Infrared absorption related to the metastable state of arsenic antisite defects in electron-irradiated GaAs

Positron-annihilation and infrared-absorption experiments have been performed to study the metastable defects in electron-irradiated semi-insulating GaAs. The positron results show that an irradiation-induced metastable vacancy can be generated by illumination with 1.1-eV light at 25 K. The vacancy can be optically recovered by either 0.85- or 1.3-eV photons at 25 K. These generation and recovery bands are identical to those detected earlier for irradiation-induced As antisite defects in magnetic circular dichroism of absorption experiments. We thus conclude that the metastable vacancy belongs to the atomic structure of the metastable state of the As antisite. The metastable As antisite absorbs infrared light, suggesting that its ionization level is in the energy gap and not in the conduction band as in as-grown GaAs. This difference can be explained by the presence of other defects complexed with the As antisite in electron-irradiated GaAs.