Two-dimensional semiconductor in-plane integration method and device

Abstract

The application discloses a two-dimensional semiconductor in-plane integration method and device, and the method comprises the following steps: providing a first two-dimensional single-layer material and placing the first two-dimensional single-layer material on a target substrate; stacking a second two-dimensional single-layer material on the first two-dimensional single-layer material to form a van der Waals heterojunction comprising a stacking area and a single-layer area; and using an excitation light source with a photon energy greater than the luminescence band gap of the first two-dimensional single-layer material and / or the second two-dimensional single-layer material to make the van der Waals heterojunction undergo a selective photochemical reaction, so that the second two-dimensional single-layer material in the stacking area is selectively removed, and the first two-dimensional single-layer material and the second two-dimensional single-layer material are integrated and spliced in the same plane. The two-dimensional semiconductor in-plane integration method and device provided by the application realizes the in-plane splicing of two-dimensional materials by utilizing the difference in the electronic state distribution of different two-dimensional materials in the stacking area and the single-layer area and selectively removing the upper-layer material in the stacking area through photochemical reaction.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of semiconductor technology, and particularly relates to a two-dimensional semiconductor in-plane integration method and device. BACKGROUND

[0002] Existing in-plane heterojunction preparation techniques usually rely on traditional single-step or multi-step growth methods, including chemical vapor deposition (CVD), atomic layer deposition (ALD), physical vapor deposition (PVD), electrochemical deposition, hydrothermal synthesis, and epitaxial growth, etc. These methods have certain applications in the preparation of two-dimensional materials and heterojunctions, but they face some technical bottlenecks. These growth methods usually rely on the crystal face structure of the substrate, resulting in the inability to obtain a patterned heterojunction array during the synthesis process. Due to the problem of random nucleation, the growth of heterojunctions cannot be precisely controlled at the microscale.

[0003] Moreover, these processes often need to be carried out at extremely high temperatures, usually between 600℃ and 1200℃. Such high temperatures pose extremely high requirements on the preparation process, especially in terms of compatibility with the integrated circuit process of the current semiconductor industry.

[0004] In order to solve the above-mentioned problem of random nucleation, existing technologies also attempt to prepare a heterojunction array by combining material growth with modern micro-nano processing technology. Common micro-nano processing means include electron beam lithography, photolithography, laser ablation, etc. Through these technologies, the patterning of the heterojunction region can be achieved. However, although these technologies can partially solve the patterning problem, in actual operation, there are still limitations in material design freedom, processing precision, and the need for high-temperature environment.

[0005] Therefore, in view of the above technical problems, it is necessary to provide a new solution. SUMMARY

[0006] The purpose of the present application is to provide a two-dimensional semiconductor in-plane integration method and device, which can realize the construction of in-plane heterojunctions at room temperature, has high material design freedom and processing precision, has a simple preparation process, and can realize low-cost integration.

[0007] To achieve the above-mentioned purpose, the technical solutions provided by the present application are as follows:

[0008] In a first aspect, the present application provides a two-dimensional semiconductor in-plane integration method, comprising: providing a first two-dimensional monolayer material and placing it on a target substrate; stacking a second two-dimensional monolayer material on the first two-dimensional monolayer material to form a van der Waals heterojunction comprising a stacked region and a monolayer region; and performing a selective photochemical reaction on the van der Waals heterojunction using an excitation light source with a photon energy greater than the light emission band gap of the first two-dimensional monolayer material and / or the second two-dimensional monolayer material, so that the second two-dimensional monolayer material in the stacked region is selectively removed by the reaction to integrate and splice the first two-dimensional monolayer material and the second two-dimensional monolayer material in the same plane.

[0009] In one or more embodiments, the first two-dimensional monolayer material is made of molybdenum sulfide, tungsten sulfide, molybdenum selenide or tungsten selenide; and / or the second two-dimensional monolayer material is made of molybdenum sulfide, tungsten sulfide, molybdenum selenide or tungsten selenide.

[0010] In one or more embodiments, the target substrate is a gold substrate, a SiO2 / Si substrate, a sapphire substrate, a quartz substrate, a boron nitride substrate or a graphene substrate.

[0011] In one or more embodiments, the first two-dimensional monolayer material is obtained on the target substrate by physical vapor deposition, chemical vapor deposition or exfoliation; and / or the second two-dimensional monolayer material is obtained by physical vapor deposition, chemical vapor deposition or exfoliation, and is transferred to the first two-dimensional monolayer material using a flexible polymer as an auxiliary substrate to stack the second two-dimensional monolayer material on the first two-dimensional monolayer material to form the van der Waals heterojunction.

[0012] In one or more embodiments, the two-dimensional semiconductor in-plane integration method further comprises: adjusting the interlayer spacing of the first two-dimensional monolayer material and the second two-dimensional monolayer material to enhance the photochemical reaction activity of the second two-dimensional monolayer material in the stacked region.

[0013] In one or more embodiments, the reaction medium of the selective photochemical reaction is a neutral or acidic aqueous solution.

[0014] In one or more embodiments, under the action of the excitation light source, the photo-generated electrons in the second two-dimensional monolayer material in the stacked region are transferred to the first two-dimensional monolayer material to accumulate photo-generated holes in the second two-dimensional monolayer material in the stacked region.

[0015] In one or more embodiments, the first two-dimensional monolayer material is patterned before stacking the second two-dimensional monolayer material.

[0016] In a second aspect, the present application provides a semiconductor device comprising a two-dimensional in-plane spliced material prepared by the two-dimensional semiconductor in-plane integration method as described above.

