Method for preparing oxide semiconductor heterostructure and optoelectronic device

Abstract

This invention discloses a method for fabricating an oxide semiconductor heterostructure and its optoelectronic device. Based on micro-nano fabrication and oxide semiconductor thin film deposition processes, the resulting heterostructure is composed of p-type and n-type semiconductor materials arranged in a checkerboard pattern, forming a unique heterojunction array. This heterostructure effectively promotes the spatial separation of charge carriers, significantly shortening the transport distance and thus effectively maintaining high-energy charge carriers with strong reduction (electron) and oxidation (hole) capabilities distributed in different semiconductor materials, significantly improving the performance of semiconductor photoelectrodes. This invention represents a significant advancement in solving the bottleneck problem of charge carrier separation and transport in semiconductor photoelectrodes, and also possesses advantages such as simple structure, strong controllability, wide applicability, and high flexibility, showing broad application prospects.

Description

Technical Field

[0001] This invention relates to the field of photoelectric conversion semiconductor materials, specifically to a thin film preparation method based on oxide semiconductor heterostructure and its optoelectronic device, which enhances carrier separation and transport efficiency and improves photoelectrode performance by periodically built-in electric fields. Background Technology

[0002] In semiconductor photoelectrodes, electron-hole pairs generated by illumination need to be effectively separated and directionally transported to the electrode surface to participate in the reaction, preventing recombination before reaching the reaction site. Studies indicate that charge carriers successfully reaching the surface and participating in the reaction mainly originate from the space charge region within a few nanometers below the electrode surface. This region possesses a significant built-in electric field, which efficiently separates photogenerated charge carriers and drives electrons and holes to migrate in opposite directions—in n-type semiconductors, electrons are guided to the conductive substrate, while holes migrate to the surface for oxidation; the opposite occurs in p-type semiconductors. However, in the deeper bulk region (or quasi-neutral region), the built-in electric field weakens significantly or even disappears, resulting in slow carrier separation, severe recombination, and a significant reduction in transport efficiency. Due to the generally high recombination rate in semiconductor materials (mainly originating from defect recombination centers in the bandgap) and poor carrier migration ability, charge carriers excited deep within the material almost completely recombine during diffusion, making it difficult for them to contribute to the surface reaction. This bulk recombination loss is particularly prominent in thick-film photoelectrodes, severely restricting carrier separation and transport efficiency and leading to low photocurrent response. Therefore, suppressing bulk recombination and improving carrier separation and transport efficiency have become key strategies for optimizing photoelectrode performance.

[0003] To address the above issues, we propose a method to enhance carrier separation and transport in photoelectrodes by fabricating oxide-semiconductor heterostructures. These heterostructures, based on conventional micro / nano fabrication processes, construct periodic built-in potentials, significantly enhancing the carrier separation and transport efficiency of semiconductor photoelectrodes. Furthermore, this structure is highly versatile and can be applied to various combinations of p-type and n-type semiconductors, as well as superstructures of different sizes, demonstrating significant application prospects and value. Summary of the Invention

[0004] This invention proposes a method for fabricating oxide semiconductor heterostructures, which enhances carrier separation and transport efficiency and improves photoelectrode performance by increasing the spatial separation area and shortening the transport distance of carriers. This invention not only broadens the avenues for improving carrier separation and transport in semiconductor photoelectrodes and enhances the ability to control carriers in pn-type semiconductors, but also provides a reference and direction for performance optimization of other semiconductor optoelectronic devices.

[0005] The specific core technical solutions are as follows.

[0006] 1. Preparation method:

[0007] A method for fabricating oxide semiconductor heterostructures is mainly based on semiconductor micro / nano patterning and oxide semiconductor thin film deposition processes, specifically including:

[0008] Step (1) n-type thin film preparation: n-type semiconductor thin films are prepared on a conductive substrate using any film preparation process (spin coating, magnetron sputtering, etc.) to completely cover the entire conductive substrate. The film thickness is 50-500 nm.

