Propagation Of Basal Plane Dislocations Research Articles

Macro Step Bunching/Debunching Engineering on 4° off 4H-SiC (0001) to Control the BPD-TED Conversion Ratio by Dynamic AGE-Ing<sup>®</sup>

This paper presents an investigation into the surface morphology control of 4H-SiC (0001) wafers cut to 4º off during thermal processing, aiming to suppress the propagation of basal plane dislocations (BPD) into the epitaxial growth layer. Developing methods for debunching rough surfaces with macro step bunching (MSB) using thermal processes removes many of the limitations of the conventional epitaxial growth process. This study presents a surface morphology control method that includes debunching of steps by thermal sublimation etching/growth using the Dynamic AGE-ing® (DA) method. By controlling the surface morphology before and after growth using this method, the dependence of the BPD-threading edge dislocation (TED) conversion ratio on surface morphology was systematically revealed. By selecting the optimal pre- and post-growth surface morphology, a 100 % BPD-TED conversion ratio was obtained for the 10 mm × 25 mm area. It was indicated that an innovative and stable surface morphology control technique using the DA sublimation process could solve numerous technological challenges in various fields.

Effect of temperature on conversion of basal plane dislocations to treading edge dislocations during 4H-SiC homoepitaxiy

Abstract 4H-SiC homoepitaxial layer grown on 4° off-axis substrates is performed at various growth temperature by using the traditional chemical vapor deposition. The effect of growth temperature on propagation of basal plane dislocations from substrate to epitaxy was studied using the deep KOH etching and Synchrotron reflection X-ray topography, and the conversion mechanism was also investigated. It is found that the majority basal plane dislocations are converted to threading edge dislocations during epitaxial growth. Meanwhile, the two types of threading edge dislocations in epitaxial layer are observed after KOH etch. By the optimization of growth temperature, high quality epitaxial wafer with extremely low basal plane dislocations density (

Direct observation of dislocation formation and plastic anisotropy in Nb2AlC MAX phase using in situ nanomechanics in transmission electron microscopy

We report on the direct observation of nucleation and propagation of basal plane dislocations in Nb2AlC, a member of MAX phases, using nanomechanical testing inside a transmission electron microscope. Different loading directions with respect to the basal plane resulted in completely different plastic response due to the pronounced anisotropy of the layered crystal. Discrete dislocation activities were correlated to distinct events in the force-displacement curves. In situ observations together with post-mortem contrast analyses of deformed regions show no indication of cross-slip or entanglement of dislocations during the indentations.

Effect of Low Pressure on Surface Roughness and Morphological Defects of 4H-SiC Epitaxial Layers.

In this work, 4H-SiC epilayers are performed on 4° off-axis substrates under low pressure condition by horizontal hot wall chemical vapor deposition (HWCVD) with a standard chemistry of silane-propane-hydrogen, which focuses on the effects of growth pressure on morphology, basal plane dislocations (BPDs) and crystalline quality. It is found that morphological defects reduce with the decreasing of growth pressure, since the surface diffusion length of absorbed adatoms increases under low growth pressure, which suppresses the nucleation of adatoms on terraces and the formation of morphological defects. However, as the surface diffusion length increases under low growth pressure, the difference of growth velocity at steps is enhanced, which leads to the extension of the steps’ width and the formation of step-bunching. Besides variation of surface diffusion length, the phenomenon described above can be correlated with different dominate modes for the minimization of surface energy at varied growth pressure. Because of the contrary influence of increased C/Si ratio and enhanced step-flow growth on the propagation of BPDs, the dislocation densities of BPDs and threading edge dislocations (TEDs) in epilayers grown at varied pressures remain basically unchanged. The crystalline quality is almost independent of growth pressure based on high resolution X-ray diffraction (HRXRD) measurements.

Imaging and Strain Analysis of Threading-Edge and Basal-Plane Dislocations in 4H-SiC Using X-Ray Three-Dimensional Topography

This paper demonstrates the X-ray three-dimensional topography of basal-plane dislocations (BPDs) and threading edge dislocations (TEDs) in 4H-SiC. Cross-sectional imaging shows the propagation of BPDs from a substrate to an epilayer and the conversion of BPDs into TEDs near the epilayer/substrate interface. The strain analysis of TEDs exhibits the image of strains in the order of ±10-5. The observed strain images correlate well to simulation results.

X-Ray Three-Dimensional Topography Imaging of Basal-Plane and Threading-Edge Dislocations in 4H-SiC

This paper demonstrates the X-ray three-dimensional (3D) topography of basal-plane dislocations (BPDs) and threading edge dislocations (TEDs) in 4H-SiC for the first time. Stereographic topographs are obtained for BPDs and TEDs, showing the propagation of BPDs from a substrate to an epilayer and the conversion of BPDs into TEDs near the epilayer/substrate interface. Strain analysis is also demonstrated for a TED, providing the image of strains in the order of ±10-5. It is verified that the 3D topography is successfully applicable to BPDs and TEDs.

Fast Epitaxial Growth of 4H-SiC and Analysis of Defect Transfer

The transfer and generation of extended defects in 4H-SiC epitaxial growth at a high growth rate are examined. An epilayer with virtually no basal plane dislocations (BPDs) is obtained using 4º off Si-face substrates, although the formation of 3C-polytype inclusions is occasionally observed. The behavior of BPDs and threading screw dislocations (TSDs) in epitaxial growth is also investigated by X-ray topography and transmission electron microscopy, and the propagation of BPDs and conversion and generation of TSDs in the epilayers are discussed.

Dislocation conversion in 4H silicon carbide epitaxy

The propagation of basal plane dislocations from off-axis 4H silicon carbide substrates into the homo-epitaxial layers has been investigated using chemical etching, optical microscopy, and transmission electron microscopy (TEM). The etch pit densities of threading edge and basal plane dislocations changed significantly across the epilayer/substrate interface. We have observed conversion of basal plane dislocations in the substrates into threading edge dislocations in the epilayers. TEM observation revealed that the threading dislocations in the epilayers are inclined from the c-axis toward the down-step direction. The conversion is interpreted as a result of the image force in the epilayers between flowing growth steps and basal plane dislocations. This effect can lead to an apparent improvement of the structural quality of epilayers compared to that of substrates.

High-temperature deformation and fracture of Bi–Sr–Ca–Cu–O superconductors

Dense polycrystalline Bi2Sr2Cu2Ox (2201), Bi2Sr2CaCu2Ox (2212), and (Bi, Pb)2Sr2Ca2Cu3Ox (2223) specimens were compressed in air at 730–835 °C. All of the materials exhibited an apparent steady-state creep response. Strain rate was proportional to stress to the 3.1–3.8 power. Apparent activation energies for the deformation processes were 520 ± 50 kJ/mole for the 2201, 630 ± 210 kJ/mole for the 2212, and 960 ± 210 kJ/mole for the 2223. Transmission electron microscopy revealed substantial generation and propagation of basal-plane dislocations during deformation. Few nonbasal-plane dislocations were observed. Intergranular fracture was evident in all deformed samples, and intragianular fracture was evident along the basal planes of some grains. It is suggested that the kinetics of fracture were determined by dislocation motion within the grains.