Method for constructing Van der Waals heterojunction by using reverse energy band bending strategy

Abstract

The invention discloses a method for constructing a Van der Waals heterojunction by using a reverse energy band bending strategy, and belongs to the field of two-dimensional material photoelectric devices. According to the Van der Waals heterojunction constructed by using the reverse energy band bending strategy, Bi2O2Se is used as an n-type semiconductor material, In2Se3 is used as a p-type semiconductor material, and the Van der Waals heterojunction with II-type energy band arrangement is formed. The energy band structures of Bi2O2Se and In2Se3 are regulated and controlled by constructing the Van der Waals heterojunction, and the conduction band bottom and the valence band top of the Bi2O2Se and In2Se3 are respectively positioned in different materials, so that II-type energy band arrangement is formed, reverse energy band bending occurs, the carrier recombination probability is reduced, the charge separation efficiency is remarkably improved, the dark current is reduced, and the light absorption efficiency is enhanced. The photoelectric detector made of the Van der Waals heterojunction constructed by the invention has the characteristics of high detection rate and wide band.

Description

Technical Field

[0001] The present invention relates to the field of optoelectronic devices based on two-dimensional materials, and particularly to a method for constructing a van der Waals heterojunction by using a reverse band bending strategy. Background Art

[0002] Two-dimensional materials are a class of material systems in which electrons can only move freely in two non-nano-scale dimensions. Among them, two-dimensional materials such as graphene, transition metal dichalcogenides (TMDs), and black phosphorus (BP) have shown significant application potential in the optoelectronic field due to their unique electronic structures and physicochemical properties. The carrier transport and heat conduction behaviors of these materials are strictly restricted within the two-dimensional plane, making them of great application value in the directions of field-effect transistors, optoelectronic devices, and thermoelectric devices.

[0003] In terms of heterostructure construction, traditional heterostructures have high lattice matching requirements, limited material selection, and will introduce dangling bonds and interface states. Therefore, their performance upper limit is lower than that of van der Waals heterostructures. Compared with traditional heterostructures, different two-dimensional materials can be freely stacked together to form van der Waals heterostructures. Van der Waals heterostructures are stacked by weak van der Waals forces, do not require lattice matching, have the unique characteristics of atomic thickness and no dangling bonds on the surface, can obtain high-quality heterojunction interfaces, and thus effectively improve the carrier transport efficiency and device performance.

[0004] However, current traditional two-dimensional materials such as graphene, transition metal dichalcogenides, and black phosphorus still have disadvantages such as insufficient electrical properties, limited spectral response, and poor environmental stability, and still need to be further improved. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for constructing a van der Waals heterojunction by using a reverse band bending strategy to solve the above problems in the background art. The present invention utilizes the characteristic of no dangling bonds of van der Waals forces. After Bi2O2Se and In2Se3 are in contact, a type-II band structure is formed, and reverse band bending occurs, which inhibits the interfacial recombination of photo-generated electron-hole pairs and promotes the separation of photo-generated carriers, reduces the dark current, and thus overcomes the technical problems of insufficient electrical properties, limited spectral response, and poor environmental stability of existing two-dimensional materials.

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

[0007] One of the technical solutions of the present invention: Provide a van der Waals heterojunction constructed by using a reverse band bending strategy, using Bi2O2Se as an n-type semiconductor material and In2Se3 as a p-type semiconductor material to form a van der Waals heterojunction with a type-II band arrangement.

[0008] Preferably, the band gap of Bi2O2Se in the van der Waals heterojunction is 0.8 - 1.5 eV, the band gap of In2Se3 is 1.3 - 2.0 eV, and the potential difference between the surfaces of Bi2O2Se and In2Se3 is 89 mV.

[0009] The second technical solution of the present invention: Provide a preparation method of the van der Waals heterojunction constructed by using the reverse band bending strategy as described above, including the following steps:

[0010] Grow Bi2O2Se on the surface of substrate A by chemical vapor deposition to obtain a substrate with Bi2O2Se nanosheets grown thereon;

[0011] Peel the In2Se3 single crystal onto substrate B to obtain a substrate with an In2Se3 layer;

[0012] Transfer the In2Se3 nanosheets on the substrate with the In2Se3 layer to the substrate with the Bi2O2Se nanosheets grown thereon to prepare a Bi2O2Se / In2Se3 van der Waals heterojunction, thus completing the preparation.

[0013] Preferably, the method of peeling the In2Se3 single crystal onto substrate B includes the following steps: Use blue tape to peel the In2Se3 single crystal and stick it on substrate B to obtain a substrate with an In2Se3 layer; The number of peeling times is 4 - 5 times.

[0014] Preferably, the thickness of the Bi2O2Se nanosheets on the substrate with the Bi2O2Se nanosheets grown thereon is 20 - 120 nm, and the thickness of the In2Se3 nanosheets on the substrate with the In2Se3 layer is 20 - 100 nm.

[0015] Preferably, substrate A is a mica sheet.

[0016] Preferably, substrate B is SiO2 / Si.

[0017] Preferably, the preparation method of the substrate with the Bi2O2Se nanosheets grown thereon includes the following steps: Place substrate A and Bi2Se3 powder and Bi2O3 powder with a mass ratio of 1:7 in a heating device, and heat at 700 °C for 30 min in a protective atmosphere with a carrier gas flow rate of 80 - 120 sccm to obtain the substrate with the Bi2O2Se nanosheets grown thereon.

