The Interstitial Carbon–Dioxygen Center in Irradiated Silicon

We investigated, experimentally as well as theoretically, defect structures in electron irradiated Czochralski-grown silicon (Cz-Si) containing carbon. Infrared spectroscopy (IR) studies observed a band at 1020 cm ⁻¹ arisen in the spectra around 300 ^◦C. Its growth occurs concomitantly with the decay out of the well-known vacancy-oxygen (VO) defect, with a Local Vibrational Mode (LVM) at 830 cm ⁻¹ and carbon interstitial-oxygen interstitial (C _iO _i) defect with a LVM at 862 cm ⁻¹, in silicon (Si). The main purpose of this work is to establish the origin of the 1020 cm ⁻¹ band. One potential candidate is the carbon interstitial-dioxygen (C _iO _2i) defect since it is expected to form upon annealing out of the C _iO _i pair. To this end, systematic density functional theory (DFT) calculations were used to predict the lowest energy structure of the (C _iO _2i) defect in Si. Thereafter, we employed the dipole–dipole interaction method to calculate the vibrational frequencies of the structure. We found that C _iO _2i defect has an LVM at ~1006 cm ⁻¹, a value very close to our experimental one. The analysis and study of the results lead us to tentatively correlate the 1020 cm ⁻¹ band with the C _iO _2i defect.