Silicon carbide single crystal flexible film with p / n junction structure and preparation method and application thereof

Abstract

The present invention relates to the technical field of single crystal flexible film manufacturing, and specifically discloses a silicon carbide single crystal flexible film with a p / n junction structure and a preparation method and application thereof. The preparation method of the silicon carbide single crystal flexible film with a p / n junction structure provided by the present invention comprises the following steps: homoepitaxially growing n on the surface of an n-type silicon carbide substrate; ‑ The silicon carbide epitaxial wafer is then subjected to photoelectrochemical etching by photoelectrochemical etching. By controlling specific photoelectrochemical etching parameters, the silicon carbide film with a p / n junction structure can be efficiently stripped without causing damage to the stripped silicon carbide film. The silicon carbide single crystal flexible film obtained by stripping can be used as a flexible substrate material, and flexible optoelectronic components such as flexible chips and flexible sensors can be designed based on the film, which can be applied to wearable devices, flexible displays, flexible detection and other fields.

Description

Technical Field

[0001] The present invention relates to the technical field of single crystal flexible film manufacturing, and in particular to a silicon carbide single crystal flexible film with a p / n junction structure, a preparation method thereof, and applications thereof. Background Art

[0002] Flexible electronics refer to electronic devices that retain their original performance after being twisted, folded, stretched, or otherwise deformed. Currently, flexible electronic and optoelectronic devices with p / n junction structures have attracted significant interest in applications such as wearable devices, flexible displays, and flexible sensing.

[0003] Compared to organic materials, single-crystal silicon carbide (SiC), a third-generation semiconductor material, boasts exceptional properties such as a wide bandgap, high breakdown field strength, high thermal conductivity, high electron mobility, and excellent thermal and chemical stability. It has demonstrated significant application potential in fields such as photodetection, medium- and high-voltage power electronics, and quantum sensing. Due to its high hardness and chemical inertness, the preparation of flexible SiC thin films with p / n junction structures and micro- and nanometer-scale thicknesses is typically accomplished through grinding and polishing, ion implantation / stripping, and ion thinning. However, these processes not only have long processing cycles and high costs, but also generate mechanical stress and damage during processing, which can easily break the SiC thin films. Therefore, when preparing flexible SiC thin films with p / n junction structures and micro- and nanometer-scale thicknesses, the challenge remains to remove the thin films without inducing external forces and damage, thereby expanding the application of SiC in flexible electronics and optoelectronic devices. Summary of the Invention

[0004] To address the technical issues of existing methods for preparing silicon carbide single crystal thin films with a p / n junction structure, such as long processing cycles and high processing costs, as well as the poor flexibility and fragility of the resulting silicon carbide single crystal, the present invention provides a flexible silicon carbide single crystal film with a p / n junction structure, as well as its preparation method and application. The present invention involves homoepitaxially growing a low-nitrogen-doped epitaxial layer on the surface of an n-type silicon carbide substrate, then homoepitaxially growing a high-nitrogen-doped epitaxial layer on the low-nitrogen-doped epitaxial layer, and finally growing an Al-doped layer. The silicon carbide epitaxial wafer is immersed in an etching solution, and photoelectrochemical etching is performed using a two-electrode system with the silicon carbide epitaxial wafer as the working electrode to achieve exfoliation of the single crystal layer, thereby obtaining a silicon carbide single crystal thin film with a p / n junction structure. This method is simple to operate, and the resulting silicon carbide single crystal thin film with a p / n junction structure is highly flexible, meeting the performance requirements of flexible electronic and optoelectronic devices.

[0005] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions:

[0006] In a first aspect, the present invention provides a method for preparing a silicon carbide single crystal flexible film having a p / n junction structure, comprising the following steps:

[0007] S1, homoepitaxially grow n on the Si surface of n-type silicon carbide substrate - type epitaxial layer, n-type epitaxial layer and p-type epitaxial layer to obtain a silicon carbide epitaxial wafer;

[0008] S2, placing the silicon carbide epitaxial wafer in an etching solution, using the silicon carbide epitaxial wafer as an anode and providing a cathode in the etching solution based on a two-electrode system;

[0009] S3, irradiating the silicon carbide epitaxial wafer with ultraviolet light of a preset wavelength, and applying a preset voltage to the silicon carbide epitaxial wafer to perform selective etching to obtain a silicon carbide single crystal flexible film with a p / n junction structure;

[0010] The preset wavelength is smaller than a critical value of the absorption wavelength corresponding to the n-type silicon carbide substrate.