[0018] Preferably, the transfer includes the following steps: Transfer the In2Se3 nanosheets on the substrate with the In2Se3 layer to a PVA film to obtain a PVA film containing In2Se3;

[0019] Bond the Bi₂O₂Se-containing surface of the substrate on which Bi₂O₂Se nanosheets are grown to the In₂Se₃-containing surface of the PVA film containing In₂Se₃, heat at 90 - 100 °C for 3 - 5 min, and then remove the PVA film on the surface, thus completing the transfer.

[0020] Technical solution three of the present invention: Provide an application of the van der Waals heterojunction constructed by the reverse band bending strategy in the field of photodetectors as described above.

[0021] Technical solution four of the present invention: Provide a Bi₂O₂Se / In₂Se₃ van der Waals heterojunction photodetector, which includes the van der Waals heterojunction constructed by the reverse band bending strategy as described above.

[0022] Preferably, the Bi₂O₂Se / In₂Se₃ van der Waals heterojunction photodetector includes a substrate, a Bi₂O₂Se layer on the substrate, an In₂Se₃ layer on the Bi₂O₂Se layer, and a Bi₂O₂Se / In₂Se₃ van der Waals heterojunction formed by the overlapping part of the Bi₂O₂Se layer and the In₂Se₃ layer; the source electrode of the Bi₂O₂Se / In₂Se₃ van der Waals heterojunction photodetector is In₂Se₃, and the drain electrode is Bi₂O₂Se.

[0023] Technical solution five of the present invention: Provide a preparation method of the Bi₂O₂Se / In₂Se₃ van der Waals heterojunction photodetector as described above, including the following steps:

[0024] Coat a photoresist on the van der Waals heterojunction constructed by the reverse band bending strategy, and then lithograph the electrode pattern on a lithography machine to obtain the lithographed heterojunction;

[0025] Evaporate a metal electrode on the lithographed heterojunction, and then anneal to obtain the Bi₂O₂Se / In₂Se₃ van der Waals heterojunction photodetector.

[0026] Preferably, the process parameters of the lithography are: the scanning speed of the lithography machine is 0.06 - 0.5 mm / s, the power is 6 - 19 mW, the developer is an aqueous solution of tetramethylammonium hydroxide with a concentration of 3 - 6%, and the development time is 18 - 25 s

[0027] Preferably, during the evaporation of the metal electrode, the material of the metal electrode independently includes one or more of Au, Cr, Ag, Ti, Ni, Pd, and Pt.

[0028] Preferably, the annealing temperature is 100 - 200 °C, the annealing time is 30 - 120 min, and the atmosphere is an Ar / N₂ mixed gas.

[0029] The beneficial technical effects of the present invention are as follows:

[0030] By utilizing the characteristic of van der Waals force without dangling bonds, the present invention forms a type-II energy band structure after the contact of Bi2O2Se and In2Se3, and reverse band bending occurs, which inhibits the interfacial recombination of photo-generated electron-hole pairs and promotes the separation of photo-generated carriers, reducing the dark current. The responsivity of the prepared Bi2O2Se / In2Se3 van der Waals heterojunction photodetector can reach 4.53 A / W, and the rise / fall time can reach 5.7 ms / 2.8 ms. Compared with traditional photodetectors, it has a higher detectivity, and the detectivity can reach 3.07×10 12 Jones, with good weak light detection ability; according to the calculation of photocurrent and optical power, it also has a high external quantum efficiency, which can reach 1.39×10 5 %, with a strong ability to convert incident photons into effective electrons. And the on / off ratio can reach four orders of magnitude, and the maximum on / off ratio is 5.28×10 4 . And it has a wide spectral response and responds in the wavelength range of 405 - 1000 nm. The construction of the Bi2O2Se / In2Se3 van der Waals heterojunction designed by the present invention can greatly improve the response performance of the photodetector.

[0031] The two-dimensional materials selected in the present invention exhibit different optoelectronic conversion mechanisms. The selected Bi2O2Se relies on bulk photoabsorption and high-mobility electron transport, and In2Se3 utilizes spontaneous ferroelectric polarization to form a built-in electric field to separate photo-generated carriers. And the potential difference between Bi2O2Se and In2Se3 is moderate and will not cause negative impacts.

[0032] The two-dimensional Bi2O2Se material is grown and prepared by the method of chemical vapor deposition. This preparation process is simple, and the prepared Bi2O2Se material has high quality and controllable thickness, which is conducive to mass production and popularization.

[0033] By constructing a van der Waals heterojunction, the present invention regulates the energy band structures of Bi2O2Se and In2Se3. Their conduction band bottoms and valence band tops are located in different materials respectively, thus forming a type-II energy band arrangement, reducing the probability of carrier recombination, significantly improving the charge separation efficiency, reducing the dark current, and enhancing the light absorption efficiency. The photodetector made of the van der Waals heterojunction constructed by the present invention has the characteristics of high detectivity and wide band. Description of the Drawings

[0034] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the accompanying drawings required in the embodiments. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can be obtained based on these drawings.

[0035] Figure 1 It is the energy band structure diagrams of Bi2O2Se and In2Se3 before and after contact in Embodiment 1 of the present invention.

[0036] Figure 2 It is the optical image of the Bi2O2Se / In2Se3 van der Waals heterojunction photodetector prepared in Embodiment 1 of the present invention.

[0037] Figure 3 It is the thickness images of In2Se3 nanosheets and Bi2O2Se nanosheets in the Bi2O2Se / In2Se3 van der Waals heterojunction photodetector prepared in Embodiment 1 of the present invention. Among them, (A) is the In2Se3 nanosheet, and (B) is the Bi2O2Se nanosheet.

