A rapid series of recent performance advances have established the interband cascade laser (ICL) as a practical midwave infrared (mid-IR) diode source that may be expected to find broad use in a variety of applications ranging from infrared countermeasures to chemical spectroscopy. The ICL is effectively a hybrid of the conventional diode laser, in that injected electrons and holes recombine to create photons, and the quantum cascade laser (QCL), in that a multi-stage staircase of active quantum wells is connected in series. The ICL also differs from both, however, in that most of the electrons and holes needed for lasing are created internally at semimetallic interfaces separating the stages rather than being injected from the contacts. The ICL performance recently improved dramatically when “carrier rebalancing”, via heavy n-type doping of the electron injector regions, was introduced to equalize the electron and hole populations in the active quantum wells [1]. Recent publications have reported cw operation up to 109 °C, cw output power up to 158 mW at room temperature (RT, taken here to be 25 °C), RT cw wallplug efficiency up to 13.5%, RT cw drive power as low as 29 mW (more than 20 times lower than the best QCLs results reported to date), and RT cw operation to wavelengths as long as 5.7 μm [1,2]. Here we discuss further improvements of the lasing characteristics that occur when the ICLs are mounted epitaxial-side-down (epi-down), using a proprietary NRL procedure that combines high performance with high processing yield.
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