Native and irradiation-induced monovacancies in<i>n</i>-type and semi-insulating GaAs

Abstract

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 1.5--3 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 -\ensuremath{\rightarrow}0 or 0\ensuremath{\rightarrow}+ of the native monovacancy defects in the upper half of the band gap. We propose that irradiation produces negative ${\mathrm{Ga}}_{\mathrm{As}}$ antisites and negative ${\mathit{V}}_{\mathrm{Ga}}$ vacancies. In n-type GaAs the behavior of the native defects under irradiation is in agreement with their earlier assignment to ${\mathit{V}}_{\mathrm{As}}$.