bluuebunny/crossref_metadata_2025_split huggingface dataset:
Photoresponse Study of Polycrystalline Diamond thin Film Schottky Diodes
Authors: Zhao G. , Stacy T. , Charlson E. M. , Charlson E. J. , Hajsaid M. , Roychoudhury R. , Khan A. H. , Meese J. M. , He Z. , Prelas M. 
Published: April 2011

ABSTRACTWe are reporting the first quantitative photoresponse characteristics of boron doped hot-filament CVD (HFCVD) diamond based Schottky diodes using semi-transparent aluminum contacts in the spectral range of 300–1050 nm. Quantum efficiencies, obtained without correction for surface reflection in the visible and near UV region, were between 5 % and 10% when the diodes were unbiased. Effect of reverse bias on the photoresponse was investigated at selected photon energies. Reverse biased diodes exhibit increasing photoresponse and ultimately saturation. Quantum efficiency as high as 30% was also obtained at 500 nm, when a reverse bias of over I volt was applied. The photoresponse mechanism of CVD diamond Schottky diodes is also discussed. A Schottky barrier height of 1.15 ± 0.02 eV for Al-HFCVD diamond contacts was determined using the d.c. photoelectric method.
Comparison of Thermal Gate Oxides on Silicon and Carbon Face P-Type 6H Silicon Carbide
Authors: Zetterling Carl-Mikael , Östling Mikael 
Published: April 2011

ABSTRACTMonocrystalline 6H silicon carbide samples (n-type and p-type) with both carbon face and silicon face have been used to investigate gate oxide quality. The oxides were thermally grown in a dry oxygen ambient at 1523 K with or without the addition of TCA (Trichloroethane), or in wet pyrogenic steam at 1473 K. POCI3 doped polysilicon gates were used for electrical characterisation by capacitance-voltage measurements and breakdown field measurements. Large flatband voltage shifts indicate fixed oxide charges up to 1013 cm-2. The incorporation of aluminum in the oxides was monitored using SIMS (Secondary Ion Mass Spectrometry). Surprisingly high signals were interpreted as evidence of an aluminum-Oxygen compound having been formed (ie Al2O3).
Process Analysis of AP-CVD of Silicon Carbide
Authors: Rottner K. , Helbig R. 
Published: April 2011

AbstractThe growth of SiC epilayers by atmospheric pressure CVD (AP-CVD) is influenced by many chemical gas phase reactions and transport phenomena, and is difficult to study directly due to the high growth temperatures (up to 2100 K). To grow epilayers of good quality, it is necessary to control the silicon and carbon supply, each affected by different mechanisms. The use of graphite as the susceptor material causes a remarkable change in the carbon balance due to reactions between the graphite and the hydrogen carrier gas. This graphite-hydrogen reaction enriches the gas phase with carbon and above a certain critical temperature it is impossible to control the Si:C-ratio in the gas phase by a variation of the carbon containing input gas. The silicon supply is usually treated as transport through a stagnant layer in the gas phase determined by the transport properties of the carrier gas and the temperature gradient in the reactor. A numerical solution of the flow-equations in the reactor shows that the flow characteristics and temperature gradients in the reactor are hardly affected by the gas flow velocity.
Laser Transformed SiC Thin Films
Authors: Kreider K. G. , Burgess D. R. F. , Tarlov M. J. , Gillen G. , Wight S. , Lareau R. , Casas L. M. 
Published: April 2011

ABSTRACTSilicon carbide has excellent physical and electronic properties for use in devices when higher temperatures or higher power densities are required. We have investigated a direct laser conversion technique to create electrical conductors on the high band-gap silicon carbide. Thin films of silicon carbide (SiC) were sputter deposited on AI2O3, SiO2, and Si substrates using a SiC target with an RF planar magnetron. These films were irradiated at 308 nm with multiple 15 ns excimer laser pulses creating 0.5 to 2 mm wide electrically conducting paths. Both the irradiated and unirradiated films were evaluated as a function of substrate type, deposition temperature, finish, stoichiomelry, annealing temperature, sputter gas, film thickness, and laser processing conditions. The lowest resistivity films, originally 10 ohm-m, were calculated to be 160 μohm-m obtained after irradiation, which compares to a value of 50 μohm-m obtained after irradiating bulk SiC. The films were characterized using XPS, SIMS, AES, SEM, and Raman spectroscopy. We were able to characterize the composition of the films and conducting traces, the surface oxide, the critical binding energies, the lattice structure, and the morphology of the microstructure. Models for the phase transformations and conductivity have been formulated.
Fundamental Materials-Issues involved in the Growth of GaN by Molecular Beam Epitaxy
Authors: Newman N. , Fu T.C , Liu X. , Liliental-Weber Z. , Rubin M. , Chan J. S. , Jones E. , Ross J. T. , Tidswell I. , Yu K. M. , Cheung N. , Weber E. R. 
Published: April 2011

