A bismuth-based single-crystal self-oxidizing dielectric layer, a preparation method and application thereof

Abstract

The application provides a single-crystal beta-Bi2SeO5 as well as a preparation method and application thereof, and belongs to the field of chemical synthesis and semiconductor microelectronic devices. The single-crystal beta-Bi2SeO5 is obtained by ultraviolet-assisted oxidation of single-crystal Bi2O2Se nanosheets or single-crystal Bi2O2Se thin films. The beta-Bi2SeO5 is a single crystal, Bi is trivalent, Se is tetravalent, and O is divalent, the chemical formula is Bi2SeO5, has a Bi-O layered skeleton structure, and the interlayer is a Se-O layer. The field effect transistor with the single-crystal beta-Bi2SeO5 as a dielectric layer has extremely strong gate control ability, low gate-drain current and high interface quality.

Description

Technical Field

[0001] This invention relates to the fields of chemical synthesis and semiconductor microelectronic devices, specifically to a single-crystal β-Bi2SeO5, its preparation method, and its applications. Background Technology

[0002] Two-dimensional semiconductors exhibit weak interactions between their layers, maintaining high mobility even at nanometer-scale thicknesses and effectively suppressing short-channel effects. Therefore, they are considered a key candidate material for the channel of next-generation field-effect transistors (FETs) in integrated circuits. During transistor miniaturization, not only the channel but also the dielectric layer must be miniaturized to maintain switching performance, a significant challenge for two-dimensional semiconductors. In recent years, some research has attempted to combine various dielectric materials with two-dimensional semiconductors, such as hBN, CaF2, Bi2SeO5, and commercially available HfO2. However, limited by dielectric constants or leakage current, the equivalent oxide thickness (EOT) can only be miniaturized to the 0.9 nm level (lower EOT results in stronger gate control), and various issues related to interface quality and process compatibility also exist. To date, gate dielectric layers compatible with two-dimensional semiconductors have not yet met the requirements of next-generation field-effect transistors.

[0003] Bismuth selenide oxide (Bi₂O₂Se) is a two-dimensional semiconductor material discovered in recent years, belonging to the tetragonal crystal system. From [Bi2O2] n 2n+ Layers and [Se] n 2n- It consists of alternating layers. Its band gap is moderate, approximately 0.85 eV, and its room-temperature electron mobility (measured by the Hall effect) is as high as 450 cm⁻¹. 2 V -1 s -1 Furthermore, it is environmentally stable and unaffected by water and oxygen corrosion at room temperature, making it a promising candidate for applications in high-performance logic circuits and flexible devices. Its oxide product, bismuth oxysene selenite (Bi₂SeO₅), has a bandgap exceeding 3.5 eV and a relative permittivity κ as high as approximately 21, making it an excellent self-oxidizing dielectric layer. In previous studies, polycrystalline and amorphous Bi₂SeO₅ have been successfully used as dielectric layers in two-dimensional field-effect transistors; however, when the equivalent oxide layer thickness is reduced to 0.9 nm, the leakage current already exceeds the low-power requirement (0.015 A / cm²). -2 At a gate voltage of 1V, its main weakness, insulation, needs further improvement. Summary of the Invention

[0004] The purpose of this invention is to provide a single-crystal β-Bi₂SeO₅, its preparation method, and its applications. This invention uses active oxygen generated from ultraviolet radiation pyrolysis of oxygen as an oxidant to oxidize bismuth [Se] in two-dimensional selenium.n 2n- Layer-intercalation oxidation, while maintaining [Bi2O2] n 2n+ The intact oxide layer structure allowed the oxide products to maintain the single-crystallinity of the bismuth selenide precursor, resulting in single-crystal β-Bi₂SeO₅. It exhibits a high dielectric constant of 22 and excellent insulation properties; even with an equivalent oxide layer thickness as thin as 0.41 nm (physical thickness 2.3 nm), its leakage current remains as low as 0.015 A / cm² at a gate voltage of 1 V. 2 The following features meet low power consumption requirements. The bismuth selenide oxide-based two-dimensional field-effect transistor, constructed with monocrystalline β-Bi2SeO5 as the dielectric layer, has stronger gate control capability (low EOT), lower gate leakage current, and a high-quality semiconductor / dielectric layer interface (low subthreshold swing and low hysteresis) compared to other two-dimensional field-effect transistors.

[0005] The present invention first provides a single-crystal β-Bi2SeO5, wherein β-Bi2SeO5 is a single crystal, Bi is positive trivalent, Se is positive tetravalent, O is negative divalent, and the chemical formula is Bi2SeO5. It has a Bi-O layered framework structure with Se-O layers between the layers.

[0006] The preparation method of the above-mentioned single-crystal β-Bi2SeO5 includes the following steps: performing ultraviolet-assisted oxidation on single-crystal Bi2O2Se nanosheets or Bi2O2Se single-crystal thin films to obtain the single-crystal β-Bi2SeO5.

[0007] In the above preparation method, the ultraviolet-assisted oxidation is to use active oxygen generated by ultraviolet decomposition of oxygen as an oxidant to oxidize the single-crystal Bi2O2Se nanosheets or Bi2O2Se single-crystal thin films.

[0008] Specifically, the wavelength of the ultraviolet light used in the ultraviolet-assisted oxidation is 185 nm and / or 254 nm;

[0009] The atmosphere for ultraviolet-assisted oxidation can be pure oxygen, air, or ozone;

[0010] The reaction temperature of the ultraviolet-assisted oxidation can be 25-300℃, specifically 200-280℃, more specifically 230℃ or 270℃; the reaction time can be specifically 5 seconds to 120 minutes, specifically 0.5 minutes to 3 minutes.

[0011] The ultraviolet-assisted oxidation is carried out in an ultraviolet ozone cleaning machine.

[0012] The present invention also provides the application of the above-mentioned single-crystal β-Bi2SeO5 in the fabrication of field-effect transistors.

[0013] Specifically, the field-effect transistor can be a top-gate field-effect transistor, a dual-gate field-effect transistor, a gate-all-around field-effect transistor, or a fin field-effect transistor;

[0014] The single-crystal β-Bi2SeO5 is used as the dielectric layer of the field-effect transistor.

[0015] The present invention further provides a field-effect transistor, which includes a substrate, a channel material on the substrate, a dielectric layer on the channel material, a gate electrode on the dielectric layer, and source and drain electrodes in direct contact with the channel material;

[0016] The material constituting the dielectric layer is the single-crystal β-Bi2SeO5;

[0017] The channel material is a single-crystal Bi2O2Se nanosheet or a Bi2O2Se single-crystal thin film;

[0018] The source and drain electrodes are located at both ends of the dielectric layer and are in contact with the channel material.

