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Abstract
In this opinion we trace the evolution of the quantum dot mid-infrared photodetector, from epitaxially-grown self-assembled quantum dot detectors, to a new generation of colloidal nano-crystal based devices. We opine on the advantages and challenges associated with these colloidal quantum dot materials and discuss their potential for commercial device applications.
© 2023 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement
Nano-structured semiconductors, or quantum dots (QDs), have long been proposed as possible materials systems for mid-infrared (mid-IR, $\lambda =3-{30}\;\mathrm{\mu}\textrm{m}$) photodetection. In an idealized QD, three dimensional charge confinement leads to a $\delta$-function electronic density of states (DOS), and thus the description of QDs as ‘artificial atoms’. Much of the earliest experimental QD work achieved this carrier confinement by epitaxial growth of lattice-mismatched, compressively strained, narrow band gap material on and in a wider band gap material matrix, where the narrow band gap material forms self-assembled quantum dots (SAQDs) to relieve strain, a process known as Stranski-Krastanow growth [1,2]. Though the original arguments in favor of QD optoelectronics touted the favorable characteristics of QDs for semiconductor laser development [3], interest quickly grew in their potential for mid-IR photodetectors, leveraging QD intersublevel transitions. The quantum dot infrared photodetector (QDIP) was a natural evolution of the quantum well infrared photodetector (QWIP) [4], where light absorption occurs via intersubband transition (ISBTs) in semiconductor quantum wells. Both the QDIP and the QWIP were viewed as potential replacements for HgCdTe-based mid-IR photodetectors, which remain to this day the mid-IR detectors of choice, despite long-standing concerns regarding HgCdTe uniformity and toxicity [5]. Nonetheless, at the time, the strength of the QD optical transition, the possibility that a phonon bottleneck [6] (since largely disproved [7]) could quench of thermionic excitation of intersublevel transitions (ISLTs), as well as the favorable orientation of the ISLT with respect to the growth direction (unlike QWIPs, which require coupling structures to excite the ISBT), all conspired to make QDIPs an exciting frontier in mid-IR detection [8].
The first QDIPs consisted of SAQDs in (Al)GaAs matrices and showed mid-IR photoconductivity upon excitation of the confined electrons in the QD [9–13]. The epitaxial nature of the SAQDs, allowing for integration into semiconductor heterostructures, proved to be a significant selling point of these nano-structured detectors, and led to the development of new device designs and material combinations looking to reduce dark current, control energy states in the dots, improve detector response and operating temperature, and potentially integrate directly onto silicon substrates [14–20]. Using such material and device designs, QDIP focal plane arrays (FPAs) were demonstrated [21–24]. While band-structure engineering in the growth direction provided significant benefits in QDIP performance, the heterogeneous broadening of the QD ensemble absorption and the diminished fill factor of the absorbing QD material (when compared to both QWIPs and bulk narrow band gap semiconductors), limited QDIP absorption efficiency. This, combined with intrinsic trade-offs between absorption and dark current, conspired to limit QDIP performance, particularly for higher temperature applications [25].
As is the case for all epitaxial III-V semiconductor-based mid-IR detectors, transitioning single-element detectors to FPA architectures requires a non-trivial epi-down bonding to a read-out integrated circuit (ROIC). In such a process, each FPA pixel must be bonded to isolated ROIC contacts, and light brought into the detector array from the substrate side. For highly efficient detectors, the advantage of superior detector performance is well worth the complexity of this integration process. But absent high-efficiency detection, continued development of a detector technology must be driven by other potential advantages (such as reduced cost or the opportunity for straightforward integration with Si electronics). This can be observed in the trajectory of microbolometer FPA development. While bolometric detection cannot typically match the sensitivity or time response of semiconductor photon detectors, advances in nano-fabrication and micro electromechanical (MEMs) technology, as well as the ability to be directly integrated with CMOS architectures, have led to dramatic improvements in, and rapid and widespread commercialization of, microbolometer FPA technology [26–33]. The inability of a photon detector architecture to dramatically outperform bolometer-based FPAs, arguably leaves only niche applications to drive the technology forward.
Fig. 1. (A) Ag$_{2}$Se CQD solution and corresponding transmission electron microscopy (TEM) image. Reprinted with permission from [34]. © 2019 American Chemical Society (ACS). (B) CQD film deposited on wafer, followed by the ligand exchange process. Reprinted with permission from [34]. © 2019 ACS. (C) Schematic illustration of HgTe CQD detector integrated with Helmholtz-like resonator. Reprinted with permission from [35]. © 2022 ACS. (D) A MWIR image captured by the HgTe CQD FPA. Reprinted with permission from [36]. © 2018 ACS.