AbstractGallium nitride is one of the most promising materials for ultraviolet and blue light-emitting diodes and lasers. Both Molecular Beam Epitaxy (MBE) and Metal-Organic Chemical Vapor Deposition (MOCVD) have recently made strong progress in fabricating high-quality epitaxial GaN thin films. In this paper, we review materials-related issues involved in MBE growth. We show that a strong understanding of the unique meta-stable growth process allows us to correctly predict the optimum conditions for epitaxial GaN growth. The resulting structural, electronic and optical properties of the GaN films are described in detail.
Structural Characterization of GaN Grown By Electron Cyclotron Resonance-Metalorganic Molecular Beam Epitaxy (ECR-MOMBE)
Authors: Bharatan S. , Jones K. S. , Pearton S. J. , Abernathy C. R. , Ren F. 
Published: April 2011

ABSTRACTElectron cyclotron resonance-metalorganic molecular beam epitaxy (ECR-MOMBE) has been used to deposit cubic and hexagonal gallium nitride (GaN) on various substrates, namely GaAs, ZnO and Al2O3. This paper will report on the effect of the growth rate of the GaN layer on the surface morphology, as analyzed using scanning electron microscopy (SEM). Structural characterization of this material was conducted using cross-sectional transmission electron microscopy (XTEM) and x-ray diffraction. Conditions such as pre-deposition annealing, growth rate and growth temperature are critical in determining the phase and crystallinity of the deposited layers. These parameters were optimized to obtain the cubic GaN phase on GaAs substrates and single crystal wurtzitic GaN on ZnO and Al2O3 substrates.
Raman Scattering and X-Ray Diffraction Studies of Gallium Nitride Films Grown on (100) Gallium Arsenide
Authors: Brown S. W. , Rand S. C. , Hong C.-H. , Pavlidis D. 
Published: April 2011

ABSTRACTRaman spectroscopy and x-ray diffraction are used to characterize Gallium Nitride (GaN) films grown on (100) Gallium Arsenide (GaAs) substrates. Reflection X-ray diffraction data from (200) planes of GaAs and cubic GaN are presented. The linewidth of the cubic GaN diffraction peak is shown to be a strong function of the growth temperature. Raman spectra are presented for a series of samples grown at different temperatures. Raman scattering is characterized by strong peaks at 560 cm-1 and at 736 cm-1, corresponding to TO and LO phonon modes of cubic GaN, respectively. An additional, unexplained feature at 768 cm-1 is clearly observed in Raman spectra of c-GaN samples grown at lower temperatures. The polarization dependence of the intensity of the GaN LO phonon mode is presented and compared with the GaAs LO phonon mode to establish the relative orientation of the c-GaN epitaxy on GaAs.
IR-Absorption Spectra of Impurities in 6H-SiC
Authors: Engelbrecht F. , Helbig R. 
Published: April 2011

ABSTRACTWe performed infrared absorption and reflectivity measurements on serverai 6H-SiC samples at variable temperatures between T=5K and T=300K. From the temperature dependence of the observed absorption lines we separated electronic from vibronic transitions. The electronic transitions are assumed to be due to transitions from the neutral nitrogen donor occupying the three different carbon lattice sites in 6H-SiC into excited states. We determined polarization and the oscillator strengths of these transitions. From the temperature dependence of the electronic transitions we determined the valley-orbit-splitting energy and we demonstrated the influence of compensation. For the different vibronic transitions we determined the Grüneisen constants.
Correlations Between Electrical and Material Properties of CVD Diamond
Authors: White C. , Zhao S. , Gan K. K. , Kagan H. , Kass R. , Malchow R. , Morrow F. , Palmer W. , Han S. , Kania D. , Pan L. S. , Schnetzer S. , Stone R. , Teserek R. , Angus J. , Ma S. J. , Sugimoto Y. 
Published: April 2011

