Charge-density-wave (CDW) materials with strongly correlated electrons have broadband light absorption and ultrafast response to light irradiation, and hence hold great potential in photodetection. 1T-TaS₂ is a typical CDW material with various thermodynamically CDW ground states at different temperatures and fertile out-of-equilibrium intermediate/hidden states. In particular, the light pulses can trigger melting of CDW ordering and also forms hidden states, which exhibits strikingly different electrical conductivity compared to the ground phase. Here, we review the recent research on phase transitions in 1T-TaS₂ and their potential applications in photodetection. We also discuss the ultrafast melting of CDW ordering by ultrafast laser irradiation and the out-of-equilibrium intermediate/hidden states by optical/electrical pulse. For photodetection, demonstrations of photoconductors and bolometers are introduced. Finally, we discuss some of the challenges that remain.

Ultraviolet (UV) photodetectors have attracted more and more attention due to their great potential applications in missile tracking, flame detecting, pollution monitoring, ozone layer monitoring, and so on. Owing to the special characteristics of large bandgap, solution processable, low cost, environmentally friendly, etc., wide bandgap oxide semiconductor materials, such as ZnO, ZnMgO, Ga₂O₃, TiO₂, and NiO, have gradually become a series of star materials in the field of semiconductor UV detection. In this paper, a review is presented on the development of UV photodetectors based on wide bandgap oxide semiconductor films.

After approximately half a century of development, HgCdTe infrared detectors have become the first choice for high performance infrared detectors, which are widely used in various industry sectors, including military tracking, military reconnaissance, infrared guidance, infrared warning, weather forecasting, and resource detection. Further development in infrared applications requires future HgCdTe infrared detectors to exhibit features such as larger focal plane array format and thus higher imaging resolution. An effective approach to develop HgCdTe infrared detectors with a larger array format size is to develop the small pixel technology. In this article, we present a review on the developmental history and current status of small pixel technology for HgCdTe infrared detectors, as well as the main challenges and potential solutions in developing this technology. It is predicted that the pixel size of long-wave HgCdTe infrared detectors can be reduced to 5 μm, while that of mid-wave HgCdTe infrared detectors can be reduced to 3 μm. Although significant progress has been made in this area, the development of small pixel technology for HgCdTe infrared detectors still faces significant challenges such as flip-chip bonding, interconnection, and charge processing capacity of readout circuits. Various approaches have been proposed to address these challenges, including three-dimensional stacking integration and readout circuits based on microelectromechanical systems.

Small-molecule organic semiconductor crystals (SMOSCs) combine broadband light absorption (ultraviolet-visible-near infrared) with long exciton diffusion length and high charge carrier mobility. Therefore, they are promising candidates for realizing high-performance photodetectors. Here, after a brief resume of photodetector performance parameters and operation mechanisms, we review the recent advancements in application of SMOSCs as photodetectors, including photoconductors, phototransistors, and photodiodes. More importantly, the SMOSC-based photodetectors are further categorized according to their detection regions that cover a wide range from ultraviolet to near infrared. Finally, challenges and outlooks of SMOSC-based photodetectors are provided.

This paper presents a review of recent advances in quantum well and quantum cascade infrared photodetectors developed in Shanghai Institute of Technical Physics, Chinese Academy of Sciences (SITP/CAS). Firstly, the temperature- and bias-dependent photocurrent spectra of very long wavelength (VLW) GaAs/AlGaAs quantum well infrared photodetectors (QWIPs) are studied using spectroscopic measurements and corresponding theoretical calculations in detail. We confirm that the first excited state, which belongs to the quasi-bound state, can be converted into a quasi-continuum state induced by bias and temperature. Aided by band structure calculations, we propose a model of the double excited states that determine the working mechanism in VLW QWIPs. Secondly, we present an overview of a VLW QWIP focal plane array (FPA) with 320×256 pixels based on the bound to quasi-bound (BTQB) design. The technology of the manufacturing FPA based on the QWIP structures has been demonstrated. At the operating temperature of 45 K, the detectivity of QWIP FPA is larger than 1.4×10¹⁰ cm·Hz^1/2/W with a cutoff wavelength larger than 16 μm. Finally, to meet the needs of space applications, we proposed a new long wavelength quantum cascade detector with a broadband detection ranging from 7.6 μm to 10.4 μm. With a pair of identical coupled quantum wells separated by a thin barrier, acting as absorption regions, the relative linewidth (Δ E/E) of response can be dramatically broadened to 30.7%. It is shown that the spectral shape and linewidth can be tuned by the thickness of the thin barrier, while it is insensitive to the working temperature. The device can work above liquid nitrogen temperature with a peak responsivity of 63 mA/W and Johnson noise limited detectivity of 5.1×10⁹ cm·Hz^1/2/W.

