Fabrication of 1D Te/2D ReS2 Mixed-Dimensional van der Waals p-n Heterojunction for High-Performance Phototransistor

Enhancing nitrate electroreduction to ammonia via electronic gas channel-driven photoelectron transfer in artificial heterojunctions

The electrochemical nitrate reduction reaction (NRR) acts as a pivotal factor in closing nitrogen cycle along with enabling a sustainable route for ammonia production. While significant progress has been made in developing cost-effective NRR catalysts through structural engineering, this research introduced a facile photo-electro activation approach that significantly improves NRR efficiency. We presented a photo-enhanced effect on electrocatalytic NRR activity in core-shell ReS2/CdS heterostructures. This junction device, featuring spherical CdS cores and tunable ReS2 shells, formed a well-defined heterojunction interface that established a two-dimensional electron gas system. This electron expressway accelerated electron transfer, facilitating rapid participation in the electrochemical NRR process. As a result, the ReS2/CdS-1 heterostructures demonstrated exceptional catalytic activity, reaching a peak Faradaic efficiency of 92.56 % with an ammonia production rate of 0.44 mmol h-1 cm-2 at -0.5 V vs. RHE. These outcomes furnish valuable perspectives into the synergistic compatibility between photo-electro activation and heterointerface engineering, paving the way for advanced catalytic NRR with steering photocarrier dynamics.

Band Tailoring Enabled Perovskite Devices for X-Ray to Near-Infrared Photodetection

Perovskite semiconductors have shown significant promise for photodetection due to their low effective carrier masses and long carrier lifetimes. However, achieving balanced detection across a broad spectrum-from X-rays to infrared-within a single perovskite photodetector presents challenges. These challenges stem from conflicting requirements for different wavelength ranges, such as the narrow bandgap needed for infrared detection and the low dark current necessary for X-ray sensitivity. To address this, this study have designed a type-II FAPbI3 perovskite-based heterojunction featuring a large energy band offset utilizing narrow bandgap tellurium (Te) semiconductor. This innovative design broadens the detection range into the infrared while simultaneously reducing dark current noise. As-designed device allows for the detection of near infrared band, achieving a detectivity of 6.8 × 109 Jones at 1550 nm. The low dark current enables X-ray sensitivity of up to 1885.1 µC Gy⁻¹ cm⁻2. First-principles calculations confirm the type-II band structure alignment of the heterojunction, and a self-driven response behavior is realized. Moreover, this study have developed a scalable 40 × 1 sensor array, demonstrating the potential for wide-spectrum imaging applications. This work is expected to advance the application of perovskite-based wide-spectrum devices.

Two-Dimensional Materials for Brain-Inspired Computing Hardware

Recent breakthroughs in brain-inspired computing promise to address a wide range of problems from security to healthcare. However, the current strategy of implementing artificial intelligence algorithms using conventional silicon hardware is leading to unsustainable energy consumption. Neuromorphic hardware based on electronic devices mimicking biological systems is emerging as a low-energy alternative, although further progress requires materials that can mimic biological function while maintaining scalability and speed. As a result of their diverse unique properties, atomically thin two-dimensional (2D) materials are promising building blocks for next-generation electronics including nonvolatile memory, in-memory and neuromorphic computing, and flexible edge-computing systems. Furthermore, 2D materials achieve biorealistic synaptic and neuronal responses that extend beyond conventional logic and memory systems. Here, we provide a comprehensive review of the growth, fabrication, and integration of 2D materials and van der Waals heterojunctions for neuromorphic electronic and optoelectronic devices, circuits, and systems. For each case, the relationship between physical properties and device responses is emphasized followed by a critical comparison of technologies for different applications. We conclude with a forward-looking perspective on the key remaining challenges and opportunities for neuromorphic applications that leverage the fundamental properties of 2D materials and heterojunctions.

Selenium Interface Layers Boost High Mobility and Switch Ratios in van der Waals Electronics

Achieving high mobility while minimizing off-current and static power consumption is critical for applications of two-dimensional field-effect transistors. Herein, a selenium (Se) sacrificial layer is introduced between the rhenium sulfide (ReS2) semiconductor and source/drain electrode. With the Se layer and postannealing process, the ReS2 transistor significantly decreases the off-state current with a substantial increase in the on-state current density. Notably, the mobility reaches 237 cm2 V-1 s-1, which is accompanied by an extraordinary current on/off ratio of 1011 at 7 K. The theoretical calculations and noise analysis show that the improvement in device performance is ascribed to the Se protective layer, which effectively shields the semiconductor from direct exposure to high-energy metal particles, reducing the Schottky barrier and the number of defect states at the interface. Finally, Se sacrificial ReS2 transistor-based versatile logic circuits including NAND and NOR logic are executed, which can be widely applied in integrated circuits.

Catalyst-Free Polymorphic β-Ga2O3 Nanomaterials for Solar-Blind Optoelectronic Devices: Applications in Imaging and Neural Communication

The continuous advancements in ultraviolet-C (UV-C) optoelectronics are poised to meet the growing demand for efficient and innovative optoelectronic devices, particularly in image sensing and neural communication. This study proposes a low-cost tube sealing and muffle calcination process for the catalyst-free synthesis of polymorphic β-Ga2O3 nanomaterials. These nanomaterials are synthesized via a vapor-solid (VS) growth mechanism, enabling the formation of high-quality nanowires (NWs), nanobelts (NBs), and nanosheets (NSs). UV-C photodetectors (PDs) fabricated with β-Ga2O3 nanobelts demonstrated exceptional performance, exhibiting a responsivity of 4.62 × 105 A W-1 and a specific detectivity of 4.78 × 1012 Jones under 254 nm light. This PD enabled high-sensitivity and high-contrast UV-C imaging, effectively capturing the letters "CNU" and a "Panda" pattern. Additionally, the β-Ga2O3 nanowire-based optoelectronic synapse (OES) device displayed efficient light sensing and significant persistent photoconductivity, accurately mimicking synaptic behaviors such as short-term to long-term memory transitions and memory reinforcement. The OES device is successfully integrated into a wireless optical communication system, effectively simulating neural signal transmission by outputting the current waveform signal of "CNU 1954" and exhibiting notable UV-C light sensing and learning abilities. This work not only introduces a method for synthesizing polymorphic β-Ga2O3 nanomaterials but also underscores their potential in advanced UV-C optoelectronic applications, including image sensing and neural communication.

