POSITRON STUDY OF DEFECTS IN AS-GROWN AND PLASTICALLY DEFORMED GAAS-TE

Point defects were studied by positron-lifetime spectroscopy in highly Te-doped GaAs, in the as-grown state, and after plastic deformation. In as-grown GaAs:Te, positron trapping to vacancy-like defects, supposed to be the compensating centers TeAsVGa-, was observed. At low temperatures (T<200 K), additional trapping is caused by shallow positron traps, probably by Ga-As(-) antisite defects. In two differently deformed samples, additional defects were identified as microvoids, consisting of not less than ten vacancies. The dominating vacancy supply mechanism for vacancy agglomeration is the dragging of jogs on screw dislocations. The microvoids almost completely anneal after thermal treatment at 1075 K. The density of shallow traps increased after deformation by about one order of magnitude as a result of dislocation climb. These shallow traps additionally formed during plastic deformation exhibit the same positron binding energy, E(b) = 43 meV, as found in as-grown material. This part could be annealed at 1000 K, whereas the part of shallow traps originally present is determined by the nonstoichiometry and is therefore thermally stable. The density of the compensating centers remains almost unchanged after deformation. They are thermally stable up to 1075 K.