Abstract Quantum cascade lasers (QCLs) are unipolar quantum devices based on inter-sub-band transitions. They break the electron-hole recombination mechanism in traditional semiconductor lasers, overcome the long-lasting bottleneck which is that the emission wavelength of semiconductor laser is completely dependent on the bandgap of semiconductor materials. Therefore, their emission wavelength is able to cover the mid-infrared (mid-IR) range and the “Terahertz gap” that is previously inaccessible by any other semiconductor lasers. After thirty years development, QCLs have become the most promising light source in the mid-IR and THz regime. In this paper, we are going to present the strategies and methodologies to achieve high-power, high-wall-plug-efficiency (WPE) QCLs with high-brightness in room temperature continuous-wave (cw) operation at 3–300 μm. We will also review the recent breakthroughs in QCL community, especially the high-power, high WPE intersubband lasers in room temperature cw operation.
Razeghi et al. (2025) studied this question.