Gallium interstitial contributions to diffusion in gallium arsenide

Abstract

Enthalpies of formation of gallium interstitials and all the other native point defects in gallium arsenide are calculated using the same well-converged \emph{ab initio} techniques. Using these results, equilibrium concentrations of these defects are computed as a function of chemical potential from the arsenic rich limit to the gallium rich limit and as a function of the doping level from $p$-type to $n$-type. Gallium interstitial diffusion paths and migration barriers for diffusion are determined for all the interstitial charge states which are favored for Fermi levels anywhere in the gap, and the charge states which dominate diffusion as a function of Fermi level are identified. The effects of chemical potential, doping level, and non-equilibrium defect concentrations produced by ion implantation or irradiation on gallium self-diffusion are examined. Results are consistent with experimental results across the ranges of doping and stoichometry where comparisons can be made. Finally, these calculations shed some light on the complex situation for gallium diffusion in gallium arsenide that is gallium-rich and doped heavily $p$-type.