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 ${\mathrm{(V}}_{\mathrm{Si}})$ 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 $V_{\mathrm{Si}}$ in 3C–SiC are stabilized in a high-spin configuration with $\text{S=1}$ giving rise to a ground state, which is a many-electron orbital singlet ${}^3{T}_1.$ For the singly negative $V_{\mathrm{Si}},$ we find a high-spin ground-state ${}^4{A}_2$ with $\text{S=3/2.}$ In the high-spin configuration, $V_{\mathrm{Si}}$ 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 $V_{\mathrm{Si}}$ has a low-spin configuration.