Heterojunction with liquid-liquid interface in-situ growth and preparation method thereof

Abstract

The invention provides a liquid-liquid interface in-situ growth heterojunction and a preparation method thereof, and belongs to the technical field of semiconductor thin film materials. Gallium atoms on the surface of liquid metal gallium react with oxygen in the atmospheric environment to generate an amorphous gallium oxide thin film; then putting the gallium oxide thin film into a metal nitrate and hexamethylenetetramine precursor solution which is prepared in advance, and growing a layer of metal oxide on the gallium oxide thin film in situ through chemical bath deposition to form a heterojunction; a gallium oxide thin film is formed on the surface of liquid metal gallium to serve as a growth substrate, then metal oxide grows on the gallium oxide thin film in situ, cleanliness and high quality of a heterojunction interface are ensured, the high-quality interface is beneficial to reducing interface defects, and therefore the overall performance of a heterojunction device is improved; in the preparation process, the in-situ growth of the metal oxide on the gallium oxide film can be realized without expensive instruments and strict growth environment, and the method has the characteristics of simplicity in operation, economy and wide application range.

Description

Technical Field

[0001] The invention relates to the technical field of semiconductor thin film materials, and in particular to a liquid-liquid interface in-situ grown heterojunction and a preparation method thereof. Background Art

[0002] In the semiconductor field, heterojunction is an important structure, which is usually used to manufacture high-performance solar cells, photodetectors and photocatalytic materials. People have studied many methods for preparing heterojunctions, such as physical vapor deposition (PVD), chemical vapor deposition (CVD) and molecular beam epitaxy (MBE), but these methods are often costly and have strict requirements on equipment, and are not suitable for large-scale production.

[0003] In recent years, a method called Van der Waals printing technology has emerged to prepare two-dimensional semiconductor films. Although this method can produce high-quality films at a very low cost, the only way to use this method to prepare heterojunctions is to rely on van der Waals forces to stack multiple layers of films to form a van der Waals heterojunction. Therefore, during the stacking process, due to the lattice mismatch between the materials, defects and dislocations will be formed at the heterojunction interface, causing carriers to be scattered at the junction interface, thereby reducing carrier mobility and affecting the electronic transmission performance and overall efficiency of the device.

[0004] An article titled "Liquid metal gallium-based printing of Cu-doped p-type Ga2O3semiconductor and Ga2O3 homojunction diodes" prepared a gallium oxide homojunction by printing n-Ga2O3 and copper-doped p-Ga2O3 using van der Waals printing technology, and deposited Au electrodes on the prepared homojunction to make a high-power diode. Although the gallium oxide diode prepared in this article has good performance, it still cannot avoid the impact of lattice mismatch because its interface is van der Waals contact. Summary of the invention

