Positive and Negative Oxygen Vacancies in Amorphous Silica

We modeled all stable positive and negative charge states of oxygen vacancies originating from the neutral O3 Si=Si O3 defect in amorphous SiO2 (a-SiO2) using an embedded cluster method on a distribution of structural sites. For the first time, we predict the geometry, electronic structure and spectroscopic properties of doubly ionized and negatively charged oxygen vacancies in a-SiO2 and demonstrate that negatively charged vacancies serve as deep electron traps. The results demonstrate that oxygen vacancies can be responsible for both the electron and hole trapping in silica. We compare our findings with the previous calculations and with the recent experimental data.