Graphene-based mid-infrared room-temperature pyroelectric bolometers with ultrahigh temperature coefficient of resistance

Ultrasensitive Graphene Field-Effect Biosensors Based on Ferroelectric Polarization of Lithium Niobate for Breast Cancer Marker Detection

Herein, we present a novel ultrasensitive graphene field-effect transistor (GFET) biosensor based on lithium niobate (LiNbO3) ferroelectric substrate for the application of breast cancer marker detection. The electrical properties of graphene are varied under the electrostatic field, which is generated through the spontaneous polarization of the ferroelectric substrate. It is demonstrated that the properties of interface between graphene and solution are also altered due to the interaction between the electrostatic field and ions. Compared with the graphene field-effect biosensor based on the conventional Si/SiO2 gate structure, our biosensor achieves a higher sensitivity to 64.7 mV/decade and shows a limit of detection down to 1.7 fM (equivalent to 12 fg·mL-1) on the detection of microRNA21 (a breast cancer marker). This innovative design combining GFETs with ferroelectric substrates holds great promise for developing an ultrahigh-sensitivity biosensing platform based on graphene that enables rapid and early disease diagnosis.

Progress in Advanced Infrared Optoelectronic Sensors

Infrared optoelectronic sensors have attracted considerable research interest over the past few decades due to their wide-ranging applications in military, healthcare, environmental monitoring, industrial inspection, and human-computer interaction systems. A comprehensive understanding of infrared optoelectronic sensors is of great importance for achieving their future optimization. This paper comprehensively reviews the recent advancements in infrared optoelectronic sensors. Firstly, their working mechanisms are elucidated. Then, the key metrics for evaluating an infrared optoelectronic sensor are introduced. Subsequently, an overview of promising materials and nanostructures for high-performance infrared optoelectronic sensors, along with the performances of state-of-the-art devices, is presented. Finally, the challenges facing infrared optoelectronic sensors are posed, and some perspectives for the optimization of infrared optoelectronic sensors are discussed, thereby paving the way for the development of future infrared optoelectronic sensors.

Ultra-broadband absorbance of nanometer-thin pyrolyzed-carbon film on silicon nitride membrane

Fifty percents absorption by thin film, with thickness is much smaller than the skin depth and optical thickness much smaller than the wavelength, is a well-known concept of classical electrodynamics. This is a valuable feature that has been numerously widely explored for metal films, while chemically inert nanomembranes are a real fabrication challenge. Here we report the 20 nm thin pyrolyzed carbon film (PyC) placed on 300 nm thick silicon nitride (Si3N4) membrane demonstrating an efficient broadband absorption in the terahertz and near infrared ranges. While the bare Si3N4membrane is completely transparent in the THz range, the 20 nm thick PyC layer increases the absorption of the PyC coated Si3N4membrane to 40%. The reflection and transmission spectra in the near infrared region reveal that the PyC film absorption persists to a level of at least 10% of the incident power. Such a broadband absorption of the PyC film opens new pathways toward broadband bolometric radiation detectors.

Transparent integrated pyroelectric-photovoltaic structure for photo-thermo hybrid power generation

Thermal losses in photoelectric devices limit their energy conversion efficiency, and cyclic input of energy coupled with pyroelectricity can overcome this limit. Here, incorporating a pyroelectric absorber into a photovoltaic heterostructure device enables efficient electricity generation by leveraging spontaneous polarization based on pulsed light-induced thermal changes. The proposed pyroelectric-photovoltaic device outperforms traditional photovoltaic devices by 2.5 times due to the long-range electric field that occurs under pulse illumination. Optimization of parameters such as pulse frequency, scan speed, and illumination wavelength enhances power harvesting, as demonstrated by a power conversion efficiency of 11.9% and an incident-photon-to-current conversion efficiency of 200% under optimized conditions. This breakthrough enables reconfigurable electrostatic devices and presents an opportunity to accelerate technology that surpasses conventional limits in energy generation.

Bionic visual-audio photodetectors with in-sensor perception and preprocessing

Serving as the "eyes" and "ears" of the Internet of Things, optical and acoustic sensors are the fundamental components in hardware systems. Nowadays, mainstream hardware systems, often comprising numerous discrete sensors, conversion modules, and processing units, tend to result in complex architectures that are less efficient compared to human sensory pathways. Here, a visual-audio photodetector inspired by the human perception system is proposed to enable all-in-one visual and acoustic signal detection with computing capability. This device not only captures light but also optically records sound waves, thus achieving "watching" and "listening" within a single unit. The gate-tunable positive, negative, and zero photoresponses lead to highly programmable responsivities. This programmability enables the execution of diverse functions, including visual feature extraction, object classification, and sound wave manipulation. These results showcase the potential of expanding perception approaches in neuromorphic devices, opening up new possibilities to craft intelligent and compact hardware systems.

Recent Advances in Low-Dimensional Nanomaterials for Photodetectors

New emerging low-dimensional such as 0D, 1D, and 2D nanomaterials have attracted tremendous research interests in various fields of state-of-the-art electronics, optoelectronics, and photonic applications due to their unique structural features and associated electronic, mechanical, and optical properties as well as high-throughput fabrication for large-area and low-cost production and integration. Particularly, photodetectors which transform light to electrical signals are one of the key components in modern optical communication and developed imaging technologies for whole application spectrum in the daily lives, including X-rays and ultraviolet biomedical imaging, visible light camera, and infrared night vision and spectroscopy. Today, diverse photodetector technologies are growing in terms of functionality and performance beyond the conventional silicon semiconductor, and low-dimensional nanomaterials have been demonstrated as promising potential platforms. In this review, the current states of progress on the development of these nanomaterials and their applications in the field of photodetectors are summarized. From the elemental combination for material design and lattice structure to the essential investigations of hybrid device architectures, various devices and recent developments including wearable photodetectors and neuromorphic applications are fully introduced. Finally, the future perspectives and challenges of the low-dimensional nanomaterials based photodetectors are also discussed.

