -1} and a resistivity of 1.3 {omega} cm. At 580 K, the corresponding values were 2.6x10{sup 19} cm{sup -3}, 1.2 cm{sup 2} V{sup -1} s{sup -1}, and 0.21 {omega} cm, respectively. Even under strong white light, the sample remained p-type with little change in the electrical parameters.

  13. Influence of Silicate Melt Composition on Metal/Silicate Partitioning of W, Ge, Ga and Ni

    NASA Technical Reports Server (NTRS)

    Singletary, S. J.; Domanik, K.; Drake, M. J.

    2005-01-01

    The depletion of the siderophile elements in the Earth's upper mantle relative to the chondritic meteorites is a geochemical imprint of core segregation. Therefore, metal/silicate partition coefficients (Dm/s) for siderophile elements are essential to investigations of core formation when used in conjunction with the pattern of elemental abundances in the Earth's mantle. The partitioning of siderophile elements is controlled by temperature, pressure, oxygen fugacity, and by the compositions of the metal and silicate phases. Several recent studies have shown the importance of silicate melt composition on the partitioning of siderophile elements between silicate and metallic liquids. It has been demonstrated that many elements display increased solubility in less polymerized (mafic) melts. However, the importance of silicate melt composition was believed to be minor compared to the influence of oxygen fugacity until studies showed that melt composition is an important factor at high pressures and temperatures. It was found that melt composition is also important for partitioning of high valency siderophile elements. Atmospheric experiments were conducted, varying only silicate melt composition, to assess the importance of silicate melt composition for the partitioning of W, Co and Ga and found that the valence of the dissolving species plays an important role in determining the effect of composition on solubility. In this study, we extend the data set to higher pressures and investigate the role of silicate melt composition on the partitioning of the siderophile elements W, Ge, Ga and Ni between metallic and silicate liquid.

  14. Chemical Forms of Heavy Metals in Bottom Sediments of the Mitręga Reservoir

    NASA Astrophysics Data System (ADS)

    Dąbrowska, Lidia

    2016-06-01

    Bottom sediments originating from the Mitręga water reservoir were studied. It was assayed, in what chemical forms heavy metals (zinc, copper, nickel, cadmium and lead) occur in sediments, using the method of sequential extraction BCR. According to the geochemical criteria with respect to the content of Zn, Cu and Ni, the sediments in all measuring points were classified as uncontaminated, however because of the Cd content - as moderately contaminated. The highest Cu and Ni content was found in the sediment collected in the southern part of the reservoir, 15 and 11 mg/kg d.m, respectively. In the case of Zn, Pb and Cd, the sediment collected at the outflow of the Mitręga river was the most contaminated; metal content amounted to 136; 35; 3 mg/kg d.m., respectively. Based on the conducted fractionation of heavy metals, it was found that the potential mobility of metals, hence the possibility of secondary pollution of the reservoir open water, are arranged in the following order: Zn> Cd> Ni> Cu ~ Pb.

  15. Low-temperature growth of AlN and GaN by metal organic vapor phase epitaxy for polarization engineered water splitting photocathode

    NASA Astrophysics Data System (ADS)

    Nakamura, Akihiro; Suzuki, Michihiro; Fujii, Katsushi; Nakano, Yoshiaki; Sugiyama, Masakazu

    2017-04-01

    Crystal properties of low-temperature grown AlN (LT-AlN) combined with low temperature GaN (LT-GaN) grown by metal organic vapor phase epitaxy (MOVPE) were investigated to obtain a high quality GaN/AlN/GaN structure with a few-nm-thick AlN layer. LT-AlN suppresses unintentional Ga incorporation and can be pseudomorphically grown on GaN with a relatively smooth surface morphology. The lattice of LT-AlN coherent to GaN, however, was found to relax after reactor conditions were changed to grow the subsequent GaN layer at higher temperature. The top GaN layer grown on the relaxed LT-AlN, thus, exhibited a rough surface morphology and a threading dislocation density (TDD) higher than 109 cm-2 estimated from an X-ray diffraction measurement. An LT-GaN capping layer was found to be highly effective for avoiding such lattice relaxation of LT-AlN. The combination of LT-AlN and LT-GaN enables us to obtain a GaN/AlN/GaN junction with high Al content, a low TDD, and abrupt interfaces. As a result, introducing an LT-GaN layer improved the photoelectrochemical (PEC) property of a polarization engineered un-doped GaN/AlN/n-type GaN (u-GaN/AlN/n-GaN) photocathode for water splitting.

  16. Droplet etched GaAs quantum dots close to surfaces and metallic interfaces

    NASA Astrophysics Data System (ADS)

    Heyn, Ch.; Zocher, M.; Pudewill, L.; Runge, H.; Küster, A.; Hansen, W.

    2017-01-01

    GaAs quantum dots (QDs) with a thin cap layer are studied as building blocks for self-aligned hybrids with a metallic nanostructure (MN). Both constituents are filled into a nanohole template that is drilled into an AlGaAs surface by self-assembled local droplet etching during molecular beam epitaxy. In a first series of samples, the interaction of a near AlGaAs surface with a single QD at varied distance is studied using microphotoluminescence (PL) spectroscopy. With decreasing distance down to 12.5 nm, surface charges cause an increase in the exciton radiative lifetime, the formation of charged excitons, and a broadening of the exciton PL peaks. The PL peak broadening is quantitatively analyzed on the basis of an analytical model assuming temporal fluctuations of the surface charge. In a second sample series, the nanoholes are filled in addition with an Au nanostructure. The optical spectra are similar to those from QDs without a metal but with a slightly stronger PL peak broadening. For a small distance of 12.5 nm clearly within the optical near-field of the MN, the QDs show a typical PL linewidth of 430 μeV that is still small enough to separate different excitonic lines.

  17. Effect of hydrogen on the device performance and stability characteristics of amorphous InGaZnO thin-film transistors with a SiO2/SiNx/SiO2 buffer

    NASA Astrophysics Data System (ADS)

    Han, Ki-Lim; Ok, Kyung-Chul; Cho, Hyeon-Su; Oh, Saeroonter; Park, Jin-Seong

    2017-08-01

    We investigate the influence of the multi-layered buffer consisting of SiO2/SiNx/SiO2 on amorphous InGaZnO (a-IGZO) thin-film transistors (TFTs). The multi-layered buffer inhibits permeation of water from flexible plastic substrates and prevents degradation of overlying organic layers. The a-IGZO TFTs with a multi-layered buffer suffer less positive bias temperature stress instability compared to the device with a single SiO2 buffer layer after annealing at 250 °C. Hydrogen from the SiNx layer diffuses into the active layer and reduces electron trapping at loosely bound oxygen defects near the SiO2/a-IGZO interface. Quantitative analysis shows that a hydrogen density of 1.85 × 1021 cm-3 is beneficial to reliability. However, the multi-layered buffer device annealed at 350 °C resulted in conductive characteristics due to the excess carrier concentration from the higher hydrogen density of 2.12 × 1021 cm-3.

  18. Detailed evaluation on the effect of metal ion impurities on complexation of generator eluted 68Ga with different bifunctional chelators.

    PubMed

    Chakravarty, Rubel; Chakraborty, Sudipta; Dash, Ashutosh; Pillai, M R A

    2013-02-01

    The introduction of (68)Ga-based positron emission tomography (PET) to clinical practice using (68)Ge/(68)Ga generator represents a developmental milestone in the field of molecular imaging. Herein, we report a systematic study on (68)Ga complexes with different bifunctional chelators (BFCs) and the effect of metal ion impurities on the radiochemical yields in order to identify the most suitable BFC to be used for the development of (68)Ga-based target specific radiopharmaceuticals. Radiolabeling of four commonly used BFCs namely p-isothiocyanato benzyl derivatives of diethylenetriaminepentacetic acid (DTPA), 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA), 1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA) and 3,6,9,15-tetraazabicyclo [9.3.1]pentadeca-1(15),11,13-triene-3,6,9-triacetic acid (PCTA) with (68)Ga was studied with respect to optimal radiolabeling conditions, effect of metal ion impurities on radiochemical yield, in vitro stability and in vivo clearance properties in biological system. Out of the four BFCs studied, p-isothiocyanato benzyl-1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA-NCS) could be radiolabeled instantly with (68)Ga at room temperature with >98% yield, even in presence of up to 10 ppm of other metal ion impurities (such as Zn, Cu, Fe, Al, Sn and Ti ions). The (68)Ga-complex of NOTA-NCS demonstrated high in vitro stability even in the presence of 1000 times molar excess of metal ions (such as Fe, Cu, Zn and Ca ions). In contrast, other (68)Ga-labeled BFCs (DTPA-NCS, DOTA-NCS and PCTA-NCS) showed reduced radiochemical yields when incubated with the above concentration of metal ions. The biodistribution studies in Swiss mice revealed that (68)Ga-NOTA-NCS cleared rapidly through the kidneys with minimum retention in any major organ. The simple and rapid approach for preparation of (68)Ga-radiopharmaceuticals using NOTA based bifunctional chelators would render (68)Ga-radiopharmaceutical chemistry more convenient with

  19. Surface half-metallicity of half-Heusler compound FeCrSe and interface half-metallicity of FeCrSe/GaP

    NASA Astrophysics Data System (ADS)

    Khalaf Al-zyadi, Jabbar M.; Jolan, Mudhahir H.; Yao, Kai-Lun

    2016-04-01

    Recent studies showed that half-Heusler FeCrSe exhibits half-metallic ferromagnetism (Huang et al. [20]). In this paper, we investigate extensively the electronic, magnetic, and half-metallic properties of the half-Heusler alloy FeCrSe (111) and (001) surfaces and the interface with GaP (111) substrate by using the first-principles calculations within the density functional theory. The atomic density of states demonstrates that the half-me tallicity verified in the bulk FeCrSe is maintained at the CrSe-terminated (001) and Se-terminated (111) surfaces, but lost at both Cr- and Fe-terminated (111) surfaces and the Fe-terminated (001) surface. Alternatively, for the interface of FeCrSe/GaP (111), the bulk half-metallicity is destroyed at Se-P configuration while Se-Ga interface and subinterface show nearly 100% spin polarization. Moreover, the calculated interfacial adhesion energies exhibit that Se-Ga shape is more stable than the Se-P one. The calculated magnetic moments of Se, Ga at the Se-Ga (111) interface and P at the Se-P (111) interface increase with respect to the corresponding bulk values while the atomic magnetic moment of Se atom at the Se-P (111) interface decreases. We also notice that the magnetic moments of subinterface Fe at both Se-Ga and Se-P (111) interfaces decrease compared to the bulk values.

  20. Development of a four-zone carousel process packed with metal ion-imprinted polymer for continuous separation of copper ions from manganese ions, cobalt ions, and the constituent metal ions of the buffer solution used as eluent.

    PubMed

    Jo, Se-Hee; Park, Chanhun; Yi, Sung Chul; Kim, Dukjoon; Mun, Sungyong

    2011-08-19

    A three-zone carousel process, in which Cu(II)-imprinted polymer (Cu-MIP) and a buffer solution were employed as adsorbent and eluent respectively, has been developed previously for continuous separation of Cu²⁺ (product) from Mn²⁺ and Co²⁺ (impurities). Although this process was reported to be successful in the aforementioned separation task, the way of using a buffer solution as eluent made it inevitable that the product stream included the buffer-related metal ions (i.e., the constituent metal ions of the buffer solution) as well as copper ions. For a more perfect recovery of copper ions, it would be necessary to improve the previous carousel process such that it can remove the buffer-related metal ions from copper ions while maintaining the previous function of separating copper ions from the other 2 impure heavy-metal ions. This improvement was made in this study by proposing a four-zone carousel process based on the following strategy: (1) the addition of one more zone for performing the two-step re-equilibration tasks and (2) the use of water as the eluent of the washing step in the separation zone. The operating conditions of such a proposed process were determined on the basis of the data from a series of single-column experiments. Under the determined operating conditions, 3 runs of carousel experiments were carried out. The results of these experiments revealed that the feed-loading time was a key parameter affecting the performance of the proposed process. Consequently, the continuous separation of copper ions from both the impure heavy-metal ions and the buffer-related metal ions could be achieved with a purity of 91.9% and a yield of 92.8% by using the proposed carousel process based on a properly chosen feed-loading time.

  1. The interplay of blocking properties with charge and potential redistribution in thin carbon-doped GaN on n-doped GaN layers

    NASA Astrophysics Data System (ADS)

    Koller, Christian; Pobegen, Gregor; Ostermaier, Clemens; Huber, Martin; Pogany, Dionyz

    2017-07-01

    In carbon-doped GaN (GaN:C) buffers used in a GaN-on-Si technology, the buffer is embedded in between transition and channel layers. This makes the analysis of buffer properties difficult due to e.g., carrier injection from or potential drop at these adjacent layers. Here, we analyze capacitance- and current-voltage characteristics of 200-300 nm thick GaN:C ([C] = 1019 cm-3) layers which are embedded between a top metal electrode and bottom n-doped GaN (n-GaN). Such structures allow a better potential control in GaN:C and thus determination of the band diagram quantitatively. The accumulation of negative charge (concentration up to 6 × 1017 cm-3) with bias is observed in GaN:C at both polarities. For biases Vappl < +1.7 V at the top electrode, negative charges accumulate in GaN:C near to its interface with n-GaN so that GaN:C exhibits no potential drop and blocks leakage current. For Vappl > +1.7 V, accumulated negative charges in GaN:C raise an energy barrier of ˜1.1 eV for electron injection from n-GaN to GaN:C. This causes a potential drop in GaN:C leading to a significant leakage current increase. The Fermi level pinning in GaN:C at a commonly referred acceptor at EV + 0.7(±0.2) eV is extracted only from electrostatic considerations. The occupancy change of carbon acceptors is attributed to trapping processes where the dislocation-related conductive paths are supposed to be involved in carrier transport from the top metal electrode to the carbon defect.

  2. Rare-metal-free high-performance Ga-Sn-O thin film transistor.

    PubMed

    Matsuda, Tokiyoshi; Umeda, Kenta; Kato, Yuta; Nishimoto, Daiki; Furuta, Mamoru; Kimura, Mutsumi

    2017-03-14

    Oxide semiconductors have been investigated as channel layers for thin film transistors (TFTs) which enable next-generation devices such as high-resolution liquid crystal displays (LCDs), organic light emitting diode (OLED) displays, flexible electronics, and innovative devices. Here, high-performance and stable Ga-Sn-O (GTO) TFTs were demonstrated for the first time without the use of rare metals such as In. The GTO thin films were deposited using radiofrequency (RF) magnetron sputtering. A high field effect mobility of 25.6 cm(2)/Vs was achieved, because the orbital structure of Sn was similar to that of In. The stability of the GTO TFTs was examined under bias, temperature, and light illumination conditions. The electrical behaviour of the GTO TFTs was more stable than that of In-Ga-Zn-O (IGZO) TFTs, which was attributed to the elimination of weak Zn-O bonds.

  3. Rare-metal-free high-performance Ga-Sn-O thin film transistor

    PubMed Central

    Matsuda, Tokiyoshi; Umeda, Kenta; Kato, Yuta; Nishimoto, Daiki; Furuta, Mamoru; Kimura, Mutsumi

    2017-01-01

    Oxide semiconductors have been investigated as channel layers for thin film transistors (TFTs) which enable next-generation devices such as high-resolution liquid crystal displays (LCDs), organic light emitting diode (OLED) displays, flexible electronics, and innovative devices. Here, high-performance and stable Ga-Sn-O (GTO) TFTs were demonstrated for the first time without the use of rare metals such as In. The GTO thin films were deposited using radiofrequency (RF) magnetron sputtering. A high field effect mobility of 25.6 cm2/Vs was achieved, because the orbital structure of Sn was similar to that of In. The stability of the GTO TFTs was examined under bias, temperature, and light illumination conditions. The electrical behaviour of the GTO TFTs was more stable than that of In-Ga-Zn-O (IGZO) TFTs, which was attributed to the elimination of weak Zn-O bonds. PMID:28290547

  4. Rare-metal-free high-performance Ga-Sn-O thin film transistor

    NASA Astrophysics Data System (ADS)

    Matsuda, Tokiyoshi; Umeda, Kenta; Kato, Yuta; Nishimoto, Daiki; Furuta, Mamoru; Kimura, Mutsumi

    2017-03-01

    Oxide semiconductors have been investigated as channel layers for thin film transistors (TFTs) which enable next-generation devices such as high-resolution liquid crystal displays (LCDs), organic light emitting diode (OLED) displays, flexible electronics, and innovative devices. Here, high-performance and stable Ga-Sn-O (GTO) TFTs were demonstrated for the first time without the use of rare metals such as In. The GTO thin films were deposited using radiofrequency (RF) magnetron sputtering. A high field effect mobility of 25.6 cm2/Vs was achieved, because the orbital structure of Sn was similar to that of In. The stability of the GTO TFTs was examined under bias, temperature, and light illumination conditions. The electrical behaviour of the GTO TFTs was more stable than that of In-Ga-Zn-O (IGZO) TFTs, which was attributed to the elimination of weak Zn-O bonds.

  5. Effect of unsintered gadolinium-doped ceria buffer layer on performance of metal-supported solid oxide fuel cells using unsintered barium strontium cobalt ferrite cathode

    NASA Astrophysics Data System (ADS)

    Kim, Yu-Mi; Kim-Lohsoontorn, Pattaraporn; Bae, Joongmyeon

    In this study, a Gd 0.1Ce 0.9O 1.95 (GDC) buffer layer and a Ba 0.5Sr 0.5Co 0.8Fe 0.2O 3- δ (BSCF) cathode, fabricated without pre-sintering, are investigated (unsintered GDC and unsintered BSCF). The effect of the unsintered GDC buffer layer, including the thickness of the layer, on the performance of solid oxide fuel cells (SOFCs) using an unsintered BSCF cathode is studied. The maximum power density of the metal-supported SOFC using an unsintered BSCF cathode without a buffer layer is 0.81 W cm -2, which is measured after 2 h of operation (97% H 2 and 3% H 2O at the anode and ambient air at the cathode), and it significantly decreases to 0.63 W cm -2 after 50 h. At a relatively low temperature of 800 °C, SrZrO 3 and BaZrO 3, arising from interaction between BSCF and yttria-stabilized zirconia (YSZ), are detected after 50 h. Introducing a GDC interlayer between the cathode and electrolyte significantly increases the durability of the cell performance, supporting over 1000 h of cell usage with an unsintered GDC buffer layer. Comparable performance is obtained from the anode-supported cell when using an unsintered BSCF cathode with an unsintered GDC buffer layer (0.75 W cm -2) and sintered GDC buffer layer (0.82 W cm -2). When a sintered BSCF cathode is used, however, the performance increases to 1.23 W cm -2. The adhesion between the BSCF cathode and the cell can be enhanced by an unsintered GDC buffer layer, but an increase in the layer thickness (1-6 μm) increases the area specific resistance (ASR) of the cell, and the overly thick buffer layer causes delamination of the BSCF cathode. Finally, the maximum power densities of the metal-supported SOFC using an unsintered BSCF cathode and unsintered GDC buffer layer are 0.78, 0.64, 0.45 and 0.31 W cm -2 at 850, 800, 750 and 700 °C, respectively.

  6. Investigation of 'surface donors' in Al2O3/AlGaN/GaN metal-oxide-semiconductor heterostructures: Correlation of electrical, structural, and chemical properties

    NASA Astrophysics Data System (ADS)

    Ťapajna, M.; Stoklas, R.; Gregušová, D.; Gucmann, F.; Hušeková, K.; Haščík, Š.; Fröhlich, K.; Tóth, L.; Pécz, B.; Brunner, F.; Kuzmík, J.

    2017-12-01

    III-N surface polarization compensating charge referred here to as 'surface donors' (SD) was analyzed in Al2O3/AlGaN/GaN metal-oxide-semiconductor (MOS) heterojunctions using scaled oxide films grown by metal-organic chemical vapor deposition at 600 °C. We systematically investigated impact of HCl pre-treatment prior to oxide deposition and post-deposition annealing (PDA) at 700 °C. SD density was reduced down to 1.9 × 1013 cm-2 by skipping HCl pre-treatment step as compared to 3.3 × 1013 cm-2 for structures with HCl pre-treatment followed by PDA. The nature and origin of SD was then analyzed based on the correlation between electrical, micro-structural, and chemical properties of the Al2O3/GaN interfaces with different SD density (NSD). From the comparison between distributions of interface traps of MOS heterojunction with different NSD, it is demonstrated that SD cannot be attributed to interface trapped charge. Instead, variation in the integrity of the GaOx interlayer confirmed by X-ray photoelectron spectroscopy is well correlated with NSD, indicating SD may be formed by border traps at the Al2O3/GaOx interface.

  7. Study of solid-phase reactions of metals on GaAs with a TiN diffusion barrier

    NASA Astrophysics Data System (ADS)

    Liew, B.-K.; Tandon, J. L.; Nicolet, M.-A.

    1987-06-01

    To make stable and reproducible contacts to GaAs, metals which react with GaAs in the solid phase should be favored. In this study, contacts with configuration: Pd/TiN/Pd/Ag, Pd:Mg/TiN/Pd:Mg/Ag and Ru/TiN/Ru/Ag are studied. The TiN layer is included to investigate its application as a diffusion barrier layer in these metallizations. Contacts to n-GaAs are rectifying and the value of barrier height is modified upon annealing. Contacts to p-GaAs are initially rectifying but exhibit ohmic behaviour after annealing. The modifications in the electrical properties are attributed to the solid-phase reaction of metal with GaAs. In addition, we also observe a significant reduction in contact resistivity by adding Mg in the Pd metallization system, which is consistent with the fact that Mg is a p-type dopant in GaAs. The integrity of these contacts relies critically on the success of the TiN diffusion barrier in preventing the intermixing of the top Ag layer with the underlying layers. At elevated annealing temperatures (450°C), TiN fails to function as a diffusion barrier. As a result, the properties of the contact deteriorate.

  8. AlGaN/GaN metal oxide semiconductor heterostructure field-effect transistors with 4 nm thick Al2O3 gate oxide

    NASA Astrophysics Data System (ADS)

    Gregušová, D.; Stoklas, R.; Čičo, K.; Lalinský, T.; Kordoš, P.

    2007-08-01

    AlGaN/GaN metal-oxide-semiconductor heterostructure field-effect transistors (MOSHFETs) with 4 nm thick Al2O3 gate oxide were prepared and their performance was compared with that of AlGaN/GaN HFETs. The MOSHFETs yielded ~40% increase of the saturation drain current compared with the HFETs, which is larger than expected due to the gate oxide passivation. Despite a larger gate-channel separation in the MOSHFETs, a higher extrinsic transconductance than that of the HFETs was measured. The drift mobility of the MOSHFETs, evaluated on large-gate FET structures, was significantly higher than that of the HFETs. The zero-bias mobility for MOSHFETs and HFETs was 1950 cm2 V-1 s-1 and 1630 cm2 V-1 s-1, respectively. These features indicate an increase of the drift velocity and/or a decrease of the parasitic series resistance in the MOSHFETs. The current collapse, evaluated from pulsed I-V measurements, was highly suppressed in the MOSHFETs with 4 nm thick Al2O3 gate oxide. This result, together with the suppressed frequency dispersion of the capacitance, indicates that the density of traps in the Al2O3/AlGaN/GaN MOSHFETs was significantly reduced.

  9. A comparative study of the annealing behavior of Cu(In,Ga)(S,Se){sub 2} based solar cells with an indium sulfide buffer layer, partly submitted to wet chemical treatments

    SciTech Connect

    Hönes, C.; Hackenberg, J.; Zweigart, S.; Wachau, A.; Hergert, F.; Siebentritt, S.

    2015-03-07

    Indium sulfide thin films deposited via thermal evaporation from compound source material have been successfully utilized as a cadmium free buffer layer for Cu(In,Ga)Se{sub 2} based solar cells. However, high efficiencies are only reached after an additional annealing step. In this work, the annealing behavior of Cu(In,Ga)(S,Se){sub 2} based indium sulfide buffered solar cells is compared to the annealing behavior of similar cells, which were submitted to wet chemical treatments partly containing cadmium ions. Upon annealing a significant improvement of the initial solar cell characteristics is observed for the untreated cell and is related to the increase of activation energy for the carrier recombination process and a decrease of the ideality factor within the one diode model. It is shown here that this improvement can also be achieved by wet treatments of the absorber prior to buffer layer deposition. Upon annealing these treated cells still gain in collection length but lose open circuit voltage, which is explained here within a model including a highly p-doped absorber surface layer and supported by simulations showing that a decrease in doping density of such a surface layer would lead to the observed effects.

  10. Improved Off-State Stress Critical Voltage on AlGaN/GaN High Electron Mobility Transistors Utilizing Pt/Ti/Au Based Gate Metallization

    SciTech Connect

    Lo, C. F.; Liu, L.; Kang, Tsung Sheng; Davies, Ryan; Gila, Brent P.; Pearton, S. J.; Kravchenko, Ivan I; Laboutin, O.; Cao, Yu; Johnson, Wayne J.; Ren, F.

    2011-01-01

    The critical voltage for degradation of AlGaN/GaN high electron mobility transistors (HEMTs) employed with the Pt/Ti/Au gate metallization instead of the commonly used Ni/Au was significantly increased during the off-state stress. The typical critical voltage for HEMTs with Ni/Au gate metallization was around -60V. By sharp contrast, no critical voltage was observed for the HEMTs with Pt/Ti/Au gate metallization, even up to -100V, which was the instrumental limitation in this experiment. Both Schottky forward and reverse gate characteristics of the Ni/Au degraded once the gate voltage passed the critical voltage of around -60V. There was no degradation exhibited for the HEMTs with Pt-gated HEMTs.

  11. Rectification and Photoconduction Mapping of Axial Metal-Semiconductor Interfaces Embedded in GaAs Nanowires

    NASA Astrophysics Data System (ADS)

    Orrù, Marta; Piazza, Vincenzo; Rubini, Silvia; Roddaro, Stefano

    2015-10-01

    Semiconductor nanowires have emerged as an important enabling technology and are today used in many advanced device architectures, with an impact both for what concerns fundamental science and in view of future applications. One of the key challenges in the development of nanowire-based devices is the fabrication of reliable nanoscale contacts. Recent developments in the creation of metal-semiconductor junctions by thermal annealing of metallic electrodes offer promising perspectives. Here, we analyze the optoelectronic properties of nano-Schottky barriers obtained thanks to the controlled formation of metallic AuGa regions in GaAs nanowire. The junctions display a rectifying behavior and their transport characteristics are analyzed to extract the average ideality factor and barrier height in the current architecture. The presence, location, and properties of the Schottky junctions are cross-correlated with spatially resolved photocurrent measurements. Broadband light emission is reported in the reverse breakdown regime; this observation, combined with the absence of electroluminescence at forward bias, is consistent with the device unipolar nature.

  12. Elemental diffusion during the droplet epitaxy growth of In(Ga)As/GaAs(001) quantum dots by metal-organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Chen, Z. B.; Lei, W.; Chen, B.; Wang, Y. B.; Liao, X. Z.; Tan, H. H.; Zou, J.; Ringer, S. P.; Jagadish, C.

    2014-01-01

    Droplet epitaxy is an important method to produce epitaxial semiconductor quantum dots (QDs). Droplet epitaxy of III-V QDs comprises group III elemental droplet deposition and the droplet crystallization through the introduction of group V elements. Here, we report that, in the droplet epitaxy of InAs/GaAs(001) QDs using metal-organic chemical vapor deposition, significant elemental diffusion from the substrate to In droplets occurs, resulting in the formation of In(Ga)As crystals, before As flux is provided. The supply of As flux suppresses the further elemental diffusion from the substrate and promotes surface migration, leading to large island formation with a low island density.

