Van der Waals heterojunction with unipolar potential barrier and polarization sensitivity and application thereof

Abstract

The invention belongs to the technical field of two-dimensional material photoelectric devices, and particularly relates to a Van der Waals heterojunction with a unipolar barrier and polarization sensitivity and application of the Van der Waals heterojunction. A p-type material Ta2NiSe5 with anisotropy is used as a collection layer of a bottom layer carrier, an n-type material ReS2 with anisotropy is used as an upper light absorption layer, WSe2 is used as a middle barrier layer, a Van der Waals heterojunction with a unipolar barrier and polarization sensitivity is constructed, and then the photoelectric detector is prepared. The photoelectric detector made of the constructed Van der Waals heterojunction has the characteristics of low dark current, high detection rate, wide band and polarized light response.

Description

Technical Field

[0001] The present invention belongs to the technical field of two-dimensional material optoelectronic devices, and more specifically relates to a van der Waals heterojunction with a unipolar barrier and polarization sensitivity and applications thereof. Background Art

[0002] Photodetectors play a vital role in a variety of fields, including optoelectronic communications, imaging, remote sensing, and environmental monitoring. With the increasing demand for high-performance photodetectors, expanding their response band, improving detection sensitivity, and reducing dark current have become hot research topics. Traditional photodetectors often use a single material or a simple type-II bandgap heterojunction structure. However, these structures often face challenges such as difficult bandgap tuning, narrow response bands, and high dark current.

[0003] In the field of broadband photodetection, existing semiconductor materials often face technical bottlenecks such as limited band gaps and significant interface recombination effects. These issues not only limit the detector's response range but also hinder further improvements in device performance. Therefore, effectively expanding the photodetector's response range, particularly in the infrared, ultraviolet, and visible light bands, while maintaining low dark current and high response speed, remains a challenge for photodetector technology.

[0004] In traditional type II bandgap two-dimensional heterojunction structures, both photogenerated electrons and holes can cross the heterojunction interface, resulting in two major bottlenecks: interfacial recombination and low photogenerated carrier collection efficiency. Although the built-in electric field between the materials can separate photogenerated carriers, this bandgap arrangement leads to the rapid flow of intrinsic electrons and holes, resulting in large dark currents and low photoelectric conversion efficiency. Summary of the Invention

[0005] The purpose of the present invention is to provide a van der Waals heterojunction with a unipolar barrier and polarization sensitivity and its application, and more specifically to provide a polarization-sensitive photodetector constructed with a unipolar barrier layer and a dark current suppression method to solve the problems existing in the above-mentioned prior art.

[0006] To achieve the above object, the present invention provides the following solutions:

[0007] One of the technical solutions of the present invention is to provide a van der Waals heterojunction with a unipolar barrier and polarization sensitivity, with an anisotropic p-type material Ta2NiSe5 as the bottom carrier collection layer, an anisotropic n-type material ReS2 as the upper light absorption layer, and WSe2 as the intermediate barrier layer.

[0008] Furthermore, the conduction band bottom of Ta2NiSe5 is at 4.6 eV, and the valence band top is at 4.93 eV.

[0009] Furthermore, the bottom of the conduction band of ReS2 is 4.5 eV, and the top of the valence band is 5.84 eV.

[0010] Furthermore, the bottom of the conduction band of WSe2 is 3.5 eV, and the top of the valence band is 5 eV.

[0011] The second technical solution of the present invention is to provide a method for preparing the above-mentioned van der Waals heterojunction with a unipolar barrier and polarization sensitivity, comprising the following steps:

[0012] WSe2 was grown on the surface of substrate A by physical vapor deposition to obtain a substrate with WSe2 (triangular and hexagonal) nanosheets;

[0013] Transferring the WSe2 nanosheets on the substrate having the WSe2 nanosheets grown thereon to a substrate D to obtain a substrate with a WSe2 layer;

[0014] Peeling the Ta2NiSe5 single crystal onto substrate B to obtain a substrate with a Ta2NiSe5 layer;

[0015] Peeling the ReS2 single crystal onto substrate C to obtain a substrate with a ReS2 layer;

[0016] Transferring the WSe2 on the substrate with the WSe2 layer to the substrate with the Ta2NiSe5 layer to obtain a substrate with a Ta2NiSe5 / WSe2 heterojunction;

[0017] The ReS2 nanosheets on the substrate with the ReS2 layer are transferred to a substrate with a Ta2NiSe5 / WSe2 heterojunction to obtain a Ta2NiSe5 / WSe2 / ReS2 heterojunction (a van der Waals heterojunction with a unipolar barrier and polarization sensitivity).

[0018] The two-dimensional materials selected in this paper exhibit different photoelectron conversion mechanisms. The selected Ta2NiSe5 has anisotropy and high mobility, while ReS2 has anisotropic light absorption and good photoelectric conversion efficiency. WSe2 grown by physical vapor deposition has low mobility and a relatively large band gap, making it suitable for a unipolar barrier in the intermediate layer.

[0019] Furthermore, the step of growing WSe2 on the surface of substrate A by physical vapor deposition includes:

[0020] Place substrate A and WSe2 powder in a heating device, use inert gas to exhaust the air, and the air flow direction is from the substrate to the reactant. Then adjust the inert gas flow rate to 30-40sccm, and heat it to 1100-1130℃ at a heating rate of 12-12.5℃ / min. Then change the air flow direction from the reactant to the substrate, adjust the flow rate to 100-120sccm, keep warm for 10-15 minutes, and finally adjust the flow rate to 20-30sccm. Cool it to room temperature to obtain a substrate with WSe2 nanosheets grown on it.

