Oxide semiconductor plane p / n superstructure and preparation method thereof

Abstract

The invention discloses an oxide semiconductor plane p / n superstructure and a preparation method thereof. According to the method, a latticed mask is formed on the surface of an oxide thin film based on a photoetching process, O2 atmosphere annealing (100-300 DEG C, 15-40 min) is combined, the local oxygen vacancy concentration of a mask covering area and an exposed area is precisely regulated and controlled, and precise in-situ conversion of a p type (oxygen-rich area) and an n type (oxygen-poor area) in a homogeneous material is achieved. The planar p / n superstructure breaks through the strict limitation of a traditional vertical multi-junction structure on material doping and interface quality, the width of a depletion region is expanded to the micron order through the p / n homojunction arrays alternately distributed in the plane, and the bulk recombination effect of photon-generated carriers is remarkably inhibited. According to the method, an innovative technical route of photoetching-assisted in-situ construction of the planar multi-junction photoelectrode is created, the method has the advantages of interface atomic-scale lattice matching, simple process, high compatibility, accurate and controllable space charge distribution and the like, and a technical foundation is laid for non-assisted solar water decomposition, research and development of self-driven optoelectronic devices and the like.

Description

Technical Field

[0001] The present invention belongs to the field of photoelectric conversion semiconductor materials, and specifically relates to a method for preparing a planar p / n superstructure of an oxide semiconductor thin film based on photolithography mask-guided oxygen vacancy regulation. The method is particularly suitable for fields such as photoelectrochemical water decomposition, solar fuel production, and self-driven optoelectronic devices. Background Art

[0002] Photoelectrochemical technology, with its unique photo-electro-chemical coupling effect, offers a promising approach for solar energy conversion and storage, and exhibits multi-dimensional application potential in areas such as environmental remediation, biomedicine, and green agriculture. However, conventional single-junction semiconductor photoelectrodes are generally limited by low light absorption efficiency and high carrier recombination rates. The construction of multi-junction structures (homo- and heterojunctions) has become a mainstream strategy for performance optimization. By forming a wide depletion region to efficiently separate photogenerated carriers and generate higher photovoltages, they are expected to promote unassisted solar-to-fuel conversion. Current research on multi-junction photoelectrodes focuses primarily on vertically stacked pin junction configurations. However, this technology faces two major challenges: 1. Controllable p / n-type doping and high-quality growth are extremely challenging for most oxide semiconductors; 2. Conventional heteroepitaxial growth techniques are limited by lattice constant differences, which can easily induce defect states such as interface dislocations and dangling bonds, leading to a disordered distribution of the space charge barrier and severely restricting carrier mobility. Furthermore, vertical multi-junction structures require complex multilayer epitaxial growth processes, which are costly and difficult to fabricate on a large scale.

[0003] To address these key bottlenecks, the present invention innovatively proposes a method for fabricating planar p / n superstructures in oxide semiconductor thin films based on photolithography-guided oxygen vacancy control. This method forms a grid-like mask on the surface of the oxide film using photolithography, and combines it with O2 atmosphere annealing to precisely control the local oxygen vacancy concentration, achieving in situ integration of the p / n superstructure within an atomically smooth interface. This method effectively addresses key challenges in traditional multi-junction fabrication, offers low technical difficulty, minimal equipment requirements, and is readily scalable, providing a technological paradigm for the integrated design of a new generation of high-performance optoelectronic devices for cross-scale applications. Summary of the Invention

[0004] The present invention provides a method for preparing a p / n superstructure in an oxide thin film. The method uses photolithography technology to perform nanometer-level precision positioning, and achieves precise control of the local oxygen vacancy concentration by annealing in an O2 atmosphere in specific areas (submerged covered areas and exposed areas). As a result, n-type regions (oxygen-poor regions) and p-type regions (oxygen-rich regions) are induced in situ on the same thin film, constructing a planar p / n superstructure, which provides new ideas and new directions for the construction and application of solar energy conversion devices.

