Theory of hydrogen-decorated gallium vacancies in GaAs and of their radiative complexes

Complexes formed by neutral or charged Ga vacancies and one or more H atoms have been investigated by using a pseudopotential-local-density-functional approach. Stable and metastable configurations have been found with some hydrogen atoms saturating As dangling bonds around the Ga vacancy. In this case, the electronic energy levels of the vacancy, although slightly lowered toward the valence band, remain in the energy gap. When one H atom is located at a bond center position next to a H-decorated vacancy, a donor level appears in the energy gap. The donor-acceptor pairs formed by this H atom and the Ga vacancy can account for the low-energy luminescence bands reported in hydrogenated p-type GaAs.