Positron annihilation techniques were used to study vacancy defects in specimens which had been grown at low temperatures. The vacancies in as-grown samples were identified as being Ga monovacancies, according to their positron lifetime and annihilation momentum distribution. The charge state of the vacancies was neutral. This was attributed to the presence of positively charged AsGa+ antisite defects in the vicinity of the vacancies. Theoretical calculations of the annihilation parameters showed that this assumption was consistent with the data. The density of VGa was related to the growth stoichiometry, in that it increased with the As/Ga beam equivalent pressure and saturated at 2 x 1018/cm3 for beam equivalent pressures above 20, at a growth temperature of 200C. Annealing at 600C removed VGa. Instead, larger vacancy agglomerates consisting of some 4 vacancies were found. These vacancy clusters were associated with As precipitates which formed during annealing.

Defect Identification in GaAs Grown at Low Temperatures by Positron Annihilation J.Gebauer, F.Börner, R.Krause-Rehberg, T.E.M.Staab, W.Bauer-Kugelmann, G.Kögel, W.Triftshäuser, P.Specht, R.C.Lutz, E.R.Weber, M.Luysberg: Journal of Applied Physics, 2000, 87[12], 8368-79