GeSe/WSe2 mixed dimensional p-n junction photoelectric properties

Heterojunctions prepared utilizing diverse 2D materials enhance a variety of optoelectronic devices. Here, we present GeSe/WSe2 mixed-dimensional p-n heterojunctions, which broaden the possibility of material combination and selection in 2D/layered heterojunction devices, while also providing material parameters to facilitate the development of optoelectronic devices based on 2D/layered semiconductor materials.

High-Performance Gate-Voltage-Tunable Photodiodes Based on Nb2Pd3Se8/WSe2 Mixed-Dimensional Heterojunctions

The mixed-dimensional (MD) van der Waals (vdWs) heterojunction for photodetectors has garnered significant attention owing to its exceptional compatibility and superior quality. Low-dimensional material heterojunctions exhibit unique photoelectric properties attributed to their nanoscale thickness and vdWs contact surfaces. In this work, a novel MD vdWs heterojunction composed of one-dimensional (1D) Nb2Pd3Se8 nanowires and two-dimensional (2D) WSe2 nanosheets is proposed. The heterojunction's energy band engineering is accomplished by manipulating the Fermi level of the bipolar 2D material via gate voltage, resulting in a rectification characteristic that can be adjusted with gate voltage. Under 685 nm laser irradiation, it demonstrates exceptional self-powered photodetection performance, attaining a photoresponsivity of 1.45 A W-1, an ultrahigh detectivity of 6.8 × 1012 Jones, and an ultrafast response time of 37/64 μs at zero bias. In addition, a broadband photodetector from 255 to 1064 nm is realized. These results demonstrate the great potential of Nb2Pd3Se8/WSe2 MD heterostructures for advanced electronic and optoelectronic devices.

Oriented Epitaxial Growth of Mixed-Dimensional van der Waals Heterostructures with One-Dimensional (1D) Bi2S3 Nanowires and Two-Dimensional (2D) WS2 Monolayers for Performance-Enhanced Photodetectors

The synthesis of mixed-dimensional van der Waals heterostructures with controlled alignment by chemical vapor deposition (CVD) technique remains a big challenge due to the complex epitaxial growth mechanism. Herein, we report the epitaxial growth of mixed-dimensional Bi2S3/WS2 heterostructures by a two-step CVD method. Bi2S3 crystals grown on 2D WS2 monolayers exhibit 1D feature with the preferred orientation, indicating a strong epitaxial growth behavior at the 1D/2D interface. Furthermore, the heterostructure was carefully characterized by transmission electron microscopy, which reveals the preferential growth of Bi2S3 nanowires along the zigzag edge of WS2 monolayers. The experimental results are also consistent with the theoretical calculations by DFT, where the preferred orientation possesses minimal surface energy. The strong interaction between Bi2S3 and WS2 enables efficient charge transfer of photogenerated carriers at the heterointerface, which leads to a largely improved light harvesting capability with the highest responsivity of ∼48.1 AW-1 and detectivity of ∼5.9 × 1012 Jones.

Electronics and Optoelectronics Based on Tellurium

As a true 1D system, group-VIA tellurium (Te) is composed of van der Waals bonded molecular chains within a triangular crystal lattice. This unique crystal structure endows Te with many intriguing properties, including electronic, optoelectronic, thermoelectric, piezoelectric, chirality, and topological properties. In addition, the bandgap of Te exhibits thickness dependence, ranging from 0.31 eV in bulk to 1.04 eV in the monolayer limit. These diverse properties make Te suitable for a wide range of applications, addressing both established and emerging challenges. This review begins with an elaboration of the crystal structures and fundamental properties of Te, followed by a detailed discussion of its various synthesis methods, which primarily include solution phase, and chemical and physical vapor deposition technologies. These methods form the foundation for designing Te-centered devices. Then the device applications enabled by Te nanostructures are introduced, with an emphasis on electronics, optoelectronics, sensors, and large-scale circuits. Additionally, performance optimization strategies are discussed for Te-based field-effect transistors. Finally, insights into future research directions and the challenges that lie ahead in this field are shared.

1D/2D Heterostructures: Synthesis and Application in Photodetectors and Sensors

Two-dimensional (2D) semiconductor components have excellent physical attributes, such as excellent mechanical ductility, high mobility, low dielectric constant, and tunable bandgap, which have attracted much attention to the fields of flexible devices, optoelectronic conversion, and microelectronic devices. Additionally, one-dimensional (1D) semiconductor materials with unique physical attributes, such as high surface area and mechanical potency, show great potential in many applications. However, isolated 1D and 2D materials often do not meet the demand for multifunctionality. Therefore, more functionality is achieved by reconstructing new composite structures from 1D and 2D materials, and according to the current study, it has been demonstrated that hybrid dimensional integration yields a significant enhancement in performance and functionality, which is widely promising in the field of constructing novel electronic and optoelectronic nanodevices. In this review, we first briefly introduce the preparation methods of 1D materials, 2D materials, and 1D/2D heterostructures, as well as their advantages and limitations. The applications of 1D/2D heterostructures in photodetectors, gas sensors, pressure and strain sensors, as well as photoelectrical synapses and biosensors are then discussed, along with the opportunities and challenges of their current applications. Finally, the outlook of the emerging field of 1D/2D heterojunction structures is given.

Spatially Resolved Light-Induced Ferroelectric Polarization in α-In2Se3/Te Heterojunctions

Light-induced ferroelectric polarization in 2D layered ferroelectric materials holds promise in photodetectors with multilevel current and reconfigurable capabilities. However, translating this potential into practical applications for high-density optoelectronic information storage remains challenging. In this work, an α-In2Se3/Te heterojunction design that demonstrates spatially resolved, multilevel, nonvolatile photoresponsivity is presented. Using photocurrent mapping, the spatially localized light-induced poling state (LIPS) is visualized in the junction region. This localized ferroelectric polarization induced by illumination enables the heterojunction to exhibit enhanced photoresponsivity. Unlike previous reports that observe multilevel polarization enhancement in electrical resistance, the device shows nonvolatile photoresponsivity enhancement under illumination. After polarization saturation, the photocurrent increases up to 1000 times, from 10-12 to 10-9 A under the irradiation of a 520 nm laser with a power of 1.69 nW, compared to the initial state in a self-driven mode. The photodetector exhibits high detectivity of 4.6×1010 Jones, with a rise time of 27 µs and a fall time of 28 µs. Furthermore, the device's localized poling characteristics and multilevel photoresponse enable spatially multiplexed optical information storage. These results advance the understanding of LIPS in 2D ferroelectric materials, paving the way for optoelectronic information storage technologies.

