Blackbody-sensitive room-temperature infrared photodetectors based on low-dimensional tellurium grown by chemical vapor deposition

Cytoskeleton-modulating nanomaterials and their therapeutic potentials

The cytoskeleton, an intricate network of protein fibers within cells, plays a pivotal role in maintaining cell shape, enabling movement, and facilitating intracellular transport. Its involvement in various pathological states, ranging from cancer proliferation and metastasis to the progression of neurodegenerative disorders, underscores its potential as a target for therapeutic intervention. The exploration of nanotechnology in this realm, particularly the use of nanomaterials for cytoskeletal modulation, represents a cutting-edge approach with the promise of novel treatments. Inorganic nanomaterials, including those derived from gold, metal oxides, carbon, and black phosphorus, alongside organic variants such as peptides and proteins, are at the forefront of this research. These materials offer diverse mechanisms of action, either by directly interacting with cytoskeletal components or by influencing cellular signaling pathways that, in turn, modulate the cytoskeleton. Recent advancements have introduced magnetic field-responsive and light-responsive nanomaterials, which allow for targeted and controlled manipulation of the cytoskeleton. Such precision is crucial in minimizing off-target effects and enhancing therapeutic efficacy. This review explores the importance of research into cytoskeleton-targeting nanomaterials for developing therapeutic interventions for a range of diseases. It also addresses the progress made in this field, the challenges encountered, and future directions for using nanomaterials to modulate the cytoskeleton. The continued exploration of nanomaterials for cytoskeleton modulation holds great promise for advancing therapeutic strategies against a broad spectrum of diseases, marking a significant step forward in the intersection of nanotechnology and medicine.

High-Sensitive Uncooled Mid-Wave Infrared Detector Based on TiS3 Nanoribbon

High-sensitive uncooled mid-wave infrared (MWIR) photodetection with fast speed is highly desired for biomedical imaging, optical communication, and night vision technology. Low-dimensional materials with low dark current and broadband photoresponse hold great promise for use in MWIR detection. Here, this study reports a high-performance MWIR photodetector based on a titanium trisulfide (TiS3) nanoribbon. This device demonstrates an ultra-broadband photoresponse ranging from the visible spectrum to the MWIR spectrum (405-4275 nm). In the MWIR spectral range, the photodetector achieves competitive high photoresponsivity (R) of 21.1 A W-1, and an impressive specific detectivity (D*) of 5.9 × 1010 cmHz1/2 W-1 in ambient air. Remarkably, the photoresponse speed in the MWIR with τr = 1.3 ms and τd = 1.5 ms is realized which is much faster than the thermal time constant of 15 ms. These findings pave the way for highly sensitive, room-temperature MWIR photodetectors with exceptionally fast response speed.

Spectrum-Dependent Image Convolutional Processing via a Two-Dimensional Polarization-Sensitive Photodetector

Currently, the improvement in the processing capacity of traditional processors considerably lags behind the demands of real-time image processing caused by the advancement of photodetectors and the widespread deployment of high-definition image sensors. Therefore, achieving real-time image processing at the sensor level has become a prominent research domain in the field of photodetector technology. This goal underscores the need for photodetectors with enhanced multifunctional integration capabilities than can perform real-time computations using optical or electrical signals. In this study, we employ an innovative p-type semiconductor GaTe0.5Se0.5 to construct a polarization-sensitive wide-spectral photodetector. Leveraging the wide-spectral photoresponse, we realize three-band imaging within a wavelength range of 390-810 nm. Furthermore, real-time image convolutional processing is enabled by configuring appropriate convolution kernels based on the polarization-sensitive photocurrents. The innovative design of the polarization-sensitive wide-spectral GaTe0.5Se0.5-based photodetector represents a notable contribution to the domain of real-time image perception and processing.

Electrically Tunable Multiple-Effects Synergistic and Boosted Photoelectric Performance in Te/WSe2 Mixed-Dimensional Heterojunction Phototransistors

Mix-dimensional heterojunctions (MDHJs) photodetectors (PDs) built from bulk and 2D materials are the research focus to develop hetero-integrated and multifunctional optoelectronic sensor systems. However, it is still an open issue for achieving multiple effects synergistic characteristics to boost sensitivity and enrich the prospect in artificial bionic systems. Herein, electrically tunable Te/WSe2 MDHJs phototransistors are constructed, and an ultralow dark current below 0.1 pA and a large on/off rectification ratio of 106 is achieved. Photoconductive, photovoltaic, and photo-thermoelectric conversions are simultaneously demonstrated by tuning the gate and bias. By these synergistic effects, responsivity and detectivity respectively reach 13.9 A W-1 and 1.37 × 1012 Jones with 400 times increment. The Te/WSe2 MDHJs PDs can function as artificial bionic visual systems due to the comparable response time to those of the human visual system and the presence of transient positive and negative response signals. This work offers an available strategy for intelligent optoelectronic devices with hetero-integration and multifunctions.

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.

High-Performance Visible to Mid-Infrared Photodetectors Based on HgTe Colloidal Quantum Dots under Room Temperature

HgTe colloidal quantum dots (CQDs) are one of few materials that can realize near-to-midwave infrared photodetection. And the quality of HgTe CQD directly affects the performance of photodetection. In this work, we optimize the method of synthesizing HgTe CQDs to reduce the defect concentration, therefore improving the photoelectric properties. The photodetector based on HeTe CQD can respond to the light from the visible to mid-infrared band. Notably, a photoresponse to 4000 nm light at room temperature is realized. The responsivity and detectivity are 90.6 mA W-1 and 6.9 × 107 Jones under 1550 nm light illumination, which are better than these of most reported HgTe CQD photodetectors. The response speed reaches a magnitude of microseconds with a rising time of τr = 1.9 μs and a falling time of τf = 1.5 μs at 10 kHz under 1550 nm light illumination.

Anisotropic Te/PdSe2 Van Der Waals Heterojunction for Self-Powered Broadband and Polarization-Sensitive Photodetection

Polarization-sensitive broadband optoelectronic detection is crucial for future sensing, imaging, and communication technologies. Narrow bandgap 2D materials, such as Te and PdSe2, show promise for these applications, yet their polarization performance is limited by inherent structural anisotropies. In this work, a self-powered, broadband photodetector utilizing a Te/PdSe2 van der Waals (vdWs) heterojunction, with orientations meticulously tailored is introduced through polarized Raman optical spectra and tensor calculations to enhance linear polarization sensitivity. The device exhibits anisotropy ratios of 1.48 at 405 nm, 3.56 at 1550 nm, and 1.62 at 4 µm, surpassing previously-reported photodetectors based on pristine Te and PdSe2. Additionally, it exhibits high responsivity (617 mA W-1 at 1550 nm), specific detectivity (5.27 × 1010 Jones), fast response (≈4.5 µs), and an extended spectral range beyond 4 µm. The findings highlight the significance of orientation-engineered heterostructures in enhancing polarization-sensitive photodetectors and advancing optoelectronic technology.