[0019] In the aforementioned field-effect transistor, the thickness of the channel material is 1.2–15 nm;

[0020] The thickness of the dielectric layer is 2–15 nm;

[0021] The material constituting the gate electrode is a metal; specifically, the metal is selected from at least one of gold and palladium.

[0022] The thickness of the gate electrode is 30–50 nm;

[0023] The source and drain electrodes include a contact layer and a protective layer;

[0024] The material constituting the contact layer is selected from at least one of palladium, iron, and titanium; the material constituting the protective layer is gold.

[0025] The thickness of the source and drain electrodes is 35–55 nm;

[0026] Specifically, the thickness of the contact layer is 5 nm; the thickness of the protective layer is 30–50 nm.

[0027] The aforementioned field-effect transistor uses commercially available fluorophlogopite or strontium titanate as the substrate material; the chemical formula of the fluorophlogopite substrate is KMg3(AlSi3O4). 10 F2, the chemical formula of the strontium titanate substrate is SrTiO3.

[0028] The single-crystal Bi2O2Se nanosheets or Bi2O2Se single-crystal thin films are prepared by chemical vapor deposition or molecular beam epitaxy.

[0029] Specifically, the chemical vapor deposition method uses Bi2Se3 bulk and Bi2O3 powder as raw materials, argon-oxygen mixture as carrier gas, and is carried out in a tube furnace; the substrate used is commercially available fluorophlogopite (for preparing nanosheets) or strontium titanate substrate (for preparing single crystal thin films).

[0030] More specifically, the mass ratio of the Bi2Se3 bulk to the Bi2O3 powder is 2:3;

[0031] The Bi2Se3 bulk and Bi2O3 powder are placed in the center and 5-8 cm upstream of the quartz tube of the tubular furnace.

[0032] The substrate is positioned 9–12 cm downstream of the center of the tubular furnace.

[0033] The molecular beam epitaxy (MBE) method uses Bi, Se, and O2 as raw materials and strontium titanate as a substrate to prepare Bi2O2Se single crystal thin films.

[0034] The present invention also provides a method for fabricating the field-effect transistor, including method one or method two;

[0035] Method 1 includes the following steps:

[0036] (1) UV-assisted oxidation of single-crystal Bi2O2Se nanosheets or Bi2O2Se single-crystal films on a substrate to obtain single-crystal β-Bi2SeO5 as a dielectric layer on its surface;

[0037] (2) A gate electrode is fabricated on the dielectric layer obtained in step (1);

[0038] (3) Remove the dielectric layer in the regions on both sides of the gate electrode, and deposit the source and drain electrodes by evaporation or sputtering to obtain the field-effect transistor.

[0039] Method 2 includes the following steps:

[0040] (1) The source and drain electrodes are deposited by vapor deposition or sputtering on a single-crystal Bi2O2Se nanosheet or Bi2O2Se single-crystal thin film on a substrate;

[0041] (2) The area not covered by the electrode in step (1) is subjected to ultraviolet-assisted oxidation to obtain β-Bi2SeO5 as a single crystal as a dielectric layer;

[0042] (3) A gate electrode is fabricated on the dielectric layer to obtain the field-effect transistor.

[0043] In the above preparation method, in the ultraviolet-assisted oxidation step, active oxygen generated by ultraviolet decomposition of oxygen is used as an oxidant to carry out the oxidation reaction;

[0044] Specifically, the wavelength of the ultraviolet light used in the ultraviolet-assisted oxidation is 185 nm and / or 254 nm;

[0045] The atmosphere for ultraviolet-assisted oxidation can be pure oxygen, air, or ozone;

[0046] The reaction temperature of the ultraviolet-assisted oxidation can be 25-300℃, specifically 200-280℃, more specifically 230℃ or 270℃; the reaction time can be specifically 5 seconds to 120 minutes, specifically 0.5 minutes to 3 minutes.

[0047] In the above preparation method, after the ultraviolet-assisted oxidation, there is an annealing step; the annealing is specifically carried out in air, the annealing temperature is 210-270°C, and the annealing time is 15-60 minutes.

[0048] After the gate electrode is prepared, there is an annealing step; the annealing is specifically carried out in air, the annealing temperature is 210-270°C, and the annealing time is 15-60 minutes.

[0049] The gate electrode is prepared by thermal evaporation or electron beam evaporation.

[0050] The source and drain electrodes used are prepared by thermal evaporation, electron beam evaporation or magnetron sputtering deposition.

[0051] Finally, the present invention provides the application of the above-described field-effect transistor in the fabrication of logic circuits, sensors, or integrated circuits, as well as logic circuits, sensors, or integrated circuits containing the field-effect transistor.

[0052] This invention uses two-dimensional Bi₂O₂Se single-crystal nanosheets or single-crystal thin films synthesized by chemical vapor deposition or molecular beam epitaxy as precursors, and uses reactive oxygen species generated by ultraviolet radiation to decompose oxygen as an oxidant for intercalation oxidation, thereby obtaining single-crystal β-Bi₂SeO₅ through in-situ transformation on its surface. The field-effect transistor prepared by this invention, using single-crystal β-Bi₂SeO₅ as the dielectric layer, exhibits extremely strong gate control capability, with an equivalent oxide thickness (EOT) as low as 0.41 nm; and low gate leakage current, reaching as low as 0.015 Acm at a gate voltage of 1 V. -2 The following features meet low power consumption requirements; high interface quality; and subthreshold swing (SS) as low as 65mV dec. -1 Hysteresis can be as low as 70mV or less.

[0053] The present invention has the following beneficial effects:

[0054] (1) This invention uses two-dimensional semiconductor Bi2O2Se as raw material and uses ultraviolet light to decompose oxygen in the air to provide oxidant for intercalation oxidation, thereby obtaining a single crystal high dielectric constant self-oxide β-Bi2SeO5 dielectric layer that maintains the Bi-O skeleton in the precursor structure, and uses it to construct a high-performance field-effect transistor.

[0055] (2) The equipment and processes of this invention are inexpensive and easy to operate. The thickness of the oxide layer can be controlled layer by layer and can be selectively applied using photomasks. The resulting dielectric layer has excellent performance: strong gate control capability, and the equivalent oxide layer thickness can be as thin as 0.41 nm; the gate leakage current can be as low as 0.015 Acm at a gate voltage of 1 V. -2 The following features meet low power consumption requirements; high interface quality; and subthreshold swing (SS) as low as 65mV dec. -1 Hysteresis can be as low as 70mV; it is expected to be applied to future ultra-miniaturized integrated circuits based on two-dimensional semiconductors. Attached Figure Description

[0056] Figure 1 The images show the ultraviolet ozone cleaning machine used in this invention, the gas phase photochemical reaction that occurs therein, and optical microscope images of Bi2O2Se nanosheets before and after partial oxidation in Example 1.

