A method for constructing van der Waals heterojunctions using a reverse band bending strategy

Abstract

The present invention discloses a method for constructing a van der Waals heterojunction using a reverse band bending strategy, which belongs to the field of two-dimensional material optoelectronic devices. The van der Waals heterojunction photodetector constructed using the reverse band bending strategy of the present invention uses Bi2O2Se as an n-type semiconductor material and In2Se3 as a p-type semiconductor material to form a van der Waals heterojunction photodetector with a type II energy band arrangement. In the van der Waals heterojunction photodetector, the bottom of the conduction band of Bi2O2Se is lower than the bottom of the conduction band of In2Se3, the top of the valence band of Bi2O2Se is lower than the top of the valence band of In2Se3, the energy band of In2Se3 bends upward, and the energy band of Bi2O2Se bends downward, generating a built-in electric field directed from In2Se3 toward Bi2O2Se, forming reverse band bending. The photodetector made of the van der Waals heterojunction constructed by the present invention has the characteristics of high detectivity and wide bandwidth.

Description

Technical Field

[0001] The present invention relates to the field of two-dimensional material optoelectronic devices, and in particular to a method for constructing a van der Waals heterojunction using a reverse energy band bending strategy. Background Art

[0002] Two-dimensional materials are a class of materials in which electrons can move freely only in two non-nanoscale dimensions. Graphene, transition metal dichalcogenides (TMDs), and black phosphorus (BP) are examples of these materials, demonstrating significant potential in optoelectronics due to their unique electronic structures and physicochemical properties. These materials exhibit significant application potential in fields such as field-effect transistors, optoelectronic devices, and thermoelectric devices, as their charge transport and heat conduction behavior are strictly confined within the two-dimensional plane.

[0003] In terms of heterostructure construction, traditional heterostructures have high lattice matching requirements, limited material selection, and the introduction of dangling bonds and interface states, resulting in a lower performance ceiling than van der Waals heterostructures. However, compared to traditional heterostructures, different two-dimensional materials can be freely stacked together to form van der Waals heterostructures. Van der Waals heterostructures are stacked through weak van der Waals forces, eliminating the need for lattice matching. They have the unique characteristics of atomic thickness and the absence of dangling bonds on the surface, resulting in high-quality heterojunction interfaces, which effectively improve carrier transport efficiency and device performance.

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

[0005] The present invention aims to provide a method for constructing a van der Waals heterojunction using a reverse band bending strategy to address the aforementioned problems in the background art. By utilizing the van der Waals force's lack of dangling bonds, the present invention forms a type II band structure upon contact between Bi2O2Se and In2Se3, with reverse band bending. This suppresses the interfacial recombination of photogenerated electron-hole pairs, promotes photogenerated carrier separation, and reduces dark current, thereby overcoming technical issues such as the insufficient electrical performance, limited spectral response, and poor environmental stability of existing two-dimensional materials.

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

[0007] One of the technical solutions of the present invention is to provide a van der Waals heterojunction photodetector constructed 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 photodetector with a type II energy band arrangement;

[0008] In the van der Waals heterojunction photodetector, the bottom of the conduction band of Bi2O2Se is lower than the bottom of the conduction band of In2Se3, the top of the valence band of Bi2O2Se is lower than the top of the valence band of In2Se3, the energy band of In2Se3 bends upward, and the energy band of Bi2O2Se bends downward, generating a built-in electric field (E) directed from In2Se3 to Bi2O2Se. bi ), forming a reverse band bending.

[0009] Preferably, the band gap of Bi2O2Se in the van der Waals heterojunction photodetector 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.

[0010] The second technical solution of the present invention is to provide a method for preparing the van der Waals heterojunction photodetector constructed using the reverse band bending strategy, comprising the following steps:

[0011] Bi2O2Se is grown on the surface of substrate A by chemical vapor deposition to obtain a substrate with Bi2O2Se nanosheets grown thereon;

[0012] Peeling the In2Se3 single crystal onto substrate B to obtain a substrate with an In2Se3 layer;

[0013] The In2Se3 nanosheets on the substrate with the In2Se3 layer are transferred to the substrate with the Bi2O2Se nanosheets grown thereon to obtain a Bi2O2Se / In2Se3 van der Waals heterojunction, thereby completing the preparation.

[0014] Preferably, the method of peeling the In2Se3 single crystal onto the substrate B includes the following steps: using blue tape to peel the In2Se3 single crystal, sticking it to the substrate B, and obtaining a substrate with an In2Se3 layer; the peeling is performed 4-5 times.

[0015] Preferably, the thickness of the Bi2O2Se nanosheets on the substrate on which the Bi2O2Se nanosheets are grown is 20-120 nm, and the thickness of the In2Se3 nanosheets on the substrate with the In2Se3 layer is 20-100 nm.

[0016] Preferably, the substrate A is a mica sheet.

[0017] Preferably, the substrate B is SiO2 / Si.

