A method for preparing two-dimensional wide-bandgap bismuth tungstate semiconductor nanofilms by chemical vapor deposition

Abstract

This invention discloses a method for preparing two-dimensional wide-bandgap bismuth tungstate semiconductor nanofilms by chemical vapor deposition (CVD). The CVD preparation method for this Bi₂WO₆ semiconductor single-crystal nanofilm includes the following steps: using WCl₆ powder and Bi₂O₃ powder as raw materials, and a mixture of argon and trace amounts of hydrogen as the carrier gas, chemical vapor deposition is performed on a mica substrate. After deposition, the layered Bi₂WO₆ semiconductor single-crystal thin film is obtained. This method is economical, simple, and easy to implement. The obtained single-crystal nanosheets not only have controllable thickness and good crystal quality, but also allow for controlled planar growth or easy transfer of self-supported upright growth. Two-dimensional bismuth tungstate semiconductors possess excellent properties such as wide bandgap, ferroelectricity, high dielectric constant, and ultrathin thickness, making them of significant value in the field of microelectronics.

Description

Technical Field

[0001] This invention belongs to the field of two-dimensional semiconductor materials, specifically relating to a method for preparing Bi2WO6 semiconductor nanofilms with a wide bandgap. Background Technology

[0002] Currently, Moore's Law is approaching its limits, and integrated circuits are entering the post-Moore era. Miniaturization, high density, and intelligence of devices have become the trends and pursuits in the field of microelectronics. Two-dimensional materials refer to layered materials with few or no layers. Their potential for miniaturization in next-generation electronic devices and their rich physical properties have attracted great interest. Wide-bandgap semiconductors are characterized by a large bandgap (>2.3 eV), high electron mobility, and low carrier concentration, making them valuable for applications in high-power electronic devices, ultraviolet optoelectronic devices, and other fields.

[0003] Bi₂WO₆ is a unique wide-bandgap layered semiconductor, belonging to bismuth-based layered oxides. It possesses excellent properties comparable to gallium nitride and silicon carbide, including a direct bandgap (3.0 eV), in-plane ferroelectricity, high dielectric constant, and excellent air stability, attracting widespread attention in photocatalysis, ferroelectricity, ferromagnetism, and dielectric applications. Ultrathin Bi₂WO₆ nanofilms are crucial for device miniaturization and eliminating depolarization field limitations through in-plane polarization. However, the reported synthesis methods for Bi₂WO₆ mainly include hydrothermal synthesis and pulsed laser deposition (PLD). Hydrothermal synthesis produces Bi₂WO₆ with low crystal quality and small area, while PLD synthesis is costly and slow, both failing to meet the application requirements of electronic devices. Chemical vapor deposition (CVD) offers advantages such as low cost, high speed, wide applicability, simple equipment, and the ability to synthesize high-quality crystalline thin films over large areas. To date, no method has been reported internationally for the controlled synthesis of high-quality Bi2WO6 single-crystal thin films with a thickness of less than 10 nm and their self-supporting upright single crystals using CVD.

[0004] How to synthesize high-quality ultrathin Bi2WO6 nanofilms in a low-cost, convenient, and efficient manner is an urgent problem to be solved. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing Bi2WO6 semiconductor nanofilms with wide bandgap.

[0006] The Bi2WO6 provided by this invention is a layered semiconductor material, and this phase belongs to the orthorhombic crystal system. It is composed of positive charge [Bi₂O₂] n 2n+ Layers and negative charge [WO4] n2n- The Bi₂WO₆ crystal is a non-neutral layered crystal structure formed by alternating stacking of layers along the c-axis. Optical absorption testing and fitting indicate that the Bi₂WO₆ crystal has a suitable bandgap of ~3.0 eV, consistent with theoretical reports, making it a wide-bandgap semiconductor material with potential applications in ferroelectric memories, power devices, optoelectronic devices, and photosynapses.

[0007] The method for preparing layered Bi2WO6 semiconductor thin films provided by the present invention includes the following steps:

[0008] Using WCl6 and Bi2O3 powders as raw materials, chemical vapor deposition was performed to obtain the ultrathin layered Bi2WO6 semiconductor film after deposition.

[0009] In the above method, the mass ratio of WCl6 powder to Bi2O3 powder is 0.1 to 0.6:1. Specifically, it can be 0.1 or 0.2:1.

[0010] The chemical vapor deposition is performed on a substrate;

[0011] The substrate is specifically mica, with the chemical formula KMg3(AlSi3O4). 10 )F2.

[0012] In the chemical vapor deposition step, argon is used as the carrier gas, and the process is carried out with the assistance of trace amounts of hydrogen. The carrier gas flow rate is 50–400 sccm.

