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Sample records for ga metal buffer

  1. 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.

  2. 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. PMID:27483845

  3. 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.

  4. Electrically Active Defects in GaN Layers Grown With and Without Fe-doped Buffers by Metal-organic Chemical Vapor Deposition

    NASA Astrophysics Data System (ADS)

    Umana-Membreno, G. A.; Parish, G.; Fichtenbaum, N.; Keller, S.; Mishra, U. K.; Nener, B. D.

    2008-05-01

    Electrically active defects in n-GaN films grown with and without an Fe-doped buffer layer have been investigated using conventional and optical deep-level transient spectroscopy (DLTS). Conventional DLTS revealed three well- defined electron traps with activation energies E a of 0.21, 0.53, and 0.8 eV. The concentration of the 0.21 and 0.8 eV defects was found to be slightly higher in the sample without the Fe-doped buffer, whereas the concentration of the 0.53 eV trap was higher in the sample with the Fe-doped buffer. A minority carrier trap with E a ≈ 0.65 eV was detected in both samples using optical DLTS; its concentration was ˜40% higher in the sample without the Fe-doped buffer. Mobility spectrum analysis and multiple magnetic-field measurements revealed that the electron mobility in the topmost layer of both samples was similar, but that the sample without the Fe-doped buffer layer was affected by parallel conduction through underlying layers with lower electron mobility.

  5. 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.

  6. Optimisation of a carbon doped buffer layer for AlGaN/GaN HEMT devices

    NASA Astrophysics Data System (ADS)

    Gamarra, Piero; Lacam, Cedric; Tordjman, Maurice; Splettstösser, Jörg; Schauwecker, Bernd; di Forte-Poisson, Marie-Antoinette

    2015-03-01

    This work reports on the optimisation of carbon doping GaN buffer layer (BL) for AlGaN/GaN HEMT (high electron mobility transistor) structures, grown by low pressure metal-organic vapour phase epitaxy (LP-MOVPE) on 3 in. SiC semi-insulating substrates. The incorporation of carbon impurities in GaN is studied as a function of the growth conditions, without using an external carbon source. We observed that the C incorporation can be effectively controlled over more than one order of magnitude by tuning the reactor pressure and the growth temperature, without degradation of the crystalline properties of the GaN layers. HEMT structures with a specific barrier design were grown with different carbon dopings in the GaN BL and processed into transistors to evaluate the impact of the BL doping on the device performances. A significant improvement of the HEMT drain leakage current and of the breakdown voltage was obtained by increasing the carbon incorporation in the GaN BL. The RF performances of the devices show a trade-off between leakage currents and trapping phenomena which are enhanced by the use of carbon doping, limiting the delivered output power. An output power as high as 6.5 W/mm with a Power Added Efficiency of 70% has been achieved at 2 GHz by the HEMT structures with the lowest carbon doping in the BL.

  7. 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.

  8. 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.

  9. 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.

  10. Optimization of a Common Buffer Platform for Monolithic Integration of InGaN/GaN Light-Emitting Diodes and AlGaN/GaN High-Electron-Mobility Transistors

    NASA Astrophysics Data System (ADS)

    Liu, Chao; Cai, Yuefei; Jiang, Huaxing; Lau, Kei May

    2016-04-01

    For the development of a metal-interconnection-free integration scheme for monolithic integration of InGaN/GaN light-emitting diodes (LEDs) and AlGaN/GaN high-electron-mobility transistors (HEMTs), a common buffer to achieve high brightness, low leakage current, and high breakdown in the integrated HEMT-LED device is essential. Different buffer structures have been investigated, and their impacts upon both the LED and HEMT parts of the HEMT-LED device have been analyzed. Results indicated that a GaN/AlN buffer structure is the most ideal to serve as a common buffer platform, offering both the excellent crystalline quality and superior buffer resistivity required by the HEMT-LED device. Growth of the AlN layer was particularly crucial for engineering the dislocation density, surface morphology, as well as resistivity of the buffer layer. Using the optimized GaN/AlN buffer structure, the LED part of the HEMT-LED device was improved, showing greatly enhanced light output power and suppressed reverse leakage current, while the breakdown characteristics of the HEMT part were also improved.

  11. Lattice curvature generation in graded InxGa1-xAs/GaAs buffer layers

    NASA Astrophysics Data System (ADS)

    Natali, M.; Romanato, F.; Napolitani, E.; de Salvador, D.; Drigo, A. V.

    2000-10-01

    Position dependent lattice tilts in InGaAs/GaAs(001) compositionally graded buffer layers are investigated. The lateral dependence of the tilt defines a concave buffer layer curvature of up to 3 deg cm-1. The buffer layer curvature is associated with a distribution of the misfit dislocation Burgers vectors that varies nearly linearly across the sample. The origin of this peculiar distribution is discussed and is explained in terms of a Burgers-vector selection rule, which governs the cross slip of gliding threading dislocations and that has been experimentally observed by Capano in Phys. Rev. B 45, 11 768 (1992). A quantitative model of lattice curvature formation is presented that satisfactorily accounts for the main features of the observed buffer layer curvature.

  12. 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.

  13. 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.

  14. Characterization of AlInN/AlN/GaN Heterostructures with Different AlN Buffer Thickness

    NASA Astrophysics Data System (ADS)

    Çörekçi, S.; Dugan, S.; Öztürk, M. K.; Çetin, S. Ş.; Çakmak, M.; Özçelik, S.; Özbay, E.

    2016-05-01

    Two AlInN/AlN/GaN heterostructures with 280-nm- and 400-nm-thick AlN buffer grown on sapphire substrates by metal-organic chemical vapor deposition (MOCVD) have been investigated by x-ray diffraction (XRD), atomic force microscopy (AFM), photoluminescence (PL) and Hall-effect measurements. The symmetric (0002) plane with respect to the asymmetric (10bar{1} 2) plane in the 280-nm-thick AlN buffer has a higher crystal quality, as opposed to the 400-nm-thick buffer. The thinner buffer improves the crystallinity of both (0002) and (10bar{1} 2) planes in the GaN layers, it also provides a sizeable reduction in dislocation density of GaN. Furthermore, the lower buffer thickness leads to a good quality surface with an rms roughness of 0.30 nm and a dark spot density of 4.0 × 108 cm-2. The optical and transport properties of the AlInN/AlN/GaN structure with the relatively thin buffer are compatible with the enhancement in its structural quality, as verified by XRD and AFM results.

  15. Characterization of AlInN/AlN/GaN Heterostructures with Different AlN Buffer Thickness

    NASA Astrophysics Data System (ADS)

    Çörekçi, S.; Dugan, S.; Öztürk, M. K.; Çetin, S. Ş.; Çakmak, M.; Özçelik, S.; Özbay, E.

    2016-07-01

    Two AlInN/AlN/GaN heterostructures with 280-nm- and 400-nm-thick AlN buffer grown on sapphire substrates by metal-organic chemical vapor deposition (MOCVD) have been investigated by x-ray diffraction (XRD), atomic force microscopy (AFM), photoluminescence (PL) and Hall-effect measurements. The symmetric (0002) plane with respect to the asymmetric (10bar{1}2) plane in the 280-nm-thick AlN buffer has a higher crystal quality, as opposed to the 400-nm-thick buffer. The thinner buffer improves the crystallinity of both (0002) and (10bar{1}2) planes in the GaN layers, it also provides a sizeable reduction in dislocation density of GaN. Furthermore, the lower buffer thickness leads to a good quality surface with an rms roughness of 0.30 nm and a dark spot density of 4.0 × 108 cm-2. The optical and transport properties of the AlInN/AlN/GaN structure with the relatively thin buffer are compatible with the enhancement in its structural quality, as verified by XRD and AFM results.

  16. 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.

  17. 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.

  18. 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.

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

    DOE PAGESBeta

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

    2015-04-21

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

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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}.

  8. 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.

  9. Vertically Oriented Growth of GaN Nanorods on Si Using Graphene as an Atomically Thin Buffer Layer.

    PubMed

    Heilmann, Martin; Munshi, A Mazid; Sarau, George; Göbelt, Manuela; Tessarek, Christian; Fauske, Vidar T; van Helvoort, Antonius T J; Yang, Jianfeng; Latzel, Michael; Hoffmann, Björn; Conibeer, Gavin; Weman, Helge; Christiansen, Silke

    2016-06-01

    The monolithic integration of wurtzite GaN on Si via metal-organic vapor phase epitaxy is strongly hampered by lattice and thermal mismatch as well as meltback etching. This study presents single-layer graphene as an atomically thin buffer layer for c-axis-oriented growth of vertically aligned GaN nanorods mediated by nanometer-sized AlGaN nucleation islands. Nanostructures of similar morphology are demonstrated on graphene-covered Si(111) as well as Si(100). High crystal and optical quality of the nanorods are evidenced through scanning transmission electron microscopy, micro-Raman, and cathodoluminescence measurements supported by finite-difference time-domain simulations. Current-voltage characteristics revealed high vertical conduction of the as-grown GaN nanorods through the Si substrates. These findings are substantial to advance the integration of GaN-based devices on any substrates of choice that sustains the GaN growth temperatures, thereby permitting novel designs of GaN-based heterojunction device concepts. PMID:27124605

  10. 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.

  11. Control of threading dislocations by Al(Ga)InAs reverse-graded buffers grown on GaAs substrates

    NASA Astrophysics Data System (ADS)

    He, Yang; Sun, Yurun; Song, Yan; Zhao, Yongming; Yu, Shuzhen; Dong, Jianrong

    2016-06-01

    High-quality strain-relaxed InP layers with undulating step-graded Al(Ga)InAs buffers were grown on GaAs substrates by metal–organic chemical vapor deposition. Transmission electron microscopy, high-resolution electron microscopy (HREM), atom force microscopy, and photoluminescence were carried out to characterize the metamorphic buffers. V-shaped dislocations in [001] Al(Ga)InAs reverse-graded layers were observed by HREM and the behavior of reverse-graded layers was simulated theoretically using analytical models. Both the experimental and theoretical results indicated that the insertion of reverse-graded layers with appropriately designed thicknesses and In grading coefficients promotes the annihilation and coalescence reactions between threading dislocations and reduces threading dislocations density.

  12. High-quality InN films on GaN using graded InGaN buffers by MBE

    NASA Astrophysics Data System (ADS)

    Islam, SM; Protasenko, Vladimir; Rouvimov, Sergei; (Grace Xing, Huili; Jena, Debdeep

    2016-05-01

    The growth of high-quality thick InN films is challenging because of the lack of native substrates. In this work, we demonstrate the use of a linearly graded InGaN buffer layer for the growth of InN films on GaN substrates. A 500 nm InN film with <0.1 nm RMS roughness is obtained with a peak mobility of 1410 cm2/(V·s) at 300 K. A strong room temperature photoluminescence showing a bandgap of 0.65 eV with 79 meV linewidth is observed. A graded InGaN buffer is found to lead to extremely smooth and high-quality InN films.

  13. Growth of InSb on GaAs Substrates Using InAlSb Buffers for Magnetic Field Sensor Applications

    SciTech Connect

    BIEFELD,ROBERT M.; PHILLIPS,J.D.

    1999-12-08

    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 {approx}0.55{micro}m thick InSb layers with resistive InAlSb buffers on GaAs substrates with measured electron mobilities of {approx}40,000 cm{sup 2}/V.s. We have investigated the In{sub 1-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.

  14. 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.

  15. 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.

  16. Controlling optical polarization of {11-22} semipolar multiple quantum wells using relaxed underlying InGaN buffer layers

    NASA Astrophysics Data System (ADS)

    Okada, Narihito; Okamura, Yasuhiro; Uchida, Katsumi; Tadatomo, Kazuyuki

    2016-08-01

    We successfully fabricated {11-22} multiple quantum wells (MQWs) having different emission peak wavelengths on partially or completely relaxed thick InGaN buffer layers with different In contents formed on a semipolar {11-22} GaN layer, which was grown on a patterned r-plane sapphire substrate. The polarization properties changed significantly with changing in In content and thickness for InGaN buffer layer. For the same In content of the InGaN buffer layer, the optical polarization changed with an increase in the thickness of the underlying InGaN buffer layer, indicating a change in the relaxation ratio of the InGaN buffer layer. Similarly, for the same thickness of the InGaN buffer layer, the optical polarization changed by changing In content of the InGaN buffer layer. Thus, the degree of optical polarization could be controlled by varying the In content of the underlying InGaN buffer layer.

  17. Relaxed InxGa1-xAs graded buffers grown with organometallic vapor phase epitaxy on GaAs

    NASA Astrophysics Data System (ADS)

    Bulsara, Mayank T.; Leitz, Chris; Fitzgerald, Eugene A.

    1998-03-01

    InxGa1-xAs structures with compositionally graded buffers were grown with organometallic vapor phase epitaxy on GaAs substrates and characterized with plan-view and cross-sectional transmission electron microscopy, atomic force microscopy, and x-ray diffraction. The results show that surface roughness experiences a maximum at growth temperatures where phase separation occurs in InxGa1-xAs. The strain fields from misfit dislocations induce this phase separation in the <110> directions. At growth temperatures above and below this temperature, the surface roughness is decreased significantly; however, only growth temperatures above this regime ensure nearly complete relaxed graded buffers with the most uniform composition caps. With the optimum growth temperature for grading InxGa1-xAs determined to be 700 °C, it was possible to produce In0.33Ga0.67As diode structures on GaAs with threading dislocation densities <8.5×106/cm2.

  18. AlGaN/GaN HEMTs with very thin buffer on Si (111) for nanosystems applications

    NASA Astrophysics Data System (ADS)

    Leclaire, P.; Chenot, S.; Buchaillot, L.; Cordier, Y.; Théron, D.; Faucher, M.

    2014-11-01

    In the present work, AlGaN/GaN high electron mobility transistors (HEMTs) have been grown with very thin buffer layers on silicon substrates in view of developing nano electromechanical systems (NEMS) for sensors applications. To ensure transducer operation in the MHz range together with low mechanical stiffness, epitaxial structures with thickness below 1 μm have to be developed. We report on the evolution of the material and electrical properties of AlGaN/GaN HEMTs with thicknesses varying from 2 μm to 0.5 μm. The set of parameters obtained includes in-plane Young modulus of 250 GPa in association with carrier density of 6 × 1012 cm-2 and mobility above 1000 cm2 V-1 s-1. The resulting behavior of demonstration transistors validates these epilayers for electromechanical resonators operation.

  19. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-06-01

    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.

  1. The influences of AlN/GaN superlattices buffer on the characteristics of AlGaN/GaN-on-Si (1 1 1) template

    NASA Astrophysics Data System (ADS)

    Ni, Yiqiang; He, Zhiyuan; Zhou, Deqiu; Yao, Yao; Yang, Fan; Zhou, Guilin; Shen, Zhen; Zhong, Jian; Zhen, Yue; Zhang, Baijun; Liu, Yang

    2015-07-01

    The influence of AlN/GaN superlattices (SL) buffer on the characteristics of AlGaN/GaN-on-Si (1 1 1) template was studied in detail. There existed an optimized Relative AlN Thickness (RAT) in the superlattices buffer which can not only further filtering the edge- and screw-type dislocations to the upper epilayer and lead to a good crystal quality with narrowest (0 0 0 2) and (1 0 -1 2) full width of half maximum (FWHMs), 439″ and 843″, but also improve the surface roughness to enhance the Two dimensional electron gas (2DEG) mobility and superior electrical properties were achieved. Moreover, an optimized RAT in SL can induce a proper compressive stress to the subsequently grown GaN epilayer and protect it from crack during the cooling step, which can also lead to a better wafer bending.

  2. High growth rate of AlGaN for buffer structures for GaN on Si to increase throughput

    NASA Astrophysics Data System (ADS)

    Matsumoto, Koh; Ubukata, Akinori; Ikenaga, Kazutada; Naito, Kazuki; Yamamoto, Jun; Yano, Yoshiki; Tabuchi, Toshiya; Yamaguchi, Akira; Ban, Yuzaburo; Uchiyama, Kosuke

    2012-03-01

    Throughput requirement of the epitaxial process of GaN on Si is described. The impact of the growth rate of AlGaN for the buffer layer of GaN on Si is highlighted. In the attempt of growing GaN on Si, we have tested a production scale high flow speed MOVPE reactor (TAIYO NIPPON SANSO UR25k) for 6 inch X 7 wafers. Al0.58Ga0.42N was grown with the growth rate of 1.85μm/hr at 30 kPa. AlN was grown with the growth rate of 1.4μm/hr at 13kPa. AlN/GaN SLS (5nm/20nm) was also grown at the growth rate of 1.4μm/hr. An excellent uniformity of aluminum concentration of less than 0.5% was also obtained for Al0.58Ga0.42N. The challenge which we are facing to further increase of the throughput is summarized.

  3. 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.

  4. β-Ga2O3 thin films on sapphire pre-seeded by homo-self-templated buffer layer for solar-blind UV photodetector

    NASA Astrophysics Data System (ADS)

    Liu, X. Z.; Guo, P.; Sheng, T.; Qian, L. X.; Zhang, W. L.; Li, Y. R.

    2016-01-01

    Gallium oxide thin films were grown on c-plane sapphire substrate by molecular beam epitaxy. The homo-self-templated buffer layer was introduced for the gallium oxide thin film growth, and accordingly the FWHM of the on-axis (2 bar 0 1) β-Ga2O3 diffraction peak of the X-ray diffraction rocking curve was reduced from 1.9° to 0.9°, proving an improvement in the crystalline quality of β-Ga2O3 thin film. In addition, the planar-geometry metal-semiconductor-metal photoconductive detectors (PDs) were manufactured by using the 100 nm β-Ga2O3 thin films. Accordingly, the PDs based on the β-Ga2O3 thin films with homo-self-templated buffer layer performed obviously improved device properties, such as small dark current of 0.04 nA, high photo- to dark- current ratio in the order of 104, large photoresponsivity of 259 A/W, high external quantum efficiency of 7.9 × 104%, weak persistent photoconductivity, and excellent solar-blind UV responsivity. Hence, it is reasonable to believe that the β-Ga2O3 thin film grown with homo-self-templated buffer layer is a promising candidate for the application in solar-blind UV camera.

  5. Transition metal oxide as anode interface buffer for impedance spectroscopy

    NASA Astrophysics Data System (ADS)

    Xu, Hui; Tang, Chao; Wang, Xu-Liang; Zhai, Wen-Juan; Liu, Rui-Lan; Rong, Zhou; Pang, Zong-Qiang; Jiang, Bing; Fan, Qu-Li; Huang, Wei

    2015-12-01

    Impedance spectroscopy is a strong method in electric measurement, which also shows powerful function in research of carrier dynamics in organic semiconductors when suitable mathematical physical models are used. Apart from this, another requirement is that the contact interface between the electrode and materials should at least be quasi-ohmic contact. So in this report, three different transitional metal oxides, V2O5, MoO3 and WO3 were used as hole injection buffer for interface of ITO/NPB. Through the impedance spectroscopy and PSO algorithm, the carrier mobilities and I-V characteristics of the NPB in different devices were measured. Then the data curves were compared with the single layer device without the interface layer in order to investigate the influence of transitional metal oxides on the carrier mobility. The careful research showed that when the work function (WF) of the buffer material was just between the work function of anode and the HOMO of the organic material, such interface material could work as a good bridge for carrier injection. Under such condition, the carrier mobility measured through impedance spectroscopy should be close to the intrinsic value. Considering that the HOMO (or LUMO) of most organic semiconductors did not match with the work function of the electrode, this report also provides a method for wide application of impedance spectroscopy to the research of carrier dynamics.

  6. 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.

  7. Strain-driven synthesis of <112> direction InAs nanowires in V-grooved trenches on Si using InP/GaAs buffer layers

    NASA Astrophysics Data System (ADS)

    Li, Shiyan; Zhou, Xuliang; Kong, Xiangting; Li, Mengke; Mi, Junping; Wang, Mengqi; Pan, Jiaoqing

    2016-09-01

    The catalyst-free metal organic vapor phase epitaxial growth of InAs nanowires on silicon (001) substrates is investigated by using selectively grown InP/GaAs buffer layers in V-grooved trenches. A strain-driven mechanism of self-aligned <112> direction InAs nanowires growing is proposed and demonstrated by the transmission electron microscopy measurement. The morphology of InAs nanowires is tapered in diameter and exhibits a hexagonal cross-section. The defect-free InAs nanowire shows a pure zinc blende crystal structure and an epitaxial relationship with InP buffer layer.

  8. Effects of continuously or step-continuously graded buffer on the performance of wavelength extended InGaAs photodetectors

    NASA Astrophysics Data System (ADS)

    Du, B.; Gu, Y.; Zhang, Y. G.; Chen, X. Y.; Xi, S. P.; Ma, Y. J.; Ji, W. Y.; Shi, Y. H.; Li, X.; Gong, H. M.

    2016-04-01

    High In content In0.83Ga0.17As photodetector structures with a new kind of buffer scheme have been grown on InP substrate by gas source molecular beam epitaxy. The effects of buffer scheme on material properties and device performances have been investigated both experimentally and theoretically. The structures with the combination of step and continuously graded buffers show reduced surface roughness, improved photoluminescence intensity and lower device dark current than those with simplex continuously graded buffer at the same buffer thickness. The mechanisms have been discussed from X-ray diffraction, photoluminescence, dark current measurements and model analysis.

  9. Ga2Se3 and (InGa)2Se3 as novel buffer layers in the GaAs on Si system

    NASA Astrophysics Data System (ADS)

    Kojima, Nobuaki; Morales, Crisóforo; Ohshita, Yoshio; Yamaguchi, Masafumi

    2013-09-01

    III-V compound solar cells on Si are attractive structure with expectations of the significant cost reduction of high efficiency multi-junction solar cells. However, the large lattice mismatch and thermal expansion coefficient difference between GaAs and Si generate a high density of threading dislocations in III-V overlayers grown on Si. In this paper, novel buffer layers consisting of Ga2Se3 and (InGa)2Se3 III-VI compounds for the GaAs on Si system are proposed. In-rich (InGa)2Se3 has a layered defect zincblende structure. The van der Waals interface of the layered structure should absorb any strain caused by lattice mismatch and thermal expansion coefficient difference between Si and GaAs. As the first step in studying the MBE growth of (InGa)2Se3 compounds, the epitaxial growth of defect zincblende structure Ga2Se3 and layered defect zincblende structure In2Se3 on GaAs(111) was confirmed.

  10. 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

  11. 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.

  12. 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.

  13. 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.

  14. 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)

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

    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 CBr4 beam equivalent pressure of 1.86 × 10-7 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.

  15. 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.

  16. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

    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.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

  18. Effects of low-temperature buffer-layer thickness and growth temperature on the SEE sensitivity of GaAs HIGFET circuits

    SciTech Connect

    Weatherford, T.R.; Fouts, D.J.; Marshall, P.W. |; Marshall, C.J.; Mathes, B.; LaMacchia, M.

    1997-12-01

    Heavy-ion Single Event Effects (SEE) test results reveal the role of growth temperature and buffer layer thickness in the use of a low-temperature grown GaAs (LT GaAs) buffer layer for suppressing SEE sensitivity in GaAs HIGFET circuits.

  19. Effects of buffer layer and back-surface field on MBE-grown InGaAsP/InGaAs solar cells

    NASA Astrophysics Data System (ADS)

    Wu, Yuanyuan; Ji, Lian; Dai, Pai; Tan, Ming; Lu, Shulong; Yang, Hui

    2016-02-01

    Solid-state molecular beam epitaxy (MBE)-grown InGaAsP/InGaAs dual-junction solar cells on InP substrates are reported. An efficiency of 10.6% under 1-sun AM1.5 global light intensity is realized for the dual-junction solar cell, while the efficiencies of 16.4 and 12.3% are reached for the top InGaAsP and bottom InGaAs cells, respectively. The effects of the buffer layer and back-surface field on the performance of solar cells are discussed. High device performance is achieved in the case of a low concentration of oxygen and weak recombination when InGaAs buffers and InP back-surface field layers are used, respectively.

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

    SciTech Connect

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

    2013-09-21

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

  1. 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.

  2. Growth and characterization of metamorphic InxGa1-xAs/InAlAs (x >= 0.8) modulation doped heterostructures on GaAs using a linearly graded In(AlGa)as buffer layer

    NASA Astrophysics Data System (ADS)

    Wang, S. M.; Karlsson, C.; Rorsman, N.; Bergh, M.; Olsson, E.; Andersson, T. G.

    1997-01-01

    Metamorphic InxGa1-xAs/InAlAs (x >= 0.8) modulation doped heterostructures have been grown on GaAs using a linearly graded In(AlGa)As buffer layer, and their structural and electric properties have been investigated. Surface morphology was found to depend on growth temperature and graded buffer thickness. Low growth temperature resulted in a relatively smooth surface with a minimum root-mean-square roughness value of 4-7 nm. The In(AlGa)As graded buffer effectively prevented dislocations from threading into the top layers. The epilayer grown on the graded buffer was tilted and not fully relaxed. High electron mobility and sheet density were achieved. The highest mobility value was 13740 cm2/Vs with a carrier density of 1.9 · 1012 cm-2 at 300 K. These values are comparable with InP-based InGaAs/InAlAs modulation doped heterostructures.

  3. 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

  4. 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.

  5. 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.

  6. InP-based InxGa1-xAs metamorphic buffers with different mismatch grading rates

    NASA Astrophysics Data System (ADS)

    Xiang, Fang; Yi, Gu; Xingyou, Chen; Li, Zhou; Yuanying, Cao; Haosibaiyin, Li; Yonggang, Zhang

    2013-07-01

    Linearly graded InxGa1-xAs metamorphic buffers with different mismatch grading rates were grown on InP substrate by gas source molecular beam epitaxy. Room temperature photoluminescence spectra show that the sample with lower mismatch grading rate in the buffer has stronger photoluminescence signal, indicating the improved optical property. Atomic force microscope images show that the lower mismatch grading rate in the buffer leads to a slightly rougher surface. The relaxation procedure with two steps in the buffer layers has been observed by X-ray diffraction reciprocal space mapping. The measurements of X-ray diffraction also reveal that the lower mismatch grading rate in the buffer is beneficial for the lattice relaxation and release of residual strain. To further increase the relaxation degree, a lower mismatch grading rate and composition “overshoot" are suggested.

  7. 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.

  8. 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

    2016-06-01

    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. PMID:27181758

  9. 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.

  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

    2016-01-01

    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. PMID:26794268

  11. 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.

  12. 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

  13. High-Quality AgGaTe2 Layers on Si Substrates with Ag2Te Buffer Layers

    NASA Astrophysics Data System (ADS)

    Uruno, Aya; Kobayashi, Masakazu

    2016-05-01

    AgGaTe2 layers were successfully grown on Si substrates by the close-spaced sublimation method. The Si substrates were confirmed to be etched during AgGaTe2 layer growth when the layer was grown directly on the substrate. To eliminate melt-back etching, a buffer layer of Ag2Te was introduced. It was found that the Ag2Te buffer layer changed into the AgGaTe2 layer during the growth process, and a uniform AgGaTe2 layer with an abrupt interface was formed. Both the diffusion of Ga into Ag2Te and the growth of AgGaTe2 occurred simultaneously. It was confirmed that uniform AgGaTe2 layers could be formed without any traces of the Ag2Te layer or melt-back etching by tuning the growth parameters. A solar cell was also fabricated using the p-AgGaTe2/n-Si heterojunction. This solar cell showed conversion efficiency of approximately 3%.

  14. High-Quality AgGaTe2 Layers on Si Substrates with Ag2Te Buffer Layers

    NASA Astrophysics Data System (ADS)

    Uruno, Aya; Kobayashi, Masakazu

    2016-09-01

    AgGaTe2 layers were successfully grown on Si substrates by the close-spaced sublimation method. The Si substrates were confirmed to be etched during AgGaTe2 layer growth when the layer was grown directly on the substrate. To eliminate melt-back etching, a buffer layer of Ag2Te was introduced. It was found that the Ag2Te buffer layer changed into the AgGaTe2 layer during the growth process, and a uniform AgGaTe2 layer with an abrupt interface was formed. Both the diffusion of Ga into Ag2Te and the growth of AgGaTe2 occurred simultaneously. It was confirmed that uniform AgGaTe2 layers could be formed without any traces of the Ag2Te layer or melt-back etching by tuning the growth parameters. A solar cell was also fabricated using the p-AgGaTe2/n-Si heterojunction. This solar cell showed conversion efficiency of approximately 3%.

  15. 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

  16. 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

    2016-01-01

    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 × 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. PMID:27412372

  17. 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.

  18. 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.

  19. 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.

  20. Optical properties of InGaAs linear graded buffer layers on GaAs grown by metalorganic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Lee, B.; Baek, J. H.; Lee, J. H.; Choi, S. W.; Jung, S. D.; Han, W. S.; Lee, E. H.

    1996-05-01

    We report optical characteristics of linear graded InxGa1-xAs (XIn=0-0.58) buffer layers grown on GaAs by low-pressure metalorganic chemical vapor deposition. Two types of wirelike surface structures were observed from the layers grown at two different temperatures. Low-temperature photoluminescence (PL) and double-crystal x-ray diffractometric measurements indicate that the PL energy and the relaxation of the graded layers were strongly dependent on the top surface structure. InGaAs cap layers were grown on top of the graded buffer layers with a variation of indium composition. A strong PL signal was observed from the top region of the graded layer grown with a lattice-matched cap layer. It suggests that the top region of the grade, similar to a graded well structure, is compressively strained but is of high structural quality without dislocations.

  1. Non-polar a-plane ZnO films grown on r-Al2O3 substrates using GaN buffer layers

    NASA Astrophysics Data System (ADS)

    Xu, C. X.; Chen, W.; Pan, X. H.; Chen, S. S.; Ye, Z. Z.; Huang, J. Y.

    2016-09-01

    In this work, GaN buffer layer has been used to grow non-polar a-plane ZnO films by laser-assisted and plasma-assisted molecular beam epitaxy. The thickness of GaN buffer layer ranges from ∼3 to 12 nm. The GaN buffer thickness effect on the properties of a-plane ZnO thin films is carefully investigated. The results show that the surface morphology, crystal quality and optical properties of a-plane ZnO films are strongly correlated with the thickness of GaN buffer layer. It was found that with 6 nm GaN buffer layer, a-plane ZnO films display the best crystal quality with X-ray diffraction rocking curve full-width at half-maximum of only 161 arcsec for the (101) reflection.

  2. 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.

  3. Hydride vapor phase epitaxy growth of GaN on sapphire with ZnO buffer layers

    NASA Astrophysics Data System (ADS)

    Gu, S.; Zhang, R.; Shi, Y.; Zheng, Y.; Zhang, L.; Kuech, T. F.

    The initial stages and subsequent growth of GaN on sapphire using ZnO buffer layers is reported for the hydride vapor phase epitaxy technique. A high gas-phase supersaturation in the growth ambient was used to favor a rapid initial growth on the substrate. A subsequent growth step was employed under conditions that favor a high lateral growth rate in order to promote the coalescence of the initial islands and provide optimal material properties. The specific gas-phase mole fractions of the GaCl and NH3 at the growth front control both the vertical and lateral growth rates. The use of a two-step growth process in the GaN growth leads to a controlled morphology and improved material properties for GaN materials when grown with a ZnO buffer layer. An optimized set of growth conditions, utilizing this two-step process, was found to also improve the growth directly on sapphire without a ZnO buffer layer.

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

    SciTech Connect

    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.

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

    SciTech Connect

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

    2005-01-24

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

  6. Reduction of Crosshatch Roughness and Threading Dislocation Density in Metamorphic GaInP Buffers and GaInAs Solar Cells

    SciTech Connect

    France, R. M.; Geisz, J. F.; Steiner, M. A.; To, B.; Romero, M. J.; Olavarria, W. J.; King, R. R.

    2012-05-15

    Surface crosshatch roughness typically develops during the growth of lattice-mismatched compositionally graded buffers and can limit misfit dislocation glide. In this study, the crosshatch roughness during growth of a compressive GaInP/GaAs graded buffer is reduced by increasing the phosphine partial pressure throughout the metamorphic growth. Changes in the average misfit dislocation length are qualitatively determined by characterizing the threading defect density and residual strain. The decrease of crosshatch roughness leads to an increase in the average misfit dislocation glide length, indicating that the surface roughness is limiting dislocation glide. Growth rate is also analyzed as a method to reduce surface crosshatch roughness and increase glide length, but has a more complicated relationship with glide kinetics. Using knowledge gained from these experiments, high quality inverted GaInAs 1 eV solar cells are grown on a GaInP compositionally graded buffer with reduced roughness and threading dislocation density. The open circuit voltage is only 0.38 V lower than the bandgap potential at a short circuit current density of 15 mA/cm{sup 2}, suggesting that there is very little loss due to the lattice mismatch.

  7. 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.

  8. 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.

  9. 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.

  10. Magnetic properties of nano-patterned GaMnAs films grown on ZnCdSe buffer layers

    NASA Astrophysics Data System (ADS)

    Dong, Sining; Li, Xiang; Kanzyuba, Vasily; Yoo, Taehee; Liu, Xinyu; Dobrowolska, Malgorzata; Furdyna, Jacek

    Magnetic semiconductor nanostructures are attracting intense attention, both because of their fundamental physical properties, and because of the promise which they hold for building smaller, faster and more energy-efficient devices. In this study we report successful MBE growth of GaMnAs films on the GaAs (100) substrates with ZnCdSe buffer layers, which results in perpendicular magnetic easy axis in the GaMnAs films. The GaMnAs/ZnCdSe films have been etched into nano-stripe shapes with various widths below 200nm by e-beam lithography, which resulted in a new geometry of interest for perpendicular magnetic recording. Magnetic anisotropy of as-grown GaMnAs films and nano-stripes was then studied by SQUID magnetometry. The results indicate that the GaMnAs films consist of magnetic domains with magnetization normal to the film plane, having rather high coercivety, which survives after nanofabrication. This is also confirmed by the dynamics of the domain motion as shown by AC susceptibility measurements. These findings are of interest for understanding the magnetic anisotropy mechanisms in GaMnAs and its domain structures, as well as for designing of nano-sized spintronic devices which require hard ferromagnetic behavior with perpendicular easy axes. This work was supported by the National Science Foundation Grant DMR1400432.

  11. 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.

  12. 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.

  13. Leaching with Penicillium simplicissimum: Influence of Metals and Buffers on Proton Extrusion and Citric Acid Production

    PubMed Central

    Franz, Andreas; Burgstaller, Wolfgang; Schinner, Franz

    1991-01-01

    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. Surface phenomena possibly involving the plasma membrane H+-ATPase are thought to participate in the induction of citric acid excretion by P. simplicissimum in the presence of industrial filter dust. PMID:16348442

  14. Ligand-enhanced electrokinetic remediation of metal-contaminated marine sediments with high acid buffering capacity.

    PubMed

    Masi, Matteo; Iannelli, Renato; Losito, Gabriella

    2016-06-01

    The suitability of electrokinetic remediation for removing heavy metals from dredged marine sediments with high acid buffering capacity was investigated. Laboratory-scale electrokinetic remediation experiments were carried out by applying two different voltage gradients to the sediment (0.5 and 0.8 V/cm) while circulating water or two different chelating agents at the electrode compartments. Tap water, 0.1 M citric acid and 0.1 M ethylenediaminetetraacetic acid (EDTA) solutions were used respectively. The investigated metals were Zn, Pb, V, Ni and Cu. In the unenhanced experiment, the acid front could not propagate due to the high acid buffering capacity of the sediments; the production of OH(-) ions at the cathode resulted in a high-pH environment causing the precipitation of CaCO3 and metal hydroxides. The use of citric acid prevented the formation of precipitates, but solubilisation and mobilisation of metal species were not sufficiently achieved. Metal removal was relevant when EDTA was used as the conditioning agent, and the electric potential was raised up to 0.8 V/cm. EDTA led to the formation of negatively charged complexes with metals which migrated towards the anode compartment by electromigration. This result shows that metal removal from sediments with high acid buffering capacity may be achieved by enhancing the electrokinetic process by EDTA addition when the acidification of the medium is not economically and/or environmentally sustainable. PMID:26490900

  15. 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.

  16. CdTe buffered GaAs thin-slab IR waveguide modulators and T/R filter

    NASA Astrophysics Data System (ADS)

    Cheo, P. K.; Brown, R. T.; Carrier, G.; Glueck, W.; Wagner, R.; Gilden, M.

    1989-07-01

    Broadband electrooptic modulation and frequency shifting of CO2 lasers using GaAs thin-slab waveguides have been described previously. The performance of an unbuffered GaAs waveguide traveling-wave modulator has been found to yield a sideband power conversion efficiency of 4.5 + or - .0000045 or -43.6 dB for one watt of microwave drive power. This paper presents the performance of CdTe buffered GaAs waveguide modulator and describes the structural parameters that have been modified to gain 5 dB improvement from that provided by unbuffered IR waveguide modulators. CdTe buffered GaAs thin-slab waveguide modulators with very low optical and microwave insertion losses, have been fabricated. The measured single sideband power that can be converted from the CO2 laser input power is -39 dB for one watt microwave driver power, as compared to a measured value of -44 dB from an unbuffered modulator. The output beam quality has also been improved significantly. A transmission/reflection filter designed to separate the sidebands from the carrier has been fabricated and tested. The rejection ratio of carrier power to sideband power is -19 dB.

  17. 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.

  18. 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.

  19. Growth of wurtzite and zinc-blende phased GaN on silicon (100) substrate with sputtered AlN buffer layer

    NASA Astrophysics Data System (ADS)

    Pang, Wen-Yuan; Lo, Ikai; Wu, Sean; Lin, Zhi-Xun; Shih, Cheng-Hung; Lin, Yu-Chiao; Wang, Ying-Chieh; Hu, Chia-Hsuan; Hsu, Gary Z. L.

    2013-11-01

    GaN films were grown by plasma-assisted molecular beam epitaxy with a sputtered AlN buffer layer on Si (100) substrate. From the analyses of X-ray diffraction (XRD), transmission electron microscopy (TEM) and photoluminescence (PL) measurements, we showed that the variant M-plane, A-plane and c-plane GaN wurtzite structures can be achieved by the selection of crystalline orientation of sputtered AlN buffer layer and the control of epitaxial growth temperature. We also found that the GaN layer grown on sputtered AlN buffer layer can be converted to GaN zinc-blende structure at the epitaxial growth temperature higher than 750 °C and under Ga-rich condition.

  20. 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.

  1. Catalyst-free growth of InP nanowires on patterned Si (001) substrate by using GaAs buffer layer

    NASA Astrophysics Data System (ADS)

    Li, Shiyan; Zhou, Xuliang; Kong, Xiangting; Li, Mengke; Mi, Junping; Pan, Jiaoqing

    2016-04-01

    The catalyst-free metal organic vapor phase epitaxial growth of InP nanowires on silicon (001) substrate is investigated using selectively grown GaAs buffer layers in V-shaped trenches. A yield up to 70% of nanowires is self-aligned in uncommon <112> directions under the optimized growth conditions. The evolution mechanism of self-aligned <112> directions for nanowires is discussed and demonstrated. Using this growth method, we can achieve branched and direction switched InP nanowires by varying the V/III ratio in situ. The structure of the nanowires is characterized by scanning electron microscope and transmission electron microscopy measurements. The crystal structure of the InP nanowires is stacking-faults-free wurtzite with its c axis perpendicular to the nanowire axis.

  2. Photoelectric characteristics of metal/InGaN/GaN heterojunction structure

    NASA Astrophysics Data System (ADS)

    Sun, X.; Liu, W. B.; Jiang, D. S.; Liu, Z. S.; Zhang, S.; Wang, L. L.; Wang, H.; Zhu, J. J.; Duan, L. H.; Wang, Y. T.; Zhao, D. G.; Zhang, S. M.; Yang, H.

    2008-08-01

    A heterojunction structure photodetector was fabricated by evaporating a semitransparent Ni/Au metal film on the InGaN/GaN structure. The photocurrent (PC) spectra show that both the Schottky junction (NiAu/InGaN) and the InGaN/GaN isotype heterojunction contribute to the PC signal which suggests that two junctions are connected in series and result in a broader spectral response of the device. Secondary electron, cathodoluminescence and electron-beam-induced current images measured from the same area of the edge surface clearly reveal the profile of the layer structure and distribution of the built-in electric field around the two junctions. A band diagram of the device is drawn based on the consideration of the polarization effect at the InGaN/GaN interface. The analysis is consistent with the physical mechanism of a tandem structure of two junctions connected in series.

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

    NASA Astrophysics Data System (ADS)

    Sun, Shichuang; Fu, Kai; Yu, Guohao; Zhang, Zhili; Song, Liang; Deng, Xuguang; Qi, Zhiqiang; Li, Shuiming; Sun, Qian; Cai, Yong; Dai, Jiangnan; Chen, Changqing; Zhang, Baoshun

    2016-01-01

    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 × 1014 cm-2) and 90 keV (dose: 1 × 1014 cm-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 IDSmax at a gate voltage of 3 V was 701 mA/mm and the maximum transconductance gmmax was 83 mS/mm.