  13. Elemental diffusion during the droplet epitaxy growth of In(Ga)As/GaAs(001) quantum dots by metal-organic chemical vapor deposition

    SciTech Connect

    Chen, Z. B.; Chen, B.; Wang, Y. B.; Liao, X. Z.; Lei, W.; Tan, H. H.; Jagadish, C.; Zou, J.; Ringer, S. P.

    2014-01-13

    Droplet epitaxy is an important method to produce epitaxial semiconductor quantum dots (QDs). Droplet epitaxy of III-V QDs comprises group III elemental droplet deposition and the droplet crystallization through the introduction of group V elements. Here, we report that, in the droplet epitaxy of InAs/GaAs(001) QDs using metal-organic chemical vapor deposition, significant elemental diffusion from the substrate to In droplets occurs, resulting in the formation of In(Ga)As crystals, before As flux is provided. The supply of As flux suppresses the further elemental diffusion from the substrate and promotes surface migration, leading to large island formation with a low island density.

  14. Enhanced effect of diffused Ohmic contact metal atoms for device scaling in AlGaN/GaN heterostructure field-effect transistors

    NASA Astrophysics Data System (ADS)

    Liu, Huan; Cheng, Aijie; Lin, Zhaojun; Cui, Peng; Liu, Yan; Fu, Chen; Lv, Yuanjie; Feng, Zhihong; Luan, Chongbiao

    2017-03-01

    Using measured capacitance-voltage and current-voltage curves for the AlGaN/GaN heterostructure field-effect transistors with different source-drain spacing, the electron mobility under the gate region was obtained. By comparing mobility variation and analyzing polarization charge distribution, it is found that with device scaling, the effect of the diffused Ohmic contact metal atoms on the electron mobility is enhanced. Then, a theoretical calculation related to different scattering mechanisms was adopted and it was verified this enhanced effect is due to the enhanced polarization Coulomb field (PCF) scattering.

  15. Non-invasively improving the Schottky barriers of metal-MoS2 interfaces: effects of atomic vacancies in a BN buffer layer.

    PubMed

    Su, Jie; Feng, Liping; Liu, Siyang; Liu, Zhengtang

    2017-08-09

    Using first-principles calculations within density functional theory, vacancies in the BN buffer layer have been predicted to improve the Schottky barrier of the metal-MoS2 interface without deteriorating the intrinsic properties of the MoS2 layer. Here, the effects of concentrations, sizes and types of vacancies on the contact properties of metal/BN-MoS2 sandwich interfaces are comparatively studied. The results show that vacancies in the BN buffer layer not only don't deteriorate the charge scatterings and electronic properties of the MoS2 layer at the metal/BN-MoS2 interface, but also improve the charge density and contact resistance between the metal surface and the BN layer. Although these vacancies have a negligible influence on the Fermi level pinning effect of the metal/BN-MoS2 interface, both N-vacancies and B-vacancies significantly change the position of the Fermi level of the metal/BN-MoS2 interface and then tune the Schottky barriers. Moreover, the Schottky barriers of metal/BN-MoS2 interfaces can decrease at first with the increasing concentrations and sizes of vacancies. When the concentration of vacancies increases to 4%, the Schottky barriers of metal/BN-MoS2 interfaces can reduce to the minimum value. The lowest n-type and p-type Schottky barriers of Au/BN-MoS2 and Pt/BN-MoS2 interfaces can reduce to -0.16 and 0.28 eV, respectively. However, the Schottky barriers are deteriorated when the sizes and concentrations of vacancies continue to increase because vacancies with large sizes and concentrations obviously change the interfacial structures of metal/BN-MoS2 interfaces and disarrange the directions of interface dipoles. The predictions in this work provide a non-invasive method to achieve high performance metal-MoS2 interfaces with low Schottky barriers.

  16. Optical Properties of Novel GaN 3D Structures Grown by Metal-Organic Chemical Vapor Deposition (MOCVD)

    NASA Astrophysics Data System (ADS)

    Sacilotti, Marco; Imhoff, Luc; Dumas, Colette; Viste, Pierre; Vial, Jean-Claude; Baldeck, Patrice; Colombier, Isabelle; Donatini, Fabrice

    2004-06-01

    Optical properties of novel micrometer-size Ga and GaN three-dimensional structures obtained by the metal-organic chemical vapour deposition (MOCVD) technique are presented in this letter. These structures are obtained as metallic three dimensions (3D) micrometer-size objects on an appropriate substrate by metalorganic (TMGa) pyrolisis and then GaN transformed on annealing under NH3 atmosphere at 650-750°C. These 3D GaN structures are analysed by optical means, using two-photon excitation (800 nm) and by UV Hg lamp fluorescent spectroscopy techniques, adapted to two-optical-microscopes apparatus. Very intense and blue/yellow light emission is observed from these 3D structures under 800 nm two-photon laser excitation and under UV Hg lamp excitation.

  17. Free Carrier Induced Spectral Shift for GaAs Filled Metallic Hole Arrays

    DTIC Science & Technology

    2012-03-13

    Bahae , G. I . Stegeman, K. Al-hemyari, J. S. Aitchison, and C. N. Ironside, “Limitation due to three-photon absorption on the useful spectral range...Free carrier induced spectral shift for GaAs filled metallic hole arrays Jingyu Zhang 1,2,* , Bin Xiang 3 , Mansoor Sheik- Bahae 4 , and S. R. J...OCIS codes: (310.6628) Subwavelength structures;(190.4350) Nonlinear optics at surfaces References and links 1. J. M. Luther, P. K. I . Jain, T. Ewers

  18. Transmission electron microscopy, photoluminescence, and capacitance spectroscopy on GaAs/Si grown by metal organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Bremond, Georges E.; Said, Hicham; Guillot, Gerard; Meddeb, Jaafar; Pitaval, M.; Draidia, Nasser; Azoulay, Rozette

    1991-03-01

    We present a complete characterization study of GaAs/Si heteroepitaxial layers grown by metalorganic chemical vapor deposition (MOCVD) at 750C using the two-step method. High resolution transmission electron microscopy secondary ion mass spectroscopy deep level transient spectroscopy (DLTS) and photoluminescence (PL) spectroscopy have been performed to study the initial stage of growth misfit and threading dislocations Si diffusion and the deep levels in the GaAs layer. We describe the influence of GaAs/AlAs superlattices in the buffer layer on the decrease of dislocation density and on Si diffusion from the substrate and the existence of deep electron traps induced by the heteroepitaxy. DLTS reveals hole traps attributed to Si incorporation on the basis of PL measurements which could contribute to the reduction of the minority carrier lifetime. We also show an improvement of the layer quality by the use of selective epitaxy.

  19. Characterization and modeling analysis for metal-semiconductor-metal GaAs diodes with Pd/SiO₂ mixture electrode.

    PubMed

    Tan, Shih-Wei; Lai, Shih-Wen

    2012-01-01

    Characterization and modeling of metal-semiconductor-metal (MSM) GaAs diodes using to evaporate SiO₂ and Pd simultaneously as a mixture electrode (called M-MSM diodes) compared with similar to evaporate Pd as the electrode (called Pd-MSM diodes) were reported. The barrier height (φ(b)) and the Richardson constant (A*) were carried out for the thermionic-emission process to describe well the current transport for Pd-MSM diodes in the consideration of the carrier over the metal-semiconductor barrier. In addition, in the consideration of the carrier over both the metal-semiconductor barrier and the insulator-semiconductor barrier simultaneously, thus the thermionic-emission process can be used to describe well the current transport for M-MSM diodes. Furthermore, in the higher applied voltage, the carrier recombination will be taken into discussion. Besides, a composite-current (CC) model is developed to evidence the concepts. Our calculated results are in good agreement with the experimental ones.

  20. GaN HEMT with AlGaN back barrier for high power MMIC switch application

    NASA Astrophysics Data System (ADS)

    Chunjiang, Ren; Hongchang, Shen; Zhonghui, Li; Tangsheng, Chen; Bin, Zhang; Tao, Gao

    2015-01-01

    0.25 μm GaN HEMT with AlGaN back barrier for high power switch application has been presented. By introducing AlGaN back barrier, the buffer layer breakdown voltage for the metal-organic chemical vapor deposited AlGaN/GaN hetero-structure on 3-inch SiC substrate showed a considerable increment, which was nearly 4× and 2× of that for the conventional GaN buffer layer and GaN buffer layer with Fe doped, respectively. GaN switch HEMTs with source to drain spacing of 2, 2.5, 3, 3.5 and 4 μm were fabricated on the AlGaN/GaN epitaxial material with AlGaN back barrier and estimated off state power handling for the GaN switch HEMTs were 25.0, 46.2, 64.0, 79.2, and 88.4 W, respectively. A demonstrator DC-12 GHz GaN SPDT MMIC switch was designed in reflective series-shunt-shunt configuration based on the GaN HEMT, with a source to drain spacing of 2.5 μm. The developed SPDT MMIC switch showed a maximum insertion loss of 1.0 dB and a minimum isolation of 30 dB at a frequency range of DC-12 GHz. A power handling capability of 44.1 dBm was achieved at 10 GHz for the MMIC switch with continuous wave power compression measurement.

  1. Nanometre-sized GaAs wires grown by organo-metallic vapour-phase epitaxy

    NASA Astrophysics Data System (ADS)

    Hiruma, Kenji; Haraguchi, Keiichi; Yazawa, Masamitsu; Madokoro, Yuuichi; Katsuyama, Toshio

    2006-06-01

    We grew GaAs wires as thin as 20 nm on a GaAs(111)B substrate using organo-metallic vapour-phase epitaxy (OMVPE), with Au as a growth catalyst. To investigate the growth characteristics, we compared two methods of depositing Au. In the first, Au was deposited by vacuum evaporation, and the deposition thickness was varied to form a planar Au layer. We found that an Au layer thickness of 1 nm was best for forming cylindrical shaped wires. Next, a new method of injecting Au onto an area of a few micrometres was tested using a focused ion beam (FIB), and this method was found to be effective for growing wires as thin as 30-80 nm. However, the wire width did not depend on the injected density of Au. We based our analysis of the results on an ion implantation model. GaAs wires with a p-n junction along the \\langle 111\\rangle \\mathrm {B} direction were formed by changing dopants from silicon to carbon during growth. We observed an optical emission with a peak intensity at the wavelength of 910-920 nm during continuous current injection into the wires at 300 K. A spectral blue-shift in the light emission and a polarization along the wire growth direction were also revealed at 77 K.

  2. The half-metallicity of zinc-blende CaC/GaAs(001) heterojunction: A density functional theory study

    NASA Astrophysics Data System (ADS)

    Moradi, M.; Mohammadi, A.; Afshari, M.; Soltani, Z.

    2013-04-01

    First principles calculations, based on spin density functional theory (SDFT) as implemented in the PWscf code of the QUANTUM-ESPRESSO package, are performed to study electronic and magnetic properties of CaC/GaAs(001) heterojunction. We simulate the interface of CaC in Zinc-Blende (ZB) structure and GaAs semiconductor to see whether this electrode could be a good choice for spin current injection or not. For this purpose, we calculate the spin-polarized density of states for ZB-CaC, in-plane strained ZB-CaC (tetragonal phase) and also for ZB-CaC/GaAs(001) heterojunction. It is shown that ZB-CaC, is a half-metal ferromagnet with large half-metallic gap. The half-metallicity is found to be robust with respect to the lattice deformation to the tetragonal phase and is maintained in the range of 0.59< c/a <1.22. Calculations with supercell scheme for simulation ZB-CaC/GaAs(001) heterojunction show that the spin polarization at the Fermi energy reduced at the CaC/GaAs(001) heterojunction. But due to large difference of density of states of spin channels around the Fermi energy, the spin polarization is large yet. So the CaC/GaAs(001) heterojunction can be used in spintronics applications as a spin current injector but it is not 100% spin-polarized.

  3. Structural, electronic, and magnetic properties of transition-metal atom adsorbed two-dimensional GaAs nanosheet

    NASA Astrophysics Data System (ADS)

    Luo, Jia; Xiang, Gang; Yu, Tian; Lan, Mu; Zhang, Xi

    2016-09-01

    By using first-principles calculations within the framework of density functional theory, the electronic and magnetic properties of 3d transitional metal (TM) atoms (from Sc to Zn) adsorbed monolayer GaAs nanosheets (GaAsNSs) are systematically investigated. Upon TM atom adsorption, GaAsNS, which is a nonmagnetic semiconductor, can be tuned into a magnetic semiconductor (Sc, V, and Fe adsorption), a half-metal (Mn adsorption), or a metal (Co and Cu adsorption). Our calculations show that the strong p-d hybridization between the 3d orbit of TM atoms and the 4p orbit of neighboring As atoms is responsible for the formation of chemical bonds and the origin of magnetism in the GaAsNSs with Sc, V, and Fe adsorption. However, the Mn 3d orbit with more unpaired electrons hybridizes not only with the As 4p orbit but also with the Ga 4p orbit, resulting in a stronger exchange interaction. Our results may be useful for electronic and magnetic applications of GaAsNS-based materials. Project supported by the National Natural Science Foundation of China (Grant No. 11174212).

  4. Measurement and simulation of top- and bottom-illuminated solar-blind AlGaN metal-semiconductor-metal photodetectors with high external quantum efficiencies

    SciTech Connect

    Brendel, Moritz Helbling, Markus; Knigge, Andrea; Brunner, Frank; Weyers, Markus

    2015-12-28

    A comprehensive study on top- and bottom-illuminated Al{sub 0.5}Ga{sub 0.5}N/AlN metal-semiconductor-metal (MSM) photodetectors having different AlGaN absorber layer thickness is presented. The measured external quantum efficiency (EQE) shows pronounced threshold and saturation behavior as a function of applied bias voltage up to 50 V reaching about 50% for 0.1 μm and 67% for 0.5 μm thick absorber layers under bottom illumination. All experimental findings are in very good accordance with two-dimensional drift-diffusion modeling results. By taking into account macroscopic polarization effects in the hexagonal metal-polar +c-plane AlGaN/AlN heterostructures, new insights into the general device functionality of AlGaN-based MSM photodetectors are obtained. The observed threshold/saturation behavior is caused by a bias-dependent extraction of photoexcited holes from the Al{sub 0.5}Ga{sub 0.5}N/AlN interface. While present under bottom illumination for any AlGaN layer thickness, under top illumination this mechanism influences the EQE-bias characteristics only for thin layers.

  5. Semiconducting chalcogenide buffer layer for oxide heteroepitaxy on Si(001)

    NASA Astrophysics Data System (ADS)

    Schmidt, D. A.; Ohta, Taisuke; Lu, C.-Y.; Bostwick, Aaron A.; Yu, Q.; Rotenberg, Eli; Ohuchi, F. S.; Olmstead, Marjorie A.

    2006-05-01

    We report controlled laminar growth of a crystalline transition metal oxide on Si(001) without SiOx or silicide formation by utilizing the chalcogenide semiconductor gallium sesquiselenide (Ga2Se3) as a nonreactive buffer layer. Initial nucleation of both pure and Co-doped anatase (TiO2) is along Ga2Se3 nanowire structures, coalescing to a flat, multidomain film within two molecular layers. Arsenic-terminated Si(001) [Si(001):As] is stable against pure O2, but oxidizes when both Ti and O2 are present. The Si -TiO2 valence band offset using either buffer layer is about 2.8eV, producing a staggered band alignment.

  6. 2D SWIR image sensor with extended wavelength cutoff of 2.5 μm on InP/InGaAs epitaxial wafers with graded buffer layers

    NASA Astrophysics Data System (ADS)

    Mushini, Prabhu; Huang, Wei; Morales, Manuel; Brubaker, Robert; Nguyen, Thuc-Uyen; Dobies, Matt; Zhang, Wei; Gustus, William; Mathews, Gary; Endicter, Scott; Paik, Namwoong

    2016-05-01

    Two-dimensional photo detector arrays with a cutoff wavelength of 2.5 μm were fabricated on InP/InGaAs epitaxial wafers with graded buffer layers in a 320x256 geometry on a 12.5μm pitch. Novel growth and fabrication techniques were employed to fabricate these arrays and optimize the performance. The dark current of the detector was investigated for a wide range of temperatures. The fabricated detector array was mated with a ROIC and packaged with a multi-stage TEC and investigated further at the FPA level. The effect of the graded buffer layers on the sensor performance was investigated and the results were compared to other methods used to develop and fabricate 2D image sensors on extended wavelength materials.

  7. Effect of heavy metals on pH buffering capacity and solubility of Ca, Mg, K, and P in non-spiked and heavy metal-spiked soils.

    PubMed

    Najafi, Sarvenaz; Jalali, Mohsen

    2016-06-01

    In many parts of the world, soil acidification and heavy metal contamination has become a serious concern due to the adverse effects on chemical properties of soil and crop yield. The aim of this study was to investigate the effect of pH (in the range of 1 to 3 units above and below the native pH of soils) on calcium (Ca), magnesium (Mg), potassium (K), and phosphorus (P) solubility in non-spiked and heavy metal-spiked soil samples. Spiked samples were prepared by cadmium (Cd), copper (Cu), nickel (Ni), and zinc (Zn) as chloride salts and incubating soils for 40 days. The pH buffering capacity (pHBC) of each sample was determined by plotting the amount of H(+) or OH(-) added (mmol kg(-1)) versus the related pH value. The pHBC of soils ranged from 47.1 to 1302.5 mmol kg(-1) for non-spiked samples and from 45.0 to 1187.4 mmol kg(-1) for spiked soil samples. The pHBC values were higher in soil 2 (non-spiked and spiked) which had higher calcium carbonate content. The results indicated the presence of heavy metals in soils generally decreased the solution pH and pHBC values in spiked samples. In general, solubility of Ca, Mg, and K decreased with increasing equilibrium pH of non-spiked and spiked soil samples. In the case of P, increasing the pH to about 7, decreased the solubility in all soils but further increase of pH from 7, enhanced P solubility. The solubility trends and values for Ca, Mg, and K did not differed significantly in non-spiked and spiked samples. But in the case of P, a reduction in solubility was observed in heavy metal-spiked soils. The information obtained in this study can be useful to make better estimation of the effects of soil pollutants on anion and cation solubility from agricultural and environmental viewpoints.

  8. Half-metallic properties of the Co 2Ti 1- xFe xGa Heusler alloys and Co 2Ti 0.5Fe 0.5Ga (0 0 1) surface

    NASA Astrophysics Data System (ADS)

    Ahmadian, F.; Boochani, A.

    2011-07-01

    Electronic and magnetic properties of the bulk Co 2Ti 1- xFe xGa Heusler alloys and Co 2Ti 0.5Fe 0.5Ga (0 0 1) surfaces are studied within the framework of density functional theory using the augmented plane wave plus local orbital (APW+lo) approach. It will be shown that all alloys have the spin polarization of the ideal 100% value except the Co 2FeGa alloy with spin polarization about 98%. Co 2Ti 0.5Fe 0.5Ga is an example that is stable against the effects destroying the half-metallicity due to the position of the Fermi energy ( EF) in the middle of the minority band gap. The phase diagram obtained by ab-initio atomistic thermodynamics shows that in the higher limit of μGa three surfaces of FeGa, TiGa and TiFeGa are accessible in the Co 2Ti 0.5Fe 0.5Ga alloy but on decreasing μGa, the accessible region gradually moves towards FeGa termination. It is discussed that, at the ideal surfaces, half-metallicity of the alloy is lost, although the TiGa surface keeps high spin polarization (about 95%).

  9. Impact of the deposition conditions of buffer and windows layers on lowering the metastability effects in Cu(In,Ga)Se2/Zn(S,O)-based solar cell

    NASA Astrophysics Data System (ADS)

    Naghavi, Negar; Hildebrandt, Thibaud; Bouttemy, Muriel; Etcheberry, Arnaud; Lincot, Daniel

    2016-02-01

    The highest and most reproducible (Cu(In,Ga)Se2 (CIGSe) based solar-cell efficiencies are obtained by use of a very thin n-type CdS layer deposited by chemical bath deposition (CBD). However because of both Cadmium's adverse environmental impact and the narrow bandgap of CdS (2.4-2.5 eV) one of the major objectives in the field of CIGSe technology remains the development and implementation in the production line of Cd-free buffer layers. The CBDZn( S,O) remains one the most studied buffer layer for replacing the CdS in Cu(In,Ga)Se2-based solar cells and has already demonstrated its potential to lead to high-efficiency solar cells up to 22.3%. However one of the key issue to implement a CBD-Zn(S,O) process in a CIGSe production line is the cells stability, which depends both on the deposition conditions of CBD-Zn(S,O) and on a good band alignment between CIGSe/Zn(S,O)/windows layers. The most common window layers applied in CIGSe solar cells consist of two layers : a thin (50-100 nm) and highly resistive i-ZnO layer deposited by magnetron sputtering and a transparent conducting 300-500 nm ZnO:Al layer. In the case of CBD-Zn(S,O) buffer layer, the nature and deposition conditions of both Zn(S,O) and the undoped window layer can strongly influence the performance and stability of cells. The present contribution will be specially focused on the effect of condition growth of CBD-Zn(S,O) buffer layers and the impact of the composition and deposition conditions of the undoped window layers such as ZnxMgyO or ZnxSnyO on the stability and performance of these solar cells.

  10. Systematic study of interfacial reactions induced by metal electrodes in high-k/InGaAs gate stacks

    NASA Astrophysics Data System (ADS)

    Yoshida, S.; Lin, D.; Vais, A.; Alian, A.; Franco, J.; El Kazzi, S.; Mols, Y.; Miyanami, Y.; Nakazawa, M.; Collaert, N.; Watanabe, H.; Thean, A.

    2016-10-01

    We systematically studied the effects of metal electrodes on high-k/InGaAs gate stacks and observed that the remote reactions—both oxidation and reduction—at the interface between the high-k dielectrics and InGaAs were thermodynamically initiated by the metal electrodes. Metal electrodes with negative Gibbs free energies (e.g., Pd) resulted in the oxidation of the InGaAs surface during the forming-gas annealing. In contrast, with TiN electrodes, which have a positive Gibbs free energy, the native III-V oxides underwent the reduction between the high-k dielectrics and InGaAs. We demonstrated that the reduction of native III-V oxides by metal electrodes improved the interface quality of the high-k/InGaAs gate stacks and produced an interface trap density (Dit) at the mid-gap with a value as low as 5.2 × 1011 cm-2 eV-1 with a scaled capacitance-equivalent thickness.

  11. Auger electron spectroscopy investigation of degradation effect in GaAs metal-insulator-semiconductor solar cells

    SciTech Connect

    Pandelisev, K.A.; Wang, E.Y.

    1982-01-01

    Au-interfacial oxide layer (GeO/sub 2/, Sb/sub 2/O/sub 3/, Bi/sub 2/O/sub 3/, SnO/sub 2/ and native oxide mixture of AS/sub 2/O/sub 3/ and Ga/sub 2/O/sub 3/)-semiconductor (GaAs) structures were investigated by the Auger Electron Spectroscopy Method. The results of depth profiling with Ar/sup +/-ion sputtering are presented for all metal-insulator-semiconductor (MIS) structures. ''Metal'' atoms from deposited interfacial oxide layers (Ge from Ge/sub 2/O/sub 3/, Sb from Sb/sub 2/O/sub 3/, Bi from Bi/sub 2/O/sub 3/, and Sn from SnO/sub 2/) were observed on the surface. Only As atoms were observed for the native oxide mixture of As/sub 2/O/sub 3/ and Ga/sub 2/O/sub 3/ interfacial layer. These findings suggest that As/sub 2/O/sub 3/ is the dominating oxide at the metal-oxide interface for native oxide GaAs MIS solar cells. The interfacial reaction takes place between Au and the interfacial layer at room temperature. The ''diffusion'' of metal atoms from the interfacial layer towards the surface is suspected to play a role in degradation effect in GaAs MIS solar cells.

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

    SciTech Connect

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

    2014-09-01

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

  13. Growth and characterization of highly tensile strained Ge{sub 1−x}Sn{sub x} formed on relaxed In{sub y}Ga{sub 1−y}P buffer layers

    SciTech Connect

    Wang, Wei; D'Costa, Vijay Richard; Dong, Yuan; Liang, Gengchiau; Yeo, Yee-Chia; Loke, Wan Khai; Yoon, Soon Fatt; Yin, Tingting; Shen, Zexiang; Zhang, Zheng; Pan, Jisheng; Tok, Eng Soon

    2016-03-28

    Ge{sub 0.94}Sn{sub 0.06} films with high tensile strain were grown on strain-relaxed In{sub y}Ga{sub 1−y}P virtual substrates using solid-source molecular beam epitaxy. The in-plane tensile strain in the Ge{sub 0.94}Sn{sub 0.06} film was varied by changing the In mole fraction in In{sub x}Ga{sub 1−x}P buffer layer. The tensile strained Ge{sub 0.94}Sn{sub 0.06} films were investigated by transmission electron microscopy, x-ray diffraction, and Raman spectroscopy. An in-plane tensile strain of up to 1% in the Ge{sub 0.94}Sn{sub 0.06} was measured, which is much higher than that achieved using other buffer systems. Controlled thermal anneal experiment demonstrated that the strain was not relaxed for temperatures up to 500 °C. The band alignment of the tensile strained Ge{sub 0.94}Sn{sub 0.06} on In{sub 0.77}Ga{sub 0.23}P was obtained by high resolution x-ray photoelectron spectroscopy. The Ge{sub 0.94}Sn{sub 0.06}/In{sub 0.77}Ga{sub 0.23}P interface was found to be of the type I band alignment, with a valence band offset of 0.31 ± 0.12 eV and a conduction band offset of 0.74 ± 0.12 eV.

  14. Influence of metal choice on (010) β-Ga2O3 Schottky diode properties

    NASA Astrophysics Data System (ADS)

    Farzana, Esmat; Zhang, Zeng; Paul, Pran K.; Arehart, Aaron R.; Ringel, Steven A.

    2017-05-01

    A systematic study of Schottky barriers fabricated on (010) β-Ga2O3 substrates is reported. Schottky barrier heights (SBHs) and current transport modes were analyzed using a combination of current-voltage (I-V), capacitance-voltage (C-V) and internal photoemission (IPE) measurements for Pd, Ni, Pt and Au Schottky diodes. Diodes fabricated for each metal choice displayed nearly ideal I-V characteristics with room temperature ideality factors ranging from 1.03 to 1.09, reverse leakage currents below detection limits and thermionic emission as the dominant current transport mode for Ni, Pt and Pd. The SBH values varied depending on the metal choice, ranging from 1.27 V for Pd and 1.54 V for Ni to 1.58 V for Pt and 1.71 V for Au, as determined using IPE measurements. Close agreement was observed between these IPE-determined SBH values and the barrier height values from I-V and C-V measurements for the Ni, Pd and Pt Schottky barriers. In contrast, for Au, a lack of general agreement was seen between the SBH measurement methods, the trends of which appear to be consistent with the presence of an inhomogeneous barrier that implies a more complex interface for the Au Schottky barrier. The dependence of the SBH on metal work function suggests that metal-(010) β-Ga2O3 interfaces are not fully pinned, and this assertion was supported by scanning Kelvin probe microscopy measurements made on this sample set.

  15. Atomic Layer Deposition of Gallium Oxide Films as Gate Dielectrics in AlGaN/GaN Metal-Oxide-Semiconductor High-Electron-Mobility Transistors.

