Generation and behavior of pure-edge threading misfit dislocations in InxGa1-xN/GaN multiple quantum wells

The relaxation of the misfit strain by the formation of misfit dislocations in InxGa1-xN/GaN multiple quantum wells grown by metal-organic chemical-vapor deposition was investigated by the cross-sectional transmission electron microscopy, double crystal x-ray diffraction, and temperature-dependent photoluminescence. It is found that the misfit dislocations generated from strain relaxation are all pure-edge threading dislocations with burgers vectors of b=1/3<11 (2) over bar0>. The misfit dislocations arise from the strain relaxation due to the thickness of strained layer greater than the critical thickness. The relaxation of strained layer was mainly achieved by the formation of dislocations and localization of In, while the dislocations changed their slip planes from {0001} to {10 (1) over bar0}. With the increasing temperature, the efficiency of photoluminescence decrease sharply. It indicates that the relaxation of the misfit strain has a strong effect on optical efficiency of film. (C) 2004 American Institute of Physics.

Abnormal alignment of misfit dislocations in In0.52Al0.48As/InxGa1-xAs/In0.52Al0.48As/InP heterostructure

It was observed with transmission electron microscopy in the In0.52Al0.48As/InxGa1-xAs/In0.52Al0.48As/InP heterostructure that misfit dislocation lines deviate from the [110] directions at a certain angle depending on the indium content x. Such an abnormal alignment of misfit dislocations is explained in terms of an alloy effect on the formation of single jogs on the misfit dislocations in the interface between the III-V ternary compounds.

Alignment of misfit dislocations in the In0.52Al0.48As/InxGa1-xAs/In0.52Al0.48As/InP heterostructure

It was observed with transmission electron microscopy in the In0.52Al0.48As/InxGa1-xAs/In0.52Al0.48As system grown on the (001) InP substrate that misfit dislocation lines deviate [110] directions at an angle with its value depending on the gallium content. Such an abnormal alignment of misfit dislocations is explained in terms of an alloy effect on the formation of single jogs on misfit dislocations in the interface between the III-V ternary compounds. (C) 1998 American Institute of Physics.

BREAKING UP OF MISFIT DISLOCATIONS IN GAASIN0.3GA0.7AS/GAAS HETEROSTRUCTURE

The effect of GaAs cap layer with different thicknesses in the GaAs/In0.3Ga0.7As/GaAs heterostructure on misfit dislocation is investigated with transmission electron microscopy, and it is found that lines of misfit dislocation break up and move out of the structure when the GaAs cap layer thickness exceeds a certain amount. The breaking up and moving out of misfit dislocations, initially confined in the (001) substrate/InGaAs epilayer interface, occur mainly along the [110] direction on the interface in the structure. (C) 1995 American Institute of Physics.

The modified Peierls-Nabarro model of interfacial misfit dislocation

The Peierls-Nabarro model of the interfacial misfit dislocation array is analytically extended to a family of dislocations of greater widths. By adjusting a parameter, the width of the misfit dislocations, the distribution of the shear stress, and the restoring force law can be systematically varied. The smaller the amplitude of the restoring force, the wider the misfit dislocations and the lower the interfacial energy.

Distribution of dislocations in GaSb and InSb epilayers grown on GaAs (001) vicinal substrates

GaSb and InSb epilayers grown on GaAs (001) vicinal substrates misoriented toward (111) plane were studied using high resolution x-ray diffraction. The results show that GaSb and InSb epilayers take on positive crystallographic tilt, and the asymmetric distribution of 60 degrees misfit dislocations in {111} glide planes have an effect on the tilt. In addition, the vicinal substrate influences the distribution of the threading dislocations in {111} glide planes, and the density of dislocation in the (111) plane is higher than in the ((1) over bar(1) over bar1) plane. A model was proposed to interpret the distribution of full width at half maximum, which can help us understand the formation and glide process of the dislocations. (C) 2009 American Institute of Physics. [DOI 10.1063/1.3115450]

