Intersubband linewidths in quantum cascade laser designs

We present a model to a priori calculate the temperature and field dependent intersubband linewidth of the optical transition in quantum cascade laser designs. Besides intra- and intersubband lifetime broadening, it comprises interface roughness scattering based on the approach of Tsujino et al. [Appl. Phys. Lett. 86, 062113 (2005)]. We verified our model with experimental data of quantum cascade lasers having different linewidths. Excellent agreement with the experiment was found for the two-phonon resonance design. Linewidths are slightly overestimated in the bound-to-continuum design. Differential gain and threshold current density are in excellent agreement for the two-phonon resonance design. Although the slope efficiency is somewhat underestimated at low temperatures, there is still reasonable agreement with the experiment.