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 annealed at temperatures from 300 to 600 °C were measured. A gallium vacancy concentration of approximately 3×1017 cm−3 is inferred for the as-grown material. The S parameter increased significantly upon anneal to 500 °C. The dominant positron traps in samples annealed at and below 400 °C are distinct from those acting for samples annealed to 500 or 600 °C. The change in S parameter for the 600 °C annealed sample compared to the GaAs substrate, SLT,600=1.047Ssub, is consistent with divacancies or larger open volume defects.