Modeling of layered structures with stacking faults

A method for modeling unit cells of layered structures containing stacking faults is considered by the example of silicon carbide. A rotating-crystal pattern is calculated by the proposed method for silicon carbide with pseudorandom violation of the sequence of close-packed layers. The results of the calculation show that the intensity and shape of reflections of an X-ray diffraction pattern of a layered structure is determined by the configuration of stacking faults.     

Intergrowth and stacking faults in the Sm5Co19 Phase

An electron microscope observation was made on the binary Sm-Co alloy. One-dimensional lattice images of Sm₅Co₁₉ taken with the incident beam parallel to the [010] and [110] directions of the hexagonal axis showed many stacking faults. The intergrowth with the Sm₂Co₇ phase was observed in the matrix of the Sm₅Co₁₉ phase, the analysis being based on the thickness of blockj layers estimated by the distance of lattice fringes.     

Diffusion of self-point defects in body-centered cubic iron crystal containing dislocations

The energetic, crystallographic, and diffusion characteristics of self-point defects (SPDs) (vacancies and self-interstitial atoms (SIAs)) in body-centered cubic (bcc) iron crystal in the absence of stress fields have been obtained by the molecular statics and molecular dynamics methods. The effect of elastic stress fields of dislocations on the characteristics of SPDs (elastic dipoles) has been calculated by the methods of the anisotropic linear theory of elasticity. The SPD diffusion in the elastic fields of edge and screw dislocations (with Burgers vectors 1/2 〈111〉 and 〈100〉) at 293 K has been studied by the kinetic Monte Carlo method. The values of the SPD sink strength of dislocations of different types are obtained. Dislocations are more effective sinks for SIAs than for vacancies. The difference in the sink strengths for SIAs and vacancies in the case of edge dislocations is larger than the screw dislocations.     

Crystal structure of stacking faults in InGaAs/InAlAs/InAs heterostructures

Stacking faults and dislocations in InGaAs/InAlAs/InAs heterostructures have been studied by electron microscopy. The use of different techniques of transmission electron microscopy (primarily, highresolution dark-field scanning transmission electron microscopy) has made it possible to determine the defect structure at the atomic level.     

Ab initio study of the effect of doping on stacking faults in GaN

The influence of impurities on the basal plane stacking fault energy in GaN is investigated using density functional theory. It is found that silicon, indium, magnesium and carbon impurities each reduce the stacking fault energy by introducing changes to the bonding properties of the material. These bonding properties are analysed in terms of Mulliken charges and bond populations. It is found that the reduction in stacking fault energy correlates both with a reduction in the average anion charge and with an increase in the overlap population.     

Inhibition of neutron irradiation on oxidation stacking faults on the surface of Si wafers

The generation of stacking faults (SF) during thermal oxidation of Czochralski Si (CZ-Si) were investigated. It has been shown that oxidation-induced stacking faults (OSF) have been retarded seriously in neutron-irradiated Si. Our studies suggest that the inhibition of OSF results from the interaction of neutron-irradiated defects with oxygen in Si.     

Stacking faults in semi‐polar 6H‐SiC single crystals

6H‐SiC single crystals have been successfully grown on (1015) plane seed by sublimation method. High density stacking faults (SFs) were observed by transmission synchrotron radiation X‐ray topography. Based on the invisibility criteria of stacking faults, the displacement vectors of most SFs were determined to be the type of 1/6[1120]. Laser scanning confocal microscopy (LSCM) was used to observe the etching morphology of (0115) wafer. The etching steps of SFs were found and their density decreased from 3.6×10³ cm^‐1 to 2.0×10² cm^‐1 along the <0001> projection direction. The inclination angles of the SFs etching step plane to (10‐15) plane were measured by line scanning of LSCM. It was found that the inclination angles decreased from 20° to 10° along the <0001> projection direction. Different etching characteristics of SFs along radial direction of 6H‐SiC (1015) wafer should be attributed to different displacement vectors and different stacking fault energies for these stacking faults. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

An X-ray investigation of growth and deformation faults in a vapour grown 2H SiC crystal

