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Review

Advancements and Challenges in Colloidal Quantum Dot Infrared Photodetectors: Strategies for Short-Wave Infrared, Mid-Wave Infrared, and Long-Wave Infrared Applications

by
Lijing Yu
1,
Pin Tian
2 and
Kun Liang
3,*
1
Key Laboratory of Materials and Surface Technology (Ministry of Education), Sichuan Energy Equipment Intelligent Engineering Research Center, School of Materials Science and Engineering, Xihua University, Chengdu 610039, China
2
Kunming Institute of Physics, Kunming 650223, China
3
Zhejiang Key Laboratory of Data-Driven High-Safety Energy Materials and Applications, Ningbo Key Laboratory of Special Energy Materials and Chemistry, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo 315201, China
*
Author to whom correspondence should be addressed.
Quantum Beam Sci. 2025, 9(1), 9; https://doi.org/10.3390/qubs9010009
Submission received: 7 November 2024 / Revised: 25 January 2025 / Accepted: 19 February 2025 / Published: 3 March 2025
(This article belongs to the Special Issue Quantum Beam Science: Feature Papers 2024)
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Abstract

Colloidal quantum dots (QDs) have emerged as promising materials for the development of infrared photodetectors owing to their tunable band gaps, cost-effective manufacturing, and ease of processing. This paper provides a comprehensive overview of the fundamental properties of quantum dots and the operating principles of various infrared detectors. We review the latest advancements in short-wave infrared (SWIR), mid-wave infrared (MWIR), and long-wave infrared (LWIR) detectors employing colloidal quantum dots. Despite their potential, these detectors face significant challenges compared to conventional infrared technologies. Current commercial applications are predominantly limited to the near-infrared and short-wave bands, with medium- and long-wave applications still under development. The focus has largely been on lead and mercury-based quantum dots, which pose environmental concerns, underscoring the need for high-performance, non-toxic materials. Looking forward, the development of large array and small pixel detectors and improving compatibility with readout circuits are critical for future progress. This paper discusses these hurdles and offers insight into potential strategies to overcome them, paving the way for next-generation infrared sensing technologies.

1. Introduction

The study of infrared radiation began in the early 1800s with the discovery of infrared radiation by the British astronomer Herschel, who investigated the spectral properties of sunlight’s photothermal effect [1]. Infrared radiation is ubiquitous, and all objects with temperatures above absolute zero emit infrared light. Infrared radiation bands are typically categorized into short wave infrared (SWIR, 1–2.5 μm), medium wave infrared (MWIR, 3–5 μm), and long wave infrared (LWIR, 8–12 μm) based on their wavelengths [2]. However, as human eyes lack sensitivity to infrared radiation, infrared light can be detected using infrared detectors designed to respond to this form of radiation. The function of an infrared detector is to convert the received light signal into easily detectable electrical signals such as current or voltage.
The first practical infrared detector was the PbS infrared detector developed by Germany during World War II. With the development of infrared detection technology, the application of infrared technology has become increasingly widespread and is now playing an important role in the military, industrial, medical, and communication fields [3,4,5,6,7]. Currently, the most widely used infrared detectors are those based on materials such as mercury cadmium telluride (HgCdTe) and indium gallium arsenic (InGaAs). However, the growth of HgCdTe materials often requires the use of technologies such as Metal-organic Chemical Vapor Deposition (MOCVD), Molecular Beam Epitaxy (MBE), and Liquid Phase Epitaxy (LPE), which leads to high growth costs and can only be used in the high-end market. In addition, mercury cadmium telluride (HgCdTe) and indium gallium arsenic (InGaAs) photodetectors often need refrigeration when working, and the existence of refrigeration equipment leads to an increase in device volume, power consumption, and an increase in cost. What must be considered is that these two materials also have lattice mismatches with the silicon readout circuits, and the connection to the readout circuits can only be realized through the flip-flop interconnect process, which further increases the process difficulty and reduces the yield [2]. These harsh conditions have limited the wide application and development of conventional photodetectors. Therefore, to further reduce the system cost; decrease the size, weight, and power consumption of the system; and increase the operating temperature of the detectors, considerable efforts are required to find new infrared detection materials with high performance and low costs [8].
A lot of research has also been carried out on emerging two-dimensional materials, such as graphene. However, due to the intrinsic gapless characteristics of two-dimensional materials, infrared photodetectors based on two-dimensional materials usually have high dark currents [9]. As one of the candidate materials for next-generation photodetection, colloidal quantum dots (CQDs) have become a hotspot for research in the field of infrared photodetection technology due to their tunable bandgap, substrate compatibility, liquid-phase processability, and high performance. The quantum confinement effect of quantum dots (QDs) enables the bandgap width of quantum dots to be controlled by adjusting their size. The multi-exciton effect of quantum dots enables performance enhancement through carrier multiplication, thus enabling the application of quantum dots in high-performance optoelectronic detection [10,11]. The phonon bottleneck effect [12,13] of quantum dots makes the relaxation time of electrons in the discrete state of quantum dots longer, and quantum dot detectors can realize high-temperature or even room-temperature operation, which makes quantum dots conducive to the fabrication of devices with high operating temperatures and can largely reduce the power consumption and volume of the detector arrays and the whole imaging system. The compatibility between quantum dots and silicon allows for direct integration with readout electronics to form an imaging array without indium bumps flip-bonding technology, which greatly simplifies the device manufacturing process. Conventional material and readout circuitry connection require a flip-flop interconnect process to be realized. To ensure the reliability of the bonding, an indium column needs to be large enough, which makes the detector’s pixel size limited by the achievable aspect ratio and pixel pitch. The compatibility of quantum dots and silicon allows for direct integration with readout electronics without the need for an indium column flip-flop interconnect process, thus greatly simplifying the device fabrication process. More importantly, flexible or wearable CQD photodetectors show great potential in medical devices and consumer electronics. Printing methods for flexible substrates give advantages that traditional semiconductor photodetectors cannot match.
There have been prior review articles on infrared detectors with different colloidal quantum dot materials [14] and different hybrid structures [15,16], but no articles have been introduced according to different wavebands. In this review, we begin by introducing the fundamental properties of quantum dots in Section 2. Subsequently, in Section 3, we describe the working principles of two distinct types of infrared detectors, with a particular focus on the latest advancements in quantum dot infrared detectors across various bands (SWIR/MWIR/LWIR). Finally, Section 4 discusses the challenges and prospects of quantum dot infrared photodetectors.

2. Characterization of QDs

Quantum dots are zero-dimensional nanomaterials with sizes almost or less than their Bohr exciton radius, typically ranging from 1 to 10 nm. Hence, they are also referred to as nanocrystals. In quantum dots, electron movement is restricted in all spatial directions, converting the continuous band structure into discrete energy levels. This alteration allows the band gap to be adjusted by adjusting their size, offering significantly different physical and chemical properties from bulk materials due to their unique quantum confinement effect.

2.1. Fundamentals of QDs

The research on quantum dots began at Bell Labs in 1983. L.E. Brus [17] et al. discovered that CdS microcrystals of different sizes could produce different colors, and based on this, proposed the theory of the “quantum confinement effect”. This work has enabled people to begin to understand and recognize quantum dots, laying the foundation for the development of quantum dots. The quantum confinement effect refers to the fact that when the particle size of the quantum dot is smaller than the exciton bore radius of the material, the motion of the electron and hole wavefunctions in the quantum dot is confined in all three directions. Both the conduction and valence bands of a single quantum dot become discontinuous, and the energy levels near the Fermi energy level become discrete. By establishing a theoretical model, the impact of size, shape, and chemical composition on the band gap can be numerically analyzed [18]. As shown in Figure 1, for bulk materials, the band gap is an inherent property of the material and does not change with its size. For quantum dots, quantum confinement makes the dispersion of energy levels near the conduction band (CB) and valence band (VB) of the material and makes the bandgap width Eg dependent on the size of the quantum dots. As the size of quantum dots decreases, the quantum confinement effect increases and the bandgap also increases. Therefore, the band gap of quantum dots can be adjusted by adjusting the size, shape, and chemical composition of the quantum dot and then adjusting its optical properties, including absorption and emission spectra, which is especially attractive for infrared detector applications.
Taking PbS quantum dots as an example, the exciton Bohr radius of PbS bulk materials is ~21 nm [19]. When the crystal size of PbS decreases to less than the exciton Bohr radius, both electron and hole wave functions are strongly constrained, resulting in discrete quantized energy states. This quantum confinement leads to size-dependent optoelectronic properties of PbS quantum dots, allowing for the adjustment of emission and absorption bands by changing the size of the quantum dots, thereby achieving optoelectronic response and multi-band detection in different bands. Figure 2 shows the tunable optical properties of PbS quantum dots. It can be observed that as the particle size of PbS quantum dots increases, the absorption spectrum exhibits a red shift phenomenon. This tunable optical property makes it possible for PbS quantum dots to be applied in infrared devices in various wavelength bands.