Surfactant-Free Ultrasonication-Assisted Synthesis of 2d Tellurium Based on Metastable 1T'-MoTe2

Elemental 2D materials (E2DMs) have been attracting considerable attention owing to their chemical simplicity and excellent/exotic properties. However, the lack of robust chemical synthetic methods seriously limits their potential. Here, a surfactant-free liquid-phase synthesis of high-quality 2D tellurium is reported based on ultrasonication-assisted exfoliation of metastable 1T'-MoTe2. The as-grown 2D tellurium nanosheets exhibit excellent single crystallinity, ideal 2D morphology, surfactant-free surface, and negligible 1D by-products. Furthermore, a unique growth mechanism based on the atomic escape of Te atoms from metastable transition metal dichalcogenides and guided 2D growth in the liquid phase is proposed and verified. 2D tellurium-based field-effect transistors show ultrahigh hole mobility exceeding 1000 cm2 V-1 s-1 at room temperature attributing to the high crystallinity and surfactant-free surface, and exceptional chemical and operational stability using both solid-state dielectric and liquid-state electrical double layer. The facile ultrasonication-assisted synthesis of high-quality 2D tellurium paves the way for further exploration of E2DMs and expands the scope of liquid-phase exfoliation (LPE) methodology toward the controlled wet-chemical synthesis of functional nanomaterials.

Recent Advances in Broadband Photodetectors from Infrared to Terahertz

The growing need for the multiband photodetection of a single scene has promoted the development of both multispectral coupling and broadband detection technologies. Photodetectors operating across the infrared (IR) to terahertz (THz) regions have many applications such as in optical communications, sensing imaging, material identification, and biomedical detection. In this review, we present a comprehensive overview of the latest advances in broadband photodetectors operating in the infrared to terahertz range, highlighting their classification, operating principles, and performance characteristics. We discuss the challenges faced in achieving broadband detection and summarize various strategies employed to extend the spectral response of photodetectors. Lastly, we conclude by outlining future research directions in the field of broadband photodetection, including the utilization of novel materials, artificial microstructure, and integration schemes to overcome current limitations. These innovative methodologies have the potential to achieve high-performance, ultra-broadband photodetectors.

Touchless Thermosensation Enabled by Flexible Infrared Photothermoelectric Detector for Temperature Prewarning Function of Electronic Skin

Artificial skin, endowed with the capability to perceive thermal stimuli without physical contact, will bring innovative interactive experiences into smart robotics and augmented reality. The implementation of touchless thermosensation, responding to both hot and cold stimuli, relies on the construction of a flexible infrared detector operating in the long-wavelength infrared range to capture the spontaneous thermal radiation. This imposes rigorous requirements on the photodetection performance and mechanical flexibility of the detector. Herein, a flexible and wearable infrared detector is presented, on basis of the photothermoelectric coupling of the tellurium-based thermoelectric multilayer film and the infrared-absorbing polyimide substrate. By suppressing the optical reflection loss and aligning the destructive interference position with the absorption peak of polyimide, the fabricated thermopile detector exhibits high sensitivity to the thermal radiation over a broad source temperature range from -50 to 110 °C, even capable of resolving 0.05 °C temperature change. Spatially resolved radiation distribution sensing is also achieved by constructing an integrated thermopile array. Furthermore, an established temperature prewarning system is demonstrated for soft robotic gripper, enabling the identification of noxious thermal stimuli in a contactless manner. A feasible strategy is offered here to integrate the infrared detection technique into the sensory modality of electronic skin.

Synergistic-potential engineering enables high-efficiency graphene photodetectors for near- to mid-infrared light

High quantum efficiency and wide-band detection capability are the major thrusts of infrared sensing technology. However, bulk materials with high efficiency have consistently encountered challenges in integration and operational complexity. Meanwhile, two-dimensional (2D) semimetal materials with unique zero-bandgap structures are constrained by the bottleneck of intrinsic quantum efficiency. Here, we report a near-mid infrared ultra-miniaturized graphene photodetector with configurable 2D potential well. The 2D potential well constructed by dielectric structures can spatially (laterally and vertically) produce a strong trapping force on the photogenerated carriers in graphene and inhibit their recombination, thereby improving the external quantum efficiency (EQE) and photogain of the device with wavelength-immunity, which enable a high responsivity of 0.2 A/W-38 A/W across a broad infrared detection band from 1.55 to 11 µm. Thereafter, a room-temperature detectivity approaching 1 × 109 cm Hz1/2 W-1 is obtained under blackbody radiation. Furthermore, a synergistic effect of electric and light field in the 2D potential well enables high-efficiency polarization-sensitive detection at tunable wavelengths. Our strategy opens up alternative possibilities for easy fabrication, high-performance and multifunctional infrared photodetectors.

From Material to Cameras: Low-Dimensional Photodetector Arrays on CMOS

The last two decades have witnessed a dramatic increase in research on low-dimensional material with exceptional optoelectronic properties. While low-dimensional materials offer exciting new opportunities for imaging, their integration in practical applications has been slow. In fact, most existing reports are based on single-pixel devices that cannot rival the quantity and quality of information provided by massively parallelized mega-pixel imagers based on complementary metal-oxide semiconductor (CMOS) readout electronics. The first goal of this review is to present new opportunities in producing high-resolution cameras using these new materials. New photodetection methods and materials in the field are presented, and the challenges involved in their integration on CMOS chips for making high-resolution cameras are discussed. Practical approaches are then presented to address these challenges and methods to integrate low-dimensional material on CMOS. It is also shown that such integrations could be used for ultra-low noise and massively parallel testing of new material and devices. The second goal of this review is to present the colossal untapped potential of low-dimensional material in enabling the next-generation of low-cost and high-performance cameras. It is proposed that low-dimensional materials have the natural ability to create excellent bio-inspired artificial imaging systems with unique features such as in-pixel computing, multi-band imaging, and curved retinas.

Tunable Contacts of Bi2 O2 Se Nanosheets MSM Photodetectors by Metal-Assisted Transfer Approach for Self-Powered Near-Infrared Photodetection

Owing to the Fermi pinning effect arose in the metal electrodes deposition process, metal-semiconductor contact is always independent on the work function, which challenges the next-generation optoelectronic devices. In this work, a metal-assisted transfer approach is developed to transfer Bi2 O2 Se nanosheets onto the pre-deposited metal electrodes, benefiting to the tunable metal-semiconductor contact. The success in Bi2 O2 Se nanosheets transfer is contributed to the stronger van der Waals adhesion of metal electrodes than that of growth substrates. With the pre-deposited asymmetric electrodes, the self-powered near-infrared photodetectors are realized, demonstrating low dark current of 0.04 pA, high Ilight /Idark ratio of 380, fast rise and decay times of 4 and 6 ms, respectively, under the illumination of 1310 nm laser. By pre-depositing the metal electrodes on polyimide and glass, high-performance flexible and omnidirectional self-powered near-infrared photodetectors are achieved successfully. This study opens up new opportunities for low-dimensional semiconductors in next-generation high-performance optoelectronic devices.

