A p-type tetragonal phase beta-bi2o3 thin film and a method for preparing the same by mocvd

Abstract

The application discloses a p-type tetragonal phase beta-Bi2O3 film and a MOCVD preparation method thereof, and the method is characterized by the following core process: in-situ oxygen pretreatment of a substrate (temperature interval is 300-425 DEG C, and low pressure interval is 5-80 mbar) + low-temperature oxygen-rich epitaxial growth (temperature interval is 725-845 DEG C, low pressure interval is 5-80 mbar, and Bi / O molar flow is 1:160-1:6000), so that key process elements of the beta-Bi2O3 film are precisely controlled, thereby realizing epitaxial growth of the p-type tetragonal phase beta-Bi2O3 single crystal film by using the MOCVD, and the film has super-high uniformity and can be adapted to 8-inch to 12-inch large-size substrates.

Description

Technical Field

[0001] This invention relates to the field of semiconductor epitaxial technology, and in particular to a p-type tetragonal phase β-Bi2O3 thin film and its MOCVD preparation method. Background Technology

[0002] Tetragonal β-Bi₂O₃ is an intrinsic p-type oxide semiconductor with great application potential. Its valence band apex is formed by the hybridization of Bi 6s and O 2p orbitals, which endows it with excellent hole transport capabilities and a broad-spectrum visible light response, making it a core material for next-generation all-oxide CMOS, visible light detection, and Z-type photocatalytic heterojunctions. However, current technologies have significant limitations in preparing high-quality β-Bi₂O₃ thin films: First, the hydrothermal / solvothermal method is only suitable for preparing micron-sized sheet-like powders and cannot be used to epitaxially grow continuous thin films on single-crystal substrates. Furthermore, the large number of interface defects that are easily introduced during the powder transfer process can lead to device leakage. Secondly, methods such as magnetron sputtering and pulsed laser deposition (PLD) have the disadvantage of poor composition uniformity, which can easily form a large thickness gradient on large-area substrates. Furthermore, due to Bi deficiency or uncontrolled oxygen vacancies, α impurity phases are easily induced, leading to unstable p-type properties. Furthermore, Mist-CVD atomization deposition requires acidic solvents, which can corrode equipment, and the precursor is prone to condensation during transport, making it difficult to precisely control the Bi / O molar flow ratio and thus impossible to obtain pure phase films.

[0003] In summary, existing technologies cannot effectively solve the technical challenges in the preparation of β-Bi2O3 thin films, such as the coexistence of α-imperfection phases, unstable conductivity, difficulty in single-crystal epitaxy, poor large-area uniformity, and difficulty in adapting to large-size substrates ranging from 8 inches to 12 inches. Therefore, it is urgent to develop a completely new preparation process. Summary of the Invention

[0004] Based on this, the present invention provides a p-type tetragonal β-Bi2O3 thin film and its MOCVD preparation method, which uses metal-organic vapor deposition to replace the traditional hydrothermal, spray pyrolysis and magnetron sputtering processes, and accurately and stably prepares intrinsic p-type tetragonal β-Bi2O3 single crystal thin film with no α impurity phase and high hole conductivity.

[0005] To achieve the above objectives, the present invention provides the following technical solution: On one hand, this invention discloses a MOCVD preparation method for p-type tetragonal phase β-Bi2O3 thin films, comprising the following steps: S1. In-situ oxygen pretreatment of substrate: In the reaction chamber of the MOCVD equipment, oxygen precursor is continuously introduced into the first temperature range and the first low pressure range to perform in-situ oxidation pretreatment of the substrate material for 5-60 minutes to remove surface carbon impurities, adsorbed water and surface defects, eliminating the need for traditional offline acid and alkali cleaning steps and avoiding the introduction of external contamination. S2. Low-temperature oxygen-enriched epitaxial growth: The temperature of the reaction chamber is adjusted to the second temperature range and the first low-pressure range is maintained. Bismuth organic precursor and oxygen precursor are introduced into the reaction chamber simultaneously according to the preset molar flow rate ratio. The thermal decomposition reaction epitaxially grows a p-type tetragonal β-Bi2O3 thin film on the surface of the substrate material. The epitaxial growth is carried out in an oxygen-enriched atmosphere throughout the process. The first temperature range is 300-425℃; the second temperature range is 725-845℃; the first low pressure range is 5-80mbar; the preset molar flow ratio is the molar flow ratio of bismuth organic precursor to oxygen precursor (Bi / O), and the Bi / O molar flow ratio range is 1:160-1:6000; the substrate material is a single crystal oxide substrate that matches the β-Bi2O3 lattice, preferably selected from any one of C-plane sapphire, R-plane sapphire, M-plane sapphire, MgO single crystal, SrTiO3(100) single crystal, and β-Ga2O3(-201) single crystal, which can be adapted to large-size substrates from 8 inches to 12 inches.

