Nonparabolicity Effects in Quantum Cascade Lasers

We calculate electron-LO phonon and interface roughness scattering rates in a GaAs/Al_xGa_1-xAs quantum cascade laser taking into account conduction subband nonparabolicity. In this work we investigate the Al concentration and the k_|| dependence of nonparabolicity effects. It is shown that the subband nonparabolicity may increase the electron-LO phonon scattering rates significantly, but the scattering rates are not qualitatively different from those in the parabolic approximation. Especially, we show that nonparabolicity leads to noticeable changes even for transitions involving electrons at the bottom of the subband and that this behaviour follows from the phonon wave vector and the electron phonon overlap.