Heterojunction photoelectric detector based on Te nanosheet and WS2 and preparation method thereof

Abstract

The invention discloses a Te nanosheet and 2-based heterojunction photoelectric detector and a preparation method thereof, and belongs to the technical field of semiconductor photoelectric detectors, and the preparation method comprises the steps: preparing a metal electrode on a substrate; te nanosheets are synthesized through a hydrothermal method, and the Te nanosheets are positioned and transferred to the metal electrode by adopting a first polydimethylsiloxane (PDMS) mediated dry transfer process; the preparation method comprises the following steps: preparing a Te nano-sheet by using a Te / WS2 Van der Waals heterojunction, obtaining a WS2 thin layer by using a mechanical stripping method, covering the surface of the Te nano-sheet with the WS2 thin layer by using a second polydimethylsiloxane (PDMS) mediated dry transfer process, and forming the Te / WS2 Van der Waals heterojunction by heating and applying pressure at the temperature of 50-80 DEG C in the transfer process of the WS2 thin layer; through the precisely controlled Van der Waals integration process, the heterojunction with a clean interface and good energy band matching is constructed without high-temperature growth, so that the common problems of high dark current and low response speed of a traditional device are solved.

Description

Technical Field

[0001] This invention relates to the field of semiconductor photodetector technology, and in particular to a heterojunction photodetector based on Te nanosheets and WS2 and its fabrication method. Background Technology

[0002] Tellurium (Te) is a group VIA quasi-one-dimensional semiconductor material with a hexagonal crystal structure. Single nanowires grow along the

[0001] direction, formed by covalently bonded helical chains stacked together via van der Waals forces, exhibiting unique anisotropic structural characteristics. This structure endows Te nanowires with not only excellent mechanical flexibility but also high carrier mobility (~1000 cm⁻¹). 2 V -1 s -1 Te exhibits a tunable band structure with an intrinsic band gap of approximately 0.35 eV, providing broad-spectrum absorption capabilities, making it particularly suitable for mid-infrared photoelectric detection. Furthermore, Te materials demonstrate excellent environmental and chemical stability, maintaining stable photoelectric properties even after prolonged exposure to air.

[0003] In recent years, Te nanomaterials have attracted widespread attention in the field of photodetectors. Field-effect devices based on Te nanowires have achieved controllable photoelectric responses in the mid-infrared band, but their performance still has significant limitations. Single-material Te devices exhibit slow response speeds, high dark currents, severe carrier recombination, and inefficient separation of photogenerated carriers, thus limiting photoelectric conversion efficiency, detection sensitivity, and broadband response capabilities. Constructing heterojunction structures is an important means to improve the performance of Te devices. Through the effects of interface band bending and built-in electric fields, rapid separation and efficient transport of photogenerated carriers can be promoted, reducing dark current and noise, while simultaneously improving response speed and signal-to-noise ratio.

[0004] Two-dimensional transition metal sulfides (TMDs) WS2 possess a moderate band gap (approximately 1.3–2.1 eV, layer-dependent), strong photo-matter interactions, and good carrier mobility, making them ideal materials for constructing photodetectors. Te and WS2 can form Type-II heterojunctions, whose band alignment facilitates the spatial separation of photogenerated electrons and holes, creating a built-in electric field that promotes carrier extraction, thereby improving the device's photoresponsivity and response speed. However, existing heterojunction fabrication techniques (such as epitaxial growth and wet etching) suffer from complex processes, interface contamination, and poor material compatibility, making it difficult to achieve the goals of high performance, low cost, and scalable fabrication. Summary of the Invention

[0005] One of the objectives of this invention is to provide a heterojunction photodetector based on Te nanosheets and WS2 and its fabrication method, so as to solve the problems of limited photodetector performance and complex heterojunction fabrication process in the prior art.

[0006] This invention provides a method for fabricating a heterojunction photodetector based on Te nanosheets and WS2 through the following technical solution, comprising:

[0007] Fabricating metal electrodes on a substrate;

[0008] Te nanosheets were synthesized by a hydrothermal method and then positioned and transferred onto the metal electrode using a dry transfer process mediated by polydimethylsiloxane PDMS.