Ultrabroadband High Photoresponsivity at Room Temperature Based on Quasi-1D Pseudogap System (TaSe4 )2 I

Narrow bandgap materials have garnered significant attention within the field of broadband photodetection. However, the performance is impeded by diminished absorption near the bandgap, resulting in a rapid decline in photoresponsivity within the mid-wave infrared (MWIR) and long-wave infrared (LWIR) regions. Furthermore, they mostly worked in cryogenic temperature. Here, without the assistance of any complex structure and special environment, it is realized high responsivity covering ultra-broadband wavelength range (Ultraviolet (UV) to LWIR) in a single quasi-1D pseudogap (PG) system (TaSe4 )2 I nanoribbon, especially high responsivity (From 23.9 to 8.31 A W-1 ) within MWIR and LWIR region at room temperature (RT). Through direct probing the carrier relaxation process with broadband time-resolved transient absorption spectrum measurement, the underlying mechanism of majorly photoconductive effect is revealed, which causes an increased spectral weight extended to PG region. This work paves the way for realizing high-performance uncooled MWIR and LWIR detection by using quasi-1D PG materials.

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.

Functional MXenes: Progress and Perspectives on Synthetic Strategies and Structure-Property Interplay for Next-Generation Technologies

MXenes are a class of 2D materials that include layered transition metal carbides, nitrides, and carbonitrides. Since their inception in 2011, they have garnered significant attention due to their diverse compositions, unique structures, and extraordinary properties, such as high specific surface areas and excellent electrical conductivity. This versatility has opened up immense potential in various fields, catalyzing a surge in MXene research and leading to note worthy advancements. This review offers an in-depth overview of the evolution of MXenes over the past 5 years, with an emphasis on synthetic strategies, structure-property relationships, and technological prospects. A classification scheme for MXene structures based on entropy is presented and an updated summary of the elemental constituents of the MXene family is provided, as documented in recent literature. Delving into the microscopic structure and synthesis routes, the intricate structure-property relationships are explored at the nano/micro level that dictate the macroscopic applications of MXenes. Through an extensive review of the latest representative works, the utilization of MXenes in energy, environmental, electronic, and biomedical fields is showcased, offering a glimpse into the current technological bottlenecks, such asstability, scalability, and device integration. Moreover, potential pathways for advancing MXenes toward next-generation technologies are highlighted.

Next-Generation Photodetectors beyond Van Der Waals Junctions

With the continuous advancement of nanofabrication techniques, development of novel materials, and discovery of useful manipulation mechanisms in high-performance applications, especially photodetectors, the morphology of junction devices and the way junction devices are used are fundamentally revolutionized. Simultaneously, new types of photodetectors that do not rely on any junction, providing a high signal-to-noise ratio and multidimensional modulation, have also emerged. This review outlines a unique category of material systems supporting novel junction devices for high-performance detection, namely, the van der Waals materials, and systematically discusses new trends in the development of various types of devices beyond junctions. This field is far from mature and there are numerous methods to measure and evaluate photodetectors. Therefore, it is also aimed to provide a solution from the perspective of applications in this review. Finally, based on the insight into the unique properties of the material systems and the underlying microscopic mechanisms, emerging trends in junction devices are discussed, a new morphology of photodetectors is proposed, and some potential innovative directions in the subject area are suggested.

Ultrasensitive Room Temperature Infrared Photodetection Using a Narrow Bandgap Conjugated Polymer

Photodetectors operating across the short-, mid-, and long-wave infrared (SWIR-LWIR, λ = 1-14 µm) underpin modern science, technology, and society in profound ways. Narrow bandgap semiconductors that form the basis for these devices require complex manufacturing, high costs, cooling, and lack compatibility with silicon electronics, attributes that remain prohibitive for their widespread usage and the development of emerging technologies. Here, a photoconductive detector, fabricated using a solution-processed narrow bandgap conjugated polymer is demonstrated that enables charge carrier generation in the infrared and ultrasensitive SWIR-LWIR photodetection at room temperature. Devices demonstrate an ultralow electronic noise that enables outstanding performance from a simple, monolithic device enabling a high detectivity (D*, the figure of merit for detector sensitivity) >2.44 × 109 Jones (cm Hz1/2  W-1 ) using the ultralow flux of a blackbody that mirrors the background emission of objects. These attributes, ease of fabrication, low dark current characteristics, and highly sensitive operation overcome major limitations inherent within modern narrow-bandgap semiconductors, demonstrate practical utility, and suggest that uncooled detectivities superior to many inorganic devices can be achieved at high operating temperatures.

A mixed-dimensional quasi-1D BiSeI nanowire-2D GaSe nanosheet p-n heterojunction for fast response optoelectronic devices

Due to the unique combination configuration and the formation of a built-in electric field, mixed-dimensional heterojunctions present fruitful possibilities for improving the optoelectronic performances of low-dimensional optoelectronic devices. However, the response times of most photodetectors built from mixed-dimensional heterojunctions are within the millisecond range, limiting their applications in fast response optoelectronic devices. Herein, a mixed-dimensional BiSeI/GaSe van der Waals heterostructure is designed, which exhibits visible light detection ability and competitive photoresponsivity of 750 A W-1 and specific detectivity of 2.25 × 1012 Jones under 520 nm laser excitation. Excitingly, the device displays a very fast response time, e.g., the rise time and decay time under 520 nm laser excitation are 65 μs and 190 μs, respectively. Our findings provide a prospective approach to mixed-dimensional heterojunction photodetection devices with rapid switching capabilities.

Flexible and broadband colloidal quantum dots photodiode array for pixel-level X-ray to near-infrared image fusion

Combining information from multispectral images into a fused image is informative and beneficial for human or machine perception. Currently, multiple photodetectors with different response bands are used, which require complicated algorithms and systems to solve the pixel and position mismatch problem. An ideal solution would be pixel-level multispectral image fusion, which involves multispectral image using the same photodetector and circumventing the mismatch problem. Here we presented the potential of pixel-level multispectral image fusion utilizing colloidal quantum dots photodiode array, with a broadband response range from X-ray to near infrared and excellent tolerance for bending and X-ray irradiation. The colloidal quantum dots photodiode array showed a specific detectivity exceeding 1012 Jones in visible and near infrared range and a favorable volume sensitivity of approximately 2 × 105 μC Gy-1 cm-3 for X-ray irradiation. To showcase the advantages of pixel-level multispectral image fusion, we imaged a capsule enfolding an iron wire and soft plastic, successfully revealing internal information through an X-ray to near infrared fused image.