[0057] Figure 2 The above are X-ray photoelectron spectroscopy (XPS) spectra of the Bi2O2Se thin film sample before and after UV-assisted oxidation in Example 2 of this invention, with Bi2SeO5 powder as the reference.

[0058] Figure 3 The images and schematic diagrams of the ultraviolet-assisted oxidation process in Embodiment 3 of the present invention are: scanning transmission electron microscope-high angle annular dark field image (STEM-HAADF) photographs and schematic diagrams of the crystal structures of Bi2O2Se and the self-oxide β-Bi2SeO5.

[0059] Figure 4 These are high-resolution transmission electron microscope (TEM) and selected area electron diffraction (SAED) images of the present invention before UV-assisted oxidation, after partial oxidation on both sides, and after complete oxidation.

[0060] Figure 5 This is a selected area electron diffraction pattern of various regions on the same fully oxidized Bi2O2Se nanosheet in Example 4 of the present invention.

[0061] Figure 6 The rate of ultraviolet-assisted oxidation at 25–300°C in Example 5 of this invention;

[0062] Figure 7The X-ray diffraction (XRD) spectra of the ultraviolet-assisted oxidation products prepared at different temperatures in Example 6 of the present invention, and their phase transformation relationship with the air thermal oxidation product α-Bi2SeO5;

[0063] Figure 8 The images show the thickness-time relationship of Bi2O2Se nanosheets on fluorophlogopite in Example 7 of this invention at 25°C, as well as atomic force microscopy (AFM) images of the upper surface of β-Bi2SeO5 and the Bi2O2Se / β-Bi2SeO5 interface.

[0064] Figure 9 This is a schematic diagram, photograph, and optical microscope image of wafer-level ultraviolet-assisted selective oxidation of Bi2O2Se thin film using a photomask as a mask, as shown in Embodiment 8 of the present invention.

[0065] Figure 10 This is a schematic diagram of the apparatus and measurement results for measuring the dielectric constant of ultrathin β-Bi2SeO5 nanosheets in the GHz band using microwave impedance microscopy (MIM) in Embodiment 9 of the present invention.

[0066] Figure 11 This is a flowchart and a schematic diagram of the measurement circuit for the fabrication of the Bi2O2Se / β-Bi2SeO5 self-oxidized dielectric layer field-effect transistor in Embodiment 10 of the present invention.

[0067] Figure 12 The thickness measurement results and leakage current measurement results of the single-crystal β-Bi2SeO5 dielectric layer obtained in Example 10 of the present invention are shown.

[0068] Figure 13 The optical microscope images, output characteristic curves, transfer characteristic curves, dielectric layer thickness measurement results, gate leakage current and subthreshold swing measurement results of the Bi2O2Se / β-Bi2SeO5 self-oxidized dielectric layer field-effect transistor obtained in Example 10 of the present invention are shown.

[0069] Figure 14 The output characteristic curve, transfer characteristic curve, and dielectric layer thickness measurement results of the Bi2O2Se / β-Bi2SeO5 self-oxidized dielectric layer field-effect transistor obtained in Example 11 of the present invention are shown.

[0070] Figure 15 The output and transfer characteristic curves and cross-sectional TEM images of the Bi2O2Se / β-Bi2SeO5 self-oxidized dielectric layer field-effect transistor obtained in Example 12 of the present invention are shown.

[0071] Figure 16The transfer characteristic curves and hysteresis of the Bi2O2Se / β-Bi2SeO5 self-oxidized dielectric layer field-effect transistor obtained in Example 12 of the present invention at different scan rates;

[0072] Figure 17 The electrical performance uniformity of the 12 Bi2O2Se / β-Bi2SeO5 self-oxidized dielectric layer field-effect transistors obtained in Example 12 of the present invention is characterized by transfer characteristic curves and statistics on subthreshold swing and on / off ratio. Detailed Implementation

[0073] The present invention will be further described in detail below with reference to specific embodiments. The embodiments given are only for illustrating the present invention and are not intended to limit the scope of the present invention.

[0074] Unless otherwise specified, the experimental methods described in the following examples are conventional methods.

[0075] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0076] Example 1

[0077] (1) Growth of Bi2O2Se nanosheets: Weigh 1.5 g of Bi2O3 powder and 1.0 g of Bi2Se3 bulk material (20-25 sheets), and place them in the center and 5-8 cm upstream of the quartz tube of the tubular furnace. Place 3 fluorophlogopite substrates 9-12 cm downstream of the center of the tubular furnace. After two gas purgings, introduce carrier gas at an argon flow rate of 200-300 standard mL / min (sccm) and an argon-oxygen mixture (O2 volume fraction 0.1%) flow rate of 0.3-2.5 standard mL / min, so that the oxygen content is 1-10 ppm. Control the system pressure at 50-800 Torr using an electric valve. Raise the temperature to 620-680 degrees Celsius over 20 minutes and maintain it for 5-30 minutes for chemical vapor deposition. Allow the reaction to cool naturally to room temperature afterward. Remove the fluorophlogopite substrate with the deposited Bi2O2Se film to obtain layered Bi2O2Se nanosheets on its surface.

[0078] (2) Oxidation step: Bi2O2Se nanosheets grown on fluorophlogopite substrate were placed in an ultraviolet ozone cleaner. After setting the temperature (25°C), the ultraviolet lamp (low-pressure mercury lamp) was turned on. The active oxygen generated by ultraviolet decomposition of oxygen was used as the oxidant to perform ultraviolet-assisted oxidation on the Bi2O2Se nanosheets. The oxidation time was 35 minutes to obtain Bi2O2Se with partial surface oxidation.

[0079] Figure 1 Photo a shows the UV ozone cleaner used in the oxidation process, with the gas phase reaction indicated below. Figure 1In the image, b represents optical microscope images of Bi2O2Se nanosheets before and after partial oxidation, indicating that Bi2O2Se has been partially transformed into a substance with a larger band gap and lower absorbance of visible light.

