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

Abstract

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.

Room temperature operation of single mode GaSb‐based DFB interband cascade lasers beyond 6.1 µm

“…It was shown in ref. [8] that the intersubband absorption in the valence band can be reduced with this h‐QW thickness for emission wavelengths around 6 µm. The GaInSb is sandwiched between InAs layers that are 2.72 and 2.27 nm thick.…”

“…Because interband cascade lasers (ICLs) are able to emit over a wide range in the mid-infrared and have rather low power consumption [2], they are important building blocks for mobile and compact sensor systems used in applications ranging from environmental monitoring and process analysis to biomedical diagnostics [3][4][5][6]. While the performance sweet spot for ICLs is between 3 and 4 µm, the upper wavelength limit has recently been pushed further [7,8]. With InAs-based ICLs emission wavelengths up to 14 µm at cryogenic temperatures in pulsed mode are possible [9,10].…”

“…In this work, we present a GaSb-based distributed feedback (DFB) ICL with single mode emission beyond 6.1 µm based on an optimized epitaxial design. Within this design, the intersubband absorption in the valence band was minimized [7,8] and the carrier densities were balanced by adjusting the doping concentration in the electron injector [13].…”

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

“…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.…”