In non-annealed 6H-SiC samples that were electron irradiated at low temperature, a new EPR signal due to a S=1 defect center with exceptionally large zero-field splitting (D=+652 x 10−4/cm, E=−8 x 10−4/cm) was observed under illumination. A positive sign of D demonstrated that the spin–orbit contribution to the zero-field splitting exceeds by far that of the spin–spin interaction. A principal axis of the fine-structure tilted by 59° against the crystal c-axis as well as the exceptionally high zero-field splitting D could be qualitatively understood by the occurrence of additional close-lying defect levels in defect clusters resulting in comparatively large second-order spin–orbit coupling. A tentative assignment to vacancy clusters was supported by the observed annealing behaviour.

Vacancy Clusters Created via Room Temperature Irradiation in 6H-SiC. A.Scholle, S.Greulich-Weber, E.Rauls, W.G.Schmidt, U.Gerstmann: Physica B, 2009, 404[23-24], 4742-4