The plane-wave pseudopotential method was used to study point-defect complexes. The results revealed that defect complexes, which consisted of dominant donors that were bound to cation vacancies, were likely to form in both materials. The position of the electronic levels in the band-gap, due to these defect complexes, was shown to agree well with an experimentally observed broad-band luminescence in both materials.

T.Mattila, R.M.Nieminen: Physical Review B, 1997, 55[15], 9571-6