Monopolar barrier and polarization sensitive van der waals heterojunctions and applications thereof

Abstract

The application belongs to the technical field of two-dimensional material photoelectric devices, and more particularly relates to a van der Waals heterojunction with unipolar barrier and polarization sensitivity and application thereof. The van der Waals heterojunction with unipolar barrier and polarization sensitivity is constructed by taking the anisotropic p-type material Ta2NiSe5 as a bottom layer carrier collection layer, taking the anisotropic n-type material ReS2 as an upper light absorption layer, and taking WSe2 as an intermediate barrier layer, and then a 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 waveband and polarized light response.

Description

Technical Field

[0001] This invention belongs to the field of two-dimensional material optoelectronic device technology, and more specifically relates to a van der Waals heterojunction with a unipolar barrier and polarization sensitivity and its applications. Background Technology

[0002] Photodetectors play a crucial role in various fields such as optoelectronic communication, imaging, remote sensing, and environmental monitoring. With the increasing demand for high-performance photodetectors, expanding the detector's response band, improving detection sensitivity, and reducing dark current have become current research hotspots. Traditional photodetectors often employ single-material or simple type II bandgap heterojunction structures; however, these structures often face problems such as difficulty in bandgap tuning, narrow response spectrum, and large dark current.

[0003] Especially in the field of broadband photodetectors, existing semiconductor materials often suffer from technical bottlenecks such as limited band gaps and significant interfacial recombination effects. These problems not only limit the response range of the detectors but also make it difficult to further improve device performance. Therefore, how to effectively extend the response range of photodetectors, especially in the infrared, ultraviolet, and visible light bands, while maintaining low dark current and high response speed, has become a challenge that needs to be addressed in photodetector technology.

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

[0005] The purpose of this 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, so as to solve the problems existing in the prior art.

[0006] To achieve the above objectives, the present invention provides the following solution:

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

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

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

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

[0011] The second technical solution of the present invention provides 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] The WSe2 nanosheets on the substrate on which WSe2 nanosheets are grown are transferred to substrate D to obtain a substrate with a WSe2 layer.

[0014] The Ta2NiSe5 single crystal was stripped onto substrate B to obtain a substrate with a Ta2NiSe5 layer.

[0015] The ReS2 single crystal was stripped onto substrate C to obtain a substrate with a ReS2 layer;

[0016] The WSe2 on the substrate with the WSe2 layer is transferred 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 invention exhibit different photoelectron conversion mechanisms. Ta2NiSe5 exhibits anisotropy and high mobility, while ReS2 shows 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] Substrate A and WSe2 powder were placed in a heating device, and air was purged using inert gas with the airflow direction from substrate to reactants. The inert gas flow rate was then adjusted to 30-40 sccm, and the temperature was increased to 1100-1130℃ at a heating rate of 12-12.5℃ / min. The airflow direction was then changed from reactants to substrate, and the flow rate was adjusted to 100-120 sccm. The temperature was maintained for 10-15 min, and finally the flow rate was adjusted to 20-30 sccm. The temperature was then cooled to room temperature to obtain a substrate with WSe2 nanosheets grown on it.

[0021] This invention produces two-dimensional WSe2 materials by physical vapor deposition. The preparation process is simple, and the WSe2 materials produced are of high quality and have controllable thickness, which is beneficial for mass production and promotion.

[0022] Furthermore, the step of transferring the WSe2 nanosheets on the substrate with grown WSe2 nanosheets onto the substrate D includes:

[0023] A polymethyl methacrylate (PMMA) solution was spin-coated onto a substrate with grown WSe2 nanosheets. After baking at 100-150°C for 3-7 minutes, the substrate was immersed in 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 was then attached to substrate D and baked at 150-200°C for 30-60 minutes. The polymethyl methacrylate (PMMA) film was removed by immersion in acetone and then dried 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 adhesive tape to peel off the Ta2NiSe5 single crystal and stick it onto the substrate B to obtain a substrate with a Ta2NiSe5 layer; the peeling is performed 3-5 times.