ABSTRACTThe electrical properties associated with diamond charged particle- and photo-detectors were studied using charged particle-induced conductivity (CPIC) and photo-induced conductivity (PIC). The collection distance d, the product of the excess carrier mobility μ excess carrier lifetime T and electric field E, was used to characterize the diamonds. X-ray diffraction, Raman spectroscopy, photoluminescence, SEM and TEM were performed on CVD diamond detectors to investigate the limitations of the electrical properties. Correlations were found between the electrical properties and the material characterizations.
Conductivity Anisotropy in Epitaxial 6H and 4H Sic
Authors: Schaffer William J. , Negley G. H. , Irvine K. G. , Palmour J. W. 
Published: April 2011

ABSTRACTA measure of the electron mobility anisotropy in n-type 4H and 6H-SiC has been obtained using the Hall effect over the temperature range 80K<T<600K. Hall mobility and resistivity data are collected from appropriately oriented bar patterns fabricated into high quality epitaxial material grown on (1100) or (1120)surfaces having total impurity concentrations 1017-1018 cm-3. The observed mobility ratio for 4H is μ[1120]/[0001] and is independent of temperature. For 6H, the ratio μ[1100]/[0001] decreases from ∼6.2 at 80K to ∼5.0 at 150K and is essentially constant (∼4.8) above 200K. A donor level near 0.6 eV is occasionally observed in 4H which reduces the high temperature electron mobility and introduces an apparent temperature dependence to the mobility ratio if nonuniformly distributed.
Diffusion of Impurities Under Bias in CVD Diamond Films
Authors: Popovici G. , Sung T. , Prelas M. A. , Khasawinah S. , Wilson R. G. 
Published: April 2011

AbstractThe diffusion of oxygen, lithium, chlorine, and fluorine in CVD diamond films was performed under bias at 700 and 1000 °C. SIMS and Auger analyses were used to determine the impurity concentration. After diffusion, the concentrations of Li and O in the diamond films were found to be of the order of (3–4)×1019 cm-3. The fluorine concentration was of order of (l-2)×1017 cm-3. The conductivity was p-type. The change in the resistivity due to diffusion was nearly nine orders of magnitude for the sample diffused under electric field, and six orders of magnitude for the samples diffused without field. No dependence of the impurity concentration on the applied bias was observed except for fluorine. The fluorine concentration dependence on the electric field indicates that fluorine may have formed a shallow level in the diamond band gap. The fact that large concentrations of impurities can be diffused into diamond films at relatively low temperatures indicates the presence in the films of many lattice defects (including grain boundaries).
Band-Offsets Between Group-III-Nitrides
Authors: Albanesi E. A. , Lambrecht W. R. L. , Segall B. 
Published: April 2011

ABSTRACTThe valence-band offset at the zincblende AIN/GaN. AIN/InN and InN/GaN (110) interfaces are calculated self-consistently by means of the linear muffin-tin orbital method using up to 5+5 layer supercells. All interfaces have a type I-offset. Assuming interface orientation and polytype effects on the valence-band maximum to be reasonably small, a type I offset can also be expected for wurtzite interfaces. Our results are in very good agreement with experimental values for AIN/GaN, the only nitride interface for which they are available.Subject index terms: band offsets, interfaces, hetero junctions, superlattices. III-nitrides.
Nickel Related Absorption Lines in High-Pressure Synthetic Diamond
Authors: Nazaré M. H. , Lopes J. C. , Kanda H. 
Published: April 2011

ABSTRACTDiamonds grown by the temperature gradient method using a nickel catalyst show an optical absorption band, extending from 2.5 eV to 2.56 eV, with a zero-phonon line at 2.51 eV. At 4 K this line exhibits fine structure; it is made up of 3 components at 2.509 eV, 2.510 eV and 2.511 eV. In absorption the fine structure components have the same relative intensity at different temperatures. We report on the effects of uniaxial stress on the zero-phonon transition at 77 K. We propose an interpretation of the results according to which the optical defect has a tetrahedral symmetry, and the 2.51 eV line occurs between two T2 states.
Native Defects and Impurities in Cubic and Wurtzite Gan
Authors: Neugebauer Jö;Rg , Van De Walle Chris G. 
Published: April 2011

ABSTRACTUsing state-of-the-art total energy calculations we investigate defect formation energies and electronic structure for native defects in wurtzite and cubic GaN.The defect formation energies and electronic structures are very similar in both structures. The main difference is a split in the p-like defect states in wurtzite GaN, which are degenerate in cubic GaN.|The role of the Ga 3d electrons on the chemical bonding in GaN is discussed in detail. We explain why the deep lying Ga 3d electrons have a remarkably strong influence on defect formation energies and atomic relaxation for some of the defects.
Characterization Of sic Layer Formed by C Ion Implantation ( ESR And IR Studies)
Authors: Show Y. , Izumi T. , Deguchi M. , Kitabatake M. , Hirao T. 
Published: April 2011

