Structure and diffusion of oxygen and silicon interstitials in silicon

Ab initio quantum chemical simulation of silicon interstitials and oxygen-related defects O_i, V-O₂, and V-O₄ in oxygen-containing silicon was performed using the embedded molecular cluster model. The defect geometry and electronic structure were studied. The migration activation energy for O_i defect was estimated as 2.73 eV at the atmospheric pressure, and 2.70, 2.68, and 1.92 eV for the lattice compressed by 0.25, 0.37, or 5.0 per cent, respectively. The activation energy of silicon interstitial is not changing with pressure. The molecular cluster used to simulate V-O₄ defect with C_2v symmetry was shown to have only slight deviation from D_2d at atmospheric pressure, a strong deviation at 5.0 per cent lattice compression, and two energetically near (by 0.15 eV) configurations at lattice compression 0.37 per cent, the less distorted configuration being lower in energy. The cluster used for V-O₂ defect (C_2v symmetry again) was shown to have only slight deviation from D_2d for all studied pressure values. The topographs showed significantly smaller size and higher concentration of defects in case of high-pressure treatment. Both theoretical and experimental results support our suggestion that high pressure increases the effective radius of O_i interaction with nucleation centre and yields a lower preexponential factor of the diffusion coefficient due to O capture by nucleation centres.