Silicon carbide single crystal flexible film with p / n junction structure as well as preparation method and application of silicon carbide single crystal flexible film
By homoepitizing different nitrogen-doped layers on n-type silicon carbide substrates and using photoelectrochemical corrosion, the problem of long processing cycle and easy breakage of silicon carbide single crystal film in the prior art is solved, and high efficiency and low cost are achieved The non-damage peeling of the p/n junction structure silicon carbide single crystal film is suitable for flexible electronic and optoelectronic devices.
Patent Information
- Application Number
- CN202411676380.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-11-22
- Publication Date
- 2024-12-24
- Estimated Expiration
- 2044-11-22
AI Technical Summary
In the prior art, when preparing a silicon carbide single crystal flexible film with a p/n junction structure, the processing cycle is long and the cost is high. The silicon carbide single crystal film is prone to shattering, making it difficult to avoid external forces and damage during the peeling process.
The homoequitaxial different nitrogen-doped layers on the n-type silicon carbide substrate are peeled off by photoelectrochemical corrosion method, and the corrosion process is controlled by built-in electric field to achieve a damage-free p/n-junction structure silicon carbide single crystal film. Peel off.
The preparation process is simplified, the cost is reduced, and a high flexibility, damage-free silicon carbide single crystal film is obtained, suitable for flexible electronic and optoelectronic devices.
Smart Images
Figure CN119181634A_ABST
Abstract
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, and a preparation method and application thereof. Background Art
[0002] Flexible electronics refers to electronic devices that can maintain their original performance after being twisted, folded, stretched, etc. At present, the application of flexible electronic and optoelectronic devices with p / n junction structure in wearable devices, flexible display and flexible detection has aroused great interest.
[0003] Compared with organic materials, single-crystal silicon carbide, as a third-generation semiconductor material, has excellent properties such as large bandgap, high breakdown field strength, high thermal conductivity, high electron mobility, high thermal stability and chemical stability. It has demonstrated important application potential in the fields of photoelectric detection, medium and high voltage power electronics and quantum sensing. Due to the characteristics of high hardness and high chemical inertness of single-crystal silicon carbide, the preparation of silicon carbide single-crystal flexible films with p / n junction structure and micro / nano-level thickness generally adopts grinding and polishing process, ion implantation / stripping process and ion thinning process. However, these processes not only have long processing cycles and high processing costs, but also the mechanical stress and damage generated during the processing will make the silicon carbide single-crystal film easy to break. Therefore, when preparing silicon carbide single-crystal flexible films with p / n junction structure and micro / nano-level thickness, how to peel off the silicon carbide single-crystal flexible film without generating external force and damage, so as to expand the application of silicon carbide single crystal in the field of flexible electronics and optoelectronic devices, this is still a huge challenge. Summary of the invention
[0004] In view of the technical problems of long processing cycle and high processing cost in the existing method for preparing silicon carbide single crystal thin film with p / n junction structure, poor flexibility and easy breakage of the obtained silicon carbide single crystal, the present invention provides a silicon carbide single crystal flexible film with p / n junction structure and its preparation method and application. The present invention homoepitaxially grows a low nitrogen doped epitaxial layer on the surface of an n-type silicon carbide substrate, then homoepitaxially grows a high nitrogen doped epitaxial layer on the low nitrogen doped epitaxial layer, and finally epitaxially grows an Al doped layer, immerses the silicon carbide epitaxial wafer in an etching solution, and based on a two-electrode system, uses the silicon carbide epitaxial wafer as a working electrode to perform photoelectrochemical etching, thereby realizing the peeling of the single crystal layer and obtaining a silicon carbide single crystal thin film with a p / n junction structure. The method is simple to operate, and the obtained silicon carbide single crystal thin film with a p / n junction structure has high flexibility, which meets 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: 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: S1, homoepitaxially grow n on the Si surface of the 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 to perform selective etching to obtain a silicon carbide single crystal flexible film with a p / n junction structure; The preset wavelength is smaller than a critical value of an absorption light wavelength corresponding to an n-type silicon carbide substrate.
