Oxygen defect in silicon studied by semi-empirical calculations

The atomic and electronic structure of interstitial oxygen in bulk silicon is studied by a semi-empirical Hartree--Fock technique. The calculations are performed in real space on a hydrogen terminated cluster in combination with a new parameterization of oxygen within the framework of the modified neglect of diatomic overlap (MNDO) technique. We find that the results on the silicon cluster are in good agreement with experiment as well as with the results of ab initio calculations. Moreover, the various charge states of the oxygen have been analyzed. It has been found that interstitial oxygen in both neutral and double negative charge state forms a stable configuration but the single negative state forms an instable configuration with a strong level in the band gap at Ev +0.55 eV.