[0017] Compared with the prior art, the two-dimensional semiconductor in-plane integration method and device provided by the application realizes in-plane splicing of two-dimensional materials by utilizing the difference in electronic state distribution of different two-dimensional materials in the stacking area and the single-layer area, and combining with selective removal of the upper layer material in the stacking area through photochemical reaction. The whole process can be carried out at room temperature, avoiding the limitation of high-temperature process. Meanwhile, through accurate control of the photochemical reaction area, high-precision heterojunction patterning can be directly realized, so that additional micro-nano processing steps are not needed. BRIEF DESCRIPTION OF DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description are only some embodiments described in the application, and for those skilled in the art, other drawings can also be obtained without creative labor on the basis of these drawings.

[0019] Figure 1 The flow chart of the two-dimensional semiconductor in-plane integration method in an embodiment of the application;

[0020] Figure 2 The schematic diagram of constructing WS2-MoS2 in-plane heterojunction by selective photohydrolysis in an embodiment of the application;

[0021] Figure 3 The schematic diagram of in-situ photochemical reaction device in an embodiment of the application;

[0022] Figure 4 The optical image of the WS2 / MoS2 van der Waals heterojunction sample prepared in embodiment 1 of the application;

[0023] Figure 5 The optical image of the WS2-MoS2 in-plane heterojunction sample prepared in embodiment 1 of the application;

[0024] Figure 6 The Raman imaging diagram of the WS2-MoS2 in-plane heterojunction sample prepared in embodiment 1 of the application;

[0025] Figure 7 The fluorescence image at each moment in the photohydrolysis reaction process in embodiment 1 of the application;

[0026] Figure 8 The kinetic curve analysis diagram of the photohydrolysis reaction process in embodiment 1 of the application;

[0027] Figure 9 The optical images of the sample before and after photohydrolysis in the process of preparing WSe2-WS2 in-plane heterojunction in embodiment 2 of the application;

[0028] Figure 10 Optical images of the sample before and after photohydrolysis in the preparation of WSe2-MoSe2 in-plane heterojunction in Example 2 of the present application;

[0029] Figure 11 Optical images of the sample before and after photohydrolysis in the preparation of WSe2-MoS2 in-plane heterojunction in Example 2 of the present application;

[0030] Figure 12 Optical images and Raman imaging images of the WSe2-WS2-MoS2 in-plane heterojunction sample prepared in Example 3 of the present application;

[0031] Figure 13 Surface potential difference (CPD) images and tip-enhanced Raman imaging images of the one-dimensional nanoscale MoS2-WS2NR-MoS2 in-plane superlattice sample prepared in Example 4 of the present application;

[0032] Figure 14 Raman imaging images of the micrometer-scale WS2-MoS2 in-plane heterojunction array prepared in Example 5 of the present application;

[0033] Figure 15 Optical images and fluorescence images of the sample before and after photohydrolysis in the preparation of WS2-MoS2 in-plane heterojunction in Example 6 of the present application;

[0034] Figure 16 Optical images and fluorescence images of the sample before and after photohydrolysis in the preparation of WS2-MoS2 in-plane heterojunction in Example 7 of the present application;

[0035] Figure 17 Electrical performance test images of the in-plane heterojunction electrical device prepared in Example 7 of the present application. DETAILED DESCRIPTION

[0036] In order to enable persons skilled in the art to better understand the technical solutions in the present application, the technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by persons skilled in the art without creative labor should fall within the scope of protection of the present application.

[0037] It is to be understood that all numbers and parameters set forth in the specification and claims are to be understood as approximations because some fabricating, measuring and other errors can occur. Accordingly, unless otherwise indicated, the numerical parameters set forth in the specification and claims are approximations that can vary from the numerical values stated in various reports, articles and other documents. In this application, the suffixes "approximately" and "about" are used as exceptions to the conventional meaning of terms when used in connection with a measurement of a quantity. The terms "approximately" and "about" are used interchangeably herein and refer to quantities that are nearly the same as a true value. Therefore, in some aspects, the numerical parameters set forth in the specification and claims are approximations that can vary from the numerical values stated in various reports, articles and other documents. Unless otherwise indicated, one or more of the numerical parameters set forth in the specification and claims could be an approximation that can vary from the numerical values stated in various documents. Numerical ranges include all numbers and ranges between the numbers inclusive of the numbers. For example, a range from 1 to 10 includes all numbers between 1 and 10, for example, 1, 1.5, 2, 2.75, 3, 3.80, 4, 5, 6.12, 7, 8, 9, 9.95, 10, etc. The summits of the ranges are not included in the ranges. Ranges of numbers ending with a term such as "less than", "greater than", "less than or equal to", "greater than or equal to", "between" and the like include all numbers falling within the range inclusive of the summits of the ranges unless the context clearly indicates otherwise. The phrases "approximately" and "about" can be used to describe values that can vary, preferably, by as much as 10% or more of the stated value, unless otherwise stated. For example, "approximately 25%" can mean values between 22.5% and 27.5% or any other number falling within the range of 10% of 25%.

[0038] The technology of the present application is generated to solve the bottleneck and limitation of the existing two-dimensional material in-plane splicing technology, and can be widely applied to the preparation of two-dimensional in-plane heterojunction. In the design and manufacture of nanomaterials and electronic devices, two-dimensional transition metal dichalcogenide (TMD) as an important material has excellent electrical and optical properties, which can meet the demand of the next generation of high-performance electronic and optoelectronic devices. In-plane heterojunction as a key material structure form can produce new physical effects through the interface interaction between different materials, and is widely used in high-performance optoelectronic devices and integrated circuits. However, the existing heterojunction preparation method usually depends on high-temperature process, crystal face limitation, etc., and it is difficult to realize flexible preparation under low temperature conditions, and it is greatly limited in patterning, material selection and corner freedom.

[0039] In the analysis of the prior art, it can be found that the current heterojunction preparation technology mostly adopts chemical vapor deposition (CVD) or other vapor deposition methods, which usually need to be carried out at a high temperature of 600-1200℃, limiting its compatibility with modern integrated circuit manufacturing process. In addition, since these methods depend on the crystal face structure of the substrate, the growth of the heterojunction is affected by the substrate crystal phase, and the in-plane heterostructure with free corner cannot be realized.