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

[0026] Furthermore, the step of transferring WSe2 from 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 side of the substrate with the obtained Ta2NiSe5 layer is bonded to the WSe2 side of the polyvinyl alcohol (PVA) film containing WSe2, heated at 90-95℃ for 3-4 min, 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 from 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 side of the substrate with the Ta2NiSe5 / WSe2 heterojunction is bonded to the ReS2 side of the polyvinyl alcohol (PVA) film containing ReS2, heated at 90-95℃ for 3-4 min, and then the polyvinyl alcohol (PVA) film on the surface is removed to obtain the Ta2NiSe5 / WSe2 / ReS2 heterojunction.

[0030] The third technical solution of the present invention provides an application of the above-mentioned van der Waals heterojunction with 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 van der Waals heterojunction with a unipolar barrier and polarization sensitivity as described above.

[0032] The core functional layer of the photodetector provided by this 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] Fifth technical solution of the present invention: A method for preparing the above-mentioned photodetector, comprising the following steps:

[0034] Photoresist is coated onto a van der Waals heterojunction with a unipolar barrier and polarization sensitivity, and then electrode patterns are etched on a photolithography machine to obtain the etched heterojunction.

[0035] Metal electrodes are deposited 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 a 3-6 wt% tetramethylammonium hydroxide aqueous solution, and development time is 18-25 s.

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

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

[0039] Optionally, the inert atmosphere may include an Ar / N2 mixture.

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

[0041] This invention constructs a van der Waals heterojunction to modulate the band structure of Ta2NiSe5, ReS2, and WSe2. WSe2 forms a high electron barrier in the middle layer, hindering the flow of thermally excited electrons between Ta2NiSe5 and ReS2 under dark conditions, thus reducing dark current. Under illumination, holes generated in ReS2 can flow smoothly into Ta2NiSe5 and rapidly recombine with their photogenerated electrons, reducing the probability of recombination between photogenerated electrons and holes in ReS2. Simultaneously, utilizing the anisotropic light absorption inherent in Ta2NiSe5 and ReS2, polarized light response is achieved in the 635 nm and 808 nm wavelength bands. In summary, this device overcomes the technical problems of existing two-dimensional material photodetectors, such as large dark current, low photoelectric conversion efficiency, limited spectral response, and poor environmental stability.

[0042] The dark current of the photodetector prepared by this invention is 2.23 × 10⁻⁶. -10 A, with a responsivity of up to 23.3 A / W, exhibits a high detectivity of up to 3.03 × 10⁻⁶. 12 Jones; Calculations based on photocurrent and optical power show that it also possesses a high external quantum efficiency, reaching 7.16 × 10⁻⁶. 3 It boasts a high degree of efficiency, effectively converting incident photons into usable current. Furthermore, its optical on / off ratio can reach three orders of magnitude, with a maximum optical on / off ratio of 6.09 × 10⁻⁶. 3 It exhibits a broad spectral response, with a wavelength range of 405-808 nm, and polarized light responses at 635 nm and 808 nm, with polarization ratios of 1.9 and 2.45, respectively.

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

[0044] The photodetector fabricated from the van der Waals heterojunction constructed in this invention has the characteristics of low dark current, high detectivity, wide spectral band, and polarized light response. Attached Figure Description

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

[0046] Figure 1 The diagrams show the band structure 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 Optical image of the Ta2NiSe5 / WSe2 / ReS2 van der Waals photodetector prepared in Example 2.

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

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

[0050] Figure 5 Comparison of 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.

[0051] Figure 6 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 wavelength range.

[0052] Figure 7 The responsivity, detectivity, optical on / off 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 are shown. Among them, (a) is the responsivity and detectivity curve, and (b) is the optical on / off ratio and optical gain curve.

