Structure and dynamics of the diarsenic complex in crystalline silicon

Abstract

Based on first-principles density functional theory (DFT) calculations within the generalized gradient approximation (GGA), we propose a structural model for a diarsenic $({\mathrm{As}}_{s}\ensuremath{-}{\mathrm{As}}_{i})$ complex in Si and a mechanism for its reorientation, diffusion and dissociation. We find that the lowest-energy structure of ${\mathrm{As}}_{s}\ensuremath{-}{\mathrm{As}}_{i}$ consists of two As atoms bonded together in a single lattice site with a bond axis which is tilted slightly from the [110] direction. Our study demonstrates the ${\mathrm{As}}_{s}\ensuremath{-}{\mathrm{As}}_{i}$ pair may undergo reorientations within a lattice site and diffusion, with energy barriers of 1.05 and $1.33\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$, respectively. Dissociation of an ${\mathrm{As}}_{s}\ensuremath{-}{\mathrm{As}}_{i}$ pair is likely to occur predominantly by the liberation of an $\mathrm{As}\ensuremath{-}{\mathrm{Si}}_{i}$ pair to leave behind a substititional As atom. The dissociation barrier is predicted to be $1.33\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$, and the ${\mathrm{As}}_{s}\ensuremath{-}{\mathrm{As}}_{i}$ binding energy is calculated to be $1.00\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ relative to dissociation products ${\mathrm{As}}^{0}$ and $\mathrm{As}\mathrm{Si}_{i}{}^{0}$. We also discuss the role of ${\mathrm{As}}_{s}\ensuremath{-}{\mathrm{As}}_{i}$ pairs in As transient enhanced diffusion and clustering.