[0009] Step (2) Checkerboard Patterning: Spin-coat photoresist onto the n-type thin film, expose it with a checkerboard photomask to obtain a checkerboard photoresist pattern. The checkerboard photomask should include different sizes, ranging from 2 to 30 μm;

[0010] Step (3) Wet etching: Perform pre-wet etching on the patterned n-type semiconductor thin film obtained in step (2), selecting the optimal etchant and parameters for etching. Note: The etching should ensure that the edge cell regions of the pn-type are slightly etched to allow for incomplete contact of the pn-type semiconductor thin film;

[0011] Step (4) Sputtering metal substrate and p-type semiconductor: Sputter metal substrate and p-type oxide semiconductor thin film sequentially on the sample obtained in step (3) using magnetron sputtering. The thickness of the metal substrate is 10-50 nm and the thickness of the p-type thin film is 50-300 nm.

[0012] Step (5) Ultrasound: The sample obtained in step (4) is placed in acetone and alcohol in sequence for ultrasound, the time of which depends on the ultrasound effect;

[0013] The ultrasound must ensure that the photoresist, the overlying metal substrate, and the p-type semiconductor are completely removed by ultrasound to obtain clear cells.

[0014] Step (6) Annealing: Place the sample obtained in step (5) into a muffle furnace for annealing (the specific annealing parameters depend on the deposited semiconductor thin film) to obtain an oxide semiconductor heterostructure.

[0015] Furthermore, the heterogeneous superstructure consists of horizontally distributed pn-phase checkerboard-shaped cells, with adjacent cells not in complete contact and leaving minute gaps. The gaps contain the initial conductive substrate, and the specific gap size is adjusted according to the cell size.

[0016] 2. Structural Design Principles:

[0017] By constructing an oxide semiconductor heterostructure, electron-hole exchange between pn-type semiconductors is achieved, eliminating competition between carrier transfer paths and greatly improving carrier separation efficiency.

[0018] Horizontally distributed heterogeneous superstructures can maximize light absorption and improve carrier generation rate.

[0019] 3. Technical and performance advantages:

[0020] Advantage (1): It expands the spatial separation interface of charge carriers, eliminates the competition between charge carrier transfer paths, and greatly improves the separation efficiency of charge carriers;

[0021] Advantage (2): Compared with the limited spectral response of conventional heterojunctions, planar structures can maximize the spectral response and enhance the concentration of photogenerated carriers;

[0022] Advantage (3): Compared with conventional heterojunctions which need to consider lattice matching, the superstructure described in this paper has no interface mismatch problem, has wide applicability and high flexibility, and can be constructed from p-type and n-type semiconductors of various structures;

[0023] Advantage (4): The superstructure fabrication method described in this paper is simple and can be achieved with conventional coating and photolithography equipment, with a low fabrication threshold;

[0024] Advantage (5): Based on the strong carrier generation and separation efficiency, the structure can generate hydrogen peroxide without the need for an external voltage, which has low application cost and is an environmentally friendly and green method for producing hydrogen peroxide;

[0025] Advantage (6): Wide range of applications and strong adaptability. Different pn-type semiconductors with different properties can be selected to prepare heterostructures according to different application requirements, so as to adapt to various types of environmental needs. Attached Figure Description

[0026] Figure 1 These are the UPS diagrams and band structure schematics of the heterogeneous superstructures (p-type: CuBi2O4; n-type: BiVO4) of the present invention, illustrating the theoretical support for the preparation of superstructures using BiVO4 and CuBi2O4 and the direction of carrier motion.

[0027] Figure 2 This is a flowchart illustrating the preparation process of the BiVO4-CuBi2O4 heterostructure of the present invention.

[0028] Figure 3 These are SEM images of the heterogeneous superstructures (p-type: CuBi2O4; n-type: BiVO4) of the present invention, showing the alternation and checkerboard distribution of BiVO4 and CuBi2O4 films in the superlattice.

[0029] Figure 4 The curves showing the hydrogen peroxide generation rate of the heterogeneous superstructures (p-type: CuBi2O4; n-type: BiVO4) in the embodiments of the present invention demonstrate the performance advantages of the superstructure.

