Mitigating Valence Intersubband Absorption in Interband Cascade Lasers

Abstract

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 (Formula presented.) InxSb hole-quantum well (h-QW) is confirmed. This is reflected in the improvement of the laser's characteristic temperature T0, threshold current density Jth, 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.