[0040] Transition and metal dichalcogenide (TMD) belongs to a class of two-dimensional materials. The chemical formula is MX2, M refers to transition metal elements (for example: molybdenum, tungsten, niobium, rhenium, titanium), and X refers to chalcogen elements (for example: sulfur, selenium, tellurium). Single-layer transition metal sulfide is a sandwich structure of X-M-X. The interlayer of bulk TMD is connected by weak van der Waals force, while the atoms in the plane are connected by strong covalent bond, so TMD can be peeled into single-layer or multi-layer nanosheet. Many TMDs exhibit semiconductor properties, and the energy band of multi-layer material is indirect band gap. When peeled into single layer, the energy band structure changes to direct band gap.

[0041] An in-plane heterojunction refers to a structure formed by seamlessly connecting two or more different materials in the same plane. This structure is different from the traditional vertically stacked van der Waals heterojunction, as it involves direct chemical bonding between different materials within the same plane. In-plane heterojunctions have a wide range of applications in electronic devices, optics and optoelectronic applications, and quantum technology. The research and development of in-plane heterojunctions are at the forefront of materials science and nanotechnology, opening up new possibilities for material performance control and new device design by precisely controlling material combinations and interfaces.

[0042] Two-dimensional monolayer semiconductor materials represented by transition metal dichalcogenides (TMDs), such as WS2 (tungsten sulfide), WSe2 (tungsten selenide), MoS2 (molybdenum sulfide), MoSe2 (molybdenum selenide), etc., have important applications in thin film transistors, large-scale field effect transistors (FETs), flexible electronic products, complementary metal oxide semiconductor (CMOS) logic, optical emitters, photodetectors, and light collection devices, etc. due to their tunable band gap and excellent electrical and optical properties.

[0043] Compared with traditional silicon-based and germanium-based semiconductors, TMDs can maintain high carrier mobility at atomic thickness (<1 nm), making them one of the most competitive candidate channel materials in the post-Moore era. Two or more TMD monolayers can be assembled in the horizontal direction to form an in-plane heterojunction. In the heterojunction, the characteristics of each monolayer component are maintained, and the electrons of each monolayer component are exposed to the heterojunction interface and interact with each other, resulting in many novel exciton physics and photoelectric synergistic effects. This makes them have great application value and potential in new functional devices (such as photodetectors, light-emitting diodes, photovoltaic cells, artificial superlattice devices, valley electron transistors, etc.) and integrated circuit industries.

[0044] Based on in-depth analysis of the aforementioned fields, the present application proposes a two-dimensional semiconductor in-plane integration method based on selective photochemical reaction (such as photohydrolysis). This method takes advantage of the difference in electronic state distribution between different two-dimensional materials in the stacking region and the monolayer region, and selectively removes the upper layer material in the stacking region through photochemical reaction, achieving in-plane splicing of two-dimensional materials and being applicable to the construction of two-dimensional in-plane heterojunctions.

[0045] Moreover, the entire process can be carried out at room temperature, avoiding the limitations of high-temperature processes. At the same time, by precisely controlling the photochemical reaction area, high-precision heterojunction patterning can be directly realized, eliminating the need for additional micro-nano processing steps. This method breaks through the limitations of existing technologies in terms of temperature, material selection, and patterning, and can improve the freedom of material selection and twist angle design, providing a mild, flexible, and highly controllable technical means for the preparation of two-dimensional in-plane heterojunctions.

[0046] Referring to Figure 1 FIG. 1 shows a flowchart of a two-dimensional semiconductor in-plane integration method according to an embodiment of the present application. The two-dimensional semiconductor in-plane integration method specifically includes the following steps:

[0047] S101: Provide a first two-dimensional monolayer material and place it on a target substrate.

[0048] It should be noted that in order to successfully place the two-dimensional material on the target substrate, an appropriate target substrate material can be selected. The selection of the target substrate affects the transfer effect and stability of the two-dimensional material. The optional substrate materials include gold substrate, SiO2 / Si substrate, sapphire substrate, quartz substrate, boron nitride substrate, graphene substrate, etc. These substrates have good flatness and chemical stability, and can provide good support for two-dimensional materials.

[0049] The gold substrate, as a metal material with excellent electrical conductivity, can be used for the preparation of optoelectronic and electronic devices. Gold has good chemical inertness and excellent electrical properties, and can form a stable van der Waals heterojunction with a variety of two-dimensional materials. For example, in a photodetector or a nano-electronic device, two-dimensional semiconductor materials such as MoS2 or WS2 can be stacked on a gold substrate, which can utilize the high electrical conductivity of gold as an electrode material to ensure high transmission performance of the device. At the same time, the optical properties of the gold substrate also make it have advantages in optical applications, such as enhancing the light absorption or emission efficiency of two-dimensional materials.

[0050] The SiO2 / Si substrate is the carrier of silicon-based integrated circuits, which provides good mechanical stability and chemical inertness, and the SiO2 layer acts as an insulating layer to help control the electronic properties of the material. In two-dimensional material research, the SiO2 / Si substrate can be used to build field effect transistors (FETs), which can isolate electrons through the SiO2 layer to form a current switching effect. For example, when preparing a MoS2-based FET device, the MoS2 monolayer material is transferred to the SiO2 / Si substrate, which can use the Si substrate as a back gate electrode to achieve precise control of the electron transport channel.

[0051] The graphene substrate is a structure based on the combination of a graphene layer with copper, SiO2 / Si, quartz, sapphire substrate. Graphene, as a two-dimensional material, has unique electrical conductivity and mechanical flexibility, making it a popular candidate material for the next generation of electronic devices. In the graphene substrate, the graphene layer can be grown on the copper, SiO2 / Si, quartz, sapphire substrate through chemical vapor deposition (CVD), and the lower substrate provides high thermal conductivity and stable substrate structure, while the graphene layer can be used as a support layer or as an electron transport layer for two-dimensional materials. For example, in the construction of high-performance optoelectronic devices, the graphene layer can be used as a transparent electrode or a charge transport layer, which can utilize its excellent electrical conductivity and transparency to improve the photoelectric conversion efficiency of the device.

