bluuebunny/crossref_metadata_2025_split huggingface dataset:
Properties of 4H-SiC by Sublimation Close Space Technique
Authors: Nishino S. , Matsumoto K. , Chen Y. , Nishio Y. 
Published: April 2011

ABSTRACTSiC is suitable for power devices but high quality SiC epitaxial layers having a high breakdown voltage are needed and thick epilayer is indispensable. In this study, CST method (Close Space Technique) was used to rapidly grow thick epitaxial layers. Source material used was 3C-SiC polycrystalline plate of high purity while 4H-SiC(0001) crystals inclined 8° off toward <1120> was used for the substrate. Quality of the epilayer was influenced significantly by pressure during growth and polarity of the substrate. A p-type conduction was obtained by changing the size of p-type source material. The carrier concentration of epilayer decreased when a lower pressure was employed. Schottky diode was also fabricated.
The comparative studies of chemical vapor deposition grown epitaxial layers and of sublimation sandwich method grown 4H-SiC samples
Authors: Evwaraye A. O. , Smith S. R. , Mitchel W. C. 
Published: April 2011

ABSTRACTThermal admittance spectroscopy was used to characterize the shallow dopants in chemical vapor deposition ( CVD) grown thin films and in sublimation sandwich method ( SSM) grown 4H-SiC layers. The values of the activation energy levels of EC − 0.054 eV for Nitrogen at the hexagonal site and of EC − 0.10 eV for Nitrogen at the cubic site were indices of comparison. The net carrier concentrations ( ND − NV ) of the films were determined by capacitance-voltage measurements. The net carrier concentrations for the SSM films ranged from 2 × 1017 to 7 × 1017 cm−3. The two Nitrogen levels were observed in the CVD films. Hopping conduction with an activation energy of EC −0.0058 eV was observed in one SSM sample having ND − NV = 7 × 1017 cm−3.
Impurity Effects in the Growth of 4H-SiC Crystals by Physical Vapor Transport
Authors: Balakrishna V. , Augustine G. , Hopkins R. H. 
Published: April 2011

ABSTRACTSiC is an important wide bandgap semiconductor material for high temperature and high power electronic device applications. Purity improvements in the growth environment has resulted in a two-fold benefit during growth: (a) minimized inconsistencies in the background doping resulting in high resistivity (>5000 ohm-cm) wafer yield increase from 10–15% to 70-85%, and (b) decrease in micropipe formation. Growth parameters play an important role in determining the perfection and properties of the SiC crystals, and are extremely critical in the growth of large diameter crystals. Several aspects of growth are vital in obtaining highly perfect, large diameter crystals, such as: (i) optimized furnace design, (ii) high purity growth environment, and (iii) carefully controlled growth conditions. Although significant reduction in micropipe density has been achieved by improvements in the growth process, more stringent device requirements mandate further reduction in the defect density. In-depth understanding of the mechanisms of micropipe formation is essential in order to devise approaches to eliminate them. Experiments have been performed to understand the role of growth conditions and ambient purity on crystal perfection by intentionally introducing arrays of impurity sites on one half of the growth surface. Results clearly suggest that presence of impurities or second phase inclusions during start or during growth can result in the nucleation of micropipes. Insights obtained from these studies were instrumental in the growth of ultra-low micropipe density (less than 2 micropipes cm−2 ) in 1.5 inch diameter boules.
Synchrotron X-ray Topography Studies of Epitaxial Lateral Overgrowth of GaN on Sapphire
Authors: Mcnally Patrick J. , Tuomi T. , Rantamaki R. , Jacobs K. , Considine L. , O'hare M. , Lowney D. , Danilewsky A. N. 
Published: April 2011