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

[0006] 1. Preparation method:

[0007] Step (1) Material preparation: Grow an oxide semiconductor on a conductive substrate using thin film preparation technology (pulsed laser deposition, magnetron sputtering, spin coating-gel method, etc.), and anneal and crystallize in air. The film thickness is d and satisfies 50≤d≤200nm.

[0008] Step (2) Photolithography patterning: Use photolithography technology (UV lithography or laser direct writing, etc.) to form a grid mask on the surface of the film, and select a high-temperature resistant photoresist (≥100°C), such as AZ series positive photoresist. The grid mask spacing is l, which is determined by the selected photolithography process parameters and the high-temperature resistance of the photoresist.

[0009] Step (3) atmosphere annealing to control p / n: annealing in an oxygen environment, by introducing oxygen (purity ≥99.99%) into a vacuum (≤1Pa) tube furnace, at atmospheric pressure, with an oxygen flow rate between 10 and 30 sccm; or annealing directly in air, with the p-type performance slightly affected. The annealing temperature is T, the annealing time is t, and they meet the requirements of 100°C ≤ T ≤ 200°C, and 15min ≤ t ≤ 40min. In the n-type region, the photoresist-covered area forms high-concentration oxygen vacancies due to oxygen deficiency, and the carrier type is n-type; in the p-type region, the uncovered area forms low-concentration oxygen vacancies in an oxygen-rich environment, and the carrier type is p-type.

[0010] Step (4) degumming and post-processing: The photoresist is removed by ultrasonic treatment with acetone and alcohol to obtain an in-plane alternatingly distributed p / n homojunction superstructure array.

[0011] Furthermore, the superstructure is composed of n-type regions and p-type regions alternately distributed in a plane, the n-type regions and the p-type regions form a grid-like homojunction array, and adjacent grid units are connected by atomically matched homojunction interfaces.

[0012] 2. Structural design principles:

[0013] Band engineering: Oxygen vacancy engineering is used to achieve Fermi level shift in oxide semiconductors, resulting in controllable switching of semiconductor conductivity types.

[0014] Depletion region expansion: The grid-like p / n superstructure forms a continuous depletion region in the horizontal direction with a densely distributed built-in electric field, which effectively separates the photogenerated carriers.

[0015] 3.Technical and performance advantages:

[0016] Advantage (1): Atomic-level matching of homojunction interfaces—eliminating lattice mismatch and defect states at heterojunction interfaces.

[0017] Advantage (2): Improved carrier collection efficiency - the depletion region width is extended to micron-scale spatial array distribution, and the bulk recombination rate is sharply reduced.

[0018] Advantage (3): Photovoltage multiplication effect - planar multi-junction series connection greatly increases the photovoltage, meeting the needs of unassisted water splitting.

[0019] Advantage (4): Simple equipment, simple steps, and low cost. Compared with conventional complex heterojunction growth or doping, the present invention does not require complex equipment connections and numerous steps. It only requires growing a single material once. The superstructure preparation process only requires lithography and heating equipment. It has low technical difficulty, simple operation, and better scalability.

[0020] Advantage (5): The preparation area of ​​the p / n superstructure described in the present invention is limited by the lithography accuracy and area. The minimum homogeneous array with nanometer-level precision can be constructed, and the device area can be achieved within 6 inches. The area limit of industrial-grade lithography equipment is even higher. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a schematic diagram of an oxide semiconductor planar p / n superstructure and its preparation method according to the present invention (summary attached);

[0022] Figure 2 Schematic diagram of the preparation process of the oxide semiconductor thin film planar p / n superstructure of the present invention, including photolithography, annealing and stripping steps;

[0023] Figure 3 The KPFM test results of the BiFeO3 thin film planar p / n superstructure according to the embodiment of the present invention show the alternating distribution of the surface potential in the p / n region;

[0024] Figure 4 The present invention calculates and analyzes the hydrogen peroxide generation rate comparison curve of the BiFeO3 thin film planar p / n superstructure, proving the performance advantage of the superstructure;

