BE DIFFUSION MECHANISM IN GAAS INVESTIGATED BY SLOW POSITRON BEAM

The slow positron beam technique was applied on undoped and Be-doped GaAs to study the effects of Be impurities on both creation and migration of Ga vacancies, V(Ga), during annealing. It is observed that a monovacancy of V(Ga) is created in Be-doped GaAs to result in enhanced Coulombic interaction between As vacancy, V(As), and Be acceptor, Be(Ga). In undoped GaAs, the formation of divacancies, V(Ga)-V(As), is dominant. The migration depth of vacancies is shorter in Be-doped GaAs than in undoped GaAs. This suggests the existence of Ga interstitials, I(Ga), in the Be diffused layer which interact with V(Ga) introduced from the surface. Based on these observations, we suggest the kick-out mechanism for Be diffusion in GaAs.