ANNEALING OF LOW-TEMPERATURE GAAS STUDIED USING A VARIABLE-ENERGY POSITRON BEAM

The annihilation characteristics of monoenergetic positrons implanted in a molecular beam epitaxy layer of low-temperature (LT) GaAs anneale d at temperatures from 300 to 600-degrees-C were measured. A gallium v acancy concentration of approximately 3 X 10(17) cm-3 is inferred for the as-grown material. The S parameter increased significantly upon an neal to 500-degrees-C. The dominant positron traps in samples annealed at and below 400-degrees-C are distinct from those acting for samples annealed to 500 or 600-degrees-C. The change in S parameter for the 6 00-degrees-C annealed sample compared to the GaAs substrate, S(LT,600) = 1.047S(sub), is consistent with divacancies or larger open volume d efects.