First-principles calculations of boron-related defects inSiO2

Abstract

We report first-principle total-energy calculations that provide stable and metastable geometries and diffusion mechanisms of boron in ${\mathrm{SiO}}_{2}$ with point defects which contain O vacancies and O interstitials. We find that a B atom forms various stable and metastable geometries in ${\mathrm{SiO}}_{2}$ 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 ${\mathrm{SiO}}_{2}.$ 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 ${\mathrm{SiO}}_{2}$ are decisive factors to the bond configuration around the B atom. In the case of B in ${\mathrm{SiO}}_{2}$ 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 ${\mathrm{SiO}}_{2}$ 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.