WO2023098902A1 - N-type doped two-dimensional stratified bismuth oxyhalide material, and preparation method therefor and application thereof - Google Patents

Abstract

An n-type doped two-dimensional stratified bismuth oxyhalide material, and a preparation method therefor and the application thereof, which belong to the technical field of semiconductor photoelectric materials. Bismuth atoms are replaced with carbon atoms, n-type doping is generated on a two-dimensional stratified bismuth oxyhalide material, an n-type doped two-dimensional stratified bismuth oxyhalide material is then prepared, and the photoelectric effect of a resistive device of the material under ultraviolet irradiation can be significantly enhanced; and when a photocarrier density exceeds a specific value, i.e. an ultraviolet irradiation intensity is greater than a specific value, avalanche-type photocurrent multiplication occurs, and when a small operating voltage is applied to the resistive device of the material, a photocurrent such as a photocurrent of an avalanche current magnitude can be generated. The n-type doped two-dimensional stratified bismuth oxyhalide material is a new photoelectric material for detecting ultraviolet light, and has the commercial application value in the application market of ultraviolet photoelectric detection.

Description

N-type doped two-dimensional layered bismuth oxyhalide material and its preparation method and application technical field

The invention relates to the technical field of semiconductor optoelectronic materials, in particular to an n-type doped two-dimensional layered bismuth oxyhalide material and a preparation method and application thereof.

Background technique

The ultraviolet light in all bands in nature basically comes from sunlight. The wavelength range of ultraviolet light is between X-rays and visible light, and the wavelength range is 10-400nm. As shown in Figure 1, it can be divided into vacuum ultraviolet bands (VUV, 10～200nm), ultraviolet C band (UVC, 100～280nm), ultraviolet B band (UVB, 280～315nm) and ultraviolet A band (UVA, 315～400nm). There are very few UVC band components in the light received by the earth's surface, because the atmospheric ozone in the earth's stratosphere absorbs the deep ultraviolet rays with the shortest wavelength in sunlight, especially the light in the 200-280nm band. The wavelength band is also often called solar-blind ultraviolet (SBUV, solar-blind ultraviolet), that is, detectors with detection wavelengths in this band are not affected by the background noise of sunlight, so that the solar-blind ultraviolet detector can work around the clock and avoid sunlight the impact. Therefore, the development of solar-blind ultraviolet detectors is of great value to national defense security and civilian technology fields such as missile tracking, flame detection, corona discharge, space communication, deep space detection imaging and satellite tracking.

_In recent years, a new generation of sun-blind zone ultraviolet photodetection materials such as β- _Ga2O3 , _{MgxZn1 -xO} and diamond have been intensively researched and developed, although they are not effective when applied to existing conventional photodetectors. It has good performance, but when the device scale is reduced to the atomic level, the interface effect caused by the dangling bonds on the surface of these non-layered semiconductor materials will greatly weaken the material performance. In contrast to non-layered semiconductors, 2D layered semiconductors have perfectly planar surfaces without any dangling bonds at the atomic thickness. Therefore, finding and researching two-dimensional materials for ultraviolet photodetection in the sun-blind zone is of great significance for the development of detection devices to the atomic scale.

The previous literature research "Highly ConDucting, N-Type Bi ₁₂ O ₁₅ CL ₆ Nanosheets with Superlaticelike Structure", "Synthesis and Internet Electric Field DependentphotoreActivity of BI ₃ O ₄ Cl Single-Crystallinenanosheets with High {001} Facet ExposurePercentages " The method only synthesizes bismuth oxyhalide materials with different stoichiometric ratios without doping; while the two-dimensional layered bismuth oxyhalide materials in "Giant Enhancement of Internal Electric Field Boosting BulkCharge Separation for Photocatalysis" adjust the interlayer The electric field experiment also uses the method of hydrothermal synthesis. BiOCl is first synthesized by hydrothermal method, and then converted into Bi ₃ O ₄ Cl through another reaction, and then carbon modified for carbon doping. This doped bismuth oxychloride powder manufacturing scheme is very effective for photocatalytic applications, but the whole process is too cumbersome, the preparation cycle is long, and the reaction impurities generated are also very polluted. In view of these problems, the present invention provides a preparation method based on two-dimensional layered bismuth oxyhalide material for gas phase treatment, which is efficient and environmentally friendly, and the obtained doped two-dimensional layered bismuth oxyhalide material contributes to the ultraviolet photoelectric Detector devices are further developed to the nanoscale.

Contents of the invention

The object of the present invention is to provide n-type doped two-dimensional layered bismuth oxyhalide material, its preparation method and its application on ultraviolet detectors.

To achieve this goal, the present invention adopts the following technical solutions:

The first aspect of the present invention provides an n-type doped two-dimensional layered bismuth oxyhalide material, whose general chemical formula is Z _i -Bi _l O _m X _n , wherein X is a halogen, and Z is an element of group IVA; the element Metering ratio (i+l):m:n is 12:15:6, 3:4:1, or 12:17:2, i/(i+l+m+n)≤7%; The two-dimensional layered bismuth oxyhalide material is a single crystal nanosheet or a single crystal continuous film.