[0005] The purpose of the present invention is to provide a liquid-liquid interface in-situ grown heterojunction and a preparation method thereof, so as to overcome the problems existing in the prior art. The present invention utilizes gallium atoms on the surface of liquid metal gallium to react with oxygen in the atmosphere to generate an amorphous gallium oxide film, and then puts the amorphous gallium oxide film into a metal nitrate and hexamethylenetetramine precursor solution prepared in advance, and in-situ grows a layer of metal oxide, such as zinc oxide (ZnO), copper oxide (CuO), cerium oxide (CeO2) and titanium dioxide (TiO2) on the gallium oxide film through chemical bath deposition (CBD) to form a heterojunction; the preparation process of the present invention does not require expensive instruments and a strict growth environment, and can realize the in-situ growth of metal oxides on the gallium oxide film, and has the characteristics of simple operation, economy and wide application range.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is as follows: A method for preparing a heterojunction grown in situ at a liquid-liquid interface comprises the following steps: (1) Dropping photoresist onto the pretreated substrate, spinning it evenly on a spin coating device and drying it, then dropping liquid metal gallium, and after forming a gallium oxide film A, peeling off the gallium oxide film A, and allowing it to stand to form a gallium oxide film B, thereby obtaining a substrate with metal gallium; (2) immersing the substrate with metal gallium obtained in (1) in a precursor solution and performing a heating reaction to obtain a layer of metal oxide grown in situ on the gallium oxide film B; (3) drying the metal oxide obtained in (2) under an inert gas, absorbing the metal in the metal oxide layer after drying, and then removing the photoresist, flushing with water, and when the surface of the metal oxide is separated from the surface of the substrate, the surface of the metal oxide is picked up from the water with the substrate to obtain a substrate with a heterojunction; (4) etching the substrate with the heterojunction obtained in (3) to obtain an in-situ grown heterojunction; Furthermore, the pretreatment in (1) is specifically as follows: the substrate is ultrasonically treated in acetone, ethanol and deionized water for 10 min respectively, and then dried with nitrogen to obtain a cleaned substrate, and the cleaned substrate is placed in an oxygen plasma cleaning machine for 5 to 10 min at a power of 70 to 90 W; Furthermore, the standing time in (1) is 1 to 2 min; Furthermore, the precursor solution in (2) is a mixed solution of metal nitrate and hexamethylenetetramine; the heating reaction temperature is 60-70°C, and the heating reaction time is 10-60 min; Furthermore, the preparation method of the precursor solution is specifically as follows: weigh hexamethylenetetramine and metal nitrate in a molar ratio of 2:1, pour them into deionized water in turn, stir and dissolve; Furthermore, in said (3), a stripping liquid is used to remove the photoresist; Furthermore, the etching in (4) is specifically as follows: placing the substrate with the heterojunction obtained in (3) into an iodine ion solution and heating it; Furthermore, the iodide ion solution is specifically an ethanol solution of lithium iodide and iodine; wherein the mass ratio of lithium iodide, iodine and ethanol is 1.34:2.54:394.5; Furthermore, the heating is specifically: heating at 60-80°C for 6-8 hours.

[0007] A liquid-liquid interface in-situ grown heterojunction is obtained based on the above-mentioned method for preparing a liquid-liquid interface in-situ grown heterojunction.

[0008] The above technical solution has the following advantages or beneficial effects: The invention provides a method for preparing a heterojunction by in-situ growth at a liquid-liquid interface. By forming a gallium oxide film on the surface of a liquid metal gallium as a growth substrate and then in-situ growing a metal oxide thereon, the cleanliness and high quality of the heterojunction interface are ensured. The high-quality interface helps to reduce interface defects and improve charge transfer efficiency, thereby improving the overall performance of the heterojunction device. The in-situ growth technology enables the metal oxide to grow directly on the gallium oxide film, which helps to achieve good lattice matching, reduces stress and defects caused by lattice mismatch, and helps to improve the stability and reliability of the material. The in-situ growth of the heterojunction is achieved through simple steps such as spin coating, drying, soaking and heating. Compared with the traditional method, no complex equipment and cumbersome process are required, the preparation process is greatly simplified, and the production cost is reduced. By adjusting the components in the precursor solution, the method of the invention can be easily extended to the growth of other metal oxides, providing the possibility for preparing a variety of heterojunction materials. In the preparation process, the materials and solvents used in the invention are mostly environmentally friendly and can be recycled and reused through proper treatment, which helps to reduce environmental pollution and achieve green production.

[0009] Furthermore, ultrasonic cleaning with acetone, ethanol and deionized water can effectively remove organic pollutants, grease and other impurities on the substrate surface, ensuring that the substrate surface is clean and free of contamination; nitrogen drying further prevents secondary contamination of the surface after cleaning and maintains the cleanliness of the substrate; oxygen plasma cleaning treatment can generate high-energy oxygen ions on the substrate surface, which can bombard the substrate surface, remove residual organic and inorganic matter, and at the same time increase the surface roughness and hydrophilicity, making the surface more activated; the activated surface is conducive to the subsequent adhesion of photoresist and the uniform distribution of liquid metal gallium, thereby improving the uniformity and quality of heterojunction growth.