[0030] Figure 5 This is a schematic diagram of the heterogeneous superstructure of the present invention. Detailed Implementation

[0031] To further illustrate the technical means of this invention, the specific implementation steps and details of the method for preparing oxide semiconductor heterostructures proposed in this invention are described in detail, and the application of the prepared optoelectronic devices is given, taking heterostructures (p-type: CuBi2O4 (CBO); n-type: BiVO4 (BVO)) as an example.

[0032] Example 1:

[0033] Ultraviolet photoelectron spectroscopy (UPS) was used to characterize individual CuBi₂O₄ and BiVO₄ thin films, which can measure the Fermi level, valence band peak, and work function of the material surface. Based on the characterization results, the principle of constructing heterostructures from BiVO₄ and CuBi₂O₄ can be explained.

[0034] UPS characterization results are as follows Figure 1 As shown, the work function of the BiVO4 film is 4.07 eV, and the valence band apex is -6.25 eV. The work function of CuBi2O4 is 4.8 eV, and the valence band apex is -6.31 eV. The work function of FTO is typically 4.4 eV, and that of Au is typically 5.1 eV. Therefore, electrons in the BiVO4 film are transported to the CuBi2O4 film through the higher work functions of FTO and Au, reaching the CuBi2O4 film surface to participate in the ORR reaction. Holes in the CuBi2O4 film are transported to the BiVO4 film through the lower work functions of Au and FTO, reaching the BiVO4 film surface to participate in the WOR reaction.

[0035] Example 2:

[0036] Preparation and characterization of checkerboard-like heterostructures:

[0037] 1. Substrate pretreatment: Fluorine-doped tin oxide (FTO) conductive glass was selected as the substrate, and it was ultrasonically cleaned with acetone and ethanol for 15 min in sequence, then rinsed with deionized water 3 times, dried with nitrogen, and finally treated in an O2 plasma cleaner for 3 min.

[0038] 2. BiVO4 Thin Film Preparation: Polycrystalline BiVO4 thin films were prepared using the sol-gel method. First, 16.5 mL and 2.5 mL of acetylacetone solution were drawn and placed into reagent bottles No. 1 and No. 2, respectively, for later use. 0.131 g of vanadium acetylacetone and 0.2425 g of bismuth nitrate pentahydrate were weighed and placed into reagent bottles No. 1 and No. 2, respectively, and mixed with the acetylacetone solution. Reagent bottles No. 1 and No. 2 were sonicated for 20 min each, then mixed and sonicated for 10 min to obtain 19 mL of clear, blue-black BiVO4 solution. FTO was then fixed on a spin coater, and an appropriate amount of the prepared BiVO4 solution was added. The mixture was filtered through a 0.25 μm PTFE filter and spin-coated at 1000 rpm for 20 s. After spin-coating, the film was pyrolyzed on a 300℃ heating plate for 10 min. This process was repeated 6 times to obtain a 60 nm thick BiVO4 thin film.

[0039] 3. Checkerboard patterning: Positive photoresist (AZ601) is spin-coated onto the surface of the BiVO4 thin film. The pre-baking temperature is 120℃ and the time is 2 min. A checkerboard mask is used and exposed to ultraviolet light for 3.8 s. The film is then immersed in a developer solution (AZ300MIF) for 50 s to form a checkerboard-shaped photoresist protection area.

[0040] 4. Wet etching: Immerse the BiVO4 film with the exposed pattern in a 0.1M hydrochloric acid solution for 6-15 seconds, then rinse with deionized water. Next, immerse it in alcohol for 10 seconds to remove the photoresist, rinse thoroughly with deionized water, and dry with an air gun. Observe the etching process under a microscope. Repeat this process several times to obtain the optimal etching parameters. Use these parameters for subsequent etching. After the final etching, it is not necessary to remove the photoresist.