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.

Self-Rolled-Up WSe2 One-Dimensional/Two-Dimensional Homojunctions: Enabling High-Performance Self-Powered Polarization-Sensitive Photodetectors

Mixed-dimensional heterostructures integrate materials of diverse dimensions with unique electronic functionalities, providing a new platform for research in electron transport and optoelectronic detection. Here, we report a novel covalently bonded one-dimensional/two-dimensional (1D/2D) homojunction structure with robust junction contacts, which exhibits wide-spectrum (from the visible to near-infrared regions), self-driven photodetection, and polarization-sensitive photodetection capabilities. Benefiting from the ultralow dark current at zero bias voltage, the on/off ratio and detectivity of the device reach 1.5 × 103 and 3.24 × 109 Jones, respectively. Furthermore, the pronounced anisotropy of the WSe2 1D/2D homojunction is attributed to its low symmetry, enabling polarization-sensitive detection. In the absence of any external bias voltage, the device exhibits strong linear dichroism for wavelengths of 638 and 808 nm, with anisotropy ratios of 2.06 and 1.96, respectively. These results indicate that such mixed-dimensional structures can serve as attractive building blocks for novel optoelectronic detectors.

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.

Dual-Junction Field-Effect Transistor with Ultralow Subthreshold Swing Approaching the Theoretical Limit

Metal-oxide-semiconductor field-effect transistors as basic electronic devices of integrated circuits have been greatly developed and widely used in the past decades. However, as the thickness of the conducting channel decreases, the interface electronic scattering between the gate oxide layer and the channel significantly impacts the performance of the transistor. To address this issue, van der Waals heterojunction field-effect transistors (vdWJFETs) have been proposed using two-dimensional semiconductors, which utilize the built-in electric field at the sharp van der Waals interface to regulate the channel conductance without the need of a complex gate oxide layer. In this study, a novel dual-junction vdWJFET composed of a MoS2 channel and a Te nanosheet gate has been developed. This device achieves an ultralow subthreshold swing (SS) and an extremely low current hysteresis, greatly surpassing the single-junction vdWJFET. In the transistor, the SS decreases from 475.04 to 68.3 mV dec-1, nearly approaching the theoretical limit of 60 mV dec-1 at room temperature. The pinch-off voltage (Vp) decreases from -4.5 to -0.75 V, with a current hysteresis of ∼10 mV and a considerable field-effect mobility (μ) of 36.43 cm2 V-1 s-1. The novel dual-junction vdWJFET provides a new approach to realize a transistor with a theoretical ideal SS and a negligible current hysteresis toward low-power electronic applications.

Tellurium and Nano-Tellurium: Medicine or Poison?

Tellurium (Te) is the heaviest stable chalcogen and is a rare element in Earth's crust (one to five ppb). It was discovered in gold ore from mines in Kleinschlatten near the present-day city of Zlatna, Romania. Industrial and other applications of Te focus on its inorganic forms. Tellurium can be toxic to animals and humans at low doses. Chronic tellurium poisoning endangers the kidney, liver, and nervous system. However, Te can be effective against bacteria and is able to destroy cancer cells. Tellurium can also be used to develop redox modulators and enzyme inhibitors. Soluble salts that contain Te had a role as therapeutic and antimicrobial agents before the advent of antibiotics. The pharmaceutical use of Te is not widespread due to the narrow margin between beneficial and toxic doses, but there are differences between the measure of toxicity based on the Te form. Nano-tellurium (Te-NPs) has several applications: it can act as an adsorptive agent to remove pollutants, and it can be used in antibacterial coating, photo-catalysis for the degradation of dyes, and conductive electronic materials. Nano-sized Te particles are the most promising and can be produced in both chemical and biological ways. Safety assessments are essential to determine the potential risks and benefits of using Te compounds in various applications. Future challenges and directions in developing nano-materials, nano-alloys, and nano-structures based on Te are still open to debate.

Engineering surface state density of monolayer CVD grown 2D MoS2 for enhanced photodetector performance

This study demonstrates the effect of nitrogen doping on the surface state densities (Nss) of monolayer MoS2 and its effect on the responsivity and the response time of the photodetector. Our experimental results shows that by doping monolayer MoS2 by nitrogen, the surface state (Nss) increases thereby increasing responsivity. The mathematical model included in the paper supports the relation of photocurrent gain and its dependency on trap level which states that the increasing the trap density increases the photocurrent gain and the same is observed experimentally. The experimental results at room temperature revealed that nitrogen doped MoS2 have a high NSS of 1.63 X 1013 states/m2/eV compared to undoped MoS2 of 4.2 x 1012 states/m2/eV. The increase in Nss in turn is the cause for rise in trap states which eventually increases the value of photo responsivity from 65.12 A/W (undoped MoS2) to 606.3 A/W (nitrogen doped MoS2). The response time calculated for undoped MoS2 was 0.85 sec and for doped MoS2 was 0.35 sec. Finally, to verify the dependence of surface states on the responsivity, the surface states were varied by varying temperature and it was observed that upon increment in temperature, the surface states decreases which causes the responsivity values also to decrease.

