High-efficiency, high-power mid-infrared quantum cascade lasers [Invited]

The step-taper active-region (STA) design concept is implemented for similar to 5.0 mu m-emitting quantum cascade lasers (QCLs) grown by metal-organic chemical vapor deposition (MOCVD). Carrier-leakage suppression yields high characteristic temperatures for the threshold-current density J(th), T-0, and for the slope efficiency eta(s1), T-1: 226 K and 653 K. Resonant-tunneling extraction from the lower level results in miniband-like extraction. In turn, the internal efficiency eta(i) is found, from a variable mirror-loss study, to be similar to 77%; thus approaching the similar to 90% upper limit, when employing only inelastic scattering. Considering interface-roughness and alloy-disorder scattering, the transition efficiency reaches values of similar to 95%. Then, the injection efficiency is similar to 81%, and, for lambda = 4.6 mu m, the wallplug-efficiency eta(wp) upper limit reaches 41.2%. Results include 4.2 W/A single-facet eta(s1) and 0.96 kA/cm(2) J(th) values. Buried-heterostructure (BH) QCLs provide single-facet 2.6 W continuous-wave (CW) power and 12% CW eta(wp). Optimized 8 mu m-emitting, STA-design QCLs provide 2 W/A eta(s1), and 1.1 kA/cm(2) J(th); and BH devices yield single-facet 1 W CW power and 6% CW eta(wp). (C) 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement