Microscopic nature and optical properties of metastable defects in electron-irradiated GaAs

Systematic correlation of infrared absorption and positron annihilation experiments allows us to identify two metastable defects in electron-irradiated GaAs. The first one is present already in as-grown material, and can be identified as the native EL2 defect by its photoquenching and subsequent thermal-annealing properties. The second one is introduced by irradiation at 300 K, and it disappears in thermal annealing at 520 K. Its metastable state is optically active, anneals at 70 K, and exhibits optical recovery at 25 K. Positron experiments indicate that both of these defects have a vacancy in their metastable state in good agreement with the vacancy-interstitial model of the As antisite defect. Therefore, the native defect is here attributed to an As antisite and the irradiation-induced one to an As antisite complex. The metastable state of the AsGa complex can be generated with 1.075-eV photons and recovered with 1.35-eV photons with optical cross sections of 2×{}10^-20 and 5×{}10^-19 cm², respectively. The metastable state of the AsGa complex absorbs 0.7-1.2-eV photons, indicating that it has ionization levels in the band gap.