Characterization of residual stress in bulk crystals is of vital importance since it can provide abundant information on the crystal growth and process techniques. In this paper, the residual stress in 4H-SiC bulk crystals was investigated by neutron diffraction. Detailed strain and stress calculations were performed using the Bragg equation and Hooke's law. The (0004), (11−20) and (1−100) plane diffraction profiles were measured. The strain and stress in three directions were found to be on the order of 10−4–10−3 and 100–1000 MPa, respectively. Moreover, the stress distributions in different directions were anisotropic. Amongst the stresses in these three directions, the stresses in the <1−100> direction were tensile and the maximum value was up to 2953 MPa, which indicated that there was a high risk of the grown crystals cracking in this direction.

Non-destructive characterization of diamond plate can provide abundant information. Consequently, it will help improve the growth technique. In this paper, unintentionally doped {100} diamond single crystal (type Ib) was synthesized by the temperature gradient growth (TGG) method under high pressure (~6.5 GPa) and high temperature (~1500 °C) condition. The crystal morphology was observed by confocal laser scanning microscope (CLSM). The result indicated there was a pit on diamond surface. UV/Vis transmission measurement indicated the maximum transmittance of our sample was about 9% lower than that of theoretical value. Fourier-transformation infrared spectroscopy (FTIR) measurement confirmed that the nitrogen concentration was about 53 ppm. High resolution X-Ray diffractometer (HRXRD) was employed to evaluated the crystalline quality, and result showed that the full width of half maximum (FWHM) at (400) and (111) rocking curves were 56.9′′, 23.7′′, respectively, which revealed the good crystalline quality. In addition, the diffraction peak of (400) lattice plane exhibited an increase trend with the X-ray beam position, showing the (100) lattice surface was convex bended.

4H-SiC single crystals with different nitrogen doping concentrations were grown by sublimation method. After processing, the standard 4H-SiC substrates were obtained. The carrier and nitrogen concentrations in 4H-SiC single crystals were measured by Raman spectroscopy and secondary ion mass spectrometry, respectively. The resistivities of 4H-SiC single crystals were measured by a noncontact resistivity testing system. The influence of nitrogen concentration on the resistivity of 4H-SiC single crystal was assessed. In addition, the structural qualities of 4H-SiC single crystals were investigated by high resolution X-ray diffractometry. The 004, 008 symmetric reflection rocking curves and 102, 204 skew symmetric reflection rocking curves of 4H-SiC single crystals were measured and the lattice constants of 4H-SiC single crystals were accurately determined. The effect of nitrogen concentration on the lattice constants was discussed.

The resistivities of vanadium-doped semi-insulating 4H-SiC wafers were measured by a contactless resistivity measurement system. Anomalous resistivity was found in semi-insulating 4H-SiC wafer. Raman spectra of semi-insulating 4H-SiC wafer indicated that the anomalous resistivity was caused by polytype inclusion. Based on the activation energies of different SiC polytypes calculated from resistivity versus temperature data measured by COREMA-VT, the resistivities in the vanadium-doped semi-insulating 4H-SiC wafer with 6H polytype inclusion were calculated. The calculated resistivities are quite consistent with the measured resistivities. Furthermore, the compensation mechanism for the formation of anomalous resistivity was proposed.

Hierarchical porous patterns have been fabricated on the C face, Si face, and cross section of n-type 6H–SiC crystal via photo-electrochemical etching using HF/C2H5OH and HF/H2O2 as electrolytes. The porous layer displayed multiple and multiscale microstructures on different faces, including stalactite-like, sponge-like and dendritic porous structures on C face, echinoid micro-patterns on Si face, and columnar and keel-shaped micro-patterns on the cross section. The formation of hierarchical porous pattern is ascribed to the dynamic competition balance between the electrochemical oxidation rate and the oxide removal rate. It was found that increasing the ionic strength of the electrolyte can obviously disturb the surface morphology of the porous SiC during the photo-electrochemical etching. Possible mechanisms for selective etching were further discussed.

