n-Type Ge–SiGe Quantum Cascade Structure Utilizing Quantum Wells for Electrons in the L and Γ Valleys

In this letter, we propose an n-type vertical transition bound-to-continuum Ge-SiGe quantum cascade structure utilizing electronic quantum wells in the L and Gamma valleys of the Ge layers. The optical transition levels are located in the quantum wells in the L valley. Under a bias of 80 kV/cm, the carriers in the lower level are extracted by miniband transport and L -Y tunneling into the subband in the Gamma well of the next period. And then the electrons are injected into the upper level by ultrafast intervalley scattering, which not only effectively increases the tunneling rate and suppresses the thermal backfilling of electrons, but also enhances the injection efficiency of the upper level. The performance of the laser is discussed.