Interestingly, there does exist a material system which may be able to combine the advantages of semiconductor-based photon detection with the CMOS compatibility of bolometer architectures. Colloidal quantum dots (CQDs) are poised to serve as the next-generation material for photodetection owing to their cost-effectiveness and synthesis-tunable optical properties (Fig. 1(A),(B)) [37–39]. The CQD detector market has grown rapidly, with companies demonstrating uncooled thin-film infrared (IR) CQD photodetectors capable of capturing short-wavelength infrared (SWIR) images [40,41]. The majority of CQD detector research has focused on visible and near-infrared (NIR) wavelengths (${400}\;\textrm{nm}-{1.5}\;\mathrm{\mu}\textrm{m}$) [42–45]. Extending CQD photoresponse to the mid-wave infrared (MWIR, $3-{5}\;\mathrm{\mu}\textrm{m}$) proved challenging due to the lack of narrow bandgap materials having both strong MWIR absorption and compatibility with colloidal synthesis techniques.
The earliest MWIR-sensitive CQDs were synthesized from HgTe, which has zero bandgap energy as a bulk crystal [46]. However, an effective bandgap in the MWIR can be achieved in nano-scale HgTe, leveraging the quantum confinement effect. Since the first photoconductive MWIR detectors using HgTe CQDs showed relatively poor responsivities even at high voltages, much of the interest moved to the development of HgTe-based photovoltaic device architectures, which could reach close to the background limited IR photodetection (BLIP, $D_{BLIP}^*=1/h\nu \sqrt {2\phi }$) without a bias [47–50]. By leveraging photovoltaic response and Ag$_{2}$Te nanocrystals as a p-type layer, the HgTe CQD photodetector performance improved to be comparable to that of epitaxially-grown QD detectors, as measured by specific detectivity (Fig. 1(D)) [36]. Although MWIR CQD detectors have developed rapidly over the past decade, they still fall short of the performance of the commercial, bulk semiconductor-based MWIR detectors, suffering from weak photon collection due to the insufficient packing density (maximum reported photon collection, to date, is $\sim$ 45 %) [51]. Increasing the thickness (and thus absorption) of the CQD layers is practically challenging due to the increased likelihood of crack formation in the CQD film and the limited diffusion length of photoexcited charge carriers in CQD films. Hence, many recent efforts have focused on integrating thin CQD films with resonant optical structures for near-field enhancement of light absorption. Photonic structures such as back reflectors, gold gratings, and a simplified Helmholtz resonator were all demonstrated to confine and concentrate incident electromagnetic fields and thus increase the CQD detector external quantum efficiency (Fig. 1(C)) [35,36,51,52]. New device architectures have been developed in order to better integrate with the reduced volume associated with the resonant photonic structures. Research on CQD integration with resonant optical structures has thus far been limited, leaving significant opportunity for the exploration of photonic architectures leveraging a range of optical resonances, to fully maximize the advantages, and overcome the challenges, associated with CQD-based photodetection.
The ability to deposit CQDs above Si-based read-out electronics is a significant advantage, when compared to traditional III-V detector integration, however, achieving simultaneous optical and electrical access is non-trivial. Solving the MWIR electrode challenge is vital to the continued development of MWIR CQD detectors. Early MWIR CQD detectors used NiCr electrodes, with 30% transmission in the MWIR, which have more recently been replaced with indium tin oxide (ITO) electrodes, which show greater transparency and have a work function more compatible with the HgTe CQD conduction band [36]. However, ITO still absorbs a fair amount of MWIR light. Developing suitable electrodes for MWIR CQD detectors is a seemingly mundane and largely overlooked challenge, but one which, if solved, could pave the way for the next big jump in MWIR detection leveraging CQDs.