[0052] The material of the first two-dimensional monolayer material can be selected from transition metal dichalcogenides (TMDs), such as molybdenum disulfide (MoS2), tungsten disulfide (WS2), molybdenum diselenide (MoSe2), and tungsten diselenide (WSe2), etc. These materials are selected as the two-dimensional monolayer material mainly because their excellent properties match the construction method of two-dimensional materials, and can play an outstanding function in different application scenarios.

[0053] MoS2 has good semiconductor properties. In the monolayer state, MoS2 exhibits direct band gap characteristics, enabling it to exhibit high light absorption and emission capabilities in optoelectronic devices (such as photodetectors and light-emitting diodes). In addition, MoS2 has high electron mobility and excellent conductive performance in field effect transistors (FETs). As the first two-dimensional monolayer material, MoS2 can provide a solid foundation for heterojunctions, and through stacking with the second layer material, more abundant electronic and optical properties can be achieved.

[0054] WS2 is a material with a relatively high band gap, which not only has excellent photoelectric response, but also has high thermal stability and mechanical strength under extreme conditions. MoSe2 has high photoelectric conversion efficiency, and its band gap can be adjusted by stress and layer number, so it also has wide application in flexible electronic devices. These materials as the first two-dimensional monolayer material can form van der Waals heterojunctions through stacking with the second layer material.

[0055] WSe2 has a direct band gap characteristic, which can form an efficient heterojunction with other TMD materials, especially in photovoltaic devices and light-emitting devices. Due to its high carrier mobility and low surface recombination rate, WSe2 can greatly improve the efficiency of the device. In the construction of in-plane heterojunctions, WSe2 can optimize the photoelectric performance when stacked with other materials such as MoS2 or WS2, especially having a significant impact on exciton physics and charge transfer.

[0056] In an exemplary embodiment, the first two-dimensional monolayer material is provided and placed on a target substrate, and the implementation specifically includes: obtaining the first two-dimensional monolayer material on the target substrate by physical vapor deposition, chemical vapor deposition or exfoliation method.

[0057] For example, a flexible polymer can be used as an auxiliary substrate to obtain the first two-dimensional monolayer material by mechanical exfoliation method, and the first two-dimensional monolayer material is transferred from the flexible polymer auxiliary substrate to the target substrate by combining a two-dimensional material transfer platform.

[0058] For example, polydimethylsiloxane (PDMS), a hydrophobic type of silicone material, is also known as dimethicone. PDMS is commonly used as an auxiliary substrate to assist in transferring two-dimensional materials to other substrates due to its mechanical softness and stretchability, which allow it to make good contact with thin and fragile two-dimensional materials without causing damage.

[0059] The use of PDMS as an auxiliary substrate is mainly due to its mechanical flexibility and good elasticity, which can effectively make seamless contact with two-dimensional materials, avoiding the problem of stress concentration in the transfer process of hard substrates. When the two-dimensional material is mechanically peeled off, the PDMS wraps the material through its flexibility and fully adheres to the surface of the material under the action of appropriate external force. This adhesion ensures that the material will not crack or break due to the mismatch between the substrates.

[0060] In the mechanical peeling process, the material is peeled off by applying appropriate external force. Taking MoS2 as an example, the interlayer of this material is combined by van der Waals force, which makes them can be separated into single layer or a few layers by mechanical peeling method. In operation, first place the PDMS on the material surface, adhere the PDMS to the material surface by slight pressure, and then gently lift the PDMS with a mechanical peeling device to take away the two-dimensional material.

[0061] After the material is peeled off, the two-dimensional material is attached to the surface of the PDMS. In order to finally transfer it to the target substrate, a two-dimensional material transfer platform can be used. The design of the transfer platform combines precise temperature control and mechanical control to ensure that the material will not be disturbed by excessive physical interference during the transfer process.

[0062] During the transfer process, the PDMS is adhered to the target substrate, and by adjusting the heating temperature of the platform (for example, it can be controlled at about 80°C) and keeping it for a certain period of time (such as 10 minutes), the flexibility and adhesion of the PDMS material will change, so that the two-dimensional material can be smoothly transferred from the PDMS surface to the target substrate. The control of temperature in this process can ensure the stability of the two-dimensional material and make the PDMS material maintain good elasticity, avoiding damage to the material.

[0063] S102: Stack a second two-dimensional single-layer material on the first two-dimensional single-layer material to form a van der Waals heterojunction comprising a stacked region and a single-layer region.

[0064] It should be noted that the second two-dimensional single-layer material is different in material from the first two-dimensional single-layer material, and the material thereof can be selected from transition metal dichalcogenides (TMD). The valence band top of the second two-dimensional single-layer material is higher than the valence band top of the first two-dimensional single-layer material.

[0065] A van der Waals heterojunction is a multilayer structure composed of different two-dimensional material layers combined by van der Waals forces. The characteristic of this structure is that there is no chemical bonding between the layers, only van der Waals forces (i.e. weak intermolecular attraction) interaction. This allows the manufacture of new material systems by precisely stacking two-dimensional materials of different properties to achieve or optimize electronic, optical and mechanical properties. Van der Waals heterojunctions both retain the inherent properties of the individual materials and introduce unique electronic and optical behavior at the interface. A van der Waals heterojunction includes a stacking region (heterojunction region) and a single-layer region, and the stacking region described in the present invention refers to the region where the upper and lower two layers of single-layer materials overlap, and the single-layer region refers to the region without overlap.

[0066] In a two-dimensional single-layer van der Waals heterojunction, due to the atomic-level thickness of the two-dimensional single-layer, the electrons are exposed to the surface and interact at the interface, resulting in differences in the electronic state distribution of the heterojunction double-layer region and the single-layer region, ultimately leading to different chemical activities. By adjusting the interlayer distance between the two single-layer components, the photochemical reaction activity of the upper layer material in the heterojunction region can be made higher.

