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We demonstrate the bias-selectable mid- or long-wave infrared detectors composed by back-to-back pin-nip diodes with “M” barrier inserted in two diodes to suppress the dark current. Mid-wave infrared (MWIR) and long-wave infrared (LWIR) active region (π layer) are composed by 8 ML/8 ML and 12.5 ML/7 ML InAs/GaSb superlattices. The cutoff wavelength is 4.8 μm under forward bias called MWIR channel and expands to 10 μm under reverse bias called LWIR channels. The responsivities are 0.27 A/W at 4.2 μm at forward 300 mV bias, while 0.31 A/W at 9 μm at reverse 400 mV bias at 77 K. The dependence of the response on the bias is due to the competition of the built-in electric field from the two junctions. The current–voltage curve and the quantum efficiency were measured at 77 K. The dark current densities are 22.7×10−5 A/cm2 and 4.51×10−2 A/cm2 for two channels under different bias. The peak detectivity of MWIR diode is calculated to 2.0×1012 cm·Hz1/2/W at 4.2 μm and 1.0×1010 cm·Hz1/2/W at 9 μm for LWIR channel.

We compared the photoluminescence (PL) properties of AlInAsSb digital alloy samples with different periods grown on GaSb (001) substrates by molecular beam epitaxy. Temperature-dependent S-shape behavior is observed and explained using a thermally activated redistribution model within a Gaussian distribution of localized states. There are two different mechanisms for the origin of the PL intensity quenching for the AlInAsSb digital alloy. The high-temperature activation energy E 1 is positively correlated with the interface thickness, whereas the low-temperature activation energy E 2 is negatively correlated with the interface thickness. A quantitative high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) study shows that the interface quality improves as the interface thickness increases. Our results confirm that E 1 comes from carrier trapping at a state in the InSb interface layer, while E 2 originates from the exciton binding energy due to the roughness of the AlAs interface layer.

By optimizing the V/III beam-equivalent pressure ratio, a high-quality InAs/GaSb type-II superlattice material for the long-wavelength infrared (LWIR) range is achieved by molecular beam epitaxy (MBE). High-resolution x-ray diffraction (HRXRD), atomic force microscopy (AFM), and Fourier transform infrared (FTIR) spectrometer are used to characterize the material growth quality. The results show that the full width at half maximum (FWHM) of the superlattice zero-order diffraction peak, the mismatching of the superlattice zero-order diffraction peak between the substrate diffraction peaks, and the surface roughness get the best results when the beam-equivalent pressure (BEP) ratio reaches the optimal value, which are 28 arcsec, 13 arcsec, and 1.63 Å, respectively. The intensity of the zero-order diffraction peak is strongest at the optimal value. The relative spectral response of the LWIR detector shows that it exhibits a 100% cut-off wavelength of 12.6 μm at 77 K. High-quality epitaxial materials have laid a good foundation for preparing high-performance LWIR detector.

The etching and passivation processes of very long wavelength infrared (VLWIR) detector based on the InAs/GaSb/AlSb type-II superlattice have been studied. By studying the effect of each component in the citric acid solution (citric acid, phosphoric acid, hydrogen peroxide, deionized water), the best solution ratio is obtained. After comparing different passivation materials such as sulfide + SiO2, Al2O3, Si3N4 and SU8, it is found that SU8 passivation can reduce the dark current of the device to a greater degree. Combining this wet etching and SU8 passivation, the R 0 A of VLWIR detector with a mesa diameter of 500 μm is about 3.6 Ω⋅cm2 at 77 K.