[0010] Furthermore, metal nitrate, as a metal source, can stably decompose under heating conditions to provide the required metal ions, and hexamethylenetetramine (HMTA) acts as a reducing agent and chelating agent to form a complex with the metal ions in the solution, which helps to control the release rate and reaction process of the metal ions. This combination makes the reaction process relatively mild and controllable, which is conducive to the formation of a uniform and high-quality metal oxide film; since the components in the precursor solution can directly react on the gallium oxide film B under heating conditions to form a metal oxide, this in-situ growth method helps to reduce interface contamination and defects and improve the interface quality of the heterojunction; at the same time, since the growth process is carried out on the surface of liquid metal gallium, the metal oxide can be tightly attached to the substrate to form a stable heterojunction structure; compared with other complex growth methods, the in-situ growth method using metal nitrate and HMTA solution as precursor solutions has a faster growth rate, which helps to shorten the preparation cycle, improve production efficiency, and reduce production costs.

[0011] Furthermore, by strictly controlling the molar ratio of hexamethylenetetramine and metal nitrate, the precise proportion of each component in the precursor solution can be ensured, which is beneficial to the uniform generation of metal oxides in subsequent reactions; dissolving the solid raw material in deionized water to form a solution helps to evenly disperse the components in the solution, improve the stability and uniformity of the solution, and help to form a uniform and high-quality metal oxide film.

[0012] Furthermore, the stripping solution is a chemical solvent specially designed for removing photoresist. It can effectively penetrate into the interface between the photoresist and the substrate, weaken the adhesion between them, thereby achieving efficient removal of the photoresist and avoiding damage to the heterojunction structure that may be caused by the use of mechanical methods. Compared with other removal methods that may damage the heterojunction surface, such as dry etching or strong acid and alkali treatment, the stripping solution is usually milder and can reduce physical and chemical damage to the heterojunction structure, helping to maintain the high quality and integrity of the heterojunction.

[0013] Furthermore, the iodine ion solution can selectively react with the metal oxide under heating conditions, thereby achieving the etching of specific components in the heterojunction, which helps to precisely control the structure and morphology of the heterojunction and meet specific device design requirements; compared with other etching methods (such as strong acid and alkali treatment in dry etching or wet etching), the etching process of the iodine ion solution under heating conditions is relatively mild, which helps to reduce physical and chemical damage to the heterojunction structure and maintain its high quality and integrity.

[0014] Furthermore, the ethanol solution of lithium iodide and iodine can form an active substance with strong etching ability under heating conditions. Since the two are mixed and dissolved in ethanol in an equimolar ratio, they can fully react and release sufficient iodide ions, thereby enhancing the etching effect on specific components in the heterojunction, helping to more thoroughly remove unnecessary materials and improve the clarity and accuracy of the heterojunction structure. In the ethanol solution of lithium iodide and iodine with a molar ratio of 1:1, the etching process can be more selectively carried out on the target material and reduce damage to non-target materials. This high selectivity helps to maintain the integrity and performance of the heterojunction structure.

[0015] Furthermore, by setting the heating time to 6 to 8 hours, the extent of the etching reaction can be precisely controlled. Too short a heating time may lead to incomplete etching, while too long a heating time may lead to over-etching or damage the heterojunction structure. This time range helps to achieve precise control of the etching rate and ensure the accuracy and integrity of the heterojunction structure.