Single crystals of 2H SiC grown by hydrogen reduction of methyltrichlorosilane at 1400°C frequently contain a high concentration of random stacking faults in their hexagonal closepacked | AB | AB | … structure. This given rise to diffuse streaks along reciprocal lattice rows parallel to the c¹ axis for h ? k ≠ 0 mod 3. To investigate the nature of stacking faults in these crystals, the intensity distribution along the 10. l reciprocal lattice row of a 2H SiC crystal was recorded on a 4-circle computer-controlled single crystal diffractometer. The halfwidths of 10. l reflections with l even and l odd were found to be 0.36 and 0.24 reciprocal units respectively. It is observed (i) that the 10. l reflections with l even are highly broadened and (ii) that the halfwidths of l even and l odd reflections are in the ratio of 3 : 2. This suggests that the stacking faults present are predominantly growth and deformation faults. Since the fault concentration is very high, exact theoretical expressions for the halfwidths of 10. l reflections were used to calculate the growth and deformation fault probabilities (α and β) from the observed half widths, without neglecting the second and higher order terms in α and β. It is found that α = 0.11 and β = 0.20. The deformation fault probability (β) is surprisingly high for hard and brittle material like SiC which does not undergo plastic deformation easily. It is suggested that several deformation fault configurations have resulted from a clustering of growth faults.     

Electron microscope study of intrinsic and extrinsic stacking faults,and twins in SOS at the early stage of epitaxial growth

Fine structures of the Si films on (1$\text{1}$02) sapphire have been studied by a lattice resolution TEM. The Si was deposited by the pyrolysis of silane in H₂ at 1000°C at a growth rate of 0.1μm/min. The samples for TEM were prepared by peeling off the Si films from the substrates after HF treatment. A film having a mean thickness of 500 Å was composed of (100) and {110} domains. The volume fraction of the {110} domains was more than 50% and about constant as a function of growth time. The {110} domains contained much higher density of microtwins than the (100) domains. These microtwins had various thicknesses including one atomic layer (intrinsic stacking faults) and two atomic layers (extrinsic stacking faults). The density of the intrinsic stacking faults was higher than those of extrinsic stacking faults and other twins. The {110} and (100) islands were nucleated independently and the microtwins were also present in the islands smaller than 500 Å in diameter.     

MOVPE of AlN-free hexagonal GaN/cubic SiC/Si heterostructures for vertical devices

The heterostructures of GaN/SiC/Si were prepared without using AlN or AlGaN buffer layers (AlN buffers) in the metalorganic vapor phase epitaxy of GaN on SiC. GaN (0 0 0 1) with specular surface was obtained. The AlN buffers are usually used in the conventional growth of GaN on SiC due to the poor nucleation of GaN on SiC. Instead, the nucleation of GaN was controlled by varying the partial pressure of H₂ in the carrier gas, the mixture of H₂ and N₂, during the low-temperature (600 °C) growth of GaN (LT-GaN). After the LT-GaN, the high-temperature (1000 °C) growth of GaN was performed using pure H₂ as the carrier gas. The epitaxial film of cubic SiC (1 1 1) on a Si (1 1 1) substrate was used as the SiC template. Increasing the partial pressure of H₂ in the carrier gas decreased the coverage of SiC surface by LT-GaN. It is suggested that the hydrogen atoms adsorbed on the surface of SiC is preventing the nucleation of GaN.     

Propagation behavior of threading dislocations during physical vapor transport growth of silicon carbide (SiC) single crystals

The dislocation formation and propagation processes in physical vapor transport (PVT) grown 4H silicon carbide (4H–SiC) single crystals have been investigated using defect selective etching and transmission electron microscopy (TEM). It was found that while the growth initiation process generally increased the density of threading dislocations in the grown crystal, for certain areas of the crystal, threading dislocations were terminated at the growth initiation. Foreign polytype inclusions also introduced a high density of dislocations at the polytype boundary. In the polytype-transformed areas of the crystal, almost no medium size hexagonal etch pits due to threading screw dislocations were observed, indicating that the foreign polytype inclusions had ceased the propagation of threading screw dislocations. Based on these results, we argued the formation and propagation of the threading dislocations in PVT grown SiC crystals, and proposed the dislocation conversion process as a plausible cause of the density reduction of threading dislocations during the PVT growth of SiC single crystals.     

Electron diffraction study of lizardite 1<Emphasis Type="Italic">T</Emphasis> with stacking faults

The stacking faults observed in the structure of the mineral lizardite 1T belonging to the polytype group A are investigated using the digital oblique-texture electron diffraction patterns, difference Fourier-potential maps, and model diffraction patterns obtained for this compound. Numerical simulation of the diffraction profiles along the first (the 02l and 11l reflections) and second (the 20l and 13l reflections) ellipses in the oblique-texture electron diffraction patterns is performed for finite sequences of ten layers with the use of the Markovian statistical model in the quasi-homogeneous approximation. The specific features of the intensity distributions along the first and second ellipses are associated with the manifestation of translational (displacements of the layers by ±b/3) and orientational (rotations of the layers through an angle of 180°) defects of the layer stacking, respectively. For both ellipses, the experimentally observed intensity distributions are in the best agreement with the diffraction profiles calculated for stacking faults at a content of approximately 25%, the short-range order parameter S = 1, and the maximum degree of ordering in the layer alternation. It is demonstrated that the irregularities revealed in the layer alternation in the structure of lizardite 1T (which is characterized by an identical orientation of the adjacent layers) arise from layer displacements by ±b/3 and, to a considerable extent, from the formation of sequences with opposite orientations of the adjacent layers. As a result, the structure of lizardite 1T nanocrystals involves a combination of layer sequences that are typical of structures belonging to the polytype groups A and D.     