2.2. Solution Process of QDs

The colloidal quantum dots we use are usually synthesized using the chemical method: the whole synthesis process is carried out in a glass flask, and by controlling the concentration of the reaction reagents, the growth temperature and time, and the selection of different ligands, the quantum dots of the desired size and shape can be obtained. The colloidal structure can effectively reduce the cost and facilitate large-scale solution processing. The colloidal quantum dots are often dispersed in solvents such as oleyl amine and oleic acid to maintain their stability and dispersibility during the synthesis of quantum dots. To improve the utilization rate of quantum dot materials and reduce the defects of the materials, it is even possible to carry out liquid phase ligand exchange of colloidal quantum dots. Figure 3 is the diagram of the surface of a quantum dot coated with oleic acid-capped and passivated by ligand exchange. The surface of the synthesized colloidal quantum dots is covered with long chains of oleic acid. To improve charge transport, long and insulated surface ligands are exchanged through short ligands so that they are packed tightly in the film. However, the surface passivation decreases in the ligand exchange process, and defects appear in the quantum dots. The defects can be reduced by a surface passivation strategy [21]. By carrying out ligand exchange of colloidal quantum dots in the solution phase, the rate of ligand exchange of colloidal quantum dots can be improved, and the resulting ink-like colloidal quantum dots are called colloidal quantum dot inks.
After the synthesized colloidal quantum dots are prepared as colloidal quantum dot inks, they can be easily deposited directly onto a variety of substrates by methods such as jet coating, spin coating, and inkjet printing, as shown in Figure 4a. These methods do not require consideration of lattice mismatch and even enable roll-to-roll large-area processing on flexible substrates. Spin-coating technology [15,22,23] is the most widely adopted technique, which is favored for its low requirements on colloidal quantum dot solutions and its ability to achieve wafer-level film preparation. Drip coating technology [24] is mainly used in the preparation of colloidal quantum dot films, and heating is often introduced to make the solvent of colloidal quantum dots fully volatilize to ensure the density and electrical performance requirements of colloidal quantum dots. This technology is often used in the preparation of small-size devices, such as photoelectric devices with interdigital electrodes. Spraying technology [25] has high requirements on colloidal quantum dot solution. The solvent required for spraying colloidal quantum dots is easy to volatilize, and the solution is easy to vaporize to achieve a high density of colloidal quantum dots. Spraying technology has high efficiency and uniformity in preparing film, which has also become an important technology for the preparation of colloidal quantum dot film. Printing technology [26,27,28] is an advanced technology for the preparation of thin films by solution processing. Colloidal quantum dot solution is prepared into colloidal quantum dot ink. Through printing technology, the colloidal quantum dot film can be patterned and printed without selectivity to the substrate.
Figure 4b,c show the preparation process diagram and cross-section diagram of colloidal quantum dot focal plane arrays, respectively. Quantum dot ink is deposited directly on the readout circuit to achieve sub-micron pixel size. Integrating a colloidal quantum dot detector into a readout integrated circuit (ROIC) does not require any flip interconnection steps, and the size of a single pixel is defined by a region of metal electrodes on the upper surface of the ROIC. And the preparation time of the focal plane photodetector chip is much less than that of the traditional bulk phase focal plane photodetector, which needs to flip the interconnection process. Therefore, detectors based on colloidal quantum dots have the potential to break through the optical diffraction limit and achieve higher resolution, higher integration, and smaller pixels.

3. QD Infrared Photodetectors

There are various types of quantum detectors, such as quantum dot infrared photodetectors (QDIPs) and quantum well infrared photodetectors (QWIPs), both of which operate on similar principles. Extensive studies have been carried out on QWIP [31,32,33,34,35,36]. However, since the carriers in QWIP are confined within multiple quantum wells, this leads to a series of drawbacks. These include low quantum efficiency and the necessity of a light coupling scheme for incident light detection. To overcome these limitations, researchers have shifted their focus toward the development of quantum dot photodetectors.
Quantum dot photodetectors have evolved significantly from theoretical concepts to fully developed focal plane arrays. Herron et al. [37] proposed the theory of applying colloidal quantum dots to the field of photodetectors in 1992, but due to the introduction of oleyl amine or oleic acid ligands to stabilize the state of quantum dots in the early colloidal quantum dot synthesis techniques, the conductivity of colloidal quantum dots is poor, and the conductivity of the prepared films is not ideal, which greatly hinders the development of colloidal quantum dots in the field of photodetectors.
With the development of colloidal quantum dot synthesis technology, in 2003, Philippe et al. [38] proposed that exchanging oleic acid or oleyl amine on the surface of colloidal quantum dots for short-chained ligands could improve the electrical conductivity of colloidal quantum dot thin films, allowing them to be transformed from insulators to semiconductors, which was a milestone event for the application of colloidal quantum dots in semiconductor photonics. Although the ligand exchange strategy for colloidal quantum dots was proposed at this time, the application of colloidal quantum dots in photodetectors did not appear in the true sense of focal plane detector arrays until 2009 [39].
Research on the synthesis of colloidal quantum dots has been carried out from the initial cadmium-based material to the lead-based material and then to the mercury-based material. Since the bulk phase of mercury telluride is a zero-band gap material, the band gap of mercury telluride colloidal quantum dots can be adjusted to the long-wave band [40], which attracts many researchers to turn their attention to this material system, and many mercury telluride colloidal quantum dot infrared detectors have been developed. At the same time, for different application fields, researchers have also begun to explore other semiconductor materials, such as copper indium sulfide (CuInSe2) [41] and silver selenide (Ag2Se) [42], which are promising nanomaterials in biomedical applications due to their non-toxic and environmentally friendly.
Due to the use of dispersants such as oleic acid in the synthesis process of quantum dots, the surface of quantum dots is coated with long chain ligands, so the charge carrier mobility of quantum dots is low. At the same time, unsaturated suspended bonds on the surface of quantum dots lead to the formation of intermediate states with different energies near the band gap, which are also easy to trap charge carriers [16]. Many new device structures have been designed to address these issues, while many new materials have been introduced into quantum dot detectors, such as by introducing high mobility materials and quantum dots for hybridization. Hybrid CQDs, combined with advanced 2D materials, have shown potential in infrared detector applications. The currently reported materials hybridized with quantum dots include graphene [43], molybdenum ditelluride (MoTe2) [44], black phosphorus (BP) [45], transition metal disulfides (TMDs) [15], and two-dimensional transition metal carbides and/or nitrides (MXene) [25]).

3.1. Mechanisms of QD Photodetectors

According to the different working principles, quantum dot infrared detectors are mainly divided into three categories: photoconductive, photovoltaic, and phototransistor. As the photosensitive layer of the detector, quantum dots generate electron hole pairs after absorbing photon energy and generate photocurrent after charge separation and extraction.
In the case of photoconductive detectors, the electrodes are symmetrical ohmic contacts that require an external voltage to be applied for operation. Under the action of an electric field, electrons and holes separate and move to the electrodes in the direction of the electric field, resulting in a current signal. Photoconductive photodetectors can achieve high gain because in photoconductive devices, one type of carrier is trapped and the other is cycled under the influence of an electric field (for example, electrons are trapped). If the hole lifetime exceeds the time it takes for the hole to pass through the device, the long lifetime of the trapped electrons ensures that the hole can be cycled through the external circuit multiple times, resulting in a gain.
As for the photovoltaic type of infrared detector, it works on the principle of the photovoltaic effect, which allows for the rapid separation and collection of photogenerated electron–hole pairs due to the presence of a built-in electric field. After light is absorbed, the energy of the photon is transferred to the electrons in the semiconductor, lifting them into the conduction band and leaving a hole in the valence band. The drift and diffusion of electrons and holes are utilized in the photovoltaic detector, and the electron–hole pairs are separated by the action of the built-in electric field, which gives the photovoltaic detector a much faster response time.
Whereas a phototransistor is a three-terminal device with a source, a drain, and a gate, the current in the channel can be adjusted by adjusting the gate voltage, and the photogenerated carriers in the quantum dot photosensitive layer can be transferred under gate bias to a material with high carrier mobility, and then collected by the drain and the source. Therefore, this structure is often applied to device structures hybridized with other high-mobility materials. As opposed to photoconductive detectors, phototransistors have three electrodes for better control of semiconductor conductivity [46]. As a result, phototransistors have a slow response and high gain.

3.2. States-of-the-Art for QD Infrared Photodetectors

As an emerging technology in the field of infrared detection, colloidal quantum dots such as lead sulfur (PbE, E = S, Se, Te) [47], mercury–sulfur compounds (HgE, E = S, Se, Te) [48,49], and silver–sulfur compounds (Ag2E, E = S, Se, Te) [50,51] are gradually emerging as alternatives to traditional infrared bulk semiconductor materials. Various new quantum dot materials and novel device structures have been developed to structure them in order to provide more affordable and high-performance infrared technology.

