TOPICAL REVIEW — Photodetector: Materials, physics, and applications
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.
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.
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.
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.
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.
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.
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.