[0011] Compared with the prior art, the present invention provides a method for preparing a silicon carbide single crystal flexible film with a p / n junction structure, wherein a first epitaxial layer (n - At the interface between the first and second epitaxial layers, electrons dissociated from the n-type SiC substrate diffuse and accumulate on the first epitaxial layer, leaving behind nitrogen cations on the n-type SiC substrate. This creates a built-in electric field similar to that at a "p / n junction" interface, with the electric field directed from the n-type SiC substrate (highly nitrogen-doped substrate) toward the first epitaxial layer (lowly nitrogen-doped layer). Furthermore, a second epitaxial layer (n-type epitaxial layer) is grown, and a similar built-in electric field similar to that at a "p / n junction" interface is spontaneously generated at the interface between the first and second epitaxial layers, with the electric field directed from the second epitaxial layer (highly nitrogen-doped layer) toward the first epitaxial layer (lowly nitrogen-doped layer). Then, a third doped layer (p-type epitaxial layer) is grown on the surface of the second epitaxial layer (highly nitrogen-doped layer), forming a p / n junction at the interface between the second and third epitaxial layers, with the built-in electric field directed from the second epitaxial layer toward the third epitaxial layer. The silicon carbide epitaxial wafer is placed in an etching solution, and the energy band of the single crystal region of the third epitaxial layer close to the etching solution bends downward, so that a built-in electric field directed from the etching solution to the interior of the crystal is generated at the solid / liquid interface.

[0012] When ultra-gap light is applied to this silicon carbide epitaxial wafer, the built-in electric field at the interface causes photogenerated holes to accumulate within the first and third epitaxial layers, while photogenerated electrons accumulate in the substrate, the second epitaxial layer, and the surface of the third epitaxial layer. Under ultra-gap light irradiation, the distribution of photogenerated holes and electrons on both sides of the interface can instantly reach a steady state. At this point, in the presence of an etching solution, electrochemical corrosion of the silicon carbide occurs in the hole-rich regions, but the corrosion rate is very slow. Applying a positive voltage to the bottom of the substrate rapidly conducts the accumulated photogenerated electrons away from the substrate. This increases the generation rate of photogenerated hole-electron pairs at the substrate / first epitaxial layer interface, rapidly increasing the concentration of photogenerated holes within the first epitaxial layer and accelerating the electrochemical corrosion rate of the silicon carbide in this region. However, since the first epitaxial layer is a low-nitrogen doped layer with an electrical conductivity close to semi-insulating, the photogenerated electrons enriched inside the second epitaxial layer and on the surface of the third epitaxial layer cannot be conducted out of the body through the first epitaxial layer. Therefore, during the photoelectrochemical etching process of the silicon carbide epitaxial wafer, only the first epitaxial layer undergoes electrochemical corrosion and is sacrificed, while the second and third epitaxial layers do not corrode. This allows the silicon carbide single crystal flexible film with a p / n junction structure to be detached from the substrate without external force, and the surface of the obtained silicon carbide single crystal flexible film is undamaged.

[0013] The remaining n-type silicon carbide substrate after stripping only needs to be properly polished before the next step of preparing a silicon carbide single crystal flexible film with a p / n junction structure can be directly carried out. This realizes the reuse of the n-type silicon carbide substrate, greatly reduces the preparation cost of the silicon carbide single crystal flexible film with a p / n junction structure, and does not cause waste of resources or damage to the environment.

[0014] Furthermore, in step S1, the nitrogen doping concentration in the n-type silicon carbide substrate is 1×10 18 / cm 3 ~2×10 19 / cm 3 .

[0015] Furthermore, in step S1, the n - The nitrogen doping concentration in the epitaxial layer is 4×10 14 / cm 3 ~5×10 15 / cm 3 .

[0016] Furthermore, in step S1, the nitrogen doping concentration in the n-type epitaxial layer is 1×10 18 / cm 3 ~5×10 19 / cm 3 .

[0017] Furthermore, in step S1, the concentration of the doping element in the p-type epitaxial layer is 1×10 18 / cm 3 ~5×10 19 / cm 3 .

[0018] Furthermore, in step S1, the n - The thickness of the n-type epitaxial layer is 1 μm to 5 μm, the thickness of the n-type epitaxial layer is 0.5 μm to 20 μm, and the thickness of the p-type epitaxial layer is 0.5 μm to 20 μm.

