A systematic correlation of infra-red absorption and positron annihilation data permitted the identification of 2 metastable defects in electron-irradiated samples. The first defect was already present in as-grown material, and was identified as being the native EL2 defect; due to its photo-quenching and subsequent annealing behaviors. The second defect was introduced by irradiation at 300K, and disappeared during annealing at 520K. Its metastable state was optically active, annealed out at 70K, and underwent optical recovery at 25K. Positron techniques indicated that both of the defects had a vacancy in their metastable state; in good agreement with the vacancy/interstitial model for the As antisite defect. Therefore, the native defect was attributed to an As antisite, and the irradiation-induced defect was attributed to an As antisite complex. The metastable state of the AsGa complex could be produced by 1.075eV photons, and recovered with 1.35eV photons; with optical cross-sections of 2 x 10-20 and 5 x 10-19cm2, respectively. The metastable state of the AsGa complex absorbed 0.7 to 1.2eV photons; thus indicating that it had ionization levels in the band-gap.

S.Kuisma, K.Saarinen, P.Hautojärvi, C.Corbel: Physical Review B, 1997, 55[15], 9609-20