[0025] Figure 5 This is a graph showing changes in hydrogen and oxygen evolution bubbles and their visible area over time observed using an optical microscope on a planar p / n superstructure of a BiFeO 3 film according to an embodiment of the present invention. DETAILED DESCRIPTION

[0026] In order to further illustrate the technical means of the present invention, the specific implementation steps and details of the method for preparing the p / n superstructure in the plane of the oxide semiconductor thin film proposed in the present invention are described in detail, and the application of the prepared optoelectronic devices is given, taking BiFeO3 (BFO) polycrystalline thin film as an example.

[0027] Example 1:

[0028] Preparation and characterization of grid-like p / n superstructures.

[0029] 1. Substrate pretreatment: Fluorine-doped tin oxide (FTO) conductive glass was selected as the substrate and ultrasonically cleaned with acetone and ethanol for 15 minutes, then rinsed with deionized water three times, blown dry with nitrogen, and finally treated in an O2 plasma cleaner for 3 minutes.

[0030] 2. BFO Film Preparation: Polycrystalline BFO films were prepared using a sol-gel method. First, 10 mL of ethylene glycol methyl ether solution was extracted and placed in a reagent bottle for later use. 1.0253 g of ferric nitrate nonahydrate and 1.2402 g of bismuth nitrate pentahydrate were weighed separately and placed in a reagent bottle, mixed with the ethylene glycol methyl ether solution, and stirred for 5 minutes to achieve a clear, reddish-brown BFO solution. Subsequently, the FTO film was placed on a spin-coating table and an appropriate amount of the prepared BFO solution was added dropwise. The film was filtered through a 0.25 μm PTFE filter and spin-coated at 4500 rpm for 20 seconds. After spin-coating, the film was pyrolyzed on a 350°C hotplate for 3 minutes. After pyrolysis, the film was annealed in a muffle furnace at 600°C for 5 minutes. The spin-coating, pyrolysis, and annealing steps were repeated five times, with the final annealing time extended to 10 minutes, to obtain a 150 nm thick polycrystalline BFO sample.

[0031] 3. Photolithography patterning: Spin-coat a positive photoresist (AZ601) on the surface of the BFO film with a pre-bake temperature of 120°C for 2 minutes. Use a grid mask and expose it to UV light for 3.8 seconds. Immerse the film in a developer (AZ300MIF) for 50 seconds to form a grid-like photoresist protection area.

[0032] 4. Oxygen atmosphere annealing: Place the sample in a tube furnace and heat it to 150°C in an O2 atmosphere at a rate of 5°C / minute (if the flipping effect is poor, the annealing temperature can be increased appropriately). Hold the temperature for 30 minutes, then cool to room temperature before removing the sample. At this point, a p / n homojunction array has been successfully constructed, with the area under the photoresist being n-type and the area without photoresist being p-type.

[0033] 5. Remove the photoresist: Soak the sample in acetone for 2 minutes, rinse it 10 times to remove the photoresist, and then use alcohol ultrasonic for 5 seconds to remove the surface stains to obtain the BFO film planar p / n superstructure. The p / n superstructure preparation process is as follows Figure 2 shown.

[0034] p / n superstructure characterization test:

[0035] The prepared p / n superstructure was characterized by Kelvin probe force microscopy (KPFM), and the scanning potential results are shown in the figure below. Figure 3 As shown, the staggered distribution structure of the surface potential (work function) can be clearly seen, proving the successful construction of the superstructure.

[0036] Example 2:

[0037] Bias-free optoelectronic devices for hydrogen peroxide production.

[0038] This example conducts an unbiased hydrogen peroxide production test based on the p / n superstructure optoelectronic device prepared in Example 1, realizing the synergistic reaction of water oxidation (n-BFO) and oxygen reduction (p-BFO) under unbiased conditions, significantly improving the H2O2 yield.