TEM study of dislocations in ZnTe/GaAs heterostructure grown by hot-wall epitaxy

A ZnTe layer grown on GaAs substrate by hot-wall epitaxy (HWE) was studied using transmission electron microscopy (TEM). For a (110) cross-sectional specimen, its (001) ZnTe/GaAs interface was analysed by large angle stereo-projection (LASP) and high resolution electron microscopy (HREM). In the LASP, a double diffraction occurred and moire fringes were formed, meanwhile misfit dislocations were revealled clearly by weak beam technique. In HREM, not only Lomer and 60 degrees types of misfit dislocations were observed, but also two types of stacking faults were analysed. The residual strain was estimated by both methods.

Dislocations in InAs epilayers grown by MBE on GaAs substrates under various conditions

Using Transmission Electron Microscopy, we studied the misfit and threading dislocations in InAs epilayers. All the samples, with thickness around 0.5 mu m, were grown on GaAs(001) substrates by molecular beam epitaxy under As-rich or in-rich conditions. The As-rich growth undergoes 2D-3D mode transition process, which was inhibited under In-rich surface. High step formation energy under As-deficient reconstruction inhibits the formation of 3D islands and leads to 2D growth. The mechanism of misfit dislocations formation was different under different growth condition which caused the variation of threading dislocation density in the epilayers.

Electron microscopy and diffraction of ordering in Ni---W alloys

Electron microscopy and diffraction studies of ordering in stoichiometric Ni-20%W and off-stoichiometric Ni-15%W alloys have been carried out. The specimens of Ni-20%W were first disordered at 1398 K for 4 h and then quenched rapidly into water. Short range order (SRO) spots were observed at {1 1/2 0}* positions. Two hitherto unknown metastable phases: D-2h(25)-Ni2W and DO22-Ni3W were observed in the diffraction patterns. Long range order (LRO) transformations were studied at 1103 and 1213 K. Kinetics and mechanism of transformations have been identified. Ni-15%W specimens were solution treated at 1523 K for 1 h followed by quenching in water. SRO spots similar to those found in Ni-20%W were observed in this alloy as well. The transition to LRO was studied at 1093 K. Distinct Ni4W precipitates could be observed after 5 h of annealing at this temperature. After 100 h of annealing precipitates were found to grow into faceted shape coherent with the disordered matrix. After prolonged annealing for over 150 h the Ni4W precipitates began to lose coherency by the generation of misfit dislocations. The microstructural observations have been compared for the stoichiometric and off-stoichiometric alloys.

Role of thermal annealing on SiGe thin films fabricated by PECVD

Amorphous Silicon Germanium (a-SiGe) thin films of 500 nm thickness are deposited on silicon substrates using Plasma Enhanced Chemical Vapour Deposition (PECVD). To obtain polycrystalline nature of films, thermal annealing is done at various temperature (450-600 degrees C) and time (1-10 h). The surface morphology of the pre- and post-annealed films is investigated using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The crystallographic structure of the film is obtained by X-ray diffraction method. Raman spectroscopy is carried out to quantify the Ge concentration and the degree of strain relaxation in the film. Nano-indentation is performed to obtain the mechanical properties of the film. It is found that annealing reduces the surface roughness of the film and increases the Ge concentration in the film. The grain size of the film increases with increase in annealing temperature. The grain size is found to decrease with increase in annealing time up to 5 h and then increased. The results show that 550 degrees C for 5 h is the critical annealing condition for variation of structural and mechanical properties of the film. Recrystallization starts at this condition and results in finer grains. An increase in hardness value of 7-8 GPa has been observed. Grain growth occurs above this critical annealing condition and degrades the mechanical properties of the film. The strain in the film is only relaxed to about 55% even for 10 h of annealing at 600 degrees C. Transmission Electron Microscopy (TEM) observations show that the strain relaxation occurs by forming misfit dislocations and these dislocations are confined to the SiGe/Si interface. (C) 2015 Elsevier Ltd. All rights reserved.

