VACANCY-TYPE DEFECTS IN SI+-IMPLANTED GAAS AND ITS EFFECTS ON ELECTRICAL ACTIVATION BY RAPID THERMAL ANNEALING

The depth distributions of vacancy-type defects in Si+ -implanted and thermally activated GaAs were studied by a slow positron beam technique and were compared with the results observed with a transmission electron microscope. In as-implanted GaAs, the concentration of vacancy-type defects decreased monotonically with increasing depth below the surface and the generation of point defects was demonstrated by the lattice image of transmission electron microscopy. The vacancy concentration is not dependent upon activation conditions; however, the electrical activation coefficiency obtained from Hall measurements is enhanced with increasing activation annealing time. This indicates that the electrical activation of Si+ -implanted GaAs is proceeding by the exchange of interstitial Si with substitutional Ga rather than the recombination of interstitial Si into Ga-related vacancies. The maximum number of extrinsic-type stacking faults was observed at 70-80 nm below the surface after the activation annealing, which is compared with that of vacancy-type defects, at 25-35 nm, obtained by the slow positron beam technique. This discrepancy in both of the damage distributions could originate in different types of defects existing along the depth below the surface, which was discussed with the high-energy recoil theory.