Native and irradiation-induced monovacancies in n-type and semi-insulating GaAs

Defects induced by electron irradiation in semi-insulating and n-type GaAs crystals have been characterized by positron-lifetime measurements. We conclude that electron irradiation with energies of 1.53 MeV produces negative monovacancies and negative ions at low and room temperature. The results also show that the native monovacancy defects in lightly n-type GaAs change their properties under irradiation. We relate this change to the existence of an ionization level 0 or 0 of the native monovacancy defects in the upper half of the band gap. We propose that irradiation produces negative GaAs antisites and negative VGa vacancies. In n-type GaAs the behavior of the native defects under irradiation is in agreement with their earlier assignment to VAs.