Progress in the Synthesis and Application of Tellurium Nanomaterials

In recent decades, low-dimensional nanodevices have shown great potential to extend Moore's Law. The n-type semiconductors already have several candidate materials for semiconductors with high carrier transport and device performance, but the development of their p-type counterparts remains a challenge. As a p-type narrow bandgap semiconductor, tellurium nanostructure has outstanding electrical properties, controllable bandgap, and good environmental stability. With the addition of methods for synthesizing various emerging tellurium nanostructures with controllable size, shape, and structure, tellurium nanomaterials show great application prospects in next-generation electronics and optoelectronic devices. For tellurium-based nanomaterials, scanning electron microscopy and transmission electron microscopy are the main characterization methods for their morphology. In this paper, the controllable synthesis methods of different tellurium nanostructures are reviewed, and the latest progress in the application of tellurium nanostructures is summarized. The applications of tellurium nanostructures in electronics and optoelectronics, including field-effect transistors, photodetectors, and sensors, are highlighted. Finally, the future challenges, opportunities, and development directions of tellurium nanomaterials are prospected.

Long-wave infrared photothermoelectric detectors with ultrahigh polarization sensitivity

Filter-free miniaturized polarization-sensitive photodetectors have important applications in the next-generation on-chip polarimeters. However, their polarization sensitivity is thus far limited by the intrinsic low diattenuation and inefficient photon-to-electron conversion. Here, we implement experimentally a miniaturized detector based on one-dimensional tellurium nanoribbon, which can significantly improve the photothermoelectric responses by translating the polarization-sensitive absorption into a large temperature gradient together with the finite-size effect of a perfect plasmonic absorber. Our devices exhibit a zero-bias responsivity of 410 V/W and an ultrahigh polarization ratio (2.5 × 10⁴), as well as a peak polarization angle sensitivity of 7.10 V/W•degree, which is one order of magnitude higher than those reported in the literature. Full linear polarimetry detection is also achieved with the proposed device in a simple geometrical configuration. Polarization-coded communication and optical strain measurement are demonstrated showing the great potential of the proposed devices. Our work presents a feasible solution for miniaturized room-temperature infrared photodetectors with ultrahigh polarization sensitivity.

Strong interlayer coupling in p-Te/n-CdSe van der Waals heterojunction for self-powered photodetectors with fast speed and high responsivity

Self-driven photodetectors, which can detect optical signals without external voltage bias, are highly attractive in the field of low-power wearable electronics and internet of things. However, currently reported self-driven photodetectors based on van der Waals heterojunctions (vdWHs) are generally limited by low responsivity due to poor light absorption and insufficient photogain. Here, we report p-Te/n-CdSe vdWHs utilizing non-layered CdSe nanobelts as efficient light absorption layer and high mobility Te as ultrafast hole transporting layer. Benefiting from strong interlayer coupling, the Te/CdSe vdWHs exhibit stable and excellent self-powered characteristics, including ultrahigh responsivity of 0.94 A W^-1, remarkable detectivity of 8.36 × 10¹² Jones at optical power density of 1.18 mW cm^-2 under illumination of 405 nm laser, fast response speed of 24 µs, large light on/off ratio exceeding 10⁵, as well as broadband photoresponse (405-1064 nm), which surpass most of the reported vdWHs photodetectors. In addition, the devices display superior photovoltaic characteristics under 532 nm illumination, such as large V_oc of 0.55 V, and ultrahigh I_sc of 2.73 µA. These results demonstrate the construction of 2D/non-layered semiconductor vdWHs with strong interlayer coupling is a promising strategy for high-performance and low-power consumption devices.

Tex Se1-x Photodiode Shortwave Infrared Detection and Imaging

Short-wave infrared detectors are increasingly important in the fields of autonomous driving, food safety, disease diagnosis, and scientific research. However, mature short-wave infrared cameras such as InGaAs have the disadvantage of complex heterogeneous integration with complementary metal-oxide-semiconductor (CMOS) readout circuits, leading to high cost and low imaging resolution. Herein, a low-cost, high-performance, and high-stability Te_x Se_{1- x} short-wave infrared photodiode detector is reported. The Te_x Se_{1- x} thin film is fabricated through CMOS-compatible low-temperature evaporation and post-annealing process, showcasing the potential of direct integration on the readout circuit. The device demonstrates a broad-spectrum response of 300-1600 nm, a room-temperature specific detectivity of 1.0 × 10¹⁰ Jones, a -3 dB bandwidth up to 116 kHz, and a linear dynamic range of over 55 dB, achieving the fastest response among Te-based photodiode devices and a dark current density 7 orders of magnitude smaller than Te-based photoconductive and field-effect transistor devices. With a simple Si₃ N₄ packaging, the detector shows high electric stability and thermal stability, meeting the requirements for vehicular applications. Based on the optimized Te_x Se_{1- x} photodiode detector, the applications in material identification and masking imaging is demonstrated. This work paves a new way for CMOS-compatible infrared imaging chips.

Ternary GePdS3: 1D van der Waals Nanowires for Integration of High-Performance Flexible Photodetectors

One-dimensional (1D) van der Waals (vdW) materials are anticipated to leverage for high-performance, giant polarized, and hybrid-dimension photodetection owing to their dangling-bond free surface, intrinsic crystal structure, and weak vdW interaction. However, only a few related explorations have been conducted, especially in the field of flexible and integrated applications. Here, high-quality 1D vdW GePdS₃ nanowires were synthesized and proven to be an n-type semiconductor. The Raman vibration and band gap (1.37-1.68 eV, varying from bulk to single chain) of GePdS₃ were systemically studied by experimental and theoretical methods. The photodetector based on a single GePdS₃ nanowire possesses fast photoresponse at a broadband spectrum of 254-1550 nm. The highest responsivity and detectivity reach up to ∼219 A/W and ∼2.7 × 10¹⁰ Jones (under 254 nm light illumination), respectively. Furthermore, an image sensor with 6 × 6 pixels based on GePdS₃ nanowires is integrated on a flexible polyethylene terephthalate (PET) substrate and exhibits sensitive and homogeneous detection at 808 nm light. These results indicate that the ternary noble metal chalcogenides show great potential in flexible and broadband optoelectronics applications.

Ultrabroadband Imaging Based on Wafer-Scale Tellurene

High-resolution imaging is at the heart of the revolutionary breakthroughs of intelligent technologies, and it is established as an important approach toward high-sensitivity information extraction/storage. However, due to the incompatibility between non-silicon optoelectronic materials and traditional integrated circuits as well as the lack of competent photosensitive semiconductors in the infrared region, the development of ultrabroadband imaging is severely impeded. Herein, the monolithic integration of wafer-scale tellurene photoelectric functional units by exploiting room-temperature pulsed-laser deposition is realized. Taking advantage of the surface plasmon polaritons of tellurene, which results in the thermal perturbation promoted exciton separation, in situ formation of out-of-plane homojunction and negative expansion promoted carrier transport, as well as the band bending promoted electron-hole pair separation enabled by the unique interconnected nanostrip morphology, the tellurene photodetectors demonstrate wide-spectrum photoresponse from 370.6 to 2240 nm and unprecedented photosensitivity with the optimized responsivity, external quantum efficiency and detectivity of 2.7 × 10⁷  A W^-1 , 8.2 × 10⁹ % and 4.5 × 10¹⁵  Jones. An ultrabroadband imager is demonstrated and high-resolution photoelectric imaging is realized. The proof-of-concept wafer-scale tellurene-based ultrabroadband photoelectric imaging system depicts a fascinating paradigm for the development of an advanced 2D imaging platform toward next-generation intelligent equipment.