[0053] Figure 8The image shows the polarization response of the Ta2NiSe5 / WSe2 / ReS2 van der Waals heterojunction photodetector prepared in Example 2 at 635 nm. In the image, (a) is a graph of source and drain current as a function of angle, and (b) is a polar coordinate graph of normalized photocurrent as a function of polarization angle.

[0054] Figure 9 The image shows the polarization response of the Ta2NiSe5 / WSe2 / ReS2 van der Waals heterojunction photodetector prepared in Example 2 at 808 nm. In the image, (a) is a graph of source and drain current as a function of angle, and (b) is a polar coordinate graph of normalized photocurrent as a function of polarization angle.

[0055] Figure 10 Optical image of the Ta2NiSe5 / WSe2 / ReS2 van der Waals photodetector prepared in Example 4.

[0056] Figure 11 Comparison of 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.

[0057] Figure 12 Optical image of the Ta2NiSe5 / ReS2 van der Waals heterojunction photodetector prepared for Comparative Example 2. Detailed Implementation

[0058] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of 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 terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0060] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0061] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

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

[0063] In the specific embodiments of the present invention, substrates A-D are all SiO2 / Si substrates.

[0064] Unless otherwise specified, room temperature and ambient temperature in the specific embodiments of this invention refer to 20-30℃.

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

[0066] It should be noted that any aspects not described in detail in this invention are conventional practices in the field and are not the focus of this invention.

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

[0068] S1. Two-dimensional WSe2 is prepared by physical vapor deposition: 100 mg of reactant WSe2 powder is weighed and placed in a quartz boat, which is placed in the heating center of a high-temperature tube furnace. A SiO2 / Si substrate with a size of 10 mm × 10 mm is placed downstream of the heating center. The carrier gas is an inert gas (N2). The air is discharged by using an inert gas with a flow rate of 100-120 sccm. The airflow direction is from the substrate to the reactant. Then the flow rate is adjusted to 30-40 sccm, and the temperature is raised to 1100-1130℃ at a heating rate of 12-12.5℃ / min. Then the airflow direction is changed from the reactant to the substrate. The flow rate is adjusted to 100-120 sccm, and the temperature is held for 10-15 min. Finally, the flow rate is adjusted to 20-30 sccm, and the temperature is cooled to room temperature. Two-dimensional WSe2 nanosheets are formed on the substrate surface, and a SiO2 / Si substrate with WSe2 nanosheets is obtained.

[0069] S2. Remove Ta2NiSe5 using mechanical peeling method: Using Ta2NiSe5 single crystal as raw material, peel the single crystal repeatedly (3-5 times) with blue tape and stick it on SiO2 / Si substrate to obtain SiO2 / Si substrate with Ta2NiSe5 layer.

[0070] S3. Remove ReS2 using mechanical peeling method: Using ReS2 single crystal as raw material, peel the single crystal repeatedly (3-5 times) with blue tape and stick it on SiO2 / Si substrate to obtain SiO2 / Si substrate with ReS2 layer.

[0071] S4. Spin-coat a 4% PMMA solution onto a SiO2 / Si substrate with grown WSe2 nanosheets. Bake at 100-150℃ for 3-7 min, then immerse it in a BOE solution (BOE:H2O = 1:10) for 4-6 min 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 at 150-200℃ for 30-60 min, then immerse it in acetone to remove the PMMA film and dry it with nitrogen. This completes the transfer of WSe2 nanosheets to the surface of the new SiO2 / Si substrate, resulting in 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 stage; drop a polydimethylsiloxane (PDMS) film capable of covering the material onto a PVA solution (concentration of 4%), gently scrape it flat with a glass slide, dry it at 55 ℃ for 10 min to form a cured PVA film, place it on a clean glass slide, fix it in the slot of the transfer stage, adjust the control platform to align it with the WSe2 on the SiO2 / Si substrate with the WSe2 layer, and transfer the WSe2 onto 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 stage, fix the PVA film containing WSe2 in the slot of the transfer stage, observe the overlapping part through the microscope of the transfer stage, select a suitable junction area, and continuously bring the two together by controlling the transfer platform. Heat at 90-95 ℃ for 3-4 min, then remove and soak in 55 ℃ deionized water for 15-30 min. After taking it out, remove the PVA film on the surface of the mica sheet, blow it dry with a nitrogen gun, and obtain the SiO2 / Si substrate with the Ta2NiSe5 / WSe2 van der Waals heterojunction.