Investigation of GaSb epilayer grown on vicinal GaAs(001) substrate by high resolution x-ray diffraction

GaSb epilayers grown on GaAs(001) vicinal substrate misoriented towards (111) plane were studied using high-resolution x-ray diffraction (HRXRD). The results show that GaSb epilayers exhibit positive crystallographic tilt and the distribution of 60 degrees misfit dislocations (MDs) is imbalanced. The vicinal substrate also leads to the anisotropy of the mosaic structure, i.e. the lateral coherent lengths in [1 (1) over bar0] directions are larger than those in [110] directions. Furthermore, the full-width at half maximum (FWHM) of the off-axis peaks varies with the inclination angle, which is a result of different dislocation densities in the {111} glide planes.

Nature of interfacial defects and their roles in strain relaxation at highly lattice mismatched 3C-SiC/Si (001) interface

Misfit defects in a 3C-SiC/Si (001) interface were investigated using a 200 kV high-resolution electron microscope with a point resolution of 0.194 nm. The [110] high-resolution electron microscopic images that do not directly reflect the crystal structure were transformed into the structure map through image deconvolution. Based on this analysis, four types of misfit dislocations at the 3C-SiC/Si (001) interface were determined. In turn, the strain relaxation mechanism was clarified through the generation of grow-in perfect misfit dislocations (including 90 degrees Lomer dislocations and 60 degrees shuffle dislocations) and 90 partial dislocations associated with stacking faults. (C) 2009 American Institute of Physics. [doi:10.1063/1.3234380]

Reduction of tensile stress in GaN grown on Si(111) by inserting a low-temperature AlN interlayer

This study describes the growth of a low-temperature AlN interlayer for crack-free GaN growth on Si(111). It is demonstrated that, in addition to the lower growth temperature, growth of the AlN interlayer under Al-rich conditions is a critical factor for crack-free GaN growth on Si(111) substrates. The effect of the AlN interlayer thickness and NH3/TMA1 ratios on the lattice constants of subsequently grown high temperature GaN was investigated by X-ray triple crystal diffraction. The results show that the elimination of micro-cracks is related to the reduction of the tensile stress in the GaN epitaxial layers. This was also coincident with a greater number of pits formed in the AlN interlayer grown under Al rich conditions. It is proposed that these pits act as centers for the generation of misfit dislocations, which in turn leads to the reduction of tensile stress. (C) 2004 Elsevier B.V. All rights reserved.

MBE InAs quantum dots grown on metamorphic InGaAs for long wavelength emitting

GaAs-based InAs quantum dots using InGaAs composition-graded metamorphic layers have been investigated by molecular beam epitaxy. Emission with the wavelength similar to 1.5 mu m from the dots was obtained at room temperature with the relatively large full width at half maximum. The emission wavelength is relatively stable when subjected to fast annealing. The number density of dots reached similar to 6 x 10(10) cm(-2). Undulated morphology was observed on the surface of the sample, which has some influence on the dot size and distribution. In epilayers, misfit dislocations were confined within the step-graded InGaAs metamorphic buffer layer. (c) 2006 Elsevier B.V. All rights reserved.

Influence of dislocation stress field on distribution of quantum dots

InAs quantum dots (QDs) were grown on In0.15Ga0.85As strained layers by molecular beam epitaxy on GaAs (0 0 1) substrates. Atomic force microscopy and transmission electron microscopy study have indicated that In0.15Ga0.85As ridges and InAs QDs formed at the inclined upside of interface misfit dislocations (MDs). By testifying the MDs are mixed 60 degrees dislocations and calculating the surface stress over them when they are 12-180 nm below the surface, we found the QDs prefer nucleating on the side with tensile stress of the MDs and this explained why the ordering of QDs is weak when the InGaAs layer is relatively thick. (c) 2006 Elsevier B.V. All rights reserved.