Implementation of the step-taper active-region (STA) design to 8-9 μm-emitting quantum cascade lasers (QCLs) has resulted in both high T0 and T1 values: 220 K and 665 K, and short lower-level lifetimes: 0.12 ps. In turn, the internal differential efficiency ηid, which is the product of the injection efficiency and the differential laser-transition efficiency, reaches values as high as 86 % for both 8.4 μm- and 8.8 μm-emitting QCLs. Such ηid values are 30-50% higher than those obtained from conventional QCLs emitting in the 7-11 μm wavelength range. Achieving both carrier-leakage suppression and miniband-like carrier extraction in mid-infrared (IR) QCLs leads to ηid values close to the fundamental limit of ~ 90 %. In turn, the currently employed fundamental wallplug-efficiency limits over the mid-IR wavelength range have to be increased by ~ 34 % (e.g., the wallplug-efficiency limit at λ= 4.6 μm increases from 29 % to 39 %). Preliminary results from STA-type 4.8-5.0 μm-emitting QCLs include 1.5 W CW operation, and 77 % internal differential efficiency; that is, 30-50% higher than the ηid values obtained from conventional 4.0-6.5μm-emitting QCLs.
Dan Botez, Jeremy D. Kirch, Chun-Chieh Chang, Colin Boyle, Honghyuk Kim, Kevin M. Oresick, Chris Sigler, Luke J. Mawst, Minhyeok Jo, Jae Cheol Shin, Gun-Kim Doo, Don F. Lindberg, and Thomas L. Earles, "High internal differential efficiency mid-infrared quantum cascade lasers," Proc. SPIE 10123, Novel In-Plane Semiconductor Lasers XVI, 101230Q (Presented at SPIE OPTO: February 01, 2017; Published: 20 February 2017); https://doi.org/10.1117/12.2249537.
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