[0006] By adopting the above technical solution, and focusing on the core process of in-situ oxygen pretreatment of the substrate followed by low-temperature oxygen-enriched epitaxial growth, the key process elements of β-Bi₂O₃ thin films are precisely controlled, thereby achieving the epitaxial growth of p-type tetragonal β-Bi₂O₃ single-crystal thin films using MOCVD. These films exhibit ultra-high uniformity and are suitable for large-size substrates ranging from 8 inches to 12 inches. The key process elements and main process principles are explained below: (1) In-situ oxidation pretreatment of substrate at 300-425℃ is used to replace the traditional offline acid and alkali cleaning operation, so as to clean and activate the substrate surface and avoid introducing external contamination.

[0007] (2) The second temperature (i.e. the epitaxial growth temperature) of 725-845℃ is the thermodynamic stability window of tetragonal β-Bi2O3, which can effectively suppress the formation of α-Bi2O3 impurity phase; if the growth temperature is below 725℃, the precursor will not be completely decomposed and the film will not be single crystal; if the temperature is above 845℃, an irreversible phase transformation will occur to generate n-type monoclinic α-Bi2O3. (3) The first low pressure of 5-80 mbar can significantly improve the migration ability of bismuth organic molecules on the substrate surface, which is conducive to achieving large-area uniform epitaxial growth; (4) A high Bi / O molar flow ratio (1:160-1:6000) and an oxygen-rich atmosphere throughout the process effectively suppress oxygen vacancy defects and bismuth precipitation, which is the key to achieving stable intrinsic p-type conductivity.

[0008] In some embodiments, step S2, low-temperature oxygen-enriched epitaxial growth, specifically includes the following steps S21-S23: S21. Constant temperature and pressure: Adjust the reaction chamber to the second temperature range and maintain the first low pressure range. Maintain constant temperature and pressure for 30 minutes. This step helps to eliminate thermal inertia and pressure fluctuations caused by the heating stage and ensures a uniform distribution of temperature field and airflow field in the reaction chamber. S22. Epitaxial growth: Bismuth organic precursor and oxygen precursor are simultaneously introduced into the reaction chamber according to the predetermined bismuth-oxygen molar ratio. The thermal decomposition reaction is carried out to epitaxially grow a p-type tetragonal β-Bi2O3 thin film on the substrate surface. S23. Post-growth treatment: First, stop feeding the bismuth organic precursor into the reaction chamber, then rapidly cool down to below 300°C under an oxygen-rich atmosphere for no more than 25 minutes, and then stop feeding the oxygen precursor into the reaction chamber; rapid cooling can effectively avoid high-temperature phase transition.

[0009] In some embodiments, the bismuth organic precursor is selected from trimethylbismuth TMBi, tris(2,2,6,6-tetramethyl-3,5-heptadecyl)bismuth Bi(tmhd)3, tert-butanol bismuth Bi(O t At least one of Bu)3 and triphenylbismuthBiPh3.

[0010] In some embodiments, the oxygen precursor is selected from any one of high-purity oxygen (O2), nitrous oxide (N2O), and ozone (O3).

[0011] In some embodiments, in step S1, the in-situ oxidation pretreatment time for the substrate material is 10-30 minutes; the oxygen precursor flow rate in the in-situ oxygen pretreatment stage of step S1 is higher than the oxygen precursor flow rate in the low-temperature oxygen-enriched epitaxial growth stage of step S2, which is beneficial to fully oxidize and remove organic contaminants on the substrate surface.

[0012] In some embodiments, the first low-pressure range is preferably 10-50 mbar. The low-pressure environment improves the surface mobility of the bismuth precursor, thereby improving the quality of single-crystal epitaxy of thin films.