    PubMed

    Shih, Huan-Yu; Chu, Fu-Chuan; Das, Atanu; Lee, Chia-Yu; Chen, Ming-Jang; Lin, Ray-Ming

    2016-12-01

    In this study, films of gallium oxide (Ga2O3) were prepared through remote plasma atomic layer deposition (RP-ALD) using triethylgallium and oxygen plasma. The chemical composition and optical properties of the Ga2O3 thin films were investigated; the saturation growth displayed a linear dependence with respect to the number of ALD cycles. These uniform ALD films exhibited excellent uniformity and smooth Ga2O3-GaN interfaces. An ALD Ga2O3 film was then used as the gate dielectric and surface passivation layer in a metal-oxide-semiconductor high-electron-mobility transistor (MOS-HEMT), which exhibited device performance superior to that of a corresponding conventional Schottky gate HEMT. Under similar bias conditions, the gate leakage currents of the MOS-HEMT were two orders of magnitude lower than those of the conventional HEMT, with the power-added efficiency enhanced by up to 9 %. The subthreshold swing and effective interfacial state density of the MOS-HEMT were 78 mV decade(-1) and 3.62 × 10(11) eV(-1) cm(-2), respectively. The direct-current and radio-frequency performances of the MOS-HEMT device were greater than those of the conventional HEMT. In addition, the flicker noise of the MOS-HEMT was lower than that of the conventional HEMT.

  16. Thermodynamic properties of La-Ga-Al and U-Ga-Al alloys and the separation factor of U/La couple in the molten salt-liquid metal system

    NASA Astrophysics Data System (ADS)

    Novoselova, A.; Smolenski, V.; Volkovich, V. A.; Ivanov, A. B.; Osipenko, A.; Griffiths, T. R.

    2015-11-01

    The electrochemical behaviour of lanthanum and uranium was studied in fused 3LiCl-2KCl eutectic and Ga-Al eutectic liquid metal alloy between 723 and 823 K. Electrode potentials were recorded vs. Cl-/Cl2 reference electrode and the temperature dependencies of the apparent standard potentials of La-(Ga-Al) and U-(Ga-Al) alloys were determined. Lanthanum and uranium activity coefficients and U/La couple separation factor were calculated. Partial excess free Gibbs energy, partial enthalpy of mixing and partial excess entropy of La-(Ga-Al) and U-(Ga-Al) alloys were estimated.

  17. Photoinduced current in n-AlGaAs/GaAs heterojunction field-effect transistor driven by local illumination in edge regions of Schottky metal gate

    NASA Astrophysics Data System (ADS)

    Kawazu, Takuya; Noda, Takeshi; Sakuma, Yoshiki

    2017-04-01

    We investigated the photoresponses of the Schottky gate region of an n-AlGaAs/GaAs field-effect transistor (FET) by local illumination with a near-infrared (IR) laser beam. We examined (1) the Schottky photocurrent J SG from the source to the metal gate and (2) the lateral photocurrent J SD from the source to the drain under the open gate condition. We found that the magnitudes of J SG and J SD rapidly increase as the laser spot approaches the edges of the metal gate; IR photoresponses are enhanced in the regions near the gate edges. Experimental findings are well explained by a simple model considering the IR photoresponses with the gate edge effect.

  18. Surface passivation and interface properties of bulk GaAs and epitaxial-GaAs/Ge using atomic layer deposited TiAlO alloy dielectric.

    PubMed

    Dalapati, G K; Chia, C K; Tan, C C; Tan, H R; Chiam, S Y; Dong, J R; Das, A; Chattopadhyay, S; Mahata, C; Maiti, C K; Chi, D Z

    2013-02-01

    High quality surface passivation on bulk-GaAs substrates and epitaxial-GaAs/Ge (epi-GaAs) layers were achieved by using atomic layer deposited (ALD) titanium aluminum oxide (TiAlO) alloy dielectric. The TiAlO alloy dielectric suppresses the formation of defective native oxide on GaAs layers. X-ray photoelectron spectroscopy (XPS) analysis shows interfacial arsenic oxide (As(x)O(y)) and elemental arsenic (As) were completely removed from the GaAs surface. Energy dispersive X-ray diffraction (EDX) analysis and secondary ion mass spectroscopy (SIMS) analysis showed that TiAlO dielectric is an effective barrier layer for reducing the out-diffusion of elemental atoms, enhancing the electrical properties of bulk-GaAs based metal-oxide-semiconductor (MOS) devices. Moreover, ALD TiAlO alloy dielectric on epi-GaAs with AlGaAs buffer layer realized smooth interface between epi-GaAs layers and TiAlO dielectric, yielding a high quality surface passivation on epi-GaAs layers, much sought-after for high-speed transistor applications on a silicon platform. Presence of a thin AlGaAs buffer layer between epi-GaAs and Ge substrates improved interface quality and gate dielectric quality through the reduction of interfacial layer formation (Ga(x)O(y)) and suppression of elemental out-diffusion (Ga and As). The AlGaAs buffer layer and TiAlO dielectric play a key role to suppress the roughening, interfacial layer formation, and impurity diffusion into the dielectric, which in turn largely enhances the electrical property of the epi-GaAs MOS devices.

  19. Nanostructured surface morphology of ZnO grown on p-type GaN and Si by metal organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Hung, S. C.; Huang, P. J.; Chan, C. E.; Uen, W. Y.; Ren, F.; Pearton, S. J.; Yang, T. N.; Chiang, C. C.; Lan, S. M.; Chi, G. C.

    2008-12-01

    The surface morphology of ZnO grown on p-GaN templates and p-Si (1 1 1) substrates at various temperatures by metal organic chemical vapor deposition (MOCVD) in a vertical reactor at atmospheric pressure is reported. A low temperature ZnO buffer was deposited initially at 200 °C for 15 min as a nucleation layer. Epitaxial ZnO was grown at 500 °C, 550 °C, 600 °C for 40 min, respectively. Uniformly distributed and well-aligned ZnO nanorods with diameter in the range 80-120 nm and length ˜0.7 μm were observed for deposition on p-GaN template. By contrast, the morphology of ZnO epilayers grown on p-Si (1 1 1) transitioned from 2D to 3D with increasing growth temperature. X-ray diffraction (XRD) spectra showed all the ZnO epilayers had the hexagonal wurtzite structure but different preferred orientation. PL spectra showed only free-exciton emission at 378 nm (˜3.28 eV) with a full width at half maximum of 13 nm without defect-related green emission in the epitaxial ZnO grown at 550 °C and 600 °C. The epitaxial ZnO layers grown on p-GaN and p-Si at the same temperature have similar PL spectra. The PL measurement also exhibits strong exciton-related emission without defect peak, which showed that the ZnO nanostructures grown at 550 °C and 600 °C have good optical properties with excellent crystal quality.

  20. The interface analysis of GaN grown on 0° off 6H-SiC with an ultra-thin buffer layer

    NASA Astrophysics Data System (ADS)

    Sun, Zheng; Ohta, Akio; Miyazaki, Seiichi; Nagamatsu, Kentaro; Lee, Hojun; Olsson, Marc; Ye, Zheng; Deki, Manato; Honda, Yoshio; Amano, Hiroshi

    2016-01-01

    Previously, we reported a growth method by metalorganic vapor phase epitaxy using a single two-dimensional growth step, resulting in 1.2-µm crack-free GaN directly grown on 6H-SiC substrate. The introduction of Al-treatment prior to the standard GaN growth step resulted in improved surface wetting of gallium on the SiC substrate. Transmission electron microscope and energy dispersive spectrometer analysis of the epitaxial interface to the SiC determined that an ultra-thin AlGaN interlayer had formed measuring around 2-3 nm. We expect our growth technique can be applied to the fabrication of GaN/SiC high frequency and high power devices.

  1. Epitaxial Growth of GaN Nanowires with High Structural Perfection on a Metallic TiN Film.

    PubMed

    Wölz, M; Hauswald, C; Flissikowski, T; Gotschke, T; Fernández-Garrido, S; Brandt, O; Grahn, H T; Geelhaar, L; Riechert, H

    2015-06-10

    Vertical GaN nanowires are grown in a self-induced way on a sputtered Ti film by plasma-assisted molecular beam epitaxy. Both in situ electron diffraction and ex situ ellipsometry show that Ti is converted to TiN upon exposure of the surface to the N plasma. In addition, the ellipsometric data demonstrate this TiN film to be metallic. The diffraction data evidence that the GaN nanowires have a strict epitaxial relationship to this film. Photoluminescence spectroscopy of the GaN nanowires shows excitonic transitions virtually identical in spectral position, line width, and decay time to those of state-of-the-art GaN nanowires grown on Si. Therefore, the crystalline quality of the GaN nanowires grown on metallic TiN and on Si is equivalent. The freedom to employ metallic substrates for the epitaxial growth of semiconductor nanowires in high structural quality may enable novel applications that benefit from the associated high thermal and electrical conductivity as well as optical reflectivity.

  2. Improvement of electrical and optical properties of p-GaN Ohmic metals under ultraviolet light irradiation annealing processes

    SciTech Connect

    Chae, S.W.; Yoon, S.K.; Kwak, J.S.; Park, Y.H.; Kim, T.G.

    2006-05-15

    We report the improvement of electrical and optical properties of p-GaN Ohmic metals, ZnNi(10 nm)/Au(10 nm), by ultraviolet (UV) light irradiation. After UV light irradiation, the specific contact resistance of p-GaN decreased slightly from 2.99x10{sup -4} to 2.54x10{sup -4} {omega} cm{sup 2}, while the transmittance of the contact layer increased form 75% to 85% at a wavelength of 460 nm. In addition, the forward voltage of InGaN/GaN light-emitting diode chip at 20 mA decreased from 3.55 to 3.45 V, and the output power increased form 18 to 25 mW by UV light irradiation. The low resistance and high transmittance of the p-GaN Ohmic metals are attributed to the reduced Shottky barrier by the formation of gallium oxide and the increased oxidation of p-Ohmic metals, respectively, due to ozone generated form oxygen during UV light irradiation.

  3. Study of Ni{sub 2}-Mn-Ga phase formation by magnetron sputtering film deposition at low temperature onto Si substrates and LaNiO{sub 3}/Pb(Ti,Zr)O{sub 3} buffer

    SciTech Connect

    Figueiras, F.; Rauwel, E.; Amaral, V. S.; Vyshatko, N.; Kholkin, A. L.; Soyer, C.; Remiens, D.; Shvartsman, V. V.; Borisov, P.; Kleemann, W.

    2010-01-15

    Film deposition of Ni{sub 2}MnGa phaselike alloy by radio frequency (rf) magnetron sputtering was performed onto bare Si(100) substrates and LaNiO{sub 3}/Pb(Ti,Zr)O{sub 3} (LNO/PZT) ferroelectric buffer layer near room temperature. The prepared samples were characterized using conventional x-ray diffraction (XRD), superconducting quantum interference device, and electron dispersive x-ray spectroscopy from scanning electron microscope observations. The optimized films deposited under high rf power and low argon pressure present good surface quality and highly textured phase crystallization. The positioning distance between the substrate and the target-holder axis has some limited effect on the film's composition due to the specific diffusion behavior of each element in the sputtering plasma. Extended four pole high resolution XRD analysis allowed one to discriminate the intended Ni-Mn-Ga tetragonal martensitic phase induced by the (100) LNO/PZT oriented buffer. This low temperature process appears to be very promising, allowing separate control of the functional layer's properties, while trying to achieve high electromagnetoelastic coupling.

  4. Effects of Ga substitution on the structural and magnetic properties of half metallic Fe2MnSi Heusler compound

    NASA Astrophysics Data System (ADS)

    Pedro, S. S.; Caraballo Vivas, R. J.; Andrade, V. M.; Cruz, C.; Paixão, L. S.; Contreras, C.; Costa-Soares, T.; Caldeira, L.; Coelho, A. A.; Carvalho, A. Magnus G.; Rocco, D. L.; Reis, M. S.

    2015-01-01

    The so-called half-metallic magnets have been proposed as good candidates for spintronic applications due to the feature of exhibiting a hundred percent spin polarization at the Fermi level. Such materials follow the Slater-Pauling rule, which relates the magnetic moment with the valence electrons in the system. In this paper, we study the bulk polycrystalline half-metallic Fe2MnSi Heusler compound replacing Si by Ga to determine how the Ga addition changes the magnetic, the structural, and the half-metal properties of this compound. The material does not follow the Slater-Pauling rule, probably due to a minor structural disorder degree in the system, but a linear dependence on the magnetic transition temperature with the valence electron number points to the half-metallic behavior of this compound.

  5. Growth and characterization aluminum gallium nitride/gallium nitride heterostructures on silicon(111) wafers using various buffer layers

    NASA Astrophysics Data System (ADS)

    Venugopal, Rajesh

    Devices based on nitride wide bandgap semiconductors are suitable for several promising applications such as blue lasers, LEDs, HEMTs etc. Due to the absence of bulk nitride crystals, nitride films are grown on lattice mismatched substrates like Al2O3 and 6H-SiC. However from a cost and integration standpoint silicon would be the substrate of choice for the growth of these materials. Nitride heterostructure growth on large area Si(111) is hence attempted by Metal Organic Chemical Vapor Deposition (MOCVD) in an modified AIX 200/4 system. The large lattice and thermal mismatch prevents the direct deposition of GaN on Si and also causes GaN layers grown on Si to crack severely. It is hence necessary to use buffer layers to alleviate this lattice and thermal mismatch. Several buffer layer schemes are used for this purpose. The crystal quality of the AlGaN/GaN heterostructures grown under various conditions on these buffers are studied using several methods like Photoluminescence, X-ray diffraction, Electron Microscopy etc. The quality of heterostructures grown on these buffers is compared in order to identify the strengths and weaknesses of each buffer and to also map the effects of process parameters on nitride layers deposited on each buffer.

  6. Interface states and internal photoemission in p-type GaAs metal-oxide-semiconductor surfaces

    NASA Technical Reports Server (NTRS)

    Kashkarov, P. K.; Kazior, T. E.; Lagowski, J.; Gatos, H. C.

    1983-01-01

    An interface photodischarge study of p-type GaAs metal-oxide-semiconductor (MOS) structures revealed the presence of deep interface states and shallow donors and acceptors which were previously observed in n-type GaAs MOS through sub-band-gap photoionization transitions. For higher photon energies, internal photoemission was observed, i.e., injection of electrons to the conduction band of the oxide from either the metal (Au) or from the GaAs valence band; the threshold energies were found to be 3.25 and 3.7 + or - 0.1 eV, respectively. The measured photoemission current exhibited a thermal activation energy of about 0.06 eV, which is consistent with a hopping mechanism of electron transport in the oxide.

  7. Interface states and internal photoemission in p-type GaAs metal-oxide-semiconductor surfaces

    NASA Technical Reports Server (NTRS)

    Kashkarov, P. K.; Kazior, T. E.; Lagowski, J.; Gatos, H. C.

    1983-01-01

    An interface photodischarge study of p-type GaAs metal-oxide-semiconductor (MOS) structures revealed the presence of deep interface states and shallow donors and acceptors which were previously observed in n-type GaAs MOS through sub-band-gap photoionization transitions. For higher photon energies, internal photoemission was observed, i.e., injection of electrons to the conduction band of the oxide from either the metal (Au) or from the GaAs valence band; the threshold energies were found to be 3.25 and 3.7 + or - 0.1 eV, respectively. The measured photoemission current exhibited a thermal activation energy of about 0.06 eV, which is consistent with a hopping mechanism of electron transport in the oxide.

  8. High responsivity in molecular beam epitaxy grown β-Ga2O3 metal semiconductor metal solar blind deep-UV photodetector

    NASA Astrophysics Data System (ADS)

    Singh Pratiyush, Anamika; Krishnamoorthy, Sriram; Vishnu Solanke, Swanand; Xia, Zhanbo; Muralidharan, Rangarajan; Rajan, Siddharth; Nath, Digbijoy N.

    2017-05-01

    In this report, we demonstrate high spectral responsivity (SR) in MBE grown epitaxial β-Ga2O3-based solar blind metal-semiconductor-metal (MSM) photodetectors (PD). The (-201)-oriented β-Ga2O3 thin film was grown using plasma-assisted MBE on c-plane sapphire substrates. MSM devices fabricated with Ni/Au contacts in an interdigitated geometry were found to exhibit peak SR > 1.5 A/W at 236-240 nm at a bias of 4 V with a UV to visible rejection ratio > 105. The devices exhibited very low dark current < 10 nA at 20 V and showed no persistent photoconductivity (PPC) as evident from the sharp transients with a photo-to-dark current ratio > 103. These results represent the state-of-art performance for the MBE-grown β-Ga2O3 MSM solar blind detector.

  9. Enhanced output power of near-ultraviolet LEDs with AlGaN/GaN distributed Bragg reflectors on 6H-SiC by metal-organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Tao, Pengcheng; Liang, Hongwei; Xia, Xiaochuan; Liu, Yang; Jiang, Jianhua; Huang, Huishi; Feng, Qiuju; Shen, Rensheng; Luo, Yingmin; Du, Guotong

    2015-09-01

    Near-ultraviolet (UV) InGaN/AlGaN multiple quantum well (MQW) LEDs with 30 pairs AlGaN/GaN distributed Bragg reflectors (DBRs) were grown on 6H-SiC substrate by metal-organic chemical vapor deposition. A thin SiNx interlayer was introduced between the DBRs and n-GaN layer of the LED to reduce the threading dislocation density and result in enhancement the internal quantum efficiency (ηint) of the InGaN/AlGaN LED. The result indicates that the light output power for the LED with DBRs and SiNx interlayer was approximately 56% higher (at 350 mA) than the LED without DBRs and SiNx interlayer on 6H-SiC substrate, and this significant improvement in performance is attributed not only to the light extraction enhancement via the DBRs but also due to improve epilayer crystalline quality.

  10. Doped LZO buffer layers for laminated conductors

    DOEpatents

    Paranthaman, Mariappan Parans [Knoxville, TN; Schoop, Urs [Westborough, MA; Goyal, Amit [Knoxville, TN; Thieme, Cornelis Leo Hans [Westborough, MA; Verebelyi, Darren T [Oxford, MA; Rupich, Martin W [Framingham, MA

    2010-03-23

    A laminated conductor includes a metallic substrate having a surface, a biaxially textured buffer layer supported by the surface of the substrate, the biaxially textured buffer layer comprising LZO and a dopant for mitigating metal diffusion through the LZO, and a biaxially textured conductor layer supported by the biaxially textured buffer layer.

  11. Light-soaking effects and capacitance profiling in Cu(In,Ga)Se2 thin-film solar cells with chemical-bath-deposited ZnS buffer layers.

    PubMed

    Yu, Hye-Jung; Lee, Woo-Jung; Wi, Jae-Hyung; Cho, Dae-Hyung; Han, Won Seok; Chung, Yong-Duck; Kim, Tae-Soo; Song, Jung-Hoon

    2016-12-07

    We fabricated Cu(In,Ga)Se2 (CIGS) solar cells with chemical-bath deposited (CBD) ZnS buffer layers with different deposition times. The conversion efficiency and the fill factor of the CIGS solar cells reveal a strong dependence on the deposition time of CBD-ZnS films. In order to understand the detailed relationship between the heterojunction structure and the electronic properties of CIGS solar cells with different deposition times of CBD-ZnS films, capacitance-voltage (C-V) profiling measurements with additional laser illumination were performed. The light-soaking effects on CIGS solar cells with a CBD-ZnS buffer layer were investigated in detail using current density-voltage (J-V) and C-V measurements with several different lasers with different emission wavelengths. After light-soaking, the conversion efficiency changed significantly and the double diode feature in J-V curves disappeared. We explain that the major reason for the improvement of efficiency by light-soaking is due to the fact that negatively charged and highly defective vacancies in the CIGS absorber near the interface of CBD-ZnS/CIGS were formed and became neutral due to carriers generated by ultra-violet absorption in the buffer layer.

  12. Comparison of InGaAs(100) Grown by Chemical Beam Epitaxy and Metal Organic Chemical Vapor Deposition

    NASA Technical Reports Server (NTRS)

    Williams, M. D.; Greene, A. L.; Daniels-Race, T.; Lum, R. M.

    2000-01-01

    Secondary ion mass spectrometry is used to study the effects of substrate temperature on the composition and growth rate of InGaAs/InP(100) multilayers grown by chemical beam epitaxy, metal-organic chemical vapor deposition and solid source molecular beam epitaxy. The growth kinetics of the material grown by the different techniques are analyzed and compared.

  13. Comparison of InGaAs(100) Grown by Chemical Beam Epitaxy and Metal Organic Chemical Vapor Deposition

    NASA Technical Reports Server (NTRS)

    Williams, M. D.; Greene, A. L.; Daniels-Race, T.; Lum, R. M.

    2000-01-01

    Secondary ion mass spectrometry is used to study the effects of substrate temperature on the composition and growth rate of InGaAs/InP(100) multilayers grown by chemical beam epitaxy, metal-organic chemical vapor deposition and solid source molecular beam epitaxy. The growth kinetics of the material grown by the different techniques are analyzed and compared.

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

    SciTech Connect

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

    2015-08-07

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

  15. Giant positive magnetoresistance and field-induced metal insulator transition in Cr2NiGa

    NASA Astrophysics Data System (ADS)

    Pramanick, S.; Dutta, P.; Chatterjee, S.; Giri, S.; Majumdar, S.

    2017-01-01

    We report the magneto-transport properties of the newly synthesized Heusler compound Cr2NiGa which crystallizes in a disordered cubic B2 structure belonging to the Pm\\bar{3} m space group. The sample is found to be paramagnetic down to 2 K with metallic characteristics. On application of a magnetic field, a significantly large increase in resistivity is observed which corresponds to magnetoresistance as high as 112% at 150 kOe of field at the lowest temperature. Most remarkably, the sample shows a negative temperature coefficient of resistivity below about 50 K under the application of field  ⩾80 kOe, signifying a field-induced metal to ‘insulating’ transition. The observed magnetoresistance follows Kohler’s rule below 20 K indicating the validity of the semiclassical model of electronic transport in metals with a single relaxation time. A multi-band model for electronic transport, originally proposed for semimetals, is found to be appropriate to describe the magneto-transport behavior of the sample.

  16. As-grown deep-level defects in n-GaN grown by metal-organic chemical vapor deposition on freestanding GaN

    SciTech Connect

    Chen Shang; Ishikawa, Kenji; Hori, Masaru; Honda, Unhi; Shibata, Tatsunari; Matsumura, Toshiya; Tokuda, Yutaka; Ueda, Hiroyuki; Uesugi, Tsutomu; Kachi, Tetsu

    2012-09-01

    Traps of energy levels E{sub c}-0.26 and E{sub c}-0.61 eV have been identified as as-grown traps in n-GaN grown by metal-organic chemical vapor deposition by using deep level transient spectroscopy of the Schottky contacts fabricated by resistive evaporation. The additional traps of E{sub c}-0.13 and E{sub c}-0.65 eV have been observed in samples whose contacts are deposited by electron-beam evaporation. An increase in concentration of the E{sub c}-0.13 and E{sub c}-0.65 eV traps when approaching the interface between the contact and the GaN film supports our argument that these traps are induced by electron-beam irradiation. Conversely, the depth profiles of as-grown traps show different profiles between several samples with increased or uniform distribution in the near surface below 50 nm. Similar profiles are observed in GaN grown on a sapphire substrate. We conclude that the growth process causes these large concentrations of as-grown traps in the near-surface region. It is speculated that the finishing step in the growth process should be an essential issue in the investigation of the surface state of GaN.

  17. P-Channel InGaN/GaN heterostructure metal-oxide-semiconductor field effect transistor based on polarization-induced two-dimensional hole gas

    PubMed Central

    Zhang, Kexiong; Sumiya, Masatomo; Liao, Meiyong; Koide, Yasuo; Sang, Liwen

    2016-01-01

    The concept of p-channel InGaN/GaN heterostructure field effect transistor (FET) using a two-dimensional hole gas (2DHG) induced by polarization effect is demonstrated. The existence of 2DHG near the lower interface of InGaN/GaN heterostructure is verified by theoretical simulation and capacitance-voltage profiling. The metal-oxide-semiconductor FET (MOSFET) with Al2O3 gate dielectric shows a drain-source current density of 0.51 mA/mm at the gate voltage of −2 V and drain bias of −15 V, an ON/OFF ratio of two orders of magnitude and effective hole mobility of 10 cm2/Vs at room temperature. The normal operation of MOSFET without freeze-out at 8 K further proves that the p-channel behavior is originated from the polarization-induced 2DHG. PMID:27021054

  18. First order Raman scattering analysis of transition metal ions implanted GaN

    NASA Astrophysics Data System (ADS)

    Majid, Abdul; Rana, Usman Ali; Shakoor, Abdul; Ahmad, Naeem; Hassan, Najam al; Khan, Salah Ud-Din

    2016-03-01

    Transition Metal (TM) ions V, Cr, Mn and Co were implanted into GaN/sapphire films at fluences 5×1014, 5×1015 and 5×1016 cm-2. First order Raman Scattering (RS) measurements were carried out to study the effects of ion implantation on the microstructure of the materials, which revealed the appearance of disorder and new phonon modes in the lattice. The variations in characteristic modes 1GaN i.e. E2(high) and A1(LO), observed for different implanted samples is discussed in detail. The intensity of nitrogen vacancy related vibrational modes appearing at 363 and 665 cm-1 was observed for samples having different fluences. A gallium vacancy related mode observed at 277/281 cm-1 for TM ions implanted at 5×1014 cm-2 disappeared for all samples implanted with rest of fluences. The fluence dependent production of implantation induced disorder and substitution of TM ions on cationic sites is discussed, which is expected to provide necessary information for the potential use of these materials as diluted magnetic semiconductors in future spintronic devices.

  19. The effects of buffer layers on the performance and stability of flexible InGaZnO thin film transistors on polyimide substrates

    SciTech Connect

    Ok, Kyung-Chul; Park, Jin-Seong E-mail: jsparklime@hanyang.ac.kr; Ko Park, Sang-Hee; Kim, H. E-mail: jsparklime@hanyang.ac.kr; Hwang, Chi-Sun; Soo Shin, Hyun; Bae, Jonguk

    2014-02-10

    We demonstrated the fabrication of flexible amorphous indium gallium zinc oxide thin-film transistors (TFTs) on high-temperature polyimide (PI) substrates, which were debonded from the carrier glass after TFT fabrication. The application of appropriate buffer layers on the PI substrates affected the TFT performance and stability. The adoption of the SiN{sub x}/AlO{sub x} buffer layers as water and hydrogen diffusion barriers significantly improved the device performance and stability against the thermal annealing and negative bias stress, compared to single SiN{sub x} or SiO{sub x} buffer layers. The substrates could be bent down to a radius of curvature of 15 mm and the devices remained normally functional.

  20. Technology of GaAs metal-oxide-semiconductor solar cells

    NASA Technical Reports Server (NTRS)

    Stirn, R. J.; Yeh, Y. C. M.

    1977-01-01

    The growth of an oxide interfacial layer was recently found to increase the open-circuit voltage (OCV) and efficiency by up to 60 per cent in GaAs metal-semiconductor solar cells. Details of oxidation techniques to provide the necessary oxide thickness and chemical structure and using ozone, water-vapor-saturated oxygen, or oxygen gas discharges are described, as well as apparent crystallographic orientation effects. Preliminary results of the oxide chemistry obtained from X-ray, photoelectron spectroscopy are given. Ratios of arsenic oxide to gallium oxide of unity or less seem to be preferable. Samples with the highest OVC predominantly have As(+3) in the arsenic oxide rather than As(+5). A major difficulty at this time is a reduction in OCV by 100-200 mV when the antireflection coating is vacuum deposited.

  1. Nuclear spin relaxation in n -GaAs: From insulating to metallic regime

    NASA Astrophysics Data System (ADS)

    Vladimirova, M.; Cronenberger, S.; Scalbert, D.; Kotur, M.; Dzhioev, R. I.; Ryzhov, I. I.; Kozlov, G. G.; Zapasskii, V. S.; Lemaître, A.; Kavokin, K. V.

