High Photoresponsivity Research Articles

High Mechanical Strength and Multifunctional Microphase-Separated Supramolecular Hydrogels Fabricated by Liquid-Crystalline Block Copolymer.

The development of multifunctional supramolecular hydrogels with high mechanical strength and multifunction is in high demand. In this work, the diblock copolymer poly(acrylamide-co-1-benzyl-3-vinylimidazolium bromide)-block-polyAzobenzene is synthesized through reversible addition-fragmentation chain transfer polymerization. The dynamic host-guest interactions between the host molecule cucurbit[8] uril and guest units are used to fabricate a 3D network of supramolecular hydrogels. Investigations on the properties of the supramolecular hydrogels show that the tensile stress of the sample is 1.46MPa, eight times higher than that of hydrogel without liquid-crystalline block copolymer, and the self-healing efficiency of the supramolecular hydrogels at room temperature is 88.3% (fracture stress) and 100% (fracture strain) after 24h. Results show that microphase-separated structure plays a key role in the high-strength hydrogel, whereas the host-guest interaction endows the hydrogel with self-healing properties. The supramolecular hydrogels with high mechanical strength, photo-responsivity, injectability, and biocompatibility can be used in various potential applications.

ReS2 Nanosheet-Based Channels for Two-Dimensional Field Effect Transistors and Phototransistors with High Photoresponsivity

ReS₂ Nanosheet-Based Channels for Two-Dimensional Field Effect Transistors and Phototransistors with High Photoresponsivity

Retina-inspired in-sensor broadband image preprocessing for accurate recognition via the flexophototronic effect

•3DSS process can achieve permanent polarization, integration, and practical application •The enhanced photosensors have realized broadband perception and high photoresponsivity •The light-dosage-tunable synaptic characteristics have been simulated by the sensors •An artificial visual system can perform preprocessing tasks for accurate recognition Neuromorphic visual systems are promising candidates for emulating vision perception and recognition tasks, especially for two-dimensional (2D) semiconductor-based imaging sensors due to their tunable electrical/optical properties and compatibility for heterogeneous integration. The device integration of sensing-memory-processing units and accurate recognition for image sensors become critical obstacles to simulating visual systems; thus, developing more advanced neuromorphic structures is required. Here, we demonstrate a retina-inspired 2D molybdenum disulfide (MoS2)-based vision sensor capable of both broadband perception and preprocessing functions by exploiting the flexophototronic effect. Three-dimensional stress stabilization (3DSS) is consciously introduced into the flexophototronic sensor to achieve broadband sensing and high photoresponsivity, resulting in distinctive UV information extraction for image preprocessing. Furthermore, the artificial neural network can remarkably enhance the recognition accuracy from 35% to 90% due to preprocessing validity. This work lays the foundation for developing emerging flexophototronics for artificial visual systems endowed with real-time interaction and efficient execution. Neuromorphic visual systems are promising candidates for emulating vision perception and recognition tasks, especially for two-dimensional (2D) semiconductor-based imaging sensors due to their tunable electrical/optical properties and compatibility for heterogeneous integration. The device integration of sensing-memory-processing units and accurate recognition for image sensors become critical obstacles to simulating visual systems; thus, developing more advanced neuromorphic structures is required. Here, we demonstrate a retina-inspired 2D molybdenum disulfide (MoS2)-based vision sensor capable of both broadband perception and preprocessing functions by exploiting the flexophototronic effect. Three-dimensional stress stabilization (3DSS) is consciously introduced into the flexophototronic sensor to achieve broadband sensing and high photoresponsivity, resulting in distinctive UV information extraction for image preprocessing. Furthermore, the artificial neural network can remarkably enhance the recognition accuracy from 35% to 90% due to preprocessing validity. This work lays the foundation for developing emerging flexophototronics for artificial visual systems endowed with real-time interaction and efficient execution.

