Tapered active-region quantum cascade lasers (λ = 4.8 μm) for virtual suppression of carrier-leakage currents

A new deep-well quantum-cascade laser (QCL) design, for which the barrier layers in the active region are tapered such that their conduction band edges increase in energy from the injection barrier to the exit barrier, results in significant suppression of the carrier leakage in 4.8 μm-emitting devices. For heatsink temperatures in the 20-60°C range, the characteristic temperature coefficients for threshold, T₀, and slope efficiency, T₁, reach values as high as 231 K and 797 K, respectively. The T₁ values are more than a factor of two higher than the best reported values for high-performance, 4.6-4.9 μm -emitting QCLs of similar injector-doping level. At 20°C, the threshold-current density for uncoated, 30-period, 3-mm-long devices is only ~1.55 kA/cm².