[0080] Example 2

[0081] (1) Preparation of Bi₂O₂Se single crystal thin film: Weigh 1.5 g of Bi₂O₃ powder and 1.0 g of Bi₂Se₃ bulk (20-25 pieces), place them in the center of the quartz tube of the tube furnace and 5-8 cm upstream, and place the strontium titanate substrate 11-14 cm downstream of the center of the tube furnace. After two gas purgings, introduce carrier gas. The argon flow rate is 200-300 standard mL / min (sccm), and the argon-oxygen mixture (O₂ volume fraction 0.1%) flow rate is 0.3-2.5 standard mL / min, so that the oxygen content is 1-10 ppm. Maintain the pressure at about 400 Torr. Raise the temperature to 670-700 degrees Celsius over 20 minutes and maintain it for 5-30 minutes for chemical vapor deposition. After the reaction, allow it to cool naturally to room temperature. Remove the strontium titanate substrate with the deposited Bi₂O₂Se thin film to obtain the Bi₂O₂Se single crystal thin film.

[0082] (2) Oxidation step: The Bi2O2Se single crystal film with a thickness of about 10 nm grown on the strontium titanate substrate was placed in an ultraviolet ozone cleaner, the temperature was set (120℃), and after the temperature stabilized, the ultraviolet lamp (low-pressure mercury lamp) was turned on. The active oxygen generated by the ultraviolet decomposition of oxygen was used as the oxidant to perform ultraviolet-assisted oxidation on the Bi2O2Se single crystal film. The oxidation time was 1 hour, and a fully oxidized Bi2O2Se film was obtained.

[0083] Figure 2 These are the X-ray photoelectron spectroscopy (XPS) spectra of the Bi2O2Se single crystal thin film before and after oxidation in this embodiment. The reference material is Bi2SeO5 powder (prepared by mixing commercially available Bi2O3 and SeO2 powders at a molar ratio of 1:1, loading the mixture into a quartz tube, sealing the tube opening with an oxyhydrogen flame, sintering at 850°C for 12 hours, breaking the quartz tube, removing the white solid sample, and grinding it into powder). Figure 2 It can be seen that in the UV-assisted oxidation product, Se has a positive four-valent oxidation state, bismuth has a positive three-valent oxidation state, and oxygen has a negative two-valent oxidation state. The elemental ratio is approximately Bi:Se:O ~ 2:1:5. Therefore, it can be determined that the chemical formula of the oxidation product is Bi2SeO5.

[0084] Example 3

[0085] (1) The growth steps of the Bi2O2Se nanosheet sample were the same as those in Example 1.

[0086] (2) Oxidation step: The Bi2O2Se nanosheets grown on the fluorophlogopite substrate were placed in an ultraviolet ozone cleaner, the temperature was set (120℃), and after the temperature stabilized, the ultraviolet lamp (low-pressure mercury lamp) was turned on. The active oxygen generated by the ultraviolet decomposition of oxygen was used as the oxidant to perform ultraviolet-assisted oxidation on the Bi2O2Se nanosheets. The oxidation time was 10 minutes, and partially oxidized Bi2O2Se nanosheets were obtained.

[0087] Figure 3 The images show a cross-sectional scanning transmission electron microscope (STEM) image of the Bi2O2Se / β-Bi2SeO5 heterostructure obtained in this example (i.e., the partially oxidized Bi2O2Se nanosheets obtained in (2)) at the oxidation front at the interface, along with a high-angle annular dark-field image (HAADF) and a schematic diagram of the crystal structure of Bi2O2Se and the self-oxidized product β-Bi2SeO5. As shown in the figure, this UV-assisted oxidation is an intercalation oxidation. The Bi-O framework of the precursor remains intact, and the interlayer spacing expands from 0.61 nm to 0.78 nm, resulting in a new layered oxide that inherits the Bi-O framework of the Bi2O2Se precursor and is different from the bulk Bi2SeO5. Combined with the chemical formula of Bi2SeO5 determined by X-ray photoelectron spectroscopy in Example 2, it is named β-Bi2SeO5 here to reflect the difference between its crystal structure and that of the bulk Bi2SeO5 (here referred to as α-Bi2SeO5).

[0088] Example 4

[0089] (1) The growth steps of the Bi2O2Se nanosheet sample were the same as those in Example 1.

[0090] (2) Transfer steps: A layer of PMMA (polymethyl methacrylate) was spin-coated onto the Bi2O2Se nanosheets on fluorophlogopite at 4000 rpm. The substrate was then immersed in a 5% HF solution to slightly etch the fluorophlogopite substrate. After 5 minutes, the substrate was retrieved into water, where the surface tension of the water allowed the PMMA to float and detach from the fluorophlogopite substrate, thus carrying away some of the Bi2O2Se nanosheets. The PMMA was then transferred to a transmission electron microscope (TEM) grid (gold grid), and dissolved in acetone, leaving the Bi2O2Se nanosheets on the grid. The nanosheets were characterized by TEM and selected area electron diffraction (SAED) before oxidation, after partial oxidation, and after complete oxidation.

[0091] (2) Oxidation Step: The transmission electron microscope (TEM) screen was placed in an ultraviolet ozone cleaner, and the temperature was set to 120℃. After the temperature stabilized, the ultraviolet lamp (low-pressure mercury lamp) was turned on. The active oxygen generated by the decomposition of oxygen by ultraviolet light was used as the oxidant to perform ultraviolet-assisted oxidation of the Bi2O2Se sample for 15 minutes. After one side was oxidized, the TEM screen was flipped over, and the other side was oxidized under the same conditions. This resulted in a β-Bi2SeO5 / Bi2O2Se / β-Bi2SeO5 stacked heterostructure with partial oxidation on both sides. After TEM characterization, the temperature was set to 150℃ and oxidized for 1 hour to completely oxidize the sample. TEM characterization was then performed again.

[0092] Figure 4 It is the Bi2O2Se nanosheets on the carrier network before oxidation ( Figure 4 a) After partial oxidation on both sides (b) After complete oxidation ( Figure 4 The transmission electron microscope (TEM) image and selected area electron diffraction (SED) pattern in (c) are shown. The image shows only one lattice and one set of diffraction points, indicating that the UV-assisted oxidation product β-Bi₂SeO₅ completely inherits the heavy atom framework of the Bi₂O₂Se precursor and maintains a strict lattice match with it. Therefore, for a single-crystal Bi₂O₂Se precursor, the UV-assisted oxidation product is also a single crystal.

[0093] Figure 5 This is a selected area electron diffraction pattern of the same Bi₂O₂Se nanosheet at different locations on the web after complete oxidation. The pattern shows only one set of diffraction points, and they remain parallel at different locations, indicating that the UV-assisted oxidation product β-Bi₂SeO₅ of the single-crystal Bi₂O₂Se nanosheet is indeed single-crystal.