  4. 10Gbps operation of a metamorphic InGaP buffered In 0.53Ga 0.47As p-i-n photodetector grown on GaAs substrate

    NASA Astrophysics Data System (ADS)

    Liao, Yu-Sheng; Lin, Gong-Ru; Lin, Chi-Kuan; Chu, Yi-Shiang; Kuo, Hao-Chung; Feng, Milton

    2005-11-01

    A novel top-illuminated In 0.53Ga 0.47As p-i-n photodiodes (MM-PINPD) grown on GaAs substrate by using a linearly graded metamorphic In xGa 1-xP (x graded from 0.49 to 1) buffer layer has been demonstrated on the SONET OC-192 receiving performance. With a cost-efficient TO-46 package, the MM-PINPD at data rate of 10 Gbit/s can be obtained at minimum optical power of -19.5 dBm. At wavelength of 1550nm, the dark current, optical responsivities, noise equivalent power, and operational bandwidth of the MM-PINPD with aperture diameter of 60 μm are 13 pA, 0.6 A/W, 3.4×10 -15 W/Hz 1/2, and 8 GHz, respectively. All the parameters are comparable to those of similar devices made on InP substrate or other InGaAs products epitaxially grown on an InGaAlAs buffered GaAs substrate. The performances of the MM-PINPD on GaAs are analyzed by impulse injecting of 1.2-ps pulse-train, eye pattern at 10Gbps, and frequency response from VNA.

  5. Comparison of different pathways in metamorphic graded buffers on GaAs substrate: Indium incorporation with surface roughness

    NASA Astrophysics Data System (ADS)

    Kumar, Rahul; Mukhopadhyay, P.; Bag, A.; Jana, S. Kr.; Chakraborty, A.; Das, S.; Mahata, M. Kr.; Biswas, D.

    2015-01-01

    In this work, compositionally graded In(Al,Ga)As metamorphic buffers (MBs) on GaAs substrate have been grown by MBE through three different paths. A comparative study has been done to comprehend the effect of underlying MB on the constant composition InAlAs healing layer by analyzing the relaxation behaviour, composition and surface morphology of the grown structures. The compositional variation between the constant composition healing layers on top of graded MB has been observed in all three samples although the growth conditions have been kept same. Indium incorporation rate has been found to be dependent on underlying MB. By combining the result of atomic force microscopy, photo-luminescence and X-ray reciprocal space mapping, varying surface roughness has been proposed as the probable driving force behind different Indium incorporation rate.

  6. Buffer-gas-induced shift and broadening of hyperfine resonances in alkali-metal vapors

    NASA Astrophysics Data System (ADS)

    Oreto, P. J.; Jau, Y.-Y.; Post, A. B.; Kuzma, N. N.; Happer, W.

    2004-04-01

    We review the shift and broadening of hyperfine resonance lines of alkali-metal atoms in buffer gases. We present a simple theory both for the shift and the broadening induced by He gas. The theory is parametrized by the scattering length of slow electrons on He atoms and by the measured hyperfine intervals and binding energies of the S states of alkali-metal atoms. The calculated shifts and their temperature dependence are in good agreement with the published experimental data. The calculated broadening is 1.6 times smaller than the recent measurements, and more than 20 times smaller than the earlier measurements. We attribute much of the linewidth in the earlier experiments to possible small temperature gradients and the resulting inhomogeneous line broadening from the temperature dependence of hyperfine frequency shift at constant buffer-gas pressure.

  7. ZnO buffer layer for metal films on silicon substrates

    DOEpatents

    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.

  8. Elastic properties of Pu metal and Pu-Ga alloys

    SciTech Connect

    Soderlind, P; Landa, A; Klepeis, J E; Suzuki, Y; Migliori, A

    2010-01-05

    We present elastic properties, theoretical and experimental, of Pu metal and Pu-Ga ({delta}) alloys together with ab initio equilibrium equation-of-state for these systems. For the theoretical treatment we employ density-functional theory in conjunction with spin-orbit coupling and orbital polarization for the metal and coherent-potential approximation for the alloys. Pu and Pu-Ga alloys are also investigated experimentally using resonant ultrasound spectroscopy. We show that orbital correlations become more important proceeding from {alpha} {yields} {beta} {yields} {gamma} plutonium, thus suggesting increasing f-electron correlation (localization). For the {delta}-Pu-Ga alloys we find a softening with larger Ga content, i.e., atomic volume, bulk modulus, and elastic constants, suggest a weakened chemical bonding with addition of Ga. Our measurements confirm qualitatively the theory but uncertainties remain when comparing the model with experiments.

  9. The effect of AlN buffer growth parameters on the defect structure of GaN grown on sapphire by plasma-assisted molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Wong, Yuen-Yee; Chang, Edward Yi; Yang, Tsung-Hsi; Chang, Jet-Rung; Chen, Yi-Cheng; Ku, Jui-Tai; Lee, Ching-Ting; Chang, Chun-Wei

    2009-03-01

    The defect structure of GaN film grown on sapphire by plasma-assisted molecular beam epitaxy (PAMBE) depends on the growth temperature and thickness of the aluminum nitride (AlN) buffer layer. High-resolution X-ray diffraction was used to measure symmetric (0 0 0 2) and asymmetric (1 0 1¯ 2) rocking curve (ω-scans) broadening, which allowed the estimation of screw threading dislocation (TD) and edge TD densities, respectively. For GaN grown on lower-temperature buffer, the density of screw TD was increased while the density of edge TD was decreased. Further examinations revealed that the edge TD was closely related to stress in GaN film and the screw TD was controlled by AlN surface roughness. Since the GaN defect was dominated by edge TD, the total TD was also effectively suppressed with the use of lower-temperature buffer with appropriate thickness.

  10. Single-junction GaAsP solar cells grown on SiGe graded buffers on Si

    NASA Astrophysics Data System (ADS)

    Faucher, J.; Gerger, A.; Tomasulo, S.; Ebert, C.; Lochtefeld, A.; Barnett, A.; Lee, M. L.

    2013-11-01

    We have investigated the microstructure and device characteristics of GaAs0.82P0.18 solar cells grown on Si0.20Ge0.80/Si graded buffers. Anti-phase domains (APDs) were largely self-annihilated within the In0.39Ga0.61P initiation layer although a low density of APDs was found to propagate to the surface. A combination of techniques was used to show that the GaAs0.82P0.18 cells have a threading dislocation density of 1.2 ± 0.2 × 107 cm-2. Despite these extended defects, the devices exhibited high open-circuit voltages of 1.10-1.12 V. These results indicate that cascading a GaAs0.82P0.18 top cell with a lower-bandgap Si0.20Ge0.80 cell is a promising approach for high-efficiency dual-junction devices on low-cost Si substrates.

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

    SciTech Connect

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

    2011-09-01

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

  12. Thick (>20 µm) and high-resistivity carbon-doped GaN-buffer layers grown by metalorganic vapor phase epitaxy on n-type GaN substrates

    NASA Astrophysics Data System (ADS)

    Tsuchiya, Tomonobu; Terano, Akihisa; Mochizuki, Kazuhiro

    2016-05-01

    To improve the performance of GaN power devices, we have investigated the crystalline quality of thick (>20 µm) carbon-doped GaN layers on n-type GaN substrates and templates. The surface morphologies and X-ray rocking curves of carbon-doped GaN layers were improved by using GaN substrates. However, the crystalline quality degraded when the carbon concentration was too high (1 × 1020 cm‑3), even in the case of GaN substrates. High breakdown voltages (approximately 7 kV under a lateral configuration) were obtained for the carbon-doped GaN layers on n-type GaN substrates when the carbon concentration was 5 × 1019 cm‑3. These results indicate that lateral power devices with high breakdown voltage can be fabricated by using thick carbon-doped GaN buffer layers, even on n-type GaN substrates.

  13. 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. PMID:18778107

  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. 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.

  16. Comparative research on reflection-mode GaAs photocathode with graded AlxGa1-xAs buffer layer

    NASA Astrophysics Data System (ADS)

    Chen, Liang; Shen, Yang; Zhang, Shuqin; Qian, Yunsheng; Xu, Sunan

    2015-11-01

    The graded Al compositional AlxGa1-xAs buffer layer can not only form continuous internal electric field from buffer layer to active layer but also optimize the interface properties by decreasing the misfit dislocations and stacking faults arising from lattice mismatch. By measuring the spectral response current (SRC) for two reflection-mode (r-mode) designed samples of graded and stationary Al compositional structure, we can find the special phenomenon that the graded structure had quite influence at the middle wavelength band from 550 nm to 850 nm, but not the short wavelength band from 400 nm to 550 nm, though the buffer layer can only absorb photon energy at the short wavelength band. Through the comparative research for designed samples through SPV before Cs-O activation and SRC after Cs-O activation, the graded structure can well optimize the key parameters such as LD, Ln, Sv and P. For the photon absorption lengths are relative little at the short wavelength band and relative long at the middle wavelength band, so the optimizations of key parameters have little influence on photo-excited electrons at the short wavelength band which are mainly excited from the region in active layer near surface barriers. The optimizations of key parameter, mainly the back interface recombination velocity (Sv), can have quite impact on photo-excited electrons at the middle short wavelength band which are mainly excited from the internal active layer near the back interface. This comparative research can help to well study the photo-emission theory and structure design on graded Al compositional design for r-mode GaAs photocathodes in the future research.

  17. Comparison of different grading schemes in InGaAs metamorphic buffers on GaAs substrate: Tilt dependence on cross-hatch irregularities

    NASA Astrophysics Data System (ADS)

    Kumar, Rahul; Bag, Ankush; Mukhopadhyay, Partha; Das, Subhashis; Biswas, Dhrubes

    2015-12-01

    InGaAs graded metamorphic buffers (MBs) with different grading strategies have been grown by molecular beam epitaxy (MBE) on GaAs (0 0 1) substrate. A detailed comparative analysis of surface using atomic force microscopy (AFM), and bulk properties using high resolution X-ray diffraction (HRXRD) and room temperature photoluminescence (RTPL) of grown MBs have been presented to comprehend the effectiveness of different grading scheme on InGaAs MBs. Conventional, statistical and fractal analysis on measured AFM data has been performed for in-depth investigation of these surfaces. The grading scheme has been found to have little impact on residual strain while it affects the epitaxial tilt significantly. Moreover, the tilt has been found to depend on growth front irregularities. Tilt magnitude in a graded MB has been found to vary with composition while tilt azimuth has been found to be almost same in the graded layers. PL Intensity and a shift in the PL peaks have been used to study the quality of the MB and residual strain comparatively.

  18. Reduction in edge dislocation density in corundum-structured α-Ga2O3 layers on sapphire substrates with quasi-graded α-(Al,Ga)2O3 buffer layers

    NASA Astrophysics Data System (ADS)

    Jinno, Riena; Uchida, Takayuki; Kaneko, Kentaro; Fujita, Shizuo

    2016-07-01

    Efforts have been made to reduce the density of defects in corundum-structured α-Ga2O3 thin films on sapphire substrates by applying quasi-graded α-(Al x Ga1‑ x )2O3 buffer layers. Transmission electron microscopy images revealed that most strains were located in the α-(Al x Ga1‑ x )2O3 buffer layers, and that the total density of dislocations in the α-Ga2O3 thin films was successfully decreased by more than one order of magnitude compared with that without buffer layers, that is, the screw and edge dislocation densities were about 3 × 108 and 6 × 108 cm‑2, respectively.

  19. 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.

  20. 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.

  1. 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

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

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

    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.

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

    PubMed

    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

  4. Zn0.85Cd0.15Se active layers on graded-composition InxGa1-xAs buffer layers

    NASA Astrophysics Data System (ADS)

    Müller, B. H.; Lantier, R.; Sorba, L.; Heun, S.; Rubini, S.; Lazzarino, M.; Franciosi, A.; Napolitani, E.; Romanato, F.; Drigo, A. V.; Lazzarini, L.; Salviati, G.

    1999-06-01

    We investigated the structural and optical properties of Zn0.85Cd0.15Se epilayers for blue optical emission on lattice-matched InxGa1-xAs buffer layers. Both the II-VI layers and the III-V buffers were grown by molecular beam epitaxy on GaAs(001) wafers. A parabolic In concentration profile within the graded-composition InxGa1-xAs buffers was selected to control strain relaxation and minimize the concentration of threading dislocations. Dislocation-free II-VI growth was readily achieved on the graded buffers, with a Rutherford backscattering yield ratio reduced by a factor of 3 and a deep-level emission intensity reduced by over two orders of magnitude relative to those observed following direct II-VI growth on GaAs. The surface morphology of the materials, however, was found to replicate the crosshatched pattern of the underlying InxGa1-xAs substrates.

  5. 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.

  6. Fabrication of vertical GaN/InGaN heterostructure nanowires using Ni-Au bi-metal catalysts

    PubMed Central

    2013-01-01

    We have fabricated the vertically aligned coaxial or longitudinal heterostructure GaN/InGaN nanowires. The GaN nanowires are first vertically grown by vapor–liquid-solid mechanism using Au/Ni bi-metal catalysts. The GaN nanowires are single crystal grown in the [0001] direction, with a length and diameter of 1 to 10 μm and 100 nm, respectively. The vertical GaN/InGaN coaxial heterostructure nanowires (COHN) are then fabricated by the subsequent deposition of 2 nm of InxGa1-xN shell on the surface of GaN nanowires. The vertical GaN/InGaN longitudinal heterostructure nanowires (LOHN) are also fabricated by subsequent growth of an InGaN layer on the vertically aligned GaN nanowires using the catalyst. The photoluminescence from the COHN and LOHN indicates that the optical properties of GaN nanowires can be tuned by the formation of a coaxial or longitudinal InGaN layer. Our study demonstrates that the bi-metal catalysts are useful for growing vertical as well as heterostructure GaN nanowires. These vertically aligned GaN/InGaN heterostructure nanowires may be useful for the development of high-performance optoelectronic devices. PMID:23803283

  7. Metal contacts on ZnSe and GaN

    SciTech Connect

    Duxstad, K J

    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.

  8. 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. PMID:24803243

  9. 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.

  10. 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.

  11. Air-bridged lateral growth of an Al0.98Ga0.02N layer by introduction of porosity in an AlN buffer

    NASA Astrophysics Data System (ADS)

    Wang, T.; Bai, J.; Parbrook, P. J.; Cullis, A. G.

    2005-10-01

    We demonstrated air-bridged lateral growth of an Al0.98Ga0.02N layer with significant dislocation reduction by introduction of a porous AlN buffer underneath via metalorganic chemical vapor deposition. By modifying growth conditions, a porous AlN layer and an atomically flat AlN layer have been obtained for comparison, confirmed by atomic force microscopy. An Al0.98Ga0.02N layer was subsequently grown on both the porous AlN layer and the atomically flat AlN layer under identical conditions. Significant dislocation reduction was achieved for the Al0.98Ga0.02N layer grown on the porous AlN buffer layer, compared to the layer grown on the atomically flat AlN layer, as observed by transmission electron microscopy. Clear bubbles from the layer grown on the porous AlN buffer layer have been observed, while in contrast, there was not any bubble from the layer on the flat AlN buffer, confirming the mechanism of lateral growth for dislocation reduction. Asymmetric x-ray diffraction studies also indicated that the crystal quality was dramatically improved using the porous AlN buffer layer.

  12. 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.

  13. Strain-free GaN thick films grown on single crystalline ZnO buffer layer with in situ lift-off technique

    SciTech Connect

    Lee, S. W.; Minegishi, T.; Lee, W. H.; Goto, H.; Lee, H. J.; Lee, S. H.; Lee, Hyo-Jong; Ha, J. S.; Goto, T.; Hanada, T.; Cho, M. W.; Yao, T.

    2007-02-05

    Strain-free freestanding GaN layers were prepared by in situ lift-off process using a ZnO buffer as a sacrificing layer. Thin Zn-polar ZnO layers were deposited on c-plane sapphire substrates, which was followed by the growth of Ga-polar GaN layers both by molecular beam epitaxy (MBE). The MBE-grown GaN layer acted as a protecting layer against decomposition of the ZnO layer and as a seeding layer for GaN growth. The ZnO layer was completely in situ etched off during growth of thick GaN layers at low temperature by hydride vapor phase epitaxy. Hence freestanding GaN layers were obtained for the consecutive growth of high-temperature GaN thick layers. The lattice constants of freestanding GaN agree with those of strain-free GaN bulk. Extensive microphotoluminescence study indicates that strain-free states extend throughout the high-temperature grown GaN layers.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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

    2016-02-01

    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. PMID:26674458

  19. 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

    NASA Astrophysics Data System (ADS)

    Hayashi, Hiroaki; Konno, Yuta; Kishino, Katsumi

    2016-02-01

    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.

  20. 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. PMID:27483934

  1. 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.

  2. 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.

  3. A resin-buffered nutrient solution for controlling metal speciation in the algal bottle assay.

    PubMed

    Verheyen, L; Merckx, R; Smolders, E

    2012-06-15

    Metal speciation in solution is uncontrolled during algal growth in the traditional algal bottle assay. A resin-buffered nutrient solution was developed to overcome this problem and this was applied to test the effect of chloride (Cl⁻) on cadmium (Cd) uptake. Standard nutrient solution was enriched with 40 mM of either NaNO₃ or NaCl, and was prepared to contain equal Cd²⁺ but varying dissolved Cd due to the presence of CdCl(n)(2-n) complexes. Both solutions were subsequently used in an algal assay in 100 mL beakers that contained only the solution (designated "-R") or contained the solution together with a cation exchange sulfonate resin (2 g L⁻¹, designated "+R") as a deposit on the bottom of the beaker. Pseudokirchneriella subcapitata was grown for 72 h (1.4 × 10⁵-1.4 × 10⁶ cells mL⁻¹) in stagnant solution and shaken three times a day. Growth was unaffected by the presence of the resin (p>0.05). The Cd concentrations in solution of the -R devices decreased with 50-58% of initial values due to Cd uptake. No such changes were found in the +R devices or in abiotic controls. Cd uptake was unaffected by either NaNO₃ or NaCl treatment in the +R device, confirming that Cd²⁺ is the preferred Cd species in line with the general concept of metal bioavailability. In contrast, Cd uptake in the -R devices was two-fold larger in the NaCl treatment than in the NaNO₃ treatment (p<0.001), suggesting that CdCl(n)(2-n) complexes are bioavailable in this traditional set-up. However this bioavailability is partially, but not completely, an apparent one, because of the considerable depletion of solution ¹⁰⁹Cd in this set-up. Resin-buffered solutions are advocated in the algal bottle assay to control trace metal supply and to better identify the role of metal complexes on bioavailability. PMID:22447105

  4. Comparative Structural Characterization of Thin Al0.2Ga0.8 N/GaN and In0.17Al0.83N/GaN Heterostructures Grown on Si(111), by MBE, with Variation of Buffer Thickness

    NASA Astrophysics Data System (ADS)

    Chowdhury, Subhra; Borisov, Boris; Chow, Peter; Biswas, Dhrubes

    2015-11-01

    We report growth, by plasma-assisted molecular beam epitaxy, of thin Al0.2Ga0.8N/GaN and In0.17Al0.83N/GaN heterostructures on Si(111) substrate with three different buffer thickness (600, 400, and 200 nm). Successful growth by critical optimization of growth conditions was followed by comparative characterization of these heterostructures by use of high resolution x-ray diffraction (HRXRD), including reciprocal space mapping (RSM), room-temperature photoluminescence (RT-PL), and high resolution transmission electron microscopy (HRTEM). The effect of different buffer thickness on the threading dislocation (TD) density of a thin 1.5 nm Al0.2Ga0.8N/In0.17Al0.83N-1.25 nm GaN-1.5 nm Al0.2Ga0.8N/In0.17Al0.83N heterostructure, was also studied. Analysis revealed increasing tensile strain with decreasing buffer thickness for AlGaN-based samples; this was confirmed by the red-shift of the GaN RT-PL peak. Reduced strain in lattice-matched InAlN-based samples resulted in a blue-shift of the GaN RT-PL peak; this was indicative of better crystallographic quality than for the AlGaN/GaN samples, which was proved by XRD-FWHM and RSM results. A substantial reduction of TD density from approximately 1010 to 108 cm-2 with increasing buffer thickness resulted in a smooth thin active region for both thick buffer structures whereas the lattice-matched InAlN/GaN-based thick buffer resulted in less effect on TD and a smooth and prominent thin active region.

  5. 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. PMID:25656795

  6. 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.

  7. Metal organic vapour phase epitaxy of GaN and lateral overgrowth

    NASA Astrophysics Data System (ADS)

    Gibart, Pierre

    2004-05-01

    Gallium nitride (GaN) is an extremely promising wide band gap semiconductor material for optoelectronics and high temperature, high power electronics. Actually, GaN is probably the most important semiconductor since silicon. However, achievement of its full potential has still been limited by a dramatic lack of suitable GaN bulk single crystals. GaN has a high melting temperature and a very high decomposition pressure; therefore it cannot be grown using conventional methods used for GaAs or Si like Czochraslski or Bridgman growths. Since there is no GaN bulk single crystal commercially available, all technological development of GaN-based devices relies on heteroepitaxy. Most of the current device structures are grown on sapphire or 6H-SiC. However, since their lattice parameters and thermal expansion coefficients are not well-matched to GaN, the epitaxial growth generates huge densities of defects, with threading dislocations (TDs) being the most prevalent (109-1011 cm-2). As a comparison, homoepitaxially grown GaAs exhibits ~102-104 dislocation cm-2, and homoepitaxial Si almost 0. Actually this large density of TDs in GaN drastically limits the performance and operating lifetime of nitride-based devices. Therefore, there is currently a tremendous technological effort to reduce these defects. Metal organic vapour phase epitaxy (MOVPE) is currently the most widely used technology. Actually, all optoelectronic commercial device structures are fabricated using MOVPE. In MOVPE, the most appropriate precursor for nitrogen is ammonia (NH3), whereas either trimethyl or triethylgallium may be used as a gallium source. MOVPE of GaN requires a high partial pressure of NH3, high growth temperatures (~1000-1100°C) and a growth chamber specially designed to avoid premature reactions between the ammonia and gallium alkyls. Since sapphire (or 6H-SiC) and GaN are highly mismatched, direct growth of GaN is impossible. Therefore, the growth of GaN on any substrate first requires

  8. GaN Metal Oxide Semiconductor Field Effect Transistors

    SciTech Connect

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

    1999-03-02

    A GaN based depletion mode metal oxide semiconductor field effect transistor (MOSFET) was demonstrated using Ga{sub 2}O{sub 3}(Gd{sub 2}O{sub 3}) as the gate dielectric. The MOS gate reverse breakdown voltage was > 35V which was significantly improved from 17V of Pt Schottky gate on the same material. A maximum extrinsic transconductance of 15 mS/mm was obtained at V{sub ds} = 30 V and device performance was limited by the contact resistance. A unity current gain cut-off frequency, f{sub {tau}}, and maximum frequency of oscillation, f{sub max} of 3.1 and 10.3 GHz, respectively, were measured at V{sub ds} = 25 V and V{sub gs} = {minus}20 V.

  9. 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.

  10. 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. PMID:27483938

  11. 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.

  12. Low-temperature grown GaAs heterojunction metal-semiconductor-metal photodetectors improve speed and efficiency

    NASA Astrophysics Data System (ADS)

    Currie, Marc; Quaranta, Fabio; Cola, Adriano; Gallo, Eric M.; Nabet, Bahram

    2011-11-01

    Low-temperature-grown GaAs (LT-GaAs) has a picosecond recombination lifetime, making a fast photodetector material but limiting carrier mobility and collection efficiency. Here, a metal-semiconductor-metal photodetector with a thin channel of regular-temperature GaAs (RT-GaAs) above LT-GaAs provides fast transit between contacts. A p-type delta doping layer below these layers produces a vertical electric field forcing optically generated electrons towards the channel. The AlGaAs/RT-GaAs heterojunction increases Schottky contacts, and the resulting 8-22 μm pitch photodetectors have low (<1-nA) dark current, 12-ps (oscilloscope-limited) pulsewidth, and 0.15-A/W responsivity. The devices demonstrate that fast LT-GaAs pulses are achievable with responsivity similar to RT-GaAs.

  13. Growth and characterization of highly tensile strained Ge1-xSnx formed on relaxed InyGa1-yP buffer layers

    NASA Astrophysics Data System (ADS)

    Wang, Wei; Loke, Wan Khai; Yin, Tingting; Zhang, Zheng; D'Costa, Vijay Richard; Dong, Yuan; Liang, Gengchiau; Pan, Jisheng; Shen, Zexiang; Yoon, Soon Fatt; Tok, Eng Soon; Yeo, Yee-Chia

    2016-03-01

    Ge0.94Sn0.06 films with high tensile strain were grown on strain-relaxed InyGa1-yP virtual substrates using solid-source molecular beam epitaxy. The in-plane tensile strain in the Ge0.94Sn0.06 film was varied by changing the In mole fraction in InxGa1-xP buffer layer. The tensile strained Ge0.94Sn0.06 films were investigated by transmission electron microscopy, x-ray diffraction, and Raman spectroscopy. An in-plane tensile strain of up to 1% in the Ge0.94Sn0.06 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 Ge0.94Sn0.06 on In0.77Ga0.23P was obtained by high resolution x-ray photoelectron spectroscopy. The Ge0.94Sn0.06/In0.77Ga0.23P 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. High-quality eutectic-metal-bonded AlGaAs-GaAs thin films on Si substrates

    NASA Astrophysics Data System (ADS)

    Venkatasubramanian, R.; Timmons, M. L.; Humphreys, T. P.; Keyes, B. M.; Ahrenkiel, R. K.

    1992-02-01

    Device quality GaAs-AlGaAs thin films have been obtained on Si substrates, using a novel approach called eutectic-metal-bonding (EMB). This involves the lattice-matched growth of GaAs-AlGaAs thin films on Ge substrates, followed by bonding onto a Si wafer. The Ge substrates are selectively removed by a CF4/O2 plasma etch, leaving high-quality GaAs-AlGaAs thin films on Si substrates. A minority-carrier lifetime of 103 ns has been obtained in a EMB GaAs-AlGaAs double heterostructure on Si, which is nearly forty times higher than the state-of-the-art lifetime for heteroepitaxial GaAs on Si, and represents the largest reported minority-carrier lifetime for a freestanding GaAs thin film. In addition, a negligible residual elastic strain in the EMB GaAs-AlGaAs films has been determined from Raman spectroscopy measurements.

  15. Fermi level pinning in metal/Al2O3/InGaAs gate stack after post metallization annealing

    NASA Astrophysics Data System (ADS)

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

    2015-08-01

    The effect of post metal deposition annealing on the effective work function in metal/Al2O3/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/Al2O3 interface.

  16. Metal-semiconductor-metal UV photodetector based on Ga doped ZnO/graphene interface

    NASA Astrophysics Data System (ADS)

    Kumar, Manoj; Noh, Youngwook; Polat, Kinyas; Kemal Okyay, Ali; Lee, Dongjin

    2015-12-01

    Fabrication and characterization of metal-semiconductor-metal (MSM) ultraviolet (UV) photodetector (PD) based on Ga doped ZnO (ZnO:Ga)/graphene is presented in this work. A low dark current of 8.68 nA was demonstrated at a bias of 1 V and a large photo to dark contrast ratio of more than four orders of magnitude was observed. MSM PD exhibited a room temperature responsivity of 48.37 A/W at wavelength of 350 nm and UV-to-visible rejection ratio of about three orders of magnitude. A large photo-to-dark contrast and UV-to-visible rejection ratio suggests the enhancement in the PD performance which is attributed to the existence of a surface plasmon effect at the interface of the ZnO:Ga and underlying graphene layer.

  17. High detectivity GaN metal semiconductor metal UV photodetectors with transparent tungsten electrodes

    NASA Astrophysics Data System (ADS)

    Wang, C. K.; Chang, S. J.; Su, Y. K.; Chiou, Y. Z.; Chang, C. S.; Lin, T. K.; Liu, H. L.; Tang, J. J.

    2005-06-01

    GaN metal-semiconductor-metal (MSM) ultraviolet photodetectors with transparent tungsten (W) electrodes were fabricated and characterized. It was found that the 10 nm thick W film deposited with a 250 W RF power could provide a reasonably high transmittance of 68.3% at 360 nm, a low resistivity of 1.5 × 10-3 Ω cm and an effective Schottky barrier height of 0.777 eV on u-GaN. We also achieved a peak responsivity of 0.15 A W-1 and a quantum efficiency of 51.8% at 360 nm from the GaN MSM UV photodetector with W electrodes. With a 2 V applied bias, it was found that the minimum noise equivalent power (NEP) and the maximum D* of our detector were 1.745 × 10-10 W and 7.245 × 109 cm Hz0.5 W-1, respectively.

  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. Growth of lanthanum manganate buffer layers for coated conductors via a metal-organic decomposition process

    NASA Astrophysics Data System (ADS)

    Venkataraman, Kartik

    LaMnO3 (LMO) was identified as a possible buffer material for YBa2Cu3O7-x conductors due to its diffusion barrier properties and close lattice match with YBa2Cu 3O7-x. Growth of LMO films via a metal-organic decomposition (MOD) process on Ni, Ni-5at.%W (Ni-5W), and single crystal SrTiO3 substrates was investigated. Phase-pure LMO was grown via MOD on Ni and SrTiO 3 substrates at temperatures and oxygen pressures within a thermodynamic "process window" wherein LMO, Ni, Ni-5W, and SrTiO3 are all stable components. LMO could not be grown on Ni-5W in the "process window" because tungsten diffused from the substrate into the overlying film, where it reacted to form La and Mn tungstates. The kinetics of tungstate formation and crystallization of phase-pure LMO from the La and Mn acetate precursors are competitive in the temperature range explored (850--1100°C). Temperatures <850°C might mitigate tungsten diffusion from the substrate to the film sufficiently to obviate tungstate formation, but LMO films deposited via MOD require temperatures ≥850°C for nucleation and grain growth. Using a Y2O3 seed layer on Ni-5W to block tungsten from diffusing into the LMO film was explored; however, Y2O3 reacts with tungsten in the "process window" at 850--1100°C. Tungsten diffusion into Y2O3 can be blocked if epitaxial, crack-free NiWO4 and NiO layers are formed at the interface between Ni-5W and Y2O3. NiWO 4 only grows epitaxially if the overlying NiO and buffer layers are thick enough to mechanically suppress (011)-oriented NiWO4 grain growth. This is not the case when a bare 75 nm-thick Y2O3 film on Ni-5W is processed at 850°C. These studies show that the Ni-5W substrate must be at a low temperature to prevent tungsten diffusion, whereas the LMO precursor film must be at elevated temperature to crystallize. An excimer laser-assisted MOD process was used where a Y2O 3-coated Ni-5W substrate was held at 500°C in air and the pulsed laser photo-thermally heated the Y2O3 and LMO

  20. 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

  1. 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.

  2. 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.

  3. Graphene on a metal surface with an h-BN buffer layer: gap opening and N-doping

    NASA Astrophysics Data System (ADS)

    Wang, Tao; Lu, Yunhao; Feng, Y. P.

    2016-04-01

    Graphene grown on a metal surface, Cu(111), with a boron-nitride (h-BN) buffer layer is studied. Our first-principles calculations reveal that charge is transferred from the copper substrate to graphene through the h-BN buffer layer which results in n-doped graphene in the absence of a gate voltage. More importantly, a gap of 0.2 eV, which is comparable to that of a typical narrow gap semiconductor, opens just 0.5 eV below the Fermi level at the Dirac point. The Fermi level can be easily shifted inside this gap to make graphene a semiconductor, which is crucial for graphene-based electronic devices. A graphene-based p-n junction can be realized with graphene eptaxially grown on a metal surface.

  4. 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)

  5. Effects of postgrowth rapid thermal annealing on InAlAs/InGaAs metamorphic high-electron-mobility transistor grown on a compositionally graded InAlAs/InGaAlAs buffer

    SciTech Connect

    Ihn, Soo-Ghang; Jo, Seong-June; Song, Jong-In

    2005-07-25

    Effects of postgrowth rapid thermal annealing (RTA) on structural and electrical properties of an In{sub 0.52}Al{sub 0.48}As/In{sub 0.52}Ga{sub 0.48}As metamorphic high-electron-mobility transistor (MHEMT) structure grown on a GaAs substrate utilizing a compositionally graded InAlAs/InGaAlAs buffer layer were investigated. High-resolution triple-axis x-ray diffraction, photoluminescence, and van der Pauw-Hall measurements were used for the investigation. While the RTA improved the structural property of the MHEMT, it degraded the channel mobility of the MHEMT due to defect-assisted impurity redistribution.

  6. Vacuum Violet Photo-Response of AlGaN-Based Metal-Semiconductor-Metal Photodetectors

    NASA Astrophysics Data System (ADS)

    Zhou, Dong; Lu, Hai; Chen, Dun-Jun; Ren, Fang-Fang; Zhang, Rong; Zheng, You-Dou; Li, Liang

    2013-11-01

    Al0.5Ga0.5 N-based metal-semiconductor-metal photodetectors (PDs) with a large device area of 5 × 5 mm2 are fabricated on a sapphire substrate, which are tested for vacuum ultraviolet light detection by using a synchrotron radiation source. The PD exhibits low dark current of less than 1 pA under 30 V bias and a spectral cutoff around 260 nm, corresponding to the energy bandgap of Al0.5Ga0.5N. A peak photo-responsivity of 14.68 mA/W at 250 nm with a rejection ratio (250/360 nm) of more than four orders of magnitude is obtained under 30 V bias. For wavelength less than 170 nm, the photoresponsivity of the PD is found to increase as wavelength decreases, which is likely caused by the enhanced photoemission effect.

  7. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-11-01

    We report the growth of thin ScN layers deposited by plasma-assisted molecular beam epitaxy on Sc2O3/Y2O3/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/Sc2O3/Y2O3 buffer system a very promising template for the growth of high quality GaN layers on silicon.

  9. 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.

  10. 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.

  11. Threading dislocation reduction in a GaN film with a buffer layer grown at an intermediate temperature

    NASA Astrophysics Data System (ADS)

    Cho, Youngji; Chang, Jiho; Ha, Joonseok; Lee, Hyun-jae; Fujii, Katsushi; Yao, Takafumi; Lee, Woong; Sekiguchi, Takashi; Yang, Jun-Mo; Yoo, Jungho

    2015-01-01

    Remarkable reduction of the threading dislocation (TD) density has been achieved by inserting a GaN layer grown at an intermediate temperature (900 °C) (IT-GaN layer), just prior to the growth of GaN at 1040 °C by using a hydride vapor phase epitaxy. The variation in the dislocation density variation along the growth direction was observed by using cathodoluminescence (CL) and transmission electron microscopy (TEM). A cross-sectional CL image revealed that the reduction of the TD density happened during the growth of IT-GaN layer. The TEM measurement provided the proof that the TD reduction could be ascribed to the masking of the TD by stacking faults in the IT-GaN layer.

  12. 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.

  13. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

    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 SiO2 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.

  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. InGaN laser diode with metal-free laser ridge using n+-GaN contact layers

    NASA Astrophysics Data System (ADS)

    Malinverni, Marco; Tardy, Camille; Rossetti, Marco; Castiglia, Antonino; Duelk, Marcus; Vélez, Christian; Martin, Denis; Grandjean, Nicolas

    2016-06-01

    We report on InGaN edge emitting laser diodes with a top metal electrode located beside the laser ridge. Current spreading over the ridge is achieved via a highly doped n+-type GaN layer deposited on top of the structure. The low sheet resistance of the n+-GaN layer ensures excellent lateral current spreading, while carrier injection is confined all along the ridge thanks to current tunneling at the interface between the n+-GaN top layer and the p++-GaN layer. Continuous-wave lasing at 400 nm with an output power of 100 mW is demonstrated on uncoated facet devices with a threshold current density of 2.4 kA·cm‑2.

  17. Equilibrium Lattice Relaxation and Misfit Dislocations in Step-Graded In x Ga1- x As/GaAs (001) and In x Al1- x As/GaAs (001) Metamorphic Buffer Layers

    NASA Astrophysics Data System (ADS)

    Kujofsa, Tedi; Ayers, John E.

    2016-06-01

    The inclusion of metamorphic buffer layers (MBLs) in the design of lattice-mismatched semiconductor heterostructures is important in enhancing reliability and performance of optoelectronic and electronic devices through proper control of threading dislocations; threading dislocation can be reduced by allowing the distribution of the misfit dislocations throughout the MBL, rather than concentrating them at the interface where substrate defects and tangling can pin dislocations or otherwise reduce their mobility. Compositionally graded layers have been particularly used for this purpose and in this work we considered heterostructures involving a step-graded In x Ga1- x As or In x Al1- x As epitaxial layer on a GaAs (001) substrate. For each structure type, we present minimum energy calculations including (i) the surface and (ii) average in-plane strain and (iii) the misfit dislocation density profile with various grading coefficients (thickness and indium composition variation). In both types of structures, the average in-plane strain and misfit dislocation density profile scale with the average grading coefficient, but In x Al1- x As structures with a greater average elastic stiffness constants exhibit slightly higher average compressive in-plane strain (absolute valued) which is associated with higher misfit dislocation densities. However, the rate of change in the normalized relaxation percentage per unit thickness of each step with respect to the lattice mismatch of the step is lower in the In x Al1- x As material system. The difference of the in-plane strain is small (<3%), however, so that these material systems are virtually interchangeable in terms of their mechanical behavior (<5.1% change in elastic constants).

  18. Investigation of noble metal substrates and buffer layers for BiSrCaCuO thin films

    NASA Astrophysics Data System (ADS)

    Matthiesen, M. M.; Rubin, L. M.; Williams, K. E.; Rudman, D. A.

    Noble metal buffer layers and substrates for Bi2Sr2CaCu2O8 (BSCCO) films were investigated using bulk ceramic processing and thin-film techniques. Highly oriented, superconducting BSCCO films were fabricated on polycrystalline Ag substrates and on Ag/MgO and Ag/YSZ structures. Such films could not be produced on Au or Pt substrates under any annealing conditions. In addition, superconducting BSCCO films could not be produced on Ag/Al2O3, Ag/SiO2/Si, or Ag/(Haynes 230 alloy) structures using high annealing temperatures (870 C). However, oriented although poorly connected, superconducting BSCCO films were fabricated on Ag/Al2O3 structures by using lower annealing temperatures (820 C). Once lower processing temperatures are optimized, Ag may be usable as a buffer layer for BSCCO films.

  19. First-principles study of d0 ferromagnetism in alkali-metal doped GaN

    NASA Astrophysics Data System (ADS)

    Zhang, Yong

    2016-08-01

    The d0 ferromagnetism in GaN has been studied based on density functional theory. Our results show that GaN with sufficient hole become spin-polarized. Alkali-metal doping can introduce holes in GaN. Among them, both of Li- and Na-doping induce ferromagnetism in GaN and Na-doped GaN behaves as half-metallic ferromagnet. Moreover, at a growth temperature of 2000 K under N-rich condition, both concentrations can exceed 18%, which is sufficient to produce detectable macroscopic magnetism in GaN. The Curie temperature of Li- and Na-doped GaN is estimated to be 304 and 740 K, respectively, which are well above room temperature.

  20. High voltage trapping effects in GaN-based metal-insulator-semiconductor transistors

    NASA Astrophysics Data System (ADS)

    Meneghesso, Gaudenzio; Meneghini, Matteo; Silvestri, Riccardo; Vanmeerbeek, Piet; Moens, Peter; Zanoni, Enrico

    2016-01-01

    This paper presents an analysis of the high voltage trapping processes that take place in high-electron mobility transistors based on GaN, with a metal-insulator-semiconductor (MIS) structure. The study is based on combined pulsed and transient measurements, carried out with trapping voltages in the range from 50 to 500 V. The results indicate that: (i) dynamic Ron is maximum for trapping voltages between 200 and 300 V, and decreases for higher voltage levels; (ii) Ron-transient measurements reveal the presence of a dominant trap with activation energy Ea1 = 0.93 eV and of a second trap with activation energy equal to Ea2 = 0.61 eV; (iii) the deep level transient spectroscopy (DLTS) signal associated to trap Ea1 is completely suppressed for high trapping voltages (VDS = 500 V). The results are interpreted by considering that the trap Ea1 is located in the buffer, and originates from CN defects. The exposure to high drain voltages may favor the depletion of such traps, due to a field-assisted de-trapping process or to the presence of vertical leakage paths.

  1. Magnetic Slowing Down of Spin Relaxation due to Binary Collisions of Alkali-Metal Atoms with Buffer-Gas Atoms

    NASA Astrophysics Data System (ADS)

    Walter, D. K.; Griffith, W. M.; Happer, W.

    2002-03-01

    We report the first studies of magnetic decoupling of the spin relaxation of alkali-metal atoms due to binary collisions with buffer gases. When binary collisions are the dominant relaxation mechanism, the relaxation and its magnetic decoupling are well described by the S-damping rate ΓSD due to the spin-rotation interaction γN˙S, the spin exchange rate ΓEX for collisions between alkali atoms, and a new ``Carver rate'' ΓC, due to the pressure-shift interaction δAİS, which can substantially broaden the magnetic decoupling curve while having no influence on the zero-field rates.

  2. 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.

