Optimization of terahertz quantum cascade lasers by suppressing carrier leakage channel via high-energy state

Terahertz quantum cascade lasers (THz QCLs) are theoretically analyzed using the non-equilibrium Green's function method. Simulations reveal a carrier leakage channel from the upper laser level to the first high-energy state in the emitting double well of the next period. This leakage channel is due to unintentional alignment of the two states, and is distinct from the thermally activated leakage channels. By tuning the energy of this high-energy state, the leakage current is clearly suppressed. The optimized THz QCL shows significant improvement, with a peak power of 350 mW, compared with the value of 220 mW for the non-optimized structure. (C) 2018 The Japan Society of Applied Physics