[0013] In some embodiments, the molar flow ratio of the bismuth organic precursor to the oxygen precursor (Bi / O) is preferably 1:200-1:4000; the oxygen-rich atmosphere suppresses the oxygen vacancy concentration during growth to a level insufficient to compensate for the p-type carriers.

[0014] On the other hand, this invention discloses a method for preparing a p-type tetragonal β-Bi₂O₃ thin film, which is a pure-phase single-crystal structure; the in-plane thickness non-uniformity of the film is determined by the coefficient of variation. Define the coefficient of variation The calculation formula is =σ / Tavg×100%, where σ is the standard deviation of the in-plane multi-point thickness measurement, and Tavg is the average value of the multi-point thickness. <1%; the thin film exhibits stable p-type conductivity.

[0015] Furthermore, the thin film was prepared by an MOCVD method for preparing a p-type tetragonal phase β-Bi2O3 thin film disclosed in this invention.

[0016] Furthermore, its stable p-type conductivity was verified by the Mott-Schottky test, showing that within the frequency range of 1-10 kHz, 1 / C 2 - The slope of the V curve is negative.

[0017] In summary, the beneficial effects of this application are as follows: 1. High and controllable crystal phase purity: By precisely controlling the growth temperature window, the formation of impurity phases such as α-Bi2O3 is effectively suppressed, and pure tetragonal β-Bi2O3 thin films are obtained.

[0018] 2. Stable intrinsic p-type conductivity: Through a full-process oxygen-rich atmosphere with a high bismuth-oxygen flow ratio (1:160-1:6000), oxygen vacancies and metallic bismuth precipitation are effectively suppressed, achieving stable intrinsic p-type conductivity.

[0019] 3. High quality of epitaxial single crystal: The low-pressure environment (5-80mbar) promotes the migration of precursor molecules on the surface, realizing high-quality single crystal epitaxy; the process can be adapted to large-size substrates from 8 inches to 12 inches to meet the needs of industrial mass production.

[0020] 4. Good process compatibility: It can be directly adapted to oxide MOCVD production lines, supporting one-step in-situ growth of β-Bi2O3 / n type gallium oxide and TiO2 heterojunctions. It can be directly applied to optoelectronic device manufacturing without complicated post-processing, simplifying the device process flow.

[0021] 5. No corrosion or pollution: The process employs MOCVD and in-situ oxygen pretreatment and low-pressure oxygen-enriched epitaxial growth. The entire process does not require the use of corrosive chemicals, making it green and environmentally friendly.

[0022] 6. Simple operation and good repeatability: The process flow, including the core process (in-situ oxygen pretreatment of substrate + low temperature oxygen-enriched epitaxial growth), is completed in-situ in the MOCVD reaction chamber. The process is simple, the process parameters are controllable, and the consistency between batches is good. Attached Figure Description

[0023] The accompanying drawings are provided to further understand this application and form part of the specification. They are used together with the embodiments of this application to explain this application and do not constitute a limitation thereof.

[0024] In the attached diagram: Figure 1 This is a process flow diagram for this application; Figure 2 This is another process flow diagram for this application; Figure 3 A schematic diagram of an exemplary MOCVD device structure is shown. Figure 4 Mapping images of the β-Bi2O3 films prepared in the three examples; Figure 5 XRD diffraction patterns of β-Bi2O3 films prepared in the three examples; Figure 6 Mott-Schottky curves of β-Bi2O3 films prepared for the three examples.

[0025] Figure label annotations: 1. Reaction chamber; 11. Gas equalization device; 12. Graphite tray; 13. Heater; 14. Exhaust pipe; 2. Substrate; 3. Oxygen source; 31. Oxygen channel; 4. Bismuth source; 41. Bismuth channel. Detailed Implementation

[0026] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. Rather, they are merely examples of apparatuses and methods consistent with some aspects disclosed in this embodiment as detailed in the appended claims.