[0041] 5. Sputtering the metal substrate and CuBi₂O₄: The subsequent metal substrate and CuBi₂O₄ were prepared by magnetron sputtering, with the base vacuum evacuated to 8*10⁻⁶. -4 First, Ar gas at a flow rate of 15 sccm was introduced into the sputtering chamber, maintaining a sputtering pressure of 0.4 Pa. The sample platform was set to rotate at a rate of 10 r / min, and the DC source sputtering current was 0.1 A. A Ti layer of approximately 10 nm thickness was first sputtered onto the film surface. Then, the RF source sputtering power was set to 15 W, and an Au layer of approximately 30 nm thickness was sputtered, completing the metal substrate fabrication. Next, the Ar gas flow rate was changed to 34-36 sccm, the sputtering pressure was maintained at 1 Pa, the sample platform rotation speed was set to 10 r / min, and the RF source power was set to 60 W, sputtering a CuBi₂O₄ layer of 100 nm thickness, thus completing the entire sputtering process.

[0042] 6. Ultrasonication: First, immerse the sputtered film in acetone solution for 1-3 hours to induce cracks in the photoresist. Then, sonicate it for 10 seconds at 50 W in an ultrasonic machine. Remove the film and sonicate it in alcohol for 1-3 minutes, continuously observing the film during this time to completely remove the photoresist and the Ti, Au, and CuBi2O4 films on it. The time should not be too long, otherwise it will damage the BiVO4 film. After ultrasonication, rinse the sample with deionized water and dry it with an air gun. Observe it under a microscope to confirm the integrity of the checkerboard p / n structure.

[0043] 7. Annealing: The ultrasonically treated sample was placed in a muffle furnace and heated to 500℃ in air at a heating rate of 5℃ / min, and held at that temperature for 1 h. This successfully yielded the BiVO4-CuBi2O4 heterostructure. The preparation process is as follows: Figure 2 As shown.

[0044] Characterization tests of heterogeneous superstructures:

[0045] The prepared heterostructure with a side length of 8 μm was characterized by scanning electron microscopy (SEM). The scanning results are as follows: Figure 3 As shown, the horizontally alternating distribution of characteristic peaks of BiVO4 and CuBi2O4 materials is clearly visible, proving the successful construction of the superstructure.

[0046] Example 3: A biasless optoelectronic device applied to the production of hydrogen peroxide.

[0047] This example is based on the BiVO4-CuBi2O4 heterostructure optoelectronic device prepared in Example 1. It conducts a test on the production of hydrogen peroxide (H2O2) without bias voltage, realizing the synergistic reaction of water oxidation (BiVO4) and oxygen reduction (CuBi2O4) under no bias voltage conditions, which significantly improves the yield of H2O2.

[0048] 1. Electrolyte preparation: A 0.1M potassium bicarbonate (KHCO3) solution was used as the reaction medium, and 15 mL was injected into the quartz reactor. Before the reaction, high-purity O2 (99.9%) was purged for 30 min to remove residual air from the system and ensure that the reaction was carried out in an oxygen-rich environment.

[0049] 2. Placement of photoelectrode: The BiVO4-CuBi2O4 heterostructured thin film prepared in Example 1 was placed at the bottom of the reactor and vertically irradiated by a light source (simulating AM 1.5 G sunlight) at a distance of 10 cm from the sample surface to control the light intensity.

[0050] 3. Temperature control: The electrolyte temperature is maintained at 5℃ by an external cooling system to inhibit H2O2 decomposition and improve detection accuracy.

[0051] 4. Quantitative Analysis of H2O2: The amount of H2O2 produced was quantitatively determined using the ferrous chloride (FeCl2) oxidation colorimetric method. 5 mL of hydrochloric acid (HCl, 3 M) and 0.2982 g of FeCl2 were added to 10 mL of aqueous solution, labeled as solution #1. The mixture was then stirred for 5 min. Subsequently, 1 mL of the reaction solution was periodically sampled, and 1.8 mL of hydrochloric acid (3 M) and 0.2 mL of solution #1 were added, shaken well, and allowed to stand for 10 min. The generated H2O2 can oxidize FeCl2... 2+ Oxidized to Fe 3+ The absorbance at 340 nm was measured using UV-visible absorption spectroscopy (Shimadzu UV-2550) to evaluate the results.