ABSTRACTSynchrotron white beam x-ray topography techniques, in section and large-area transmission modes, have been applied to the evaluation of ELOG GaN on A12O3. Using the openings in 100 nm thick SiO2 windows, a new GaN growth took place, which resulted in typical overgrowth thicknesses of 6.8 μm. Measurements on the recorded Laue patterns indicate that the misorientation of GaN with respect to the sapphire substrate (excluding a 30° rotation between them) varies considerably along various crystalline directions, reaching a maximum of a ∼0.66° rotation of the (0001) plane about the [01•1] axis. This is ∼3% smaller than the misorientation measured in the non-ELOG reference, which reached a maximum of 0.68°. This misorientation varies measurably as the stripe or window dimensions are changed. The quality of the ELOG epilayers is improved when compared to the non- ELOG samples, though some local deviations from lattice coherence were observed. Long range and large-scale (order of 100 μm long) strain structures were observed in all multi quantum well epilayers.
Investigation of the Morphology of AlN Films Grown on Sapphire by MOCVD Using Transmission Electron Microscopy
Authors: Samey W. L. , Salamanca-Ribal L. , Zhou P. , Wilson S. , Spencer M. G. , Jones K. A. 
Published: April 2011

ABSTRACTTo determine the effect of growth conditions on AlN film morphology, we investigated several AlN films grown on sapphire by MOCVD with various V/III ratios. Transmission electron microscopy was used to characterize the film's crystalline quality and defect morphology. TEM results show that the resulting film morphology depends on the V/III ratio. Films grown with NH3 flow rates below 170 sccm have high crystalline quality. In contrast, we observe columnar growth and secondary interfaces in films grown with NH3 flow rates at or above 170 sccm. The secondary interfaces are likely to be inversion domain boundaries (IDBs) and may be associated with strain relaxation. We discuss the V/III ratio's effect on crystalline quality, surface roughness, and IDB and columnar structure formation.
Temperature Dependent Morphology Transition of GaN Films
Authors: Zauner A. R. A. , Theue F. K. De , Hageman P. R. , Van W. J. P. , Schermer J. J. , Larsen P. K. 
Published: April 2011

ABSTRACTThe temperature dependence of the surface morphology of GaN epilayers was studied with AFM. The layers were grown by low pressure MOCVD on (0001) sapphire substrates in the temperature range of 980°C-1085°C. In this range the (0001) and {1101} faces completely determine the morphology of 1.5 μm thick Ga-faced GaN films. For specimens grown at 20 mbar and temperatures below 1035°C the {1101} faces dominate the surface, which results in matt-white layers. At higher growth temperatures the morphology is completely determined by (0001) faces, which lead to smooth and transparent samples. For growth at 50 mbar, this transition takes place between 1000°C and 1015°C. It is shown that the morphology of the films can be described using a parameter αGaN, which is proportional to the relative growth rates of the (0001) and the {1101} faces.
Atomic Scale Analysis of InGaN Multi-Quantum Wells
Authors: Benamara M. , Liliental-Weber Z. , Swider W. , Washburn J. , Dupuis R. D. , Grudowski P. A. , Eiting C. J. , Yang J. W. , Khan M. A. 
Published: April 2011

ABSTRACTInGaN multiquantum wells grown by MOCVD on GaN have been investigated by transmission electron microscopy techniques and numerical analysis of high resolution (HREM) images. One objective of this research was to correlate the atomic structure and emission mechanisms of InGaN quantum well. The studied layers contained 13% or 20% In. It was shown that GaN/InGaN interfaces are rather rough and exhibit an oscillating contrast. Structural defects were found on these interfaces. The relative c-lattice parameter variation in the well was determined using numerical processing of HREM images. The lattice spacings appear to be larger than that expected from Vegard's law suggesting the presence of a biaxial strain. Further observations also revealed a redistribution of In within the well. Instead of a continous In-rich layer, quantum dots were often observed along the well with a regular spacing. The formation of these In-rich dots was not intented and their presence suggests either a periodic modulation of strain along the well or In-rich cluster formation.
Deformation-Induced Dislocations in 4H-SiC and GaN
Authors: Hong M. H. , Samant A. V. , Orlov V. , Farber B. , Kisielowski C. , Pirouz P. 
Published: April 2011