[0009] A WS2 thin layer was obtained by mechanical exfoliation and then coated onto the surface of the Te nanosheet using a dry transfer process mediated by second polydimethylsiloxane (PDMS). During the transfer of the WS2 thin layer, heating and pressure were applied at a temperature of 50-80°C to form a Te / WS2 van der Waals heterojunction.

[0010] Furthermore, the hydrothermal synthesis of Te nanosheets includes:

[0011] A mixed solution containing sodium tellurite, polyvinylpyrrolidone, liquid ammonia, and hydrazine hydrate is reacted at 150-200°C for 3-6 hours.

[0012] Furthermore, the amount of polyvinylpyrrolidone (PVP) used is controlled at 50-150 g / L of deionized water.

[0013] Furthermore, the fabrication of the metal electrode on the substrate includes: forming an Au, Ti / Au, or Cr / Au metal electrode with a thickness of 50-100 nm by photolithography, electron beam evaporation deposition, and lift-off processes.

[0014] Another aspect of the present invention provides a heterojunction photodetector based on Te nanosheets and WS2, wherein the heterojunction photodetector is fabricated by any one of the methods described above, comprising: a substrate; a metal electrode fabricated on the substrate; a Te nanosheet layer located on the substrate and forming an ohmic contact with the metal electrode, the Te nanosheet layer being synthesized by a hydrothermal method; and a WS2 thin layer stacked on the Te nanosheet layer, the WS2 thin layer being obtained by a mechanical exfoliation method; wherein the Te nanosheet layer and the WS2 thin layer form a van der Waals heterojunction in the overlapping region.

[0015] Furthermore, the Te nanosheets and the WS2 thin layer constitute a Type-II band heterojunction.

[0016] Furthermore, the Te nanosheets have a thickness of 50-300 nm and a side length of 10 nm-50 μm.

[0017] Furthermore, the number of layers in the WS2 thin layer is 1-5.

[0018] Furthermore, the overlap area of ​​the heterojunction interface is 10-50 μm².

[0019] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0020] 1. This invention combines hydrothermally synthesized Te nanosheets with mechanically exfoliated WS2 to construct a Type-II van der Waals heterojunction. By utilizing band crossing to promote carrier separation, it overcomes the performance limitations of single Te materials. The narrow bandgap of Te and the wide bandgap of WS2 complement each other, achieving a broad spectral response.

[0021] 2. This invention employs dry transfer technology, avoiding interface contamination and damage introduced by wet processes, significantly improving interface quality and device repeatability; it eliminates the need for high-temperature epitaxy or complex etching, is compatible with flexible substrates, and the core equipment consists only of a hydrothermal reactor, a lithography machine, and an evaporation coating machine, thus reducing manufacturing costs.

[0022] 3. This invention optimizes light absorption and carrier transport paths by controlling the thickness and size of Te nanosheets, achieves a balance between response speed and sensitivity by controlling the number of WS2 layers, and realizes extremely low dark current by combining Te with WS2. High on / off ratio (>10) 4 The combined performance improvement of ) and fast response (200 / 9μs) is significantly better than that of single-material devices. Attached Figure Description

[0023] The accompanying drawings, which are included to provide a further understanding of embodiments of the invention and form part of this application, do not constitute a limitation thereof. In the drawings:

[0024] Figure 1 This is a schematic diagram of the structure of the Te / WS2 heterojunction photodetector prepared in this invention.

[0025] Figure 2 This is a schematic optical micrograph of the Te / WS2 heterojunction photodetector prepared in this invention.

[0026] Figure 3 This is an optical microscope image of the Te nanomaterials prepared according to the present invention.

[0027] Figure 4 This is a scanning electron microscope (SEM) image of the Te nanomaterials prepared according to the present invention.

[0028] Figure 5 The image shows the energy dispersive spectroscopy (EDS) spectrum of the Te nanomaterials prepared in this invention.

[0029] Figure 6This is the X-ray diffraction (XRD) pattern of the Te nanosheets in this invention.

[0030] Figure 7 This is the X-ray photoelectron energy (XPS) spectrum of the Te nanosheets in this invention.

[0031] Figure 8 This is a schematic diagram of the transfer of Te nanosheets in this invention.

[0032] Figure 9 This is a current-voltage (IV) characteristic curve of the Te / WS2 heterojunction photodetector prepared in this invention.