[0038] Figure 4 It is the surface potential difference image of In2Se3 nanosheets and Bi2O2Se nanosheets in the Bi2O2Se / In2Se3 van der Waals heterojunction photodetector prepared in Embodiment 1 of the present invention.

[0039] Figure 5 It is the Raman spectra of the Bi2O2Se / In2Se3 van der Waals heterojunction photodetector, In2Se3, and Bi2O2Se in Embodiment 1 of the present invention.

[0040] Figure 6 It is the PL photoluminescence images of the Bi2O2Se / In2Se3 van der Waals heterojunction photodetector, In2Se3, Bi2O2Se, and fluorophlogopite flakes in Embodiment 1 of the present invention.

[0041] Figure 7 It is the variation diagram of photocurrent of the Bi2O2Se / In2Se3 van der Waals heterojunction photodetector prepared in Embodiment 1 of the present invention at different powers.

[0042] Figure 8 It is the variation curves of photocurrent corresponding to different power densities and different source-drain voltages of the Bi2O2Se / In2Se3 van der Waals heterojunction photodetector prepared in Embodiment 1 of the present invention.

[0043] Figure 9Respectively, the responsivity, detectivity curves and on / off ratio curves of the Bi2O2Se / In2Se3 van der Waals heterojunction photodetector prepared in Example 1 of the present invention under different power densities. Among them, (A) are the responsivity and detectivity curves, and (B) is the on / off ratio curve.

[0044] Figure 10 Time response curves of the products of Example 1 and Comparative Examples 1-3 under different powers of 405 nm light illumination. Among them, (A) is Example 1, (B) is Comparative Example 1, (C) is Comparative Example 2, and (D) is Comparative Example 3.

[0045] Figure 11 Rise / fall time images of a single period of the Bi2O2Se / In2Se3 van der Waals heterojunction photodetector prepared in Example 1 of the present invention at 405 nm. Detailed implementation manners

[0046] Now, various exemplary implementation manners of the present invention will be described in detail. This detailed description should not be regarded as a limitation of the present invention, but should be understood as a more detailed description of certain aspects, characteristics and implementation schemes of the present invention. It should be understood that the terms described in the present invention are only used to describe specific implementation manners and are not used to limit the present invention.

[0047] In addition, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded from the range.

[0048] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the implementation or testing of the present invention. It should be noted that the operations not detailed in the present invention are all conventional operation means in the art and are not the focus of the present invention.

[0049] Regarding the use of "comprising", "including", "having", "containing", etc. in the present invention, they are all open-ended terms, that is, they mean including but not limited to.

[0050] As a core parameter determining the electrical, optical, and thermal properties of devices, the energy band structure has a direct impact on key indicators such as carrier mobility, optoelectronic device efficiency, power consumption, and on-off ratio. In terms of interface effects, the formation of Ohmic contacts or Schottky barriers will significantly change the contact resistance characteristics of devices. By precisely regulating the energy band structure, the multifunctional integration of a single device can be achieved. Among the types of energy band alignments, a type-II energy band structure is formed when the energy band alignment of two materials is such that the bottom of the conduction band of one material is lower than the top of the valence band of the other material. Compared with the disadvantages of a narrow spectral response range in type-I energy band structures and low carrier separation efficiency in type-III energy band structures, at the type-II heterojunction interface, strong charge transfer may change the electrostatic potential at the interface, resulting in a reversal of the energy band bending direction. The reverse energy band bending may strengthen the electric field in the space charge region of the type-II structure, further promoting the movement of electrons and holes in opposite directions, and enabling efficient carrier separation and broad-spectrum light response.

[0051] In the present invention, the layers of Bi2O2Se selected are combined by van der Waals forces, stable in air, not easily degraded, and have the characteristics of high mobility, stability, broad-spectrum response, and process compatibility, and are suitable for practical applications such as photodetectors, solar cells, and light-emitting diodes.

[0052] The present invention discloses a method for constructing a van der Waals heterojunction using the reverse energy band bending strategy. Bi2O2Se is selected as the n-type semiconductor material, and In2Se3 is selected as the p-type semiconductor material to form a type-II energy band alignment (that is, the bottom of the conduction band and the top of the valence band of the constructed heterojunction are both located on different materials), thereby obtaining the van der Waals heterojunction.

[0053] Furthermore, the method for constructing a van der Waals heterojunction using the reverse energy band bending strategy includes the following steps:

[0054] Growing and preparing two-dimensional Bi2O2Se by chemical vapor deposition: Weigh 0.1 g of Bi2Se3 powder and place it in a quartz boat, which is placed upstream of a high-temperature tube furnace. Weigh 0.7 g of Bi2O3 powder and place it in the quartz boat, which is placed at the thermal center. Place a mica sheet with a size of 15 mm × 15 mm downstream of the thermal center. The carrier gas is a mixed gas of Ar / N2, and the carrier gas flow rate is 80 - 120 sccm. Heat up to 700 °C within 30 min of heating time and keep it at this temperature for 30 min, then naturally cool to below 100 °C and turn off the carrier gas, and then naturally cool to room temperature. It is found under a microscope that there are several rectangles grown on the mica sheet, that is, a mica sheet with two-dimensional Bi2O2Se nanosheets grown on it is prepared;

[0055] Peeling In2Se3 by mechanical exfoliation: Using an In2Se3 single crystal as the raw material, repeatedly peel the single crystal with blue tape and stick it on a SiO2 / Si substrate to obtain a SiO2 / Si substrate with an In2Se3 layer.