In some embodiments of the present invention, the general chemical formula of the n-type doped two-dimensional layered bismuth oxyhalide material is C _i -Bi _3-i O ₄ X, i≤0.56. When the resistive device has a voltage of ≤1V and an ultraviolet light intensity of ≥100mW/cm ² , photocarriers will undergo an avalanche multiplication phenomenon. In some preferred embodiments of the present invention, the lifetime of the photocarriers is ≥91 ns.

The second aspect of the present invention provides a method for preparing the above-mentioned n-type doped two-dimensional layered bismuth oxyhalide material.

The preparation method of the n-type doped two-dimensional layered bismuth oxyhalide material provided by the present invention uses two-dimensional layered BiOX as a precursor, and simultaneously performs phase conversion and doping in the gas phase.

In some embodiments of the present invention, the phase inversion specifically includes the following steps:

Step 1. Place the substrate loaded with BiOX in a quartz boat, and put the quartz boat into the quartz tube of the tube furnace;

Step 2. Vacuumize the quartz tube of the tube furnace, remove impurity gases in the system, feed the carrier gas, program the temperature to the required reaction temperature, feed the carrier gas and reaction gas to adjust the chamber pressure, and carry out phase inversion;

Step 3. Cool naturally after the reaction, and take out the substrate to obtain two-dimensional layered nanomaterials that have been phase-transformed into Bi ₁₂ O ₁₅ X ₆ , Bi ₃ O ₄ X , or Bi ₁₂ O ₁₇ X ₂ on the surface of the substrate.

In some embodiments of the present invention, the carrier gas introduced in step 2 is specifically nitrogen gas with a flow rate of 100-300 sccm.

In some embodiments of the present invention, when the carrier gas and reaction gas are introduced in step 2, when the temperature is about to reach the target temperature, the oxygen flow rate of one path is set to 50-150 sccm, and the nitrogen flow rate of the other path is set to 50-150 sccm.

In some embodiments of the present invention, the required temperature in step 2 is 390-410°C, 440-460°C or 490-510°C.

In some embodiments of the present invention, the phase inversion time in step 2 is 50-150 min.

In some embodiments of the present invention, the preparation method of the two-dimensional layered BiOX includes: using BiX ₃ , water vapor or oxygen as the precursor source, at a pressure of 0.1-0.8 atm and a temperature of 260-400°C, a chemical vapor phase The deposition method prepares BiOX single-crystal nanosheets or single-crystal continuous films.

In some embodiments of the present invention, the doping is carbon element doping, which includes the following steps: using a polymer sacrificial layer method to transfer a two-dimensional layered BiOX material sample, while generating carbon residue on the surface, and then using a high temperature phase The conversion diffuses and implants carbon into the sample to obtain a carbon-doped two-dimensional layered Bi ₃ O ₄ X material.

The third aspect of the present invention provides the application of the above-mentioned n-type doped two-dimensional layered bismuth oxyhalide material in an ultraviolet detector.

In some embodiments of the present invention, the ultraviolet detector includes a high temperature resistant substrate or a flexible substrate, and the n-type doped two-dimensional layered bismuth oxyhalide material is applied on the high temperature resistant substrate or flexible substrate.

In some embodiments of the present invention, the method for applying the n-type doped two-dimensional layered bismuth oxyhalide material to a high temperature resistant substrate is: transferring the two-dimensional layered BiOCl material by using a polymer sacrificial layer method Put it on any high-temperature-resistant substrate for thermally driven phase transition to produce Zi _- Bi _12-i O ₁₅ Cl ₆ , Zi _- Bi _3-i O ₄ Cl or Zi _- Bi _12-i O ₁₇ Cl _2nm sheet or film.

In some embodiments of the present invention, the method for applying the n-type doped two-dimensional layered bismuth oxyhalide material to a flexible substrate is: using a polymer sacrificial layer method to transfer the two-dimensional layered BiOCl material to On a high-temperature-resistant silicon substrate, thermally driven phase conversion is performed first to produce Z _i -Bi _12-i O ₁₅ Cl ₆ , Z _i -Bi _3-i O ₄ Cl or Z _i -Bi _12-i O ₁₇ Cl _2nm sheet or film, and then transfer Zi _- Bi _12-i O ₁₅ Cl ₆ , Zi _- Bi _3-i O ₄ Cl or Zi _- Bi _12-i O ₁₇ Cl ₂ nanosheet or film to a flexible substrate.

The fourth aspect of the present invention provides an ultraviolet detection device, including a substrate, an ultraviolet sensitive layer and an electrode layer; the ultraviolet sensitive layer is arranged on the substrate, and the electrode layer is arranged on the ultraviolet sensitive layer; the ultraviolet sensitive layer is the n-type doped two-dimensional layered bismuth oxyhalide material.

In some embodiments of the present invention, when the working voltage of the ultraviolet detection device is ≤1V and the intensity of 266nm ultraviolet light is greater than or equal to 100mW/cm ² , an avalanche photocurrent phenomenon occurs.

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

1. The n-type doped two-dimensional layered bismuth oxyhalide material provided by the present invention realizes the acquisition of low-power avalanche photocurrent, breaks through the mechanism framework of traditional avalanche photocurrent, and can realize the multiplication of photocurrent at low voltage Effect.