ABSTRACTCharacterization of C ion implanted silicon layers were performed by fourier transformation infrared ( FT-IR ) spectroscopy and electron spin resonance ( ESR ) methods. Microcrystalline β-SiC including amorphous Si are formed in the Si surface region by annealing at 1200 °C following hot ( 450 °C ) implantation. The ESR analysis revealed the presence of two kinds of defect centers in SiC layer formed by implantation, i.e. Si dangling bond ( g=2.0060, ΔHpp=6 Oe) in the amorphous Si and Si dangling bond with C atom neighbors ( g=2.0032, ΔHpp=3 Oe). Heating substrate during implantation prevents the formation of carbon clusters on the Si surface.
Tight-Binding Study of the {211} Σ=3 Grain Boundary in Cubic Silicon-Carbide
Authors: Kohyama M. , Yamamoto R. 
Published: April 2011

ABSTRACTIn grain boundaries in compound semiconductors such as SiC, the interface stoichiometry and the wrong bonds between like atoms are of much importance. Firstly, a general definition of the interface stoichiometry in such grain boundaries has been discussed. Secondly, the atomic and electronic structures of the {211} Σ=3 boundary in SiC have been examined by using the self-consistent tight-binding method, based on the atomic models with bonding networks similar to those in the models of the same boundary in Si or Ge. The wrong bonds have significant effects through the large electrostatic repulsion and the generation of localized states as well as those in the {122} Σ=9 boundary in SiC. And the different bond lengths of the wrong bonds very much affect the local bond distortions at the interfaces, which determines the relative stability among the present models.
Sulfide Passivated GaAs/AlGaAs Microdisk Lasers
Authors: Hobson W. S. , Mohideen U. , Pearton S. J. , Slusher R. E. , Ren F. , Schnoes M. Lamont 
Published: April 2011

ABSTRACTSulfide passivation of optically pumped GaAs/AlGaAs microdisks (at 77K) was examined. The microdisks had diameters between 2 and 10 µm and thicknesses of 0.2 µm. The layer structure was grown by organometallic vapor phase epitaxy. An ammonium sulfide solution was used for the passivation. The GaAs/AlGaAs microdisks without the sulfide treatment did not lase when optically pumped, even at the highest pump power densities of 10 kW/cm2. With sulfide treatment cw lasing was achieved with a lifetime of several seconds. A dramatic increase in the laser lifetime was obtained when the sulfide treated samples were encapsulated with silicon nitride in order to prevent loss of sulfur and surface oxidation. In addition to the lifetime increase, the laser output could be increased by nearly an order of magnitude by annealing at 400°C for 300 s or by cw operation over a period of hours at pumping powers near 10 kW/cm2.
Characterization and Control of Surface Morphology and Defect Density for MBE GaAs Surfaces in the Production MBE Environment
Authors: Patterson George A. , Chang James S.C. 
Published: April 2011

ABSTRACTIn the production MBE environment it is important to maintain low densities of oval defects and particle induced defects in epitaxial films that are used for the fabrication ofGaAs ICs. Most often, the grown layers are characterized on a sample basis by use of an optical microscope. The disadvantages of this technique are the time and labor involved.The data obtained is incomplete, dependent on training, and subjective. A preferred method would be to develop an inspection method that characterizes the surface morphology ofall MBE grown GaAs wafers and the resulting defect density. The use of a laser wafer surface scanning system has allowed us to reproducably inspect 100% of wafers. Rapid diagnosis of epitaxial problems has resulted in an improved understanding of how to routinely produce high quality epitaxial films for GaAs IC production. This work will highlight the production benefits derived from employing 100% inspection of MBE grown GaAs wafers and provide 2D maps. The relationship between gallium source operation and defect sizes will be discussed.
AFM and STM Studies of Large Scale Unstable Growth Formed During GaAs (001) Homoepitaxy
Authors: Orme C. , Johnson M.D. , Leung K.T. , Orr B.G. 
Published: April 2011

ABSTRACTAtomic force and scanning tunneling microscopy studies have been performed on GaAs(001) films grown by molecular beam epitaxy. Multilayered mounds are seen to evolve when the growth conditions favor island nucleation. As the epilayer thickness is increased, these features grow in all dimensions but the angle of inclination remains approximately constant at 1°. The mounding does not occur on surfaces grown in stepflow. We propose that the multi-layered features are due to an unstable growth mode which relies on island nucleation and the presence of a step edge barrier.
Doping in III-V Semiconductors
Authors: Schubert E. F. 
Published: April 2011

