| Quantum cascade lasers (QCLs) are electrically driven, unipolar semiconductor devices that achieve lasing based on intersubband transitions. They are compact and high-power light sources promising for many technological applications in the mid-infrared (mid-IR) and terahertz (THz) spectral regimes. However, QCLs experience self-heating problems due to its fundamental design, and the high active core temperature increases the threshold current, lowers the wall-plug efficiency (WPE), and may prevent the room-temperature continuous-wave (RT-CW) operation.;To address the thermal issues of QCLs, a self-consistent heat diffusion simulator, a single-stage coupled ensemble Monte Carlo (EMC) simulator, and a multiscale device-level simulator for nonequilibrium electron-phonon transport in QCLs have been developed. The simulators are capable of capturing both microscopic physics in the active core and the heat transfer over the entire device structure to provide insights to QCL performance metrics critical for further developments.;The heat diffusion simulator is used to study a GaAs-based mid- IR QCL. A lattice temperature increase of over 150 K with respect to the heat-sink temperature was obtained from the simulation, indicating a severe self-heating effect in the active region.;The single-stage coupled EMC simulator is used to investigate the effects of nonequilibrium phonon dynamics on the operation of the same QCL. Nonequilibrium phonon effects are shown to be important below 200 K, and they improve modal gain and threshold current density by enhancing the injection efficiency through increasing the interstage electron scattering rate. By amplifying phonon absorption, nonequilibrium phonons also hinder electron energy relaxation and lead to elevated electronic temperatures.;Finally, we demonstrate the multiscale device-level electrothermal simulation technique on capturing realistic device electrothermal performance directly comparable to experiments. The effects of device geometry, including substrate thickness, contact thickness, and ridge width on the active core temperature and current density-voltage characteristics have been studied. |