2. The present invention provides two-dimensional layered bismuth oxyhalide materials prepared in the gas phase, such as BiOCl, Bi ₁₂ O ₁₅ Cl ₆ , Bi ₃ O ₄ Cl and Bi ₁₂ O ₁₇ Cl ₂ , which can be produced by using a low-cost tube furnace Two-dimensional layered bismuth oxyhalide materials with different stoichiometric ratios of elements are prepared, and the preparation process is simple and easy to operate.

3. The present invention provides a widely applicable doping method for replacing bismuth atoms with carbon atoms in a large area, completes phase transformation while doping and diffusing, and can also explore the doping of different group IV elements, such as silicon, germanium, etc., by means of The method is simple and less impurity.

4. The two-dimensional layered Bi ₃ O ₄ Cl provided by the present invention is a new type of optoelectronic material, which has excellent photocurrent switching ratio and specified spectral photosensitive responsivity to ultraviolet light, especially ultraviolet light in the solar blind zone, so it is used in ultraviolet detection When on the device, it can promote more diverse applications of ultraviolet detectors.

Description of drawings

Figure 1 shows the wavelength distribution of ultraviolet light and the division of specific bands.

Figure 2 shows the morphology of nanosheets under the optical microscope before and after heat treatment: (a) BiOCl nanosheets transferred to silicon dioxide (300nm)/silicon wafer substrate; (b) same sample as (a), heat treated at 440-460°C (c) BiOCl nanosheets grown on mica substrate; (d) _the same sample as (c), Bi ₃ O ₄ Cl nanosheets after heat treatment at 440-460℃; ₍ e) Topography of BiOCl film grown on mica substrate

Figure 3 shows the results of AFM characterization of the thickness change of nanosheet samples before and after heat treatment at 440-460°C.

Figure 4 shows the phase transformation of bismuth oxychloride material after heat treatment at different temperatures by XRD.

Fig. 5 is a flowchart of the transfer of two-dimensional layered bismuth oxyhalide materials.

FIG. 6 is a structure diagram of a field effect transistor (FET) device.

Fig. 7 is a diagram of a FET device prepared from BiOCl.

FIG. 8 is a diagram of a FET device prepared by C-doped Bi ₃ O ₄ Cl (C:Bi ₃ O ₄ Cl).

Figure 9 shows the characterization results of I _ds -V _g transfer characteristic curves of BiOCl nanosheets and C:Bi ₃ O ₄ Cl nanosheets field effect tube devices, showing that BiOCl nanosheets are p-type, and C:Bi ₃ O ₄ Cl nanosheets are n type.

Figure 10 shows the test results of transfer characteristic curves of other six C:Bi ₃ O ₄ Cl nanosheet field effect transistor devices, showing that C:Bi ₃ O ₄ Cl is n-type.

Figure 11 is the photoelectric performance test results of C:Bi ₃ O ₄ Cl and BiOCl: (a) I _ds -time (It) curves of C:Bi ₃ O ₄ Cl and BiOCl under different power 266nm laser irradiation; (b) C: Variation of optical switching ratio, optical responsivity, and specific detectivity of Bi ₃ O ₄ Cl devices with material thickness.

Figure 12 shows the It test results of four C:Bi ₃ O ₄ Cl devices.

Figure 13 is the DFT calculation results of the C:Bi ₃ O ₄ Cl model with carbon atoms replacing bismuth atoms: (a) energy band structure diagram; (b) density of state diagram; (c) interlayer potential distribution diagram.

Fig. 14 is a diagram of photoconductivity (σ _ph ) and photon density (G) of C: Bi ₃ O ₄ Cl and BiOCl.

Figure 15 is a vacuum tube furnace, BiOCl chemical vapor deposition system.

Fig. 16 is a schematic diagram of the spatial confinement of BiCl ₃ vapor in chemical vapor deposition.

Figure 17 is the TEM characterization results of BiOCl (before phase inversion) and C:Bi ₃ O ₄ Cl (after phase inversion): (a) (d) TEM topography; (b) (e) selected area electron diffraction lattice; (c)(f) High-resolution TEM images and respective crystal structure images.

Figure 18 shows the cross-section TEM characterization results of C:Bi ₃ O ₄ Cl (after phase inversion) after FIB treatment: (a) TEM topography; (b) enlarged TEM topography of the selected area; (c) Fourier transform electron diffraction lattice based on high-resolution TEM image; (d) High-resolution TEM image with atomic resolution (e) EDS result.

Figure 19 is the XPS characterization results of BiOCl and C:Bi ₃ O ₄ Cl.

Figure 20 is the Raman spectrum characterization results of BiOCl and C:Bi ₃ O ₄ Cl.

Figure 21 is the UV-Vis characterization results of BiOCl and C:Bi ₃ O ₄ Cl.

Fig. 22 is the ultrafast femtosecond transient absorption spectra of C: Bi ₃ O ₄ Cl and BiOCl.

Detailed ways

The n-type doped two-dimensional layered bismuth oxyhalide material of the present invention and its preparation method and application in ultraviolet detectors are described in detail below.