  3. Dual-wavelength sensitive AlGaN/GaN metal-insulator-semiconductor-insulator-metal ultraviolet sensor with balanced ultraviolet/visible rejection ratios

    NASA Astrophysics Data System (ADS)

    Lee, Chang-Ju; Kwon, Young-Jin; Won, Chul-Ho; Lee, Jung-Hee; Hahm, Sung-Ho

    2013-09-01

    We proposed and fabricated a metal-insulator-semiconductor-insulator-metal type dual-wavelength sensitive UV sensor by using an AlGaN/GaN hetero-structure layer epitaxially grown on a sapphire substrate and a thin Al2O3 layer inserted between AlGaN and Ni Schottky electrodes to reduce dark current and improve the UV/visible rejection ratio. The proposed sensor shows high photo-responsive current to both UV wavelength regimes with a significantly improved UV/visible rejection ratio under the regime of the GaN-related UV response. Cut-off wavelengths can be controlled by changing the bias below and above 10 V.

  4. Slow and fast traps in metal-oxide-semiconductor capacitors fabricated on recessed AlGaN/GaN heterostructures

    NASA Astrophysics Data System (ADS)

    Fiorenza, Patrick; Greco, Giuseppe; Iucolano, Ferdinando; Patti, Alfonso; Roccaforte, Fabrizio

    2015-04-01

    In this letter, slow and fast trap states in metal-oxide-semiconductor (MOS) capacitors fabricated on recessed AlGaN/GaN heterostructures were studied by frequency dependent conductance measurements. In particular, the comparison of devices before and after annealing in forming gas allowed to ascribe the fast states (with characteristic response time in the range of 5-50 μs) to SiO2/GaN "interface traps," and the slow states (50-100 μs) to "border traps" located few nanometers inside the SiO2 layer. These results can be important to predict and optimize the threshold voltage stability of hybrid MOS-based transistors on GaN.

  5. Optoelectronic properties of eutectic-metal-bonded (EMB) GaAs-AlGaAs structures on Si substrates

    NASA Astrophysics Data System (ADS)

    Venkatasubramanian, R.; Timmons, M. L.

    1994-11-01

    Device-quality GaAsAlGaAs thin-film hetero-structures have been obtained on Si substrates using a novel approach called eutectic-metal-bonding (EMB). The optoelectronic material properties of the thin-films have been evaluated by a variety of techniques including, Raman spectroscopy, room temperature photoluminescence (PL), and cathodoluminescence (CL) imaging. Transient PL measurement indicates that the minority-carrier lifetime in an EMB GaAs-on-Si thin-film is about 40 times higher than that in state-of-the-art hetero-epitaxial GaAs-on-Si layer. The PL characteristics of the EMB GaAs-on-Si structures have been used to obtain the long-wavelength dispersion values for GaAs thin-film structures. The minority carrier device quality of these thin-films have been evaluated using dark log I- V measurements on n+- p GaAs diodes, spectral-response characterization and solar cell performance data.

  6. Structural and optical investigations of AlGaN MQWs grown on a relaxed AlGaN buffer on AlN templates for emission at 280 nm

    NASA Astrophysics Data System (ADS)

    Li, X.; Le Gac, G.; Bouchoule, S.; El Gmili, Y.; Patriarche, G.; Sundaram, S.; Disseix, P.; Réveret, F.; Leymarie, J.; Streque, J.; Genty, F.; Salvestrini, J.-P.; Dupuis, R. D.; Li, X.-H.; Voss, P. L.; Ougazzaden, A.

    2015-12-01

    10-period Al0.57Ga0.43N/Al0.38Ga0.62N multi-quantum wells (MQWs) were grown on a relaxed Al0.58Ga0.42N buffer on AlN templates on sapphire. The threading dislocations and V-pits were characterized and their origin is discussed. The influence of V-pits on the structural quality of the MQWs and on optical emission at 280 nm was analyzed. It was observed that near-surface V-pits were always associated with grain boundaries consisting of edge threading dislocations originating from the AlN/Al2O3 interface. Although the high density of V-pits disrupted MQWs growth, it did not affect the internal quantum efficiency which was measured to be ~1% at room temperature even when V-pit density was increased from 7×107 cm-2 to 2×109 cm-2. The results help to understand the origin, propagation and influences of the typical defects in AlGaN MQWs grown on AlN/Al2O3 templates which may lead to further improvement of the performance of DUV devices.

  7. 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. PMID:25781866

  8. IR spectroscopy of lattice vibrations and comparative analysis of the ZnTe/CdTe quantum-dot superlattices on the GaAs substrate and with the ZnTe and CdTe buffer layers

    SciTech Connect

    Kozyrev, S. P.

    2009-07-15

    A comparative analysis of multiperiod ZnTe/CdTe superlattices with the CdTe quantum dots grown by molecular beam epitaxy on the GaAs substrate with the ZnTe and CdTe buffer layers is carried out. The elastic-stress-induced shifts of eigenfrequencies of the modes of the CdTe- and ZnTe-like vibrations of materials forming similar superlattices but grown on different buffer ZnTe and CdTe layers are compared. The conditions of formation of quantum dots in the ZnTe/CdTe superlattices on the ZnTe and CdTe buffer layers differ radically.

  9. 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.

  10. Characterization of ZnInxSey Thin Films as a Buffer Layer for High Efficiency Cu(InGa)Se2 Thin-Film Solar Cells

    NASA Astrophysics Data System (ADS)

    Ohtake, Yasutoshi; Chaisitsak, Sutichai; Yamada, Akira; Konagai, Makoto

    1998-06-01

    The structural, optical and electrical properties of ZnInxSey (ZIS) thin films on Cu(InGa)Se2 (CIGS) thin films and glass substrates were characterized. Polycrystalline ZIS thin films were grown by the coevaporation method using three constituent elements. We confirmed the formation of ZnIn2Se4 from the X-ray diffraction patterns of the ZIS thin films on glass substrates. From the transmittance and reflectance measurements of these films, the bandgap of ZIS is estimated at around 2.0 eV in this study. In addition, the ZIS films on glass substrates show low dark conductivity and high photosensitivity, which are suitable for the buffer layer in CIGS thin-film solar cells. We also fabricated the CIGS thin-film solar cells with a ZnO/ZIS/CIGS structure, and investigated the relationship between the cell performance and the beam intensity ratio of zinc to indium.

  11. Investigation of buffer traps in an AlGaN/GaN/Si high electron mobility transistor by backgating current deep level transient spectroscopy

    NASA Astrophysics Data System (ADS)

    Marso, M.; Wolter, M.; Javorka, P.; Kordoš, P.; Lüth, H.

    2003-01-01

    The influence of a substrate voltage on the dc characteristics of an AlGaN/GaN high electron mobility transistor (HEMT) on silicon (111) substrate is profited to investigate traps that are located between the substrate and the two-dimensional electron gas channel. The transient of the drain current after applying a negative substrate voltage is evaluated in the temperature range from 30 to 100 °C. With this method, known as backgating current deep level transient spectroscopy, majority carrier traps with activation energy of 200 meV as well as minority carrier traps at 370 meV are identified. The experiments are performed on completed HEMTs, allowing the investigation of the influence of device fabrication technology.

  12. 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.

  13. Molecular beam epitaxy and characterizations of PbTe grown on GaAs(211) substrates using CdTe/ZnTe buffers

    NASA Astrophysics Data System (ADS)

    Shu, Tianyu; Lu, Pengqi; Zhang, Bingpo; Wang, Miao; Chen, Lu; Fu, Xiangliang; Xu, Gangyi; Wu, Huizhen

    2015-06-01

    Narrow-gap semiconductor PbTe has exhibited versatility in both mid-infrared optoelelctronics and thermoelectrics. However, the absence of commercially obtainable PbTe crystal substrates limits its wide applications. In this paper, heteroepitaxy of high-quality PbTe crystal on GaAs(211) using CdTe/ZnTe buffers by molecular beam epitaxy is presented for the first time. Optimal growth parameters have been obtained by both in-situ and ex-situ characterizations. In-situ reflection high-energy electron diffraction observed a transition of growth mode from 2D to 3D, which is in agreement with the results of atomic force microscope and scanning electron microscope characterizations. High resolution X-ray diffraction revealed that the growth of PbTe crystal is along [531] direction which is different from the [211] substrate orientation. Multiple phonon modes related to PbTe were observed by Raman scattering while mid-infrared light emission from epitaxial PbTe is observed at a peak of 3.5 μm by photoluminescence. Different from PbTe grown on BaF2(111), n-type conductivity with electron densities of ~5×1017 cm-3 and mobilities of 675 cm2/V s at room temperature and 4300 cm2/V s at 2 K is observed. The high quality PbTe grown on GaAs(211) substrates using CdTe/ZnTe buffers renders promising applications in both optoelectronics and thermoelectrics.

  14. 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.

  15. Metal{endash}insulator{endash}semiconductor structure on GaAs using a pseudomorphic Si/GaP interlayer

    SciTech Connect

    Park, D.; Mohammad, S.N.; Chen, Z.; Morkoc, H.

    1997-03-01

    We report on a novel GaAs metal{endash}insulator{endash}semiconductor (MIS) structure exhibiting the interface state densities in the 9.2{times}10{sup 10} eV{sup {minus}1}cm{sup {minus}2} with a Si (10 {Angstrom})/GaP (12 {Angstrom}) layer on GaAs. The structure was grown by a combination of molecular beam epitaxy and chemical vapor deposition. The hysteresis and frequency dispersion of the MIS capacitor were lower than 100 mV, some of them as low as 70 mV under a field swing of about {plus_minus}1.4 MV/cm. {ital Ex situ} solid phase annealing around 500{endash}550{degree}C in N{sub 2} using rapid thermal annealing was high enough to recrystallize the as-deposited Si interlayer at low temperature ({approximately}300{degree}C). The 100 kHz frequency response at 77 K suggests that the interface pinning levels are close to the conduction band edge of GaAs. This article reports the first application of a pseudomorphic Si/GaP interlayer to ideal GaAs MIS diodes and exhibits a favorable interface stability with high temperature annealing. {copyright} {ital 1997 American Vacuum Society.}

  16. Evolution of epilayer tilt in thick InxGa1-xAs metamorphic buffer layers grown by hydride vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    Schulte, K. L.; Strand, M. T.; Kuech, T. F.

    2015-09-01

    Tilt behavior in thick InxGa1-xAs metamorphic buffer layers (MBLs) grown by hydride vapor phase epitaxy (HVPE) was measured by high-resolution reciprocal space mapping. Step-graded and continuously-graded structures, grown on nominally (001) oriented GaAs substrates, were analyzed. Tilt was measured as a function of position in a step-graded MBL. It was found that the tilt was strongest near the edges and tended to point toward the sample center. Step-grading induced a nearly linear tilt increase with xInAs, while tilt increased slowly below xInAs~0.10 then increased more sharply with In concentration in continuously-graded samples. The tilt behavior could be described by a model in which the tilt is attributed to imbalances in dislocations that result from cross-slip within a glide length of the sample edge. This finding implies that dislocation multiplication by cross slip is an important strain relief mechanism during the growth of these MBLs. Strategies for minimizing tilt in HVPE MBLs are discussed.

  17. Role of dislocations in the degradation of metal-GaAs structures

    NASA Astrophysics Data System (ADS)

    Ptashchenko, A. A.; Sik, Em Ren

    A study is made of the effect of uniaxial pressure, forward and reverse current transmission, and of the combined effect of these factors on the electrical and photoelectrical properties of metal-GaAs structures. It is found that the prolonged application of uniaxial pressure and direct current transmission produce defects in the surface layer of Au-GaAs, Sn-GaAs, and Au-GaAlAs structures, which significantly increases the excess current of the structures and reduces the minority carrier lifetimes. The annealing behavior of the defects is discussed.

  18. 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.

  19. 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.

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

    DOE PAGESBeta

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

    2015-08-18

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

  1. 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.

  2. Some characteristics of Ureaplasma urealyticum. Urease activity in a simple buffer: effect of metal ions and sulphydryl inhibitors.

    PubMed

    Swanberg, S L; Masover, G K; Hayflick, L

    1978-10-01

    Urealytic activity of the cytoplasmic fraction of Ureaplasma urealyticum prepared by digitonin lysis was assayed in a simple buffer system (HEPES plus EDTA) by measuring the release of 14CO2 from [14C]urea. The Km of this preparation agreed with our previous observations of the same activity measured in a more complex reaction mixture. The substrate concentration at which maximum velocity occurred was approximately 20 mM. The activity was sensitive to heavy metals and inhibitors which react with sulphydryl groups such as N-ethylmaleimide and p-chloromercuribenzoate. It was not inhibited by Ca2+ or Mg2+ or by the reaction products, ammonia and carbon dioxide. PMID:31413

  3. Effects of radiation and temperature on gallium nitride (GaN) metal-semiconductor-metal ultraviolet photodetectors

    NASA Astrophysics Data System (ADS)

    Chiamori, Heather C.; Angadi, Chetan; Suria, Ateeq; Shankar, Ashwin; Hou, Minmin; Bhattacharya, Sharmila; Senesky, Debbie G.

    2014-06-01

    The development of radiation-hardened, temperature-tolerant materials, sensors and electronics will enable lightweight space sub-systems (reduced packaging requirements) with increased operation lifetimes in extreme harsh environments such as those encountered during space exploration. Gallium nitride (GaN) is a ceramic, semiconductor material stable within high-radiation, high-temperature and chemically corrosive environments due to its wide bandgap (3.4 eV). These material properties can be leveraged for ultraviolet (UV) wavelength photodetection. In this paper, current results of GaN metal-semiconductor-metal (MSM) UV photodetectors behavior after irradiation up to 50 krad and temperatures of 15°C to 150°C is presented. These initial results indicate that GaN-based sensors can provide robust operation within extreme harsh environments. Future directions for GaN-based photodetector technology for down-hole, automotive and space exploration applications are also discussed.

  4. Microstructure of a high Jc, laser-ablated YBa 2Cu 3O 7- δ/sol-gel deposited NdGaO 3 buffer layer/(001) SrTiO 3 multi-layer structure

    NASA Astrophysics Data System (ADS)

    Yang, Chau-Yun; Ichinose, Ataru; Babcock, S. E.; Morrell, J. S.; Mathis, J. E.; Verebelyi, D. T.; Paranthaman, M.; Beach, D. B.; Christen, D. K.

    A YBa 2Cu 3O 7- δ (YBCO) film with a transport critical current density ( Jc) value of 1 mA/cm 2 (77 K, 0 T) was grown on a solution deposited NdGaO 3 (NGO) buffer layer on (100) SrTiO 3 (STO). The 25-nm thick NGO buffer layer was dip-coated onto the STO single crystal from a solution of metal methoxyethoxides in 2-methoxyethanol. Pulsed laser deposition (PLD) was used to grow a 250-nm-thick YBCO film on the NGO. The epitaxial relationships are cube-on-cube throughout the structure when the pseudo cubic and pseudo tetragonal unit cells are used to describe the NGO and YBCO crystal structures, respectively: (001) YBCO∥(001) NGO∥(001) STO and [100] YBCO∥[100] NGO∥[100] STO. High resolution scanning electron microscopy (SEM) of the bare NGO surface revealed ∼40 nm diameter pinholes with number density of ∼2×10 13 m -2, corresponding to an area fraction coverage of 2.5%, in an otherwise featureless surface. Cross-sectional transmission electron microscopy (TEM) showed that these pinholes penetrate to the STO; otherwise the NGO layer was uniformly thick to within approximately ±5 nm and defect free. The X-ray diffraction φ- and ω-scans indicated that the YBCO film was highly oriented with a full-width-half maximum peak breadth of 1.14° for in-plane and 0.46° for out-of-plane alignment, respectively. The film contained sparse a-axis oriented grains, an appreciable density of (001) stacking faults and apparently insulating second phase precipitates of the type that typically litter the surface of PLD films. All of these defects are typical of YBCO thin films. High-resolution cross-sectional TEM images indicate that no chemical reaction occurs at the YBCO/NGO interface.

  5. 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.

  6. GaN metal-oxide-semiconductor field-effect transistors on AlGaN/GaN heterostructure with recessed gate

    NASA Astrophysics Data System (ADS)

    Wang, Qingpeng; Ao, Jin-Ping; Wang, Pangpang; Jiang, Ying; Li, Liuan; Kawaharada, Kazuya; Liu, Yang

    2015-04-01

    GaN metal-oxide-semiconductor field-effect transistors (MOSFETs) on AlGaN/GaN heterostructure with a recess gate were fabricated and characterized. The device showed good pinch-off characteristics and a maximum field-effect mobility of 145.2 cm2·V-1·s-1. The effects of etching gas of Cl2 and SiCl4 were investigated in the gate recess process. SiCl4-etched devices showed higher channel mobility and lower threshold voltage. Atomic force microscope measurement was done to investigate the etching profile with different etching protection mask. Compared with photoresist, SiO2-masked sample showed lower surface roughness and better profile with stepper sidewall and weaker trenching effect resulting in higher channel mobility in the MOSFET.

  7. A photovoltaic effect in the metal-high-resistive GaAs:Cr contact

    NASA Astrophysics Data System (ADS)

    Budnitskii, D. L.; Novikov, V. A.; Prudaev, I. A.; Тоlbanov, О. P.; Yaskevich, Т. М.

    2012-12-01

    The results of studies of photovoltaic effect in the contacts of a number of metals with high-resistive GaAs:Cr are reported. High-resistive (HR) GaAs was obtained by diffusion of chromium in n-GaAs. V, Cr, and Al were used as metals. In was employed in order to produce ohmic contacts. Photovoltage was excited by red light (hν = 1.85 eV), and the excitation intensity amounted to 1.5ṡ1021 сm-2ṡs-1. Photovoltage was measured in the presence of asymmetric pairs of contacts to HR-GaAs: V-In, Cr-In, and Al-In. It is shown that V, Cr, and Al form barriers for electrons in the contact with high-resistive GaAs:Cr. The photovoltage of the contacts is determined by the inversion of conductivity type of the near-surface GaAs layer under the metal contact. The hole concentration in the inversion layer can be as high as ≈1015 сm-3. An In contact to high-resistive GaAs:Cr is an ohmic injecting contact for electrons with the barrier height for holes ≈0.9 eV.

  8. 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.

  9. Enhanced Lifetime of Polymer Solar Cells by Surface Passivation of Metal Oxide Buffer Layers.

    PubMed

    Venkatesan, Swaminathan; Ngo, Evan; Khatiwada, Devendra; Zhang, Cheng; Qiao, Qiquan

    2015-07-29

    The role of electron selective interfaces on the performance and lifetime of polymer solar cells were compared and analyzed. Bilayer interfaces consisting of metal oxide films with cationic polymer modification namely poly ethylenimine ethoxylated (PEIE) were found to enhance device lifetime compared to bare metal oxide films when used as an electron selective cathode interface. Devices utilizing surface-modified metal oxide layers showed enhanced lifetimes, retaining up to 85% of their original efficiency when stored in ambient atmosphere for 180 days without any encapsulation. The work function and surface potential of zinc oxide (ZnO) and ZnO/PEIE interlayers were evaluated using Kelvin probe and Kelvin probe force microscopy (KPFM) respectively. Kelvin probe measurements showed a smaller reduction in work function of ZnO/PEIE films compared to bare ZnO films when aged in atmospheric conditions. KPFM measurements showed that the surface potential of the ZnO surface drastically reduces when stored in ambient air for 7 days because of surface oxidation. Surface oxidation of the interface led to a substantial decrease in the performance in aged devices. The enhancement in the lifetime of devices with a bilayer interface was correlated to the suppressed surface oxidation of the metal oxide layers. The PEIE passivated surface retained a lower Fermi level when aged, which led to lower trap-assisted recombination at the polymer-cathode interface. Further photocharge extraction by linearly increasing voltage (Photo-CELIV) measurements were performed on fresh and aged samples to evaluate the field required to extract maximum charges. Fresh devices with a bare ZnO cathode interlayer required a lower field than devices with ZnO/PEIE cathode interface. However, aged devices with ZnO required a much higher field to extract charges while aged devices with ZnO/PEIE showed a minor increase compared to the fresh devices. Results indicate that surface modification can act as a

  10. Microstructural evaluation of Sb-adjusted Al{sub 0.5}Ga{sub 0.5}As{sub 1{minus}y}Sb{sub y} buffer layer systems for IR applications

    SciTech Connect

    Chen, E.; Paine, D.C.; Uppal, P.; Ahearn, J.S.; Nichols, K.; Charache, G.W.

    1998-06-01

    The authors report on a transmission electron microscopy (TEM) study of Sb-adjusted quaternary Al{sub 0.5}Ga{sub 0.5}As{sub 1{minus}y}Sb{sub y} buffer-layers grown on <001> GaAs substrates. A series of structures were grown by MBE at 470 C that utilize a multilayer grading scheme in which the Sb content of Al{sub 0.5}Ga{sub 0.5}As{sub 1{minus}y}Sb{sub y} buffer-layers grown on <001> GaAs substrates. A series of structures were grown by MBe at 470 C that utilize a multilayer grading scheme in which the Sb content of Al{sub 0.5}Ga{sub 0.5}As{sub 1{minus}y}Sb{sub y} is successively increased in a series of 125 nm thick layers. Post growth analysis using conventional bright field and weak beam dark field imaging of these buffer layers in cross-section reveals that the interface misfit dislocations are primarily of the 60{degree} type and are distributed through out the interfaces of the buffer layer. When optimized, the authors have shown, using plan view and cross-sectional TEM, that this approach can reduce the threading defect density to below the detectability limit of TEM (< 10{sup 5}/cm{sup 2}) and preserve growth surface planarity. The Sb-graded approach was used to fabricate two 2.2 {micro}m power converter structures fabricated using InGaAs grown on Sb-based buffer layers on GaAs substrates. A microstructural and electrical characterization was performed on these device structures and the results are contrasted with a sample in which InP was selected as the substrate. Microstructure, defect density and device performance in these not-yet-optimized Sb-based buffer layers compares favorably to equivalent devices fabricated using InP substrates.

  11. 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.

  12. Electronic structure and magnetic properties of substitutional transition-metal atoms in GaN nanotubes

    NASA Astrophysics Data System (ADS)

    Zhang, Min; Shi, Jun-Jie

    2014-01-01

    The electronic structure and magnetic properties of the transition-metal (TM) atoms (Sc—Zn, Pt and Au) doped zigzag GaN single-walled nanotubes (NTs) are investigated using first-principles spin-polarized density functional calculations. Our results show that the bindings of all TM atoms are stable with the binding energy in the range of 6-16 eV. The Sc- and V-doped GaN NTs exhibit a nonmagnetic behavior. The GaN NTs doped with Ti, Mn, Ni, Cu and Pt are antiferromagnetic. On the contrary, the Cr-, Fe-, Co-, Zn- and Au-doped GaN NTs show the ferromagnetic characteristics. The Mn- and Co-doped GaN NTs induce the largest local moment of 4μB among these TM atoms. The local magnetic moment is dominated by the contribution from the substitutional TM atom and the N atoms bonded with it.

  13. 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.

  14. 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.

  15. High-efficiency organometallic vapor phase epitaxy AlGaAs/GaAs monolithic cascade solar cell using metal interconnects

    SciTech Connect

    Ludowise, M.J.; LaRue, R.A.; Borden, P.G.; Gregory, P.E.; Dietze, W.T.

    1982-09-15

    A two-junction solar cell has been fabricated using an Al/sub 0.30/Ga/sub 0.70/As (1.82 eV) tap cell and a GaAs (1.43 eV) bottom cell. A processed metal interconnect is used to connect the two cells together in series. An efficiency of 21.5% at 980 mW/cm/sup 2/ has been measured in a solar simulator with an open circuit voltage of 2.35 V, a short circuit current of 118.6 mA/cm/sup 2/, and a fill factor of 0.76. An efficiency of 22% has been measured under 130 AM3 sun in a solar tracking concentrator. Organometallic vapor phase epitaxy is used to grow the entire nine-layer device.

  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. Growth and characterization of an In0.53Ga0.47As-based Metal-Oxide-Semiconductor Capacitor (MOSCAP) structure on 300 mm on-axis Si (001) wafers by MOCVD

    NASA Astrophysics Data System (ADS)

    Orzali, Tommaso; Vert, Alexey; Kim, Tae-Woo; Hung, P. Y.; Herman, Joshua L.; Vivekanand, Saikumar; Huang, Gensheng; Kelman, Max; Karim, Zia; Hill, Richard J. W.; Rao, Satyavolu S. Papa

    2015-10-01

    We report on the development of a metamorphic In0.53Ga0.47As-based heterostructure grown on 300 mm on-axis Si (001) wafers by metal-organic chemical vapor deposition (MOCVD), and the fabrication of a Metal-Oxide-Semiconductor Capacitor (MOSCAP) with C-V characteristics and interfacial trap density (Dit) values comparable to those of an equivalent structure grown on an InP substrate. A 1.15 μm thick GaAs/InP buffer with a defect density in the low 109 cm-2 range and a surface roughness rms value <2 nm was used to accommodate the large lattice mismatch between In0.53Ga0.47As and Si.

  18. Analysis of aluminum nano-gratings assisted light reflection reduction in GaAs metal-semiconductor-metal photodetectors

    NASA Astrophysics Data System (ADS)

    Fan, Zhenzhu; Su, Yahui; Zhang, Huayong; Han, Xiaohu; Ren, Feifei

    2015-09-01

    Plasmonics-based GaAs metal-semiconductor-metal photodetector (MSM-PD) with aluminum nano-gratings was proposed. A detailed numerical study of subwavelength nanogratings behavior to reduce the light reflection is performed by finite-difference time domain (FDTD) algorithm. The geometric parameters of nano-gratings, such as aperture width, the nano-gratings height, the duty cycles are optimized for subwavelength metal nanogratings on GaAs substrate and their impact on light reflection below the conventional MSM-PD is confirmed. Simulation results show that a light reflection factor around 15% can be obtained near the wavelength of 900 nm with optimized MSM-PDs, and in visible light spectrum, the Al nano-gratings show better performance than Au nano-gratings.

  19. 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

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

    NASA Astrophysics Data System (ADS)

    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

    2016-03-01

    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.

  1. Emergence of half-metallic ferromagnetism in Ga1- x Cr x As

    NASA Astrophysics Data System (ADS)

    Rani, Anita; Kumar, Ranjan

    2016-08-01

    We have studied the structural, electronic and half-metallic ferromagnetic properties of Ga1- x Cr x As compounds at dopant concentrations x = 0.25, 0.125 and 0.0625. First principle calculations based on density functional theories as implemented in SIESTA code using LDA + U (local density approximation + U) as exchange correlation potential have been used to study the properties of these compounds. Here, U is the Hubbard's parameter. The calculated results predict that Cr-doped GaAs diluted magnetic semiconductors exhibit half-metallic properties at different concentrations, in which Cr atoms form deep levels in forbidden energy gap. The results also predict that with increase of fraction of Cr atoms, half-metallic energy band gap of Ga1- x Cr x As decreases. Total magnetic moment of these compounds is due to Cr states, and also p-d hybridization between Ga-p and Cr-d induces small magnetic moment on nonmagnetic atoms (Ga and As) for all concentrations.

  2. 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.

  3. 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.

  4. 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.

  5. Study of the influence of strained superlattices introduced into a metamorphic buffer on the electrophysical properties and the atomic structure of InAlAs/InGaAs MHEMT heterostructures

    SciTech Connect

    Galiev, G. B.; Pushkarev, S. S.; Vasil'evskii, I. S.; Zhigalina, O. M.; Klimov, E. A.; Zhigalina, V. G.; Imamov, R. M.

    2013-04-15

    The results of studying the influence of strained superlattices introduced into a metamorphic buffer on the electrophysical properties and atomic crystal structure of In{sub 0.70}Al{sub 0.30}As/In{sub 0.76}Ga{sub 0.24}As/In{sub 0.70}Al{sub 0.30}As metamorphic high-electron-mobility transistor (MHEMT) nanoheterostructures on GaAs substrates are presented. Two types of MHEMT structures are grown by molecular beam epitaxy, namely, one with a linear increase in x in the In{sub x}Al{sub 1-x}As metamorphic buffer, and the second with two mismatched superlattices introduced inside the metamorphic buffer. The electrophysical and structural parameters of the grown samples are studied by the van der Pauw method, transmission electron microscopy (including scanning and high-resolution microscopy), atomic-force microscopy, and energy dispersive X-ray analysis. It is revealed that the introduction of superlattices into a metamorphic buffer substantially improves the electrophysical and structural characteristics of MHEMT structures.

  6. Metal-insulator transition in AlxGa1-xAs/GaAs heterostructures with large spacer width

    NASA Astrophysics Data System (ADS)

    Gold, A.

    1991-10-01

    Analytical results are presented for the mobility of a two-dimensional electron gas in a heterostructure with a thick spacer layer α. Due to multiple-scattering effects a metal-insulator transition occurs at a critical electron density Nc=N1/2i/(4π1/2α) (Ni is the impurity density). The transport mean free path l(t) (calculated in Born approximation) at the metal-insulator transition is l(t)c=2α. A localization criterion in terms of the renormalized single-particle mean free path l(sr) is presented: kFcl(sr)c=(1/2)1/2 (kFc is the Fermi wave number at the critical density). I compare the theoretical results with recent experimental results found in AlxGa1-xAs/GaAs heterostructures with large spacer width: 1200<α<2800 Å. Remote impurity doping and homogeneous background doping are considered. The only fitting parameter used for the theoretical results is the background doping density NB=6×1013 cm-3. My theory is in fair agreement with the experimental results.

  7. A study of the impact of gate metals on the performance of AlGaN/AlN/GaN heterostructure field-effect transistors

    NASA Astrophysics Data System (ADS)

    Zhao, Jingtao; Lin, Zhaojun; Chen, Quanyou; Yang, Ming; Cui, Peng; Lv, Yuanjie; Feng, Zhihong

    2015-09-01

    The fabrication processes of heterostructure field-effect transistors (HFETs) often introduce stresses into the device structures. These stresses can significantly affect the electrical characteristics of the device. We investigated the additional strain induced by the gate metals (in this study, Au, Cu, Fe, Al, and Ni) in AlGaN/AlN/GaN HFETs using the measured capacitance-voltage and current-voltage characteristics. We found that the intensity of the additional strain of the AlGaN barrier layer is greatly affected by the types of gate metals. For those metals that mainly undergo a physical interaction with the AlGaN barrier layer, there is a negative correlation between the intensity of the additional strain and the Young's modulus of the gate metal. Therefore, the gate metal with a larger Young's modulus will be more favorable for weakening polarization Coulomb field scattering and increasing both the carrier mobility and the sheet carrier density in AlGaN/AlN/GaN HFETs.

  8. Novel alkali metal amidogallates as intermediates in ammonothermal GaN crystal growth

    NASA Astrophysics Data System (ADS)

    Zhang, Shiyu; Alt, Nicolas S. A.; Schlücker, Eberhard; Niewa, Rainer

    2014-10-01

    Single crystals of lithium tetra-amidogallate, Li[Ga(NH2)4], were obtained from the reaction of Ga metal and LiNH2 in supercritical ammonia at a pressure of 250 MPa and temperature of 400 °C. Two structural modifications were characterized by single crystal X-ray diffraction: a=5.849(1) Å, b=12.640(3) Å, c=6.858(1) Å, β=92.56(3)°, Z=4, space group P21/n; a=6.005(1) Å, b=7.394(2) Å, c=6.005(1) Å, β=103.51(3)°, Z=2, space group P21. Disodium tetra-amidogallate amide, Na2[Ga(NH2)4]NH2 (a=11.748(2) Å, b=6.681(1) Å, c=9.665(2) Å, Z=4, space group Pnma), was grown ammonothermally (p=130 MPa, T=580 °C) as single crystals in the course of synthesizing wurzite GaN employing NaNH2 as an ammono-basic mineralizer. Like known Na[Ga(NH2)4], all three novel compounds contain isolated tetra-amidogallate ions [Ga(NH2)4]- as constituents and likely candidates for dominant dissolved gallium-containing species in ammonothermal GaN synthesis and crystal growth under ammono-basic conditions, accomplishing the material transport. Raman spectroscopy data for Li[Ga(NH2)4] in both modifications as well as Na2[Ga(NH2)4]NH2 are provided and discussed.

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

    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.

  10. 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.

  11. Comparison of electrical properties and deep traps in p-Al{sub x}Ga{sub 1-x}N grown by molecular beam epitaxy and metal organic chemical vapor deposition

    SciTech Connect

    Polyakov, A. Y.; Smirnov, N. B.; Govorkov, A. V.; Kozhukhova, E. A.; Dabiran, A. M.; Chow, P. P.; Wowchak, A. M.; Lee, In-Hwan; Ju, Jin-Woo; Pearton, S. J.

    2009-10-01

    The electrical properties, admittance spectra, microcathodoluminescence, and deep trap spectra of p-AlGaN films with an Al mole fraction up to 45% grown by both metal organic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE) were compared. The ionization energy of Mg increases from 0.15 to 0.17 eV in p-GaN to 0.3 eV in 45% Al p-AlGaN. In p-GaN films grown by MBE and MOCVD and in MOCVD grown p-AlGaN, we observed additional acceptors with a concentration an order lower than that of Mg acceptors, with a higher hole capture cross section and an ionization energy close to that of Mg. For some of the MBE grown p-AlGaN, we also detected the presence of additional acceptor centers, but in that case the centers were located near the p-AlGaN layer interface with the semi-insulating AlGaN buffer and showed activation energies considerably lower than those of Mg.

  12. Stability of metal/GaAs-lnterfaces: A phase diagram survey

    NASA Astrophysics Data System (ADS)

    Schmid-Fetzer, Rainer

    1988-03-01

    Calculated phase diagrams of ternary Ga-As-metal systems for the metals Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Re, Os, Rh, Ir, Ni, Pd, Pt, Cu, Ag and Au are presented. The predictive calculations are based on the following simplifications: Ternary phases and solid solubilities are disregarded and the Gibbs energy of formation of binary compounds is estimated by the enthalpy of formation and calculated from Miedema’s model. The predicted diagrams agree surprisingly well with experimental data and they may be useful for the many cases where data are lacking or fragmentary. The phase diagrams and the thermodynamic data are shown to be a powerful tool for the understanding of interface reactions of metallic contacts to GaAs and hence for the development of improved contact materials.

  13. The electrochemical evaluation of a Zr-based bulk metallic glass in a phosphate-buffered saline electrolyte.

    PubMed

    Morrison, M L; Buchanan, R A; Leon, R V; Liu, C T; Green, B A; Liaw, P K; Horton, J A

    2005-09-01

    Bulk metallic glasses (BMGs) represent an emerging class of materials with an amorphous structure and a unique combination of properties. The objectives of this investigation were to define the electrochemical behavior of a specific Zr-based BMG alloy in a physiologically relevant environment and to compare these properties to standard, crystalline biomaterials as well as other Zr-based BMG compositions. Cyclic-anodic-polarization studies were conducted with a Zr52.5Cu17.9Ni14.6Al10.0Ti5.0 (at %) BMG in a phosphate-buffered saline electrolyte with a physiologically relevant oxygen content at 37 degrees C. The results were compared to three common, crystalline biomaterials: CoCrMo, 316L stainless steel, and Ti-6Al-4V. The BMG alloy was found to have a lower corrosion penetration rate (CPR), as compared to the 316L stainless steel, and an equivalent CPR, as compared to the CoCrMo and Ti-6Al-4V alloys. Furthermore, the BMG alloy demonstrated better localized corrosion resistance than the 316L stainless steel. However, the localized corrosion resistance of the BMG alloy was not as high as those of the CoCrMo and Ti-6Al-4V alloys in the tested environment. The excellent electrochemical properties demonstrated by the BMG alloy are combined with a low modulus and unparalleled strength. This unique combination of properties dramatically demonstrates the potential for amorphous alloys as a new generation of biomaterials. PMID:16013063

  14. The electrochemical Evaluation of a Zr-Based Bulk Metallic Glass in a Phosphate-Buffered Saline Electrolyte

    SciTech Connect

    Morrison, M. L.; Buchanan, R. A.; Leon, R. V.; Liu, Chain T; Green, B. A.; Liaw, Peter K; Horton Jr, Joe A

    2005-01-01

    Bulk metallic glasses (BMGs) represent an emerging class of materials with an amorphous structure and a unique combination of properties. The objectives of this investigation were to define the electrochemical behavior of a specific Zr-based BMG alloy in a physiologically relevant environment and to compare these properties to standard, crystalline biomaterials as well as other Zr-based BMG compositions. Cyclic-anodic-polarization studies were conducted with a Zr{sub 52.5}Cu{sub 17.9}Ni{sub 14.6}Al{sub 10.0}Ti{sub 5.0} (at %) BMG in a phosphate-buffered saline electrolyte with a physiologically relevant oxygen content at 37 C. The results were compared to three common, crystalline biomaterials: CoCrMo, 316L stainless steel, and Ti-6Al-4V. The BMG alloy was found to have a lower corrosion penetration rate (CPR), as compared to the 316L stainless steel, and an equivalent CPR, as compared to the CoCrMo and Ti-6Al-4V alloys. Furthermore, the BMG alloy demonstrated better localized corrosion resistance than the 316L stainless steel. However, the localized corrosion resistance of the BMG alloy was not as high as those of the CoCrMo and Ti-6Al-4V alloys in the tested environment. The excellent electrochemical properties demonstrated by the BMG alloy are combined with a low modulus and unparalleled strength. This unique combination of properties dramatically demonstrates the potential for amorphous alloys as a new generation of biomaterials.

  15. 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.

  16. 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.

  17. The influence of V/III ratio in the initial growth stage on the properties of GaN epilayer deposited on low temperature AlN buffer layer

    NASA Astrophysics Data System (ADS)

    Zhao, D. G.; Jiang, D. S.; Zhu, J. J.; Liu, Z. S.; Zhang, S. M.; Yang, Hui; Liang, J. W.

    2007-05-01

    The V/III ratio in the initial growth stage of metalorganic chemical vapor deposition has an important influence on the quality of a GaN epilayer grown on a low-temperature AlN buffer layer and c-plane sapphire substrate. A weaker yellow luminescence, a narrower half-width of the X-ray diffraction peak, and a higher electron mobility result when a lower V/III ratio is taken. The intensity of in situ optical reflectivity measurements indicates that the film surface is rougher at the beginning of GaN growth, and a longer time is needed for the islands to coalesce and for a quasi-two dimensional mode growth to start. A comparison of front- and back-illuminated photoluminescence spectra confirms that many threading dislocations are bent during the initial stage, leading to a better structural quality of the GaN layer.

  18. Heteroepitaxial growth and multiferroic properties of Mn-doped BiFeO3 films on SrTiO3 buffered III-V semiconductor GaAs

    NASA Astrophysics Data System (ADS)

    Gao, G. Y.; Yang, Z. B.; Huang, W.; Zeng, H. Z.; Wang, Y.; Chan, H. L. W.; Wu, W. B.; Hao, J. H.

    2013-09-01

    Epitaxial Mn-doped BiFeO3 (MBFO) thin films were grown on GaAs (001) substrate with SrTiO3 (STO) buffer layer by pulsed laser deposition. X-ray diffraction results demonstrate that the films show pure (00l) orientation, and MBFO (100)//STO(100), whereas STO (100)//GaAs (110). Piezoresponse force microscopy images and polarization versus electric field loops indicate that the MBFO films grown on GaAs have an effective ferroelectric switching. The MBFO films exhibit good ferroelectric behavior (2Pr ˜ 92 μC/cm2 and 2EC ˜ 372 kV/cm). Ferromagnetic property with saturated magnetization of 6.5 emu/cm3 and coercive field of about 123 Oe is also found in the heterostructure at room temperature.

  19. Formation of Ni Diffusion-Induced Surface Traps in GaN/Al x Ga1- x N/GaN Heterostructures on Silicon Substrate During Gate Metal Deposition

    NASA Astrophysics Data System (ADS)

    Kajen, R. S.; Bera, L. K.; Tan, H. R.; Dolmanan, S. B.; Cheong, Z. W.; Tripathy, S.

    2016-01-01

    The diffusion of the Schottky metal (Ni) in GaN is known to occur at elevated temperatures and as a result of prolonged electric field-driven stress. This leads to device degradation and reliability issues in Al x Ga1- x N/GaN-on-silicon high electron mobility transistors (HEMTs). In this study, we have investigated the formation of Ni-induced deep level traps across the Ni-GaN interface in Al x Ga1- x N/GaN HEMT-based Schottky diodes on Si substrates during the Schottky metal deposition process prior to any gate/Schottky metal annealing step. Two deep level traps were detected at 0.14 eV and 0.54 eV using Fourier deep level transient spectroscopy, which correlated well with nitrogen vacancies and nitrogen antisite defects, respectively. Our results are further supported by transmission electron microscopy-based energy dispersive x-ray analysis and electron energy loss spectroscopy measurements which confirm the interdiffusion of Ga and Ni across the Ni/GaN interface on the HEMT structure. Understanding the nature of such defects may help to employ suitable growth or passivation schemes for development of improved GaN-based electronic devices.

  20. Optimising uniformity of InAs/(InGaAs)/GaAs quantum dots grown by metal organic vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    Höglund, Linda; Petrini, E.; Asplund, C.; Malm, H.; Andersson, J. Y.; Holtz, P. O.

