Temperature dependence of the key electro-optical characteristics for midinfrared emitting quantum cascade lasers

The equations for threshold-current density Jth, differential quantum efficiency ηd, and maximum wallplug efficiency ηwp,max for quantum-cascade lasers (QCLs) are modified for electron leakage and backfilling. A thermal-excitation model of “hot” injected electrons from the upper laser state to upper active-region states is used to calculate leakage currents. The calculated characteristic temperature T0 for Jth is found to agree well with experiment for both conventional and deep-well (DW) QCLs. For conventional QCLs ηwp,max is found to be strongly temperature dependent; explaining experimental data. At 300 K for optimized DW-QCLs, front-facet, continuous-wave ηwp,max values >20% are projected.