The first aspect of the present invention provides an n-type doped two-dimensional layered bismuth oxyhalide material, whose general chemical formula is Z _i -Bi _l O _m X _n , wherein X is a halogen, and Z is an element of group IVA; the element Metering ratio (i+l):m:n is 12:15:6, 3:4:1, or 12:17:2, i/(i+l+m+n)≤7%; The two-dimensional layered bismuth oxyhalide material is a single crystal nanosheet or a single crystal continuous film. Compared with the undoped n-type doped two-dimensional layered bismuth oxyhalide material resistive device provided by the present invention, the photoelectric effect under ultraviolet light can be significantly enhanced, and when the photocarrier density exceeds a certain Value, that is, the ultraviolet light intensity is greater than a specific value, and an avalanche photocurrent multiplication occurs. The n-type doped two-dimensional layered bismuth oxyhalide material provided by the present invention is a new photoelectric material for detecting the intensity of ultraviolet light, and its resistive device has excellent photocurrent switching ratio, high ultraviolet light sensitivity, and ultraviolet Photodetectors can perform detection work under low voltage and low power.

In some embodiments of the present invention, the general chemical formula of the n-type doped two-dimensional layered bismuth oxyhalide material is C _i -Bi _3-i O ₄ X , wherein X is halogen, and i≤0.56. In the carbon-doped two-dimensional layered bismuth oxyhalide material, carbon atoms replace bismuth atoms, and the electric field (or potential) between the atomic layers of the bismuth oxyhalide material increases, thereby increasing the lifetime of n-type photoelectrons and enhancing its photoelectric effect, and its photocurrent switch The ratio is 20-1500, and the photosensitive responsivity of the specified ultraviolet spectrum (wavelength is 266nm) is 0.003-0.45A/W (ampere per watt). Its resistive device is strongly ionized under low voltage below 1V and high photon density, resulting in avalanche photocurrent phenomenon. Avalanche photocurrent is a method to improve the photosensitive photocurrent switch ratio. In the previous literature research, the device needs to be in the The avalanche photocurrent phenomenon will only appear when the breakdown voltage is approaching. For example, when the voltage of the resistive device is ≤1V and the ultraviolet light intensity is ≥100mW/cm ² , the photocarriers will undergo an avalanche multiplication phenomenon.

In some preferred embodiments of the present invention, the lifetime of the photocarriers is ≥91 ns. Photocarriers have a longer lifespan, and they are excited under a specific high light intensity, which not only maintains the photocarrier density, but also produces an avalanche effect, exciting more carriers, thereby generating photocurrent multiplication. The photocarrier has a high lifespan, because the carbon atom replaces the bismuth atom, which causes the electric field (or potential) between the atomic layers of the bismuth oxyhalide material to increase, thereby inhibiting the recombination of electrons and holes, and achieving the effect of increasing the lifespan of the carrier .

The n-type doped two-dimensional layered bismuth oxyhalide material provided by the invention has a low-power avalanche photocurrent effect. Usually, when a semiconductor diode is applied with a sufficiently high reverse bias voltage, the carriers moving in the depletion layer may cause an avalanche multiplication of photo-generated carriers due to the impact ionization effect of strong ionization. It was first discovered in 1953 Photocurrent multiplication of a germanium-silicon PN junction near breakdown. In the present invention, based on the carbon-doped Bi ₃ O ₄ Cl ultraviolet detection device, only a 1V bias voltage is applied to find the phenomenon of avalanche photocurrent, which provides the possibility for the application of future semiconductor devices in various fields.

The second aspect of the present invention provides a method for preparing an n-type doped two-dimensional layered bismuth oxyhalide material.

The preparation method of the n-type doped two-dimensional layered bismuth oxyhalide material provided by the present invention is to use two-dimensional layered BiOX as a precursor, and simultaneously perform phase transformation and doping in the gas phase.

The preparation method of the present invention adopts a complete gas phase system, and compared with the hydrothermal method, no redundant reaction waste will be generated, less pollution, less impurity, lower reaction energy consumption, and better crystal quality.

In some embodiments of the present invention, the phase inversion specifically includes the following steps:

Step 1. Place the substrate loaded with BiOX in a quartz boat, and put the quartz boat into the quartz tube of the tube furnace;

Step 2. Vacuumize the quartz tube of the tube furnace, remove impurity gases in the system, feed the carrier gas, program the temperature to the required reaction temperature, feed the carrier gas and reaction gas to adjust the chamber pressure, and carry out phase inversion;

Step 3. Cool naturally after the reaction, and take out the substrate to obtain two-dimensional layered nanomaterials that have been phase-transformed into Bi ₁₂ O ₁₅ X ₆ , Bi ₃ O ₄ X , or Bi ₁₂ O ₁₇ X ₂ on the surface of the substrate.

In some embodiments of the present invention, the carrier gas introduced in step 2 is specifically nitrogen gas with a flow rate of 100-300 sccm.

In some embodiments of the present invention, when the carrier gas and reaction gas are introduced in step 2, when the temperature is about to reach the target temperature, the oxygen flow rate of one path is set to 50-150 sccm, and the nitrogen flow rate of the other path is set to 50-150 sccm.