    2006-05-01

    A route towards optimisation of uniformity and density of InAs/(InGaAs)/GaAs quantum dots grown by metal organic vapor phase epitaxy (MOVPE) through successive variations of the growth parameters is reported. It is demonstrated that a key parameter in obtaining a high density of quantum dots is the V/III ratio, a fact which was shown to be valid when either AsH 3 (arsine) or tertiary-butyl-arsine (TBA) were used as group V precursors. Once the optimum V/III ratio was found, the size distribution was further improved by adjusting the nominal thickness of deposited InAs material, resulting in an optimum thickness of 1.8 monolayers of InAs in our case. The number of coalesced dots was minimised by adjusting the growth interruption time to approximately 30 s. Further, the uniformity was improved by increasing the growth temperature from 485 °C to 520 °C. By combining these optimised parameters, i.e. a growth temperature of 520 °C, 1.8 monolayers InAs thickness, 30 s growth stop time and TBA as group V precursor, a full-width-half-maximum (FWHM) of the low temperature luminescence band of 40 meV was achieved, indicating a narrow dot size distribution.

  1. Design and characterization of thick InxGa1-xAs metamorphic buffer layers grown by hydride vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    Schulte, K. L.; Zutter, B. T.; Wood, A. W.; Babcock, S. E.; Kuech, T. F.

    2014-03-01

    Thick InxGa1-xAs metamorphic buffer layers (MBLs) grown by hydride vapor phase epitaxy (HVPE) were studied. Relationships between MBL properties and growth parameters such as grading rate, cap layer thickness, final xInAs, and deposition temperature (TD) were explored. The MBLs were characterized by measurement of in-plane residual strain (ɛ¦¦), surface etch pit density (EPD), and surface roughness. Capping layer thickness had a strong effect on strain relaxation, with thickly capped samples exhibiting the lowest ɛ¦¦. EPD was higher in samples with thicker caps, reflecting their increased relaxation through dislocation generation. ɛ¦¦ and EPD were weakly affected by the grading rate, making capping layer thickness the primary structural parameter which controls these properties. MBLs graded in discrete steps had similar properties to MBLs with continuous grading. In samples with identical thickness and 10-step grading style, ɛ¦¦ increased almost linearly with final xInAs, while total relaxation stayed relatively constant. Relaxation as a function of xInAs could be described by an equilibrium model in which dislocation nucleation is impeded by the energy of the existing dislocation array. EPD was constant from xInAs = 0 to 0.24 then increased exponentially, which is related to the increased dislocation interaction and blocking seen at higher dislocation densities. RMS roughness increased with xInAs above a certain strain rate (0.15%/µm) samples grown below this level possessed large surface hillocks and high roughness values. The elimination of hillocks at higher values of xInAs is attributed to increased density of surface steps and is related to the out-of-plane component of the burgers vector of the dominant type of 60° dislocation. TD did not affect ɛ¦¦ for samples with a given xInAs. EPD tended to increase with TD, indicating dislocation glide likely is impeded at higher temperatures.

  2. 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. PMID:27168329

  3. 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.

  4. 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

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

    NASA Astrophysics Data System (ADS)

    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

    2015-09-01

    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.

  6. 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

    2015-01-01

    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

  7. The effects of buffer layers on the performance and stability of flexible InGaZnO thin film transistors on polyimide substrates

    NASA Astrophysics Data System (ADS)

    Ok, Kyung-Chul; Ko Park, Sang-Hee; Hwang, Chi-Sun; Kim, H.; Soo Shin, Hyun; Bae, Jonguk; Park, Jin-Seong

    2014-02-01

    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 SiNx/AlOx 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 SiNx or SiOx buffer layers. The substrates could be bent down to a radius of curvature of 15 mm and the devices remained normally functional.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. Improved dielectric properties of lead zirconate titanate thin films deposited on metal foils with LaNiO3 buffer layers

    NASA Astrophysics Data System (ADS)

    Zou, Q.; Ruda, H. E.; Yacobi, B. G.

    2001-02-01

    Improved dielectric properties of lead zirconate titanate (PZT) films deposited on a variety of foils using buffer layers are reported. Foils include titanium, stainless steel, and nickel with LaNiO3(LNO) buffer layers which were prepared by sol-gel processing. High dielectric constant (330 for stainless steel, 420 for titanium, and 450 for nickel foils), low dielectric loss (<2.2% for titanium and 8% for stainless steel), symmetric ferroelectric C-V characteristics and P-E curves were obtained. The LNO layers are shown to provide an effective diffusion barrier for Ni and Cr and to restrict oxide layer formation (i.e., TiOx or NiOx) between the PZT film and the metallic foils during annealing in air.

  15. 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.

  16. High linearly polarized light emission from GaN-based LED with patterned dielectric/metal structures

    NASA Astrophysics Data System (ADS)

    Wang, Miao; Cao, Bing; Xu, Fuyang; Hu, Jingpei; Wang, Jianfeng; Xu, Ke; Wang, Chinhua

    2015-07-01

    We proposed and demonstrated an integrated high linearly polarized InGaN/GaN green LED grown on (0001) oriented sapphire with a structure of combined dielectric/metal wire grids (CDMWG). Both theoretical and experimental results show that the CDMWG can effectively loosen the requirement on the dimension of the grating, and the introduction of a low-refractive dielectric layer can further enhance both TMT and ER significantly for the GaN-type LED. An InGaN/ GaN green LED with an integrated CDMWG of 220 nm period has been fabricated, and a measured extinction ratio(ER) of higher than 20 dB and TMT of 65% within an angle of +/-40° is obtained directly from a InGaN/GaN LED.

  17. 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.

  18. 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.

  19. 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.

  20. Pure AlN layers in metal-polar AlGaN/AlN/GaN and AlN/GaN heterostructures grown by low-temperature ammonia-based molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Kaun, Stephen W.; Mazumder, Baishakhi; Fireman, Micha N.; Kyle, Erin C. H.; Mishra, Umesh K.; Speck, James S.

    2015-05-01

    When grown at a high temperature (820 °C) by ammonia-based molecular beam epitaxy (NH3-MBE), the AlN layers of metal-polar AlGaN/AlN/GaN heterostructures had a high GaN mole fraction (∼0.15), as identified by atom probe tomography in a previous study (Mazumder et al 2013 Appl. Phys. Lett. 102 111603). In the study presented here, growth at low temperature (<740 °C) by NH3-MBE yielded metal-polar AlN layers that were essentially pure at the alloy level. The improved purity of the AlN layers grown at low temperature was correlated to a dramatic increase in the sheet density of the two-dimensional electron gas (2DEG) at the AlN/GaN heterointerface. Through application of an In surfactant, metal-polar AlN(3.5 nm)/GaN and AlGaN/AlN(2.5 nm)/GaN heterostructures grown at low temperature yielded low 2DEG sheet resistances of 177 and 285 Ω/□, respectively.

  1. 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.

  2. Growth and characterisation of Ga(NAsBi) alloy by metal-organic vapour phase epitaxy

    NASA Astrophysics Data System (ADS)

    Bushell, Z. L.; Ludewig, P.; Knaub, N.; Batool, Z.; Hild, K.; Stolz, W.; Sweeney, S. J.; Volz, K.

    2014-06-01

    This paper summarises results of the epitaxial growth of Ga(NAsBi) by metal-organic vapour phase epitaxy (MOVPE) and the subsequent optical and structural characterisations of the samples. Ga(NAsBi)/GaAs multi-quantum well (MQW) samples are grown at 400 °C and single layers at 450 °C on GaAs (001) substrates. Triethylgallium (TEGa), tertiarybutylarsine (TBAs), trimethylbismuth (TMBi) and unsymmetrical dimethylhydrazine (UDMHy) are used as precursors. Secondary ion mass spectrometry (SIMS) shows that the Bi content is independent of the N content in the alloy. It is found that the N content depends on both UDMHy and TMBi supply during growth. High resolution X-ray diffraction (HR-XRD), scanning transmission electron microscopy (STEM) and atomic force microscopy (AFM) measurements show that samples with good crystalline quality can be realised. For samples containing 1.8% Bi and up to 1.8% N grown at 450 °C, photoreflectance spectroscopy (PR) shows a decrease in the band gap with increasing N content of 141±22 meV/% N.

  3. Effects of HCl treatment and predeposition vacuum annealing on Al2O3/GaSb/GaAs metal-oxide-semiconductor structures

    NASA Astrophysics Data System (ADS)

    Gotow, Takahiro; Fujikawa, Sachie; Fujishiro, Hiroki I.; Ogura, Mutsuo; Yasuda, Tetsuji; Maeda, Tatsuro

    2015-02-01

    The effects of HCl treatment and predeposition vacuum annealing (VA) on n-type GaSb/GaAs metal-oxide-semiconductor (MOS) structures with the atomic layer deposition (ALD) of Al2O3 dielectrics are studied. We obtained MOS structures with good Fermi level modulation by HCl treatment prior to the deposition of Al2O3. From X-ray photoelectron spectroscopy (XPS) analysis, we found that the Ga2O3 content increases during the Al2O3 deposition, whereas the amounts of Sb components are reduced. The excess growth of Ga2O3 is inhibited by the reductions in the amounts of Sb components by the HCl treatment. Further reductions in the amounts of Sb components are observed following predeposition VA, indicating a lower density of states (Dit). However, the frequency dispersion in the capacitance-voltage (C-V) characteristics increases with predeposition VA at higher temperatures.

  4. 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).

  5. P-Channel InGaN/GaN heterostructure metal-oxide-semiconductor field effect transistor based on polarization-induced two-dimensional hole gas

    NASA Astrophysics Data System (ADS)

    Zhang, Kexiong; Sumiya, Masatomo; Liao, Meiyong; Koide, Yasuo; Sang, Liwen

    2016-03-01

    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.

  6. 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

    2016-01-01

    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 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. PMID:27021054

  7. 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).

  8. 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.

  9. High Jc YBCO coated conductors on non-magnetic metallic substrate using YSZ-based buffer layer architecture

    NASA Astrophysics Data System (ADS)

    Celentano, G.; Boffa, V.; Ciontea, L.; Fabbri, F.; Galluzzi, V.; Gambardella, U.; Mancini, A.; Petrisor, T.; Rogai, R.; Rufoloni, A.; Varesi, E.

    2002-08-01

    Biaxially aligned YBa 2Cu 3O 7- δ (YBCO) thick films were deposited by pulsed laser ablation technique on cube textured non-magnetic Ni 89V 11 (Ni-V) substrate, using CeO 2/YSZ/CeO 2/NiO buffer layer architecture. The first NiO seed layer was formed by epitaxial oxidation of the Ni-V substrate. Structural analyses show typical full width at half maximum values of φ- and ω-scans less than 10° and 8°, respectively. The highest value obtained for the critical current density at 77 K and zero magnetic field was 6×10 5 A cm -2, which is close to that obtained for YBCO films grown on CeO 2/NiO buffer layer architecture.

  10. 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)

  11. 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.

  12. 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.

  13. 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.

  14. 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

  15. Structural and optical studies of GaN pn-junction with AlN buffer layer grown on Si (111) by RF plasma enhanced MBE

    NASA Astrophysics Data System (ADS)

    Yusoff, Mohd Zaki Mohd; Hassan, Zainuriah; Woei, Chin Che; Hassan, Haslan Abu; Abdullah, Mat Johar

    2012-06-01

    GaN pn-junction grown on silicon substrates have been the focus in a number of recent reports and further effort is still necessary to improve its crystalline quality for practical applications. GaN has the high n-type background carrier concentration resulting from native defects commonly thought to be nitrogen vacancies. In this work, we present the growth of pn-junction of GaN on Si (111) substrate using RF plasma-enhanced molecular beam epitaxy (MBE). Both of the layers show uniformity with an average thickness of 0.709 μm and 0.095 μm for GaN and AlN layers, respectively. The XRD spectra indicate that no sign of cubic phase of GaN are found, so it is confirmed that the sample possessed hexagonal structure. It was found that all the allowed Raman optical phonon modes of GaN, i.e. the E2 (low), E1 (high) and A1 (LO) are clearly visible.

  16. Structural and optical studies of GaN pn-junction with AlN buffer layer grown on Si (111) by RF plasma enhanced MBE

    SciTech Connect

    Yusoff, Mohd Zaki Mohd; Hassan, Zainuriah; Woei, Chin Che; Hassan, Haslan Abu; Abdullah, Mat Johar

    2012-06-29

    GaN pn-junction grown on silicon substrates have been the focus in a number of recent reports and further effort is still necessary to improve its crystalline quality for practical applications. GaN has the high n-type background carrier concentration resulting from native defects commonly thought to be nitrogen vacancies. In this work, we present the growth of pn-junction of GaN on Si (111) substrate using RF plasma-enhanced molecular beam epitaxy (MBE). Both of the layers show uniformity with an average thickness of 0.709 {mu}m and 0.095 {mu}m for GaN and AlN layers, respectively. The XRD spectra indicate that no sign of cubic phase of GaN are found, so it is confirmed that the sample possessed hexagonal structure. It was found that all the allowed Raman optical phonon modes of GaN, i.e. the E2 (low), E1 (high) and A1 (LO) are clearly visible.

  17. Coupling of single InGaAs quantum dots to the plasmon resonance of a metal nanocrystal

    SciTech Connect

    Urbanczyk, A.; Hamhuis, G. J.; Noetzel, R.

    2010-07-26

    The authors report the coupling of single InGaAs quantum dots (QDs) to the surface plasmon resonance of a metal nanocrystal. Clear enhancement of the photoluminescence (PL) in the spectral region of the surface plasmon resonance is observed which splits up into distinct emission lines from single QDs in micro-PL. The hybrid metal-semiconductor structure is grown by molecular beam epitaxy on GaAs (100) utilizing the concept of self-organized anisotropic strain engineering for realizing ordered arrays with nanometer-scale precise positioning of the metal nanocrystals with respect to the QDs.

  18. Tunable Magnetism and Half-Metallicity in Hole-Doped Monolayer GaSe

    NASA Astrophysics Data System (ADS)

    Cao, Ting; Li, Zhenglu; Louie, Steven G.

    2015-06-01

    We find, through first-principles calculations, that hole doping induces a ferromagnetic phase transition in monolayer GaSe. Upon increasing hole density, the average spin magnetic moment per carrier increases and reaches a plateau near 1.0 μB per carrier in a range of 3 ×1013/cm2-1 ×1014/cm2 , with the system in a half-metal state before the moment starts to descend abruptly. The predicted itinerant magnetism originates from an exchange splitting of electronic states at the top of the valence band, where the density of states exhibits a sharp van Hove singularity in this quasi-two-dimensional system.

  19. 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.

  20. 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.

  1. Structural and optical analyses of AlxGa1-xN thin films grown by metal organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Kucukgok, Bahadir; Lu, Na; Ferguson, Ian T.; Wang, Shu Chang; Zhang, Xiong; Feng, Zhe Chuan

    2015-02-01

    A series of AlxGa1-xN thin films with x = 0.20-0.60 were grown by metal organic chemical vapor deposition (MOCVD) on sapphire (0001) substrate using AlN buffer layer. High resolution X-ray diffraction (HRXRD) was performed for (0002), (0004), and (0006) reflections to investigate the threading dislocation density in variation with Al composition by X-ray analysis technique; Williamson-Hall (WH) plot. A symmetric high resolution 2θ-ω scans exhibit high crystal quality for all the AlGaN samples. A room temperature deep ultraviolet (DUV) photoluminescence (PL) spectroscopy (excitation at 248 nm) has also been employed to investigate the effect of various Al compositions on crystal structure of the thin film layers. It was observed that the band edge transition peak energy blueshifts from 3.87 eV for x = 0.23 to 4.55 eV for x = 0.47. In addition to the band edge transition, each spectrum also shows deep impurity transitions.

  2. The structural and optical properties of metal ion-implanted GaN

    NASA Astrophysics Data System (ADS)

    Macková, A.; Malinský, P.; Sofer, Z.; Šimek, P.; Sedmidubský, D.; Veselý, M.; Böttger, R.

    2016-03-01

    The practical development of novel optoelectronic materials with appropriate optical properties is strongly connected to the structural properties of the prepared doped structures. We present GaN layers oriented along the (0 0 0 1) crystallographic direction that have been grown by low-pressure metal-organic vapour-phase epitaxy (MOVPE) on sapphire substrates implanted with 200 keV Co+, Fe+ and Ni+ ions. The structural properties of the ion-implanted layers have been characterised by RBS-channelling and Raman spectroscopy to obtain a comprehensive insight into the structural modification of implanted GaN layers and to study the subsequent influence of annealing on crystalline-matrix recovery. Photoluminescence was measured to control the desired optical properties. The post-implantation annealing induced the structural recovery of the modified GaN layer depending on the introduced disorder level, e.g. depending on the ion implantation fluence, which was followed by structural characterisation and by the study of the surface morphology by AFM.

  3. Superconducting state parameters of La100-C GaC binary metallic glasses

    NASA Astrophysics Data System (ADS)

    Vora, Aditya

    2008-06-01

    The theoretical investigations of the superconducting state parameters (SSP) viz. electron-phonon coupling strength λ, Coulomb pseudopotential μ*, transition temperature T C, isotope effect exponent α and effective interaction strength N O V of six binary La100-C GaC (C = 16, 20, 22, 24, 26 and 28 at. %) metallic glasses have been reported using Ashcroft's empty core (EMC) model potential for the first time. Five local field correction functions proposed by Hartree (H), Taylor (T), Ichimaru-Utsumi (IU), Farid et al. (F) and Sarkar et al. (S) are used in the present investigation to study the screening influence on the aforesaid properties. It is observed that the electron-phonon coupling strength λ and the transition temperature T C are quite sensitive to the selection of the local field correction functions, whereas the Coulomb pseudopotential μ*, isotope effect exponent α and effective interaction strength N O V show weak dependences on the local field correction functions. The T C obtained from H-local field correction function are found in qualitative agreement with available experimental data and show almost linear nature with the concentration (C) of `Ga' element. A linear T C equation is proposed by fitting the present outcomes for H-local field correction function, which is in conformity with other results for the experimental data. Also, the present results are found to be in qualitative agreement with other such earlier reported data, which confirms the superconducting phase in the metallic glasses.

  4. The metallic interface between insulating NdGaO3 and SrTiO3 perovskites

    NASA Astrophysics Data System (ADS)

    Li, Chen; Xu, Qinfang; Wen, Zheng; Zhang, Shantao; Li, Aidong; Wu, Di

    2013-11-01

    Perovskite NdGaO3 (NGO) films, 2-20 unit cells in thickness, have been deposited epitaxially on {001} TiO2-terminated SrTiO3 substrates at different O2 pressures. The {001} NdGaO3/SrTiO3 (STO) interface becomes metallic as the NdGaO3 overlayer is more than 4 unit cells in thickness. The sheet carrier density is above 1013 cm-2 and temperature-independent from 300 down to 7 K. Similar metallic interface has also been achieved in {111} NdGaO3/SrTiO3. Post-annealing in O2 does not change the transport characteristics significantly. These indicate that oxygen vacancies may not have a predominant contribution to the observed interfacial conduction in NGO/STO heterostructures deposited at high oxygen pressure.

  5. Improved linearity in AlGaN/GaN metal-insulator-semiconductor high electron mobility transistors with nonlinear polarization dielectric

    SciTech Connect

    Gao, Tao; Xu, Ruimin; Kong, Yuechan Zhou, Jianjun; Kong, Cen; Dong, Xun; Chen, Tangsheng

    2015-06-15

    We demonstrate highly improved linearity in a nonlinear ferroelectric of Pb(Zr{sub 0.52}Ti{sub 0.48})-gated AlGaN/GaN metal-insulator-semiconductor high electron mobility transistor (MIS-HEMT). Distinct double-hump feature in the transconductance-gate voltage (g{sub m}-V{sub g}) curve is observed, yielding remarkable enhancement in gate voltage swing as compared to MIS-HEMT with conventional linear gate dielectric. By incorporating the ferroelectric polarization into a self-consistent calculation, it is disclosed that in addition to the common hump corresponding to the onset of electron accumulation, the second hump at high current level is originated from the nonlinear polar nature of ferroelectric, which enhances the gate capacitance by increasing equivalent dielectric constant nonlinearly. This work paves a way for design of high linearity GaN MIS-HEMT by exploiting the nonlinear properties of dielectric.

  6. Highly reflective GaN/Al0.34Ga0.66N quarter-wave reflectors grown by metal organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Someya, T.; Arakawa, Y.

    1998-12-01

    Quarter-wave reflectors consisting of sets of GaN and Al0.34Ga0.66N layers have been grown on sapphire substrates by atmospheric-pressure metal organic chemical vapor deposition. A periodic structure with flat interfaces was observed by high-resolution scanning electron microscopy. X-ray diffraction measurements were performed to characterize the structures, from which the Al content x in the AlxGa1-xN layers was determined to be 0.34. No cracks could be seen on the surface of the reflectors by optical microscopy. The measured peak reflectivity at 390 nm increases with the number of pairs and reaches as high as 96±2% in the 35-pair reflector.

  7. 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.

  8. 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.

  9. 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.

  10. Growth of GaN Layers on Sapphire by Low-Temperature-Deposited Buffer Layers and Realization of p-type GaN by Magesium Doping and Electron Beam Irradiation (Nobel Lecture).

    PubMed

    Amano, Hiroshi

    2015-06-26

    This Review is a personal reflection on the research that led to the development of a method for growing gallium nitride (GaN) on a sapphire substrate. The results paved the way for the development of smart 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 that enables the growth of GaN and the realization of p-type GaN was established are reviewed. PMID:26032024

  11. 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.

  12. Atomic Layer Deposition of Gallium Oxide Films as Gate Dielectrics in AlGaN/GaN Metal-Oxide-Semiconductor High-Electron-Mobility Transistors

    NASA Astrophysics Data System (ADS)

    Shih, Huan-Yu; Chu, Fu-Chuan; Das, Atanu; Lee, Chia-Yu; Chen, Ming-Jang; Lin, Ray-Ming

    2016-04-01

    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 × 1011 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.

  13. 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. PMID:27129687

  14. High-crystalline GaSb epitaxial films grown on GaAs(001) substrates by low-pressure metal-organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Wang, Lian-Kai; Liu, Ren-Jun; Lü, You; Yang, Hao-Yu; Li, Guo-Xing; Zhang, Yuan-Tao; Zhang, Bao-Lin

    2015-01-01

    Orthogonal experiments of GaSb films growth on GaAs(001) substrates have been designed and performed by using a low-pressure metal-organic chemical vapor deposition (LP-MOCVD) system. The crystallinities and microstructures of the produced films were comparatively analyzed to achieve the optimum growth parameters. It was demonstrated that the optimized GaSb thin film has a narrow full width at half maximum (358 arc sec) of the (004) ω-rocking curve, and a smooth surface with a low root-mean-square roughness of about 6 nm, which is typical in the case of the heteroepitaxial single-crystal films. In addition, we studied the effects of layer thickness of GaSb thin film on the density of dislocations by Raman spectra. It is believed that our research can provide valuable information for the fabrication of high-crystalline GaSb films and can promote the integration probability of mid-infrared devices fabricated on mainstream performance electronic devices. Project supported by the National Natural Science Foundation of China (Grant No. 61076010) and the International Science and Technology Cooperation Program of Science and Technology Bureau of Changchun, China (Grant No. 12ZX68).

  15. Investigation of ZnO thin films deposited on ferromagnetic metallic buffer layer by molecular beam epitaxy toward realization of ZnO-based magnetic tunneling junctions

    SciTech Connect

    Belmoubarik, M.; Nozaki, T.; Sahashi, M.; Endo, H.

    2013-05-07

    Deposition of ZnO thin films on a ferromagnetic metallic buffer layer (Co{sub 3}Pt) by molecular beam epitaxy technique was investigated for realization of ZnO-based magnetic tunneling junctions with good quality hexagonal ZnO films as tunnel barriers. For substrate temperature of 600 Degree-Sign C, ZnO films exhibited low oxygen defects and high electrical resistivity of 130 {Omega} cm. This value exceeded that of hexagonal ZnO films grown by sputtering technique, which are used as tunnel barriers in ZnO-MTJs. Also, the effect of oxygen flow during deposition on epitaxial growth conditions and Co{sub 3}Pt surface oxidation was discussed.

  16. 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.

  17. Low current operation of GaN-based blue-violet laser diodes fabricated on sapphire substrate using high-temperature-grown single-crystal AlN buffer layer

    NASA Astrophysics Data System (ADS)

    Ohba, Yasuo; Gotoda, Toru; Kaneko, Kei

    2007-01-01

    Low current laser operation at 405 nm has been demonstrated for the first time for the devices fabricated on sapphire substrates by metalorganic chemical vapor deposition (MOCVD) using a high-temperature-grown single-crystal AlN buffer. The thick optical guiding layers were adopted to improve optical confinement. The device structure was the 2-μm-wide ridge-stripe type without facet coating. The minimum threshold current and current density were 60 mA and 3.8 kA/cm 2 for cavity lengths of 500 mm and 1 mm, respectively. These data were comparable to those reported using the special dislocation reduction techniques. The threshold current density linearly decreases with decreasing inverse of cavity length. It was expected that the low threshold current density ranging from 1 to 2 kA/cm 2 could be realized by adapting high reflection coating for laser facets. This expected current density was comparable to values realized for devices grown on the thick freestanding GaN as substrates. These findings support the promising potential of the HT-AlN buffer technique for production of advanced short-wavelength light-emitting devices on sapphire substrates.

  18. 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. PMID:27494649

  19. 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.

  20. 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.

  1. Plasma-induced-damage of GaAs during etching of refractory metal contacts

    SciTech Connect

    Shul, R.J.; Lovejoy, M.L.; Baca, A.G.; Zolper, J.C.; Rieger, D.J.; Hafich, M.J.; Corless, R.F.; Vartuli, C.R.

    1994-10-01

    The effect of plasma-induced-damage on the majority carrier transport properties of GaAs has been studied by monitoring changes in sheet resistance (R{sub s}) of thin conducting layers under various plasma conditions including etch conditions for refractory metal contacts. R{sub s} determined from transmission line measurements are used to evaluate plasma-induced-damage for electron cyclotron resonance (ECR) and reactive ion etch (RIE) conditions by varying the thickness of doped epitaxial layers. The authors speculate that plasma-induced-damage in the near surface region plays a major role in explaining the damage mechanism observed in this study. Very consistent trends have been observed where R{sub s} increases with increasing ECR and RIE dc-bias, increasing microwave power, and decreasing pressure, thus showing R{sub s} increases as either the ion energy or ion flux increases. The authors have also observed that R{sub s} is lower for samples exposed to the RIE than the ECR, possibly due to higher ion and electron densities generated in the ECR and higher pressures in the RIE. It has also been observed R{sub s} dependence on ECR plasma chemistry where, R{sub s} is lower in SF{sub 6}/Ar plasmas than Ar and N{sub 2} plasmas possibly related to interactions of F or S atoms with the GaAs surface. Moderate anneal temperatures (200 to 500{degrees}C) have shown significant R{sub s} recovery.

  2. 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.

  3. Tunable Magnetism and Half-Metallicity in Hole-Doped Monolayer GaSe.

    PubMed

    Cao, Ting; Li, Zhenglu; Louie, Steven G

    2015-06-12

    We find, through first-principles calculations, that hole doping induces a ferromagnetic phase transition in monolayer GaSe. Upon increasing hole density, the average spin magnetic moment per carrier increases and reaches a plateau near 1.0 μB per carrier in a range of 3×10(13)/cm(2)-1×10(14)/cm(2), with the system in a half-metal state before the moment starts to descend abruptly. The predicted itinerant magnetism originates from an exchange splitting of electronic states at the top of the valence band, where the density of states exhibits a sharp van Hove singularity in this quasi-two-dimensional system. PMID:26196815

  4. 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.

  5. 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. PMID:26001039

  6. 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.

  7. The 310 340 nm ultraviolet light emitting diodes grown using a thin GaN interlayer on a high temperature AlN buffer

    NASA Astrophysics Data System (ADS)

    Wang, T.; Lee, K. B.; Bai, J.; Parbrook, P. J.; Ranalli, F.; Wang, Q.; Airey, R. J.; Cullis, A. G.; Zhang, H. X.; Massoubre, D.; Gong, Z.; Watson, I. M.; Gu, E.; Dawson, M. D.

    2008-05-01

    Previously, we reported that a thin GaN interlayer approach has been developed for growth of 340 nm ultraviolet light emitting diodes (UV-LEDs) with significantly improved performance. In this paper, more recent results on the further development of UV-LEDs with shorter wavelengths are reported, and the limitation of the wavelength of the UV-LEDs that can be pushed to, while retaining high device performance using the approach has been investigated. Transmission electron microscopy and device-performance data, including electrical and optical characteristics, indicated that the thin GaN interlayer approach can be effectively employed for growth of UV-LEDs to an emission wavelength approaching at least 300 nm. The approach should be taken into account in growth of UV-LEDs on sapphire substrates, as it provides a simple but effective growth method to achieve UV-LEDs with high performance. This paper also reports that a micro-LED array using the UV-LED wafer has been successfully fabricated, offering versatile micro-structured UV light sources for a wide range of applications.

  8. The physical origin of dispersion in accumulation in InGaAs based metal oxide semiconductor gate stacks

    NASA Astrophysics Data System (ADS)

    Krylov, Igor; Ritter, Dan; Eizenberg, Moshe

    2015-05-01

    Dispersion in accumulation is a widely observed phenomenon in technologically important InGaAs gate stacks. Two principal different interface defects were proposed as the physical origin of this phenomenon—disorder induced gap states and border traps. While the gap states are located at the semiconductor side of the interface, the border traps are related to the dielectric side. The study of Al2O3, HfO2, and an intermediate composition of HfxAlyO deposited on InGaAs enabled us to find a correlation between the dispersion and the dielectric/InGaAs band offset. At the same time, no change in the dispersion was observed after applying an effective pre-deposition treatment which results in significant reduction of the interface states. Both observations prove that border traps are the physical origin of the dispersion in accumulation in InGaAs based metal-oxide-semiconductor gate stacks.

  9. High-performance GaAs metal-insulator-semiconductor field-effect transistors enabled by self-assembled nanodielectrics

    NASA Astrophysics Data System (ADS)

    Lin, H. C.; Ye, P. D.; Xuan, Y.; Lu, G.; Facchetti, A.; Marks, T. J.

    2006-10-01

    High-performance GaAs metal-insulator-semiconductor field-effect-transistors (MISFETs) fabricated with very thin self-assembled organic nanodielectrics (SANDs), deposited from solution at room temperature, are demonstrated. A submicron gate-length depletion-mode n-channel GaAs MISFET with SAND thicknesses ranging from 5.5to16.5nm exhibit a gate leakage current density <10-5A/cm2 at a gate bias smaller than 3V, a maximum drain current of 370mA/mm at a forward gate bias of 2V, and a maximum intrinsic transconductance of 170mS/mm. The importance of appropriate GaAs surface chemistry treatments on SAND/GaAs interface properties is also presented. Application of SANDs to III-V compound semiconductors affords more opportunities to manipulate the complex III-V surface chemistry with broad materials options.

  10. 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.

  11. InAs/GaSb core-shell nanowires grown on Si substrates by metal-organic chemical vapor deposition.

    PubMed

    Ji, Xianghai; Yang, Xiaoguang; Du, Wenna; Pan, Huayong; Luo, Shuai; Ji, Haiming; Xu, H Q; Yang, Tao

    2016-07-01

    We report the growth of InAs/GaSb core-shell heterostructure nanowires with smooth sidewalls on Si substrates using metal-organic chemical vapor deposition with no assistance from foreign catalysts. Sb adatoms were observed to strongly influence the morphology of the GaSb shell. In particular, Ga droplets form on the nanowire tips when a relatively low TMSb flow rate is used, whereas the droplets are missing and the radial growth of the GaSb is enhanced due to a reduction in the diffusion length of the Ga adatoms when the TMSb flow rate is increased. Moreover, transmission electron microscopy measurements revealed that the GaSb shell coherently grew on the InAs core. The results obtained here show that the InAs/GaSb core-shell nanowires grown using the Si platform have strong potential in the fabrication of future nanometer-scale devices and in the study of fundamental quantum physics. PMID:27232079

  12. Poole Frenkel current and Schottky emission in SiN gate dielectric in AlGaN/GaN metal insulator semiconductor heterostructure field effect transistors

    NASA Astrophysics Data System (ADS)

    Hanna, Mina J.; Zhao, Han; Lee, Jack C.

    2012-10-01

    We analyze the anomalous I-V behavior in SiN prepared by plasma enhanced chemical vapor deposition for use as a gate insulator in AlGaN/GaN metal insulator semiconductor heterostructure filed effect transistors (HFETs). We observe leakage current across the dielectric with opposite polarity with respect to the applied electric field once the voltage sweep reaches a level below a determined threshold. This is observed as the absolute minimum of the leakage current does not occur at minimum voltage level (0 V) but occurs earlier in the sweep interval. Curve-fitting analysis suggests that the charge-transport mechanism in this region is Poole-Frenkel current, followed by Schottky emission due to band bending. Despite the current anomaly, the sample devices have shown a notable reduction of leakage current of over 2 to 6 order of magnitudes compared to the standard Schottky HFET. We show that higher pressures and higher silane concentrations produce better films manifesting less trapping. This conforms to our results that we reported in earlier publications. We found that higher chamber pressure achieves higher sheet carrier concentration that was found to be strongly dependent on the trapped space charge at the SiN/GaN interface. This would suggest that a lower chamber pressure induces more trap states into the SiN/GaN interface.

  13. 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

  14. Chromatography of alkaline earths and transition metals on tin(iv) arsenosilicate and arsenophosphate thin layers in buffered EDTA solutions

    SciTech Connect

    Varshney, K.G.; Anwar, S.; Khan, A.A.

    1985-01-01

    The complex forming ability of ethylene diamine tetraacetic acid at various pH values and the ion exchange behavior of tin(IV) arsenosilicate and arsenophosphate cation exchangers have been combined in a chromatographic study of some metal ions. As a result some interesting observations have been made, which have led to certain analytically difficult separations such as Ca/sup 2 +/ -Sr/sup 2 +/, Ca/sup 2 +/ -Ba/sup 2 +/ and Hg/sup 2 +/ from Cu/sup 2 +/, Ni/sup 2 +/, Zn/sup 2 +/, Co/sup 2 +/ and Mn/sup 2 +/.

  15. Superconducting state parameters of La100- C Ga C binary metallic glasses

    NASA Astrophysics Data System (ADS)

    Vora, Aditya M.

    2008-06-01

    The theoretical investigations of the superconducting state parameters (SSP) viz. electron-phonon coupling strength λ, Coulomb pseudopotential μ*, transition temperature T C , isotope effect exponent α and effective interaction strength N O V of six binary La100- C Ga C ( C = 16, 20, 22, 24, 26 and 28 at. %) metallic glasses have been reported using Ashcroft’s empty core (EMC) model potential for the first time. Five local field correction functions proposed by Hartree (H), Taylor (T), Ichimaru-Utsumi (IU), Farid et al. (F) and Sarkar et al. (S) are used in the present investigation to study the screening influence on the aforesaid properties. It is observed that the electron-phonon coupling strength λ and the transition temperature T C are quite sensitive to the selection of the local field correction functions, whereas the Coulomb pseudopotential μ*, isotope effect exponent α and effective interaction strength N O V show weak dependences on the local field correction functions. The T C obtained from H-local field correction function are found in qualitative agreement with available experimental data and show almost linear nature with the concentration ( C) of ‘Ga’ element. A linear T C equation is proposed by fitting the present outcomes for H-local field correction function, which is in conformity with other results for the experimental data. Also, the present results are found to be in qualitative agreement with other such earlier reported data, which confirms the superconducting phase in the metallic glasses.

  16. Temperature dependent surface photovoltage spectroscopy characterization of highly strained InGaAs/GaAs double quantum well structures grown by metal organic vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    Chan, C. H.; Wu, J. D.; Huang, Y. S.; Su, Y. K.; Tiong, K. K.

    2009-08-01

    Highly strained InxGa1-xAs/GaAs double quantum well (DQW) structures grown by metal organic vapor phase epitaxy with different In compositions are investigated by surface photovoltage spectroscopy (SPS) in the temperature range 20-300 K. A lineshape fit of spectral features in the differential surface photovoltage (SPV) spectra determines the transition energies accurately. A comprehensive analysis of the anomalous phenomena appearing in lower temperature SPV spectra enable us to evaluate directly the band lineup of DQW and to remove the ambiguity in the identification of spectral features. The process of separation of carriers within the QW with possible capture by the interface defect traps plays an important role for phase change in SPV signal in the vicinity of light-hole related feature at low temperature. The results demonstrate the considerable diagnostic values of the SPS technique for characterizing these highly strained DQW structures.

  17. 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.

  18. 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.

  19. High-performance AlGaN metal-semiconductor-metal solar-blind ultraviolet photodetectors by localized surface plasmon enhancement

    NASA Astrophysics Data System (ADS)

    Zhang, Wei; Xu, Jin; Ye, Wei; Li, Yang; Qi, Zhiqiang; Dai, Jiangnan; Wu, Zhihao; Chen, Changqing; Yin, Jun; Li, Jing; Jiang, Hao; Fang, Yanyan

    2015-01-01

    AlGaN-based solar-blind ultraviolet photodetectors have attractive potential applications in the fields of missile plume detection, biochemical sensing, solar astronomy, etc. In this work, significant deep ultraviolet detection enhancement is demonstrated on AlGaN-based metal-semiconductor-metal (MSM) solar-blind ultraviolet photodetectors by introducing the coupling of localized surface plasmon from Al nanoparticles with the high-Al-content AlGaN epilayer. The size-controlled Al nanoparticle arrays fabricated by nanosphere lithography can not only reduce the detectors' dark current but also bring about greatly enhanced responsivity. The peak responsivity of AlGaN-based MSM solar-blind ultraviolet photodetectors with Al nanoparticles can reach 2.34 A/W at 269 nm under 20 V bias, enhanced more than 25 times than that without Al nanoparticles. Our approach shows an efficient fabrication technique of high-performance and low-cost plasmonic enhanced AlGaN solar-blind MSM ultraviolet photodetectors.

  20. Au-Free GaN High-Electron-Mobility Transistor with Ti/Al/W Ohmic and WN X Schottky Metal Structures for High-Power Applications

    NASA Astrophysics Data System (ADS)

    Hsieh, Ting-En; Lin, Yueh-Chin; Chu, Chung-Ming; Chuang, Yu-Lin; Huang, Yu-Xiang; Shi, Wang-Cheng; Dee, Chang-Fu; Majlis, Burhanuddin Yeop; Lee, Wei-I.; Chang, Edward Yi

    2016-04-01

    In this study, an Au-free AlGaN/GaN high-electron-mobility transistor (HEMT) with Ti/Al/W ohmic and WNx Schottky metal structures is fabricated and characterized. The device exhibits smooth surface morphology after metallization and shows excellent direct-current (DC) characteristics. The device also demonstrates better performance than the conventional HEMTs under high voltage stress. Furthermore, the Au-free AlGaN/GaN HEMT shows stable device performance after annealing at 400°C. Thus, the Ti/Al/W ohmic and WN X Schottky metals can be applied in the manufacturing of GaN HEMT to replace the Au based contacts to reduce the manufacturing costs of the GaN HEMT devices with comparable device performance.

  1. Au-Free GaN High-Electron-Mobility Transistor with Ti/Al/W Ohmic and WN X Schottky Metal Structures for High-Power Applications

    NASA Astrophysics Data System (ADS)

    Hsieh, Ting-En; Lin, Yueh-Chin; Chu, Chung-Ming; Chuang, Yu-Lin; Huang, Yu-Xiang; Shi, Wang-Cheng; Dee, Chang-Fu; Majlis, Burhanuddin Yeop; Lee, Wei-I.; Chang, Edward Yi

    2016-07-01

    In this study, an Au-free AlGaN/GaN high-electron-mobility transistor (HEMT) with Ti/Al/W ohmic and WN x Schottky metal structures is fabricated and characterized. The device exhibits smooth surface morphology after metallization and shows excellent direct-current (DC) characteristics. The device also demonstrates better performance than the conventional HEMTs under high voltage stress. Furthermore, the Au-free AlGaN/GaN HEMT shows stable device performance after annealing at 400°C. Thus, the Ti/Al/W ohmic and WN X Schottky metals can be applied in the manufacturing of GaN HEMT to replace the Au based contacts to reduce the manufacturing costs of the GaN HEMT devices with comparable device performance.

  2. The role of AsH3 partial pressure on anti-phase boundary in GaAs-on-Ge grown by MOCVD - Application to a 200 mm GaAs virtual substrate

    NASA Astrophysics Data System (ADS)

    Kohen, David; Bao, Shuyu; Lee, Kwang Hong; Lee, Kenneth Eng Kian; Tan, Chuan Seng; Yoon, Soon Fatt; Fitzgerald, Eugene A.