Multilayer Bolometric Structures for Efficient Wideband Communication Signal Reception

It is known that the dielectric layer (resonator) located behind the conducting plate of the bolometer system can significantly increase its sensitivity near the resonance frequencies. In this paper, the possibility of receiving broadband electromagnetic signals in a multilayer bolometric meta-material made of alternating conducting (e.g., silicon semiconductor) and dielectric layers is demonstrated both experimentally and numerically. It is shown that such a multilayer structure acts as a lattice of resonators and can significantly increase the width of the frequency band of efficient electromagnetic energy absorption. The parameters of the dielectric and semiconductor layers determine the frequency bands. Numerical modeling of the effect has been carried out under the conditions of our experiment. The numerical results show acceptable qualitative agreement with the experimental data. This study develops the previously proposed technique of resonant absorption of electromagnetic signals in bolometric structures.

Multifunctional carbon nitride nanoarchitectures for catalysis

Catalysis is at the heart of modern-day chemical and pharmaceutical industries, and there is an urgent demand to develop metal-free, high surface area, and efficient catalysts in a scalable, reproducible and economic manner. Amongst the ever-expanding two-dimensional materials family, carbon nitride (CN) has emerged as the most researched material for catalytic applications due to its unique molecular structure with tunable visible range band gap, surface defects, basic sites, and nitrogen functionalities. These properties also endow it with anchoring capability with a large number of catalytically active sites and provide opportunities for doping, hybridization, sensitization, etc. To make considerable progress in the use of CN as a highly effective catalyst for various applications, it is critical to have an in-depth understanding of its synthesis, structure and surface sites. The present review provides an overview of the recent advances in synthetic approaches of CN, its physicochemical properties, and band gap engineering, with a focus on its exclusive usage in a variety of catalytic reactions, including hydrogen evolution reactions, overall water splitting, water oxidation, CO2 reduction, nitrogen reduction reactions, pollutant degradation, and organocatalysis. While the structural design and band gap engineering of catalysts are elaborated, the surface chemistry is dealt with in detail to demonstrate efficient catalytic performances. Burning challenges in catalytic design and future outlook are elucidated.

One-step rolling fabrication of VO2 tubular bolometers with polarization-sensitive and omnidirectional detection

Uncooled infrared detection based on vanadium dioxide (VO2) radiometer is highly demanded in temperature monitoring and security protection. The key to its breakthrough is to fabricate bolometer arrays with great absorbance and excellent thermal insulation using a straightforward procedure. Here, we show a tubular bolometer by one-step rolling VO2 nanomembranes with enhanced infrared detection. The tubular geometry enhances the thermal insulation, light absorption, and temperature sensitivity of freestanding VO2 nanomembranes. This tubular VO2 bolometer exhibits a detectivity of ~2 × 108 cm Hz1/2 W-1 in the ultrabroad infrared spectrum, a response time of ~2.0 ms, and a calculated noise-equivalent temperature difference of 64.5 mK. Furthermore, our device presents a workable structural paradigm for polarization-sensitive and omnidirectional light coupling bolometers. The demonstrated overall characteristics suggest that tubular bolometers have the potential to narrow performance and cost gap between photon detectors and thermal detectors with low cost and broad applications.

Direct Induction of Porous Graphene from Mechanically Strong and Waterproof Biopaper for On-Chip Multifunctional Flexible Electronics

Graphene with a 3D porous structure is directly laser-induced on lignocellulosic biopaper under ambient conditions and is further explored for multifunctional biomass-based flexible electronics. The mechanically strong, flexible, and waterproof biopaper is fabricated by surface-functionalizing cellulose with lignin-based epoxy acrylate (LBEA). This composite biopaper shows as high as a threefold increase in tensile strength and excellent waterproofing compared with pure cellulose one. Direct laser writing (DLW) rapidly induces porous graphene from the biopaper in a single step. The porous graphene shows an interconnected carbon network, well-defined graphene domains, and high electrical conductivity (e.g., ≈3 Ω per square), which can be tuned by lignin precursors and loadings as well as lasing conditions. The biopaper in situ embedded with porous graphene is facilely fabricated into flexible electronics for on-chip and paper-based applications. The biopaper-based electronic devices, including the all-solid-state planer supercapacitor, electrochemical and strain biosensors, and Joule heater, show great performances. This study demonstrates the facile, versatile, and low-cost fabrication of multifunctional graphene-based electronics from lignocellulose-based biopaper.

A molecular pyroelectric enabling broadband photo-pyroelectric effect towards self-driven wide spectral photodetection

Broadband spectral photoresponse has shown bright prospects for various optoelectronic devices, while fulfilling high photoactivity beyond the material bandgap is a great challenge. Here, we present a molecular pyroelectric, N-isopropylbenzylaminium trifluoroacetate (N-IBATFA), of which the broadband photo-pyroelectric effects allow for self-driven wide spectral photodetection. As a simple organic binary salt, N-IBATFA possesses a large polarization (~9.5 μC cm-2), high pyroelectric coefficient (~6.9 μC cm-2 K-1) and figures-of-merits (FV = 187.9 × 10-2 cm2 μC-1; FD = 881.5 × 10-5 Pa-0.5) comparable to the state-of-art pyroelectric materials. Particularly, such intriguing attributes endow broadband photo-pyroelectric effect, namely, transient currents covering ultraviolet (UV, 266 nm) to near-infrared (NIR, 1950 nm) spectral regime, which breaks the restriction of its optical absorption and thus allows wide UV-NIR spectral photodetection. Our finding highlights the potential of molecular system as high-performance candidates toward self-powered wide spectral photodetection.

In-sensor computing using a MoS2 photodetector with programmable spectral responsivity

Optical spectroscopy is an indispensable technique in almost all areas of scientific research and industrial applications. After its acquisition, an optical spectrum is usually further processed using a mathematical algorithm to classify or quantify the measurement results. Here we present the design and realization of a smart photodetector that provides such information directly without the need to explicitly record a spectrum. This is achieved by tailoring the spectral responsivity of the device to a specific purpose. In-sensor computation is performed at the lowest possible level of the sensor system hierarchy - the physical level of photon detection - and does not require any external processing of the measurement data. The device can be programmed to cover different types of spectral regression or classification tasks. We present the analysis of spectral mixtures as an example, but the scheme can also be applied to any other algorithm that can be represented by a linear operator. Our prototype physical implementation utilizes an ensemble of optical cavity-enhanced MoS₂ photodetectors with different center wavelengths and individually adjustable peak responsivities. This spectroscopy method represents a significant advance in miniaturized and energy-efficient optical sensing.

