Effects of doping concentration on terahertz quantum-cascade lasers

Quantum-cascade lasers are sophisticated devices for a large number of applications such as imaging, spectroscopy and heterodyne detection. Significant steps forward in the temperature performance and available frequencies have been made over the last years. Nonetheless the influence of the doping concentration is not yet completely understood. The investigations which carried out by H.C. Liu et. al., show a monotonic, but non-linear dependency of the threshold current density on the doping concentration which was attributed to the free-carrier-absorption in the active region. The maximum lasing temperature was also affected by the doping concentration.