[0016] The present invention also provides a liquid-liquid interface in-situ grown heterojunction, which is obtained based on the above-mentioned liquid-liquid interface in-situ grown heterojunction preparation method. The in-situ grown heterojunction preparation method ensures that different material layers are directly combined during the growth process, avoiding the performance degradation caused by interface contamination and defects that may exist in traditional methods. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 The optical microscope image and Raman spectrum of the heterojunction film prepared in Example 1 of the present invention; wherein, Figure 1 (a) is an optical microscope image. Figure 1 (b) is the Raman spectrum; Figure 2 This is a transmission electron microscope image of a single-layer gallium oxide film; Figure 2 (a) is a transmission electron image of a gallium oxide film peeled off from the surface of liquid metal gallium; Figure 2 (b) is the distribution diagram of gallium atoms in the EDS scanning area; Figure 2 (c) is the distribution diagram of oxygen atoms in the EDS scanning area; Figure 2 (d) HRTEM image of gallium oxide film; Figure 2(e) is the selected area electron diffraction image of the gallium oxide film; Figure 3 is a SEM image of the heterojunction film prepared by the present invention; wherein, Figure 3 (a) is a low-magnification SEM image of the heterojunction film prepared in the present invention; Figure 3 (b) is a high-magnification SEM image of the interior of the heterojunction film prepared in the present invention; Figure 3 (c) is a high-magnification SEM image of the boundary of the heterojunction film prepared in the present invention; Figure 3 (d) is a high-magnification SEM image of the boundary of the heterojunction film prepared by the present invention after being etched by an iodine ion solution; Figure 4 The SEM image and EDS spectrum of the heterojunction film prepared by the present invention; wherein, Figure 4 (a) is the SEM image of the EDS spectrum scanning area of ​​the heterojunction film; Figure 4 (b) is the distribution diagram of gallium atoms in the EDS scanning area; Figure 4 (c) is the distribution map of zinc atoms in the EDS scanning area; Figure 4 (d) is the distribution diagram of oxygen atoms in the EDS scanning area; Figure 5 This is the XPS spectrum of the heterojunction film prepared by the present invention; wherein, Figure 5 (a) is the 2p orbital of Zn; Figure 5 (b) is the 3d orbital of Ga; Figure 5 (c) is the 1s orbital of O; Figure 6 HRTEM image of the heterojunction film prepared in the present invention. DETAILED DESCRIPTION

[0017] The present invention is further described in detail below in conjunction with specific embodiments, which are intended to explain the present invention rather than to limit it. In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention. It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0018] The present invention provides a method for preparing a liquid-liquid interface in-situ grown heterojunction, comprising the following steps: (1) Use a pipette to drop photoresist onto the pretreated substrate, rotate it evenly on a spreader and dry it, then drop liquid metal gallium. After gallium oxide film A is formed, use a glass rod to push away the gallium oxide film A to expose a new surface. After standing for 1 to 2 minutes, gallium oxide film B is formed to obtain a substrate with metal gallium. The pretreatment is as follows: the substrate is ultrasonically treated in acetone, ethanol and deionized water for 10 minutes respectively, and then dried with nitrogen to obtain a cleaned substrate. The cleaned substrate is placed in an oxygen plasma cleaning machine and treated at a power of 70-90 W for 5-10 minutes. O2 plasma (oxygen plasma cleaning) treatment can make the surface of the substrate hang with abundant -OH groups, forming a hydrophilic surface, which is conducive to the adhesion of the photoresist to the substrate. (2) placing the substrate with metal gallium obtained in (1) into a clean glass weighing bottle, adding hexamethylenetetramine (HMT) and metal nitrate precursor solution, so that the surface of the metal gallium is completely immersed in the precursor solution, covering the weighing bottle with a cap, placing it on a heating table at 60-70°C for reaction for 10-60 min, and obtaining a layer of metal oxide in situ grown on the gallium oxide film B; The preparation method of the precursor solution is as follows: weigh hexamethylenetetramine and metal nitrate in a molar ratio of 2:1, pour them into deionized water in turn, and stir and dissolve them with a glass rod; (3) drying the metal oxide obtained in (2) under an inert gas, and after drying, using a syringe to absorb the metal in the metal oxide layer, and then removing the photoresist with a stripping solution, and flushing with water, until the surface of the metal oxide is separated from the surface of the substrate, and using a substrate to pick up the surface of the metal oxide from the water, thereby obtaining a substrate with a heterojunction; (4) Placing the substrate with the heterojunction obtained in (3) into an ethanol solution of lithium iodide and iodine, and heating it at 60-80 °C for 6-8 h to etch away the metal gallium remaining on the film to obtain an in-situ grown heterojunction; wherein the mass ratio of lithium iodide, iodine and ethanol solution is 1.34:2.54:394.5.

