Self-vacancies in gallium arsenide: Anab initiocalculation

We report here a reexamination of the static properties of vacancies in GaAs by means of first-principles density-functional calculations using localized basis sets. Our calculated formation energies yields results that are in good agreement with recent experimental and ab initio calculation and provide a complete description of the relaxation geometry and energetic for various charge states of vacancies from both sublattices. Gallium vacancies are stable in the 0, \ensuremath{-}, $\ensuremath{-}2$, $\ensuremath{-}3$ charge states, but ${V}_{\mathrm{Ga}}^{\ensuremath{-}3}$ remains the dominant charge state for intrinsic and $n$-type GaAs, confirming results from positron annihilation. Interestingly, arsenic vacancies show two successive negative-$U$ transitions making only $+1$, $\ensuremath{-}1$, and $\ensuremath{-}3$ charge states stable, while the intermediate defects are metastable. The second transition $(\ensuremath{-}∕\ensuremath{-}3)$ brings a resonant bond relaxation for ${V}_{\mathrm{As}}^{\ensuremath{-}3}$ similar to the one identified for silicon and GaAs divacancies.