Large-scale ab initio simulation methods were employed to investigate the configurations and properties of defects in SiC. Atomic structures, formation energies and binding energies of small vacancy clusters have also been studied as a function of cluster size, and their relative stabilities were determined. The calculated formation energies of point defects were in good agreement with previously theoretical calculations. The results showed that the di-vacancy cluster consists of two C vacancies located at the second nearest neighbour sites was stable up to 1300K, while a di-vacancy with two Si vacancies was not stable and may dissociate at room temperature. In general, the formation energies of small vacancy clusters increased with size, but the formation energies for clusters with a Si vacancy and nC vacancies (VSi–nVC) were much smaller than those with a C vacancy and nSi vacancies (VC–nVSi). These results demonstrated that the VSi–nVC clusters were more stable than the VC–nVSi clusters in SiC, and provide possible nucleation sites for larger vacancy clusters or voids to grow. For these small vacancy clusters, the binding energy decreased with increasing cluster size, and ranges from 2.5 to 4.6eV. These results indicated that the small vacancy clusters in SiC were stable at up to 1900K, which was consistent with experimental observations.

Formation and Properties of Defects and Small Vacancy Clusters in SiC - Ab initio calculations. F.Gao, W.J.Weber, H.Y.Xiao, X.T.Zu: Nuclear Instruments and Methods in Physics Research B, 2009, 267[18], 2995-8