Theoretical study of vacancy diffusion and vacancy-assisted clustering of antisites in SiC -: art. no. 155208

Using the self-consistent-charge density-functional-based tight-binding (SCC-DFTB) method, we have investigated the migration of vacancies at high temperatures, taking into account the entropy contribution to the Gibbs free energy. We have found that the energy barrier for sublattice migration of V-Si is lower than that for V-C, so that V-Si should anneal out at lower temperatures, which agrees with the experimental observations for as-grown SiC. In irradiated material, vacancies and interstitials are expected to appear in high concentrations. In the early stages of annealing, their recombination can also result in antisites. We show that at annealing temperatures at which vacancies are mobile, their motion can mediate the migration of antisites. The vacancy-assisted diffusion of carbon antisites is much faster than that of silicon antisites and may lead to the formation of carbon antisite clusters. We propose a mechanism for the formation of antisite clusters during the migration of silicon vacancies. The role of these complexes in the formation of very stable defects, observed in irradiated SiC, is discussed, additionally.