[0056] Place the SiO2 / Si substrate with the In2Se3 layer on the sample stage of the transfer stage; Drop polyvinyl alcohol solution (PVA) on the polydimethylsiloxane (PDMS) film that can cover the material, scrape it gently with a glass slide until it is flat, dry it at 55 - 70 °C for 5 - 10 min to form a cured PVA film, place it on a clean glass slide, fix it in the card slot of the transfer stage, align it with the In2Se3 on the SiO2 / Si substrate with the In2Se3 layer through the adjustment control platform, and transfer the In2Se3 to the PVA film to obtain a PVA film containing In2Se3;

[0057] Place the mica sheet growing two-dimensional Bi2O2Se nanosheets on the sample stage of the transfer stage, fix the PVA film containing In2Se3 in the card slot of the transfer stage, observe the overlapping part through the microscope of the transfer stage, select a suitable junction area, and continuously fit the two by controlling the transfer platform, heat at 90 - 100 °C for 3 - 5 min, then remove it and soak it in deionized water at 55 °C for 10 - 15 min, remove the PVA film on the surface of the mica sheet after taking it out, and dry it with a nitrogen gun to obtain a Bi2O2Se / In2Se3 van der Waals heterojunction;

[0058] Lithographically pattern the electrodes on the Bi2O2Se / In2Se3 van der Waals heterojunction; Use a spin coater to spin-coat photoresist on the Bi2O2Se / In2Se3 van der Waals heterojunction, then heat it at 100 - 105 °C for 3 - 6 min, and then use electron beam lithography technology to accurately position and expose the pattern of the electrodes. Then develop the exposed heterojunction with a developer, fix it with deionized water, and dry it with a nitrogen gun; The parameters are: the scanning speed of the lithography machine is 0.06 - 0.5 mm / s, the power is 6 - 19 mW, the developer is a 3 - 6% aqueous solution of tetramethylammonium hydroxide, and the development time is 18 - 25 s;

[0059] Evaporate metal source electrodes and drain electrodes on the Bi2O2Se / In2Se3 van der Waals heterojunction, so that part of the metal source electrode is on the surface of the In2Se3 material, and the other part is on the surface of the mica substrate, and part of the drain electrode is on the surface of the Bi2O2Se material, and the other part is on the surface of the mica substrate;

[0060] After evaporation, remove the photoresist with acetone solution, soak it in deionized water to remove the residual acetone solution, then dry it with a nitrogen gun, and finally perform vacuum high-temperature annealing; The conditions for the high-temperature annealing are: the annealing temperature is 100 - 200 °C, the atmosphere is an Ar / N2 mixed gas, and the annealing time is 30 - 120 min to obtain a Bi2O2Se / In2Se3 van der Waals heterojunction photodetector.

[0061] All raw materials used in the following examples and comparative examples of the present invention are commercially available products.

[0062] Example 1

[0063] A method for constructing a van der Waals heterojunction using a reverse band bending strategy. Select n-type Bi2O2Se two-dimensional material and p-type In2Se3 two-dimensional material to build the van der Waals heterojunction. That is, prepare Bi2O2Se by chemical vapor deposition, and then build the van der Waals heterojunction with In2Se3 material through PVA dry transfer. Finally, an optical device is obtained by photolithography, metal evaporation, and high-temperature annealing treatment.

[0064] The specific steps are as follows:

[0065] (1) Cut the fluorophlogopite sheet with a blade to obtain a fresh mica sheet, and prepare a fluorophlogopite sheet with a size of 15 mm × 15 mm.

[0066] Grow and prepare two-dimensional Bi2O2Se by chemical vapor deposition: Weigh 0.1 g of Bi2Se3 powder and place it in a quartz boat at the upstream of a high-temperature tube furnace. Weigh 0.7 g of Bi2O3 powder in a quartz boat and place it at the thermal center. Place the prepared fluorophlogopite sheet at the downstream of the quartz tube, with the fresh side facing up. The carrier gas is a mixed gas of Ar / N2, and the carrier gas flow rate is 100 sccm. Heat up to 700 °C within 30 min of heating time and keep it at this temperature for 30 min, then naturally cool to below 100 °C and turn off the carrier gas, and then naturally cool to room temperature. It is found under a microscope that several rectangles grow on the mica sheet, that is, a mica sheet with two-dimensional Bi2O2Se nanosheets grown on it is obtained.

[0067] (2) Cut the SiO2 / Si substrate into a size of 10 mm × 10 mm, clean it in acetone, ethanol, and deionized water for 15 min respectively, and finally dry it with a nitrogen gun for standby.

[0068] Exfoliate In2Se3 by mechanical exfoliation method: In order to obtain two-dimensional In2Se3 material with as thin a thickness as possible, use In2Se3 single crystal as the raw material, repeatedly exfoliate it with blue tape, and then stick it on the SiO2 / Si substrate. Then observe it under a microscope to obtain a SiO2 / Si substrate with an In2Se3 layer, and keep it for standby.

[0069] Transfer the two-dimensional Bi2O2Se nanosheets and two-dimensional In2Se3 materials on a transfer platform to obtain a heterojunction; Place the SiO2 / Si substrate with the In2Se3 layer on the sample stage of the transfer platform. Drop polyvinyl alcohol solution (PVA) on a small piece of polydimethylsiloxane (PDMS) film that can cover the material, scrape it gently with a glass slide until it is flat, dry it at 55 °C for 10 min to form a cured PVA film, place it on a clean glass slide, fix it in the card slot of the transfer platform, align it with the In2Se3 material on the substrate by adjusting the control platform, and transfer the In2Se3 to the PVA film to obtain a PVA film containing In2Se3.

