Uniaxial-stress symmetry studies on the E1, E2 and E3 irradiation-induced defects in gallium arsenide

To obtain information on the crystallographic symmetries of the E1, E2 and E3 irradiation-induced defects in n-GaAs we have investigated the effects of uniaxial-stress upto 0.4 GPa on the DLTS spectra of epitaxial n-GaAs irradiated by 1.0 MeV protons. We find that for each of those three defect levels, uniaxial stress applied along a [100] direction of the GaAs caused increase but no broadening of the DLTS-measured electron ionisation energy, but that [110] applied stress produced both broadening of the DLTS peaks and increase in the mean ionisation energy of each defect. For the Fl defect the effect of 0.4 GPa [110] stress was to produce clearly observable splitting of its peak into two peaks. By detailed analysis of the DLTS peak shapes we deduce that [110] stress causes splitting of each of the El, E2 and E3 electronic energy levels into two levels of equal populations. These data strongly suggest that the El, E2 and E3 defects each have C-3v (trigonal) crystallographic symmetry, ie that each is an atomic arrangement that contains a single [111] symmetry axis. The data do not support the identification of the E1 and E2 defects as simple arsenic vacancies of T-d symmetry, but are consistent with a previous proposal that E3 defects are arsenic Frenkel pairs. We believe these to be the first uniaxial-stress studies on any irradiation-induced defect in GaAs.