In some embodiments of the present invention, the required temperature in step 2 is 390-410°C, 440-460°C or 490-510°C.

In some embodiments of the present invention, the phase inversion time in step 2 is 50-150 min.

In some embodiments of the present invention, the preparation method of the two-dimensional layered BiOX includes: using BiX ₃ , water vapor or oxygen as the precursor source, at a pressure of 0.1-0.8 atm and a temperature of 260-400°C, a chemical vapor phase The deposition method prepares BiOX single-crystal nanosheets or single-crystal continuous films. In some embodiments of the present invention, the size of the BiOX single crystal nanosheet is larger than 10 μm, and the thickness is between 0.7 and 300 nm; the size of the BiOX single crystal continuous film is larger than 2.54 cm, and the thickness is between 0.1 and 5 μm. Figures 2(a) and 2(c) show the morphology of BiOCl nanosheets on silica/silicon wafer substrate (transferred sample) and mica substrate (native sample), respectively. Figure 2(e) shows the morphology of the grown single crystal continuous film.

In the present invention, the preparation method of two-dimensional layered bismuth oxyhalide materials (Bi ₁₂ O ₁₅ X ₆ , Bi ₃ O ₄ X , or Bi ₁₂ O ₁₇ X ₂ ) with different stoichiometric ratios of elements is the same as the above phase transformation steps.

The two-dimensional layered bismuth oxyhalide material Bi ₃ O ₄ Cl is a Bi ₃ O ₄ Cl single crystal nanosheet or a single crystal continuous film; in some embodiments of the present invention, the Bi ₃ O ₄ Cl single crystal nano The sheet size is greater than 10 μm, and the thickness is between 0.7 and 300 nm; Figure 2(b) and 2(d) respectively show Bi ₃ O ₄ Cl nanosheets on silica/silicon wafer substrate (phase-inverted sample) and mica substrate ( Phase-inverted sample) morphology; Figure 3 is the phase inversion before (BiOCl), after (Bi ₃ O ₄ Cl), using AFM to characterize the thickness change of the nanosheet sample, Figure 4 is using X-ray diffraction (X-ray diffraction; XRD) confirmed Bi ₃ O ₄ Cl crystals.

The two-dimensional layered bismuth oxyhalide material Bi ₁₂ O ₁₅ Cl ₆ is Bi ₁₂ O ₁₅ Cl ₆ single crystal nanosheet or single crystal continuous thin film. FIG. 4 is a confirmation of Bi ₁₂ O ₁₅ Cl ₆ crystals using X-ray diffraction (XRD).

The two-dimensional layered bismuth oxyhalide material Bi ₁₂ O ₁₇ Cl ₂ is Bi ₁₂ O ₁₇ Cl ₂ single crystal nanosheet or single crystal continuous thin film. FIG. 4 is a confirmation of Bi ₁₂ O ₁₇ Cl ₂ crystals using X-ray diffraction (XRD).

The two-dimensional layered Bi ₃ O ₄ Cl material provided by the present invention has ultra-high photocurrent (photocurrent) response to ultraviolet (ultraviolet, abbreviated as UV) light with a wavelength range of 100-400nm, and its photocurrent-off ratio ) is 20-1500, and its specified spectrum (wavelength is 266nm) photosensitive responsivity (specific spectral responsivity) is 0.003-0.45A/W (Ampere per Watt), which is an excellent ultraviolet detector material. Described ultraviolet light comprises three kinds of ultraviolet light bands (shown in Figure 1): UV-A band (wavelength range: 400～320nm), UV-B band (wavelength range: 320～280nm) and UV-C band (wavelength range : 100-280nm).

The Bi ₁₂ O ₁₅ Cl ₆ , Bi ₃ O ₄ Cl or Bi ₁₂ O ₁₇ Cl ₂ provided by the present invention is a material converted from BiOCl under certain conditions, which has a layered structure similar to BiOCl and is superior to BiOCl. Photodetection performance.

In some embodiments of the present invention, the doping described in the present invention is carbon element doping, including the following steps: using the polymer sacrificial layer method to transfer the two-dimensional layered BiOX material sample, while generating carbon residue on the surface, and then using The high-temperature phase transformation diffuses and implants carbon into the sample, resulting in a carbon-doped two-dimensional layered Bi ₃ O ₄ X material. In the present invention, the precursor source for the preparation of the two-dimensional layered Bi ₃ O ₄ Cl material sample may be a BiOCl single crystal nanosheet, or a BiOCl single crystal nanofilm.

In a preferred embodiment of the present invention, the operation of transferring the two-dimensional layered bismuth oxyhalide material to the target substrate by the polymer sacrificial layer method is shown in Figure 5, and the steps are as follows: the prepared two-dimensional layered The surface of the bismuth oxyhalide material is uniformly coated with a polymer sacrificial layer, baked on a hot plate, then soaked in water, and ultrasonically treated to float the polymer sacrificial layer film containing a two-dimensional layered bismuth oxyhalide material on the water surface for the purpose of Substrate The polymer sacrificial layer film containing two-dimensional layered bismuth oxyhalide material is picked up from the water surface, soaked in glue remover to remove the polymer sacrificial layer, soaked in isopropanol, taken out, and blown with nitrogen. Just dry.