[0070] Place the mica sheet growing two-dimensional Bi2O2Se nanosheets on the sample stage of the transfer platform. Fix the PVA film containing In2Se3 in the card slot of the transfer platform. Observe the overlapping part through the microscope of the transfer platform, select a suitable junction area, and continuously fit the two by controlling the transfer platform. Heat it at 90 °C for 3 min, then remove it and soak it in deionized water at 55 °C for 15 min. After taking it out, remove the PVA film on the surface of the mica sheet, and blow dry the remaining water on the surface with a nitrogen gun to obtain a Bi2O2Se / In2Se3 van der Waals heterojunction.

[0071] (3)Lithograph the electrode pattern on the Bi2O2Se / In2Se3 van der Waals heterojunction; Use a spin coater to spin coat the photoresist on the Bi2O2Se / In2Se3 van der Waals heterojunction, then heat it at 100 °C for 3 min. Then use electron beam lithography technology to accurately position and expose the pattern of the electrode. Then develop the exposed heterojunction with a developer, fix it with deionized water, and blow it dry with a nitrogen gun. The specific process parameters are: the scanning speed of the lithography machine is 0.3 mm / s, the power is 19 mW, the developer is a 3% aqueous solution of tetramethylammonium hydroxide, and the developing time is 25 s.

[0072] (4)Evaporate the Ti / Au source electrode and drain electrode on the Bi2O2Se / In2Se3 van der Waals heterojunction, so that part of the metal source electrode is located on the surface of the In2Se3 material, and the other part is located on the surface of the mica substrate. Part of the drain electrode is located on the surface of the Bi2O2Se material, and the other part is located on the surface of the mica substrate.

[0073] Then, remove the photoresist with acetone solution, soak it in deionized water to remove the remaining acetone solution, then blow it dry with a nitrogen gun, and finally perform vacuum high-temperature annealing. The specific conditions for high-temperature annealing are: the annealing temperature is set at 150 °C, the atmosphere is a mixed gas of Ar / N2, and the annealing time is set at 60 min to obtain a Bi2O2Se / In2Se3 van der Waals heterojunction photodetector.

[0074] Comparative Example 1 (omitting the steps of preparing Bi2O2Se nanosheets and constructing Bi2O2Se / In2Se3 heterojunctions)

[0075] A method for preparing a photodetector, the steps are as follows:

[0076] Cut the SiO2 / Si substrate into pieces of 10 mm×10 mm, wash them in acetone, ethanol, and deionized water for 15 min respectively, and finally dry them with a nitrogen gun for standby.

[0077] Exfoliate In2Se3 by mechanical exfoliation method: using In2Se3 single crystal as raw material, repeatedly exfoliate with blue tape, then stick it on the SiO2 / Si substrate, and then observe under a microscope to obtain a two-dimensional In2Se3 material with as thin a thickness as possible, obtaining a SiO2 / Si substrate with an In2Se3 layer for standby.

[0078] Lithograph the electrode pattern on the In2Se3 nanosheets; use a spin coater to spin-coat the photoresist on the SiO2 / Si substrate with an In2Se3 layer, then heat it at 100 °C for 3 min, and then use electron beam lithography technology to accurately position and expose the electrode pattern, and then develop the exposed raw material system with a developer, then fix it with deionized water, and then dry it with a nitrogen gun. The specific process parameters are: the scanning speed of the lithography machine is 0.3 mm / s, the power is 19 mW, the developer is a 3% aqueous solution of tetramethylammonium hydroxide, and the development time is 25 s.

[0079] Evaporate metal electrodes on the lithographed SiO2 / Si substrate with an In2Se3 layer, so that part of the metal electrodes are on the surface of the In2Se3 material and the other part is on the surface of the SiO2 / Si substrate.

[0080] Then, remove the photoresist with an acetone solution, soak it in deionized water to remove the residual acetone solution, then dry it with a nitrogen gun, and finally perform vacuum high-temperature annealing. The specific conditions for high-temperature annealing are: the annealing temperature is set at 150 °C, the atmosphere is an Ar / N2 mixed gas, and the annealing time is set at 60 min to obtain an In2Se3 single-element photodetector.

[0081] Comparative Example 2 (omitting the steps of preparing In2Se3 nanosheets and constructing Bi2O2Se / In2Se3 heterojunctions)

[0082] A method for preparing a photodetector, the steps are as follows:

[0083] Cut the fluorophlogopite sheet with a blade to obtain a fresh mica sheet, and prepare a fluorophlogopite sheet with a size of 15 mm×15 mm.

[0084] Growth and preparation of two-dimensional Bi2O2Se by chemical vapor deposition: Weigh 0.1 g of Bi2Se3 powder and place it in a quartz boat at the upstream of a high-temperature tube furnace. Weigh 0.7 g of Bi2O3 powder and place it in a quartz boat at the thermal center. Place the prepared fluorophlogopite sheet at the downstream of the quartz tube with the fresh side facing up. The carrier gas is a mixture of Ar / N2 with a flow rate of 100 sccm. Heat it to 700 °C within 30 min of heating time and hold at this temperature for 30 min, then naturally cool it to below 100 °C and turn off the carrier gas, and then naturally cool it to room temperature. It is found under a microscope that several rectangles grow on the mica sheet, that is, a mica sheet with two-dimensional Bi2O2Se nanosheets grown on it is obtained.

