0.8-eV photoluminescence of GaAs grown by molecular-beam epitaxy at low temperatures

We report deep-center photoluminescence of GaAs grown at low temperatures between 200 and 400 °C by molecular-beam epitaxy. Changes of temperature and excitation intensity were used in addition to heat-treatment and photoluminescence-excitation measurements. The type of photoluminescence transition strongly depends on the growth temperature and the [${\mathrm{As}}_4$]/[Ga] ratio. The layers grown at 200–300 °C show a dominant emission at 0.68 eV (EL2) and an emission at 1.1 eV related to a ${\mathit{V}}_{\mathrm{Ga}}$ center. The layers grown at 325–400 °C show one transition at 0.75–0.81 eV (designated as the 0.8-eV emission). We attribute the 0.8-eV emission to the ${\mathrm{As}}_{\mathit{i}}$-${\mathit{V}}_{\mathrm{Ga}}$ center. The center shows the large lattice relaxation exemplified by the Franck-Condon shift of 0.34 eV. The thermal ionization energy is determined to be 0.36 eV. We discuss our assignment of the ${\mathrm{As}}_{\mathit{i}}$-${\mathit{V}}_{\mathrm{Ga}}$ center to the well-known EL6 center.