Interband cascade lasers (ICLs), especially valued for their low power consumption, are particularly appealing for portable, compact, and battery-driven trace gas sensors. However, their performance notably degrades outside the 3-4 µm region. Here, a solution to overcome current performance limitations is presented. Simulation results based on the eight-band k⋅p method employing a generalized momentum matrix element model identify resonant intersubband absorption in the valence band as the causative underlying mechanism. Experimentally, a direct dependence of this resonant absorption on the thickness of the Ga 1−x In x Sb hole-quantum well (h-QW) is confirmed. This is reflected in the improvement of the laser's characteristic temperature T 0 , threshold current density J th , slope efficiency 𝜼, and output power. Extracted waveguide losses from length-dependent measurements substantiate the key role of the valence intersubband absorption. While the performance improvement is experimentally verified at 4.35 µm, the simulation results additionally show how to mitigate undesired absorption at longer wavelengths, paving the way towards high-performance continuous-wave (cw) operation above 6 µm.

GaSb‐based interband cascade lasers (ICLs) emitting at a center wavelength of 6.12 µm at 20 °C in continuous‐wave operation up to a maximum operating temperature of 40 °C are presented. Pulsed measurements based on broad area devices show improved performance by applying the recently published approach of adjusting the Ga1−x$_{1-x}$InxSb layer thickness in the active region to reduce the valence intersubband absorption. The W‐quantum well design adjustment and the optimization of the electron injector, to rebalance the electron and hole concentrations in the active quantum wells, improved the device performance, yielding room temperature current densities as low as 0.5 kA cm−2 for broad area devices under pulsed operation. As a direct result of this improvement together with optimizations of the waveguide design, the long wavelength limit for GaSb‐based ICLs in continuous‐wave operation could be extended. For an epi‐side down mounted 23 µm wide and 2 mm long device with nine active stages and high‐reflectivity back facet, the threshold power is below 1 W and the optical output power is over 25 mW at 20 °C in continuous‐wave mode. Such low‐threshold and low‐power consumption ICLs are especially attractive for mobile and compact sensing systems.

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We present GaSb-based interband cascade lasers emitting at a center wavelength of 6.12 µm at 20°C in continuous-wave operation up to a maximum operating temperature of 40°C. Pulsed measurements based on broad area devices show improved performance by applying the recently published approach of adjusting the Ga1−xInxSb layer thickness in the active region to reduce the valence intersubband absorption. The W-quantum well design adjustment and the optimization of the electron injector, to rebalance the electron and hole concentrations in the active quantum wells, improved the device performance, yielding room temperature current densities as low as 0.5 kA/cm 2 for broad area devices under pulsed operation. As a direct result of this improvement the long wavelength limit for GaSb-based ICLs in continuous wave operation could be extended. For an epi-side down mounted 23 µm wide and 2 mm long device with 9 active stages and high-reflectivity back facet the threshold power is below 1 W and the optical output power is over 25 mW at 20°C in continuous-wave mode. Such low-threshold and low-power consumption interband cascade lasers are especially attractive for mobile and compact sensing systems.