While the problem of photon collection has been tackled largely by approaches designed to better confine and control incident light, improvements in photon collection must be accompanied by commensurate improvements in photoexcited carrier collection. The low carrier mobility in CQD films ($10^{-4} - 10^{0}$ cm$^{2}$/Vs) is another obstacle to improved performance of MWIR CQD detectors [37,53–55]. Overcoming this hurdle requires improvements in the chemical treatment of the CQDs. Because the ligands, which most differentiates the CQDs from the SAQDs, serve as a high potential barrier to charge transport, they must be replaced by other short or atomic ligands [56]. The solid-state ligand exchange method has been intensively used due to its manufacturing process compatibility [36,48–51]. However, incomplete ligand exchange results in a remainder of unexchanged organic ligands on the nanocrystal surface, which reduce carrier mobility. This obstacle could be addressed by leveraging solution-state ligand exchange [53,57]. The replacement of surface ligands leads to a dramatic change in the dielectric property of the nanocrystal, which allows a physical transfer of the nanocrystals from the non-polar to the polar phase solution. Through this process, long organic ligands can be efficiently replaced with short ligands. Implementing such a method increased the carrier mobility of the HgTe CQD film by two orders of magnitude [53].
Ligand exchange not only facilitates charge transport by lowering the potential energy barrier between nanocrystals but also significantly affects their fundamental properties, including dielectric constant, crystal structure, absolute energy levels (vs. vacuum), degree of wavefunction overlap between nanocrystals in the film, packing density, surface trap density, and doping density [43,53,58–64]. For example, the surface dipole of a nanocrystal is readily changed by the species of surface ligands. Depending on the direction of the surface dipole, the position of the electronic energy state (vs. vacuum) varies substantially [58,65,66]. Exploiting this phenomenon, gradient homojunction HgTe CQD detectors were successfully fabricated, achieving improved rectifying behavior via the gradual change of doping level. This led to increased room temperature specific detectivity ($D^*>10^{9}$ Jones) [59]. Thus, the ligand exchange process is perhaps the most critical step in determining the ultimate performance of CQD detectors. Improved ligand exchange methods, combined with enhanced photon collection, resulted in the best detectivity for HgTe CQD MWIR detectors to date: $4\times 10^{11}$ Jones at ${85}\;\textrm{K}$, $7.6\times 10^{9}$ Jones at $ {300}\;\textrm{K}$ (photodiode), and $\sim 10^{11}$ Jones at ${80}\;\textrm{K}$ (photoconductor) [35,51,59]. The device with $D^*=4\times 10^{11}$ Jones showed noise equivalent temperature difference (NETD) of 14 mK.
The choice of the ligand is not the only consideration when looking to optimize charge transport in CQD detector structures. The shape of CQDs is mostly non-cubic, and therefore vacant sites are inevitably created during the CQD film fabrication process. Once the vacancy is filled with an inorganic charge transport matrix, or the packing density of nanocrystals is sufficiently large, with high positional and energetic order of nanocrystals, the charge transport properties can be further enhanced.
While the performance of the heavy metal-based CQD detectors has rapidly improved, their toxicity should be considered to meet the Restriction of Hazardous Substances (ROHS) regulations which require heavy metal composition below $0.1\%$ by weight of inseparable components. The silver chalcogenide CQDs [Ag$_{2}$E (E$=$S, Se, Te)] have evolved as an alternative to Hg-based CQDs due to their facile synthesis with widely tunable energy from NIR to MWIR [34,67–70]. From the first self-doped Ag$_{x}$Se (x$\geq$2) CQD MWIR thin film transistor to an electrolyte-gated transistor and photoconductive structure, there has been significant development in silver chalcogenide CQD detector responsivity. However, detectors based on self-doped Ag$_{x}$Se (x$\geq$2) CQDs still face obstacles for further improvement: excess Ag ions in the CQD film, leading to instability of devices, slow response time of several tens of seconds, and limited selection of surface ligands due to the surface sensitivity of doping density [34,68]. Thus, the non-toxic and self-doped Ag$_{2}$Se CQD photodetectors require further optimization by chemical treatment to make them comparable to other CQD MWIR photodetectors.
The CQDs hold significant advantages over epitaxially-grown SAQDs for MWIR light detection, most directly observed when considering the cost and flexibility (literally and figuratively) of colloidal systems. CQDs offer direct coating on a range of substrates without concern for lattice matching or surface topography. Large areas can be coated at minimal cost and with excellent control over the CQD optical and electronic properties, enabling both low-cost IR sensors and imaging systems, as well as integration with curved or flexible electronics and, thus, next-generation wearable sensors or lens-free photodetectors. While commercial mid-IR detectors based on bulk or heterostructured II-VI or III-V semiconductors still out-perform CQD-based MWIR detectors, there remains a range of opportunities to improve CQD detector performance and bring them into direct competition with more traditional detector materials (as measured by technical metrics such as responsivity, specific detectivity, and bandwidth). Most generally, the co-design of the CQD optical, electronic, and photonic properties (encompassing CQD bandstructure, device architecture, and charge transport, as well as the surrounding photonic environment), provides a broad parameter space to explore and significant opportunity for optimization of CQD detector performance. Future efforts to further develop CQD MWIR photodetectors require a focus on the efficient integration with both photonic structures (resonant cavities, dielectric and plasmonic waveguides, antennas, and plasmonic resonators), device electrodes, and read-out electronics, as well as improvements to intrinsic nanocrystal properties (decreasing defects, increasing homogeneity and CQD stability). With such advances, CQDs could potentially be the material system to dethrone HgCdTe for mid-IR photodetection.