[0018] Preferably, the preparation method of the substrate on which Bi2O2Se nanosheets are grown comprises the following steps: placing substrate A and Bi2Se3 powder and Bi2O3 powder in a mass ratio of 1:7 in a heating device, heating them at 700°C for 30 min in a protective atmosphere with a carrier gas flow rate of 80-120 sccm to obtain the substrate on which Bi2O2Se nanosheets are grown.

[0019] Preferably, the transfer comprises the following steps: transferring the In2Se3 nanosheets on the substrate with the In2Se3 layer to a PVA film to obtain a PVA film containing In2Se3;

[0020] The Bi2O2Se-containing surface of the substrate on which the Bi2O2Se nanosheets are grown is laminated to the In2Se3-containing surface of the In2Se3-containing PVA film, heated at 90-100°C for 3-5 minutes, and then the PVA film on the surface is removed to complete the transfer.

[0021] 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 of the Bi2O2Se / In2Se3 van der Waals heterojunction photodetector is In2Se3, and the drain is Bi2O2Se.

[0022] Preferably, the process parameters of the photolithography are: the scanning speed of the photolithography machine is 0.06-0.5 mm / s, the power is 6-19 mW, the developer is a tetramethylammonium hydroxide aqueous solution with a concentration of 3-6%, and the developing time is 18-25 s.

[0023] Preferably, in the process of evaporating the metal electrode, the material of the metal electrode independently includes one or more of Au, Cr, Ag, Ti, Ni, Pd and Pt.

[0024] Preferably, the annealing temperature is 100-200° C., the annealing time is 30-120 min, and the atmosphere is an Ar / N 2 mixed gas.

[0025] The beneficial technical effects of the present invention are as follows:

[0026] This invention utilizes the van der Waals' lack of dangling bonds to form a type II band structure with reverse band bending upon contact between Bi2O2Se and In2Se3, suppressing the interfacial recombination of photogenerated electron-hole pairs and promoting photogenerated carrier separation, thereby reducing dark current. The resulting Bi2O2Se / In2Se3 van der Waals heterojunction photodetector has a responsivity of up to 4.53 A / W and rise / fall times of 5.7 ms / 2.8 ms. Compared to traditional photodetectors, it has a higher detectivity of up to 3.07×10 12 Jones, has good weak light detection capability; according to the calculation of photocurrent and optical power, it can be seen that it also has a high external quantum efficiency, which can reach 1.39×10 5 %, and has a strong ability to convert incident photons into effective electrons. The on-off ratio can reach four orders of magnitude, with a maximum on-off ratio of 5.28×10 4 It also has a wide spectral response, with a response within the wavelength range of 405-1000 nm. The Bi2O2Se / In2Se3 van der Waals heterojunction designed in the present invention can greatly improve the response performance of the photodetector.

[0027] The two-dimensional materials selected in this paper exhibit different photoelectron conversion mechanisms. The selected Bi2O2Se relies on bulk light absorption and high-mobility electron transport, while In2Se3 uses spontaneous ferroelectric polarization to form a built-in electric field to separate photogenerated carriers. Furthermore, the potential difference between Bi2O2Se and In2Se3 is moderate, preventing any negative impact.

[0028] The present invention grows and prepares a two-dimensional Bi2O2Se material by a chemical vapor deposition method. The preparation process is simple, and the Bi2O2Se material grown and prepared is of high quality and controllable thickness, which is conducive to mass production and promotion.

[0029] By constructing a van der Waals heterojunction, the present invention modulates the band structures of Bi2O2Se and In2Se3. The conduction band bottom and valence band top reside in different materials, forming a type II band arrangement. This reduces the probability of carrier recombination, significantly improves charge separation efficiency, reduces dark current, and enhances light absorption efficiency. The photodetector constructed using this van der Waals heterojunction exhibits high detectivity and a wide bandwidth. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0031] Figure 1 This is the energy band structure diagram after Bi2O2Se and In2Se3 come into contact in Example 1 of the present invention.

[0032] Figure 2 This is an optical image of the Bi2O2Se / In2Se3 van der Waals heterojunction photodetector prepared in Example 1 of the present invention.

[0033] Figure 3 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. (A) shows an In2Se3 nanosheet, and (B) shows a Bi2O2Se nanosheet.

[0034] Figure 4 This is an image of the surface potential difference between In2Se3 nanosheets and Bi2O2Se nanosheets in the Bi2O2Se / In2Se3 van der Waals heterojunction photodetector prepared in Example 1 of the present invention.

[0035] Figure 5 2 , which are Raman images of the Bi2O2Se / In2Se3 van der Waals heterojunction photodetector, In2Se3 and Bi2O2Se in Example 1 of the present invention.

[0036] Figure 6 PL photoluminescence images of the Bi2O2Se / In2Se3 van der Waals heterojunction photodetector, In2Se3, Bi2O2Se and fluorophlogopite sheet in Example 1 of the present invention.

[0037] Figure 7 This is a graph showing the change in photocurrent of the Bi2O2Se / In2Se3 van der Waals heterojunction photodetector prepared in Example 1 of the present invention at different powers.

[0038] Figure 8 This is a curve showing the change in photocurrent of 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.