Electronic/Optoelectronic Memory Device Enabled by Tellurium-based 2D van der Waals Heterostructure for in-Sensor Reservoir Computing at the Optical Communication Band

Although 2D materials are widely explored for data storage and neuromorphic computing, the construction of 2D material-based memory devices with optoelectronic responsivity in the short-wave infrared (SWIR) region for in-sensor reservoir computing (RC) at the optical communication band still remains a big challenge. In this work, an electronic/optoelectronic memory device enabled by tellurium-based 2D van der Waals (vdW) heterostructure is reported, where the ferroelectric CuInP₂ S₆ and tellurium channel endow this device with both the long-term potentiation/depression by voltage pulses and short-term potentiation by 1550 nm laser pulses (a typical wavelength in the conventional fiber optical communication band). Leveraging the rich dynamics, a fully memristive in-sensor RC system that can simultaneously sense, decode, and learn messages transmitted by optical fibers is demonstrated. The reported 2D vdW heterostructure-based memory featuring both the long-term and short-term memory behaviors using electrical and optical pulses in SWIR region has not only complemented the wide spectrum of applications of 2D materials family in electronics/optoelectronics but also paves the way for future smart signal processing systems at the edge.

Synergistic effects of extrinsic photoconduction and photogating in a short-wavelength ZrS3 infrared photodetector

Two-dimensional (2D) material-based photodetectors, especially those working in the infrared band, have shown great application potential in the thermal imaging, optical communication, and medicine fields. Designing 2D material photodetectors with broadened detection band and enhanced responsivity has become an attractive but challenging research direction. To solve this issue, we report a zirconium trisulfide (ZrS₃) infrared photodetector with enhanced and broadened response with the assistance of the synergistic effects of extrinsic photoconduction and photogating effect. The ZrS₃ photodetectors can detect infrared light up to 2 μm by extrinsic photoconduction and exhibit a responsivity of 100 mA W^-1 under 1550 nm illumination. Furthermore, the ZrS₃ infrared photodetectors with an oxide layer show a triple enhanced responsivity due to the photogating effect. Additionally, the infrared imaging capability of the ZrS₃ infrared photodetectors is also demonstrated. This work provides a potential way to extend the response range and improve the responsivity for nanomaterial-based photodetectors at the same time.

How to characterize figures of merit of two-dimensional photodetectors

Photodetectors based on two-dimensional (2D) materials have been the focus of intensive research and development over the past decade. However, a gap has long persisted between fundamental research and mature applications. One of the main reasons behind this gap has been the lack of a practical and unified approach for the characterization of their figures of merit, which should be compatible with the traditional performance evaluation system of photodetectors. This is essential to determine the degree of compatibility of laboratory prototypes with industrial technologies. Here we propose general guidelines for the characterization of the figures of merit of 2D photodetectors and analyze common situations when the specific detectivity, responsivity, dark current, and speed can be misestimated. Our guidelines should help improve the standardization and industrial compatibility of 2D photodetectors.

High-Performance and Polarization-Sensitive Imaging Photodetector Based on WS2 /Te Tunneling Heterostructure

Next-generation imaging systems require photodetectors with high sensitivity, polarization sensitivity, miniaturization, and integration. By virtue of their intriguing attributes, emerging 2D materials offer innovative avenues to meet these requirements. However, the current performance of 2D photodetectors is still below the requirements for practical application owing to the severe interfacial recombination, the lack of photoconductive gain, and insufficient photocarrier collection. Here, a tunneling dominant imaging photodetector based on WS₂ /Te heterostructure is reported. This device demonstrates competitive performance, including a remarkable responsivity of 402 A W^-1 , an outstanding detectivity of 9.28 × 10¹³ Jones, a fast rise/decay time of 1.7/3.2 ms, and a high photocurrent anisotropic ratio of 2.5. These outstanding performances can be attributed to the type-I band alignment with carrier transmission barriers and photoinduced tunneling mechanism, allowing reduced interfacial trapping effect, effective photoconductive gains, and anisotropic collection of photocarriers. Significantly, the constructed photodetector is successfully integrated into a polarized light imaging system and an ultra-weak light imaging system to illustrate the imaging capability. These results suggest the promising application prospect of the device in future imaging systems.

Infrared Photodetection from 2D/3D van der Waals Heterostructures

An infrared photodetector is a critical component that detects, identifies, and tracks complex targets in a detection system. Infrared photodetectors based on 3D bulk materials are widely applied in national defense, military, communications, and astronomy fields. The complex application environment requires higher performance and multi-dimensional capability. The emergence of 2D materials has brought new possibilities to develop next-generation infrared detectors. However, the inherent thickness limitations and the immature preparation of 2D materials still lead to low quantum efficiency and slow response speeds. This review summarizes 2D/3D hybrid van der Waals heterojunctions for infrared photodetection. First, the physical properties of 2D and 3D materials related to detection capability, including thickness, band gap, absorption band, quantum efficiency, and carrier mobility, are summarized. Then, the primary research progress of 2D/3D infrared detectors is reviewed from performance improvement (broadband, high-responsivity, fast response) and new functional devices (two-color detectors, polarization detectors). Importantly, combining low-doped 3D and flexible 2D materials can effectively improve the responsivity and detection speed due to a significant depletion region width. Furthermore, combining the anisotropic 2D lattice structure and high absorbance of 3D materials provides a new strategy in high-performance polarization detectors. This paper offers prospects for developing 2D/3D high-performance infrared detection technology.

Fast near-infrared photodetectors from p-type SnSe nanoribbons

Low-dimensional tin selenide nanoribbons (SnSe NRs) show a wide range of applications in optoelectronics fields such as optical switches, photodetectors, and photovoltaic devices due to the suitable band gap, strong light-matter interaction, and high carrier mobility. However, it is still challenging to grow high-quality SnSe NRs for high-performance photodetectors so far. In this work, we successfully synthesized high-quality p-type SnSe NRs by chemical vapor deposition and then fabricated near-infrared photodetectors. The SnSe NR photodetectors show a high responsivity of 376.71 A W^-1, external quantum efficiency of 5.65 × 10⁴%, and detectivity of 8.66 × 10¹¹Jones. In addition, the devices show a fast response time with rise and fall time of up to 43μs and 57μs, respectively. Furthermore, the spatially resolved scanning photocurrent mapping shows very strong photocurrent at the metal-semiconductor contact regions, as well as fast generation-recombination photocurrent signals. This work demonstrated that p-type SnSe NRs are promising material candidates for broad-spectrum and fast-response optoelectronic devices.