[0085] Lithograph the electrode pattern on the Bi2O2Se nanosheet; Use a spin coater to spin coat the photoresist on the mica sheet with two-dimensional Bi2O2Se nanosheets grown on it, then heat it at 100 °C for 3 min, and then use electron beam lithography technology to accurately position and expose the electrode pattern. Then develop the exposed raw material system with a developer, fix it with deionized water, and then blow it dry with a nitrogen gun. The specific process parameters are: the scanning speed of the lithography machine is 0.3 mm / s, the power is 19 mW, the developer is an aqueous solution of tetramethylammonium hydroxide with a concentration of 3%, and the development time is 25 s.

[0086] Evaporate metal electrodes on the lithographed mica sheet with two-dimensional Bi2O2Se nanosheets grown on it, so that part of the metal electrodes are on the surface of the Bi2O2Se material and the other part is on the surface of the mica sheet substrate.

[0087] Then, remove the photoresist with acetone solution, soak it in deionized water to remove the residual acetone solution, then blow it dry with a nitrogen gun, and finally perform vacuum high-temperature annealing. The specific conditions for high-temperature annealing are: the annealing temperature is set at 150 °C, the atmosphere is a mixture of Ar / N2, and the annealing time is set at 60 min to obtain a Bi2O2Se single-element photodetector.

[0088] Comparative Example 3 (replace In2Se3 with ReS2)

[0089] A method for preparing a photodetector, the steps are as follows:

[0090] (1) Cut the fluorophlogopite sheet with a blade to obtain a fresh mica sheet, and prepare a fluorophlogopite sheet with a size of 15 mm × 15 mm.

[0091] Growth and preparation of two-dimensional Bi2O2Se by chemical vapor deposition: Weigh 0.1 g of Bi2Se3 powder and place it in a quartz boat, which is placed upstream in a high-temperature tube furnace. Weigh 0.7 g of Bi2O3 powder and place it in the quartz boat, which is placed at the thermal center. Place the prepared fluorophlogopite sheet downstream in the quartz tube, with the fresh side facing up. The carrier gas is a mixture of Ar / N2, and the carrier gas flow rate is 100 sccm. Heat up to 700 °C within 30 min of heating time and hold at this temperature for 30 min, then naturally cool to below 100 °C and turn off the carrier gas, and then naturally cool to room temperature. It is found under a microscope that several rectangles grow on the mica sheet, and thus the mica sheet with two-dimensional Bi2O2Se nanosheets grown on it is obtained.

[0092] (2)Cut the SiO2 / Si substrate into pieces of 10 mm×10 mm size, clean them in acetone, ethanol, and deionized water for 15 min respectively, and finally dry them with a nitrogen gun for standby.

[0093] Exfoliation of ReS2 by mechanical exfoliation method: Using a ReS2 single crystal as the raw material, repeatedly exfoliate it with blue tape, then stick it on the SiO2 / Si substrate, and then observe it under a microscope to obtain a two-dimensional ReS2 material with as thin a thickness as possible, and obtain a SiO2 / Si substrate with a ReS2 layer for standby.

[0094] Transfer the above two-dimensional Bi2O2Se nanosheets and two-dimensional ReS2 material on a transfer platform to obtain a heterojunction; Place the SiO2 / Si substrate with a ReS2 layer on the sample stage of the transfer platform. Drop polyvinyl alcohol solution (PVA) on a small piece of polydimethylsiloxane (PDMS) film that can cover the material, and gently scrape it flat with a glass slide, dry it at 55 °C for 10 min to form a cured PVA film, place it on a clean glass slide, fix it in the card slot of the transfer platform, align it with the ReS2 material on the substrate by adjusting the control platform, and transfer the ReS2 to the PVA film to obtain a PVA film containing ReS2.

[0095] Place the mica sheet with two-dimensional Bi2O2Se nanosheets grown on it 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 a suitable junction area, and continuously fit the two by controlling the transfer platform. Heat at 90 °C for 3 min, then remove it and soak it in 55 °C deionized water for 15 min. After taking it out, remove the PVA film on the surface of the mica sheet, and dry the remaining water on the surface with a nitrogen gun to obtain a Bi2O2Se / ReS2 van der Waals heterojunction.

[0096] (3) Lithographically pattern the electrode on the Bi2O2Se / ReS2 van der Waals heterojunction; use a spin coater to spin coat the photoresist on the Bi2O2Se / ReS2 van der Waals heterojunction, then heat it at 100 °C for 3 min, and then use electron beam lithography technology to accurately position and expose the pattern of the electrode. Then, develop the exposed heterojunction with a developer, fix it with deionized water, and dry it with a nitrogen gun. The specific process parameters are as follows: the scanning speed of the lithography machine is 0.3 mm / s, the power is 19 mW, the developer is a 3% aqueous solution of tetramethylammonium hydroxide, and the development time is 25 s.

[0097] (4) Evaporate the metal source electrode and drain electrode on the Bi2O2Se / ReS2 van der Waals heterojunction, 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 mica substrate. Part of the drain electrode is located on the surface of the Bi2O2Se material, and the other part is located on the surface of the mica substrate.

[0098] Then, remove the photoresist with acetone solution, soak it in deionized water to remove the residual acetone solution, then dry it with a nitrogen gun, and finally perform vacuum high-temperature annealing. The specific conditions for high-temperature annealing are as follows: the annealing temperature is set at 150 °C, the atmosphere is a mixed gas of Ar / N2, and the annealing time is set at 60 min to obtain a Bi2O2Se / ReS2 van der Waals heterojunction photodetector.

