First-principles calculations were made of Se -doped material, and a carrier compensation mechanism at high Se concentrations was proposed. It was found that the introduction of Ga vacancies near to Se atoms made the system extremely stable and semiconducting. In the high-concentration region, where the Se atoms were close to each other, the latter were expected to come together upon introducing Ga vacancies and form clusters which consisted of three Se atoms and one Ga vacancy. The extra electrons of the Se atoms were transferred to the dangling bonds of the Se or As atoms, and became electrically inactive.

J.Nara, T.Sasaki, T.Ohno: Applied Physics Letters, 1997, 70[26], 3534-6