[0039] Figure 9 The responsivity and detectivity curves and on / off ratio curves of the Bi2O2Se / In2Se3 van der Waals heterojunction photodetector prepared in Example 1 of the present invention at different power densities are shown in Figure 1. (A) shows the responsivity and detectivity curves, and (B) shows the on / off ratio curve.

[0040] Figure 10The time response curves of the products of Example 1 and Comparative Examples 1-3 under different powers of 405nm light irradiation are shown. Among them, (A) is Example 1, (B) is Comparative Example 1, (C) is Comparative Example 2, and (D) is Comparative Example 3.

[0041] Figure 11 This is a single-cycle rise / fall time image of the Bi2O2Se / In2Se3 van der Waals heterojunction photodetector prepared in Example 1 of the present invention at 405nm. DETAILED DESCRIPTION

[0042] Various exemplary embodiments of the present invention are now described in detail. This detailed description should not be considered as a limitation of the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention. It should be understood that the terms used in the present invention are only for describing specific embodiments and are not intended to limit the present invention.

[0043] In addition, for numerical ranges in the present invention, it is understood that each intervening value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any stated value or stated range, and any other stated value or intervening value in the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges may independently be included or excluded in the range.

[0044] Unless otherwise specified, all technical and scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the art to which the present invention pertains. Although preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present invention. It should be noted that any details not described herein are conventional procedures in the art and are not the focus of the present invention.

[0045] The terms “include,” “including,” “have,” “contain,” etc. used in the present invention are open-ended terms, meaning including but not limited to.

[0046] As a core parameter that determines the electrical, optical and thermal properties of a device, the band structure has a direct impact on key indicators such as carrier mobility, optoelectronic device efficiency, power consumption and switching ratio. In terms of interface effects, the formation of ohmic contacts or Schottky barriers will significantly change the contact resistance characteristics of the device. By precisely controlling the band structure, multifunctional integration of a single device can be achieved. Compared with the narrow spectral response range of the type I band structure and the low carrier separation efficiency of the type III band structure, at the type II heterojunction interface, strong charge transfer may change the electrostatic potential at the interface, resulting in a reversal of the band bending direction. Reverse band bending may strengthen the electric field in the space charge region of the type II structure, further pushing electrons and holes to move in opposite directions, thereby achieving efficient carrier separation and wide-spectrum light response.

[0047] The Bi2O2Se layers selected in the present invention are bonded by van der Waals forces, are stable in air, are not easily degraded, have the characteristics of high mobility, stability, wide spectrum response and process compatibility, and are suitable for practical applications such as photodetectors, solar cells and light-emitting diodes.

[0048] The present invention discloses a method for constructing a van der Waals heterojunction photodetector using a reverse band bending strategy. Bi2O2Se is selected as an n-type semiconductor material and In2Se3 is selected as a p-type semiconductor material to form a type II band arrangement (i.e., the bottom of the conduction band and the top of the valence band of the constructed heterojunction are located on different materials), thereby obtaining the van der Waals heterojunction photodetector.

[0049] In the van der Waals heterojunction photodetector, the conduction band bottom of Bi2O2Se is lower than the conduction band bottom of In2Se3, the valence band top of Bi2O2Se is lower than the valence band top of In2Se3, the energy band of In2Se3 bends upward, and the energy band of Bi2O2Se bends downward, generating a built-in electric field from In2Se3 to Bi2O2Se, forming reverse energy band bending.

[0050] Furthermore, the method for constructing a van der Waals heterojunction photodetector using a reverse band bending strategy comprises the following steps:

[0051] Two-dimensional Bi2O2Se was grown by chemical vapor deposition: 0.1 g of Bi2Se3 powder was weighed and placed in a quartz boat, which was placed upstream of a high-temperature tube furnace. 0.7 g of Bi2O3 powder was weighed and placed in a quartz boat, which was placed at the hot center. A mica sheet with a size of 15 mm × 15 mm was placed downstream of the hot center. The carrier gas was an Ar / N2 mixed gas with a carrier gas flow rate of 80-120 sccm. The temperature was raised to 700 °C within 30 minutes and kept at this temperature for 30 minutes. The mixture was then naturally cooled to below 100 °C, the carrier gas was turned off, and the mixture was naturally cooled to room temperature. Several rectangles were found growing on the mica sheet under a microscope, indicating that a mica sheet with two-dimensional Bi2O2Se nanosheets was prepared.

[0052] Mechanical exfoliation: Using an In2Se3 single crystal as the raw material, the single crystal is repeatedly exfoliated using blue tape and then adhered to a SiO2 / Si substrate to obtain a SiO2 / Si substrate with an In2Se3 layer.

