Using the self-consistent-charge density-functional-based tight-binding (SCC-DFTB) method, the migration of vacancies at high temperatures was investigated; taking into account the entropy contribution to the Gibbs free energy. It was found that the energy barrier for sub-lattice migration of VSi was lower than that for VC, so that VSi should anneal out at lower temperatures, which agrees with the experimental observations for as-grown SiC. In irradiated material, vacancies and interstitials were expected to appear in high concentrations. In the early stages of annealing, their recombination could also result in antisites. It was shown that at annealing temperatures at which vacancies were mobile, their motion could mediate the migration of antisites. The vacancy-assisted diffusion of C antisites was much faster than that of Si antisites and may lead to the formation of C antisite clusters. A mechanism was proposed for the formation of antisite clusters during the migration of Si vacancies. The role of these complexes in the formation of very stable defects, observed in irradiated SiC, was discussed, additionally.

Theoretical Study of Vacancy Diffusion and Vacancy-Assisted Clustering of Antisites in SiC. E.Rauls, T.Frauenheim, A.Gali, P.Deák: Physical Review B, 2003, 68[15], 155208 (9pp)