Mechanism for the Enhanced Diffusion of Charged Oxygen Ions in SiO2

Based on real-space multigrid electronic structure calculations, we find that a double Si-O-Si bridge structure is the lowest energy configuration of interstitial oxygen ions ( O^- and O^2-) in SiO₂, where two additional Si-O bonds are formed with almost no interaction between the interstitial and host O atoms, while the peroxy linkage is the most stable structure for neutral interstitial O. We propose a diffusion mechanism of interstitial O ions generated from molecular O₂ under UV radiation, and find extremely low energy barriers of 0.11-0.27 eV for migration in the form of the double-bridge structure, in good agreement with enhanced oxidation experiments.