Shockproof Deformable Infrared Radiation Sensors Based on a Polymeric Rubber and Organic Semiconductor H2Pc-CNT Composite

Polymeric rubber and organic semiconductor H₂Pc-CNT-composite-based surface- and sandwich-type shockproof deformable infrared radiation (IR) sensors were fabricated using a rubbing-in technique. CNT and CNT-H₂Pc (30:70 wt.%) composite layers were deposited on a polymeric rubber substrate as electrodes and active layers, respectively. Under the effect of IR irradiation (0 to 3700 W/m²), the resistance and the impedance of the surface-type sensors decreased up to 1.49 and 1.36 times, respectively. In the same conditions, the resistance and the impedance of the sandwich-type sensors decreased up to 1.46 and 1.35 times, respectively. The temperature coefficients of resistance (TCR) of the surface- and sandwich-type sensors are 1.2 and 1.1, respectively. The novel ratio of the H₂Pc-CNT composite ingredients and comparably high value of the TCR make the devices attractive for bolometric applications meant to measure the intensity of infrared radiation. Moreover, given their easy fabrication and low-cost materials, the fabricated devices have great potential for commercialization.

Intersubband Transitions in Lead Halide Perovskite-Based Quantum Wells for Mid-Infrared Detectors

Due to their excellent optical and electrical properties as well as versatile growth and fabrication processes, lead halide perovskites have been widely considered as promising candidates for green energy and applications related to optoelectronics. Here, we investigate their potential applications at infrared wavelengths by modeling the intersubband transitions in perovskite-based quantum well systems. Both single-well and double-well structures are studied, and their energy levels as well as the corresponding wave functions and intersubband transition energies are calculated by solving the one-dimensional Schrödinger equations. Via adjustment of the quantum well and barrier thicknesses, the intersubband transition energies can be tuned to cover a broad infrared wavelength range. We also find that the lead halide perovskite-based quantum wells possess high absorption coefficients. The widely tunable transition energies and high absorption coefficients of the perovskite-based quantum well systems, combined with their unique material and electrical properties, may enable an alternative material system for infrared photodetector applications.

Peculiarities of Resonant Absorption of Electromagnetic Signals in Multilayer Bolometric Sensors

We examine the effect of resonant absorption of electromagnetic signals in a silicon semiconductor plasma layer when the dielectric plate is placed behind it both experimentally and numerically. It is shown that such plate acts as a dielectric resonator and can significantly increase the electromagnetic energy absorption in the semiconductor for certain frequencies determined by the dielectric plate parameters. Numerical modelling of the effect is performed under the conditions of conducted experiment. The numerical results are found to be in qualitative agreement with experimental ones. This study confirms the proposed earlier method of increasing the efficiency of bolometric-type detectors of electromagnetic radiation.

Broadband Photoresponses from Ultraviolet to Near-Infrared (II) Region through Light-induced Pyroelectric Effects in a Hybrid Perovskite

Broadband photodetection has shown a great promise for diverse applications, while the realization of plateau photoresponse from ultraviolet (UV) to near-infrared (NIR) spectral region is very challenging. Herein, we exploit photoexcited pyroelectric effect in a chiral hybrid perovskite, (N, N-dimethylcyclohexylammonium)PbBr₃ (1), serving as a new pathway to drive broadband photoactivities. It is a room-temperature pyroelectric with large polarization of ≈6.4 μC cm^-2 and high pyroelectric figure-of-merits (F_V =1.0×10^-2  cm²   μC^-1 and F_D =7.1×10^-5  Pa^-1/2 ). Strikingly, light-induced pyroelectric effect arising from spontaneous polarization is observed in 1, which cover UV (266 nm) to NIR-II (1950 nm) full spectral region. The broadband photoresponses actualized by pyroelectricity break the limit of optical band gap. As the first demonstration of photo-pyroelectricity covering UV-to-NIR spectral region in hybrid perovskites, this work paves a pathway to assemble high-performance smart devices.

Contribution of Sub-Gap States to Broadband Infrared Response in Organic Bulk Heterojunctions

This work studied a series of infrared detectors comprised of organic bulk heterojunctions to explain the origin of their broadband spectral response from the visible to the infrared spanning 1 to 8 μm and the transition from photonic to bolometric operation. Through comparisons of the detector current and the sub-bandgap density of states, the mid- and long-wave infrared response was attributed to charge trap-and-release processes that impact thermal charge generation and the activation energy of charge mobility. We further demonstrate how the sub-bandgap characteristics, mobility activation energy, and effective bandgap are key design parameters for controlling the device temperature coefficient of resistance, which reached up to -7%/K, better than other thin-film materials such as amorphous silicon and vanadium oxide.

Room-temperature plasmonic mid-infrared photodetector based on PtSi/p-Si low Schottky-barrier junction

In this study, a low Schottky-barrier photodetector with a plasmonic assist using a two-dimensional (2D) nanohole array was demonstrated, which receives mid-infrared (MIR) light at room temperature. In the structural design, it was confirmed that the 2D nanohole-array photodetector has high absorbance in the MIR region using rigorous coupled-wave analysis. The result showed that the nanoholes formed in p-type silicon (p-Si), platinum silicide (PtSi), to form Schottky barriers, and gold (Au), for photocurrent extraction, had high absorbance in the MIR region along with the Fabry-Perot resonance mode toward the depth of the nanohole. The 2D nanohole array, with Au/PtSi/p-Si layers, has high absorbance for illuminating MIR light near 3.46 µm from the backside. The current-voltage characteristics indicated a low Schottky barrier of 0.32 eV, confirming the photoresponsive potential in the MIR photodetection. The photocurrent response to the modulation signal was obtained at room temperature. In addition, signal processing through transimpedance and lock-in amplifiers enabled us to obtain characteristics with high linearity for light intensities in milliwatts. Light acquisition for 2.5-3.8-µm-long MIR wavelength became possible, and applications in gas sensing, including vibrational absorption bands of alkane groups, are expected.