[0074] S7. Place the SiO2 / Si substrate with the ReS2 layer on the sample stage of the transfer stage; drop a polydimethylsiloxane (PDMS) film capable of covering the material onto a PVA solution (concentration of 4%), gently scrape it flat with a glass slide, dry it at 55 ℃ for 10 min to form a cured PVA film, place it on a clean glass slide, fix it in the slot of the transfer stage, adjust the control platform to align it with the ReS2 on the SiO2 / Si substrate with the ReS2 layer, transfer the ReS2 onto the PVA film, and 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 stage. Fix the PVA film containing ReS2 in the slot of the transfer stage. Observe the overlapping part through the microscope of the transfer stage, select a suitable junction area, and continuously bring the two together by controlling the transfer platform. Heat at 90-95 ℃ for 3-4 min, then remove and soak in 55 ℃ deionized water for 15-30 min. After removal, remove the PVA film on the surface of the mica sheet and blow dry with a nitrogen gun to obtain the Ta2NiSe5 / WSe2 / ReS2 van der Waals heterojunction.

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

[0077] S1. Photolithography of electrode patterns on Ta2NiSe5 / WSe2 / ReS2 van der Waals heterojunction: Photoresist is spin-coated onto the Ta2NiSe5 / WSe2 / ReS2 van der Waals heterojunction using a spin coater, then heated at 105 ℃ for 4-5 min. Electron beam lithography is then used to precisely position and expose the electrode patterns. The exposed heterojunction is then developed with a developer, fixed with deionized water, and dried with a nitrogen gun to obtain the photolithographically lithographic heterojunction. The parameters are: scanning speed of the photolithography machine is 0.06-0.5 mm / s, power is 6-19 mW, the developer is a 3-6 wt% tetramethylammonium hydroxide aqueous solution, and the development time is 18-25 s.

[0078] S2. Metal drain and source electrodes are deposited on the heterojunction after photolithography, such 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 deposition is completed, the photoresist is removed with acetone solution, and the residue is removed by immersing in deionized water. Then, it is dried with a nitrogen gun and finally vacuum high-temperature annealing is performed. The conditions for the high-temperature annealing are: annealing temperature of 100-200 ℃, atmosphere of Ar / N2 mixed gas, and annealing time of 30-120 min, to obtain the Ta2NiSe5 / WSe2 / ReS2 van der Waals heterojunction photodetector.

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

[0080] In the specific embodiments of the present invention, the SiO2 / Si substrates used are all 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. Two-dimensional WSe2 was prepared 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 heating center. The carrier gas was an inert gas (N2). The air was discharged by using an inert gas with a flow rate of 120 sccm. The air flow direction was from the substrate to the reactant. Then the flow rate was adjusted to 35 sccm, and the temperature was raised to 1130℃ at a heating rate of 12.5℃ / min. The air flow direction was changed from the reactant to the substrate. The flow rate was adjusted to 120 sccm and held for 12 min. Finally, the flow rate was adjusted to 25 sccm and cooled to room temperature. Two-dimensional WSe2 nanosheets were obtained on the substrate surface, resulting in a SiO2 / Si substrate with WSe2 (triangular and hexagonal) nanosheets grown on it.