Solar-blind ultraviolet photodetectors have many advantages, such as low false alarm rates, the ability to detect weak signals, and high signal-to-noise ratios. Among the various functional solar-blind ultraviolet photodetectors, Ga-based alloys of AlGaN and Ga₂O₃ are the most commonly adopted channel semiconductor materials and have attracted extensive research attention in the past decades. This review presents an overview of the recent progress in Ga-based solar-blind photodetectors. In case of AlGaN-based solar-blind ultraviolet photodetectors, the response properties can be improved by optimizing the AlN nucleation layer and designing the avalanche structure. On the other hand, we also discuss the morphology and growth methods of Ga₂O₃ nanomaterials and their effect on the performance of the corresponding solar-blind photodetectors. The mechanically exfoliated Ga₂O₃ flakes show good potential for ultraviolet detection. Also, Ga₂O₃ nanoflowers and nanowires reveal perfect response to ultraviolet light. Finally, the challenges and future development of Ga-based functional solar-blind ultraviolet photodetectors are summarized.

Commercial photodetectors based on silicon are extensively applied in numerous fields. Except for their high performance, their maximum absorption wavelength is not over than 1100 nm and incident light with longer wavelengths cannot be detected; in addition, their cost is high and their manufacturing process is complex. Therefore, it is meaningful and significant to extend absorption wavelength, to decrease cost, and to simplify the manufacturing process while maintaining high performance for photodetectors. Due to the properties of size-dependent bandgap tunability, low cost, facile processing, and substrate compatibility, solution-processed colloidal quantum dots (CQDs) have recently gained significant attention and become one of the most competitive and promising candidates for optoelectronic devices. Among these CQDs, lead chalcogenide CQDs are getting very prominent and are widely investigated. In this paper, the recent progress of infrared (IR) photodetectors based on lead sulfide (PbS), lead selenide (PbSe), and ternary PbS_xSe_1-x CQDs, and their underlying concepts, breakthroughs, and remaining challenges are reviewed, thus providing guidance for designing high-performance quantum-dot IR photodetectors.

Infrared detection technology has greatly expanded the ability of mankind to study the earth and the universe. In recent years, the demand for long-wavelength infrared detectors is increasing for their advantages in exploring the earth and the universe. A variety of long-wavelength infrared detectors have been made based on thermal resistive effect, photoelectric effect, etc., in the past few decades. Remarkable achievements have been made in infrared materials, device fabrication, readout circuit, and device package. However, high performance long-wavelength infrared detectors, especially those for large format long-wavelength infrared detector focus plane array, are still unsatisfactory. Low noise, high detectivity, and large format long-wavelength infrared detector is necessary to satisfy space-based application requirements.

Narrow-gap Hg_1-xCd_xTe material with a composition x of about 0.3 plays an extremely important role in mid-infrared detection applications. In this work, the optical properties of doped HgCdTe with x≈ 0.3 are reviewed, including the defects and defect levels of intrinsic V_Hg and the extrinsic amphoteric arsenic (As) dopants, which can act as shallow/deep donors and acceptors. The influence of the defects on the determination of band-edge electronic structure is discussed when absorption or photoluminescence spectra are considered. The inconsistency between these two optical techniques is demonstrated and analyzed by taking into account the Fermi level position as a function of composition, doping level, conductivity type, and temperature. The defect level and its evolution, especially in As-doped HgCdTe, are presented. Our results provide a systematic understanding of the mechanisms and help for optimizing annealing conditions towards p-type As-activation, and eventually for fabricating high performance mid-infrared detectors.