    2017-03-01

    Nuclear spin relaxation is studied in n -GaAs thick layers and microcavity samples with different electron densities. We reveal that both in metallic samples where electrons are free and mobile, and in insulating samples where electrons are localized, nuclear spin relaxation is strongly enhanced at low magnetic fields. The origin of this effect could reside in the quadrupole interaction between nuclei and fluctuating electron charges, that has been proposed to govern nuclear spin dynamics at low magnetic fields in the insulating samples. The characteristic values of these magnetic fields are given by dipole-dipole interaction between nuclei in bulk samples, and are greatly enhanced in microcavities, presumably due to additional strain, inherent to microstructures and nanostructures.

  2. Technology of GaAs metal-oxide-semiconductor solar cells

    NASA Technical Reports Server (NTRS)

    Stirn, R. J.; Yeh, Y. C. M.

    1977-01-01

    The growth of an oxide interfacial layer was recently found to increase the open-circuit voltage (OCV) and efficiency by up to 60 per cent in GaAs metal-semiconductor solar cells. Details of oxidation techniques to provide the necessary oxide thickness and chemical structure and using ozone, water-vapor-saturated oxygen, or oxygen gas discharges are described, as well as apparent crystallographic orientation effects. Preliminary results of the oxide chemistry obtained from X-ray, photoelectron spectroscopy are given. Ratios of arsenic oxide to gallium oxide of unity or less seem to be preferable. Samples with the highest OVC predominantly have As(+3) in the arsenic oxide rather than As(+5). A major difficulty at this time is a reduction in OCV by 100-200 mV when the antireflection coating is vacuum deposited.

  3. Ferromagnetism in Transition Metal Doped GaN and Related Materials

    NASA Astrophysics Data System (ADS)

    Abernathy, Cammy

    2005-03-01

    There is high current interest in the development of dilute magnetic semiconductor (DMS) materials exhibiting ferromagnetic behavior for spin-based light-emitting diodes, sensors, and transistors. Such materials are formed through the introduction of transition metal (TM) ions, such as Mn and Cr, into semiconductor hosts. Unfortunately many DMS materials, such as GaMnAs, have a relatively low magnetic ordering temperature ( 170 K for GaMnAs), which severely limits their usefulness. In the past few years, several groups have reported achieving ferromagnetism at room temperature in wide bandgap materials, such as GaMnN. This property makes these materials attractive for use as ultra-low-power switching elements, where the bit state of the device is determined through control of electron spin. Furthermore, these materials may also allow for the integration of photonic (laser and light-emitting diodes), electronic (field-effect and bipolar transistors) and magnetic (information storage) devices on a single substrate, leading to a new class of electronic devices that offer multi-purpose functionality. However, to realize such devices, several challenges remain. One concern to date has been the relatively low thermal stability of the III-Mn-N compounds. Doping with Cr in place of Mn, however, appears to greatly enhance the ability of the material to retain its magnetic properties even after annealing at temperatures up to 700C, easing the road to practical device fabrication. In addition, the ability to achieve magnetic behavior in a semi-insulating barrier material such as AlCrN opens new device possibilities. The most evident application of ferromagnetic AlN is as a ferromagnetic tunnel barrier, similar to EuS, but unlike EuS should allow for operation at room temperature. Growth of tunnel devices using Al-TM-N as a barrier and Ga-TM-N as a spin injector will be discussed. This work is supported by the Army Research Office under ARO-DAAD19-01-0-0701 and NSF under ECS

  4. Comparison of ohmic metallization schemes for InGaAlN

    SciTech Connect

    Ren, F.; Vartuli, C.B.; Pearton, S.J.; Abernathy, C.R.; Donovan, S.M.; MacKenzie, J.D.; Shul, R.J.; Zolper, J.C.; Lovejoy, M.L.; Baca, A.G.; Hagerott-Crawford, M.; Jones, K.A.

    1997-05-01

    W, WSi{sub 0.44}, and Ti/Al contacts were examined on n{sup +}In{sub 0.65}Ga{sub 0.35}N, InN, and In{sub 0.75}Al{sub 0.25}N. W was found to produce low specific contact resistance (q{sub c}{approximately}10{sup {minus}7}{Omega}cm{sup 2}) ohmic contacts to InGaN, while WSi{sub x} showed an as-deposited q{sub c} of 4{times}10{sup {minus}7}{Omega}cm{sup 2} but this degraded significantly with subsequent annealing, reaching 10{sup {minus}5}{Omega}cm{sup 2} at 700{degree}C. Ti/Al contacts on InGaN were stable to {approximately}600{degree}C (q{sub c}{approximately}4{times}10{sup {minus}7}{Omega}cm{sup 2} at {le}600{degree}C). InN contacted with W and Ti/Al produced ohmic contacts with q{sub c}{approximately}10{sup {minus}7}{Omega}cm{sup 2} and for WSi{sub x} q{sub c}{approximately}10{sup {minus}6}{Omega}cm{sup 2} and all three metallization schemes retained values {le}10{sup {minus}6}{Omega}cm{sup 2} up to 600{degree}C. The contact resistances for all of the metals were {ge}10{sup {minus}4}{Omega}cm{sup 2} on InAlN, and degraded with subsequent annealing. WSi{sub x} contacts on InN grown graded from In{sub 0.6}Al{sub 0.4}N were also examined. The specific contact resistance was an order of magnitude lower (q{sub c}{approximately}10{sup {minus}5}{Omega}cm{sup 2}) after 500{degree}C anneal than that measured for WSi{sub x} deposited directly on In{sub 0.6}Al{sub 0.4}N. Measurements of the temperature dependence of these contact structures showed that field emission was generally the most important conduction mechanism. {copyright} {ital 1997 American Vacuum Society.}

  5. Optical study of a-plane InGaN/GaN multiple quantum wells with different well widths grown by metal-organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Ko, T. S.; Lu, T. C.; Wang, T. C.; Chen, J. R.; Gao, R. C.; Lo, M. H.; Kuo, H. C.; Wang, S. C.; Shen, J. L.

    2008-11-01

    a-plane InGaN/GaN multiple quantum wells of different widths ranging from 3 to 12 nm grown on r-plane sapphire by metal-organic chemical vapor deposition were investigated. The peak emission intensity of the photoluminescence (PL) reveals a decreasing trend as the well width increases from 3 to 12 nm. Low temperature (9 K) time-resolved PL (TRPL) study shows that the sample with 3-nm-thick wells has the best optical property with a fastest exciton decay time of 0.57 ns. The results of cathodoluminescence and micro-PL scanning images for samples of different well widths further verify that the more uniform and stronger luminescence intensity distribution are observed for the samples of thinner quantum wells. In addition, more effective capturing of excitons due to larger localization energy Eloc and shorter radiative lifetime of localized excitons are observed in thinner well width samples in the temperature dependent TRPL.

  6. Growth of GaN on Sapphire via Low-Temperature Deposited Buffer Layer and Realization of p-Type GaN by Mg Doping Followed by Low-Energy Electron Beam Irradiation

    NASA Astrophysics Data System (ADS)

    Amano, Hiroshi

    2015-12-01

    This is a personal history of one of the Japanese researchers engaged in developing a method for growing GaN on a sapphire substrate, paving the way for the realization of smart television and display systems using blue LEDs. The most important work was done in the mid- to late 80s. The background to the author's work and the process by which the technology enabling the growth of GaN and the realization of p-type GaN was established are reviewed.

  7. Nobel Lecture: Growth of GaN on sapphire via low-temperature deposited buffer layer and realization of p -type GaN by Mg doping followed by low-energy electron beam irradiation*

    NASA Astrophysics Data System (ADS)

    Amano, Hiroshi

    2015-10-01

    This is a personal history of one of the Japanese researchers engaged in developing a method for growing GaN on a sapphire substrate, paving the way for the realization of smart television and display systems using blue LEDs. The most important work was done in the mid to late 1980s. The background to the author's work and the process by which the technology enabling the growth of GaN and the realization of p -type GaN was established are reviewed.

  8. Low-frequency noise in AlN/AlGaN/GaN metal-insulator-semiconductor devices: A comparison with Schottky devices

    SciTech Connect

    Le, Son Phuong; Nguyen, Tuan Quy; Shih, Hong-An; Kudo, Masahiro; Suzuki, Toshi-kazu

    2014-08-07

    We have systematically investigated low-frequency noise (LFN) in AlN/AlGaN/GaN metal-insulator-semiconductor (MIS) devices, where the AlN gate insulator layer was sputtering-deposited on the AlGaN surface, in comparison with LFN in AlGaN/GaN Schottky devices. By measuring LFN in ungated two-terminal devices and heterojunction field-effect transistors (HFETs), we extracted LFN characteristics in the intrinsic gated region of the HFETs. Although there is a bias regime of the Schottky-HFETs in which LFN is dominated by the gate leakage current, LFN in the MIS-HFETs is always dominated by only the channel current. Analyzing the channel-current-dominated LFN, we obtained Hooge parameters α for the gated region as a function of the sheet electron concentration n{sub s} under the gate. In a regime of small n{sub s}, both the MIS- and Schottky-HFETs exhibit α∝n{sub s}{sup −1}. On the other hand, in a middle n{sub s} regime of the MIS-HFETs, α decreases rapidly like n{sub s}{sup −ξ} with ξ ∼ 2-3, which is not observed for the Schottky-HFETs. In addition, we observe strong increase in α∝n{sub s}{sup 3} in a large n{sub s} regime for both the MIS- and Schottky-HFETs.

  9. Sputtered Inx(O,S)y Buffer Layers for Cu(In,Ga)Se2 Thin-Film Solar Cells: Engineering of Band Alignment and Interface Properties.

    PubMed

    Ho, Wei-Hao; Hsu, Chia-Hao; Wei, Shih-Yuan; Cai, Chung-Hao; Huang, Wei-Chih; Lai, Chih-Huang

    2017-05-24

    We propose a simple approach to engineering the sputtered Inx(O,S)y/Cu(In,Ga)Se2 heterojunction, in terms of band alignment and interface properties. The band alignment was tailored by tuning the base pressure of the sputtering deposition to incorporate oxygen into deposited In2S3 layers (termed as Inx(O,S)y). The interface properties were improved by optimizing the air-annealing temperature on Inx(O,S)y/Cu(In,Ga)Se2 stacked layers. Increasing the base pressure raises the O/(S + O) ratio contained in deposited Inx(O,S)y films and thus widens the band gaps. This could effectively tailor the conduction band offset (ΔEC) at the Inx(O,S)y/Cu(In,Ga)Se2 interface from a cliff (-0.25 eV) to a nearly flat band (0.07 eV) alignment. On the other hand, the extra air annealing at 235 °C did not significantly change the band alignment but did ameliorate the interface properties by reducing the Cu content at the Cu(In,Ga)Se2 surface and diminish the interface defect density induced by sputtering damages. The former might enhance the type of inversion and increase the hole barrier at the interface, preventing the detrimental recombination behavior. The latter could effectively strengthen the junction quality. Consequently, our approach substantially enhances the cell efficiency from 2.30% to 11.04%.

  10. Metal insulator transition induced by the magnetic field in n-type GaSb

    NASA Astrophysics Data System (ADS)

    Ghezzi, C.; Magnanini, R.; Parisini, A.

    2005-10-01

    The metal-insulator (MI) transition induced by a magnetic field was evidenced for the first time in compensated n-type GaSb layers grown by molecular beam epitaxy. The free electron densities were in the low 10 16 cm -3 range or even slightly lower, so that the zero-field 3D electron gas was degenerate and, at the BMI magnetic field of the MI transition, it populates only the spin-split 0 (+) Landau level (extreme quantum limit). On the metallic side of the MI transition a T1/3 dependence of the conductivity was assumed to fit the low- T data and to estimate the BMI value, which resulted of 9.1 T in the purest sample. The MI transition manifests in a strong increase of the diagonal resistivity with the magnetic field, but not of the Hall coefficient, suggesting that the apparent electron density is practically constant, whereas the mobility varies strongly. The evidence of a maximum in the temperature dependence of the Hall coefficient has been explained through a two channels transport mechanism involving localized and extended states.

  11. Thermal and microwave characterization of GaAs to Si metal-bonded structures

    NASA Astrophysics Data System (ADS)

    Bickford, Justin R.; Yu, P. K. L.; Lau, S. S.

    2013-09-01

    Isothermal solidification metal waferbonding is well suited to heterogeneously integrate high-speed/high-power density RF and microwave devices with standard CMOS technology. It is capable of forming efficient electrical and thermal interconnects as well as bonded-microstrip waveguide structures. Accurate means of characterizing the electrical, thermal, and microwave properties of these structures are necessary to enable heterogeneous monolithic microwave integrated circuits (HMMICs). This article describes a bond layer thermal conductivity measurement method, a bond-metal microstrip microwave waveguide characterization method, and the fabrication method developed to support the measurement structures. As a result, an In-Pd bond alloy thermal conductivity of 2.51 W/(m K) was measured for GaAs devices bonded to Si. Also, an optimized bonded-microstrip waveguide was simulated based upon measured microwave results of the measurement structure, projecting a 0.56 dB/mm loss, a microwave index of 2.91, and a characteristic impedance of 41.3+6i Ω at 15 GHz, thus advocating this approach as a means of realizing high power HMMICs.

  12. Investigating compositional effects of atomic layer deposition ternary dielectric Ti-Al-O on metal-insulator-semiconductor heterojunction capacitor structure for gate insulation of InAlN/GaN and AlGaN/GaN

    SciTech Connect

    Colon, Albert; Stan, Liliana; Divan, Ralu; Shi, Junxia

    2016-11-01

    Gate insulation/surface passivation in AlGaN/GaN and InAlN/GaN heterojunction field-effect transistors is a major concern for passivation of surface traps and reduction of gate leakage current. However, finding the most appropriate gate dielectric materials is challenging and often involves a compromise of the required properties such as dielectric constant, conduction/valence band-offsets, or thermal stability. Creating a ternary compound such as Ti-Al-O and tailoring its composition may result in a reasonably good gate material in terms of the said properties. To date, there is limited knowledge of the performance of ternary dielectric compounds on AlGaN/GaN and even less on InAlN/GaN. To approach this problem, the authors fabricated metal-insulator-semiconductor heterojunction (MISH) capacitors with ternary dielectrics Ti-Al-O of various compositions, deposited by atomic layer deposition (ALD). The film deposition was achieved by alternating cycles of TiO2 and Al2O3 using different ratios of ALD cycles. TiO2 was also deposited as a reference sample. The electrical characterization of the MISH capacitors shows an overall better performance of ternary compounds compared to the pure TiO2. The gate leakage current density decreases with increasing Al content, being similar to 2-3 orders of magnitude lower for a TiO2:Al2O3 cycle ratio of 2:1. Although the dielectric constant has the highest value of 79 for TiO2 and decreases with increasing the number of Al2O3 cycles, it is maintaining a relatively high value compared to an Al2O3 film. Capacitance voltage sweeps were also measured in order to characterize the interface trap density. A decreasing trend in the interface trap density was found while increasing Al content in the film. In conclusion, our study reveals that the desired high-kappa properties of TiO2 can be adequately maintained while improving other insulator performance factors. The ternary compounds may be an excellent choice as a gate material for both

  13. Metal/Silicate Partitioning of W, Ge, Ga and Ni: Dependence on Silicate Melt Composition

    NASA Astrophysics Data System (ADS)

    Singletary, S.; Drake, M. J.

    2004-12-01

    Metal/silicate partition coefficients (Dm/s) for siderophile elements are essential to investigations of core formation when used in conjunction with the pattern of elemental abundances in the Earth's mantle (Drake and Righter, 2002; Jones and Drake, 1986; Righter et al. 1997). The partitioning of siderophile elements is controlled by temperature, pressure, oxygen fugacity, and by the compositions of the metal and silicate phases. In this work, we investigate the role of silicate melt composition on the partitioning of the siderophile elements W, Ge, Ga and Ni between metallic and silicate liquid. Experiments were performed in the Experimental Geochemistry Laboratory at the University of Arizona utilizing a non-end loaded piston cylinder apparatus with a barium carbonate pressure medium. Starting materials were created by combining the mafic and silicic compositions of Jaeger and Drake (2000) with Fe powder (~25 wt% of the total mixture) to achieve metal saturation. Small amounts of W, Ge, Ga2O3 and NiO powder (less than 2 wt% each) were also added to the starting compositions. The experiments were contained in a graphite capsule and performed with temperature and pressure fixed at 1400ºC and 1.5 GPa. Experimental run products were analyzed with the University of Arizona Cameca SX50 electron microprobe with four wavelength dispersive spectrometers and a PAP ZAF correction program. All experiments in our set are saturated with metal and silicate liquid, indicating that oxygen fugacity is below IW. Several of the runs also contain a gallium-rich spinel as an additional saturating phase. Quench phases are also present in the silicate liquid in all runs. The experimentally produced liquids have nbo/t values (calculated using the method of Mills, 1993) that range from 1.10 to 2.97. These values are higher than those calculated for the liquids in the Jaeger and Drake (2000) study. The higher nbo/t values are due to uptake of Fe by the melt. The initial silicate

  14. An energy-harvesting scheme employing CuGaSe2 quantum dot-modified ZnO buffer layers for drastic conversion efficiency enhancement in inorganic-organic hybrid solar cells.

    PubMed

    Ho, Cherng-Rong; Tsai, Meng-Lin; Jhuo, Hung-Jun; Lien, Der-Hsien; Lin, Chin-An; Tsai, Shin-Hung; Wei, Tzu-Chiao; Huang, Kun-Ping; Chen, Show-An; He, Jr-Hau

    2013-07-21

    We demonstrated a promising route to enhance the performance of inverted organic photovoltaic (OPV) devices by the incorporation of CuGaSe2 (CGS) quantum dots (QDs) into the ZnO buffer layer of P3HT:PCBM-based devices. The modification of QDs provides better band alignment between the organic/cathode interface, improves ZnO crystal quality, and increases photon absorption, leading to more effective carrier transport/collection. By employing this energy-harvesting scheme, short-circuit current density, open-circuit voltage, and fill factor of the OPV device after CGS QD modification are improved by 9.43%, 7.02% and 6.31%, respectively, giving rise to a 23.8% enhancement in the power conversion efficiency.

  15. Growth of wurtzite InP/GaP core-shell nanowires by metal-organic molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Halder, Nripendra N.; Kelrich, Alexander; Kauffmann, Yaron; Cohen, Shimon; Ritter, Dan

    2017-04-01

    We report on the selective area vapor-liquid-solid (SA-VLS) growth of InP/GaP core shell nano-wires (NWs) by metal organic molecular beam epitaxy. Wurtzite crystal structure of the core InP was transferred to the GaP shell through layer by layer radial growth which eliminated bending of the NWs in random directions. Low growth temperature restricted surface segregation and kept the shell free from indium. Strain in the GaP shell was partially relaxed through formation of periodic misfit dislocations. From the periodicity of Moiré fringes and splitting of the fast-Fourier-transform of the transmission electron micrographs, the radial and axial strain were determined as 4.5% and 6.2%, respectively.

  16. Electric, dielectric and optical properties of Ga2O3 grown by metal organic chemical vapour deposition

    NASA Astrophysics Data System (ADS)

    Paskaleva, A.; Spassov, D.; Terziyska, P.

    2017-01-01

    Thin film (15-130 nm) of gallium oxide were grown by the industry relevant metal organic chemical vapour deposition (MOCVD) technique on p-type Si to check the possibility for integration of newly rediscovered wide bandgap material with the Si technology. Electric, dielectric and optical properties were studied and analyzed. To perform electrical characterization, Ga2O3 films were integrated into Al/Ga2O3/p-Si metal–oxide–semiconductor (MOS) capacitors. Relative dielectric permittivity, flat-band voltage shift and effective oxide charge density were obtained from C-V measurements. Spectroscopic ellipsometry measurements reveal that Ga2O3 deposited by MOCVD is a direct bandgap material with a large optical bandgap of about 5.1 eV. Both ellipsometrical and electrical results show formation of a thick interfacial SiO2.

  17. The realization of ferro-ferrimagnetic transition and half-metallicity in half-Heusler CoMnGa alloy

    NASA Astrophysics Data System (ADS)

    Wang, L. Y.; Dai, X. F.; Wang, X. T.; Liu, X. F.; Li, P. P.; Cui, Y. T.; Liu, E. K.; Wang, W. H.; Wu, G. H.; Liu, G. D.

    2014-11-01

    We theoretically predicted that half-Heusler CoMnGa alloy to be half-metallic ferrimagnet at the equilibrium lattice parameter. With the lattice expansion, a local energy minimum occurs at a larger lattice parameter where CoMnGa alloy is in a metastable ferromagnetic state. However, a ferro-ferrimagnetic transition (Fo-Fi-T) is not observed in experiment. We found the Co-Mn antisites can induce the Fo-Fi-T by adjusting the driving force of magnetic transition and the energy barrier. The antisites are sensitive to the preparation methods and annealing temperatures. The highly ordered CoMnGa is achieved by annealing at 1073 K. The Fo-Fi-T occurs in a sample annealed at 1083 K.

  18. Buffer Biology.

    ERIC Educational Resources Information Center

    Morgan, Kelly

    2000-01-01

    Presents a science experiment in which students test the buffering capacity of household products such as shampoo, hand lotion, fizzies candy, and cola. Lists the standards addressed in this experiment and gives an example of a student lab write-up. (YDS)

  19. Buffer Biology.

    ERIC Educational Resources Information Center

    Morgan, Kelly

    2000-01-01

    Presents a science experiment in which students test the buffering capacity of household products such as shampoo, hand lotion, fizzies candy, and cola. Lists the standards addressed in this experiment and gives an example of a student lab write-up. (YDS)

  20. Chemical bonding, adatom-adatom interaction, and replacement reaction of column-3 metals on GaAs(110)

    NASA Astrophysics Data System (ADS)

    Skeath, Perry; Lindau, I.; Su, C. Y.; Spicer, W. E.

    1983-12-01

    Studies of the electronic states associated with column-3 (Al, Ga, and In) overlayers on cleaved GaAs(110) surfaces by photoemission electron spectroscopy (PES) and low-energy electron diffraction are reported. Deposition of In or Ga leaves the valence-band spectra devoid of structure other than that characteristic of clean GaAs(110). Comparison with theory shows that the models assumed previously in calculations are in error and that a fundamentally new understanding of the metal-semiconductor bonding is needed. The most significant result is that a strong interaction between the column-3 adatoms leads to cluster formation on the surface. It is shown that at submonolayer coverage Ga most likely forms flat (one- or two-atom-thick) clusters on the surface, which are not in registry with the GaAs surface lattice, while In shows a greater tendency toward three-dimensional cluster formation. As a result, the electronic structure of the overlayer is free-electron-like even at submonolayer coverage. As a contrasting example, Sb (a column-5 element), which forms an ordered overlayer, produces quite significant changes in the surface valence band. The room-temperature reaction between Al adsorbate atoms and a GaAs(110) surface is observed by means of soft-x-ray photoemission techniques using core-level spectroscopy. Evidence of two states of Al which are distinct from the bulk Al metal is seen at submonolayer coverages. The sequential appearance of these states suggests that Al, as deposited at room temperature, tends to replace Ga below the surface layer first; but, as monolayer coverage of Al is reached, a large degree of replacement in the top or surface layer may take place. This interpretation is consistent with the finding by Kahn, Duke, and co-workers that (in thermodynamic equilibrium) Al tends to replace Ga below the GaAs(110) surface layer before much replacement in the first layer occurs. It is concluded that the differences between the room-temperature data of

  1. InP/InGaAlAs distributed Bragg reflectors grown by low-pressure metal organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Lu, T. C.; Tsai, J. Y.; Chu, J. T.; Chang, Y. S.; Wang, S. C.

    2003-04-01

    Long-wavelength vertical cavity surface emitting lasers (VCSELs) are considered the best candidate for the future low-cost reliable light sources in fiber communications. However, the absence of high refractive index contrast in InP-lattice-matched materials impeded the development of 1.3-1.5 μm VCSELs. Although wafer fusions provided the alternative approaches to integrate the InP-based gain materials with the GaAs/AlAs materials for their inherent high refractive index contrast, the monolithic InP-based lattice-matched distributed Bragg reflectors (DBRs) are still highly attractive and desirable. In this report, we demonstrate InP/InGaAlAs DBRs with larger refractive index contrast than InP/InGaAsP and InAlAs/InGaAlAs DBRs. The switching between InP and InGaAlAs layers and growth rate control have been done by careful growth interruption technique and accurate in situ optical monitoring in low-pressure metal organic chemical vapor deposition. A 35 pairs 1.55 μm centered InP/InGaAlAs DBRs has the stopband of more than 100 nm and the highest reflectivity of more than 99%. A VCSEL structure incorporating 35 pairs InP/InGaAlAs DBR as the bottom mirror combined with a 2 λ thick periodic gain cavity and 10 pairs SiO 2/TiO 2 top dielectric mirrors was fabricated. The VCSELs lased at 1.56 μm by optical pumping at room temperature with the threshold pumping power of 30 mW.

  2. Heteroepitaxial VO{sub 2} thin films on GaN: Structure and metal-insulator transition characteristics

    SciTech Connect

    Zhou You; Ramanathan, Shriram

    2012-10-01

    Monolithic integration of correlated oxide and nitride semiconductors may open up new opportunities in solid-state electronics and opto-electronics that combine desirable functional properties of both classes of materials. Here, we report on epitaxial growth and phase transition-related electrical properties of vanadium dioxide (VO{sub 2}) thin films on GaN epitaxial layers on c-sapphire. The epitaxial relation is determined to be (010){sub vo{sub 2}} parallel (0001){sub GaN} parallel (0001){sub A1{sub 2O{sub 3}}} and [100]{sub vo{sub 2}} parallel [1210]{sub GaN} parallel [0110]{sub A1{sub 2O{sub 3}}} from x-ray diffraction. VO{sub 2} heteroepitaxial growth and lattice mismatch are analyzed by comparing the GaN basal plane (0001) with the almost close packed corrugated oxygen plane in vanadium dioxide and an experimental stereographic projection describing the orientation relationship is established. X-ray photoelectron spectroscopy suggests a slightly oxygen rich composition at the surface, while Raman scattering measurements suggests that the quality of GaN layer is not significantly degraded by the high-temperature deposition of VO{sub 2}. Electrical characterization of VO{sub 2} films on GaN indicates that the resistance changes by about four orders of magnitude upon heating, similar to epitaxial VO{sub 2} films grown directly on c-sapphire. It is shown that the metal-insulator transition could also be voltage-triggered at room temperature and the transition threshold voltage scaling variation with temperature is analyzed in the framework of a current-driven Joule heating model. The ability to synthesize high quality correlated oxide films on GaN with sharp phase transition could enable new directions in semiconductor-photonic integrated devices.

  3. Behavior of Photocarriers in the Light-Induced Metastable State in the p-n Heterojunction of a Cu(In,Ga)Se2 Solar Cell with CBD-ZnS Buffer Layer.

