Intersubband Quantum-Box Lasers: Progress and Potential as Uncooled Mid-Infrared Sources
Reed Center for Photonics, University of Wisconsin, Madison, WI 53706, U.S.A.
Naval Research Laboratory, Washington, DC 20375, U.S.A.
MIT Lincoln Laboratory, Lexington, MA 02420, U.S.A.
University of Florida, Gainesville, FL 32611, U.S.A
Semiconductor lasers operating in continuous wave (cw) at or near room temperature (RT) and emitting in the mid- and far-infrared wavelength ranges, 3-13 μm, are critically needed for a vast array of applications. Intersubband (IS) transition emitters are the most likely solution. The first implementation of the concept for using IS transitions for laser action was realized in early 19941 and named quantum cascade (QC) laser. Current QC devices have demonstrated high-power, RT cw operation in the 4.0-6.0 μm range,2,3 but with relatively low wall-plug efficiency (~10%) due to inherently high operating voltages (10-11 V). Furthermore, the devices have highly temperature-sensitive characteristics2–4 at and above RT, due to severe carrier leakage out of their active regions, which in turn raises serious issues of long-term device reliability. To suppress the carrier leakage we have employed the deep-well QC laser concept.5,6
Quantum cascade lasers have fundamentally poor radiative efficiencies ...