Defects in highly Si-doped material were identified, and their concentrations were determined by means of positron lifetime spectroscopy and scanning tunnelling microscopy. It was observed that, with increasing Si concentration, there was an increase in the concentration of a deep positron trap which was identified as being a SiGa-donor-Ga-vacancy complex. The concentration of shallow positron traps also increased with the Si concentration. The shallow traps were found to be SiAs acceptors and Si clusters.

J.Gebauer, R.Krause-Rehberg, C.Domke, P.Ebert, K.Urban: Physical Review Letters, 1997, 78[17], 3334-7