6th International Conference on Photonics
University of Wisconsin-Madison, USA
Title: High-internal-efficiency quantum cascade lasers: the road to mid-infrared lasers of 40% CW wall-plug efficiency
Biography: Dan Botez
The internal efficiency hi of quantum cascade lasers (QCLs) is the factor in the expression for the external differential efficiency that encompasses all differential carrier-usage (i.e., the injection efficiency) and lasing-photon-transition efficiencies. For conventional QCLs the hI values have been found to be rather low: 50-60% in the 4.5-6.0 μm wavelength range and 57-67% in the 7-11 μm wavelength range; with, until recently, no clear explanation why that was the case. With the advent of combining carrier-leakage suppression with fast, efficient carrier extraction out of the active regions of QCLs, the hi values have steadily increased and are approaching their fundamental upper limit of ~ 90% for mid-infrared (IR)-emitting devices. We will review the developments that led to high hi values throughout the mid-IR wavelength range. Conduction-band engineering has led to the so-called step-taper active-region (STA) QCLs which have provided hi values 30-50% higher than in conventional QCLs over both the 4.5-6.0 μm and 7-11 μm wavelength ranges. A record-high, single-facet, continuous-wave (CW) power, for 8.0 μm-emitting QCLs, of 1.0 Watt has been achieved from STA-type QCLs. Furthermore, the recognition that the fundamental limit for hi (i.e., 90%) is 34% higher than the hi value employed a decade ago when determining the fundamental limit for the wall-plug efficiency of mid-IR QCLs, has led to the realization that wall-plug efficiencies ≥ 40% can be achieved for 4.5-5.0 μm-emitting QCLs. The practical benefits of achieving such high performance from mid-IR emitting semiconductor lasers will be discussed as well.
Wall-plug-efficiency fundamental limits for mid-infrared-emitting QCLs
- Kirch J et al (2016) 86% internal differential efficiency from 8-9 µm-emitting, step-taper active-region quantum cascade lasers. Optics Express 24: 24483-24494.
- Botez D, Chang C-C, Mawst L J (2016) Temperature sensitivity of the electro-optical characteristics for mid-infrared-emitting quantum cascade lasers. J. Phys. D: Applied Physics 49: 043001.
- Botez D et al. (2013) Multidimensional conduction-band engineering for maximizing the continuous-wave (cw) wallplug efficiencies of mid-infrared quantum cascade lasers. IEEE Journal Selected Topics in Quantum Electronics 19 (4): 1200312.
- Kirch J et al. (2012) Tapered active-region quantum cascade lasers for suppression of carrier-leakage currents. Electron Lett. 48: 234.
5. Botez D et al. (2010) Temperature dependence of the key electro-optical characteristics for mid-infra-red emitting quantum cascade lasers. Applied Physics Letters 97: 071101.