[0006] Compared with the prior art, the method for preparing a silicon carbide single crystal flexible film with a p / n junction structure provided by the present invention comprises homogeneously growing a first epitaxial layer (n - Type epitaxial layer), at the interface between the two, the electrons dissociated from the n-type silicon carbide substrate will diffuse and accumulate on the first epitaxial layer side, while nitrogen cations will be left on the n-type silicon carbide substrate side, forming a built-in electric field similar to the "p / n junction" interface, and the direction of the electric field is from the n-type silicon carbide substrate (high nitrogen doped substrate) to the first epitaxial layer side (low nitrogen doped layer). Further, the second epitaxial layer (n-type epitaxial layer) is epitaxially grown, and a built-in electric field similar to the "p / n junction" interface is also spontaneously generated at the interface between the first epitaxial layer and the second epitaxial layer, and the direction of the electric field is from the second epitaxial layer (high nitrogen doped layer) to the first epitaxial layer (low nitrogen doped layer). Then, the third doped layer (p-type epitaxial layer) is epitaxially grown on the surface of the second epitaxial layer (high nitrogen doped layer), and a p / n junction is formed at the interface between the second epitaxial layer and the third epitaxial layer, and the direction of the built-in electric field is from the second epitaxial layer to 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 inside of the crystal is generated at the solid / liquid interface.
[0007] When the silicon carbide epitaxial wafer is irradiated with ultra-gap light, under the action of the built-in electric field at the interface, the photogenerated holes are enriched in the first epitaxial layer and the third epitaxial layer, and the photogenerated electrons are enriched in the substrate, the second epitaxial layer and the surface of the third epitaxial layer. Under ultra-gap light irradiation, the distribution state of photogenerated holes and photogenerated electrons on both sides of the interface can instantly reach a steady state. At this time, with the participation of the etching solution, the area where the photogenerated holes are enriched can undergo electrochemical corrosion of silicon carbide, but the corrosion rate is very slow. After applying a positive voltage at the bottom of the substrate, the photogenerated electrons enriched in the substrate are quickly conducted out of the body, which can increase the generation rate of photogenerated hole-electron pairs at the substrate / first epitaxial layer interface, so that the concentration of photogenerated holes in the first epitaxial layer increases rapidly, accelerating the electrochemical corrosion rate of silicon carbide in this area. However, since the first epitaxial layer is a low-nitrogen doped layer with a 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 corrosion 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 the action of external force, and the surface of the obtained silicon carbide single crystal flexible film is undamaged.
[0008] 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, thus realizing the reuse of the n-type silicon carbide substrate, greatly reducing the preparation cost of the silicon carbide single crystal flexible film with a p / n junction structure, and will not cause waste of resources or damage to the environment.
[0009] 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 .
[0010] Further, in step S1, the n - The nitrogen doping concentration in the epitaxial layer is 4×10 14 / cm 3 ~5×10 15 / cm 3 .
[0011] 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 .
[0012] 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 .
[0013] Further, 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.
[0014] The present invention creatively proposes a method for homoepitaxially growing n-type silicon carbide substrates with different nitrogen doping concentrations on the n-type silicon carbide substrate. - / 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), so that the silicon carbide single crystal flexible film with a p / n structure is peeled off from the substrate, and the peeled flexible film is undamaged. This provides a simple and efficient new process for preparing silicon carbide single crystal flexible film with a p / n structure, which can be applied to wearable devices, flexible displays, flexible detection and other fields.
[0015] 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.
[0016] The n-type silicon carbide substrate in the present invention can directly adopt 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 limitation.
[0017] It should be noted that, in the present invention, when homoepitaxially growing a p-type silicon carbide layer, the doping element may be Al or B.
[0018] Furthermore, in step S2, the etching solution is a mixed solution of hydrofluoric acid and hydrogen peroxide.
[0019] As a specific embodiment of the present invention, the hydrofluoric acid and hydrogen peroxide are both commercially available products, wherein the concentration of the hydrofluoric acid is 40wt%, and the concentration of the hydrogen peroxide is 30wt%.