Tailoring the epitaxial growth of oriented Te nanoribbon arrays

As an elemental semiconductor, tellurium (Te) has been famous for its high hole-mobility, excellent ambient stability and topological states. Here, we realize the controllable synthesis of horizontal Te nanoribbon arrays (TRAs) with an angular interval of 60°on mica substrates by physical vapor deposition strategy. The growth of Te nanoribbons (TRs) is driven by two factors, where the intrinsic quasi-one-dimensional spiral chain structure promotes the elongation of their length; the epitaxy relationship between [110] direction of Te and [110] direction of mica facilitates the oriented growth and the expansion of their width. The bending of TRs which have not been reported is induced by grain boundary. Field-effect transistors based on TRs demonstrate high mobility and on/off ratio corresponding to 397 cm² V^-1 s^-1 and 1.5×10⁵, respectively. These phenomena supply an opportunity to deep insight into the vapor-transport synthesis of low-dimensional Te and explore its underlying application in monolithic integration.

Substrate engineering for wafer-scale two-dimensional material growth: strategies, mechanisms, and perspectives

The fabrication of wafer-scale two-dimensional (2D) materials is a prerequisite and important step for their industrial applications. Chemical vapor deposition (CVD) is the most promising approach to produce high-quality films in a scalable way. Recent breakthroughs in the epitaxy of wafer-scale single-crystalline graphene, hexagonal boron nitride, and transition-metal dichalcogenides highlight the pivotal roles of substrate engineering by lattice orientation, surface steps, and energy considerations. This review focuses on the existing strategies and underlying mechanisms, and discusses future directions in epitaxial substrate engineering to deliver wafer-scale 2D materials for integrated electronics and photonics.

Mid-infrared single-pixel imaging at the single-photon level

Single-pixel cameras have recently emerged as promising alternatives to multi-pixel sensors due to reduced costs and superior durability, which are particularly attractive for mid-infrared (MIR) imaging pertinent to applications including industry inspection and biomedical diagnosis. To date, MIR single-pixel photon-sparse imaging has yet been realized, which urgently calls for high-sensitivity optical detectors and high-fidelity spatial modulators. Here, we demonstrate a MIR single-photon computational imaging with a single-element silicon detector. The underlying methodology relies on nonlinear structured detection, where encoded time-varying pump patterns are optically imprinted onto a MIR object image through sum-frequency generation. Simultaneously, the MIR radiation is spectrally translated into the visible region, thus permitting infrared single-photon upconversion detection. Then, the use of advanced algorithms of compressed sensing and deep learning allows us to reconstruct MIR images under sub-Nyquist sampling and photon-starving illumination. The presented paradigm of single-pixel upconversion imaging is featured with single-pixel simplicity, single-photon sensitivity, and room-temperature operation, which would establish a new path for sensitive imaging at longer infrared wavelengths or terahertz frequencies, where high-sensitivity photon counters and high-fidelity spatial modulators are typically hard to access.

Visible and infrared photodiode based on γ-InSe/Ge van der Waals heterojunction for polarized detection and imaging

Broadband photodetectors are a category of optoelectronic devices that have important applications in modern communication information. γ-InSe is a newly developed two-dimensional (2D) layered semiconductor with an air-stable and low-symmetry crystal structure that is suitable for polarization-sensitive photodetection. Herein, we report a P-N photodiode based on 3D Ge/2D γ-InSe van der Waals heterojunction (vdWH). A built-in electric field is introduced at the p-Ge/n-InSe interface to suppress the dark current and accelerate the separation of photogenerated carriers. Moreover, the heterojunction belongs to the accumulation mode with a well-designed type-II band arrangement, which is suitable for the fast separation of photogenerated carriers. Driven by these advantages, the device exhibits excellent photovoltaic performance within the detection range of 400 to 1600 nm and shows a double photocurrent peak at around 405 and 1550 nm. In particular, the responsivity (R) is up to 9.78 A W^-1 and the specific detectivity (D*) reaches 5.38 × 10¹¹ Jones with a fast response speed of 46/32 μs under a 1550 nm laser. Under blackbody radiation, the room temperature R and D* in the mid-wavelength infrared region are 0.203 A W^-1 and 5.6 × 10⁸ Jones, respectively. Moreover, polarization-sensitive light detection from 405-1550 nm was achieved, with the dichroism ratios of 1.44, 3.01, 1.71, 1.41 and 1.34 at 405, 635, 808, 1310 and 1550 nm, respectively. In addition, high-resolution single-pixel imaging capability is demonstrated at visible and near-infrared wavelengths. This work reveals the great potential of the γ-InSe/Ge photodiode for high-performance, broadband, air-stable and polarization-sensitive photodetection.

Polarity-Reversible Te/WSe2 van der Waals Heterodiode for a Logic Rectifier and Polarized Short-Wave Infrared Photodetector

As a p-type elemental material with high carrier mobility, superior ambient stability, and anisotropic crystal structure, emerging two-dimensional (2D) tellurium (Te) has been considered a successor to black phosphorus for developing infrared-related optoelectronics. Nevertheless, the lack of a scalable thickness engineering strategy remains an obstacle to unleashing its full potential. Te-based electronics with logic functions are also less explored. Herein, we propose a novel wet-chemical thinning method for 2D Te, with the merits of scalability and site-specific thickness patterning capability. A polarity-switchable van der Waals (vdW) heterodiode with a high rectification ratio of 2.4 × 10³ is realized on the basis of Te/WSe₂. The electronic application of this unique characteristic is demonstrated by fabricating a logic half-wave rectifier, in which the rectifying states are switchable via electrostatic gating control. Besides, the narrow band gap of Te endows the device with a broad spectral response from visible to short-wave infrared. The room-temperature responsivity reaches 5.2 A W^-1 at the telecom wavelength of 1.55 μm, with an external quantum efficiency of 420% and detectivity of 6.8 × 10⁹ Jones. In particular, owing to the intrinsic in-plane anisotropy of Te, the device exhibits a favorable photocurrent anisotropic ratio of ∼3. Our study demonstrates the enormous potential of Te for novel electronics, promoting the development of elemental 2D materials.

Large-Scale MoS2 Pixel Array for Imaging Sensor

Two-dimensional molybdenum disulfide (MoS₂) has been extensively investigated in the field of optoelectronic devices. However, most reported MoS₂ phototransistors are fabricated using the mechanical exfoliation method to obtain micro-scale MoS₂ flakes, which is laboratory- feasible but not practical for the future industrial fabrication of large-scale pixel arrays. Recently, wafer-scale MoS₂ growth has been rapidly developed, but few results of uniform large-scale photoelectric devices were reported. Here, we designed a 12 × 12 pixels pixel array image sensor fabricated on a 2 cm × 2 cm monolayer MoS₂ film grown by chemical vapor deposition (CVD). The photogating effect induced by the formation of trap states ensures a high photoresponsivity of 364 AW^-1, which is considerably superior to traditional CMOS sensors (≈0.1 AW^-1). Experimental results also show highly uniform photoelectric properties in this array. Finally, the concatenated image obtained by laser lighting stencil and photolithography mask demonstrates the promising potential of 2D MoS₂ for future optoelectrical applications.

