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

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 InAs_0.91Sb_0.09 and AlAs_0.1Sb_0.9∕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·Hz^1∕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 · Hz^1∕2∕W.