Direct growth Bi2O2Se nanosheets on SiO2/Si substrate for high-performance and broadband photodetector

Bi2O2Se, a newly emerging two-dimensional (2D) material, has attracted significant attention as a promising candidate for optoelectronics applications due to its exceptional air stability and high mobility. Generally, mica and SrTiO3substrates with lattice matching are commonly used for the growth of high-quality 2D Bi2O2Se. Although 2D Bi2O2Se grown on these insulating substrates can be transferred onto Si substrate to ensure compatibility with silicon-based semiconductor processes, this inevitably introduces defects and surface states that significantly compromise the performance of optoelectronic devices. Herein we employ Bi2Se3as the evaporation source and oxygen reaction to directly grow Bi2O2Se nanosheets on Si substrate through a conventional chemical vapor deposition method. The photodetector based on the Bi2O2Se nanosheets on Si substrate demonstrates outstanding optoelectronics performance with a responsivity of 379 A W-1, detectivity of 2.9 × 1010Jones, and rapid response time of 0.28 ms, respectively, with 532 nm illumination. Moreover, it also exhibits a broadband photodetection capability across the visible to near-infrared range (532-1300 nm). These results suggest that the promising potential of Bi2O2Se nanosheets for high-performance and broadband photodetector applications.

Electrical and optoelectronic anisotropy and surface electron accumulation in ReS2 nanostructures

Two interesting electronic transport properties including in-plane anisotropy and nonhomogeneous carrier distribution were observed in ReS2 nanoflakes. The electrical conductivity defined by the current parallel to the b-axis (‖b) is 32 times higher than that perpendicular to the b-axis (⊥b). Similar anisotropy was also observed in optoelectronic properties in which the ratio of responsivity ‖b to ⊥b reaches 20. In addition, conductivity and thermal activation energy with substantial thickness dependence were observed, which indicates a surface-dominant 2D transport in ReS2 nanoflakes. The presence of surface electron accumulation (SEA) in ReS2 has been confirmed by angle-resolved photoemission spectroscopy and scanning tunneling spectroscopy. The electron concentration (∼1019 cm-3) at the surface is over three orders of magnitude higher than that of the bulks. Sulfur vacancies which are sensitive to air molecules are suggested to be the major factor resulting in SEA and high conductivity in ReS2 nanostructures.

MXene based flexible photodetectors: progress, challenges, and opportunities

The growing interest in applying 2D transition-metal carbides and nitrides (MXenes) to diverse application fields such as energy storage and harvesters, catalysts, sensors, optoelectronics, electromagnetic interference shielding and antennas since its first discovery in 2011 is clearly evident. Their intrinsic high conductivity limits the development of MXenes in photodetectors that rely on the semiconducting properties of active materials, while the abundant functional groups on the surface of MXenes provide opportunities for using MXenes as sensing materials in the fabrication of flexible photodetectors. Considerable studies on MXene based photodetectors have been carried out, but the main obstacles include seeking novel semiconducting materials in MXene families, the manufacturing technology, etc. This review highlights the progress, challenges and opportunities in MXene based flexible photodetectors and discusses novel materials, architectures, and approaches that capitalize on our growing understanding of MXenes.

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.

Reveal Ultrafast Electron Relaxation across Sub-bands of Tellurium by Time- and Energy-Resolved Photoemission Microscopy

Exploring ultrafast carrier dynamics is crucial for the materials' fundamental properties and device design. In this work, we employ time- and energy-resolved photoemission electron microscopy with tunable pump wavelengths from visible to near-infrared to reveal the ultrafast carrier dynamics of the elemental semiconductor tellurium. We find that two discrete sub-bands around the Γ point of the conduction band are involved in excited-state electron ultrafast relaxation and reveal that hot electrons first go through ultrafast intra sub-band cooling on a time scale of about 0.3 ps and then transfer from the higher sub-band to the lower one on a time scale of approximately 1 ps. Additionally, theoretical calculations reveal that the lower one has flat-band characteristics, possessing a large density of states and a long electron lifetime. Our work demonstrates that TR- and ER-PEEM with broad tunable pump wavelengths are powerful techniques in revealing the details of ultrafast carrier dynamics in time and energy domains.

Photoelectric performance of InSe vdW semi-floating gate p-n junction transistor

Semi-floating gate transistors based on vdW materials are often used in memory and programmable logic applications. In this paper, we propose a semi-floating gate photoelectric p-n junction transistor structure which is stacked by InSe/h-BN/Gr. By modulating gate voltage, InSe can be presented as N-type and P-type respectively on different substrates, and then combined into p-n junction. Moreover, InSe/h-BN/Gr device can be switched freely between N-type resistance and p-n junction. The resistance value of InSe resistor and the photoelectric properties of the p-n junction are also sensitively modulated by laser. Under dark conditions, the rectification ratio of p-n junction can be as high as 107. After laser modulation, the device has a response up to 1.154 × 104A W-1, a detection rate up to 5.238 × 1012Jones, an external quantum efficiency of 5.435 × 106%, and a noise equivalent power as low as 1.262 × 10-16W/Hz1/2. It lays a foundation for the development of high sensitivity and fast response rate tunable photoelectric p-n junction transistor.

Controllable Synthesis of 2H-1T' Mox Re(1- x ) S2 Lateral Heterostructures and Their Tunable Optoelectronic Properties

Constructing heterostructures and doping are valid ways to improve the optoelectronic properties of transition metal dichalcogenides (TMDs) and optimize the performance of TMDs-based photodetectors. Compared with transfer techniques, chemical vapor deposition (CVD) has higher efficiency in preparing heterostructures. As for the one-step CVD growth of heterostructures, cross-contamination between the two materials may occur during the growth process, which may provide the possibility of one-step simultaneous realization of controllable doping and formation of alloy-based heterostructures by finely tuning the growth dynamics. Here, 2H-1T' Mox Re(1- x ) S2 alloy-to-alloy lateral heterostructures are synthesized through this one-step CVD growth method, utilizing the cross-contamination and different growth temperatures of the two alloys. Due to the doping of a small amount of Re atoms in 2H MoS2 , 2H Mox Re(1- x ) S2 has a high response rejection ratio in the solar-blind ultraviolet (SBUV) region and exhibits a positive photoconductive (PPC) effect. While the 1T' Mox Re(1- x ) S2 formed by heavily doping Mo atoms into 1T' ReS2 will produce a negative photoconductivity (NPC) effect under UV laser irradiation. The optoelectronic property of 2H-1T' Mox Re(1- x ) S2 -based heterostructures can be modulated by gate voltage. These findings are expected to expand the functionality of traditional optoelectronic devices and have potential applications in optoelectronic logic devices.

