Various large-area growth methods for two-dimensional transition metal dichalcogenides have been developed recently for future electronic and photonic applications. However, they have not yet been employed for synthesizing active pixel image sensors. Here, we report on an active pixel image sensor array with a bilayer MoS2 film prepared via a two-step large-area growth method. The active pixel of image sensor is composed of 2D MoS2 switching transistors and 2D MoS2 phototransistors. The maximum photoresponsivity (Rph) of the bilayer MoS2 phototransistors in an 8 × 8 active pixel image sensor array is statistically measured as high as 119.16 A W−1. With the aid of computational modeling, we find that the main mechanism for the high Rph of the bilayer MoS2 phototransistor is a photo-gating effect by the holes trapped at subgap states. The image-sensing characteristics of the bilayer MoS2 active pixel image sensor array are successfully investigated using light stencil projection.

Highly sensitive and system integrable gas sensors play a significant role in industry and daily life, and MoS2 has emerged as one of the most promising two-dimensional nanomaterials for gas sensor technology. In this study, we demonstrate a scalable and monolithically integrated active-matrix gas sensor array based on large-area bilayer MoS2 films synthesized via two-successive steps: radio-frequency magnetron sputtering and thermal sulfurization. The fabricated thin-film transistors exhibit consistent electrical performance over a few centimeters area and resulting gas sensors detect NO2 with ultra-high sensitivity across a wide detection range, from 1 to 256 ppm. This is due to the abundant grain boundaries of the sputtered MoS2 channel, which perform as active sites for absorption of NO2 gas molecules. The demonstrated active-matrix gas sensor arrays display good switching capabilities and are anticipated to be readily integrated with additional circuitry for different gas sensing and monitoring applications.

The epitaxial growth of functional oxides using a substrate with a graphene layer is a highly desirable method for improving structural quality and obtaining freestanding epitaxial nanomembranes for scientific study, applications, and economical reuse of substrates. However, the aggressive oxidizing conditions typically used in growing epitaxial oxides can damage graphene. Here, we demonstrate the successful use of hybrid molecular beam epitaxy for SrTiO 3 growth that does not require an independent oxygen source, thus avoiding graphene damage. This approach produces epitaxial films with self-regulating cation stoichiometry. Furthermore, the film (46-nm-thick SrTiO 3 ) can be exfoliated and transferred to foreign substrates. These results open the door to future studies of previously unattainable freestanding oxide nanomembranes grown in an adsorption-controlled manner by hybrid molecular beam epitaxy. This approach has potentially important implications for the commercial application of perovskite oxides in flexible electronics and as a dielectric in van der Waals thin-film electronics.

chemical doping, elemental doping, and electrostatic gating techniques. The photoresponsive performances of PN-junction photodiodes have thus been effectively increased compared to intrinsic 2D material-based photodiodes. [18,19] Although PN-homojunction photodiodes exhibit better optical properties than intrinsic 2D materials photodiodes, there are many challenges present in fabricating the junctions. Chemical doping techniques are highly dependent on environmental conditions, [12,13] the elemental doping method causes limited vertical junction formation which leads to lower charge mobility, [5] and the electrostatic doping method has led to devices with slow photoresponses. [14] Heterojunction photodiodes with dissimilar materials and unequal bandgap have also been studied, using MoS 2 /Si, [20,21] MoS 2 /GaN, [22] MoS 2 / graphene, [23,24] MoS 2 /Black Phosphorous (BP), [6,25] and MoS 2 /pentacene, [26,27] and show improved electrical and optical properties compared to homojunction photodiodes. However, despite notable performance improvements in terms of photoresponsivity and sensitivity, homo-and heterojunction photodiodes are limited by low carrier mobility, difficult processing techniques, and unstable photoresponsive behavior. [18,19] In these designs, the chosen fabrication technique also has a significant influence on the device performance.Many studies have also been reported on Schottky barrier phototransistors, which incorporate a gate terminal to a metal-semiconductor-metal (M-S-M) design to obtain reliable electrical and optical properties along with a stable photoresponse and easier processing methods. [28,29] The gating effect is a key device function in these devices as it tunes the Schottky barrier, which controls charge transfer in the device. [30,31] The forward and reverse saturation currents can be determined by modulating the Schottky barrier by applying positive, negative, or zero bias. [28] However, electrical characteristics are often limited by the interface properties of the materials used, and more generally by fabrication techniques. The investigation of the Schottky contact between metals and MoS 2 is now gaining interest due to possible applications in photodetectors, biosensors, photovoltaics, as well as field-effect transistors (FETs).In this work, we introduce a unique design for MoS 2 photodiodes. This design uses a multilayer MoS 2 semiconductor layer 2D materials, specifically MoS 2 semiconductors, have received tremendous attention for photo-sensing applications due to their tunable bandgap and low noise levels. A unique photodetector using multilayer MoS 2 as the semiconductor channel, in which the gate electrode of the device is permanently connected to the grounded source electrode to introduce rectification, is reported. The proposed grounded-gate photodiode exhibits high photoresponsivity of 1.031 A W −1 , excellent photodetectivity (>6 × 10 10 jones), and highly stable rise/fall time response (100-200 ms) under illumination of visible light (at the wavelengths of 405,...

