Substitutional carbon-dioxygen center in irradiated silicon

This work reports theoretical and experimental studies of the substitutional carbon-dioxygen (CsO2i) defect in silicon (Si). To this end, density functional theory (DFT) calculations were used to predict the lowest energy structure of the defect. Thereafter, the dipole-dipole interaction method was employed to calculate the local vibration modes (LVM) of this lowest energy structure. We found that the CsO2i defect is characterized by two LVM frequencies at 1064.7 and 1140.1 cm−1. These values are quite close to experimental bands of earlier studies at 1048 and 1094 cm−1 (deviation ~1.6 and 4.2%) reported in the literature, both attributed to the CsO2i defect. Next, infrared Spectroscopy (IR) measurements were carried, out at room temperature (RT), on electron irradiated Si samples. A band at 1048 cm−1 was observed. It is grown in the spectra upon annealing out of the 830 cm−1 band of the vacancy-oxygen center (VO) and the 861 cm−1 band of the carbon interstitial-oxygen interstitial center (CiOi). Furthermore, isochronal anneals were carried out to monitor the evolution of the band. The analysis and examination of the results lead us to suggest that the 1048 cm−1 band originates from the CsO2i complex, formed according to the reaction: VO + CiOi → CsO2i. The other band at 1094 cm−1 is most probably masked by the very strong band of Oi (1107 cm−1, at RT) in Si.