High Photoresponsivity and Response Speed of Visible‐Light Photodetectors Based on Tin Disulfide/Indium‐Doped Tin Disulfide Homostructures

AbstractTin disulfide (SnS2) is an emerging 2D‐layered metal dichalcogenide with promising application potential for highly sensitive and fast‐response‐speed photodetectors. However, SnS2‐based photodetectors still have drawbacks that limit their practical and commercial applications. Herein, an effective route is proposed for constructing SnS2/indium‐doped SnS2 homostructures to improve photodetector performance. Vertical SnS2/Sn0.991In0.009S2 homostructures and photodetectors based on these homostructures were fabricated via a polydimethylsiloxane‐assisted dry‐transfer method. The photodetectors exhibit excellent performance, including a high photoresponsivity of up to 271.7 A W−1, high normalized detectivity of up to 2.13 × 1012 cm Hz1/2 W−1, and fast response time of ≈10 ms. The pseudo‐built‐in electrical field of the SnS2/Sn0.991In0.009S2 homostructure results in the superior performance of the photodetectors based on this material compared to that based on individual SnS2 and Sn0.991In0.009S2 thin layers, most 2D materials, and commercial photodetectors (e.g., THORLABS FD11A Si, and FGA01 InGaAs). This study provides a facile and effective approach to enhance the performance of SnS2‐based photodetectors and paves the way for future applications of photodetectors based on SnS2 and other 2D materials.

High Responsivity Vacuum Nano-Photodiode Using Single-Crystal CsPbBr3 Micro-Sheet.

Field electron emission vacuum photodiode is promising for converting free-space electromagnetic radiation into electronic signal within an ultrafast timescale due to the ballistic electron transport in its vacuum channel. However, the low photoelectric conversion efficiency still hinders the popularity of vacuum photodiode. Here, we report an on-chip integrated vacuum nano-photodiode constructed from a Si-tip anode and a single-crystal CsPbBr3 cathode with a nano-separation of ~30 nm. Benefiting from the nanoscale vacuum channel and the high surface work function of the CsPbBr3 (4.55 eV), the vacuum nano-photodiode exhibits a low driving voltage of 15 V with an ultra-low dark current (50 pA). The vacuum nano-photodiode demonstrates a high photo responsivity (1.75 AW-1@15 V) under the illumination of a 532-nm laser light. The estimated external quantum efficiency is up to 400%. The electrostatic field simulation indicates that the CsPbBr3 cathode can be totally depleted at an optimal thickness. The large built-in electric field in the depletion region facilitates the dissociation of photoexcited electron-hole pairs, leading to an enhanced photoelectric conversion efficiency. Moreover, the voltage drop in the vacuum channel increases due to the photoconductive effect, which is beneficial to the narrowing of the vacuum barrier for more efficient electron tunneling. This device shows great promise for the development of highly sensitive perovskite-based vacuum opto-electronics.

Self-powered, ultra-fast and high photoresponsivity of MoTe2/HfSe2 heterostructure broadband photovoltaic device

Due to their multifunctionality and tunable properties in electronic devices, the transition-metal dichalcogenides (TMDs) based van der Waals (vdW) heterostructures have attracted much attention and are considered a potential candidate for advanced nanoelectronics. In this work, a self-powered molybdenum ditelluride (MoTe2)/hafnium diselenide (HfSe2) vdW heterostructure-based photodetector with ohmic contacts is designed. The high rectification ratio is attained as 1.9×106, rising from the clean interface and small barrier height. Photovoltaic experiments are also carried out using laser light with a wavelength of 532–1064 nm in visible and near-infrared (VNIR) regions with different power intensities ranging from 10 to 120 nW. The photoresponsivity of MoTe2/HfSe2 is enhanced remarkably up to 1.3×103A/W with detectivity 2.6 × 1013 Jones and external quantum efficiency of 68% because of band-to-band and interlayer TMDs charge transition at a longer wavelength (1064 nm). Under incoming light with an intensity of 120 nW, rapid growth (6.8 μs) and decay times (8.7 μs) are projected because of interlayer TMDs charge transition at the longer wavelength. The obtained results showed significantly higher values than the reported vdW heterostructures. The fast response time, low recombination rate and astonishing value of photoresponsivity are the key parameters to developing highly efficient TMDs-based solar devices.