The present invention adopts a large-area doping method. By coating a layer of polymer on the nanosheet as a carbon source, carbon doping is carried out at high temperature. This method can realize the whole nanosheet or large-area continuous film. Uniform doping can also achieve phase inversion and carbon doping at the same time. This method is easy to operate, low pollution, less impurities, and low energy consumption.

In the present invention, the carbon element is diffused and doped into the bismuth oxyhalide material, and the doping of the carbon element is that carbon atoms replace bismuth atoms in the crystal structure. The carbon-doped bismuth oxyhalide material was found to have an avalanche photocurrent phenomenon caused by strong ionization at a low voltage of 1V and a high photon density. The avalanche photocurrent is a method to improve the photosensitive photocurrent switch ratio. Previously In the literature research, the device needs to be close to the breakdown voltage (10V or higher) before the avalanche photocurrent phenomenon will appear. The present invention produces an avalanche photocurrent under high light intensity, which is different from the avalanche dark current caused by traditional high voltage.

In the field of microelectronics, Si and Ge have always been common semiconductor materials in the semiconductor industry. Through the theory of similar properties of elements in the same group, as elements of the same main group as C, using the same method, it may be possible to use silicon atoms, germanium atoms, etc. In the doping of bismuth oxyhalide materials, it is expected to obtain new semiconductor materials with higher carrier mobility and adjust the forbidden band width of certain semiconductor materials.

The third aspect of the present invention provides the application of the above-mentioned n-type doped two-dimensional layered bismuth oxyhalide material in an ultraviolet detector.

In some embodiments of the present invention, the ultraviolet detector includes a high temperature resistant substrate or a flexible substrate, and the n-type doped two-dimensional layered bismuth oxyhalide material is applied on the high temperature resistant substrate or flexible substrate.

In some embodiments of the present invention, the method for applying the n-type doped two-dimensional layered bismuth oxyhalide material to a high temperature resistant substrate is: transferring the two-dimensional layered BiOCl material by using a polymer sacrificial layer method Put it on any high-temperature-resistant substrate for thermally driven phase transition to produce Zi _- Bi _12-i O ₁₅ Cl ₆ , Zi _- Bi _3-i O ₄ Cl or Zi _- Bi _12-i O ₁₇ Cl _2nm sheet or film.

In some embodiments of the present invention, the method for applying the n-type doped two-dimensional layered bismuth oxyhalide material to a flexible substrate is: using a polymer sacrificial layer method to transfer the two-dimensional layered BiOCl material to On a high-temperature-resistant silicon substrate, thermally driven phase conversion is performed first to produce Z _i -Bi _12-i O ₁₅ Cl ₆ , Z _i -Bi _3-i O ₄ Cl or Z _i -Bi _12-i O ₁₇ Cl _2nm sheet or film, and then transfer Zi _- Bi _12-i O ₁₅ Cl ₆ , Zi _- Bi _3-i O ₄ Cl or Zi _- Bi _12-i O ₁₇ Cl ₂ nanosheet or film to a flexible substrate.

The fourth aspect of the present invention provides an ultraviolet detection device, including a substrate, an ultraviolet sensitive layer and an electrode layer; the ultraviolet sensitive layer is arranged on the substrate, and the electrode layer is arranged on the ultraviolet sensitive layer; the ultraviolet sensitive layer is the n-type doped two-dimensional layered bismuth oxyhalide material.

In some embodiments of the present invention, when the working voltage of the ultraviolet detection device is ≤1V and the intensity of 266nm ultraviolet light is greater than or equal to 100mW/cm ² , an avalanche photocurrent phenomenon occurs.

Avalanche photocurrent means that the value of the photoelectric characteristic constant (α) is greater than 1. When α=0.5, it means that electrons and holes recombine through the band gap edge; when α=1, electrons and holes recombine at the defect state in the energy band gap; when α>1, it means that photoelectric carriers are multiplied, greater than The number of photoelectrons and holes recombined. In a preferred embodiment of the invention, α = 2.5.

The two-dimensional layered Bi ₃ O ₄ Cl of the present invention, other two-dimensional layered bismuth oxychloride materials with different stoichiometric ratios, and carbon-doped Bi ₃ O ₄ Cl materials can be prepared as a field effect transistor (field effect transistor; FET) device, its structural diagram is shown in Figure 6; when the device is not applied with a gate voltage, it is a resistance device; Figure 7 is the morphology of the FET device prepared by BiOCl; Morphology of FET devices fabricated from carbon-doped Bi ₃ O ₄ Cl.

The field effect transistors of the two-dimensional layered BiOCl and carbon-doped Bi ₃ O ₄ Cl materials provided by the present invention are respectively p-type and n-type semiconductors, as shown in FIG. 9 and FIG. 10 . In the carbon-doped Bi ₃ O ₄ Cl material, bismuth atoms are replaced by carbon atoms, and the doped carbon atoms donate one more electron to achieve the effect of n-type semiconductor doping.