[0019] The present invention creatively proposes a method for homoepitaxially growing n-type silicon carbide substrates with different nitrogen doping concentrations. - / n-type epitaxial layer and p-type epitaxial layer, using epitaxial layers with different nitrogen doping concentrations to construct a built-in electric field similar to the "p / n junction" interface, using the photoelectrochemical etching method to make n - The epitaxial layer is etched away (as a sacrificial layer), allowing the silicon carbide single crystal flexible film with a p / n structure to be peeled off from the substrate without damage. This provides a simple and efficient new process for preparing silicon carbide single crystal flexible films with a p / n structure, which can be applied to wearable devices, flexible displays, flexible detection and other fields.

[0020] Furthermore, in step S1, the size of the n-type silicon carbide substrate is 1 inch to 8 inches, and the thickness is 0.3 mm to 0.5 mm.

[0021] The n-type silicon carbide substrate in the present invention can directly use a commercially available n-type silicon carbide substrate (4H or 6H), or a conventional vapor deposition method (CVD method) in the art can be used to prepare an n-type silicon carbide layer on the surface of the silicon carbide substrate, and the present invention does not make any special restrictions.

[0022] It should be noted that, when performing homoepitaxial growth of the p-type silicon carbide layer in the present invention, the doping element may be Al or B.

[0023] Furthermore, in step S2, the etching solution is a mixed solution of hydrofluoric acid and hydrogen peroxide.

[0024] As a specific embodiment of the present invention, the hydrofluoric acid and hydrogen peroxide are both commercially available products, wherein the concentration of hydrofluoric acid is 40 wt % and the concentration of hydrogen peroxide is 30 wt %.

[0025] Furthermore, in step S2, the mass concentration of HF in the etching solution is 2% to 15%, the mass concentration of H2O2 is 2% to 15%, and the balance is water.

[0026] Furthermore, in step S2, the cathode is a graphite sheet electrode.

[0027] Furthermore, in step S2, before placing the silicon carbide epitaxial wafer in the etching solution, the step further includes: preparing a conductive layer on the carbon surface of the n-type silicon carbide substrate of the silicon carbide epitaxial wafer, and preparing an insulating layer on the surface of the conductive layer.

[0028] It should be noted that the conductive layer is a metal material layer, specifically a Pt layer, an Au layer, a Ti layer, or a Ni layer, etc., as long as the metal material has good conductivity, and the present invention does not specifically limit it. The method for preparing the conductive layer can be sputtering, or a conventional method for preparing metal layers in the art, as long as it does not significantly damage the n-type silicon carbide substrate, and the present invention does not specifically limit it.

[0029] As a specific embodiment of the present invention, the insulating layer is prepared by coating black wax on the surface of the conductive layer. The insulating layer plays the role of insulation and protection.

[0030] Specifically, in step S2, the voltage output end of the wire is connected to the conductive layer, and the voltage input end is connected to the cathode, forming a two-electrode system.

[0031] In a two-electrode system, when ultra-gap ultraviolet light is used to irradiate the silicon carbide epitaxial wafer, the photogenerated holes accumulated inside the first epitaxial layer selectively erode the silicon carbide there with the assistance of the etchant HF and the oxidant H2O2. The reaction that occurs is:

[0032] SiC+2H2O2+4 h + →SiO2+CO2↑+4H +

[0033] SiO2+6HF→(SiF6) 2- +2H2O+ 2H +

[0034] The photogenerated electrons enriched in the n-type silicon carbide substrate are transferred to the counter electrode under the action of the external electric field to participate in the hydrogen evolution reaction. The reaction equation is:

[0035] 2H + +H2O2+2 e - =2H2O

[0036] Furthermore, in step S3, the preset wavelength is 200 nm to 380 nm.

[0037] In one embodiment of the present invention, a filter is used on the light source to filter the light so that the wavelength of light reaching the silicon carbide epitaxial wafer is less than the critical value of the light absorption wavelength corresponding to the n-type silicon carbide substrate, preferably in the wavelength range of 200nm to 380nm. Specifically, a xenon lamp or a mercury lamp can be used as the light source.

[0038] As a specific embodiment of the present invention, it also includes using an organic glass sheet above the etching liquid to block the vapor formed after the etching liquid evaporates, so as to prevent the evaporated etching liquid from corroding the filter.

[0039] Furthermore, in step S3, the preset voltage is 0.1V~3V vs. cathode.

[0040] Furthermore, in step S3, the height of the light source emitting the incident light from the surface of the etching liquid is 5 cm to 10 cm, the flow rate of the etching liquid is 1 mL / min to 5 mL / min, and the stirring speed during the etching process is 300 r / min to 500 r / min.

