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Misfit Dislocations (misfit + dislocation)
Selected AbstractsMisfit dislocations and surface morphology of InGaAs/GaAs heterostructures grown by MOVPEPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 8 2009ukasz Gelczuk Abstract A two-dimensional network of misfit dislocations at the interface of the partially relaxed Inx Ga1- xAs epitaxial layers grown on (001)-oriented GaAs substrates by metalorganic vapor-phase epitaxy (MOVPE) has been revealed by transmission electron microscopy (TEM). A close correspondence between the distribution of interfacial misfit dislocations and undulating surface morphology in the form of a characteristic cross-hatch pattern has been observed by means of atomic force microcopy (AFM). Anisotropic strain relaxation attributed to the asymmetry in the formation of misfit dislocations has been also reproduced on the surface in the form of a fine pattern, cutting the cross-hatch one. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Microstructure-Lattice Thermal Conductivity Correlation in Nanostructured PbTe0.7S0.3 Thermoelectric MaterialsADVANCED FUNCTIONAL MATERIALS, Issue 5 2010Jiaqing He Abstract The reduction of thermal conductivity, and a comprehensive understanding of the microstructural constituents that cause this reduction, represent some of the important challenges for the further development of thermoelectric materials with improved figure of merit. Model PbTe-based thermoelectric materials that exhibit very low lattice thermal conductivity have been chosen for this microstructure,thermal conductivity correlation study. The nominal PbTe0.7S0.3 composition spinodally decomposes into two phases: PbTe and PbS. Orderly misfit dislocations, incomplete relaxed strain, and structure-modulated contrast rather than composition-modulated contrast are observed at the boundaries between the two phases. Furthermore, the samples also contain regularly shaped nanometer-scale precipitates. The theoretical calculations of the lattice thermal conductivity of the PbTe0.7S0.3 material, based on transmission electron microscopy observations, closely aligns with experimental measurements of the thermal conductivity of a very low value, ,0.8,W,m,1,K,1 at room temperature, approximately 35% and 30% of the value of the lattice thermal conductivity of either PbTe and PbS, respectively. It is shown that phase boundaries, interfacial dislocations, and nanometer-scale precipitates play an important role in enhancing phonon scattering and, therefore, in reducing the lattice thermal conductivity. [source] Strain Mapping at the Atomic Scale in Highly Mismatched Heterointerfaces,ADVANCED FUNCTIONAL MATERIALS, Issue 14 2007M. Sánchez Abstract A complete characterization of dislocation network in a highly mismatched interface with high spatial resolution has been performed. The interface between InN quantum dots and a (0001) GaN substrate contains three noninteracting sets of regularly-spaced misfit dislocations lying along <110> directions. The network has a "Star of David" form, with each star bounding a hexagonal region which is pseudomorphic. These misfit dislocations form a threading dislocation network at the island edges due to free surface forces. [source] Synchrotron X-ray topography of electronic materialsJOURNAL OF SYNCHROTRON RADIATION, Issue 3 2002T. Tuomi Large-area transmission, transmission section, large-area back-reflection, back-reflection section and grazing-incidence topography are the geometries used when recording high-resolution X-ray diffraction images with synchrotron radiation from a bending magnet, a wiggler or an undulator of an electron or a positron storage ring. Defect contrast can be kinematical, dynamical or orientational even in the topographs recorded on the same film at the same time. In this review article limited to static topography experiments, examples of defect studies on electronic materials cover the range from voids and precipitates in almost perfect float-zone and Czochralski silicon, dislocations in gallium arsenide grown by the liquid-encapsulated Czochralski technique, the vapour-pressure controlled Czochralski technique and the vertical-gradient freeze technique, stacking faults and micropipes in silicon carbide to misfit dislocations in epitaxic heterostructures. It is shown how synchrotron X-ray topographs of epitaxic laterally overgrown gallium arsenide layer structures are successfully explained by orientational contrast. [source] Interface Structure of an Epitaxial Cubic Ceria Film on Cubic ZirconiaJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2003Chong-Min Wang A cubic CeO2 (001) film with a thickness of ,58 nm was grown epitaxially on Y2O3 -stablized cubic ZrO2 by oxygen-plasma-assisted molecular-beam epitaxy (OPA-MBE). The interface was characterized using high-resolution transmission electron microscopy (HRTEM). The interface exhibited coherent regions separated by equally