[0067] In an exemplary embodiment, the second two-dimensional single-layer material can be obtained by physical vapor deposition, chemical vapor deposition or exfoliation method, and a flexible polymer is used as an auxiliary substrate to transfer the second two-dimensional single-layer material to the first two-dimensional single-layer material, so that the second two-dimensional single-layer material is partially stacked on the first two-dimensional single-layer material to form a van der Waals heterojunction.

[0068] For example, PDMS can be used as an auxiliary substrate to extract the second two-dimensional single-layer material from the original substrate by mechanical exfoliation method, and stack it on the first layer material through a two-dimensional material transfer platform. In this process, part of the second two-dimensional single-layer material overlaps with the first two-dimensional single-layer material to form a stacking region, while the remaining part remains as a single-layer region. This structure design allows the two materials to produce a heterojunction effect in the stacking region, while maintaining the individual properties of each material in the single-layer region.

[0069] In specific operations, the stacking position, area and angle of the two-dimensional material can be adjusted according to actual application requirements. By precisely aligning and controlling the size of the stacking region, different types of in-plane heterostructures can be achieved.

[0070] In an exemplary embodiment, during the transfer process, the interlayer distance of the first two-dimensional single-layer material and the second two-dimensional single-layer material is adjusted by the heating function of the two-dimensional material transfer platform to enhance the photochemical reaction activity of the second two-dimensional single-layer material in the stacking region.

[0071] The interlayer spacing between two-dimensional materials has a significant impact on their electronic structure and physical and chemical properties. In van der Waals heterojunctions, the van der Waals force between materials is weak, so regulating the interlayer spacing can effectively affect the electronic interaction between layers, especially in photochemical reactions, where the transfer behavior of electrons and holes between layers is significantly affected by changes in spacing. By precisely controlling the interlayer spacing through a heating platform, the electronic state of the material can be optimized, resulting in enhanced photochemical reactivity of the upper material in the stacking region.

[0072] In specific operations, when two-dimensional materials are stacked together to form a van der Waals heterojunction, the spacing between the materials is not fixed. By using the heating function of the two-dimensional material transfer platform, this spacing can be precisely adjusted. Typically, by heating the platform to a moderate temperature range (e.g., 80°C), thermal expansion or surface energy adjustment of the materials can be induced, thereby changing the van der Waals force between the materials. This heating process does not destroy the layered structure of the materials, but it does have a slight impact on the physical state of the materials.

[0073] The use of a heating platform allows for fine-tuned control through gentle thermal treatment without affecting the structural integrity of the materials. Unlike traditional mechanical control methods, thermal control can more uniformly and controllably change the interlayer spacing, avoiding potential mechanical damage to the materials during operation.

[0074] S103: Using an excitation light source with photon energy greater than the luminescence band gap of the first or second two-dimensional monolayer material, the van der Waals heterojunction is subjected to selective photochemical reaction, causing the second two-dimensional monolayer material in the stacking region to be selectively removed by reaction, thereby integrating and splicing the first and second two-dimensional monolayer materials in the same plane.

[0075] To initiate a photochemical reaction, the photon energy of the selected light source must be greater than the luminescence band gap of at least one of the stacked materials. For example, for transition metal dichalcogenides (TMDs) such as MoS2 or WS2, the band gap of monolayer materials is typically between 1.2 and 2.1 electron volts, so a light source with a wavelength around 530 nm can be used to excite electron transitions in these materials. In this case, a power-adjustable laser or mercury lamp is typically used as the excitation light source, and by precisely controlling the photon energy, it can be ensured that photochemical reactions only occur in the stacking region.

[0076] When the energy of the photons is greater than the bandgap of the stacked material, the illumination will induce the transition of electrons from the valence band to the conduction band. At this time, the electrons will leave a hole after jumping from the valence band, and the electrons will enter the conduction band and conduct in the material. The holes are left in the valence band, and they can participate in oxidation reactions, so the distribution of holes is directly related to the photochemical reactivity of the material. In a single-layer material, holes accumulate locally in the valence band inside the material, but due to the absence of charge transfer processes, the holes in the single-layer material are relatively stable and do not induce significant photochemical reactions.

[0077] However, in the double-layer region, the situation is different. The stacked double-layer material usually has different valence band structures, especially in the heterojunction, the valence band top of the upper layer material is often higher than that of the lower layer material. Because the holes tend to transfer to the material with a higher valence band top, the charge distribution in the double-layer region becomes asymmetric. Specifically, the holes will transfer from the material with a lower valence band (such as the lower layer of MoS2) to the material with a higher valence band (such as the upper layer of WS2). This transfer process significantly increases the hole density of the upper layer material, resulting in a significant increase in the photochemical reactivity of the upper layer material, thereby inducing photochemical reactions.

[0078] This hole accumulation effect is the key to the photochemical reaction in the double-layer region. In the stacked region, the hole density of the upper layer material is much higher than that of the lower layer material, so the chemical reaction activity of the upper layer material is greatly enhanced. In the photochemical reaction, the holes will react with the surrounding water molecules, causing the upper layer material to be oxidized into water-soluble products (such as molybdate or tungstate), which are then hydrolyzed and removed from the material surface. In this way, the upper layer material in the stacked region is selectively removed, while the lower layer material remains intact.

[0079] Through this mechanism, the difference in electronic state distribution between the double-layer and single-layer regions makes the selective photochemical reaction highly selective. Specifically, only in the double-layer region, due to the transfer and accumulation of holes, the upper layer material will undergo photochemical reactions. This reaction spontaneously stops at the material boundary, ensuring the precise boundary of the material after being partially removed, thereby forming a heterojunction structure in the double-layer region, while the other unstacked regions remain intact.

