Vacancies in low-temperature-grown GaAs: observations by positron annihilation

Positron annihilation will be used to study vacancy defects in GaAs grown at low temperatures (LT-GaAs), the vacancies in as-grown LT-GaAs can be identified to be Ga monovacancies, V_Ga, the density of V_Ga is related to the nonstoichiometry in LT-GaAs, established by decreasing the growth temperature or increasing the As/Ga beam equivalent pressure (BEP) ratio, a maximum of about 2×10¹⁸ V_Ga/cm³ was observed at the lowest growth temperature (200°C), annealing at elevated temperatures (≈600°C) removes V_Ga, instead, larger vacancy agglomerates are found, they are most likely associated with the As-precipitates commonly found in annealed LT-GaAs