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/sub Ga/, the density of V/sub 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/spl times/10/sup 18/ V/sub Ga//cm/sup 3/ was observed at the lowest growth temperature (200/spl deg/C), annealing at elevated temperatures (/spl ap/600/spl deg/C) removes V/sub Ga/, instead, larger vacancy agglomerates are found, they are most likely associated with the As-precipitates commonly found in annealed LT-GaAs.