Construction of a High‐Quality Organic‐Inorganic Hybrid Heterostructure and Its Photo‐response Performance

Comprehensive SummaryThe combination of metal oxide and organic semiconductor for constructing organic–inorganic hybrid heterostructure is promising to offer unique optoelectronic properties. However, the distinct difference in electron structure and processing technology of the two types of materials makes it usually difficult to fully deliver their complementary advantages. Herein, we report the construction of a high quality organic/In2O3 hybrid heterostructure presenting a good ambipolar transport with average electron mobility >1 cm2·V–1·s–1 and hole mobility up to 0.4 cm2·V–1·s–1, respectively, together with a high‐gain inverter. In addition, the incorporation with organic film on top of In2O3 remarkably reduces the dark current, enabling the realization of high photoconductivity response with photosensitivity of two magnitudes higher than that of pure In2O3. The photoconductor and phototransistor of the hybrid structure demonstrate high photoresponsivity >103 AW–1 and detectivity up to 1014 Jones, demonstrating the promising functionality of such a high quality hybrid heterostructure.

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.

Experimental and DFT study of structural and optical properties of Ni-doped ZnO nanofiber thin films for optoelectronic applications

As an important metal oxide semiconductor, transition metal-doped zinc oxide (ZnO) has attracted great interest for various applications in optoelectronic, spintronic photovoltaic and photodetectors due to its significant chemical and physical properties. In this research study, pure and nickel (Ni)-doped ZnO nanostructured films were synthesized via the sol-gel method using the spin coating technique on glass substrates. The structural results revealed that all samples exhibited a polycrystalline wurtzite structure and a (002) plane preferred orientation. The crystallite size was reduced by Ni doping. The morphology micrographs indicate that the surface of thin films shows nanofiber structures. An optical study revealed the high transparency of the films. The photoluminescence (PL) showed one ultraviolet (UV) emission at 387 nm and different defect emissions for all films. The absorption, band gap and PL emissions intensities were influenced by Ni doping. Ni-doped ZnO nanostructured thin films revealed high UV sensitivity and photoresponse. Therefore, these thin films are a promising material for a UV photodetector. The dielectric function, absorption coefficient and energy band gap were also calculated and discussed by density functional theory (DFT), using the Ultra Soft Pseudo Potential (US-PP) approach implemented in the CASTEP code.

Tuning the Layered Thickness of MoTe2 Thin Film for Dye‐Sensitized Solar Cells, UV and Visible Spectrum Photodetectors, and Hydrogen Evolution Reaction

Atomically thick van der Waals (VdW)‐bonded layered transition metal dichalcogenide (TMD) structures have influenced the investigation of novel phenomena for modern electronics and energy devices immensely. Herein, the fabrication of atomically thick tunable mollybednum ditelluride thin films on substrates through a chemical bath methodology is shown for the first time. The proposed methodology can be used to fine tune the atomic layer thickness of MoTe2 with highly modified surface characteristics, which is a greatly interesting feature for multifunctional nanodevice fabrication. Microscopic images confirm the atomic layer thickness‐tuned MoTe2. Furthermore, a photodetector assembled using few‐layer‐thick (S4) MoTe2 shows a high photoresponsivity of 3.21 A W−1 under ultraviolet light and an excellent detectivity of 5.4 × 1011 Jones, and a dye‐sensitized solar cell constructed using a photocathode made from S4 MoTe2 atomic layers shows a high power conversion efficiency of 8.44%, which is much greater than that of many other layered TMD structures. In addition, synthesized S4 MoTe2 atomic layers exhibit excellent hydrogen evolution characteristics in alkaline and acidic media. The resulting outcomes obviously establish the advantages of developed layered thick MoTe2 to produce the outstanding interface characteristics between the vdW‐bonded atomic layers to achieve outstanding energy and semiconductor devices.

