High-performance continuous-wave operation of λ ∼ 4.6 μm quantum-cascade lasers above room temperature

We report the high-performance continuous-wave (CW) operation of 10-mum-wide quantum-cascade lasers (QCLs) emitting at λ ∼ 4.6 μm, based on the GaInAs-AlInAs material without regrowth, in epilayer-up and -down bonding configurations. The operational characteristics of QCLs such as the maximum average power, peak output power, CW output power, and maximum CW operating temperature are investigated, depending on cavity length. Also, important device parameters, i.e., the waveguide loss, the transparency current density, the modal gain, and the internal quantum efficiency, are calculated from length-dependent results. For a high-reflectivity (HR) coated 4-mm-long cavity with epilayer-up bonding, the highest maximum average output power of 633 mW is measured at 65% duty cycle, with 469 mW still observed at 100%. The laser exhibits the maximum wall-plug efficiencies of 8.6% and 3.1% at 298 K, in pulsed and CW operatons, respectively. From 298 to 393 K, the temperature dependent threshold current density in pulsed operation shows a high characteristic temperature of 200 K. The use of an epilayer-down bonding further improves the device performance. A CW output power of 685 mW at 288 K is achieved for the 4-mm-long cavity. At 298 K, the output power of 590 mW, threshold current density of 1.52 kA/cm², and maximum wall-plug efficiency of 3.73% are obtained under CW mode, operating up to 363 K (90°C). For HR coated 3-mm-long cavities, laser characteristics across the same processed wafer show a good uniformity across the area of 2 × 1 cm², giving similar output powers, threshold current densities, and emission wavelengths. The CW beam full-width at half-maximum of far-field patterns are 25° and 46° for the parallel and the perpendicular directions, respectively.