The carbon-doped two-dimensional layered Bi ₃ O ₄ Cl material provided by the present invention is sensitive to solar-blind ultraviolet (abbreviated as SBUV) with a wavelength range of 220-280 nm, photocurrent switching ratio and specified spectral photosensitive response. The degrees are shown in Figure 11 and Figure 12, respectively.

The ultraviolet light detector provided by the present invention can detect work under low voltage, low power, for example voltage is 1V (volt) or less voltage, under 266nm ultraviolet light intensity 100mW/cm ² (milliwatts per square centimeter), resistance The power of the device is 1nW (nanowatt), and the power of the resistive device is about 7nW (nanowatt) under the 266nm ultraviolet light intensity of 200mW/cm ² (milliwatt per square centimeter).

The avalanche ultraviolet photoelectric response principle and the avalanche photocurrent device (ultraviolet light detector) working mode of the n-type doped two-dimensional layered bismuth oxyhalide material in the present invention are as follows:

Taking carbon-doped two-dimensional layered Bi ₃ O ₄ Cl nanosheets as an example, the main reason why the traditional avalanche photodiode can obtain the photocurrent multiplication effect is to rely on the high voltage as the driving force, so that the photogenerated carriers are driven by the high electric field. Acceleration interacts with phonons inside the material, and ionization occurs to generate secondary carriers. New carriers continue to be driven by high voltage to interact with phonons, so that carriers are continuously generated to achieve photocurrent multiplication. The avalanche photocurrent device in the present invention is driven by high photon density and carbon doping:

(1) In the carbon-doped Bi ₃ O ₄ Cl nanosheets obtained in the present invention, C atoms replace Bi atoms in the crystal structure, resulting in an enhanced potential (electric field) between layers of Bi atoms in a layered structure. As shown in Figure 13(c), in the DFT theoretical simulation results, it is found that the interlayer built-in electric field of the Bi-O atomic layer is greater than that of the undoped The built-in electric field between Bi ₃ O ₄ Cl and the Bi-O atomic layer of BiOCl.

(2) When ultraviolet light with high photon density is irradiated on Bi ₃ O ₄ Cl nanosheets, the photogenerated carriers hinder the recombination process under the enhanced interlayer electric field, and a lifetime of up to 91ns is obtained. As in Table 3.

(3) As shown in Fig. 6 and Fig. 11, the thickness of Bi ₃ O ₄ Cl nanosheets is 20 nanometers, the electrode spacing is about 1.5 microns, and the metal contact is chromium (Cr) 3nm/gold (Au) 80nm.

(4) For the Bi ₃ O ₄ Cl device shown in Figure 11, when a voltage of 1V is applied, the 266nm ultraviolet light intensity is between 100-200mW/cm ² , and an avalanche photocurrent is generated, and the device power is between 1-7nW.

(5) At the same time, the high photon density makes the nanosheets have a high concentration of photo-generated carriers. These high-concentration photo-generated carriers will strongly interact with the internal phonons of the material, and the carrier concentration will be higher after strong ionization. , so the high-concentration and long-life carriers only need a driving voltage of 1V to multiply the photocurrent and achieve an avalanche phenomenon (as shown in Figures 11 and 12).

(6) The photoelectric characteristic constant (α) mentioned in the present invention comes from the relationship between photocurrent (I _ds ) and optical power density (F _ir. ), which can be converted into the relationship between photoconductivity (σ _ph ) and photon density (G) relation. According to the traditional photogenerated carrier recombination mechanism, photoconductivity and photon density have a relationship of σ _ph ∝ G ^α . When α=0.5, it means that electrons and holes recombine through the band gap edge; when α=1, electrons and holes Recombination at the defect state in the energy band gap, and the device in the present invention exhibits α=2.5 under high photon density, as shown in Figure 14, which means that the photocurrent multiplication phenomenon is far greater than the electron-hole recombination phenomenon, and avalanche light has been produced. current phenomenon.

The specific implementation manners of the present invention will be further described in detail below in conjunction with preferred embodiments. When the examples give numerical ranges, it should be understood that, unless otherwise stated in the present invention, the two endpoints of each numerical range and any value between the two endpoints can be selected. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. In addition to the specific methods, equipment, and materials used in the embodiments, as those skilled in the art grasp the prior art and the records of the present invention, the methods, equipment, and materials described in the embodiments of the present invention can also be used Any methods, apparatus and materials of the prior art similar or equivalent to the practice of the present invention.

Embodiment 1: prepare BiOCl in gas phase

(1) The tube furnace system used in the preparation of BiOCl is shown in Figure 15. When the raw materials are put into the furnace tube (1 inch in diameter and 1 meter in length), in order to prevent the _BiCl3 powder from absorbing too much water in the air, the The time spent must be as short as possible;

(2) Use an electronic balance to weigh about 3 mg of BiCl ₃ powder, place the BiCl ₃ powder on a quartz boat through a small funnel with an outlet cut to a diameter of 2 mm, and take a piece of mica cut into a size of about 1.5 cm × 5 cm split it into two pieces of mica with the help of a medical blade, blow the fresh face of the split mica with high-purity nitrogen, and place the fresh face of the newly split mica on top of the BiCl ₃ powder source, the quartz boat The cross-section is approximately circular, and the surface of the mica placed on it and the surface of the quartz boat forms a narrow confinement space with a height of about 2-4 mm, as shown in Figure 16. After the assembly is completed, it is placed into the furnace tube;