[0094] Example 5

[0095] (1) The growth steps of the Bi2O2Se nanosheet sample were the same as those in Example 1.

[0096] (2) Oxidation step: Place the Bi2O2Se nanosheet sample on fluorophlogopite in an ultraviolet ozone cleaner, set the temperature (25℃~300℃), and turn on the ultraviolet lamp (low-pressure mercury lamp) after the temperature stabilizes. Use the active oxygen generated by ultraviolet decomposition of oxygen as the oxidant to perform ultraviolet-assisted oxidation of the Bi2O2Se sample for 1~35 minutes.

[0097] Thickness measurement procedure: The thickness of the partially oxidized Bi2O2Se nanosheets was measured using an atomic force microscope (AFM). Then, the β-Bi2SeO5 oxide layer was etched away with a 0.2% HF solution for 20 seconds. The remaining thickness of the Bi2O2Se nanosheets was measured again, and the difference was the oxide layer thickness.

[0098] Figure 6The figure shows the oxide layer thickness of Bi₂O₂Se nanosheets on fluorophlogopite after UV-assisted oxidation at 25–300 °C for 1–35 minutes. As shown in the figure, UV-assisted oxidation is initially controlled by interfacial reaction, but changes to diffusion control as the oxide layer thickens. Based on the oxidation rate-temperature relationship, the activation energy of the UV-assisted oxidation process can be read as approximately 19.8 kJ / mol.

[0099] Example 6

[0100] (1) The growth steps of the Bi2O2Se single crystal thin film sample are the same as those in Example 2.

[0101] (2) Oxidation step: Place the Bi2O2Se single crystal thin film sample (about 10nm) on SrTiO3 in an ultraviolet ozone cleaner, set the temperature (50℃~300℃), and turn on the ultraviolet lamp (low-pressure mercury lamp) after the temperature stabilizes. Use the active oxygen generated by ultraviolet decomposition of oxygen as the oxidant to perform ultraviolet-assisted oxidation on the Bi2O2Se single crystal thin film sample until it is completely oxidized and transformed into β-Bi2SeO5 (visibly white and transparent to the naked eye).

[0102] (3) Heat annealing step: The sample that has been completely oxidized to β-Bi2SeO5 is heated in a tube furnace at 340-380℃ for 30 minutes in air atmosphere and then taken out.

[0103] Figure 7 These are X-ray diffraction patterns of Bi₂O₂Se single-crystal thin film samples on SrTiO₃ after complete UV-assisted oxidation at different temperatures, resulting in complete conversion to β-Bi₂SeO₅. Figure 7 (a) and the X-ray diffraction pattern after high-temperature annealing in an air atmosphere in a tube furnace ( Figure 7 (b) The references are Bi₂O₂Se and the product of Bi₂O₂Se thermal oxidation in air at 400℃ (the same bulk phase, referred to here as α-Bi₂SeO₅). As shown in the figure, the UV-assisted oxidation product from 50℃ to 300℃ is β-Bi₂SeO₅, and it can withstand air annealing at 340℃, indicating that it has sufficient thermal stability in air. However, when heated to 360℃ or above, β-Bi₂SeO₅ transforms into the high-temperature stable phase α-Bi₂SeO₅.

[0104] Example 7

[0105] (1) The growth steps of the Bi2O2Se nanosheet sample were the same as those in Example 1.

[0106] (2) Oxidation step: The Bi2O2Se nanosheets grown on the fluorophlogopite substrate were placed in an ultraviolet ozone cleaner, the temperature was set to 25℃ (room temperature), and the ultraviolet lamp (low-pressure mercury lamp) was turned on. The active oxygen generated by the ultraviolet decomposition of oxygen was used as the oxidant to perform ultraviolet-assisted oxidation on the Bi2O2Se sample. The oxidation time was 6 to 30 minutes to obtain partially oxidized Bi2O2Se nanosheets.

[0107] The oxide layer thickness measurement procedure is the same as in Example 5.

[0108] Figure 8 These are atomic force microscopy (AFM) images of the thickness-time relationship of Bi₂O₂Se nanosheets on fluorophlogopite at 25°C, as well as the surface of β-Bi₂SeO₅ and the Bi₂O₂Se / β-Bi₂SeO₅ interface. As shown, layer-by-layer oxidation can be achieved by precisely controlling the time; furthermore, the interfaces obtained through UV-assisted oxidation are atomically smooth.

[0109] Example 8

[0110] (1) The growth steps of the Bi2O2Se single crystal thin film sample are the same as those in Example 2.

[0111] (2) Self-made photomask processing steps: Using a commercially available quartz ultraviolet window as a substrate, gold with a thickness of 230nm is deposited by magnetron sputtering. Then, using commercially available photoresist as the processing target, the surface pattern is processed by laser direct writing technology. Using the photoresist as a mask, the gold is selectively etched using the reverse sputtering function of a magnetron sputtering instrument at a power of 50W and an argon flow rate of 100sccm until it becomes transparent. Afterwards, the photoresist is removed in a plasma cleaner using oxygen plasma (500W, 10sccm for 2h), thus obtaining the self-made gold photomask.

[0112] (3) Oxidation step: In a Class 100 cleanroom, the UV lamp (square with a side length of 10cm) of the UV ozone cleaner is wrapped with aluminum foil, leaving only a circular hole with a diameter of about 2.5cm in the center. The Bi2O2Se single crystal thin film sample (10nm) on the 1-inch wafer SrTiO3 is placed in the UV ozone cleaner. The self-made gold photomask is carefully covered on the sample wafer (no photoresist required), the distance is set to the farthest, the temperature is set to 100℃, and the oxidation is carried out for 16h. The photomask is then removed and the sample is taken out.

[0113] Figure 9 This is a schematic diagram of the ultraviolet selective oxidation process of a photolithography plate. Figure 9 (a) A heterostructure image of a 1-inch wafer-level Bi₂O₂Se single-crystal thin film on a SrTiO₃ surface, fabricated by selective oxidation using a UV-assisted photolithography (see image a). Figure 9In b), the white area represents the region oxidized to β-Bi₂SeO₅, and the brown area represents the unoxidized Bi₂O₂Se; a local optical microscope image of its surface (see...) Figure 9 (c) As shown in the figure, the UV-assisted oxidation method is compatible with advanced photolithography technology and does not require photoresist, directly achieving wafer-level region-selective oxidation.

[0114] Example 9

[0115] (1) The growth steps of the Bi2O2Se nanosheet sample were the same as those in Example 1.