Funding
Directorate for Mathematical and Physical Sciences (DMR-2004422); National Research Foundation of Korea (2021M3H4A3A01062964, 2021R1A2C2092053, 2022M3H4A1A03076626, NRF-2019M3D1A1078299).
Disclosures
The authors declare that there are no conflicts of interest related to this article.
Data availability
No data were generated or analyzed in the presented manuscript.
References
1. D. J. Eaglesham and M. Cerullo, “Dislocation-free stranski-krastanow growth of ge on si(100),” Phys. Rev. Lett. 64(16), 1943–1946 (1990). [CrossRef]
2. D. Leonard, M. Krishnamurthy, C. M. Reaves, S. P. Denbaars, and P. M. Petroff, “Direct formation of quantum-sized dots from uniform coherent islands of InGaAs on GaAs surfaces,” Appl. Phys. Lett. 63(23), 3203–3205 (1993). [CrossRef]
3. Y. Arakawa and H. Sakaki, “Multidimensional quantum well laser and temperature dependence of its threshold current,” Appl. Phys. Lett. 40(11), 939–941 (1982). [CrossRef]
4. B. Levine, “Quantum-well infrared photodetectors,” J. Appl. Phys. 74(8), R1–R81 (1993). [CrossRef]
5. “Directive 2011/65/EU of The European Parliament and of the Council of 8 June 2011 on the restriction of the use of certain hazardous substances in electrical and electronic equipment,” Official JournalL174, 88–100 (2011).
6. J. Urayama, T. B. Norris, J. Singh, and P. Bhattacharya, “Observation of phonon bottleneck in quantum dot electronic relaxation,” Phys. Rev. Lett. 86(21), 4930–4933 (2001). [CrossRef]
7. Y. Toda, O. Moriwaki, M. Nishioka, and Y. Arakawa, “Efficient carrier relaxation mechanism in InGaAs/GaAs self-assembled quantum dots based on the existence of continuum states,” Phys. Rev. Lett. 82(20), 4114–4117 (1999). [CrossRef]
8. V. Ryzhii, “The theory of quantum-dot infrared phototransistors,” Semicond. Sci. Technol. 11(5), 759–765 (1996). [CrossRef]
9. K. W. Berryman, S. A. Lyon, and M. Segev, “Mid-infrared photoconductivity in InAs quantum dots,” Appl. Phys. Lett. 70(14), 1861–1863 (1997). [CrossRef]
10. J. Phillips, K. Kamath, and P. Bhattacharya, “Far-infrared photoconductivity in self-organized InAs quantum dots,” Appl. Phys. Lett. 72(16), 2020–2022 (1998). [CrossRef]
11. S. Sauvage, P. Boucaud, F. Julien, J.-M. Gerard, and J.-Y. Marzin, “Infrared spectroscopy of intraband transitions in self-organized InAs/GaAs quantum dots,” J. Appl. Phys. 82(7), 3396–3401 (1997). [CrossRef]
12. S. Maimon, E. Finkman, G. Bahir, S. E. Schacham, J. M. Garcia, and P. M. Petroff, “Intersublevel transitions in InAs/GaAs quantum dots infrared photodetectors,” Appl. Phys. Lett. 73(14), 2003–2005 (1998). [CrossRef]
13. H. C. Liu, M. Gao, J. McCaffrey, Z. R. Wasilewski, and S. Fafard, “Quantum dot infrared photodetectors,” Appl. Phys. Lett. 78(1), 79–81 (2001). [CrossRef]
14. Z. Ye, J. C. Campbell, Z. Chen, E.-T. Kim, and A. Madhukar, “InAs quantum dot infrared photodetectors with in0.15ga0.85as strain-relief cap layers,” J. Appl. Phys. 92(12), 7462–7468 (2002). [CrossRef]
15. S. Krishna, S. Raghavan, G. von Winckel, P. Rotella, A. Stintz, C. P. Morath, D. Le, and S. W. Kennerly, “Two color InAs/InGaAs dots-in-a-well detector with background-limited performance at 91 K,” Appl. Phys. Lett. 82(16), 2574–2576 (2003). [CrossRef]