ABSTRACTBulk single crystals of 4H-SiC have been deformed in compression in the temperature range 550–1300°C, whereas a GaN thin film grown on a (0001) sapphire substrate was deformed by Vickers indentation in the temperature range 25–800°C. The TEM observations of the deformed crystals indicate that deformation-induced dislocations in 4H-SiC all lie on the (0001) basal plane but depending on the deformation temperature, are one of two types. The dislocations induced by deformation at temperatures above ∼1 100°C are complete, with a Burgers vector, b, of but are all dissociated into two partials bounding a ribbon of stacking fault. On the other 3 hand, the dislocations induced by deformation in the temperature range 550<T<∼ 1100°C were predominantly single leading partials each dragging a stacking fault behind them. From the width of dissociated dislocations in the high-temperature deformed crystals, the stacking fault energy of 4H-SiC has been estimated to be 14.7±2.5 mJ/m2. Vickers indentations of the [0001]-oriented GaN film produced a dense array of dislocations along the three 〈1120〉 directions at all temperatures. The dislocations were slightly curved with their curvature increasing as the deformation temperature increased. Most of these dislocations were found to have a screw nature with their b parallel to 〈1120〉. Also, within the resolution of the weak-beam method, they were not found to be dissociated. Tilting experiment show that these dislocations lie on the {1100} prism plane rather than the easier (0001) glide plane.
Nondegenerate Optical Pump-Probe Spectroscopy of Highly Excited Group III Nitrides
Authors: Schmidt T. J. , Song J. J. , Keller S. , Mishra U. K. , DenBaars S. P. , Yang Wei 
Published: April 2011

ABSTRACTWe report the results of nondegenerate optical pump-probe absorption experiments performed on GaN and InGaN thin films and quantum wells under the conditions of strong optical band to band excitation. The evolution of the band edge in these materials was monitored as the number of photoexcited free carriers was increased beyond that required to achieve population inversion and observe stimulated emission. The band edge of InGaN is shown to exhibit markedly different high excitation behavior than that of GaN, explaining in part the reduction in stimulated emission threshold that typically accompanies the incorporation of indium into GaN to form InGaN. A comparison of the band edge absorption changes observed in pump-probe experiments to the gain spectra measured in variable-stripe gain experiments is also given.
Comparative Study of GaN Growth Process by MOVPE
Authors: Sun Jingxi , Redwing J. M. , Kuech T. F. 
Published: April 2011

ABSTRACTA comparative study of two different MOVPE reactors used for GaN growth is presented. Computational fluid dynamics (CFD) was used to determine common gas phase and fluid flow behaviors within these reactors. This paper focuses on the common thermal fluid features of these two MOVPE reactors with different geometries and operating pressures that can grow device-quality GaN-based materials. Our study clearly shows that several growth conditions must be achieved in order to grow high quality GaN materials. The high-temperature gas flow zone must be limited to a very thin flow sheet above the susceptor, while the bulk gas phase temperature must be very low to prevent extensive pre-deposition reactions. These conditions lead to higher growth rates and improved material quality. A certain range of gas flow velocity inside the high-temperature gas flow zone is also required in order to minimize the residence time and improve the growth uniformity. These conditions can be achieved by the use of either a novel reactor structure such as a two-flow approach or by specific flow conditions. The quantitative ranges of flow velocities, gas phase temperature, and residence time required in these reactors to achieve high quality material and uniform growth are given.
IIIB- Nitride Semiconductors for High Temperature Electronic Applications
Authors: Bai X. , Hill D. M. , Kordesch M. E. 
Published: April 2011

ABSTRACTThin films of ScN and YN were grown on silicon, quartz and sapphire using metal evaporation and an RF atomic nitrogen source. YN decomposes on contact with water vapor, and only AlN capped films could be stabilized. ScN is stable in air and water, and thin films of this material deposited at temperatures between 300 and 900 °C show a substrate-dependent film texture. Typical growth rates were ∼ 0.1 nm/second with a 300W N discharge at about 0.1 mTorr Nitrogen pressure. Structural characterization by x-ray diffraction, infrared transmission spectroscopy and Hall effect measurements on n-type ScN and the fabrication of p-n junctions of n- type ScN with silicon are presented.
Characterization of GaS-Passivated Quantum-Well Laser Diodes
Authors: Vaughn L. G. , Newell T. C. , Lester L. F. , Macinnes A. N. 
Published: April 2011

