Influence of indium-tin-oxide thin-film quality on reverse leakage current of indium-tin-oxide/n-GaN Schottky contacts

Indium-tin-oxide (ITO)/n-GaN Schottky contacts were prepared by e-beam evaporation at 200 degrees C under various partial pressures of oxygen. X-ray photoemission spectroscopy and positron beam measurements were employed to obtain chemical and structural information of the deposited ITO films. The results indicated that the observed variation in the reverse leakage current of the Schottky contact and the optical transmittance of the ITO films were strongly dependent on the quality of the ITO film. The high concentration of point defects at the ITO-GaN interface is suggested to be responsible for the large observed leakage current of the ITO/n-GaN Schottky contacts. (c) 2006 American Institute of Physics.

Void formation and failure in InGaN/AlGaN double heterostructures

Condensed clusters of point defects within an InGaN/AlGaN double heterostructure grown by metal-organic vapor phase epitaxy on sapphire substrate have been observed using transmission electron microscopy. The existence of voids results in failure of the heterostructure in electroluminescence. The voids are 50-100 nm in diameter and are distributed inhomogeneously within In0.25Ga0.75N/AlGaN active layers. The density of the voids was measured as 10(15) cm(-3), which corresponds to a density of dangling bonds of 10(20) cm(-3). These dangling bonds may fully deplete free carriers in this double heterostructure and result in the heterostructure having high resistivity as confirmed by electrical measurement. (C) 2003 Elsevier Science B.V. All rights reserved.

Content analyses in GaMnAs by double-crystal X-ray diffraction

A model for analyzing point defects in compound crystals was improved. Based on this modified model, a method for measuring Mn content in GaMnAs was established. A technique for eliminating the zero-drift-error was also established in the experiments of X-ray diffraction. With these methods, the Mn content in GaMnAs single crystals fabricated by the ion-beam epitaxy system was analyzed.

Study of self-assembled InAs quantum dots grown on low temperature GaAs epi-layer

InAs self-organized quantum dots (QDs) grown on annealed low temperature GaAs (LT-GaAs) epi-layer were investigated by transmission electron microscopy (TEM) and photoluminescence (PL) measurement. TEM showed that QDs formed on annealed LT-GaAs epi-layer have a smaller size and a higher density than QDs formed on normal GaAs buffer layer. In addition, the PL spectra analysis showed that the LT-GaAs epi-layer resulted in a blue shift in peak energy, and a narrower linewidth in the PL peak. The differences were attributed to the point defects and As precipitates in annealed LT-GaAs epi-layer for the point defects and As precipitates change the strain field of the surface. The results provide a method to improve the uniformity and change the energy band structure of the QDs by controlling the defects in the LT-GaAs epi-layer.

Effect of arsenic precipitates on Fermi level in GaAs grown by molecular-beam epitaxy at low temperature

A simple model is presented to discuss the effect of As precipitates on the Fermi level in GaAs grown by molecular-beam epitaxy at low temperature (LT-GaAs). This model implements the compensation between point defects and the depletion of arsenic precipitates. The condition that the Fermi level is pinned by As precipitates is attained. The shifts of the Fermi level in LT-GaAs with annealing temperature are explained by our model. Additionally, the role of As precipitates in conventional semi-insulating GaAs is discussed. (C) 2000 American Institute of Physics. [S0021-8979(00)09905-9].

Temperature dependence of the Fermi level in low-temperature-grown GaAs

A variable-temperature reflectance difference spectroscopy study of GaAs grown by molecular beam epitaxy at low-temperature GaAs (LT-GaAs) shows that the Fermi level is mostly determined by the point defects in samples annealed at below 600 degrees C and can be shifted by photoquenching the defects. The Fermi level is otherwise almost temperature independent, leading to an estimated width of the defect band of 150 meV in the as-grown sample, For LT-GaAs annealed at 850 degrees C, the Fermi level is firmly pinned, most Likely by the As precipitates. (C) 1998 American Institute of Physics.

Electronic, structural, and optical properties of crystalline yttria

The electronic structure of crystalline Y2O3 is investigated by first-principles calculations within the local-density approximation (LDA) of the density-functional theory. Results are presented for the band structure, the total density of states (DOS), the atom-and orbital-resolved partial DOS. effective charges, bond order, and charge-density distributions. Partial covalent character in the Y-O bonding is shown, and the nonequivalency of the two Y sites is demonstrated. The calculated electronic structure is compared with a variety of available experimental data. The total energy of the crystal is calculated as a function of crystal volume. A bulk modulus B of 183 Gpa and a pressure coefficient B' of 4.01 are obtained, which are in good agreement with compression data. An LDA band gap of 4.54 eV at Gamma is obtained which increases with pressure at a rate of dE(g)/dP = 0.012 eV/Gpa at the equilibrium volume. Also investigated are the optical properties of Y2O3 up to a photon energy of 20 eV. The calculated complex dielectric function and electron-energy-loss function are in good agreement with experimental data. A static dielectric constant of epsilon(O)= 3.20 is obtained. It is also found that the bottom of the conduction band consists of a single band, and direct optical transition at Gamma between the top of the valence band and the bottom of the conduction band may be symmetry forbidden.