[0053] The SiO2 / Si substrate with the In2Se3 layer is placed on the sample stage of the transfer table; a polyvinyl alcohol solution (PVA) is dropped on a polydimethylsiloxane (PDMS) film that can cover the material, and the film is gently scraped with a glass slide until it is flat. The film is dried at 55-70°C for 5-10 minutes to form a solidified PVA film, which is placed on a clean glass slide and fixed in the card slot of the transfer table. The control platform is adjusted to align it with the In2Se3 on the SiO2 / Si substrate with the In2Se3 layer, and the In2Se3 is transferred to the PVA film to obtain a PVA film containing In2Se3;

[0054] A mica sheet with two-dimensional Bi2O2Se nanosheets grown on it was placed on the sample stage of a transfer platform. A PVA film containing In2Se3 was fixed in a slot on the transfer platform. The overlapping portion was observed through a microscope on the transfer platform. The appropriate junction area was selected and the two were continuously bonded by controlling the transfer platform. The mica sheet was heated at 90-100°C for 3-5 minutes, then removed and immersed in 55°C deionized water for 10-15 minutes. The PVA film on the surface of the mica sheet was removed and dried with a nitrogen gun to obtain a Bi2O2Se / In2Se3 van der Waals heterojunction.

[0055] Photolithography of an electrode pattern on a Bi2O2Se / In2Se3 van der Waals heterojunction; spin coating of photoresist on the Bi2O2Se / In2Se3 van der Waals heterojunction using a spin coater, followed by heating at 100-105°C for 3-6 minutes, and precise exposure of the electrode pattern using electron beam lithography. The exposed heterojunction is then developed with a developer, fixed with deionized water, and dried with a nitrogen gun. The photolithography parameters are: a scan speed of 0.06-0.5 mm / s, a power of 6-19 mW, a developer of 3-6% tetramethylammonium hydroxide aqueous solution, and a development time of 18-25 seconds.

[0056] Depositing a metal source electrode and a drain electrode on the Bi2O2Se / In2Se3 van der Waals heterojunction, such that part of the metal source electrode is located on the surface of the In2Se3 material and another part is located on the surface of the mica substrate, and part of the drain electrode is located on the surface of the Bi2O2Se material and another part is located on the surface of the mica substrate;

[0057] After the evaporation is completed, the photoresist is removed with an acetone solution, and the residual acetone solution is removed by immersing in deionized water. Then, the surface is blown dry with a nitrogen gun, and finally vacuum high-temperature annealing is performed. The conditions of the high-temperature annealing are: annealing temperature of 100-200 ° C, atmosphere of Ar / N2 mixed gas, annealing time of 30-120 min, and a Bi2O2Se / In2Se3 van der Waals heterojunction photodetector is obtained.

[0058] The raw materials used in the following examples and comparative examples of the present invention are all commercially available products.

[0059] Example 1

[0060] A method for constructing a van der Waals heterojunction using a reverse band bending strategy, wherein n-type Bi2O2Se two-dimensional material and p-type In2Se3 two-dimensional material are selected to construct the van der Waals heterojunction, that is, Bi2O2Se is prepared by chemical vapor deposition, and then the van der Waals heterojunction is constructed with In2Se3 material through PVA dry transfer. Finally, the optical device is manufactured by photolithography, metal evaporation, and high-temperature annealing.

[0061] The specific steps are as follows:

[0062] (1) Use a blade to cut the fluorophlogopite mica sheet to obtain fresh mica sheets and prepare fluorophlogopite mica sheets with a size of 15 mm × 15 mm.

[0063] Two-dimensional Bi2O2Se was grown by chemical vapor deposition: 0.1 g of Bi2Se3 powder was weighed and placed in a quartz boat upstream of a high-temperature tube furnace. 0.7 g of Bi2O3 powder was also weighed and placed in a quartz boat at the hot center. A prepared fluorophlogopite sheet was placed downstream of the quartz tube, fresh side up. The carrier gas was an Ar / N2 mixture at a flow rate of 100 sccm. The temperature was raised to 700°C over 30 minutes and held at this temperature for 30 minutes. The sheet was then cooled naturally to below 100°C, the carrier gas was turned off, and the sample was allowed to cool naturally to room temperature. Microscopic observation revealed several rectangular structures growing on the mica sheet, indicating the formation of two-dimensional Bi2O2Se nanosheets.

[0064] (2) Cut the SiO2 / Si substrate into 10 mm × 10 mm pieces, clean them in acetone, ethanol, and deionized water for 15 min respectively, and finally blow dry them with a nitrogen gun for later use.

[0065] In2Se3 is peeled off using a mechanical peeling method: In order to obtain a two-dimensional In2Se3 material with the thinnest possible thickness, an In2Se3 single crystal is used as the raw material, which is repeatedly peeled off using blue tape and then glued to a SiO2 / Si substrate. After observation under a microscope, a SiO2 / Si substrate with an In2Se3 layer is obtained and set aside.

[0066] Two-dimensional Bi2O2Se nanosheets and two-dimensional In2Se3 materials are transferred on a transfer platform to obtain a heterojunction; a SiO2 / Si substrate with an In2Se3 layer is placed on the sample stage of the transfer platform, and a small piece of polydimethylsiloxane (PDMS) film that can cover the material is dropped with a polyvinyl alcohol solution (PVA), which is gently scraped with a glass slide until it is flat, and dried at 55°C for 10 minutes to form a layer of solidified PVA film. The film is placed on a clean glass slide and fixed in the slot of the transfer platform. By adjusting the control platform, it is aligned with the In2Se3 material on the substrate, and the In2Se3 is transferred to the PVA film to obtain a PVA film containing In2Se3.