[0116] (2) Oxidation step: Select Bi2O2Se nanosheets (2-6 nm) of different thicknesses grown on fluorophlogopite substrate under an optical microscope, place them in an ultraviolet ozone cleaner, set the temperature to 120℃, and after the temperature stabilizes, turn on the ultraviolet lamp (low-pressure mercury lamp) to use the active oxygen generated by ultraviolet decomposition of oxygen as the oxidant to perform ultraviolet-assisted oxidation on the Bi2O2Se nanosheet samples until the selected Bi2O2Se nanosheets are completely oxidized (transparent under an optical microscope).

[0117] Dielectric constant measurement using microwave impedance microscopy: A microwave impedance microscopy (MIM) mounted on an atomic force microscope (AFM) instrument was used to scan the vicinity of the edge of a fully oxidized nanosheet (β-Bi₂SeO₅), simultaneously obtaining dielectric property information of the β-Bi₂SeO₅ nanosheet and the fluorophlogopite substrate (dielectric constant 5.5). The instrument emitted 1.0 GHz microwaves, and the microwave impedance signal was measured while the morphology and thickness were being measured. The imaginary part was extracted and fitted to the thickness. Finite element analysis was then performed, combining the substrate dielectric constant and the relative value of the signal, to obtain the dielectric constant of β-Bi₂SeO₅ nanosheets of various thicknesses.

[0118] Figure 10 This is a schematic diagram of the process of measuring the dielectric constant using microwave impedance microscopy. Figure 10 In part a), the directly measured thickness is related to the imaginary part of the microwave signal. Figure 10 b) in the figure, for thickness fitting ( Figure 10 c) and the measured dielectric constant results ( Figure 10 (d) As shown in the figure, the dielectric constant of β-Bi2SeO5 nanosheets is as high as 22 and does not decrease with the thinning of the sample, even when the thickness is less than 3 nm.

[0119] Example 10

[0120] (1) The growth steps of the Bi2O2Se nanosheet sample were the same as those in Example 1.

[0121] (2) Oxidation step: Select Bi2O2Se nanosheets with a thickness of 10-15 nm grown on a fluorophlogopite substrate and place them in an ultraviolet ozone cleaner. Set the temperature (270℃), and after the temperature stabilizes for 1 minute, turn on the ultraviolet lamp (low-pressure mercury lamp). Use the active oxygen generated by the decomposition of oxygen by ultraviolet light as the oxidant to perform ultraviolet-assisted oxidation on the Bi2O2Se nanosheet samples. The oxidation time is 75 s, resulting in Bi2O2Se nanosheets with the surface partially oxidized to single-crystal β-Bi2SeO5 (thickness 2.3-3.1 nm) (Bi2O2Se / single-crystal β-Bi2SeO5 nanosheets). After oxidation, perform air thermal annealing for 30 minutes on a hot stage at 270℃.

[0122] (3) Field-effect transistor fabrication steps

[0123] For the Bi2O2Se / single-crystal β-Bi2SeO5 nanosheets after thermal annealing in step (2), the gate region (30kV, 350μC / cm) was exposed by electron beam exposure using commercial PMMA (950K)-A4.5 electron beam photoresist and commercial PMMA-MMA copolymer additive as a mask. 2 The developing solution is methyl isobutyl ketone:isopropanol (volume ratio 1:3), developing for approximately 2 seconds. The top grid electrode is thermally deposited at a specific evaporation rate. Afterwards, it was annealed on a 270℃ hot stage for 30 minutes. Then, the source and drain electrode regions were exposed by electron beam exposure using the same method. The self-oxidized layer of the source and drain electrode regions was removed by argon plasma sputtering (20W, 100sccm argon flow rate, 120s, etching rate of approximately 2nm oxide / min). Subsequently, the source and drain electrodes were thermally vaporized at a evaporation rate of...

[0124] The Bi2O2Se-based single-crystal in-situ oxide top-gate field-effect transistor obtained in this embodiment includes a fluorophlogopite substrate, a channel material on the substrate, a dielectric layer on the channel material, a gate electrode on the dielectric layer, and source and drain electrodes that are in direct contact with the channel material and are located at both ends of the dielectric layer.

[0125] The channel material is a two-dimensional Bi2O2Se crystal;

[0126] The thickness of the channel material is approximately 10–15 nm.

[0127] The material constituting the dielectric layer is single-crystal β-Bi2SeO5;

[0128] The thickness of the dielectric layer is 2.3–3.1 nm;

[0129] The material constituting the gate electrode is gold;

[0130] The thickness of the gate electrode is 40 nm;

[0131] The source and drain electrodes comprise a 5nm contact layer and a 50nm protective layer. The contact layer is made of iron, and the protective layer is made of gold.

[0132] The oxide layer thickness measurement method is as follows: first, measure the total thickness of Bi2O2Se / β-Bi2SeO5 exposed between the gate and the source / drain; then, immerse and etch the β-Bi2SeO5 dielectric layer in a 0.2% HF solution for 20 seconds to completely etch away the β-Bi2SeO5 dielectric layer; measure the remaining thickness, and the difference is the thickness of the β-Bi2SeO5 dielectric layer.

[0133] Figure 11 This embodiment describes the manufacturing process and measurement circuit for a Bi2O2Se-based single-crystal self-oxidized dielectric layer top-gate field-effect transistor.

[0134] Figure 12 The figures show the thickness and gate leakage current measurements of the thinnest working single-crystal self-oxidizing dielectric layer (β-Bi₂SeO₅) in this embodiment. As can be seen, even at a thickness of 2.3 nm (corresponding to exactly 3 layers of β-Bi₂SeO₅), the equivalent oxide thickness (EOT) of the single-crystal self-oxidizing dielectric layer β-Bi₂SeO₅ is as low as 0.41 nm based on a dielectric constant of 22. At a gate voltage of 1 V, its gate leakage current density is still as low as 0.015 A / cm². 2 The following meets the semiconductor industry's requirements for low power limit of the gate dielectric layer.

[0135] Figure 13 The output characteristic curve of the transistor obtained in this example ( Figure 13 a) Transfer characteristic curve ( Figure 13 b) Thickness measurement results ( Figure 13 c) Gate leakage current measurement results ( Figure 13 d) and subthreshold swing measurement results ( Figure 13 (e). Its self-oxidized dielectric layer thickness is 2.7 nm, and the equivalent oxide layer thickness (EOT) calculated based on a dielectric constant of 22 is as low as 0.48 nm, with a gate leakage current as low as 0.015 A / cm at a gate voltage of 1 V. 2 Below, the field-effect mobility is approximately 10² cm⁻¹. 2 V -1 s -1 The subthreshold swing can be as low as 65mV / dec, close to the theoretical limit.

