Local electronic structure around vacancies and vacancy-antisite complexesin beta-SiC

The local electronic structure around vacancies and vacancy-antisite comple xes in cubic SiC has been calculated by means of the LMTO (linear muffin-ti n orbital) method and the supercell approach. In order to improve the descr iption of the electronic structure near the energy gap, the orbital-depende nt LDA + U potential has been used. Different models for the displacement o f the atoms around the defects are discussed. It has been shown that the at oms surrounding a silicon vacancy (V-Si) relax outwards from the vacancy, w hile for a carbon vacancy (V-C) a distortion of the tetrahedral arrangement of atoms is the more reliable model. The calculations of the local electro nic structure performed for the vacancy-antisite complexes show that the V- Si +Si-C complex is characterized by a repulsive interaction between the Si c antisite and the three carbon atoms surrounding the vacancy. In contrast, the stability of the V-C + C-Si complex is determined by the bonding of th e atoms surrounding the vacancy. In all cases the appearance of the localiz ed electron state in the middle region of the energy gap is a characteristi c feature of the vacancy-antisite complex. Some possible mechanisms of the annealing out of the vacancies in beta-SiC are discussed.