[0021] The present invention grows and prepares two-dimensional WSe2 material by physical vapor deposition. The preparation process is simple, and the WSe2 material grown and prepared is of high quality and controllable thickness, which is conducive to mass production and promotion.

[0022] Furthermore, the step of transferring the WSe2 nanosheets on the substrate having the WSe2 nanosheets grown thereon to the substrate D comprises:

[0023] The substrate with WSe2 nanosheets grown on it is spin-coated with a polymethyl methacrylate (PMMA) solution, baked at 100-150°C for 3-7 minutes, and then immersed in a BOE solution for 4-6 minutes to obtain a polymethyl methacrylate (PMMA) film / two-dimensional WSe2 nanosheet separated from the substrate; the polymethyl methacrylate (PMMA) film / two-dimensional WSe2 nanosheet is attached to a substrate D, baked at 150-200°C for 30-60 minutes, immersed in acetone to remove the polymethyl methacrylate (PMMA) film, and blown dry with nitrogen to obtain a substrate with a WSe2 layer.

[0024] Furthermore, the step of peeling the Ta2NiSe5 single crystal onto the substrate B includes: using blue tape to peel the Ta2NiSe5 single crystal, sticking it on the substrate B, and obtaining a substrate with a Ta2NiSe5 layer; the number of peeling times is 3-5 times.

[0025] Furthermore, the step of peeling the ReS2 single crystal onto the substrate C includes: using blue tape to peel the ReS2 single crystal, sticking it to the substrate C, and obtaining a substrate with a ReS2 layer; the peeling is performed 3-5 times.

[0026] Furthermore, the step of transferring the WSe2 on the substrate with the WSe2 layer to the substrate with the Ta2NiSe5 layer includes:

[0027] The WSe2 nanosheets on the substrate with the WSe2 layer are transferred to a polyvinyl alcohol (PVA) film to obtain a polyvinyl alcohol (PVA) film containing WSe2; the Ta2NiSe5 surface of the substrate with the Ta2NiSe5 layer is laminated with the WSe2 surface of the polyvinyl alcohol (PVA) film containing WSe2, and the mixture is heated at 90-95°C for 3-4 minutes, and then the polyvinyl alcohol (PVA) film on the surface is removed to obtain a substrate with a Ta2NiSe5 / WSe2 heterojunction.

[0028] Furthermore, the step of transferring the ReS2 nanosheets on the substrate with the ReS2 layer to the substrate with the Ta2NiSe5 / WSe2 heterojunction includes:

[0029] The ReS2 nanosheets on the substrate with the ReS2 layer are transferred to a polyvinyl alcohol (PVA) film to obtain a polyvinyl alcohol (PVA) film containing ReS2; the Ta2NiSe5 / WSe2 surface of the substrate with the Ta2NiSe5 / WSe2 heterojunction is laminated with the ReS2 surface of the polyvinyl alcohol (PVA) film containing ReS2, and the mixture is heated at 90-95°C for 3-4 minutes, and then the polyvinyl alcohol (PVA) film on the surface is removed to obtain a Ta2NiSe5 / WSe2 / ReS2 heterojunction.

[0030] The third technical solution of the present invention is to provide an application of the above-mentioned van der Waals heterojunction with a unipolar barrier and polarization sensitivity in the field of photodetectors.

[0031] The fourth technical solution of the present invention: provides a photodetector, wherein the core functional layer of the photodetector is the above-mentioned van der Waals heterojunction with a unipolar barrier and polarization sensitivity.

[0032] The core functional layer of the photodetector provided by the present invention is a Ta2NiSe5 / WSe2 / ReS2 heterojunction (a van der Waals heterojunction with a unipolar barrier and polarization sensitivity), wherein the source is ReS2 and the drain is Ta2NiSe5.

[0033] A fifth technical solution of the present invention is to provide a method for preparing the above-mentioned photodetector, comprising the following steps:

[0034] Coating photoresist on the van der Waals heterojunction with unipolar barrier and polarization sensitivity, and then photolithography electrode pattern on a photolithography machine to obtain the heterojunction after photolithography;

[0035] A metal electrode is evaporated on the heterojunction after photolithography, and after annealing, the photodetector (Ta2NiSe5 / WSe2 / ReS2 van der Waals heterojunction photodetector) is obtained.

[0036] Furthermore, the photolithography parameters are: scanning speed 0.06-0.5 mm / s, power 6-19 mW, developer is tetramethylammonium hydroxide aqueous solution with a concentration of 3-6 wt%, and development time is 18-25 s.

[0037] Furthermore, the metal electrode in the evaporated metal electrode includes at least one of Au, Cr, Ag, Ti, Ni, Pd and Pt.

[0038] Furthermore, the annealing temperature is 100-200° C., the time is 30-120 min, and the atmosphere is an inert atmosphere.

[0039] Optionally, the inert atmosphere includes an Ar / N2 mixed gas.

[0040] The present invention discloses the following technical effects:

[0041] The present invention regulates the band structure of Ta2NiSe5, ReS2, and WSe2 by constructing a van der Waals heterojunction. WSe2 forms a high electron barrier in the middle layer, which can hinder the mutual flow of thermally excited electrons in Ta2NiSe5 and ReS2 under dark conditions, thereby reducing the dark current. Under light, the holes generated by ReS2 can flow smoothly into Ta2NiSe5 and quickly recombine with its photogenerated electrons, reducing the probability of recombination between photogenerated electrons and holes in ReS2. At the same time, the anisotropic light absorption of Ta2NiSe5 and ReS2 is utilized to achieve polarized light response in the 635 nm and 808 nm bands. In summary, this device overcomes the technical problems of existing two-dimensional material photodetectors, such as large dark current and low photoelectric conversion efficiency, limited spectral response, and poor environmental stability.

