A systematic positron annihilation investigation was made of layers which had been grown at low temperatures. The vacancy defects in undoped as-grown material were identified as being mainly VGa. This was done by comparing the annihilation parameters with those for Ga vacancies in highly Si-doped material. The characteristic S parameter for positron annihilation in Ga vacancies was determined to be 1.024. The VGa concentration increased to 1018/cm3 upon decreasing the growth temperature to 200C. It was concluded that the vacancy concentration could account for the compensation of AsGa+ antisites.

J.Gebauer, R.Krause-Rehberg, S.Eichler, M.Luysberg, H.Sohn, E.R.Weber: Applied Physics Letters, 1997, 71[5], 638-40