Self-powered broadband photodetector based on MoS2/Sb2Te3 heterojunctions: a promising approach for highly sensitive detection

Abstract Topological insulators have shown great potential for future optoelectronic technology due to their extraordinary optical and electrical properties. Photodetectors, as one of the most widely used optoelectronic devices, are crucial for sensing, imaging, communication, and optical computing systems to convert optical signals to electrical signals. Here we experimentally show a novel combination of topological insulators (TIs) and transition metal chalcogenides (TMDs) based self-powered photodetectors with ultra-low dark current and high sensitivity. The photodetector formed by a MoS2/Sb2Te3 heterogeneous junction exhibits a low dark current of 2.4 pA at zero bias and 1.2 nA at 1V. It shows a high photoresponsivity of >150 mA W−1 at zero bias and rectification of 3 times at an externally applied bias voltage of 1V. The excellent performance of the proposed photodetector with its innovative material combination of TMDs and TIs paves the way for the development of novel high-performance optoelectronic devices. The TIs/TMDs transfer used to form the heterojunction is simple to incorporate into on-chip waveguide systems, enabling future applications on highly integrated photonic circuits.

High-Responsivity Multiband and Polarization-Sensitive Photodetector Based on the TiS3/MoS2 Heterojunction.

Two-dimensional (2D) material photodetectors have received considerable attention in optoelectronics as a result of their extraordinary properties, such as passivated surfaces, strong light-matter interactions, and broad spectral responses. However, single 2D material photodetectors still suffer from low responsivity, large dark current, and long response time as a result of their atomic-level thickness, large binding energy, and susceptibility to defects. Here, a transition metal trichalcogenide TiS3 with excellent photoelectric characteristics, including a direct bandgap (1.1 eV), high mobility, high air stability, and anisotropy, is selected to construct a type-II heterojunction with few-layer MoS2, aiming to improve the performance of 2D photodetectors. An ultrahigh photoresponsivity of the TiS3/MoS2 heterojunction of 48 666 A/W at 365 nm, 20 000 A/W at 625 nm, and 251 A/W at 850 nm is achieved under light-emitting diode illumination. The response time and dark current are 2 and 3 orders of magnitude lower than those of the current TiS3 photodetector with the highest photoresponsivity (2500 A/W), respectively. Furthermore, polarized four-wave mixing spectroscopy and polarized photocurrent measurements verify its polarization-sensitive characteristics. This work confirms the excellent potential of TiS3/MoS2 heterojunctions for air-stable, high-performance, polarization-sensitive, and multiband photodetectors, and the excellent type-II TiS3/MoS2 heterojunction system may accelerate the design and fabrication of other 2D functional devices.

Ultraviolet to near infrared wavelength independent SnS-graphene hybrid thin film photodetector from nanocolloids

It is crucial and imperative to produce wavelength-independent photodetectors as most of the reported devices are limited by their operating wavelength region. We report graphene incorporated tin sulfide (SnS) hybrid thin films as photodetectors operational in the ultrabroadband range of wavelength using their nanocolloids. SnS nanocolloids obtained by Pulsed Laser Irradiation in Liquid (PLIL) performed by irradiating SnS powder using 532 nm laser output (Nd:YAG) is the first report on SnS by PLIL. Into this nanocolloid, graphene was ultrasonically dispersed. SnS-graphene hybrid films were deposited by spin-coating followed by annealing in vacuum. The morphological study of the films revealed graphene layers hybridized with spherical SnS nanoparticles. Raman analysis, X-ray diffraction and X-ray photoelectron spectroscopy results confirmed the phase, structure and chemical composition. A bandgap of 2.1–2.0 eV was obtained for the annealed SnS films and graphene addition helped in extending the absorption range over the entire UV–Vis-NIR reducing the bandgap values to 1.8–1.5 eV. The films showed high photoresponse independent of the different wavelengths of illumination. The hybrid photodetector exhibits a specific detectivity of 107 Jones and a responsivity of 10-5 AW−1. The SnS-graphene hybrid photodetectors, being wavelength-independent, are a promising candidate for optoelectronic applications.

