Transition metal defects were studied in different polytypes of silicon carbide by ab initio super-cell calculations. Asymmetrical split-vacancy complexes were found for defects that formed preferentially at only one site in hexagonal polytypes, and might not be detectable at all in cubic polytype. Electron spin resonance studies demonstrated the existence of an asymmetric split-vacancy complex in niobium doped 4H polytype of SiC.

Asymmetric Split-Vacancy Defects in SiC Polytypes: a Combined Theoretical and Electron Spin Resonance Study. V.Ivády, A.Gällström, N.T.Son, E.Janzén, A.Gali: Physical Review Letters, 2011, 107[19], 195501