[0020] Furthermore, in step S2, the mass concentration of HF in the etching solution is 2%-15%, the mass concentration of H2O2 is 2%-15%, and the balance is water.
[0021] Furthermore, in step S2, the cathode is a graphite sheet electrode.
[0022] 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.
[0023] It should be noted that the conductive layer is a metal material layer, and specifically a Pt layer, an Au layer, a Ti layer or a Ni layer can be selected, as long as the metal material has a good conductive effect, the present invention does not make any special restrictions. The method for preparing the conductive layer can be a sputtering method, or a conventional method for preparing a metal layer in the art, as long as it does not significantly damage the n-type silicon carbide substrate, the present invention does not make any special restrictions.
[0024] 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.
[0025] 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 to form a two-electrode system.
[0026] In a two-electrode system, when ultra-bandgap ultraviolet light is used to irradiate the silicon carbide epitaxial wafer, the photogenerated holes enriched in the first epitaxial layer selectively erode the silicon carbide at this location with the assistance of the etchant HF and the oxidant H2O2, and the reaction that occurs is: SiC+2H2O2+4 h + →SiO2+CO2↑+4H + SiO2+6HF→(SiF6) 2- +2H2O+ 2H + 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: 2H + +H2O2+2 e - =2H2O Furthermore, in step S3, the preset wavelength is 200nm~380nm.
[0027] As a specific embodiment of the present invention, a filter is used on the light source to filter so that the wavelength reaching the silicon carbide epitaxial wafer is smaller than the critical value of the light absorption wavelength corresponding to the n-type silicon carbide substrate, and the preferred wavelength range is 200nm~380nm. Specifically, a xenon lamp or a mercury lamp can be selected as the light source.
[0028] As a specific implementation of the present invention, it also includes using an organic glass sheet above the etching liquid to block the steam formed after the etching liquid evaporates, so as to prevent the evaporated etching liquid from corroding the filter.
[0029] Further, in step S3, the preset voltage is 0.1V~3V vs. cathode.
[0030] Furthermore, 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.
[0031] 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.
[0032] 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.
[0033] 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.
[0034] 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 the fields of 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 prior art cannot prepare a silicon carbide single crystal flexible film with a p / n junction structure. BRIEF DESCRIPTION OF THE DRAWINGS
[0035] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. 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 creative work.
[0036] 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; Figure 2Schematic diagram of a stripping device for preparing a silicon carbide single crystal flexible film with a p / n junction structure according to the present invention; wherein: 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; 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 in accordance with an embodiment of the present invention; 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; Figure 5 This is a Raman graph of a silicon carbide single crystal flexible film with a p / n junction structure prepared in accordance with an embodiment of the present invention. DETAILED DESCRIPTION
[0037] In order to make the purpose, technical solution 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 used to limit the present invention.
[0038] The peeling device used in the following examples for preparing the silicon carbide single crystal flexible film with a p / n junction structure is as follows: Figure 2 The stripping device comprises a flow-type electrolytic cell 8 and a light source. The electrolytic cell is provided with an open hole structure and a stirring structure 3. The open hole structure is used to fix the silicon carbide epitaxial wafer 1 and the cathode graphite sheet electrode 2. One end of the silicon carbide epitaxial wafer 1 is connected to the voltage output terminal 4, and the cathode graphite sheet electrode 2 is connected to the voltage input terminal 5. The light source is set at 5 cm to 10 cm above the surface of the etching liquid. The light emitted by the light source is filtered by a filter and then vertically irradiated on the surface of the silicon carbide epitaxial wafer.
[0039] The method for preparing a silicon carbide single crystal flexible film having a p / n junction structure using the above device comprises the following steps: S1, homoepitaxially grow n on the Si surface of the 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 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.