16. Z. Chen, O. Baklenov, E. Kim, I. Mukhametzhanov, J. Tie, A. Madhukar, Z. Ye, and J. Campbell, “Normal incidence InAs/Al x Ga 1−x As quantum dot infrared photodetectors with undoped active region,” J. Appl. Phys. 89(8), 4558–4563 (2001). [CrossRef]
17. M. S. Park, V. Jain, E. Lee, S. Kim, H. Pettersson, Q. Wang, J. Song, and W. J. Choi, “InAs/GaAs p–i–p quantum dots-in-a-well infrared photodetectors operating beyond 200 K,” Electron. Lett. 50(23), 1731–1733 (2014). [CrossRef]
18. W. Chen, Z. Deng, D. Guo, Y. Chen, Y. I. Mazur, Y. Maidaniuk, M. Benamara, G. J. Salamo, H. Liu, J. Wu, and B. Chen, “Demonstration of InAs/InGaAs/GaAs quantum dots-in-a-well mid-wave infrared photodetectors grown on silicon substrate,” J. Lightwave Technol. 36(13), 2572–2581 (2018). [CrossRef]
19. H. Kim, S.-Y. Ahn, S. Kim, G. Ryu, J. H. Kyhm, K. W. Lee, J. H. Park, and W. J. Choi, “InAs/GaAs quantum dot infrared photodetector on a si substrate by means of metal wafer bonding and epitaxial lift-off,” Opt. Express 25(15), 17562–17570 (2017). [CrossRef]
20. J. Wu, Q. Jiang, S. Chen, M. Tang, Y. I. Mazur, Y. Maidaniuk, M. Benamara, M. P. Semtsiv, W. T. Masselink, K. A. Sablon, G. J. Salamo, and H. Liu, “Monolithically integrated InAs/GaAs quantum dot mid-infrared photodetectors on silicon substrates,” ACS Photonics 3(5), 749–753 (2016). [CrossRef]
21. J. Jiang, K. Mi, S. Tsao, W. Zhang, H. Lim, T. O’Sullivan, T. Sills, M. Razeghi, G. J. Brown, and M. Z. Tidrow, “Demonstration of a 256×256 middle-wavelength infrared focal plane array based on InGaAs/InGaP quantum dot infrared photodetectors,” Appl. Phys. Lett. 84(13), 2232–2234 (2004). [CrossRef]
22. S.-F. Tang, C.-D. Chiang, P.-K. Weng, Y.-T. Gau, J.-J. Luo, S.-T. Yang, C.-C. Shih, S.-Y. Lin, and S.-C. Lee, “High-temperature operation normal incident 256/spl times/256 InAs-GaAs quantum-dot infrared photodetector focal plane array,” IEEE Photonics Technol. Lett. 18(8), 986–988 (2006). [CrossRef]
23. S. Krishna, D. Forman, S. Annamalai, P. Dowd, P. Varangis, T. Tumolillo, A. Gray, J. Zilko, K. Sun, M. Liu, J. Campbell, and D. Carothers, “Demonstration of a 320×256 two-color focal plane array using InAs/InGaAs quantum dots in well detectors,” Appl. Phys. Lett. 86(19), 193501 (2005). [CrossRef]
24. S. Gunapala, S. Bandara, C. Hill, D. Ting, J. Liu, S. Rafol, E. Blazejewski, J. Mumolo, S. Keo, S. Krishna, Y.-C. Chang, and C. Shott, “Demonstration of 640×512 pixels long-wavelength infrared (LWIR) quantum dot infrared photodetector (QDIP) imaging focal plane array,” Infrared Phys. & Technol. 50(2-3), 149–155 (2007). [CrossRef]
25. P. Martyniuk and A. Rogalski, “Comparison of performance of quantum dot and other types of infrared photodetectors,” Proc. SPIE 6940, 694004 (2008). [CrossRef]
26. M. García, R. Ambrosio, A. Torres, and A. Kosarev, “Ir bolometers based on amorphous silicon germanium alloys,” J. Non-Cryst. Solids 338-340, 744–748 (2004). [CrossRef]
27. E. Iborra, M. Clement, L. Herrero, and J. Sangrador, “Ir uncooled bolometers based on amorphous gex/si1−xoy on silicon micromachined structures,” J. Microelectromech. Syst. 11(4), 322–329 (2002). [CrossRef]
