Strain-free Ge∕GeSiSn quantum cascade lasers based on L-valley intersubband transitions

The authors propose a Ge∕Ge0.76Si0.19Sn0.05 quantum cascade laser using intersubband transitions at L valleys of the conduction band which has a “clean” offset of 150meV situated below other energy valleys (Γ,X). The entire structure is strain-free because the lattice-matched Ge and Ge0.76Si0.19Sn0.05 layers are to be grown on a relaxed Ge buffer layer on a Si substrate. Longer lifetimes due to the weaker scattering of nonpolar optical phonons reduce the threshold current and potentially lead to room temperature operation.