Enhanced indirect-to-direct inter-valley scattering in germanium under tensile strain for improving the population of electrons in direct valley

A theoretical model is proposed to analyze the inter-valley electron transferring between direct Gamma and indirect L valleys, which sheds light on the electron conduction dynamics in (001) tensile strained Ge. Inter-valley scattering is included to calculate average scattering time between Gamma and L valleys based on a time-dependent Hamiltonian describing the electron-phonon interaction. Numerical results indicate that enhanced indirect-to-direct inter-valley scattering and reduced direct-to-indirect inter-valley scattering are reliable by introducing tensile strain in Ge material. The population ratio of electrons in Gamma and L valleys in strained Ge will increase one to two orders of magnitude compared to the model without the inter-valley scattering. The results offer fundamental understanding of phonon engineering for further improvement of performance in strained germanium light sources.