3.2.1. SWIR Applications

Due to the limitation of material bandgap, the studies carried out for colloidal quantum dots infrared detectors that can be seen in the short-wave band are mainly focused on lead-based and mercury-based quantum dots. Among them, the synthesis methods of lead-based systems were studied earlier, and the PbS and PbSe in lead-based quantum dots, with band gaps of 0.41 and 0.26 eV for bulk materials [52], responded to the wavelength bands mainly in the near-infrared photovoltaic and short-wave infrared bands, and thus have been the most widely developed in near-infrared photovoltaic and short-wave infrared sensing.
The performance of colloidal quantum dot photodetectors has been limited by the material properties of colloidal quantum dots, especially the low carrier mobility and low external quantum efficiency, which make the practical applications of colloidal quantum dot photodetectors extremely limited. To solve this problem, a series of studies have been carried out.
Ligand exchange can affect the surface trap state of the quantum dot, and the type of ligand can also change the carrier lifetime [53]. Yang et al. [54] studied the effects of sodium sulfide (Na2S), tetrabutylammonium iodide (TBAI), 1, 2-ethylene glycol (EDT), cetyltrimethyl ammonium bromide (CTAB), and four different ligands on PbS QD films. In the experiment, PbS QD films were prepared by means of solid-state ligand exchange, and the results showed that the devices with sodium sulfide ligand exchange for light conduction showed a wider detection range (from 400 nm to 2300 nm) and the best sensitivity. Hybridization of low-mobility quantum dots and high-mobility materials can also effectively enhance the mobility and quantum efficiency of quantum dots. In 2017, Goossens et al. [55] in Spain found that graphene materials have high mobility, while PbS colloidal quantum dots have low mobility, which makes internal gain possible. So, they combined the two to achieve internal gain, improving the external quantum efficiency and responsiveness of the colloidal quantum dot photodetector and finally achieving the response in ultraviolet, visible, and infrared light (300–2000 nm). The prepared short-wave infrared focal plane array is 388 × 288, and its responsivity is up to 107 A·W−1 with a gain of 108.
Ligand exchange is an effective method to improve the carrier mobility of quantum dots. In 2020, Mi et al. [56] reported a high-performance photodetector based on PbS-QDs with the hybrid perovskite ligand exchange process. Figure 5a–c show the absorption spectrum of PbS CQDs, the combining process of PbS-QDs and hybrid perovskite, and the energy level diagram of PbS-QDs + hybrid perovskite structure, respectively. Hybrid perovskite treatment can effectively improve carrier transport behavior between QDs and passivate the defects of PbS quantum dots. The photodetector based on Au/PbS-QD + hybrid perovskite/Au structure exhibits low noise current, high sensitivity, and high stability in the spectrum range of 300–1200 nm at an applied bias voltage of and detectivity of 1015.
To obtain shortwave infrared detectors with wider bands, people began to study quantum dots other than PbS. PbSe CQDs have the potential to shift the operating range of photodetectors to a wider band. In 2022, He et al. [57] reported a wide-spectrum photodetector with a spectral range of 400–2600 nm. PbSe CQDs were synthesized by a simple solution process. During the synthesis process, the size of the colloidal quantum dots was precisely adjusted by controlling the reaction temperature, and the relationship between the size of the quantum dots and the reaction temperature was obtained. The oleic acid ligands on the surface of the quantum dots were replaced by 1, 2-ethyldimercaptan. During the deposition process, the oleic acid ligands on the surface of QDs were substituted by 1, 2-ethylene dithiol, and the CQDs films were obtained by a layer-by-layer (LbL) spin coating method. The device has a responsivity of ~320 m A/W at room temperature and an external quantum efficiency (EQE) of about 14% at 2520 nm. High-performance devices were obtained by a simple and inexpensive method of preparation, indicating that PbSe colloidal quantum dots are a promising material for broadband spectral photoelectric detection.
HgTe CQD has shown great potential in SWIR photodetection. Yang et al. [58] developed a novel p-i-n photodiode using bismuth sulfide (Bi2S3) film as the electron transport layer (ETL). The electron transport layer is conducive to uniform deposition of absorbent, charge extraction, and suppression of interface loss. At −400 mV, the photodiode has a room-temperature dark current density as low as 1.6 × 10−5 A/cm2 and detectivity (D*) of about 1011 Jones. Figure 5d–f show the device structure, simulated current−voltage characteristics, and energy band of the solar cell capacitance simulator (SCAPS) model of the HgTe CQD photodetector, respectively. The results demonstrate that the selection of appropriate ETL is highly crucial for the performance of the device.
Until now, colloidal quantum dots applied to short-wave infrared detectors have mainly been based on compounds of lead and mercury series, which contain toxic heavy metals and have some regulatory problems in consumer electronics.
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Figure 5. SWIR detector based on colloidal quantum dots. (a) Absorption spectrum of PbS CQDs [56]. (b) The process of combining PbS-QDs with the hybrid perovskite. (c) Energy level diagram for the PbS-QD + hybrid perovskite structure. (d) Device architecture of HgTe CQD photodetectors with ETL [58]. (e) Simulated current−voltage characteristics in the dark (dashed) and the light (solid). (f) The energy band from SCAPS modeling for HgTe CQD photodetectors. (g) Schematic of ROIC-integrated Ag2Te QD SWIR imager [59]. (h) Photograph of the imager and zoomed-in view of the ROIC die.
Figure 5. SWIR detector based on colloidal quantum dots. (a) Absorption spectrum of PbS CQDs [56]. (b) The process of combining PbS-QDs with the hybrid perovskite. (c) Energy level diagram for the PbS-QD + hybrid perovskite structure. (d) Device architecture of HgTe CQD photodetectors with ETL [58]. (e) Simulated current−voltage characteristics in the dark (dashed) and the light (solid). (f) The energy band from SCAPS modeling for HgTe CQD photodetectors. (g) Schematic of ROIC-integrated Ag2Te QD SWIR imager [59]. (h) Photograph of the imager and zoomed-in view of the ROIC die.
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Wang et al. [59] reported a photodetector based on environmentally friendly silver telluride (Ag2Te) CQDs, which were synthesized by thermal injection method. Ag2Te quantum dots were synthesized by a thermal injection method, and the synthesized quantum dots had well-controlled size distributions, with exciton peaks in a wide range. The detectors are sensitive in the spectral range of 350 nm to 1600 nm, with a room temperature detectivity of 1012 Jones orders of magnitude, a 3 dB bandwidth of more than 0.1 MHz, and a linear dynamic range of more than 118 dB. The preparation process is based on solution processing, which allows for low-cost preparation as well as easy monolithic integration in the back end. Figure 5g,h show the Ag2Te CQD photodetector, which is integrated into the ROIC to form a focal plane array. Using Au as the top electrode of the image sensor, the die can be manufactured in an electronic printed circuit board enclosure.
Group-IV photonics is also attracting attention, especially about the GeSn-based devices [60,61,62,63,64], which are compatible with the Si-based CMOS technology and also show very promising performance in the SWIR region. Atalla et al. [65] demonstrated a photodiode fabricated by growing GeSn on a silicon wafer, exhibiting a cutoff wavelength of 2.6 μm and a peak responsivity of 0.3 A/W at room temperature. As suitable for high-speed applications, the device was used to diagnose ultra-short pulses of a supercontinuum laser in the picosecond range of 2.5 μm, highlighting the potential of GeSn photodiodes for high-speed extended SWIR applications.
Based on the research results of previous decades, European and American countries have begun to turn the application of colloidal quantum dot infrared detectors to industry. Mainly led by SWIR company in the United States, it has developed a short-wave infrared focal plane device with a pixel pitch of 7 μm and an array specification of 2 K × 3 K.
Many studies have been carried out on the application of colloidal QDS in SWIR; Table 1 summarizes the device structure and performance of typical CQD-based SWIR detectors.

