Calculations were made of the electronic and atomic structures of neutral and charged di-vacancies by using the first-principles Car-Parrinello method. It was found that the di-vacancy relaxed inwards in all of the charge states (2-, 1-, 0, 1+) which were studied. It was found that the defect-induced electron levels lay in the lower half of the fundamental band gap. The doubly-negative di-vacancy was the most stable one for nearly all values

of the electron chemical potential within the band-gap. The deep-level electron density was localized at the Ga-vacancy end of the di-vacancy, and the ionic relaxation was stronger there than at the As-vacancy end. The thermodynamic concentrations of several native defects were also calculated.

S.Pöykkö, M.J.Puska, R.M.Nieminen: Physical Review B, 1996, 53[7], 3813-9