Seminarium Fizyki Politechniki Wrocławskiej
PWr, bud. A1, sala 322
THz Quantum Cascade Lasers: How Much Headroom Is Left?
Prof. Zbig Wasilewski
Department of Electrical and Computer Engineering, Department of Physics and Astronomy, Waterloo Institute for Nanotechnology and Institute for Quantum Computing, University of Waterloo
For more than two decades, the terahertz quantum cascade laser (THz QCL) community has chased room-temperature operation, driven by applications in communications, sensing, and spectroscopy, and by capabilities—frequency combs, amplifiers, heterodyne local oscillators—that nonlinear up-/down-conversion sources struggle to match. At cryogenic temperatures, THz QCLs already deliver watt-level pulsed power, tens of milliwatts of CW power, and near-percent efficiencies. Broadband room-temperature operation, however, has remained out of reach.
After years of stagnation, the maximum operating temperature has recently jumped to Tmax ~ 250 K on a portable thermoelectric cooler [1], and then to 261 K [2]. How much headroom is left, and what now sets the practical ceiling?
In this talk, I argue that further progress depends on tightly coupling active-region design with MBE growth precision—and on making that optimized growth reproducible and transferable between systems. Across the hundreds of layers in a THz QCL stack, small deviations in thickness, composition, and dopant placement accumulate, broadening resonances and eroding gain. Flux stability, lateral uniformity (including rotation-related effects), dopant placement, and interface control are decisive.
I will close by discussing complementary directions, including our exploratory work on THz QCL heterostructures grown on high-index GaAs(411)A substrates. High-index surfaces are known to produce exceptionally flat heterointerfaces and have been shown to improve resonant-tunneling structures and mid-IR QCLs [3]; we are investigating whether these benefits extend to the THz regime.
[1] A. Khalatpour, A. K. Paulsen, C. Deimert, Z. R. Wasilewski, and Q. Hu, "High-power portable terahertz laser systems," Nature Photonics 15, 16-20 (2021).
[2] A. Khalatpour, M. C. Tam, S. J. Addamane, J. Reno, Z. Wasilewski, and Q. Hu, "Enhanced operating temperature in terahertz quantum cascade lasers based on direct phonon depopulation," Applied Physics Letters 122, 161101 (2023).
[3] M. P. Semtsiv, S. S. Kurlov, D. Alcer, Y. Matsuoka, J.-F. Kischkat, O. Bierwagen, and W. T. Masselink, "Reduced interface roughness scattering in InGaAs/InAlAs quantum cascade lasers grown on (411)A InP substrates", Appl Phys Lett 113, 121110 (2018).
