Home  About us  Contact
 

High Dislocation Density (high + dislocation_density)

Distribution by Scientific Domains
Physics and Astronomy75%

Selected Abstracts

UV emission on a Si substrate: Optical and structural properties of ,-CuCl on Si grown using liquid phase epitaxy techniques

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 5 2009
A. Cowley
Abstract Considerable research is being carried out in the area of wide band gap semiconductor materials for light emission in the 300,400 nm spectral range. Current materials being used for such devices are typically based on II,VI and III-nitride compounds and variants thereof. However, one of the major obstacles to the successful fabrication of III-N devices is lattice mismatch-induced high dislocation densities for epitaxially grown layers on non-native substrates. ,-CuCl is a direct bandgap material and an ionic wide bandgap I,VII semiconductor with a room temperature free exciton binding energy of ,190 meV (compared to ,25 meV and ,60 meV for GaN and ZnO, respectively) and has a band gap of 3.4 eV (, , 366 nm). The lattice constant of ,-CuCl (0.541 nm) is closely matched to that of Si (0.543 nm). This could, in principle, lead to the development of optoelectronic systems based on CuCl grown on Si. Research towards this end has successfully yielded polycrystalline ,-CuCl on Si(100) and Si(111) using vacuum-based deposition techniques [1]. We report on developments towards achieving single crystal growth of CuCl from solution via Liquid Phase Epitaxy (LPE) based techniques. Work is being carried out using alkali halide flux compounds to depress the liquidus temperature of the CuCl below its solid phase wurtzite-zincblende transition temperature (407 °C [2]) for solution based epitaxy on Si substrates. Initial results show that the resulting KCl flux-driven deposition of CuCl onto the Si substrate has yielded superior photoluminescence (PL) and X-ray excited optical luminescence (XEOL) behavior relative to comparitively observed spectra for GaN or polycrystalline CuCl. This enhancement is believed to be caused by an interaction between the KCl and CuCl material subsequent to the deposition process, perhaps involving a reduction in Cl vacancy distributions in CuCl. This paper presents a detailed discussion of a CuCl LPE growth system as well as the characterization of deposited materials using X-ray diffraction (XRD), room temperature and low temperature PL, and XEOL. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Reliability and degradation mechanism of AlGaAs/InGaAs and InAlAs/InGaAs HEMTs

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2003
M. Dammann
Abstract The long-term stability of AlGaAs/GaAs and InAlAs/InGaAs high electron mobility transistors (HEMTs), tested under high drain voltage and/or high temperature operation is reported. HEMTs with high In content in the active channel, alternatively fabricated on InP substrates and on GaAs substrates covered by a metamorphic buffer (MHEMT), are compared. Despite the high dislocation density in the buffer layer MHEMTs and InP based HEMTs exhibit comparable reliability. AlGaAs/GaAs HEMTs are more reliable than their InAlAs/InGaAs counterparts, especially when operated at high drain voltage. Failure mechanisms are thermally activated gate sinking, Ohmic contact degradation and hot electron induced degradation. [source]

Cathodoluminescence, High-Resolution X-Ray Diffraction and Transmission-Electron-Microscopy Investigations of Cubic AlGaN/GaN Quantum Wells

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2003
D.J. As
Abstract The structural and optical properties of cubic Al0.25Ga0.75N/GaN multi quantum well structures grown on GaAs (001) substrates by radio-frequency plasma-assisted molecular beam epitaxy (MBE) are reported. Transmission electron microscopy (TEM), high resolution X-ray diffraction (HRXRD), and cathodoluminescence (CL) measurements are used to characterize the cubic Al0.25Ga0.75N/GaN quantum wells. The interfaces between the quantum-well and barrier layers are well resolved, abrupt and the entire structure shows an excellent periodicity. Due to the high dislocation density of about 1010 cm,2 a severe broadening of the XRD-reflection is observed and superlattice satellite peaks are only weakly indicated. Further, a wavy structure is seen in TEM at the coalescence of submicron-size grains. Nevertheless, CL at room temperature shows a strong emission of quantized states at 3.352 eV. [source]

High-efficiency solar cells on phosphorus gettered multicrystalline silicon substrates

PROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 8 2006
O. Schultz
Abstract Measurements of the dislocation density are compared with locally resolved measurements of carrier lifetime for p-type multicrystalline silicon. A correlation between dislocation density and carrier recombination was found: high carrier lifetimes (>100,µs) were only measured in areas with low dislocation density (<105,cm,2), in areas of high dislocation density (>106,cm,2) relatively low lifetimes (<20,µs) were observed. In order to remove mobile impurities from the silicon, a phosphorus diffusion gettering process was applied. An increase of the carrier lifetime by about a factor of three was observed in lowly dislocated regions whereas in highly dislocated areas no gettering efficiency was observed. To test the effectiveness of the gettering in a solar cell manufacturing process, five different multicrystalline silicon materials from four manufacturers were phosphorus gettered. Base resistivity varied between 0·5 and 5,,,cm for the boron- and gallium-doped p-type wafers which were used in this study. The high-efficiency solar cell structure, which has led to the highest conversion efficiencies of multicrystalline silicon solar cells to date, was used to fabricate numerous solar cells with aperture areas of 1 and 4,cm2. Efficiencies in the 20% range were achieved for all materials with an average value of 18%. Best efficiencies for 1,cm2 (20·3%) and 4,cm2 (19·8%) cells were achieved on 0·6 and 1·5,,,cm, respectively. This proves that multicrystalline silicon of very different material specification can yield very high efficiencies if an appropriate cell process is applied. Copyright © 2006 John Wiley & Sons, Ltd. [source]