Preparation method of bismuth ferrite-based homojunction superlattice based on molecular beam epitaxy as well as product and application of bismuth ferrite-based homojunction superlattice

Abstract

The invention discloses a preparation method of a bismuth ferrite-based homojunction superlattice based on molecular beam epitaxy. The preparation method comprises the following steps: transferring a substrate into an MBE (Molecular Beam Epitaxial) growth chamber, wherein the temperature of the substrate is lower than the evaporation temperature of a Bi source; the Bi source and the Fe source are heated, and the beam size is adjusted; ozone is adopted as an epitaxial growth atmosphere, a Bi source and a Fe source are mixed in a growth chamber, an oxygen-vacancy-free bismuth ferrite epitaxial film is firstly grown in an epitaxial mode to serve as a ferroelectric phase, and after oxygen pressure is reduced, an oxygen-vacancy-containing bismuth ferrite film is grown in an epitaxial mode to serve as a defect ferroelectric phase; the two times of epitaxial growth are alternately and respectively grown to obtain the bismuth ferrite-based homojunction superlattice. The oxygen vacancy content in each layer of bismuth ferrite is regulated and controlled by controlling ozone partial pressure of bismuth ferrite in the epitaxial process, a depolarization field is provided at a homogeneous interface by introducing a bismuth ferrite layer containing oxygen vacancies, and the bismuth ferrite / oxygen vacancy bismuth ferrite homojunction superlattice is prepared; and the surface of the prepared superlattice has clear and parallel atomic steps.

Description

Technical Field

[0001] The present invention belongs to the field of information storage technology, and in particular to ferroelectric superlattice polarization topological storage, and in particular to a preparation method of bismuth ferrite-based homojunction superlattice based on molecular beam epitaxy, and its products and applications. Background Art

[0002] Ferroelectric memory is a storage device that can quickly write and read information by regulating polarization reversal. Compared with traditional magnetic storage and semiconductor storage that read and write through electric current, ferroelectric storage uses external voltage to achieve short-range displacement of ions in the lattice, which can effectively reduce Joule heat dissipation during information reading and writing, and has broad development prospects in the field of low-power information storage devices. The ferroelectric memory cell is a ferroelectric domain structure with consistent polarization direction. Among various ferroelectric domains, the ferroelectric topological domain effectively reduces the size of the ferroelectric domain by bending polarization, so that its storage density can be theoretically increased by 100,000 times compared with traditional ferroelectric memory. In 2009, researchers proposed to make racetrack memory by domain flipping in ferroelectric materials, which has important properties such as low heat dissipation and non-volatility (Science, 2009, 320, 190-194). Since then, logic devices (Sci. Rep., 2015, 5, 9400) and brain-like devices (Nanotechnology, 2017, 28, 08LT02; Nanotechnology, 2017, 28, 31LT01) developed based on ferroelectric materials have milestone significance for the development of current fields such as artificial intelligence. Ferroelectric topological structures have been widely studied in perovskite ferroelectric / dielectric superlattice materials, such as lead titanate / strontium titanate (PTO / STO) (Nature, 2016, 530, 198-201), barium titanate / strontium titanate (BTO / STO) (ACS Nano, 2021, 15, 13380-13388), bismuth ferrite / strontium titanate (BFO / STO) (Nat. Commun., 2023, 14, 4178), etc. Among them, PTO, BTO and BFO as ferroelectric layer materials provide strong polarization properties, and STO is a commonly used dielectric layer material to bind the charges generated by polarization and provide a strong depolarization field.

[0003] However, most commonly used superlattices are heterogeneous structures, and multiple evaporation sources are required during the epitaxial preparation of the material, which increases the complexity of the process. In addition, heteroepitaxiality also places higher requirements on the material epitaxial conditions. Therefore, how to achieve homogeneous epitaxy of high-quality ferroelectric superlattices and simplify the process is an urgent problem to be solved. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing a bismuth ferrite-based homojunction superlattice based on molecular beam epitaxy, by controlling the ozone partial pressure of bismuth ferrite during the epitaxial process to regulate the oxygen defect content in each layer of bismuth ferrite, on the basis of not changing the type of material, by introducing a bismuth ferrite layer containing oxygen vacancies, providing a depolarization field at the homogeneous interface, and preparing a bismuth ferrite / oxygen vacancy bismuth ferrite homojunction superlattice; and the prepared superlattice surface has clear and parallel atomic steps.

