Positron annihilation studies of defects in molecular beam epitaxy grown III–V layers

Abstract

A summary of recent positron annihilation experiments on molecular beam epitaxy (MBE) grown III–V layers is presented. Variable energy positron beam measurements on Al 0.32Ga 0.68As undoped and Si-doped have been completed. Positron trapping at an open volume defect in Al 0.32Ga 0.68As:Si for temperatures from 300 to 25 K in the dark was observed. The positron trap was lost after 1.3 eV illumination at 25 K. These results indicate an open volume defect is associated with the local structure of the deep donor state of the DX center. Stability of MBE GaAs to thermal annealing was investigated over the temperature range 230–700°C. Proximity wafer furnace anneals in flowing argon were used. Samples grown above 450°C were shown to be stable but for samples below this temperature an anneal-induced vacancy-related defect was produced for anneals between 400 and 500°C. The nature of the defect was shown to be different for materials grown at 350 and 230°C. Activation energies of 2.5-2.3 eV were obtained from isochronal anneal experiments for samples grown at 350 and 230°C, respectively.