POSITRON-ANNIHILATION STUDIES OF DEFECTS IN MOLECULAR-BEAM EPITAXY-GROWN III-V LAYERS

A summary of recent positron annihilation experiments on molecular bea m epitaxy (MBE) grown III-V layers is presented. Variable energy posit ron beam measurements on Al0.32Ga0.68As undoped and Si-doped have been completed. Positron trapping at an open volume defect in Al0.32Ga0.68 As: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 result s indicate an open volume defect is associated with the local structur e of the deep donor state of the DX center. Stability of MBE GaAs to t hermal annealing was investigated over the temperature range 230-700 d egrees C. Proximity wafer furnace anneals in flowing argon were used. Samples grown above 450 degrees C were shown to be stable but for samp les below this temperature an anneal-induced vacancy-related defect wa s produced for anneals between 400 and 500 degrees C. The nature of th e defect was shown to be different for materials grown at 350 and 230 degrees C. Activation energies of 2.5-2.3 eV were obtained from isochr onal anneal experiments for samples grown at 350 and 230 degrees C, re spectively.