[0005] The present invention provides the following technical solutions:

[0006] A method for preparing a bismuth ferrite-based homojunction superlattice based on molecular beam epitaxy, the preparation method comprising:

[0007] (1) The substrate is introduced into the MBE growth chamber, and the substrate temperature is lower than the Bi source evaporation temperature;

[0008] (2) Raising the temperature of the Bi source and the Fe source to the evaporation temperature, and adjusting the beam current of the Bi source and the Fe source;

[0009] (3) using ozone as the epitaxial growth atmosphere, a Bi source and a Fe source are mixed in a growth chamber to first epitaxially grow a bismuth ferrite film without oxygen vacancies as a ferroelectric phase, and then epitaxially grow a bismuth ferrite film containing oxygen vacancies as a defective ferroelectric phase after reducing the oxygen pressure;

[0010] (4) The two epitaxial growths in step (3) are grown alternately to obtain a bismuth ferrite-based homojunction superlattice.

[0011] The preparation method provided by the present invention regulates the oxygen defect content in each layer of bismuth ferrite by controlling the ozone partial pressure of bismuth ferrite during the epitaxial growth process. On the basis of not changing the type of material, a bismuth ferrite layer containing oxygen vacancies is introduced to provide a depolarization field at the homogeneous interface, and an oxygen vacancy layer is introduced between different layers of bismuth ferrite to provide a depolarization field, thereby constructing a bismuth ferrite / oxygen vacancy bismuth ferrite homojunction superlattice, avoiding the operation of replacing the evaporation source during the thin film growth process, and only by adjusting the ozone partial pressure operation, the preparation process of the superlattice is simplified, and the preparation efficiency of the superlattice is improved.

[0012] In step (1), the substrate is a (110)-oriented scandate single crystal substrate, and the substrate is a substrate having an atomically flat surface after being treated by chemical wet processing and annealing.

[0013] Specifically, the chemical wet treatment includes organic solvent cleaning and strong alkali etching, and the particles adsorbed on the surface of the substrate are removed by alternate cleaning with ketone and alcohol, and then the surface of the substrate is etched by a strong alkaline solution under ultrasonic action to remove the dysprosium oxide and obtain a surface with a single scandium cutoff. The annealing treatment is to perform a high-temperature heat preservation treatment on the alkali-treated substrate in an oxidizing atmosphere to rearrange the surface atoms and obtain an atomically flat substrate with clear steps.

[0014] Specifically, an organic solvent (acetone and isopropanol) is used to alternately ultrasonically clean the substrate. The amount of solvent should be able to completely cover the substrate. After each cleaning, the waste liquid is removed, but the surface of the substrate should be kept moist. After the organic solvent cleaning is completed, pure water is used to ultrasonically clean the substrate again to remove the organic solvent. Using sodium hydroxide solution as an etchant, the cleaned substrate is successively placed in NaOH solutions of different concentrations for ultrasonic etching to remove the dysprosium oxide exposed on the surface, thereby preparing a substrate material with a single scandium cutoff surface. The treated substrate is washed with pure water to remove the alkaline solution remaining on the surface, and then the substrate is quickly dried at room temperature. In order to make the film grow in a step flow manner during the molecular beam epitaxy process, the substrate needs to be annealed at high temperature to rearrange the surface ScO2 and produce parallel atomic steps.

[0015] Preferably, the annealing temperature should meet the energy required for atomic migration on the substrate surface but prevent the substrate from deteriorating at high temperature, and the annealing time should allow the atoms to fully rearrange, so the annealing temperature is usually 1000-1200° C. and the annealing time is 1 hour.

[0016] Atomic steps with a width of about 200 nm and arranged in parallel can be observed on the surface of the substrate, and the overall surface roughness should be less than 0.4 nm, thereby ensuring the quality of bismuth ferrite homojunction superlattice epitaxy.

[0017] In step (1), the substrate temperature satisfies: 300° C. ≤ substrate temperature < 600° C. The growth temperature should be lower than the evaporation temperature of the evaporation source and provide sufficient energy to promote the migration of epitaxial ions on the substrate surface, and should be 300° C. ≤ substrate temperature < 600° C.