[0067] A mica sheet with two-dimensional Bi2O2Se nanosheets grown on it was placed on the sample stage of a transfer platform. A PVA film containing In2Se3 was fixed in the card slot of the transfer platform. The overlapping part was observed through a microscope on the transfer platform, and the appropriate junction area was selected. The two were continuously bonded by controlling the transfer platform. They were heated at 90°C for 3 minutes, then removed and soaked in 55°C deionized water for 15 minutes. After removal, the PVA film on the surface of the mica sheet was removed, and the residual water on the surface was blown dry with a nitrogen gun to obtain a Bi2O2Se / In2Se3 van der Waals heterojunction.

[0068] (3) Photolithography of electrode patterns on the Bi2O2Se / In2Se3 van der Waals heterojunction. Spin-coat the Bi2O2Se / In2Se3 van der Waals heterojunction with photoresist, then heat at 100°C for 3 minutes. Electron beam lithography is then used to precisely position and expose the electrode pattern. The exposed heterojunction is then developed with a developer, fixed with deionized water, and dried with a nitrogen gun. Specific process parameters are: a lithography scan speed of 0.3 mm / s, a power of 19 mW, a 3% tetramethylammonium hydroxide aqueous solution as the developer, and a development time of 25 seconds.

[0069] (4) Ti / Au source and drain electrodes are evaporated 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, and 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.

[0070] The photoresist was then removed with acetone, and the remaining acetone was removed by soaking in deionized water. The sample was then dried with a nitrogen gun and finally subjected to vacuum high-temperature annealing. The specific conditions for the high-temperature annealing were: 150°C, an Ar / N2 mixture atmosphere, and 60 minutes of annealing time, resulting in a Bi2O2Se / In2Se3 van der Waals heterojunction photodetector.

[0071] Comparative Example 1 (Omitting the steps of preparing Bi2O2Se nanosheets and constructing Bi2O2Se / In2Se3 heterojunction)

[0072] A method for preparing a photoelectric detector comprises the following steps:

[0073] The SiO2 / Si substrate was cut into 10 mm × 10 mm sizes, cleaned in acetone, ethanol, and deionized water for 15 min respectively, and finally dried with a nitrogen gun for later use.

[0074] Use mechanical exfoliation to peel off In2Se3: Use In2Se3 single crystal as raw material, use blue tape to peel it repeatedly, and then stick it to SiO2 / Si substrate. Then observe it under a microscope to obtain the thinnest two-dimensional In2Se3 material possible, and obtain SiO2 / Si substrate with In2Se3 layer for later use.

[0075] Electrode patterns were photolithographically patterned onto In2Se3 nanosheets. A photoresist was spin-coated onto the SiO2 / Si substrate with the In2Se3 layer using a spin coater. The substrate was then heated at 100°C for 3 minutes. Electron beam lithography was then used to precisely position and expose the electrode pattern. The exposed material system was then developed with a developer, fixed with deionized water, and dried with a nitrogen gun. Specific process parameters included a scan speed of 0.3 mm / s, a power of 19 mW, a 3% tetramethylammonium hydroxide solution as the developer, and a development time of 25 seconds.

[0076] A metal electrode is evaporated on the SiO2 / Si substrate with the In2Se3 layer after photolithography, so that part of the metal electrode is located on the surface of the In2Se3 material and the other part is located on the surface of the SiO2 / Si substrate.

[0077] The photoresist was then removed with acetone, and the remaining acetone was removed by soaking in deionized water. The film was then dried with a nitrogen gun and finally annealed at high temperature in a vacuum. The specific conditions for the high-temperature annealing were: 150°C, an Ar / N2 mixture atmosphere, and 60 minutes of annealing time, resulting in an In2Se3 single-element photodetector.

[0078] Comparative Example 2 (Omitting the steps of preparing In2Se3 nanosheets and constructing Bi2O2Se / In2Se3 heterojunction)

[0079] A method for preparing a photoelectric detector comprises the following steps:

[0080] The fluorophlogopite sheet was cut with a blade to obtain fresh mica sheets, and fluorophlogopite sheets with a size of 15 mm × 15 mm were prepared.

[0081] Two-dimensional Bi2O2Se was grown by chemical vapor deposition: 0.1 g of Bi2Se3 powder was weighed and placed in a quartz boat upstream of a high-temperature tube furnace. 0.7 g of Bi2O3 powder was also weighed and placed in a quartz boat at the hot center. A prepared fluorophlogopite sheet was placed downstream of the quartz tube, fresh side up. The carrier gas was an Ar / N2 mixture at a flow rate of 100 sccm. The temperature was raised to 700°C over 30 minutes and held at this temperature for 30 minutes. The sheet was then cooled naturally to below 100°C, the carrier gas was turned off, and the sample was allowed to cool naturally to room temperature. Microscopic observation revealed several rectangular structures growing on the mica sheet, indicating the formation of two-dimensional Bi2O2Se nanosheets.