Bi2O2Se Nanowire/MoSe2 Mixed-Dimensional Polarization-Sensitive Photodiode with a Nanoscale Ultrafast-Response Channel

In recent years, polarization-sensitive photodiodes based on one-dimensional/two-dimensional (1D/2D) van der Waals (vdWs) heterostructures have garnered significant attention due to the high specific surface area, strong orientation degree of 1D structures, and large photo-active area and mechanical flexibility of 2D structures. Therefore, they are applicable in wearable electronics, electrical-driven lasers, image sensing, optical communication, optical switches, etc. Herein, 1D Bi₂O₂Se nanowires have been successfully synthesized via chemical vapor deposition. Impressively, the strongest Raman vibration modes can be achieved along the short edge (y-axis) of Bi₂O₂Se nanowires with high crystalline quality, which originate from Se and Bi vacancies. Moreover, the Bi₂O₂Se/MoSe₂ photodiode designed with type-II band alignment demonstrates a high rectification ratio of 10³. Intuitively, the photocurrent peaks are mainly distributed in the overlapped region under the self-powered mode and reverse bias, within the wavelength range of 400-nm. The resulting device exhibits excellent optoelectrical performances, including high responsivities (R) and fast response speed of 656 mA/W and 350/380 μs (zero bias) and 17.17 A/W and 100/110 μs (-1 V) under 635 nm illumination, surpassing the majority of reported mixed-dimensional photodiodes. The most significant feature of our photodiode is its highest photocurrent anisotropic ratio of ∼2.2 (-0.8 V) along the long side (x-axis) of Bi₂O₂Se nanowires under 635 nm illumination. The above results reveal a robust and distinctive correlation between structural defects and polarized orientation for 1D Bi₂O₂Se nanowires. Furthermore, 1D Bi₂O₂Se nanowires appear to be a great potential candidate for high-performance rectifiers, polarization-sensitive photodiodes, and phototransistors based on mixed vdWs heterostructures.

Emerging Trends in 2D TMDs Photodetectors and Piezo-Phototronic Devices

The piezo-phototronic effect shows promise with regards to improving the performance of 2D semiconductor-based flexible optoelectronics, which will potentially open up new opportunities in the electronics field. Mechanical exfoliation and chemical vapor deposition (CVD) influence the piezo-phototronic effect on a transparent, ultrasensitive, and flexible van der Waals (vdW) heterostructure, which allows the use of intrinsic semiconductors, such as 2D transition metal dichalcogenides (TMD). The latest and most promising 2D TMD-based photodetectors and piezo-phototronic devices are discussed in this review article. As a result, it is possible to make flexible piezo-phototronic photodetectors, self-powered sensors, and higher strain tolerance wearable and implantable electronics for health monitoring and generation of piezoelectricity using just a single semiconductor or vdW heterostructures of various nanomaterials. A comparison is also made between the functionality and distinctive properties of 2D flexible electronic devices with a range of applications made from 2D TMDs materials. The current state of the research about 2D TMDs can be applied in a variety of ways in order to aid in the development of new types of nanoscale optoelectronic devices. Last, it summarizes the problems that are currently being faced, along with potential solutions and future prospects.

Controlled Bipolar Doping of One-Dimensional van der Waals Nb2Pd3Se8

Tailoring the electrical properties of one-dimensional (1D) van der Waals (vdW) materials is desirable for their applications toward electronic devices by exploiting their unique characteristics. However, 1D vdW materials have not been extensively investigated for modulation of their electrical properties. Here we control doping levels and types of 1D vdW Nb₂Pd₃Se₈ over a wide energy range by immersion in AuCl₃ or β-nicotinamide adenine dinucleotide (NADH) solutions, respectively. Through spectroscopic analyses and electrical characterizations, we confirm that the charges were effectively transferred to Nb₂Pd₃Se₈, and the dopant concentration was adjusted to the immersion time. Furthermore, we make the axial p-n junction of 1D Nb₂Pd₃Se₈ by a selective area p-doping using the AuCl₃ solution, which exhibits rectifying behavior with an I_forward/I_reverse of 81 and an ideality factor of 1.2. Our findings could pave the way to more practical and functional electronic devices based on 1D vdW materials.

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.

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.

Locally Thinned, Core-Shell Nanowire-Integrated Multi-gate MoS2 Transistors for Active Control of Extendable Logic

Field-effect transistor (FET) devices with multi-gate coupled structures usually exhibit special electrical properties and are suitable for fabricating multifunctional devices. Among them, the 1D nanowire gate configuration has become a promising gate design to tailor 2D FET performances. However, due to possible short circuiting induced by nanowire contact and the high requirement for precision manipulation, the integration of multi-nanowires as gates in a single 2D electronic system remains a grand challenge. Herein, local laser--thinned multiple core-shell SiC@SiO₂ nanowires are successfully integrated into MoS₂ transistors as multi-gates for active control of extendable logic applications. Nanowire gates (NGs) locally enhance the carrier transportation, and the use of multiple NGs can achieve designed band structures to tune the performance of the device. For core-shell structures, a semiconducting core is used to introduce a gate bias, and the insulating shell provides protection against short circuiting between NGs, facilitating nanowire assembly. Furthermore, a global control gate is introduced to co-tune the overall electrical characteristics, while active control of logic devices and extendable inputs are achieved based on this model. This work proposes a novel nanowire multi-gate configuration, which provides possibilities for localized, precise control of band structures and the fabrication of highly integrated, multifunctional, and controllable nano-devices.

High-Performance UV-Vis Broad-Spectra Photodetector Based on a β-Ga2O3/Au/MAPbBr3 Sandwich Structure

The UV-vis photodetector (PD), a detector that can simultaneously detect light in the ultraviolet region and the visible region, has a wide range of applications in military and civilian fields. Currently, it is very difficult to obtain good detection performance in the UV region (especially in the solar-blind range) like in the visible region with most UV-vis PDs. This severely affects the practical application of UV-vis broad-spectra PDs. Here, a simple sandwich structure PD (SSPD) composed of β-Ga₂O₃, Au electrodes, and the MAPbBr₃ perovskite is designed and fabricated to simultaneous enhance the detection performance in the UV and visible light regions. The β-Ga₂O₃/Au/MAPbBr₃ SSPD exhibits enhanced optoelectronic performance with high responsivities of 0.47 and 1.43 A W^-1 at 240 and 520 nm under a bias of 6 voltage (V), respectively, which are 8.5 and 23 times than that of the metal-semiconductor-metal (MSM) structure MAPbBr₃ PD at 6 V, respectively. The enhanced performance was attributed to the effective suppression of carrier recombination due to the efficient interface charge separation in the device structure. In addition, the self-powered response characteristic is also realized by forming a type-II heterojunction between β-Ga₂O₃ and MAPbBr₃, which gives the β-Ga₂O₃/Au/MAPbBr₃ SSPD superior single-pixel photo-imaging ability without an external power supply. This work provides a simple and effective method for the preparation of high-performance self-powered imaging PDs in the UV-visible region.

