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Artificial optic-neural synapse for colored and color-mixed pattern recognition
摘要： The priority of synaptic device researches has been given to prove the device potential for the emulation of synaptic dynamics and not to functionalize further synaptic devices for more complex learning. Here, we demonstrate an optic-neural synaptic device by implementing synaptic and optical-sensing functions together on h-BN/WSe2 heterostructure. This device mimics the colored and color-mixed pattern recognition capabilities of the human vision system when arranged in an optic-neural network. Our synaptic device demonstrates a close to linear weight update trajectory while providing a large number of stable conduction states with less than 1% variation per state. The device operates with low voltage spikes of 0.3 V and consumes only 66 fJ per spike. This consequently facilitates the demonstration of accurate and energy efficient colored and color-mixed pattern recognition. The work will be an important step toward neural networks that comprise neural sensing and training functions for more complex pattern recognition.
关键词： optic-neural synaptic device,human vision system,pattern recognition,energy efficiency,h-BN/WSe2 heterostructure
更新于2025-09-23 15:21:21
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[IEEE 2019 Device Research Conference (DRC) - Ann Arbor, MI, USA (2019.6.23-2019.6.26)] 2019 Device Research Conference (DRC) - Tunable WSe <sub/>2</sub> phototransistor enabled by electrostatically doped lateral p-n homojunction
摘要： This study demonstrates an approach to tune the responsivity and detectivity of a WSe2 phototransistor by incorporating an electrostatically doped lateral p-n junction in the form of side gates to the transistor channel. The resulting decrease in dark current and enhancement in photocurrent by externally injected carriers into the conduction channel leads to improved photodetection with a fast response time (τ).
关键词： photodetection,phototransistor,lateral p-n junction,electrostatic doping,WSe2
更新于2025-09-23 15:21:01
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Influence of WSe2 buffer layer at back electrode on performance of Cu2ZnSn(S,Se)4 solar cells
摘要： CZTSSe-based solar cells with a structure of Al/ITO/ZnO/CdS/CZTSSe/p-WSe2/Mo (denoted as WSe2-CZTSSe solar cell) were prepared on the Mo-coated soda-lime glass (SLG) with a pre-sputtering metal tungsten (W) layer. Comparing with the conventional CZTSSe solar cell with a structure of Al/ITO/ZnO/CdS/CZTSSe/n-MoSe2/Mo (denoted as CZTSSe solar cell), the WSe2-CZTSSe solar cell shows a significant improvement in open-circuit voltage (VOC), short-circuit current density (JSC) and fill factor (FF), and so its power conversion efficiency (PCE) enhances. The largest enhancement of the PCE is from 4.13% of the CZTSSe solar cell to 5.45% of the WSe2-CZTSSe solar cell. The increased VOC and JSC are mainly due to the enhancement of photogenerated current density (JL) and decrease of reversion saturation current density (J0), while the increased FF is ascribed to the increase of shunt resistance (RSh). The influence mechanism of the WSe2 buffer layer on JL, J0 and RSh is also investigated in detail. Our results present a route of increment of PCE by reducing and even removing back contact barrier between CZTSSe and MoSe2 layers.
关键词： Cu2ZnSn(S,Se)4,Solar cell,MoSe2,Contact potential barrier,Interface,WSe2
更新于2025-09-23 15:19:57
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Layer-dependent signatures for exciton dynamics in monolayer and multilayer WSe2 revealed by fluorescence lifetime imaging measurement
摘要： Two-dimensional (2D) transition-metal dichalcogenide (TMD) materials have aroused noticeable interest due to their distinguished electronic and optical properties. However, little is known about their complex exciton properties together with the exciton dynamics process which have been expected to influence the performance of optoelectronic devices. The process of fluorescence can well reveal the process of exciton transition after excitation. In this work, the room-temperature layer-dependent exciton dynamics properties in layered WSe2 are investigated by the fluorescence lifetime imaging microscopy (FLIM) for the first time. This paper focuses on two mainly kinds of excitons including the direct transition neutral excitons and trions. Compared with the lifetime of neutral excitons (< 0.3 ns within four-layer), trions possess a longer lifetime (~ 6.6 ns within four-layer) which increases with the number of layers. We attribute the longer-lived lifetime to the increasing number of trions as well as the varieties of trion configurations in thicker WSe2. Besides, the whole average lifetime increases over 10% when WSe2 flakes added up from monolayer to four-layer. This paper provides a novel tuneable layer-dependent method to control the exciton dynamics process and finds a relatively longer transition lifetime of trions at room temperature, enabling to investigate in the charge transport in TMD-based optoelectronics devices in the future.
