Symmetry, spin state and hyperfine parameters of vacancies in cubic SiC

Cluster calculation of carbon and silicon vacancies in cubic SiC has been performed for the charge states of +1, 0 and −1 and possible spin states. The density functional theory has been used with the B3LYP exchange-correlation functional and Gaussian basis set applied to the 52- and 70-atom clusters. Being suitable for a comparison with EPR data, the calculations of hyperfine coupling parameters for atoms of the first and second shells of vacancies have been performed. The test calculations have been done to check the validity of applied approximations, and reasonable agreement between calculated and experimental data has been obtained. The ground spin state and the defect point symmetry for all the above-mentioned charge states have been determined along with the hyperfine parameters for atoms of the first and second shells. In the ground state, spins of VC−, VSi− and VSi+ have the value of S=32, while S=1 for VC0 and VSi0, and S=12 for VC+. Optimization of geometry leads to a minimum with the Td symmetry only for VC−, VSi− and VSi+ centers. At the same time, VSi0 and VC+ defects have D2d symmetry, while VC0 has C3V symmetry. All the considered charge states of the carbon vacancy exhibit remarkably stronger hyperfine interaction with the nearest and next-nearest neighbors as compared to the silicon vacancy.