Competitiveness between direct and indirect radiative transitions of Ge

Both direct and indirect transitions of photoluminescence and electroluminescence are observed in a Ge n + p diode. The relative intensity of direct radiative recombination with respect to indirect radiative recombination increases with the increase in the optical pumping power, injection current density, and temperature. The increase in electron population in the direct valley is responsible for the enhancement. The spectra can be fitted by the combination of direct and indirect transition models. The direct radiative transition rate is ∼ 1600 times of the indirect transition, estimated by electroluminescence and photoluminescence spectra near room temperature.