    PubMed

    Lee, Woo-Jung; Yu, Hye-Jung; Wi, Jae-Hyung; Cho, Dae-Hyung; Han, Won Seok; Yoo, Jisu; Yi, Yeonjin; Song, Jung-Hoon; Chung, Yong-Duck

    2016-08-31

    We fabricated Cu(In,Ga)Se2 (CIGS) solar cells with a chemical bath deposition (CBD)-ZnS buffer layer grown with varying ammonia concentrations in aqueous solution. The solar cell performance was degraded with increasing ammonia concentration, due to actively dissolved Zn atoms during CBD-ZnS precipitation. These formed interfacial defect states, such as hydroxide species in the CBD-ZnS film, and interstitial and antisite Zn defects at the p-n heterojunction. After light/UV soaking, the CIGS solar cell performance drastically improved, with a rise in fill factor. With the Zn-based buffer layer, the light soaking treatment containing blue photons induced a metastable state and enhanced the CIGS solar cell performance. To interpret this effect, we suggest a band structure model of the p-n heterojunction to explain the flow of photocarriers under white light at the initial state, and then after light/UV soaking. The determining factor is a p+ defect layer, containing an amount of deep acceptor traps, located near the CIGS surface. The p+ defect layer easily captures photoexcited electrons, and then when it becomes quasi-neutral, attracts photoexcited holes. This alters the barrier height and controls the photocurrent at the p-n junction, and fill factor values, determining the solar cell performance.

  4. In vitro corrosion properties and cytocompatibility of Fe-Ga alloys as potential biodegradable metallic materials.

    PubMed

    Wang, Henan; Zheng, Yang; Liu, Jinghua; Jiang, Chengbao; Li, Yan

    2017-02-01

    The in vitro biodegradable properties and cytocompatibility of Fe-Ga alloys including Fe81Ga19, (Fe81Ga19)98B2 and (Fe81Ga19)99.5(TaC)0.5, and pure Fe were investigated for biomedical applications. The microstructure of the alloys was characterized using X-ray diffraction spectroscopy and optical microscopy. The results showed that A2 and D03 phases were detected for the three types of Fe-Ga alloys, and additional Fe2B and TaC phases were found in the (Fe81Ga19)98B2 and (Fe81Ga19)99.5(TaC)0.5 alloys, respectively. The corrosion rates of the Fe-Ga alloys were higher than that of pure Fe, as demonstrated by both potentiodynamic polarization measurements and immersion tests in simulated body fluid. The alloying element Ga lowered the corrosion potential of the Fe matrix and made it more susceptible to corrosion. Severe pitting corrosion developed on the surface of the Fe81Ga19 alloy after the addition of ternary B or TaC due to the multi-phase microstructures. The MC3T3-E1 cells exhibited good adhesion and proliferation behavior on the surfaces of the Fe-Ga alloys after culture for 4h and 24h.

  5. High Growth Rate Metal-Organic Molecular Beam Epitaxy for the Fabrication of GaAs Space Solar Cells

    NASA Technical Reports Server (NTRS)

    Freundlich, A.; Newman, F.; Monier, C.; Street, S.; Dargan, P.; Levy, M.

    2005-01-01

    In this work it is shown that high quality GaAs photovoltaic devices can be produced by Molecular Beam Epitaxy (MBE) with growth rates comparable to metal-organic chemical vapor deposition (MOCVD) through the subsitution of group III solid sources by metal-organic compounds. The influence the III/V flux-ratio and growth temperatures in maintaining a two dimensional layer by layer growth mode and achieving high growth rates with low residual background impurities is investigated. Finally subsequent to the study of the optimization of n- and p doping of such high growth rate epilayers, results from a preliminary attempt in the fabrication of GaAs photovoltaic devices such as tunnel diodes and solar cells using the proposed high growth rate approach are reported.

  6. Resonant metallic nanostructure for enhanced two-photon absorption in a thin GaAs p-i-n diode

    SciTech Connect

    Portier, Benjamin; Pardo, Fabrice; Péré-Laperne, Nicolas; Steveler, Emilie; Dupuis, Christophe; Bardou, Nathalie; Lemaître, Aristide; Pelouard, Jean-Luc; Vest, Benjamin; Jaeck, Julien; Rosencher, Emmanuel; Haïdar, Riad

    2014-07-07

    Degenerate two-photon absorption (TPA) is investigated in a 186 nm thick gallium arsenide (GaAs) p-i-n diode embedded in a resonant metallic nanostructure. The full device consists in the GaAs layer, a gold subwavelength grating on the illuminated side, and a gold mirror on the opposite side. For TM-polarized light, the structure exhibits a resonance close to 1.47 μm, with a confined electric field in the intrinsic region, far from the metallic interfaces. A 109 times increase in photocurrent compared to a non-resonant device is obtained experimentally, while numerical simulations suggest that both gain in TPA-photocurrent and angular dependence can be further improved. For optimized grating parameters, a maximum gain of 241 is demonstrated numerically and over incidence angle range of (−30°; +30°).

  7. Performance improvement of GaN-based metal-semiconductor-metal photodiodes grown on Si(111) substrate by thermal cycle annealing process

    NASA Astrophysics Data System (ADS)

    Lin, Jyun-Hao; Huang, Shyh-Jer; Su, Yan-Kuin

    2014-01-01

    A simple thermal cycle annealing (TCA) process was used to improve the quality of GaN grown on a Si substrate. The X-ray diffraction (XRD) and etch pit density (EPD) results revealed that using more process cycles, the defect density cannot be further reduced. However, the performance of GaN-based metal-semiconductor-metal (MSM) photodiodes (PDs) prepared on Si substrates showed significant improvement. With a two-cycle TCA process, it is found that the dark current of the device was only 1.46 × 10-11 A, and the photo-to-dark-current contrast ratio was about 1.33 × 105 at 5 V. Also, the UV/visible rejection ratios can reach as high as 1077.

  8. Ferroelectric BaTiO3 thin films on Ni metal tapes using NiO as buffer layer

    NASA Astrophysics Data System (ADS)

    Yuan, Z.; Liu, J.; Weaver, J.; Chen, C. L.; Jiang, J. C.; Lin, B.; Giurgiutiu, V.; Bhalla, A.; Guo, R. Y.

    2007-05-01

    Ferroelectric BaTiO3 (BTO) thin films were deposited on NiO buffered polycrystalline Ni tapes by pulsed laser deposition. Microstructural studies by x-ray diffractometer and transmission electron microscopy reveal that the as-grown BTO films have the nanopillar structures with an average size of approximately 80nm in diameter and the good interface structures with no interdiffusion or reaction. The dielectric and ferroelectric property measurements exhibit that the BTO films have a relatively large dielectric constant, a small dielectric loss, and an extremely large piezoelectric response with a symmetric hysteresis loop. These excellent properties indicate that the as-fabricated BTO films are promising for the development of the structural health monitoring systems.

  9. Damage-Free Smooth-Sidewall InGaAs Nanopillar Array by Metal-Assisted Chemical Etching.

    PubMed

    Kong, Lingyu; Song, Yi; Kim, Jeong Dong; Yu, Lan; Wasserman, Daniel; Chim, Wai Kin; Chiam, Sing Yang; Li, Xiuling

    2017-09-29

    Producing densely packed high aspect ratio In0.53Ga0.47As nanostructures without surface damage is critical for beyond Si-CMOS nanoelectronic and optoelectronic devices. However, conventional dry etching methods are known to produce irreversible damage to III-V compound semiconductors because of the inherent high-energy ion-driven process. In this work, we demonstrate the realization of ordered, uniform, array-based In0.53Ga0.47As pillars with diameters as small as 200 nm using the damage-free metal-assisted chemical etching (MacEtch) technology combined with the post-MacEtch digital etching smoothing. The etching mechanism of InxGa1-xAs is explored through the characterization of pillar morphology and porosity as a function of etching condition and indium composition. The etching behavior of In0.53Ga0.47As, in contrast to higher bandgap semiconductors (e.g., Si or GaAs), can be interpreted by a Schottky barrier height model that dictates the etching mechanism constantly in the mass transport limited regime because of the low barrier height. A broader impact of this work relates to the complete elimination of surface roughness or porosity related defects, which can be prevalent byproducts of MacEtch, by post-MacEtch digital etching. Side-by-side comparison of the midgap interface state density and flat-band capacitance hysteresis of both the unprocessed planar and MacEtched pillar In0.53Ga0.47As metal-oxide-semiconductor capacitors further confirms that the surface of the resultant pillars is as smooth and defect-free as before etching. MacEtch combined with digital etching offers a simple, room-temperature, and low-cost method for the formation of high-quality In0.53Ga0.47As nanostructures that will potentially enable large-volume production of In0.53Ga0.47As-based devices including three-dimensional transistors and high-efficiency infrared photodetectors.

  10. Influence of vicinal sapphire substrate on the properties of N-polar GaN films grown by metal-organic chemical vapor deposition

    SciTech Connect

    Lin, Zhiyu; Zhang, Jincheng Xu, Shengrui; Chen, Zhibin; Yang, Shuangyong; Tian, Kun; Hao, Yue; Su, Xujun; Shi, Xuefang

    2014-08-25

    The influence of vicinal sapphire substrates on the growth of N-polar GaN films by metal-organic chemical vapor deposition is investigated. Smooth GaN films without hexagonal surface feature are obtained on vicinal substrate. Transmission electron microscope results reveal that basal-plane stacking faults are formed in GaN on vicinal substrate, leading to a reduction in threading dislocation density. Furthermore, it has been found that there is a weaker yellow luminescence in GaN on vicinal substrate than that on (0001) substrate, which might be explained by the different trends of the carbon impurity incorporation.

  11. Electrical and optical properties of p-GaN films implanted with transition metal impurities

    NASA Astrophysics Data System (ADS)

    Polyakov, A. Y.; Smirnov, N. B.; Govorkov, A. V.; Khanna, Rohit; Pearton, S. J.

    2005-05-01

    The electrical and optical properties and the spectra of deep hole traps in p-GaN films implanted with Co, Mn, Fe and Cr and annealed at 700 °C were studied. The amount of increase in the series resistance of TM implanted and annealed p-GaN films can be reduced for samples with higher Mg doping and higher Mg acceptor activation efficiency. This is of primary importance for practical use in fabricating GaN spin-LEDs by TM ion implantation into the top p-GaN layer of a spin-LED structure involving injection from GaMnN into a InGaN MQW structure. The Fermi level after the implantation of these TM elements into p-GaN is found not to be shifted far away from the Mg acceptors band where it is pinned in the virgin samples. The main deep defects generated by implantation are found to be the 0.3 eV hole traps and the 0.9 eV hole traps as in the case of p-GaN samples heavily implanted with protons.In practical terms it is found that for fabricating GaN-based spin-LEDs by implantation of TM ions the best results should be expected for the Cr implantation which has also been shown to produce the highest Curie temperature (>350 K in p-GaN,by both implantation or MBE growth).

  12. Nanoscale Skyrmions in a Nonchiral Metallic Multiferroic: Ni2MnGa

    DOE PAGES

    Phatak, Charudatta; Heinonen, Olle; De Graef, Marc; ...

    2016-05-17

    Magnetic skyrmions belong to a set of topologically nontrivial spin textures at the nanoscale that have received increased attention due to their emergent behavior and novel potential spintronic applications. Discovering materials systems that can host skyrmions at room temperature in the absence of external magnetic field is of crucial importance not only from a fundamental aspect, but also from a technological point of view. So far, the observations of skyrmions in bulk metallic ferromagnets have been limited to low temperatures and to materials that exhibit strong chiral interactions. In this paper, we show the formation of nanoscale skyrmions in amore » nonchiral multiferroic material, which is ferromagnetic and ferroelastic, Ni2MnGa at room temperature without the presence of external magnetic fields. By using Lorentz transmission electron microscopy in combination with micromagnetic simulations, we elucidate their formation, behavior, and stability under applied magnetic fields at room temperature. Finally, the formation of skyrmions in a multiferroic material with no broken inversion symmetry presents new exciting opportunities for the exploration of the fundamental physics of topologically nontrivial spin textures.« less

  13. Nanoscale Skyrmions in a Nonchiral Metallic Multiferroic: Ni2MnGa

    SciTech Connect

    Phatak, Charudatta; Heinonen, Olle; De Graef, Marc; Petford-Long, Amanda

    2016-05-17

    Magnetic skyrmions belong to a set of topologically nontrivial spin textures at the nanoscale that have received increased attention due to their emergent behavior and novel potential spintronic applications. Discovering materials systems that can host skyrmions at room temperature in the absence of external magnetic field is of crucial importance not only from a fundamental aspect, but also from a technological point of view. So far, the observations of skyrmions in bulk metallic ferromagnets have been limited to low temperatures and to materials that exhibit strong chiral interactions. In this paper, we show the formation of nanoscale skyrmions in a nonchiral multiferroic material, which is ferromagnetic and ferroelastic, Ni2MnGa at room temperature without the presence of external magnetic fields. By using Lorentz transmission electron microscopy in combination with micromagnetic simulations, we elucidate their formation, behavior, and stability under applied magnetic fields at room temperature. Finally, the formation of skyrmions in a multiferroic material with no broken inversion symmetry presents new exciting opportunities for the exploration of the fundamental physics of topologically nontrivial spin textures.

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

    SciTech Connect

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

    2015-07-15

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

  15. Fabrication of full-color GaN-based light-emitting diodes on nearly lattice-matched flexible metal foils.

    PubMed

    Kim, Hyeryun; Ohta, Jitsuo; Ueno, Kohei; Kobayashi, Atsushi; Morita, Mari; Tokumoto, Yuki; Fujioka, Hiroshi

    2017-05-18

    GaN-based light-emitting diodes (LEDs) have been widely accepted as highly efficient solid-state light sources capable of replacing conventional incandescent and fluorescent lamps. However, their applications are limited to small devices because their fabrication process is expensive as it involves epitaxial growth of GaN by metal-organic chemical vapor deposition (MOCVD) on single crystalline sapphire wafers. If a low-cost epitaxial growth process such as sputtering on a metal foil can be used, it will be possible to fabricate large-area and flexible GaN-based light-emitting displays. Here we report preparation of GaN films on nearly lattice-matched flexible Hf foils using pulsed sputtering deposition (PSD) and demonstrate feasibility of fabricating full-color GaN-based LEDs. It was found that introduction of low-temperature (LT) grown layers suppressed the interfacial reaction between GaN and Hf, allowing the growth of high-quality GaN films on Hf foils. We fabricated blue, green, and red LEDs on Hf foils and confirmed their normal operation. The present results indicate that GaN films on Hf foils have potential applications in fabrication of future large-area flexible GaN-based optoelectronics.

  16. Intermixing at the absorber-buffer layer interface in thin-film solar cells: The electronic effects of point defects in Cu(In,Ga)(Se,S){sub 2} and Cu{sub 2}ZnSn(Se,S){sub 4} devices

    SciTech Connect

    Varley, J. B.; Lordi, V.

    2014-08-14

    We investigate point defects in the buffer layers CdS and ZnS that may arise from intermixing with Cu(In,Ga)(S,Se){sub 2} (CIGS) or Cu{sub 2}ZnSn(S,Se){sub 4} (CZTS) absorber layers in thin-film photovoltaics. Using hybrid functional calculations, we characterize the electrical and optical behavior of Cu, In, Ga, Se, Sn, Zn, Na, and K impurities in the buffer. We find that In and Ga substituted on the cation site act as shallow donors in CdS and tend to enhance the prevailing n-type conductivity at the interface facilitated by Cd incorporation in CIGS, whereas they are deep donors in ZnS and will be less effective dopants. Substitutional In and Ga can favorably form complexes with cation vacancies (A-centers) which may contribute to the “red kink” effect observed in some CIGS-based devices. For CZTS absorbers, we find that Zn and Sn defects substituting on the buffer cation site are electrically inactive in n-type buffers and will not supplement the donor doping at the interface as in CIGS/CdS or ZnS devices. Sn may also preferentially incorporate on the S site as a deep acceptor in n-type ZnS, which suggests possible concerns with absorber-related interfacial compensation in CZTS devices with ZnS-derived buffers. Cu, Na, and K impurities are found to all have the same qualitative behavior, most favorably acting as compensating acceptors when substituting on the cation site. Our results suggest one beneficial role of K and Na incorporation in CIGS or CZTS devices is the partial passivation of vacancy-related centers in CdS and ZnS buffers, rendering them less effective interfacial hole traps and recombination centers.

  17. Modification of opto-electronic properties of ZnO by incorporating metallic tin for buffer layer in thin film solar cells

    SciTech Connect

    Deepu, D. R.; Jubimol, J.; Kartha, C. Sudha; Louis, Godfrey; Vijayakumar, K. P.; Kumar, K. Rajeev

    2015-06-24

    In this report, the effect of incorporation of metallic tin (Sn) on opto-electronic properties of ZnO thin films is presented. ZnO thin films were deposited through ‘automated chemical spray pyrolysis’ (CSP) technique; later different quantities of ‘Sn’ were evaporated on it and subsequently annealed. Vacuum annealing showed a positive effect on crystallinity of films. Creation of sub band gap levels due to ‘Sn’ diffusion was evident from the absorption and PL spectra. The tin incorporated films showed good photo response in visible region. Tin incorporated ZnO thin films seem to satisfy the desirable criteria for buffer layer in thin film solar cells.

  18. Annealing behaviors of vacancy-type defects near interfaces between metal contacts and GaN probed using a monoenergetic positron beam

    SciTech Connect

    Uedono, Akira Yoshihara, Nakaaki; Fujishima, Tatsuya; Piedra, Daniel; Palacios, Tomás; Ishibashi, Shoji; Sumiya, Masatomo; Laboutin, Oleg; Johnson, Wayne

    2014-08-04

    Vacancy-type defects near interfaces between metal contacts and GaN grown on Si substrates by metal organic chemical vapor deposition have been studied using a monoenergetic positron beam. Measurements of Doppler broadening spectra of the annihilation radiation for Ti-deposited GaN showed that optically active vacancy-type defects were introduced below the Ti/GaN interface after annealing at 800 °C. Charge transition of those defects due to electron capture was observed and was found to correlate with a yellow band in the photoluminescence spectrum. The major defect species was identified as vacancy clusters such as three to five Ga-vacancies coupled with multiple nitrogen-vacancies. The annealing behaviors of vacancy-type defects in Ti-, Ni-, and Pt-deposited GaN were also examined.

  19. Electrical characteristics and thermal stability of HfO{sub 2} metal-oxide-semiconductor capacitors fabricated on clean reconstructed GaSb surfaces

    SciTech Connect

    Miyata, Noriyuki Mori, Takahiro; Yasuda, Tetsuji; Ohtake, Akihiro; Ichikawa, Masakazu

    2014-06-09

    HfO{sub 2}/GaSb interfaces fabricated by high-vacuum HfO{sub 2} deposition on clean reconstructed GaSb surfaces were examined to explore a thermally stable GaSb metal-oxide-semiconductor structure with low interface-state density (D{sub it}). Interface Sb-O bonds were electrically and thermally unstable, and post-metallization annealing at temperatures higher than 200 °C was required to stabilize the HfO{sub 2}/GaSb interfaces. However, the annealing led to large D{sub it} in the upper-half band gap. We propose that the decomposition products that are associated with elemental Sb atoms act as interface states, since a clear correlation between the D{sub it} and the Sb coverage on the initial GaSb surfaces was observed.

  20. Temperature dependence of trapping effects in metal gates/Al2O3/InGaAs stacks

    NASA Astrophysics Data System (ADS)

    Palumbo, F.; Pazos, S.; Aguirre, F.; Winter, R.; Krylov, I.; Eizenberg, M.

    2017-06-01

    The influence of the temperature on Metal Gate/Al2O3/n-InGaAs stacks has been studied by means of capacitance-voltage (C-V) hysteresis and flat band voltage as function of both negative and positive stress fields. It was found that the de-trapping effect decreases at low-temperature, indicating that the de-trapping of trapped electrons from oxide traps may be performed via Al2O3/InGaAs interface defects. The dependence of the C-V hysteresis on the stress field at different temperatures in our InGaAs stacks can be explained in terms of the defect spatial distribution. An oxide defect distribution can be found very close to the metal gate/Al2O3 interface. On the other side, the Al2O3/InGaAs interface presents defects distributed from the interface into the bulk of the oxide, showing the influence of InGaAs on Al2O3 in terms of the spatial defect distribution. At the present, he is a research staff of the National Council of Science and Technology (CONICET), working in the National Commission of Atomic Energy (CNEA) in Buenos Aires, Argentina, well embedded within international research collaboration. Since 2008, he is Professor at the National Technological University (UTN) in Buenos Aires, Argentina. Dr. Palumbo has received research fellowships from: Marie Curie Fellowship within the 7th European Community Framework Programme, Abdus Salam International Centre for Theoretical Physics (ICTP) Italy, National Council of Science and Technology (CONICET) Argentina, and Consiglio Nazionale delle Ricerche (CNR) Italy. He is also a frequent scientific visitor of academic institutions as IMM-CNR-Italy, Minatec Grenoble-France, the Autonomous University of Barcelona-Spain, and the Israel Institute of Technology-Technion. He has authored and co-authored more than 50 papers in international conferences and journals.

  1. Process dependency on threshold voltage of GaN MOSFET on AlGaN/GaN heterostructure

    NASA Astrophysics Data System (ADS)

    Wang, Qingpeng; Jiang, Ying; Miyashita, Takahiro; Motoyama, Shin-ichi; Li, Liuan; Wang, Dejun; Ohno, Yasuo; Ao, Jin-Ping

    2014-09-01

    GaN metal-oxide-semiconductor field-effect transistors (MOSFETs) with recessed gate on AlGaN/GaN heterostructure are reported in which the drain and source ohmic contacts were fabricated on the AlGaN/GaN heterostructure and the electron channel was formed on the GaN buffer layer by removing the AlGaN barrier layer. Negative threshold voltages were commonly observed in all devices. To investigate the reasons of the negative threshold voltages, different oxide thickness, etching gas and bias power of inductively-coupled plasma (ICP) system were utilized in the fabrication process of the GaN MOSFETs. It is found that positive charges of around 1 × 1012 q/cm2 exist near the interface at the just threshold condition in both silane- and tetraethylorthosilicate (TEOS)-based devices. It is also found that the threshold voltages do not obviously change with the different etching gas (SiCl4, BCl3 and two-step etching of SiCl4/Cl2) at the same ICP bias power level (20-25 W) and will become deeper when higher bias power is used in the dry recess process which may be related to the much serious ion bombardment damage. Furthermore, X-ray photoelectron spectroscopy (XPS) experiments were done to investigate the surface conditions. It is found that N 1s peaks become lower with higher bias power of the dry etching process. Also, silicon contamination was found and could be removed by HNO3/HF solution. It indicates that the nitrogen vacancies are mainly responsible for the negative threshold voltages rather than the silicon contamination. It demonstrates that optimization of the ICP recess conditions and improvement of the surface condition are still necessary to realize enhancement-mode GaN MOSFETs on AlGaN/GaN heterostructure.

  2. Unexpected bismuth concentration profiles in metal-organic vapor phase epitaxy-grown Ga(As{sub 1−x}Bi{sub x})/GaAs superlattices revealed by Z-contrast scanning transmission electron microscopy imaging

    SciTech Connect

    Wood, A. W.; Babcock, S. E.; Guan, Y.; Forghani, K.; Anand, A.; Kuech, T. F.

    2015-03-01

    A set of GaAs{sub 1−x}Bi{sub x}/GaAs multilayer quantum-well structures was deposited by metal-organic vapor phase epitaxy at 390 °C and 420 °C. The precursor fluxes were introduced with the intent of growing discrete and compositionally uniform GaAs{sub 1−x}Bi{sub x} well and GaAs barrier layers in the epitaxial films. High-resolution high-angle annular-dark-field (or “Z-contrast”) scanning transmission electron microscopy imaging revealed concentration profiles that were periodic in the growth direction, but far more complicated in shape than the intended square wave. The observed composition profiles could explain various reports of physical properties measurements that suggest compositional inhomogeneity in GaAs{sub 1−x}Bi{sub x} alloys as they currently are grown.

  3. Preparation of AlGaN/GaN Heterostructures on Sapphire Using Light Radiation Heating Metal-Organic Chemical Vapor Deposition at Low Pressure

    NASA Astrophysics Data System (ADS)

    Zhou, Yu-Gang; Shen, Bo; Zhang, Rong; Li, Wei-Ping; Chen, Peng; Chen, Zhi-Zhong; Gu, Shu-Lin; Shi, Yi; Z, Huang C.; Zheng, You-Dou

    2000-08-01

    AlGaN/GaN heterostructures on sapphire substrate were fabricated by using light radiation heating metalorganic chemical vapor deposition. Photoluminescence excitation spectra show that there are two abrupt slopes corresponding to the absorption edges of AlGaN and GaN, respectively. X-ray diffraction spectra clearly exhibit the GaN (0002), (0004), and AlGaN (0002), (0004) diffraction peaks, and no diffraction peak other than those from the GaN {0001} and AlGaN {0001} planes is found. Reciprocal space mapping indicates that there is no tilt between the AlGaN layer and the GaN layer. All results also indicate that the sample is of sound quality and the Al composition in the AlGaN layer is of high uniformity.

  4. Self-assembled growth and structural analysis of inclined GaN nanorods on nanoimprinted m-sapphire using catalyst-free metal-organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Lee, Kyuseung; Chae, Sooryong; Jang, Jongjin; Min, Daehong; Kim, Jaehwan; Nam, Okhyun

    2016-04-01

    In this study, self-assembled inclined (1-10-3)-oriented GaN nanorods (NRs) were grown on nanoimprinted (10-10) m-sapphire substrates using catalyst-free metal-organic chemical vapor deposition. According to X-ray phi-scans, the inclined GaN NRs were tilted at an angle of ˜57.5° to the [10-10]sapp direction. Specifically, the GaN NRs grew in a single inclined direction to the [11-20]sapp. Uni-directionally inclined NRs were formed through the one-sided (10-11)-faceted growth of the interfacial a-GaN plane layer. It was confirmed that a thin layer of a-GaN was formed on r-facet nanogrooves of the m-sapphire substrate by nitridation. The interfacial a-GaN nucleation affected both the inclined angle and the growth direction of the inclined GaN NRs. Using X-ray diffraction and selective area electron diffraction, the epitaxial relationship between the inclined (1-10-3) GaN NRs and interfacial a-GaN layer on m-sapphire substrates was systematically investigated. Moreover, the inclined GaN NRs were observed to be mostly free of stacking fault-related defects using high-resolution transmission electron microscopy.

  5. Self-assembled growth and structural analysis of inclined GaN nanorods on nanoimprinted m-sapphire using catalyst-free metal-organic chemical vapor deposition

    SciTech Connect

    Lee, Kyuseung; Chae, Sooryong; Jang, Jongjin; Min, Daehong; Kim, Jaehwan; Nam, Okhyun

    2016-04-15

    In this study, self-assembled inclined (1-10-3)-oriented GaN nanorods (NRs) were grown on nanoimprinted (10-10) m-sapphire substrates using catalyst-free metal-organic chemical vapor deposition. According to X-ray phi-scans, the inclined GaN NRs were tilted at an angle of ∼57.5° to the [10-10]{sub sapp} direction. Specifically, the GaN NRs grew in a single inclined direction to the [11-20]{sub sapp}. Uni-directionally inclined NRs were formed through the one-sided (10-11)-faceted growth of the interfacial a-GaN plane layer. It was confirmed that a thin layer of a-GaN was formed on r-facet nanogrooves of the m-sapphire substrate by nitridation. The interfacial a-GaN nucleation affected both the inclined angle and the growth direction of the inclined GaN NRs. Using X-ray diffraction and selective area electron diffraction, the epitaxial relationship between the inclined (1-10-3) GaN NRs and interfacial a-GaN layer on m-sapphire substrates was systematically investigated. Moreover, the inclined GaN NRs were observed to be mostly free of stacking fault-related defects using high-resolution transmission electron microscopy.

  6. Realization of improved metallization-Ti/Al/Ti/W/Au ohmic contacts to n-GaN for high temperature application

    NASA Astrophysics Data System (ADS)

    Motayed, A.; Davydov, A. V.; Boettinger, W. J.; Josell, D.; Shapiro, A. J.; Levin, I.; Zheleva, T.; Harris, G. L.

