Barrier Height Tuning of Terahertz Quantum Cascade Lasers for High-Temperature Operation

Terahertz quantum cascade lasers (QCLs) are excellent coherent light sources, but are still limited to an operating temperature below 200 K. To tackle this, we analyze the influence of the barrier height for the identical three-well terahertz QCL layer sequence by comparing different aluminum concentrations (x = 0.12-0.24) in the GaAs/AlxGai_ As material system, and then we present an optimized structure based on these findings. Electron injection and extraction mechanisms as well as LO-phonon depopulation processes play crucial roles in the efficient operation of these lasers and are investigated in this study. Experimental results of the barrier height study show the highest operating temperature of 186.5 K for the structure with 21% aluminum barriers, with a record lcBT max/ hco value of 1.36 for a three-well active region design. An optimized heterostructure with 21% aluminum concentration and reduced cavity waveguide losses is designed and enables a record operating temperature of 196 K for a 3.8 THz QCL.