(Invited, Digital Presentation) Ternary III-Sb Nanowires: Synthesis and Their Electronic and Optoelectronics Applications

Nowadays, the increasing demand for low power and highly efficient electronics and optoelectronics has driven the semiconductor industry to look for the alternatives of Si which is approaching its physical limit. Materials like graphene, carbon nanotube, III-V materials and so on, are the most promising candidates as the replacement of silicon. Among them, III-Sb materials, a sub-group of III-V materials, have been extensively researched due to their narrow and direct bandgap, high charge carrier mobility and high g-factor which makes them suitable for transistor, infra red detection and so on. Their nanowire counterparts have also been explored as the geometry of nanowire provide unique advantages.One of the research directions of III-Sb nanowire is to study their ternary counterpart (III-V-Sb or III-III’-Sb) like InAsSb, GaAsSb and InGaSb. Compares with binary compounds, ternary compound provides more room for engineering freedom like lattice parameter engineering and bandgap tuning. In this presentation, the synthesis and the electronic and optoelectronic applications of ternary III-Sb nanowires will be introduced. The high-crystal quality and high-aspect ratio ternary III-Sb nanowires were synthesized by using solid-source chemical vapor deposition method. Composition tunability was demonstrated successfully by adjusting the precursor ratio which allowed us to control the physical properties. We further integrated these nanowires into transistors and photodetectors which exhibit good performance like high carrier mobility and good photoresponse.

Mid-Infrared Photoconductive Detectors Fabricated from Solution-Processed PbSe Nanocrystals

Lead selenide (PbSe) was the first semiconductor used for photosensors operating in the mid-wavelength infrared spectral region (3-5 um) and is still the primary choice for low-cost, uncooled photoconductive detector applications. Even through PbSe has been studied for over 70 years, more understandings on its physical mechanism for high photoresponsivity is still emerging. Common methods of fabricating PbSe detectors involve physical/chemical vapor deposition or chemical bath deposition (CBD) techniques, followed by post-deposition sensitization processes including oxygen annealing and iodization. Here, we present a new approach to fabricating photoconductive devices based on PbSe colloidal nanocrystals. This infrared colloidal ink can serve as a critical component to enabling digital additive manufacturing of mid-infrared sensor arrays and simultaneously lower the fabrication cost by removing multiple masking steps required in conventional approaches. We report on the synthesis and fabrication of PbSe nanostructured film and the effects of thermal annealing as well as oxygen and iodide incorporation on the photoconductive properties.

Rationally designed state-of-the-art approach for enhancing the ultraviolet photon detection performance of ZnO thin film

Here, we demonstrate a simple and effective state-of-the-art (surface passivation) approach for enhancing the UV photo detection performance of ZnO thin films synthesized via spray pyrolysis. The surface passivated Ag/ZnO/Ag device (using polyvinyl alcohol layer) has low dark current of 1.1 nA as compared with the device without surface passivation (0.04 μA). The significant decay in the dark current after surface passivation is due the reduction in the density of surface oxygen vacancies confirmed by PL measurements. The UV photon detection capability of the surface passivated ZnO thin film exhibits a significantly high photo response (3675), high photosensitivity (3.6 × 105), photo-responsivity (0.6 A/W) and fast response time (0.6 ms) under UV light (340 nm, 140 μW/cm2). This straightforward approach superimposes surface defects, making the ZnO thin film more suitable for a wide range of electronic device applications while preserving the material's intrinsic properties.

Ferroelectric-gated MoSe2 photodetectors with high photoresponsivity

Ferroelectric transistors with semiconductors as the channel material and ferroelectrics as the gate insulator have potential applications in nanoelectronics. We report in-situ modulation of optoelectronic properties of MoSe2 thin flakes on ferroelectric 0.7PbMg1/3Nb2/3O3–0.3PbTiO3 (PMN-PT). Under the excitation of 638 nm laser, the photoresponsivity can be greatly boosted to 59.8 A W−1 and the detectivity to 3.2 × 1010 Jones, with the improvement rates of about 1500% and 450%, respectively. These results suggest hybrid structure photodetector of two-dimensional layered material and ferroelectric has great application prospects in photoelectric detector.