    2015-07-01

    We demonstrate the influence of the arsine partial pressure (p(AsH3)) on the quality of a GaAs layer grown on Ge substrate by metal organic chemical vapor deposition. The GaAs quality improves with p(AsH3) used during the 100 nm thick GaAs buffer layer. By growing a GaAs buffer layer at 630 °C with p(AsH3) of 5 mbar, we obtain a smooth GaAs layer with a root mean square roughness of 4.7 Å. This GaAs layer does not contain anti-phase boundaries. With these optimized growth parameters, we fabricate a virtual GaAs substrate on a 200 mm silicon wafer as a first step towards the integration of III-V devices on silicon.

  3. Plasma-induced damage of GaAs during etching of refractory metal contacts

    SciTech Connect

    Shul, R.J.; Lovejoy, M.L.; Baca, A.G.; Zolper, J.C.; Rieger, D.J.; Hafich, M.J.; Corless, R.F.; Vartuli, C.B.

    1995-05-01

    The effect of plasma-induced damage on the majority carrier transport properties of {ital p}-type GaAs has been studied by monitoring changes in sheet resistance ({ital R}{sub {ital s}}) of thin conducting layers under various plasma conditions including etch conditions for refractory metal contacts. {ital R}{sub {ital s}} determined from transmission line measurements are used to evaluate plasma-induced damage for electron cyclotron resonance (ECR) and reactive ion etch (RIE) conditions by varying the thickness and doping of epitaxial layers. Damage depths calculated from {ital R}{sub {ital s}} data show a strong dependence on doping levels. This can be explained by a plasma-damage-induced trap density profile which tails off into the sample. Consistent trends have been observed where {ital R}{sub {ital s}} increases with increasing dc bias, increasing microwave power, and decreasing pressure, thus showing {ital R}{sub {ital s}} increases as either the ion energy or ion flux increases. The lowest plasma-induced damage observed in this study occurs with ECR at low microwave power and no rf biasing. Under rf-bias conditions, samples exposed to the ECR (1 mTorr total pressure) show more damage than those exposed to the RIE (8 mTorr total pressure) at comparable dc bias. We have also observed {ital R}{sub {ital s}} dependence on ECR plasma chemistry where {ital R}{sub {ital s}} is lower in SF{sub 6}/Ar plasmas than Ar and N{sub 2} plasmas possibly related to interactions of F or S atoms with the GaAs surface. Moderate anneal temperatures (200--500 {degree}C) have shown significant {ital R}{sub {ital s}} recovery. {copyright} {ital 1995} {ital American} {ital Vacuum} {ital Society}

  4. 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. PMID:23331503

  5. Studies on metal/n-GaAs Schottky barrier diodes: The effects of temperature and carrier concentrations

    SciTech Connect

    Mangal, Sutanu; Banerji, P.

    2009-04-15

    Metal/Semiconductor Schottky diodes were fabricated to study the effect of temperature and carrier concentrations on diode parameters, such as ideality factor and barrier heights. The diodes were formed on the epitaxial layers of metal organic chemical vapor deposition (MOCVD) grown n-GaAs with metals such as Al, Pd, and Zn-Pd deposited onto n-GaAs by thermal evaporation technique. Trimethyl gallium and AsH{sub 3} were used as Ga and As precursors, respectively, to grow GaAs on semi-insulating GaAs substrates at 600 deg. C and H{sub 2}S was used for n-type doping in a horizontal reactor atmospheric pressure MOCVD system. The Schottky diodes were characterized by forward bias current-voltage measurements in the temperature range 130-300 K and capacitance-voltage measurement at room temperature and diode parameters such as ideality factor and barrier height have been evaluated. It is found that the Schottky barrier height decreases with decrease in temperature while the ideality factor increases. It is also observed that the barrier height increases linearly with the applied forward bias voltage and the rate of change of barrier height with voltage increases for higher carrier concentration of the semiconductor. The carrier concentration of n-GaAs was chosen in the regime 1x10{sup 16}-8.2x10{sup 16} cm{sup -3} so that the depletion region extends inside the semiconductor and the diode can be used as a III-V photovoltaic device.

  6. 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.

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

    DOE PAGESBeta

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

    2015-11-16

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-11-01

    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 films grown 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. Here, we use a combination of aberration-corrected scanning transmission electron microscopy and first-principles density functional theory modeling to examine the role of interfacial oxygen vacancies on the ferroelectric polarization of a BaTiO3 thin film grown on GaAs. 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.

  9. 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.

  10. Epitaxial ferromagnetic thin films and heterostructures of Mn-based metallic and semiconducting compounds on GaAs

    NASA Astrophysics Data System (ADS)

    Tanaka, Masaaki

    1998-07-01

    We present two approaches to integrate magnetic materials with III-V semiconductors. One is epitaxial ferromagnetic metallic films and heterostructures on GaAs (0 0 1) substrates. Although crystal structure, lattice constant, chemical bonding and other properties are dissimilar, ferromagnetic hexagonal MnAs thin films and MnAs/NiAs ferromagnet/nonmagnet heterostructures (HSs) are grown on GaAs by molecular beam epitaxy (MBE). Multi-stepped magnetic hysteresis are controllably realized in MnAs/NiAs HSs, making this material promising for the application to multi-level nonvolatile recording on semiconductors. The other approach is to prepare a new class of GaAs based magnetic semiconductor, GaMnAs, by low-temperature molecular beam epitaxy (LT-MBE) on GaAs (0 0 1). New III-V based superlattices consisting of ferromagnetic semiconductor GaMnAs and nonmagnetic semiconductor AlAs are also successfully grown. Structural and magnetic properties of these new heterostructures are presented.

  11. In-situ wafer bowing measurements of GaN grown on Si (111) substrate by reflectivity mapping in metal organic chemical vapor deposition system

    NASA Astrophysics Data System (ADS)

    Yang, Yi-Bin; Liu, Ming-Gang; Chen, Wei-Jie; Han, Xiao-Biao; Chen, Jie; Lin, Xiu-Qi; Lin, Jia-Li; Luo, Hui; Liao, Qiang; Zang, Wen-Jie; Chen, Yin-Song; Qiu, Yun-Ling; Wu, Zhi-Sheng; Liu, Yang; Zhang, Bai-Jun

    2015-09-01

    In this work, the wafer bowing during growth can be in-situ measured by a reflectivity mapping method in the 3×2″ Thomas Swan close coupled showerhead metal organic chemical vapor deposition (MOCVD) system. The reflectivity mapping method is usually used to measure the film thickness and growth rate. The wafer bowing caused by stresses (tensile and compressive) during the epitaxial growth leads to a temperature variation at different positions on the wafer, and the lower growth temperature leads to a faster growth rate and vice versa. Therefore, the wafer bowing can be measured by analyzing the discrepancy of growth rates at different positions on the wafer. Furthermore, the wafer bowings were confirmed by the ex-situ wafer bowing measurement. High-resistivity and low-resistivity Si substrates were used for epitaxial growth. In comparison with low-resistivity Si substrate, GaN grown on high-resistivity substrate shows a larger wafer bowing caused by the highly compressive stress introduced by compositionally graded AlGaN buffer layer. This transition of wafer bowing can be clearly in-situ measured by using the reflectivity mapping method. Project supported by the National Natural Science Foundation of China (Grant Nos. 61274039 and 51177175), the National Basic Research Program of China (Grant No. 2011CB301903), the Ph.D. Programs Foundation of Ministry of Education of China (Grant No. 20110171110021), the International Science and Technology Collaboration Program of China (Grant No. 2012DFG52260), the International Science and Technology Collaboration Program of Guangdong Province, China (Grant No. 2013B051000041), the Science and Technology Plan of Guangdong Province, China (Grant No. 2013B010401013), the National High Technology Research and Development Program of China (Grant No. 2014AA032606), and the Opened Fund of the State Key Laboratory on Integrated Optoelectronics, China (Grant No. IOSKL2014KF17).

  12. Tuning the gallium content of metal precursors for Cu(In,Ga)Se2 thin film solar cells by electrodeposition from a deep eutectic solvent.

    PubMed

    Malaquias, João C; Regesch, David; Dale, Phillip J; Steichen, Marc

    2014-02-14

    Controlling the Ga incorporation of Cu-In-Ga metal precursors for Cu(In,Ga)Se2 (CIGS) solar cells is one of the main challenges for low cost electrodeposition processes, mainly due to the difficulty in electrodepositing metallic Ga from aqueous electrolytes. In this work we use the deep eutectic solvent (DES) Choline Chloride : Urea (ChCl : U - 1 : 2) to efficiently codeposit In-Ga on Cu and Mo electrodes. We control the Ga/(Ga+In) (Ga/III) ratio of the films via the mass fluxes. The electrochemical behavior of ChCl : U containing GaCl3 and InCl3 is studied by rotating disk electrode cyclic voltammetry (CV) on Mo and Cu electrodes. CV revealed on both Mo and Cu electrodes that the electrochemical behavior of the ChCl : U-GaCl3-InCl3 system is the superposition of the individual In and Ga electrochemistry. On a Cu electrode the morphology, crystal structure and element distribution of the deposits were a function of the Ga/III ratio. We demonstrate the precise control of Ga incorporation over a large composition range from 0.1 ≤ Ga/III ≤ 0.9 and proved that ED from DES is a straightforward, robust and efficient process. First solar cells based on Mo/Cu/In-Ga metal stacks achieved efficiencies as high as 7.9% with a Voc of 520 mV. PMID:24382400

  13. Effect of interface and bulk traps on the C–V characterization of a LPCVD-SiNx/AlGaN/GaN metal-insulator-semiconductor structure

    NASA Astrophysics Data System (ADS)

    Bao, Qilong; Huang, Sen; Wang, Xinhua; Wei, Ke; Zheng, Yingkui; Li, Yankui; Yang, Chengyue; Jiang, Haojie; Li, Junfeng; Hu, Anqi; Yang, Xuelin; Shen, Bo; Liu, Xinyu; Zhao, Chao

    2016-06-01

    Silicon nitride (SiNx) film grown by low-pressure chemical vapor deposition (LPCVD) is utilized as a gate dielectric for AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistors (MIS-HEMTs). Trap distribution at the gate-dielectric/III-nitrides interface is characterized by a temperature-dependent ac-capacitance technique. The extracted interface state density D it decreases from 2.92 × 1013 to 1.59 × 1012 cm‑2 eV‑1 as the energy level depth (E C-E T) increases from 0.29 to 0.50 eV, and then levels off to E C-E T = 0.80 eV. Capacitance-mode deep level transient spectroscopy (C-DLTS) and energy band diagram simulations reveal that deep levels with E C-E T > 0. 83 eV are responsible for the dispersion of capacitances at high temperature (>125 °C) and low frequencies (<1 kHz). A high-resolution transmission electron microscope (TEM) reveals that re-oxidation of the RCA-treated AlGaN barrier surface may be responsible for the relatively high density of shallow states at the LPCVD-SiNx/III-nitride interface.

  14. Wet oxidation of AlxGa1 - xAs: Temporal evolution of composition and microstructure and the implications for metal-insulator-semiconductor applications

    NASA Astrophysics Data System (ADS)

    Ashby, Carol I. H.; Sullivan, John P.; Newcomer, Paula P.; Missert, Nancy A.; Hou, Hong Q.; Hammons, B. E.; Hafich, Michael J.; Baca, Albert G.

    1997-05-01

    Three important processes dominate the wet thermal oxidation of AlxGa1-xAs on GaAs: (1) oxidation of Al and Ga in the AlxGa1-xAs alloy to form an amorphous oxide, (2) formation and elimination of crystalline and amorphous elemental As and of amorphous As2O3, and (3) crystallization of the amorphous oxide film. Residual As can lead to strong Fermi-level pinning at the oxidized AlGaAs/GaAs interface, up to a 100-fold increase in leakage current, and a 30% increase in the dielectric constant of the oxide layer. Thermodynamically favored interfacial As may impose a fundamental limitation on the use of AlGaAs wet oxidation in metal-insulatorsemiconductor devices in the GaAs material system.

  15. Top-down, in-plane GaAs nanowire MOSFETs on an Al2O3 buffer with a trigate oxide from focused ion-beam milling and chemical oxidation.

    PubMed

    Lee, S C; Neumann, A; Jiang, Y-B; Artyushkova, K; Brueck, S R J

    2016-09-16

    The top-down fabrication of an in-plane nanowire (NW) GaAs metal-oxide-semiconductor field-effect transistor (MOSFET) with a trigate oxide implemented by liquid-phase chemical-enhanced oxidation (LPCEO) is reported. A 2 μm long channel having an effective cross section ∼70 × 220 nm(2) is directly fabricated into an epitaxial n (+)-GaAs layer. This in-plane NW structure is achieved by focused ion beam (FIB) milling and hydrolyzation oxidation resulting in electronic isolation from the substrate through a semiconductor-on-insulator structure with an n (+)-GaAs/Al2O3 layer stack. The channel is epitaxially connected to the μm-scale source and drain within a single layer for a planar MOSFET to avoid any issues of ohmic contact and LPCEO to the NW. To fabricate a MOSFET, the top and the two sidewalls of the in-plane NW are oxidized by LPCEO to relieve the surface damage from FIB as well as to transform these surfaces to a ∼15 nm thick gate oxide. This trigate device has threshold voltage ∼0.14 V and peak transconductance ∼35 μS μm(-1) with a subthreshold swing ∼150 mV/decade and on/off ratio of drain current ∼10(3), comparable to the performance of bottom-up NW devices. PMID:27504931

  16. New Semiconductor Alloy GaAs1-xBix Grown by Metal Organic Vapor Phase Epitaxy

    NASA Astrophysics Data System (ADS)

    Oe, Kunishige; Okamoto, Hiroshi

    1998-11-01

    A new semiconductor alloy material, GaAs1-xBix has been created by Metal Organic Vapor Phase Epitaxial (MOVPE) growth. A low growth temperature, such as 365°C, is required to obtain the alloy. X-ray diffraction measurements of alloy layers reveal that the diffraction patterns are satisfactory. The maximum GaBi content in the GaAsBi alloy estimated from the lattice constant is around 2%, which is consistent with that estimated from secondary ion mass spectroscopy (SIMS) measurements. In a photoluminescence (PL) measurement, a single peak spectrum is observed from 10 to 300 K. The temperature variation of the PL peak energy is as small as 0.1 meV/K.

  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. Photoionization spectroscopy of traps in GaN metal-semiconductor field-effect transistors

    NASA Astrophysics Data System (ADS)

    Klein, P. B.; Binari, S. C.; Freitas, J. A.; Wickenden, A. E.

    2000-09-01

    Measurements of the spectral and intensity dependences of the optically-induced reversal of current collapse in a GaN metal-semiconductor field-effect transistor (MESFET) have been compared to calculated results. The model assumes a net transfer of charge from the conducting channel to trapping states in the high-resistivity region of the device. The reversal, a light-induced increase in the trap-limited drain current, results from the photoionization of trapped carriers and their return to the channel under the influence of the built-in electric field associated with the trapped charge distribution. For a MESFET in which two distinct trapping centers have been spectrally resolved, the experimentally measured dependence upon light intensity was fitted using this model. The two traps were found to have very different photoionization cross-sections but comparable concentrations (4×1011 cm-2 and 6×1011 cm-2), suggesting that both traps contribute comparably to the observed current collapse.

  19. Nanoscale Skyrmions in a Nonchiral Metallic Multiferroic: Ni2MnGa.

    PubMed

    Phatak, Charudatta; Heinonen, Olle; De Graef, Marc; Petford-Long, Amanda

    2016-07-13

    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. Here 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. 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. PMID:27186990

  20. Effect of temperature on the mutual diffusion of Ge/GaAs and GaAs/Ge

    NASA Astrophysics Data System (ADS)

    Bosi, Matteo; Attolini, Giovanni; Ferrari, Claudio; Frigeri, Cesare; Calicchio, Marco; Rossi, Francesca; Vad, Kálmán; Csik, Attila; Zolnai, Zsolt

    2011-03-01

    We studied the diffusion of Ge, As and Ga in GaAs/Ge and Ge/GaAs epilayers grown at different temperatures by metal-organic vapor phase epitaxy using iso-butylgermane, arsine and trimethylgallium in hydrogen atmosphere at low pressure. The use of low temperature buffer layers was investigated in order to overcome the diffusion problem. High-resolution X-ray diffraction and transmission electron microscopy were used to assess the crystal quality, while secondary neutral mass spectrometry has been employed to investigate diffusion profiles in the samples. As it is well known, the diffusivity of the atoms (e.g. Ga, As, Ge) and intermixing of layers during sample preparation strongly depend on the substrate temperature. We found that the use of a low temperature GaAs buffer layer reduced the diffusion in GaAs/Ge epitaxy at 600 °C; while a Ge low temperature buffer layer was not effective in reducing the interdiffusion in Ge/GaAs epitaxy at 700 °C.

  1. 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.

  2. 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.

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

    NASA Astrophysics Data System (ADS)

    Yin, Wenlong; Wang, Wendong; Kang, Lei; Lin, Zheshuai; Feng, Kai; Shi, Youguo; Hao, Wenyu; Yao, Jiyong; Wu, Yicheng

    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.

  4. 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.

  5. 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

    Technology Transfer Automated Retrieval System (TEKTRAN)

    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...

  6. Comparison between chemical vapor deposited and physical vapor deposited WSi2 metal gate for InGaAs n-metal-oxide-semiconductor field-effect transistors

    NASA Astrophysics Data System (ADS)

    Ong, B. S.; Pey, K. L.; Ong, C. Y.; Tan, C. S.; Antoniadis, D. A.; Fitzgerald, E. A.

    2011-05-01

    We compare chemical vapor deposition (CVD) and physical vapor deposition (PVD) WSi2 metal gate process for In0.53Ga0.47As n-metal-oxide-semiconductor field-effect transistors using 10 and 6.5 nm Al2O3 as dielectric layer. The CVD-processed metal gate device with 6.5 nm Al2O3 shows enhanced transistor performance such as drive current, maximum transconductance and maximum effective mobility. These values are relatively better than the PVD-processed counterpart device with improvement of 51.8%, 46.4%, and 47.8%, respectively. The improvement for the performance of the CVD-processed metal gate device is due to the fluorine passivation at the oxide/semiconductor interface and a nondestructive deposition process.

  7. Magnetometory Measurement of AlGaN/GaN 2DEG

    NASA Astrophysics Data System (ADS)

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

    2004-03-01

    AlGaN/GaN heterostructure devices have been attracting much attention 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 magnetometory measurement of AlGaN/GaN 2DEG 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 9,540 cm^2/Vs and 6.6 × 10^12 cm-2, respectively. When the temperature is lower than 4.5 K the hysteresis of magnetometric data is observed near zero magnetic field. At the temperature larger than 4.5 K, the hysteresis of magnetometric data disappears and the slope of magnetometric data with respect to magnetic field becomes lower as obeying Currie-Weiss law. In general the hysteresis and Currie-Weiss law behavior in magnetometric data imply the possibility of the ferromagnetism, but the conformation of the ferromagnetism of AlGaN/GaN heterostructure is still difficult and the detailed physical mechanism is still unclear.

  8. FIFO Buffer for Asynchronous Data Streams

    NASA Technical Reports Server (NTRS)

    Bascle, K. P.

    1985-01-01

    Variable-rate, asynchronous data signals from up to four measuring instruments or other sources combined in first-in/first-out (FIFO) buffer for transmission on single channel. Constructed in complementary metal-oxide-semiconductor (CMOS) logic, buffer consumes low power (only 125 mW at 5V) and conforms to aerospace standards of reliability and maintainability.

  9. Investigation of flat band voltage shift in recessed-gate GaN MOSHFETs with post-metallization-annealing in oxygen atmosphere

    NASA Astrophysics Data System (ADS)

    Lee, Jae-Gil; Kim, Hyun-Seop; Lee, Jung-Yeon; Seo, Kwang-Seok; Cha, Ho-Young

    2015-11-01

    We have investigated the effects of post-metallization-annealing (PMA) in oxygen atmosphere on recessed-gate GaN metal-oxide-semiconductor heterostructure field effect transistors (MOSHFETs). The flat band voltage of MOS is a function of bulk and interface charges in the oxide, which strongly depends on a post-annealing process as well as deposition conditions. A positive threshold voltage shift enabling normally-off operation has been achieved by an O2 PMA process where the GaN MOSHFET employed an ICPCVD SiO2 gate oxide with a Ni/Au metal gate. According to the analysis using energy dispersive x-ray spectroscopy in transmission electron microscopy and x-ray photoelectron spectroscopy, it is suggested that the improved SiO2/GaN interface quality with an enhanced metallic-like Ga level was responsible for the positive shift in threshold voltage.

  10. Coplanar metal–semiconductor–metal light-emitting devices with an n++ InGaN layer and their application to display

    NASA Astrophysics Data System (ADS)

    Long, H.; Zeng, Y. P.; Mei, Y.; Ying, L. Y.; Zhang, B. P.

    2016-06-01

    We demonstrated a new kind of InGaN/GaN multi-quantum well (MQW) light-emitting diode (LED) with simplified fabrication processes, where only one round of photolithography and electrode deposition is necessary. The electrical and optical properties of this LED, which is defined as a coplanar metal–semiconductor–metal (CMSM) LED, were characterized. The electroluminescence spectrum only exhibits blue emission at 450 nm, meaning that the light comes exclusively from MQWs. The optical output at 20 mA was comparable to that of conventional LEDs. A shunt circuit model with a surface thin film resistance, an n++ InGaN/p-GaN/n-GaN structure and a p-GaN/n-GaN junction was proposed to explain the working mechanism of the CMSM LED. A proof-of–concept display was demonstrated, exploiting the promising application of CMSM LED to display.

  11. Reactions of cationic transition metal acetonitrile complexes [M(CH3CN)n]m+ with GaCp*: novel gallium complexes of iron, cobalt, copper and silver.

    PubMed

    Bollermann, Timo; Puls, Arik; Gemel, Christian; Cadenbach, Thomas; Fischer, Roland A

    2009-02-28

    The reactions of the cationic transition metal acetonitrile complexes [M(CH3CN)n]m+ (m = 2: M = Fe, Co and m = 1: M = Cu, Ag) with GaCp* were investigated. The reaction of [Fe(CH3CN)6][BArF]2 (BAr(F) = [B{C6H3(CF3)2}4) with GaCp* leads to [Cp*Fe(GaCp*)3][BAr(F)] (1) via a redox neutral Cp* transfer and [Ga2Cp*][BAr(F)] as a by-product while the formation of [Cp*Co(GaCp*)3][BAr(F)]2 (2) from [Co(CH3CN)6][BAr(F)]2 is accompanied by oxidation of Co(II) to Co(III) with GaCp* as the oxidant. The reactions of [Cu(CH3CN)4][BAr(F)] and Ag[BPh4] with GaCp* lead to the formation of the homoleptic compounds [Cu(GaCp*)4][BAr(F)] (4) and [Ag(GaCp*)4][BPh4] (5), while treatment of Ag[CF3SO3] with GaCp* leads to the dimeric complex [Ag2(GaCp*)3(micro-GaCp*)2][CF3SO3]2 (6). All compounds were characterized by NMR spectroscopy, single crystal X-ray diffraction and elemental analysis. PMID:19462658

  12. Pulsed laser deposition of c-axis untilted YBCO films on c-axis tilted ISD MgO-buffered metallic substrates

    NASA Astrophysics Data System (ADS)

    Li, M.; Ma, B.; Koritala, R. E.; Fisher, B. L.; Venkataraman, K.; Maroni, V. A.; Vlasko-Vlasov, V.; Berghuis, P.; Welp, U.; Gray, K. E.; Balachandran, U.

    2003-05-01

    Biaxially textured MgO template layer was deposited on nontextured metal substrates by inclined-substrate deposition (ISD) at a deposition rate of 24-600 nm/min. c-axis untilted YBa 2Cu 3O 7- x (YBCO) films were deposited on these MgO-buffered substrates by pulsed laser deposition. The crystalline structures of the YBCO films and MgO layers were examined by X-ray pole figure analysis, X-ray φ-scans, and χ-scans. A tilt angle of 33° of the MgO[0 0 1] with respect to the substrate normal and c-axis untilted YBCO films were observed, respectively. Good biaxial texture of these films with full-width-at-half-maximum values of 13.8° and 10.6° for the φ-scans of YBCO(1 0 3) and MgO(2 2 0), respectively, were obtained. Morphologies were examined by scanning electron microscopy, which revealed a unique roof-tile feature and columnar grain growth for the ISD MgO layer. Raman spectroscopy and magneto-optical image technique were also used to evaluate the quality of the YBCO film. An angular dependence of Jc on the direction of an applied magnetic field confirmed the c-axis untilted orientation of the YBCO films. Tc=90 K with sharp transition and Jc=3.0×10 5 A/cm 2 at 77 K in zero field were obtained on 0.4-μm-thick YBCO films.

  13. Metal-oxide buffer layer for maintaining topological bumpy surface underlayer of columnar CoPt-SiO2 granular media deposited at high substrate temperature

    NASA Astrophysics Data System (ADS)

    Tham, Kim Kong; Hinata, Shintaro; Saito, Shin; Takahashi, Migaku

    2015-05-01

    Investigation of surface topography for underlayer with various metal-oxide buffer layer (BL) materials for magnetic recording media is reported. In the previous study, it was found out that the application of a high substrate temperature deposition process to a granular layer with a magnetic alloy and a non-magnetic oxide material, such as CoPtCr-SiO2, will induce lamellar and spherical grains due to the flattening of the underlayer bumpy surface by recrystallization. By depositing a CoCr-SiO2 BL onto the Ru underlayer at room temperature, CoCr grains grow epitaxially onto Ru grains and SiO2 segregates to Ru boundaries. Consequently, bumpy surface morphology of the underlayer is maintained even though heated to around 400 °C before depositing the granular layer. Therefore, CoPt magnetic grains of a Co82.4Pt17.6- 27.7 vol. % SiO2 granular film deposited on the underlayer grow epitaxially on CoCr grains with columnar structure. As a result, high average Ku⊥ of around 6.7 × 106 erg/cm3 can be obtained. Among the studied BL materials, CoCr-SiO2 shows the highest thermal resistance with root mean square surface roughness (Rq) of around 1.7 nm after heating at around 400 °C. To obtain columnar magnetic grains with critical thickness more than 13 nm, underlayer with Rq more than 1.6 nm is needed.

  14. 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

  15. 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).

  16. Fabrication of 160-nm T-gate metamorphic AlInAs/GaInAs HEMTs on GaAs substrates by metal organic chemical vapour deposition

    NASA Astrophysics Data System (ADS)

    Li, Hai-Ou; Huang, Wei; Tang Chak, Wah; Deng, Xiao-Fang; Lau Kei, May

    2011-06-01

    The fabrication and performance of 160-nm gate-length metamorphic AlInAs/GaInAs high electron mobility transistors (mHEMTs) grown on GaAs substrate by metal organic chemical vapour deposition (MOCVD) are reported. By using a novel combined optical and e-beam photolithography technology, submicron mHEMTs devices have been achieved. The devices exhibit good DC and RF performance. The maximum current density was 817 mA/mm and the maximum transconductance was 828 mS/mm. The non-alloyed Ohmic contact resistance Rc was as low as 0.02 Ω-mm. The unity current gain cut-off frequency (fT) and the maximum oscillation frequency (fmax) were 146 GHz and 189 GHz, respectively. This device has the highest fT yet reported for a 160-nm gate-length HEMTs grown by MOCVD. The output conductance is 28.9 mS/mm, which results in a large voltage gain of 28.6. Also, an input capacitance to gate-drain feedback capacitance ratio, Cgs/Cgd, of 4.3 is obtained in the device.

  17. Performance of GaN Metal-Oxide-Semiconductor Field-Effect Transistor with Regrown n+-Source/Drain on a Selectively Etched GaN

    NASA Astrophysics Data System (ADS)

    Kim, Do-Kywn; Kim, Dong-Seok; Chang, Sung-Jae; Lee, Chang-Ju; Bae, Youngho; Cristoloveanu, Sorin; Lee, Jung-Hee; Hahm, Sung-Ho

    2013-06-01

    We proposed and fabricated normally off GaN MOSFETs with an epitaxially regrown n+ GaN source/drain after a short period of dry etching on a sapphire substrate. The regrown S/D MOSFET after dry etching (MOSFET A) exhibited enhanced performance in terms of current drivability and access resistance compared with the same MOSFET without the surface etching before the regrowth (MOSFET B). While MOSFET A has a saturation drain current of 10 mA/mm at VG = 8 V, a field-effect mobility of 22 cm2 V-1 s-1, and a series resistance RSD of 0.57 kΩ, MOSFET B has 3 mA/mm, 12 cm2 V-1 s-1, and 0.93 kΩ, respectively. The electrical characteristic of MOSFET A was also much more improved than that of MOSFET B at low temperatures. Mobility degradation at low temperatures was related to the effect of impurity scattering caused by crystal defects generated during the metal organic chemical vapor deposition (MOCVD) growth.

  18. 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.

  19. Low-frequency noise in AlTiO/AlGaN/GaN metal-insulator-semiconductor heterojunction field-effect transistors

    NASA Astrophysics Data System (ADS)

    Le, Son Phuong; Ui, Toshimasa; Nguyen, Tuan Quy; Shih, Hong-An; Suzuki, Toshi-kazu

    2016-05-01

    Using aluminum titanium oxide (AlTiO, an alloy of Al2O3 and TiO2) 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.

  20. 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.

  1. 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.

  2. Parameters influencing interfacial morphology in GaAs/Ge superlattices grown by metal organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Jia, Roger; Fitzgerald, Eugene A.

    2016-02-01

    We investigated the epitaxy and morphology of GaAs/Ge superlattices grown by metal organic chemical vapor deposition (MOCVD) under a range of conditions. The surfaces of Ge layers deposited on GaAs at 650 °C and 100 Torr are observed to be rough in cross-sectional transmission electron microscopy. When either the temperature is lowered to 500 °C or the pressure is increased to 250 Torr, the surface of the first deposited Ge layer is observed to be smooth. This behavior suggests that Ge roughening is a thermodynamically favorable process that can be kinetically limited with appropriate growth conditions. At 500 °C, GaAs islands on Ge do not completely coalesce into one film. This may result from poor surface coverage; the short depositions would not be sufficient to coarsen and completely coalesce the islands. At 650 °C, growth on offcut substrates did not suppress antiphase boundaries, likely due to the unique conditions for GaAs/Ge superlattice growth. A wide-range of two- and three- dimensional nanostructures are formed and should allow insight in structure-property correlations in semiconducting thermoelectric materials.

  3. Emission channeling studies on transition-metal doped GaN and ZnO: Cation versus anion substitution

    NASA Astrophysics Data System (ADS)

    Pereira, L. M. C.; Wahl, U.; Correia, J. G.; Amorim, L. M.; Silva, D. J.; Decoster, S.; da Silva, M. R.; Temst, K.; Vantomme, A.

    2014-08-01

    The magnetic and electric properties of impurities in semiconductors are strongly dependent on the lattice sites which they occupy. While the majority site can often be predicted based on chemical similarities with the host elements and is usually simple to confirm experimentally, minority sites are far more complicated to predict, detect and identify. We have carried out extensive β- emission channeling studies on the lattice location of transition metal impurities in wide-gap dilute magnetic semiconductors, namely Co and Mn in GaN and ZnO, making use of radioactive 61Co and 56Mn implanted at the ISOLDE facility at CERN. In addition to the majority occupation of cation (Ga, Zn) sites, we located significant fractions (of the order of 20%) of the Co and Mn impurities in anion (N, O) sites, which are virtually unaffected by thermal annealing up to 900 °C. Here, we present the β- emission channeling experiments on 61Co-implanted GaN. We discuss these results in the context of our recent reports of minority anion substitution in Mn-implanted GaN Pereira et al. (2012) [19] and Mn/Co-implanted ZnO Pereira et al. (2011) [20], particularly in terms of the advantages of the emission channeling technique in such cases of multi-site occupancy.

  4. 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.

  5. 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.

  6. Enhancing the orthorhombicity and antiferromagnetic-insulating state in epitaxial La0.67Ca0.33MnO3/NdGaO3(001) films by inserting a SmFeO3 buffer layer

    NASA Astrophysics Data System (ADS)

    Tan, Xuelian; Gao, Guanyin; Chen, Pingfan; Xu, Haoran; Zhi, Bowen; Jin, Feng; Chen, Feng; Wu, Wenbin

    2014-11-01

    Structural and magnetotransport properties of epitaxial La0.67Ca0.33MnO3(30 nm)/NdGaO3(001) [LCMO/NGO(001)] films are tuned by inserting an insulating SmFeO3 (SFO) buffer layer at various thicknesses (t). All the layers and the NGO substrates have the same Pbnm symmetry with the octahedra tilting about the b-axis, but different orthorhombicity (d). We found that as t increases, the fully strained (≤15 nm) or partially relaxed (30-60 nm) SFO layers can produce different d in the upper LCMO films. Correspondingly, the induced antiferromagnetic-insulating (AFI) state in LCMO is greatly enhanced with TAFI shifted from ˜250 K for t ≤ 15 nm to ˜263 K for t = 30-60 nm. We also show that the strain relaxation for t ≥ 30 nm is remarkably anisotropic, with a stable lattice constant a as that of the NGO substrates but increasing b of both SFO and LCMO layers. This indicates the octahedral coupling across the interfaces, leaving the strain along the a-axis accommodated by the octahedral tilts, while along the b-axis most probably by the octahedral deformations. The AFI state in the LCMO layer could be ascribed to the enhanced orthorhombicity with cooperatively increased Jahn-Teller-like distortions and tilting of the MnO6 octahedra. The results strongly suggest that the interfacial octahedral coupling plays a crucial role in epitaxial growth and in tuning functionalities of the perovskite oxide films.

  7. Facet recovery and light emission from GaN/InGaN/GaN core-shell structures grown by metal organic vapour phase epitaxy on etched GaN nanorod arrays

    NASA Astrophysics Data System (ADS)

    Le Boulbar, E. D.; Gîrgel, I.; Lewins, C. J.; Edwards, P. R.; Martin, R. W.; Šatka, A.; Allsopp, D. W. E.; Shields, P. A.

    2013-09-01

    The use of etched nanorods from a planar template as a growth scaffold for a highly regular GaN/InGaN/GaN core-shell structure is demonstrated. The recovery of m-plane non-polar facets from etched high-aspect-ratio GaN nanorods is studied with and without the introduction of a hydrogen silsesquioxane passivation layer at the bottom of the etched nanorod arrays. This layer successfully prevented c-plane growth between the nanorods, resulting in vertical nanorod sidewalls (˜89.8°) and a more regular height distribution than re-growth on unpassivated nanorods. The height variation on passivated nanorods is solely determined by the uniformity of nanorod diameter, which degrades with increased growth duration. Facet-dependent indium incorporation of GaN/InGaN/GaN core-shell layers regrown onto the etched nanorods is observed by high-resolution cathodoluminescence imaging. Sharp features corresponding to diffracted wave-guide modes in angle-resolved photoluminescence measurements are evidence of the uniformity of the full core-shell structure grown on ordered etched nanorods.

  8. Role of ultra thin pseudomorphic InP layer to improve the high-k dielectric/GaAs interface in realizing metal-oxide-semiconductor capacitor

    NASA Astrophysics Data System (ADS)

    Kundu, Souvik; Halder, Nripendra N.; Biswas, D.; Banerji, P.; Shripathi, T.; Chakraborty, S.

    2012-08-01

    In this article, we report GaAs metal-oxide-semiconductor (MOS) capacitors with a metal organic chemical vapor deposited ultrathin (1.5 nm) pseudomorphic InP interface passivation layer (IPL) and a thin (5 nm) ZrO2 high-k dielectric. Reduction of the surface states on InP passivated GaAs surfaces was observed from the photoluminescence study. The x-ray photoelectron spectra confirmed the dramatic reduction of GaAs native oxides (Ga-O and As-O) from the interface of ZrO2 and p-GaAs, implying that the Fermi level at the high-k/GaAs interface can be unpinned with good interface quality. As a result, very low values of interface trap density (1.1 × 1011 cm-2 eV-1) and hysteresis (8.21 mV) were observed. The same was done for directly deposited ZrO2 on GaAs surface to understand the efficacy of InP interface passivation layer on GaAs MOS devices. A systematic capacitance-voltage and current density-voltage studies were performed on bothAl/ZrO2/InP/p-GaAs and Al/ZrO2/p-GaAs structures. It was found that insertion of 1.5 nm InP ultrathin layer in-between ZrO2 and GaAs improves the essential parameters of GaAs MOS such as dielectric constant, frequency dispersion, leakage current, etc. The dielectric reliability has been studied with constant voltage stressing. A very small flatband voltage shift with stress time was observed in InP passivated GaAs MOS capacitors.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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 %. PMID:25959012

  14. GaN-Based Trench Gate Metal Oxide Semiconductor Field-Effect Transistor Fabricated with Novel Wet Etching

    NASA Astrophysics Data System (ADS)

    Kodama, Masahito; Sugimoto, Masahiro; Hayashi, Eiko; Soejima, Narumasa; Ishiguro, Osamu; Kanechika, Masakazu; Itoh, Kenji; Ueda, Hiroyuki; Uesugi, Tsutomu; Kachi, Tetsu

    2008-02-01

    A novel method for fabricating trench structures on GaN was developed. A smooth non-polar (1100) plane was obtained by wet etching using tetramethylammonium hydroxide (TMAH) as the etchant. A U-shape trench with the (1100) plane side walls was formed with dry etching and the TMAH wet etching. A U-shape trench gate metal oxide semiconductor field-effect transistor (MOSFET) was also fabricated using the novel etching technology. This device has the excellent normally-off operation of drain current-gate voltage characteristics with the threshold voltage of 10 V. The drain breakdown voltage of 180 V was obtained. The results indicate that the trench gate structure can be applied to GaN-based transistors.

  15. 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. PMID:25607316

  16. Resonant conversion based on GaAs-metal metamaterials within terahertz range

    NASA Astrophysics Data System (ADS)

    Cao, Xiaolong; Che, Yongli; Yao, Jianquan

    2015-07-01

    In this paper, by utilizing the variable conductivity with photo-injection in gallium arsenide (GaAs), we have designed an asymmetrical planar terahertz (THz) metamaterial, which is connected with two single-gap split ring resonator (SRR) by GaAs strip and demonstrated the resonant conversion of SRR within the THz range under appropriate optical pumping. As central trailing arm of the structure, GaAs is skillfully inserted between the two cross arms of the THz metamaterial and plays a key role in resonant conversion. Through modulation of its conductivity (σGaAs), the variable conductivity of GaAs can make one dual-gap SRR into two connective single-gap SRRs in physical structure, at the same time, the state conversion of two different resonances in the THz metamaterial has been achieved. The simulation results show that the resonant states of THz metamaterial can be switched from one LC and one dipole (state 1) to two LC and one new dipole (state 2) through the intermediate state with the increasing σGaAs. This structural design provides a new example to apply variable conductivity to achieve state conversion of resonance and can be extended to the additional application in THz devices.

  17. 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.

  18. Hexagonal phase-pure wide band gap ɛ-Ga2O3 films grown on 6H-SiC substrates by metal organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Xia, Xiaochuan; Chen, Yuanpeng; Feng, Qiuju; Liang, Hongwei; Tao, Pengcheng; Xu, Mengxiang; Du, Guotong

    2016-05-01

    In this paper, hexagonal structure phase-pure wide-band gap ɛ-Ga2O3 films were grown by metal organic chemical vapor deposition on 6H-SiC substrates. The ɛ-Ga2O3 films with good crystal quality were verified by high-resolution X-ray diffraction. The out-of-plane epitaxial relationship between ɛ-Ga2O3 films and 6H-SiC substrates is confirmed to be ɛ-Ga2O3 (0001)//6H-SiC (0001), and the in-plane epitaxial relationship is also confirmed to be ɛ-Ga2O3 ⟨ 11 2 ¯ 0 ⟩//6H-SiC ⟨ 11 2 ¯ 0 ⟩. The SEM and AFM images show that the ɛ-Ga2O3 films are uniform and flat. The ɛ-Ga2O3 films are thermally stable up to approximately 800 °C and begin to transform into β-phase Ga2O3 at 850 °C. Then, they are completely converted to β-Ga2O3 films under 900 °C. The high-quality ɛ-Ga2O3 films with hexagonal structure have potential application in the optoelectronic field.

  19. 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.

  20. Chemical lift-off and direct wafer bonding of GaN/InGaN P-I-N structures grown on ZnO

    NASA Astrophysics Data System (ADS)

    Pantzas, K.; Rogers, D. J.; Bove, P.; Sandana, V. E.; Teherani, F. H.; El Gmili, Y.; Molinari, M.; Patriarche, G.; Largeau, L.; Mauguin, O.; Suresh, S.; Voss, P. L.; Razeghi, M.; Ougazzaden, A.

    2016-02-01

    p-GaN/i-InGaN/n-GaN (PIN) structures were grown epitaxially on ZnO-buffered c-sapphire substrates by metal organic vapor phase epitaxy using the industry standard ammonia precursor for nitrogen. Scanning electron microscopy revealed continuous layers with a smooth interface between GaN and ZnO and no evidence of ZnO back-etching. Energy Dispersive X-ray Spectroscopy revealed a peak indium content of just under 5 at% in the active layers. The PIN structure was lifted off the sapphire by selectively etching away the ZnO buffer in an acid and then direct bonded onto a glass substrate. Detailed high resolution transmission electron microscoy and grazing incidence X-ray diffraction studies revealed that the structural quality of the PIN structures was preserved during the transfer process.

