Long Wavelength, Coherent Injector GaAs/AlGaAs Quantum Cascade Lasers

Abstract

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 hazardous and potentially carcinogenic trace gases such as xylene, benzene, or toluene, which are released during the combustion of gasoline or 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 optical power performance, the coherent injector behavior exhibited by a well-researched In$_{0.53}$Ga$_{0.47}$As/Al$_{0.52}$In$_{0.48}$As QC laser structure was successfully recreated in GaAs/Al$_{0.33}$Ga$_{0.67}$As via simulations using a Schrödinger solver. Our GaAs/Al$_{0.33}$Ga$_{0.67}$As QC laser has a theoretical emission wavelength of 12.4 μm; and, indeed, initial experiments show a peak electroluminescence wavelength of 11.9 μm and full width at half maximum ($\gamma_{32}$) of 169.7 cm$^{-1}$ (21 meV). Future designs will scale the peak wavelength towards the critical wavelength of 16 μm and will be optimized for lasing at high optical power.