[0042] The dark current of the photodetector prepared by the present invention is 2.23×10 -10 A, the response can reach 23.3A / W, with a high detection rate of up to 3.03×10 12 Jones; According to the calculation of photocurrent and optical power, it can be seen that it also has a high external quantum efficiency, which can reach 7.16×10 3 %, and has a strong ability to convert incident photons into effective current. The optical switching ratio can reach 3 orders of magnitude, with a maximum optical switching ratio of 6.09×10 3 It has a wide spectral response, with a response in the wavelength range of 405-808 nm, and has polarized light response at 635 nm and 808 nm with polarization ratios of 1.9 and 2.45.

[0043] The Ta2NiSe5 / WSe2 / ReS2 van der Waals heterojunction provided by the present invention can significantly reduce dark current and improve the response performance of the photodetector.

[0044] The photodetector made of the van der Waals heterojunction constructed in the present invention has the characteristics of low dark current, high detection rate, wide band and polarized light response. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] The accompanying drawings, which constitute part of the present invention, are provided to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are provided to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0046] Figure 1 These are the energy band structure diagrams of Ta2NiSe5 / WSe2 / ReS2 before and after contact in Example 1, where (a) is before contact, (b) is under dark conditions after contact, and (c) is under light conditions after contact.

[0047] Figure 2 This is an optical image of the Ta2NiSe5 / WSe2 / ReS2 van der Waals heterojunction photodetector prepared in Example 2.

[0048] Figure 3 These are the polarization Raman images of the Ta2NiSe5 / WSe2 / ReS2 van der Waals heterojunction photodetector prepared in Example 2, where (a) is the polarization Raman image of Ta2NiSe5, and (b) is the polarization Raman image of ReS2.

[0049] Figure 4 This is a source-drain voltage-source-drain current diagram of the Ta2NiSe5 / WSe2 / ReS2 van der Waals heterojunction photodetector prepared in Example 2 at different light powers in the 405 nm band.

[0050] Figure 5 This is a comparison diagram of the source-drain voltage-source-drain current of the photodetectors prepared in Example 2 and Comparative Example 2 under dark and light conditions in the 405 nm band.

[0051] Figure 6 This is a source-drain voltage-source-drain current diagram of the Ta2NiSe5 / WSe2 / ReS2 van der Waals heterojunction photodetector prepared in Example 2 in the 405-808 nm band.

[0052] Figure 7 The responsivity, detectivity curves, optical switching ratio, and optical gain curves of the Ta2NiSe5 / WSe2 / ReS2 van der Waals heterojunction photodetector prepared in Example 2 at different power densities in the 405 nm band, where (a) is the responsivity and detectivity curves, and (b) is the optical switching ratio and optical gain curves.

[0053] Figure 8This is the polarized light response diagram of the Ta2NiSe5 / WSe2 / ReS2 van der Waals heterojunction photodetector prepared in Example 2 in the 635 nm band, where (a) is a curve diagram of the source-drain current changing with angle, and (b) is a polar coordinate diagram of the normalized photocurrent changing with polarization angle.

[0054] Figure 9 This is the polarized light response diagram of the Ta2NiSe5 / WSe2 / ReS2 van der Waals heterojunction photodetector prepared in Example 2 in the 808 nm band, where (a) is a curve diagram of the source-drain current changing with angle, and (b) is a polar coordinate diagram of the normalized photocurrent changing with polarization angle.

[0055] Figure 10 This is an optical image of the Ta2NiSe5 / WSe2 / ReS2 van der Waals heterojunction photodetector prepared in Example 4.

[0056] Figure 11 This is a comparison diagram of the source-drain voltage-source-drain current of the photodetectors prepared in Example 4 and Comparative Example 2 under dark and light conditions in the 405 nm band.

[0057] Figure 12 This is the optical image of the Ta2NiSe5 / ReS2 van der Waals heterojunction photodetector prepared in comparative example 2. DETAILED DESCRIPTION

[0058] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0059] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. The intermediate value within any stated value or stated range, and each smaller range between any other stated value or intermediate value within the stated range, is also encompassed within the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0060] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0061] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be illustrative only.

[0062] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0063] Substrates A to D involved in the specific embodiments of the present invention are all SiO2 / Si substrates.

[0064] Unless otherwise specified, the room temperature and normal temperature involved in the specific embodiments of the present invention refer to 20-30°C.

[0065] Unless otherwise specified, the raw materials and reagents involved in the specific embodiments of the present invention are commercially available products.

[0066] It should be pointed out that the matters not described in detail in the present invention are conventional operating means in this field and are not the focus of the present invention.