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.

Controllable Inverse Photoconductance in Semiconducting Nanowire Films

As a typical p-type semiconductor, tellurium (Te) has been widely studied for the construction of photodetectors. However, only the positive photoconductance of Te-based photodetectors based on the photoconductive effect has been observed in the reported literature. Herein, an unusual but interesting phenomenon, in that tellurium nanowires (NWs) behave with negative photoresponse to positive photoresponse under enlarged optical intensities from the UV to VIS-IR region is reported. According to the experiments and simulations, adsorbed oxygen on the surface of Te NWs plays a significant role in the abnormal photoresponse. The inverse photoconductance can be attributed to the competition between the photoconductive effect and the oxygen desorption effect. Moreover, the influence of the size and layers of Te NWs is also discussed. This inverse photoconductance phenomenon is further explored by introducing the Te-Au heterojunction system. Hot-electron injection at the Te-Au heterojunction interface induces a more obvious tendency to behave with a negative photoresponse. These findings will be beneficial for potential applications of Te-NW-based photodetectors.

Synthesis of a Selectively Nb-Doped WS2-MoS2 Lateral Heterostructure for a High-Detectivity PN Photodiode

In this study, selective Nb doping (P-type) at the WS₂ layer in a WS₂-MoS₂ lateral heterostructure via a chemical vapor deposition (CVD) method using a solution-phase precursor containing W, Mo, and Nb atoms is proposed. The different chemical activity reactivity (MoO₃ > WO₃ > Nb₂O₅) enable the separation of the growth temperature of intrinsic MoS₂ to 700 °C (first grown inner layer) and Nb-doped WS₂ to 800 °C (second grown outer layer). By controlling the Nb/(W+Nb) molar ratio in the solution precursor, the hole carrier density in the p-type WS₂ layer is selectively controlled from approximately 1.87 × 10⁷/cm² at 1.5 at.% Nb to approximately 1.16 × 10¹³/cm² at 8.1 at.% Nb, while the electron carrier density in n-type MoS₂ shows negligible change with variation of the Nb molar ratio. As a result, the electrical behavior of the WS₂-MoS₂ heterostructure transforms from the N-N junction (0 at.% Nb) to the P-N junction (4.5 at.% Nb) and the P-N tunnel junction (8.1 at.% Nb). The band-to-band tunneling at the P-N tunnel junction (8.1 at.% Nb) is eliminated by applying negative gate bias, resulting in a maximum rectification ratio (10⁵) and a minimum channel resistance (10⁸ Ω). With this optimized photodiode (8.1 at.% Nb at V_g = -30 V), an I_photo/I_dark ratio of 6000 and a detectivity of 1.1 × 10¹⁴ Jones are achieved, which are approximately 20 and 3 times higher, respectively, than the previously reported highest values for CVD-grown transition-metal dichalcogenide P-N junctions.

Inducing Strong Light-Matter Coupling and Optical Anisotropy in Monolayer MoS2 with High Refractive Index Nanowire

Mixed-dimensional heterostructures combine the merits of materials of different dimensions; therefore, they represent an advantageous scenario for numerous technological advances. Such an approach can be exploited to tune the physical properties of two-dimensional (2D) layered materials to create unprecedented possibilities for anisotropic and high-performance photonic and optoelectronic devices. Here, we report a new strategy to engineer the light-matter interaction and symmetry of monolayer MoS₂ by integrating it with one-dimensional (1D) AlGaAs nanowire (NW). Our results show that the photoluminescence (PL) intensity of MoS₂ increases strongly in the mixed-dimensional structure because of electromagnetic field confinement in the 1D high refractive index semiconducting NW. Interestingly, the 1D NW breaks the 3-fold rotational symmetry of MoS₂, which leads to a strong optical anisotropy of up to ∼60%. Our mixed-dimensional heterostructure-based phototransistors benefit from this and exhibit an improved optoelectronic device performance with marked anisotropic photoresponse behavior. Compared with bare MoS₂ devices, our MoS₂/NW devices show ∼5 times enhanced detectivity and ∼3 times higher photoresponsivity. Our results of engineering light-matter interaction and symmetry breaking provide a simple route to induce enhanced and anisotropic functionalities in 2D materials.

A Submicrosecond-Response Ultraviolet-Visible-Near-Infrared Broadband Photodetector Based on 2D Tellurosilicate InSiTe3

2D material (2DM) based photodetectors with broadband photoresponse are of great value for a vast number of applications such as multiwavelength photodetection, imaging, and night vision. However, compared with traditional photodetectors based on bulk material, the relatively slow speed performance of 2DM based photodetectors hinders their practical applications. Herein, a submicrosecond-response photodetector based on ternary telluride InSiTe₃ with trigonal symmetry and layered structure was demonstrated in this study. The InSiTe₃ based photodetectors exhibit an ultrafast photoresponse (545-576 ns) and broadband detection capabilities from the ultraviolet (UV) to the near-infrared (NIR) optical communication region (365-1310 nm). Besides, the photodetector presents an outstanding reversible and stable photoresponse in which the response performance remains consistent within 200 000 cycles of switch operation. These significant findings suggest that InSiTe₃ can be a promising candidate for constructing fast response broadband 2DM based optoelectronic devices.

