The equilibrium geometries, phonon spectra, electronic structures and optical properties of the CiOi defect in bulk Si and Si1-xGex systems were calculated using the ab initio plane wave density-functional method. It was found that in a Ge-doped Si crystal it was more energetically favorable for the defect to stabilize in a configuration with no Ge atoms in the first sphere. The calculations showed that the vibrational properties of the defect in the Si1-xGex alloy were similar to those in the pure Si bulk crystal and only one local vibrational mode was sensitive to the presence of the Ge substitutions. The effect of C, O, Si and Ge isotopes upon the phonon spectra were also investigated and were found to be in good agreement with available experimental data. It also followed, from the calculations of the singlet–triplet splitting and a position of the gap state of the defect with respect to the top of the valence band, that the optical energies of the CiOi defect were expected to increase due to Ge doping; in agreement with available experimental data.

The Interstitial CiOi Defect in Bulk Si and Si1-xGex. S.Hao, L.Kantorovich, G.Davies: Journal of Physics - Condensed Matter, 2004, 16[47], 8545-55