First-principles total-energy calculations were described which provided stable and metastable geometries and diffusion mechanisms of B in SiO2 with point defects which contain O vacancies and O interstitials. It was found that a B atom forms various stable and metastable geometries in SiO2 with point defects, depending on its charge state and surrounding environments. Calculations were also performed that clarify the chemical feasibility of bonding configurations between a B atom and constituent atoms in SiO2. It was found that wave function distribution around the impurity and its occupation were essential to determine the geometry for each charge state. Binding energies of a B atom with constituent atoms in SiO2 were decisive factors to the bond configuration around the B atom. In the case of B in SiO2 with an O interstitial, a B atom forms a very stable B-O complex in which the B atom was bound to the O interstitial. Once the B-O complex was formed, the B atom diffused via the SiO2 network keeping this B-O unit with unexpectedly small activation energies of 2.1 to 2.3eV. The calculated activation energies agreed well with the data experimentally available.

First-Principles Calculations of Boron-Related Defects in SiO2. M.Otani, K.Shiraishi, A.Oshiyama: Physical Review B, 2003, 68[18], 184112