[0040] 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 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 epitaxial layer and the third epitaxial layer, and the built-in electric field is directed from n-type doping to p-type doping. A built-in electric field is generated at the solid-liquid interface between the third epitaxial layer and the etching solution, which is directed from the etching solution to the interior of the crystal. Under photoelectrochemical corrosion, the silicon carbide of the first epitaxial layer is electrochemically corroded and sacrificed. Since the first epitaxial layer is a low-nitrogen doped layer with a conductivity close to semi-insulating, the electrons inside the second epitaxial layer and on the surface of the third epitaxial layer cannot pass through the first epitaxial layer and be conducted out of the body. Therefore, they will not be etched during the photochemical corrosion process. Finally, when the first epitaxial layer is completely corroded, a single crystal flexible film formed by the second epitaxial layer (n-type) and the third epitaxial layer (p-type) can be obtained, and the surface of the obtained silicon carbide single crystal flexible film is not damaged.
[0041] 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 prepared silicon carbide single crystal flexible film with a p / n junction structure has no damage on the surface, meets 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 thin films in the field of flexible electronic or optoelectronic equipment.
[0042] 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.
[0043] Example 1 A method for preparing a silicon carbide single crystal flexible film having a p / n junction structure comprises the following steps: 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. - The n-type silicon carbide epitaxial layer, the n-type silicon carbide epitaxial layer and the p-type silicon carbide epitaxial layer are provided; 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; S2, preparing an etching solution, mixing a hydrofluoric acid solution with a mass concentration of 40% and a hydrogen peroxide solution with a mass concentration of 30% with ultrapure water in 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%; 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, coating the conductive layer with black wax to play an insulating and protective role, using the silicon carbide epitaxial wafer as the anode and the graphite electrode sheet as the cathode, connecting the silicon carbide epitaxial wafer to the output end of the voltage, and connecting the graphite electrode sheet to the input end of the voltage; S4, under room temperature conditions, a xenon lamp is used as a light source, and 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 is applied to the silicon carbide epitaxial wafer, and the potential is 0.5V (vs. the counter electrode) for selective etching to obtain a silicon carbide single crystal flexible film with a p / n junction structure; The height of the light source from 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.
[0044] Example 2 A method for preparing a silicon carbide single crystal flexible film having a p / n junction structure comprises the following steps: 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. - The n-type silicon carbide epitaxial layer, the n-type silicon carbide epitaxial layer and the p-type silicon carbide epitaxial layer are provided; 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 2μm; S2, preparing an etching solution, mixing a hydrofluoric acid solution with a mass concentration of 40% and a hydrogen peroxide solution with a mass concentration of 30% with ultrapure water in 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 15%, and the mass fraction of H2O2 is 15%; 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, coating the conductive layer with black wax to play an insulating and protective role, using the silicon carbide epitaxial wafer as the anode and the graphite electrode sheet as the cathode, connecting the silicon carbide epitaxial wafer to the output end of the voltage, and connecting the graphite electrode sheet to the input end of the voltage; S4, under room temperature conditions, a xenon lamp is used as a light source, and 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, and the wavelength of the light irradiated onto the silicon carbide epitaxial wafer is 200nm after filtering. At the same time, a voltage is applied to the silicon carbide epitaxial wafer, and the potential is 1.0V (vs. the counter electrode), and selective etching is performed to obtain a silicon carbide single crystal flexible film with a p / n junction structure; The height of the light source from 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.
[0045] Example 3 A method for preparing a silicon carbide single crystal flexible film having a p / n junction structure comprises the following steps: 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. - The n-type silicon carbide epitaxial layer, the n-type silicon carbide epitaxial layer and the p-type silicon carbide epitaxial layer are provided; wherein the nitrogen doping concentration in the n-type silicon carbide substrate is 5×10 18 / 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 6μm; S2, preparing an etching solution, mixing a hydrofluoric acid solution with a mass concentration of 40% and a hydrogen peroxide solution with a mass concentration of 30% with ultrapure water in 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%; 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, coating the conductive layer with black wax to play an insulating and protective role, using the silicon carbide epitaxial wafer as the anode and the graphite electrode sheet as the cathode, connecting the silicon carbide epitaxial wafer to the output end of the voltage, and connecting the graphite electrode sheet to the input end of the voltage; S4, under room temperature conditions, a xenon lamp is used as a light source, and the light emitted from the light source is filtered by a filter and 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 250nm. At the same time, a voltage is applied to the silicon carbide epitaxial wafer, and the potential is 2.0V (vs. the counter electrode) to perform selective etching to obtain a silicon carbide single crystal flexible film with a p / n junction structure; 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.