Gallium oxide (Ga₂O₃), a typical ultra wide bandgap semiconductor, with a bandgap of~4.9 eV, critical breakdown field of 8 MV/cm, and Baliga's figure of merit of 3444, is promising to be used in high-power and high-voltage devices. Recently, a keen interest in employing Ga₂O₃ in power devices has been aroused. Many researches have verified that Ga₂O₃ is an ideal candidate for fabricating power devices. In this review, we summarized the recent progress of field-effect transistors (FETs) and Schottky barrier diodes (SBDs) based on Ga₂O₃, which may provide a guideline for Ga₂O₃ to be preferably used in power devices fabrication.

Ultraviolet (UV) photodetectors (PDs) have drawn great attention in recent years due to their potential application in civil and military fields. Because of its ultrawide bandgap, low cost, strong radiation hardness, and high thermal and chemical stability with high visible-light transparency, Ga₂O₃ is regarded as the most promising candidate for UV detection. Furthermore, the bandgap of Ga₂O₃ is as high as 4.7-4.9 eV, directly corresponding to the solar-blind UV detection band with wavelength less than 280 nm. There is no need of doping in Ga₂O₃ to tune its bandgap, compared to AlGaN, MgZnO, etc, thereby avoiding alloy composition fluctuations and phase separation. At present, solar-blind Ga₂O₃ photodetectors based on single crystal or amorphous Ga₂O₃ are mainly focused on metal-semiconductor-metal and Schottky photodiodes. In this work, the recent achievements of Ga₂O₃ photodetectors are systematically reviewed. The characteristics and performances of different photodetector structures based on single crystal Ga₂O₃ and amorphous Ga₂O₃ thin film are analyzed and compared. Finally, the prospects of Ga₂O₃ UV photodetectors are forecast.

We review our recent efforts on developing HgCdSe infrared materials on GaSb substrates via molecular beam epitaxy (MBE) for fabricating next generation infrared detectors with features of lower production cost and larger focal plane array format size. In order to achieve high-quality HgCdSe epilayers, ZnTe buffer layers are grown before growing HgCdSe, and the study of misfit strain in ZnTe buffer layers shows that the thickness of ZnTe buffer layer needs to be below 300 nm in order to minimize the generation of misfit dislocations. The cut-off wavelength/alloy composition of HgCdSe materials can be varied in a wide range by varying the ratio of Se/Cd beam equivalent pressure during the HgCdSe growth. Growth temperature presents significant impact on the material quality of HgCdSe, and lower growth temperature leads to higher material quality for HgCdSe. Typically, long-wave infrared HgCdSe (x = 0.18, cut-off wavelength of 10.4 μm at 80 K) presents an electron mobility as high as 1.3×10⁵ cm²·V^-1·s^-1, a background electron concentration as low as 1.6×10¹⁶ cm^-3, and a minority carrier lifetime as long as 2.2 μs. These values of electron mobility and minority carrier lifetime represent a significant improvement on previous studies of MBE-grown HgCdSe reported in the open literatures, and are comparable to those of counterpart HgCdTe materials grown on lattice-matched CdZnTe substrates. These results indicate that HgCdSe grown at the University of Western Australia, especially long-wave infrared can meet the basic material quality requirements for making high performance infrared detectors although further effort is required to control the background electron concentration to below 10¹⁵ cm^-3. More importantly, even higher quality HgCdSe materials on GaSb are expected by further optimizing the growth conditions, using higher purity Se source material, and implementing postgrowth thermal annealing and defect/impurity gettering/filtering. Our results demonstrate the great potential of HgCdSe infrared materials grown on GaSb substrates for fabricating next generation infrared detectors with features of lower cost and larger array format size.

In recent years, the rapid progress of metal halide perovskite solar cells has been witnessed by the rocketing power conversion efficiency. In addition, perovskites have opened up a great opportunity for high performance photodetectors (PDs), due to their attractive optical and electrical properties. This review summarizes the latest progress of perovskite-based PDs, aiming to give a comprehensive understanding of the material design and device engineering in perovskite PDs. To begin with, the performance parameters and device configurations of perovskite PDs are introduced, which are the basis for the next discussion. Next, various PDs based on perovskites in different morphologies are discussed from two aspects:the preparation method, and device performance. Then, several device engineering strategies to enhance the performance of perovskite-based PDs are highlighted, followed by the introduction of flexible and narrow-band perovskite PDs. Finally, key issues and major challenges of perovskite PDs that need to be addressed in the future are outlined.