[0027] like Figure 3 As shown, the MOCVD equipment used in this embodiment of the invention includes a reaction chamber 1, an oxygen source 3, and a bismuth source 4. A gas equalization device 11 is provided in the reaction chamber 1. The oxygen source 3 is connected to the gas equalization device 11 through an oxygen channel 31, and the bismuth source 4 is connected to the gas equalization device 11 through a bismuth channel 41. The substrate 2 is placed on a rotatable graphite tray 12. A control heater 13 controls the temperature in the reaction chamber 1. The oxygen precursor and the bismuth organic precursor enter the reaction chamber 1 through the oxygen channel 31 and the bismuth channel 41, respectively, and undergo a chemical deposition reaction on the surface of the substrate 2. The exhaust gas after the reaction is discharged from the exhaust pipe 14.

[0028] like Figure 1 , Figure 2 , Figure 3 As shown, the method in this application embodiment includes the following steps: Step S1, In-situ Oxygen Pretreatment of Substrate: Place substrate 2 on graphite tray 12, control heater 13 to keep reaction chamber 1 of MOCVD equipment in the first temperature range (300-425℃, such as 300℃) and the first low pressure range (5-80mbar, such as 10mbar), continuously introduce oxygen precursor, and perform in-situ oxidation pretreatment of substrate 2 material for 5-60 minutes (such as 30 minutes) to remove surface carbon impurities, adsorbed water and surface defects. This operation can eliminate the traditional offline acid and alkali cleaning steps and avoid the introduction of external contamination. Step S21, Constant Temperature and Pressure: Adjust the temperature of reaction chamber 1 to the second temperature range (725-845℃, such as 800℃) and maintain the first low pressure range (such as 10mbar). After maintaining constant temperature and pressure for 30 minutes, proceed to step S22. This step helps to eliminate thermal inertia and pressure fluctuations caused by the heating stage, avoid excessive deviation between the actual local temperature and the set value on the surface of substrate 2, and ensure the uniform distribution of temperature field and flow field in reaction chamber 1. Step S22, Epitaxial Growth: The reaction chamber 1 is in the second temperature range (e.g., 800℃) and the first low pressure range (e.g., 10mbar). Bismuth organic precursor and oxygen precursor are simultaneously introduced into the reaction chamber 1 according to the preset molar flow ratio (Bi / O molar flow ratio 1:160-1:6000, e.g., 1:2000). The thermal decomposition reaction epitaxially grows a p-type tetragonal β-Bi2O3 thin film on the surface of the substrate 2 material. The epitaxial growth is carried out in an oxygen-rich atmosphere throughout the process. Step S23, Post-growth treatment: After growth, first stop the input of bismuth organic precursor, and rapidly cool reaction chamber 1 to below 300°C under an oxygen-rich atmosphere for no more than 25 minutes, then stop the input of oxygen precursor. Rapid cooling ensures that the film has a very short residence time in the high-temperature range where the β-phase to α-phase transition is likely to occur (especially around 725-845°C), shorter than the incubation period for the phase transition, thus kinetically suppressing the initiation of the high-temperature phase transition. When the temperature drops below 300°C, the atomic diffusion ability is significantly reduced at this temperature, making it difficult for the phase transition to occur. At this point, the oxygen precursor is shut off and the film is allowed to cool naturally to room temperature. This operation effectively suppresses the high-temperature phase transition and yields a high-crystallinity p-type tetragonal β-Bi₂O₃ film.

[0029] Substrate 2 is a single-crystal oxide substrate that matches the β-Bi₂O₃ lattice, preferably selected from any one of C-plane sapphire, R-plane sapphire, M-plane sapphire, MgO single crystal, SrTiO₃(100) single crystal, and β-Ga₂O₃(-201) single crystal, and can be adapted to large-size substrates from 8 inches to 12 inches; the bismuth organic precursor is selected from trimethylbismuth™Bi, tris(2,2,6,6-tetramethyl-3,5-heptanedione)bismuthBi(tmhd)₃, and tert-butanolbismuthBi(O tAt least one of Bu)3 and triphenylbismuthBiPh3; the oxygen precursor is selected from any one of high-purity oxygen O2, nitrous oxide N2O, and ozone O3.

[0030] To further understand the content, features, and effects of this application, the following embodiments are provided, and detailed descriptions are given below in conjunction with the accompanying drawings: All embodiments used a low-pressure MOCVD equipment (model: stellar oxide 2), with a C-plane sapphire substrate and high-purity nitrogen (N2) as the carrier gas.

