Numerical Simulation of Tunneling Transmission Spectra of Quantum Cascade Lasers

Resonant tunneling is the main transport mechanism in quantum cascade lasers and has direct effects on the L-I characteristics. In this study, the tunneling transmission spectra of the active region of InP lattice- matched In0.53Ga0.47As/In0.52Al0.48As and In0.53Ga0.47As/AlAs0.56Sb0.44 quantum cascade lasers (QCLs) with vertical transitions were simulated using the transfer matrix method with various design parameters: quantum well numbers, layer thicknesses, and the choice of materials. Generally, we aim for a high tunneling transmission coefficient with a low transmission peak-to-valley ratio. The simulation results reveal that the number of transmission peaks increases with increasing well width and the number of quantum wells. Moreover, the transmission peak-to-valley ratio increases as the number of quantum wells increases. The simulations also suggest increases in both the transmission coefficient and the peak-to-valley ratio by reducing the barrier thicknesses. By comparing QCLs composed of different materials, we also show that different material systems have different optimum operational voltages that can improve the resonant tunneling properties.