The positron 2-dimensional angular correlation of annihilation radiation technique was coupled with optical excitation methods in order to study native point defects in semi-insulating material. The As vacancy was observed at temperatures below about 170K, when illuminated with 1.41eV photons. The temperature dependence of the annihilation, with and without illumination, was studied. Data were also obtained at 25K, as a function of the intensity of infra-red light. The annihilation spectra reflected the e+-e- pair momentum distribution at, or near to, the vacancy and provided symmetry and electronic structure data which could be used to provide a unique defect signature for the vacancy.

J.P.Peng, K.G.Lynn, M.T.Umlor, D.J.Keeble, D.R.Harshman: Physical Review B, 1994, 50[15], 11247-50