The effect of misorientation of 6H–SiC substrate on the structural quality of GaN epilayer grown by organometallic vapor phase epitaxy (MOVPE) has been investigated. The results reveal that the structural quality of GaN epilayer is significantly influenced by the misorientation of 6H–SiC substrate. Larger misorientation angle of 6H–SiC substrate results in better structural quality of GaN epilayer, such as narrower atomic step widths of GaN surface, less yellow luminescence band/edge emission (Iy/Ib) ratio of PL, and lower dislocations density. It is also found that the Iy/Ib ratio of GaN epilayer is affected only by the misorientation angle of 6H–SiC substrate, but the screw dislocation density and edge dislocation density are influenced by both the misorientation angle and the misorientation direction of 6H–SiC substrate. GaN epilayer grown on 6H–SiC substrate with 2.3° misorientation angle towards [1 1 2¯ 0] direction has the best structural quality.Research highlights▶ Larger substrate misorientation results in better crystal quality of GaN epilayer. ▶ The dislocations density was influenced not only by the misorientation angle but also by the misorientation direction, while the point defects were affected only by the misorientation angle. ▶ GaN grown on 6H–SiC substrate with 2.3° misorientation angle and [1 1 2¯ 0] misorientation direction has the best crystal quality.

The influence of AlN buffer growth temperature on the quality and stress of 4.5 μm GaN epilayer on 6H–SiC substrate by organometallic vapor phase epitaxy (MOVPE) has been investigated. The crystalline quality and the atomic surface morphology were improved, the density of the pits and the stress of the GaN epilayer were reduced by increasing the growth temperature of the AlN buffer in the range from 950 °C to 1100 °C. By employing the optimized 1100 °C growth temperature of AlN buffer, very high quality of GaN epilayer was achieved. The X-ray full width of half maximums (FWHMs) of (0 0 2) and (1 0 2) reflection rocking curves of the GaN epilayer have been improved to 159 arcsec and 194 arcsec, respectively, and the surface RMS to only 0.31 nm in the 5 μm × 5 μm atomic force microscopy (AFM) scan. The stress of GaN epilayer was investigated by X-ray diffraction and Raman scattering as well. The degree of the tensile stress in GaN epilayer could be suppressed by increasing the growth temperature of AlN buffer. Finally, a high quality of crack-free 4.5 μm thick GaN epilayer was obtained on 6H–SiC substrate using the optimized 1100 °C AlN growth temperature.

The chemical mechanical polishing (CMP) of the Si face (0 0 0 1), the C face (0 0 0 1¯), the a face (1 1 2¯ 0) and the m face (1 1¯ 0 0) of silicon carbide (SiC) wafers was investigated. It was found that the removal rate and surface quality varied greatly with the different crystal face orientations during the CMP. Surface quality was characterized with atomic force microscopy (AFM) in terms of root mean square (RMS) roughness and high-resolution X-ray diffractometry (HRXRD). The optimum CMP process yielded a superior Si face finish with 0.096 nm RMS roughness, while no polishing action was observed on the C face. Results were explained in light of the atomic structure. CMP mechanisms of four faces were analyzed based on different polishing results.

•We find that the low angle grain boundary extends along the direction whose projection on C plane is just 〈101¯0〉.•We conclude that the edge of low angle grain boundary area is formed by the ordered arrangement of dislocations.•The low angle grain boundary was detected by the synchrotron white-beam X-ray topography.•The orientation angle of low angle grain boundary was calculated from the SWBXT and the angle difference is 2–3°.Low angle grain boundaries (LAGB) are one of the most commonly seen defects in sapphire crystals. In this paper, we have studied the origin, topography and orientation of LAGB in large sapphire crystals grown by the Kyropoulos method through etching, polaroscopy, optical microscopy as well as synchrotron white-beam X-ray topography. The results show that the LAGB starts mainly from the atomic layers mismatch caused by environmental fluctuations. The misorientation angle of the grain boundaries is 2–3°, and the grain boundaries are distributed around 〈101¯0〉 direction.

•The patterned seeds were used to improve the structural perfection of SiC crystals by PVT.•Anisotropy in lateral growth rates was observed.•The dependence of lateral growth rate on growth conditions was investigated.Growth of 6H–SiC on patterned seeds with the vertical sidewalls composed of {11–20} and {1–100} faces by a sublimation method at 1700–2000 °C was studied. Anisotropy in lateral growth rates was observed, i.e the growth rate towards <11–20> was faster than that along <1–100>. It was found that free lateral growth on mesas was accompanied by a sharp decrease in the density of threading dislocation. The dependence of lateral growth rate on growth conditions such as reactor pressure and growth temperature was investigated. The factors governing the process of lateral growth of 6H–SiC on patterned seeds were discussed.