[0084] S2. Remove Ta2NiSe5 using mechanical peeling method: Using Ta2NiSe5 single crystal as raw material, peel the single crystal repeatedly (5 times) with blue tape and stick it on SiO2 / Si substrate to obtain SiO2 / Si substrate with Ta2NiSe5 layer.

[0085] S3. Remove ReS2 using mechanical peeling method: Using ReS2 single crystal as raw material, peel the single crystal repeatedly (5 times) with blue tape and stick it on SiO2 / Si substrate to obtain SiO2 / Si substrate with ReS2 layer.

[0086] S4. Spin-coat a 4% PMMA solution onto a SiO2 / Si substrate with grown WSe2 (triangular) nanosheets. After baking at 120°C for 3 min, immerse it in a BOE solution (BOE:H2O = 1:10) for 5 min 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 at 150°C for 30 min, immerse it in acetone to remove the PMMA film, and dry it with nitrogen gas. This completes the transfer of WSe2 nanosheets to the surface of the new SiO2 / Si substrate, resulting in 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 stage; drop a polydimethylsiloxane (PDMS) film capable of covering the material onto a PVA solution (concentration of 4%), gently scrape it flat with a glass slide, dry it at 55 ℃ for 10 min to form a cured PVA film, place it on a clean glass slide, fix it in the slot of the transfer stage, adjust the control platform to align it with the WSe2 on the SiO2 / Si substrate with the WSe2 layer, and transfer the WSe2 onto 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 stage, fix the PVA film containing WSe2 in the slot of the transfer stage, observe the overlapping part through the microscope of the transfer stage, select a suitable junction area, and continuously bring the two together by controlling the transfer platform. Heat at 90 ℃ for 3 min, then remove and soak in 55 ℃ deionized water for 15 min. After taking it out, remove the PVA film on the surface of the mica sheet, blow it dry with a nitrogen gun, and obtain the SiO2 / Si substrate with the Ta2NiSe5 / WSe2 van der Waals heterojunction.

[0089] S7. Place the SiO2 / Si substrate with the ReS2 layer on the sample stage of the transfer stage; drop a polydimethylsiloxane (PDMS) film capable of covering the material onto a PVA solution (concentration of 4%), gently scrape it flat with a glass slide, dry it at 55 ℃ for 10 min to form a cured PVA film, place it on a clean glass slide, fix it in the slot of the transfer stage, adjust the control platform to align it with the ReS2 on the SiO2 / Si substrate with the ReS2 layer, transfer the ReS2 onto the PVA film, and 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 stage. Fix the PVA film containing ReS2 in the slot of the transfer stage. Observe the overlapping part through the microscope of the transfer stage, select a suitable junction area, and continuously bring the two together 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 removal, remove the PVA film on the surface of the mica sheet and blow dry with a nitrogen gun to obtain the Ta2NiSe5 / WSe2 / ReS2 van der Waals heterojunction.

[0091] Example 2

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

[0093] S1. Photolithographic electrode patterning on the Ta2NiSe5 / WSe2 / ReS2 van der Waals heterojunction prepared in Example 1: Photoresist was spin-coated onto the Ta2NiSe5 / WSe2 / ReS2 van der Waals heterojunction using a spin coater, then heated at 105 °C for 4 min, and then the electrode pattern was precisely positioned and exposed using electron beam lithography. The exposed heterojunction was then developed with a developer, fixed with deionized water, and dried with a nitrogen gun to obtain the photolithographic heterojunction. The parameters were: scanning speed of the photolithography machine was 0.3 mm / s, power was 19 mW, the developer was a 3 wt% tetramethylammonium hydroxide aqueous solution, and the development time was 25 s.

[0094] S2. Ti / Au drain and source electrodes are deposited on the heterojunction after photolithography, such 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 deposition is completed, the photoresist is removed with acetone solution, and the residue is removed by immersion in deionized water. Then, it is dried with a nitrogen gun and finally subjected to vacuum high-temperature annealing. The conditions for high-temperature annealing are: annealing temperature of 150 ℃, atmosphere of Ar / N2 mixed gas, and annealing time of 60 min, to obtain the Ta2NiSe5 / WSe2 / ReS2 van der Waals heterojunction photodetector.