[0136] Example 11

[0137] (1) The growth steps of the Bi2O2Se nanosheet sample were the same as those in Example 1.

[0138] (2) Field-effect transistor fabrication steps

[0139] Bi₂O₂Se nanosheets of approximately 10 nm grown on a fluorophlogopite substrate were selected. Using PMMA (950K)-A4.5 electron beam photoresist and PMMA-MMA copolymer as a mask, electron beam exposure was performed (30 kV, 350 μC / cm²). 2 The developer is methyl isobutyl ketone:isopropanol (volume ratio 1:3), and development takes approximately 2 seconds to expose the source / drain electrode regions. Source / drain electrodes are then deposited using thermal evaporation.

[0140] The sample was then placed in an ultraviolet ozone cleaner, where active oxygen generated by ultraviolet decomposition of oxygen was used as an oxidant to perform ultraviolet-assisted oxidation of the Bi2O2Se sample: the ultraviolet lamp (low-pressure mercury lamp) was turned on, and the sample was oxidized at room temperature for 20 minutes. Then the temperature was raised to 150°C and oxidized for 0.5 minutes. This oxidized the area except for the area covered by the source and drain electrodes into single-crystal β-Bi2SeO5.

[0141] The gate electrode region is then exposed using the same electron beam exposure method, and the gate electrode is deposited by electron beam evaporation at a certain rate.

[0142] The Bi2O2Se-based single-crystal self-oxidizing dielectric layer top-gate field-effect transistor obtained in this embodiment includes a fluorinated phlogopite substrate, a channel material on the substrate, a dielectric layer on the channel material, a gate electrode on the dielectric layer, and source and drain electrodes that are in direct contact with the channel material and are located at both ends of the dielectric layer.

[0143] The channel material is a two-dimensional Bi2O2Se crystal with a thickness of approximately 8.0 nm;

[0144] The material constituting the dielectric layer is single-crystal β-Bi2SeO5;

[0145] The dielectric layer is approximately 3.0 nm thick;

[0146] The material constituting the gate electrode is gold;

[0147] The thickness of the gate electrode is 40 nm;

[0148] The source and drain electrodes comprise a 5nm contact layer and a 50nm protective layer. The contact layer is made of iron, and the protective layer is made of gold.

[0149] The method for measuring oxide layer thickness is the same as in Example 10.

[0150] Figure 14The figures show the output characteristic curves, transfer characteristic curves, and dielectric layer thickness measurement results of the Bi₂O₂Se / β-Bi₂SeO₅ single-crystal self-oxidized dielectric layer field-effect transistor obtained in Example 11 of this invention. Figure 14 It can be seen that its dielectric layer thickness is approximately 3.0 nm, corresponding to EOT = 0.53 nm; the channel thickness is approximately 8.0 nm; and the leakage current of its dielectric layer at a gate voltage of -1 V is 0.05 A / cm. 2 To meet the gate leakage current requirements of high-performance devices (<1A / cm) 2 ).

[0151] Example 12

[0152] (1) The sample was prepared using Bi, O2, and Se as sources in 10 -2 A single-crystal Bi₂O₂Se thin film with a thickness of approximately 10 nm was grown on SrTiO₃ using molecular beam epitaxy at Pa. Specific fabrication method: First, the strontium titanate substrate was annealed in situ at 950°C under high vacuum for 1 hour in a molecular beam epitaxy apparatus, followed by... Se and Bi (measured on the crystal oscillator of the instrument), maintaining the substrate temperature at 290°C, and introducing O2 to achieve a pressure of 10. -2 By growing at Pa for 18 hours, a 10 nm thick Bi₂O₂Se single crystal film can be prepared on a strontium titanate substrate.

[0153] (2) Oxidation step: The sample was placed in a UV ozone cleaner, the temperature was set (230℃), and after the temperature stabilized for 1 minute, the UV lamp (low-pressure mercury lamp) was turned on. The active oxygen generated by the decomposition of oxygen by UV light was used as the oxidant to perform UV-assisted oxidation on the Bi2O2Se sample for 1.5 minutes, resulting in a Bi2O2Se single crystal film with the surface partially oxidized to single crystal β-Bi2SeO5 ((Bi2O2Se / single crystal β-Bi2SeO5 single crystal film)). After oxidation, it was then subjected to air heat annealing for 30 minutes on a hot stage at 230℃.

[0154] (3) Field-effect transistor fabrication steps

[0155] For the annealed Bi2O2Se / single-crystal β-Bi2SeO5 single-crystal thin film in (2), using PMMA (950K)-A4.5 electron beam photoresist and PMMA-MMA copolymer additive as a mask, electron beam exposure (30kV, 350μC / cm) was performed. 2 The developer is methyl isobutyl ketone:isopropanol, volume ratio 1:3 (development time approximately 2 seconds) to expose the gate region, and then thermally vaporizes the top gate (evaporation rate...). Afterwards, it was annealed on a hot stage at 230°C for 15 minutes. Then, the source and drain electrode regions were exposed by electron beam exposure using the same method. The self-oxidized layer of the source and drain electrode regions was removed by argon plasma sputtering (20W, 100sccm argon flow rate, 150s, etching rate approximately 2nm oxide / min). Subsequently, the source and drain electrodes were deposited by electron beam evaporation (evaporation rate approximately 2nm oxide / min). ).

[0156] The Bi2O2Se-based single-crystal in-situ oxide top-gate field-effect transistor obtained in this embodiment includes a strontium titanate substrate, a channel material on the substrate, a dielectric layer on the channel material, a gate electrode on the dielectric layer, and source and drain electrodes that are in direct contact with the channel material and are located at both ends of the dielectric layer.

[0157] The channel material is a two-dimensional Bi2O2Se single crystal;

[0158] The thickness of the channel material is approximately 5–7 nm;

[0159] The material constituting the dielectric layer is single-crystal β-Bi2SeO5;

[0160] The dielectric layer has a thickness of approximately 3.5–5.5 nm.

[0161] The material constituting the gate electrode is gold;

[0162] The thickness of the gate electrode is 30 nm;

[0163] The source and drain electrodes include a 5nm contact layer and a 30nm protective layer. The contact layer is made of titanium, and the protective layer is made of gold.