Enhanced room-temperature terahertz detection and imaging derived from anti-reflection 2D perovskite layer on MAPbI3 single crystals

Terahertz (THz) detection technology is getting increasing attention from scientists and industries alike due to its superiority in imaging, communication, and defense. Unfortunately, the detection of THz electromagnetic waves under room temperature requires a complicated device architecture design or additional cryogenic cooling units, which increase the cost and complexity of devices, subsequently imposing an impediment in its universal application. In this work, THz detectors operated under room temperature are designed based on the thermoelectric effect with MAPbI₃ single crystals (SCs) as active layers. With solution-processed molecular growth engineering, the anti-reflection 2D perovskite layers were constructed on SCs' surfaces to suppress THz reflection loss. Simultaneously, by finely regulating the main carrier types and the direction of the applied bias across the inclined energy level, the thermoelectric effect is further promoted. As a result, THz-induced ΔT in MAPbI₃ SCs reaches 4.6 °C, while the enhancement in the bolometric and photothermoelectric effects reach ∼4.8 times and ∼16.9 times, respectively. Finally, the devices achieve responsivity of 88.8 μA W^-1 at 0.1 THz under 60 V cm^-1, noise equivalent power (NEP) less than 2.16 × 10^-9 W Hz^-1/2, and specific detectivity (D*) of 1.5 × 10⁸ Jones, which even surpasses the performance of state-of-the-art graphene-based room-temperature THz thermoelectric devices. More importantly, proof-of-concept imaging gives direct evidence of perovskite-based THz sensing in practical applications.

Germanium nanowire microbolometer

Near-infrared detection is widely used for nondestructive and non-contact inspections in various areas, including thermography, environmental and chemical analysis as well as food and medical diagnoses. Common room temperature bolometer-type infrared sensors are based on architectures in theμm range, limiting miniaturization for future highly integrated 'More than Moore' concepts. In this work, we present a first principle study on a highly scalable and CMOS compatible bolometer-type detector utilizing Ge nanowires as the thermal sensitive element. For this approach, we implemented the Ge nanowires on top of a low thermal conducting and highly absorptive membrane as a near infrared (IR) sensor element. We adopted a freestanding membrane coated with an impedance matched platinum absorber demonstrating wavelength independent absorptivity of 50% in the near to mid IR regime. The electrical characteristics of the device were measured depending on temperature and biasing conditions. A strong dependence of the resistance on the temperature was shown with a maximum temperature coefficient of resistance of -0.07 K^-1atT = 100 K. Heat transport simulations using COMSOL were used to optimize the responsivity and temporal response, which are in good agreement with the experimental results. Further, lock-in measurements were used to benchmark the bolometer device at room temperature with respect to detectivity and noise equivalent power. Finally, we demonstrated that by operating the bolometer with a network of parallel nanowires, both detectivity and noise equivalent power can be effectively improved.

Further Advancement of Perovskite Single Crystals

Halide perovskite (HP) single crystals (SCs) are garnering extensive attention as active materials to substitute polycrystalline counterparts in solar cells, photodiodes, and photodetectors, etc. Nevertheless, the large thickness and defect-rich surface results in severe carrier recombination and becomes the major bottleneck for augmented performance. In this perspective, we are looking forward to explaining in detail why the SCs hardly unleash their engrossing potential and introduce two parallel paths for further advancement. First is the modification of thick SCs by reducing the prepared thickness or surface passivation. Second is the large thickness that is conducive to the sufficient absorption of high-energy rays with strong penetrating ability and is beneficial to the thermoelectric effect due to the ultralow thermal conductivity of HPs. These applications provide a roundabout strategy to exploit freestanding SCs with a large thickness. Herein, direct modification and application of thick SCs are systematically introduced, expecting to give rise to the prosperity of HP SCs.

Highly Sensitive and Ultra-Broadband VO2(B) Photodetector Dominated by Bolometric Effect

In this study, Wadsley B phase vanadium oxide (VO₂(B)) with broad-band photoabsorption ability, a large temperature coefficient of resistance (TCR), and low noise was developed for uncooled broad-band detection. By using a freestanding structure and reducing the size of active area, the VO₂(B) photodetector shows stable and excellent performances in the visible to the terahertz region (405 nm to 0.88 mm), with a peak TCR of -4.77% K^-1 at 40 °C, a peak specific detectivity of 6.02 × 10⁹ Jones, and a photoresponse time of 83 ms. A terahertz imaging ability with 30 × 30 pixels was demonstrated. Scanning photocurrent imaging and real-time temperature-photocurrent measurements confirm that a photothermal-type bolometric effect is the dominating mechanism. The study shows the potential of VO₂(B) in applications as a new type of uncooled broad-band photodetection material and the potential to further raise the performance of broad-band photodetectors by structural design.

Recent Advances in Pyroelectric Materials and Applications

As one important subclass of piezoelectric materials, pyroelectric materials have caused increasing attention owing to the unique pyroelectric effect induced by spontaneous polarization, showing broad promising application prospects due to various electrical responses induced by time-dependent temperature variation. This review systematically introduces the pyroelectric effect and evaluation of pyroelectric materials and follows by analyzing and concluding the novel properties corresponding to four kinds of main pyroelectric materials. The emphasis of this review focuses on several significant and practical applications of pyroelectric materials in thermal energy harvesting from the external environment, pyroelectric sensing, and imaging, even some electrochemical applications including hydrogen generation, wastewater treatment, sterilization, and disinfection. Finally, the development direction of pyroelectric materials, potential challenges and opportunities in the future are all discussed and proposed. Through systematical conclusion and analysis of the latest research progress in the recent two decades, this review may provide significant guide and inspiration in the development of pyroelectric materials.

Chip-Scalable, Room-Temperature, Zero-Bias, Graphene-Based Terahertz Detectors with Nanosecond Response Time

The scalable synthesis and transfer of large-area graphene underpins the development of nanoscale photonic devices ideal for new applications in a variety of fields, ranging from biotechnology, to wearable sensors for healthcare and motion detection, to quantum transport, communications, and metrology. We report room-temperature zero-bias thermoelectric photodetectors, based on single- and polycrystal graphene grown by chemical vapor deposition (CVD), tunable over the whole terahertz range (0.1-10 THz) by selecting the resonance of an on-chip patterned nanoantenna. Efficient light detection with noise equivalent powers <1 nWHz^-1/2 and response time ∼5 ns at room temperature are demonstrated. This combination of specifications is orders of magnitude better than any previous CVD graphene photoreceiver operating in the sub-THz and THz range. These state-of-the-art performances and the possibility of upscaling to multipixel architectures on complementary metal-oxide-semiconductor platforms are the starting points for the realization of cost-effective THz cameras in a frequency range still not covered by commercially available microbolometer arrays.