[0099] Figure 1 This is the energy band structure diagram of Bi2O2Se and In2Se3 before and after contact in Example 1 of the present invention.

[0100] Figure 1 Among them, before contact refers to the energy band structures of Bi2O2Se on the surface of the mica sheet growing two-dimensional Bi2O2Se nanosheets and In2Se3 on the surface of the SiO2 / Si substrate containing In2Se3 respectively; after contact refers to the energy band structure of the Bi2O2Se / In2Se3 van der Waals heterojunction photodetector.

[0101] As Figure 1 shown, when Bi2O2Se and In2Se3 are not in contact, the difference in Fermi energy levels between the two is 89 mV. When Bi2O2Se and In2Se3 are in contact, the Fermi levels reach the same level and form a reverse energy band bending.

[0102] Figure 2 This is the optical image of the Bi2O2Se / In2Se3 van der Waals heterojunction photodetector prepared in Example 1 of the present invention.

[0103] As Figure 2 shown, the drain electrode of the heterojunction optoelectronic device prepared in Example 1 is Bi2O2Se, and the source electrode is In2Se3.

[0104] Figure 3 The thickness images of In2Se3 nanosheets and Bi2O2Se nanosheets in the Bi2O2Se / In2Se3 van der Waals heterojunction photodetector prepared in Example 1 of the present invention. Among them, (A) is the In2Se3 nanosheet, and (B) is the Bi2O2Se nanosheet.

[0105] As Figure 3 shown, in Example 1, the thicknesses of the junction region materials In2Se3 and Bi2O2Se were measured by atomic force microscopy (AFM). Among them, the measured thickness of In2Se3 was 63 nm, and the thickness of Bi2O2Se was 118 nm.

[0106] Figure 4 The surface potential difference image of In2Se3 nanosheets and Bi2O2Se nanosheets in the Bi2O2Se / In2Se3 van der Waals heterojunction photodetector prepared in Example 1 of the present invention.

[0107] As Figure 4 shown, in Example 1, the surface potential difference between the junction region materials In2Se3 and Bi2O2Se was measured. Among them, the measured potential difference between the two was 89 mV.

[0108] Figure 5 The Raman spectra of the Bi2O2Se / In2Se3 van der Waals heterojunction photodetector, In2Se3, and Bi2O2Se in Example 1 of the present invention.

[0109] Figure 5 And in the subsequent Figure 6 The Raman spectra of In2Se3 and Bi2O2Se and the PL photoluminescence images were obtained by detecting In2Se3 on the surface of the SiO2 / Si substrate containing In2Se3 and Bi2O2Se on the surface of the mica sheet grown with two-dimensional Bi2O2Se nanosheets, respectively.

[0110] Figure 5 The Raman images of Bi2O2Se / In2Se3, In2Se3, and Bi2O2Se in Example 1 were provided. It can be seen from the dotted line in the figure that the Raman shift of the Bi2O2Se / In2Se3 heterojunction is in the approximate Raman shift range corresponding to Bi2O2Se and In2Se3, indicating that the prepared heterojunction is a combination of Bi2O2Se and In2Se3, that is, the successful preparation of the heterojunction region.

[0111] Figure 6 The PL photoluminescence images of the Bi2O2Se / In2Se3 van der Waals heterojunction photodetector, In2Se3, Bi2O2Se, and fluorophlogopite sheet in Example 1 of the present invention.

[0112] As Figure 6 shown, Example 1 provides the photoluminescence images of Bi2O2Se, In2Se3, Bi2O2Se / In2Se3, and fluorophlogopite flakes, indicating that both In2Se3 and Bi2O2Se / In2Se3 can be excited at infrared wavelengths. As Figure 6 can be seen, the device also has a certain response in the near-infrared region and has a wide spectral response.

[0113] Figure 7 This is the variation diagram of the photocurrent of the Bi2O2Se / In2Se3 van der Waals heterojunction photodetector prepared in Example 1 of the present invention at different powers.

[0114] As Figure 7 shown, Example 1 provides the Bi2O2Se / In2Se3 van der Waals heterojunction photodetector at different power densities (0.008 mW / cm ds = -2 V, wavelength of 405 nm), 0.03 mW / cm 2 , 0.1 mW / cm 2 , 0.2 mW / cm 2 , 3.4 mW / cm 2 , 22 mW / cm 2 , 31.8 mW / cm 2 , 31.8 mW / cm 2 , 69.6 mW / cm 2 and 106.7 mW / cm 2 ), and the corresponding photocurrent magnitudes. As Figure 7 can be seen, there is a good linear relationship between the power density and the photocurrent.

[0115] Figure 8 This is the variation curve of the photocurrent corresponding to the Bi2O2Se / In2Se3 van der Waals heterojunction photodetector prepared in Example 1 of the present invention at different power densities and different source-drain voltages.

[0116] As Figure 8 shown, Example 1 provides the variation curves of the photocurrent corresponding to Bi2O2Se / In2Se3 at different power densities with different source-drain voltages applied (-2V to 2V). As Figure 8 can be seen, when the source-drain voltage V ds is constant, the dark current is the smallest, and the photocurrent increases with the increase of the power density. When the power density reaches the maximum of 106 mW / cm 2 , the photocurrent is the largest, indicating that this heterojunction photodetector has a high on-off ratio.

[0117] Figure 9Respectively shown are the responsivity, detectivity curves, and on / off ratio curves of the Bi2O2Se / In2Se3 van der Waals heterojunction photodetector prepared in Example 1 of the present invention under different power densities. Among them, (A) shows the responsivity and detectivity curves, and (B) shows the on / off ratio curves.

