Open AccessMultidimensional Conduction-Band Engineering for Maximizing the Continuous-Wave (CW) Wallplug Efficiencies of Mid-Infrared Quantum Cascade Lasers
Author(s) -
Dan Botez,
Jae Cheol Shin,
Jeremy Daniel Kirch,
Chun-Chieh Chang,
Luke James Mawst,
Thomas Earles
Publication year - 2013
Publication title -
ieee journal of selected topics in quantum electronics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.131
H-Index - 159
eISSN - 1558-4542
pISSN - 1077-260X
DOI - 10.1109/jstqe.2012.2237387
Subject(s) - engineered materials, dielectrics and plasmas , photonics and electrooptics
By tailoring the active-region quantum wells and barriers of 4.5-5.0-μm-emitting quantum cascade lasers (QCLs), the device performances dramatically improve. Deep-well QCLs significantly suppress carrier leakage, as evidenced by high values for the threshold-current characteristic temperature T0 (253 K) and the slope-efficiency characteristic temperature T1 (285 K), but, due to stronger quantum confinement, the global upper-laser-level lifetime τ4g decreases, resulting in basically the same room-temperature (RT) threshold-current density Jth as conventional QCLs. Tapered active-region (TA) QCLs, devices for which the active-region barrier heights increase in energy from the injection to the exit barriers, lead to recovery of the τ4g value while further suppressing carrier leakage. As a result, experimental RT Jth values from moderate-taper TA 4.8-μm emitting QCLs are ~14% less than for conventional QCLs and T1 reaches values as high as 797 K. A step-taper TA (STA) QCL design provides both complete carrier-leakage suppression and an increase in the τ4g value, due to Stark-effect reduction and strong asymmetry. Then, the RT Jth value decreases by at least 25% compared to conventional QCLs of same geometry. In turn, single-facet, RT pulsed and continuous-wave maximum wallplug-efficiency values of 29% and 27% are projected for 4.6-4.8-μm-emitting QCLs.