Positron-lifetime and Doppler-broadening investigations of γ-irradiated GaAs

γ irradiation of four differently doped GaAs samples results in significant changes in the Doppler parameter S depending on the type of dopants. For Cd-doped GaAs, S increases (by 1.2%) after irradiation by only 10${}^1$ ${}^6$ photons/cm${}^2$, while for Si-doped GaAs, S decreases. Lifetime measurements indicate that upon irradiation an unresolved lifetime component appears with a value shorter than that for the monovacancy. The results are explained in terms of radiation-enhanced vacancy migration toward impurities.