Molybdenum disulfide (MoS2) synthesis methods have become diverse and enable wafer‐scale growth for high‐performance optoelectronic applications. However, there has been limited research on the carrier transports of wafer‐scale deposited MoS2 thin‐film transistors (TFTs). In this paper, the first demonstration of the electron transport mechanism in top‐gated polycrystalline crystalline MoS2 (poly‐MoS2) TFTs grown by a wafer‐scale deposition method is presented. The MoS2 is synthesized via radio frequency (RF) magnetron sputtering and gas flow chemical vapor sulfurization. A surface analysis is performed to determine the basic ingredients and grain size of the grown MoS2. Furthermore, the electrical properties and charge transport behaviors of the poly‐MoS2 TFTs are characterized using current–voltage measurement at low temperatures (93–273 K). The extracted parameters (e.g., field‐effect mobility, contact and channel resistance, activation energy, and hopping distance) and 2D Mott variable range hopping (VRH) of the poly‐MoS2 TFTs support the notion that the primary mechanism of carrier transport in the poly‐MoS2 TFTs involves thermally active hopping and grain effects. For advanced poly‐MoS2‐based devices, an increase of grain size will be the principal factor using the relationship between the grain size and electron hopping distance of poly‐MoS2.

We report the low-temperature characterization of back-gated multilayer molybdenum disulfide (MoS2) thin-film transistors (TFTs) based on mechanically exfoliated natural MoS2 crystals. Although all the tested MoS2 TFTs are fabricated with the same processes and materials, the current-voltage characteristics of MoS2 TFTs between 77 K and 300 K indicate the existence of two distinct transport behaviors in MoS2 TFTs. One group with a negligible Schottky barrier shows temperature-independent large field-effect mobility, whereas the other group with a high Schottky barrier exhibits significantly lower mobility with a large dependence on temperature variation. We have revealed that the temperature dependence originates from the different carrier injection mechanisms at the source-channel junction, where the intrinsic variation of electronic properties of natural MoS2 crystals can strongly influence the Schottky barrier. Given that sample-to-sample variations are commonly observed in MoS2 TFTs, the metal-semiconductor junction of the as-fabricated device is of paramount importance, and so the low-temperature measurement of current-voltage characteristics of a multilayer MoS2 transistor can be a practical means to investigate the contact properties of natural MoS2 TFTs. Our comprehensive study advances the fundamental knowledge of the transport mechanisms particularly through the metal-MoS2 interface, which will be a critical step toward high-performance electronics based on 2D semiconductors.

The demand for renewable energy resources has led to the development of water electrolysis technology. Various transitional metal chalcogenides are investigated to adopt water electrolysis. Nickel telluride, from the family of transition metal chalcogenides, is attractive as a new cathode material for the hydrogen evolution reaction due to its metallic property. However, conventional approaches mainly focus on the solvothermal method and these have difficulty in controlling the alignment of nickel telluride. Therefore, another route to synthesize this material is necessary. In this study, for the first time, a radio-frequency (RF) magnetron sputtering method is used to synthesize a nickel telluride thin film and this method has the benefit of controlling the alignment of the nickel telluride thin film. By RF magnetron sputtering, a nickel telluride thin film is deposited on the substrate along the direction normal to the plane of the substrate, forming a columnar structure with vertical alignment. Its microstructure enables fast flow of electrons, having the advantage of hydrogen evolution reaction as a cathode material. The sample in optimized conditions shows a good performance with an overpotential of 416 mV and a Tafel slope of 63.79 mV dec−1. Therefore, the RF magnetron sputtering method can be adopted as a new approach to synthesize a vertically aligned electrocatalyst.

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