The electron-positron momentum distributions in the Ga vacancy (VGa3-) and Ga antisite (GaAs2-) were obtained by performing 2-dimensional angular correlation of positron annihilation radiation measurements on electron-irradiated semi-insulating material. The results were compared with previous data on the As vacancy. It was found that all of the vacancy distributions were structure-less, although their anisotropies indicated that there was a residual bulk-like component. The magnitude of this component varied from vacancy to vacancy and indicated how far the localized positron wave-function extended into the crystal bulk around the vacancy. The present results showed that this extension of the wave-function in VGa3- and VAs- was similar to, and clearly greater than, that in VAs0. The momentum distribution, as sampled by the positron in a Rydberg state about GaAs2-, was very similar to that in the bulk but could nevertheless be distinguished from the latter.

R.Ambigapathy, C.Corbel, P.Hautojärvi, A.A.Manuel, K.Saarinen: Journal of Physics - Condensed Matter, 1995, 7[49], L683-8