[0164] Figure 15 The figures show the output characteristic curves, transfer characteristic curves, and interface transmission electron microscopy (TEM) images of the Bi₂O₂Se / β-Bi₂SeO₅ single-crystal self-oxidized dielectric layer top-gate field-effect transistor obtained in this embodiment. The figure shows that its mobility is 10⁸ cm⁻¹. 2 V -1 s -1 Subthreshold swing as low as 70–74 mV / dec; on / off ratio as high as 2 × 10⁻⁶ 6 Its gate leakage current is as low as 1.3 × 10⁻⁶ at a gate voltage of 1V. -3 A / cm 2 The Bi2O2Se channel thickness is 6.6 nm, and the thickness of the single-crystal self-oxidized dielectric layer β-Bi2SeO5 is 3.9 nm (EOT = 0.69 nm).

[0165] Figure 16The figure shows the transfer characteristic curves and hysteresis of the Bi2O2Se / β-Bi2SeO5 single-crystal self-oxidized dielectric top-gate field-effect transistor obtained in this embodiment at different scan rates. As can be seen from the figure, the hysteresis is less than 70mV, indicating that the number of defects in the single-crystal oxide layer is small and the oxide layer quality is high.

[0166] Figure 17 The electrical performance uniformity of the 12 identical Bi2O2Se / β-Bi2SeO5 self-oxidized dielectric top-gate field-effect transistors obtained in this embodiment is statistically analyzed, including the transfer characteristic curves, subthreshold swing, and on / off ratio. As shown in the figure, the transistors exhibit good parallelism, and the subthreshold swing is generally between 70 and 80 mV / dec, indicating high interface quality and few defects in the Bi2O2Se / β-Bi2SeO5 structure.

Claims

1. A single-crystal state β -Bi2SeO5, characterized in that: The β -Bi2SeO5 is a single crystal with Bi in the positive trivalent, Se in the positive tetravalent, and O in the negative divalent. Its chemical formula is Bi2SeO5. It has a Bi-O layered framework structure with Se-O layers between the layers.

2. The single-crystal state as described in claim 1 β The preparation method of -Bi2SeO5 includes the following steps: UV-assisted oxidation of single-crystal Bi2O2Se nanosheets or Bi2O2Se single-crystal thin films to obtain the single-crystal state. β -Bi2SeO5; The wavelength of the ultraviolet light used in the ultraviolet-assisted oxidation is 185 nm and / or 254 nm.

3. The preparation method according to claim 2, characterized in that: The ultraviolet-assisted oxidation involves using active oxygen generated by ultraviolet radiation to pyrolyze oxygen as an oxidant to oxidize single-crystal Bi2O2Se nanosheets or Bi2O2Se single-crystal thin films. The atmosphere for the ultraviolet-assisted oxidation is pure oxygen, air, or ozone; The reaction temperature for the UV-assisted oxidation is 25~300℃; the reaction time is 5 seconds~120 minutes.

4. The single-crystal state as described in claim 1 β Application of Bi2SeO5 in the fabrication of field-effect transistors.

5. The application according to claim 4, characterized in that: The field-effect transistor is a top-gate field-effect transistor, a dual-gate field-effect transistor, a gate-all-around field-effect transistor, or a fin field-effect transistor; The single crystal state β -Bi2SeO5 is used as the dielectric layer of a field-effect transistor.

6. A field-effect transistor, characterized in that: The field-effect transistor includes a substrate, a channel material on the substrate, a dielectric layer on the channel material, a gate electrode on the dielectric layer, and source / drain electrodes in direct contact with the channel material. The material constituting the dielectric layer is the single-crystal state as described in claim 1. β -Bi2SeO5; The channel material is a single-crystal Bi2O2Se nanosheet or a Bi2O2Se single-crystal thin film; The source and drain electrodes are located at both ends of the dielectric layer and are in contact with the channel material.

7. The field-effect transistor according to claim 6, characterized in that: The thickness of the channel material is 1.2~15nm; The thickness of the dielectric layer is 2~15 nm; The material constituting the gate electrode is a metal; The thickness of the gate electrode is 30~50 nm; The source and drain electrodes include a contact layer and a protective layer; The material constituting the contact layer is selected from at least one of palladium, iron, and titanium; the material constituting the protective layer is gold. The thickness of the source and drain electrodes is 35~55 nm.

8. The field-effect transistor according to claim 7, characterized in that: The metal is selected from at least one of gold and palladium; The thickness of the contact layer is 5 nm; the thickness of the protective layer is 30~50 nm.

9. A method for fabricating a field-effect transistor according to any one of claims 6-8, comprising method one or method two; Method 1 includes the following steps: (1) UV-assisted oxidation of single-crystal Bi2O2Se nanosheets or Bi2O2Se single-crystal films on a substrate to obtain single-crystal Bi2O2Se as a dielectric layer on its surface. β -Bi2SeO5; The wavelength of the ultraviolet light used in the ultraviolet-assisted oxidation is 185 nm and / or 254 nm; (2) Fabricate a gate electrode on the dielectric layer obtained in step (1); (3) Remove the dielectric layer in the regions on both sides of the gate electrode, and deposit the source and drain electrodes by evaporation or sputtering to obtain the field-effect transistor. Method 2 includes the following steps: (1) The source and drain electrodes are deposited by vapor evaporation or sputtering on a single-crystal Bi2O2Se nanosheet or Bi2O2Se single-crystal thin film on a substrate; (2) Perform ultraviolet-assisted oxidation on the area not covered by the electrode in step (1) to obtain a single-crystal state as the dielectric layer. β -Bi2SeO5; The wavelength of the ultraviolet light used in the ultraviolet-assisted oxidation is 185 nm and / or 254 nm; (3) A gate electrode is fabricated on the dielectric layer to obtain the field-effect transistor.

10. The preparation method according to claim 9, characterized in that: In the ultraviolet-assisted oxidation step, active oxygen generated by ultraviolet decomposition of oxygen is used as an oxidant to carry out the oxidation reaction. The atmosphere for the ultraviolet-assisted oxidation is pure oxygen, air, or ozone; The reaction temperature for the UV-assisted oxidation is 25~300℃; the reaction time is 5 seconds~120 minutes.

11. The preparation method according to claim 9 or 10, characterized in that: The ultraviolet-assisted oxidation is followed by an annealing step; the annealing is carried out in air at a temperature of 210~270℃ for 15~60 minutes. After the gate electrode is prepared, there is an annealing step; the annealing is carried out in air, the annealing temperature is 210~270℃, and the annealing time is 15~60 minutes. The gate electrode is prepared by thermal evaporation or electron beam evaporation. The source and drain electrodes used are prepared by thermal evaporation, electron beam evaporation or magnetron sputtering deposition.

12. The use of the field-effect transistor according to any one of claims 6-8 in the fabrication of logic circuits, sensors or integrated circuits.

13. A logic circuit, sensor, or integrated circuit comprising a field-effect transistor according to any one of claims 6-8.

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