Threshold Current Density Reduction by Utilizing High-Al-Composition Barriers in 3.7 THz GaAs/AlₓGa₁₋ₓAs Quantum Cascade Lasers

The temperature dependence of threshold current density ( J th ) for GaAs/Al x Ga 1- x As terahertz quantum cascade lasers (THz-QCLs) with different Al barrier compositions is studied. We achieved a maximum operation temperature ( T max ) of 143 K for a 3.7 THz QCL by employing a longitudinal-optical (LO) phonon depopulation scheme. High-Al-composition barriers are used for increasing averaged LO-phonon energy. A significant reduction in J th of approximately 30% was obtained by increasing the Al composition from 15 to 35%, when we used the same energy separation of the depopulation stats ( E 21 ). T max could be increased by using high-Al-composition structures due to the reduction of thermally-activated LO-phonon scattering.