A first-principles total-energy investigation was made of the geometries, formation energies, and electronic structures of N which occupied As or Ga sites (NAs or NGa). It was found that both neutral defects induced impurity-like empty levels, in the band-gap, which acted as acceptors. Whereas NAs produced an s-like a1 level in the middle of the band-gap, NGa produced a p-like t2 level which was close to the bottom of the conduction band. The gap level of NAs provided theoretical support for an experimentally observed band-edge red-shift in GaAsN having a N concentration of about 3%. Strong inward relaxations which preserved Td symmetry characterized the NAs equilibrium geometry in all of the charge states which were investigated. On the other hand, NGa exhibited a structural metastability in the neutral charge state, and Jahn-Teller off-center distortions in the negative charge states; forming a negative-U center.

Ab Initio Study of Substitutional Nitrogen in GaAs. W.Orellana, A.C.Ferraz: Applied Physics Letters, 2001, 78[9], 1231-3