[0067] In some specific embodiments, the present invention provides a method for preparing a Ta2NiSe5 / WSe2 / ReS2 van der Waals heterojunction, comprising the steps of:

[0068] S1. Preparation of two-dimensional WSe2 by physical vapor deposition: 100 mg of reactant WSe2 powder was weighed and placed in a quartz boat, which was placed in the heating center of a high-temperature tube furnace. A SiO2 / Si substrate with a size of 10 mm × 10 mm was placed downstream of the hot center. The carrier gas was an inert gas (N2). The air was exhausted with an inert gas flow rate of 100-120 sccm. The air flow direction was from substrate to reactant. The flow rate was then adjusted to 30-40 sccm. The temperature was raised to 1100-1130°C at a heating rate of 12-12.5°C / min. The air flow direction was changed from reactant to substrate. The flow rate was adjusted to 100-120 sccm. The temperature was kept at this temperature for 10-15 minutes. Finally, the flow rate was adjusted to 20-30 sccm. The mixture was cooled to room temperature. Two-dimensional WSe2 nanosheets were prepared on the surface of the substrate, and a SiO2 / Si substrate with WSe2 nanosheets was obtained.

[0069] S2. Mechanical exfoliation of Ta2NiSe5: Using Ta2NiSe5 single crystal as raw material, repeatedly exfoliate (3-5 times) the single crystal using blue tape and stick it on a SiO2 / Si substrate to obtain a SiO2 / Si substrate with a Ta2NiSe5 layer.

[0070] S3. Mechanical exfoliation of ReS2: Using a ReS2 single crystal as the raw material, use blue tape to repeatedly exfoliate (3-5 times) the single crystal and stick it on a SiO2 / Si substrate to obtain a SiO2 / Si substrate with a ReS2 layer.

[0071] S4. Spin-coat the SiO2 / Si substrate with WSe2 nanosheets grown on it with a PMMA solution (concentration of 4%), bake it at 100-150°C for 3-7 minutes, and then immerse it in a BOE solution (specification BOE:H2O=1:10) for 4-6 minutes to obtain a PMMA film / two-dimensional WSe2 nanosheet separated from the substrate; attach the PMMA film / two-dimensional WSe2 nanosheet to a new SiO2 / Si substrate, bake it at 150-200°C for 30-60 minutes, immerse it in acetone to remove the PMMA film, and blow dry it with nitrogen to complete the transfer of the WSe2 nanosheet to the surface of the new SiO2 / Si substrate, and obtain a SiO2 / Si substrate with a WSe2 layer;

[0072] S5. Place the SiO2 / Si substrate with the WSe2 layer on the sample stage of the transfer table; drip a PVA solution (concentration of 4%) onto the polydimethylsiloxane (PDMS) film that can cover the material, gently scrape it with a glass slide until it is flat, and dry it at 55°C for 10 minutes to form a solidified PVA film. Place it on a clean glass slide, fix it in the card slot of the transfer table, align it with the WSe2 on the SiO2 / Si substrate with the WSe2 layer by adjusting the control platform, and transfer the WSe2 to the PVA film to obtain a PVA film containing WSe2;

[0073] S6. Place the SiO2 / Si substrate with the Ta2NiSe5 layer on the sample stage of the transfer platform, fix the PVA film containing WSe2 in the card slot of the transfer platform, observe the overlapping part through the microscope of the transfer platform, select the appropriate junction area, and continuously fit the two by controlling the transfer platform, heat at 90-95°C for 3-4 minutes, then remove and soak in 55°C deionized water for 15-30 minutes, remove the PVA film on the surface of the mica sheet, and blow dry with a nitrogen gun to obtain a SiO2 / Si substrate with a Ta2NiSe5 / WSe2 van der Waals heterojunction;

[0074] S7. Place the SiO2 / Si substrate with the ReS2 layer on the sample stage of the transfer table; drip a PVA solution (concentration of 4%) onto the polydimethylsiloxane (PDMS) film that can cover the material, gently scrape it with a glass slide until it is flat, and dry it at 55°C for 10 minutes to form a solidified PVA film. Place it on a clean glass slide, fix it in the card slot of the transfer table, align it with the ReS2 on the SiO2 / Si substrate with the ReS2 layer by adjusting the control platform, and transfer the ReS2 to the PVA film to obtain a PVA film containing ReS2;

[0075] S8. Place the SiO2 / Si substrate with the Ta2NiSe5 / WSe2 van der Waals heterojunction on the sample stage of the transfer platform, fix the PVA film containing ReS2 in the card slot of the transfer platform, observe the overlapping part through the microscope of the transfer platform, select the appropriate junction area, and continuously fit the two by controlling the transfer platform, heat at 90-95°C for 3-4 min, then remove and soak in 55°C deionized water for 15-30 min, remove the PVA film on the surface of the mica sheet after taking it out, blow dry with a nitrogen gun to obtain a Ta2NiSe5 / WSe2 / ReS2 van der Waals heterojunction.

[0076] In some specific embodiments, the present invention provides a method for preparing a Ta2NiSe5 / WSe2 / ReS2 van der Waals heterojunction photodetector, comprising the steps of:

[0077] S1. Photolithography of electrode patterns on Ta2NiSe5 / WSe2 / ReS2 van der Waals heterojunctions: Spin-coat the Ta2NiSe5 / WSe2 / ReS2 van der Waals heterojunction with photoresist using a spin coater, then heat at 105°C for 4-5 minutes. Use electron beam lithography to precisely position and expose the electrode pattern. Develop the exposed heterojunction with a developer, fix it with deionized water, and blow dry it with a nitrogen gun to obtain the photolithographic heterojunction. The parameters are: a scan speed of 0.06-0.5 mm / s, a power of 6-19 mW, a 3-6 wt% tetramethylammonium hydroxide aqueous solution as the developer, and a development time of 18-25 seconds for the photolithography machine.