ABSTRACTThe degradation of AlGaAs/GaAs diode laser performance during operation is typically due to catastrophic optical damage of the facets caused when thermal runaway occurs. These heating effects are due to the presence of non-radiative recombination sites at and near the facets. MOCVD GaS is deposited on the facets of 825-nm ridge waveguide AlGaAs/GaAs quantumwell laser diodes as an electronic passivation to reduce the number of surface states available for non-radiative recombination. For passivated devices, a peak pulsed power nearly double that of unpassivated devices was achieved. The passivated devices also exhibit a longer lifetime before degradation. The impact of the passivation process on other optical characteristics of the laser diodes will also be discussed.
One-Step Silicon Nitride Passivation by ECR-CVD for Heterostructure Transistors and MIS Devices
Authors: Diniz J. A. , Barros L. E. M. de , Yoshioka R. T. , Lujan G. S. , Danilov I. , Swart J. W. 
Published: April 2011

ABSTRACTSilicon nitride (SiNx) films with extremely low interface charge densities have been developed by electron cyclotron resonance-chemical vapor deposition (ECR-CVD) deposition on GaAs substrates. The procedure is a one-step process and does not involve H2and/or N2pre-treatment of the sample surface. Characterization by Fourier transform infrared (FTIR) and ellipsometry analysis indicate good properties of the film revealing N-H and Si-N bonds. Results of capacitance-voltage (C–V) measurements show surface charge densities on the order of 5 × 1010cm−2, which we believe is the lowest surface charge density achieved so far over GaAs.
Chemical Vapor Deposited Tungsten Film on Molecular Layer Epitaxially-Grown GaAs and its Application to Low Resistivity Contact
Authors: Oyama Y. , Oshida Y. , Nishizawa J. , Matsumoto F. , Plotka P. 
Published: April 2011

ABSTRACTW CVD process was caried out on molecular layer epitaxially-grown GaAs just after in-situ surface treatment under optimized AsH3 pressure followed by ex-situ photolithography process. The precursor for W CVD used is W(CO)6. The W/GaAs interface is analyzed using SIMS and RBS/channeling technique. Interface structure was directly observed by cross sectional HRTEM. Plan view HRTEM observation was also carried out. From these physical analyses, it is shown that the mixed layer at W/GaAs interface is estimated to be about 2–3 ML and that the deposited W layer is epitaxially aligned with underlying GaAs lattice. The contact resistance in W/GaAs is obtained by the transmission line measurements (TLM) of patterned W on heavily doped GaAs grown by (molecular layer epitaxy) MLE. The dependence of the contact resistance on the surface treatment prior to the W CVD is also studied. Barrier height of W/GaAs structure is measured by the temperature dependence of I-V characteristics. Contact resistance of non-alloyed structure achieved are 3 × 10−7 Ωcm2 for n-type GaAs:Te and below 5 ×10−8 Ωcm2 for p-type GaAs:C respectively.
Advances in GaAs Mosfet's Using Ga2O3(Gd2O3) as Gate Oxide
Authors: Wang Y. C. , Hong M. , Kuo J. M. , Mannaerts J. P. , Kwo J. , Tsai H. S. , Krajewski J. J. , Weiner J. S. , Chen Y. K. , Cho A. Y. 
Published: April 2011

ABSTRACTIn this article, we review the recent progress on GaAs MOSFET's using in-situ MBE-grown Ga2O3(Gd2O3) as the gate dielectric. Both depletion-mode (D-mode) and inversion-mode (I-mode) GaAs MOSFET's with negligible drain current drift and hysteresis are demostrated. The absence of drain current drift and hysteresis indicates that the excellent stability of the oxide and low oxide/GaAs interface state density have been achieved. The drain current density and transconductance are about one order of magnitude higher than the best previous reported data in the literature for an inversion-mode GaAs MOSFET. Excellent high frequency and power performances were also measured from the depletion-mode devices. These improvements are attributed to the excellent Ga2O3(Ga2O3) oxide properties and novel processing techniques.
Anodic sulfidation and model characterisation of GaAs (100) in (NH4)2 Sx solution
Authors: Elbahnasawy R. F. , Mclnerney J. G. , Ryan P. , Hughes G. , Murtagh M. 
Published: April 2011

