Fig. 1. History of the development of infrared detectors

Fig. 2. （a）Bandgap diagram of nBn barrier detector，（b）spatial makeups of the various current components and barrier blocking in nBn detector，（c）bandgap diagram of the p-n photodiode，（d）the schematic Arrhenius plot of the dark current in a p-n photodiode and nBn device and comparision with Rule 07 & Law 19

Fig. 3. （a）Conduction（filled）and valence（open）band offsets for the 12 binaries，（b）valence band offset as a function of lattice constant ^［52］

Fig. 4. （a）Arrhenius plot of dark current at different reverse bias values for a 300×300 μm nBn detector，（b）photoresponse spectra at 150 K（the calculated spectral response（solid line）and the measured spectral response at a reverse bias of -0.6 V（dotted line）），（c）image captured by a 320×256 nBn FPA detector（BF ROIC）operating at 150 K and f/3，（d）the device structure of InAsSb/AlAsSb nBn MWIR detector，（e）the stimulated energy band diagram under reverse bias conditions of InAsSb/AlAsSb nBn MWIR detector，（f）the dark current density vs bias voltage as a function of the temperature of the InAsSb/AlAsSb nBn MWIR detector^{［54，58，60］}

Fig. 5. Design of the InSb nBn barrier detector，（a）design of InSb nBn structure with InAlSb barrier layer including Al grading from 15% to 35%，（b）calculated energy band diagram at T = 110 K and V = 0 V of InSb/InAlSb/InSb nBn structure with 50 nm-thick InAlSb graded composition barrier layer，（c）Arrhenius plot of the dark current density collected at -50 mV where thermionic emission regime is identified，（d）J-V curves performed at 77 K of InSb-based nBn detector（solid line）and InSb PIN diode（dashed line），（e）J-V characteristics of nBn structure for different operating temperatures，from 105 K to 175 K，（f）Arrhenius behavior of three different types of InSb-based photodetectors^{［64，65，67］}

Fig. 6. （a）Alignment between mini-bands in the active and barrier layers of a T2SLs XBp device，superimposed on the band gaps of InAs，GaSb，and AlSb，（b）the schematic diagram of the SWIR nBn photodetector with the inset showing the superlattice band alignment of the H-structure electron barrier^{［71，72］}

Fig. 7. Design of the HgCdTe nBn barrier detector，（a）the schematic illustration of the structure of the HgCdTe nBn photodetector device，（b）cross-sectional device diagram and structural parameters，（c）measured dark and unfiltered blackbody illuminated I-V characteristics of planar MWIR HgCdTe nBn device at 77 K^{［30，79］}

Fig. 8. Design of the two-dimensional materials nBn barrier detector，（a）the schematic diagram of the WS₂ nBn vdW unipolar barrier photodetector，（b）simulated band diagrams of the device under different source-drain bias（V_ds）conditions（WS₂，h-BN，and PdSe₂ flakes act as the absorber，barrier，and contact layer，respectively），（c）output characteristic curves of the nBn vdW unipolar barrier device under 520 nm laser illumination with increasing powers^［94］