[0013] The system pressure is 100-700 Torr, specifically 400 or 700 Torr.

[0014] The deposition temperature is 600-950℃, specifically 600℃, 700℃ or 900℃.

[0015] The deposition time is 5-40 minutes, specifically 10 or 30 minutes.

[0016] The chemical vapor deposition can be carried out in a tube furnace, and more specifically, the raw material is located at the center of the tube furnace, and the mica substrate is located about 0.1 to 2 cm above the raw material.

[0017] The method further includes the following step: after the chemical vapor deposition step, the system is allowed to cool naturally to room temperature.

[0018] The Bi2WO6 layered semiconductor thin film material belongs to the N-type semiconductor and has a film thickness between 5-200nm. In addition to synthesizing nanostructures with planar growth, it also synthesizes self-supporting upright structures.

[0019] Under ultraviolet light irradiation, the Bi2WO6 device exhibits >10 5It exhibits an excellent current on / off ratio and an ultra-low dark current of ~0.1pA. In addition, it demonstrates an ultra-long continuous photoconductivity (~7h).

[0020] The layered Bi2WO6 semiconductor thin film prepared by the above method and its application in the preparation of optoelectronic devices, field-effect transistors and photoelectric synaptic devices are also within the scope of protection of this invention.

[0021] The technical effects of this invention are:

[0022] This invention introduces a method for epitaxially growing two-dimensional wide-bandgap Bi2WO6 semiconductor single-crystal thin films on mica substrates via chemical vapor deposition (CVD). The thinnest thickness can reach 5.5 nm, and the number of crystal domains can reach 309 μm. Furthermore, self-supporting upright Bi2WO6 crystals that are easy to transfer can be grown in a controlled manner. The developed and synthesized Bi2WO6 semiconductor thin film material possesses an ultra-large bandgap (3.0 eV), an ultra-thin thickness (5.5 nm), and the synthesis method is economical, simple, and easy to implement. The resulting nanoscale thin film has controllable thickness, good crystal quality, excellent ferroelectric properties, ultra-high dielectric constant, and a self-supporting upright structure that is easy to transfer and stack. Therefore, it provides a material option for the development of novel ferroelectric memories, high-k gate transistors, high-power semiconductor devices, ultraviolet optoelectronic devices, and retinal photosynaptic devices in future sub-3nm advanced processes. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the chemical vapor deposition method for growing Bi2WO6 thin films according to the present invention. The growth method is simple and convenient.

[0024] Figure 2 This is an optical microscope image of the Bi2WO6 thin film obtained in Example 1 of the present invention, showing uniform crystal size;

[0025] Figure 3 This is a micro-area energy dispersive X-ray spectroscopy analysis diagram of the Bi2WO6 thin film obtained in Example 1 of this invention.

[0026] (EDX-mapping) shows that Bi, W, and O elements are evenly distributed inside the sample.

[0027] Figure 4 These are the X-ray diffraction (XRD) spectra of the Bi2WO6 thin film obtained in Example 1 of this invention and the theoretically calculated spectra.

[0028] Compare;

[0029] Figure 5 This is the Raman spectrum of the Bi2WO6 thin film obtained in Example 1 of this invention;

[0030] Figure 6The selected region electron diffraction (SAED) and high-resolution HRTEM (HRTEM) patterns of the Bi2WO6 thin film ab plane obtained in Embodiment 1 of the present invention show clearly visible interplanar spacing and high-quality crystal structure.

[0031] Figure 7 This is a cross-sectional transmission electron microscope (TEM) image of the Bi₂WO₆ thin film obtained in Example 1 of this invention along the c-axis. It is clearly visible that the Bi₂WO₆ thin film is composed of positively charged [Bi₂O₂]. n 2n+ Layers and negative charge [WO4] n 2n- A non-neutral layered crystal structure formed by alternating stacking of layers along the c-axis;

[0032] Figure 8 This is a graph showing the relationship between the sustained photoconductivity (PPC) characteristics of the optoelectronic device constructed from the Bi2WO6 thin film obtained in Example 1 of this invention and time after being excited by an ultraviolet laser with a wavelength of 405nm for 10s. The Bi2WO6 thin film synthesized by this method has ultra-long-term sustained photoconductivity (PPC) characteristics.

[0033] Figure 9 The figure shows the transfer characteristic curves of the field-effect transistor (FET) constructed from the Bi2WO6 thin film obtained in Example 1 of this invention before and after ultraviolet light irradiation. It can be seen that the synthesized Bi2WO6 thin film belongs to the N-type semiconductor.

