Radiative Recombination in Annealed Electron-Irradiated GaAs

Broad-band emission peaking near 1.39 eV appears in Zn-doped GaAs in addition to the narrow bound-exciton emission at 1.49 eV. Electron irradiations at energies between 0.6 and 2.0 MeV for time-integrated fluxes of 1.3×{}10¹⁸ e/cm² quench all luminescence. For bombardment energies below a critical value, which lies between 1.0 and 1.5 MeV, isochronal annealing near 190^∘{}C causes the reappearance of the broad-band emission, which now is found to possess structure. The structure consists of three no-phonon lines at 1.4433, 1.4415, and 1.4402 eV which are repeated at intervals of the transverse acoustic phonon energy. The emission intensity is greatest for temperatures near 220^∘{}C. Further annealing at higher temperatures diminishes the intensity of the fine structure and the associated broad-band emission; complete disappearance occurs above 260^∘{}C. The emission is not regained upon annealing when the bombardment energy exceeds the critical value. It is suggested that direct lattice displacement occurs at the critical bombarding energy. This would correspond to a threshold displacement energy of 50-60 eV. It is also suggested that previous measurements of threshold energy (10-20 eV) in GaAs and other experimental observations may be due to known large concentrations ({≈}10¹⁹ cm³) of defects in as-grown GaAs, in the form of Ga-As interstitial pairs.