High-performance quantum cascade lasers in the 7.3- to 7.8-μm wavelength band using strained active regions

We consider the use of strained quantum cascade (QC) laser designs in the 7.3- to 7.8-µm wavelength region to improve the cw operating characteristics of these lasers at room temperature. We compare the performance of a QC laser with a strain-balanced active region with that of two similarly designed QC lasers with lattice-matched active-region layers, and we show that the strain-balanced design significantly outperforms the unstrained-layer designs in terms of threshold-current density, power slope efficiency, and cw output power at room temperature. A epi-side-down-mounted, double-channel ridge-geometry laser that was fabricated from the strained design with a ridge width of 13 µm and a cavity length of 3 mm produced cw output power in excess of 500 mW at room temperature. The characteristic temperature T0 for the strained-layer design as determined from pulsed measurements between 25 and 80°C is 221.5 K, compared with a value of 194.0 K for one of the unstrained designs.