A Heterostructured Graphene Quantum Dots/β-Ga2O3 Solar-Blind Photodetector with Enhanced Photoresponsivity

The superior optical and electronic characteristics of quasi-two-dimensional β-Ga₂O₃ make it suitable for solar-blind (200-280 nm) photodetectors (PDs). The metal-semiconductor-metal (MSM) PDs commonly suffer from low photoresponsivity, slow response speed, and a narrow detection wavelength range despite their simple fabrication process. Herein, we report a high-performance MSM PD by integrating exfoliated β-Ga₂O₃ flakes with zero-dimensional graphene quantum dots (GQDs), which exhibits the advantages of enhancing the photoresponsivity, shortening the photoresponse time, and stimulating a broad range of photon detection. The hybrid GQDs/β-Ga₂O₃ heterostructure PD is sensitive to deep-ultraviolet (DUV) light (250 nm) with an ultrahigh responsivity (R of ∼2.4 × 10⁵ A/W), a large detectivity (D* of ∼4.3 × 10¹³ Jones), an excellent external quantum efficiency (EQE of ∼1.2 × 10⁸%), and a fast photoresponse (150 ms), which is superior to the bare β-Ga₂O₃ PD. These improvements result from effective charge transfer due to the introduction of GQDs, which enhance the light absorption and the generation of electron-hole pairs. In addition, the hybrid GQDs/β-Ga₂O₃ PD also exhibits better photoelectric performance than the bare β-Ga₂O₃ PD at a 1000 nm wavelength. As a conclusion, the hybrid GQDs/β-Ga₂O₃ DUV photodetector shows potential applications in commercial optoelectronic products and provides an alternative solution for the design and preparation of high-performance photodetectors.

Broadband, Ultra-High-Responsive Monolayer MoS2/SnS2 Quantum-Dot-Based Mixed-Dimensional Photodetector

Atomically thin two-dimensional (2D) materials have gained significant attention from the research community in the fabrication of high-performance optoelectronic devices. Even though there are various techniques to improve the responsivity of the photodetector, the key factor limiting the performance of the photodetectors is constrained photodetection spectral range in the electromagnetic spectrum. In this work, a mixed-dimensional 0D/2D SnS₂-QDs/monolayer MoS₂ hybrid is fabricated for high-performance and broadband (UV-visible-near-infrared (NIR)) photodetector. Monolayer MoS₂ is deposited on SiO₂/Si using chemical vapor deposition (CVD), and SnS₂-QDs are prepared using a low-cost solution-processing method. The high performance of the fabricated 0D/2D photodetector is ascribed to the band bending and built-in potential created at the junction of SnS₂-QDs and MoS₂, which enhances the injection and separation efficiency of the photoexcited charge carriers. The mixed-dimensional structure also suppresses the dark current of the photodetector. The decorated SnS₂-QDs on monolayer MoS₂ not only improve the performance of the device but also extends the spectral range to the UV region. Photoresponsivity of the device for UV, visible, and NIR region is found to be ∼278, ∼ 435, and ∼189 A/W, respectively. Fabricated devices showed maximum responsivity under the visible region attributed to the high absorbance of monolayer MoS₂. The response time of the fabricated device is measured as ∼100 ms. These results reveal that the development of a mixed-dimensional (0D/2D) SnS₂-QDs/MoS₂-based high-performance and broadband photodetector is technologically promising for next-generation optoelectronic applications.

2D Heterostructures for Ubiquitous Electronics and Optoelectronics: Principles, Opportunities, and Challenges

A grand family of two-dimensional (2D) materials and their heterostructures have been discovered through the extensive experimental and theoretical efforts of chemists, material scientists, physicists, and technologists. These pioneering works contribute to realizing the fundamental platforms to explore and analyze new physical/chemical properties and technological phenomena at the micro-nano-pico scales. Engineering 2D van der Waals (vdW) materials and their heterostructures via chemical and physical methods with a suitable choice of stacking order, thickness, and interlayer interactions enable exotic carrier dynamics, showing potential in high-frequency electronics, broadband optoelectronics, low-power neuromorphic computing, and ubiquitous electronics. This comprehensive review addresses recent advances in terms of representative 2D materials, the general fabrication methods, and characterization techniques and the vital role of the physical parameters affecting the quality of 2D heterostructures. The main emphasis is on 2D heterostructures and 3D-bulk (3D) hybrid systems exhibiting intrinsic quantum mechanical responses in the optical, valley, and topological states. Finally, we discuss the universality of 2D heterostructures with representative applications and trends for future electronics and optoelectronics (FEO) under the challenges and opportunities from physical, nanotechnological, and material synthesis perspectives.

Ultrabroadband Tellurium Photoelectric Detector from Visible to Millimeter Wave

Ultrabroadband photodetection is of great significance in numerous cutting-edge technologies including imaging, communications, and medicine. However, since photon detectors are selective in wavelength and thermal detectors are slow in response, developing high performance and ultrabroadband photodetectors is extremely difficult. Herein, one demonstrates an ultrabroadband photoelectric detector covering visible, infrared, terahertz, and millimeter wave simultaneously based on single metal-Te-metal structure. Through the two kinds of photoelectric effect synergy of photoexcited electron-hole pairs and electromagnetic induced well effect, the detector achieves the responsivities of 0.793 A W-1 at 635 nm, 9.38 A W-1 at 1550 nm, 9.83 A W-1 at 0.305 THz, 24.8 A W-1 at 0.250 THz, 87.8 A W-1 at 0.172 THz, and 986 A W-1 at 0.022 THz, respectively. It also exhibits excellent polarization detection with a dichroic ratio of 468. The excellent performance of the detector is further verified by high-resolution imaging experiments. Finally, the high stability of the detector is tested by long-term deposition in air and high-temperature aging. The strategy provides a recipe to achieve ultrabroadband photodetection with high sensitivity and fast response utilizing full photoelectric effect.