[0031] Example 1 A C-plane sapphire substrate was selected; TMBi was chosen as the bismuth organic precursor, and pure oxygen O2 was chosen as the oxygen precursor.

[0032] S1. In-situ substrate pretreatment: Place the C-side sapphire substrate on a graphite tray, set the reaction chamber pressure to 5 mbar, the first temperature to 300℃, and introduce high-purity oxygen (O2) as an oxygen precursor. The pretreatment time is 30 min to remove contaminants from the substrate surface.

[0033] S21, Constant temperature and pressure: The pressure in the reaction chamber is kept constant at 5mbar±2mbar, and the temperature is raised to 725℃±2℃[1], and the temperature and pressure are kept constant for 30min.

[0034] S22. Epitaxial growth: TMBi was selected as the bismuth organic precursor. The source bottle was heated to 25°C, the TMBi flow rate was 125 sccm, the O2 flow rate was 10000 sccm, the bismuth-oxygen (Bi / O) molar flow rate ratio was 1:160, and deposition was carried out for 90 min.

[0035] S23. Post-growth treatment: After growth is completed, first stop the bismuth organic precursor, then rapidly cool the reaction chamber to below 300°C in an oxygen-rich atmosphere for no more than 25 minutes, then stop the oxygen precursor to complete the film growth.

[0036] Sample 1 was finally obtained. Tests on Sample 1 showed that XRD matched tetragonal β-Bi2O3, ellipsometry showed an inhomogeneity of 0.47%, MS tests confirmed p-type characteristics, and the film thickness was approximately 570 nm.

[0037] Example 2 A C-plane sapphire substrate was selected; TMBi was chosen as the bismuth organic precursor, and pure oxygen O2 was chosen as the oxygen precursor.

[0038] S1. In-situ substrate pretreatment: Place the C-side sapphire substrate on a graphite tray, set the reaction chamber pressure to 50 mbar, the first temperature to 350°C, and introduce high-purity oxygen (O2) as an oxygen precursor. The pretreatment time is 30 min to remove contaminants from the substrate surface.

[0039] S21. Constant temperature and pressure: The pressure in the reaction chamber is kept constant at 50mbar±2mbar. The temperature is increased to 775℃±2℃ and kept constant at the same temperature and pressure for 30 minutes.

[0040] S22. Epitaxial growth: TMBi was selected as the bismuth organic precursor. The source bottle was heated to 25°C, the TMBi flow rate was 10 sccm, the O2 flow rate was 10000 sccm, the bismuth-oxygen (Bi / O) molar flow rate ratio was 1:2000, and deposition was carried out for 90 min.

[0041] S23. Post-growth treatment: After growth is completed, first stop the bismuth organic precursor, then rapidly cool the reaction chamber to below 300°C in an oxygen-rich atmosphere for no more than 25 minutes, then stop the oxygen precursor to complete the film growth.

[0042] Sample 2 was finally obtained. Tests on sample 2 showed that XRD matched tetragonal β-Bi2O3, ellipsometry showed an inhomogeneity of 0.56%, MS tests confirmed p-type characteristics, and the film thickness was approximately 560 nm.

[0043] Example 3 A C-plane sapphire substrate was selected; TMBi was chosen as the bismuth organic precursor, and pure oxygen O2 was chosen as the oxygen precursor.

[0044] S1. In-situ substrate pretreatment: The C-side sapphire substrate is placed on a graphite tray. The reaction chamber pressure is 80 mbar and the temperature is 420℃. High-purity oxygen (O2) is introduced as an oxygen precursor. The pretreatment time is 30 min to remove contaminants from the substrate surface.

[0045] S21. Constant temperature and pressure: The pressure in the reaction chamber is kept constant at 80mbar±2mbar. The temperature is raised to 845℃±2℃ and kept constant at the same temperature and pressure for 30 minutes before the precursor is introduced.

[0046] S22. Epitaxial growth: TMBi was selected as the organic bismuth precursor. The source bottle was heated to 25°C, the TMBi flow rate was 5 sccm, the O2 flow rate was 10000 sccm, the bismuth-oxygen (Bi / O) molar flow rate ratio was 1:4000, and deposition was carried out for 90 min.