[0080] The selective photochemical reaction in the present application is a self-terminating photochemical reaction process, which is based on the charge transfer mechanism between different two-dimensional materials in the stacked region, and the difference in electronic state distribution between the double-layer and single-layer regions. At the beginning of the selective photochemical reaction, a light source with an energy greater than the bandgap of the second two-dimensional single-layer material (upper layer) and / or the first two-dimensional single-layer material (lower layer) is used to irradiate the stacked region.

[0081] Please refer to Figure 2As shown, in the WS2-MoS2 van der Waals heterojunction, WS2 serves as the upper layer material and MoS2 as the lower layer material. Upon photoexcitation, electrons in the upper layer WS2 are excited to the conduction band, forming electron-hole pairs. Due to the band difference in the heterojunction region, the conduction and valence bands of WS2 and MoS2 are located differently. Electrons are more likely to transfer from the conduction band of WS2 to the lower layer MoS2, while holes remain in the upper layer WS2. As the photoexcitation time increases, holes gradually accumulate in WS2, leading to an increase in its chemical reactivity.

[0082] The accumulation of holes makes the upper layer material of WS2 extremely active, enabling it to undergo an oxidation reaction with water molecules in the reaction medium, such as ultrapure water or dilute sulfuric acid solution. Specifically, holes react with oxygen atoms in water molecules, gradually oxidizing WS2 into water-soluble tungsten acid.

[0083] As the photochemical reaction progresses, the upper layer material of WS2 is gradually removed from the edges. When the photochemical reaction reaches the boundary of the stacking region, i.e., the hydrolysis of WS2 progresses to the edge of the lower layer MoS2, the reaction spontaneously stops. This is because the boundary of the upper and lower layer materials is coupled, and the accumulated holes in the upper layer material WS2 meet the electrons in the lower layer material MoS2 at the boundary, forming a charge binding. This charge binding effect prevents further accumulation of holes and blocks the continuation of the hydrolysis reaction. After the reaction is complete, the sample is dried with nitrogen, and an in-plane heterojunction sample with the upper and lower single-layer materials spliced together is obtained.

[0084] Repeating the above steps S102 and S103, other two-dimensional single-layer materials are sequentially transferred and subjected to selective photochemical reaction, enabling the construction of a multi-element two-dimensional in-plane splicing material containing multiple interfaces.

[0085] The first two-dimensional single-layer material or the second two-dimensional single-layer material can be a single-component two-dimensional material or a multi-component splicing two-dimensional material. A single-component two-dimensional material refers to a two-dimensional structure composed of a specific material. Common single-component two-dimensional materials include transition metal dichalcogenides (TMDs), such as molybdenum sulfide, tungsten sulfide, and molybdenum selenide. A multi-component splicing two-dimensional material refers to a material formed by splicing two or more different two-dimensional materials. This splicing can be performed on the same plane through the aforementioned method or other methods to form an in-plane heterojunction. The advantage of multi-component splicing materials lies in their ability to combine the characteristics of different materials, achieving synergistic optimization in functionality. For example, by splicing materials with different band gaps, a heterostructure with superior optoelectronic performance can be constructed.

[0086] In an exemplary embodiment, the first two-dimensional monolayer material can be patterned before stacking the second two-dimensional monolayer material. The purpose of patterning is to selectively treat the first layer material with a pre-designed geometry or pattern, forming specific patterns or structures, so as to achieve the desired functional effect when stacking the second layer material.

[0087] The purpose of patterning is to provide a customized structural basis for the preparation of stacked heterojunctions. By patterning the first layer material, the arrangement and layout of the material in the subsequent stacking process can be precisely controlled. This precise control not only affects the geometry of the material, but also regulates the physical and chemical properties of the material. For example, patterning can form specific channels, interfaces or functional areas, thereby providing the possibility for functional optimization of heterojunctions in electronic or optoelectronic devices.

[0088] The heterostructure building process in the present application does not rely on synchronous growth technology, but is achieved by mechanical exfoliation and transfer stacking of two-dimensional materials. In operation, the first two-dimensional monolayer material (such as MoS2) is exfoliated and transferred to a substrate, and then the second two-dimensional monolayer material (such as WS2) is partially stacked on the first layer material by the same exfoliation and transfer steps. Since the transfer stacking is a physical process, the operator can precisely control the angle of the second layer material relative to the first layer material when transferring the second layer material, and can freely adjust the twist angle between the two layers of material.

[0089] After stacking two-dimensional monolayer materials with different twist angles, the upper layer material (which is more active in photochemical reaction) in the stacked area can be selectively removed by selective photochemical reaction. Since the upper layer material in the stacked area is removed, the originally stacked area becomes a direct splicing of two different materials in the same plane, forming an in-plane heterojunction. Since the twist angle between the two materials has been set during stacking, the newly formed in-plane heterojunction interface naturally has this twist angle.

[0090] Traditional CVD methods usually cannot achieve the regulation of twist angle between layers due to the limitation of lattice matching requirements of the growth substrate. However, the two-dimensional material transfer platform in the present application can artificially regulate the stacking angle, so that different twist angles can be generated between the upper layer material and the lower layer material.

[0091] The present application also provides a semiconductor device comprising the two-dimensional in-plane splicing material prepared by the aforementioned two-dimensional semiconductor in-plane integration method.

[0092] The present application will be further described in conjunction with specific embodiments.

[0093] The application selects four kinds of transition metal chalcogenide (TMD) monolayers: molybdenum sulfide (MoS2), tungsten sulfide (WS2), molybdenum selenide (MoSe2), and tungsten selenide (WSe2) two-dimensional monolayer materials.

[0094] The specific preparation process is as follows:

[0095] (1) Obtain the TMD monolayer on the PDMS substrate by the method of mechanical exfoliation.

[0096] (2) Transfer the TMD monolayer material to the flat gold substrate by combining the two-dimensional material transfer platform. After the sample is attached to the substrate, the heating temperature of the transfer platform is set to 80℃, and after being kept for 10 min, the PDMS is lifted by the transfer platform, so that the monolayer on the PDMS is transferred to the target substrate.

