Temperature performance of terahertz quantum-cascade lasers with resonant-phonon active-regions

Abstract

Significant progress has recently been made toward improving the power output, beam quality and spectral characteristics of terahertz quantum cascade lasers (QCLs). However, the maximum operating temperature of the best-performing devices has become relatively stagnant and is in the range of 150-200 K for QCLs designed to emit in the frequency range of 2-4 THz. Such QCLs are primarily designed with resonant-phonon depopulation schemes. The requirement to cryogenically cool terahertz QCLs leads to stringent limitations on their use for various applications. Although significant advances have been made to model quantum transport in quantum cascade superlattices, the relative role of various electron transport mechanisms as a function of temperature is not clear. This article discusses temperature behavior of resonantphonon terahertz QCLs with respect to a variety of active-region design schemes, and argues that precise understanding of high-temperature transport remains elusive for terahertz QCLs. The role of electron-phonon scattering, collisional-broadening, thermal leakage, and interface-roughness scattering towards the degradation of intersubband optical gain at higher temperatures is discussed for the popular terahertz QCL designs.

Large static tuning of narrow-beam terahertz plasmonic lasers operating at 78K

“…30, and was grown by molecular-beam epitaxy. The QCL superlattice is 10 µm thick with an average n-doping of 5.5 × 10 15 cm −3 , and surrounded by 0.05 µm and 0.1 µm thick highly doped GaAs contact layers at 5 × 10 18 cm −3 on either side of the superlattice.…”

“…30 The metallic QCL cavities with antennafeedback gratings were fabricated using standard wafer-wafer thermocompression bonding and contact lithography technique. Fig.…”

Simple electron-electron scattering in non-equilibrium Green's function simulations

“…The main temperature degrading mechanism of the THz QCLs is currently not fully understood and is still debated by the community [4]. This is a challenge to theory and there is a great need of realistic modeling tools that are able to treat all important quantum effects on the same footing.…”

“…This can be overcome via difference frequency generation which recently has been demonstrated at powers in the milli-watt range [3]. Direct THz-QCLs still generate a lot of interest in the research community due to the promise of higher wall-plug efficiency and the prospects of miniaturization of cryo-coolers.The main temperature degrading mechanism of the THz QCLs is currently not fully understood and is still debated by the community [4]. This is a challenge to theory and there is a great need of realistic modeling tools that are able to treat all important quantum effects on the same footing.…”

Split-well direct-phonon terahertz quantum cascade lasers

“…6,7 Additional potential limiting mechanisms for the performance of THz-QCLs are thermal backfilling 8 and line broadening. 9 In both resonant-phonon (RP) 10,11 and direct-phonon two-well (TW) schemes, 12,13 the phonon well is the widest in the structure. As such, a higher level in this well is not far above the upper laser level (ULL), so it provides a leakage channel at high temperatures.…”