[0019] The present invention also provides a liquid-liquid interface in-situ grown heterojunction, which is obtained based on the above-mentioned method for preparing a liquid-liquid interface in-situ grown heterojunction.

[0020] Embodiment 1: The present invention provides a method for preparing a liquid-liquid interface in-situ grown heterojunction, comprising the following steps: (1) Use a pipette to drop photoresist onto the pretreated silicon wafer, rotate it evenly on a spreader and dry it, then drop liquid metal gallium. After gallium oxide film A is formed, use a glass rod to push away the gallium oxide film A to expose a new surface. After standing for 1 minute, gallium oxide film B is formed, and a silicon wafer with metal gallium is obtained; The pretreatment is as follows: the silicon wafer is ultrasonicated in acetone, ethanol and deionized water for 10 min respectively, and then dried with nitrogen to obtain a cleaned silicon wafer, and the cleaned silicon wafer is placed in an oxygen plasma cleaning machine and treated at a power of 90 W for 5 min; (2) Place the silicon wafer with metal gallium obtained in (1) into a clean glass weighing bottle, add hexamethylenetetramine (HMT) and zinc nitrate precursor solution, so that the surface of the metal gallium is completely immersed in the precursor solution, cover the weighing bottle with a cap, and place it on a heating table at 60°C for reaction for 60 minutes to obtain a layer of metal oxide grown in situ on the gallium oxide film B; The specific method for preparing the precursor solution is as follows: weigh 0.175 g (CH2)6N4 and 0.186 g Zn(NO3)2·6H2O respectively, pour them into 50 ml deionized water and stir with a glass rod to dissolve; the hexamethylenetetramine in the precursor solution is 25 mmol / L and the zinc nitrate is 12.5 mmol / L; (3) drying the metal oxide obtained in (2) under an inert gas, and after drying, using a syringe to absorb the metal in the metal oxide layer, and then removing the photoresist with a stripping solution, and flushing with water, until the surface of the metal oxide is separated from the surface of the substrate, and using a substrate to pick up the surface of the metal oxide from the water, thereby obtaining a substrate with a heterojunction; (4) The substrate with the heterojunction obtained in (3) was placed in an ethanol solution of 0.268 g lithium iodide, 0.508 g iodine and 78.9 g ethanol, and heated at 60 °C for 8 h to obtain an in-situ grown heterojunction.

[0021] like Figure 1 As shown, Figure 1 (a) The optical microscopic image of the heterojunction film shows that the film has good continuity and uniformity with clear boundaries. The vertical and horizontal dimensions can reach several hundred microns. In addition, larger oxide heterojunction films can be obtained by increasing the size of the liquid metal. Figure 1 (b) The Raman spectrum shows that the -1 The characteristic peaks of gallium oxide at 333 cm -1 The characteristic peak of zinc oxide is shown in Figure 2, proving that the film is composed of gallium oxide and zinc oxide.

[0022] like Figure 2 As shown, Figure 2 (a) is a TEM image of a single-layer gallium oxide film peeled off from the surface of liquid metal gallium. It can be observed that the surface of the gallium oxide film is smooth, continuous and uniform; Figure 2 (b) is the distribution of gallium atoms in the EDS spectrum; Figure 2 (c) is the distribution of oxygen atoms in the EDS spectrum, from which we can know that the film is composed of gallium atoms and oxygen atoms; Figure 2 (d) is a HRTEM image of a single-layer gallium oxide film. No obvious lattice fringes are observed in the image, which proves that the film is amorphous gallium oxide. Figure 2 (e) is the selected area electron diffraction image of a single-layer gallium oxide film. No obvious diffraction spots or diffraction rings are observed in the image, which further proves that the film on the surface of liquid metal gallium is amorphous gallium oxide.