[0095] Example 3

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

[0097] Example 4

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

[0099] Comparative Example 1

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

[0101] S1. Using mechanical peeling method to peel off Ta2NiSe5: Using Ta2NiSe5 single crystal as raw material, the single crystal is repeatedly peeled off (5 times) with blue tape and attached to SiO2 / Si substrate to obtain SiO2 / Si substrate with Ta2NiSe5 layer.

[0102] S2. ReS2 is removed by mechanical peeling: Using ReS2 single crystal as raw material, the single crystal is repeatedly peeled (5 times) with blue tape and attached to the SiO2 / Si substrate to obtain a SiO2 / Si substrate with ReS2 layer.

[0103] S3. Place the SiO2 / Si substrate with the ReS2 layer on the sample stage of the transfer stage; drop a polydimethylsiloxane (PDMS) film capable of covering the material onto a PVA solution (concentration of 4%), gently scrape it flat with a glass slide, dry it at 55 ℃ for 10 min to form a cured PVA film, place it on a clean glass slide, fix it in the slot of the transfer stage, adjust the control platform to align it with the ReS2 on the SiO2 / Si substrate with the ReS2 layer, and transfer the ReS2 onto 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 stage, fix the PVA film containing ReS2 in the slot of the transfer stage, observe the overlapping part through the microscope of the transfer stage, select a suitable junction area, and continuously bring the two together 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 removal, remove the PVA film on the surface of the mica sheet, blow dry with a nitrogen gun, and obtain the 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 with the Ta2NiSe5 / ReS2 van der Waals heterojunction prepared in Comparative Example 1, and the resulting photodetector is a Ta2NiSe5 / ReS2 van der Waals heterojunction photodetector.

[0107] Test case

[0108] Figure 1 The diagrams show the band structure 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.

[0109] Figure 1 Before contact, it refers to the band structure of the three two-dimensional materials Ta2NiSe5, WSe2, and ReS2 respectively; after contact, it refers to the 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 intermediate layer, which can prevent the flow of thermally excited electrons from Ta2NiSe5 to ReS2 under dark conditions, while the thermally excited holes from ReS2 can flow to Ta2NiSe5. Ta2NiSe5 is a p-type semiconductor, and holes are majority carriers; therefore, the holes flowing to Ta2NiSe5 cannot recombine, thus reducing the dark current. Under illumination, both Ta2NiSe5 and ReS2 generate photogenerated carriers. Due to the high potential barrier of WSe2, electrons at Ta2NiSe5 cannot flow to ReS2, resulting in a large accumulation. When enough photogenerated electrons accumulate at Ta2NiSe5, they recombine with the holes flowing from ReS2 to Ta2NiSe5, thereby improving the device's photoelectric response.

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

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

[0113] Figure 4 The figure shows the source-drain voltage-source-drain current curves of the Ta2NiSe5 / WSe2 / ReS2 van der Waals photodetector prepared in Example 2 at different optical powers in the 405 nm band. As can be seen from the figure, the photocurrent changes corresponding to different source-drain voltages (-3V to 3V) at different power densities. At source-drain voltages V... ds At a given power density, the dark-state current is minimum, and the photocurrent increases with increasing power density, reaching a maximum of 101 mW / cm². 2 The photocurrent is at its maximum, indicating that the heterojunction photodetector has a high on / off ratio.

[0114] Figure 5 The graph shows a comparison of source-drain voltage and source-drain current of the photodetectors prepared in Example 2 and Comparative Example 2 under dark and illuminated conditions at the 405 nm wavelength. As can be seen from the graph, at a source-drain voltage of -3V, the dark current of Example 2 is significantly lower than that of Comparative Example 2, which is 4.17 × 10⁻⁶. -10 A decreased to 2.33 × 10 -10 A, Under illumination, the source-drain current of Example 2 compared to Comparative Example 2 is 3.54 × 10⁻⁶. -8 A increased to 1.35 × 10 -6A indicates that the high barrier of WSe2 in the middle plays a role in reducing dark current and increasing photocurrent.