[0018] Specifically, in step (1), the processed substrate is placed on a molybdenum metal support, fixed with tantalum foil by spot welding, and then inverted in the MBE growth chamber. The substrate is heated and degassed to a temperature 50°C higher than the predetermined temperature, and the degassing is performed until the pressure in the growth chamber is 10 -9 Torr level, and after the degassing is completed, the temperature is reduced to the predetermined temperature.

[0019] In step (2), the evaporation temperature of the Bi source is 600-700° C., and the evaporation temperature of the Fe source is 1200-1500° C. Preferably, the Bi source is Bi metal particles, and the Fe source is Fe metal particles.

[0020] The beam ratio of the Bi source to the Fe source is greater than or equal to 4:1.

[0021] In step (2), the Bi / Fe beam ratio should be greater than 4:1 to compensate for the Bi x O y Volatilization at high temperature improves the crystal quality and purity of bismuth ferrite epitaxial film.

[0022] Preferably, the beam ratio of the Bi source to the Fe source is 4-16:1.

[0023] Specifically, in step (2), the temperature of the evaporation source is increased to a predetermined temperature to provide a predetermined beam current, and the beam current size is measured by a quartz microbalance (QCM).

[0024] In step (3), the oxygen pressure of the epitaxial growth is 10 -6 -10 -5 Torr, the oxygen pressure drop of the epitaxially grown bismuth ferrite epitaxial film without oxygen vacancies is no more than 1×10 -6 Torr, and then epitaxially grow bismuth ferrite thin films containing oxygen vacancies. The growth oxygen pressure should be controlled at 10 -6 -10 -5 Torr to provide sufficient oxidation capacity and ensure a long atomic free path. To ensure the oxidation capacity of ozone, the oxygen pressure of the growth of the bismuth ferrite layer containing oxygen vacancies should be reduced by no more than 1×10 -6 Torr.

[0025] As a preference, the oxygen pressure control accuracy should be 10 -8 Torr.

[0026] In step (3), the oxygen pressure is the ozone pressure, which is obtained by high-pressure ionization of pure oxygen and fractionation of liquid nitrogen. The partial pressure should be less than 10 -5 Torr, thus ensuring that the molecular beam has a long mean free path.

[0027] The specific operation process is: open the micro-leak valve, adjust the ozone pressure in the growth chamber to a predetermined value, and open the baffles of the Bi source and the Fe source at the same time. After stabilization, open the growth chamber baffle to carry out epitaxial growth of the thin film, and control the thickness of the film by controlling the growth time and the beam size; after the growth is completed, close the growth chamber baffle to stop the film growth and obtain a bismuth ferrite epitaxial film.

[0028] Preferably, in step (4), the thickness of the epitaxially grown oxygen vacancy-free bismuth ferrite epitaxial film is 0.8-20 nm.

[0029] Preferably, the film surface should have atomic steps similar to those of the substrate, and the surface roughness should be less than 0.4 nm.

[0030] In step (4), the growth is performed alternately 2 to 16 times.

[0031] It should be understood that the epitaxial growth sequence should be to grow the bismuth ferrite epitaxial film first, and then grow the bismuth ferrite film containing oxygen vacancies, alternating the growth for 2-16 times. Each time the alternation occurs, the evaporation source should be turned off first, and the oxygen pressure should be adjusted to be stable before growing the next layer.

[0032] The steps (3) to (4) are specifically described as follows: a bismuth ferrite film without oxygen vacancies of a certain thickness is grown on a substrate; after the growth of the bismuth ferrite film without oxygen vacancies is completed, the baffle of the growth chamber is closed to reduce the oxygen pressure to the required growth condition; after the oxygen pressure is stabilized, the baffle of the growth chamber is opened to perform homoepitaxial growth of the oxygen vacancy bismuth ferrite; after the epitaxial growth is completed, the baffle is closed and the growth of the bismuth ferrite film without oxygen vacancies is repeated; after 2-16 cycles of cyclic growth, the molybdenum support is taken out to obtain BFO (V o )-SL homojunction superlattice.

[0033] In the present invention, the ferroelectric phase is prepared by controlling the substrate temperature, growth oxygen pressure and Bi / Fe beam ratio by oxide molecular beam epitaxy; the defective ferroelectric phase is prepared by adjusting the growth oxygen pressure so that the lattice oxygen content of bismuth ferrite is reduced on the basis of maintaining the original phase: specifically, by calculating the element content and ratio of the film, the linear region where the element ratio changes with the oxygen pressure is found, thereby realizing the adjustability of the oxygen vacancy concentration in the bismuth ferrite film.