[0041] The selective etching using the above process conditions can improve the stripping efficiency of the silicon carbide single crystal flexible film with a p / n junction structure and ensure that the surface of the silicon carbide single crystal flexible film with a p / n junction structure obtained by stripping is not damaged.

[0042] In a second aspect, the present invention provides a silicon carbide single crystal flexible film having a p / n junction structure, which is prepared by the method for preparing a silicon carbide single crystal flexible film having a p / n junction structure.

[0043] In a third aspect, the present invention further provides a flexible electronic device comprising the silicon carbide single crystal flexible film having a p / n junction structure.

[0044] The method for preparing a silicon carbide single crystal flexible film with a p / n junction structure provided by the present invention has a simple process and a short operation cycle. The prepared silicon carbide single crystal flexible film with a p / n junction structure has good flexibility and can be used as a flexible substrate material in fields such as wearable devices, flexible displays, and flexible detection. It provides a new idea for preparing a silicon carbide single crystal flexible film with a p / n junction structure, and solves the defect that the existing technology cannot prepare a silicon carbide single crystal flexible film with a p / n junction structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0046] Figure 1 Schematic diagram of the peeling mechanism of the silicon carbide single crystal flexible film with a p / n junction structure of the present invention;

[0047] Figure 2Schematic diagram of the stripping apparatus for preparing a silicon carbide single crystal flexible film with a p / n junction structure according to the present invention; 1, silicon carbide epitaxial wafer; 2, graphite sheet electrode; 3, stirring structure; 4, voltage output terminal; 5, voltage input terminal; 6, etching solution inlet; 7, etching solution outlet; 8, flow-type electrolytic cell;

[0048] Figure 3 An AFM image of the upper surface (upper surface of the third epitaxial layer) of a silicon carbide single crystal flexible film having a p / n junction structure prepared according to an embodiment of the present invention;

[0049] Figure 4 An AFM image of the lower surface (lower surface of the second epitaxial layer) of a silicon carbide single crystal flexible film having a p / n junction structure prepared in accordance with an embodiment of the present invention;

[0050] Figure 5 This is a Raman graph of a silicon carbide single crystal flexible film with a p / n junction structure prepared in an embodiment of the present invention. DETAILED DESCRIPTION

[0051] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0052] The peeling device used in the following examples for preparing the silicon carbide single crystal flexible film with p / n junction structure is as follows: Figure 2 The stripping device includes a flow-type electrolytic cell 8 and a light source. The electrolytic cell is provided with an open-pore structure and a stirring structure 3. The open-pore structure is used to fix a silicon carbide epitaxial wafer 1 and a cathode graphite sheet electrode 2. One end of the silicon carbide epitaxial wafer 1 is connected to a voltage output terminal 4, and the cathode graphite sheet electrode 2 is connected to a voltage input terminal 5. The light source is positioned 5 to 10 cm above the surface of the etching solution. The light emitted by the light source is filtered by a filter and then vertically illuminates the surface of the silicon carbide epitaxial wafer.

[0053] The method for preparing a silicon carbide single crystal flexible film having a p / n junction structure using the above-mentioned device comprises the following steps:

[0054] S1, homoepitaxially grow n on the Si surface of n-type silicon carbide substrate - type epitaxial layer, n-type epitaxial layer and p-type epitaxial layer to obtain a silicon carbide epitaxial wafer;

[0055] S2, placing the silicon carbide epitaxial wafer in an etching solution, using the silicon carbide epitaxial wafer as an anode and providing a cathode in the etching solution based on a two-electrode system;

[0056] S3, irradiating the silicon carbide epitaxial wafer with ultraviolet light of a preset wavelength, and at the same time, applying a preset voltage to the silicon carbide epitaxial wafer to perform selective etching to obtain a silicon carbide single crystal flexible film with a p / n junction structure.

[0057] The schematic diagram of the stripping principle of the above-mentioned photoelectrochemical corrosion is as follows Figure 1 As shown. n-type silicon carbide substrate (high nitrogen doping) and n - A built-in electric field similar to the "p / n junction" interface can be formed between the type silicon carbide substrate (low nitrogen doping), and the direction of the electric field is from the substrate to the first epitaxial layer (n - A built-in electric field similar to that at the "p / n junction" interface can also be formed between the first epitaxial layer (low nitrogen doping) and the second epitaxial layer (high nitrogen doping), and the direction of the electric field is from the second epitaxial layer (n-type epitaxial layer) to the first epitaxial layer (n - Type epitaxial layer). A p / n junction is formed at the interface between the second and third epitaxial layers, with the built-in electric field directed from the n-type doping layer to the p-type doping layer. A built-in electric field is generated at the solid-liquid interface between the third epitaxial layer and the etchant, directed from the etchant toward the interior of the crystal. Under photoelectrochemical etching, the silicon carbide in the first epitaxial layer undergoes electrochemical corrosion and is sacrificed. Because the first epitaxial layer is a low-nitrogen doped layer with near-semi-insulating conductivity, electrons within the second epitaxial layer and on the surface of the third epitaxial layer cannot pass through the first epitaxial layer and out of the body, thus remaining unetched during the photochemical etching process. Ultimately, once the first epitaxial layer has been completely etched, a single-crystalline flexible film formed by the second epitaxial layer (n-type) and the third epitaxial layer (p-type) is obtained, with an undamaged surface.

