A positron lifetime spectroscopic study was made of the depth distribution of vacancy-type defects in molecular beam epitaxial material which had been grown at low temperatures. The lifetime spectra were measured as a function of the positron energy. From an analysis of the positron lifetimes in as-grown material, and in annealed material which had been grown at low temperatures, the concentrations of Ga mono-vacancies and voids were estimated. The results showed that, in as-grown samples, the Ga mono-vacancy concentration was greater than 3 x 1018/cm3. It was recalled that the vacancy-cluster concentration in annealed samples exceeded 1018/cm3, with a non-uniform spatial distribution.

J.Störmer, W.Triftshäuser, N.Hozhabri, K.Alavi: Applied Physics Letters, 1996, 69[13], 1867-9