Native vacancies were identified by using positron annihilation techniques. Particular emphasis was placed on As vacancy-related defects. In the case of annealed highly Si-doped material, a neutral vacancy defect was observed; with a positron lifetime of 280 to 285ps and a high intensity of core annihilation. This was contrasted with the behavior of Ga vacancies, which exhibited a lifetime of about 260ps and a lower intensity of core annihilation. This defect was identified, by means of scanning tunnelling microscopic measurements, to be an As-vacancy SiGa donor complex. It was found that the same defect was also present in low n-doped material, where it had been previously attributed to a neutral As vacancy. The high positron lifetime was explained in terms of a large outward lattice relaxation. Theoretical calculations of the momentum distribution, which involved free atomic wave functions, were in good agreement with the experimental results, provided that only relative changes were considered and an outward lattice relaxation was included which yielded the experimentally observed positron lifetime. The calculations also yielded annihilation parameters, for Ga vacancies, which were in good agreement with experiment. The results demonstrated that vacancies in both sub-lattices could be directly and unambiguously identified by means of positron annihilation, provided that the annihilation characteristics were first calibrated by using a complementary method. The abundances of As vacancies were considered in terms of stoichiometry and formation energies.

Direct Identification of As Vacancies in GaAs using Positron Annihilation Calibrated by Scanning Tunnelling Microscopy. J.Gebauer, R.Krause-Rehberg, C.Domke, P.Ebert, K.Urban, T.E.M.Staab: Physical Review B, 2001, 63[4], 045203 (9pp)