Positron Annihilation Spectroscopy of As Vacancies in As-Grown GaAs

Positron lifetime measurements give direct evidence on positron trapping in monovacancy defects in n-type, but not in p-type nor in semi-insulating LEC-grown GaAs. The defects are identified as As vacancies. Two Fermi level controlled transitions have been found in positron lifetime spectra at 0.03+—0.01 eV and at 0.10±0.01 eV below the conduction band. We attribute them to the 2-/- and - / 0 ionisation levels of the As vacancy.