Computational study of interstitial oxygen and vacancy-oxygen complexes in silicon

The formation and binding energies, the ionization levels, the structures, and the local vibrations of Oᵢ, O₂ᵢ, O₃ᵢ, VO, VO₂, and V₂O $(V$=vacancy) in silicon are calculated using a self-consistent total-energy pseudopotential method. The most important results are as follows: The ionization levels and associated structures are given for VO and V₂O as well as the local vibration modes for the negative charge states of VO. The experimental frequency of Oᵢ at 517 cm^-1 is associated tentatively with an oxygen-induced silicon mode of weakly interacting Oᵢ's. We find two competing structures for O₂ᵢ: the staggered configuration and the skewed Oᵢ-Si-Si-Oᵢ configuration with the binding energies of 0.2 and 0.1 eV, respectively. The experimental frequencies of O₂ᵢ at 1060, 1012, 690, and 556 cm^-1 are found to originate from the staggered O₂ᵢ. The experimental frequency of O₂ᵢ at 1105 cm^-1 is found to originate from the skewed Oᵢ-Si-Si-Oᵢ configuration of O₂ᵢ. The calculated effects of pressure on the structures and local vibration frequencies (Gr\"uneisen parameters) of Oᵢ and O₂ᵢ are presented.