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10 March 2016 Step-taper active-region quantum cascade lasers for carrier-leakage suppression and high internal differential efficiency
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Proceedings Volume 9767, Novel In-Plane Semiconductor Lasers XV; 976713 (2016)
Event: SPIE OPTO, 2016, San Francisco, California, United States
By stepwise tapering both the barrier heights and quantum-well depths in the active regions of 8.7 μm- and 8.4 μm-emitting quantum cascade lasers (QCLs) virtually complete carrier-leakage suppression is achieved, as evidenced by high values for both the threshold-current characteristic temperature coefficient T0 (283 K and 242 K) and the slope-efficiency characteristic temperature coefficient T1 (561 K and 279 K), over the 20–60 °C heatsink-temperature range, for low- and high-doped devices, respectively. Such high values are obtained while the threshold-current density is kept relatively low for 35-period, low- and high-doped devices: 1.58 kA/cm2 and 1.88 kA/cm2, respectively. In addition, due to resonant extraction from the lower laser level, high differential-transition-efficiency values (89-90%) are obtained. In turn, the slope-efficiency for 3 mm-long, 35-period high-reflectivity (HR)-coated devices are: 1.15-1.23 W/A; that is, 30- 40 % higher than for same-geometry and similar-doping conventional 8-9 μm-emitting QCLs. As a result of both efficient carrier-leakage suppression as well as fast and efficient carrier extraction, the values for the internal differential efficiency are found to be ≈ 86%, by comparison to typical values in the 58-67 % range for conventional QCLs emitting in the 7-11 μm wavelength range.
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J. D. Kirch, C.-C. Chang, C. Boyle, L. J. Mawst, D. Lindberg III, T. Earles, and D. Botez "Step-taper active-region quantum cascade lasers for carrier-leakage suppression and high internal differential efficiency", Proc. SPIE 9767, Novel In-Plane Semiconductor Lasers XV, 976713 (10 March 2016);

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