Observation of a monovacancy in the metastable state of theEL2 defect in GaAs by positron annihilation

Abstract
A monovacancy defect is observed by positron-lifetime and Doppler-broadening experiments in semi-insulating GaAs after photoquenching the EL2 defects. The monovacancy exhibits the same thermal and optical recoveries as the metastable state of EL2 and its concentration is proportional to that of the EL2 defect. It is concluded that the metastable state of the EL2 defect involves the monovacancy. The results indiacte that the monovacancy or its immediate surroundings is negatively charged.