3.2.2. MWIR Applications

The most studied mid-wave colloidal quantum dot material is HgTe. HgTe is a zero-bandgap semiconductor that exhibits quantum confinement-induced interband transition [75], with a spectral absorption range tuned to cover the entire infrared wavelength band, as well as high absorption coefficients and unique photovoltaic properties [76]. HgTe colloidal quantum dots have a lower auger coefficient than bulk HgCdTe materials with similar energy gaps, and detectors based on HgTe colloidal quantum dots can perform infrared detection at a higher temperature than bulk semiconductor materials, which reduces the requirements for refrigeration equipment [77]. Therefore, the characteristics of HgTe colloidal quantum dots, such as low cost, strong compatibility with substrates, wide infrared spectrum adjustability, and higher operating temperature, make HgTe colloidal quantum dots become a research hotspot.
In 2011, Keuleyan et al. [78] reported for the first time a photoconductive detector based on HgTe colloidal quantum dots, which was prepared by drop-coating the quantum dots onto electrodes, with a detectivity of 2 × 109 Jones at 130 K and the incident wavelength of 5 µm. This work verifies that low-cost HgTe CQDs are promising materials for mid-infrared detection applications.
In 2016, Buurma et al. [79] from the University of Chicago reported a low-cost mid-wave infrared HgTe colloidal quantum dot focal plane array prepared by a solution processing technique with a noise equivalent temperature difference (NETD) of 120 mK at 100 K, which is of great importance for mid-wave quantum dot infrared focal plane array devices, even though the signal needs to be improved.
To investigate the effect of ligand exchange on the performance of quantum dots, Chen et al. [80] improved a mid-infrared photodetector based on colloidal HgTe quantum dots by a hybrid ligand exchange and polar phase transfer. Compared with the previous “solid-state ligand exchange” method, the new ligand exchange process has increased the electron and hole mobility by ~100-fold, detectivity by ~10-fold, and the responsivity by ~100-fold, while the optical properties are basically unchanged.
The quality of quantum dots is a key factor affecting the performance of the devices, and a lot of research has also been carried out to obtain high-quality quantum dots. Xia et al. [81] optimized the synthesis method of HgTe CQDs using HgBr2 as the Hg source and the thermal injection method, which effectively reduces the concentration of defects in the quantum dots. The prepared high-performance HgTe CQDs photodetectors achieved a broad optical response of 450~4000 nm at room temperature. The responsivity and detectivity were 90.6 mA W−1 and 6.9 × 107 Jones under 1550 nm illumination. The rise and fall times of the device were 1.9 μs and 1.5 μs, respectively. Figure 6a–c show the characteristics of HgTe quantum dots using HgBr2 as a mercury source and the structure of a photoconductive detector.
Based on continuous efforts, a breakthrough has been achieved in the infrared detection technology of medium-wave quantum dots. Recently, Tang et al. [82] proposed a stacked lead sulfide/mercury telluride colloidal quantum dot photodetector, which can achieve an ultra-wideband spectral response of 0.4 to 5.0 µm. The detectivity is 3.15 × 1010 Jones, and the responsivity at 0.4, 0.7, 2.2, and 4.2 µm wavelengths are 0.23, 0.31, 0.83, and 0.71 A W−1, respectively. This structure has also been applied to 640 × 512 focal plane arrays with a photoresponse non-uniformity as low as 6% and a noise-equivalent temperature difference of 34 mK. Figure 6d–f show the structure of the ultra-broadband imager, photographs of the detector, and thermal images.
In addition to HgTe quantum dots, the applications of HgSe, HgS, and Ag2Se quantum dots in the medium wave band have also been studied. In order to improve the carrier mobility of HgSe quantum dots, Chen et al. [83] reported a room-temperature mixed-phase ligand exchange method, which made the carrier mobility of HgSe colloidal quantum dots reach 1 cm2/(V s). As shown in Figure 6g–i, the characteristics of HgSe quantum dots and the performance of the HgSe detector are presented. Using the 1 Se to 1 Pe transition, the response speed of the mid-infrared photodetector can reach several μs (a 1000-fold increase), the response rate can reach 77 mA/W (a 55-fold increase), and the specific detection rate can reach more than 1.7 × 109 Jones at 80 K (a 10-fold increase).
At present, there are limited reports on HgS CQD infrared detectors, and more studies focus on the synthesis and properties of HgS quantum dots. A dual-phase synthesis method of HgS and HgS/CdS nanoparticles was reported by Kim et al. [84]. The synthesis was carried out under ambient conditions in air and at room temperature, and the synthesized HgS CQDs showed n-doping, good air stability, and infrared in-band absorption, and their electron mobility was as high as 1.29 cm2/(V s). The same synthesis method was applied to the HgS/CdS core/shell. Encapsulation of HgS in a CdS shell eliminates the natural n doping of the HgS core. The core/shell also greatly improves the thermal stability of the HgS core, allowing annealing temperatures up to 200 °C.
There are studies on medium-wave colloidal quantum dots without heavy metal elements. Shihab et al. [85] reported a photodetector based on Ag2Se CQDs intraband absorption, as well as the preparation of a binary mixture film containing Ag2Se quantum dots and a p-n heterojunction diode with strong rectification properties. The detector effectively reduces dark and noisy current densities by mixing two different types of quantum dots to control the electrical properties of the mixture film. Without cooling, the detector achieves a detection rate of 7.8 × 106 Jones at 4.5 μm. Compared with the previous generation of intraband quantum dot detectors, it is an order of magnitude higher. Table 2 summarizes the device structure and performance of typical CQD-based MWIR detectors.

3.2.3. For LWIR Applications

LWIR imagers are particularly effective in areas such as human detection, where human emission is maximized at around 9 μm according to the Plank distribution. LWIR has a function that cannot be fulfilled by detectors in other wavelength bands, though in recent years, there has been increasing interest in longer wavelengths stimulated by space applications [91].
HgTe quantum dots are the most studied long-wavelength colloidal quantum dots due to their broad-band tunability. The intraband transition of the CQD is important for infrared applications. Zhang et al. [92] optimized the synthesis process of n-doped HgTe colloidal quantum dots to produce samples with a 1Se-1Pe intraband transition in the long-wave infrared (8~12 μm). At a temperature of 80 K, a photoconductive film with a thickness of 80 nm on a quarter-wave reflector substrate shows a detectivity of ~107 Jones (D*) in the range of 500 Hz and 8–12 μm when doping ~2 electrons/dot doping.
Ramiro et al. [93] demonstrated that by heavy doping, PbS colloidal quantum dots can achieve intraband absorption and photodetection in the 5–9 μm range beyond the PbS bulk band gap. Because PbS bulk crystals have relatively large band gaps, intraband absorption in PbS CQD can enter ranges of the spectrum that are not accessible by interband conversion. This band-gap modulation strategy further expands the availability of solution-processed materials in MWIR and LWIR infrared applications.
Currently, colloidal quantum dots photodetection wavelengths are mainly in the mid-wave infrared, and one may wonder about the upper limit of the wavelength region of CQDs. Xue et al. [94] developed a regrowth method and ionic doping modification to achieve photodetection at wavelengths up to 18 μm on HgTe CQDs. At liquid nitrogen temperature, the 10 μm and 18 μm HgTe CQD photoconductors achieved responsivity of 0.13 A/W and 0.3 A/W, respectively, and detectivity of 2.3 × 109 Jones and 6.6 × 108 Jones, respectively.
Another important research direction of colloidal quantum dots is multi-band detection, which can cover a wider band and realize more device application scenarios. In 2019, Tang et al. [95] achieved short- and medium-wave responses at different bias voltages by adjusting the size of HgTe colloidal quantum dots and realized scanning-type imaging with a single component, which is an important advancement, hinting at the potential value of colloidal quantum dots for dual- or multicolor applications.
In 2023, Tang et al. [96] reported a three-band infrared detector that used Ag2Te nanocrystals to bring spatially stable doping. HgTe CQDs with varying band gaps are used to construct a three-band infrared detector with short-wave infrared of 1.7 and 2.4 μm and medium-wave infrared of 4 μm. The detector switches between the three-band mode and the dual-band mode by adjusting the bias polarity. The detector exhibits excellent performance, with detectivity of more than 3 × 1010 Jones in three-band mode.
Doping strategies can also effectively extend operational wavelengths and minimize defects. By optimizing the synthesis process of n-doped HgTe colloidal quantum dots et al. [92] prepared long-wave infrared (8–12 μm) samples with intraband transitions (1Se−1Pe) that have stronger absorption, tunable in the LWIR detection range of 8–12 μm, and less temperature-dependent.

4. Conclusions and Prospects

Colloidal quantum dots (QDSs) are considered promising materials for infrared photodetectors due to their adjustable band gap, low manufacturing cost, and solution processability. This paper introduces the basic properties of quantum dots and outlines the working principles of several types of infrared detectors, reviewing the latest progress in SWIR/MWIR/LWIR detectors. However, compared to traditional infrared detectors, those based on colloidal quantum dots still face several challenges.
(1)
Wavelength Range Limitations: Currently, the commercial applications of colloidal quantum dot infrared detectors are mainly concentrated in the near-infrared and short-wave bands. There remains a significant gap in their effectiveness for medium- and long-wave band applications. While focal plane detectors have been reported for the medium-wave band, current research primarily focuses on HgTe quantum dots. To achieve a long-wavelength response, quantum dots must be of considerable size, even approaching the Bohr radius. Consequently, such large quantum dots typically exhibit poor stability. The relatively low stability of HgTe quantum dots poses challenges for their application of colloidal quantum dots in the long-wave band, and there are few reports on long-wave application. Perhaps doping strategies or hybrid material designs are feasible solutions to extend the detection wavelength.
(2)
Material Limitations: Research on colloidal quantum dots has predominantly focused on lead- and mercury-based quantum dots, both of which contain heavy metals. Although there are reports on environmentally friendly quantum dot materials, their performance remains at a relatively low level. Therefore, there is a need to actively search for new materials that offer non-toxic and high-performance quantum dots. InP quantum dots and other materials that do not contain heavy metals (Hg, Pb, etc.) have gradually entered people’s field of vision due to their excellent optical properties.
(3)
Future Developments: The future development of colloidal quantum dot infrared detectors should focus on large arrays and small pixels. Scalable and precise fabrication methods, such as 3D nanoprinting and roll-to-roll manufacturing, have great potential for applications in low-cost, large-scale CQD production. Many challenges remain, such as ensuring compatibility between the quantum dot and the readout circuit and realizing the process realization; the inherent complexity of the deposition process often affects the quality of the film. Recent advancements in encapsulation and passivation techniques can improve the lifespan of photodetectors. For instance, studies employing atomic layer deposition (ALD) coatings or surface functionalization would be valuable additions.

Author Contributions

Conceptualization, L.Y. and K.L.; investigation, L.Y. and P.T.; writing—original draft preparation, L.Y.; writing—review and editing, P.T. and K.L. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Conflicts of Interest

The authors declare no conflicts of interest.

