The effect of injector barrier thickness and doping level on current transport and optical transition width in a λ ∼ 8.0 μm quantum cascade structure

We experimentally study the optical transition width and current transport properties of a set of λ ∼ 8.0 μm quantum cascade (QC) structures with varying injector barrier thickness and doping level. For this high-performance QC laser structure, a 50% reduction in doping level and a 33% reduction in injection barrier thickness yield five times stronger luminescence, 20% smaller optical transition linewidth, and improved current-voltage characteristics. These results demonstrate how high-performance QC laser structures can be engineered to produce narrow gain spectra at and above room temperature.