High-power ∼ 4.1 μm quantum cascade lasers grown by metal-organic chemical vapor deposition

The authors report the development of a λ ∼ 4.1 μm quantum cascade laser grown by metal-organic chemical vapor deposition using strain-balanced InGaAs/InAlAs materials. A device with a 7.5 mm cavity length and 6.5 μm ridge width, bonded to an aluminum nitride heatsink, achieves maximum output powers of 3.4 W at 288 K in pulsed mode and 1.6 W at 288 K in continuous-wave (CW) operation, with corresponding maximum wall-plug efficiencies of 14.8% and 9.3%. A kink is observed in the power–current curve under CW operation, which is absent in pulsed operation. Near-field results show that in CW operation, the horizontal beam quality factor M² fluctuates with current, indicating mode instability and high-order lateral mode excitation, while in pulsed mode, the horizontal M² remains stable around 1.3 as the current increases from 1.4 A to 1.9 A.