[0033] Figure 10 The image shows the rise and fall times of the transient optical response curve of the Te / WS2 heterojunction photodetector prepared in this invention.

[0034] Figure 11 The image shows the photocurrent-time (IT) response curves of the Te / WS2 heterojunction photodetector prepared in this invention under different light intensities. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0036] As core devices for converting optical signals to electrical signals, photodetectors play an irreplaceable role in information sensing, communication, and intelligent systems. Traditional silicon-based or III-V compound photodetectors, limited by material band gaps and carrier recombination mechanisms, suffer from slow response speeds, high dark currents, low detection limits, and narrow spectral response ranges, making it difficult to meet the demands of emerging applications for high-performance, wide-band detection. For example, silicon-based detectors exhibit low absorption efficiency in the near-infrared band, while III-V materials such as InGaAs are expensive and complex to manufacture, limiting their large-scale application.

[0037] Low-dimensional materials (such as two-dimensional and quasi-one-dimensional materials) have become key to overcoming the bottlenecks of traditional devices due to their unique quantum confinement effects and photoelectric properties. Te, as a typical quasi-one-dimensional semiconductor material, has a helical chain structure and an tunable bandgap (approximately 0.35 eV), theoretically enabling efficient detection in the mid-infrared band. However, single Te-based devices face bottlenecks such as high dark current and insufficient photogenerated carrier separation efficiency, making it difficult to improve their detection sensitivity and signal-to-noise ratio. Constructing heterojunction structures is an effective strategy to improve photoelectric detection performance. Through band engineering at the heterojunction interface, the separation and transport of photogenerated carriers can be enhanced, and recombination can be suppressed, thereby significantly improving detection sensitivity. However, traditional heterojunction fabrication processes (such as high-temperature epitaxial growth) are prone to introducing interface defects, and the process flow is complex and costly, posing serious challenges to the device's on / off ratio, response speed, and large-scale fabrication.

[0038] The purpose of this invention is to overcome the inherent defects of the existing technical solutions and provide a heterojunction photodetector based on Te nanosheets and WS2 and its fabrication method. Specifically, this invention aims to solve the key problems of the prior art in the following ways:

[0039] Two-dimensional semiconductor materials, due to their moderate band gap, high electron mobility, and excellent light absorption properties, have become ideal choices for constructing high-performance heterojunctions. Among them, WS2, as a typical two-dimensional material, can form a high-quality interface with Te. Through synergistic band gap modulation and interface optimization, the separation efficiency of photogenerated carriers is enhanced, recombination losses are reduced, and photoelectric conversion efficiency is improved. Therefore, using the Te / WS2 material system, a clean and tightly coupled heterojunction was successfully constructed by synthesizing Te nanosheets via a hydrothermal method and combining it with a dry transfer process of mechanically exfoliating WS2. This effectively utilizes the characteristic of band matching between the two materials to promote carrier separation. Through a precisely controlled van der Waals integration process, a heterojunction with a clean interface and good band matching was constructed without the need for high-temperature growth. This solves the common problems of high dark current and slow response speed in traditional devices, and significantly improves the overall performance of the device, including dark current, on / off ratio, and response speed.

[0040] Example 1

[0041] This embodiment provides a method for fabricating a heterojunction photodetector based on Te nanosheets and WS2, which addresses the problems existing in the prior art, and includes the following steps:

[0042] Step 1: Fabricate metal electrodes on a substrate;

[0043] Step 2: Te nanosheets are synthesized by hydrothermal method, and the Te nanosheets are positioned and transferred onto the metal electrode by a dry transfer process mediated by polydimethylsiloxane (PDMS) to form an ohmic contact.

[0044] Step 3: Obtain a WS2 thin layer by mechanical exfoliation and use a dry transfer process mediated by polydimethylsiloxane (PDMS) to cover the surface of the Te nanosheet. Then, enhance the interfacial coupling by heating and applying pressure to form a clean and tightly coupled Te / WS2 van der Waals heterojunction.

