Introduction of metastable vacancy defects in electron irradiated semi-insulating GaAs

Positron lifetime measurements on electron irradiated SI GaAs indicate the presence of Ga vacancies and Ga antisites in a negative charge state. Illumination of the sample reveals another vacancy defect, which is metastable at 30 K and anneals out at temperatures 100 - 120 K. The introduction rate of this defect is about 0.3 cm^-1. The metastable properties of the defect resemble those of the EL2 center in as-grown GaAs. We associate the defects to As antisites, which in the metastable configuration relax away from the lattice site leaving a Ga site vacant.