spaced misfit dislocations. When imaged from the [100] direction, the dislocation spacing is 3.3 ± 0.5 nm, which is slightly shorter than the expected value of 4.9 nm calculated from the differences in lattice constants given in the literature, but is fairly consistent with that of 3.9 nm which was calculated using the lattice mismatch measured by electron diffraction. Thus, the results presented here indicate that the lattice mismatch between the film and the substrate is accommodated mainly by interface misfit dislocations above some critical thickness. [source] Low-temperature growth of high quality AlN films on carbon face 6H-SiCPHYSICA STATUS SOLIDI - RAPID RESEARCH LETTERS, Issue 1 2008Myunghee Kim Abstract AlN films have been grown on atomically flat carbon face 6H-SiC (000) substrates by pulsed laser deposition and their structural properties have been investigated. In-situ reflection high-energy electron diffraction observations have revealed that growth of AlN at 710 °C proceeds in a Stranski,Krastanov mode, while typical layer-by-layer growth occurs at room temperature (RT) with atomically flat surfaces. It has been revealed that the crystalline quality of the AlN film is dramatically improved by the reduction in growth temperature down to RT and the full width at half maximum values in the X-ray rocking curves for 0004 and 102 diffractions of the RT-grown AlN film are 0.05° and 0.07°, respectively. X-ray reciprocal space mapping has revealed that the introduction of misfit dislocations is suppressed in the case of RT growth, which is probably responsible for the improvement in crystalline quality. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Various misfit dislocations in green and yellow GaInN/GaN light emitting diodesPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 6 2010Mingwei Zhu Abstract We report the growth and structural characteristics of green and yellow (529,576,nm) GaInN/GaN light emitting diodes (LEDs) grown on two types of c -plane substrates , bulk GaN and sapphire. In this longer wavelength range, depending on the substrate, we find different strain relaxation mechanisms within the GaInN/GaN quantum well (QW) region. In optimized epitaxy, structures on sapphire that contain a low density of threading dislocations (TDs) within the n -GaN show virtually no generation of additional misfit dislocations (MDs) (<108,cm,2) or V -defects within the QW region for emission wavelengths up to 571,nm. On bulk GaN substrate, however, where much fewer TDs reach the QWs, strain relaxation is observed by inclined dislocation pairs in green emitters and a high density of edge-type MDs in yellow emitters. The electroluminescence line width, as well as the efficiency droop, was found to increase with dislocation density in the QWs. [source] Theoretical investigations of polytypism in AlN thin filmsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 6 2010Tomonori Ito Abstract The polytypism in AlN is theoretically investigated using ab initio pseudopotential, empirical interatomic potential, and Monte Carlo simulation. In bulk form, 2H-AlN is stable without polytypes because of its large energy profit to 3C, 6H, and 4H structures. On the Si(001) substrate, the AlN thin films varies their structures from 3C at the film thickness h,,,4 monolayers (MLs) to (0001)-oriented 2H tilted 5° at the h,,,2345,MLs via (0001)-oriented 2H with two misfit dislocations. This reveals that the large lattice mismatch system destabilizes the metastable 3C-AlN(001) to make the stable 2H-AlN appear with different orientation. The 4H-AlN can be stably formed on the 4H-SiC(11-20) under Al-rich condition, whereas the 2H-AlN may appear under N-rich condition. This results from the distinctive behavior of Al (N) after N (Al) pre-depositions. These results are consistent with experimental findings for the polytypism in AlN thin films grown on various substrates. [source] Strain relaxation in AlN/GaN heterostructures grown by molecular beam epitaxyPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 11 2008G. P. Dimitrakopulos Abstract The strain distribution and defects in a graded AlN/GaN heterostructure comprising AlN layers from 3 nm up to 100 nm grown by plasma-assisted MBE were studied using transmission electron microscopy techniques. Gradual strain relaxation was observed as well as strain partitioning between the GaN spacers and the thicker AlN layers. Elastic strain is retained even in the thicker layers of the heterostructure. Extensive introduction of threading and misfit dislocations is observed at and above the 7 nm AlN layer. The threading dislocations adopt inclined zig-zag line directions thus contributing to the relief of alternating compressive-tensile elastic strain across the the layers of the heterostructure. