Fig. 1. Infrared detection technology of HgTe colloidal quantum dots^[14-27]

Fig. 2. Optoelectronic properties of infrared materials. (a) Current main studied infrared materials and their response ranges^[34]; (b) band diagram for bulk HgTe^[33]; (c) impact of quantum confinement effect on the optical and electrical properties of CQDs^[35]

Fig. 3. Synthesis of HgTe QDs in polar media. (a) Absorption and photoluminescence (PL) spectra of HgTe nanocrystals synthesized in aqueous solvent [inset: transmission electron microscope (TEM) image]^[36]; (b) TEM and absorption spectra of DT-capped HgTe NCs in CCl₄^[37]; (c) PL spectra obtained from a series of aliquots taken from the DMSO-based HgTe QD synthesis^[38]; (d) various processes that can occur during HgTe QD growth in aprotic solvents (above curves correspond to the possible particle size distribution at each step)^[39]

Fig. 4. Synthesis of HgTe quantum dots in nonpolar media. (a) Absorption spectra of HgTe capped with octadecylamine and TOPO, prepared at 70 ℃ (inset: TEM image)^[40]; (b) absorption spectra of different-sized colloidal HgTe (inset: TEM image of HgTe CQDs with an absorption onset at 5 µm. Scale bar: 100 nm)^[41]; (c) TEM image of HgTe QDs with PL peak at 2460 cm^-1 (0.305 eV), and the absorption and PL of HgTe CQDs solutions with different sizes dispersed in C₂Cl₄^[14]

Fig. 5. Synthesis of monodisperse HgTe quantum dots. (a) TEM image and absorption spectra of HgTe CQDs synthesized with TMSTe^[43]; (b) TEM and absorption spectra of spherical dots synthesized using the 0.05 mmol∶0.05 mmol TMSTe∶TMSTe protocol and tetrahedral dots synthesized using the 0.025 mmol∶0.075 mmol TMSTe∶TOPTe protocol at 92 ℃^[44]; (c) TEM of HgTe CQDs synthesized through ligand-engineered strategy and absorption spectra of HgTe CQD films after ligand exchange with different sizes^[17]

Fig. 6. Synthesis of HgTe quantum dots with sharp excitonic absorption. (a) TEM image and the tunable absorption spectra of tetrapod HgTe CQDs synthesized by continuous-drop method^[18]; (b) TEM image and the absorption spectra of branched HgTe CQDs synthesized by hot-injection method^[46]; (c) absorption spectra of 2.5 μm HgTe CQDs with TOPTe, TMSTe, and TMSTe+TOPTe CQD, respectively, and HgTe CQD morphology effect on infrared photoconductors^[47]

Fig. 7. Mechanism diagrams of electronic transition. (a) Interband transition; (b) intraband transition

Fig. 8. Synthesis of large-sized HgTe quantum dots. (a) multiple exciton characteristics, TEM image, absorption and PL spectra of LWIR of HgTe CQDs synthesized by regrowth method^[51]; (b) LWIR HgTe CQDs with a response of 18 μm synthesized by high activity Te source^[52]

Fig. 9. Scalable synthesis of HgTe quantum dots. (a) High-concentration HgTe CQDs synthesis based on liquid Hg drop^[19]; (b) continuous-drop synthesis of HgTe CQDs^[18]

Fig. 10. Preparation method of HgTe CQD solids. (a) Schematic of solid-state ligand exchange; (b) energy of the valence band, conduction band, and vacuum level for HgTe CQDs with a 1.7 μm cutoff wavelength and different capping ligands^[53]; (c) schematic of solution ligand exchange and doping^[54]; (d) absorption spectra of CQD with different doping^[54]; (e) energy diagram of the HgTe CQDs at different doping concentrations of HgCl₂^[55]

Fig. 11. Research on the mobility of HgTe quantum dot thin films. (a) Resolvable quantum state electron filling and bandlike transport^[20]; (b) high mobility achieved by liquid phase exchange and the effect of mobility on specific detectability of devices^[55]; (c) mobility characterization of HgTe CQD solids synthesized by ligand engineering strategies^[17]; (d) currently the highest electron mobility of HgTe quantum dot thin films ^[16]

