For the next-generation 8 to 14μm long-wavelength infrared (LWIR) sensing, type-II superlattices (T2SLs) detectors have enormous potential to appeal to various applications including space, medical imaging, and defense. In typical absorber design, the sufficiently thick active layer (AL) is required to achieve high quantum efficiency (QE), whereas it can cause a high dark current and increase the cost. Moreover, a simple increase in AL thickness does not provide an increase in QE due to the limited carrier lifetime in T2SLs. A possible solution to the weak absorption in the AL of the T2SL-based detectors involves incorporating the AL into an optically resonant cavity. In this work, optically enhanced QE for the broadband T2SL nBn detectors will be presented through the guided-mode-resonance (GMR) structures on the top surface of the T2SL. We fabricated T2SL nBn detectors with periodic gratings on the top surface. The devices showed much-enhanced QE due to multiple resonances, as well as Fabry-Perot resonance in the thin AL with a lower dark current characteristic than the reference T2SL detector. Furthermore, we also found the broadening of the cutoff wavelength, which is typically limited by the material property, by scaling the dimension of the diffraction grating for a strong resonance beyond the cut-off region. In conclusion, the GMR-based LWIR T2SL detectors can show a significant performance enhancement in QE and extend the detection range beyond the cut-off wavelength while maintaining a low dark current.
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