[0034] The present invention also provides a bismuth ferrite-based homojunction superlattice obtained according to the above preparation method.

[0035] The bismuth ferrite-based homojunction superlattice is a (001)-oriented bismuth ferrite / oxygen vacancy bismuth ferrite homojunction superlattice, comprising a substrate, a ferroelectric phase and a defective ferroelectric phase.

[0036] Preferably, the bismuth ferrite-based homojunction superlattice is (001) oriented (BiFeO3)x / (BiFeO3-V o ) y (x and y are the number of alternating growths, ranging from 2 to 16) epitaxial superlattice (BFO (V o )-SL),

[0037] The present invention uses the oxide molecular beam epitaxy method to prepare BFO (V o)-SL has high single crystal quality (diffraction peak half-width FWHM < 0.02°), a smooth surface and clear atomic steps (roughness RMS < 200pm).

[0038] The present invention also provides an application of the bismuth ferrite-based homojunction superlattice in a ferroelectric memory.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] The preparation method provided by the present invention is to prepare BFO (V o )-SL, can effectively reduce Bi x O y The volatilization of oxygen vacancy defects can be precisely controlled.

[0041] The preparation method provided by the present invention uses oxide molecular beam epitaxy (O-MBE) to precisely control the temperature, oxygen partial pressure and beam current ratio during the BFO growth process (wherein the growth oxygen pressure accuracy of bismuth ferrite reaches 1×10 -8 Torr), which can further improve the BFO (V o )-SL's physical purity and crystal quality (high-resolution thin-film XRD and XPS are also used to detect the film quality during the preparation process). BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 The molecular beam epitaxy method provided in the embodiment of the present invention is used to prepare BFO (V o ) Schematic diagram of the principle of SL;

[0043] Figure 2 BFO (V) provided in the embodiment of the present invention o ) Schematic diagram of homojunction superlattice structure;

[0044] Figure 3 BFO (V) provided in the embodiment of the present invention o )SL high-resolution XRD pattern:

[0045] Figure 4 XPS graph and phase diagram of the effect of oxygen pressure on the element content in BFO provided by the embodiment of the present invention;

[0046] Figure 5 AFM images and TEM images of the BFO surface grown under different oxygen pressures provided by the embodiment of the present invention;

[0047] Figure 6 AFM images of the substrate and superlattice surface provided by the embodiments of the present invention. DETAILED DESCRIPTION

[0048] Various additional advantages and benefits will become apparent to those of ordinary skill in the art from a reading of the following detailed description of the preferred embodiments.

[0049] Specifically, the method for preparing a bismuth ferrite-based homojunction superlattice based on molecular beam epitaxy provided in an embodiment of the present invention includes:

[0050] (1) Surface treatment process of dysprosium scandate substrate, specifically including:

[0051] The dysprosium scandate substrate was soaked in 30mL of acetone and ultrasonically cleaned for 20min. The substrate was taken out and placed in 30mL of isopropanol, and ultrasonic cleaning was continued for 20min, and the above cleaning process was repeated. After the last round of isopropanol cleaning, the substrate was placed in pure water and ultrasonically cleaned to remove the residual organic solvent. 10mol / L and 1mol / L NaOH etching solutions were prepared respectively, and the substrate was ultrasonically etched in 10mol / L and 1mol / L alkaline etching solutions for 30min, and then washed with pure water for 3 times to remove the residual alkaline solution on the surface. The cleaned substrate was adsorbed on a spin coater and the surface moisture was dried at room temperature at a speed of 5000r / min. The dried substrate was placed in a tube furnace, heated to 1100℃ at a speed of 5℃ / min in an oxygen atmosphere, kept warm for 1h, and then cooled to 800℃ at a speed of 5℃ / min, and finally cooled to room temperature with the furnace to obtain a dysprosium scandate substrate with parallel atomic steps and a roughness of less than 0.2nm on the surface.

