Structural variations and defects in epitaxial 4H-SiC layers on 6H-SiC or 15R-SiC Lely wafers were investigated by means of X-ray differential diffractometry and Lang X-ray topographical methods. It was shown that the deposits consisted of several sub-layers. These 3 sub-layers were differentiated by the degree to which they relaxed the interfacial elastic strains. There was a deformed sub-layer at the interface, a middle sub-layer with randomly distributed dislocations, and an upper sub-layer which was composed of blocks that were surrounded by dislocation boundaries. The existence of a deformed sub-layer, and the extent of its relaxation, depended in general upon the type of substrate. It was assumed that the greater lattice mismatch between 4H- and 6H-SiC (as compared to 4H- and 15R-SiC) resulted in a more highly strained deformed sub-layer. This led to a more rapid relaxation process and a thinner deformed sub-layer. A misorientation between the perfect blocks of the upper sub-layer (which was larger in 4H- on 6H-, than in 4H- on 15R-) was also suggested to be caused by this. No effect of the growth conditions, particularly no effect of the growth temperature, was evident. A difference in the structural properties of transformed and epitaxial layers was explained by the differing natures of nucleation of 4H-SiC, which was probably associated with the effect of Sn or Sc doping upon the nucleation process. This made it clear that the 2 substrates produced differing effects, and that even a slight lattice mismatch could be a key factor in determining the extent and quality of the transformation of one polytype into another.

I.P.Nikitina, R.C.Glass, E.Janzén, N.B.Guseva, A.A.Maltsev: Journal of Crystal Growth, 1995, 152[4], 292-9