[0097] (3) Align the second layer of TMD monolayer material according to the requirement, and then attach it to the first layer of monolayer. Then, the heating temperature of the transfer platform is set to 80℃, and after being kept for 13 min, the PDMS is lifted by the transfer platform. At this time, the second layer of monolayer is stacked on the first layer of monolayer, so as to obtain a weakly coupled van der Waals heterojunction sample.

[0098] The photolysis reaction is carried out under a fluorescence microscope equipped with a high-sensitivity scientific-grade camera, and the dynamic changes of the reaction process are observed in situ. The experimental device is as shown in Figure 3 The photolysis experiment steps include:

[0099] (1) One end of the PDMS is attached to the stage of the microscope, and the other end is used to fix the substrate with the sample attached.

[0100] (2) A drop of ultrapure water is dropped on the sample, and a cover glass is placed on it. In order to offset the influence of the cover glass on imaging, an objective lens with a correction ring can be selected to optimize the imaging quality.

[0101] (3) The whole system is placed under the fluorescence microscope, and a power-adjustable mercury lamp or other light with energy greater than the band gap energy of the TMD monolayer material is used as the excitation light source to irradiate the van der Waals heterojunction sample, so that the sample performs selective photolysis reaction. The image of the sample is recorded and collected by a high-speed S-CMOS camera after passing through a long-pass filter, so as to obtain the dynamic fluorescence image or video of the heterojunction sample during the photolysis process. After the reaction is completed, the sample is dried by nitrogen, and the in-plane heterojunction sample with the upper and lower two monolayer materials spliced together is obtained.

[0102] Example 1

[0103] The WS2 / MoS2 weakly coupled van der Waals heterojunction sample is prepared by the foregoing method (as shown in Figure 4(As shown), then a photohydrolysis experiment was performed to compare the results before and after hydrolysis (as shown). Figure 5 As shown in the optical photograph, the heterojunction bilayer region after hydrolysis ( Figure 5 The contrast of the area within the dashed box in the image is reduced to the contrast of a single layer, combined with the Raman imaging of the sample (e.g., Figure 6 As shown in the figure, the formation of the WS2-MoS2 in-plane heterostructure was demonstrated.

[0104] Fluorescence microscopy can record fluorescence images of the sample at various moments during the reaction process in Example 1, thereby enabling the analysis of information on the photohydrolysis reaction kinetics. Figure 7 As can be seen, the photohydrolysis reaction starts from the edge of the upper WS2 heterojunction region. This can be observed by extracting the perimeter of the reactants (WS2 monolayer in the stacked region) over time (e.g., [image of the curve showing the change in perimeter over time]). Figure 8 As shown in the figure, the results indicate that the perimeter of the reactants decreases linearly with time, meaning that the photohydrolysis reaction in this selected area is a zero-order reaction.

[0105] Example 2

[0106] WSe2 / WS2, WSe2 / MoSe2, and WSe2 / MoS2 van der Waals heterostructures were prepared using the aforementioned method, and then subjected to photohydrolysis. Optical photographs before and after hydrolysis were compared (e.g., ...). Figure 9 , Figure 10 and Figure 11 As shown in the figure, it is demonstrated that WSe2-WS2, WSe2-MoSe2, and WSe2-MoS2 in-plane heterojunctions were successfully constructed through selected area photohydrolysis reaction.

[0107] Example 3

[0108] MoS2, WS2, and WSe2 monolayers on a PDMS substrate were obtained by mechanical exfoliation.

[0109] A two-dimensional material transfer platform was used to transfer a MoS2 monolayer onto a flat gold substrate. After the sample was attached to the substrate, the heating temperature of the transfer platform was set to 80°C and maintained for 10 minutes. Then, the PDMS was lifted using the transfer platform, and the MoS2 monolayer on the PDMS was transferred to the target substrate.

[0110] The WS2 monolayer was stacked onto the MoS2 monolayer using the same method. Then, the heating temperature of the transfer platform was set to 80°C and held for 13 minutes. The PDMS was then lifted using the transfer platform to obtain a WS2 / MoS2 weakly coupled van der Waals heterojunction sample.

[0111] Selective photohydrolysis was performed on a WS2 / MoS2 weakly coupled van der Waals heterojunction sample to obtain a WS2-MoS2 in-plane heterojunction.

[0112] WSe2 monolayer was stacked on WS2-MoS2 in-plane heterojunction, and the interface boundary of WS2 and MoS2, one edge of WS2 and one edge of MoS2 were simultaneously partially covered by WSe2 monolayer. After lamination, the heating temperature of the transfer platform was set to 80℃, and after 13 min, the PDMS was lifted by the transfer platform, and the weakly coupled van der Waals heterojunction samples of WS2 / WSe2 and MoS2 / WSe2 were obtained.

[0113] The above heterojunction samples were subjected to selective photohydrolysis reaction, and WSe2-WS2-MoS2 in-plane heterojunction with three different interface boundaries (WSe2-WS2, WSe2-MoS2, WS2-MoS2) and three boundaries intersecting at a point was obtained, as shown in Figure 12 .

[0114] Example 4

[0115] Combined with electron beam exposure technology and plasma etching technology, MoS2 monolayer on the gold substrate was etched into a one-dimensional array composed of MoS2 nanogap with a width of 180 nm. Then a layer of monolayer WS2 was stacked on it using it as a template to obtain a weakly coupled WS2 / MoS2 van der Waals heterojunction, and finally a one-dimensional nanoscale MoS2-WS2 NR-MoS2 in-plane superlattice was constructed by selective photohydrolysis reaction, as shown in Figure 13 .