[0052] (2) Bismuth ferrite epitaxial film prepared by molecular beam epitaxy, specifically comprising:

[0053] First, the processed substrate was placed on a molybdenum metal holder, fixed with tantalum foil by spot welding, and then inverted in the MBE growth chamber. The substrate was slowly heated and degassed, and the final degassing temperature was 400°C. When the pressure in the growth chamber was 10 -9 The degassing was completed at the Torr level, and the substrate temperature was reduced to 350°C for film growth. The Bi source was heated to 650°C and the Fe source was heated to 1350°C. At this time, the beam current ratio J measured by QCM was Bi / J Fe The ratio is about 8:1. Ozone is prepared by high-pressure ionization of pure oxygen, and the temperature is controlled at -170°C by liquid nitrogen for fractionation to improve the purity of ozone. Open the micro-leak valve and adjust the ozone pressure in the growth chamber to 4×10 -6 Torr, open the baffles of Bi source and Fe source at the same time, and after stabilization, open the growth chamber baffle to start epitaxial film growth. After the film grows for 5 minutes, the epitaxial thickness is 4nm. Turn off the growth chamber baffle to stop the film growth and obtain bismuth ferrite epitaxial film (ferroelectric phase).

[0054] (3) Bismuth ferrite-based homojunction superlattice prepared by molecular beam epitaxy, with [(BiFeO3) 4nm / (BiFeO3-V o ) 4nm ]8 as an example, specifically including:

[0055] After the growth of the 4 nm bismuth ferrite film was completed, the growth chamber baffle was closed and the ozone end micro-leak valve was slowly adjusted to reduce the oxygen pressure to 3.5×10 -6 Torr, after the pressure stabilizes, open the growth chamber baffle to start the oxygen vacancy layer growth (defective ferroelectric phase). After growing for 5 minutes, turn off the growth chamber baffle to obtain a cycle of bismuth ferrite homojunction. Repeat the above process for eight cycles, turn off the growth chamber baffle and the two evaporation source baffles, cool the substrate to room temperature with the furnace and take it out, and obtain 8 cycles of bismuth ferrite-based homojunction superlattice with 8nm in each cycle.

[0056] The above embodiment uses oxide molecular beam epitaxy (O-MBE) to control the ozone partial pressure and growth time of the growth of bismuth ferrite (BiFeO3), and in the dysprosium scandate (DyScO3-(110) pc ) single crystal substrate (001) oriented (BiFeO3 / BiFeO3-V o )8 epitaxial superlattice (BFO (V o )-SL).

[0057] Figure 1 The molecular beam epitaxy method provided in the embodiment of the present invention is used to prepare BFO (V o )Schematic diagram of SL principle: Figure 1 (a) is the molecular beam epitaxy flow chart. Figure 1 (b) is the molecular beam epitaxial growth mechanism diagram; Figure 1 It can be seen that the growth mechanism of BFO is an oxidation adsorption diffusion mechanism. Since Bi oxide has strong volatility, it needs to be adsorbed and deposited based on Fe oxide. Therefore, within a certain range, increasing the beam current of Bi will be beneficial to the purity of the BFO phase.

[0058] Figure 2 BFO (V) provided in the embodiment of the present invention o ) Schematic diagram of homojunction superlattice structure: Figure 2 (a) is BFO (V o )SL devices, Figure 2 (b) is BFO (V o )SL atomic model; Figure 2 Given BFO(V o ) The application of homojunction superlattice can use voltage and needle tip force to write and erase the topological structure in the superlattice to achieve information storage.

[0059] Figure 3 BFO (V) provided in the embodiment of the present invention o )SL high-resolution XRD pattern; Figure 3 It can be seen that BFO has good epitaxy and crystallinity.

[0060] Figure 4 XPS graph and phase diagram of the effect of oxygen pressure on the element content in BFO provided by the embodiment of the present invention: Figure 4 (a)-(c) are the X-ray photoelectron spectra of Fe, Bi, and O in BFO grown under 4e-6. Figure 4 (d) The content of each element and the corresponding phase diagram under different oxygen pressures, Figure 4 (e) O / Bi ratio phase diagram at different oxygen pressures, Figure 4 (f) is an enlarged phase image of region I in (d) and (e); Figure 4 It can be seen that by finely controlling the ozone pressure, the phase and oxygen vacancy content in BFO can be precisely controlled.

[0061] Figure 5 AFM and TEM images of the BFO surface grown under different oxygen pressures provided in the embodiment of the present invention: Figure 5 (a) and (b) are atomic force microscope images. Figure 5 (c) and (d) are transmission electron microscope cross-sectional images; Figure 5 It can be seen that the surface of the BFO superlattice is flat, with an atomic step at the unit cell level, and the contrast in layers with different oxygen contents is different.