High-performance photodetectors are expected to open up revolutionary opportunities in many application fields, such as environment monitoring, military, optical communication and biomedical science. Combining two-dimensional materials (which have tunable optical absorption and high carrier mobility) with organic materials (which are abundant with low cost, high flexibility and large-area scalability) to form thin-film heterojunctions, high-responsivity photodetectors could be predicted with fast response speed in a wide spectra region. In this review, we give a comprehensive summary of photodetectors based on two-dimensional materials and organic thin-film heterojunctions, which includes hybrid assisted enhanced devices, single-layer enhanced devices, vertical heterojunction devices and tunable vertical heterojunction devices. We also give a systematic classification and perspectives on the future development of these types of photodetectors.

Two-dimensional (2D) materials, such as graphene, transition metal dichalcogenides (TMDs), black phosphorus (BP), and related derivatives, have attracted great attention due to their advantages of flexibility, strong light-matter interaction, broadband absorption, and high carrier mobility, and have become a powerful contender for next-generation infrared photodetectors. However, since the thickness of 2D materials is on the order of nanometers, the absorption of 2D materials is very weak, which limits the detection performance of 2D materials-based infrared photodetectors. In order to solve this problem, scientific researchers have tried to use optimized device structures to combine with 2D materials for improving the performance of infrared photodetectors. In this review, we review the progress of room-temperature infrared photodetectors with hybrid structure based on 2D materials in recent years, focusing mainly on 2D-nD (n=0, 1, 2) heterostructures, the integration between 2D materials and on-chip or plasmonic structure. Finally, we summarize the current challenges and point out the future development direction.

The newly emerging metal halide perovskites have attracted considerable attention due to their exceptional optoelectronic properties. This upsurge was initially driven when the power conversion efficiency of perovskite-based photovoltaic devices exceeded 23%. Due to their optoelectronic properties, perovskite materials have also been used in light-emitting diodes, photodetectors, lasers, and memory devices. This study comprehensively discusses the recent progress of all-inorganic perovskite-based photodetectors, focusing on their structures, morphologies of their constituent materials, and diverse device architectures that improve the performance metrics of these photodetectors. A brief outlook, highlighting the main existing problems, possible solutions to these problems, and future development directions, is also provided herein.

Ultraviolet (UV) photodetectors based on wide band gap semiconductor have attracted much attention for their small volume, low working voltage, long lifetime, good chemical and thermal stability. Up to now, many researches have been done on the semiconductors based UV detectors and some kinds of detectors have been made, such as metal-semiconductor-metal (MSM), Schottky, and PIN-type detectors. However, the sensitivity values of those detectors are still far from the expectation. Recent years, surface plasmon (SP) has been considered to be an effective way to enhance the sensitivity of semiconductor based UV photodetector. When the light is matched with the resonance frequency of surface plasmon, the localized field enhancement or scattering effect will happen and thus the spectral response will be enhanced. Here, we present an overview of surface plasmon enhancing the performance of UV detectors, including the GaN, ZnO, and other wide band gap semiconductor UV detectors. Both fundamental and experimental achievements are contained in this review.

In this article, unique spectral features of short-wave infrared band of 1 μ-3 μm, and various applications related to the photodetectors and focal plane arrays in this band, are introduced briefly. In addition, the different material systems for the devices in this band are outlined. Based on the background, the development of lattice-matched and wavelength-extended InGaAs photodetectors and focal plane arrays, including our continuous efforts in this field, are reviewed. These devices are concentrated on the applications in spectral sensing and imaging, exclusive of optical fiber communication.

The perovskite photodetectors can be used for image sensing, environmental monitoring, optical communication, and chemical/biological detection. In the recent five years, the perovskite photoelectric detectors with various devices are well-designed and have made unprecedented progress of light detection. It is necessary to emphasize the most interesting works and summarize them to provide researchers with systematic information. In this review, we report the recent progress in perovskite photodetectors, including highly sensitive, ultrafast response speed, high gain, low noise, flexibility, and narrowband, concentrating on the photodetection performance of versatile halide perovskites (organic-inorganic hybrid and all inorganic compositions). Currently, organic-inorganic hybrid and all-inorganic halide microcrystals with polycrystalline film, nanoparticle/wire/chip, and block monocrystalline morphology control show important performance in response rate, decomposition rate, noise equivalent power, linear dynamic range, and response speed. It is expected that a comprehensive compendium of the research status of perovskite photodetectors will contribute to the development of this area.