[0116] Example 5

[0117] Combined with electron beam exposure technology and plasma etching technology, MoS2 monolayer on the gold substrate was etched into a two-dimensional array composed of MoS2 square holes with a side length of 20 μm. Then a layer of monolayer WS2 was stacked on it using it as a template to obtain a weakly coupled WS2 / MoS2 van der Waals heterojunction, and finally a millimeter-scale WS2-MoS2 in-plane heterojunction array was constructed by selective photohydrolysis reaction, as shown in Figure 14 .

[0118] Example 6

[0119] A weakly coupled van der Waals WS2 / MoS2 heterojunction was prepared on a graphene / Cu substrate using the aforementioned method, and then subjected to selective photohydrolysis reaction. The optical and fluorescence photos before and after hydrolysis proved the successful preparation of WS2-MoS2 in-plane heterojunction, as shown in Figure 15 .

[0120] Example 7

[0121] The weakly coupled van der Waals WS2 / MoS2 heterojunction is prepared on a SiO2 / Si substrate by the foregoing method, and then a selective photohydrolysis reaction is performed on the weakly coupled van der Waals WS2 / MoS2 heterojunction, and the optical photographs before and after hydrolysis prove the successful preparation of the WS2-MoS2 in-plane heterojunction, as shown in Figure 16 .

[0122] Then, the in-plane heterojunction is made into an electrical device by combining electron beam exposure technology and plasma etching technology, and the I-V curves (as shown in Figure 17 ) of the device under different back gates (V g = 0, 10, 20, 30, 40, 50 V) and different excitation light powers (P laser = 0, 4, 22, 67 muW) prove the feasibility of the in-plane heterojunction prepared by the selective photohydrolysis method in the application of semiconductor devices.

[0123] In summary, the two-dimensional semiconductor in-plane integration method and device provided by the application realizes the in-plane splicing of two-dimensional materials by utilizing the difference in the electronic state distribution of different two-dimensional materials in the stacking region and the single-layer region, combining the selective removal of the upper layer material in the stacking region by photochemical reaction, the whole process can be carried out at room temperature, avoiding the limitation of high-temperature process, and at the same time, by accurately controlling the photochemical reaction area, high-precision heterojunction patterning can be directly realized, so that additional micro-nano processing steps are not needed.

[0124] It is apparent for those skilled in the art that the application is not limited to the details of the foregoing exemplary embodiments, and the application can be implemented in other specific forms without departing from the spirit or essential characteristics of the application. Therefore, the embodiments should be regarded as exemplary and non-limiting, the scope of the application is defined by the appended claims rather than the foregoing description, and all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the application. Any reference signs in the claims should not be regarded as limiting the claims involved.

[0125] In addition, it should be understood that although the present specification is described in terms of embodiments, each embodiment does not contain only one independent technical solution, and the description manner of the specification is only for the sake of clarity, and those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for in-plane integration of two-dimensional semiconductors, characterized in that, include: Provide a first two-dimensional monolayer material and place it on the target substrate; A second two-dimensional monolayer material is partially stacked on the first two-dimensional monolayer material to form a van der Waals heterojunction including a stacked region and a monolayer region. Using an excitation source with photon energy greater than the luminescence bandgap of the first two-dimensional monolayer material and / or the second two-dimensional monolayer material, the van der Waals heterojunction undergoes a selective photochemical reaction, causing the second two-dimensional monolayer material in the stacked region to be selectively removed, thereby integrating and splicing the first two-dimensional monolayer material and the second two-dimensional monolayer material in the same plane.

2. The two-dimensional semiconductor in-plane integration method according to claim 1, characterized in that, The first two-dimensional monolayer material is made of molybdenum sulfide, tungsten sulfide, molybdenum selenide, or tungsten selenide; and / or The second two-dimensional monolayer material is made of molybdenum sulfide, tungsten sulfide, molybdenum selenide, or tungsten selenide.

3. The two-dimensional semiconductor in-plane integration method according to claim 1, characterized in that, The target substrate is a gold substrate, a SiO2 / Si substrate, a sapphire substrate, a quartz substrate, a boron nitride substrate, or a graphene substrate.

4. The two-dimensional semiconductor in-plane integration method according to claim 1, characterized in that, A first two-dimensional monolayer material is obtained on the target substrate using physical vapor deposition, chemical vapor deposition, or exfoliation; and / or A second two-dimensional monolayer material is obtained by physical vapor deposition, chemical vapor deposition, or exfoliation. A flexible polymer is used as an auxiliary substrate to transfer the second two-dimensional monolayer material onto the first two-dimensional monolayer material, so that the second two-dimensional monolayer material is partially stacked on the first two-dimensional monolayer material to form a van der Waals heterojunction.

5. The two-dimensional semiconductor in-plane integration method according to claim 4, characterized in that, The two-dimensional semiconductor in-plane integration method further includes: The interlayer spacing between the first two-dimensional monolayer material and the second two-dimensional monolayer material is adjusted to enhance the photochemical reactivity of the second two-dimensional monolayer material in the stacked region.

6. The two-dimensional semiconductor in-plane integration method according to claim 1, characterized in that, The reaction medium for the selected area photochemical reaction is a neutral or acidic aqueous solution.

7. The two-dimensional semiconductor in-plane integration method according to claim 1, characterized in that, Under the action of the excitation light source, photogenerated electrons in the second two-dimensional monolayer material of the stacked region are transferred to the first two-dimensional monolayer material, so that the second two-dimensional monolayer material of the stacked region accumulates photogenerated holes.

8. The two-dimensional semiconductor in-plane integration method according to claim 1, characterized in that, Before stacking the second two-dimensional monolayer material, the first two-dimensional monolayer material is patterned.

9. The two-dimensional semiconductor in-plane integration method according to claim 1, characterized in that, The first or second two-dimensional monolayer material is a single-component two-dimensional material or a multi-component spliced ​​two-dimensional material.

10. A semiconductor device, characterized in that, Includes two-dimensional in-plane splicing materials prepared by the two-dimensional semiconductor in-plane integration method as described in any one of claims 1 to 9.

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