  1. 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.

  2. Highly aligned vertical GaN nanowires using submonolayer metal catalysts

    DOEpatents

    Wang, George T.; Li, Qiming; Creighton, J. Randall

    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.

  3. 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. PMID:27352143

  4. 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.

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

    DOE PAGESBeta

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

    2015-04-27

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

  6. 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.

  7. Growth kinetics of Al xGa 1- xN grown via ammonia-based metal-organic molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Billingsley, Daniel; Henderson, Walter; Pritchett, David; Alan Doolittle, W.

    2010-01-01

    The structural characteristics and growth regimes of AlGaN grown by ammonia-based metal-organic molecular beam epitaxy (NH 3-MOMBE) on GaN templates were investigated. The NH 3 utilization efficiency for the growth of AlGaN was estimated to be 2-2.5 times greater than the growth of GaN. Increasing the Al gas phase composition lead to an increase in the utilization efficiency as a result of increased NH 3 catalyzation. Despite the increased pyrolysis of ammonia, AlGaN films grown at 860 °C had significant active species desorption, leading to slower growth rates as well as lower calculated utilization efficiencies. AlGaN films grown with constant Al gas phase compositions showed an increase in the solid Al composition when grown more metal-rich, because of the preferential Al incorporation over Ga in N-limited growth environments. AlGaN surface morphologies became smoother with higher V/III ratios since surface pitting, which is attributed to decoration of threading dislocations, was reduced with increasing NH 3 flux.

  8. 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. PMID:27409958

  9. Indium-Tin-Oxide Metal-Insulator-Semiconductor GaN Ultraviolet Photodetectors Using Liquid-Phase-Deposition Oxide

    NASA Astrophysics Data System (ADS)

    Yang, Gow-Huei; Hwang, Jun-Dar; Lan, Chih-Hsueh; Chan, Chien-Mao; Chen, Hone-Zem; Chang, Shoou-Jinn

    2007-08-01

    A low-cost and reliable SiO2 insulating layer was successfully deposited onto GaN by liquid-phase deposition (LPD) using supersaturated H2SiF6 and H3BO3 solutions. The interface-trap density, Dit, was estimated to be 1.2× 1012 cm-2 eV-1 for the as-grown, not annealed LPD-SiO2 layers. It was found that the leakage current density was 2.06× 10-5 A/cm2 at a negative bias of 10 V for the as-grown Al/20 nm LPD-SiO2/GaN metal-insulator-semiconductor (MIS) capacitors. It was also found that the LPD-SiO2 layer could be used to suppress the dark current of nitride-based photodetectors. A large photocurrent to dark-current contrast ratio higher than four orders of magnitude and a maximum responsivity of 0.65 A/W were observed from the fabricated indium-tin-oxide (ITO)/LPD-SiO2/GaN MIS UV photodetectors. These results could be explained by defect-assisted tunneling.

  10. Effects of forming gas anneal on ultrathin InGaAs nanowire metal-oxide-semiconductor field-effect transistors

    NASA Astrophysics Data System (ADS)

    Si, Mengwei; Gu, Jiangjiang J.; Wang, Xinwei; Shao, Jiayi; Li, Xuefei; Manfra, Michael J.; Gordon, Roy G.; Ye, Peide D.

    2013-03-01

    InGaAs gate-all-around metal-oxide-semiconductor field-effect transistors (MOSFETs) with 6 nm nanowire thickness have been experimentally demonstrated at sub-80 nm channel length. The effects of forming gas anneal (FGA) on the performance of these devices have been systematically studied. The 30 min 400 °C FGA (4% H2/96% N2) is found to improve the quality of the Al2O3/InGaAs interface, resulting in a subthreshold slope reduction over 20 mV/dec (from 117 mV/dec in average to 93 mV/dec). Moreover, the improvement of interface quality also has positive impact on the on-state device performance. A scaling metrics study has been carried out for FGA treated devices with channel lengths down to 20 nm, indicating excellent gate electrostatic control. With the FGA passivation and the ultra-thin nanowire structure, InGaAs MOSFETs are promising for future logic applications.

  11. VIRTUAL FRAME BUFFER INTERFACE

    NASA Technical Reports Server (NTRS)

    Wolfe, T. L.

    1994-01-01

    Large image processing systems use multiple frame buffers with differing architectures and vendor supplied user interfaces. This variety of architectures and interfaces creates software development, maintenance, and portability problems for application programs. The Virtual Frame Buffer Interface program makes all frame buffers appear as a generic frame buffer with a specified set of characteristics, allowing programmers to write code which will run unmodified on all supported hardware. The Virtual Frame Buffer Interface converts generic commands to actual device commands. The virtual frame buffer consists of a definition of capabilities and FORTRAN subroutines that are called by application programs. The virtual frame buffer routines may be treated as subroutines, logical functions, or integer functions by the application program. Routines are included that allocate and manage hardware resources such as frame buffers, monitors, video switches, trackballs, tablets and joysticks; access image memory planes; and perform alphanumeric font or text generation. The subroutines for the various "real" frame buffers are in separate VAX/VMS shared libraries allowing modification, correction or enhancement of the virtual interface without affecting application programs. The Virtual Frame Buffer Interface program was developed in FORTRAN 77 for a DEC VAX 11/780 or a DEC VAX 11/750 under VMS 4.X. It supports ADAGE IK3000, DEANZA IP8500, Low Resolution RAMTEK 9460, and High Resolution RAMTEK 9460 Frame Buffers. It has a central memory requirement of approximately 150K. This program was developed in 1985.

  12. Methods for improved growth of group III nitride buffer layers

    DOEpatents

    Melnik, Yurity; Chen, Lu; Kojiri, Hidehiro

    2014-07-15

    Methods are disclosed for growing high crystal quality group III-nitride epitaxial layers with advanced multiple buffer layer techniques. In an embodiment, a method includes forming group III-nitride buffer layers that contain aluminum on suitable substrate in a processing chamber of a hydride vapor phase epitaxy processing system. A hydrogen halide or halogen gas is flowing into the growth zone during deposition of buffer layers to suppress homogeneous particle formation. Some combinations of low temperature buffers that contain aluminum (e.g., AlN, AlGaN) and high temperature buffers that contain aluminum (e.g., AlN, AlGaN) may be used to improve crystal quality and morphology of subsequently grown group III-nitride epitaxial layers. The buffer may be deposited on the substrate, or on the surface of another buffer. The additional buffer layers may be added as interlayers in group III-nitride layers (e.g., GaN, AlGaN, AlN).

  13. 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.

  14. 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.

  15. Impact of atomic layer deposition temperature on HfO2/InGaAs metal-oxide-semiconductor interface properties

    NASA Astrophysics Data System (ADS)

    Suzuki, Rena; Taoka, Noriyuki; Yokoyama, Masafumi; Kim, Sang-Hyeon; Hoshii, Takuya; Maeda, Tatsuro; Yasuda, Tetsuji; Ichikawa, Osamu; Fukuhara, Noboru; Hata, Masahiko; Takenaka, Mitsuru; Takagi, Shinichi

    2012-10-01

    We have studied the impact of atomic-layer-deposition (ALD) temperature on the HfO2/InGaAs metal-oxide-semiconductor (MOS) interface with a comparison to the Al2O3/InGaAs interface. It is found that the interface properties such as the C-V characteristics and the interface trap density (Dit) and the interface structure of HfO2/InGaAs have strong dependence on the ALD temperature, while the Al2O3/InGaAs interfaces hardly depend on it. As a result, we have achieved the HfO2/InGaAs interfaces with low Dit comparable to that in the Al2O3/InGaAs interface by lowering the ALD temperature down to 200 °C or less. Also, we have found that As2O3 and Ga2O3 formed at the interface during ALD increase with a decrease in the ALD temperature. Combined with the ALD temperature dependence of the electrical characteristics, the better C-V characteristics and the lower Dit obtained at the lower ALD temperature can be explained by the As2O3 and Ga2O3 passivation of the HfO2/InGaAs interfaces, which is consistent with a reported theoretical result on the effective passivation of III-V MOS interfaces by trivalent oxides.

  16. Interface engineering with an MOCVD grown ZnO interface passivation layer for ZrO 2-GaAs metal-oxide-semiconductor devices

    NASA Astrophysics Data System (ADS)

    Kundu, Souvik; Shripathi, T.; Banerji, P.

    2011-12-01

    This work deals with the fabrication of a GaAs metal-oxide-semiconductor device with an unpinned interface environment. An ultrathin ( ˜2 nm) interface passivation layer (IPL) of ZnO on GaAs was grown by metal organic chemical vapor deposition to control the interface trap densities and to prevent the Fermi level pinning before high-k deposition. X-ray photoelectron spectroscopy and high resolution transmission electron microscopy results show that an ultra thin layer of ZnO IPL can effectively suppress the oxides formation and minimize the Fermi level pinning at the interface between the GaAs and ZrO 2. By incorporating ZnO IPL, GaAs MOS devices with improved capacitance-voltage and reduced gate leakage current were achieved. The charge trapping behavior of the ZrO 2/ZnO gate stack under constant voltage stressing exhibits an improved interface quality and high dielectric reliability.

  17. Unusual M2-mediated metal-insulator transition in epitaxial VO2 thin films on GaN substrates

    NASA Astrophysics Data System (ADS)

    Yang, Hyoung Woo; Inn Sohn, Jung; Yang, Jae Hoon; Jang, Jae Eun; Cha, Seung Nam; Kim, Jongmin; Kang, Dae Joon

    2015-01-01

    We report on the epitaxial growth of vanadium dioxide (\\text{VO}2) thin films on (0001) GaN substrates using a radio frequency magnetron sputtering method and discuss their unusual M2-mediated metal-insulator transition (MIT) properties. We found that large lattice misfits between the \\text{VO}2 film and the GaN substrate could favor the stabilization of the intermediate insulating \\text{M}2 phase, which is known to be observed only in either doped or uniaxially strained samples. We demonstrated that the MIT in \\text{VO}2 films on GaN substrates could be mediated via a monoclinic \\text{M}2 phase during the transition from a monoclinic \\text{M}1 to a rutile R phase. This was confirmed by temperature-dependent Raman studies that exhibited both an evident upshift of a high-frequency phonon mode (ω\\text{V-O}) from 618 \\text{cm}-1 (\\text{M}1) to 645 \\text{cm}-1 (\\text{M}2) and a distinct peak splitting of a low-frequency phonon mode (ω\\text{V-V}) at 221 \\text{cm}-1 (\\text{M}2) for increasing temperatures. Moreover, a resistance change of four orders of magnitude was observed for \\text{VO}2 thin films on GaN substrates, being indicative of the high quality of \\text{VO}2 thin films. This study may offer great opportunities not only to improve the understanding of M2-mediated MIT behavior in \\text{VO}2 thin films, but also to realize novel electronic and optoelectronic devices.

  18. 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.

  19. Effect of temperature on Ga{sub 2}O{sub 3}(Gd{sub 2}O{sub 3})/GaN metal{endash}oxide{endash}semiconductor field-effect transistors

    SciTech Connect

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

    1998-12-01

    Ga{sub 2}O{sub 3}(Gd{sub 2}O{sub 3}) was deposited on GaN for use as a gate dielectric in order to fabricate a depletion metal{endash}oxide{endash}semiconductor field-effect transistor (MOSFET). Analysis of the effect of temperature on the device shows that gate leakage is significantly reduced at elevated temperature relative to a conventional metal{endash}semiconductor field-effect transistor fabricated on the same GaN layer. MOSFET device operation in fact improved upon heating to 400 {degree}C. Modeling of the effect of temperature on contact resistance suggests that the improvement is due to a reduction in the parasitic resistances present in the device. {copyright} {ital 1998 American Institute of Physics.}

  20. New metal atom laser transitions in As, Bi, Ga, Ge, Hg, In, Pb, Sb, and Tl

    NASA Technical Reports Server (NTRS)

    Chou, M. S.; Cool, T. A.

    1976-01-01

    A double discharge technique was used in the investigation. An initial discharge established between parallel arrays of tungsten pin electrodes was followed, after a variable time delay, by a high voltage (180 kV), short duration (50 nsec) secondary discharge between two aluminum main electrodes. Metal compounds, including metal alkyls, hydrides, and halides, were used to obtain the required metal atom concentrations. Twenty-four new laser transitions involving 9 different metal atoms were observed. The observed relations are shown in a number of partial energy-level diagrams.

  1. 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

  2. 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.

  3. 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. PMID:26418767

  4. Thermal annealing effect on material characterizations of β-Ga2O3 epilayer grown by metal organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Huang, Chiung-Yi; Horng, Ray-Hua; Wuu, Dong-Sing; Tu, Li-Wei; Kao, Hsiang-Shun

    2013-01-01

    In this work, a single-crystalline β-Ga2O3 epilayer was grown on (0001) sapphire at low temperature by low-pressure metal organic chemical vapor deposition. The optimized parameters for the chamber pressure, oxygen flow, and growth temperature were 15 Torr, 200 sccm, and 500 °C, respectively. The β-Ga2O3 epilayer was fabricated as a metal-semiconductor-metal solar-blind deep ultraviolet photodetector. Due to the gallium oxide grown at low temperature, the as-grown β-Ga2O3 epilayer was annealed at 800 °C in atmosphere or in a nitrogen environment. The effects of defects of the β-Ga2O3 epilayer before and after N2 annealing were studied using x-ray diffraction system, cathodoluminescence at differential temperature, and Hall measurement. The β-Ga2O3 epilayer that was N2 annealed for 15 min presented better photodetector performance than the as-grown β-Ga2O3 epilayer. The annealed epilayer exhibited a dark current of 1.6 × 10-13 A under 5 V bias.

  5. 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

  6. In situ synchrotron x-ray studies of strain and composition evolution during metal-organic chemical vapor deposition of InGaN.

    SciTech Connect

    Richard, M.-I.; Highland, M. J.; Fister, T. T.; Munkholm, A.; Mei, J.; Streiffer, S. K.; Thompson, C.; Fuoss, P. H.; Stephenson, G. B.; Univ. Paul Cezanne; Philips Lumileds Lighting Co.; Northern Illinois Univ.; Faculte des Sciences de St. Jerome

    2010-01-01

    Composition and strain inhomogeneities strongly affect the optoelectronic properties of InGaN but their origin has been unclear. Here we report real-time x-ray reciprocal space mapping that reveals the development of strain and composition distributions during metal-organic chemical vapor deposition of In{sub x}Ga{sub 1-x}N on GaN. Strong, correlated inhomogeneities of the strain state and In fraction x arise during growth in a manner consistent with models for instabilities driven by strain relaxation.

  7. 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.

  8. 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.

  9. Tunnelling magnetoresistance of the half-metallic compensated ferrimagnet Mn2RuxGa

    NASA Astrophysics Data System (ADS)

    Borisov, K.; Betto, D.; Lau, Y.-C.; Fowley, C.; Titova, A.; Thiyagarajah, N.; Atcheson, G.; Lindner, J.; Deac, A. M.; Coey, J. M. D.; Stamenov, P.; Rode, K.

    2016-05-01

    Tunnel magnetoresistance ratios of up to 40% are measured between 10 K and 300 K when the highly spin-polarized compensated ferrimagnet, Mn2RuxGa, is integrated into MgO-based perpendicular magnetic tunnel junctions. Temperature and bias dependences of the tunnel magnetoresistance effect, with a sign change near -0.2 V, reflect the structure of the Mn2RuxGa interface density of states. Despite magnetic moment vanishing at a compensation temperature of 200 K for x ≈ 0.8 , the tunnel magnetoresistance ratio remains non-zero throughout the compensation region, demonstrating that the spin-transport is governed by one of the Mn sub-lattices only. Broad temperature range magnetic field immunity of at least 0.5 T is demonstrated in the same sample. The high spin polarization and perpendicular magnetic anisotropy make Mn2RuxGa suitable for applications in both non-volatile magnetic random access memory cells and terahertz spin-transfer oscillators.

  10. 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.

  11. Demonstration of InAlN/AlGaN high electron mobility transistors with an enhanced breakdown voltage by pulsed metal organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Xue, JunShuai; Zhang, JinCheng; Hao, Yue

    2016-01-01

    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 cm2/V s along with a sheet carrier density of 1.88 × 1013 cm-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.

  12. Effects of growth temperature on the properties of InGaN channel heterostructures grown by pulsed metal organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Zhang, Yachao; Zhou, Xiaowei; Xu, Shengrui; Wang, Zhizhe; Chen, Zhibin; Zhang, Jinfeng; Zhang, Jincheng; Hao, Yue

    2015-12-01

    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 × 1013 cm-2 and Hall electron mobility of 1025 cm2/(Vṡs) 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.

  13. A Transmission Electron Microscopy Observation of Dislocations in GaN Grown on (0001) Sapphire by Metal Organic Chemical Vapor Deposition

    NASA Astrophysics Data System (ADS)

    Huang, Shih-Yao; Yang, Jer-Ren

    2008-10-01

    A transmission electron microscopy (TEM) observation of dislocations in GaN grown on (0001) sapphire by metal organic chemical vapor deposition (MOCVD) was carried out in this study. The GaN film was rotated 30° around the c-axis in the growth plane against the substrate. The finding of this research, according to TEM analysis, is that about 3% (or less) of the threading dislocations are pure screw (b = <0001 >) and 20% are pure edge (b = 1/3 <1120 >). The remaining threading dislocations, about 77%, are mixed-type dislocations; that is the major dislocation type in the GaN epitaxial layer grown on (0001) sapphire is the mixed type. In addition, to further understand the dislocation configuration on the interface of GaN/sapphire, a plane-view TEM sample of the GaN/sapphire interface was prepared. The plane-view TEM image of the GaN/sapphire interface reveals an extremely high density of kink dislocations lying on the interface, with a dislocation density of about 8×109 cm-2, involving high strain and stress. A comparison of the 8×109 cm-2 dislocation density with another plane-view TEM image (6×108 cm-2) near the GaN free surface revealed that approximately 7.5% of the dislocations lying on the substrate coalesce into threading dislocations generated from the interface to the GaN surface.

  14. Evaluation of excess In during metal organic vapor-phase epitaxy growth of InGaN by monitoring via in situ laser scattering

    NASA Astrophysics Data System (ADS)

    Yamamoto, Tetsuya; Tamura, Akira; Usami, Shigeyoshi; Mitsunari, Tadashi; Nagamatsu, Kentaro; Nitta, Shugo; Honda, Yoshio; Amano, Hiroshi

    2016-05-01

    Using an in situ laser absorption and scattering method, the surface roughness and incorporation of In in InGaN layers grown by metal organic vapor-phase epitaxy (MOVPE) were monitored. We observed that the laser light with energy higher than the GaN bandgap was fully absorbed in a GaN layer with a smooth film surface. On the other hand, we observed that the scattering laser light from the surface when the roughness of the InGaN surface increased owing to the formation of In droplets. Laser light with energy lower than the GaN bandgap was weakly absorbed by the GaN layer and was scattered at the back surface of the wafer. Furthermore, laser light intensity decreased during InGaN growth because of In incorporation. The threshold of trimethyl-In (TMIn) for the formation of In droplets as a function of growth temperature was determined using our in situ system. Moreover, we observed that the In droplets were removed by thermal or H2 treatment. The results indicate that multiwavelength laser absorption and scattering enable the optimization of the growth conditions for In-rich InGaN.

  15. Surface morphology of Cr:Ga2Se3 heteroepitaxy on Si(001)

    NASA Astrophysics Data System (ADS)

    Yitamben, E. N.; Lovejoy, T. C.; Paul, D. F.; Callaghan, J. B.; Ohuchi, F. S.; Olmstead, M. A.

    2009-08-01

    Addition of the transition-metal dopant Cr to Ga2Se3 during heteroepitaxial growth on Si(001), a system of interest as a prototype silicon-compatible, dilute magnetic semiconductor, has been studied with scanning-tunneling microscopy and scanning Auger microscopy as a function of Cr concentration and the presence or absence of an undoped buffer or capping layer. Chromium incorporates into laminar Ga2Se3 films up to a solubility limit of several atomic percent, after which Cr-rich islands nucleate. At low Cr concentrations, the vacancy-ordered nanoridge structure characteristic of pure Ga2Se3 remains but nanoridge aspect ratios decrease with Cr concentration; this is likely associated with Cr removing intrinsic vacancies. At higher Cr concentrations, faceted, Cr-rich islands nucleate, often surrounded by trenches, and the terrace morphology no longer resembles pure Ga2Se3 . Growth of Cr-doped Ga2Se3 directly on Si(001):As is qualitatively similar to growth on a pure Ga2Se3 buffer layer; however, the island structure changes dramatically upon coverage of a highly doped layer with undoped Ga2Se3 . Addition of Cr stabilizes cubic overlayer growth under Se-poor growth conditions beyond that of pure Ga2Se3 ; no growth of the hexagonal layered structure characteristic of bulk GaSe was observed.

  16. Growth of III-V nitrides and buffer layer investigation by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Huang, Tzu-Fang

    1999-11-01

    III-V nitrides have been investigated intensively due to the enormous interest in optoelectronic device applications in the green, blue, violet, and near-ultraviolet regions. Advances in III-V nitride materials for short wavelength light sources will lead to both a revolution in optical disk storage, as higher densities can be achieved with short wavelengths, and a major impact on imaging and graphic technology as high quality red, green, and blue light-emitting diodes (LED) and lasers become available. High quality GaN films have mostly been prepared by metal-organic vapor phase epitaxy (MOCVD), molecular beam epitaxy (MBE) and vapor phase epitaxy (VPE). Compared to these techniques, pulsed laser deposition (PLD) is a relatively new growth technique used widely for the growth of oxide thin films. However, several advantages of PLD make it worthy of study as a method of growing nitrides. The congruent ablation achieved with short UV-laser pulses allows deposition of a multicomponent material by employing a single target and the ability for depositing a wide variety of materials. This advantage makes PLD very suitable for growing multilayer structures sequentially in the same chamber and investigating the effect of buffer layers. Moreover, the strong nonequilibrium growth conditions of PLD may lead to different nucleation and growth processes. In this work, GaN and (Al,Ga)N films have been epitaxially grown on (0001) sapphire substrate by PLD, which has been successfully applied to controlling the lattice constant and band gap of (Al,Ga)N. Room-temperature photoluminescence of PLD-GaN exhibits a strong band edge emission at 3.4eV. The threading dislocations of GaN are predominantly screw dislocations with Burgers vector of <0001> while edge dislocations with Burgers vector of 1/3<11-20> are the dominant ones in GaN grown by MBE, MOCVD and VPE. This variation observed in defect characteristics may come from the difference in nucleation and growth kinetics between PLD

  17. Gallium Pnictides of the Alkaline Earth Metals, Synthesized by Means of the Flux Method: Crystal Structures and Properties of CaGa[subscript 2]Pn[subscript 2], SrGa[subscript 2]As[subscript 2], Ba[subscript 2]Ga[subscript 5]As[subscript 5], and Ba[subscript 4]Ga[subscript 5]Pn[subscript 8] (Pn = P or As)

    SciTech Connect

    He, Hua; Stearrett, Ryan; Nowak, Edmund R.; Bobev, Svilen

    2014-05-28

    The focus of this paper is on the structural characterization of the new Zintl phases CaGa{sub 2}P{sub 2}, CaGa{sub 2}As{sub 2}, SrGa{sub 2}As{sub 2}, and Ba{sub 2}Ga{sub 5}As{sub 5}, and the solid solution (Ba{sub 0.85(1)}Sr{sub 0.15}){sub 2}Ga{sub 5}As{sub 5}, all of which were synthesized from molten metal fluxes.CaGa{sub 2}P{sub 2}, CaGa{sub 2}As{sub 2}, and SrGa{sub 2}As{sub 2} have layered structures with polyanionic layers made of ethane-like Ga{sub 2}P6 and Ga{sub 2}As6 motifs fused through common edges; the polyanionic substructure in Ba{sub 2}Ga{sub 5}As{sub 5} consists of condensed Ga{sub 2}As6 units and GaAs{sub 4} tetrahedra. Ba{sub 4}Ga{sub 5}P{sub 8} and Ba{sub 4}Ga{sub 5}As{sub 8}, another pair of new compounds with channel-like 3D structures, were also synthesized from metal fluxes, and their structures were established from single-crystal X-ray and synchrotron powder diffraction. They are based on GaP{sub 4} and GaAs{sub 4} tetrahedra, with parts of their structures being heavily disordered. The electronic structures computed with the linear muffin-tin orbital (LMTO) method are discussed as well, alongside the thermopower and the electrical conductivity, measured on single crystals of Ba{sub 2}Ga{sub 5}As{sub 5} and the solid solution (Ba{sub 0.85(1)}Sr{sub 0.15}){sub 2} Ga{sub 5}As{sub 5}. They demonstrate that such an approach would be an effective way to fine-tune the transport properties.

  18. Temperature dependent electrical characterisation of Pt/HfO{sub 2}/n-GaN metal-insulator-semiconductor (MIS) Schottky diodes

    SciTech Connect

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

    2015-09-15

    This paper reports an improvement in Pt/n-GaN metal-semiconductor (MS) Schottky diode characteristics by the introduction of a layer of HfO{sub 2} (5 nm) between the metal and semiconductor interface. The resulting Pt/HfO{sub 2}/n-GaN metal-insulator-semiconductor (MIS) Schottky diode showed an increase in rectification ratio from 35.9 to 98.9(@ 2V), increase in barrier height (0.52 eV to 0.63eV) and a reduction in ideality factor (2.1 to 1.3) as compared to the MS Schottky. Epitaxial n-type GaN films of thickness 300nm were grown using plasma assisted molecular beam epitaxy (PAMBE). The crystalline and optical qualities of the films were confirmed using high resolution X-ray diffraction and photoluminescence measurements. Metal-semiconductor (Pt/n-GaN) and metal-insulator-semiconductor (Pt/HfO{sub 2}/n-GaN) Schottky diodes were fabricated. To gain further understanding of the Pt/HfO{sub 2}/GaN interface, I-V characterisation was carried out on the MIS Schottky diode over a temperature range of 150 K to 370 K. The barrier height was found to increase (0.3 eV to 0.79 eV) and the ideality factor decreased (3.6 to 1.2) with increase in temperature from 150 K to 370 K. This temperature dependence was attributed to the inhomogeneous nature of the contact and the explanation was validated by fitting the experimental data into a Gaussian distribution of barrier heights.

  19. Photoluminescence spectroscopy and energy-level analysis of metal-organic-deposited Ga2O3:Cr3+ films

    NASA Astrophysics Data System (ADS)

    Tokida, Yoshinori; Adachi, Sadao

    2012-09-01

    The aims of this study are (i) to demonstrate the synthesis of Cr3+-activated β-Ga2O3 films by metal-organic deposition and (ii) to report the temperature-dependent photoluminescence (PL) properties of such films from 20 to 300 K. An activation energy of ˜0.9 eV for the Cr3+ ions in β-Ga2O3 is determined from a plot of PL intensity vs calcination temperature. The red-line emission doublet R1 and R2 at ˜1.8 eV and the broad emission band with a peak at ˜1.7 eV are ascribed to the Cr3+ ions in the β-Ga2O3 host. The energies of the excited states, i.e., 2E, 4T2, 2T2, 4T1, and 4T1, in Cr3+ are determined from the experimental PL and PL excitation spectra using a newly developed analysis model. The high-energy luminescence tail of the broad 4T2 → 4A2 emission band can be explained by the hot-carrier effect of the photoexcited electrons in the 4T2 state. The relative intensities of the R-line emission doublet can also be explained very well by the population and depopulation of the electron numbers in the E¯ (R1) and 2A¯ (R2) states. PL properties, such as the temperature-dependent PL intensity, peak energy, and spectral width, are analyzed in detail.

  20. Structural stability, half-metallicity and magnetism of the CoFeMnSi/GaAs(0 0 1) interface

    NASA Astrophysics Data System (ADS)

    Feng, Yu; Chen, Xiaorui; Zhou, Ting; Yuan, Hongkuan; Chen, Hong

    2015-08-01

    The ferromagnet/semiconductor interface plays a crucial role in the performance of advanced magnetic tunnel junctions (MTJs) built of ferromagnetic electrodes and semiconductor as a spacer. We investigate the interface character between LiMgPbSb-type Heusler alloy CoFeMnSi and semiconductor GaAs by using the first-principles density functional simulations. In our calculations, we build two kinds of interface structures, namely the top-type and the bridge-type structure by connecting the termination of nine CoFeMnSi layers to the top of the As-terminated GaAs layer and the bridge site between interface As atoms, respectively. The calculated phase diagram indicated that the CoFe-terminated interface is more stable in the bridge-type structure than in the top-type structure, and a favored MnMn- or MnSi-terminated interface will appear in the top-type structure instead of the bridge-type structure under Fe-rich conditions. Besides, our calculation reveals that interface Mn and interface Fe atoms prefer to extend outward and their atom-resolved spin magnetic moments are enhanced due to the rehybridization caused by the symmetry breaking at the interface, while interface Co atoms shrink inward and their moments are decreased compared with the bulk value. Further analysis on DOS and PDOS indicates that owing to the interface effect, the half metallicity of CoFe-, MnSi-, and SiSi-terminated interfaces is completely destroyed. However, the MnMn-terminated interface in the top-type structure preserves 100% spin polarization, indicating that the CoFeMnSi/GaAs heterostructure with the top-type MnMn-terminated interface has more advantages than other atomic terminations in spintronics applications.

  1. Effect of conductive TiN buffer layer on the growth of stoichiometric VO{sub 2} films and the out-of-plane insulator–metal transition properties

    SciTech Connect

    Mian, Md. Suruz; Okimura, Kunio

    2014-07-15

    A TiN buffer film is used with a conductive interfacial layer for stoichiometric vanadium dioxide (VO{sub 2}) film growth, creating a layered device with a VO{sub 2} insulator–metal transition. Low-temperature growth (<250 °C) of the VO{sub 2} film on a Ti layer on a Si substrate is achieved using inductively coupled plasma-assisted sputtering. It is found that Ti diffusion and oxidation degrades the VO{sub 2} film quality at higher temperatures, but the introduction of a TiN buffer layer suppresses the degradation and enables growth of a stoichiometric VO{sub 2} film even at 400 °C. The high resistance of the VO{sub 2} film grown on the TiN layer suggests the benefit of using the intrinsic insulator–metal transition of VO{sub 2}. The voltage-triggered switching properties of the layered devices are examined, and the cause of the high out-of-plane resistance in this layered structure is discussed based upon the dependence of the initial resistance as a function the electrode area.

  2. Theoretical study of dilute GaN-4d transition metal alloys.

    PubMed

    de Paiva, R; Nogueira, R A; Alves, J L A

    2006-09-20

    Electronic calculations were carried out for the dilute ordered alloys Ga(0.94) (TM)(0.06)N (TM = Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, and Ag) in the zinc-blende structure. The theoretical framework used was the density functional theory, using the local spin density approximation, as implemented in the full-potential linearized augmented plane wave method. We examine energy band structures, densities of states, charge distributions, and local magnetic moments and anticipate the properties of these promising systems for applications in spin electronic devices. PMID:21690911

  3. 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.}.

  4. On trapping mechanisms at oxide-traps in Al2O3/GaN metal-oxide-semiconductor capacitors

    NASA Astrophysics Data System (ADS)

    Bisi, D.; Chan, S. H.; Liu, X.; Yeluri, R.; Keller, S.; Meneghini, M.; Meneghesso, G.; Zanoni, E.; Mishra, U. K.

    2016-03-01

    By means of combined current-voltage and capacitance-voltage sweep and transient measurements, we present the effects of forward-bias stress and charge trapping mechanisms at oxide traps in Al2O3/GaN metal-oxide-semiconductor capacitors grown in-situ by metalorganic chemical vapor deposition. Two main current-voltage regimes have been identified: a low-field regime characterized by low gate-current and low flat-band voltage instabilities, and a high-field regime triggered for oxide field greater than 3.3 MV/cm and characterized by the onset of parasitic leakage current and positive flat-band shift. In the low-voltage regime, gate current transients convey stress/relaxation kinetics based on a power-law, suggesting that tunneling trapping mechanisms occur at near-interface traps aligned with the GaN conduction-band minimum. In the high-voltage regime, devices experience parasitic conduction mechanisms and enhanced charge-trapping at oxide-traps revealed by very slow recovery transients.

  5. Investigation of cracks in GaN films grown by combined hydride and metal organic vapor-phase epitaxial method

    PubMed Central

    2011-01-01

    Cracks appeared in GaN epitaxial layers which were grown by a novel method combining metal organic vapor-phase epitaxy (MOCVD) and hydride vapor-phase epitaxy (HVPE) in one chamber. The origin of cracks in a 22-μm thick GaN film was fully investigated by high-resolution X-ray diffraction (XRD), micro-Raman spectra, and scanning electron microscopy (SEM). Many cracks under the surface were first observed by SEM after etching for 10 min. By investigating the cross section of the sample with high-resolution micro-Raman spectra, the distribution of the stress along the depth was determined. From the interface of the film/substrate to the top surface of the film, several turnings were found. A large compressive stress existed at the interface. The stress went down as the detecting area was moved up from the interface to the overlayer, and it was maintained at a large value for a long depth area. Then it went down again, and it finally increased near the top surface. The cross-section of the film was observed after cleaving and etching for 2 min. It was found that the crystal quality of the healed part was nearly the same as the uncracked region. This indicated that cracking occurred in the growth, when the tensile stress accumulated and reached the critical value. Moreover, the cracks would heal because of high lateral growth rate. PMID:21711601

  6. Controlling the interface charge density in GaN-based metal-oxide-semiconductor heterostructures by plasma oxidation of metal layers

    SciTech Connect

    Hahn, Herwig Kalisch, Holger; Vescan, Andrei; Pécz, Béla; Kovács, András; Heuken, Michael

    2015-06-07

    In recent years, investigating and engineering the oxide-semiconductor interface in GaN-based devices has come into focus. This has been driven by a large effort to increase the gate robustness and to obtain enhancement mode transistors. Since it has been shown that deep interface states act as fixed interface charge in the typical transistor operating regime, it appears desirable to intentionally incorporate negative interface charge, and thus, to allow for a positive shift in threshold voltage of transistors to realise enhancement mode behaviour. A rather new approach to obtain such negative charge is the plasma-oxidation of thin metal layers. In this study, we present transmission electron microscopy and energy dispersive X-ray spectroscopy analysis as well as electrical data for Al-, Ti-, and Zr-based thin oxide films on a GaN-based heterostructure. It is shown that the plasma-oxidised layers have a polycrystalline morphology. An interfacial amorphous oxide layer is only detectable in the case of Zr. In addition, all films exhibit net negative charge with varying densities. The Zr layer is providing a negative interface charge density of more than 1 × 10{sup 13 }cm{sup –2} allowing to considerably shift the threshold voltage to more positive values.

  7. Effects of Ga substitution on the structural and magnetic properties of half metallic Fe{sub 2}MnSi Heusler compound

    SciTech Connect

    Pedro, S. S. Caraballo Vivas, R. J.; Andrade, V. M.; Cruz, C.; Paixão, L. S.; Contreras, C.; Costa-Soares, T.; Rocco, D. L.; Reis, M. S.; Caldeira, L.; Coelho, A. A.; Carvalho, A. Magnus G.

    2015-01-07

    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 Fe{sub 2}MnSi 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.

  8. Impact of short-range scattering on the metallic transport of strongly correlated two-dimensional holes in GaAs quantum wells

    NASA Astrophysics Data System (ADS)

    Goble, Nicholas J.; Watson, John D.; Manfra, Michael J.; Gao, Xuan P. A.

    2014-07-01

    Understanding the nonmonotonic 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 20-nm-wide GaAs quantum wells with varying short-range disorder strength by changing the Al fraction x in the AlxGa1-xAs barrier. Via varying the short-range interface roughness and alloy scattering, it is observed that increasing x suppresses both the strength and characteristic temperature scale of the 2D metallicity, pointing to the distinct role of short-range vs long-range disorder in the 2D metallic transport in this correlated 2D hole system with interaction parameter rs˜20.

  9. Common data buffer

    NASA Technical Reports Server (NTRS)

    Byrne, F.

    1981-01-01

    Time-shared interface speeds data processing in distributed computer network. Two-level high-speed scanning approach routes information to buffer, portion of which is reserved for series of "first-in, first-out" memory stacks. Buffer address structure and memory are protected from noise or failed components by error correcting code. System is applicable to any computer or processing language.

  10. Micro-x-ray absorption near-edge structure imaging for detecting metallic Mn in GaN

    NASA Astrophysics Data System (ADS)

    Martínez-Criado, G.; Somogyi, A.; Homs, A.; Tucoulou, R.; Susini, J.

    2005-08-01

    In this study, we report the application of a synchrotron radiation microprobe to the analysis of Mn valencies in GaN. X-ray absorption near-edge structure (XANES) images taken around MnK-edge in fluorescence detection mode reveal the concentration of oxidation states of Mn centers. By fitting the XANES curve for each point of the image, the distributions of the Mn0, Mn2+, and Mn3+ oxidation states are obtained. At low Mn concentrations, there is a homogeneous mixture of Mn2+ and Mn3+ centers, while at high Mn content strong spatial-dependent Mn0 and Mn2+ distributions characterize the XANES maps. In a supplementary way with respect to Mn2+, the Mn0 pattern suggests the presence of specific cluster-like features, indicating surface segregation of metallic Mn centers.

  11. A top-gate GaN nanowire metal-semiconductor field effect transistor with improved channel electrostatic control

    NASA Astrophysics Data System (ADS)

    Gačević, Ž.; López-Romero, D.; Juan Mangas, T.; Calleja, E.

    2016-01-01

    A uniformly n-type doped GaN:Si nanowire (NW), with a diameter of d = 90 nm and a length of 1.2 μm, is processed into a metal-semiconductor field effect transistor (MESFET) with a semi-cylindrical top Ti/Au Schottky gate. The FET is in a normally-ON mode, with the threshold at -0.7 V and transconductance of gm ˜ 2 μS (the transconductance normalized with NW diameter gm/d > 22 mS/mm). It enters the saturation mode at VDS ˜ 4.5 V, with the maximum measured drain current IDS = 5.0 μA and the current density exceeding JDS > 78 kA/cm2.

  12. GaAs metal-oxide-semiconductor based nonvolatile memory devices embedded with ZnO quantum dots

    NASA Astrophysics Data System (ADS)

    Kundu, Souvik; Rao Gollu, Sankara; Sharma, Ramakant; Halder, Nripendra. N.; Biswas, Pranab; Banerji, P.; Gupta, D.

    2013-08-01

    Ultrathin InP passivated GaAs non-volatile memory devices were fabricated with chemically synthesized 5 nm ZnO quantum dots embedded into ZrO2 high-k oxide matrix deposited through metal organic chemical vapor deposition. In these memory devices, the memory window was found to be 6.10 V and the obtained charge loss was only 15.20% after 105 s. The superior retention characteristics and a wide memory window are achieved due to presence of ZnO quantum dots between tunneling and control oxide layers. Room temperature Coulomb blockade effect was found in these devices and it was ascertained to be the main reason for low leakage. Electronic band diagram with program and erase operations were described on the basis of electrical characterizations.

  13. Stability of In-Ga-Zn-O metal-semiconductor field-effect-transistors under bias, illumination, and temperature stress

    NASA Astrophysics Data System (ADS)

    Dang, Giang T.; Kawaharamura, Toshiyuki; Furuta, Mamoru; Saxena, Saurabh; Allen, Martin W.

    2015-10-01

    The stability of metal-semiconductor field-effect-transistors (MESFETs) with silver oxide Schottky gates on In-Ga-Zn-O (IGZO) channels, grown by mist chemical-vapor-deposition, was examined under different combinations of positive and negative bias, illumination, and temperature stress. These devices were remarkably stable, even under the most severe condition of negative-bias-illumination-temperature-stress (NBITS), where the threshold voltage shift after 10 h NBITS was only +0.12 V and was mainly attributed to a decrease in the carrier density of the channel. The stability of these IGZO MESFETs is associated with the use of a conducting Schottky gate that significantly reduces charge trapping at the gate-channel interface.

  14. Double metal waveguide InGaAs/AlInAs quantum cascade lasers emitting at 24 μm

    SciTech Connect

    Ohtani, K. Beck, M.; Faist, J.

    2014-09-22

    A study on far-infrared In{sub 0.53}Ga{sub 0.47}As/Al{sub 0.48}In{sub 0.52}As quantum cascade lasers operating with a double metal waveguide is presented. To increase the laser upper state lifetime, a diagonal bound-to-continuum transition scheme is used in the active region. The observed threshold current density at 50 K is 5.7 kA/cm{sup 2}, and the maximum operation temperature is 240 K. The laser emission wavelength is 24.4 μm, which is the longest wavelength in the mid-infrared quantum cascade lasers so far reported.

  15. Optical reflection from the Bragg lattice of AsSb metal nanoinclusions in an AlGaAs matrix

    SciTech Connect

    Ushanov, V. I.; Chaldyshev, V. V.; Preobrazhenskii, V. V.; Putyato, M. A.; Semyagin, B. R.

