EPR studies of the isolated negatively charged silicon vacancies in n-type 4H- and 6H-SiC: Identification of C3v symmetry and silicon sites

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The isolated negatively charged silicon vacancy (VSi-) in the hexagonal lattices of 4H- and 6H-SiC has been studied by electron paramagnetic resonance (EPR). The local structure was suggested to have Td symmetry from the isotropic g value within the resolution of the conventional X-band measurements, from the isotropic 29Si hyperfine interaction of the next-nearest-neighbor silicon atoms and from the absence of the zero-field splitting with the high spin state of S=3/2. From the 13C hyperfine spectrum of the nearest-neighbor carbon atoms, the two kinds of VSi-, denoted VSi-(I) and VSi-(II), respectively have been distinguished. VSi-(I) and VSi-(II) are assigned to be arising from hexagonal site (h) and quasicubic sites (k in 4H-SiC, k1 and k2 in 6H-SiC), respectively. In both VSi-(I) and VSi-(II), from the 13C hyperfine interactions, the symmetry has been revealed to be C3v with the arrangement of the four nearest-neighbor carbon atoms slightly distorted from a regular tetrahedron.
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