A first-principles local density functional cluster program was used to model N-related shallow thermal donor defects. It was found that the bonding of O with interstitial N in Ni-O2i was almost normal, but the O atoms were moved slightly out of their bond-centered sites; thus causing the deep-donor level of Ni to become shallow. The defect had properties which were consistent with those which were observed experimentally for shallow thermal donors. It was also found that a CiH-O2i defect had very similar electronic properties. It was concluded that shallow thermal donors did not have a unique composition.

C.P.Ewels, R.Jones, S.Oberg, J.Miro, P.Deák: Physical Review Letters, 1996, 77[5], 865-8