Long-wavelength, coherent injector GaAs/AlGaAs quantum cascade lasers

We report on the design, fabrication, and characterization of GaAs/AlGaAs quantum cascade (QC) lasers with an emission wavelength in the range of 12 to 16 μm. Quantum cascade lasers in this wavelength range are of major interest for the creation of sensors to detect carcinogenic trace gases such as xylene, benzene, or toluene, which are released during the combustion of gasoline and forest fires. GaAs/AlGaAs is the material of choice for these designs despite the prevalence and greater understanding of InGaAs/AlInAs because the InP substrate on which InGaAs/AlInAs designs are grown has a large two-phonon absorption near 16μm, hindering and even preventing high performance InGaAs/AlInAs QC lasers in the target wavelength range. To achieve high-power performance, the coherent injector behavior exhibited by a well-researched In_0.53Ga_0.47As/Al_0.52In_0.48As QC laser structure was successfully recreated in GaAs/Al_0.33Ga_0.67As via simulations of a Schrödinger solver. This GaAs/Al_0.33Ga_0.67As QC laser has a designed emission wavelength of 12.4 μm; and, indeed, initial experiments show an electroluminescence wavelength of 12.0 ± 0.8 μm. Further experiments will determine whether the structure lases and future designs are scaling the wavelength to 16 μm.