The epitaxial graphene growth at the 4H-SiC(0001) surface with intentionally inserted step-free basal plane regions was performed by high temperature annealing in the range of 1600-1900 C under ultrahigh vacuum. For fabricating inverted-mesa structures with the step-free regions at SiC surfaces, a combined process consisting of a direct laser digging and a Si-vapor etching at 1900 C was utilized. The graphitized surfaces were characterized by atomic force microscopy, low acceleration voltage (0.1-1.0 kV) scanning electron microscopy and Raman spectroscopy. It was found that the graphene thickness at the SiC step-free surface tends to be suppressed compared with the thickness at background SiC stepterrace surfaces where the steps are intrinsically introduced from intentional/unintentional substrate miscut angles. From the characterization by Raman mapping, 1 ML graphene was obtained at the SiC step-free surface at 1600 C graphitization in contrast to the case that multilayer graphene was grown at SiC step-terrace surfaces.
For bulk growth of SiC crystal with higher quality, it is important to control the temperature distribution inside the crucible. We have performed numerical calculations of the temperature distribution inside the growing crystal, and discussed the relationship between the calculated sheer stress and the basal plane dislocation densities. We found that growth with lower basal plane dislocation defect densities, specifically at the front edge of the crystal, is possible by lowering the temperature gradient toward the growth direction.
Epitaxial layers grown on mechanically lapped 4H-SiC (0001) substrates were analyzed by using scanning ion microscopy (SIM), photoluminescence (PL) mapping and transmission electron microscopy (TEM). Even in the use of substrates with standard nitrogen concentration of 1.3 × 1019 cm-3, double Shockley-type stacking faults were observed to be formed in the epitaxial layer from the interface between the epitaxial layer and the substrate without any external stresses. Surface damaged layer seems to cause the formation of not only 2SSFs but also threading edge dislocation (TED) half-loops during epitaxial growth.
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