Role of micropipes in the formation of pores at foreign polytype boundaries in SiC crystals

Abstract

The role of micropipes in pore formation in SiC crystals with foreign polytype inclusions is studied by means of synchrotron phase sensitive radiography, optical and scanning electron microscopies, and color photoluminescence. The pores at the inclusion boundaries are revealed, and their shapes and locations are analyzed. It is found that the pores arise due to the attraction of micropipes by the foreign polytype interfaces, followed by micropipe coalescence. The observed pores have tubular or slit shapes. Tubular pores nucleate at the inclusion corners, where the inclusion-associated stresses are concentrated. Slit pores spread between them and follow the shape of the inclusion boundaries. We explain the observations within a two-dimensional model of elastic interaction between micropipes and inclusion boundaries, which accounts for free surfaces of micropipes.