A first-principles pseudopotential method was used to study some potentially important metastable defects in N-doped material. Formation energies were deduced and were related to those of As and Ga vacancies in the intrinsic material. Of the structures considered, 2 were identified which depended critically upon the overall material

stoichiometry. These were N on a Ga site, NGa, or an NN dimer on an As site, NNAs. The NGa had a partly shallow energy-level structure with a fully occupied level lying near to the valence-band edge. The NNAs had a localized nature, with a mid-gap deep level. Both defects were suggested to be responsible for the onset of a reduction in the apparent band-gap that had been observed in heavily N-doped GaAs before alloying.

Nitrogen-Related Complexes in Gallium Arsenide. J.E.Lowther, S.K.Estreicher, H.Temkin: Applied Physics Letters, 2001, 79[2], 200-2