[0115] Figure 6 The figure shows the source-drain voltage-source-drain current curves of the Ta2NiSe5 / WSe2 / ReS2 van der Waals photodetector prepared in Example 2 in the 405-808 nm wavelength range. As can be seen from the figure, the photodetector exhibits good response in the 405-808 nm wavelength range, demonstrating that the device has a wide response range.

[0116] Figure 7 The responsivity, detectivity, optical on / off ratio, and optical gain curves of the Ta2NiSe5 / WSe2 / ReS2 van der Waals heterojunction photodetector prepared in Example 2 are shown at different power densities in the 405 nm band. (a) shows the responsivity and detectivity curves, and (b) shows the optical on / off ratio and optical gain curves. Figure 7 It can be seen that (a) simultaneously provides the photodetector at the source-drain voltage V ds The responsivity and detectivity curves for this photodetector at -3V and a wavelength of 405 nm under different power densities show that the responsivity is 22.3 A / W and the detectivity is 3.03 × 10⁻⁶. 12 Jones (b) provides the photodetector at source-drain voltage V. ds The optical on / off ratio and optical gain of this photodetector at different power densities with a voltage of -3 V and a wavelength of 405 nm are as follows: the maximum optical on / off ratio is 6.09 × 10⁻⁶. 3 The optical gain is 71.55.

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

[0118] Figure 9 The figure shows the polarization response of the Ta2NiSe5 / WSe2 / ReS2 van der Waals photodetector prepared in Example 2 at 808 nm. (a) is a graph showing the source / drain current as a function of angle, and (b) is a polar plot showing the normalized photocurrent as a function of polarization angle. As can be seen from the figure, this photodetector exhibits good polarization response performance 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 photodetector prepared in Example 4. As shown in the image, the drain is Ta2NiSe5 and the source is ReS2.

[0120] Figure 11 The graph shows a comparison of source-drain voltage and source-drain current of the photodetectors prepared in Example 4 and Comparative Example 2 under dark and illuminated conditions at the 405 nm wavelength. As can be seen from the graph, at a source-drain voltage of -3V, the dark current of Example 4 is significantly lower than that of Comparative Example 2, decreasing from 4.17 × 10⁻⁶. -10 A decreased to 2.6 × 10 -11 A, Under illumination, the source-drain current of Example 4 compared to Comparative Example 2 was 3.54 × 10⁻⁶. -8 A increased to 4.31 × 10 -7 A indicates that the high barrier of WSe2 in the middle plays a role in reducing dark current and increasing photocurrent.

[0121] Figure 12 Optical images of the Ta2NiSe5 / ReS2 van der Waals photodetector prepared for Comparative Example 2. As shown in the figure, the drain is Ta2NiSe5 and the source is ReS2.

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

[0123] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those 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 invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded 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, Anisotropic p-type material Ta2NiSe5 is used as the bottom carrier collection layer, anisotropic n-type material ReS2 is used as the top light-absorbing layer, and WSe2 is used as the intermediate barrier layer. The conduction band bottom of the Ta2NiSe5 is located at 4.6 eV, and the valence band top is located at 4.93 eV. The bottom of the conduction band of the ReS2 is located at 4.5 eV, and the top of the valence band is located at 5.84 eV. The bottom of the conduction band of WSe2 is located at 3.5 eV, and the top of the valence band is located at 5 eV.