[0058] The method for preparing a silicon carbide single crystal flexible film with a p / n junction structure provided by the present invention has a short production cycle and low cost, and can obtain a highly flexible silicon carbide single crystal flexible film with a p / n junction structure. The surface of the prepared silicon carbide single crystal flexible film with a p / n junction structure is undamaged, meeting the requirements of flexible electronic and optoelectronic devices for high-quality silicon carbide single crystal flexible films, and is of great significance for expanding the application of silicon carbide films in the field of flexible electronic or optoelectronic equipment.

[0059] In order to better illustrate the method for preparing the silicon carbide single crystal flexible film with a p / n junction structure provided by the embodiment of the present invention, further examples are given below.

[0060] Example 1

[0061] A method for preparing a silicon carbide single crystal flexible film having a p / n junction structure comprises the following steps:

[0062] S1, prepare silicon carbide epitaxial wafers, and homoepitaxially grow n on the Si surface of a 2-inch, 0.3 mm thick n-type silicon carbide substrate by chemical vapor deposition.- type silicon carbide epitaxial layer, n-type silicon carbide epitaxial layer and p-type silicon carbide epitaxial layer; wherein the nitrogen doping concentration in the n-type silicon carbide substrate is 1×10 18 / cm 3 ;n - The nitrogen doping concentration in the silicon carbide epitaxial layer is 4×10 14 / cm 3 , with a thickness of 1 μm; the nitrogen doping concentration in the n-type silicon carbide epitaxial layer is 2×10 18 / cm 3 , with a thickness of 1.0 μm; the Al doping concentration in the p-type silicon carbide layer is 5×10 19 / cm 3 , the thickness of the epitaxial layer is 15 μm;

[0063] S2, preparing an etching solution by mixing a 40% by mass concentration hydrofluoric acid solution and a 30% by mass concentration hydrogen peroxide solution with ultrapure water in a certain proportion to obtain an etching solution, and adding the etching solution into a flow-type polytetrafluoroethylene electrolytic cell; the mass fraction of HF in the etching solution is 2%, and the mass fraction of H2O2 is 2%;

[0064] S3, electrode preparation, using a two-electrode system, sputtering a Pt layer on the bottom of the silicon carbide substrate of the epitaxial wafer to form a conductive layer, which is then coated with black wax for insulation and protection. The silicon carbide epitaxial wafer serves as the anode and the graphite electrode sheet serves as the cathode. The silicon carbide epitaxial wafer is connected to the output terminal of the voltage, and the graphite electrode sheet is connected to the input terminal of the voltage;

[0065] S4, at room temperature, using a xenon lamp as the light source, the light emitted from the light source is filtered by a filter and then vertically irradiated onto the surface of the silicon carbide epitaxial wafer. After filtering, the wavelength of the light irradiating the silicon carbide epitaxial wafer is 375nm. At the same time, a voltage of 0.5V (vs. the counter electrode) is applied to the silicon carbide epitaxial wafer to perform selective etching, thereby obtaining a silicon carbide single crystal flexible film with a p / n junction structure;

[0066] The height between the light source and the surface of the etching liquid is 10 cm, the flow rate of the etching liquid is 1 mL / min, and the rotation speed of the stirring bar is 300 r / min.

