Theoretical studies on defects in SiC

Ab initio LDA calculations on a molecular cluster model of SIC(SC) has been carried out for the donors nitrogen, phosphorus, and arsenic, as well as for substitutional and interstitial oxygen. It is found that N at the C site (giving rise to a shallow donor state) is favored only by 0.35 eV over N at a Si site (giving rise to a trap), if symmetry lowering reconstruction is allowed. No such effect was found for P-Si and As-Si. Oxygen is found to be electrically inactive as an interstitial, and giving rise to hyper-deep double donor levels as substitutional. A semi-empirical quantum chemical and an LDA based tight binding Hamiltonian has been tested (for later use in more complicated defects and polytypes) on intrinsic defects. Preliminary results are given for the equilibrium geometry, electronic structure and charge state of vacancies and anti sites.