[0078] S2. Vapor-depositing a metal drain electrode and a source electrode on the heterojunction after photolithography, so that part of the metal source electrode is located on the surface of the ReS2 material and the other part is located on the surface of the SiO2 / Si substrate, and part of the drain electrode is located on the surface of the Ta2NiSe5 material and the other part is located on the surface of the SiO2 / Si substrate; after the evaporation is completed, removing the photoresist with an acetone solution, soaking in deionized water to remove the residual acetone solution, then blowing dry with a nitrogen gun, and finally performing vacuum high-temperature annealing; the conditions of the high-temperature annealing are: annealing temperature of 100-200 ° C, atmosphere of Ar / N2 mixed gas, annealing time of 30-120 min, to obtain a Ta2NiSe5 / WSe2 / ReS2 van der Waals heterojunction photodetector;

[0079] The metal electrodes in the evaporated metal drain electrode and source electrode include at least one of Au, Cr, Ag, Ti, Ni, Pd and Pt.

[0080] The SiO2 / Si substrates used in the specific embodiments of the present invention were cleaned in acetone, ethanol, and deionized water for 15 minutes, and finally dried with a nitrogen gun.

[0081] Example 1

[0082] The preparation steps of Ta2NiSe5 / WSe2 / ReS2 van der Waals heterojunction include:

[0083] S1. Preparation of two-dimensional WSe2 by physical vapor deposition: 100 mg of reactant WSe2 powder was weighed and placed in a quartz boat, which was placed in the heating center of a high-temperature tube furnace. A SiO2 / Si substrate with a size of 10 mm × 10 mm was placed downstream of the hot center. The carrier gas was an inert gas (N2). The air was exhausted with an inert gas flow rate of 120 sccm. The airflow direction was from substrate to reactant. The flow rate was then adjusted to 35 sccm. After heating to 1130°C at a heating rate of 12.5°C / min, the airflow direction was changed from reactant to substrate. The flow rate was adjusted to 120 sccm and kept at this temperature for 12 minutes. Finally, the flow rate was adjusted to 25 sccm and cooled to room temperature. Two-dimensional WSe2 nanosheets were prepared on the substrate surface, and a SiO2 / Si substrate with WSe2 (triangular and hexagonal) nanosheets was obtained.

[0084] S2. Mechanical exfoliation of Ta2NiSe5: Using a Ta2NiSe5 single crystal as the raw material, the single crystal was repeatedly exfoliated (5 times) using blue tape and then adhered to a SiO2 / Si substrate to obtain a SiO2 / Si substrate with a Ta2NiSe5 layer.

[0085] S3. Mechanical exfoliation of ReS2: Using a ReS2 single crystal as the raw material, the single crystal was repeatedly exfoliated (5 times) using blue tape and then adhered to a SiO2 / Si substrate to obtain a SiO2 / Si substrate with a ReS2 layer.

[0086] S4. Spin-coat the SiO2 / Si substrate with WSe2 (select triangle) nanosheets grown on it with PMMA solution (concentration of 4%), bake it at 120℃ for 3min, and then immerse it in BOE solution (specification BOE:H2O=1:10) for 5min to obtain PMMA film / two-dimensional WSe2 nanosheets separated from the substrate; attach the PMMA film / two-dimensional WSe2 nanosheets to a new SiO2 / Si substrate, bake it at 150℃ for 30min, immerse it in acetone to remove the PMMA film, and blow dry it with nitrogen to complete the transfer of WSe2 nanosheets to the surface of the new SiO2 / Si substrate, and obtain a SiO2 / Si substrate with a WSe2 layer;

[0087] S5. Place the SiO2 / Si substrate with the WSe2 layer on the sample stage of the transfer table; drip a PVA solution (concentration of 4%) onto the polydimethylsiloxane (PDMS) film that can cover the material, gently scrape it with a glass slide until it is flat, and dry it at 55°C for 10 minutes to form a solidified PVA film. Place it on a clean glass slide, fix it in the card slot of the transfer table, align it with the WSe2 on the SiO2 / Si substrate with the WSe2 layer by adjusting the control platform, and transfer the WSe2 to the PVA film to obtain a PVA film containing WSe2;

[0088] S6. Place the SiO2 / Si substrate with the Ta2NiSe5 layer on the sample stage of the transfer platform, fix the PVA film containing WSe2 in the card slot of the transfer platform, observe the overlapping part through the microscope of the transfer platform, select the appropriate junction area, and continuously fit the two by controlling the transfer platform, heat at 90°C for 3 minutes, then remove and soak in 55°C deionized water for 15 minutes, remove the PVA film on the surface of the mica sheet, and blow dry with a nitrogen gun to obtain a SiO2 / Si substrate with a Ta2NiSe5 / WSe2 van der Waals heterojunction;

[0089] S7. Place the SiO2 / Si substrate with the ReS2 layer on the sample stage of the transfer table; drip a PVA solution (concentration of 4%) onto the polydimethylsiloxane (PDMS) film that can cover the material, gently scrape it with a glass slide until it is flat, and dry it at 55°C for 10 minutes to form a solidified PVA film. Place it on a clean glass slide, fix it in the card slot of the transfer table, align it with the ReS2 on the SiO2 / Si substrate with the ReS2 layer by adjusting the control platform, and transfer the ReS2 to the PVA film to obtain a PVA film containing ReS2;

[0090] S8. Place the SiO2 / Si substrate with the Ta2NiSe5 / WSe2 van der Waals heterojunction on the sample stage of the transfer platform, fix the PVA film containing ReS2 in the card slot of the transfer platform, observe the overlapping part through the microscope of the transfer platform, select the appropriate junction area, and continuously fit the two by controlling the transfer platform, heat at 90°C for 3 minutes, then remove and soak in 55°C deionized water for 15 minutes, remove the PVA film on the surface of the mica sheet after taking it out, blow dry with a nitrogen gun to obtain a Ta2NiSe5 / WSe2 / ReS2 van der Waals heterojunction.