References

  1. Herschel, W., II. Experiments on the refrangibility of the invisible rays of the sun. Philos. Mag. 1800, 8, 9–15. [Google Scholar] [CrossRef]
  2. Guyot-Sionnest, P.; Ackerman, M.M.; Tang, X. Colloidal quantum dots for infrared detection beyond silicon. J. Chem. Phys. 2019, 151, 060901. [Google Scholar] [CrossRef]
  3. Rogalski, A. Recent progress in infrared detector technologies. Infrared Phys. Technol. 2011, 54, 136–154. [Google Scholar] [CrossRef]
  4. Wang, F.; Zhang, Y.; Gao, Y.; Luo, P.; Su, J.; Han, W.; Liu, K.; Li, H.; Zhai, T. 2D Metal Chalcogenides for IR Photodetection. Small 2019, 15, 1901347. [Google Scholar] [CrossRef]
  5. Bianconi, S.; Mohseni, H. Recent advances in infrared imagers: Toward thermodynamic and quantum limits of photon sensitivity. Rep. Prog. Phys. 2020, 83, 044101. [Google Scholar] [CrossRef] [PubMed]
  6. Du, K.; Li, Q.; Zhang, W.; Yang, Y.; Qiu, M. Wavelength and Thermal Distribution Selectable Microbolometers Based on Metamaterial Absorbers. IEEE Photonics J. 2015, 7, 1–8. [Google Scholar] [CrossRef]
  7. Gul, H.Z.; Sakong, W.; Ji, H.; Torres, J.; Yi, H.; Ghimire, M.K.; Yoon, J.H.; Yun, M.H.; Hwang, H.R.; Lee, Y.H.; et al. Semimetallic Graphene for Infrared Sensing. ACS Appl. Mater. Interfaces 2019, 11, 19565–19571. [Google Scholar] [CrossRef]
  8. Rogalski, A.; Martyniuk, P.; Kopytko, M. Challenges of small-pixel infrared detectors: A review. Rep. Prog. Phys. 2016, 79, 046501. [Google Scholar] [CrossRef]
  9. Yu, X.; Ji, Y.; Shen, X.; Le, X. Progress in Advanced Infrared Optoelectronic Sensors. Nanomaterials 2024, 14, 845. [Google Scholar] [CrossRef]
  10. Konstantatos, G.; Sargent, E.H. Colloidal quantum dot photodetectors. Infrared Phys. Technol. 2011, 54, 278–282. [Google Scholar] [CrossRef]
  11. Nozik, A.J.; Beard, M.C.; Luther, J.M.; Law, M.; Ellingson, R.J.; Johnson, J.C. Semiconductor quantum dots and quantum dot arrays and applications of multiple exciton generation to third-generation photovoltaic solar cells. Chem. Rev. 2010, 110, 6873–6890. [Google Scholar] [CrossRef] [PubMed]
  12. Wang, L.; Chen, Z.; Liang, G.; Li, Y.; Lai, R.; Ding, T.; Wu, K. Observation of a phonon bottleneck in copper-doped colloidal quantum dots. Nat. Commun. 2019, 10, 4532. [Google Scholar] [CrossRef]
  13. Kilina, S.V.; Neukirch, A.J.; Habenicht, B.F.; Kilin, D.S.; Prezhdo, O.V. Quantum zeno effect rationalizes the phonon bottleneck in semiconductor quantum dots. Phys. Rev. Lett. 2013, 110, 180404. [Google Scholar] [CrossRef] [PubMed]
  14. Ren, A.; Yuan, L.; Xu, H.; Wu, J.; Wang, Z. Recent progress of III–V quantum dot infrared photodetectors on silicon. J. Mater. Chem. C 2019, 7, 14441–14453. [Google Scholar] [CrossRef]
  15. Kufer, D.; Nikitskiy, I.; Lasanta, T.; Navickaite, G.; Koppens, F.H.; Konstantatos, G. Hybrid 2D-0D MoS2 -PbS quantum dot photodetectors. Adv. Mater. 2015, 27, 176–180. [Google Scholar] [CrossRef]
  16. Nakotte, T.; Luo, H.; Pietryga, J. PbE (E = S, Se) Colloidal Quantum Dot-Layered 2D Material Hybrid Photodetectors. Nanomaterials 2020, 10, 172. [Google Scholar] [CrossRef]
  17. Rossetti, R.; Nakahara, S.; Brus, L.E. Quantum size effects in the redox potentials, resonance Raman spectra, and electronic spectra of CdS crystallites in aqueous solution. J. Chem. Phys. 1983, 79, 1086–1088. [Google Scholar] [CrossRef]
  18. Lin, P.-H.; Ghosh, S.; Chang, G.-E. Theoretical Analysis of GeSn Quantum Dots for Photodetection Applications. Sensors 2024, 24, 1263. [Google Scholar] [CrossRef]
  19. Sargent, E.H. Colloidal quantum dot solar cells. Nat. Photonics 2012, 6, 133–135. [Google Scholar] [CrossRef]
  20. Weidman, M.C.; Beck, M.E.; Hoffman, R.S.; Prins, F.; Tisdale, W.A. Monodisperse, air-stable PbS nanocrystals via precursor stoichiometry control. ACS Nano 2014, 8, 6363–6371. [Google Scholar] [CrossRef]
  21. Sharma, A.; Mahajan, C.; Rath, A.K. Reduction of Trap and Polydispersity in Mutually Passivated Quantum Dot Solar Cells. ACS Appl. Energy Mater. 2020, 3, 8903–8911. [Google Scholar] [CrossRef]
  22. Wang, X.; Xu, K.; Yan, X.; Xiao, X.; Aruta, C.; Foglietti, V.; Ning, Z.; Yang, N. Amorphous ZnO/PbS Quantum Dots Heterojunction for Efficient Responsivity Broadband Photodetectors. ACS Appllied Mater. Interfaces 2020, 12, 8403–8410. [Google Scholar] [CrossRef]
  23. Tang, X.; Ackerman, M.M.; Shen, G.; Guyot-Sionnest, P. Towards Infrared Electronic Eyes: Flexible Colloidal Quantum Dot Photovoltaic Detectors Enhanced by Resonant Cavity. Small 2019, 15, e1804920. [Google Scholar] [CrossRef]
  24. Tang, X.; Chen, M.; Kamath, A.; Ackerman, M.M.; Guyot-Sionnest, P. Colloidal Quantum-Dots/Graphene/Silicon Dual-Channel Detection of Visible Light and Short-Wave Infrared. ACS Photonics 2020, 7, 1117–1121. [Google Scholar] [CrossRef]
  25. Sun, Y.; Liu, Z.; Ding, Y.; Chen, Z. Flexible Broadband Photodetectors Enabled by MXene/PbS Quantum Dots Hybrid Structure. IEEE Electron. Device Lett. 2021, 42, 1814–1817. [Google Scholar] [CrossRef]
  26. Böberl, M.; Kovalenko, M.V.; Gamerith, S.; List, E.J.W.; Heiss, W. Inkjet-Printed Nanocrystal Photodetectors Operating up to 3 μm Wavelengths. Adv. Mater. 2007, 19, 3574–3578. [Google Scholar] [CrossRef]
  27. Cook, B.; Gong, M.; Ewing, D.; Casper, M.; Stramel, A.; Elliot, A.; Wu, J. Inkjet Printing Multicolor Pixelated Quantum Dots on Graphene for Broadband Photodetection. ACS Appl. Nano Mater. 2019, 2, 3246–3252. [Google Scholar] [CrossRef]
  28. Tang, X.; Chen, M.; Ackerman, M.M.; Melnychuk, C.; Guyot-Sionnest, P. Direct Imprinting of Quasi-3D Nanophotonic Structures into Colloidal Quantum-Dot Devices. Adv. Mater. 2020, 32, e1906590. [Google Scholar] [CrossRef]
  29. García de Arquer, F.P.; Armin, A.; Meredith, P.; Sargent, E.H. Solution-processed semiconductors for next-generation photodetectors. Nat. Rev. Mater. 2017, 2, 16100. [Google Scholar] [CrossRef]
  30. Rogalski, A. Scaling infrared detectors—Status and outlook. Rep. Prog. Phys. 2022, 85, 126501. [Google Scholar] [CrossRef]
  31. Billaha, M.A.; Das, M.K. Performance analysis of AlGaAs/GaAs/InGaAs-based asymmetric long-wavelength QWIP. Appl. Phys. A 2019, 125, 457. [Google Scholar] [CrossRef]
  32. Cellek, O.O.; Ozer, S.; Besikci, C. High responsivity InP-InGaAs quantum-well infrared photodetectors: Characteristics and focal plane array performance. IEEE J. Quantum Electron. 2005, 41, 980–985. [Google Scholar] [CrossRef]
  33. Ghosh, S.; Bhattacharyya, A.; Sen, G.; Mukhopadhyay, B. Optimization of different structural parameters of GeSn/SiGeSn Quantum Well Infrared Photodetectors (QWIPs) for low dark current and high responsivity. J. Comput. Electron. 2021, 20, 1224–1233. [Google Scholar] [CrossRef]