[0045] This invention first prefabricates metal electrodes on a substrate as the integration basis, then controllably synthesizes Te nanosheets via a hydrothermal method, and precisely positions them to the electrode region to form ohmic contacts using a PDMS-mediated dry transfer technique. Subsequently, a WS2 thin layer is obtained through mechanical exfoliation, and similarly, it is integrated with the Te nanosheets under heating and pressure conditions at 50-80℃ using the PDMS dry transfer technique, forming a clean and tightly coupled heterojunction structure. This fabrication route successfully overcomes the technical bottlenecks of traditional heterojunction fabrication caused by high-temperature epitaxial growth or wet processes, such as interface contamination, lattice mismatch, and process complexity. Through a low-temperature, non-destructive van der Waals integration process, a high-quality heterojunction interface is achieved without the need for lattice matching. The final detector exhibits excellent overall performance: extremely low dark current (…). ), up to 10 4 The aforementioned on / off ratio and fast response speed of 200 / 9μs, along with its wide spectral response characteristics, provide a new technical path for the development of high-performance, low-power photodetectors, and have significant application value in fields such as infrared imaging, optical communication, and low-light detection. The following provides a detailed explanation of each step.

[0046] Step 1: Fabricate a metal electrode on the substrate.

[0047] Before constructing the Te / WS2 heterojunction, electrodes need to be fabricated on a Si / SiO2 substrate as the basis for subsequent nanosheet transfer and device integration, i.e., fabricating metal electrodes on the substrate in step one. This specifically includes the following steps:

[0048] 1) Electrode patterns are formed in a predetermined area on a Si / SiO2 substrate using standard photolithography.

[0049] 2) Deposit metal electrodes by electron beam evaporation or thermal evaporation, preferably with Au, Ti / Au or Cr / Au, and control the thickness in the range of 50-100nm to ensure good conductivity and adhesion, thereby improving the interface contact quality and reducing resistance and contact barrier.

[0050] 3) Use the lift-off process to remove excess photoresist, leaving only the metal electrode pattern in the target area, to obtain a neat and clear electrode structure;

[0051] 4) After the electrode is fabricated, Te nanosheets and WS2 thin layers are transferred sequentially to cover and connect to the electrode region, forming the active region of the heterojunction device.

[0052] Step 2: Te nanosheets are synthesized by hydrothermal method, and the Te nanosheets are positioned and transferred onto the metal electrode by a dry transfer process mediated by polydimethylsiloxane (PDMS) to form an ohmic contact.

[0053] The hydrothermal synthesis of Te nanomaterials specifically includes the following steps:

[0054] 1) Dissolve 1-3g of polyvinylpyrrolidone (PVP, Mw≈58000) and 46 mg of sodium tellurite (Na2TeO3) in 16mL of deionized water to form a homogeneous and transparent mixed solution.

[0055] 2) Add 1.66 mL of liquid ammonia with a mass fraction of 25–28% and 0.84 mL of hydrazine hydrate with a mass fraction of 80%, and stir for 2 minutes;

[0056] 3) Transfer the mixture to a 25mL polytetrafluoroethylene-lined hydrothermal reactor and react at 150-200℃ for 3-6 hours;

[0057] 4) After the reaction is complete, allow the product to cool naturally to room temperature. Remove the reaction product and centrifuge and wash it 2-4 times (6000-10000 rpm, 5-10 min) to remove PVP and other residues. Finally, Te product dispersed in deionized water is obtained.

[0058] 5) The Te nanosheet powder synthesized by hydrothermal method was placed in an appropriate amount of distilled water and ultrasonically dispersed into a suspension. Then, the dispersion was drop-coated onto a clean glass substrate using a dropper and allowed to dry naturally to obtain uniformly distributed Te nanosheets.

[0059] The morphology of the product is closely related to the amount of polyvinylpyrrolidone (PVP) in the reaction system. Under lower PVP concentrations, the generated Te nanowires are mainly slender one-dimensional nanowires; while at higher PVP concentrations, the oriented growth of Te can be effectively controlled, suppressing the formation of one-dimensional linear structures, and the product exhibits a regular two-dimensional sheet-like morphology. By precisely controlling the PVP concentration, Te nanowires of different diameters and lengths can be prepared. This controllability of size and morphology provides significant design freedom for optimizing the interfacial area, band matching, and photogenerated carrier transport paths of heterojunctions. The two-dimensional Te nanosheets have a thickness of 50-300 nm and a side length of 10 nm-50 μm, while the obtained Te nanosheets with a thickness of 80-200 nm and a side length of 1-3 μm exhibit higher uniformity and crystallinity.