[0091] Example 2

[0092] The preparation steps of Ta2NiSe5 / WSe2 / ReS2 van der Waals heterojunction photodetector include:

[0093] S1. Photolithography of an electrode pattern on the Ta2NiSe5 / WSe2 / ReS2 van der Waals heterojunction prepared in Example 1: spin-coating the Ta2NiSe5 / WSe2 / ReS2 van der Waals heterojunction with photoresist using a spin coater, then heating at 105°C for 4 minutes, and then precisely positioning and exposing the electrode pattern using electron beam exposure technology. The exposed heterojunction is then developed with a developer, fixed with deionized water, and dried with a nitrogen gun to obtain a photolithographic heterojunction. The parameters are: a scanning speed of 0.3 mm / s, a power of 19 mW, a 3 wt% tetramethylammonium hydroxide aqueous solution as the developer, and a development time of 25 seconds for the photolithography machine.

[0094] S2. Ti / Au drain electrode and source electrode are evaporated on the heterojunction after photolithography, so that part of the metal source electrode is located on the surface of the ReS2 material, the other part is located on the surface of the SiO2 / Si substrate, and part of the drain electrode is located on the surface of the Ta2NiSe5 material, and the other part is located on the surface of the SiO2 / Si substrate; after the evaporation is completed, the photoresist is removed with acetone solution, and the residual acetone solution is removed by soaking in deionized water, and then blown dry with a nitrogen gun, and finally vacuum high-temperature annealing is performed; the conditions of the high-temperature annealing are: annealing temperature is 150°C, the atmosphere is Ar / N2 mixed gas, and the annealing time is 60 min, thereby obtaining a Ta2NiSe5 / WSe2 / ReS2 van der Waals heterojunction photodetector.

[0095] Example 3

[0096] Compared with Example 1, the difference is that the shape of the middle layer WSe2 of the Ta2NiSe5 / WSe2 / ReS2 van der Waals heterojunction prepared in Example 1 is replaced from a triangle to a hexagon.

[0097] Example 4

[0098] Compared with Example 2, the difference is that the Ta2NiSe5 / WSe2 / ReS2 van der Waals heterojunction prepared in Example 3 is used for preparation.

[0099] Comparative Example 1

[0100] The preparation steps of Ta2NiSe5 / ReS2 van der Waals heterojunction include:

[0101] S1. Mechanical exfoliation of Ta2NiSe5: Using Ta2NiSe5 single crystal as raw material, repeatedly exfoliate the single crystal (5 times) using blue tape and stick it on a SiO2 / Si substrate to obtain a SiO2 / Si substrate with a Ta2NiSe5 layer.

[0102] S2. Mechanical exfoliation of ReS2: Using a ReS2 single crystal as the raw material, the single crystal was repeatedly exfoliated (5 times) using blue tape and then adhered to a SiO2 / Si substrate to obtain a SiO2 / Si substrate with a ReS2 layer.

[0103] S3. Place the SiO2 / Si substrate with the ReS2 layer on the sample stage of the transfer table; drip a PVA solution (concentration of 4%) onto the polydimethylsiloxane (PDMS) film that can cover the material, gently scrape it with a glass slide until it is flat, and dry it at 55°C for 10 minutes to form a solidified PVA film. Place it on a clean glass slide, fix it in the card slot of the transfer table, align it with the ReS2 on the SiO2 / Si substrate with the ReS2 layer by adjusting the control platform, and transfer the ReS2 to the PVA film to obtain a PVA film containing ReS2;

[0104] S4. Place the SiO2 / Si substrate with the Ta2NiSe5 layer on the sample stage of the transfer platform, fix the PVA film containing ReS2 in the card slot of the transfer platform, observe the overlapping part through the microscope of the transfer platform, select the appropriate junction area, and continuously fit the two by controlling the transfer platform. Heat at 90°C for 3 minutes, then remove and soak in 55°C deionized water for 15 minutes. After taking it out, remove the PVA film on the surface of the mica sheet and blow it dry with a nitrogen gun to obtain a Ta2NiSe5 / ReS2 van der Waals heterojunction.

[0105] Comparative Example 2

[0106] Compared with Example 2, the difference is that the Ta2NiSe5 / WSe2 / ReS2 van der Waals heterojunction prepared in Example 1 is replaced by the Ta2NiSe5 / ReS2 van der Waals heterojunction prepared in Comparative Example 1, and the obtained photodetector is a Ta2NiSe5 / ReS2 van der Waals heterojunction photodetector.

[0107] Test example

[0108] Figure 1 The energy band structure diagrams of Ta2NiSe5 / WSe2 / ReS2 before and after contact in Example 1, where (a) is before contact, (b) is after contact under dark conditions, and (c) is after contact under light conditions.

[0109] Figure 1 Before contact, it refers to the energy band structures of the three two-dimensional materials Ta2NiSe5, WSe2, and ReS2 respectively; after contact, it refers to the energy band structure of the Ta2NiSe5 / WSe2 / ReS2 van der Waals heterojunction photodetector.