2. A method for preparing a van der Waals heterojunction with a unipolar barrier and polarization sensitivity as described in claim 1, characterized in that the steps include... include: WSe2 was grown on the surface of substrate A by physical vapor deposition to obtain a substrate with WSe2 nanosheets. The WSe2 nanosheets on the substrate on which WSe2 nanosheets are grown are transferred to substrate D to obtain a substrate with a WSe2 layer. The Ta2NiSe5 single crystal was stripped onto substrate B to obtain a substrate with a Ta2NiSe5 layer. The ReS2 single crystal was stripped onto substrate C to obtain a substrate with a ReS2 layer; The WSe2 on the substrate with the WSe2 layer is transferred 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, characterized in that, The steps of growing WSe2 on the surface of substrate A by physical vapor deposition include: placing substrate A and WSe2 powder in a heating device, using inert gas to purge air, with the airflow direction from substrate to reactants, then adjusting the inert gas flow rate to 30-40 sccm, and heating to 1100-1130℃ at a heating rate of 12-12.5℃ / min, then changing the airflow direction from reactants to substrate, adjusting the flow rate to 100-120 sccm, holding at this temperature for 10-15 min, and finally adjusting the flow rate to 20-30 sccm and cooling to room temperature to obtain a substrate with WSe2 nanosheets grown on it.

4. The preparation method according to claim 2, characterized in that, The step of transferring the WSe2 nanosheets on the substrate with grown WSe2 nanosheets onto the substrate D includes: A substrate with WSe2 nanosheets is spin-coated with a polymethyl methacrylate solution, baked at 100-150°C for 3-7 min, and then immersed in BOE solution for 4-6 min to obtain a polymethyl methacrylate film / two-dimensional WSe2 nanosheet separated from the substrate. The polymethyl methacrylate film / two-dimensional WSe2 nanosheet is then attached to substrate D, baked at 150-200°C for 30-60 min, immersed in acetone to remove the polymethyl methacrylate film, and dried with nitrogen to obtain a substrate with a WSe2 layer.

5. The preparation method according to claim 2, characterized in that, The step of peeling the Ta2NiSe5 single crystal onto the substrate B includes: using blue adhesive tape to peel off the Ta2NiSe5 single crystal and stick it onto the substrate B to obtain a substrate with a Ta2NiSe5 layer; the peeling is performed 3-5 times. And / or, the step of peeling the ReS2 single crystal onto the substrate C includes: using blue adhesive tape to peel the ReS2 single crystal and stick it onto the substrate C to obtain a substrate with a ReS2 layer; the peeling is performed 3-5 times.

6. The preparation method according to claim 2, characterized in that, The step of transferring WSe2 from the substrate with the WSe2 layer to the substrate with the Ta2NiSe5 layer includes: The WSe2 nanosheets on the substrate with the WSe2 layer are transferred to a polyvinyl alcohol film to obtain a polyvinyl alcohol film containing WSe2; the Ta2NiSe5 side of the substrate with the Ta2NiSe5 layer is bonded to the WSe2 side of the polyvinyl alcohol film containing WSe2, heated at 90-95℃ for 3-4 min, 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, characterized in that, The step of transferring the ReS2 nanosheets on the substrate with the ReS2 layer to the substrate with the Ta2NiSe5 / WSe2 heterojunction includes: 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 bonded to the ReS2 surface of the polyvinyl alcohol film containing ReS2, heated at 90-95℃ for 3-4 min, and then the polyvinyl alcohol film on the surface is removed to obtain the Ta2NiSe5 / WSe2 / ReS2 heterojunction.

8. The application of the van der Waals heterojunction with unipolar barrier and polarization sensitivity as described in claim 1 in the field of photodetectors.

9. A photodetector, 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 fabricating a photodetector according to claim 9, characterized in that step... include: Photoresist is coated onto a van der Waals heterojunction with a unipolar barrier and polarization sensitivity, and then electrode patterns are etched on a photolithography machine to obtain the etched heterojunction. Metal electrodes are deposited on the heterojunction after photolithography, and then annealed to obtain the photodetector.

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