Studies of helical dislocations,polygonization and pile-ups of dislocations in magnesium orthosilicate single crystals

(010) cleavages of magnesium orthosilicate crystals have been etched in concentrated hydrochloric acid and in its vapour at room temperature and also in the melts of sodium and potassium hydroxides at 400 °. Evidences of helical dislocations with their axes along [100] and [001] directions as revealed by etching is reported. Observations of polygonizations and pile-ups of dislocations are described and the implications are discussed.     

Observation of individual dislocations in 6H and 4H SiC by means of back‐reflection methods of X‐ray diffraction topography

SiC crystals of high structural perfection were investigated with several methods of X‐ray diffraction topography in Bragg‐case geometry. The methods included section and projection synchrotron white beam topography and monochromatic beam topography. The investigated 6H and 4H samples contained in large regions dislocations of density not exceeding 10³ cm^‐2. Most of them cannot be interpreted as hollow core dislocations (micro‐ or nano‐pipes). The concentration of the latter was lower than 10² cm^‐2. The present investigation confirmed the possibility of revealing dislocations with all used methods. The quality of presently obtained Bragg‐case multi‐crystal and section images of dislocation enabled analysis based on comparison with numerically simulated images. The analysis confirmed the domination of screw‐type dislocations in the investigated crystals. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Lattice strain and misfit dislocations in GaAs-GaAlAsP heterojunctions

The lattice strain and misfit dislocations in a GaAs-GaAlAsP heterojunction were examined. The change in lattice strain with the composition ratio or the position of the crystal was measured, and it was found that some of the misfit dislocations introduced in the heterojunction were edge-type dislocations. The critical thickness of the epitaxial layer for the generation of misfit dislocations was also measured. The critical differential strain between the atomic layers was on the order of several angstroms. The distribution of lattice strain was analyzed by a two-dimensional simple cubic lattice model, and the distribution of differential strain was examined.     

Texture growth and screw dislocations in smectic A phases

The formation of the textures of smectic A phases was investigated. In planar oriented samples the A phases grow in the shape of rods without defects. The velocity of growth is strongly anisotropic with its maximum normal to the director orientation. In non oriented samples the smectic A texture is growing in batonnets with defect structure to give focal conic textures. The maximum growth velocity of the batonnets is parallel to the director orientation. Since this would contradict to the Wulff theorem we assume a growth mechanism with a screw dislocation.     

Investigation of one‐dimensionally disordered structures of AIIBVI crystals by Monte Carlo technique III. 4H structure with different kinds of stacking faults

To investigate one‐dimensionally disordered (ODD) structures in close packed (cp) crystals, the Monte Carlo computer simulation technique has been applied. Calculations of diffraction intensity distributions along the 10.L reciprocal lattice row from 4H structure with four different kinds of stacking faults (SFs): growth, deformation, layer displacement and extrinsic fault are presented. In particular, using simple frequency function of fault to fault distances, both random and non‐random distributions of SFs are considered. Distinctive features of the diffraction patterns corresponding to the chosen examples of transformations from the parent 4H structure into another small‐period polytypes are discussed in detail.     

Forest intersection of dislocations in HCP structures

The contribution to flow stress by junction reactions in hep metals is computed using a virtual displacement method. Basal glide by 0°, 30°, 60° and 90° dislocations and trees with Burgers vector length a, c and | c + a | are considered. Conceptual shortcomings of previous treatments are discussed.     

Defect generation on mechanical surface defects before and after the oxidation (I). TEM investigations on the nucleation of oxidation stacking faults at mechanically induced weak surface defects

In order to obtain information on the nucleation mechanism of oxidation stacking faults, mechanically induced weak surface defects as simulated by low-load scratches were investigated with TEM before and after a short-time wet oxidation at 1050 °C. The experimental results could not confirm the existing models which explain stacking fault nucleation by the splitting of complete dislocations. Rather it was found that clusters of silicon interstitials are generated due to strong local compression during scratching, which then act as nuclei for stacking faults in the subsequent oxydation process.