[0110] Depend on Figure 1It can be seen that after contact under dark conditions, WSe2 forms a large potential barrier in the middle layer, which can prevent the electrons thermally excited by Ta2NiSe5 from flowing to ReS2 under dark conditions, while the holes thermally excited by ReS2 can flow to Ta2NiSe5. Ta2NiSe5 is a p-type semiconductor, and holes are majority carriers. The holes flowing to Ta2NiSe5 cannot form recombination, thereby reducing the dark current. Under light conditions, both Ta2NiSe5 and ReS2 will generate photogenerated carriers. Due to the high potential barrier of WSe2, the electrons at Ta2NiSe5 cannot flow to ReS2, resulting in a large accumulation. When the photogenerated electrons at Ta2NiSe5 accumulate sufficiently, they will recombine with the holes flowing from ReS2 to Ta2NiSe5, thereby improving the photoelectric response of the device.

[0111] Figure 2 This is an optical image of the Ta2NiSe5 / WSe2 / ReS2 van der Waals heterojunction photodetector prepared in Example 2. The image shows that the drain is Ta2NiSe5 and the source is ReS2.

[0112] Figure 3 These are the polarization Raman images of the Ta2NiSe5 / WSe2 / ReS2 van der Waals heterojunction photodetector prepared in Example 2, where (a) is the polarization Raman image of Ta2NiSe5, and (b) is the polarization Raman image of ReS2.

[0113] Figure 4 This is the source-drain voltage-source-drain current diagram of the Ta2NiSe5 / WSe2 / ReS2 van der Waals heterojunction photodetector prepared in Example 2 at different light powers in the 405 nm band. As can be seen from the figure, at different power densities, the corresponding photocurrent curves are obtained when different source-drain voltages (-3V to 3V) are applied. ds When the power density is constant, the dark state current is the smallest, and the photocurrent increases with the increase of power density. When the power density reaches the maximum of 101 mW / cm 2 The photocurrent is the largest, which indicates that the heterojunction photodetector has a high on-off ratio.

[0114] Figure 5 The following is a comparison of the source-drain voltage and source-drain current of the photodetectors prepared in Example 2 and Comparative Example 2 under dark and light conditions in the 405 nm band. As can be seen from the figure, when the source-drain voltage is -3 V, the dark current of Example 2 increases from 4.17×10 -10 A decreased to 2.33×10 -10 A, under light conditions, the source-drain current of Example 2 is 3.54×10 -8 A increased to 1.35×10 -6A, which shows that the high potential barrier of WSe2 in the middle plays a role in reducing dark current and increasing photocurrent.

[0115] Figure 6 This is a graph showing the source-drain voltage versus source-drain current for the Ta2NiSe5 / WSe2 / ReS2 van der Waals heterojunction photodetector prepared in Example 2 in the 405-808 nm wavelength range. As can be seen from the figure, the photodetector has good response in the 405-808 nm wavelength range, demonstrating the device's wide-response performance.

[0116] Figure 7 The responsivity, detectivity curves, optical switching ratio, and optical gain curves of the Ta2NiSe5 / WSe2 / ReS2 van der Waals heterojunction photodetector prepared in Example 2 at different power densities in the 405 nm band, where (a) is the responsivity and detectivity curves, and (b) is the optical switching ratio and optical gain curves. Figure 7 It can be seen that (a) provides the photodetector with a source-drain voltage V ds =-3V, wavelength of 405 nm, the responsivity and detectivity curves at different power densities. The responsivity of the photodetector is 22.3 A / W, and the detectivity is 3.03×10 12 Jones. (b) provides the photodetector at source-drain voltage V ds =-3 V, the optical switching ratio and optical gain at different power densities at a wavelength of 405 nm. The maximum optical switching ratio of the photodetector is 6.09×10 3 , the optical gain is 71.55.

[0117] Figure 8 Figure 2 shows the polarization response of the Ta2NiSe5 / WSe2 / ReS2 van der Waals heterojunction photodetector prepared in Example 2 at 635 nm. (a) shows the source-drain current as a function of angle, and (b) shows the normalized photocurrent as a function of polarization angle. As can be seen from the figure, the photodetector has good polarization response at 635 nm, with a polarization angle of 1.9.

[0118] Figure 9 Figure 2 shows the polarization response of the Ta2NiSe5 / WSe2 / ReS2 van der Waals heterojunction photodetector prepared in Example 2 at 808 nm. (a) shows the source-drain current as a function of angle, and (b) shows the normalized photocurrent as a function of polarization angle. As can be seen from the figure, the photodetector has good polarization response at 808 nm, with a polarization angle of 2.45.

[0119] Figure 10This is an optical image of the Ta2NiSe5 / WSe2 / ReS2 van der Waals heterojunction photodetector prepared in Example 4. As can be seen from the figure, the drain electrode is Ta2NiSe5 and the source electrode is ReS2.

[0120] Figure 11 The following is a comparison of the source-drain voltage and source-drain current of the photodetectors prepared in Example 4 and Comparative Example 2 under dark and light conditions in the 405 nm band. As can be seen from the figure, when the source-drain voltage is -3 V, the dark current of Example 4 increases from 4.17×10 -10 A decreased to 2.6×10 -11 A, under light conditions, the source-drain current of Example 4 is 3.54×10 -8 A increased to 4.31×10 -7 A, which shows that the high potential barrier of WSe2 in the middle plays a role in reducing dark current and increasing photocurrent.

[0121] Figure 12 This is an optical image of the Ta2NiSe5 / ReS2 van der Waals heterojunction photodetector prepared in Comparative Example 2. As can be seen from the image, the drain electrode is Ta2NiSe5 and the source electrode is ReS2.

