Engineering the electron-phonon scattering rates in the active regions of quantum cascade lasers operating beyond 30 μm

This theoretical work explores an aspect of carrier scattering rate design in the active region of intersubband quantum cascade lasers operating in the far-infrared (30-300 μm) or terahertz (1-10 THz) region of the spectrum, namely the depopulation of the lower laser level. Envelope function calculations of eigenstates and non-radiative scattering rates are presented for the active layer of an intersubband laser under the influence of an electric field and at room temperature. Two methods of depopulating the lower laser level to engineer a population inversion are explored, namely depopulation by resonant longitudinal optic phonon emission and depopulation to a strongly coupled state, as can occur at an anti-crossing.