[0060] like Figures 3-5 The image shown is an optical microscope image, a SEM image, and an EDS elemental distribution map of the Te sample obtained in the embodiments of the present invention. The microscope and SEM results clearly show the coexistence and transformation trends of Te nanosheets and nanowires under different polyvinylpyrrolidone (PVP) conditions, verifying the key role of PVP dosage in regulating the morphology of the Te product. Meanwhile, the EDS results indicate that the product is mainly composed of Te, with a uniform distribution and no obvious impurities.

[0061] like Figure 6 The image shows the XRD pattern of the obtained Te nanosheets. The positions of the main diffraction peaks are consistent with the standard Te card of hexagonal crystal structure, indicating that the prepared product has good crystallinity and no impurity peaks, which proves the high purity and single phase composition of the material.

[0062] like Figure 7 The image shows the XPS spectrum of the obtained Te nanosheets. The results indicate that Te in the product mainly exists in the valence state Te. 0 The presence of this form, without obvious oxide signals, proves that its surface chemical environment is stable.

[0063] The above characterization results show that the morphology of Te nanomaterials can be effectively controlled by adjusting the amount of polyvinylpyrrolidone (PVP), transforming them from one-dimensional nanowires to two-dimensional sheet-like structures. Microscopy and SEM characterization revealed their uniformity and morphological evolution, EDS confirmed their elemental composition, XRD demonstrated their good crystallinity, and XPS further indicated their stable surface chemical state. This verifies the controllability and effectiveness of the hydrothermal synthesis process of this invention.

[0064] like Figure 8 As shown, to better fabricate high-performance optoelectronic devices, it is necessary to transfer Te nanosheets dispersed on a glass substrate to a Si / SiO2 substrate with good electrical insulation properties and stability. This process utilizes the viscoelastic properties of the PDMS film. First, gentle pressing ensures reliable adhesion to the Te nanosheets, followed by its rapid peeling capability to completely remove the nanosheets from the glass surface. Subsequently, a crucial hot-pressing treatment at 80°C for 10 minutes on the target Si / SiO2 substrate significantly enhances the van der Waals interactions between the Te nanosheets and the SiO2 surface, forming a stable, low-contact-resistance interfacial coupling. Furthermore, it effectively reduces the adhesion force of PDMS, ensuring complete peeling after cooling without bringing the nanosheets back. Specifically, the process includes the following steps:

[0065] 1) Cover the glass substrate with a fresh and clean polydimethylsiloxane (PDMS) film and Te nanosheets for about 5 minutes. Then, gently press the PDMS with a cotton swab to ensure that it is in full contact with the Te nanosheets.

[0066] 2) Rapidly peel the PDMS film off the glass substrate and use the adhesion of PDMS to remove the Te nanosheets from the glass surface;

[0067] 3) The PDMS film with Te nanosheets was flatly covered on the target Si / SiO2 substrate and heated at 80°C for 10 minutes to enhance the interfacial contact between the Te nanosheets and the Si / SiO2 substrate, while reducing the adhesion of PDMS.

[0068] 4) After cooling to room temperature, peel off the polydimethylsiloxane (PDMS) film to complete the transfer of Te nanosheets.

[0069] By using a polydimethylsiloxane (PDMS) thin film-assisted transfer step, the crystal structure and intrinsic electrical properties of Te nanosheets were preserved, avoiding surface contamination or structural damage that might be introduced by solution transfer. At the same time, an active layer for high-performance devices was successfully constructed on an electrically insulating Si / SiO2 substrate, providing an ideal platform for subsequent WS2 heterojunction integration and electrode fabrication, and ensuring that the final photodetector achieves comprehensive performance with extremely low dark current, high on / off ratio, and excellent stability.

[0070] Step 3: Obtain a WS2 thin layer by mechanical exfoliation and use a dry transfer process mediated by polydimethylsiloxane (PDMS) to cover the surface of the Te nanosheet. Then, enhance the interfacial coupling by heating and applying pressure to form a clean and tightly coupled Te / WS2 van der Waals heterojunction.