[0067] Example 2

[0068] A method for preparing a silicon carbide single crystal flexible film having a p / n junction structure comprises the following steps:

[0069] S1, prepare silicon carbide epitaxial wafers, and homoepitaxially grow n on the Si surface of a 3-inch, 0.4 mm thick n-type silicon carbide substrate by chemical vapor deposition. -type silicon carbide epitaxial layer, n-type silicon carbide epitaxial layer and p-type silicon carbide epitaxial layer; wherein the nitrogen doping concentration in the n-type silicon carbide substrate is 2×10 19 / cm 3 ;n - The nitrogen doping concentration in the silicon carbide epitaxial layer is 5×10 15 / cm 3 , with a thickness of 5 μm; the nitrogen doping concentration in the n-type silicon carbide epitaxial layer is 2×10 19 / cm 3 , with a thickness of 18 μm; the Al doping concentration in the p-type silicon carbide layer is 1×10 18 / cm 3 , the thickness of the epitaxial layer is 2 μm;

[0070] S2, preparing an etching solution by mixing a 40% by mass concentration hydrofluoric acid solution and a 30% by mass concentration hydrogen peroxide solution with ultrapure water in a certain proportion to obtain an etching solution, and adding the etching solution to a flow-type polytetrafluoroethylene electrolytic cell; the mass fraction of HF in the etching solution is 15%, and the mass fraction of H2O2 is 15%;

[0071] S3, electrode preparation, using a two-electrode system, sputtering a Pt layer on the bottom of the silicon carbide substrate of the epitaxial wafer to form a conductive layer, which is then coated with black wax for insulation and protection. The silicon carbide epitaxial wafer serves as the anode and the graphite electrode sheet serves as the cathode. The silicon carbide epitaxial wafer is connected to the output terminal of the voltage, and the graphite electrode sheet is connected to the input terminal of the voltage;

[0072] S4, at room temperature, using a xenon lamp as the light source, the light emitted from the light source is filtered by a filter and then vertically irradiated onto the surface of the silicon carbide epitaxial wafer. After filtering, the wavelength of the light irradiating the silicon carbide epitaxial wafer is reduced to 200nm. At the same time, a voltage of 1.0V (vs. the counter electrode) is applied to the silicon carbide epitaxial wafer to perform selective etching, thereby obtaining a silicon carbide single crystal flexible film with a p / n junction structure.

[0073] The height between the light source and the surface of the etching liquid is 5 cm, the flow rate of the etching liquid is 5 mL / min, and the rotation speed of the stirring bar is 500 r / min.

[0074] Example 3

[0075] A method for preparing a silicon carbide single crystal flexible film having a p / n junction structure comprises the following steps:

[0076] S1, prepare silicon carbide epitaxial wafers, and homoepitaxially grow n on the Si surface of an 8-inch, 0.5 mm thick n-type silicon carbide substrate by chemical vapor deposition. - type silicon carbide epitaxial layer, n-type silicon carbide epitaxial layer and p-type silicon carbide epitaxial layer; wherein the nitrogen doping concentration in the n-type silicon carbide substrate is 5×1018 / cm 3 ;n - The nitrogen doping concentration in the silicon carbide epitaxial layer is 8×10 14 / cm 3 , with a thickness of 3 μm; the nitrogen doping concentration in the n-type silicon carbide epitaxial layer is 6×10 18 / cm 3 , with a thickness of 8 μm; the Al doping concentration in the p-type silicon carbide layer is 3×10 18 / cm 3 , the thickness of the epitaxial layer is 6 μm;

[0077] S2, preparing an etching solution by mixing a 40% by mass concentration hydrofluoric acid solution and a 30% by mass concentration hydrogen peroxide solution with ultrapure water in a certain proportion to obtain an etching solution, and adding the etching solution into a flow-type polytetrafluoroethylene electrolytic cell; the mass fraction of HF in the etching solution is 5%, and the mass fraction of H2O2 is 10%;

[0078] S3, electrode preparation, using a two-electrode system, sputtering a Pt layer on the bottom of the silicon carbide substrate of the epitaxial wafer to form a conductive layer, which is then coated with black wax for insulation and protection. The silicon carbide epitaxial wafer serves as the anode and the graphite electrode sheet serves as the cathode. The silicon carbide epitaxial wafer is connected to the output terminal of the voltage, and the graphite electrode sheet is connected to the input terminal of the voltage;

[0079] S4, at room temperature, using a xenon lamp as the light source, the light emitted from the light source is filtered by a filter and then vertically irradiated onto the surface of the silicon carbide epitaxial wafer. After filtering, the wavelength of the light irradiating the silicon carbide epitaxial wafer is reduced to 250nm. At the same time, a voltage of 2.0V (vs. the counter electrode) is applied to the silicon carbide epitaxial wafer to perform selective etching, thereby obtaining a silicon carbide single crystal flexible film with a p / n junction structure.

[0080] The height between the light source and the surface of the etching liquid is 8 cm, the flow rate of the etching liquid is 4 mL / min, and the rotation speed of the stirring bar is 450 r / min.