    2005-05-01

    Tungsten metal layer was used for the first time as an effective diffusion barrier for the standard Ti/Al/Ti/Au ohmic metallization scheme to obtain thermally stable ohmic contact suitable for high temperature applications. Comparative studies were performed on three distinct metallization schemes: 1) standard GaN/Ti/Al/Ti/Au, 2) GaN/Ti/Al/W/Au, and 3) GaN/Ti/Al/Ti/W/Au. For the GaN with doping level of 5 × 1017 cm-3, the lowest specific contact resistance for the Ti/Al/Ti/W/Au metallization scheme annealed in argon at 750 °C for 30 sec was 5 × 10-6 .cm2, which is comparable to the standard Ti/Al/Ti/Au scheme. X-ray diffractions (XRD), auger electron spectroscopy (AES) depth profiling, field-emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), and cross-sectional transmission electron microscopy (TEM) revealed that the Ti/Al/Ti/W/Au metallization has superior morphology and microstructural properties compared to standard Ti/Al/Ti/Au metallizations. Remarkably, this metallization was able to withstand thermal aging at 500 °C for 50 hrs with only marginal morphological and electrical deterioration. These studies revealed that the utilization of a compound diffusion barrier stack, as in the Ti/Al/Ti/W/Au metallization, yields electrically, structurally, and morphologically superior metallizations with exceptional thermal stability.

  7. Growth of GaN epitaxial films on polycrystalline diamond by metal-organic vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    Jiang, Quanzhong; Allsopp, Duncan W. E.; Bowen, Chris R.

    2017-04-01

    Heat extraction is often essential in ensuring efficient performance of semiconductor devices and requires minimising the thermal resistance between the functional semiconductor layers and any heat sink. This paper reports the epitaxial growth of N-polar GaN films on polycrystalline diamond substrates of high thermal conductivity with metal-organic vapor phase epitaxy, by using a Si x C layer formed during deposition of polycrystalline diamond on a silicon substrate. The Si x C layer acts to provide the necessary structure ordering information for the formation of a single crystal GaN film at the wafer scale. It is shown that a three-dimensional island (3D) growth process removes hexagonal defects that are induced by the non-single crystal nature of the Si x C layer. It is also shown that intensive 3D growth and the introduction of a convex curvature of the substrate can be deployed to reduce tensile stress in the GaN epitaxy to enable the growth of a crack-free layer up to a thickness of 1.1µm. The twist and tilt can be as low as 0.65° and 0.39° respectively, values broadly comparable with GaN grown on Si substrates with a similar structure.

  8. Detecting the Photoexcited Carrier Distribution Across GaAs/Transition Metal Oxide Interfaces by Coherent Longitudinal Acoustic Phonons.

    PubMed

    Pollock, Kevin L; Doan, Hoang Q; Rustagi, Avinash; Stanton, Christopher J; Cuk, Tanja

    2017-03-02

    A prominent architecture for solar energy conversion layers diverse materials, such as traditional semiconductors (Si, III-V) and transition metal oxides (TMOs), into a monolithic device. The efficiency with which photoexcited carriers cross each layer is critical to device performance and dependent on the electronic properties of a heterojunction. Here, by time-resolved changes in the reflectivity after excitation of an n-GaAs/p-GaAs/TMO (Co3O4, IrO2) device, we detect a photoexcited carrier distribution specific to the p-GaAs/TMO interface through its coupling to phonons in both materials. The photoexcited carriers generate two coherent longitudinal acoustic phonons (CLAPs) traveling in opposite directions, one into the TMO and the other into the p-GaAs. This is the first time a CLAP is reported to originate at a semiconductor/TMO heterojunction. Therefore, these experiments seed future modeling of the built-in electric fields, the internal Fermi level, and the photoexcited carrier density of semiconductor/TMO interfaces within multilayered heterostructures.

  9. Investigation of stress induced interface states in Al2O3/InGaAs metal-oxide-semiconductor capacitors

    NASA Astrophysics Data System (ADS)

    Palumbo, F.; Winter, R.; Tang, K.; McIntyre, P. C.; Eizenberg, M.

    2017-05-01

    Implementation of high-k dielectrics on InGaAs for CMOS technology requires capabilities to predict long-time degradation and the impact of process changes on degradation processes. In this work, the degradation under constant voltage stress of metal gate/Al2O3/InGaAs stacks is studied for n-type and p-type As2 passivated InGaAs substrates. The results show that the degradation for both positive bias and negative bias did not produce Al2O3 oxide traps, while the distribution of interface states increased. In particular, the distribution of interface states, calculated by the distributed impedance equivalent circuit model, increased significantly after positive bias stress regardless of the doping type of the substrate. The injection of carriers from the semiconductor conduction band into the gate dielectric enhanced the generation of interface states but not the generation of oxide traps, suggesting that the interfacial degradation is related primarily to the InGaAs surface and not to the oxide layer.

  10. Studies of polycrystalline n-GaAs junctions: effects of metal ion chemisorption on the photoelectrochemical properties of n-GaAs/KOH-Se/sup -/2-/, n-GaAs/CH/sub 3/CH-ferrocene/sup +/0/, and n-GaAs/Au interfaces

    SciTech Connect

    Lunt, S.R.; Casagrande, L.G.; Tufts, B.J.; Lewis, N.S.

    1988-10-06

    Current-voltage and spectral response properties were determined for polycrystalline n-GaAs photoanodes in contact with aqueous KOH-Se/sup -2/-/ and nonaqueous CH/sub 3/CN-ferrocene/sup +/0/-LiClO/sub 4/ electrolytes. The n-GaAs/KOH-Se/sup -/2-/ system initially exhibited poor junction behavior, but chemisorption of Ru/sup III/, Rh/sup III/, Ir/sup III/, Co/sup III/, or Os/sup III/ ions onto the GaAs photoanode was found to yield improved I-V properties. The trend in I-V improvement correlated with improved electrocatalysis of Se/sup 2/minus// oxidation at p-GaAs, N/sup +/-GaAs, and In/sub 2/O/sub 3/ electrode surfaces. The n-GaAs/CH/sub 3/CH system displayed excellent junction behavior and did not respond to metal chemisorption treatments. These results are consistent with the metal-ion-induced improvements being predominantly due to electrocatalytic effects.

  11. GaAs Photovoltaics on Polycrystalline Ge Substrates

    NASA Technical Reports Server (NTRS)

    Wilt, David M.; Pal, AnnaMaria T.; McNatt, Jeremiah S.; Wolford, David S.; Landis, Geoffrey A.; Smith, Mark A.; Scheiman, David; Jenkins, Phillip P.; McElroy Bruce

    2007-01-01

    High efficiency III-V multijunction solar cells deposited on metal foil or even polymer substrates can provide tremendous advantages in mass and stowage, particularly for planetary missions. As a first step towards that goal, poly-crystalline p/i/n GaAs solar cells are under development on polycrystalline Ge substrates. Organo Metallic Vapor Phase Epitaxy (OMVPE) parameters for pre-growth bake, nucleation and deposition have been examined. Single junction p/i/n GaAs photovoltaic devices, incorporating InGaP front and back window layers, have been grown and processed. Device performance has shown a dependence upon the thickness of a GaAs buffer layer deposited between the Ge substrate and the active device structure. A thick (2 m) GaAs buffer provides for both increased average device performance as well as reduced sensitivity to variations in grain size and orientation. Illumination under IR light (lambda > 1 micron), the cells showed a Voc, demonstrating the presence of an unintended photoactive junction at the GaAs/Ge interface. The presence of this junction limited the efficiency to approx.13% (estimated with an anti-refection coating) due to the current mismatch and lack of tunnel junction interconnect.

  12. Impact of Interface Roughness on the Metallic Transport of Strongly Correlated 2D Holes in GaAs Quantum Wells

    NASA Astrophysics Data System (ADS)

    Goble, Nicholas; Watson, John; Manfra, Michael; Gao, Xuan

    2014-03-01

    Understanding the non-monotonic behavior in the temperature dependent resistance, R(T) , of strongly correlated two-dimensional (2D) carriers in clean semiconductors has been a central issue in the studies of 2D metallic states and metal-insulator transitions. We have studied the transport of high mobility 2D holes in 20nm wide GaAs quantum wells with varying interface roughness by changing the Al fraction x in the AlxGa1-xAs barrier. Prior to this work, no comprehensive study of the non-monotonic resistance peak against controlled barrier characteristics has been conducted. We show that the shape of the electronic contribution to R(T) is qualitatively unchanged throughout all of our measurements, regardless of the percentage of Al in the barrier. It is observed that increasing x or short range interface roughness suppresses both the strength and characteristic temperature scale of the 2D metallicity, pointing to the distinct role of short range versus long range disorder in the 2D metallic transport in this 2D hole system with interaction parameter rs ~ 20. N.G. acknowledges the US DOE GAANN fellowship (P200A090276 & P200A070434). M.J.M. is supported by the Miller Family Foundation and the US DOE, Office of Basic Energy Sciences, DMS (DE-SC0006671). X.P.A.G thanks the NSF for funding support (DMR-0906415).

  13. Practical realization of deeply subwavelength multilayer metal-dielectric nanostructures based on InGaAsP (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Smalley, Joseph S. T.; Vallini, Felipe; Montoya, Sergio; Fullerton, Eric E.; Fainman, Yeshaiahu

    2015-09-01

    Using established nanofabrication techniques, we realize deeply subwavelength multilayer metal-dielectric nanostructures composed of silver and indium gallium arsenide phosphide (InGaAsP). In contrast to most, if not all, subwavelength multilayer metal-dielectric systems to date, the Bloch vector of the fabricated structure is parallel to the plane of the substrate, making it suitable for waveguide integration. InGaAsP multiple quantum wells (MQWs) are epitaxially grown on InP normal to the Bloch vector of the resulting multilayer. The associated carrier population of the MQWs allows for active control of the behavior of the nanostructure via external optical pumping. Individual layer thicknesses of 30nm are repeatedly achieved via electron-beam lithography, reactive ion etching of InGaAsP, and sputter deposition of silver. Resulting 60nm periods of the one-dimensional periodic structure are 25 times smaller than telecommunication wavelengths in vacuum. The realized multilayer nanostructures hold promise as a platform for active and tunable hyperbolic metamaterials at telecommunication frequencies.

  14. The impact of the surface on step-bunching and diffusion of Ga on GaAs (001) in metal-organic vapour phase epitaxy

    NASA Astrophysics Data System (ADS)

    Pristovsek, Markus; Poser, Florian; Richter, Wolfgang

    2016-07-01

    We studied diffusion by measuring step-bunching, island spacing, and the transition from step-flow growth to two-dimensional island growth of (001) GaAs in metal-organic vapour phase epitaxy and correlated them with the surface reconstruction measured by reflectance anisotropy spectroscopy. The V/III ratio had a small effect, while the square root of the growth rate was anti-proportional to the diffusion length. The thermal activation energy was about 2.3 eV on {{c}}(4× 4) terraces and 1.6 eV on (2× 4) domains at higher temperatures. Pronounced step-bunching coincided with large (4× 2) domains at the step-edges, causing smoother steps for the [11̅0] misorientation. This Ga-rich reconstruction at the step-edges is needed for the Schwoebel barrier to induce step-bunching. At higher temperatures of (2× 4) domains grow in size, the Schwoebel barrier reduces and nucleation becomes easier on this surface which reduces diffusion length and thus step-bunching.

  15. Low-frequency noise in AlTiO/AlGaN/GaN metal-insulator-semiconductor heterojunction field-effect transistors

    SciTech Connect

    Le, Son Phuong; Ui, Toshimasa; Nguyen, Tuan Quy; Shih, Hong-An; Suzuki, Toshi-kazu

    2016-05-28

    Using aluminum titanium oxide (AlTiO, an alloy of Al{sub 2}O{sub 3} and TiO{sub 2}) as a high-k gate insulator, we fabricated and investigated AlTiO/AlGaN/GaN metal-insulator-semiconductor heterojunction field-effect transistors. From current low-frequency noise (LFN) characterization, we find Lorentzian spectra near the threshold voltage, in addition to 1/f spectra for the well-above-threshold regime. The Lorentzian spectra are attributed to electron trapping/detrapping with two specific time constants, ∼25 ms and ∼3 ms, which are independent of the gate length and the gate voltage, corresponding to two trap level depths of 0.5–0.7 eV with a 0.06 eV difference in the AlTiO insulator. In addition, gate leakage currents are analyzed and attributed to the Poole-Frenkel mechanism due to traps in the AlTiO insulator, where the extracted trap level depth is consistent with the Lorentzian LFN.

  16. The compositional, structural, and magnetic properties of a Fe3O4/Ga2O3/GaN spin injecting hetero-structure grown by metal-organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Xu, Zhonghua; Huang, Shimin; Tang, Kun; Gu, Shulin; Zhu, Shunming; Ye, Jiandong; Xu, Mingxiang; Wang, Wei; Zheng, Youdou

    2016-12-01

    In this article, the authors have designed and fabricated a Fe3O4/Ga2O3/GaN spin injecting hetero-structure by metal-organic chemical vapor deposition. The compositional, structural, and magnetic properties of the hetero-structure have been characterized and discussed. From the characterizations, the hetero-structure has been successfully grown generally. However, due to the unintentional diffusion of Ga ions from Ga2O3/GaN layers, the most part of the nominal Fe3O4 layer is actually in the form of GaxFe3-xO4 with gradually decreased x values from the Fe3O4/Ga2O3 interface to the Fe3O4 surface. Post-annealing process can further aggravate the diffusion. Due to the similar ionic radius of Ga and Fe, the structural configuration of the GaxFe3-xO4 does not differ from that of pure Fe3O4. However, the ferromagnetism has been reduced with the incorporation of Ga into Fe3O4, which has been explained by the increased Yafet-Kittel angles in presence of considerable amount of Ga incorporation. A different behavior of the magnetoresistance has been found on the as-grown and annealed samples, which could be modelled and explained by the competition between the spin-dependent and spin-independent conduction channels. This work has provided detailed information on the interfacial properties of the Fe3O4/Ga2O3/GaN spin injecting hetero-structure, which is the solid basis for further improvement and application of the structure.

  17. Metal ion displacements in noncentrosymmetric chalcogenides La3Ga1.67S7, La3Ag0.6GaCh7 (Ch=S, Se), and La3MGaSe7 (M=Zn, Cd)

    NASA Astrophysics Data System (ADS)

    Iyer, Abishek K.; Yin, Wenlong; Rudyk, Brent W.; Lin, Xinsong; Nilges, Tom; Mar, Arthur

    2016-11-01

    The quaternary Ga-containing chalcogenides La3Ag0.6GaS7, La3Ag0.6GaSe7, La3ZnGaSe7, and La3CdGaSe7, as well as the related ternary chalcogenide La3Ga1.67S7, were prepared by reactions of the elements at 950 °C. They adopt noncentrosymmetric hexagonal structures (space group P63, Z=2) with cell parameters (a=10.2 Å, c=6.1 Å for the sulfides; a=10.6 Å, c=6.4 Å for the selenides) that are largely controlled by the geometrical requirements of one-dimensional stacks of Ga-centered tetrahedra separated by the La atoms. Among these compounds, which share the common formulation La3M1-xGaCh7 (M=Ga, Ag, Zn, Cd; Ch=S, Se), the M atoms occupy sites within a stacking of trigonal antiprisms formed by Ch atoms. The location of the M site varies between extremes with trigonal antiprismatic (CN6) and trigonal planar (CN3) geometry. Partial occupation of these sites and intermediate ones accounts for the considerable versatility of these structures and the occurrence of large metal displacement parameters. The site occupations can be understood in a simple way as being driven by the need to satisfy appropriate bond valence sums for both the M and Ch atoms. Band structure calculations rationalize the substoichiometry observed in the Ag-containing compounds (La3Ag0.6GaS7, La3Ag0.6GaSe7) as a response to overbonding. X-ray photoelectron spectroscopy supports the presence of monovalent Ag atoms in these compounds, which are not charge-balanced.

  18. Influence of metal deposition on exciton-surface plasmon polariton coupling in GaAs/AlAs/GaAs core-shell nanowires studied with time-resolved cathodoluminescence.

    PubMed

    Estrin, Yevgeni; Rich, Daniel H; Kretinin, Andrey V; Shtrikman, Hadas

    2013-04-10

    The coupling of excitons to surface plasmon polaritons (SPPs) in Au- and Al-coated GaAs/AlAs/GaAs core-shell nanowires, possessing diameters of ~100 nm, was probed using time-resolved cathodoluminescence (CL). Excitons were generated in the metal coated nanowires by injecting a pulsed high-energy electron beam through the thin metal films. The Purcell enhancement factor (FP) was obtained by direct measurement of changes in the temperature-dependent radiative lifetime caused by the nanowire exciton-SPP coupling and compared with a model that takes into account the dependence of FP on the distance from the metal film and the thickness of the film covering the GaAs nanowires.

  19. Cu(In,Ga)Se2 Thin Film Preparation from a Cu(In,Ga) Metallic Alloy and Se Nanoparticles by an Intense Pulsed Light Technique

    NASA Astrophysics Data System (ADS)

    Dhage, Sanjay R.; Kim, Hak-Sung; Hahn, H. Thomas

    2011-02-01

    The main contribution of this paper is the development of a novel process for the formation of copper indium gallium diselenide (CIGS) films. CIGS films with a thickness of 4 μm and grain size from 0.3 μm to 1 μm were prepared from a Cu(In0.7Ga0.3) (CIG) metallic alloy and Se nanoparticles by the intense pulsed light (IPL) technique. The melting of the CIG and Se nanoparticles and nucleation of CIGS occurred in a very short reaction time of 2 ms. It is believed that the Se diffuses into the CIG lattice to form the CIGS chalcopyrite crystal structure. The tetragonal chalcopyrite crystal structure was confirmed by x-ray powder diffraction (XRD), while the microstructure and composition were determined by field-emission scanning electron microscopy (FESEM), energy-dispersive x-ray spectroscopy (EDAX), and x-ray fluorescence (XRF) spectroscopy.

  20. First principles study on half-metallic properties of Heusler compounds Ti2VZ (Z=Al, Ga, and In)

    NASA Astrophysics Data System (ADS)

    Galehgirian, S.; Ahmadian, F.

    2015-01-01

    First principles calculations using the self-consistent full-potential linearized augmented plane wave (FPLAPW) method in the framework of density functional theory (DFT) were performed to study the electronic structures and magnetic properties of new full-Heusler compounds Ti2VZ (Z=Al, Ga, and In). Electronic structure calculations showed that Ti2VZ (Z=Al, Ga, and In) compounds in AlCu2Mn-type are conventional ferrimagnets. The Ti2VAl, Ti2VGa, and Ti2VIn compounds in the CuHg2Ti-type structure have half-metallic characteristics with a respective majority band gap of 0.52, 0.51, and 0.59 eV at the equilibrium lattice parameter. The origin of half-metallicity in these compounds was also discussed. The total magnetic moments of Ti2VZ (Z=Al, Ga, and In) compounds in the CuHg2Ti-type structures were 2 μB per formula unit which were in agreement with Slater-Pauling rule (Mtot=18-Ztot). The Ti2VAl, Ti2VGa, and Ti2VIn compounds in the CuHg2Ti-type structure respectively showed half-metallic characteristics at lattice constants ranges of 6.12-7.17 Å, 5.99-7.12 Å, and 6.31-7.06 Å, indicating the lattice distortion did not affect the half-metallic properties of these compounds which makes them interesting materials in the spintronics field.

  1. Assessment of a metal-organic framework catalyst in air cathode microbial fuel cells over time with different buffers and solutions.

    PubMed

    Rossi, Ruggero; Yang, Wulin; Setti, Leonardo; Logan, Bruce E

    2017-06-01

    Metal-organic framework (MOF) on activated carbon (AC) enhanced the performance of cathodes but longevity needs to be considered in the presence of metal chelators or ligands, such as phosphate, present in wastewaters. MOF catalysts on AC initially produced 2.78±0.08Wm(-2), but power decreased by 26% after eight weeks in microbial fuel cells using a 50mM phosphate buffer (PBS) and acetate due to decreased cathode performance. However, power was still 41% larger than that of the control AC (no MOF). Power generation using domestic wastewater was initially 0.73±0.01Wm(-2), and decreased by 21% over time, with power 53% larger than previous reports, although changes in wastewater composition were a factor in performance. Adding phosphate salts to the wastewater did not affect the catalyst performance over time. While MOF catalysts are therefore initially adversely affected by chelators, performance remains enhanced compared to plain AC. Copyright © 2017 Elsevier Ltd. All rights reserved.

  2. Monolithic integration of GaN-based light-emitting diodes and metal-oxide-semiconductor field-effect transistors.

    PubMed

    Lee, Ya-Ju; Yang, Zu-Po; Chen, Pin-Guang; Hsieh, Yung-An; Yao, Yung-Chi; Liao, Ming-Han; Lee, Min-Hung; Wang, Mei-Tan; Hwang, Jung-Min

    2014-10-20

    In this study, we report a novel monolithically integrated GaN-based light-emitting diode (LED) with metal-oxide-semiconductor field-effect transistor (MOSFET). Without additionally introducing complicated epitaxial structures for transistors, the MOSFET is directly fabricated on the exposed n-type GaN layer of the LED after dry etching, and serially connected to the LED through standard semiconductor-manufacturing technologies. Such monolithically integrated LED/MOSFET device is able to circumvent undesirable issues that might be faced by other kinds of integration schemes by growing a transistor on an LED or vice versa. For the performances of resulting device, our monolithically integrated LED/MOSFET device exhibits good characteristics in the modulation of gate voltage and good capability of driving injected current, which are essential for the important applications such as smart lighting, interconnection, and optical communication.

  3. Effect of doped substrates on the growth of GaAs nanowires via metal organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Liu, Yan; Peng, Yan; Guo, Jingwei; La, Dongsheng; Xu, Zhaopeng; Wang, Haiyan

    2017-08-01

    Vertical GaAs nanowires were grown on different doped substrates via Metal Organic Chemical Vapor Deposition by catalyst assisted vapor-liquid-solid mechanism. It is found that both n and p type doped substrates affect catalyst distribution during the formation of alloy catalysts. The catalyst density decreases with an increase in the doping concentration of the substrates. In the growth of GaAs nanowires, the growth rate, which is mostly determined by the atoms diffusion from the pyrolysis of precursors on the surface of nanowires and substrates, is proportional to the catalyst densities. Moreover, the structures of as-grown nanowires are all pure zinc blende without any defects. These results will be valuable for the applications of nanowire-based optical and electrical devices.

  4. Synthesis and Nanostructures of Metal Selenide Precursors for Cu(In,Ga)Se2 Thin-Film Solar Cells.

    PubMed

    Cha, Ji-Hyun; Noh, Se Jin; Jung, Duk-Young

    2015-07-20

    A nanoink solution-based process was developed as a low-costing method for the fabrication of Cu(In,Ga)Se2 (CIGSe) thin-film photovoltaic cells. The sonochemical synthesis of CIGSe nanocrystals of the nanoink through step-by-step mixing of the reactants was investigated. To achieve the ideal stoichiometry of Cu(In0.7 Ga0.3 )Se2 to tune the bandgap and to fabricate high-efficiency photovoltaic cells, the synthetic parameters, the concentration of hydrazine, and the amount used of the gallium precursor were investigated. As the hydrazine concentration increased, gallium loss was observed in the CIGSe product. The gallium content in the reactant mixture strongly affected the metal stoichiometry of the prepared CIGSe nanocrystals. The nanoink solution based fabrication of thin-film photovoltaic cells was also explored, and the resulting device showed a conversion efficiency of 5.17 %.

  5. Behavior of W and WSi(x) Contact Metallization on n- and p- Type GaN

    SciTech Connect

    Abernathy, C.R.; Cao, X.A.; Cole, M.W.; Eizenberg, M.; Lothian, J.R.; Pearton, S.J.; Ren, F.; Shul, R.J.; Zeitouny, A.; Zolper, J.C.

    1999-01-05

    Sputter-deposited W-based contacts on p-GaN (N{sub A} {approximately} 10{sup 18} cm{sup {minus}3}) display non-ohmic behavior independent of annealing temperature when measured at 25 C. The transition to ohmic behavior occurs above {approximately} 250 C as more of the acceptors become ionized. The optimum annealing temperature is {approximately} 700 C under these conditions. These contacts are much more thermally stable than the conventional Ni/Au metallization, which shows a severely degraded morphology even at 700 C. W-based contacts may be ohmic as-deposited on very heavily doped n-GaN, and the specific contact resistance improves with annealing up to {approximately} 900 C.

  6. Ultra-thin flexible GaAs photovoltaics in vertical forms printed on metal surfaces without interlayer adhesives

    NASA Astrophysics Data System (ADS)

    Kim, Juho; Hwang, Jeongwoo; Song, Kwangsun; Kim, Namyun; Shin, Jae Cheol; Lee, Jongho

    2016-06-01

    Wearable flexible electronics often require sustainable power sources that are also mechanically flexible to survive the extreme bending that accompanies their general use. In general, thinner microelectronic devices are under less strain when bent. This paper describes strategies to realize ultra-thin GaAs photovoltaics through the interlayer adhesiveless transfer-printing of vertical-type devices onto metal surfaces. The vertical-type GaAs photovoltaic devices recycle reflected photons by means of bottom electrodes. Systematic studies with four different types of solar microcells indicate that the vertical-type solar microcells, at only a quarter of the thickness of similarly designed lateral-type cells, generate a level of electric power similar to that of thicker cells. The experimental results along with the theoretical analysis conducted here show that the ultra-thin vertical-type solar microcells are durable under extreme bending and thus suitable for use in the manufacturing of wearable flexible electronics.

  7. Ultra-thin flexible GaAs photovoltaics in vertical forms printed on metal surfaces without interlayer adhesives

    SciTech Connect

    Kim, Juho; Song, Kwangsun; Kim, Namyun; Lee, Jongho; Hwang, Jeongwoo; Shin, Jae Cheol

    2016-06-20

    Wearable flexible electronics often require sustainable power sources that are also mechanically flexible to survive the extreme bending that accompanies their general use. In general, thinner microelectronic devices are under less strain when bent. This paper describes strategies to realize ultra-thin GaAs photovoltaics through the interlayer adhesiveless transfer-printing of vertical-type devices onto metal surfaces. The vertical-type GaAs photovoltaic devices recycle reflected photons by means of bottom electrodes. Systematic studies with four different types of solar microcells indicate that the vertical-type solar microcells, at only a quarter of the thickness of similarly designed lateral-type cells, generate a level of electric power similar to that of thicker cells. The experimental results along with the theoretical analysis conducted here show that the ultra-thin vertical-type solar microcells are durable under extreme bending and thus suitable for use in the manufacturing of wearable flexible electronics.

  8. HfxAlyO ternary dielectrics for InGaAs based metal-oxide-semiconductor capacitors

    NASA Astrophysics Data System (ADS)

    Krylov, Igor; Ritter, Dan; Eizenberg, Moshe

    2017-07-01

    The electrical properties of HfxAlyO compound dielectric films and the HfxAlyO/InGaAs interface are reported for various dielectric film compositions. Despite the same trimethylaluminum (TMA) pre-deposition treatment, dispersion in accumulation and capacitance-voltage (C-V) hysteresis increased with hafnium content. Different kinds of border traps were identified as being responsible for the phenomena. After anneal, the density of states in the HfxAlyO/InGaAs interface varied quite weakly with dielectric film composition. The optimal composition for obtaining high inversion charge density in metal oxide semiconductor gate stacks is determined by a tradeoff between leakage and dielectric constant, with the optimum atomic cation ratio ([Hf]/[Al]) of ˜1.