[0118] As Figure 9 shown, (A) simultaneously provides the responsivity and detectivity curves of Bi2O2Se / In2Se3 in Example 1 under different power densities when the source-drain voltage V ds = -2V and the wavelength is 405 nm. It can be seen from the figure that the responsivity of this photodetector is 4.53 A / W, and the detectivity is 3.07×10 12 Jones. Figure 9 (B) provides the on / off ratio of Bi2O2Se / In2Se3 under different power densities when the source-drain voltage V ds = -2V and the wavelength is 405 nm. It can be seen from the figure that when the power density gradually increases, the on / off ratio of this photodetector also increases. When the power density is 106 mW / cm 2 , the maximum on / off ratio is 5.28×10 4 .

[0119] Figure 10 Shown are the time response curves of the products of Example 1 and Comparative Examples 1-3 under different powers of 405 nm illumination. Among them, (A) is for Example 1, (B) is for Comparative Example 1, (C) is for Comparative Example 2, and (D) is for Comparative Example 3.

[0120] Under different power densities, the photocurrent and dark current corresponding to the turn-on illumination and turn-off illumination are respectively shown. As Figure 10 shown in (A), the change in the dark current of the product of Example 1 is obvious when the illumination is turned on, increasing by one order of magnitude. The change in the dark current of Comparative Example 1 is not significant when the illumination is turned on, while the maximum power of Comparative Example 2 has almost no effect on the dark current when the illumination is turned on. The change in the dark current of Comparative Example 3 is not significant when the illumination is turned on, and the maximum on / off ratio is 5.28×10 4 . Compared with Figure 10 (A), (B), (C), and (D) only change within the same order of magnitude, indicating that the construction of the preferred heterojunction of the present invention can greatly improve the response performance of the photodetector.

[0121] Figure 11 Shown is the rising / falling time image of a single period of the Bi2O2Se / In2Se3 van der Waals heterojunction photodetector prepared in Example 1 of the present invention at 405 nm.

[0122] As Figure 11 shown, its rising / falling time is 5.7 ms / 2.8 ms.

[0123] As can be seen from the above-mentioned Example 1 and Comparative Examples 1, 2, and 3, by preferably selecting appropriate two-dimensional materials and constructing van der Waals heterostructures with different two-dimensional materials, the response performance of the device can be greatly improved.

[0124] The above-described embodiments are only descriptions of the preferred modes of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A van der Waals heterojunction constructed using a reverse band bending strategy, characterized in that, Using Bi2O2Se as the n-type semiconductor material and In2Se3 as the p-type semiconductor material, a van der Waals heterojunction with a type-II band alignment is formed.

2. The van der Waals heterojunction constructed by using the reverse band bending strategy according to claim 1, wherein In the van der Waals heterojunction, the bandgap of Bi2O2Se is 0.8 - 1.5 eV, the bandgap of In2Se3 is 1.3 - 2.0 eV, and the potential difference between the surfaces of Bi2O2Se and In2Se3 is 89 mV.

3. A method for preparing a van der Waals heterojunction constructed by using the reverse band bending strategy according to claim 1 or 2, characterized in that, It includes the following steps: Growing Bi2O2Se on the surface of substrate A by chemical vapor deposition to obtain a substrate with Bi2O2Se nanosheets grown thereon; Peeling the In2Se3 single crystal onto substrate B to obtain a substrate with an In2Se3 layer; Transferring the In2Se3 nanosheets on the substrate with the In2Se3 layer onto the substrate with the Bi2O2Se nanosheets grown thereon to prepare the Bi2O2Se / In2Se3 van der Waals heterojunction, thus completing the preparation.

4. The preparation method according to claim 3, wherein The substrate A is a mica sheet; and / or, the substrate B is SiO2 / Si.

5. The preparation method according to claim 3, wherein The preparation method of the substrate with the Bi2O2Se nanosheets grown thereon includes the following steps: placing substrate A and Bi2Se3 powder and Bi2O3 powder with a mass ratio of 1:7 in a heating device, and heating at 700 °C for 30 min in a protective atmosphere with a carrier gas flow rate of 80 - 120 sccm to obtain the substrate with the Bi2O2Se nanosheets grown thereon.

6. The preparation method according to claim 3, characterized in that, The transfer includes the following steps: transferring the In2Se3 nanosheets on the substrate with the In2Se3 layer onto a PVA film to obtain a PVA film containing In2Se3; Bringing the Bi2O2Se-containing surface of the substrate with the Bi2O2Se nanosheets grown thereon into contact with the In2Se3-containing surface of the PVA film containing In2Se3, heating at 90 - 100 °C for 3 - 5 min, and then removing the PVA film on the surface to complete the transfer.

7. Application of the van der Waals heterojunction constructed by using the reverse band bending strategy as described in claim 1 or 2 in the field of photodetectors.

8. A Bi2O2Se / In2Se3 van der Waals heterojunction photodetector, characterized in that, It contains the van der Waals heterojunction constructed by using the reverse band bending strategy as described in claim 1 or 2.

9. A method for preparing the Bi2O2Se / In2Se3 van der Waals heterojunction photodetector according to claim 8, characterized in that, It includes the following steps: Coating a photoresist on the van der Waals heterojunction constructed by using the reverse band bending strategy, and then lithographing an electrode pattern on a lithography machine to obtain a lithographed heterojunction; Evaporating a metal electrode on the lithographed heterojunction and then annealing to obtain the Bi2O2Se / In2Se3 van der Waals heterojunction photodetector.

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