  34. Ghosh, S.; Mukhopadhyay, B.; Sen, G.; Basu, P.K. Performance analysis of GeSn/SiGeSn quantum well infrared photodetector in terahertz wavelength region. Phys. E Low-Dimens. Syst. Nanostructures 2020, 115, 113692. [Google Scholar] [CrossRef]
  35. Guériaux, V.; Nedelcu, A.; Coulibaly, A.; Marcadet, X.; March, K.; Enouz-Vedrenne, S. Structural and chemical study of AlGaAs/InGaAs based QWIPs. Infrared Phys. Technol. 2011, 54, 199–203. [Google Scholar] [CrossRef]
  36. Mahmodi, H.; Hashim, M.R.; Allahyarzadeh, G. Design and study of a GeSn-SiGeSn single quantum well structure for infrared photodetection. In Proceedings of the 2012 International Conference on Enabling Science and Nanotechnology, Johor Bahru, Malaysia, 5–7 January 2012; pp. 1–2. [Google Scholar]
  37. Wang, Y.; Herron, N. Photoconductivity of CdS nanocluster-doped polymers. Chem. Phys. Lett. 1992, 200, 71–75. [Google Scholar] [CrossRef]
  38. Guyot-Sionnest, P.; Wang, C. Fast Voltammetric and Electrochromic Response of Semiconductor Nanocrystal Thin Films. J. Phys. Chem. B 2003, 107, 7355–7359. [Google Scholar] [CrossRef]
  39. Rauch, T.; Böberl, M.; Tedde, S.F.; Fürst, J.; Kovalenko, M.V.; Hesser, G.; Lemmer, U.; Heiss, W.; Hayden, O. Near-infrared imaging with quantum-dot-sensitized organic photodiodes. Nat. Photonics 2009, 3, 332–336. [Google Scholar] [CrossRef]
  40. Kobayashi, N.P.; Talin, A.A.; Islam, M.S.; Davydov, A.V.; Pimpinella, R.E.; Ciani, A.; Guyot-Sionnest, P.; Grein, C. HgTe colloidal quantum dot LWIR infrared photodetectors. In Low-Dimensional Materials and Devices; SPIE: Bellingham, WA, USA, 2015; pp. 73–79. [Google Scholar]
  41. Shen, T.; Li, F.; Zhang, Z.; Xu, L.; Qi, J. High-Performance Broadband Photodetector Based on Monolayer MoS2 Hybridized with Environment-Friendly CuInSe2 Quantum Dots. ACS Appl. Mater. Interfaces 2020, 12, 54927–54935. [Google Scholar] [CrossRef]
  42. Garcia, D.A.; Mendoza, L.; Vizuete, K.; Debut, A.; Arias, M.T.; Gavilanes, A.; Terencio, T.; Avila, E.; Jeffryes, C.; Dahoumane, S.A. Sugar-Mediated Green Synthesis of Silver Selenide Semiconductor Nanocrystals under Ultrasound Irradiation. Molecules 2020, 25, 5193. [Google Scholar] [CrossRef]
  43. Jeong, H.; Song, J.H.; Jeong, S.; Chang, W.S. Graphene/PbS quantum dot hybrid structure for application in near-infrared photodetectors. Sci. Rep. 2020, 10, 12475. [Google Scholar] [CrossRef] [PubMed]
  44. Li, Y.; Yu, J.; Wei, Y.; Wang, Y.; Cheng, L.; Feng, Z.; Yang, Y.; Wang, Z.L.; Sun, Q. Ambipolar tribotronic transistor of MoTe2. Nano Res. 2023, 16, 11907–11913. [Google Scholar] [CrossRef]
  45. Kim, J.; Baik, S.S.; Ryu, S.H.; Sohn, Y.; Park, S.; Park, B.-G.; Denlinger, J.; Yi, Y.; Choi, H.J.; Kim, K.S. Observation of tunable band gap and anisotropic Dirac semimetal state in black phosphorus. Science 2015, 349, 723–726. [Google Scholar] [CrossRef]
  46. Wang, Z.; Gu, Y.; Li, X.; Liu, Y.; Liu, F.; Wu, W. Recent Progress of Quantum Dot Infrared Photodetectors. Adv. Opt. Mater. 2023, 11, 2300970. [Google Scholar] [CrossRef]
  47. Sashchiuk, A.; Langof, L.; Chaim, R.; Lifshitz, E. Synthesis and characterization of PbSe and PbSe/PbS core–shell colloidal nanocrystals. J. Cryst. Growth 2002, 240, 431–438. [Google Scholar] [CrossRef]
  48. Keuleyan, S.; Lhuillier, E.; Guyot-Sionnest, P. Synthesis of colloidal HgTe quantum dots for narrow mid-IR emission and detection. J. Am. Chem. Soc. 2011, 133, 16422–16424. [Google Scholar] [CrossRef]
  49. Greboval, C.; Chu, A.; Goubet, N.; Livache, C.; Ithurria, S.; Lhuillier, E. Mercury Chalcogenide Quantum Dots: Material Perspective for Device Integration. Chem. Rev. 2021, 121, 3627–3700. [Google Scholar] [CrossRef]
  50. Zhang, Y.; Liu, Y.; Li, C.; Chen, X.; Wang, Q. Controlled Synthesis of Ag2S Quantum Dots and Experimental Determination of the Exciton Bohr Radius. J. Phys. Chem. C 2014, 118, 4918–4923. [Google Scholar] [CrossRef]
  51. Yu, M.-X.; Ma, J.-J.; Wang, J.-M.; Cai, W.-G.; Zhang, Z.; Huang, B.; Sun, M.-Y.; Cheng, Q.-Y.; Zhang, Z.-L.; Pang, D.-W.; et al. Ag2Te Quantum Dots as Contrast Agents for Near-Infrared Fluorescence and Computed Tomography Imaging. ACS Appl. Nano Mater. 2020, 3, 6071–6077. [Google Scholar] [CrossRef]
  52. Hu, J.; Yang, S.; Zhang, Z.; Li, H.; Perumal Veeramalai, C.; Sulaman, M.; Saleem, M.I.; Tang, Y.; Jiang, Y.; Tang, L.; et al. Solution-processed, flexible and broadband photodetector based on CsPbBr3/PbSe quantum dot heterostructures. J. Mater. Sci. Technol. 2021, 68, 216–226. [Google Scholar] [CrossRef]
  53. Liu, Y.; Gibbs, M.; Puthussery, J.; Gaik, S.; Ihly, R.; Hillhouse, H.W.; Law, M. Dependence of Carrier Mobility on Nanocrystal Size and Ligand Length in PbSe Nanocrystal Solids. Nano Lett. 2010, 10, 1960–1969. [Google Scholar] [CrossRef] [PubMed]
  54. Yang, M.; Liu, H.; Wen, S.; Du, Y.; Gao, F. Optimizing the Infrared Photoelectric Detection Performance of Pbs Quantum Dots through Solid-State Ligand Exchange. Materials 2022, 15, 9058. [Google Scholar] [CrossRef] [PubMed]
  55. Goossens, S.; Navickaite, G.; Monasterio, C.; Gupta, S.; Piqueras, J.J.; Pérez, R.; Burwell, G.; Nikitskiy, I.; Lasanta, T.; Galán, T.; et al. Broadband image sensor array based on graphene–CMOS integration. Nat. Photonics 2017, 11, 366–371. [Google Scholar] [CrossRef]
  56. Mi, L.; Chang, Y.; Zhang, Y.; Xu, E.; Jiang, Y. Hybrid perovskite exchange of PbS quantum dots for fast and high-detectivity visible–near-infrared photodetectors. J. Mater. Chem. C 2020, 8, 7812–7819. [Google Scholar] [CrossRef]
  57. He, Z.; Liu, H.; Xie, F.; Bai, M.; Wen, S.; Zhao, J.; Liu, W.; Liao, M. Lead Selenium Colloidal Quantum Dots for 400-2600 nm Broadband Photodetectors. J. Nanomater. 2022, 2022, 1–8. [Google Scholar] [CrossRef]
  58. Yang, J.; Lv, Y.; He, Z.; Wang, B.; Chen, S.; Xiao, F.; Hu, H.; Yu, M.; Liu, H.; Lan, X.; et al. Bi2S3 Electron Transport Layer Incorporation for High-Performance Heterostructure HgTe Colloidal Quantum Dot Infrared Photodetectors. ACS Photonics 2023, 10, 2226–2233. [Google Scholar] [CrossRef]
  59. Wang, Y.; Peng, L.; Schreier, J.; Bi, Y.; Black, A.; Malla, A.; Goossens, S.; Konstantatos, G. Silver telluride colloidal quantum dot infrared photodetectors and image sensors. Nat. Photonics 2024, 18, 236–242. [Google Scholar] [CrossRef]
  60. Wang, N.; Xue, C.; Wan, F.; Zhao, Y.; Xu, G.; Liu, Z.; Zheng, J.; Zuo, Y.; Cheng, B.; Wang, Q. High-Performance GeSn Photodetector Covering All Telecommunication Bands. IEEE Photonics J. 2021, 13, 1–9. [Google Scholar] [CrossRef]
  61. Ghosh, S.; Bansal, R.; Sun, G.; Soref, R.A.; Cheng, H.-H.; Chang, G.-E. Design and Optimization of GeSn Waveguide Photodetectors for 2-µm Band Silicon Photonics. Sensors 2022, 22, 3978. [Google Scholar] [CrossRef]