28. C. Chen, X. Yi, J. Zhang, and X. Zhao, “Linear uncooled microbolometer array based on vox thin films,” Infrared Phys. & Technol. 42(2), 87–90 (2001). [CrossRef]
29. B. Cole, R. Higashi, and R. Wood, “Monolithic two-dimensional arrays of micromachined microstructures for infrared applications,” Proc. IEEE 86(8), 1679–1686 (1998). [CrossRef]
30. L. Laurent, J.-J. Yon, J.-S. Moulet, M. Roukes, and L. Duraffourg, “12 − μm-pitch electromechanical resonator for thermal sensing,” Phys. Rev. Appl. 9(2), 024016 (2018). [CrossRef]
31. Y. Zhang, B. Qiu, N. Nagai, M. Nomura, S. Volz, and K. Hirakawa, “Enhanced thermal sensitivity of mems bolometers integrated with nanometer-scale hole array structures,” AIP Adv. 9(8), 085102 (2019). [CrossRef]
32. R. Kokkoniemi, J.-P. Girard, D. Hazra, A. Laitinen, J. Govenius, R. E. Lake, I. Sallinen, V. Vesterinen, M. Partanen, J. Y. Tan, K. W. Chan, K. Y. Tan, P. Hakonen, and M. Möttönen, “Bolometer operating at the threshold for circuit quantum electrodynamics,” Nature 586(7827), 47–51 (2020). [CrossRef]
33. M. Kimata, “Uncooled infrared focal plane arrays,” IEEJ Trans. Elec. Electron. Eng. 13(1), 4–12 (2018). [CrossRef]
34. S. B. Hafiz, M. R. Scimeca, P. Zhao, I. J. Paredes, A. Sahu, and D.-K. Ko, “Silver selenide colloidal quantum dots for mid-wavelength infrared photodetection,” ACS Appl. Nano Mater. 2(3), 1631–1636 (2019). [CrossRef]
35. C. Abadie, L. Paggi, A. Fabas, A. Khalili, T. H. Dang, C. Dabard, M. Cavallo, R. Alchaar, H. Zhang, Y. Prado, N. Bardou, C. Dupuis, X. Z. Xu, S. Ithurria, D. Pierucci, J. K. Utterback, and B. Fix, “Helmholtz resonator applied to nanocrystal-based infrared sensing,” Nano Lett. 22(21), 8779–8785 (2022). [CrossRef]
36. M. M. Ackerman, X. Tang, and P. Guyot-Sionnest, “Fast and sensitive colloidal quantum dot mid-wave infrared photodetectors,” ACS Nano 12(7), 7264–7271 (2018). [CrossRef]
37. P. Guyot-Sionnest, M. M. Ackerman, and X. Tang, “Colloidal quantum dots for infrared detection beyond silicon,” J. Chem. Phys. 151(6), 060901 (2019). [CrossRef]
38. H. Lu, G. M. Carroll, N. R. Neale, and M. C. Beard, “Infrared quantum dots: progress, challenges, and opportunities,” ACS Nano 13(2), acsnano.8b09815 (2019). PMID: 30648854. [CrossRef]
39. T. Nakotte, S. G. Munyan, J. W. Murphy, S. A. Hawks, S. Kang, J. Han, and A. M. Hiszpanski, “Colloidal quantum dot based infrared detectors: extending to the mid-infrared and moving from the lab to the field,” J. Mater. Chem. C 10(3), 790–804 (2022). [CrossRef]
40. V. Pejović, E. Georgitzikis, J. Lee, I. Lieberman, D. Cheyns, P. Heremans, and P. E. Malinowski, “Infrared colloidal quantum dot image sensors,” IEEE Trans. Electron Devices 69(6), 2840–2850 (2022). [CrossRef]
41. K. Lambert, I. Moreels, D. V. Thourhout, and Z. Hens, “Quantum dot micropatterning on Si,” Langmuir 24(11), 5961–5966 (2008). [CrossRef]
42. J. Leemans, V. Pejović, E. Georgitzikis, M. Minjauw, A. B. Siddik, Y.-H. Deng, Y. Kuang, G. Roelkens, C. Detavernier, I. Lieberman, P. E. Malinowski, D. Cheyns, and Z. Hens, “Colloidal iii–v quantum dot photodiodes for short-wave infrared photodetection,” Adv. Sci. 9(17), 2200844 (2022). [CrossRef]