A high-performance quasi-vertical MoSe2 photodiode with ultra-low dark current

Van der Waals heterostructure based on 2D materials is a promising technology for high-performance optoelectronic devices because of its tunable bandgaps and optical properties. However, photodetectors with a low dark current and a fast response speed commonly lose their photoresponsivity. The recovery current induced by the Schottky barrier height variation cancels out the device's reverse bias current in this paper, resulting in a quasi-vertical MoSe2 photodiode with ultralow dark current (<1 pA). Simultaneously, rapid electron–hole pair separation occurs at the interface due to the large heterojunction area and the strong interlayer coupling of MoSe2/graphene heterojunction, resulting in a fast response time of 1.5 ms and a high photoresponsivity of 19.72 A/W. Furthermore, the Au/MoSe2 forms a Schottky contact, which is asymmetrical to the Ohmic contact formed by the MoSe2/graphene, enabling the proposed device to achieve high-performance self-powered photodetection. Our work shows an alternative approach to improve the performance of future electronic and optoelectronic applications.

Robust and fast response solar-blind UV photodetectors based on the transferable 4H-SiC free-standing nanowire arrays

Wide band gap semiconductor 4 H -SiC has been considered as the most promising candidate for developing solar blind ultraviolet (UV) photodetectors (PDs). However, the absence of PDs constructed by the desired 4 H -SiC nanostructures greatly limits their performance and practical application. In this study, the free-standing 4 H -SiC bamboo-like nanowire arrays with an even diameter/height of 30 nm/35 µm prepared by the anodic oxidation of 4 H -SiC bulk single crystal in a top-down manner are used to develop the solar-blind PDs. Experiment results reveal that the developed PDs can have an excellent solar-blind detection performance such as high sensitivity to 275 and 365 nm UV light, a considerable light-dark ratio (∼44.3), remarkably low dark current, fast response (47.3 ms), excellent repeatability and stability. Additionally, the unencapsulated PDs can have an excellent high-temperature stability up to 300 ºC. It is expected that the 4 H -SiC nanowire arrays-based PDs can have more potential than their counterpart bulk material for the future optoelectronic device applications. • The MSM solar-blind UV photodetectors based on bamboo-like 4 H -SiC nanowire arrays have been successfully fabricated. • The developed photodetectors can have a large light-dark ratio, high photoresponsivity, and remarkably low dark current. • The resulting photodetectors can achieve the fast response and an excellent high-temperature stability up to 300 ºC.

Controlled two-step synthesis of nanostructured WS2 thin films for enhanced UV–visible photodetector applications

Nowadays, development of transition metal dichalcogenides (TMDs) integrated ultra-fast optoelectronics devices under broad spectral range has attracted our research community. The fabricated devices should have high photoresponsivity, specific detectivity, fast switching, and low power consumption. Herein, we put the efforts to successfully synthesize a large area of WS 2 nanostructures using sputtering and chemical vapour deposition (CVD) techniques for ultraviolet-visible (UV-Vis) photodetector applications. It is found that following the sulfurization of sputter deposited tungsten films at 800 °C for 60 min facilitated nanostructures with high surface-area to volume ratio. Promising metal-semiconductor-metal (MSM) featured photodetector test-devices based upon interdigitated symmetric Ag electrodes are fabricated. Finally, interdigitated electrode structure, ohmic contact between metal and photoactive material, and enhanced structural properties allowed the test-device accelerates the photodetector performances with 100 ms of response time under UV and visible illuminations even at a bias voltage of 2 V. • WS 2 nanostructures are successfully grown by two-step synthesis process. • Fabricated the Ag/WS 2 /Ag UV-Vis photodetector with ohmic contact behavior. • Ultrafast response time of 100 ms was achieved through interdigitated Ag electrodes. • Superior figures of merit were achieved by the WS 2 photodetector.