First-principles calculations of boron-related defects in SiO2 -: art. no. 184112

We report first-principle total-energy calculations that provide stable and metastable geometries and diffusion mechanisms of boron in SiO2 with point defects which contain O vacancies and O interstitials. We find that a B atom forms various stable and metastable geometries in SiO2 with point defects, depending on its charge state and surrounding environments. We also perform calculations that clarify the chemical feasibility of bonding configurations between a B atom and constituent atoms in SiO2. It is found that wave function distribution around the impurity and its occupation are essential to determine the geometry for each charge state. Binding energies of a B atom with constituent atoms in SiO2 are 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 is bound to the O interstitial. Once the B-O complex is formed, the B atom diffuses via the SiO2 network keeping this B-O unit with unexpectedly small activation energies of 2.1-2.3 eV. The calculated activation energies agree well with the data experimentally available.