InAs-based interband cascade lasers (ICLs) can be more easily adapted toward long wavelength operation than their GaSb counterparts. Devices made from two recent ICL wafers with an advanced waveguide structure are reported, which demonstrate improved device performance in terms of reduced threshold current densities for ICLs near 11  μm or extended operating wavelength beyond 13  μm. The ICLs near 11  μm yielded a significantly reduced continuous wave (cw) lasing threshold of 23 A/cm2 at 80 K with substantially increased cw output power, compared with previously reported ICLs at similar wavelengths. ICLs made from the second wafer incorporated an innovative quantum well active region, comprised of InAsP layers, and lased in the pulsed-mode up to 120 K at 13.2  μm, which is the longest wavelength achieved for III–V interband lasers.

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The temperature-dependent and excitation-dependent photoluminescence (PL) spectroscopy characterization of mid-wavelength infrared InAs/InAs 1-x Sb x type-II superlattices reveals evidence of carrier localization. Carrier localization is apparent in the 8 meV PL peak position blue shift from 4 K to 60 K while the peak full-width-at-half-maximum is non-monotonic, peaking at 25 K before increasing above 60 K. In addition, competition between two recombination processes is evident in the temperature-dependent behavior of the PL peak integrated intensity under low excitation conditions: the intensity decreases from 4 K to 80 K, increases from 80 K to 160 K, and decreases above 160 K. Excitation-dependent PL studies reveal the dominant recombination mechanism changes from free-tobound or donor-acceptor-like recombination to excitonic or band-to-band recombination at ~60 K. These findings suggest that carrier localization is occurring below 60 K, and the confined carriers are holes as these are unintentionally doped n-type superlattices. The localization potentials are due to variations in the InAs 1-x Sb x composition, the interfaces, and the InAs and InAs 1-x Sb x layer widths. The width of a Gaussian distribution used to describe the density of states of the band tails due to carrier localization potentials ranges from 2 meV to 4 meV. The larger energy corresponds to the smaller period superlattices, indicating the interface compositional variation is more prominent and creates larger localization potentials than in the longer period superlattices.

In order to achieve improved understanding and gain insights into the device operation of interband cascade infrared photodetectors (ICIPs) and ultimately to optimize the design, we present a comparative study of five long-wavelength (LW) ICIPs based on a type-II InAs/GaSb superlattice. This study shows how the device responsivity is affected by the individual absorber thicknesses and the number of cascade stages, through the impact of light attenuation. Additionally, this study further validates that the electrical gain universally exists in non-current-matched ICIPs. With multiple cascade stages to suppress noise, these LW ICIPs achieved superior device performance at high temperatures, in terms of Johnson-noise limited detectivities, compared to commercial MCT detectors. Furthermore, a theory is developed to quantitatively describe the electrical gain in ICIPs and our calculations are in good agreement with the experimental results. Based on the theory, the optimal number of stages for maximizing the device detectivity D* is identified with inclusion of the electrical gain. Our calculation shows that this optimal number of stages is relatively large in the presence of the gain and the maximized D* has a relatively weak dependence on the absorber thickness when it is sufficiently thin.

We report on a comparative study of narrow-bandgap (∼0.2 eV at 300 K) thermophotovoltaic (TPV) devices with InAs/GaSb type-II superlattice absorbers. By comparing the characteristics of three narrow bandgap TPV structures with a single absorber or multiple discrete absorbers, it is clearly demonstrated that the device performance of a conventional single-absorber TPV cell is limited mainly by the small collection efficiency associated with a relatively short diffusion length (1.5 μm at 300 K). Furthermore, this study revealed that multi-stage interband cascade (IC) TPV structures with thin individual absorbers can circumvent the diffusion length limitation and are capable of achieving a collection efficiency approaching 100% for photo-generated carriers. Additionally, the open-circuit voltage, the fill factor, the output power, and the power conversion efficiency can be significantly increased in IC TPV devices compared to the conventional single-absorber TPV structure. These results have further validated the potential and advantages of narrow bandgap IC structures for TPV cells.