[0039] 1. Electrolyte Preparation: Use 0.1M KHCO3 solution as the reaction medium and inject 15mL into the quartz reactor. Before the reaction, purge with high-purity O2 (99.9%) for 30 minutes to remove any residual air in the system and ensure that the reaction is carried out in an oxygen-rich environment.

[0040] 2. Photoelectrode placement: The planar p / n superstructure film prepared in Example 1 was placed at the bottom of the reactor, and the light source (simulating AM1.5G sunlight) was irradiated vertically at a distance of 10 cm from the sample surface to control the light intensity.

[0041] 3. Temperature control: The electrolyte temperature is maintained at 5°C through an external cooling system to inhibit the decomposition of H2O2 and improve detection accuracy.

[0042] 4. Quantitative analysis of H2O2: FeCl2 oxidation colorimetry was used to quantitatively determine the amount of H2O2 produced. 5 mL of hydrochloric acid (3 M) and FeCl2 (0.2982 g) were added to 10 mL of aqueous solution, referred to as solution ①. The mixture was then stirred for 5 minutes. Subsequently, 1 mL of the reaction solution was sampled at regular intervals and added to 1.8 mL of hydrochloric acid (3 M) and 0.2 mL of the above-prepared solution ①, shaken, and allowed to stand for 10 minutes. The H2O2 produced can convert FeCl2 into H2O2. 2+ Oxidized to Fe 3+ , was evaluated by measuring the absorbance at 340 nm using UV-visible absorption spectroscopy (Shimadzu UV-2550).

[0043] Test results:

[0044] Calculate and analyze the hydrogen peroxide generation rate as Figure 4 As shown, the average H2O2 generation rate of the in-plane p / n-BFO superstructure photoelectrode within a reaction time of 50 minutes is much greater than that of a single film.

[0045] Example 3:

[0046] No auxiliary solar energy conversion devices.

[0047] The unassisted solar energy conversion device provided by the present invention, based on the superstructure prepared in Example 1, achieves unbiased water splitting through the selective deposition of hydrogen / oxygen evolution catalysts. The device utilizes photoelectrochemical deposition to spatially selectively deposit the hydrogen evolution catalyst on p-BFO and the oxygen evolution catalyst on n-BFO. Through the synergistic effect between the p / n superstructure and the catalysts, the device simultaneously produces H2 and O2 without an external bias.

[0048] 1. Electrode configuration: A photoelectrochemical deposition system was constructed using the p / n superstructure sample as the working electrode (WE), platinum foil as the counter electrode (CE), and Ag / AgCl (saturated KCl) as the reference electrode (RE).

[0049] 2. Photodeposition (using Pt loading as an example): Prepare 10 ml of a 5 wt% aqueous solution of chloroplatinic acid (HPtCl6·6H2O) as the deposition solution. Under simulated sunlight, apply a constant voltage of 0.2 V to the system (a higher voltage is applied because Pt deposition is rapid, and the reaction should be slowed down as much as possible to achieve a slow deposition rate) for 100 seconds. Use a small stirrer to ensure uniform deposition. After deposition, wash the resulting product with deionized water and anhydrous ethanol to remove surface impurities, then dry it at 60°C for 12 hours to complete the Pt loading on the p-BFO.

[0050] 3. Photooxidation deposition (with CoO x For example, 100 ml of 1 wt% cobalt nitrate solution (Co(NO3)2·6H2O) was prepared as the deposition solution. A constant voltage of 0.2 V was applied under light for 600 s. The remaining washing and drying steps were the same as those for photoreduction deposition to achieve CoO x Deposition on n-BFO.

[0051] 4. Water Splitting Performance Testing: The edges of the deposited p / n superstructure were wrapped with tape. A small amount of 0.1M KHCO₃ solution was dripped onto the superstructure as the reaction medium. A glass slide was gently placed over the solution to prevent evaporation of bubbles, which would otherwise hinder observation. The growth of bubbles on the superstructure during the reaction was observed using an optical microscope and recorded for later quantitative analysis.

