First-principles characterization of native defects and oxygen impurities in GaAs

We present an investigation of native defects and oxygen impurities in GaAs using hybrid functional calculations. The point defects are characterized by their structural, electronic, and optical properties. Under thermodynamic equilibrium, dominant native defects are Ga antisites (GaAs), As antisites (AsGa), and/or Ga vacancies (VGa), depending on synthesis conditions. On the basis of the defect transition levels, the isolated AsGacan be identified with theEL2center reported in experiments. This defect, however, has a negligible nonradiative electron capture cross section and thus cannot be the 'main electron trap' as commonly believed. We find that GaAs can have multiple O-related defects, especially when prepared under As-rich conditions. The quasi-substitutional O impurity (OAs) and its complex with two AsGadefects (OAs-2AsGa) both have a metastable and paramagnetic middle (neutral) charge state; however, only the latter can be identified with the experimentally observed Ga-O-Ga or 'OX' center. These two defects have large nonradiative electron capture cross sections and can be effective carrier traps or recombination centers, which has important implications for materials design.