Slow positron beam measurements of Si-doped GaAs on Be-doped GaAs grown by molecular beam epitaxy

Slow positrons were used to study impurity diffusion mechanisms in Si-doped GaAs grown on Be-doped substrates by molecular beam epitaxy. The S parameter correlates with the concentration of VGa acceptors increases continuously with the Si doping concentration, which supports the theoretical model that the creation of VGa acceptors is related to the change of the Fermi level position in Si-doped GaAs. This implies that Si diffuses as a single Si-vacancy neutral complex (SiGa+-VGa-) rather than the paired Si (SiGa+-SiAs-). When the specimens were annealed with a face-to-face contact GaAs, the S parameter value saturated at that for trapping at a monovacancy. However the formation of divacancies (VGa--VAs+) was observed in undoped GaAs wafers annealed under the same conditions. These gives the evidence on the formation of monovacancy complexes such as (VAs+-GeGa-) and (VGa--SiGa+) in impurity-containing GaAs because of the Coulomb interaction between the two dipoles