[0023] like Figure 3 As shown, Figure 3 (a) is a low-magnification SEM image of the heterojunction film, where it can be observed that zinc oxide is overgrown and some spherical crystal particles grow on the surface; Figure 3 (b) is a high-magnification SEM image of the interior of the heterojunction film, which allows a clearer observation of the morphology of the zinc oxide surface. The image shows that zinc oxide continues to grow and arch after covering the entire gallium oxide surface, presenting an irregular shape. Figure 3 (c) is a high-magnification SEM image of the heterojunction film boundary, where the residual liquid metal can be observed during the transfer process of the film after being soaked in iodine ion solution; Figure 3 (d) It can be seen that the liquid metal has been etched away, and wrinkles appear on the surface of the film at the boundary without the support of liquid metal, indicating that immersion in iodine ion solution can effectively remove the residual metal gallium on the heterojunction.

[0024] like Figure 4 As shown, Figure 4 (a) is a SEM image of the EDS spectrum scanning area of ​​the heterojunction film prepared by the present invention, and a double-layer structure of gallium oxide and zinc oxide can be observed at the boundary; Figure 4(b) Gallium atoms in Figure 4 The distribution of heterojunction film area shown in (a); Figure 4 (c) is the zinc atom in Figure 4 (a) Distribution of heterojunction film area shown; Figure 4 (d) is the oxygen atom in Figure 4 (a) shows the distribution of the heterojunction film area. The double-layer structure of the film can be more intuitively observed from the EDS energy spectrum, further confirming that the film is a heterojunction composed of gallium oxide and zinc oxide.

[0025] like Figure 5 As shown, Figure 5 The XPS spectrum of the heterojunction film prepared in the present invention shows that the 2p orbital of zinc oxide appears at 1021.9 eV and 1044.9 eV of Zn2p orbital. 3 / 2 and 2p 1 / 2 Characteristic peaks: a characteristic peak belonging to gallium oxide appears at 20.2 eV of the Ga3d orbital, and a characteristic peak belonging to metallic gallium due to residual liquid metallic gallium appears at 18.5 eV. Characteristic peaks belonging to zinc oxide and gallium oxide appear at 530.3 eV and 531.0 eV of the O1s orbital, respectively, which correspond to the characteristic peaks of the Zn2p orbital and the Ga3d orbital, further confirming that the film is composed of gallium oxide and zinc oxide.

[0026] like Figure 6 As shown, Figure 6 The HRTEM image of the heterojunction film prepared by the present invention shows obvious lattice fringes. The crystal plane spacings of 0.28 nm and 0.26 nm marked in the image correspond to the (100) and (002) crystal planes of hexagonal zinc oxide, respectively, indicating that the zinc oxide grown by the present invention is a hexagonal crystal. In situ growth of zinc oxide on a gallium oxide film to form a heterojunction will reduce dislocations and defects between semiconductor materials, thereby improving carrier mobility. Therefore, the present method has considerable application prospects.

[0027] Embodiment 2: The present invention provides a method for preparing a liquid-liquid interface in-situ grown heterojunction, comprising the following steps: (1) Use a pipette to drop photoresist onto the pretreated silicon wafer, rotate it evenly on a spreader and dry it, then drop liquid metal gallium. After gallium oxide film A is formed, use a glass rod to push away the gallium oxide film A to expose a new surface. After standing for 1 minute, gallium oxide film B is formed, and a silicon wafer with metal gallium is obtained; The pretreatment is as follows: the silicon wafer is ultrasonicated in acetone, ethanol and deionized water for 10 min respectively, and then dried with nitrogen to obtain a cleaned silicon wafer, and the cleaned silicon wafer is placed in an oxygen plasma cleaning machine and treated at a power of 90 W for 5 min; (2) Place the silicon wafer with metal gallium obtained in (1) into a clean glass weighing bottle, add hexamethylenetetramine (HMT) and copper nitrate precursor solution, so that the surface of the metal gallium is completely immersed in the precursor solution, cover the weighing bottle with a cap, and place it on a heating table at 60°C for reaction for 60 minutes to obtain a layer of metal oxide grown in situ on the gallium oxide film B; The specific method for preparing the precursor solution is as follows: weigh 0.175 g (CH2)6N4 and 0.151 g Cu(NO3)2·3H2O respectively, pour them into 50 ml deionized water and stir with a glass rod to dissolve; the hexamethylenetetramine in the precursor solution is 25 mmol / L and the copper nitrate is 12.5 mmol / L; (3) drying the metal oxide obtained in (2) under an inert gas, and after drying, using a syringe to absorb the metal in the metal oxide layer, and then removing the photoresist with a stripping solution, and flushing with water, until the surface of the metal oxide is separated from the surface of the substrate, and using a substrate to pick up the surface of the metal oxide from the water, thereby obtaining a substrate with a heterojunction; (4) The substrate with the heterojunction obtained in (3) was placed in an ethanol solution of 0.268 g lithium iodide, 0.508 g iodine and 78.9 g ethanol, and heated at 60 °C for 8 h to obtain an in-situ grown heterojunction.

