Experimentally identified deep levels in p-type material, at about 0.9 to 1, 1.4, and 1.8 to 2eV above the valence-band maximum, were attributed to Ga vacancies. On the basis of first-principles calculations, it was concluded that it was necessary to consider the structural modification, VGa → Nanti + VN, which resulted from the transfer of a nearest-neighbor N atom to a Ga-vacancy site, in order to explain the levels at 1 and 2eV. Isolated N antisite and N-vacancy defects were found to give rise to additional deep levels at 1.4 and 0.8eV, respectively.

D.J.Chadi: Applied Physics Letters, 1997, 71[20], 2970-1