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

    DOE PAGES

    Qiao, Q.; Zhang, Y.; Contreras-Guerrero, Rocio; ...

    2015-11-16

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

  10. Effect of process pressure and substrate temperature on CdS buffer layers deposited by using RF sputtering for Cu(In,Ga)Se2 solar cells

    NASA Astrophysics Data System (ADS)

    Choi, Ji Hyun; Jung, Sung Hee; Chung, Chee Won

    2016-02-01

    The characteristics of CdS films deposited on Cu(In,Ga)Se2(CIGS)/Mo/glass and glass substrates by using RF magnetron sputtering were investigated. The deposition pressure and the substrate temperature were selected as key parameters to examine the electrical, compositional and optical properties of the films. As the deposition pressure was increased, the resistivity increased while the carrier concentration decreased owing to a stoichiometric change and Cd-O incorporation at high pressure. Field-emission scanning electron microscopy(FE-SEM) revealed that the CdS films on CIGS/Mo became denser as the pressure was increased, which was responsible for the high transmittance of the film deposited at high pressure. As the substrate temperature was increased, the deposition rate decreased, which could be explained by using Langmuir theory. As the temperature was increased from room temperature to 573 K, the resistivity increased and the carrier concentration decreased, which was attributed to an increase in [S]/[Cd] ratio. In addition, as the temperature was increased, the small grains were agglomerated to form larger grains due to the increase in the activity of grains at high temperature. CdS films were confirmed to be uniformly deposited on the CIGS layer by using RF sputtering. The large amount of interdiffusion between the CIGS and the CdS films deposited at a high substrate temperature were observed by using X-ray photoelectron spectroscopy.

  11. Selective-area growth of vertically oriented GaN nanostructures with a hafnium pre-orienting layer

    NASA Astrophysics Data System (ADS)

    Bae, S.-Y.; Lekhal, K.; Lee, H.-J.; Mitsunari, T.; Min, J.-W.; Lee, D.-S.; Kushimoto, M.; Honda, Y.; Amano, H.

    2017-06-01

    Severe melt-back etching has forced the epitaxy of GaN on Si to use an AlN buffer layer for growing high-quality two-dimensional layers, despite its high resistivity. Herein, we report a metal-based pre-orienting layer (POL) for growing GaN nanostructures (NSs) to replace the traditional AlN buffer layer. Two metals, titanium (Ti) and hafnium (Hf), were evaluated as POLs. We succeeded in fabricating arrays of GaN NSs with highly preferred orientation using selective-area growth. The crystallographic phase of the POLs critically affected the evolved orientation of the crystals. Photoluminescence measurements revealed that GaN NSs with Hf-based POLs were of reasonably high quality. We believe that this result will facilitate broader III-V semiconductor applications using alternative substrates moving beyond conventional Si-based optoelectronics.

  12. Study of gate oxide traps in HfO2/AlGaN/GaN metal-oxide-semiconductor high-electron-mobility transistors by use of ac transconductance method

    NASA Astrophysics Data System (ADS)

    Sun, X.; Saadat, O. I.; Chang-Liao, K. S.; Palacios, T.; Cui, S.; Ma, T. P.

    2013-03-01

    We introduce an ac-transconductance method to profile the gate oxide traps in a HfO2 gated AlGaN/GaN Metal-Oxide-Semiconductor High-Electron-Mobility Transistors (MOS-HEMTs) that can exchange carriers with metal gates, which in turn causes changes in analog and pulsed channel currents. The method extracts energy and spacial distributions of the oxide and interface traps under the gate from the frequency dependence of ac transconductance. We demonstrate the method using MOS-HEMTs with gate oxides that were annealed at different temperatures.

  13. A highly manufacturable 0.2 {mu}m AlGaAs/InGaAs PHEMT fabricated using the single-layer integrated-metal FET (SLIMFET) process

    SciTech Connect

    Havasy, C.K.; Quach, T.K.; Bozada, C.A.

    1995-12-31

    This work is the development of a single-layer integrated-metal field effect transistor (SLIMFET) process for a high performance 0.2 {mu}m AlGaAs/InGaAs pseudomorphic high electron mobility transistor (PHEMT). This process is compatible with MMIC fabrication and minimizes process variations, cycle time, and cost. This process uses non-alloyed ohmic contacts, a selective gate-recess etching process, and a single gate/source/drain metal deposition step to form both Schottky and ohmic contacts at the same time.

  14. Kinetic buffers.

    PubMed

    Alibrandi, Giuseppe; Fabbrizzi, Luigi; Licchelli, Maurizio; Puglisi, Antonio

    2015-01-12

    This paper proposes a new type of molecular device that is able to act as an inverse proton sponge to slowly decrease the pH inside a reaction vessel. This makes the automatic monitoring of the concentration of pH-sensitive systems possible. The device is a composite formed of an alkyl chloride, which kinetically produces acidity, and a buffer that thermodynamically modulates the variation in pH value. Profiles of pH versus time (pH-t plots) have been generated under various experimental conditions by computer simulation, and the device has been tested by carrying out automatic spectrophotometric titrations, without using an autoburette. To underline the wide variety of possible applications, this new system has been used to realize and monitor HCl uptake by a di-copper(II) bistren complex in a single run, in a completely automatic experiment. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  15. Tailoring of the Metal-N/P-Type GaSb Interface Properties for Device Production

    SciTech Connect

    Varblianska, K.; Tzeneva, S.; Comninou, Ph.; Nihtianova, D.

    2007-04-23

    There are some difficulties in producing Schottky barriers (SB) to p-type GaSb and ohmic contacts (OC) to n-type GaSb connected with the physical nature of the GaSb itself. By applying low energy Ar ion sputtering at 200-700V and (NH4)2S solution treatment of the p-type substrates we achieved a rectifying behavior of the p-GaSb/Pd contacts. The same procedure combined with a proper annealing led to the production of good n-GaSb/Pd/Ge/Au ohmic contacts. The electrical behavior of the SB and OC is inferred from their current-voltage characteristics on specially prepared diode structures. SEM and TEM investigations are conducted to specify the surface and interface reactions during the processing. We interpret these results in terms of the generation of such a Ga to Sb vacancy concentration ratio during the ion sputtering that enhances the incorporation of Ge and S as donor impurities in the GaSb surface.

  16. Study of the interface stability of the metal (Mo, Ni, Pd)/HfO2/AlN/InGaAs MOS devices

    NASA Astrophysics Data System (ADS)

    Do, Huy Binh; Luc, Quang Ho; Ha, Minh Thien Huu; Huynh, Sa Hoang; Nguyen, Tuan Anh; Lin, Yueh Chin; Chang, Edward Yi

    2017-08-01

    The degeneration of the metal/HfO2 interfaces for Mo, Ni, and Pd gate metals was studied in this paper. An unstable PdOx interfacial layer formed at the Pd/HfO2 interface, inducing the oxygen segregation for the Pd/HfO2/InGaAs metal oxide capacitor (MOSCAP). The low dissociation energy for the Pd-O bond was the reason for oxygen segregation. The PdOx layer contains O2- and OH- ions which are mobile during thermal annealing and electrical stress test. The phenomenon was not observed for the (Mo, Ni)/HfO2/InGaAs MOSCAPs. The results provide the guidance for choosing the proper metal electrode for the InGaAs based MOSFET.

  17. Ultrathin body GaSb-on-insulator p-channel metal-oxide-semiconductor field-effect transistors on Si fabricated by direct wafer bonding

    SciTech Connect

    Yokoyama, Masafumi Takenaka, Mitsuru; Takagi, Shinichi; Yokoyama, Haruki

    2015-02-16

    We have realized ultrathin body GaSb-on-insulator (GaSb-OI) on Si wafers by direct wafer bonding technology using atomic-layer deposition (ALD) Al{sub 2}O{sub 3} and have demonstrated GaSb-OI p-channel metal-oxide-semiconductor field-effect transistors (p-MOSFETs) on Si. A 23-nm-thick GaSb-OI p-MOSFET exhibits the peak effective mobility of ∼76 cm{sup 2}/V s. We have found that the effective hole mobility of the thin-body GaSb-OI p-MOSFETs decreases with a decrease in the GaSb-OI thickness or with an increase in Al{sub 2}O{sub 3} ALD temperature. The InAs passivation of GaSb-OI MOS interfaces can enhance the peak effective mobility up to 159 cm{sup 2}/V s for GaSb-OI p-MOSFETs with the 20-nm-thick GaSb layer.

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

    SciTech Connect

    Hwang, Ya-Hsi; Ahn, Shihyun; Dong, Chen; Zhu, Weidi; Kim, Byung-Jae; Le, Lingcong; Ren, Fan; Lind, Aaron G.; Dahl, James; Jones, Kevin S.; Pearton, Stephen J.; Kravchenko, Ivan I.; Zhang, Ming-Lan

    2015-04-27

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

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

    DOE PAGES

    Hwang, Ya-Hsi; Ahn, Shihyun; Dong, Chen; ...

    2015-04-27

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

  20. Evaluation of AlGaN/GaN metal-oxide-semicondutor high-electron mobility transistors with plasma-enhanced atomic layer deposition HfO2/AlN date dielectric for RF power applications

    NASA Astrophysics Data System (ADS)

    Chiu, Yu Sheng; Luc, Quang Ho; Lin, Yueh Chin; Chien Huang, Jui; Dee, Chang Fu; Yeop Majlis, Burhanuddin; Chang, Edward Yi

    2017-09-01

    A plasma enhanced atomic layer deposition (PEALD) HfO2/AlN dielectric stack was used as the gate dielectric for AlGaN/GaN metal-oxide-semiconductor high-electron-mobility transistors (MOS-HEMTs) for high-frequency power device applications. The capacitance-voltage (C-V) curves of the HfO2/AlN/GaN MOS capacitor (MOSCAP) showed a small frequency dispersion along with a very small hysteresis (˜50 mV). Moreover, the interface trap density (D it) was calculated to be 2.7 × 1011 cm-2 V-1 s-1 at 150 °C. Using PEALD-AlN as the interfacial passivation layer (IPL), the drain current of the HfO2/AlN MOS-HEMTs increased by about 46% and the gate leakage current decreased by six orders of magnitude as compared with those of the conventional Schottky gate AlGaN/GaN HEMTs processed using the same epitaxial wafer. The 0.3-µm-gate-length HfO2/AlN/AlGaN/GaN MOS-HEMTs demonstrated a 2.88 W/mm output power, a 23 dB power gain, a 30.2% power-added efficiency at 2.4 GHz, and an improved device linearity as compared with the conventional AlGaN/GaN HEMTs. The third-order intercept point at the output (OIP3) of the MOS-HEMTs was 28.4 as compared with that of 26.5 for the conventional GaN HEMTs. Overall, the MOS-HEMTs with a HfO2/AlN gate stack showed good potential for high-linearity RF power device applications.

  1. Photochemical Hydrogen Doping Induced Embedded Two-Dimensional Metallic Channel Formation in InGaZnO at Room Temperature.

    PubMed

    Kim, Myeong-Ho; Lee, Young-Ahn; Kim, Jinseo; Park, Jucheol; Ahn, Seungbae; Jeon, Ki-Joon; Kim, Jeong Won; Choi, Duck-Kyun; Seo, Hyungtak

    2015-10-27

    The photochemical tunability of the charge-transport mechanism in metal-oxide semiconductors is of great interest since it may offer a facile but effective semiconductor-to-metal transition, which results from photochemically modified electronic structures for various oxide-based device applications. This might provide a feasible hydrogen (H)-radical doping to realize the effectively H-doped metal oxides, which has not been achieved by thermal and ion-implantation technique in a reliable and controllable way. In this study, we report a photochemical conversion of InGaZnO (IGZO) semiconductor to a transparent conductor via hydrogen doping to the local nanocrystallites formed at the IGZO/glass interface at room temperature. In contrast to thermal or ionic hydrogen doping, ultraviolet exposure of the IGZO surface promotes a photochemical reaction with H radical incorporation to surface metal-OH layer formation and bulk H-doping which acts as a tunable and stable highly doped n-type doping channel and turns IGZO to a transparent conductor. This results in the total conversion of carrier conduction property to the level of metallic conduction with sheet resistance of ∼16 Ω/□, room temperature Hall mobility of 11.8 cm(2) V(-1) sec(-1), the carrier concentration at ∼10(20) cm(-3) without any loss of optical transparency. We demonstrated successful applications of photochemically highly n-doped metal oxide via optical dose control to transparent conductor with excellent chemical and optical doping stability.

  2. Novel Metal-Sulfur-Based Air-Stable Passivation of GaAs with Very Low Surface State Densities

    SciTech Connect

    Ashby, Carol I.H.; Baca, Albert G.; Chang, P.-C; Hafich, M.J.; Hammons, B.E.; Zavadil, Kevin R.

    1999-08-09

    A new air-stable electronic surface passivation for GaAs and other III-V compound semiconductors that employs sulfur and a suitable metal ion, e.g., Zn, and that is robust towards plasma dielectric deposition has been developed. Initial improvements in photoluminescence are twice that of S-only treatments and have been preserved for >11 months with SiO{sub x}N{sub y} dielectric encapsulation. Photoluminescence and X-ray photoelectron spectroscopies indicate that the passivation consists of two major components with one being stable for >2 years in air. This process improves heterojunction bipolar transistor current gain for both large and small area devices.

  3. Monitoring the dissolution process of metals in the gas phase: reactions of nanoscale Al and Ga metal atom clusters and their relationship to similar metalloid clusters.

    PubMed

    Burgert, Ralf; Schnöckel, Hansgeorg

    2008-05-14

    Formation and dissolution of metals are two of the oldest technical chemical processes. On the atomic scale, these processes are based on the formation and cleavage of metal-metal bonds. During the past 15 years we have studied intensively the intermediates during the formation process of metals, i.e. the formation of compounds containing many metal-metal bonds between naked metal atoms in the center and ligand-bearing metal atoms at the surface. We have called the clusters metalloid or, more generally, elementoid clusters. Via a retrosynthetic route, the many different Al and Ga metalloid clusters which have been structurally characterized allow us to understand also the dissolution process; i.e. the cleavage of metal-metal (M-M) bonds. However, this process can be detected much more directly by the reaction of single metal atom clusters in the gas phase under high vacuum conditions. A suitable tool to monitor the dissolution process of a metal cluster in the gas phase is FT-ICR (Fourier transform ion cyclotron resonance) mass spectrometry. Snapshots during these cleavage processes are possible because only every 1-10 s is there a contact between a cluster molecule and an oxidizing molecule (e.g. Cl2). This period is long, i.e. the formation of the primary product (a smaller metal atom cluster) is finished before the next collision happens. We have studied three different types of reaction:(1) Step-by-step fragmentation of a structurally known metalloid cluster allows us to understand the bonding principle of these clusters because in every step only the weakest bond is broken.(2) There are three oxidation reactions of an Al13(-) cluster molecule with Cl2, HCl and O2 central to this review. These three reactions represent three different reaction types, (a) an exothermic reaction (Cl2), (b) an endothermic reaction (HCl), and (c) a kinetically limited reaction based on spin conservation rules (O2).(3) Finally, we present the reaction of a metalloid cluster with Cl2

  4. Investigation of Pd-InGaAs for the formation of self-aligned source/drain contacts in InGaAs metal-oxide-semiconductor field-effect transistors

    NASA Astrophysics Data System (ADS)

    Kong, Eugene Y.-J.; Ivana; Zhang, Xingui; Zhou, Qian; Pan, Jisheng; Zhang, Zheng; Yeo, Yee-Chia

    2013-07-01

    The formation of salicide-like source/drain contacts on III-V MOSFETs necessitates a search for suitable metals that can react with III-V materials to form ohmic contacts with low sheet resistance and contact resistivity. To advance this search, the reaction between Pd and In0.53Ga0.47As is explored in this work. Reaction temperatures ranging from 200 to 400 °C were investigated, and extensive physical and electrical characterization was performed. Pd completely reacts with In0.53Ga0.47As after annealing at temperatures as low as 200 °C for 60 s to form a very smooth and uniform Pd-InGaAs film with good interfacial quality. Pd-InGaAs formed at 250 °C was found to have a work function of ˜4.6 ± 0.1 eV, sheet resistance of ˜77.3 Ω/square for a thickness of 20 nm, and contact resistivity of ˜8.35 × 10-5 Ω cm2 on In0.53Ga0.47As with n-type active doping concentration of ˜2 × 1018 cm-3. With further development, Pd-InGaAs could potentially be useful as self-aligned contacts for InGaAs transistors.

  5. Fabrication of normally-off AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistors by photo-electrochemical gate recess etching in ionic liquid

    NASA Astrophysics Data System (ADS)

    Zhang, Zhili; Qin, Shuangjiao; Fu, Kai; Yu, Guohao; Li, Weiyi; Zhang, Xiaodong; Sun, Shichuang; Song, Liang; Li, Shuiming; Hao, Ronghui; Fan, Yaming; Sun, Qian; Pan, Gebo; Cai, Yong; Zhang, Baoshun

    2016-08-01

    We characterized an ionic liquid (1-butyl-3-methylimidazolium nitrate, C8H15N3O3) as a photo-electrochemical etchant for fabricating normally-off AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistors (MIS-HEMTs). Using the ionic liquid, we achieved an etching rate of ˜2.9 nm/min, which is sufficiently low to facilitate good etching control. The normally-off AlGaN/GaN MIS-HEMT was fabricated with an etching time of 6 min, with the 20 nm low-pressure chemical vapor deposition (LPCVD) silicon nitride (Si3N4) gate dielectric exhibiting a threshold voltage shift from -10 to 1.2 V, a maximum drain current of more than 426 mA/mm, and a breakdown voltage of 582 V.

  6. Nanometer-Thick Single-Crystal Hexagonal Gd2 O3 on GaN for Advanced Complementary Metal-Oxide-Semiconductor Technology.

    PubMed

    Chang, Wen Hsin; Lee, Chih Hsun; Chang, Yao Chung; Chang, Pen; Huang, Mao Lin; Lee, Yi Jun; Hsu, Chia-Hung; Hong, J Minghuang; Tsai, Chiung Chi; Kwo, J Raynien; Hong, Minghwei

    2009-12-28

    Hexagonal-phase single-crystal Gd2 O3 is deposited on GaN in a molecular beam epitaxy system. The dielectric constant is about twice that of its cubic counterpart when deposited on InGaAs or Si. The capacitive effective thickness of 0.5 nm in hexagonal Gd2 O3 is perhaps the lowest on GaN-metal-oxide-semiconductor devices. The heterostructure is thermo dynamically stable at high temperatures and exhibits low interfacial densities of states after high-temperature annealing. Copyright © 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  7. Structural properties of Al-rich AlInN grown on c-plane GaN substrate by metal-organic chemical vapor deposition

    PubMed Central

    2014-01-01

    The attractive prospect for AlInN/GaN-based devices for high electron mobility transistors with advanced structure relies on high-quality AlInN epilayer. In this work, we demonstrate the growth of high-quality Al-rich AlInN films deposited on c-plane GaN substrate by metal-organic chemical vapor deposition. X-ray diffraction, scanning electron microscopy, and scanning transmission electron microscopy show that the films lattice-matched with GaN can have a very smooth surface with good crystallinity and uniform distribution of Al and In in AlInN. PMID:25489282

  8. The nature of catalyst particles and growth mechanisms of GaN nanowires grown by Ni-assisted metal-organic chemical vapor deposition.

    PubMed

    Weng, Xiaojun; Burke, Robert A; Redwing, Joan M

    2009-02-25

    The structure and chemistry of the catalyst particles that terminate GaN nanowires grown by Ni-assisted metal-organic chemical vapor deposition were investigated using a combination of electron diffraction, high-resolution transmission electron microscopy, and x-ray energy dispersive spectrometry. The crystal symmetry, lattice parameter, and chemical composition obtained reveal that the catalyst particles are Ni(3)Ga with an ordered L 1(2) structure. The results suggest that the catalyst is a solid particle during growth and therefore favor a vapor-solid-solid mechanism for the growth of GaN nanowires under these conditions.

  9. Metal modulation epitaxy growth for extremely high hole concentrations above 10{sup 19} cm{sup -3} in GaN

    SciTech Connect

    Namkoong, Gon; Trybus, Elaissa; Lee, Kyung Keun; Moseley, Michael; Doolittle, W. Alan; Look, David C.

    2008-10-27

    The free hole carriers in GaN have been limited to concentrations in the low 10{sup 18} cm{sup -3} range due to the deep activation energy, lower solubility, and compensation from defects, therefore, limiting doping efficiency to about 1%. Herein, we report an enhanced doping efficiency up to {approx}10% in GaN by a periodic doping, metal modulation epitaxy growth technique. The hole concentrations grown by periodically modulating Ga atoms and Mg dopants were over {approx}1.5x10{sup 19} cm{sup -3}.

  10. The optimization of interfaces in InAsSb/InGaAs strained-layer superlattices grown by metal-organic chemical vapor deposition

    SciTech Connect

    Biefeld, R.M.; Baucom, K.C.; Kurtz, S.R.

    1993-12-31

    We have prepared InAsSb/InGaAs strained-layer superlattice (SLS) semiconductors by metal-organic chemical vapor deposition (MOCVD) under a variety of conditions. Presence of an InGaAsSb interface layer is indicated by x-ray diffraction patterns. Optimized growth conditions involved the use of low pressure, short purge times, and no reactant flow during the purges. MOCVD was used to prepare an optically pumped, single heterostructure InAsSb/InGaAs SLS/InPSb laser which emitted at 3.9 {mu}m with a maximum operating temperature of approximately 100 K.

  11. Growth of InGaAs nanowires on Ge(111) by selective-area metal-organic vapor-phase epitaxy

    NASA Astrophysics Data System (ADS)

    Yoshida, Akinobu; Tomioka, Katsuhiro; Ishizaka, Fumiya; Motohisa, Junichi

    2017-04-01

    We report the growth of InGaAs nanowires (NWs) on Ge(111) substrates using selective-area metal-organic vapor-phase epitaxy (SA-MOVPE) for novel InGaAs/Ge hybrid complementary metal-oxide-semiconductor (CMOS) applications. Ge(111) substrates with periodic arrays of mask opening were prepared, and InGaAs was selectively grown on the opening region of Ge(111). A uniform array of InGaAs NWs with a diameter around 100 nm was successfully grown using appropriate preparation of the initial surfaces with an AsH3 thermal treatment and flow-rate modulation epitaxy (FME). We found that optimizing partial pressure of AsH3 and the number of FME cycles improved the yield of vertical InGaAs NWs. Line-scan profile analysis of energy dispersive X-ray (EDX) spectrometry showed that the In composition in the InGaAs NW was almost constant from the bottom to the top. Transmission electron microscope (TEM) analysis revealed that the interface between InGaAs NW and Ge had misfit dislocations, but their distance was longer than that expected from the difference in their lattice constants.

  12. Transparent Conducting ZnO:B Thin Films Grown by Ultraviolet Light Assisted Metal Organic Chemical Vapor Deposition Using Triethylboron for Cu(In,Ga)Se2 Solar Cells

    NASA Astrophysics Data System (ADS)

    Kobayashi, Taizo; Yamauchi, Kotaro; Mise, Takahiro; Nakada, Tokio

    2012-10-01

    High-efficiency cadmium-free Cu(In,Ga)Se2 (CIGS) thin-film solar cells have been fabricated using a zinc compound buffer layer deposited by the chemical bath deposition (CBD) process. However, the zinc compound buffer layers such as ZnS(O,OH) are prone to plasma-induced damage during the subsequent ZnO sputtering process. A process causing less damage such as metal-organic chemical vapor deposition (MOCVD) is thus required for ZnO-based transparent conducting oxide (TCO) layers. In the present work, the boron-doped zinc oxide (ZnO:B) films were grown by MOCVD using diethyl zinc (DEZ), H2O, and low-toxicity triethylboron (TEB). An UV-assisted MOCVD process was developed in order to reduce the resistivity of ZnO:B films. As a result, the resisitivity significantly decreased together with the increased electron mobility and carrier concentration. The comparison of performance was also carried out for the ZnS(O,OH)/CIGS solar cells with MOCVD-deposited ZnO:B and sputter-deposited ZnO:Al window layers.

  13. R{sub 5}Ga{sub 3} compounds of rare-earth metals R; structures and properties

    SciTech Connect

    Zhao, Jing-Tai; Corbett, J.D.

    1993-12-31

    The chemistry of rare-earth metals with Al family elements is important in our understanding of the bonding nature of the so-called Zintl phases and regular intermetallic compounds as well as the perspective of potential new materials. The rare-earth gallides, R{sub 5}Ga{sub 3}, has been synthesized and their structure types have been clarified by single crystal structure determinations. Among them, La{sub 5}Ga{sub 3}, Gd{sub 5}B{sub 3} and Y{sub 5}Ga{sub 3}, instead of having the Cr{sub 5}B{sub 3}- or Mn{sub 5}Si{sub 3}-type as reported, crystallize with the Ba{sub 5}Si{sub 3}-type which is a deformation variant of the Cr{sub 5}B{sub 3}-type. The structural features of these phases are compared with other Cr{sub 5}B{sub 3} deformation structures. The physical property measurements of these compounds are consistent with their structural features.

  14. Droop-Free, Reliable, and High-Power InGaN/GaN Nanowire Light-Emitting Diodes for Monolithic Metal-Optoelectronics.

    PubMed

    Zhao, Chao; Ng, Tien Khee; ElAfandy, Rami T; Prabaswara, Aditya; Consiglio, Giuseppe Bernardo; Ajia, Idris A; Roqan, Iman S; Janjua, Bilal; Shen, Chao; Eid, Jessica; Alyamani, Ahmed Y; El-Desouki, Munir M; Ooi, Boon S

    2016-07-13

    A droop-free nitride light-emitting diode (LED) with the capacity to operate beyond the "green gap" has been a subject of intense scientific and engineering interest. While several properties of nanowires on silicon make them promising for use in LED development, the high aspect ratio of individual nanowires and their laterally discontinuous features limit phonon transport and device performance. Here, we report on the monolithic integration of metal heat-sink and droop-free InGaN/GaN quantum-disks-in-nanowire LEDs emitting at ∼710 nm. The reliable operation of our uncooled nanowire-LEDs (NW-LEDs) epitaxially grown on molybdenum was evident in the constant-current soft burn-in performed on a 380 μm × 380 μm LED. The square LED sustained 600 mA electrical stress over an 8 h period, providing stable light output at maturity without catastrophic failure. The absence of carrier and phonon transport barriers in NW-LEDs was further inferred from current-dependent Raman measurements (up to 700 mA), which revealed the low self-heating. The radiative recombination rates of NW-LEDs between room temperature and 40 °C was not limited by Shockley-Read-Hall recombination, Auger recombination, or carrier leakage mechanisms, thus realizing droop-free operation. The discovery of reliable, droop-free devices constitutes significant progress toward the development of nanowires for practical applications. Our monolithic approach realized a high-performance device that will revolutionize the way high power, low-junction-temperature LED lamps are manufactured for solid-state lighting and for applications in high-temperature harsh environment.

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

    SciTech Connect

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

    2015-08-31

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

  16. Metal Preferences and Metallation*

    PubMed Central

    Foster, Andrew W.; Osman, Deenah; Robinson, Nigel J.

