A summary was presented of recent positron annihilation data on molecular beam epitaxially grown III-V layers. Variable-energy positron beam measurements of undoped or Si-doped Ga0.68Al0.32As were described. Positron trapping was observed at an open-volume defect in Si-doped material at temperatures ranging from 300 to 25K, in the dark. The positron trap was lost after 1.3eV illumination at 25K. The results suggested that an open-volume defect was associated with the local structure of the deep-donor state of the DX center. The stability of molecular beam epitaxial GaAs to thermal annealing was investigated at temperatures ranging from 230 to 700C. Proximity wafer furnace annealing in flowing Ar was used. It was shown that samples which were grown at temperatures above 450C were stable but, at lower temperatures, an annealing-induced vacancy-related defect was produced upon annealing at temperatures between 400 and 500C. The nature of the defect was shown to be different for materials which had been grown at temperatures between 350 and 230C. Activation energies of 2.5 to 2.3eV were deduced from isochronal annealing experiments on samples which had been grown at 350 and 230C, respectively.

M.T.Umlor, P.Asoka-Kumar, D.J.Keeble, P.W.Cooke, K.G.Lynn: Applied Surface Science, 1995, 85, 295-300