[0062] Figure 6 AFM images of the substrate and superlattice surface provided by the embodiment of the present invention: Figure 6 (a) and (b) are atomic steps on the surface of DSO (110) substrate, which is BFO (V o )SL surface atomic steps; from Figure 6 It can be seen that the step width of the BFO superlattice is similar to that of the substrate, and it has extremely high flatness: the superlattice surface has clear and parallel atomic steps with a roughness of about 0.2nm. The homojunction superlattice grows along the (001) orientation, which is similar to DyScO3-(110). pc The mismatch of the substrate is about -0.2%.

[0063] In summary, the present invention provides a bismuth ferrite-based homojunction superlattice based on molecular beam epitaxy. By precisely controlling the ozone pressure through molecular beam epitaxy, a bismuth ferrite / oxygen vacancy bismuth ferrite homojunction superlattice is constructed on a dysprosium scandate substrate. Bismuth ferrite containing oxygen vacancies is used to provide a depolarization field at the homojunction interface, which simplifies the preparation process of the ferroelectric superlattice and improves the preparation efficiency of the superlattice. By precisely controlling the condition parameters of the superlattice during the growth process, the crystallization quality and epitaxial quality of the superlattice are improved.

[0064] Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, and thus, the scope of the present invention should not be limited to the above embodiments.

Claims

1. A method for preparing a bismuth ferrite-based homojunction superlattice based on molecular beam epitaxy, characterized in that: The preparation method comprises: (1) The substrate is introduced into the MBE growth chamber, and the substrate temperature is lower than the Bi source evaporation temperature; (2) Raising the temperature of the Bi source and the Fe source to the evaporation temperature, and adjusting the beam current of the Bi source and the Fe source; (3) using ozone as the epitaxial growth atmosphere, a Bi source and a Fe source are mixed in a growth chamber to first epitaxially grow a bismuth ferrite film without oxygen vacancies as a ferroelectric phase, and then epitaxially grow a bismuth ferrite film containing oxygen vacancies as a defective ferroelectric phase after reducing the oxygen pressure; (4) The two epitaxial growths in step (3) are grown alternately to obtain a bismuth ferrite-based homojunction superlattice.

2. The method for preparing a bismuth ferrite-based homojunction superlattice based on molecular beam epitaxy according to claim 1, characterized in that: In step (1), the substrate is a (110)-oriented scandate single crystal substrate, and the substrate is a substrate having an atomically flat surface after being treated by chemical wet processing and annealing.

3. The method for preparing bismuth ferrite-based homojunction superlattice based on molecular beam epitaxy according to claim 1, characterized in that: In step (1), the substrate temperature satisfies: 300°C ≤ substrate temperature < 600°C.

4. The method for preparing the bismuth ferrite-based homojunction superlattice according to claim 1, characterized in that: In step (2), the evaporation temperature of the Bi source is 600-700° C., and the evaporation temperature of the Fe source is 1200-1500° C.; the beam ratio of the Bi source to the Fe source is greater than or equal to 4:

1.

5. The method for preparing bismuth ferrite-based homojunction superlattice based on molecular beam epitaxy according to claim 4, characterized in that: The beam ratio of the Bi source to the Fe source is 4-16:

1.

6. The method for preparing bismuth ferrite-based homojunction superlattice based on molecular beam epitaxy according to claim 1, characterized in that: In step (3), the oxygen pressure of the epitaxial growth is 10 -6 -10 -5 Torr, the oxygen pressure drop of the epitaxially grown bismuth ferrite epitaxial film without oxygen vacancies is no more than 1×10 -6 After the Torr treatment, epitaxial growth of bismuth ferrite thin films containing oxygen vacancies was performed.

7. The method for preparing bismuth ferrite-based homojunction superlattice based on molecular beam epitaxy according to claim 1, characterized in that: In step (4), the growth is performed alternately 2 to 16 times.

8. A bismuth ferrite-based homojunction superlattice obtained by the preparation method according to any one of claims 1 to 7.

9. The bismuth ferrite-based homojunction superlattice according to claim 8, characterized in that: The bismuth ferrite-based homojunction superlattice is a (001)-oriented bismuth ferrite / oxygen vacancy bismuth ferrite homojunction superlattice.

10. Application of the bismuth ferrite-based homojunction superlattice according to claim 8 in a ferroelectric memory.

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