[0122] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0123] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A van der Waals heterojunction with a unipolar barrier and polarization sensitivity, characterized in that The anisotropic p-type material Ta2NiSe5 is used as the bottom carrier collection layer, the anisotropic n-type material ReS2 is used as the upper light absorption layer, and WSe2 is used as the intermediate barrier layer.

2. A method for preparing a van der Waals heterojunction having a unipolar barrier and polarization sensitivity according to claim 1, characterized in that the steps include: WSe2 is grown on the surface of substrate A by physical vapor deposition to obtain a substrate with WSe2 nanosheets grown on it; Transferring the WSe2 nanosheets on the substrate having the WSe2 nanosheets grown thereon to a substrate D to obtain a substrate with a WSe2 layer; Peeling the Ta2NiSe5 single crystal onto substrate B to obtain a substrate with a Ta2NiSe5 layer; Peeling the ReS2 single crystal onto substrate C to obtain a substrate with a ReS2 layer; Transferring the WSe2 on the substrate with the WSe2 layer to the substrate with the Ta2NiSe5 layer to obtain a substrate with a Ta2NiSe5 / WSe2 heterojunction; The ReS2 nanosheets on the substrate with the ReS2 layer are transferred to a substrate with a Ta2NiSe5 / WSe2 heterojunction to obtain a Ta2NiSe5 / WSe2 / ReS2 heterojunction.

3. The preparation method according to claim 2, wherein The step of growing WSe2 on the surface of substrate A by physical vapor deposition includes: placing substrate A and WSe2 powder in a heating device, exhausting air with an inert gas, with the air flow direction from the substrate to the reactant, then adjusting the inert gas flow rate to 30-40 sccm, and heating to 1100-1130°C at a heating rate of 12-12.5°C / min, changing the air flow direction from the reactant to the substrate, adjusting the flow rate to 100-120 sccm, keeping warm for 10-15 minutes, and finally adjusting the flow rate to 20-30 sccm, cooling to room temperature, and obtaining a substrate with WSe2 nanosheets grown thereon.

4. The preparation method according to claim 2, wherein The step of transferring the WSe2 nanosheets on the substrate having the WSe2 nanosheets grown thereon to the substrate D comprises: The substrate with WSe2 nanosheets grown on it is spin-coated with a polymethyl methacrylate solution, baked at 100-150°C for 3-7 minutes, and then immersed in a BOE solution for 4-6 minutes to obtain a polymethyl methacrylate film / two-dimensional WSe2 nanosheet separated from the substrate; the polymethyl methacrylate film / two-dimensional WSe2 nanosheet is attached to a substrate D, baked at 150-200°C for 30-60 minutes, immersed in acetone to remove the polymethyl methacrylate film, and blown dry with nitrogen to obtain a substrate with a WSe2 layer.

5. The preparation method according to claim 2, wherein The step of peeling the Ta2NiSe5 single crystal onto the substrate B includes: using blue tape to peel the Ta2NiSe5 single crystal, sticking it to the substrate B, and obtaining a substrate with a Ta2NiSe5 layer; the number of times of peeling is 3-5; And / or, the step of peeling the ReS2 single crystal onto the substrate C includes: using blue tape to peel the ReS2 single crystal, sticking it to the substrate C, and obtaining a substrate with a ReS2 layer; the number of peeling is 3-5 times.

6. The preparation method according to claim 2, wherein The step of transferring the WSe2 on the substrate with the WSe2 layer to the substrate with the Ta2NiSe5 layer comprises: The WSe2 nanosheets on the substrate with the WSe2 layer are transferred to the polyvinyl alcohol film to obtain a polyvinyl alcohol film containing WSe2; the Ta2NiSe5 surface of the substrate with the Ta2NiSe5 layer is laminated with the WSe2 surface of the polyvinyl alcohol film containing WSe2, heated at 90-95°C for 3-4 minutes, and then the polyvinyl alcohol film on the surface is removed to obtain a substrate with a Ta2NiSe5 / WSe2 heterojunction.

7. The preparation method according to claim 2, wherein The step of transferring the ReS2 nanosheets on the substrate with the ReS2 layer to the substrate with the Ta2NiSe5 / WSe2 heterojunction comprises: The ReS2 nanosheets on the substrate with the ReS2 layer are transferred to a polyvinyl alcohol film to obtain a polyvinyl alcohol film containing ReS2; the Ta2NiSe5 / WSe2 surface of the substrate with the Ta2NiSe5 / WSe2 heterojunction is laminated with the ReS2 surface of the polyvinyl alcohol film containing ReS2, heated at 90-95°C for 3-4 minutes, and then the polyvinyl alcohol film on the surface is removed to obtain a Ta2NiSe5 / WSe2 / ReS2 heterojunction.

8. Use of the van der Waals heterojunction with a unipolar barrier and polarization sensitivity according to claim 1 in the field of photodetectors.

9. A photoelectric detector, characterized in that: The core functional layer of the photodetector is the van der Waals heterojunction with a unipolar barrier and polarization sensitivity as described in claim 1.

10. A method for preparing a photodetector according to claim 9, characterized in that the steps include: Coating photoresist on the van der Waals heterojunction with unipolar barrier and polarization sensitivity, and then photolithography electrode pattern on a photolithography machine to obtain the heterojunction after photolithography; A metal electrode is evaporated on the heterojunction after photolithography, and annealed to obtain the photodetector.

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