[0034] Figure 10 This is the output curve of the Bi2WO6 thin film obtained in Example 1 of the present invention. The Bi2WO6 thin film synthesized by this method has ultra-low static power consumption (dark current of ~0.1pA).

[0035] Figure 11 The chemical vapor deposition (CVD) growth of the Bi2WO6 thin film obtained in Example 1 of this invention can be controlled to synthesize thin film samples of various thicknesses and planar or vertical shapes.

[0036] Figure 12 The atomic force microscopy characterization results of the Bi2WO6 thin film obtained in Example 1 of this invention show that the controllable synthesis of ultrathin layered Bi2WO6 thin films with a thickness of 5.5 nm and an atomically smooth surface is achieved.

[0037] Figure 13 The UV-Vis absorption spectrum of the Bi2WO6 thin film obtained in Example 1 of this invention shows an optical band gap of about 3.0 eV and good absorption in the UV region.

[0038] Figure 14This is a large single-crystal optical microscope image of the Bi2WO6 thin film obtained in Example 1 of the present invention. The crystal can reach 309μm, the thickness is only 7.2nm, and it has an atomically flat surface. Detailed Implementation

[0039] Figure 1 A schematic diagram of the chemical vapor deposition method for growing Bi2WO6 thin films according to the present invention is shown. Using WCI6 powder and Bi2O3 powder as raw materials, chemical vapor deposition is performed, and the film is obtained after deposition. The present invention will be further described below with reference to specific embodiments, but the present invention is not limited to the following embodiments. Unless otherwise specified, the methods described are conventional methods. Unless otherwise specified, the raw materials can be obtained from publicly available commercial sources.

[0040] Example 1

[0041] Weigh 0.5 g of WCl6 powder and 0.6 g of Bi2O3 powder and place them in the center of a tubular furnace quartz tube. Then, a freshly dissociated fluorinated mica substrate is placed approximately 1 cm directly above the raw materials. Argon carrier gas (300 s·ccm) and a trace amount of auxiliary gas (hydrogen) (1%, 3 s·ccm) are introduced to maintain a system pressure of 400 Torr. The temperature of the central source region of the WCl6 powder is raised to 160°C, and the temperature of the central source region of the Bi2O3 powder is raised to 650°C, maintained for 30 minutes for chemical vapor deposition. After deposition, the auxiliary gas is stopped, and the mixture is allowed to cool naturally to room temperature. Then, the pressure inside the tube is reduced to atmospheric pressure, and the argon gas supply is stopped. Finally, the mica substrate with the deposited Bi2WO6 film is removed, yielding the layered Bi2WO6 semiconductor thin film provided by this invention.

[0042] Figure 2 The image shows an optical microscope photograph of the Bi2WO6 thin film obtained in Example 1. As can be seen from the image, the obtained Bi2WO6 two-dimensional crystal thin film is nearly a regular square in shape, and the domain size is approximately 50-80 micrometers.

[0043] Figure 3 The image shows the EDX mapping spectrum of the Bi2WO6 two-dimensional crystal thin film obtained in Example 1. As can be seen from the image, the obtained two-dimensional crystal contains Bi, W, and O elements, and the elements are evenly distributed.

[0044] Figure 4 The image shows the XRD pattern of the Bi2WO6 two-dimensional crystal thin film obtained in Example 1. As can be seen from the image, the diffraction peak of the (00l) crystal plane of the obtained two-dimensional crystal thin film matches the theoretically calculated peak, indicating that the synthesized Bi2WO6 pure phase is obtained.

[0045] Figure 5 The image shows the Raman spectrum of the Bi2WO6 thin film obtained in Example 1, which has very obvious characteristic peaks.

[0046] Figure 6 The image shows the ab-plane electron diffraction and high-resolution pattern of the Bi2WO6 thin film obtained in this embodiment, obtained by transferring it to a Cu mesh. This method can be used to synthesize Bi2WO6 thin films with high crystal quality.

[0047] Figure 7 This is a cross-sectional transmission electron microscope (TEM) image of the Bi₂WO₆ thin film obtained in Example 1, [Bi₂O₂]. n 2n+ and [WO4] n 2n- The alternatingly stacked layered Bi2WO6 exhibits a very neat interface, with a layer thickness in the c-direction of [missing information].

[0048] Figure 8 The optoelectronic device constructed from the Bi2WO6 thin film obtained in Example 1 exhibits >10 under 10 seconds of ultraviolet light (405nm wavelength) excitation. 4 The continuous photoconductive behavior of s.