关键词： two-dimensional (2D) WSe2,fluorescence lifetime,fluorescence lifetime imaging microscopy (FLIM),exciton dynamics,density functional theory (DFT)
更新于2025-09-23 15:19:57
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Tungsten Dichalcogenide Nanoflake/InGaZnO Thin-Film Heterojunction for Photodetector, Inverter, and AC Rectifier Circuits
摘要： Heterojunction PN diode and inverter circuits are fabricated and presented, combining two-dimensional WSe2 nanoflake and amorphous InGaZnO (a-IGZO) thin film on a glass substrate. A heterojunction p-WSe2/n-IGZO diode exhibits rectifying characteristics and effectively responds to red light (λ = 620 nm) under a reverse bias. The combination of a heterojunction PN diode and IGZO field effect transistor (FET) leads to a diode-load inverter showing a peak voltage gain of about 12 at a supply voltage of 5 V. The same integration from the PN diode and n-FET displays the capability of visible light detection when a reverse-bias voltage is applied to the PN diode. Furthermore, after oxygen plasma treatment on the PN diode, it shows dramatically enhanced on/off rectification ratio of ≈5 × 105 due to the hole doping effect on the WSe2 nanoflake. Such an improved PN diode leads to an alternating current rectifier circuit as integrated with IGZO FET.
关键词： field-effect transistor (FET),inverter,WSe2,InGaZnO (IGZO),heterojunction PN diode,AC rectifier
更新于2025-09-23 15:19:57
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A WSe <sub/>2</sub> vertical field emission transistor
摘要： We report the first observation of a gate-controlled field emission current from a tungsten diselenide (WSe2) monolayer, synthesized by chemical-vapour deposition on a SiO2/Si substrate. Ni contacted WSe2 monolayer back-gated transistors, under high vacuum, exhibit n-type conduction and drain-bias dependent transfer characteristics, which are attributed to oxygen/water desorption and drain induced Schottky barrier lowering, respectively. The gate-tuned n-type conduction enables field emission, i.e. the extraction of electrons by quantum tunnelling, even from the flat part of the WSe2 monolayers. Electron emission occurs under an electric field ～100 V μm?1 and exhibits good time stability. Remarkably, the field emission current can be modulated by the back-gate voltage. The first field-emission vertical transistor based on the WSe2 monolayer is thus demonstrated and can pave the way to further optimize new WSe2 based devices for use in vacuum electronics.
关键词： WSe2,field emission,monolayer,transistor,vacuum electronics
更新于2025-09-19 17:15:36
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Laser annealing towards high-performance monolayer MoS2 and WSe2 field effect transistors
摘要： The transition metal dichalcogenides (TMDCs) have been intensively investigated as one of promising nanoelectronic and optoelectronic materials. However, the pervasive adsorbates on the surface of monolayer TMDCs, including oxygen and water molecules from the ambient environments, predominately degrade the device performance, thus hindering the precise applications. In this work, we report the effect of laser irradiation on the transport and photoresponse of monolayer MoS2 and WSe2 devices, and this laser annealing process is demonstrated as one straightforward approach to remove the physically adsorbed contaminations. Compared with vacuum pumping and in-situ thermal annealing treatments, the field-effect transistors after the laser annealing show more than one order of magnitude higher on-state current, and no apparent degradation of device performance at low temperature. The mobility of monolayer WSe2 devices can be enhanced by 3-4 times, and for single-layered MoS2 devices with the commonly used SiO2 as the back-gate, the mobility increases by 20 times, reaching 37 cm2 ? V?1 ? s?1. The efficient cleaning effect of the laser annealing is also supported by the reduction of channel and contact resistances revealed by the transmission line experiment. Further, the enhanced photocurrent by a factor of 10 has been obtained in the laser annealed device. These findings pave the way for the high-performance monolayer TMDCs-based electronic and optoelectronic devices with the clean surface and intrinsic properties.
