Enhancements of Direct Band Radiative Recombination from Ge

Abstract

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 n type doping level, optical pumping power, injection current density, temperature, and strain. 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 reduction in bandgap difference between the direct and indirect valleys by biaxial tensile strain increases the electron population in the direct valley, and further enhances the direct transition. The bandgap reduction in the direct and indirect valleys can be extracted from the photoluminescence spectra and is consistent with the calculations using k. p and deformation potential methods for conduction bands and valence bands, respectively.