Hybrid System Combining Two-Dimensional Materials and Ferroelectrics and Its Application in Photodetection

Photodetectors are one of the most important components for a future "Internet-of-Things" information society. Compared to the mainstream semiconductor-based photodetectors, emerging devices based on two-dimensional (2D) materials and ferroelectrics as well as their hybrid systems have been extensively studied in recent decades due to their outstanding performances and related interesting physical, electrical, and optoelectronic phenomena. In this paper, we review the photodetection based on 2D materials and ferroelectric hybrid systems. The fundamentals of 2D and ferroelectric materials as well as the interaction in the hybrid system will be introduced. Ferroelectricity modulated optoelectronic properties in the hybrid system will be discussed in detail. After the basics and figures of merit of photodetectors are summarized, the 2D-ferroelectrics devices with different structures including p-n diodes, Schottky diodes, and field-effect transistors will be reviewed and compared. The polarization of ferroelectrics offers the possibility of the modulation and enhancement of the photodetection in the hybrid detectors, which will be discussed in depth. Finally, the challenges and perspectives of the photodetectors based on 2D ferroelectrics will be proposed. This Review outlines the important aspects of the recent development of the hybrid system of 2D and ferroelectric materials, which could interact with each other and thus lead to photodetectors with higher performances. Such a Review will be helpful for the research of emerging physical phenomena and for the design of multifunctional nanoscale electronic and optoelectronic devices.

Graphene oxide and polydimethylsiloxane coated quartz tuning fork for improved sensitive near- and mid-infrared detection

Sensitive and broadband infrared sensors are required for security and medical applications, as few can rapidly and sensitively detect infrared without uncooled devices. Here, we report a wideband optical-detection strategy based on the thermoelastic effect of a coating-enhanced quartz tuning fork (QTF) and study the feasibility of using an atomic force probe operating in contact mode to monitor the vibration. Graphene oxide (GO) and polydimethylsiloxane (PDMS) coating were applied on the QTF's surface to improve the light absorption and the thermal-mechanical conversion efficiency. Experimental results showed that the bi-layer coatings yielded a maximum gain factor of 8 in response amplitude and signal-to-noise ratio (SNR) than that of a bare QTF, respectively. Lasers with wavelengths of 1512 nm and 10.6 µm were used as the typical representative light source to test the photoresponse of the QTF detector. The device displays a broadband photoresponse covering the near-infrared to mid-infrared range at room temperature, high performance with the maximum photoresponsivity of 85.76 V·mW^-1, and 1σ detection limit of 0.056 µW; the lowest noise equivalent power (NEP) of 1.35 nW·Hz^-1/2 and 43.9 ms response speed is also achieved. The preparation process of detector is simple and easy to implement; the resulting device exhibits high responsivity and wide wavelength response ranging at least from 1512 to 10600 nm, compared with custom QTF; and the surface coating strategy potentially enables the construction of a new class of low-cost photodetection sensors operated at room temperature.

Optoelectronic mixing with high-frequency graphene transistors

Graphene is ideally suited for optoelectronics. It offers absorption at telecom wavelengths, high-frequency operation and CMOS-compatibility. We show how high speed optoelectronic mixing can be achieved with high frequency (~20 GHz bandwidth) graphene field effect transistors (GFETs). These devices mix an electrical signal injected into the GFET gate and a modulated optical signal onto a single layer graphene (SLG) channel. The photodetection mechanism and the resulting photocurrent sign depend on the SLG Fermi level (E_F). At low E_F (<130 meV), a positive photocurrent is generated, while at large E_F (>130 meV), a negative photobolometric current appears. This allows our devices to operate up to at least 67 GHz. Our results pave the way for GFETs optoelectronic mixers for mm-wave applications, such as telecommunications and radio/light detection and ranging (RADAR/LIDARs.).

2D Nanomaterials for Effective Energy Scavenging

The development of a nation is deeply related to its energy consumption. 2D nanomaterials have become a spotlight for energy harvesting applications from the small-scale of low-power electronics to a large-scale for industry-level applications, such as self-powered sensor devices, environmental monitoring, and large-scale power generation. Scientists from around the world are working to utilize their engrossing properties to overcome the challenges in material selection and fabrication technologies for compact energy scavenging devices to replace batteries and traditional power sources. In this review, the variety of techniques for scavenging energies from sustainable sources such as solar, air, waste heat, and surrounding mechanical forces are discussed that exploit the fascinating properties of 2D nanomaterials. In addition, practical applications of these fabricated power generating devices and their performance as an alternative to conventional power supplies are discussed with the future pertinence to solve the energy problems in various fields and applications.

Collective input impedance of micro-antenna based infrared detectors

In this article, the author leverages the concept of "input impedance" to determine in a proper manner the collective resonances of infrared devices based on square arrays of micro-dipoles, commonly obtained by the scattered field of devices under illumination. With the aid of finite-element simulations, the resistive and capacitive nature of the odd and even resonant modes of individual micro-dipoles is first unveiled. Subsequently, the micro-dipoles are incorporated into an array with lattice parameters (a_x, ay), and the dependence of the emerging collective odd and even resonant modes, on the transverse and longitudinal dipolar interaction, is evaluated. The opposite wavelength shift of these modes is unveiled and the physical mechanisms behind their behavior are discussed. By analyzing the absorbance spectra of the micro-antenna arrays, the equivalence of optical resonances counterpart, in the short and open-circuit configurations, with the odd and even modes is presented. Finally, the effect on the array's performance that results from introducing highly resistive nano-bolometers is optimized by exploiting the natural high-resistance of the collective even modes.

Plasmonic antenna coupling to hyperbolic phonon-polaritons for sensitive and fast mid-infrared photodetection with graphene

Integrating and manipulating the nano-optoelectronic properties of Van der Waals heterostructures can enable unprecedented platforms for photodetection and sensing. The main challenge of infrared photodetectors is to funnel the light into a small nanoscale active area and efficiently convert it into an electrical signal. Here, we overcome all of those challenges in one device, by efficient coupling of a plasmonic antenna to hyperbolic phonon-polaritons in hexagonal-BN to highly concentrate mid-infrared light into a graphene pn-junction. We balance the interplay of the absorption, electrical and thermal conductivity of graphene via the device geometry. This approach yields remarkable device performance featuring room temperature high sensitivity (NEP of 82 pW[Formula: see text]) and fast rise time of 17 nanoseconds (setup-limited), among others, hence achieving a combination currently not present in the state-of-the-art graphene and commercial mid-infrared detectors. We also develop a multiphysics model that shows very good quantitative agreement with our experimental results and reveals the different contributions to our photoresponse, thus paving the way for further improvement of these types of photodetectors even beyond mid-infrared range.

