The properties of several point defects in hexagonal GaN that could compensate Be shallow acceptors (BeGa) were calculated by using the AIMPRO method based upon local density functional theory. BeGa itself was predicted to have local vibrational modes very similar to Mg acceptors. The highest frequency was about 663/cm. Consistent with other recent studies, it was found that interstitial Be double donors and single-donor Be split interstitial pairs at Ga sites were very likely causes of compensation. The calculations predict that the split interstitial pairs possess three main local vibrational modes at about 1041, 789 and 738/cm. Of these, the highest was very close to the experimental observation in Be-doped GaN. Although an O donor at the nearest-neighboring site to a Be acceptor (BeGa-ON) was also a prime suspect among defects that were possibly responsible for compensation, its highest frequency was calculated to be about 699/cm and hence was not related in any way to the observed center. Another mode for this defect was estimated to be about 523/cm and was localized on the ON atom. These 2 vibrations of BeGa-ON were thus equivalent to those for the isolated substitutional centers perturbed by the presence of their impurity partners.

Calculated Properties of Point Defects in Be-Doped GaN. C.D.Latham, R.M.Nieminen, C.J.Fall, R.Jones, S.Öberg, P.R.Briddon: Physical Review B, 2003, 67[20], 205206 (8pp)