Anisotropic charge trapping in phototransistors unlocks ultrasensitive polarimetry for bionic navigation

Being able to probe the polarization states of light is crucial for applications from medical diagnostics and intelligent recognition to information encryption and bio-inspired navigation. Current state-of-the-art polarimeters based on anisotropic semiconductors enable direct linear dichroism photodetection without the need for bulky and complex external optics. However, their polarization sensitivity is restricted by the inherent optical anisotropy, leading to low dichroic ratios of typically smaller than ten. Here, we unveil an effective and general strategy to achieve more than 2,000-fold enhanced polarization sensitivity by exploiting an anisotropic charge trapping effect in organic phototransistors. The polarization-dependent trapping of photogenerated charge carriers provides an anisotropic photo-induced gate bias for current amplification, which has resulted in a record-high dichroic ratio of >10⁴, reaching over the extinction ratios of commercial polarizers. These findings further enable the demonstration of an on-chip polarizer-free bionic celestial compass for skylight-based polarization navigation. Our results offer a fundamental design principle and an effective route for the development of next-generation highly polarization-sensitive optoelectronics.

Solution-processed thickness engineering of tellurene for field-effect transistors and polarized infrared photodetectors

Research on elemental 2D materials has been experiencing a renaissance in the past few years. Of particular interest is tellurium (Te), which possesses many exceptional properties for nanoelectronics, photonics, and beyond. Nevertheless, the lack of a scalable approach for the thickness engineering and the local properties modulation remains a major obstacle to unleashing its full device potential. Herein, a solution-processed oxidative etching strategy for post-growth thickness engineering is proposed by leveraging the moderate chemical reactivity of Te. Large-area ultrathin nanosheets with well-preserved morphologies could be readily obtained with appropriate oxidizing agents, such as HNO₂, H₂O₂, and KMnO₄. Compared with the conventional physical thinning approaches, this method exhibits critical merits of high efficiency, easy scalability, and the capability of site-specific thickness patterning. The thickness reduction leads to substantially improved gate tunability of field-effect transistors with an enhanced current switching ratio of ∼10³, promoting the applications of Te in future logic electronics. The response spectrum of Te phototransistors covers the full range of short-wave infrared wavelength (1–3 μm), and the room-temperature responsivity and detectivity reach 0.96 AW^-1 and 2.2 × 10⁹ Jones at the telecom wavelength of 1.55 μm, together with a favorable photocurrent anisotropic ratio of ∼2.9. Our study offers a new approach to tackling the thickness engineering issue for solution-grown Te, which could help realize the full device potential of this emerging p-type 2D material.

Ultrasensitive Colloidal Quantum-Dot Upconverters for Extended Short-Wave Infrared

Infrared-to-visible upconverters converting low-energy infrared to higher-energy visible light without bringing in complicated readout integrated circuits have triggered enormous excitement. However, existing upconverters suffer from limited sensing wavelengths, low photon-to-photon (p-p) efficiency, and high minimum detectable infrared power. Here, we reported the colloidal quantum-dot (CQD) upconverters with unprecedented performance. By using HgTe CQDs as the sensing layer, the operation spectral ranges of the upconverters are, for the first time, extended to short-wave infrared. More importantly, the resistance-area products of the HgTe CQD photodetectors are carefully optimized by interface engineering to match with the visible light-emitting diodes so that the quantum efficiency and sensitivity of upconverters can be maximized. The integrated upconverters demonstrate a high p-p efficiency of nearly 30% and a low detection limit down to 20 μW cm^-2.

Te/SnS2 tunneling heterojunctions as high-performance photodetectors with superior self-powered properties

The tunneling heterojunctions made of two-dimensional (2D) materials have been explored to have many intriguing properties, such as ultrahigh rectification and on/off ratio, superior photoresponsivity, and improved photoresponse speed, showing great potential in achieving multifunctional and high-performance electronic and optoelectronic devices. Here, we report a systematic study of the tunneling heterojunctions consisting of 2D tellurium (Te) and Tin disulfide (SnS₂). The Te/SnS₂ heterojunctions possess type-II band alignment and can transfer to type-III one under reverse bias, showing a reverse rectification ratio of about 5000 and a current on/off ratio over 10⁴. The tunneling heterojunctions as photodetectors exhibit an ultrahigh photoresponsivity of 50.5 A W^-1 in the visible range, along with a dramatically enhanced photoresponse speed. Furthermore, due to the reasonable type-II band alignment and negligible band bending at the interface, Te/SnS₂ heterojunctions at zero bias exhibit excellent self-powered performance with a high responsivity of 2.21 A W^-1 and external quantum efficiency of 678%. The proposed heterostructure in this work provides a useful guideline for the rational design of a high-performance self-powered photodetector.

Dual sensing signal decoupling based on tellurium anisotropy for VR interaction and neuro-reflex system application

Anisotropy control of the electronic structure in inorganic semiconductors is an important step in developing devices endowed with multi-function. Here, we demonstrate that the intrinsic anisotropy of tellurium nanowires can be used to modulate the electronic structure and piezoelectric polarization and decouple pressure and temperature difference signals, and realize VR interaction and neuro-reflex applications. The architecture design of the device combined with self-locking effect can eliminate dependence on displacement, enabling a single device to determine the hardness and thermal conductivity of materials through a simple touch. We used a bimodal Te-based sensor to develop a wearable glove for endowing real objects to the virtual world, which greatly improves VR somatosensory feedback. In addition, we successfully achieved stimulus recognition and neural-reflex in a rabbit sciatic nerve model by integrating the sensor signals using a deep learning technique. In view of in-/ex-vivo feasibility, the bimodal Te-based sensor would be considered a novel sensing platform for a wide range application of metaverse, AI robot, and electronic medicine.

The accumulation of single-function sensors can increase the complexity of virtual reality systems. Here, Shen et al. exploit the intrinsic anisotropy of tellurium nanowires to design a multi-function pressure and temperature sensor, which can be used as tactile experience in the virtual world.

A tellurium short-wave infrared photodetector with fast response and high specific detectivity

Two-dimensional (2D) elementary tellurium (Te) has attracted intensive attention due to its potential applications in short-wave infrared photodetector devices. Here, we report hydrothermally synthesized 2D Te nanoflakes for short-wave infrared photodetectors with high performance. A Te-based photodetector exhibits a peak responsivity of 51.85 A W^-1 at a 1550 nm wavelength, attributed to the efficient absorption of the phonons of 2D Te nanoflakes. Besides, the rising and decay time of the Te photodetector is calculated to be ∼19 μs and ∼21 μs, respectively, due to the rapid diffusion of charge carriers. In addition, Te-photodetectors exhibit a high specific detectivity (D*) of 1.88 × 10¹⁰ Jones and a superior external quantum efficiency (EQE) of 4148%. Our findings have demonstrated the development of high-performance short-wave infrared photodetectors with fast responses based on 2D Te nanoflakes.

