A study was made of the electronic and structural properties of native defects (N vacancy, B antisite, substitutional O), in the cubic phase, by using all-electron first-principles total-energy calculations. It was found that all of the defects introduced a deep state above the middle of the energy-gap. These defects had C3v local symmetry. A Jahn-Teller distortion in the <111> direction was observed for the neutral isolated B antisite. Strong relaxation was found in the case of the neutral N vacancy. A highly localized orbital in the vacancy region (F-center precursor) and a resonant orbital in the conduction band appeared before lattice relaxation. Such relaxation, plus distortion, split the resonant orbital and led to a half-occupied level close to the conduction band. The results suggested that a strong electron paramagnetic resonance signal which was detected in cubic material could be generated by the trapping of 2 electrons by acceptor levels which were introduced by C doping.

P.Piquini, R.Mota, T.M.Schmidt, A.Fazzio: Physical Review B, 1997, 56[7], 3556-9