[0028] Embodiment 3: The present invention provides a method for preparing a liquid-liquid interface in-situ grown heterojunction, comprising the following steps: (1) Use a pipette to drop photoresist onto the pre-treated silicon wafer, rotate it evenly on a photoresist spreader and dry it, then drop liquid metal gallium. After gallium oxide film A is formed, use a glass rod to push away the gallium oxide film A to expose a new surface. After standing for 2 minutes, gallium oxide film B is formed, and a silicon wafer with metal gallium is obtained; The pretreatment is as follows: the silicon wafer is ultrasonicated in acetone, ethanol and deionized water for 10 min respectively, and then dried with nitrogen to obtain a cleaned silicon wafer, and the cleaned silicon wafer is placed in an oxygen plasma cleaning machine and treated at a power of 70 W for 10 min; (2) Place the silicon wafer with metal gallium obtained in (1) into a clean glass weighing bottle, add hexamethylenetetramine (HMT) and cerium nitrate precursor solution, make the surface of metal gallium completely immersed in the precursor solution, cover the weighing bottle with a cap, place it on a heating table at 80°C for reaction for 10 min, and obtain a layer of metal oxide grown in situ on the gallium oxide film B; The preparation method of the precursor solution is as follows: 0.175 g (CH2)6N4 and 0.271 g Ce (NO3)3·6H2O are weighed respectively, poured into 50 ml deionized water and stirred with a glass rod to dissolve; the hexamethylenetetramine in the precursor solution is 25 mmol / L, and the cerium nitrate is 12.5 mmol / L; (3) drying the metal oxide obtained in (2) under an inert gas, and after drying, using a syringe to absorb the metal in the metal oxide layer, and then removing the photoresist with a stripping solution, and flushing with water, until the surface of the metal oxide is separated from the surface of the substrate, and using a substrate to pick up the surface of the metal oxide from the water, thereby obtaining a substrate with a heterojunction; (4) The substrate with the heterojunction obtained in (3) was placed in an ethanol solution of 0.268 g lithium iodide, 0.508 g iodine and 78.9 g ethanol, and heated at 80 °C for 6 h to obtain an in-situ grown heterojunction.

[0029] According to the above implementation scheme, metal oxide is in-situ grown on an amorphous gallium oxide film naturally grown on the surface of liquid metal gallium by chemical bath deposition, and finally a heterojunction material consisting of gallium oxide and zinc oxide, copper oxide and cerium oxide is peeled off from the liquid metal surface. It is expected that the grown heterojunction has good interface quality and high carrier mobility. In addition, this method is also applicable to the growth of other metal oxides on gallium oxide films, providing a new direction for the in-situ growth of other oxide heterojunctions.