Graphene-based temperature sensors suspended by anodic aluminum oxide

In this paper, we investigate the substrate effect in graphene temperature sensors. Recently, there have been many research studies done on temperature sensors using the nanofabrication technique. However, the sensitivity and response time need to be improved. In this study, we propose a new type of temperature sensor that consists of graphene and Anodic Aluminum Oxide (AAO). In this device, graphene and AAO are used as the sensing material and the substrate, respectively. We characterize the sensitivity and the response time using the experimental results and simulation data. The real-time resistance change of graphene is monitored depending on the temperature, and the response time is also analyzed by COMSOL Multiphysics. To confirm the porous substrate effect, we compare the device performance of the AAO substrate to the performance of the glass substrate. From these results, the suspended graphene on the AAO substrate shows about two times higher sensitivity and a much faster response time than the glass substrate.

Conjuncted photo-thermoelectric effect in ZnO-graphene nanocomposite foam for self-powered simultaneous temperature and light sensing

The self-powered sensors are more and more important in current society. However, detecting both light and temperature signals simultaneously without energy waste and signal interference is still a challenge. Here, we report a ZnO/graphene nanocomposite foam-based self-powered sensor, which can realize the simultaneous detection of light and temperature by using the conjuncted photo-thermoelectric effect in ZnO-graphene nanocomposite foam sensor. The output current under light, heating and cooling of the device with the best ZnO/graphene ratio (8:1) for the foam can reach 1.75 µA, 1.02 µA and 0.70 µA, respectively, which are approximately three fold higher than them of devices with other ZnO/graphene ratios. The ZnO-graphene nanocomposite foam device also possesses excellent thermoelectric and photoelectric performances for conjuncted lighting and heating detection without mutual interference. The ZnO-graphene nanocomposite foam device exhibits a new designation on the road towards the fabrication of low cost and one-circuit-based multifunction sensors and systems.

Infrared photodetector sensitized by InAs quantum dots embedded near an Al0.3Ga0.7As/GaAs heterointerface

Mid-infrared sensors detect infrared radiation emitted from objects, and are actually widely used for monitoring gases and moisture as well as for imaging objects at or above room temperature. Infrared photodetectors offer fast detection, but many devices cannot provide high responsivity at room temperature. Here we demonstrate infrared sensing with high responsivity at room temperature. The central part of our device is an Al_0.3Ga_0.7As/GaAs heterostructure containing InAs quantum-dot (QD) layer with a 10-nm-thick GaAs spacer. In this device, the electrons that have been accumulated at the heterointerface are transferred to the conduction band of the Al_0.3Ga_0.7As barrier by absorbing infrared photons and the following drift due to the electric field at the interface. These intraband transitions at the heterointerface are sensitized by the QDs, suggesting that the presence of the QDs increases the strength of the intraband transition near the heterointerface. The room-temperature responsivity spectrum exhibits several peaks in the mid-infrared wavelength region, corresponding to transitions from the InAs QD and wetting layer states as well as the transition from the quantized state of the triangular potential well at the two-dimensional heterointerface. We find that the responsivity is almost independent of the temperature and the maximum value at 295 K is 0.8 A/W at ~ 6.6 µm for a bias of 1 V, where the specific detectivity is \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$1.8\times {10}^{10}$$\end{document}1.8×1010 cmHz^1/2/W.

Graphene Hybrid Structures for Integrated and Flexible Optoelectronics

Graphene (Gr) has many unique properties including gapless band structure, ultrafast carrier dynamics, high carrier mobility, and flexibility, making it appealing for ultrafast, broadband, and flexible optoelectronics. To overcome its intrinsic limit of low absorption, hybrid structures are exploited to improve the device performance. Particularly, van der Waals heterostructures with different photosensitive materials and photonic structures are very effective for improving photodetection and modulation efficiency. With such hybrid structures, Gr hybrid photodetectors can operate from ultraviolet to terahertz, with significantly improved R (up to 10⁹ A W^-1 ) and bandwidth (up to 128 GHz). Furthermore, integration of Gr with silicon (Si) complementary metal-oxide-semiconductor (CMOS) circuits, the human body, and soft tissues is successfully demonstrated, opening promising opportunities for wearable sensors and biomedical electronics. Here, the recent progress in using Gr hybrid structures toward high-performance photodetectors and integrated optoelectronic applications is reviewed.

On-Chip Ultrafast Plasmonic Graphene Hot Electron Bolometric Photodetector

We investigate a waveguide-integrated plasmonic graphene photodetector operating based on the hot carrier photo-bolometric effect, which is characterized simultaneously by high responsivity on the scale of hundreds of A/W and high speed on the scale of 100's of GHz that is limited only by the product of the electronic heat capacitance and thermal resistance. We develop a theory of the bolometric effect originating from the band nonparabolicity of graphene and estimate responsivity due to the bolometric effect, which is shown to significantly surpass the responsivity of the coexisting photoconductive effect, thus convincingly demonstrating the dominance of the bolometric effect. Based on the theory, we propose a novel detector configuration based on a hybrid waveguide that allows for efficient absorption in graphene over a short distance and subsequently a large change of conductivity. The results demonstrate the potential of graphene for high-speed communication systems.

Breaking symmetry in device design for self-driven 2D material based photodetectors

The advent of graphene and other two-dimensional (2D) materials offers great potential for optoelectronic applications. Various device structures and novel mechanisms have been proposed to realize photodetectors with unique detecting properties. In this minireview, we focus on a self-driven photodetector that has great potential for low-power or even powerless operation required in the internet of things and wearable electronics. To address the general principle of self-driven properties, we propose and elaborate the concept of symmetry breaking in 2D material based self-driven photodetectors. We discuss various mechanisms of breaking symmetry for self-driven photodetectors, including asymmetrical contact engineering, field-induced asymmetry, PN homojunctions, and PN heterostructures. Typical device examples based on these mechanisms are reviewed and compared. The performance of current self-driven photodetectors is critically assessed and future directions are discussed towards the target application fields.