[0082] Electrode patterns were photolithographically patterned onto Bi2O2Se nanosheets. A photoresist was spin-coated onto a mica sheet bearing the two-dimensional Bi2O2Se nanosheets using a spin coater. The sheet was then heated at 100°C for 3 minutes. Electron beam lithography was then used to precisely position and expose the electrode pattern. The exposed material system was then developed with a developer, fixed with deionized water, and dried with a nitrogen gun. Specific process parameters included a scan speed of 0.3 mm / s, a power of 19 mW, a 3% tetramethylammonium hydroxide solution as the developer, and a development time of 25 seconds.

[0083] A metal electrode is evaporated on the mica sheet on which two-dimensional Bi2O2Se nanosheets are grown after photolithography, so that part of the metal electrode is located on the surface of the Bi2O2Se material and the other part is located on the surface of the mica substrate.

[0084] The photoresist was then removed with acetone, and the remaining acetone was removed by soaking in deionized water. The sample was then dried with a nitrogen gun and finally annealed at high temperature in a vacuum. The annealing conditions were: 150°C, an Ar / N2 mixture, and 60 minutes. This resulted in a Bi2O2Se single-element photodetector.

[0085] Comparative Example 3 (Replacing In2Se3 with ReS2)

[0086] A method for preparing a photoelectric detector comprises the following steps:

[0087] (1) Use a blade to cut the fluorophlogopite mica sheet to obtain fresh mica sheets and prepare fluorophlogopite mica sheets with a size of 15 mm × 15 mm.

[0088] Two-dimensional Bi2O2Se was grown by chemical vapor deposition: 0.1 g of Bi2Se3 powder was weighed and placed in a quartz boat upstream of a high-temperature tube furnace. 0.7 g of Bi2O3 powder was also weighed and placed in a quartz boat at the hot center. A prepared fluorophlogopite sheet was placed downstream of the quartz tube, fresh side up. The carrier gas was an Ar / N2 mixture at a flow rate of 100 sccm. The temperature was raised to 700°C over 30 minutes and held at this temperature for 30 minutes. The sheet was then cooled naturally to below 100°C, the carrier gas was turned off, and the sample was allowed to cool naturally to room temperature. Microscopic observation revealed several rectangular structures growing on the mica sheet, indicating the formation of two-dimensional Bi2O2Se nanosheets.

[0089] (2) Cut the SiO2 / Si substrate into 10 mm × 10 mm pieces, clean them in acetone, ethanol, and deionized water for 15 min respectively, and finally blow dry them with a nitrogen gun for later use.

[0090] Use mechanical exfoliation to peel off ReS2: Use ReS2 single crystal as raw material, use blue tape to peel it repeatedly, and then stick it to SiO2 / Si substrate. Then observe it under a microscope to obtain the thinnest two-dimensional ReS2 material as possible, and obtain SiO2 / Si substrate with ReS2 layer for use.

[0091] The above-mentioned two-dimensional Bi2O2Se nanosheets and two-dimensional ReS2 materials are transferred on a transfer platform to obtain a heterojunction; the SiO2 / Si substrate with the ReS2 layer is placed on the sample stage of the transfer platform, and a small piece of polydimethylsiloxane (PDMS) film that can cover the material is dripped with polyvinyl alcohol solution (PVA), and gently scraped with a glass slide until it is flat, and dried at 55°C for 10 minutes to form a layer of solidified PVA film, which is placed on a clean glass slide and fixed in the card slot of the transfer platform. By adjusting the control platform, it is aligned with the ReS2 material on the substrate, and the ReS2 is transferred to the PVA film to obtain a PVA film containing ReS2.

[0092] A mica sheet with two-dimensional Bi2O2Se nanosheets grown on it was placed on the sample stage of a transfer platform, and a PVA film containing ReS2 was fixed in the card slot of the transfer platform. The overlapping part was observed through a microscope on the transfer platform, and the appropriate junction area was selected. The two were continuously bonded by controlling the transfer platform, heated at 90°C for 3 minutes, then removed and soaked in 55°C deionized water for 15 minutes. After removal, the PVA film on the surface of the mica sheet was removed, and the residual water on the surface was blown dry with a nitrogen gun to obtain a Bi2O2Se / ReS2 van der Waals heterojunction.

[0093] (3) Photolithography of electrode patterns on the Bi2O2Se / ReS2 van der Waals heterojunction. Spin-coat the Bi2O2Se / ReS2 van der Waals heterojunction with photoresist, then heat at 100°C for 3 minutes. Electron beam lithography is then used to precisely position and expose the electrode pattern. The exposed heterojunction is then developed with a developer, fixed with deionized water, and dried with a nitrogen gun. Specific process parameters are: a scan speed of 0.3 mm / s, a power of 19 mW, a 3% tetramethylammonium hydroxide aqueous solution as the developer, and a development time of 25 seconds.

[0094] (4) A metal source electrode and a drain electrode are evaporated 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 another part is located on the surface of the mica substrate, and part of the drain electrode is located on the surface of the Bi2O2Se material and another part is located on the surface of the mica substrate.

