Vacancy complexes in Cr-doped GaAs

Cr-doped semi-insulating GaAs has been investigated by means of position lifetime spectroscopy. In as-grown GaAs the dominant positron trap is a CrGa·VAs complex. Upon annealing the concentration of this complex increases around 260°C and then decreases at temperatures higher than 500°C. No vacancy agglomeration took place. In low temperature (130 K) e--irradiated (28 MeV) Cr-GaAs, di- and trivacancies were observed together with the gallium antisite, GaAs.