High performance polarization-sensitive self-powered imaging photodetectors based on a p-Te/n-MoSe2 van der Waals heterojunction with strong interlayer transition

In-plane anisotropic two-dimensional (2D) materials offer great opportunities for developing novel polarization sensitive photodetectors without being in conjunction with filters and polarizers. However, owing to low linear dichroism ratio and insufficient optical absorption of the few layer 2D materials, the comprehensive performance of the present polarization sensitive photodetectors based on 2D materials is still lower than the practical application requirements. In this work, after systematic investigation of the structural, vibrational, and optical anisotropies of layer-structured Te nanosheets, a novel polarization-sensitive self-powered imaging photodetector with high comprehensive performance based on a p-Te/n-MoSe₂ van der Waals heterojunction (vdWH) with strong interlayer transition is proposed. Owing to the high rectification ratio (10⁴) of the diode, the device shows excellent photovoltaic characteristics. As examples, the photodetectors exhibited an ultrahigh on/off ratio of 10⁵ at a relatively weak light intensity (4.73 mw cm^-2), and the highest responsivity of the device could reach 2106 mA W^-1 without any power supply. In particular, benefitting from the excellent dichroism properties of Te nanosheets synthesized in this work, the anisotropic ratio of the photocurrent (I_max/I_min) could reach as high as 16.39 (405 nm, 24.2 mw cm^-2). This value obtained under zero bias voltage is much greater than that of present 2D material photodetectors even at a bias voltage. In addition, the highest detectivity is 2.91 × 10¹³ Jones at a low bias voltage of -0.08 V. This work provides a novel building block for high resolution polarization-sensitive photodetection of weak signals in complex environments.

Atomically Thin Materials for Next-Generation Rechargeable Batteries

Atomically thin materials (ATMs) with thicknesses in the atomic scale (typically <5 nm) offer inherent advantages of large specific surface areas, proper crystal lattice distortion, abundant surface dangling bonds, and strong in-plane chemical bonds, making them ideal 2D platforms to construct high-performance electrode materials for rechargeable metal-ion batteries, metal-sulfur batteries, and metal-air batteries. This work reviews the synthesis and electronic property tuning of state-of-the-art ATMs, including graphene and graphene derivatives (GE/GO/rGO), graphitic carbon nitride (g-C₃N₄), phosphorene, covalent organic frameworks (COFs), layered transition metal dichalcogenides (TMDs), transition metal carbides, carbonitrides, and nitrides (MXenes), transition metal oxides (TMOs), and metal-organic frameworks (MOFs) for constructing next-generation high-energy-density and high-power-density rechargeable batteries to meet the needs of the rapid developments in portable electronics, electric vehicles, and smart electricity grids. We also present our viewpoints on future challenges and opportunities of constructing efficient ATMs for next-generation rechargeable batteries.

Mechanism, Material, Design, and Implementation Principle of Two-Dimensional Material Photodetectors

Two-dimensional (2D) materials may play an important role in future photodetectors due to their natural atom-thin body thickness, unique quantum confinement, and excellent electronic and photoelectric properties. Semimetallic graphene, semiconductor black phosphorus, and transition metal dichalcogenides possess flexible and adjustable bandgaps, which correspond to a wide interaction spectrum ranging from ultraviolet to terahertz. Nevertheless, their absorbance is relatively low, and it is difficult for a single material to cover a wide spectrum. Therefore, the combination of phototransistors based on 2D hybrid structures with other material platforms, such as quantum dots, organic materials, or plasma nanostructures, exhibit ultra-sensitive and broadband optical detection capabilities that cannot be ascribed to the individual constituents of the assembly. This article provides a comprehensive and systematic review of the recent research progress of 2D material photodetectors. First, the fundamental detection mechanism and key metrics of the 2D material photodetectors are introduced. Then, the latest developments in 2D material photodetectors are reviewed based on the strategies of photocurrent enhancement. Finally, a design and implementation principle for high-performance 2D material photodetectors is provided, together with the current challenges and future outlooks.

Laser-assisted micropyramid patterned PDMS encapsulation of 1D tellurium nanowires on cellulose paper for highly sensitive strain sensor and its photodetection studies

This work demonstrates the fabrication of tellurium-nanowires (Te-NWs)/paper based device encapsulated using laser assisted mircopyramid patterned polydimethylsiloxane (PDMS) films. Although there are multiple reports published on 1D Te, most of them are limited to establishing its properties and studying its behavior as a sensor and research on the utilization of Te-NWs for physical sensors remain unexplored. Further, reports on p-type photodetectors also remain scarce. The fabricated Te-NWs/paper with micropyramid structured PDMS films encapsulation was used as a strain sensor, and it exhibited considerable improvement (∼60%) in sensitivity compared to smooth PDMS films. The gauge factor of the developed strain sensor was found to be ∼15.3. In addition, fabricated Te-NWs/paper device with contacts was used as a photodetector and it showed photoresponsivity of ∼22.5 mA W^-1and ∼14.5 mA W^-1in visible and NIR regions, respectively. Furthermore, the device exhibited long-term mechanical stability under harsh deformations. Fabricated 1D Te-NWs/paper device was utilized as a strain sensor to monitor the angular movements in the human body and successfully monitored various human motions, including wrist bending, finger knuckle, elbow joint, and knee joint. The successful demonstration of Te-NWs based physical sensors and utilization in broadband photodetectors opens avenues of research for tellurium based flexible and wearable devices.

A high performance self-powered photodetector based on a 1D Te-2D WS2 mixed-dimensional heterostructure

One-dimensional (1D)-two-dimensional (2D) van der Waals (vdWs) mixed-dimensional heterostructures with advantages of an atomically sharp interface, high quality and good compatibility have attracted tremendous attention in recent years. Herein, a mixed-dimensional vertical heterostructure is constructed by transferring mechanically exfoliated 2D WS₂ nanosheets on epitaxially grown 1D tellurium (Te) microwires. According to the theoretical type-II band alignment, the device exhibits a photovoltaic effect and serves as an excellent self-powered photodetector with a maximum open-circuit voltage (V _oc) up to ∼0.2 V. Upon 635 nm light illumination, the photoresponsivity, external quantum efficiency and detectivity of the self-powered photodetector (SPPD) are calculated to be 471 mA W^-1, 91% and 1.24 × 10¹² Jones, respectively. Moreover, the dark current of the SPPD is highly suppressed to the sub-pA level due to the large lateral built-in electric field, which leads to a high I _light/I _dark ratio of 10⁴ with a rise time of 25 ms and decay time of 14.7 ms. The abovementioned properties can be further enhanced under a negative bias of -2 V. In brief, the 1D Te-2D WS₂ mixed-dimensional heterostructures have great application potential in high performance photodetectors and photovoltaics.