Broadening effects due to alloy scattering in a quantum cascade laser

We report on calculations of broadening effects in a quantum cascade laser due to alloy scattering. The output of numerical calculations of alloy-broadened Landau levels compare favorably with calculations performed at the self-consistent Born approximation. Results for Landau level width and optical absorption are presented. A disorder activated forbidden transition becomes significant in the vicinity of crossings of Landau levels which belong to different subbands. A study of the time dependent survival probability in the lowest Landau level of the excited subband is performed. It is shown that at resonance, the population relaxation occurs in a subpicosecond scale.