Analysis of limitations to wallplug efficiency and output power for quantum cascade lasers

We have carried out detailed optical and thermal simulations of quantum cascade laser (QCL) operation as a function of material and device parameters. The main objective of the study is to evaluate the potential for improvements in the cw wallplug efficiencies and output powers beyond the current state of the art, when such parameters as the internal loss, series resistance, doping level in the active region, number of QCL stages, ridge width, cavity length, current density, and operating temperature are varied within reasonable ranges. For the test case of a narrow-ridge λ=4.8μm QCL mounted epitaxial side down, we project that a maximum wallplug efficiency of >10% and cw output power of >1W may be feasible at room temperature, if the net internal loss can be reduced by 30% from its best current value.