Type-II superlattice-based extended short-wavelength infrared focal plane array with an AlAsSb/GaSb superlattice etch-stop layer to allow near-visible light detection

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A versatile infrared imager capable of imaging the near-visible to the extended short-wavelength infrared (e-SWIR) is demonstrated using e-SWIR InAs/GaSb/AlSb type-II superlattice-based photodiodes. A bi-layer etch-stop scheme consisting of bulk InAs0.91Sb0.09 and AlAs0.1Sb0.9/GaSb superlattice layers is introduced for substrate removal from the hybridized back-side illuminated photodetectors. The implementation of this new technique on an e-SWIR focal plane array results in a significant enhancement in the external quantum efficiency (QE) in the 1.8–0.8 μm spectral region, while maintaining a high QE at wavelengths longer than 1.8 μm. Test pixels exhibit 100% cutoff wavelengths of ∼2.1 and ∼2.25  μm at 150 and 300 K, respectively. They achieve saturated QE values of 56% and 68% at 150 and 300 K, respectively, under back-side illumination and without any anti-reflection coating. At 150 K, the photodetectors (27  μm×27  μm area) exhibit a dark current density of 4.7×10−7  A/cm2 under a −50  mV applied bias providing a specific detectivity of 1.77×1012  cm·Hz1/2/W. At 300 K, the dark current density reaches 6.6×10−2  A/cm2 under −50  mV bias, providing a specific detectivity of 5.17×109  cm·Hz1/2/W.