[0081] Example 4

[0082] A method for preparing a silicon carbide single crystal flexible film having a p / n junction structure comprises the following steps:

[0083] S1, prepare silicon carbide epitaxial wafers, and homoepitaxially grow n on the Si surface of a 5-inch, 0.4 mm thick n-type silicon carbide substrate by chemical vapor deposition. - type silicon carbide epitaxial layer, n-type silicon carbide epitaxial layer and p-type silicon carbide epitaxial layer; wherein the nitrogen doping concentration in the n-type silicon carbide substrate is 1×10 19 / cm 3 ;n -The nitrogen doping concentration in the silicon carbide epitaxial layer is 1×10 15 / cm 3 , with a thickness of 2 μm; the nitrogen doping concentration in the n-type silicon carbide epitaxial layer is 1×10 19 / cm 3 , with a thickness of 5 μm; the Al doping concentration in the p-type silicon carbide layer is 2×10 19 / cm 3 , the thickness of the epitaxial layer is 10 μm;

[0084] S2, preparing an etching solution by mixing a 40% by mass concentration hydrofluoric acid solution and a 30% by mass concentration hydrogen peroxide solution with ultrapure water in a certain proportion to obtain an etching solution, and adding the etching solution into a flow-type polytetrafluoroethylene electrolytic cell; the mass fraction of HF in the etching solution is 10%, and the mass fraction of H2O2 is 10%;

[0085] S3, electrode preparation, using a two-electrode system, sputtering a Pt layer on the bottom of the silicon carbide substrate of the epitaxial wafer to form a conductive layer, which is then coated with black wax for insulation and protection. The silicon carbide epitaxial wafer serves as the anode and the graphite electrode sheet serves as the cathode. The silicon carbide epitaxial wafer is connected to the output terminal of the voltage, and the graphite electrode sheet is connected to the input terminal of the voltage;

[0086] S4, at room temperature, using a xenon lamp as the light source, the light emitted from the light source is filtered by a filter and then vertically irradiated onto the surface of the silicon carbide epitaxial wafer. After filtering, the wavelength of the light irradiating the silicon carbide epitaxial wafer is reduced to 300nm. At the same time, a voltage of 1.5V (vs. the counter electrode) is applied to the silicon carbide epitaxial wafer to perform selective etching, thereby obtaining a silicon carbide single crystal flexible film with a p / n junction structure.

[0087] The height between the light source and the surface of the etching liquid is 6 cm, the flow rate of the etching liquid is 2 mL / min, and the rotation speed of the stirring bar is 400 r / min.

[0088] The AFM images of the upper and lower surfaces of the silicon carbide single crystal flexible film with p / n junction structure prepared in this embodiment are as follows: Figure 3~Figure 4 As shown in the figure, after electrochemical etching, the upper surface of the silicon carbide single-crystal flexible film with a p / n junction structure remains smooth with a roughness of Ra = 0.3nm, indicating that no corrosion occurred during the electrochemical etching process. However, the lower surface (peeled surface) of the silicon carbide single-crystal flexible film with a p / n junction structure exhibits a large step after electrochemical etching, with a roughness of Ra = 3.2nm.

[0089] Raman characterization was performed on the upper surface of the flexible silicon carbide single crystal film with a p / n junction structure prepared in this embodiment. Figure 5 As shown in the figure, it can be seen that the -1The FTA folding mode is located at 776 cm -1 The folded mode of the lateral optical branch (FTO) and the folded mode at 965 cm -1 and 985cm -1 The folding modes of the longitudinal optical branch (FLO) of 965cm -1 and 985cm -1 The folding patterns of the longitudinal optical branch (FLO) correspond to p-type and n-type doping, respectively. The flexible SiC single-crystal film with a p / n junction structure exhibits characteristic Raman peaks at the same locations before and after photoelectrochemical etching, indicating that the prepared SiC p / n single-crystal film maintains a stable crystalline structure. However, the intensity of the Raman peak decreases slightly after photoelectrochemical etching, which is attributed to the thin thickness of the SiC p / n single-crystal film.