[0046] Example 4 A method for preparing a silicon carbide single crystal flexible film having a p / n junction structure comprises the following steps: 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. - The n-type silicon carbide epitaxial layer, the n-type silicon carbide epitaxial layer and the p-type silicon carbide epitaxial layer are provided; 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; S2, preparing an etching solution, mixing a hydrofluoric acid solution with a mass concentration of 40% and a hydrogen peroxide solution with a mass concentration of 30% with ultrapure water in 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%; 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, coating the conductive layer with black wax to play an insulating and protective role, using the silicon carbide epitaxial wafer as the anode and the graphite electrode sheet as the cathode, connecting the silicon carbide epitaxial wafer to the output end of the voltage, and connecting the graphite electrode sheet to the input end of the voltage; S4, under room temperature conditions, a xenon lamp is used as a light source, and 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 300nm. At the same time, a voltage is applied to the silicon carbide epitaxial wafer, and the potential is 1.5V (vs. the counter electrode) for selective etching to obtain a silicon carbide single crystal flexible film with a p / n junction structure; The height of the light source from 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.
[0047] The AFM images of the upper and lower surfaces of the silicon carbide single crystal flexible film with a p / n junction structure prepared in this embodiment are as follows: Figure 3~Figure 4 As shown in the figure, after electrochemical corrosion, the upper surface of the silicon carbide single crystal flexible film with a p / n junction structure obtained by peeling is still a smooth plane with a roughness of Ra=0.3nm, indicating that no corrosion occurred during the electrochemical corrosion process. The lower surface (peeling surface) of the silicon carbide single crystal flexible film with a p / n junction structure has a large step after electrochemical corrosion, with a roughness of Ra=3.2nm.
[0048] The upper surface of the silicon carbide single crystal flexible film with a p / n junction structure prepared in this embodiment is characterized by Raman spectroscopy. Figure 5 As shown in the figure, it can be seen that at 204cm -1 The FTA folding mode is located at 776 cm -1 The folded mode of lateral optical branching (FTO) and the -1 and 985cm -1 The folding modes of the longitudinal optical branch (FLO) of 965cm -1 and 985cm -1 The folding modes of the longitudinal optical branch (FLO) correspond to p-type doping and n-type doping, respectively. The silicon carbide single crystal flexible film with a p / n junction structure shows Raman characteristic peaks at the same position before and after photoelectrochemical corrosion stripping, which indicates that the prepared silicon carbide p / n single crystal film has stable crystal form before and after photoelectrochemical corrosion stripping. The intensity of the Raman characteristic peak decreases slightly after photoelectrochemical corrosion stripping, which is due to the thin thickness of the silicon carbide p / n single crystal film.
[0049] It can be seen from the above embodiments that the method for preparing a silicon carbide single crystal flexible film with a p / n junction structure provided by the present invention comprises: sequentially growing n-type silicon carbide substrates on the surface of the n-type silicon carbide substrates by homoepitaxial growth; -A n-type silicon carbide substrate, an n-type silicon carbide substrate and a p-type silicon carbide layer are prepared, and then the prepared silicon carbide epitaxial wafer is subjected to photoelectrochemical etching. By controlling specific photoelectrochemical etching parameters, the efficient stripping of the silicon carbide thin film with a p / n junction structure is achieved without damaging the stripped silicon carbide thin film. The stripped silicon carbide single crystal flexible film can be used as a flexible substrate material, on the basis of 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.
[0050] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modification, equivalent substitution or improvement made within the spirit and principle of the present invention should be included in the protection scope 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.