[0049] Figure 9 The figure shows the transfer characteristic curve of the FET constructed from the Bi2WO6 thin film obtained in Example 1. The 285nm silicon oxide is used as the bottom gate, and it exhibits N-type semiconductor behavior before and after 1 second of ultraviolet light (405nm wavelength) excitation.

[0050] Figure 10 The output characteristic curve of the FET constructed from the Bi2WO6 thin film obtained in Example 1 shows that it has ultra-low static power consumption and a dark current of about 0.1pA.

[0051] Figure 13 The UV-Vis absorption spectrum of the Bi2WO6 thin film obtained in Example 1 shows an optical direct bandgap structure of ~3.0 eV.

[0052] Example 2

[0053] The steps are the same as in Example 1, except that the temperature of the central source region of the Bi2O3 powder is reduced to 600 degrees Celsius and the holding time is changed to 10 minutes.

[0054] Figure 11 (b) is an optical microscope image of the sub-10 nm high-quality Bi2WO6 single crystal obtained in Example 2.

[0055] Figure 12 The image shows the AFM characterization of the 5.5 nm high-quality Bi2WO6 single crystal obtained in Example 2. The ultra-low surface roughness of ~0.12 nm indicates that it has an atomically smooth surface.

[0056] Figure 14This is an optical microscope image of a 7.2 nm high-quality Bi2WO6 single crystal obtained in Example 2, whose single crystal domain region can reach 309 μm.

[0057] Example 3

[0058] The steps are the same as in Example 1, except that the mass of WCl6 powder is reduced to 0.05g, the temperature of the central source region of Bi2O3 powder is reduced to 600 degrees Celsius, and the gas pressure is changed to 700 torr.

[0059] Figure 11 (a) is an optical microscope image of the self-supporting upright Bi2WO6 single crystal that is easy to transfer, obtained in Example 3.

[0060] Example 4

[0061] The steps are the same as in Example 1, except that the temperature of the central source region of the Bi2O3 powder is increased to 700 degrees Celsius.

[0062] Figure 11 (c) is an optical microscope image of the ~30nm thick Bi2WO6 single crystal obtained in Example 4.

[0063] Example 5

[0064] The steps are the same as in Example 1, except that the temperature of the central source region of the Bi2O3 powder is increased to 900 degrees Celsius.

[0065] Figure 11 (d) is an optical microscope image of the Bi2WO6 single crystal with high thickness obtained in Example 4.

[0066] Although embodiments of the present invention have been described above, it is understood that these embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the present invention.

Claims

1. A method for preparing two-dimensional wide-bandgap bismuth tungstate semiconductor nanofilms by chemical vapor deposition, characterized in that: Using WCl6 powder and Bi2O3 powder as raw materials, chemical vapor deposition is performed, and the product is obtained after deposition. The mass ratio of WCl6 powder to Bi2O3 powder is 0.1~1:

1. The substrate is mica with the chemical formula KMg3(AlSi3O) 10 F2; In the chemical vapor deposition step, the carrier gas is a mixture of argon and a trace amount of hydrogen. The system pressure is 100-700 Torr; The deposition temperature is 600-950 ℃; The deposition time is 5-40 minutes; The gas flow rate is 50~400 sccm; The substrate is located 0.1 to 2 cm directly above the raw material Bi2O3.

2. The method according to claim 1, characterized in that: The chemical vapor deposition is carried out in a tube furnace.

3. The method according to claim 1, characterized in that: The method further includes the following step: after the chemical vapor deposition step, the system is naturally cooled to room temperature.

4. The ultrathin layered Bi2WO6 semiconductor nanofilm prepared by any of the methods described in claims 1-3.

5. The ultrathin layered Bi₂WO₆ semiconductor nanofilm according to claim 4, characterized in that: The thin film has a layered structure, and its crystal structure consists of [Bi₂O₂]. n 2n+ and [WO4] n 2n− The layers are stacked alternately along the c-axis, with a single layer thickness of ~0.85 nm.

6. The ultrathin layered Bi₂WO₆ semiconductor nanofilm according to claim 4, characterized in that: This thin film is a type of direct bandgap N-type semiconductor with a bandgap of ~3.0 eV and a thickness between 5-200 nm. It has a planar structure or a self-supporting structure that is easy to transfer on the substrate. Under ultraviolet light irradiation, the bismuth tungstate device exhibits a current on / off ratio >10. 5 With a dark current of ~0.1 pA, it exhibits extremely long continuous photoconductive behavior, lasting up to 7 hours.

7. The application of the wide bandgap ultrathin layered Bi2WO6 semiconductor thin film as described in any one of claims 4-6 in the fabrication of high-κ gate transistors, ferroelectric memories, photovoltaics, and photoelectric sensing synaptic devices.

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