Local electronic structure around vacancies and vacancy-antisite complexes in beta-SiC

The local electronic structure around vacancies and vacancy-antisite complexes in cubic SiC has been calculated by means of the LMTO (linear muffin-tin orbital) method and the supercell approach. In order to improve the description of the electronic structure near the energy gap, the orbital-dependent LDA+U potential has been used. Different models for the displacement of the atoms around the defects are discussed. It has been shown that the atoms surrounding a silicon vacancy (VSi ) relax outwards from the vacancy, while for a carbon vacancy (VC ) a distortion of the tetrahedral arrangement of atoms is the more reliable model. The calculations of the local electronic structure performed for the vacancy-antisite complexes show that the VSi + SiC complex is characterized by a repulsive interaction between the SiC antisite and the three carbon atoms surrounding the vacancy. In contrast, the stability of the VC + CSi complex is determined by the bonding of the atoms surrounding the vacancy. In all cases the appearance of the localized electron state in the middle region of the energy gap is a characteristic feature of the vacancy-antisite complex. Some possible mechanisms of the annealing out of the vacancies in -SiC are discussed.