  62. Ghosh, S.; Mukhopadhyay, B.; Sen, G.; Basu, P.K. Study of Si-Ge-Sn based Heterobipolar Phototransistor (HPT) exploiting Quantum Confined Stark Effect and Franz Keldysh effect with and without resonant cavity. Phys. E Low-Dimens. Syst. Nanostructures 2019, 106, 62–67. [Google Scholar] [CrossRef]
  63. Cui, J.; Fang, R.; Liu, X.; Wu, Y.; Huang, Q.; Liu, Z.; Yi, F.; Liu, Z.; Zuo, Y.; Cheng, B.; et al. Comprehensive Investigation of GeSn Metasurface Photodetector for Short-Wave Infrared Application. ACS Photonics 2024, 11, 4126–4133. [Google Scholar] [CrossRef]
  64. Atalla, M.R.M.; Lemieux-Leduc, C.; Assali, S.; Koelling, S.; Daoust, P.; Moutanabbir, O. Extended short-wave infrared high-speed all-GeSn PIN photodetectors on silicon. APL Photonics 2024, 9, 056103. [Google Scholar] [CrossRef]
  65. Atalla, M.R.M.; Assali, S.; Koelling, S.; Attiaoui, A.; Moutanabbir, O. High-Bandwidth Extended-SWIR GeSn Photodetectors on Silicon Achieving Ultrafast Broadband Spectroscopic Response. ACS Photonics 2022, 9, 1425–1433. [Google Scholar] [CrossRef]
  66. Dias, S.; Kumawat, K.; Biswas, S.; Krupanidhi, S.B. Solvothermal Synthesis of Cu2SnS3 Quantum Dots and Their Application in Near-Infrared Photodetectors. Inorg. Chem. 2017, 56, 2198–2203. [Google Scholar] [CrossRef]
  67. Xiao, X.; Xu, K.; Yin, M.; Qiu, Y.; Zhou, W.; Zheng, L.; Cheng, X.; Yu, Y.; Ning, Z. High quality silicon: Colloidal quantum dot heterojunction based infrared photodetector. Appl. Phys. Lett. 2020, 116, 101102. [Google Scholar] [CrossRef]
  68. Biondi, M.; Choi, M.-J.; Wang, Z.; Wei, M.; Lee, S.; Choubisa, H.; Sagar, L.K.; Sun, B.; Baek, S.-W.; Chen, B.; et al. Facet-Oriented Coupling Enables Fast and Sensitive Colloidal Quantum Dot Photodetectors. Adv. Mater. 2021, 33, 2101056. [Google Scholar] [CrossRef]
  69. Grotevent, M.J.; Hail, C.U.; Yakunin, S.; Bachmann, D.; Calame, M.; Poulikakos, D.; Kovalenko, M.V.; Shorubalko, I. Colloidal HgTe Quantum Dot/Graphene Phototransistor with a Spectral Sensitivity Beyond 3 microm. Adv. Sci. 2021, 8, 2003360. [Google Scholar] [CrossRef]
  70. Shikoh, A.S.; Choi, G.S.; Hong, S.; Jeong, K.S.; Kim, J. High-sensitivity hybrid PbSe/ITZO thin film-based phototransistor detecting from 2100 to 2500 nm near-infrared illumination. Nanotechnology 2022, 33, 165501. [Google Scholar] [CrossRef]
  71. Leemans, J.; Pejović, V.; Georgitzikis, E.; Minjauw, M.; Siddik, A.B.; Deng, Y.-H.; Kuang, Y.; Roelkens, G.; Detavernier, C.; Lieberman, I.; et al. Colloidal III–V Quantum Dot Photodiodes for Short-Wave Infrared Photodetection. Adv. Sci. 2022, 9, 2200844. [Google Scholar] [CrossRef]
  72. Xu, Q.; Cheong, I.T.; Song, H.; Van, V.; Veinot, J.G.C.; Wang, X. Heterogeneous Integration of Colloidal Quantum Dot Inks on Silicon Enables Highly Efficient and Stable Infrared Photodetectors. ACS Photonics 2022, 9, 2792–2801. [Google Scholar] [CrossRef]
  73. Zhang, Y.; Vafaie, M.; Xu, J.; Pina, J.M.; Xia, P.; Najarian, A.M.; Atan, O.; Imran, M.; Xie, K.; Hoogland, S.; et al. Electron-Transport Layers Employing Strongly Bound Ligands Enhance Stability in Colloidal Quantum Dot Infrared Photodetectors. Adv. Mater. 2022, 34, 2206884. [Google Scholar] [CrossRef] [PubMed]
  74. Zhang, L.; Chen, L.; Yang, J.; Liu, J.; Lu, S.; Liang, X.; Zhao, X.; Yang, Y.; Hu, J.; Hu, L.; et al. High-Performance and Stable Colloidal Quantum Dots Imager via Energy Band Engineering. Nano Lett. 2023, 23, 6489–6496. [Google Scholar] [CrossRef]
  75. Guyot-Sionnest, P.; Roberts, J.A. Background limited mid-infrared photodetection with photovoltaic HgTe colloidal quantum dots. Appl. Phys. Lett. 2015, 107, 253104. [Google Scholar] [CrossRef]
  76. Hao, Q.; Ma, H.; Xing, X.; Tang, X.; Wei, Z.; Zhao, X.; Chen, M. Mercury Chalcogenide Colloidal Quantum Dots for Infrared Photodetectors. Materials 2023, 16, 7321. [Google Scholar] [CrossRef]
  77. Melnychuk, C.; Guyot-Sionnest, P. Slow Auger Relaxation in HgTe Colloidal Quantum Dots. J. Phys. Chem. Lett. 2018, 9, 2208–2211. [Google Scholar] [CrossRef] [PubMed]
  78. Keuleyan, S.; Lhuillier, E.; Brajuskovic, V.; Guyot-Sionnest, P. Mid-infrared HgTe colloidal quantum dot photodetectors. Nat. Photonics 2011, 5, 489–493. [Google Scholar] [CrossRef]
  79. Razeghi, M.; Temple, D.S.; Brown, G.J.; Buurma, C.; Pimpinella, R.E.; Ciani, A.J.; Feldman, J.S.; Grein, C.H.; Guyot-Sionnest, P. MWIR imaging with low cost colloidal quantum dot films. In Optical Sensing, Imaging, and Photon Counting: Nanostructured Devices and Applications 2016; SPIE: Bellingham, WA, USA, 2016; Volume 9933, p. 993303. [Google Scholar]
  80. Chen, M.; Lan, X.; Tang, X.; Wang, Y.; Hudson, M.H.; Talapin, D.V.; Guyot-Sionnest, P. High Carrier Mobility in HgTe Quantum Dot Solids Improves Mid-IR Photodetectors. ACS Photonics 2019, 6, 2358–2365. [Google Scholar] [CrossRef]
  81. Xia, K.; Gao, X.D.; Fei, G.T.; Xu, S.H.; Liang, Y.F.; Qu, X.X. High-Performance Visible to Mid-Infrared Photodetectors Based on HgTe Colloidal Quantum Dots under Room Temperature. ACS Appl. Mater. Interfaces 2024, 16, 23717–23723. [Google Scholar] [CrossRef]
  82. Mu, G.; Tan, Y.; Bi, C.; Liu, Y.; Hao, Q.; Tang, X. Visible to mid-wave infrared PbS/HgTe colloidal quantum dot imagers. Nat. Photonics 2024, 18, 1147–1154. [Google Scholar] [CrossRef]
  83. Chen, M.; Hao, Q.; Luo, Y.; Tang, X. Mid-Infrared Intraband Photodetector via High Carrier Mobility HgSe Colloidal Quantum Dots. ACS Nano 2022, 16, 11027–11035. [Google Scholar] [CrossRef]
  84. Kim, J.; Yoon, B.; Kim, J.; Choi, Y.; Kwon, Y.-W.; Park, S.K.; Jeong, K.S. High electron mobility of β-HgS colloidal quantum dots with doubly occupied quantum states. RSC Adv. 2017, 7, 38166–38170. [Google Scholar] [CrossRef]
  85. Hafiz, S.B.; Al Mahfuz, M.M.; Lee, S.; Ko, D.K. Midwavelength Infrared p-n Heterojunction Diodes Based on Intraband Colloidal Quantum Dots. ACS Appl. Mater. Interfaces 2021, 13, 49043–49049. [Google Scholar] [CrossRef]
  86. Ackerman, M.M.; Tang, X.; Guyot-Sionnest, P. Fast and Sensitive Colloidal Quantum Dot Mid-Wave Infrared Photodetectors. ACS Nano 2018, 12, 7264–7271. [Google Scholar] [CrossRef] [PubMed]
  87. Qiu, J.; Weng, B.; McDowell, L.L.; Shi, Z. Low-cost uncooled MWIR PbSe quantum dots photodiodes. RSC Adv. 2019, 9, 42516–42523. [Google Scholar] [CrossRef]
  88. Luo, Y.; Zhang, S.; Tang, X.; Chen, M. Resonant cavity-enhanced colloidal quantum-dot dual-band infrared photodetectors. J. Mater. Chem. C 2022, 10, 8218–8225. [Google Scholar] [CrossRef]
  89. Zhang, S.; Bi, C.; Qin, T.; Liu, Y.; Cao, J.; Song, J.; Huo, Y.; Chen, M.; Hao, Q.; Tang, X. Wafer-Scale Fabrication of CMOS-Compatible Trapping-Mode Infrared Imagers with Colloidal Quantum Dots. ACS Photonics 2023, 10, 673–682. [Google Scholar] [CrossRef]
  90. Xue, X.; Chen, M.; Luo, Y.; Qin, T.; Tang, X.; Hao, Q. High-operating-temperature mid-infrared photodetectors via quantum dot gradient homojunction. Light Sci. Appl. 2023, 12, 2. [Google Scholar] [CrossRef]