[0095] The photoresist was then removed with acetone, and the remaining acetone was removed by immersion in deionized water. The sample was then dried with a nitrogen gun and finally annealed at high temperature in a vacuum. The annealing conditions were: 150°C, an Ar / N2 mixture, and 60 minutes. This yielded a Bi2O2Se / ReS2 van der Waals heterojunction photodetector.

[0096] Figure 1 This is the energy band structure diagram after Bi2O2Se and In2Se3 come into contact in Example 1 of the present invention.

[0097] Figure 1 In the figure, post-contact refers to the band structure of the Bi2O2Se / In2Se3 van der Waals heterojunction photodetector.

[0098] like Figure 1 As shown, when Bi2O2Se and In2Se3 come into contact, the Fermi levels reach the same level and form reverse band bending.

[0099] Figure 2 This is an optical image of the Bi2O2Se / In2Se3 van der Waals heterojunction photodetector prepared in Example 1 of the present invention.

[0100] like Figure 2 As shown, the drain of the heterojunction optoelectronic device prepared in Example 1 is Bi2O2Se, and the source is In2Se3.

[0101] Figure 3Thickness images of In2Se3 nanosheets and Bi2O2Se nanosheets in the Bi2O2Se / In2Se3 van der Waals heterojunction photodetector prepared in Example 1 of the present invention. (A) shows an In2Se3 nanosheet, and (B) shows a Bi2O2Se nanosheet.

[0102] like Figure 3 As shown, in Example 1, the thickness of the junction materials In2Se3 and Bi2O2Se was measured by atomic force microscopy (AFM), wherein the thickness of In2Se3 was measured to be 63 nm, and the thickness of Bi2O2Se was measured to be 118 nm.

[0103] Figure 4 This is an image of the surface potential difference between In2Se3 nanosheets and Bi2O2Se nanosheets in the Bi2O2Se / In2Se3 van der Waals heterojunction photodetector prepared in Example 1 of the present invention.

[0104] like Figure 4 As shown, in Example 1, the surface potential difference between the junction materials In2Se3 and Bi2O2Se was measured, and the measured potential difference between the two was 89 mV.

[0105] Figure 5 2 , which are Raman images of the Bi2O2Se / In2Se3 van der Waals heterojunction photodetector, In2Se3 and Bi2O2Se in Example 1 of the present invention.

[0106] Figure 5 and subsequent Figure 6 In the figure, the Raman images and PL photoluminescence images of In2Se3 and Bi2O2Se were obtained by detecting In2Se3 on the surface of SiO2 / Si substrate containing In2Se3 and Bi2O2Se on the surface of mica sheet with two-dimensional Bi2O2Se nanosheets grown on it, respectively.

[0107] Figure 5 The Raman images of Bi2O2Se / In2Se3, In2Se3 and Bi2O2Se in Example 1 are provided. As can be seen from the dotted lines in the figure, the Raman shift of the Bi2O2Se / In2Se3 heterojunction is approximately in the Raman shift range corresponding to Bi2O2Se and In2Se3, indicating that the prepared heterojunction is a combination of Bi2O2Se and In2Se3, that is, the heterojunction region is successfully prepared.

[0108] Figure 6 PL photoluminescence images of the Bi2O2Se / In2Se3 van der Waals heterojunction photodetector, In2Se3, Bi2O2Se and fluorophlogopite sheet in Example 1 of the present invention.

[0109] like Figure 6As shown, Example 1 provides photoluminescence images of Bi2O2Se, In2Se3, Bi2O2Se / In2Se3 and fluorophlogopite sheets, indicating that In2Se3 and Bi2O2Se / In2Se3 can be excited at infrared wavelengths. Figure 6 It can be seen that the device also has a certain response in the near-infrared and has a wide spectral response.

[0110] Figure 7 This is a graph showing the change in photocurrent of the Bi2O2Se / In2Se3 van der Waals heterojunction photodetector prepared in Example 1 of the present invention at different powers.

[0111] like Figure 7 As shown, Example 1 provides a Bi2O2Se / In2Se3 van der Waals heterojunction photodetector with a source-drain voltage V ds = -2 V, different power densities at a wavelength of 405 nm (0.008 mW / cm 2 , 0.03 mW / cm 2 , 0.1 mW / cm 2 , 0.2mW / cm 2 , 3.4 mW / cm 2 , 22 mW / cm 2 、31.8 mW / cm 2 、69.6 mW / cm 2 and 106.7 mW / cm 2 ) corresponds to the photocurrent size, which is given by Figure 7 It can be seen that the power density and the photocurrent have a good linear relationship.

[0112] Figure 8 This is a curve showing the change in photocurrent of 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.

[0113] like Figure 8 As shown in FIG, Example 1 provides a curve of photocurrent change corresponding to Bi2O2Se / In2Se3 under different power densities and different source-drain voltages (-2V to 2V). Figure 8 It can be seen that when the source-drain voltage V ds When the power density is constant, the dark current is the smallest, and the photocurrent increases with the increase of power density. When the power density reaches the maximum of 106 mW / cm 2 The photocurrent is the largest, which indicates that the heterojunction photodetector has a high on-off ratio.

