Broad gain injectorless quantum-cascade lasers with low threshold emitting around 8.6 µm

Broad gain lasers attract much interest due to the practical gas sensing applications. A step well structure with double optical transitions is implemented in the active region of injectorless quantum-cascade lasers (QCLs) to achieve extended gain bandwidth. The step well is constructed by a “short period superlattice” which provides an equivalent GaInAlAs alloy quantum step well in each active module. The fabricated devices show an ultrabroadband gain spectrum of 480 cm^-1 (4 μm) at room temperature in pulsed mode. The laser threshold current density is as low as 1.1 kA/cm² which is the lowest among the broad gain QCLs emitting at similar wavelengths and the slope efficiency is 1.6 W/A at room temperature.