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 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.

Interband cascade lasers with advanced waveguides operating in the 3 to 4 μm wavelength region

“…This might be caused by the substantial reductions in layer thicknesses from the intended design, which could narrow the interband tunneling window between the electron and hole injectors 2,25 and consequently would require a higher voltage to open and widen the tunneling window. Nevertheless, these ICLs were able to lase in pulsed mode at high temperatures (up to 390 K) with characteristic temperature (T 0 ) values in pulsed mode of 59.5 and 58.0 K in the temperature range of 200 to 360 K, respectively, which is higher than previously reported values (T 0 ∼ 45 to 55 K) from early RT ICLs 5,12 with similar lasing wavelengths.…”

“…These features of the ICL are ideal for a host of practical applications in the mid-infrared, including gas/chemical sensing, imaging, industrial process control, and free-space optical communication 7 – 11 The GaSb-based ICLs have demonstrated efficient room temperature (RT) operation in the 3 to 6 μm range but exhibited performance below their InAs-based counterparts beyond 6 μm due partially to limited effort and the difficulties associated with the waveguide traditionally used 4 , 5 , 12 , 13 . The typical waveguide used in a GaSb-based ICL consists of two Te-doped GaSb separate confinement layers (SCLs) surrounding the cascade active region, wrapped by two n-type doped InAs/AlSb superlattice (SL) cladding layers, which have a low thermal conductivity and a small contrast in refractive index with the cascade region.…”

“…[7][8][9][10][11] The GaSb-based ICLs have demonstrated efficient room temperature (RT) operation in the 3 to 6 μm range but exhibited performance below their InAs-based counterparts beyond 6 μm due partially to limited effort and the difficulties associated with the waveguide traditionally used. 4,5,12,13 The typical waveguide used in a GaSb-based ICL consists of two Te-doped GaSb separate confinement layers (SCLs) surrounding the cascade active region, wrapped by two n-type doped InAs/AlSb superlattice (SL) cladding layers, which have a low thermal conductivity and a small contrast in refractive index with the cascade region. On the other hand, the InAs-based ICLs have utilized a heavily n þ -type doped InAs plasmon-enhanced cladding layer, instead of the InAs/AlSb SL, to improve the optical confinement and the overall thermal conductivity of the device, [14][15][16][17] resulting in the wavelength coverage of ICLs extending to 11.2 μm.…”

Pushing the Room Temperature Continuous‐Wave Operation Limit of GaSb‐Based Interband Cascade Lasers beyond 6 µm

“…Compared to the published T 0 values from ref. [6], the absolute T 0 values here are smaller. It should be noted that the broad area devices in this work are completely etched through the active region to reduce current spreading.…”

“…Simulation results are based on the eight‐band k· p method using a generalized momentum matrix element model, for more details on the simulation see ref. [6]. Around the emission wavelength (depicted in gray), the widest h‐QW (3 ‐ red) should experience the lowest absorption and the narrowest (1 ‐ black) the highest absorption.…”