  91. Rogalski, A. Next Decade in Infrared Detectors; SPIE: Bellingham, WA, USA, 2017; Volume 10433, p. 10433OL. [Google Scholar]
  92. Zhang, H.; Peterson, J.C.; Guyot-Sionnest, P. Intraband Transition of HgTe Nanocrystals for Long-Wave Infrared Detection at 12 μm. ACS Nano 2023, 17, 7530–7538. [Google Scholar] [CrossRef] [PubMed]
  93. Ramiro, I.; Ozdemir, O.; Christodoulou, S.; Gupta, S.; Dalmases, M.; Torre, I.; Konstantatos, G. Mid- and Long-Wave Infrared Optoelectronics via Intraband Transitions in PbS Colloidal Quantum Dots. Nano Lett. 2020, 20, 1003–1008. [Google Scholar] [CrossRef]
  94. Xue, X.; Hao, Q.; Chen, M. Very long wave infrared quantum dot photodetector up to 18 μm. Light Sci. Appl. 2024, 13, 89. [Google Scholar] [CrossRef]
  95. Tang, X.; Ackerman, M.M.; Chen, M.; Guyot-Sionnest, P. Dual-band infrared imaging using stacked colloidal quantum dot photodiodes. Nat. Photonics 2019, 13, 277–282. [Google Scholar] [CrossRef]
  96. Zhao, P.; Mu, G.; Wen, C.; Qi, Y.; Lv, H.; Tang, X. Colloidal Quantum Dots-Based Three-Band Infrared Photodetector with the Bias-Tunable Spectral Response. Phys. Status Solidi (RRL)—Rapid Res. Lett. 2023, 18, 2300121. [Google Scholar] [CrossRef]
Table 1. The summary of SWIR photodetectors based on CQDs.
Table 1. The summary of SWIR photodetectors based on CQDs.
YearMaterialDevice StructureResponse Band (nm)Responsivity
(A/W)		Detectivity (Jones)Response TimeRef.
2017PbSGraphene/PbS300–2000107//[55]
2017Cu2SnS3ITO/Cu2SnS3/Ag15500.9 × 10−31.86 × 1094.1 s[66]
2020PbSSi/ZnO/PbS14900.224.08 × 101147.6 μs[67]
2020PbSZnO/PbS13100.473.39 × 1011/[22]
2020PbSPbS-QDs + hybrid perovskite300–12002 × 10610152/24 μs[56]
2020HgTeSi/Bi2Se3/Gr/HgTe/Ag2Te/Au24000.95 × 10913 ns[24]
2021PbSITO/ZnO/PbS/PbS-EDT/Au1550/1.6 × 10127 ns[68]
2021HgTeHgTe/Gr25008006 × 108-[69]
2022PbSeInSnZnO/PbSe21003.91 × 10−34.55 × 1070.38 s[70]
2022In(As,P)ITO/NiO/In(As,P)/TiO2/Al14007 × 10−31 × 1091.6 μs[71]
2022PbSSi/PbS-EDT/PbS/ZnO400–1500/3.2 × 10111.9 μs[72]
2022PbSITO/PbS-EDT/PbS/PbS-TFCA/Ag14500.43 × 10101.1 μs[73]
2022PbSePbSe400–26000.32/32 ms[57]
2023HgTeBi2S3/HgTe/Ag:HgTe22000.2910118 μs[58]
2023Ag2TeAg2Te/AgBiS2/SnO2350–16000.110121.3/3.3 μs[59]
2023PbSAu/NiO/PbS-EDT/PbS/C60/SnO2/ITO15300.84.1 × 10124.6 μs[74]
Table 2. The summary of MWIR photodetectors based on CQDs.
Table 2. The summary of MWIR photodetectors based on CQDs.
YearMaterialResponse Band (nm)Responsivity
(A/W)		Detectivity (Jones)Response TimeRef.
2011HgTe5000/2 × 109/[78]
2016HgTe5000/5.4 × 10101.3 μs[80]
2018HgTe48001.33.3 × 10110.3 μs[86]
2019PbSe42000.368.5 × 108/[87]
2021Ag2Se4500/7.8 × 106/[85]
2022HgSe50000.0771.7 × 109/[83]
2022HgTe40001.62 × 1011/[88]
2023HgTe5500/8 × 1010/[89]
2023HgTe42002.72.7 × 1011 [90]
2024HgTe45–40000.096.9 × 1071.9/1.5 μs[81]
2024PbS/HgTe400–42007103.15 × 1010/[82]
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Figure 1. Band gap of bulk materials and quantum dots.
Figure 1. Band gap of bulk materials and quantum dots.
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Figure 2. Absorption spectra of PbS quantum dots of different sizes [20].
Figure 2. Absorption spectra of PbS quantum dots of different sizes [20].
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Figure 3. Diagram of the surface of a quantum dot coated with oleic acid-capped and passivated by ligand exchange [21].
Figure 3. Diagram of the surface of a quantum dot coated with oleic acid-capped and passivated by ligand exchange [21].
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Figure 4. Solution-processed photodetector. (a) Method of depositing colloidal quantum dots [29]. (b) Process diagram of colloidal quantum dot infrared focal plane detector [30]. (c) Cross-section of colloidal quantum dot infrared focal plane arrays [30].
Figure 4. Solution-processed photodetector. (a) Method of depositing colloidal quantum dots [29]. (b) Process diagram of colloidal quantum dot infrared focal plane detector [30]. (c) Cross-section of colloidal quantum dot infrared focal plane arrays [30].
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Figure 6. MWIR detector based on colloidal quantum dots. (a) Synthesized HgTe quantum dots using HgBr2 as mercury source [81]. (b) TEM image of HgTe CQDs. (c) Structure diagram of the photoconductive detector. (d) Schematic of the architecture of the ultra-broadband imager [82]. (e) Photograph (above) and cross-sectional SEM image (bottom) of the ultra-broadband imager. (f) Thermal images captured by the ultra-broadband FPA imager with an MWIR optical filter. (g) Intraband transition of HgSe [83]. (h) TEM of HgSe CQDs before and after ligand exchange. (i) Photoresponse spectra of the HgSe CQD photoconductor. The right inset graph shows infrared hot images by a HgSe intraband CQD photodetector.
Figure 6. MWIR detector based on colloidal quantum dots. (a) Synthesized HgTe quantum dots using HgBr2 as mercury source [81]. (b) TEM image of HgTe CQDs. (c) Structure diagram of the photoconductive detector. (d) Schematic of the architecture of the ultra-broadband imager [82]. (e) Photograph (above) and cross-sectional SEM image (bottom) of the ultra-broadband imager. (f) Thermal images captured by the ultra-broadband FPA imager with an MWIR optical filter. (g) Intraband transition of HgSe [83]. (h) TEM of HgSe CQDs before and after ligand exchange. (i) Photoresponse spectra of the HgSe CQD photoconductor. The right inset graph shows infrared hot images by a HgSe intraband CQD photodetector.
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Yu, L.; Tian, P.; Liang, K. Advancements and Challenges in Colloidal Quantum Dot Infrared Photodetectors: Strategies for Short-Wave Infrared, Mid-Wave Infrared, and Long-Wave Infrared Applications. Quantum Beam Sci. 2025, 9, 9. https://doi.org/10.3390/qubs9010009

AMA Style

Yu L, Tian P, Liang K. Advancements and Challenges in Colloidal Quantum Dot Infrared Photodetectors: Strategies for Short-Wave Infrared, Mid-Wave Infrared, and Long-Wave Infrared Applications. Quantum Beam Science. 2025; 9(1):9. https://doi.org/10.3390/qubs9010009

Chicago/Turabian Style

Yu, Lijing, Pin Tian, and Kun Liang. 2025. "Advancements and Challenges in Colloidal Quantum Dot Infrared Photodetectors: Strategies for Short-Wave Infrared, Mid-Wave Infrared, and Long-Wave Infrared Applications" Quantum Beam Science 9, no. 1: 9. https://doi.org/10.3390/qubs9010009

APA Style

Yu, L., Tian, P., & Liang, K. (2025). Advancements and Challenges in Colloidal Quantum Dot Infrared Photodetectors: Strategies for Short-Wave Infrared, Mid-Wave Infrared, and Long-Wave Infrared Applications. Quantum Beam Science, 9(1), 9. https://doi.org/10.3390/qubs9010009

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