[0047] S23. Post-growth treatment: After growth is completed, first stop the bismuth precursor, then rapidly cool the reaction chamber to below 300°C in an oxygen-rich atmosphere for no more than 25 minutes, then stop the oxygen precursor to complete the film growth.

[0048] Sample 3 was finally obtained. Tests on sample 3 showed that XRD matched tetragonal β-Bi2O3, ellipsometry showed an inhomogeneity of 0.55%, MS tests confirmed p-type characteristics, and the film thickness was approximately 530 nm.

[0049] Sample testing and verification instructions 1. Characterization of in-plane thickness uniformity Ellipsometry was used to perform full-film thickness mapping tests on three groups of samples, covering a diameter of 200 mm. Data from 49 feature points were collected for each sample for fitting and inversion. The film thickness inhomogeneity was defined as the coefficient of variation. The calculation formula is: In the formula, The standard deviation of the thickness measurement at 49 points. The average thickness is 49 points.

[0050] like Figure 4 As shown, the average film thicknesses of samples 1-3 are 570 nm, 560 nm, and 530 nm, respectively. The values ​​were 0.47%, 0.56%, and 0.55% respectively, for all samples. All values ​​met the good grade judgment threshold of less than 1%, and all samples... The excellent performance of values ​​less than 0.6% indicates that the film prepared by this invention has extremely high in-plane thickness uniformity on an 8-inch (200mm) macroscopic scale, effectively eliminating edge effects and local stress concentrations commonly found in the processing of large-size substrates, and fully meeting the industrial application requirements of 8-inch to 12-inch large-size substrates.

[0051] 2. Phase structure and crystal quality analysis Figure 5 The X-ray diffraction (XRD) patterns of the three samples were obtained. The results showed that all three curves exhibited the strongest characteristic peak near 2θ≈28°, which belongs to the (201) crystal plane of β-Bi₂O₃. The remaining diffraction peaks, including those of the (002), (200), (222), and (400) crystal planes, matched the standard diffraction peaks of β-Bi₂O₃ in the JCPDS standard card (No. 27-0050), and no impurity phase peaks such as metallic Bi and α-Bi₂O₃ were observed. This confirms that all three samples are high-purity single β-Bi₂O₃ phases with excellent crystal quality.

[0052] 3. Characterization of conductivity type and electrical stability Figure 6 Mott-Schottky test curves (1kHz, 3kHz, 10kHz) for three groups of samples in the 1-10kHz frequency range are shown. The 1 / C values ​​for the three groups of samples are also shown. 2 - The V curves all exhibit negative slopes, confirming the intrinsic p-type conductivity of the thin film; simultaneously, 1 / C 2The slope of the -V curve changes only slightly with the test frequency and has a wide linear range, indicating that the thin film has a low interface state density and stable space charge layer behavior. This further confirms that the p-type conductivity has good frequency stability and structural stability, and there is no n-type leakage phenomenon.

[0053] In summary, the β-Bi₂O₃ thin film prepared by this invention has the following significant advantages: (1) Phase purity: All three groups of samples were single β-Bi2O3 phases without any metal impurities.

[0054] (2) Excellent electrical performance: It exhibits intrinsic p-type hole conduction, no n-type leakage channels, and low interface state density.

[0055] (3) Strong compatibility with large size: At the 8-inch substrate scale, the thickness non-uniformity, combined with the excellent crystal quality shown by XRD, proves that the film has extremely high thickness uniformity on a macroscopic scale and high crystallinity and low defect density on a microscopic scale.

[0056] Compared with existing sputtering and hydrothermal methods, this invention significantly improves thin film epitaxial quality, in-plane uniformity, and electrical properties, and has the capability for large-scale fabrication of 8-inch to 12-inch large-size substrates.

[0057] Finally, it should be noted that the above disclosure is merely a preferred embodiment of this application and is not intended to limit this application. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some technical features, such as the precursor. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application. The scope of this application is limited only by the appended claims.

