Influence of polytypism on properties of intrinsic defects in SiC

Symmetry considerations and classical-potential computer simulations are employed to perform a comparative study of properties of intrinsic defects in 3C- and 4H-SiC. Investigations of the polytype structure reveal that the number of non-equivalent point defects in 4H-SiC should be significantly higher than in 3C-SiC. Most of the potential defects are found to be stable. A considerable difference between 3C- and 4H-SiC exists for some dumbbells with a complex and anisotropic structure. This is due to the important role of lattice deformations beyond the first neighbor shell and the fact that the spatial distribution of these deformations is strongly dependent on the polytype. The interstitials between hexagonal and trigonal rings are characteristic for 4H and other hexagonal polytypes. They do not exist in 3C-SiC. In the case of more compact and isotropic defects, such as vacancies, anitisites, hexagonal interstitials and many dumbbells, the influence of polytypism is small. The properties of tetrahedral interstitials in 3C- and 4H-SiC are very similar since in both polytypes their first, second and third neighbor shells are equal. Besides the elementary defects, the structure and energetics of defect clusters is investigated.