Evidence for Self-Activated Luminescence in GaAs: The Gallium Vacancy-Donor Center

Evidence for self-activated luminescence at 1.2 eV at low temperatures in n-type GaAs was obtained by a comparison with ZnS luminescence. Both luminescence lines have a Gaussian-like shape, and a similar temperature dependence of half-width, peak energy, and intensity. The half-width temperature variation was predicted by the configurational coordinate model. A vibrational energy of 0.022 eV is calculated for the excited state of the center. The luminescence was observed in GaAs samples doped with a single donor to a carrier concentration of from 1×{}10¹⁸ to 5×{}10¹⁸/cc. The following donors were studied: C, Si, Ge, Sn, S, Se, and Te. Each donor modified the luminescence to some extent, and the emission peak energy shift of 0.02 eV of group-IV donors from group-VI donors in the same period is similar, though smaller, to the shift observed in the analogous centers in ZnS and ZnSe. This supports the conclusion that the center is a gallium vacancy bound to a donor.