High-Performance $\lambda \sim 8.6~\mu {\rm m}$ Quantum Cascade Lasers With Single Phonon-Continuum Depopulation Structures

We report high performance λ~8.6 μm m quantum cascade lasers based on 5 quantum well single phonon-continuum (SPC) depopulation scheme, grown by metal organic vapor-phase epitaxy. Devices with SPC depopulation structures exhibit high device performances in pulsed and continuous wave (CW) operation due to a large dipole matrix element (3.0 nm) and short depopulation time (0.22 ps). A 4 mm-long, 8 μm-wide, high reflective (HR)-coated buried-hetero-structure laser with 33 cascade stages, for active region, demonstrates a high output power of 313 mW, a threshold current density of 1.35 kA/cm
²
, and slope efficiency of 547 mW/A at 30°C in CW operation. The maximum CW lasing temperature of the device is observed to be 120°C. Furthermore, by using a higher number of cascade stages (N=70) in a 4 mm-long, 22 m-wide, HR-coated ridge laser, a high peak power of 6.3 W is obtained together with a high wall-plug efficiency (WPE) of 10.8%, a slope efficiency of 2.7 W/A, and a threshold current density of 0.76 kA/cm
²
in pulsed operation at 300 K. The measured WPE of over 10% at room temperature is close to the theoretical values.