[0052] Characterization and testing:

[0053] The temporal changes in the visible area of ​​bubbles in the p / n superstructure were recorded and compared with that of a control p-BFO / n-BFO with the same photolithographic pattern to verify the generation of hydrogen and oxygen during the unbiased water splitting process. Figure 5The time-dependent increasing trend of the visible area of ​​bubbles in the p / n superstructure was presented, while no bubbles were generated in the control p-BFO / n-BFO, demonstrating the effectiveness of the synergistic effect between the p / n superstructure and the catalyst, and providing a new strategy for the scalable preparation of high-performance solar energy conversion materials.

[0054] The p / n superstructure multifunctional device prepared by the present invention showed good application potential in the test, with H2O2 production and hydrogen and oxygen evolution capabilities significantly improved, and the carrier recombination rate significantly reduced.

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

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

Claims

1. An oxide semiconductor planar p / n superstructure and a method for preparing the same, characterized in that: The following steps are involved: Step (1) photolithographic patterning: forming a grid-shaped mask on the surface of the oxide semiconductor film by photolithographic technology, wherein the mask is made of a high-temperature resistant photoresist (≥100° C.), and the grid spacing l is determined by the actual photolithographic process parameters; Step (2) atmosphere annealing to in-situ control the p / n region: Annealing is performed in an oxygen atmosphere, specifically by introducing high-purity (≥99.99%) oxygen in a vacuum environment (≤1 Pa) at a controlled flow rate of approximately 10-30 sccm, with the annealing pressure being atmospheric pressure. The photoresist-covered region forms high-concentration oxygen vacancies due to oxygen deficiency, constituting an n-type conductive region; the uncovered region forms low-concentration oxygen vacancies in an oxygen-rich environment, constituting a p-type conductive region. The above process can also be performed directly in dry air. Step (3) degumming and post-processing: The photoresist is removed by ultrasonic treatment with acetone and alcohol to obtain an in-plane alternatingly distributed p / n homojunction superstructure array.

2. The preparation method according to claim 1, characterized in that In step (2), the annealing temperature is 100-300° C., the annealing time is 15-40 minutes, and the oxygen flow rate is 10-30 sccm.

3. The preparation method according to claim 1, characterized in that The superstructure consists of n-type regions and p-type regions alternately distributed in a plane, wherein the n-type regions and the p-type regions form a grid-like homojunction array, and adjacent grid units are connected through atomic-level lattice-matched homojunction interfaces.

4. The oxide thin film planar p / n superstructure according to claims 1-3, characterized in that: The superstructure pattern is not fixed, and all pn junction arrays prepared according to the present invention are superstructures.

5. The oxide thin film p / n superstructure according to claim 3, characterized in that: The preparation area of ​​the superstructure is limited by the photolithography process and the heat resistance of the photoresist. The minimum homogeneous array with nanometer-level precision can be constructed, and the device area can be expanded within the range of industrial-grade photolithography equipment at the micron level and above.

6. A solar energy conversion device, characterized in that: The invention comprises the oxide thin film planar p / n superstructure as claimed in claim 3, wherein the superstructure acts as a photoelectrode, separating photogenerated carriers by a built-in electric field under simulated sunlight, thereby achieving unbiased water decomposition or hydrogen peroxide production.

7. The solar energy conversion device according to claim 6, characterized in that Similar to hydrogen and oxygen evolution, the surface of the photoelectrode realizes spatially selective loading of catalysts by photoelectrochemical deposition: hydrogen evolution catalyst is deposited in the p-type region, and oxygen evolution catalyst is deposited in the n-type region.

8. Use of the solar energy conversion device according to any one of claims 6 to 7, characterized in that: The device is used for unassisted solar water decomposition to produce hydrogen and oxygen or unbiased photocatalytic synthesis of hydrogen peroxide. The device does not require an external bias and relies solely on solar energy to achieve efficient energy conversion.

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