    2014-01-01

    The metal binding preferences of most metalloproteins do not match their metal requirements. Thus, metallation of an estimated 30% of metalloenzymes is aided by metal delivery systems, with ∼25% acquiring preassembled metal cofactors. The remaining ∼70% are presumed to compete for metals from buffered metal pools. Metallation is further aided by maintaining the relative concentrations of these pools as an inverse function of the stabilities of the respective metal complexes. For example, magnesium enzymes always prefer to bind zinc, and these metals dominate the metalloenzymes without metal delivery systems. Therefore, the buffered concentration of zinc is held at least a million-fold below magnesium inside most cells. PMID:25160626

  17. Electronic structures, magnetic properties and half-metallicity in Heusler alloys Zr2CoZ (Z=Al, Ga, In, Sn)

    NASA Astrophysics Data System (ADS)

    Yan, Peng-Li; Zhang, Jian-Min; Xu, Ke-Wei

    2015-10-01

    The electronic structures, magnetic properties, and half-metallicity of full-Heusler alloys Zr2 CoZ (Z=Al, Ga, In, Sn) with the Hg2 CuTi -type structure have been studied by using the first-principles projector augmented wave (PAW) potential within the generalized gradient approximation (GGA). The Zr2 CoZ (Z=Al, Ga, In, Sn) are found to be half-metallic ferrimagnets within a certain range of the lattice constant. The total magnetic moments (μt) of the Zr2 CoZ alloys are calculated to be 2 for Z=Al, Ga, In and 3 for Z=Sn, linearly scaled with the total number of valence electrons (Zt) by μt =Zt - 18 . The origin of the band gap for these half-metallic alloys is well understood. These new Zr-based Heusler alloys are the ideal candidates for spintronic devices.

  18. Effects of growth temperature on the properties of InGaN channel heterostructures grown by pulsed metal organic chemical vapor deposition

    SciTech Connect

    Zhang, Yachao; Zhou, Xiaowei; Xu, Shengrui; Wang, Zhizhe; Chen, Zhibin; Zhang, Jinfeng; Zhang, Jincheng E-mail: xd-zhangyachao@163.com; Hao, Yue E-mail: xd-zhangyachao@163.com

    2015-12-15

    Pulsed metal organic chemical vapor deposition (P-MOCVD) is introduced into the growth of high quality InGaN channel heterostructures. The effects of InGaN channel growth temperature on the structural and transport properties of the heterostructures are investigated in detail. High resolution x-ray diffraction (HRXRD) and Photoluminescence (PL) spectra indicate that the quality of InGaN channel strongly depends on the growth temperature. Meanwhile, the atomic force microscopy (AFM) results show that the interface morphology between the InGaN channel and the barrier layer also relies on the growth temperature. Since the variation of material properties of InGaN channel has a significant influence on the electrical properties of InAlN/InGaN heterostructures, the optimal transport properties can be achieved by adjusting the growth temperature. A very high two dimension electron gas (2DEG) density of 1.92 × 10{sup 13} cm{sup −2} and Hall electron mobility of 1025 cm{sup 2}/(V⋅s) at room temperature are obtained at the optimal growth temperature around 740 °C. The excellent transport properties in our work indicate that the heterostructure with InGaN channel is a promising candidate for the microwave power devices, and the results in this paper will be instructive for further study of the InGaN channel heterostructures.

  19. Demonstration of InAlN/AlGaN high electron mobility transistors with an enhanced breakdown voltage by pulsed metal organic chemical vapor deposition

    SciTech Connect

    Xue, JunShuai Zhang, JinCheng; Hao, Yue

    2016-01-04

    In this work, InAlN/AlGaN heterostructures employing wider bandgap AlGaN instead of conventional GaN channel were grown on sapphire substrate by pulsed metal organic chemical vapor deposition, where the nominal Al composition in InAlN barrier and AlGaN channel were chosen to be 83% and 5%, respectively, to achieve close lattice-matched condition. An electron mobility of 511 cm{sup 2}/V s along with a sheet carrier density of 1.88 × 10{sup 13 }cm{sup −2} were revealed in the prepared heterostructures, both of which were lower compared with lattice-matched InAlN/GaN due to increased intrinsic alloy disorder scattering resulting from AlGaN channel and compressively piezoelectric polarization in barrier, respectively. While the high electron mobility transistor (HEMT) processed on these structures not only exhibited a sufficiently high drain output current density of 854 mA/mm but also demonstrated a significantly enhanced breakdown voltage of 87 V, which is twice higher than that of reported InAlN/GaN HEMT with the same device dimension, potential characteristics for high-voltage operation of GaN-based electronic devices.

  20. Growth optimization toward low angle incidence microchannel epitaxy of GaN using ammonia-based metal-organic molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Lin, Chia-Hung; Abe, Ryota; Uchiyama, Shota; Maruyama, Takahiro; Naritsuka, Shigeya

    2012-08-01

    Growth optimization toward low angle incidence microchannel epitaxy (LAIMCE) of GaN was accomplished using ammonia-based metal-organic molecular beam epitaxy (NH3-based MOMBE). Firstly, the [NH3]/[trimethylgallium (TMG)] ratio (R) dependence of selective GaN growth was studied. The growth temperature was set at 860 °C while R was varied from 5 to 200 with precursors being supplied parallel to the openings cut in the SiO2 mask. The selectivity of the growth was superior for all R, because TMG and NH3 preferably decompose on the GaN film. The formation of {112¯0}GaN or {112¯2}GaN sidewalls and (0001)GaN surface were observed by the change in R. The intersurface diffusion of Ga adatoms was also changed by a change in R. Ga adatoms migrate from the sidewalls to the top at R lower than 50, whereas the migration weakened with R greater than 100. Secondly, LAIMCE was optimized by changing the growth temperature. Consequently, 6 μm wide lateral overgrowth in the direction of precursor incidence was achieved with no pit after etching by H3PO4, which was six times wider than that in the opposite direction.

  1. Self-Catalyzed Growth of Vertical GaSb Nanowires on InAs Stems by Metal-Organic Chemical Vapor Deposition

    NASA Astrophysics Data System (ADS)

    Ji, Xianghai; Yang, Xiaoguang; Yang, Tao

    2017-06-01

    We report the first self-catalyzed growth of high-quality GaSb nanowires on InAs stems using metal-organic chemical vapor deposition (MOCVD) on Si (111) substrates. To achieve the growth of vertical InAs/GaSb heterostructure nanowires, the two-step flow rates of the trimethylgallium (TMGa) and trimethylantimony (TMSb) are used. We first use relatively low TMGa and TMSb flow rates to preserve the Ga droplets on the thin InAs stems. Then, the flow rates of TMGa and TMSb are increased to enhance the axial growth rate. Because of the slower radial growth rate of GaSb at higher growth temperature, GaSb nanowires grown at 500 °C exhibit larger diameters than those grown at 520 °C. However, with respect to the axial growth, due to the Gibbs-Thomson effect and the reduction in the droplet supersaturation with increasing growth temperature, GaSb nanowires grown at 500 °C are longer than those grown at 520 °C. Detailed transmission electron microscopy (TEM) analyses reveal that the GaSb nanowires have a perfect zinc-blende (ZB) crystal structure. The growth method presented here may be suitable for other antimonide nanowire growth, and the axial InAs/GaSb heterostructure nanowires may have strong potential for use in the fabrication of novel nanowire-based devices and in the study of fundamental quantum physics.

  2. Optical properties of highly polarized InGaN light-emitting diodes modified by plasmonic metallic grating.

    PubMed

    Chen, Hong; Fu, Houqiang; Lu, Zhijian; Huang, Xuanqi; Zhao, Yuji

    2016-05-16

    We implement finite-difference time-domain (FDTD) method to simulate the optical properties of highly polarized InGaN light emitting diodes (LEDs) coupled with metallic grating structure. The Purcell factor (Fp), light extraction efficiency (LEE), internal quantum efficiency (IQE), external quantum efficiency (EQE), and modulation frequency are calculated for different polarized emissions. Our results show that light polarization has a strong impact on Fp and LEE of LEDs due to their coupling effects with the surface plasmons (SPs) generated by metallic grating. Fp as high as 34 and modulation frequency up to 5.4 GHz are obtained for a simulated LED structure. Furthermore, LEE, IQE and EQE can also be enhanced by tuning the coupling between polarized emission and SPs. These results can serve as guidelines for the design and fabrication of high efficiency and high speed LEDs for the applications of solid-state lighting and visible-light communication.

  3. Metal-insulator transition by isovalent anion substitution in Ga1-xMnxAs: Implications to ferromagnetism

    SciTech Connect

    Stone, P.R.; Alberi, K.; Tardif, S.K.Z.; Beeman, J.W.; Yu, K.M.; Walukiewicz, W.; Dubon, O.D.

    2008-02-07

    We have investigated the effect of partial isovalent anion substitution in Ga1-xMnxAs on electrical transport and ferromagnetism. Substitution of only 2.4percent of As by P induces a metal-insulator transition at a constant Mn doping of x=0.046 while the replacement of 0.4 percent As with N results in the crossover from metal to insulator for x=0.037. This remarkable behavior is consistent with a scenario in which holes located within an impurity band are scattered by alloy disorder in the anion sublattice. The shorter mean free path of holes, which mediate ferromagnetism, reduces the Curie temperature TC from 113 K to 60 K (100 K to 65 K) upon the introduction of 3.1 percent P (1percent N) into the As sublattice.

  4. Critical metal-insulator transition due to nuclear quantum effects in Mn-doped GaAs

    NASA Astrophysics Data System (ADS)

    Bae, Soungmin; Raebiger, Hannes

    2016-12-01

    Mn-doped GaAs exhibits a critical metal-insulator transition at the Mn concentration of xcrit≈1 % . Our self-interaction corrected first principles calculation shows that for Mn concentrations x ≳1 % , hole carriers are delocalized in host valence states, and for x ≲1 % , holes tend to be trapped in impurity-band-like states. We further show that for a finite range of concentrations around xcrit the system exhibits a nonadiabatic superposition of these states, i.e., a mixing of electronic and nuclear wave functions. This means that the phase transition is continuous, and its criticality is caused by quantum effects of the atomic nuclei. In other words, the apparently electronic phase transition from the insulator to metal state cannot be described by electronic effects alone.

  5. AlGaN Metal-Semiconductor-Metal Photodetectors on Planar and Epitaxial Laterally Overgrown AlN/Sapphire Templates for the Ultraviolet C Spectral Region

    NASA Astrophysics Data System (ADS)

    Knigge, Andrea; Brendel, Moritz; Brunner, Frank; Einfeldt, Sven; Knauer, Arne; Kueller, Viola; Zeimer, Ute; Weyers, Markus

    2013-08-01

    Schottky type metal-semiconductor-metal (MSM) Al0.4Ga0.6N photodetectors (PDs) for the ultraviolet C spectral region on conventional planar AlN templates are compared with epitaxial laterally overgrown (ELO) AlN templates. On planar templates solar blind MSM PDs with state-of-the-art dark current in the pA range and a power independent responsivity are obtained. PDs on ELO templates with fingers parallel to the etched stripes have properties similar to those on planar templates. PDs on ELO templates with contact fingers oriented perpendicular to the etched stripe pattern exhibit photoconductive gain leading to external quantum efficiencies of up to 77 at 30 V applied bias surpassing that of the planar grown PDs by a factor of 100. In spite of the high gain these PDs also show low dark currents, short switching times and two operating regimes with power independent responsivity.

  6. Direct evidence of barrier inhomogeneities at metal/AlGaN/GaN interfaces using nanoscopic electrical characterizations

    NASA Astrophysics Data System (ADS)

    Kumar, Ashutosh; Kapoor, Raman; Garg, M.; Kumar, V.; Singh, R.

    2017-06-01

    The existence of barrier inhomogeneities at metal-semiconductor interfaces is believed to be one of the reasons for the non-ideal behaviour of Schottky contacts. In general, barrier inhomogeneities are modelled using a Gaussian distribution of barrier heights of nanoscale patches having low and high barrier heights, and the standard deviation of this distribution roughly estimates the level of barrier inhomogeneities. In the present work, we provide direct experimental evidence of barrier inhomogeneities by performing electrical characterizations on individual nanoscale patches and, further, obtaining the magnitude of these inhomogeneities. Localized current-voltage measurements on individual nanoscale patches were performed using conducting atomic force microscopy (CAFM) whereas surface potential variations on nanoscale dimensions were investigated using Kelvin probe force microscopy (KPFM) measurements. The CAFM measurements revealed the distribution of barrier heights, which is attributed to surface potential variations at nanoscale dimensions, as obtained from KPFM measurements. The present work is an effort to provide direct evidence of barrier inhomogeneities, finding their origin and magnitude by combining CAFM and KPFM techniques and correlating their findings.

  7. Responsivity drop due to conductance modulation in GaN metal-semiconductor-metal Schottky based UV photodetectors on Si(111)

    NASA Astrophysics Data System (ADS)

    Ravikiran, L.; Radhakrishnan, K.; Dharmarasu, N.; Agrawal, M.; Wang, Zilong; Bruno, Annalisa; Soci, Cesare; Lihuang, Tng; Kian Siong, Ang

    2016-09-01

    GaN Schottky metal-semiconductor-metal (MSM) UV photodetectors were fabricated on a 600 nm thick GaN layer, grown on 100 mm Si (111) substrate using an ammonia-MBE growth technique. In this report, the effect of device dimensions, applied bias and input power on the linearity of the GaN Schottky-based MSM photodetectors on Si substrate were investigated. Devices with larger interdigitated spacing, ‘S’ of 9.0 μm between the fingers resulted in good linearity and flat responsivity characteristics as a function of input power with an external quantum efficiency (EQE) of ˜33% at an applied bias of 15 V and an input power of 0.8 W m-2. With the decrease of ‘S’ to 3.0 μm, the EQE was found to increase to ˜97%. However, devices showed non linearity and drop in responsivity from flatness at higher input power. Moreover, the position of dropping from flatter responsivity was found to shift to lower powers with increased bias. The drop in the responsivity was attributed to the modulation of conductance in the MSM due to the trapping of electrons at the dislocations, resulting in the formation of depletion regions around them. In devices with lower ‘S’, both the image force reduction and the enhanced collection efficiency increased the photocurrent as well as the charging of the dislocations. This resulted in the increased depletion regions around the dislocations leading to the modulation of conductance and non-linearity.

  8. X-ray diffraction analysis and scanning micro-Raman spectroscopy of structural irregularities and strains deep inside the multilayered InGaN/GaN heterostructure

    SciTech Connect

    Strelchuk, V. V. Kladko, V. P.; Avramenko, E. A.; Kolomys, O. F.; Safryuk, N. V.; Konakova, R. V.; Yavich, B. S.; Valakh, M. Ya.; Machulin, V. F.; Belyaev, A. E.

    2010-09-15

    High-resolution X-ray diffraction analysis and scanning confocal Raman spectroscopy are used to study the spatial distribution of strains in the In{sub x}Ga{sub 1-x}N/GaN layers and structural quality of these layers in a multilayered light-emitting diode structure produced by metal-organic chemical vapor deposition onto (0001)-oriented sapphire substrates. It is shown that elastic strains almost completely relax at the heterointerface between the thick GaN buffer layer and In{sub x}Ga{sub 1-x}N/GaN buffer superlattice. It is established that the GaN layers in the superlattice are in a stretched state, whereas the alloy layers are in a compressed state. In magnitude, the stretching strains in the GaN layers are lower than the compressive strains in the InGaN layers. It is shown that, as compared to the buffer layers, the layers of the superlattice contain a smaller number of dislocations and the distribution of dislocations is more randomly disordered. In micro-Raman studies on scanning through the thickness of the multilayered structure, direct evidence is obtained for the asymmetric gradient distributions of strains and crystal imperfections of the epitaxial nitride layers along the direction of growth. It is shown that the emission intensity of the In{sub x}Ga{sub 1-x}N quantum well is considerably (more than 30 times) higher than the emission intensity of the GaN barrier layers, suggesting the high efficiency of trapping of charge carriers by the quantum well.

  9. High temperature electron transport properties in AlGaN/GaN heterostructures

    NASA Astrophysics Data System (ADS)

    Tokuda, H.; Yamazaki, J.; Kuzuhara, M.

    2010-11-01

    Hall electron mobility (μH) and sheet concentration (ns) in AlGaN/GaN heterostructures have been measured from 77 to 1020 K. The effect of the deposited Al2O3 layer is also investigated with varying its thickness. It is found that μH decreases monotonously with the temperature (T) and its dependence is well approximated with the function of μH=4.5×103 exp(-0.004T) in the temperatures over 350 K. The function is different from the commonly used one of μH=AT-α (α ˜1.5), which indicates that the mobility is not only governed by the polar optical phonon scattering but also the deformation potential scattering plays a role. The sheet electron concentration (ns) has a weak dependence on the temperature, that is, slightly decreases with temperature in 300-570 K and increases gradually up to 1020 K. The decrease is explained by considering the reduction in the polarization (probably both spontaneous and piezoelectric) charge and the increase seems to be due to the parallel conduction through the interface between GaN buffer layer and sapphire substrate. The dependence of sheet resistance (Rsh) in AlGaN/GaN is compared with that of n-GaN. In the low temperatures, AlGaN/GaN shows a lower Rsh due to its high mobility, however, at the temperatures higher than 350 K, Rsh of AlGaN/GaN becomes higher than that of n-GaN. This result implies that AlGaN/GaN high-electron-mobility-transistors are inferior to GaN metal-semiconductor field-effect transistors in terms of higher source, drain, and channel resistances at high temperature operations, although further investigations on other performances such as output power and reliability are needed. The Al2O3 deposited AlGaN/GaN shows about 15% higher ns than without Al2O3 layer for the whole temperatures. On the contrary, μH at 77 K shows a slight decrease with Al2O3 deposition, which degree is not affected by the layer thickness. In the temperatures higher than 400 K, μH is almost the same for with and without Al2O3 layer.

  10. The friction behavior of semiconductors Si and GaAs in contact with pure metals

    NASA Technical Reports Server (NTRS)

    Mishina, H.

    1984-01-01

    The friction behavior of the semiconductors silicon and gallium arsenide in contact with pure metals was studied. Five transition and two nontransition metals, titanium, tantalum, nickel, palladium, platinum, copper, and silver, slid on a single crystal silicon (111) surface. Four metals, indium, nickel, copper and silver, slid on a single crystal gallium arsenide (100) surface. Experiments were conducted in room air and in a vacuum of 10 to the minus 7th power N/sq cm (10 to the minus 9th power torr). The results indicate that the sliding of silicon on the transition metals exhibits relatively higher friction than for the nontransition metals in contact with silicon. There is a clear correlation between friction and Schottky barrier height formed at the metal silicon interface for the transition metals. Transition metals with a higher barrier height on silicon had a lower friction. The same effect of barrier height was found for the friction of gallium arsenide in contact with metals.

  11. An X-ray absorption spectroscopic study of the metal site preference in Al{sub 1-x}Ga{sub x}FeO{sub 3}

    SciTech Connect

    Walker, James D.S.; Grosvenor, Andrew P.

    2013-01-15

    Magnetoelectric materials have potential for being introduced into next generation technologies, especially memory devices. The AFeO{sub 3} (Pna2{sub 1}; A=Al, Ga) system has received attention to better understand the origins of magnetoelectric coupling. The magnetoelectric properties this system exhibits depend on the amount of anti-site disorder present, which is affected by the composition and the method of synthesis. In this study, Al{sub 1-x}Ga{sub x}FeO{sub 3} was synthesized by the ceramic method and studied by X-ray absorption spectroscopy. Al L{sub 2,3}-, Ga K-, and Fe K-edge spectra were collected to examine how the average metal coordination number changes with composition. Examination of XANES spectra from Al{sub 1-x}Ga{sub x}FeO{sub 3} indicate that with increasing Ga content, Al increasingly occupies octahedral sites while Ga displays a preference for occupying the tetrahedral site. The Fe K-edge spectra indicate that more Fe is present in the tetrahedral site in AlFeO{sub 3} than in GaFeO{sub 3}, implying more anti-site disorder is present in AlFeO{sub 3}. - Graphical abstract: Al{sub 1-x}Ga{sub x}FeO{sub 3} has been investigated by XANES. Through examination of Al L{sub 2,3}-, Ga K-, and Fe K-edge XANES spectra, it was found that more anti-site disorder of the Fe atoms is present in AlFeO{sub 3} compared to in GaFeO{sub 3}. Highlights: Black-Right-Pointing-Pointer Al{sub 1-x}Ga{sub x}FeO{sub 3} was investigated by X-ray absorption spectroscopy. Black-Right-Pointing-Pointer Ga prefers to occupy the tetrahedral site in Al{sub 1-x}Ga{sub x}FeO{sub 3}. Black-Right-Pointing-Pointer Fe prefers to occupy the octahedral sites in Al{sub 1-x}Ga{sub x}FeO{sub 3} as x increases. Black-Right-Pointing-Pointer More anti-site disorder is present in AlFeO{sub 3} compared to in GaFeO{sub 3.}.

  12. Growth of high N containing GaNAs/GaP/BGaAsP multi quantum well structures on Si (0 0 1) substrates

    NASA Astrophysics Data System (ADS)

    Ludewig, P.; Diederich, M.; Jandieri, K.; Stolz, W.

    2017-06-01

    GaNAs/GaP/BGaAsP-multiple quantum well heterostructures (MQWH) were deposited pseudomorphically strained on exactly oriented (0 0 1) Si-substrate plus thin GaP buffer by metal organic vapor phase epitaxy (MOVPE). The compressive strain of the GaNAs QW material enabled N fractions as high as 16.8%. Structural analyses show that the structures exhibit high crystalline quality for moderate strain values of 0.6% to 2.2%. Room temperature PL was obtained from samples with up to 11% N with an emission wavelength of up to 1130 nm. At low temperatures (15 K) even layers with 15% N showed photoluminescence from the GaNAs QW expanding the emission wavelength range to 1300 nm.

  13. β-Ga2O3 versus ε-Ga2O3: Control of the crystal phase composition of gallium oxide thin film prepared by metal-organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Zhuo, Yi; Chen, Zimin; Tu, Wenbin; Ma, Xuejin; Pei, Yanli; Wang, Gang

    2017-10-01

    Gallium oxide thin films of β and ε phase were grown on c-plane sapphire using metal-organic chemical vapor deposition and the phase compositions were analyzed using X-ray diffraction. The epitaxial phase diagram was constructed as a function of the growth temperature and VI/III ratio. A low growth temperature and low VI/III ratio were beneficial for the formation of hexagonal-type ε-Ga2O3. Further structure analysis revealed that the epitaxial relationship between ε-Ga2O3 and c-plane sapphire is ε-Ga2O3 (0001) || Al2O3 (0001) and ε-Ga2O3 || Al2O3 . The structural evolution of the mixed-phase sample during film thickening was investigated. By reducing the growth rate, the film evolved from a mixed phase to the energetically favored ε phase. Based on these results, a Ga2O3 thin film with a phase-pure ε-Ga2O3 upper layer was successfully obtained.

  14. Highly aligned vertical GaN nanowires using submonolayer metal catalysts

    DOEpatents

    Wang, George T [Albuquerque, NM; Li, Qiming [Albuquerque, NM; Creighton, J Randall [Albuquerque, NM

    2010-06-29

    A method for forming vertically oriented, crystallographically aligned nanowires (nanocolumns) using monolayer or submonolayer quantities of metal atoms to form uniformly sized metal islands that serve as catalysts for MOCVD growth of Group III nitride nanowires.

  15. Characterization and Modeling Analysis for Metal-Semiconductor-Metal GaAs Diodes with Pd/SiO2 Mixture Electrode

    PubMed Central

    Tan, Shih-Wei; Lai, Shih-Wen

    2012-01-01

    Characterization and modeling of metal-semiconductor-metal (MSM) GaAs diodes using to evaporate SiO2 and Pd simultaneously as a mixture electrode (called M-MSM diodes) compared with similar to evaporate Pd as the electrode (called Pd-MSM diodes) were reported. The barrier height (φb) and the Richardson constant (A*) were carried out for the thermionic-emission process to describe well the current transport for Pd-MSM diodes in the consideration of the carrier over the metal-semiconductor barrier. In addition, in the consideration of the carrier over both the metal-semiconductor barrier and the insulator-semiconductor barrier simultaneously, thus the thermionic-emission process can be used to describe well the current transport for M-MSM diodes. Furthermore, in the higher applied voltage, the carrier recombination will be taken into discussion. Besides, a composite-current (CC) model is developed to evidence the concepts. Our calculated results are in good agreement with the experimental ones. PMID:23226352

  16. Ballistics-Electron-Microscopy and Spectroscopy of Metal/GaN Interfaces

    NASA Technical Reports Server (NTRS)

    Bell, L. D.; Smith, R. P.; McDermott, B. T.; Gertner, E. R.; Pittman, R.; Pierson, R. L.; Sullivan, G. J.

    1997-01-01

    BEEM spectroscopy and imaging have been applied to the Au/GaN interface. In contrast to previous BEEM measurements, spectra yield a Schottky barrier height of 1.04eV that agrees well with the highest values measured by conventional methods.

  17. Ballistics-Electron-Microscopy and Spectroscopy of Metal/GaN Interfaces

    NASA Technical Reports Server (NTRS)

    Bell, L. D.; Smith, R. P.; McDermott, B. T.; Gertner, E. R.; Pittman, R.; Pierson, R. L.; Sullivan, G. J.

    1997-01-01

    BEEM spectroscopy and imaging have been applied to the Au/GaN interface. In contrast to previous BEEM measurements, spectra yield a Schottky barrier height of 1.04eV that agrees well with the highest values measured by conventional methods.

  18. Effect of Na-doped Mo on Selenization Pathways for CuGa/In Metallic Precursors

    SciTech Connect

    Krishnan, Rangarajan; Tong, Gabriel; Kim, Woo Kyoung; Payzant, E Andrew; Adelhelm, Christoph; Franzke, Enrico; Winkler, Jörg; Anderson, Timothy J

    2013-01-01

    Reaction pathways were followed for selenization of CuGa/In precursor structures using in-situ high temperature X-ray diffraction (HTXRD). Precursor films were deposited on Na-free and Na-doped Mo (3 and 5 at %)/Na-free glass. The precursor film was constituted with CuIn, In, Cu9Ga4, Cu3Ga, Cu16In9 and Mo. HTXRD measurements during temperature ramp selenization showed CIS formation occurs first, followed by CGS formation, and then mixing on the group III sub-lattice to form CIGS. CIGS formation was observed to be complete at ~450 C for samples deposited on 5 at % Na-doped Mo substrates. MoSe2 formation was evidenced after the CIGS synthesis reaction was complete. The Ga distribution in the annealed CIGS was determined by Rietveld refinement. Isothermal reaction studies were conducted for CIGS (112) formation in the temperature range 260-320 C to estimate the rate constants.

  19. Growth and doping of Al(x)Ga(1-x) nitride films by electron cyclotron resonance assisted molecular beam epitaxy. Semiannual report

    SciTech Connect

    Moustakas, T.

    1992-10-30

    Growth and doping of GaN by ECR assisted MBE is reported. We report on the role of the GaN-buffer and AlN-buffer, and their combination on the two dimensional nucleation rate and lateral growth rate. Conditions for quasi layer by layer growth were identified. XRD was used to study secondary phase, the direction and quality of orientational ordering in and out of the substrate, and homogeneous and inhomogeneous strain. Relatively high mobility autodoped films were produced and their transport mechanism was investigated. Intrinsic GaN- films were produced and were doped n- and p-type with Si and Mg respectively, without requiring annealing for dopant activation. RIE processing of GaN was developed and metal contacts were investigated. A direct correlation between the metal work function and barrier height was also found.

  20. Nonthermal inactivation of Escherichia coli K12 in buffered peptone water using a pilot-plant scale supercritical carbon dioxide system with gas-liquid porous metal contractor

    USDA-ARS?s Scientific Manuscript database

    This study evaluated the effectiveness of a supercritical carbon dioxide (SCCO2) system, with a gas-liquid CO2 contactor, for reducing Escherichia coli K12 in diluted buffered peptone water. 0.1% (w/v) buffered peptone water inoculated with E. coli K12 was processed using the SCCO2 system at CO2 con...