[0071] WS2 thin layers are two-dimensional materials, prepared by mechanical exfoliation. Their preparation and transfer include the following steps:

[0072] 1) Use blue film (blue adhesive release film) to repeatedly adhere and peel off bulk WS2 crystals to obtain single-layer or few-layer WS2 flakes;

[0073] 2) A thin layer of WS2 was adhered to a polydimethylsiloxane PDMS elastic substrate, and its positioning was performed under a microscope by utilizing the transparency and flexibility of polydimethylsiloxane PDMS.

[0074] 3) Dry transfer process: Utilizing a 2D material transfer platform, the WS2 sheet is accurately aligned with the Te nanosheet region under the assistance of an optical microscope. The sheets are then slowly bonded together and heated to 50℃-80℃, with slight pressure applied to achieve transfer. If the temperature is too low (below 50℃), the adhesion of polydimethylsiloxane (PDMS) is insufficient, making it difficult for the WS2 thin layer to completely and smoothly cover the Te nanosheet surface. This fails to provide enough energy for the two materials to overcome minor surface irregularities and achieve atomic-level close contact. Conversely, if the temperature is too high (above 80℃), thermal stress may be introduced, leading to wrinkles, cracks, or even degradation of the two-dimensional material. This is particularly problematic for heat-sensitive materials like WS2 and Te, potentially damaging the interface quality. This invention controls the temperature between 50℃ and 80℃, which can effectively reduce the adhesion of PDMS, ensure the complete release of the WS2 thin layer and achieve a tight, bubble-free bond with the Te nanosheets, and avoid thermal stress damage to the material or interface degradation caused by excessive temperature. This directly ensures that the final device can obtain the structural characteristics of a clean interface and tight coupling, thereby achieving excellent optoelectronic performance with extremely low dark current, high on / off ratio and fast response.

[0075] 4) Control the peeling speed and angle of polydimethylsiloxane (PDMS) to ensure that the WS2 sheet completely covers the Te surface, forming a heterojunction structure. The preferred overlap area of ​​the heterojunction structure is 30 μm × 15 μm. Te and WS2 form a heterojunction structure with a vertically stacked van der Waals interface in the overlap region, thus exhibiting a Type-II band arrangement, providing excellent carrier separation capability and interface coupling characteristics.

[0076] This step achieves high-quality heterojunction integration of WS2 thin layers and Te nanosheets through the synergistic effect of mechanical exfoliation and PDMS-mediated dry transfer process: First, structurally complete and surface-clean single-layer or few-layer WS2 thin sheets are obtained from bulk crystals through mechanical exfoliation, laying the foundation for constructing an ideal interface; then, taking advantage of the transparency and flexibility of the PDMS substrate, the WS2 thin layer is precisely aligned and covered onto the surface of the Te nanosheets under a microscope. By strictly controlling the transfer temperature within the range of 50-80℃ and applying slight pressure, the adhesion force of PDMS is effectively reduced and the WS2 is completely released, while avoiding thermal stress damage to the two-dimensional material, thus achieving atomically tight and contamination-free van der Waals coupling between the two materials; the resulting heterojunction with a vertical stacking structure and Type-II band arrangement (preferably with an overlap area of ​​30μm×15μm) greatly promotes efficient spatial separation and rapid transport of photogenerated carriers through its built-in electric field. This low-temperature, non-destructive integration process not only avoids the stringent requirements of lattice matching in traditional epitaxial growth and the interface contamination of wet transfer, but also endows the detector with extremely low dark current. ), up to 10 4 The above-mentioned on / off ratio and microsecond-level fast response (200 / 9μs) provide a reliable technical path for the fabrication of high-performance, scalable two-dimensional material optoelectronic devices.