Fully Depleted Self-Aligned Heterosandwiched Van Der Waals Photodetectors

Room-temperature-operating highly sensitive mid-wavelength infrared (MWIR) photodetectors are utilized in a large number of important applications, including night vision, communications, and optical radar. Many previous studies have demonstrated uncooled MWIR photodetectors using 2D narrow-bandgap semiconductors. To date, most of these works have utilized atomically thin flakes, simple van der Waals (vdW) heterostructures, or atomically thin p-n junctions as absorbers, which have difficulty in meeting the requirements for state-of-the-art MWIR photodetectors with a blackbody response. Here, a fully depleted self-aligned MoS₂ -BP-MoS₂ vdW heterostructure sandwiched between two electrodes is reported. This new type of photodetector exhibits competitive performance, including a high blackbody peak photoresponsivity up to 0.77 A W^-1 and low noise-equivalent power of 2.0 × 10^-14  W Hz^-1/2 , in the MWIR region. A peak specific detectivity of 8.61 × 10¹⁰  cm Hz^1/2  W^-1 under blackbody radiation is achieved at room temperature in the MWIR region. Importantly, the effective detection range of the device is twice that of state-of-the-art MWIR photodetectors. Furthermore, the device presents an ultrafast response of ≈4 µs both in the visible and short-wavelength infrared bands. These results provide an ideal platform for realizing broadband and highly sensitive room-temperature MWIR photodetectors.

All-van-der-Waals Barrier-Free Contacts for High-Mobility Transistors

Ultrathin 2D semiconductor devices are considered to have beyond-silicon potential but are severely troubled by the high Schottky barriers of the metal-semiconductor contacts, especially for p-type semiconductors. Due to the severe Fermi-level pinning effect and the lack of conventional semimetals with high work functions, their Schottky hole barriers are hardly removed. Here, an all-van-der-Waals barrier-free hole contact between p-type tellurene semiconductor and layered 1T'-WS₂ semimetal is reported, which achieves a zero Schottky barrier height of 3 ± 9 meV and a high field-effect mobility of ≈1304 cm² V^-1 s^-1 . The formation of such contacts can be attributed to the higher work function of ≈4.95 eV of the 1T'-WS₂ semimetal, which is in sharp contrast with low work function (4.1-4.7 eV) of conventional semimetals. The study defines an available strategy for eliminating the Schottky barrier of metal-semiconductor contacts, facilitating 2D-semiconductor-based electronics and optoelectronics to extend Moore's law.

Switchable Unipolar-Barrier Van der Waals Heterostructures with Natural Anisotropy for Full Linear Polarimetry Detection

Polarization-resolved photodetection in a compact footprint is of great interest for ultraminiaturized polarimeters to be used in a wide range of applications. However, probing the states of polarization (SOP) in materials with natural anisotropy are usually weak, limited by the material's natural dichroism or diattenuation. Here, a twisted unipolar-barrier van der Waals heterostructure (vdWH) to construct a bias-switchable polarization detection for retrieval of full SOP (from 0 to 180°) for linear polarized incident light is reported. As a demonstration example, this study realizes the concept in a b-AsP/WS₂ /b-AsP vdWH relying on the natural anisotropic properties of the materials without using additional plasmonic/metasurface nanostructures to realize linear polarimetry in the mid-infrared range. Polarimetric imaging is further demonstrated with the developed linear polarimetry by directly displaying the Jones-vector-described SOP distribution of certain target object. This method, with the capabilities of detecting full linear SOP, is promising for the next-generation on-chip miniaturized polarimeters.

Manipulating Nanowire Structures for an Enhanced Broad-Band Flexible Photothermoelectric Photodetector

The photothermoelectric effect, directly converting light energy into electrical energy, shows promising prospects in self-powered broad-band optical detection, which can extend to various applications, such as sensing, optoelectronic communications, and wide-temperature-range measurements. However, the low photosensitivity, narrow-band response, and rapid performance degeneration under continuous illumination restrict its broad application. Herein, we propose a simple bottom-up strategy to manipulate nanowires (NWs) into a well-defined multilayer Te-Ag₂Te-Ag NW film, resulting in a high-performance photothermoelectric photodetector with a broad-band responsivity (4.1 V/W), large detectivity (944 MHz^1/2 W^-1), and fast response speed (0.4-0.7 s from 365 to 1200 nm). In addition, the ultrathin structure endows this device with slow and weak transverse heat conduction, enabling a stable voltage without an obvious degeneration over 1500 s. The highly anisotropic arrangement of NWs gives this device a prominent polarization sensitivity. Prospectively, this hierarchically designed nanowire film provides a promising pathway toward engineering photodetectors with high performance.

Liquid Precursor-Assisted Chemical Vapor Deposition of One-Dimensional van der Waals Material Nb2Se9: Tunable Growth for Room-Temperature Gas Sensors

In this study, Nb₂Se₉, a one-dimensional (1D) material with van der Waals (vdWs) bonding, was synthesized by chemical vapor deposition (CVD). A liquid precursor was used to overcome the difficulty of controlling the length and density of Nb₂Se₉ by CVD due to the high melting point of Nb. Growth proceeded horizontally in a nano-ribbon shape on the substrate in the [100] direction, which had the most stable bonding distance, resulting in a preferred orientation of the (010) plane on the out-of-plane axis. Unlike that grown by conventional mechanical or chemical exfoliation, the nanoscale Nb₂Se₉ grown by CVD was uniform and did not have contaminants, such as dispersants, on its surface, meaning it could effectively induce reactions such as gas adsorption and desorption. It exhibited high sensitivity to NO₂ gas adsorption at room temperature (27 °C), and its behavior was confirmed in a high-humidity environment. For the first time, this study demonstrated the possibility of synthesizing a vdWs bonding-based 1D material by CVD, which is expected to be widely used in a variety of low-dimensional materials and devices.

Waveguide-Integrated van der Waals Heterostructure Mid-Infrared Photodetector with High Performance

Extending the operation wavelength of silicon photonics to the mid-infrared (mid-IR) band will significantly benefit critical application areas, including health care, astronomy, and chemical sensing. However, a major hurdle for mid-IR silicon photonics has been the lack of high-speed, high-responsivity, and low noise-equivalent power (NEP) photodetectors. Here, we demonstrate a van der Waals (vdW) heterostructure mid-IR photodetector integrated on a silicon-on-insulator (SOI) waveguide. The detector is composed of vertically stacked black phosphorus (BP)/molybdenum ditelluride (MoTe₂). We measured high responsivity (up to 0.85 A/W) over a 3-4 μm spectral range, indicating that waveguide-confined light could strongly interact with vdW heterostructures on top. In addition, the waveguide-integrated detector could be modulated at high speed (>10 MHz) and its switching performance shows excellent stability. These results, together with the noise analysis, indicate that the NEP of the detector is as low as 8.2 pW/Hz^1/2. This reported critical missing piece in the silicon photonic toolbox will enable the wide-spread adoption of mid-IR integrated photonic circuits.