[0090] From the above embodiments, it can be seen that the method for preparing a silicon carbide single crystal flexible film with a p / n junction structure provided by the present invention is to sequentially homoepitaxially grow n on the surface of an n-type silicon carbide substrate. - type silicon carbide substrate, n-type silicon carbide substrate and p-type silicon carbide layer, and then use the photoelectrochemical etching method to perform photoelectrochemical etching on the prepared silicon carbide epitaxial wafer. By controlling specific photoelectrochemical etching parameters, efficient stripping of the silicon carbide film with a p / n junction structure is achieved without damaging the stripped silicon carbide film. The silicon carbide single crystal flexible film obtained by stripping can be used as a flexible substrate material, based on which flexible chips, flexible sensors and other flexible optoelectronic components are designed, which are applied to wearable devices, flexible displays and flexible detection and other fields; in addition, the n-type silicon carbide substrate remaining after stripping can be reused many times after simple grinding, which effectively simplifies the production process of silicon carbide single crystal thin films and reduces production costs.

[0091] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a silicon carbide single crystal flexible film having a p / n junction structure, characterized in that: The steps include: S1, homoepitaxially grow n on the Si surface of n-type silicon carbide substrate - type epitaxial layer, n-type epitaxial layer and p-type epitaxial layer to obtain a silicon carbide epitaxial wafer; S2, placing the silicon carbide epitaxial wafer in an etching solution, using the silicon carbide epitaxial wafer as an anode and setting a cathode in the etching solution based on a two-electrode system; S3, irradiating the silicon carbide epitaxial wafer with ultraviolet light of a preset wavelength, and applying a preset voltage to the silicon carbide epitaxial wafer for selective etching to obtain a silicon carbide single crystal flexible film having a p / n junction structure; The preset wavelength is smaller than a critical value of an absorption wavelength of light corresponding to an n-type silicon carbide substrate.

2. The method for preparing a silicon carbide single crystal flexible film having a p / n junction structure according to claim 1, characterized in that: In step S1, the nitrogen doping concentration in the n-type silicon carbide substrate is 1×10 18 / cm 3 ~2×10 19 / cm 3 .

3. The method for preparing a silicon carbide single crystal flexible film having a p / n junction structure according to claim 1, characterized in that: In step S1, the n - The nitrogen doping concentration in the epitaxial layer is 4×10 14 / cm 3 ~5×10 15 / cm 3 ; and / or In step S1, the nitrogen doping concentration in the n-type epitaxial layer is 1×10 18 / cm 3 ~5×10 19 / cm 3 ; and / or In step S1, the concentration of the doping element in the p-type epitaxial layer is 1×10 18 / cm 3 ~5×10 19 / cm 3 .

4. The method for preparing a silicon carbide single crystal flexible film having a p / n junction structure according to any one of claims 1 to 3, characterized in that: In step S1, the n - The thickness of the n-type epitaxial layer is 1 μm to 5 μm, the thickness of the n-type epitaxial layer is 0.5 μm to 20 μm, and the thickness of the p-type epitaxial layer is 0.5 μm to 20 μm.

5. The method for preparing a silicon carbide single crystal flexible film having a p / n junction structure according to claim 1, characterized in that: In step S1, the size of the n-type silicon carbide substrate is 1 inch to 8 inches, and the thickness is 0.3 mm to 0.5 mm.

6. The method for preparing a silicon carbide single crystal flexible film having a p / n junction structure according to claim 1, characterized in that: In step S2, the etching solution is a mixed solution of hydrofluoric acid and hydrogen peroxide, wherein the mass concentration of HF in the etching solution is 2%-15%, and the mass concentration of H2O2 is 2%-15%.

7. The method for preparing a silicon carbide single crystal flexible film having a p / n junction structure according to claim 1, characterized in that: In step S2, the cathode is a graphite sheet electrode; and / or In step S2, before placing the silicon carbide epitaxial wafer in the etching solution, the method further includes: preparing a conductive layer on the carbon surface of the n-type silicon carbide substrate of the silicon carbide epitaxial wafer, and preparing an insulating layer on the surface of the conductive layer.

8. The method for preparing a silicon carbide single crystal flexible film having a p / n junction structure according to claim 1, characterized in that: In step S3, the preset wavelength is 200nm~380nm; and / or In step S3, the preset voltage is 0.1V~3V vs. cathode; In step S3, the light source emitting the incident light is at a height of 5 cm to 10 cm from the surface of the etching liquid, the flow rate of the etching liquid is 1 mL / min to 5 mL / min, and the stirring speed during the etching process is 300 r / min to 500 r / min.

9. A silicon carbide single crystal flexible film having a p / n junction structure, characterized in that: The flexible silicon carbide single crystal film having a p / n junction structure is prepared by the method for preparing the flexible silicon carbide single crystal film having a p / n junction structure as described in any one of claims 1 to 8.

10. A flexible electronic device, characterized in that: The invention comprises the silicon carbide single crystal flexible film having a p / n junction structure as claimed in claim 9.

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