[0077] Example 2

[0078] This embodiment provides a heterojunction photodetector based on Te nanosheets and WS2, which is fabricated using the method described in Example 1 for preparing a heterojunction photodetector based on Te nanosheets and WS2. Figure 1 and Figure 2 This paper presents a schematic diagram and corresponding optical micrograph of the Te / WS2 heterojunction photodetector constructed in this embodiment. The components of the device are clearly distinguishable from the image, including: a substrate; a metal electrode fabricated on the substrate; a Te nanosheet layer located on the substrate and forming an ohmic contact with the metal electrode, the Te nanosheet layer being synthesized via a hydrothermal method; and a WS2 thin layer stacked on top of the Te nanosheet layer, the WS2 thin layer being obtained via mechanical exfoliation. The Te nanosheet layer and the WS2 thin layer are integrated in the overlapping region by van der Waals forces, forming a heterojunction interface. The overall device structure is well-organized and the interface is clear, indicating that the fabrication process can effectively ensure the integrity of material transfer and the stability of the device structure. This embodiment will be described in detail below.

[0079] Substrate: Si / SiO2, glass, flexible polymers (such as polyimide, PET) can be selected as substrates to provide mechanical support and electrical insulation. Among them, Si / SiO2 substrates have both high thermal conductivity and low cost, while flexible substrates are suitable for wearable or flexible electronic systems. Therefore, Si / SiO2 substrates are selected in this embodiment.

[0080] The Te nanosheet layer on the substrate: The Te nanosheets, synthesized via a hydrothermal method, have a two-dimensional sheet structure with a thickness of 50–300 nm and a side length of 10 nm–50 μm, exhibiting high crystallinity and good photoelectric properties. Preferably, the Te nanosheets have a thickness of 80–200 nm and a side length of 1–3 μm, exhibiting good in-plane dimensions and a single-crystal structure, thus achieving optimal balance between light absorption and carrier transport. The morphology of the Te nanosheets can be controlled by adjusting the hydrothermal reaction temperature (150–200 °C), reaction time (3–6 hours), and polyvinylpyrrolidone (PVP) concentration (50–150 g / L deionized water). For example, reacting at 180 °C for 4.5 hours with a PVP concentration of 93.75 g / L deionized water (i.e., 1.5 g / 16 ml deionized water) yields Te nanosheets with uniform thickness and a smooth surface.

[0081] A thin layer of WS2 is transferred and stacked on top of the Te nanosheets, wherein the Te nanosheets and the WS2 layer form a heterojunction interface in the overlapping region through van der Waals forces. A single or few layers (1–5 layers) of WS2, obtained by mechanical exfoliation, cover the surface of the Te nanosheets, forming a van der Waals heterojunction interface with the Te nanosheets in the overlapping region, with an area of ​​10–50 μm². The interface is tightly bonded, without bubbles or cracks. The overlapping area can be precisely controlled by optical microscopy alignment and micro / nano fabrication techniques, thereby optimizing device performance. The number of WS2 layers can be determined by optical contrast and atomic force microscopy (AFM) characterization, preferably 1–3 layers of WS2, to balance high responsivity and transparency, and avoid increased carrier tunneling resistance due to excessive layers. The number of layers can be quickly screened by color contrast and confirmed by AFM measurements. Based on the Te / WS2 heterojunction, dark current suppression, faster response speed, and wide-spectrum detection are achieved, and it can play an important role in self-powered infrared photodetectors. This provides an effective technical path for realizing high-performance, low-noise, and wide-band photodetectors, while also expanding the potential of the device in applications such as infrared imaging, low-light detection, and intelligent sensing.

[0082] Metal electrodes that make electrical contact with the Te nanosheets and WS2 thin layer respectively: deposited on the Te nanosheets and WS2 layer to form ohmic or Schottky contacts. The electrode materials are preferably Au, Ti / Au (thickness ratio 5nm Ti + 50nm Au), or Cr / Au (thickness ratio 5nm Cr + 50nm Au), with a thickness of 50–100nm. Ti or Cr, acting as an adhesion layer, enhances the bonding force between Au and the substrate, reducing contact resistance.

[0083] Based on the heterojunction photodetector based on Te nanosheets and WS2 provided in Example 2, its device performance was tested, that is, its electrical and photoelectric properties were systematically characterized, mainly including the following aspects:

[0084] 1) Use a source meter to test its dark current and current-voltage (IV) characteristic curves, such as... Figure 9 As shown, the device exhibits extremely low dark current at zero bias, specifically as low as ~10. -12 A (pA level) means extremely low background noise, stronger detection capability for weak light signals, and good rectification characteristics.