[0052] Test results:

[0053] Calculation and analysis of H2O2 formation rate, such as Figure 4 As shown, the average H2O2 generation rate of the BiVO4-CuBi2O4 heterostructure photoelectrode is much higher than that of a single thin film within a 50-minute reaction time.

[0054] The BiVO4-CuBi2O4 heterostructure device prepared by this invention showed good application potential in the test, with a significant improvement in H2O2 production capacity and a significant improvement in carrier separation efficiency.

[0055] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention. Furthermore, various modifications can be made to the present invention for specific situations or circumstances without departing from the scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed, but should include all embodiments falling within the scope of the claims of the present invention.

[0056] It should be understood that this disclosure is not limited to the features described above, and various modifications or changes can be made without departing from its scope. The scope of this disclosure is limited only by the appended claims.

Claims

1. A method for fabricating an oxide semiconductor heterostructure and an optoelectronic device, characterized in that, The preparation method includes the following steps in sequence: Step (1) n-type thin film preparation: n-type oxide semiconductor thin film is deposited on a conductive substrate using any film preparation technique, wherein the n-type thin film completely covers the entire conductive substrate; Step (2) Checkerboard patterning: A checkerboard photoresist pattern is formed on the surface of the n-type thin film by photolithography. The size of the pattern unit is determined by the mask size design and specific photolithography process parameters. Step (3) Etching: The patterned film obtained in step (2) is etched. Specifically, the patterned film is pre-wet etched. After multiple experiments, the most suitable parameters are obtained, and the formal etching is performed using these parameters. Among them, the n-type film in the area without photoresist pattern protection is etched away, while the n-type film in the area with photoresist pattern protection is retained. There should be slight etching at the p / n junction. (4) Titanium / gold film and p-type film sputtering: Metal electrodes and p-type oxide semiconductor films are sputtered sequentially on the film obtained in step (3). (5) Ultrasonication: The sample obtained in step (4) is ultrasonically removed from the photoresist and the portion above it in acetone and alcohol. Specifically, the metal electrodes and p-type semiconductor films in the areas without photoresist patterns are retained, while the sputtered material in the areas with photoresist is removed along with the photoresist. (6) Annealing: The sample stripped in step (5) is placed in a muffle furnace for annealing to obtain the oxide semiconductor heterostructure.

2. The method for fabricating oxide semiconductor heterostructures according to claim 1, characterized in that, The method for preparing the n-type oxide semiconductor thin film in step (1) is any one of the following film-forming techniques: physical vapor deposition, chemical vapor deposition, or solution deposition.

3. The method for fabricating oxide semiconductor heterostructures according to claim 2, characterized in that, In step (2), the size of the checkerboard unit of the mask is 2-30 μm.

4. The method for fabricating an oxide semiconductor heterostructure according to claim 1, characterized in that, The etching process described in step (3) is a wet etching process.

5. The method for fabricating an oxide semiconductor heterostructure according to claim 4, characterized in that, The sputtering sequence in step (4) is to first sputter the metal substrate and then sputter the p-type oxide semiconductor thin film.

6. The method for fabricating an oxide semiconductor heterostructure according to claim 1, characterized in that, In the fabricated heterostructure, the size of the pn cell is limited by the resolution accuracy of the photolithography and etching processes.

7. The method for fabricating an oxide semiconductor heterostructure according to claim 6, characterized in that, In the prepared heterostructure, the distance between adjacent pn cells depends on the etching process parameters and etching accuracy in step (3).

8. An oxide semiconductor heterostructure, characterized in that, The oxide semiconductor heterostructure is a checkerboard-shaped photoelectrode. It enhances carrier separation and transport capabilities by spatially separating carriers and shortening their movement distance, thereby improving photoelectrode performance. It can produce hydrogen peroxide by simulating sunlight irradiation without bias voltage.

9. An oxide semiconductor heterostructure, characterized in that, The oxide semiconductor heterostructure can select high-performance pn-type semiconductor combinations and choose a metal substrate that matches the work function of the p-type semiconductor to form an ohmic contact, effectively further improving the carrier separation capability.

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