43. C. Livache, B. Martinez, N. Goubet, C. Gréboval, J. Qu, A. Chu, S. Royer, S. Ithurria, M. G. Silly, B. Dubertret, and E. Lhuillier, “A colloidal quantum dot infrared photodetector and its use for intraband detection,” Nat. Commun. 10(1), 2125 (2019). [CrossRef]
44. S.-W. Baek, S. Jun, B. Kim, A. H. Proppe, O. Ouellette, O. Voznyy, C. Kim, J. Kim, G. Walters, J. H. Song, S. Jeong, H. R. Byun, M. S. Jeong, S. Hoogland, F. P. G. Arquer, S. O. Kelly, J.-Y. Lee, and E. H. Sargent, “Efficient hybrid colloidal quantum dot/organic solar cells mediated by near-infrared sensitizing small molecules,” Nat. Energy 4(11), 969–976 (2019). [CrossRef]
45. M. Ginterseder, D. Franke, C. F. Perkinson, L. Wang, E. C. Hansen, and M. G. Bawendi, “Scalable synthesis of InAs quantum dots mediated through indium redox chemistry,” J. Am. Chem. Soc. 142(9), 4088–4092 (2020). [CrossRef]
46. T. Ramesh, V. Shubha, and P. Gopalakrishnan, “Mercury chalcogenides under pressure,” Bull. Mater. Sci. 5(3-4), 199–206 (1983). [CrossRef]
47. S. Keuleyan, E. Lhuillier, V. Brajuskovic, and P. Guyot-Sionnest, “Mid-infrared HgTe colloidal quantum dot photodetectors,” Nat. Photonics 5(8), 489–493 (2011). [CrossRef]
48. E. Lhuillier, S. Keuleyan, P. Rekemeyer, and P. Guyot-Sionnest, “Thermal properties of mid-infrared colloidal quantum dot detectors,” J. Appl. Phys. 110(3), 033110 (2011). [CrossRef]
49. E. Lhuillier, S. Keuleyan, P. Zolotavin, and P. Guyot-Sionnest, “Mid-infrared HgTe/As2S3 field effect transistors and photodetectors,” Adv. Mater. 25(1), 137–141 (2013). [CrossRef]
50. P. Guyot-Sionnest and J. A. Roberts, “Background limited mid-infrared photodetection with photovoltaic HgTe colloidal quantum dots,” Appl. Phys. Lett. 107(25), 253104 (2015). [CrossRef]
51. X. Tang, M. M. Ackerman, and P. Guyot-Sionnest, “Thermal imaging with plasmon resonance enhanced HgTe colloidal quantum dot photovoltaic devices,” ACS Nano 12(7), 7362–7370 (2018). [CrossRef]
52. T. H. Dang, C. Abadie, A. Khalili, C. Gréboval, H. Zhang, Y. Prado, X. Z. Xu, D. Gacemi, A. Descamps-Mandine, S. Ithurria, Y. Todorov, C. Sirtori, A. Vasanelli, and E. Lhuillier, “Broadband enhancement of mid-wave infrared absorption in a multi-resonant nanocrystal-based device,” Adv. Opt. Mater. 10(9), 2200297 (2022). [CrossRef]
53. M. Chen, X. Lan, X. Tang, Y. Wang, M. H. Hudson, D. V. Talapin, and P. Guyot-Sionnest, “High carrier mobility in HgTe quantum dot solids improves mid-IR photodetectors,” ACS Photonics 6(9), 2358–2365 (2019). [CrossRef]
54. Z. Deng, K. S. Jeong, and P. Guyot-Sionnest, “Colloidal quantum dots intraband photodetectors,” ACS Nano 8(11), 11707–11714 (2014). [CrossRef]
55. J. Kim, B. Yoon, J. Kim, Y. Choi, Y.-W. Kwon, S. K. Park, and K. S. Jeong, “High electron mobility of β-HgS colloidal quantum dots with doubly occupied quantum states,” RSC Adv. 7(61), 38166–38170 (2017). [CrossRef]
56. M. Jarosz, V. Porter, B. Fisher, M. Kastner, and M. Bawendi, “Photoconductivity studies of treated cdse quantum dot films exhibiting increased exciton ionization efficiency,” Phys. Rev. B 70(19), 195327 (2004). [CrossRef]