Photoninduced charge redistribution of graphene determined by edge structures in the infrared region

By using the ab initio density-functional theory method, we investigated the charge redistribution of monolayer graphene with ZigZag and/or ArmChair edges upon infrared excitation. The photoinduced charge redistribution is strongly dependent on edge types. The priority of electrons transfer has been revealed by charge density difference. To further investigate the influence of edge types on optical properties, the dielectric constants and absorption coefficient of graphene with various edge types have been calculated. The edge types have a non-negligible influence on optical properties of graphene, and the Zigzag edge graphene owns stronger optical absorption in infrared region. Our results are potentially beneficial for designing graphene nanodevices in the infrared region.

Spray Coating of Two-Dimensional Suspended Film of Vanadium Oxide-Coated Carbon Nanotubes for Fabrication of a Large Volume Infrared Bolometer

A novel spray coating and transfer method is developed for fabricating a suspended bolometer of vanadium oxide-coated multiwalled carbon nanotubes (VCNTs). A parametric study was performed to evaluate the effect of the substrate, modulation frequency, and temperature on the bolometric performance and revealed that the performance of the bolometer solely does not depend on the substrate parameter but modulation frequency and bias current as a function of temperature also play a key attribute. The TCR (temperature coefficient of resistance) of the suspended VCNT bolometer is ∼-0.41%/K which is ∼486% higher than the reported suspended multiwalled CNTs at 300 K. Moreover, the suspended bolometer has a voltage responsivity of ∼67.42 ± 5.46 V/W (∼7.68 times that of unsuspended) at 200 K. Thus, the study presents an efficient method to develop the suspended bolometer that has not been realized so far to obtain much higher TCR and responsivity.

Highly Sensitive Graphene/Polydimethylsiloxane Composite Films near the Threshold Concentration with Biaxial Stretching

Uniformly dispersed graphene effectively improves the strain-sensing capability of the composite film under a low graphene load in nanocomposites prepared with polydimethylsiloxane (PDMS) and graphene (GNP) monolayer powder. The threshold concentration of graphene was determined by loading nanocomposites at different temperatures. For different concentrations, when using traditional uniaxial stretching, the rate of resistance change of films near the threshold concentration is five times higher than the rate of films with a high concentration. Compared with traditional uniaxial stretching, the biaxial stretching we introduced can effectively improve the sensitivity of the film by an order of magnitude. The change in the resistance of the film near the threshold concentration is due to the change of the tunnel length and the cross-section of the tunnel, whereas the high concentration of the film is due to the change of the conductive path inside the film. Biaxial stretching has different effects on films with different concentrations, but the final effect of increasing sensitivity is the same. This study provides guidance for improving the strain-sensing sensitivity of GNP/PDMS composite films and the application of biaxial tension in detecting human motions.

Large-Area and Broadband Thermoelectric Infrared Detection in a Carbon Nanotube Black-Body Absorber

Room-temperature mid- and far-infrared photodetectors and energy harvesters meet diverse upcoming demands including health condition monitoring, industrial inspection, and miniaturized power-source for Internet of Things. However, the cryogenic cooling requirement for III-V semiconductors and the inefficient light absorption in two-dimensional (2D) materials, for example, graphene (2.3%) and black phosphorus (∼3%), have hindered mid- and far-infrared optoelectronics from widespread applications. Here, we demonstrate a self-powered infrared photodetector as well as energy harvester via employing vertical photothermoelectric (PTE) effect of a carbon nanotube forest (CNTF). In the self-assembled anti-reflecting CNTF, 99.4% reflection suppression is observed, resulting in a broadband detectivity of 1.9 × 10⁷ cm Hz^1/2 in 2.5-25 μm spectral range and peak detectivity of 2.3 × 10⁹ cm Hz^1/2 at 4.3 THz via nonlithography fabrication. By virtue of vertical architecture, this photodetector exhibits enhanced sensitivity to weak and unfocused infrared illumination, which mitigates the high actuating power density in conventional PTE or field-effect detectors and renders practical infrared detection in the real life.

Simulation of tuning graphene plasmonic behaviors by ferroelectric domains for self-driven infrared photodetector applications

We demonstrate a tunable longwave infrared photodetector with ultra-high sensitivity based on graphene surface plasmon polaritons controlled by ferroelectric domains. The simulated results show that the photodetector shows a tunable absorption peak, modulated by periodically polarized ferroelectric domains at the nanoscale, with an ultra-high responsivity up to 7.62 × 10⁶ A W^-1 and a detectivity of ∼6.24 × 10¹³ Jones (Jones = cm Hz^1/2 W^-1) in the wavelengths ranging from 5 to 20 μm at room temperature. The potential mechanism for the prominent performances of the proposed photodetector can be attributed to the highly confined graphene surface plasmons excited by the local electrical field across the interface of the graphene and ferroelectric layer resonant to the incident wavelength, which could be easily controlled by the features of the ferroelectric domains. Compared with the silicon-based graphene plasmonic photodetector using a complex process of micro-nano fabrication, the proposed photodetector provides the advantages of a more convenient and controllable technique without the need for patterning graphene, and lower energy consumption due to the non-volatile properties of the ferroelectrics without an additional contact electrode. The tunable spectral response and the ultra-high responsivity make the graphene plasmonic photodetector tuned by the ferroelectric domains promising in practical applications of micro-spectrometers and other light sensing devices.

Waveguide-Integrated, Plasmonic Enhanced Graphene Photodetectors

We present a micrometer-scale, on-chip integrated, plasmonic enhanced graphene photodetector (GPD) for telecom wavelengths operating at zero dark current. The GPD is designed to directly generate a photovoltage by the photothermoelectric effect. It is made of chemical vapor deposited single layer graphene, and has an external responsivity ∼12.2 V/W with a 3 dB bandwidth ∼42 GHz. We utilize Au split-gates to electrostatically create a p-n-junction and simultaneously guide a surface plasmon polariton gap-mode. This increases the light-graphene interaction and optical absorption and results in an increased electronic temperature and steeper temperature gradient across the GPD channel. This paves the way to compact, on-chip integrated, power-efficient graphene based photodetectors for receivers in tele- and datacom modules.