Defect Cluster-Induced X-Ray Diffuse Scattering in GaN Films Grown by MOCVD

High-resolution X-ray diffraction has been employed to investigate the diffuse scattering in a (0001) oriented GaN epitaxial film grown on sapphire substrate. The analysis reveals that defect clusters are present in GaN films and their concentration increases as the density of threading dislocations increases. Meanwhile, the mean radius of these defect clusters shows a reverse tendency. This result is explained by the effect of clusters preferentially forming around dislocations, which act as effective sinks for the segregation of point defects. The electric mobility is found to decrease as the cluster concentration increases.

Modulation of Photonic Bandgap and Localized States by Dielectric Constant Contrast and Filling Factor in Photonic Crystals

The band structure of 2D photonic crystals (PCs) and localized states resulting from defects are analyzed by finite-difference time-domain (FDTD) technique and Pade approximation. The effect of dielectric constant contrast and filling factor on photonic bandgap (PBG) for perfect PCs and localized states in PCs with point defects are investigated. The resonant frequencies and quality factors are calculated for PCs with different defects. The numerical results show that it is possible to modulate the location, width and number of PBGs and frequencies of the localized states only by changing the dielectric constant contrast and filling factor.

Annealing ambient controlled deep defect formation in InP

Deep defects in annealed InP have been investigated by deep level transient capacitance spectroscopy (DLTS), photo induced current transient spectroscopy (PICTS) and thermally stimulated current spectroscopy (TSC). Both DLTS results of annealed semiconducting InP and PICTS and TSC results of annealed semi-insulating InP indicate that InP annealed in phosphorus ambient has five defects, while lid? annealed in iron phospbide ambient has two defects. Such a defect formation phenomenon is explained in terms of defect suppression by the iron atom diffusion process. The correlation of the defects and the nature of the defects in annealed InP are discussed based on the results.

The SPER and characteristics of Si1-yCy alloys

\Si1-yCy alloys with carbon composition of 0.5 at.% were successfully grown on n-Si(100) substrate by solid phase epitaxy recraystallization. The result was presented in this paper. With the help of the SiO2 capping layer, rather uniform carbon profile in amorphous Si layer was obtained by dual-energy implantation. Since ion-flow was small and implantation time was long enough, the emergency of beta-SiC was avoided and the dynamic annealing effect was depressed. The pre-amorphization of the Si substrate increased the fraction of the substitutions carbon and the two-step annealing reduced point defects. As a result, Si1-yCy alloys with high quality was recrystallized on Si substrate.

Mechanical Behavior of Nanometer Ni by Simulating Nanoindentation

An indentation simulation of the crystal Ni is carried out by a molecular dynamics technique (MD) to study the mechanical behavior at nanometer scales. Indenter tips with both sphere shape and conical shape with 60 cone angle are used, and simulation samples with different crystal orientations are adopted. Some defects such as dislocations and point defects are observed. It is found that nucleated defects (dislocations, amorphous atoms) are from the local region near the pin tip or the sample surface. The temperature distribution of the local region is analyzed and it can explain our MD simulation results.

Mechanical Behavior of Nanometer Ni by MD Simulation

The indention simulation of the crystal Ni is carried out by molecular dynamics technique (MD) to study the mechanical behavior at nanometer scales, the indenter tips with sphere shape is used. Some defects such as dislocations, point defects are observed. It is found that defects (dislocations, amorphous) nucleated is from local region near the pin tip or the sample surface. The temperature distribution of local region is analyzed and it can explain our MD simulation result.

碳化硅中氦离子高温注入引入的缺陷及其退火行为的光谱研究

对氦(He)离子高温(600K)注入6H-SiC中的辐照缺陷,在阶梯温度退火后演化行为的拉曼光谱和室温光致发光谱的特征进行了分析.这两种方法的实验结果表明,离子注入所产生晶格损伤的程度与注入剂量有关;高温退火导致损伤的恢复,不同注入剂量造成的晶格损伤需要不同的退火温度才可恢复.在阶梯温度退火下呈现出了点缺陷的复合、氦-空位团的产生、氦泡的形核、长大等特性.研究表明:高温(600K)注入在一定剂量范围内是避免注入层非晶化的一个重要方法,为后续利用氦离子注入空腔掩埋层吸杂或者制备低成本、低缺陷密度的绝缘层上碳化硅(SiCOI)材料提供了可能.

Void swelling in MA956 ODS steel irradiated with 122 MeV Ne-ions at elevated temperatures

An investigation of a commercial oxide dispersion-strengthened steel (MA9561) irradiated with high energy Ne-ions to high doses at elevated temperatures is presented. Specimens of MA956 oxide dispersion strengthened steel together with a 9% Cr ferritic/martensitic steel, e.g., Grade 92 steel were irradiated simultaneously with 20Ne-ions (with 122 MeV) to successively increasing damage levels of 1, 5 and 10 dpa at the damage peak at 440 C and 570 C, respectively. Cross-sectional microstructures of the specimens were investigated with transmission electron microscopy. MA956 oxide dispersion strengthened steel showed a higher resistance to void swelling especially to void growth at the grain boundaries than the ferritic/martensitic steel, e.g., Grade 92 steel did, and thus exhibited a prominence for an application in the situation of a high He production at high temperatures. The suppression of the growth of voids especially at the grain boundaries in MA956 is ascribed to an enhanced recombination of the point defects and a trapping of Ne atoms at the interfaces of the yttrium–aluminum oxide particles and the matrix.