关键词： TMDCs,monolayer MoS2,photoresponse,field-effect transistors,laser annealing,monolayer WSe2
更新于2025-09-19 17:13:59
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Photo-response in 2D metal chalcogenide-ferroelectric oxide heterostructure controlled by spontaneous polarization
摘要： The interplay between free and bound charges in two-dimensional (2D) semiconductor/ferroelectric oxide structures is responsible for the unique opto-electrical properties of these structures. In this study, we vertically combined the 2D layered semiconductors MoS2 (n-type) and WSe2 (p-type) with a ferroelectric oxide (PbTiO3) and found that a ferroelectric polarization induced accumulation or depletion in the layered materials. The heterostructures exhibited polarization-dependent charge distribution and pinched hysteresis. We show that polarization at the interface promoted e?cient charge separation of photo-generated carriers in the 2D layers. Optical control of electrical transport was e?ectively achieved in the MoS2 layers. This study potentially opens up new applications for semiconductor/ferroelectric systems in electronic devices.
关键词： opto-electrical properties,optical control,MoS2,2D semiconductor,ferroelectric oxide,PbTiO3,charge separation,WSe2
更新于2025-09-19 17:13:59
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Photovoltaic activity of WSe2/Si hetero junction
摘要： Propelled by the development of layered transition metal dichalcogenides, heterojunctions have captivated tremendous attention due to various excitonic mechanisms assisted strong light-matter interaction. We demonstrate liquid phase exfoliation of WSe2 and fabrication of fast switchable WSe2/Si heterojunction. The heterojunction device showed obvious rectifying nature with ideality factor of 1.21 and it is explored under white illumination at power intensities varying from 5 to 18 mW/cm2. The WSe2/Si heterojunction photovoltaic device exhibited excellent transient photoresponse with highest responsivity of 86.11 mA/W and 23 ms response time under white light. Besides, heterojunction exhibited excellent photoresponse in broad spectral range from 390 to 1088 nm with highest photoresponsivity of 122.2 mA/W for 780 nm illumination. The device showed excellent response in temperature range 200 to 300 K. Eventually, the results advocate the huge significance of WSe2/Si heterojunction for photovoltaic cell and photodetection.
关键词： WSe2/Si heterojunction,Responsivity,Liquid phase exfoliation,Photovoltaic activity,Morse codes
更新于2025-09-16 10:30:52
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Hexagonal Boron Nitride for Surface Passivation of Two-dimensional van der Waals Heterojunction Solar Cells
摘要： Two-dimensional (2D) semiconductors can be promising active materials for solar cells due to their advantageous electrical and optical properties, in addition to their ability to form high-quality van der Waals (vdW) heterojunctions using a simple process. Furthermore, the atomically thin nature of these 2D materials allows them to achieve light-weighted and transparent thin-film solar cells. However, strategies appropriate for optimizing their properties have not been extensively studied yet. In this paper, we propose a method for reducing the electrical loss of 2D vdW solar cells by introducing hexagonal boron nitride (h-BN) as a surface passivation layer. This method allowed us to enhance the photovoltaic performance of a MoS2/WSe2 solar cell. In particular, we observed ~74 % improvement of the power conversion efficiency owing to a large increase in both short-circuit current and open-circuit voltage. Such a remarkable performance enhancement was due to the reduction of the recombination rate at the junction and surface of non-overlapped semiconductor regions, which was confirmed via time-resolved photoluminescence analysis. Furthermore, the h-BN top layer was found to improve the long-term stability of the tested 2D solar cell under ambient conditions. We observed the evolution of our MoS2/WSe2 solar cell for a month and found that h-BN passivation effectively suppressed its degradation speed. In particular, the degradation speed of the passivated cell was twice as low as that of a non-passivated cell. This work reveals that h-BN can successfully suppress the electrical loss and degradation of 2D vdW heterojunction solar cells under ambient conditions.
关键词： surface passivation,solar cell,MoS2,WSe2,2D material,van der Waals heterojunction,h-BN
更新于2025-09-16 10:30:52