[0085] 2) Using a modulated light source for excitation, test the transient optical response characteristics of the device, such as... Figure 10 As shown, the device exhibits rapid rise and fall times (200 / 9μs) during the illumination switching process, indicating its excellent high-speed response capability. The microsecond-level fast response suggests that the device has the potential to be applied to dynamic optical signal processing and high-speed communication.

[0086] 3) Further record the photocurrent-time (IT) curves of the device under different light intensities, such as... Figure 11 As shown, the photocurrent of the device gradually increases with increasing light intensity, and the repeated switching response remains stable, with a switching ratio (I0) of [missing information]. light / I dark >10 4 This indicates that it has a good linear response relationship and working stability. At the same time, the high switching ratio proves the device's excellent photoelectric conversion efficiency and significant signal-to-noise ratio improvement.

[0087] 4) The optical responsivity, detectivity and signal-to-noise ratio of the device were calculated. The results show that the device of the present invention exhibits high sensitivity and low noise characteristics in the visible to mid-infrared bands.

[0088] Test results show that the Te / WS2 heterojunction photodetector prepared by this invention has a low dark current (~10). - 12 A) High-gloss switching ratio (>10) 4 It features a fast response speed (200 / 9μs) and maintains stable photocurrent output under different light intensities, demonstrating excellent photoelectric detection performance and operational stability. This provides a new technical path for the development of high-performance, low-power photodetectors and has significant application value in fields such as infrared imaging, optical communication, and low-light detection.

[0089] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for fabricating a heterojunction photodetector based on Te nanosheets and WS2, characterized in that, include: Fabricating metal electrodes on a substrate; Te nanosheets were synthesized by a hydrothermal method and then positioned and transferred onto the metal electrode using a dry transfer process mediated by polydimethylsiloxane PDMS. A WS2 thin layer was obtained by mechanical exfoliation and then coated onto the surface of the Te nanosheet using a dry transfer process mediated by second polydimethylsiloxane (PDMS). During the transfer of the WS2 thin layer, heating and pressure were applied at a temperature of 50-80°C to form a Te / WS2 van der Waals heterojunction.

2. The method for fabricating a heterojunction photodetector based on Te nanosheets and WS2 according to claim 1, characterized in that, The synthesis of Te nanosheets via hydrothermal method includes: A mixed solution containing sodium tellurite, polyvinylpyrrolidone, liquid ammonia, and hydrazine hydrate is reacted at 150-200°C for 3-6 hours.

3. The method for fabricating a heterojunction photodetector based on Te nanosheets and WS2 according to claim 2, characterized in that, The amount of polyvinylpyrrolidone (PVP) used is controlled at 50-150 g / L of deionized water.

4. The method for fabricating a heterojunction photodetector based on Te nanosheets and WS2 according to claim 1, characterized in that, The preparation of metal electrodes on the substrate includes: forming Au, Ti / Au, or Cr / Au metal electrodes with a thickness of 50-100 nm by photolithography, electron beam evaporation deposition, and lift-off processes.

5. A heterojunction photodetector based on Te nanosheets and WS2, characterized in that, The heterojunction photodetector is fabricated by the method described in any one of claims 1 to 4, comprising: a substrate; a metal electrode fabricated on the substrate; a Te nanosheet layer located on the substrate and forming an ohmic contact with the metal electrode, the Te nanosheet layer being synthesized by a hydrothermal method; and a WS2 thin layer stacked on the Te nanosheet layer, the WS2 thin layer being obtained by a mechanical exfoliation method; wherein the Te nanosheet layer and the WS2 thin layer form a van der Waals heterojunction in the overlapping region.

6. The photodetector according to claim 5, characterized in that, The Te nanosheets and the WS2 thin layer form a Type-II band heterojunction.

7. A heterojunction photodetector based on Te nanosheets and WS2 according to claim 5, characterized in that, The Te nanosheets have a thickness of 50-300 nm and a side length of 10 nm-50 μm.

8. A heterojunction photodetector based on Te nanosheets and WS2 according to claim 5, characterized in that, The number of layers in the WS2 thin layer is 1-5.

9. A heterojunction photodetector based on Te nanosheets and WS2 according to claim 5, characterized in that, The overlap area of ​​the heterojunction interface is 10-50 μm².

Images