Fig. 12. Structure of HgTe quantum dot infrared detectors. (a) Schematic of photodiode structure and energy band profile of the short-wave infrared photodiode with a structure FTO/TiO₂/HgTe (ambipolar, 4000 cm^-1)/HgTe (p type, 6000 cm^-1)/MoO₃/Au^[65]; (b) schematic of the device structure, and I-V curves of device at 90 K in dark conditions (black line), ambient 295 K radiation (blue line), and 600 ℃ blackbody illumination (red line)^[64]; (c) sketch of the device structure, and D* from the HgCl₂-treated HgTe CQDs MWIR detectors (red circles) and the HgTe PV MWIR detector (black arrow line) in Ref. [44]^[21]; (d) device architecture and energy diagram of HgTe CQD photodetectors with Bi₂S₃-ETL^[24]; (e) schematic and energy diagram of PIN gradient structure based on HgTe CQDs^[54]; (f) device structure, energy band diagram and specific detectivity spectrum of the top-illuminated n-on-p type HgTe CQD infrared detector^[66]

Fig. 13. Research on multi-band HgTe quantum dot infrared detectors. (a) Illustration of the structure of a dual-band CQD imaging device (bias voltage is applied between the indium tin oxide (ITO) and the Au contact (grounded)), energy diagram of the dual-band detector under 0 V bias voltage without illumination at 85 K (ΔE_c and ΔE_v are the conduction band and valence band discontinuities. Pink and blue regions denote the MWIR and SWIR photodiodes), optical absorption of SWIR and MWIR HgTe CQDs used to fabricate the dual-band device (sizes of the SWIR and MWIR CQDs are 6 nm and 9 nm, respectively. Background: atmospheric transmission window)^[22]; (b) architecture and energy band diagram of the dual-band visible and SWIR photodetector, and absorption spectra of CdTe CQDs and HgTe CQDs^[72]; (c) structure diagram of the HgTe CQDs-based three-band infrared PD (bias voltage is applied between the indium tin oxide (ITO) and the gold (Au) electrodes, energy band structure diagram of the HgTe CQDs-based three-band infrared PD, and response spectra of the three-band infrared device under negative bias)^[73]

Fig. 14. HgTe CQD detectors FPA based on photoconductive mode. (a) Schemitic of the photoconduction in MWIR HgTe CQD detector, dark current map of the 320×256 MWIR HgTe CQD FPA, and image of a cup of warm water thrown into the air captured by the MWIR HgTe CQD FPA^[74]; (b) schematic of the HgTe QD camera, pictures of a building (Arabic fine art museum of Paris) and the tip of a soldering iron heated at 400 ℃ taken with the QD-based SWIR camera, and visible picture (smartphone camera) and SWIR images of a scene with four vials containing from left to right is tetrachloroethylene, toluene, acetone, and water (in front of the vials, an ITO covered glass slide and 2 inch silicon wafer are placed) taken with the infrared FPA based on HgTe QDs^[75]

Fig. 15. Infrared FPA based on HgTe CQDs. (a) Deposition of diode stack using spin coating method (top semi transparent Au electrode thickness of 20 nm), demonstration of imaging effects using HgTe NC photodiode arrays [standard card photos for measuring static image resolution of electronic cameras, visible images captured by smartphones, and SWIR images obtained by HgTe NC diode arrays]^[26]; (b) illustration of the working process of the capture mode photodetector, band diagram, scanning electron microscope cross-sectional image (scale: 200 nm), and comparison of dark current of the detector with and without a capture layer^[27]; (c) mid-wave infrared images captured by a 1280×1024 scale capture imaging instrument^[27]

Fig. 16. Research on the stability of infrared FPA based on HgTe CQDs^[25]. (a) Aging experiment of the sensor working continuously for more than 24 h in air without cooling (left image is taken with an integration time of 100 μs on the first day, and the right image is taken with an integration time of 40 μs on the second day); (b) statistical histogram of dark current varying with working time obtained over 50 μs of acquisition time; (c) thermogravimetric analysis of HgTe NCs; (d) X-ray diffraction pattern of HgTe nanocrystals near the (220) peak at different annealing temperatures; (e) dark current of HgTe photoconductive devices varies with annealing time at different temperatures under 100 mV