[0114] Figure 9The responsivity and detectivity curves and on / off ratio curves of the Bi2O2Se / In2Se3 van der Waals heterojunction photodetector prepared in Example 1 of the present invention at different power densities are shown in Figure 1. (A) shows the responsivity and detectivity curves, and (B) shows the on / off ratio curve.

[0115] like Figure 9 As shown, (A) also provides the Bi2O2Se / In2Se3 of Example 1 at the source-drain voltage V ds =-2V, wavelength of 405 nm, the responsivity and detectivity curves at different power densities. It can be seen from the figure that the responsivity of the photodetector is 4.53 A / W, and the detectivity is 3.07×10 12 Jones. Figure 9 (B) provides Bi2O2Se / In2Se3 at source-drain voltage V ds =-2V, wavelength of 405 nm, the on-off ratio at different power densities. As can be seen from the figure, when the power density gradually increases, the on-off ratio of the photodetector also increases. When the power density is 106 mW / cm 2 When the on / off ratio is 5.28×10 4 .

[0116] Figure 10 The time response curves of the products of Example 1 and Comparative Examples 1-3 under different powers of 405nm light irradiation are shown. Among them, (A) is Example 1, (B) is Comparative Example 1, (C) is Comparative Example 2, and (D) is Comparative Example 3.

[0117] The photocurrent and dark current under different power densities are respectively corresponding to the light on and the light off. Figure 10 As shown in (A), the dark current of the product of Example 1 changes significantly when the light is turned on, increasing by an order of magnitude. The dark current of Comparative Example 1 does not change much when the light is turned on, and the maximum power of Comparative Example 2 has almost no effect on the dark current when the light is turned on. The dark current of Comparative Example 3 does not change much when the light is turned on, and the maximum on-off ratio is 5.28×10 4 .and Figure 10 Compared with (A), (B), (C), and (D) only change at the same order of magnitude, indicating that the preferred heterojunction construction of the present invention can greatly improve the response performance of the photodetector.

[0118] Figure 11 This is a single-cycle rise / fall time image of the Bi2O2Se / In2Se3 van der Waals heterojunction photodetector prepared in Example 1 of the present invention at 405nm.

[0119] like Figure 11 As shown, its rise / fall time is 5.7 ms / 2.8 ms.

[0120] It can be seen from the above-mentioned Example 1 and Comparative Examples 1, 2 and 3 that by selecting suitable two-dimensional materials and constructing van der Waals heterostructures with different two-dimensional materials, the response performance of the device can be greatly improved.

[0121] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A van der Waals heterojunction photodetector constructed using a reverse band bending strategy, characterized in that: Bi2O2Se is used as n-type semiconductor material and In2Se3 is used as p-type semiconductor material to construct a van der Waals heterojunction photodetector with type II energy band arrangement; In the van der Waals heterojunction photodetector, the conduction band bottom of Bi2O2Se is lower than the conduction band bottom of In2Se3, the valence band top of Bi2O2Se is lower than the valence band top of In2Se3, the energy band of In2Se3 bends upward, and the energy band of Bi2O2Se bends downward, generating a built-in electric field from In2Se3 to Bi2O2Se, forming reverse energy band bending.

2. The van der Waals heterojunction photodetector constructed using the reverse band bending strategy according to claim 1, characterized in that: The band gap of Bi2O2Se in the van der Waals heterojunction photodetector 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.

3. A method for preparing a van der Waals heterojunction photodetector constructed using a reverse band bending strategy according to claim 1 or 2, characterized in that: The following steps are involved: Bi2O2Se is grown 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 to the substrate with the Bi2O2Se nanosheets grown thereon to form a Bi2O2Se / In2Se3 van der Waals heterojunction; Coating a photoresist on the Bi2O2Se / In2Se3 van der Waals heterojunction, and then photoetching an electrode pattern on a photolithography machine to obtain a photoetched heterojunction; A metal electrode is evaporated on the photolithographic heterojunction, and then annealed to obtain the van der Waals heterojunction photodetector constructed using the reverse energy band bending strategy.

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

5. The preparation method according to claim 3, characterized in that The method for preparing a substrate on which Bi2O2Se nanosheets are grown comprises the following steps: placing a substrate A and Bi2Se3 powder and Bi2O3 powder in a mass ratio of 1:7 in a heating device, heating them at 700°C for 30 minutes in a protective atmosphere with a carrier gas flow rate of 80-120 sccm to obtain the substrate on which Bi2O2Se nanosheets are grown.

6. The preparation method according to claim 3, characterized in that The transfer comprises the following steps: transferring the In2Se3 nanosheets on the substrate with the In2Se3 layer to the PVA film to obtain the In2Se3-containing PVA film; The Bi2O2Se-containing surface of the substrate on which the Bi2O2Se nanosheets are grown is laminated to the In2Se3-containing surface of the In2Se3-containing PVA film, heated at 90-100°C for 3-5 minutes, and then the PVA film on the surface is removed to complete the transfer.

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