Silicon vacancy in SiC:: A high-spin state defect

We report results from spin-polarized ab initio local spin-density calculations for the silicon vacancy (V-Si) in 3C- and 2H-SiC in all its possible charge states. The calculated electronic structure for SiC reveals the presence of a stable spin-aligned electron-state t(2) near the midgap. The neutral and doubly negative charge states of V-Si in 3C-SiC are stabilized in a high-spin configuration with S = 1 giving rise to a ground state, which is a many-electron orbital singlet T-3(1). For the singly negative V-Si, we find a high-spin ground-state (4)A(2) with S = 3/2. In the high-spin configuration,V-Si preserves the T-d symmetry. These results indicate that in neutral, singly, and doubly negative charge states a strong exchange coupling, which prefers parallel electron spins, overcomes the Jahn-Teller energy. In other charge states, the ground state of V-Si has a low-spin configuration. (C) 1999 American Institute of Physics. [S0003-6951(99)04702-6].