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Self-assembled quantum dot formation induced by surface energy change of a strained two-dimensional layerPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 3 2004Frank Tinjod Abstract To account for the occurrence (or not) of the Stranski-Krastanow (SK) transition (two-dimensional to 3D change of surface morphology) during the epitaxial growth of various lattice-mismatched semiconductor systems, we present a simple equilibrium model taking into account not only the lattice mismatch, but also the dislocation formation energy and the surface energy. It demonstrates the importance of these parameters especially for II,VI systems such as CdTe/ZnTe and CdSe/ZnSe. For II,VIs indeed, as misfit dislocations are easier to form than in III,Vs (such as InAs/GaAs) or IV systems (Ge/Si), the 3D elastic transition is short-circuited by the plastic one. Nevertheless, by lowering surface energy, telluride and selenide quantum dots can also be grown as predicted by our model and as evidenced experimentally by reflection high-energy electron diffraction (RHEED), atomic force microscopy and optical measurements. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Misfit dislocations and surface morphology of InGaAs/GaAs heterostructures grown by MOVPEPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 8 2009ukasz Gelczuk Abstract A two-dimensional network of misfit dislocations at the interface of the partially relaxed Inx Ga1- xAs epitaxial layers grown on (001)-oriented GaAs substrates by metalorganic vapor-phase epitaxy (MOVPE) has been revealed by transmission electron microscopy (TEM). A close correspondence between the distribution of interfacial misfit dislocations and undulating surface morphology in the form of a characteristic cross-hatch pattern has been observed by means of atomic force microcopy (AFM). Anisotropic strain relaxation attributed to the asymmetry in the formation of misfit dislocations has been also reproduced on the surface in the form of a fine pattern, cutting the cross-hatch one. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Microstructures, defects, and localization luminescence in InGaAsN alloy filmsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2003F. Nakajima Abstract We studied the structural and optical properties of InxGa1,xAs1,yNy (x = 0.116, ,0.3 and y = 0,0.031) alloy films grown by low-pressure metalorganic vapour epitaxy (LP-MOVPE), performing high-resolution transmission electron microscopy (HRTEM) and photoluminescece (PL) measurements. The effects of rapid thermal annealing (RTA) at 700 °C under N2 ambient were also examined. The TEM images showed that with increasing In content, not only misfit dislocations near the InGaAsN/GaAs interface due to the large lattice mismatch with the GaAs subatrate, but also many defects in the InGaAsN layer due to the relaxation of local strain increased. From energy dispersive X-ray (EDX) analysis of the high In-content layers (x = 0.3,0.355), we found a significant In fluctuation in the InGaAsN layer. The PL peaks of In0.116Ga0.884As1,yNy (y = 0,0.031) measured at 7 K shifted to the high-energy side after RTA, while those of InxGa1,xAs1,yNy (x = ,0.3, y = 0,0.015) shifted unusually to the low-energy side. This unsual behavior of the high In-content layer after RTA may be attributed to the enlargement of quantum-dot-like regions, which are formed by the compositional fluctuation in microscopic scale. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Optimizing the diffused regions of interdigitated backside buried contact solar cellsPROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 3 2007Jiun-Hua Guo Abstract Recombination and a number of other important factors must be considered in the optimization of the diffused regions of high-efficiency silicon solar cells. In this paper, we examine issues related to the four types of diffusions used in rear-junction, interdigitated backside buried contact solar cells made on n-type silicon wafers: the phosphorus-diffused front-surface field (FSF), the boron-diffused emitter, and the boron and the phosphorus diffused contact regions. Dark saturation current density, effective lifetime, implied open-circuit voltage and sheet resistance are characterized for the optimization of the above-mentioned diffused regions. Diffusion uniformity and the avoidance of the diffusion-induced dislocations are also discussed for the heavily diffused, metal coated contact diffusions. It is found that the optimal sheet resistances of the FSF for planar and textured surfaces are 120,,/, and 105,,/, respectively, whereas the optimal post-processing sheet resistance for the boron emitter is approximately 100,,/,. Moreover, sheet resistance as heavy as 10,20,,/, for the boron groove diffusion and 5,10,,/, for the phosphorus groove diffusion have been achieved without introducing the diffusion-induced misfit dislocations. Careful consideration of the issues discussed here led to an absolute efficiency improvement on the planar n-type IBBC solar cell of more than 0·6%. Copyright © 2006 John Wiley & Sons, Ltd. [source] | |||||||||||||