Extremely high T-values (∼450 K) of long-wavelength (∼15 μm), low-threshold-current-density quantum-cascade lasers based on the indirect pump scheme

The high device performance of a long-wavelength (∼15 μm), InGaAs/InAlAs, Fabry–Pérot quantum-cascade laser based on the indirect pump scheme is reported. As a result of felicitous designing of the active region and waveguide structure, a low threshold-current-density of ∼3.5 kA/cm2, a high maximum output power of ∼216 mW, and a high slope efficiency of ∼346 mW/A, all at room temperature are obtained. The observed extremely high characteristic temperature of threshold current, T0∼450 K over wide temperature range, 320–380 K is ascribed to a strong suppression of electron populations in injectors, which are specifically visualized in the indirect pump scheme.