    2013-08-15

    The optical properties of metal-semiconductor metamaterials based on an AlGaAs matrix are studied. The specific feature of these materials is that there are As and AsSb nanoinclusion arrays which modify the dielectric properties of the material. These nanoinclusions are randomly arranged in the medium or form a Bragg structure with a reflectance peak at a wavelength close to 750 nm, corresponding to the transparency region of the matrix. The reflectance spectra are studied for s- and p-polarized light at different angles of incidence. It is shown that (i) As nanoinclusion arrays only slightly influence the optical properties of the medium in the wavelength range 700-900 nm, (ii) chaotic AsSb nanoinclusion arrays cause strong scattering of light, and (iii) the spatial periodicity in the arrangement of AsSb nanoinclusions is responsible for Bragg resonance in the optical reflection.

  16. GaSb p-channel metal-oxide-semiconductor field-effect transistor and its temperature dependent characteristics

    NASA Astrophysics Data System (ADS)

    Zhao, Lian-Feng; Tan, Zhen; Wang, Jing; Xu, Jun

    2015-01-01

    GaSb p-channel metal-oxide-semiconductor field-effect transistors (MOSFETs) with an atomic layer deposited Al2O3 gate dielectric and a self-aligned Si-implanted source/drain are experimentally demonstrated. Temperature dependent electrical characteristics are investigated. Different electrical behaviors are observed in two temperature regions, and the underlying mechanisms are discussed. It is found that the reverse-bias pn junction leakage of the drain/substrate is the main component of the off-state drain leakage current, which is generation-current dominated in the low temperature regions and is diffusion-current dominated in the high temperature regions. Methods to further reduce the off-state drain leakage current are given. Project supported by the National Basic Research Program of China (Grant No. 2011CBA00602) and the National Science and Technology Major Project of the Ministry of Science and Technology of China (Grant No. 2011ZX02708-002).

  17. Electron Transport Behavior on Gate Length Scaling in Sub-50 nm GaAs Metal Semiconductor Field Effect Transistors

    NASA Astrophysics Data System (ADS)

    Han, Jaeheon

    2011-12-01

    Short channel GaAs Metal Semiconductor Field Effect Transistors (MESFETs) have been fabricated with gate length to 20 nm, in order to examine the characteristics of sub-50 nm MESFET scaling. Here the rise in the measured transconductance is mainly attributed to electron velocity overshoot. For gate lengths below 40 nm, however, the transconductance drops suddenly. The behavior of velocity overshoot and its degradation is investigated and simulated by using a transport model based on the retarded Langevin equation (RLE). This indicates the existence of a minimum acceleration length needed for the carriers to reach the overshoot velocity. The argument shows that the source resistance must be included as an internal element, or appropriate boundary condition, of relative importance in any model where the gate length is comparable to the inelastic mean free path of the carriers.

  18. Buffer Therapy for Cancer.

    PubMed

    Ribeiro, Maria de Lourdes C; Silva, Ariosto S; Bailey, Kate M; Kumar, Nagi B; Sellers, Thomas A; Gatenby, Robert A; Ibrahim-Hashim, Arig; Gillies, Robert J

    2012-08-15

    Oral administration of pH buffers can reduce the development of spontaneous and experimental metastases in mice, and has been proposed in clinical trials. Effectiveness of buffer therapy is likely to be affected by diet, which could contribute or interfere with the therapeutic alkalinizing effect. Little data on food pH buffering capacity was available. This study evaluated the pH and buffering capacity of different foods to guide prospective trials and test the effect of the same buffer (lysine) at two different ionization states. Food groups were derived from the Harvard Food Frequency Questionnaire. Foods were blended and pH titrated with acid from initial pH values until 4.0 to determine "buffering score", in mmol H(+)/pH unit. A "buffering score" was derived as the mEq H(+) consumed per serving size to lower from initial to a pH 4.0, the postprandial pH of the distal duodenum. To differentiate buffering effect from any metabolic byproduct effects, we compared the effects of oral lysine buffers prepared at either pH 10.0 or 8.4, which contain 2 and 1 free base amines, respectively. The effect of these on experimental metastases formation in mice following tail vein injection of PC-3M prostate cancer cells were monitored with in vivo bioluminescence. Carbohydrates and dairy products' buffering score varied between 0.5 and 19. Fruits and vegetables showed a low to zero buffering score. The score of meats varied between 6 and 22. Wine and juices had negative scores. Among supplements, sodium bicarbonate and Tums(®) had the highest buffering capacities, with scores of 11 and 20 per serving size, respectively. The "de-buffered" lysine had a less pronounced effect of prevention of metastases compared to lysine at pH 10. This study has demonstrated the anti-cancer effects of buffer therapy and suggests foods that can contribute to or compete with this approach to manage cancer. PMID:24371544

  19. High-quality uniaxial In(x)Ga(1-x)N/GaN multiple quantum well (MQW) nanowires (NWs) on Si(111) grown by metal-organic chemical vapor deposition (MOCVD) and light-emitting diode (LED) fabrication.

    PubMed

    Ra, Yong-Ho; Navamathavan, R; Park, Ji-Hyeon; Lee, Cheul-Ro

    2013-03-01

    This article describes the growth and device characteristics of vertically aligned high-quality uniaxial p-GaN/InxGa1-xN/GaN multiple quantum wells (MQW)/n-GaN nanowires (NWs) on Si(111) substrates grown by metal-organic chemical vapor deposition (MOCVD) technique. The resultant nanowires (NWs), with a diameter of 200-250 nm, have an average length of 2 μm. The feasibility of growing high-quality NWs with well-controlled indium composition MQW structure is demonstrated. These resultant NWs grown on Si(111) substrates were utilized for fabricating vertical-type light-emitting diodes (LEDs). The steep and intense photoluminescence (PL) and cathodoluminescence (CL) spectra are observed, based on the strain-free NWs on Si(111) substrates. High-resolution transmission electron microscopy (HR-TEM) analysis revealed that the MQW NWs are grown along the c-plane with uniform thickness. The current-voltage (I-V) characteristics of these NWs exhibited typical p-n junction LEDs and showed a sharp onset voltage at 2.75 V in the forward bias. The output power is linearly increased with increasing current. The result indicates that the pulsed MOCVD technique is an effective method to grow uniaxial p-GaN/InxGa1-xN/GaN MQW/n-GaN NWs on Si(111), which is more advantageous than other growth techniques, such as molecular beam epitaxy. These results suggest the uniaxial NWs are promising to allow flat-band quantum structures, which can enhance the efficiency of LEDs. PMID:23432423

  20. Metal nanoparticle-enhanced photocurrent in GaAs photovoltaic structures with microtextured interfaces.

    PubMed

    Dmitruk, Nicolas L; Borkovskaya, Olga Yu; Mamontova, Iryna B; Mamykin, Sergii V; Malynych, Sergii Z; Romanyuk, Volodymyr R

    2015-01-01

    The photocurrent enhancement effect caused by Au and Ag nanoparticles for GaAs-based photovoltaic structures of surface barrier or p-n junction type with microtextured interfaces has been investigated in dependence on the conditions of nanoparticles deposition and, respectively, on the shape and local dielectric environment of obtained nanoparticle arrays. Three nanoparticle deposition methods have been checked: 1) photoinduced chemical deposition of Au from aqueous AuCl3 solution forming nanowires on the ridges of quasigrating-type surface microrelief, 2) deposition of Ag nanoparticles from colloidal suspension on the GaAs substrate covered with poly(vinylpyridine), and 3) drop and dry deposition of Au/SiO2 core-shell nanoparticles from aqueous colloid solution. The comprehensive investigation of optical reflectance, photoelectric, and electrical characteristics of the fabricated barrier structures has shown the highest photovoltaic parameters for surface microrelief of quasigrating-type and electroless Au nanoparticle deposition. The analysis of characteristics obtained allowed us also to define the mechanisms of the total photocurrent enhancement. PMID:25852368

  1. 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.

  2. Growth and Structural Characteristics of CuGaSe2 Films Fabricated from Metallic Precursors Followed by an Elemental Se Reaction Process.

    PubMed

    Jung, Sangkyo; Kim, Jeha

    2016-05-01

    We investigated the growth, structural and optical characteristics of CuGaSe2 thin films prepared with the selenium reaction. Metallic precursor layers from Cu0:5Ga0.5 and Cu0.8Ga0.2 alloy targets were prepared on a sodalime glass substrate by using DC magnetron sputtering, and then annealed to form CuGaSe2 in a rapid thermal process (RTP) with selenium radicals generated by a thermal cracker. The base and sputtering pressures were < 5 x 10(-7) Torr and 30 mTorr, respectively. At ambient temperature, the precursors from the Cu0.5Ga0.5 and Cu0.8Ga0.2 targets were deposited at the rates of 42 nm/min. and 45 nm/min., respectively. The film thicknesses were about 300 nm. Selenization was carried out at different annealing temperatures of T(a) = 450 degrees C, 500 degrees C, 550 degrees C, and 600 degrees C for time periods of 15 min., 30 min., and 60 min. We found that high quality CuGaSe2 films of crystal grains (-1 μm in dia.) fabricated with a reaction using elemental Se at temperatures as low as 450 degrees C for 30 min. When T(a) ≤ 350 degrees C, the Se reaction was insufficient to form CuGaSe2. However, the annealing time had little effect on the formation of CuGaSe2 at T(a) ≥ 450 degrees C. For all the samples, the photoluminescence (PL) emission was only from the donor-acceptor interband transition D1A1 for all the composition ratios of the films [Ga]/[Cu] -1. PMID:27483915

  3. Oxidative addition of group 13 and 14 metal halides and Alkyls to Ga(DDP) (DDP = bulky bisimidinate).

    PubMed

    Kempter, Andreas; Gemel, Christian; Fischer, Roland A

    2008-08-18

    The oxidative addition of a variety of group 13 and group 14 halides and alkyls R aMX to the mono valent group 13 bis-imidinate Ga(DDP) (DDP = 2-{(2,6-diisopropyl-phenyl)amino}-4-{(2,6-diisopropylphenyl)imino}-2-pentene) is reported. Accordingly, the insertion of Ga(DDP) into the Ga-Me bond of GaMe 3 yield in the complexes [{(DDP)GaMe}GaMe 2] ( 1) and [{(DDP)GaMe} 2GaMe] ( 2), respectively, which show a temperature-dependent equilibrium between 1 at higher temperatures and 2 at lower temperatures. In the case of GaCl 3, the only isolable product is [{(DDP)GaCl} 2GaCl] ( 3). The related reaction of SnMe 2Cl 2 with Ga(DDP) yields the compound [Me 2Sn{ClGa(DDP)} 2] ( 4), whereas SnMe 4 behaves inert. In the case of SiCl 4, only the monoinsertion product [Cl 3Si{ClGa(DDP)}] ( 5) was observed. Finally, [(CH 3) 3C{ClGa(DDP)}] ( 6) is synthesized by insertion of Ga(DDP) into the C-Cl bond of ClC(CH 3) 3. All new compounds were fully characterized by elemental analysis, NMR-spectroscopy, and single-crystal X-ray diffraction analysis. PMID:18630902

  4. Operation of the GaSb p-channel metal-oxide-semiconductor field-effect transistors fabricated on (111)A surfaces

    SciTech Connect

    Nishi, K. Takenaka, M.; Takagi, S.; Yokoyama, M.; Yokoyama, H.; Hoshi, T.; Sugiyama, H.

    2014-12-08

    We demonstrate the operation of GaSb p-channel metal-oxide-semiconductor field-effect transistors (p-MOSFETs) on (111)A surfaces with Al{sub 2}O{sub 3} gate dielectrics formed by atomic-layer deposition at 150 °C. The p-MOSFETs on (111)A surfaces exhibit higher drain current and lower subthreshold swing than those on (100) surfaces. We find that the interface-state density (D{sub it}) values at the Al{sub 2}O{sub 3}/GaSb MOS interfaces on the (111)A surfaces are lower than those on the (100) surfaces, which can lead to performance enhancement of the GaSb p-MOSFETs on (111)A surfaces. The mobility of the GaSb p-MOSFETs on (111)A surfaces is 80% higher than that on (100) surfaces.

  5. Mobility enhancement of strained GaSb p-channel metal-oxide-semiconductor field-effect transistors with biaxial compressive strain

    NASA Astrophysics Data System (ADS)

    Yan-Wen, Chen; Zhen, Tan; Lian-Feng, Zhao; Jing, Wang; Yi-Zhou, Liu; Chen, Si; Fang, Yuan; Wen-Hui, Duan; Jun, Xu

    2016-03-01

    Various biaxial compressive strained GaSb p-channel metal-oxide-semiconductor field-effect transistors (MOSFETs) are experimentally and theoretically investigated. The biaxial compressive strained GaSb MOSFETs show a high peak mobility of 638 cm2/V·s, which is 3.86 times of the extracted mobility of the fabricated GaSb MOSFETs without strain. Meanwhile, first principles calculations show that the hole effective mass of GaSb depends on the biaxial compressive strain. The biaxial compressive strain brings a remarkable enhancement of the hole mobility caused by a significant reduction in the hole effective mass due to the modulation of the valence bands. Project supported by the National Basic Research Program of China (Grant No. 2011CBA00602) and the National Science and Technology Major Project of the Ministry of Science and Technology of China (Grant No. 2011ZX02708-002).

  6. Metal organic vapour-phase epitaxy growth of GaN wires on Si (111) for light-emitting diode applications

    PubMed Central

    2013-01-01

    GaN wires are grown on a Si (111) substrate by metal organic vapour-phase epitaxy on a thin deposited AlN blanket and through a thin SiNx layer formed spontaneously at the AlN/Si interface. N-doped wires are used as templates for the growth of core-shell InGaN/GaN multiple quantum wells coated by a p-doped shell. Standing single-wire heterostructures are connected using a metallic tip and a Si substrate backside contact, and the electroluminescence at room temperature and forward bias is demonstrated at 420 nm. This result points out the feasibility of lower cost nitride-based wires for light-emitting diode applications. PMID:23391377

  7. Buffer Therapy for Cancer

    PubMed Central

    Ribeiro, Maria de Lourdes C; Silva, Ariosto S.; Bailey, Kate M.; Kumar, Nagi B.; Sellers, Thomas A.; Gatenby, Robert A.; Ibrahim-Hashim, Arig; Gillies, Robert J.

    2013-01-01

    Oral administration of pH buffers can reduce the development of spontaneous and experimental metastases in mice, and has been proposed in clinical trials. Effectiveness of buffer therapy is likely to be affected by diet, which could contribute or interfere with the therapeutic alkalinizing effect. Little data on food pH buffering capacity was available. This study evaluated the pH and buffering capacity of different foods to guide prospective trials and test the effect of the same buffer (lysine) at two different ionization states. Food groups were derived from the Harvard Food Frequency Questionnaire. Foods were blended and pH titrated with acid from initial pH values until 4.0 to determine “buffering score”, in mmol H+/pH unit. A “buffering score” was derived as the mEq H+ consumed per serving size to lower from initial to a pH 4.0, the postprandial pH of the distal duodenum. To differentiate buffering effect from any metabolic byproduct effects, we compared the effects of oral lysine buffers prepared at either pH 10.0 or 8.4, which contain 2 and 1 free base amines, respectively. The effect of these on experimental metastases formation in mice following tail vein injection of PC-3M prostate cancer cells were monitored with in vivo bioluminescence. Carbohydrates and dairy products’ buffering score varied between 0.5 and 19. Fruits and vegetables showed a low to zero buffering score. The score of meats varied between 6 and 22. Wine and juices had negative scores. Among supplements, sodium bicarbonate and Tums® had the highest buffering capacities, with scores of 11 and 20 per serving size, respectively. The “de-buffered” lysine had a less pronounced effect of prevention of metastases compared to lysine at pH 10. This study has demonstrated the anti-cancer effects of buffer therapy and suggests foods that can contribute to or compete with this approach to manage cancer. PMID:24371544

  8. In-situ metalorganic chemical vapor deposition and capacitance-voltage characterizations of Al2O3 on Ga-face GaN metal-oxide-semiconductor capacitors

    NASA Astrophysics Data System (ADS)

    Liu, X.; Yeluri, R.; Kim, J.; Lal, S.; Raman, A.; Lund, C.; Wienecke, S.; Lu, J.; Laurent, M.; Keller, S.; Mishra, U. K.

    2013-07-01

    The in-situ metalorganic chemical vapor deposition of Al2O3 on Ga-face GaN metal-oxide-semiconductor capacitors (MOSCAPs) is reported. Al2O3 is grown using trimethylaluminum and O2 in the same reactor as GaN without breaking the vacuum. The in-situ MOSCAPs are subjected to a series of capacitance-voltage measurements combined with stress and ultraviolet-assisted techniques, and the results are discussed based on the presence of near-interface states with relatively fast and slow electron emission characteristics. The in-situ MOSCAPs with Al2O3 grown at 900 and 1000 °C exhibit very small hystereses and charge trappings as well as average near-interface state densities on the order of 1012 cm-2eV-1.

  9. Nd0.5Bi2.5Fe5- y Ga y O12 thin films on Gd3Ga5O12 substrates prepared by metal-organic decomposition

    NASA Astrophysics Data System (ADS)

    Sasaki, Michimasa; Lou, Gengjian; Liu, Qi; Ninomiya, Minami; Kato, Takeshi; Iwata, Satoshi; Ishibashi, Takayuki

    2016-05-01

    Highly Bi-substituted neodymium iron gallium garnet thin films with a Bi content of 2.5, Nd0.5Bi2.5Fe5- y Ga y O12 (NBIGG) with y = 0-1, on gadolinium gallium garnet (111) and (100) substrates have been prepared by metal-organic decomposition. Magnetic properties and magnetic anisotropy energies were measured using an alternating field gradient magnetometer and by magnetic torque measurement, respectively. Faraday rotation spectra and hysteresis loops were measured using a Faraday rotation spectrometer. The magnetization of NBIGG thin films exhibiting a large Faraday rotation of 10-15°/µm decreased with increasing Ga content, resulting in increased effective magnetic anisotropy energy K eff. The dependence of the magnetic anisotropies on the Ga content is discussed in terms of the reverse magnetostrictive effect caused by thermal stress as well as the magnetocrystalline and shape anisotropies.

  10. Metal-organic vapor-phase epitaxy-grown ultra-low density InGaAs/GaAs quantum dots exhibiting cascaded single-photon emission at 1.3 μm

    SciTech Connect

    Paul, Matthias Kettler, Jan; Zeuner, Katharina; Clausen, Caterina; Jetter, Michael; Michler, Peter

    2015-03-23

    By metal-organic vapor-phase epitaxy, we have fabricated InGaAs quantum dots on GaAs substrate with an ultra-low lateral density (<10{sup 7} cm{sup −2}). The photoluminescence emission from the quantum dots is shifted to the telecom O-band at 1.31 μm by an InGaAs strain reducing layer. In time-resolved measurements, we find fast decay times for exciton (∼600 ps) and biexciton (∼300 ps). We demonstrate triggered single-photon emission (g{sup (2)}(0)=0.08) as well as cascaded emission from the biexciton decay. Our results suggest that these quantum dots can compete with their counterparts grown by state-of-the-art molecular beam epitaxy.

  11. InGaP/GaAs Inverted Dual Junction Solar Cells For CPV Applications Using Metal-Backed Epitaxial Lift-Off

    SciTech Connect

    Bauhuis, Gerard J.; Mulder, Peter; Haverkamp, Erik J.; Schermer, John J.; Nash, Lee J.; Fulgoni, Dominic J. F.; Ballard, Ian M.; Duggan, Geoffrey

    2010-10-14

    The epitaxial lift-off (ELO) technique has been combined with inverted III-V PV cell epitaxial growth with the aim of employing thin film PV cells in HCPV systems. In a stepwise approach to the realization of an inverted triple junction on a MELO platform we have first grown a GaAs single junction PV cell to establish the basic layer release process and cell processing steps followed by the growth, fabrication and test of an inverted InGaP/GaAs dual junction structure.

  12. New MBE (molecular beam epitaxy) buffer used to eliminate backgating in gaas mesfets

    SciTech Connect

    Smith, F.W.; Calawa, A.R.; Chen, C.L.; Manfra, M.J.; Mahoney, L.J.

    1988-02-01

    A new buffer layer has been developed that eliminates backgating between MESFET's fabricated in active layers grown upon it. The new buffer is grown by molecular beam epitaxy (MBE) at low substrate temperatures (150-300 C) using Ga and As4 beam fluxes. It is highly resistive, optically inactive, and crystalline, and high-quality GaAs active layers can be grown on top of the new buffer. MESFET's fabricated in active layers grown on top of this new buffer show improved output resistance and breakdown voltages; the dc and Rf characteristics are otherwise comparable to MESFET's fabricated by alternative means and with other buffer layers.

  13. Hydrogenation-Induced Structure and Property Changes in the Rare-Earth Metal Gallide NdGa: Evolution of a [GaH]2- Polyanion Containing Peierls-like Ga-H Chains.

    PubMed

    Ångström, Jonas; Johansson, Robert; Sarkar, Tapati; Sørby, Magnus H; Zlotea, Claudia; Andersson, Mikael S; Nordblad, Per; Scheicher, Ralph H; Häussermann, Ulrich; Sahlberg, Martin

    2016-01-01

    The hydride NdGaH1+x (x ≈ 0.66) and its deuterized analogue were obtained by sintering the Zintl phase NdGa with the CrB structure in a hydrogen atmosphere at pressures of 10-20 bar and temperatures near 300 °C. The system NdGa/NdGaH1+x exhibits reversible H storage capability. H uptake and release were investigated by kinetic absorption measurements and thermal desorption mass spectroscopy, which showed a maximum H concentration corresponding to "NdGaH2" (0.93 wt % H) and a two-step desorption process, respectively. The crystal structure of NdGaH1+x was characterized by neutron diffraction (P21/m, a = 4.1103(7), b = 4.1662(7), c = 6.464(1) Å, β = 108.61(1)° Z = 2). H incorporates in NdGa by occupying two distinct positions, H1 and H2. H1 is coordinated in a tetrahedral fashion by Nd atoms. The H2 position displays flexible occupancy, and H2 atoms attain a trigonal bipyramidal coordination by centering a triangle of Nd atoms and bridging two Ga atoms. The phase stability and electronic structure of NdGaH1+x were analyzed by first-principles DFT calculations. NdGaH1H2 (NdGaH2) may be expressed as Nd(3+)(H1(-))[GaH2](2-). The two-dimensional polyanion [GaH](2-) features linear -H-Ga-H-Ga- chains with alternating short (1.8 Å) and long (2.4 Å) Ga-H distances, which resembles a Peierls distortion. H2 deficiency (x < 1) results in the fragmentation of chains. For x = 0.66 arrangements with five-atom moieties, Ga-H-Ga-H-Ga are energetically most favorable. From magnetic measurements, the Curie-Weiss constant and effective magnetic moment of NdGaH1.66 were obtained. The former indicates antiferromagnetic interactions, and the latter attains a value of ∼3.6 μB, which is typical for compounds containing Nd(3+) ions. PMID:26669218

  14. Quantum Griffiths singularity of superconductor-metal transition in Ga thin films.

    PubMed

    Xing, Ying; Zhang, Hui-Min; Fu, Hai-Long; Liu, Haiwen; Sun, Yi; Peng, Jun-Ping; Wang, Fa; Lin, Xi; Ma, Xu-Cun; Xue, Qi-Kun; Wang, Jian; Xie, X C

    2015-10-30

    The Griffiths singularity in a phase transition, caused by disorder effects, was predicted more than 40 years ago. Its signature, the divergence of the dynamical critical exponent, is challenging to observe experimentally. We report the experimental observation of the quantum Griffiths singularity in a two-dimensional superconducting system. We measured the transport properties of atomically thin gallium films and found that the films undergo superconductor-metal transitions with increasing magnetic field. Approaching the zero-temperature quantum critical point, we observed divergence of the dynamical critical exponent, which is consistent with the Griffiths singularity behavior. We interpret the observed superconductor-metal quantum phase transition as the infinite-randomness critical point, where the properties of the system are controlled by rare large superconducting regions. PMID:26472763

  15. Nanoscale InGaN/GaN on ZnO substrate for LED applications

    NASA Astrophysics Data System (ADS)

    Hung, I.-Hsiang; Lan, You-Ren; Wu, Tsung Han; Feng, Zhe Chuan; Li, Nola; Yu, Hongbo; Ferguson, Ian T.; Lu, Weijie

    2009-08-01

    The challenge of growing GaN and its alloys, In1-xGaxN and Al1-xGaxN, is still formidable because of the lack of close lattice match, stacking order match, and similar thermal expansion coefficient substrates, the same as GaN-based optoelectronic materials. ZnO is the most promising optoelectronic materials in the next generation, with wide band gap of 3.3eV and exciton binding energy of 60meV. In addition, ZnO also has been considered as a substrate for epitaxial growth of III-Nitrides due to its close lattice and stacking order match. Our works cover the growth of n-type InGaN and GaN epitaxial layers on lattice-matched ZnO substrates by metal-organic chemical vapor deposition (MOCVD). Since MOCVD is the dominant growth technology for GaN-based materials and devices, there is a need to more fully explore this technique for ZnO substrates. However, the thermal stability of the ZnO substrate, out-diffusion of Zn from the ZnO into the GaN, and H2 back etching into the substrate can cause growth of poor quality GaN. We use a GaN buffer layer of about 40nm to avoid Zn/O diffusion. We can investigate the Zn/O diffusion in the InGaN epilayers by means of second ion mass spectroscopy (SIMS) depth profiles, and analyze the surface bonding of different elements by x-ray photoelectron spectroscopy (XPS), and investigate optical and structural characterization of InGaN epilayers on ZnO substrates by various angles spectroscopic ellipsometry (VASE). Finally, from the Raman scattering, Photoluminescence (PL) and Photoluminescence excitation (PLE) spectra, we can determine the qualities easily and prove that we have grown the InGaN on ZnO with a GaN buffer layer successfully.

  16. Growth of non-polar InGaN quantum dots with an underlying AlN/GaN distributed Bragg reflector by metal-organic vapour phase epitaxy

    NASA Astrophysics Data System (ADS)

    Zhu, Tongtong; Griffiths, James T.; Fu, Wai Yuen; Howkins, Ashley; Boyd, Ian W.; Kappers, Menno J.; Oliver, Rachel A.

    2015-12-01

    Non-polar (11-20) InGaN quantum dots (QDs) have been grown using a modified droplet epitaxy method by metal-organic vapour phase epitaxy on top of a 15-period AlN/GaN distributed Bragg reflector (DBR) on a-plane GaN pseudo-substrate prepared by epitaxial lateral overgrowth (ELOG), in which the QDs are located at the centre of a ca. 180 nm GaN layer. The AlN/GaN DBR has shown a peak reflectivity of ∼80% at a wavelength of ∼454 nm with a 49 nm wide, flat stop-band. Variations in layer thicknesses observed by cross-sectional scanning transmission electron microscopy have been identified as the main source of degradation of the DBR reflectivity. The presence of trenches due to incomplete coalescence of the ELOG template and the formation of cracks due to relaxation of tensile strain during the DBR growth may distort the DBR and further reduce the reflectivity. The DBR top surface is very smooth and does not have a detrimental effect on the subsequent growth of QDs. Enhanced single QD emission at 20 K was observed in cathodoluminescence.

  17. Nonpolar AlGaN/GaN HFETs with a normally off operation

    NASA Astrophysics Data System (ADS)

    Ishida, M.; Kuroda, M.; Ueda, T.; Tanaka, T.

    2012-02-01

    Nonpolar AlGaN/GaN heterojunction field-effect transistors (HFETs) with a normally off operation have been demonstrated. The nonpolar (1-120) a-plane's epitaxial layers are grown on (1-102) r-plane sapphire substrates by metal organic chemical vapour deposition. We have found that a thicker AlN buffer layer achieves a GaN layer with a narrower full-width at half-maximum of the x-ray rocking curve and higher electron mobility. We have fabricated AlGaN/GaN HFETs with different gate directions. It is found that the drain current strongly depends on the gate directions, and higher drain current flows to the (0001) direction that is parallel to the hair-lined morphology. To realize a complete normally off operation, we have fabricated a-plane metal-insulator-semiconductor HFETs (MIS-HFETs) with a 2 nm-thick SiN as an insulator. The fabricated MIS-HFET exhibits a threshold voltage of +1.3 V with a high drain current of 112 mA mm-1. The presented MIS-HFETs will be desirable in next-generation power switching applications.

  18. Growth and characterization of Al xGa 1-xN via NH 3-based metal-organic molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Billingsley, Daniel; Henderson, Walter; Pritchett, David; Alan Doolittle, W.

    2009-02-01

    Growth and characterization of ammonia-based metal-organic molecular beam epitaxy (NH 3-MOMBE) Al xGa 1-xN epitaxial films has been conducted. Al xGa 1-xN films spanning the entire range of aluminum compositions were grown on GaN templates. This is the first reported successful growth of Al xGa 1-xN via NH 3-MOMBE, using triethylgallium (TEGa), triethylaluminum (TEAl) and ammonia (NH 3) as the precursors. These films were characterized via optical interferometry (OI), atomic force microscopy (AFM), X-ray diffraction (XRD) and scanning electron microscopy (SEM). High-quality Al xGa 1-xN films, as inferred by XRD, are achievable in films without cracking. The catalytic effect of Al on NH 3 is found to play a major part in the growth rate of the Al xGa 1-xN films. The excessive nitrogen produced through this catalytic effect hinders the growth rate at lower Al composition while increasing the growth rate of Al xGa 1-xN ( x>0.4) films. Stress in the deposited films is found to be partially relieved through surface cracking along the <1 1 2¯ 0> direction in the film. These cracks provide dislocation gettering centers, with the dislocation pit density decreasing with increasing Al composition. A basic understanding on the factors affecting the growth of Al xGa 1-xN is determined and will become the basis for further investigations into the optimization of Al xGa 1-xN growth.

  19. Analysis of twin defects in GaAs nanowires and tetrahedra and their correlation to GaAs(1 1 1)B surface reconstructions in selective-area metal organic vapour-phase epitaxy

    NASA Astrophysics Data System (ADS)

    Yoshida, Hiroatsu; Ikejiri, Keitaro; Sato, Takuya; Hara, Shinjiroh; Hiruma, Kenji; Motohisa, Junichi; Fukui, Takashi

    2009-12-01

    We analyzed twin defects in GaAs nanowires as thin as 100-400 nm and tetrahedral structures as small as 1.0 μm, which were selectively grown by metal organic vapour-phase epitaxy (MOVPE) within a SiO 2 mask window fabricated on GaAs(1 1 1)B substrates. In particular, we focused on the correlation between the twins and GaAs(1 1 1)B surface reconstructions. We confirmed that the shape of GaAs crystals selectively grown on GaAs(1 1 1)B substrates changed from hexagonal nanowires to truncated tetrahedra when the size of the mask opening was increased from 100 to 1000 nm under the same growth conditions. The shape also changed from tetrahedral to hexagonal with decreasing growth temperature ( Tg: 600-800 °C) and with increasing arsine (AsH 3) partial pressure (1.0×10 -4 to 5.0×10 -4 atm). Rotational twins around the <1 1 1> axis were found in the tetrahedra by transmission electron microscopy (TEM) and scanning electron microscopy observations. In addition, the probability of twins developing in the tetrahedra increased with decreasing mask opening size, with decreasing Tg, and with increasing AsH 3 partial pressure. The TEM study also revealed the existence of a high density of rotational twins in the nanowires, and their density increased with decreasing nanowire diameter, suggesting a correlation between the twins and the shape/size of GaAs crystals. These findings were semi-quantitatively compared with a reported phase diagram for GaAs(1 1 1)B surface reconstruction. By analyzing the relationship between twin development and MOVPE conditions, we found that the shape change of GaAs crystals on GaAs(1 1 1)B and the formation of twins coincided well with the transition of GaAs surface reconstruction between the (2×2) and (√19×√19) structures.

  20. Influence of thermal treatment on the formation of ohmic contacts based on Ti/Al/Ni/Au metallization to n-type AlGaN/GaN heterostructures

    NASA Astrophysics Data System (ADS)

    Macherzyński, W.; Paszkiewicz, B.; Vincze, A.; Paszkiewicz, R.; Tłaczała, M.; Kováč, J.

    2012-12-01

    Interfacial reactions between Ti/Al/Ni/Au metallization and GaN(cap)/AlGaN/GaN heterostructures at various annealing temperatures ranging from 715 to 865 °C were studied. Electrical current-voltage (I-V) characteristics, van der Pauw Hall mobility measurements and surface topography measurement with atomic force microscopy (AFM) were performed. The ohmic metallizations were annealed at various temperatures in a rapid thermal annealing system and the annealing time of 60 seconds was kept for all samples. To study the influence of the parameters of annealing process on the properties of the 2 dimensional electron gas (2DEG) the van der Pauw Hall mobility measurement was used. Interfacial reactions between the contact metals and heterostructures were analyzed through depth profiles of secondary ion mass spectroscopy. It was observed that transition from nonlinear to linear I-V behavior occurred after the annealing at 805 °C. For the studied samples, the most promising results were obtained for the annealing temperature of 805 °C. This temperatue ensured not only low contact resistance but also made possible to preserve the 2DEG.

  1. ZnO/Cu(InGa)Se.sub.2 solar cells prepared by vapor phase Zn doping

    DOEpatents

    Ramanathan, Kannan; Hasoon, Falah S.; Asher, Sarah E.; Dolan, James; Keane, James C.

    2007-02-20

    A process for making a thin film ZnO/Cu(InGa)Se.sub.2 solar cell without depositing a buffer layer and by Zn doping from a vapor phase, comprising: depositing Cu(InGa)Se.sub.2 layer on a metal back contact deposited on a glass substrate; heating the Cu(InGa)Se.sub.2 layer on the metal back contact on the glass substrate to a temperature range between about 100.degree. C. to about 250.degree. C.; subjecting the heated layer of Cu(InGa)Se.sub.2 to an evaporant species from a Zn compound; and sputter depositing ZnO on the Zn compound evaporant species treated layer of Cu(InGa)Se.sub.2.

  2. Ultraviolet photoconductive devices with an n-GaN nanorod-graphene hybrid structure synthesized by metal-organic chemical vapor deposition

    PubMed Central

    Kang, San; Mandal, Arjun; Chu, Jae Hwan; Park, Ji-Hyeon; Kwon, Soon-Yong; Lee, Cheul-Ro

    2015-01-01

    The superior photoconductive behavior of a simple, cost-effective n-GaN nanorod (NR)-graphene hybrid device structure is demonstrated for the first time. The proposed hybrid structure was synthesized on a Si (111) substrate using the high-quality graphene transfer method and the relatively low-temperature metal-organic chemical vapor deposition (MOCVD) process with a high V/III ratio to protect the graphene layer from thermal damage during the growth of n-GaN nanorods. Defect-free n-GaN NRs were grown on a highly ordered graphene monolayer on Si without forming any metal-catalyst or droplet seeds. The prominent existence of the undamaged monolayer graphene even after the growth of highly dense n-GaN NRs, as determined using Raman spectroscopy and high-resolution transmission electron microscopy (HR-TEM), facilitated the excellent transport of the generated charge carriers through the photoconductive channel. The highly matched n-GaN NR-graphene hybrid structure exhibited enhancement in the photocurrent along with increased sensitivity and photoresponsivity, which were attributed to the extremely low carrier trap density in the photoconductive channel. PMID:26028318

  3. Direct synthesis of organometallics V. Direct synthesis of isopropylcyclopentadienyl M(I) compounds of Ga, Tl, Mn and Cu via metal vapour cocondensation, and their spectroscopic characterization

    NASA Astrophysics Data System (ADS)

    Tacke, Matthias; Teuber, Roland

    1997-06-01

    The cocondensation of metal atoms of Ga, Tl, Cu and Mn with 6,6-dimethylfulvene leads to the formation of Cp iM(I) derivatives (Cp i = C 5H 4CHMe 2) which need — in the case of Cu and Mn — trimethylphosphite as a co-ligand to fill up their coordination sphere. It is remarkable that the synthesis of the thermolabile Cp iGa(I) is possible by using the newly developed cocondensation vessel with a cooled internal drain. The species is stable in solution up to -30°C and is therefore characterized by its 71Ga NMR and MS spectrum and the following reactions. The reaction is believed to pass through a metal fulvene complex in a first step, which is characterized for Ga by quantum mechanical methods. For the gallium case a tucked-in η 6 bonding mode with formation of Ga(II), instead of coordination to an η 5 cylopentadienyl or η 4 fulvene, is observed. ? Following the formation of this first intermediate, a complete mechanism is developed by using semiempirical calculations. The resulting geometries and reaction enthalpies are discussed in comparison with the reaction of tin atoms with the fulvene, which ends in the formation of ansa-stannocene. In contrast to this reaction, the cocondensation of cobalt atoms with 6,6-dimethylfulvene in the presence of trimethylphosphite ends in the formation of CoH(P(OMe) 3) 4 instead of a half-sandwich complex.

  4. Superior material qualities and transport properties of InGaN channel heterostructure grown by pulsed metal organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Ya-Chao, Zhang; Xiao-Wei, Zhou; Sheng-Rui, Xu; Da-Zheng, Chen; Zhi-Zhe, Wang; Xing, Wang; Jin-Feng, Zhang; Jin-Cheng, Zhang; Yue, Hao

    2016-01-01

    Pulsed metal organic chemical vapor deposition is introduced into the growth of InGaN channel heterostructure for improving material qualities and transport properties. High-resolution transmission electron microscopy imaging shows the phase separation free InGaN channel with smooth and abrupt interface. A very high two-dimensional electron gas density of approximately 1.85 × 1013 cm-2 is obtained due to the superior carrier confinement. In addition, the Hall mobility reaches 967 cm2/V·s, owing to the suppression of interface roughness scattering. Furthermore, temperature-dependent Hall measurement results show that InGaN channel heterostructure possesses a steady two-dimensional electron gas density over the tested temperature range, and has superior transport properties at elevated temperatures compared with the traditional GaN channel heterostructure. The gratifying results imply that InGaN channel heterostructure grown by pulsed metal organic chemical vapor deposition is a promising candidate for microwave power devices. Project supported by the National Natural Science Foundation of China (Grant Nos. 61306017, 61334002, 61474086, and 11435010) and the Young Scientists Fund of the National Natural Science Foundation of China (Grant No. 61306017).

  5. Thermodynamic stability, magnetism and half metallicity of Mn2CoAl/GaAs(0 0 1) interface

    NASA Astrophysics Data System (ADS)

    Feng, Yu; Zhou, Ting; Chen, Xiaorui; Yuan, Hongkuan; Chen, Hong

    2015-07-01

    Interface properties of the heterojunction which is composed of the inverse Heusler alloy Mn2 CoAl and semiconductor GaAs are investigated by employing the first-principles density functional simulations. Two kinds of interface structures, namely the top-type and bridge-type structure by connecting termination of nine Mn2 CoAl layers to the top of the As-terminated GaAs layer and bridge site between interface As atoms are respectively built. Our calculations reveal that, as for the structure with the same interface atoms, different atoms sitting directly on top of the interface As atom will lead to different interface magnetism and electronic structures. The calculated phase diagram reveals that the top-type structure including natural MnCo or MnAl termination is stable only when the interface Mn or interface Al atom directly locates on top of the As atom. Besides, bridge-type and top-type structures containing a pure Mn interface are always thermodynamically accessible regardless of values of the chemical potential of Mn and Co. The atom-resolved spin magnetic moments of most interface magnetic atoms are enhanced due to the rehybridization caused by symmetry breaking at the interface. Further analyses on electronic structures indicate that, owing to the interface effect, the interface half metallicity of all structures are completely destroyed. However, the top-type structure with MnAl termination where the interface Al atom directly sits on top of the As atom preserves the highest interface spin polarization of 80%, indicating that it has more advantages in spintronics application than other atomic terminations.

  6. Gate-control efficiency and interface state density evaluated from capacitance-frequency-temperature mapping for GaN-based metal-insulator-semiconductor devices

    SciTech Connect

    Shih, Hong-An; Kudo, Masahiro; Suzuki, Toshi-kazu

    2014-11-14

    We present an analysis method for GaN-based metal-insulator-semiconductor (MIS) devices by using capacitance-frequency-temperature (C-f-T) mapping to evaluate the gate-control efficiency and the interface state density, both exhibiting correlations with the linear-region intrinsic transconductance. The effectiveness of the method was exemplified by application to AlN/AlGaN/GaN MIS devices to elucidate the properties of AlN-AlGaN interfaces depending on their formation processes. Using the C-f-T mapping, we extract the gate-bias-dependent activation energy with its derivative giving the gate-control efficiency, from which we evaluate the AlN-AlGaN interface state density through the Lehovec equivalent circuit in the DC limit. It is shown that the gate-control efficiency and the interface state density have correlations with the linear-region intrinsic transconductance, all depending on the interface formation processes. In addition, we give characterization of the AlN-AlGaN interfaces by using X-ray photoelectron spectroscopy, in relation with the results of the analysis.