ABSTRACTDoping of III-V semiconductors is an essential part of growth and processing technology for optoelectronic and high speed electronic devices. This review covers several recent developments in III-V doping including (i) the high-concentration regime for p-type dopants in InP and GaAs, (ii) the sensitivity of doping incorporation on the crystal orientation, (iii) compensation mechanisms in Si-doped GaAs, and (iv) p-type carbon doping in GaAs and AlxGa1-xAs.
The Relationship between InGaAs Channel Layer Thickness and Device Performance in High Electron Mobility Transistors
Authors: Meshkinpour M. , Goorsky M. S. , Streit D. C. , Block T. , Wojtowicz M. , Rammohan K. , Rich D. H. 
Published: April 2011

ABSTRACTThe performance of InGaAs/GaAs pseudomorphic high electron mobility transistors is anticipated to improve with increased channel thickness due to reduced effects of quantum confinement. However, greater channel thicknesses increase the probability of forming misfit dislocations which have been reported to impair device properties. We characterized the composition and thickness of the active layer in Al0.25Ga0.75As / In0.21Ga0.79As structures with different channel thicknesses (75 Å - 300 Å) to within ± 0.005 and ± 8 Å using high resolution x-ray techniques. We determined, using Hall and rf measurements, that the device properties of these structures improved with increasing thickness up to about 185-205 Å; degraded properties were observed for thicker channel layers. Cathodoluminescence results indicate that the mosaic spread observed in x-ray triple axis rocking curves of these device structures is due to the presence of misfit dislocations. Thus, even though misfit dislocations are present, the device structure performs best with a channel thickness of ∼185 Å. These results demonstrate that one can fabricate functional devices in excess of critical thickness considerations, and that these x-ray techniques provide an effective means to evaluate structural properties prior to device processing.
Influence of Growth Parameters on the Properties of InxGa1-xAs Grown on GaAs by OMVPE
Authors: Dyk E. Ernest Van , Leitch Andrew W. R. , Ehlers Hendrik L. 
Published: April 2011

ABSTRACTInxGa1-xAs epilayers (x < 0.2) have been grown on GaAs substrates by atmospheric pressure OMVPE. The effects of varying the substrate temperature and the gas composition on the properties of the epilayers were investigated. The investigations have shown that higher mobilities were obtained at low growth temperatures (610°C), while optimum optical properties were obtained at higher growth temperatures (690°C). Variation of the AsH3 overpressure yielded optimum electrical and optical properties at a V/III ratio of 50. 77 K mobilities higher than 42 000 cm2/V.s and photoluminescence linewidths as low as 4.4 meV were obtained for x = 0.087 and x = 0.137 epilayers, respectively.
Surface Morphology of InxGa1-xAs/GaAs Relaxed Layers Characterized by Atomic Force Microscopy
Authors: Padeletti G. , Ingo G. M. , Imperatori P. 
Published: April 2011

ABSTRACTGa0.65In0.35As layers of a varying nominal epilayer thickness (10 – 1000 nm) have been grown by the MBE technique on GaAs (100) substrates and characterized by the combined use of atomic force microscopy (AFM) and grazing incidence X-ray diffraction (GIXD). The surface roughness and morphology have been investigated. The GIXD and AFM results show that the thinnest films are characterized by an asymmetric strain relaxation along the two <110> directions with no surface crosshatched pattern but with a misfit dislocation network. AFM images on the thickest films show also well-oriented protrusions along the [110] direction, which increase in size and become more elongated as the nominal film thickness increases.
Effects of Low-Temperature Grown GaAs Intermediate Layers on the Crystalline Quality of GaAs-on-Si Epilayers
Authors: Chong T.C. , Phua C.C. , Lau W.S. , Tan L.S. 
Published: April 2011

ABSTRACTThe incorporation of low-temperature (LT) GaAs intermediate layers grown at 230°C had been shown to have the effects of improving the crystalline quality of GaAs epilayers on Si. The use of this LT-GaAs intermediate layer between the GaAs nucleation layer and the GaAs overlayer has improved the photoluminescence (PL) peak intensity by about five times, and reduced the GaAs (004) X-ray diffraction full width at half maximum (FWHM) by 59 arcsecs. The PL results were subsequently confirmed by cathodoluminescence images. The dominant deep level electron trap in the LT-GaAs epilayer grown on Si substrate was the same as that found in LT-GaAs epilayer grown on GaAs substrate.