Size effects in the resistivity of graphene nanoribbons

The electrical resistivity of single-layer graphene nanoribbons has been studied experimentally for ribbon widths from 16 to 320 nm and is shown to validate the expected quantum scattering model for conduction through confined graphene structures. The experimental findings are that the resistivity follows a more dramatic trend than that seen for metallic nanowires of similar dimensions, due to a combination of the nature of the charge carriers in this 2D material, surface scattering from the edges, bandgap related effects and shifts in the Fermi level due to edge effects. We show that the charge neutrality point switches polarity below a ribbon width of around 50 nm, and that at this point, the thermal coefficient of resistance is a maximum. The majority doping type therefore can be controlled by altering ribbon width below 100 nm. We also demonstrate that an alumina passivation layer has a significant effect on the mean free path of the charge carriers within the graphene, which can be probed directly via measurements of the width-dependent resistivity.

Bolometric Effect in Bi2 O2 Se Photodetectors

Bi₂ O₂ Se is emerging as a photosensitive functional material for optoelectronics, and its photodetection mechanism is mostly considered to be a photoconductive regime in previous reports. Here, the bolometric effect is discovered in Bi₂ O₂ Se photodetectors. The coexistence of photoconductive effect and bolometric effect is generally observed in multiwavelength photoresponse measurements and then confirmed with microscale local heating experiments. The unique photoresponse of Bi₂ O₂ Se photodetectors may arise from a change of hot electrons during temperature rises instead of photoexcited holes and electrons. Direct proof of the bolometric effect is achieved by real-time temperature tracking of Bi₂ O₂ Se photodetectors under time evolution after light excitation. Moreover, the Bi₂ O₂ Se bolometer shows a high temperature coefficient of resistance (-1.6% K^-1 ), high bolometric coefficient (-31 nA K^-1 ), and high bolometric responsivity (>320 A W^-1 ). These findings offer a new approach to develop bolometric photodetectors based on Bi₂ O₂ Se layered materials.

Highly Sensitive, Fast Graphene Photodetector with Responsivity >106 A/W Using a Floating Quantum Well Gate

Graphene, owing to its zero-band-gap electronic structure, is promising as an absorption material for ultra-wideband photodetection applications. However, graphene-absorption-based detectors inherently suffer from poor responsivity because of weak absorption and fast photocarrier recombination, limiting their viability for low-intensity light detection. Here, we use a graphene/WS₂/MoS₂ vertical heterojunction to demonstrate a highly sensitive photodetector, where the graphene layer serves dual purposes, namely, as the light absorption layer and also as the carrier conduction channel, thus maintaining the broadband nature of the photodetector. A fraction of the photoelectrons in graphene encounter ultrafast interlayer transfer to a floating monolayer MoS₂ quantum well, providing a strong quantum-confined photogating effect. The photodetector shows a responsivity of 4.4 × 10⁶ A/W at 30 fW incident power, outperforming photodetectors reported till date where graphene is used as a light absorption material by several orders. In addition, the proposed photodetector exhibits an extremely low noise equivalent power of <4 fW/ Hz and a fast response (∼milliseconds) with zero reminiscent photocurrent. The findings are attractive toward the demonstration of a graphene-based highly sensitive, fast, broadband photodetection technology.

Mini Review on Flexible and Wearable Electronics for Monitoring Human Health Information

The application potential of wearable electronics in the healthcare field has been of great interest over the past several decades. Flexible and wearable devices based on skin-friendly soft elastic materials can be snugly attached to the surface of human skin, so that a series of vital health information such as wrist pulse, body temperature, and blood glucose can be extracted and analyzed to help the patient maintain physical fitness. Here, we outlined the most common types of wearable electronics for monitoring human health information, including force sensors, temperature sensors, physiological biochemical sensors, and multifunctional sensors. Their general working principles and structural innovations are reviewed. Then, we discussed two functional modules that make the wearable sensors more applicable in real life-self-powered module and signal processing module. The challenges and future research directions are also proposed to develop wearable electronics for monitoring human health information.

Semimetallic Graphene for Infrared Sensing

Both photothermal and photovoltaic infrared (IR) detectors employ sensing materials that have an optical band gap. Different from these conventional materials, graphene has a conical band structure that imposes zero band gap. In this study, using the semimetallic multilayer graphene, IR detection at room temperature is realized. The relatively high Seebeck coefficient, ranging from 40 to 60 μV/K, compared to that of the metal, and the large optical absorption in the mid-IR region, in the wavelength range of 7-17 μm, enable graphene to detect IR without an absorber, which is essential for most IR detectors because the band gap of the sensing materials is much larger than the energy of IR and the incident IR can be absorbed directly by the sensing material. Thus, the incident IR can be absorbed directly by the sensing material in our device. The developed detector with a SiN membrane shows high responsivity and detectivity, which are 140 V/W and 5 × 10⁸ cm·Hz^1/2/W at 5 Hz, respectively. In addition, the IR sensor shows a response time of 600 μs. In the room-temperature operation of the IR sensor array without cooling, our sensors detect IR emitted from a human body and track the movement. The availability of large-area graphene in current technology opens new applications for metallic two-dimensional materials and a possibility for scale-up.

Near-zero temperature coefficient of resistance of hybrid resistor fabricated with carbon nanotube and metal alloy

A hybrid resistor has been fabricated by parallely connecting carbon nanotube (CNT) fiber with negative temperature coefficient of resistance (TCR) and metal alloy with positive TCR to achieve near zero TCR. The CNT fibers were prepared by yarning CNTs grown on the silicone substrate by chemical vapor deposition (CVD) method. The CNT fiber resistors were fabricated by winding CNT fiber on the ceramic rod. Metal terminals were connected at both ends of the CNT fiber wound on the ceramic rod. The metal alloy resistors were fabricated with copper (Cu) and nickel (Ni) with different weight compositions. Electrical resistance and thermal stability (in terms of TCR in this work) of the CNT fiber resistors, the metal alloy resistors, and the hybrid resistors were measured as 7.94 Ω and -870 ppm/°C, 7.94 Ω and 1100 ppm/°C, and 3.97 Ω and -2 ppm/°C, respectively. In case of parallelly connected resistors with suitable combination, the resistance was lower than that of resistor with lower value, and the TCR approached to near zero. Finally, we propose a theoretical approach for adjusting resistance and TCR of the hybrid resistor composed of metal alloy and CNT fibers.