[0030] The working principle of the present invention is further described below: The purpose of the present invention is to provide a liquid-liquid interface in-situ grown heterojunction and a preparation method thereof. When using the device, taking zinc oxide as an example, the technical principle adopted by the present invention is: First, liquid gallium metal is exposed to air to allow its surface to oxidize naturally to form a smooth gallium oxide film. Then it is heated in a precursor solution of zinc nitrate and hexamethylenetetramine, and the following reaction occurs in the solution: (CH2)6N4+6H2O→4NH3↑+6HCHO↑ Hexamethylenetetramine is the first to be hydrolyzed by hot water to release ammonia and formaldehyde: NH3+H2O→NH4 + +OH - Zn 2+ +4OH - →Zn(OH)4 2- OH generated by ammonia and water - and Zn nitrate in solution 2+ The reaction generates Zn(OH)4 2-, which is a soluble complex: Zn(OH)4 2- →ZnO↓+H2O+2OH - As the reaction proceeds, when the solution is supersaturated, Zn(OH)4 2- It will dehydrate to form ZnO precipitation on gallium oxide; gallium oxide is an amorphous film, and the generated zinc oxide has a hexagonal crystal structure, realizing the in-situ growth of the heterojunction.

[0031] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a heterojunction by in-situ growth at a liquid-liquid interface, characterized in that: The following steps are involved: S1, dropping photoresist on the pre-treated substrate, spinning it evenly on a spin coating device and drying it, then dropping liquid metal gallium, and after forming a gallium oxide film A, the gallium oxide film A is pushed aside, and after standing, a gallium oxide film B is formed, thereby obtaining a substrate with metal gallium; S2, immersing the substrate with metal gallium obtained in S1 in a precursor solution, and performing a heating reaction to obtain a layer of metal oxide grown in situ on the gallium oxide film B; S3, drying the metal oxide obtained in S2 under an inert gas, absorbing the metal in the metal oxide layer after drying, and then removing the photoresist, flushing with water flow, and when the surface of the metal oxide is separated from the surface of the substrate, the surface of the metal oxide is picked up from the water with the substrate to obtain a substrate with a heterojunction; S4, etching the substrate with the heterojunction obtained in S3 to obtain an in-situ grown heterojunction.

2. The method for preparing a liquid-liquid interface in-situ growth heterojunction according to claim 1, characterized in that: The pretreatment in S1 is specifically as follows: ultrasonically treating the substrate in acetone, ethanol and deionized water for 10 min respectively, blowing it dry with nitrogen to obtain a cleaned substrate, and placing the cleaned substrate in an oxygen plasma cleaning machine for 5 to 10 min at a power of 70 to 90 W.

3. The method for preparing a liquid-liquid interface in-situ growth heterojunction according to claim 1, characterized in that: The standing time in S1 is 1 to 2 min.

4. The method for preparing a liquid-liquid interface in-situ growth heterojunction according to claim 1, characterized in that: The precursor solution in S2 is a mixed solution of metal nitrate and hexamethylenetetramine; the heating reaction temperature is 60-70°C, and the heating reaction time is 10-60 min.

5. The method for preparing a liquid-liquid interface in-situ grown heterojunction according to claim 4, characterized in that: The preparation method of the precursor solution is specifically as follows: hexamethylenetetramine and metal nitrate are weighed in a molar ratio of 2:1, poured into deionized water in turn, and stirred to dissolve.

6. The method for preparing a liquid-liquid interface in-situ grown heterojunction according to claim 1, characterized in that: In S3, a stripping liquid is used to remove the photoresist.

7. The method for preparing a liquid-liquid interface in-situ grown heterojunction according to claim 1, characterized in that: The etching in S4 is specifically as follows: placing the substrate with the heterojunction obtained in S3 into an iodine ion solution and heating it.

8. The method for preparing a liquid-liquid interface in-situ grown heterojunction according to claim 7, characterized in that: The iodide ion solution is specifically an ethanol solution of lithium iodide and iodine; wherein the mass ratio of lithium iodide, iodine and ethanol is 1.34:2.54:394.

5.

9. The method for preparing a liquid-liquid interface in-situ grown heterojunction according to claim 7, characterized in that: The heating is specifically: heating at 60-80°C for 6-8 hours.

10. A liquid-liquid interface in-situ grown heterojunction, characterized in that: The invention is obtained based on the method for preparing a heterojunction by in-situ growth of a liquid-liquid interface as described in any one of claims 1 to 9.

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