Structure of the silicon vacancy in6H−SiCafter annealing identified as the carbon vacancy–carbon antisite pair

We investigated radiation-induced defects in neutron-irradiated and subsequently annealed 6H-silicon carbide (SiC) with electron paramagnetic resonance (EPR), the magnetic circular dichroism of the absorption (MCDA), and MCDA-detected EPR (MCDA-EPR). In samples annealed beyond the annealing temperature of the isolated silicon vacancy we observed photoinduced EPR spectra of spin $S=1\mathrm{}$ centers that occur in orientations expected for nearest neighbor pair defects. EPR spectra of the defect on the three inequivalent lattice sites were resolved and attributed to optical transitions between photon energies of 999 and 1075 meV by MCDA-EPR. The resolved hyperfine structure indicates the presence of one single carbon nucleus and several silicon ligand nuclei. These experimental findings are interpreted with help of total energy and spin density data obtained from the standard local-spin density approximation of the density-functional theory, using relaxed defect geometries obtained from the self-consistent charge density-functional theory based tight binding scheme. We have checked several defect models of which only the photoexcited spin triplet state of the carbon antisite–carbon vacancy pair $({\mathrm{C}}_{\mathrm{Si}}-{\mathrm{V}}_{\mathrm{C}})$ in the doubly positive charge state can explain all experimental findings. We propose that the $({\mathrm{C}}_{\mathrm{Si}}-{\mathrm{V}}_{\mathrm{C}})$ defect is formed from the isolated silicon vacancy as an annealing product by the movement of a carbon neighbor into the vacancy.