Self-vacancies in gallium arsenide: An ab initio calculation

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, 2, -2, -3 charge states, but V _Ga ^-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, -1, and -3 charge states stable, while the intermediate defects are metastable. The second transition (-/-3) brings a resonant bond relaxation for V _As ^-3 similar to the one identified for silicon and GaAs divacancies.