Claims

1. A method for preparing p-type tetragonal phase β-Bi₂O₃ thin films by MOCVD, characterized in that, Includes the following steps: S1. In-situ oxygen pretreatment of substrate: The reaction chamber of the MOCVD equipment is in the first temperature range and the first low pressure range. Oxygen precursor is continuously introduced to perform in-situ oxidation pretreatment of the substrate material for 5-60 minutes to remove surface carbon impurities, adsorbed water and surface defects. S2. Low-temperature oxygen-enriched epitaxial growth: Adjust the temperature of the reaction chamber to the second temperature range and maintain the first low-pressure range. Simultaneously introduce bismuth organic precursor and oxygen precursor into the reaction chamber according to the preset molar flow rate ratio. The thermal decomposition reaction epitaxially grows a p-type tetragonal β-Bi2O3 thin film on the surface of the substrate material. The first temperature range is 300-425℃; the second temperature range is 725-845℃; and the first low-pressure range is 5-80 mbar. The preset molar flow rate ratio is the molar flow rate ratio of bismuth organic precursor to oxygen precursor (Bi / O), and the Bi / O molar flow rate ratio range is 1:160-1:6000. The substrate material is a single-crystal oxide substrate that matches the β-Bi2O3 lattice, preferably selected from any one of C-plane sapphire, R-plane sapphire, M-plane sapphire, MgO single crystal, SrTiO3(100) single crystal, and β-Ga2O3(-201) single crystal.

2. The MOCVD preparation method for a p-type tetragonal β-Bi₂O₃ thin film according to claim 1, characterized in that, Step S2 includes the following steps S21-S23; S21. Constant temperature and pressure: Adjust the reaction chamber to the second temperature range and maintain the first low pressure range, and maintain constant temperature and pressure for 30 minutes. S22. Epitaxial growth: Bismuth organic precursor and oxygen precursor are simultaneously introduced into the reaction chamber according to a predetermined molar ratio, and thermal decomposition reaction is carried out to epitaxially grow a p-type tetragonal β-Bi2O3 thin film on the substrate surface. S23. Post-growth treatment: First, stop feeding bismuth organic precursor into the reaction chamber, then rapidly cool down to below 300°C under an oxygen-rich atmosphere for no more than 25 minutes, and then stop feeding oxygen precursor into the reaction chamber.

3. The MOCVD preparation method for a p-type tetragonal β-Bi₂O₃ thin film according to claim 1, characterized in that: The bismuth organic precursor is selected from trimethylbismuth TMBi, tris(2,2,6,6-tetramethyl-3,5-heptanedione)bismuth Bi(tmhd)3, and tert-butanol bismuth Bi(O t At least one of Bu)3 and triphenylbismuthBiPh3.

4. The MOCVD preparation method for a p-type tetragonal β-Bi₂O₃ thin film according to claim 1, characterized in that: The oxygen precursor is selected from any one of high-purity oxygen (O2), nitrous oxide (N2O), and ozone (O3).

5. The MOCVD preparation method for a p-type tetragonal β-Bi₂O₃ thin film according to claim 1, characterized in that: In step S1, the in-situ oxidation pretreatment time for the substrate material is 10-30 minutes; In step S1, the oxygen precursor flow rate is higher than that in step S2.

6. The MOCVD preparation method for a p-type tetragonal phase β-Bi₂O₃ thin film according to claim 1, characterized in that: The first low-pressure range is preferably 10-50 mbar.

7. The MOCVD preparation method for a p-type tetragonal β-Bi₂O₃ thin film according to claim 1, characterized in that: The preferred molar flow ratio of the bismuth organic precursor to the oxygen precursor (Bi / O) is 1:200-1:4000.

8. A p-type tetragonal phase β-Bi₂O₃ thin film, characterized in that: The thin film has a pure phase single crystal structure; The in-plane thickness non-uniformity of the thin film is determined by the coefficient of variation. Define the coefficient of variation. The calculation formula is =σ / Tavg×100%, where σ is the standard deviation of the in-plane multi-point thickness measurement, and Tavg is the average value of the multi-point thickness. <1%; The thin film exhibits stable p-type conductivity.

9. A p-type tetragonal β-Bi₂O₃ thin film according to claim 8, characterized in that: The thin film is prepared by the method described in any one of claims 1-7.

10. A p-type tetragonal β-Bi₂O₃ thin film according to claim 8 or 9, characterized in that: The stable p-type conductivity was verified by the Mott-Schottky test, showing that within the frequency range of 1-10kHz, 1 / C 2 The slope of the V curve is negative.

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