Nitrogen-related complexes in gallium arsenide

A first-principles pseudopotential method has been used to study some poten tially important metastable defects in N-doped GaAs. Formation energies hav e been obtained and related to those of As and Ga vacancies in the intrinsi c material. Of the structures considered, two are identified that crucially depend on overall material stoichiometry. These are N on a Ga site (N-Ga) or a NN dimer on an As site (NNAs). N-Ga has a partly shallow energy-level structure with a fully occupied level lying near the valence-band edge, whe reas NNAs has localized character with a midgap deep level. Both defects ma y be responsible for the onset of a reduction in the apparent band gap that has been recently observed in heavily N-doped GaAs prior to alloying. (C) 2001 American Institute of Physics.