57. M. Chen, Q. Hao, Y. Luo, and X. Tang, “Mid-infrared intraband photodetector via high carrier mobility HgSe colloidal quantum dots,” ACS Nano 16(7), 11027–11035 (2022). [CrossRef]
58. K. S. Jeong, Z. Deng, S. Keuleyan, H. Liu, and P. Guyot-Sionnest, “Air-stable n-doped colloidal HgS quantum dots,” J. Phys. Chem. Lett. 5(7), 1139–1143 (2014). [CrossRef]
59. X. Xue, M. Chen, Y. Luo, T. Qin, X. Tang, and Q. Hao, “High-operating-temperature mid-infrared photodetectors via quantum dot gradient homojunction,” Light: Sci. Appl. 12(1), 2 (2023). [CrossRef]
60. E. R. Kennehan, K. T. Munson, G. S. Doucette, A. R. Marshall, M. C. Beard, and J. B. Asbury, “Dynamic ligand surface chemistry of excited PbS quantum dots,” J. Phys. Chem. Lett. 11(6), 2291–2297 (2020). [CrossRef]
61. D. Bederak, D. M. Balazs, N. V. Sukharevska, A. G. Shulga, M. Abdu-Aguye, D. N. Dirin, M. V. Kovalenko, and M. A. Loi, “Comparing halide ligands in PbS colloidal quantum dots for field-effect transistors and solar cells,” ACS Appl. Nano Mater. 1(12), 6882–6889 (2018). [CrossRef]
62. S. A. McDonald, G. Konstantatos, S. Zhang, P. W. Cyr, E. J. Klem, L. Levina, and E. H. Sargent, “Solution-processed PbS quantum dot infrared photodetectors and photovoltaics,” Nat. Mater. 4(2), 138–142 (2005). [CrossRef]
63. I. Moreels, B. Fritzinger, J. C. Martins, and Z. Hens, “Surface chemistry of colloidal PbSe nanocrystals,” J. Am. Chem. Soc. 130(45), 15081–15086 (2008). [CrossRef]
64. C. B. Murray, C. R. Kagan, and M. G. Bawendi, “Synthesis and characterization of monodisperse nanocrystals and close-packed nanocrystal assemblies,” Annu. Rev. Mater. Sci. 30(1), 545–610 (2000). [CrossRef]
65. P. R. Brown, D. Kim, R. R. Lunt, N. Zhao, M. G. Bawendi, J. C. Grossman, and V. Bulovic, “Energy level modification in lead sulfide quantum dot thin films through ligand exchange,” ACS Nano 8(6), 5863–5872 (2014). [CrossRef]
66. B. G. Jeong, J. H. Chang, D. Hahm, S. Rhee, M. Park, S. Lee, Y. Kim, D. Shin, J. W. Park, C. Lee, D. C. Lee, K. Park, E. Hwang, and W. K. Bae, “Interface polarization in heterovalent core–shell nanocrystals,” Nat. Mater. 21(2), 246–252 (2022). [CrossRef]
67. M. Park, D. Choi, Y. Choi, H.-B. Shin, and K. S. Jeong, “Mid-infrared intraband transition of metal excess colloidal Ag2Se nanocrystals,” ACS Photonics 5(5), 1907–1911 (2018). [CrossRef]
68. J. Qu, N. Goubet, C. Livache, B. Martinez, D. Amelot, C. Gréboval, A. Chu, J. Ramade, H. Cruguel, S. Ithurria, M. G. Silly, and E. Lhuillier, “Intraband mid-infrared transitions in Ag2Se nanocrystals: potential and limitations for hg-free low-cost photodetection,” J. Phys. Chem. C 122(31), 18161–18167 (2018). [CrossRef]
69. G. Kim, D. Choi, S. Y. Eom, H. Song, and K. S. Jeong, “Extended short-wavelength infrared photoluminescence and photocurrent of nonstoichiometric silver telluride colloidal nanocrystals,” Nano Lett. 21(19), 8073–8079 (2021). [CrossRef]
70. R. Bera, D. Choi, Y. S. Jung, H. Song, and K. S. Jeong, “Intraband transitions of nanocrystals transforming from lead selenide to self-doped silver selenide quantum dots by cation exchange,” J. Phys. Chem. Lett. 13(26), 6138–6146 (2022). [CrossRef]