ABSTRACTElectrochemical sulfidation of n-type GaAs (100) has been investigated under anodic conditions with a view to surface passivation for improved electronic and optical properties. This treatment has successfully removed the native oxide and formed a thick layer of gallium and arsenic sulfides displaying high durability against oxidation and optical degradation compared to conventional dipping treatment using (NH4)2S solution. X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), secondary ion mass spectroscopy (SIMS) and atomic force microscopy (AFM) have been used to characterize the treated surfaces. These studies have been used to devise a structural model of the near-surface region. The results of Raman backscattering spectroscopy measurements indicate that there is a 35% reduction of the surface barrier height compared to the untreated surface. This passivation technique has been shown to be effective in reducing surface band bending on GaAs (100) and enhancing the chemical stability of the surface, making it more suitable for electronic and optoelectronic device applications.
High-Density Plasma-Induced Etch Damage of GaN
Authors: Shul R. J. , Zhang L. , Baca A. G. , Willison C. G. , Han J. , Pearton S. J. , Ren F. , Zolper J. C. , Lester L. F. 
Published: April 2011

ABSTRACTAnisotropic, smooth etching of the group-Ill nitrides has been reported at relatively high rates in high-density plasma etch systems. However, such etch results are often obtained under high dc-bias and/or high plasma flux conditions where plasma induced damage can be significant. Despite the fact that the group-III nitrides have higher bonding energies than more conventional III–V compounds, plasma-induced etch damage is still a concern. Attempts to minimize such damage by reducing the ion energy or increasing the chemical activity in the plasma often result in a loss of etch rate or anisotropy which significantly limits critical dimensions and reduces the utility of the process for device applications requiring vertical etch profiles. It is therefore necessary to develop plasma etch processes which couple anisotropy for critical dimension and sidewall profile control and high etch rates with low-damage for optimum device performance. In this study we report changes in sheet resistance and contact resistance for n- and p-type GaN samples exposed to an Ar inductively coupled plasma (ICP). In general, plasma-induced damage was more sensitive to ion bombardment energies as compared to plasma flux. In addition, p-GaN was typically more sensitive to plasma-induced damage as compared to n-GaN.
Kinetics of the Interaction of Atomic Species With (100) Gallium Arsenide Surfaces
Authors: Gheorghita Ligia , Ogryzlo Elmer 
Published: April 2011

ABSTRACTThe interactions of atomic hydrogen, deuterium and sulfur with (100) GaAs surfaces have been studied. The atoms were produced in a remote microwave plasma and their effect on carrier recombination velocities was continuously monitored in situ by the change in photoluminescence intensity (PLI). It was observed that the PLI increased by about 1–2 orders of magnitude following a few seconds exposure to hydrogen and deuterium atoms. A subsequent treatment with sulfur atoms further increased the PLI. A kinetic analysis of the room temperature hydrogen atom interactions with the (100) GaAs surface was attempted. A similar behavior was observed at higher temperatures when hydrogen and deuterium atoms were allowed to interact with a SiSiO2 interface. A comparison of the two systems leads us to conclude that the hydrogen and deuterium atoms can be trapped at interstitial sites near these interfaces. The kinetics of the hydrogen atom loss from these semiconductors is presented and analyzed in terms of a distribution of trapping sites.
Theory of the Sulphur-Passivated InP(001) Surface
Authors: Lewis Laurent J. , Dharma-Wardana Chandré 
Published: April 2011

ABSTRACTWe present a detailed and comprenhensive theoretical investigation of the sulphur-passivated (001) surface of InP. First, the ground-state structure is determined using density-functional methods, including full relaxation of the surface. The lowest-energy structure at 0 K is a striking (2 × 2) reconstruction with the S atoms displaced from the bridge sites to form short and long dimers, belonging to two distinct sublayers. This surface structure is used to calculate the backscattering Raman spectrum; the two peaks arising from surface-layer vibrations predicted by our calculations are observed. Next, our first-principles calculations are extended to the study of a number of other stable states of the surface that can arise upon annealing. For this purpose, we construct and relax several higher-energy states of the surface, and calculate the corresponding core-level photoemission spectra. A remarkable sequence of structures is found to unfold from the fully S-covered ground state as they become energetically accessible. The surface S atoms exchange with bulk P atoms, forming new (and strong) S-P bonds while dissociating pre-existing S–S dimers. The predicted core-level spectra are found to be entirely consistent with the experimental measurements; our calculations indicate that the annealed (at about 700 K) surface is a (2 × 2) structure containing two S and two P atoms per unit cell. Finally, we have used the predicted stable surface structures to calculate the photoemission and inverse photoemission spectra. They are found to agree well with experiment if the surface is assumed to consist of a mixture of the above ground-state and annealed structures.