  7. Effective surface treatment for GaN metal-insulator-semiconductor high-electron-mobility transistors using HF plus N2 plasma prior to SiN passivation

    NASA Astrophysics Data System (ADS)

    Liu, Shih-Chien; Trinh, Hai-Dang; Dai, Gu-Ming; Huang, Chung-Kai; Dee, Chang-Fu; Yeop Majlis, Burhanuddin; Biswas, Dhrubes; Chang, Edward Yi

    2016-01-01

    An effective surface cleaning technique is demonstrated for the GaN metal-insulator-semiconductor high-electron-mobility transistor (MIS-HEMT) passivation process. In this study, dilute HF solution and in situ N2 plasma treatments were adopted to remove the native oxide and recover the nitrogen-vacancy defects at the GaN surface before device passivation. To investigate the correlation between the properties of the SiN/GaN interface and the device performance, the GaN MIS-HEMTs were characterized using current-voltage (I-V) measurement, capacitance-voltage (C-V) measurement, and X-ray photoelectron spectroscopy (XPS) analysis. With the application of this surface treatment technique, the device exhibits improved I-V characteristics with low leakage current, low dynamic ON-resistance, and good C-V response with a steep slope. Overall, the results reveal that the oxide-related bonds and nitrogen-vacancy defects at the SiN/GaN interface are the root cause of the GaN MIS-HEMTs performance degradation.

  8. Metal-assisted electroless fabrication of nanoporous p-GaN for increasing the light extraction efficiency of light emitting diodes

    SciTech Connect

    Wang Ruijun; Liu Duo; Zuo Zhiyuan; Yu Qian; Feng Zhaobin; Xu Xiangang

    2012-03-15

    We report metal-assisted electroless fabrication of nanoporous p-GaN to improve the light extraction efficiency of GaN-based light emitting diodes (LEDs). Although it has long been believed that p-GaN cannot be etched at room temperature, in this study we find that Ag nanocrystals (NCs) on the p-GaN surface enable effective etching of p-GaN in a mixture of HF and K{sub 2}S{sub 2}O{sub 8} under ultraviolet (UV) irradiation. It is further shown that the roughened GaN/air interface enables strong scattering of photons emitted from the multiple quantum wells (MQWs). The light output power measurements indicate that the nanoporous LEDs obtained after 10 min etching show a 32.7% enhancement in light-output relative to the conventional LEDs at an injection current of 20 mA without significant increase of the operating voltage. In contrast, the samples etched for 20 min show performance degradation when compared with those etched for 10 min, this is attributed to the current crowding effect and increased surface recombination rate.

  9. Effect of long anneals on the densities of threading dislocations in GaN films grown by metal-organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Chen, Z. T.; Xu, K.; Guo, L. P.; Yang, Z. J.; Su, Y. Y.; Yang, X. L.; Pan, Y. B.; Shen, B.; Zhang, H.; Zhang, G. Y.

    2006-09-01

    Effect of long anneals on densities of different types of threading dislocations (TDs) in GaN films grown onto sapphire substrate by metal-organic chemical vapor deposition was investigated by high-resolution X-ray diffraction. The results showed that the densities of both types of TDs changed obviously but oppositely, and residual stress in the GaN films was relaxed by generating edge-type TDs instead of screw-type TDs. The results obtained from chemical etching experiments and grazing-incidence X-ray diffraction (GIXRD) also supported the proposed defect structure evolution.

  10. Nitride passivation reduces interfacial traps in atomic-layer-deposited Al2O3/GaAs (001) metal-oxide-semiconductor capacitors using atmospheric metal-organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Aoki, T.; Fukuhara, N.; Osada, T.; Sazawa, H.; Hata, M.; Inoue, T.

    2014-07-01

    Using an atmospheric metal-organic chemical vapor deposition system, we passivated GaAs with AlN prior to atomic layer deposition of Al2O3. This AlN passivation incorporated nitrogen at the Al2O3/GaAs interface, improving the capacitance-voltage (C-V) characteristics of the resultant metal-oxide-semiconductor capacitors (MOSCAPs). The C-V curves of these devices showed a remarkable reduction in the frequency dispersion of the accumulation capacitance. Using the conductance method at various temperatures, we extracted the interfacial density of states (Dit). The Dit was reduced over the entire GaAs band gap. In particular, these devices exhibited Dit around the midgap of less than 4 × 1012 cm-2eV-1, showing that AlN passivation effectively reduced interfacial traps in the MOS structure.

  11. Ridge InGaAs/InP multi-quantum-well selective growth in nanoscale trenches on Si (001) substrate

    NASA Astrophysics Data System (ADS)

    Li, S.; Zhou, X.; Li, M.; Kong, X.; Mi, J.; Wang, M.; Wang, W.; Pan, J.

    2016-01-01

    Metal organic chemical vapor deposition of InGaAs/InP multi-quantum-well in nanoscale V-grooved trenches on Si (001) substrate was studied using the aspect ratio trapping method. A high quality GaAs/InP buffer layer with two convex {111} B facets was selectively grown to promote the highly uniform, single-crystal ridge InP/InGaAs multi-quantum-well structure growth. Material quality was confirmed by transmission electron microscopy and room temperature micro-photoluminescence measurements. This approach shows great promise for the fabrication of photonics devices and nanolasers on Si substrate.

  12. Zinc sensing by metal-responsive transcription factor 1 (MTF1) controls metallothionein and ZnT1 expression to buffer the sensitivity of the transcriptome response to zinc.

    PubMed

    Hardyman, J E J; Tyson, J; Jackson, K A; Aldridge, C; Cockell, S J; Wakeling, L A; Valentine, R A; Ford, D

    2016-03-01

    Only a small number of genes are known direct targets of the zinc-responsive transcription factor MTF1; therefore, the aim of this study was to gain a more complete understanding of the MTF-1 regulated zinc-responsive component of the transcriptome. A targeted siRNA was used to deplete MTF1 expression in the human intestinal cell line Caco-2. We predicted that the response to zinc of direct MTF1 target genes would be abrogated by MTF1 knockdown. Surprisingly, a greater number of genes were regulated by zinc following MFT1 knockdown, and most genes that responded to zinc under both control and MTF1-depleted conditions had an augmented response in the latter condition. Exceptions were the zinc effluxer ZnT1 and a suite of metallothionein genes, suggesting that responses of other genes to zinc are usually buffered by increases in these proteins. We propose that MTF1 heads a hierarchy of zinc sensors, and through controlling the expression of a raft of metallothioneins and other key proteins involved in controlling intracellular zinc levels (e.g. ZnT1) alters zinc buffering capacity and total cellular zinc content. We tested and validated this model by overexpressing metallothionein and observing the predicted curtailment in response of the zinc-repressed SLC30A5 (ZnT5) promoter. The model provides the framework for an integrated understanding of cellular zinc homeostasis. Because MTs can bind metals other than zinc, this framework links with overall cellular metal homeostasis. PMID:26824222

  13. Phase equilibrium modeling for high temperature metallization on GaAs solar cells

    NASA Technical Reports Server (NTRS)

    Chung, M. A.; Davison, J. E.; Smith, S. R.

    1991-01-01

    Recent trends in performance specifications and functional requirements have brought about the need for high temperature metallization technology to be developed for survivable DOD space systems and to enhance solar cell reliability. The temperature constitution phase diagrams of selected binary and ternary systems were reviewed to determine the temperature and type of phase transformation present in the alloy systems. Of paramount interest are the liquid-solid and solid-solid transformations. Data are being utilized to aid in the selection of electrical contact materials to gallium arsenide solar cells. Published data on the phase diagrams for binary systems is readily available. However, information for ternary systems is limited. A computer model is being developed which will enable the phase equilibrium predictions for ternary systems where experimental data is lacking.

  14. GaAs metal-oxide-semiconductor based non-volatile flash memory devices with InAs quantum dots as charge storage nodes

    NASA Astrophysics Data System (ADS)

    Islam, Sk Masiul; Chowdhury, Sisir; Sarkar, Krishnendu; Nagabhushan, B.; Banerji, P.; Chakraborty, S.; Mukherjee, Rabibrata

    2015-06-01

    Ultra-thin InP passivated GaAs metal-oxide-semiconductor based non-volatile flash memory devices were fabricated using InAs quantum dots (QDs) as charge storing elements by metal organic chemical vapor deposition technique to study the efficacy of the QDs as charge storage elements. The grown QDs were embedded between two high-k dielectric such as HfO2 and ZrO2, which were used for tunneling and control oxide layers, respectively. The size and density of the QDs were found to be 5 nm and 1.8×1011 cm-2, respectively. The device with a structure Metal/ZrO2/InAs QDs/HfO2/GaAs/Metal shows maximum memory window equivalent to 6.87 V. The device also exhibits low leakage current density of the order of 10-6 A/cm2 and reasonably good charge retention characteristics. The low value of leakage current in the fabricated memory device is attributed to the Coulomb blockade effect influenced by quantum confinement as well as reduction of interface trap states by ultra-thin InP passivation on GaAs prior to HfO2 deposition.

  15. GaAs metal-oxide-semiconductor based non-volatile flash memory devices with InAs quantum dots as charge storage nodes

    SciTech Connect

    Islam, Sk Masiul Chowdhury, Sisir; Sarkar, Krishnendu; Nagabhushan, B.; Banerji, P.; Chakraborty, S.

    2015-06-24

    Ultra-thin InP passivated GaAs metal-oxide-semiconductor based non-volatile flash memory devices were fabricated using InAs quantum dots (QDs) as charge storing elements by metal organic chemical vapor deposition technique to study the efficacy of the QDs as charge storage elements. The grown QDs were embedded between two high-k dielectric such as HfO{sub 2} and ZrO{sub 2}, which were used for tunneling and control oxide layers, respectively. The size and density of the QDs were found to be 5 nm and 1.8×10{sup 11} cm{sup −2}, respectively. The device with a structure Metal/ZrO{sub 2}/InAs QDs/HfO{sub 2}/GaAs/Metal shows maximum memory window equivalent to 6.87 V. The device also exhibits low leakage current density of the order of 10{sup −6} A/cm{sup 2} and reasonably good charge retention characteristics. The low value of leakage current in the fabricated memory device is attributed to the Coulomb blockade effect influenced by quantum confinement as well as reduction of interface trap states by ultra-thin InP passivation on GaAs prior to HfO{sub 2} deposition.

  16. Introduction of Artificial Pinning Center into PLD-YBCO Coated Conductor on IBAD and Self-Epitaxial CeO2 Buffered Metal Substrate

    SciTech Connect

    Kobayashi, H.; Yamada, Y.; Ishida, S.; Takahashi, K.; Konishi, M.; Ibi, A.; Miyata, S.; Kato, T.; Hirayama, T.; Shiohara, Y.

    2006-03-31

    In order to fabricate YBa2Cu3O7-x (YBCO) coated conductors with high critical current density Jc in magnetic fields, we fabricated YBCO coated conductors with artificial pinning centers by the pulsed laser deposition (PLD) method on a self epitaxial PLD-CeO2 layer and ion-beam assisted deposition (IBAD)-Gd2Zr2O7 (GZO) buffered Hastelloy tape. Artificial pinning centers were introduced by the PLD deposition using the yttria-stabilized zirconia (YSZ) oxide target (nano-dot method) and YBCO target including YSZ particles (mixed target method). In the experiments using YSZ oxide target, YSZ nano-dots were observed. They were approximately 15 nm in height and 10 nm to 70 nm in diameter. We found that the density of nano-dots was controlled by the number of laser pulses. These samples exhibited higher Jc than YBCO films in magnetic fields. Furthermore, a similar improvement of Jc was observed in the experiments using YBCO target including YSZ particles. TEM observation revealed that columnar nano-structure made of BaZrO3 was formed during YBCO deposition and it was effective for pinning. We call this new epitaxial nano-structure 'bamboo structure' from its anisotropic growth and morphology.

  17. Facile Formation of High-Quality InGaN/GaN Quantum-Disks-in-Nanowires on Bulk-Metal Substrates for High-Power Light-Emitters.

    PubMed

    Zhao, Chao; Ng, Tien Khee; Wei, Nini; Prabaswara, Aditya; Alias, Mohd S; Janjua, Bilal; Shen, Chao; Ooi, Boon S

    2016-02-10

    High-quality nitride materials grown on scalable and low-cost metallic substrates are considerably attractive for high-power light-emitters. We demonstrate here, for the first time, the high-power red (705 nm) InGaN/GaN quantum-disks (Qdisks)-in-nanowire light-emitting diodes (LEDs) self-assembled directly on metal-substrates. The LEDs exhibited a low turn-on voltage of ∼2 V without efficiency droop up to injection current of 500 mA (1.6 kA/cm(2)) at ∼5 V. This is achieved through the direct growth and optimization of high-quality nanowires on titanium (Ti) coated bulk polycrystalline-molybdenum (Mo) substrates. We performed extensive studies on the growth mechanisms, obtained high-crystal-quality nanowires, and confirmed the epitaxial relationship between the cubic titanium nitride (TiN) transition layer and the hexagonal nanowires. The growth of nanowires on all-metal stack of TiN/Ti/Mo enables simultaneous implementation of n-metal contact, reflector, and heat sink, which greatly simplifies the fabrication process of high-power light-emitters. Our work ushers in a practical platform for high-power nanowires light-emitters, providing versatile solutions for multiple cross-disciplinary applications that are greatly enhanced by leveraging on the chemical stability of nitride materials, large specific surface of nanowires, chemical lift-off ready layer structures, and reusable Mo substrates. PMID:26745217

  18. Development of a Au-free process using Mo-based metallization for high-power AlGaN/GaN-on-Si heterostructure field-effect transistors

    NASA Astrophysics Data System (ADS)

    Choi, Shinhyuk; Lee, Jae-Gil; Kang, Youngjin; Cha, Ho-Young; Kim, Hyungtak; Cho, Chun-Hyung

    2014-08-01

    A Au-free ohmic contact process for fabricating AlGaN/GaN heterostructure field-effect transistors (HFETs) on Si substrates was developed by using Mo-based metallization. We investigated Si/Ti/Al/Mo metal stacks for ohmic metallization where the Ti/Al thickness ratio and the annealing temperature were varied. The optimized metal stack and annealing conditions were a Si/Ti/Al/Mo stack with 5/40/60/50 nm thicknesses and rapid thermal annealing in a N2 ambient at 900 °C for 30 sec, which resulted in a contact resistance of 1.24 Ω·mm, a sheet resistance of 410 Ω/sq and a specific contact resistivity of 3.76 × 10-5 Ω·cm2. Devices fabricated using the optimized Mo-based, Au-free ohmic contact process exhibited comparable characteristics with higher breakdown voltage to those of devices fabricated using a conventional Au-based ohmic contact process.

  19. Metal Organic Vapor Phase Epitaxy of Monolithic Two-Color Light-Emitting Diodes Using an InGaN-Based Light Converter

    NASA Astrophysics Data System (ADS)

    Damilano, Benjamin; Kim-Chauveau, Hyonju; Frayssinet, Eric; Brault, Julien; Hussain, Sakhawat; Lekhal, Kaddour; Vennéguès, Philippe; De Mierry, Philippe; Massies, Jean

    2013-09-01

    Monolithic InGaN-based light-emitting diodes (LEDs) using a light converter fully grown by metal organic vapor phase epitaxy are demonstrated. The light converter, consisting of 10-40 InGaN/GaN quantum wells, is grown first, followed by a violet pump LED. The structure and growth conditions of the pump LED are specifically adapted to avoid thermal degradation of the light converter. Electroluminescence analysis shows that part of the pump light is absorbed by the light converter and reemitted at longer wavelength. Depending on the emission wavelength of the light converter, different LED colors are achieved. In particular, for red-emitting light converters, a color temperature of 2100 K corresponding to a tint between warm white and candle light is demonstrated.

  20. Multi-frequency inversion-charge pumping for charge separation and mobility analysis in high-k/InGaAs metal-oxide-semiconductor field-effect transistors

    SciTech Connect

    Djara, V.; Cherkaoui, K.; Negara, M. A.; Hurley, P. K.

    2015-11-28

    An alternative multi-frequency inversion-charge pumping (MFICP) technique was developed to directly separate the inversion charge density (N{sub inv}) from the trapped charge density in high-k/InGaAs metal-oxide-semiconductor field-effect transistors (MOSFETs). This approach relies on the fitting of the frequency response of border traps, obtained from inversion-charge pumping measurements performed over a wide range of frequencies at room temperature on a single MOSFET, using a modified charge trapping model. The obtained model yielded the capture time constant and density of border traps located at energy levels aligned with the InGaAs conduction band. Moreover, the combination of MFICP and pulsed I{sub d}-V{sub g} measurements enabled an accurate effective mobility vs N{sub inv} extraction and analysis. The data obtained using the MFICP approach are consistent with the most recent reports on high-k/InGaAs.

  1. Performance enhancement of GaN metal–semiconductor–metal ultraviolet photodetectors by insertion of ultrathin interfacial HfO{sub 2} layer

    SciTech Connect

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

    2015-03-15

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

  2. Direct-current and radio-frequency characterizations of GaAs metal-insulator-semiconductor field-effect transistors enabled by self-assembled nanodielectrics

    NASA Astrophysics Data System (ADS)

    Lin, H. C.; Kim, S. K.; Chang, D.; Xuan, Y.; Mohammadi, S.; Ye, P. D.; Lu, G.; Facchetti, A.; Marks, T. J.

    2007-08-01

    Direct-current and radio-frequency characterizations of GaAs metal-insulator-semiconductor field-effect transistors (MISFETs) with very thin self-assembled organic nanodielectrics (SANDs) are presented. The application of SAND on compound semiconductors offers unique opportunities for high-performance devices. Thus, 1μm gate-length depletion-mode n-channel SAND/GaAs MISFETs exhibit low gate leakage current densities of 10-2-10-5A/cm2, a maximum drain current of 260mA/mm at 2V forward gate bias, and a maximum intrinsic transconductance of 127mS/mm. These devices achieve a current cutoff frequency (fT) of 10.6GHz and a maximum oscillation frequency (fmax) of 6.9GHz. Nearly hysteresis-free Ids-Vgs characteristics and low flicker noise indicate that a high-quality SAND-GaAs interface is achieved.

  3. Fixed charge and trap states of in situ Al2O3 on Ga-face GaN metal-oxide-semiconductor capacitors grown by metalorganic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Liu, X.; Kim, J.; Yeluri, R.; Lal, S.; Li, H.; Lu, J.; Keller, S.; Mazumder, B.; Speck, J. S.; Mishra, U. K.

    2013-10-01

    In situ Al2O3 on Ga-face GaN metal-oxide-semiconductor capacitors (MOSCAPs) were grown by metalorganic chemical vapor deposition and measured using capacitance-voltage techniques. The flat band voltage and hysteresis had a linear relationship with Al2O3 thickness, which indicates the presence of fixed charge and trap states that are located at or near the Al2O3/GaN interface. In addition, slow and fast near-interface states are distinguished according to their different electron emission characteristics. Atom probe tomography was used to characterize the in situ MOSCAPs to provide information on the Al/O stoichiometric ratios, Al2O3/GaN interface abruptnesses, and C concentrations. The in situ MOSCAPs with Al2O3 deposited at 700 °C exhibited an order of magnitude higher fast near-interface states density but a lower slow near-interface states density compared with those with Al2O3 deposited at 900 and 1000 °C. Furthermore, the 700 °C MOSCAPs exhibited a net negative fixed near-interface charge, whereas the 900 and 1000 °C MOSCAPs exhibited net positive fixed near-interface charges. The possible origins of various fixed charge and trap states are discussed in accordance with the experimental data and recently reported first-principals calculations.

  4. Comparative study on interface and bulk charges in AlGaN/GaN metal-insulator-semiconductor heterostructures with Al2O3, AlN, and Al2O3/AlN laminated dielectrics

    NASA Astrophysics Data System (ADS)

    Zhu, Jie-Jie; Ma, Xiao-Hua; Chen, Wei-Wei; Hou, Bin; Xie, Yong; Hao, Yue

    2016-05-01

    In this paper, the interface and bulk charges in AlGaN/GaN metal-insulator-semiconductor (MIS) heterostructures with AlN, Al2O3, and Al2O3/AlN laminated dielectrics were studied. In situ plasma pretreatment resulted negligible interface trap states and voltage hysteresis. The fixed charge density at Al2O3/AlN (or Al2O3/barrier) interface was estimated to be 1.66 × 1013 cm-2 by using flat-band voltage shift, and the oxide bulk charge concentration was 2.86 × 1017 cm-3. The interface charge density at other interfaces were at the order of 1011 cm-2. Simulation results using the above charge density/concentration indicated that Al2O3/AlN interface fixed charges dominated the dielectric-related voltage shift in AlGaN/GaN MIS heterostructures, which caused a large voltage shift of -3 V with 10 nm Al2O3 thickness, while the flat-band voltage variety resulting from other types of charges was within 0.1 V.

  5. Influence of metamorphic buffer design on electrophysical and structural properties of MHEMT nanoheterostructures In0.7Al0.3As/In0.7Ga0.3As/In0.7Al0.3As/GaAs

    NASA Astrophysics Data System (ADS)

    Pushkarev, S. S.; Galiev, G. B.; Klimov, E. A.; Lavrukhin, D. V.; Vasil'evskii, I. S.; Imamov, R. M.; Subbotin, I. A.; Zhigalina, O. M.; Zhigalina, V. G.; Buffat, P. A.; Dwir, B.; Suvorova, E. I.

    2013-01-01

    Metamorphic InхAl1-хAs buffer design influence on electrophysical and structural properties of the MHEMT nanoheterostructures was investigated. Electrophysical properties of the nanoheterostructures were characterized by Hall measurements, while the structural features were described with the help of transmission electron microscopy. The strained superlattices inserted in the metamorphic buffer are shown to filter threading dislocations preventing their penetration in active region. Moreover, the increase of period number in superlattices enhances such effect. Step-graded metamorphic buffer permitted to reach the minimal surface roughness with rather high electron mobility.

  6. The SVT Hit Buffer

    SciTech Connect

    Belforte, S.; Dell`Orso, M.; Donati, S.

    1996-06-01

    The Hit Buffer is part of the Silicon Vertex Tracker, a trigger processor dedicated to the reconstruction of particle trajectories in the Silicon Vertex Detector and the Central Tracking Chamber of the Collider Detector at Fermilab. The Hit Buffer is a high speed data-traffic node, where thousands of words are received in arbitrary order and simultaneously organized in an internal structured data base, to be later promptly retrieved and delivered in response to specific requests. The Hit Buffer is capable of processing data at a rate of 25 MHz, thanks to the use of special fast devices like Cache-Tag RAMs and high performance Erasable Programmable Logic Devices from the XILINX XC7300 family.

  7. A modeling approach for the purification of group III metals (Ga and In) by zone refining

    SciTech Connect

    Ghosh, K.; Dhar, S.; Mani, V. N.

    2008-07-15

    An 'experimental friendly' model for zone refining process is proposed which predicts effective zone length in each refining passes that would lead to maximal solute removal, thereby leading to ultrapurification of the material for use in high-end electronic applications. The effectiveness of the model is experimentally tested and validated by purifying gallium from 4N (99.99%) to 6N5 (99.99995%) purity level at 30% yield and {approx}6 N at 70% yield with respect to targeted metallic impurities such as, Zn, Cu, Al, Ca, Bi, Si, Pb, Ni, Mn, and Fe, as analyzed by inductively coupled plasma optical emission spectrometry, graphite furnace atomic absorption spectrometry, and high resolution inductively coupled plasma mass spectrometry techniques. The distribution coefficient (k) of all the targeted impurities, detected in the purified gallium, was found to be less than 1. By comparing the experimentally obtained axial concentration profiles with the theoretical calculations, the k values of some detected impurities, such as Ca and Al, are determined to be {approx}0.8, Pb and Bi to be 0.7, Cu to be 0.65, and Fe to be 0.68, which prove the efficiency of the proposed model in reducing the concentration of these vulnerable impurities significantly. Following the model and as evidenced from the theoretical predictions, degradation of material purification containing a mixture of impurities having k less than as well as greater than 1 was elucidated experimentally by zone refining of 4N6 indium. Only a 40% yield of 5N6 indium was obtained, thereby highlighting the intricacies and problem areas in ultrapurification of these types of material.

  8. Damage free Ar ion plasma surface treatment on In0.53Ga0.47As-on-silicon metal-oxide-semiconductor device

    NASA Astrophysics Data System (ADS)

    Koh, Donghyi; Shin, Seung Heon; Ahn, Jaehyun; Sonde, Sushant; Kwon, Hyuk-Min; Orzali, Tommaso; Kim, Dae-Hyun; Kim, Tae-Woo; Banerjee, Sanjay K.

    2015-11-01

    In this paper, we investigated the effect of in-situ Ar ion plasma surface pre-treatment in order to improve the interface properties of In0.53Ga0.47As for high-κ top-gate oxide deposition. X-ray photoelectron spectroscopy (XPS) and metal-oxide-semiconductor capacitors (MOSCAPs) demonstrate that Ar ion treatment removes the native oxide on In0.53Ga0.47As. The XPS spectra of Ar treated In0.53Ga0.47As show a decrease in the AsOx and GaOx signal intensities, and the MOSCAPs show higher accumulation capacitance (Cacc), along with reduced frequency dispersion. In addition, Ar treatment is found to suppress the interface trap density (Dit), which thereby led to a reduction in the threshold voltage (Vth) degradation during constant voltage stress and relaxation. These results outline the potential of surface treatment for III-V channel metal-oxide-semiconductor devices and application to non-planar device process.

  9. The effect of post oxide deposition annealing on the effective work function in metal/Al{sub 2}O{sub 3}/InGaAs gate stack

    SciTech Connect

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

    2014-05-19

    The effect of post oxide deposition annealing on the effective work function in metal/Al{sub 2}O{sub 3}/ InGaAs gate stacks was investigated. Using a systematic method for effective work function extraction, a shift of 0.3 ± 0.1 eV was found between the effective work function of forming gas annealed samples and vacuum annealed samples. The electrical measurements enabled us to obtain the band alignment of the metal/Al{sub 2}O{sub 3}/InGaAs gate stack. This band alignment was confirmed by X-ray photoelectron spectroscopy. The measured shift in the effective work function between different annealing ambient may be attributed to indium out-diffusion during post oxide deposition annealing that is observed in forming gas anneal to a much larger extent than in vacuum.

  10. Recycling of metal-organic chemical vapor deposition waste of GaN based power device and LED industry by acidic leaching: Process optimization and kinetics study

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

    Recovery of metal values from GaN, a metal-organic chemical vapor deposition (MOCVD) waste of GaN based power device and LED industry is investigated by acidic leaching. Leaching kinetics of gallium rich MOCVD waste is studied and the process is optimized. The gallium rich waste MOCVD dust is characterized by XRD and ICP-AES analysis followed by aqua regia digestion. Different mineral acids are used to find out the best lixiviant for selective leaching of the gallium and indium. Concentrated HCl is relatively better lixiviant having reasonably faster kinetic and better leaching efficiency. Various leaching process parameters like effect of acidity, pulp density, temperature and concentration of catalyst on the leaching efficiency of gallium and indium are investigated. Reasonably, 4 M HCl, a pulp density of 50 g/L, 100 °C and stirring rate of 400 rpm are the effective optimum condition for quantitative leaching of gallium and indium.

  11. Optical conductivity measurements of GaTa4Se8 under high pressure: evidence of a bandwidth-controlled insulator-to-metal Mott transition.

    PubMed

    Ta Phuoc, V; Vaju, C; Corraze, B; Sopracase, R; Perucchi, A; Marini, C; Postorino, P; Chligui, M; Lupi, S; Janod, E; Cario, L

    2013-01-18

    The optical properties of a GaTa(4)Se(8) single crystal are investigated under high pressure. At ambient pressure, the optical conductivity exhibits a charge gap of ≈0.12 eV and a broad midinfrared band at ≈0.55 eV. As pressure is increased, the low energy spectral weight is strongly enhanced and the optical gap is rapidly filled, pointing to an insulator to metal transition around 6 GPa. The overall evolution of the optical conductivity demonstrates that GaTa(4)Se(8) is a Mott insulator which undergoes a bandwidth-controlled Mott metal-insulator transition under pressure, in remarkably good agreement with theory. With the use of our optical data and ab initio band structure calculations, our results were successfully compared to the (U/D, T/D) phase diagram predicted by dynamical mean field theory for strongly correlated systems. PMID:23373949

  12. Phosphor-free white-light emitters using in-situ GaN nanostructures grown by metal organic chemical vapor deposition

    PubMed Central

    Min, Daehong; Park, Donghwy; Jang, Jongjin; Lee, Kyuseung; Nam, Okhyun

    2015-01-01

    Realization of phosphor-free white-light emitters is becoming an important milestone on the road to achieve high quality and reliability in high-power white-light-emitting diodes (LEDs). However, most of reported methods have not been applied to practical use because of their difficulties and complexity. In this study we demonstrated a novel and practical growth method for phosphor-free white-light emitters without any external processing, using only in-situ high-density GaN nanostructures that were formed by overgrowth on a silicon nitride (SiNx) interlayer deposited by metal organic chemical vapor deposition. The nano-sized facets produced variations in the InGaN thickness and the indium concentration when an InGaN/GaN double heterostructure was monolithically grown on them, leading to white-color light emission. It is important to note that the in-situ SiNx interlayer not only facilitated the GaN nano-facet structure, but also blocked the propagation of dislocations. PMID:26626890

  13. Engel-Vosko GGA Approach Within DFT Investigations of the Optoelectronic Structure of the Metal Chalcogenide Semiconductor CsAgGa2Se4

    NASA Astrophysics Data System (ADS)

    Azam, Sikander; Khan, Saleem Ayaz; Goumri-Said, Souraya

    2016-01-01

    Metal chalcogenide semiconductors have a significant role in the development of materials for energy and nanotechnology applications. First principle calculations were applied on CsAgGa2Se4 to investigate its optoelectronic structure and bonding characteristics, using the full-potential linear augmented plane wave method within the framework of generalized gradient approximations (GGA) and Engel-Vosko GGA functionals (EV-GGA). The band structure from EV-GGA shows that the valence band maximum and conduction band minimum are situated at Γ with a band gap value of 2.15 eV. A mixture of orbitals from Ag 4 p 6/4 d 10, Se 3 d 10, Ga 4 p 1, Se 4 p 4 , and Ga 4 s 2 states have a primary role to lead to a semiconducting character of the present chalcogenide. The charge density iso-surface shows a strong covalent bonding between Ag-Se and Ga-Se atoms. The imaginary part of dielectric constant reveals that the threshold (first optical critical point) energy of dielectric function occurs 2.15 eV. It is obvious that with a direct large band gap and large absorption coefficient, CsAgGa2Se4 might be considered a potential material for photovoltaic applications.

  14. Phosphor-free white-light emitters using in-situ GaN nanostructures grown by metal organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Min, Daehong; Park, Donghwy; Jang, Jongjin; Lee, Kyuseung; Nam, Okhyun

    2015-12-01

    Realization of phosphor-free white-light emitters is becoming an important milestone on the road to achieve high quality and reliability in high-power white-light-emitting diodes (LEDs). However, most of reported methods have not been applied to practical use because of their difficulties and complexity. In this study we demonstrated a novel and practical growth method for phosphor-free white-light emitters without any external processing, using only in-situ high-density GaN nanostructures that were formed by overgrowth on a silicon nitride (SiNx) interlayer deposited by metal organic chemical vapor deposition. The nano-sized facets produced variations in the InGaN thickness and the indium concentration when an InGaN/GaN double heterostructure was monolithically grown on them, leading to white-color light emission. It is important to note that the in-situ SiNx interlayer not only facilitated the GaN nano-facet structure, but also blocked the propagation of dislocations.

  15. Parameters study on the growth of GaAs nanowires on indium tin oxide by metal-organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Wu, Dan; Tang, Xiaohong; Wang, Kai; Olivier, Aurelien; Li, Xianqiang

    2016-03-01

    After successful demonstration of GaAs nanowire (NW) epitaxial growth on indium tin oxide (ITO) by metal organic chemical vapor deposition, we systematically investigate the effect of growth parameters' effect on the GaAs NW, including temperature, precursor molar flow rates, growth time, and Au catalyst size. 40 nm induced GaAs NWs are observed with zinc-blende structure. Based on vapor-liquid-solid mechanism, a kinetic model is used to deepen our understanding of the incorporation of growth species and the role of various growth parameters in tuning the GaAs NW growth rate. Thermally activated behavior has been investigated by variation of growth temperature. Activation energies of 40 nm Au catalyst induced NWs are calculated at different trimethylgallium (TMGa) molar flow rates about 65 kJ/mol. The GaAs NWs growth rates increase with TMGa molar flow rates whereas the growth rates are almost independent of growth time. Due to Gibbs-Thomson effect, the GaAs NW growth rates increase with Au nanoparticle size at different temperatures. Critical radius is calculated as 2.14 nm at the growth condition of 430 °C and 1.36 μmol/s TMGa flow rate. It is also proved experimentally that Au nanoparticle below the critical radius such as 2 nm cannot initiate the growth of NWs on ITO. This theoretical and experimental growth parameters investigation enables great controllability over GaAs NWs grown on transparent conductive substrate where the methodology can be expanded to other III-V material NWs and is critical for potential hybrid solar cell application.

  16. Self-limiting growth when using trimethyl bismuth (TMBi) in the metal-organic vapor phase epitaxy (MOVPE) of GaAs1-yBiy

    NASA Astrophysics Data System (ADS)

    Forghani, Kamran; Guan, Yingxin; Wood, Adam W.; Anand, Amita; Babcock, Susan E.; Mawst, Luke J.; Kuech, Thomas F.

    2014-06-01

    Theoretical and experimental studies have confirmed that the GaAs1-yBiy semiconductor alloy system has potential for long wavelength applications and devices with improved performance over other materials emitting at similar wavelengths. The growth of GaAs1-yBiy by metal-organic vapor phase epitaxy (MOVPE) remains a challenge; bismuth is not easily incorporated into the GaAs matrix due the large difference in electronegativity and covalent radii between As and Bi. These differences often lead to Bi surface segregation or very low incorporation rates of Bi into the GaAs matrix. We have studied the growth of GaAs1-yBiy quantum well structures using trimethyl bismuth as the Bi source. A reduced growth rate is observed with increasing Bi precursor flux into the growth reactor. Additionally, an increase in the growth time for the Bi-containing layer at very low growth temperatures does not lead to a corresponding increase in layer thickness, which is indicative of a near self-limiting growth. Complex compositional profiles deduced from combining x-ray diffraction analysis with the transmission electron microscopy investigations are used to develop a phenomenological model of the MOVPE growth of GaAs1-yBiy heterostructures which includes a complex interplay of the chemical surface species. The presence of a methyl-terminated surface, associated with the use of trimethyl Bi, particularly at low growth temperatures, leads to an effective “site blocking” by Bi precursor inhibiting the growth of GaAs1-yBiy hetero-structures.

  17. Inclined angle-controlled growth of GaN nanorods on m-sapphire by metal organic chemical vapor deposition without a catalyst

    NASA Astrophysics Data System (ADS)

    Lee, Kyuseung; Chae, Sooryong; Jang, Jongjin; Min, Daehong; Kim, Jaehwan; Eom, Daeyong; Yoo, Yang-Seok; Cho, Yong-Hoon; Nam, Okhyun

    2015-08-01

    In this study, we have intentionally grown novel types of (11-22)- and (1-10-3)-oriented3 and self-assembled inclined GaN nanorods (NRs) on (10-10) m-sapphire substrates using metal organic chemical vapor deposition without catalysts and ex situ patterning. Nitridation of the m-sapphire surface was observed to be crucial to the inclined angle as well as the growth direction of the GaN NRs. Polarity-selective KOH etching confirmed that both (11-22) and (1-10-3) GaN NRs are nitrogen-polar. Using pole figure measurements and selective area electron diffraction patterns, the epitaxial relationship between the inclined (11-22) and (1-10-3) GaN NRs and m-sapphire substrates was systematically demonstrated. Furthermore, it was verified that the GaN NRs were single-crystalline wurtzite structures. We observed that stacking fault-related defects were generated during the initial growth stage using high-resolution transmission electron microscopy. The blue-shift of the near band edge (NBE) peak in the inclined angle-controlled GaN NRs can be explained by a band filling effect through carrier saturation of the conduction band, resulting from a high Si-doping concentration; in addition, the decay time of NBE emission in (11-22)- and (1-10-3)-oriented NRs was much shorter than that of stacking fault-related emission. These results suggest that defect-free inclined GaN NRs can be grown on m-sapphire without ex situ treatment.

  18. Inclined angle-controlled growth of GaN nanorods on m-sapphire by metal organic chemical vapor deposition without a catalyst.

    PubMed

    Lee, Kyuseung; Chae, Sooryong; Jang, Jongjin; Min, Daehong; Kim, Jaehwan; Eom, Daeyong; Yoo, Yang-Seok; Cho, Yong-Hoon; Nam, Okhyun

    2015-08-21

    In this study, we have intentionally grown novel types of (11-22)- and (1-10-3)-oriented(3) and self-assembled inclined GaN nanorods (NRs) on (10-10) m-sapphire substrates using metal organic chemical vapor deposition without catalysts and ex situ patterning. Nitridation of the m-sapphire surface was observed to be crucial to the inclined angle as well as the growth direction of the GaN NRs. Polarity-selective KOH etching confirmed that both (11-22) and (1-10-3) GaN NRs are nitrogen-polar. Using pole figure measurements and selective area electron diffraction patterns, the epitaxial relationship between the inclined (11-22) and (1-10-3) GaN NRs and m-sapphire substrates was systematically demonstrated. Furthermore, it was verified that the GaN NRs were single-crystalline wurtzite structures. We observed that stacking fault-related defects were generated during the initial growth stage using high-resolution transmission electron microscopy. The blue-shift of the near band edge (NBE) peak in the inclined angle-controlled GaN NRs can be explained by a band filling effect through carrier saturation of the conduction band, resulting from a high Si-doping concentration; in addition, the decay time of NBE emission in (11-22)- and (1-10-3)-oriented NRs was much shorter than that of stacking fault-related emission. These results suggest that defect-free inclined GaN NRs can be grown on m-sapphire without ex situ treatment. PMID:26222432

  19. Valorization of GaN based metal-organic chemical vapor deposition dust a semiconductor power device industry waste through mechanochemical oxidation and leaching: A sustainable green process

    SciTech Connect

    Swain, Basudev; Mishra, Chinmayee; Lee, Chan Gi; Park, Kyung-Soo; Lee, Kun-Jae

    2015-07-15

    Dust generated during metal organic vapor deposition (MOCVD) process of GaN based semiconductor power device industry contains significant amounts of gallium and indium. These semiconductor power device industry wastes contain gallium as GaN and Ga{sub 0.97}N{sub 0.9}O{sub 0.09} is a concern for the environment which can add value through recycling. In the present study, this waste is recycled through mechanochemical oxidation and leaching. For quantitative recovery of gallium, two different mechanochemical oxidation leaching process flow sheets are proposed. In one process, first the Ga{sub 0.97}N{sub 0.9}O{sub 0.09} of the MOCVD dust is leached at the optimum condition. Subsequently, the leach residue is mechanochemically treated, followed by oxidative annealing and finally re-leached. In the second process, the MOCVD waste dust is mechanochemically treated, followed by oxidative annealing and finally leached. Both of these treatment processes are competitive with each other, appropriate for gallium leaching and treatment of the waste MOCVD dust. Without mechanochemical oxidation, 40.11 and 1.86 w/w% of gallium and Indium are leached using 4 M HCl, 100 °C and pulp density of 100 kg/m{sup 3,} respectively. After mechanochemical oxidation, both these processes achieved 90 w/w% of gallium and 1.86 w/w% of indium leaching at their optimum condition. - Highlights: • Waste MOCVD dust is treated through mechanochemical leaching. • GaN is hardly leached, and converted to NaGaO{sub 2} through ball milling and annealing. • Process for gallium recovery from waste MOCVD dust has been developed. • Thermal analysis and phase properties of GaN to Ga{sub 2}O{sub 3} and GaN to NaGaO{sub 2} is revealed. • Solid-state chemistry involved in this process is reported.

  20. Interfacial reaction between metal-insulator transition material NbO2 thin film and wide band gap semiconductor GaN

    NASA Astrophysics Data System (ADS)

    Posadas, Agham; Kvit, Alexander; Demkov, Alexander

    Materials that undergo a metal-insulator transition (MIT) are potentially useful for a wide variety of applications including electronic and opto-electronic switches, memristors, sensors, and coatings. In most such materials, the MIT is driven by temperature. In one such material, NbO2, the MIT mechanism is primarily of the Peierls-type, in which the dimerization of the Nb atoms without electron correlation causes the transition from metallic to semiconducting. We describe our initial work at combining NbO2 and GaN in epitaxial form, which could be potentially useful in resistive switching devices operating at very high temperatures. We grow NbO2 films on GaN(0001)/Si(111) substrates using reactive molecular beam epitaxy from a metal evaporation source and molecular oxygen. X-ray diffraction shows that the films are found to grow with a single out of plane orientation but with three symmetry-related orientation domains in the plane. In situ x-ray photoelectron spectroscopy confirms that the phase pure NbO2 is formed but that a chemical reaction occurs between the GaN and NbO2 during the growth forming a polycrystalline interfacial layer. We perform STEM-EELS analysis of the film and the interface to further elucidate their chemical and structural properties.