(3) Open the ball valves at the left and right ends of the furnace, turn on the mechanical pump, and close the bubbler to prevent the mechanical pump from evacuating the furnace tube to a low vacuum due to moisture volatilization, and then remove the air in the entire system to reduce the pressure in the tube to below 10 Torr , open the gas cylinder valve, feed nitrogen, open the flow meter gas valve and set the gas flow to 50-150 sccm, and clean for 5-10 minutes. Then close the air valve of the flowmeter, and then open the air valve of the flowmeter to feed in the same amount of nitrogen when the pressure in the pipe drops below 10Torr again. Repeat this three times to fully discharge the impurity gas in the tube and the residual water vapor in the previous experimental pipeline;

(4) After the last cleaning is completed, continue to pass in nitrogen gas with a flow rate of 100-300 sccm, raise the temperature of the cavity to 90-120°C, and bake for about 20 minutes to remove the water in the raw material powder due to exposure to air. BiCl ₃ ·H ₂ O is converted to BiCl ₃ ;

(5) Pull the quartz tube slightly out of the tube furnace cavity, so that the BiCl ₃ raw material is removed from the heating zone, and then the cavity is heated from room temperature at a rate of 20 °C/min to a growth temperature between 260 and 360 °C. The purpose of the step is to prevent the powder from melting in advance due to the heat accumulated during the heating process before reaching the target temperature due to the rapid temperature rise of the chamber;

(6) Open the bubbler, and at the same time set the argon flow of the path with the bubbler to 50-150 sccm, and the nitrogen flow of the other path to 50-150 sccm, and then use the fine-tuning valve to adjust the chamber pressure to 100-300 Torr The growth pressure between;

(7) Push the quartz tube slightly so that the _BiCl3 raw material is moved into the heating area again, and start the synthesis experiment. Note that if there is a large fluctuation in the pressure inside the tube during the heating process, the fine-tuning valve should be manually adjusted in time;

(8) After the 1-10min heat preservation program is over, let the furnace body cool down to room temperature naturally. Close the proton flowmeter, gas cylinder valve, ball valve, and mechanical pump, and then open the vent valve to restore normal atmospheric pressure in the tube, then remove the quartz tube, collect the mica substrate, and obtain two-dimensional BiOCl single crystal nanosheets.

The synthesized BiOCl is observed under an optical microscope as square nanosheets of different colors. The color of the nanosheets is related to the thickness (see (a) in Figure 2). The color changes (see (b) in Figure 2). As shown in Figure 4, by X-ray diffraction analysis, the obtained BiOCl sample grows along the (001) plane of the BiOCl crystal structure.

The TEM results are shown in Fig. 17(a)(b)(c). The diffraction lattice of BiOCl nanosheets prepared in the gas phase shows complete and regular BiOCl[001] direction diffraction spots, which is consistent with the XRD results showing only the BiOCl(001) series crystal planes, and the interplanar spacing of the two directions in the high-resolution TEM image can be compared with that of The {110} and {200} interplanar spacings correspond to each other.

Example 2: Preparation of Bi ₁₂ O ₁₅ Cl ₆ /Bi ₃ O ₄ Cl/Bi ₁₂ O ₁₇ Cl ₂ by phase inversion in gas phase

(1) Put the mica grown with BiOCl nanosheets into the quartz tube, as shown in Figure 15, then assemble the quartz tube and other vacuum accessories into a high-temperature vacuum tube furnace system for high-temperature heat treatment;

(2) Open the ball valves at the left and right ends of the furnace, turn on the mechanical pump, and close the bubbler to prevent the mechanical pump from evacuating the furnace tube to a low vacuum due to moisture volatilization, and then remove the air in the entire system to reduce the pressure in the tube to below 10 Torr , open the gas cylinder valve, feed nitrogen, open the flow meter gas valve and set the gas flow to 50-150 sccm, and clean for 5-10 minutes. Then close the air valve of the flowmeter, and then open the air valve of the flowmeter to feed in the same amount of nitrogen when the pressure in the pipe drops below 10Torr again. Repeat this three times to fully discharge the impurity gas in the tube and the residual water vapor in the previous experimental pipeline;

(3) After the last cleaning is completed, continue to feed nitrogen gas with a flow rate of 100-300 sccm, and raise the temperature of the chamber from room temperature to 390-410 °C/440-460 °C/490-510 °C at a rate of 15 °C/min growth temperature;

(4) When the temperature is about to reach the target temperature, the oxygen with a flow rate of 50-150 sccm is introduced, and the nitrogen flow rate is set at 50-150 sccm at the same time, and then the chamber pressure is adjusted to a conversion pressure of about 200-400 Torr by using a fine-tuning valve;

(5) After the 50-70min heat preservation program is over, let the furnace body cool down to room temperature naturally. Turn off the proton flowmeter, gas cylinder valve, ball valve, mechanical pump, and then open the vent valve to restore the normal atmospheric pressure in the tube, then remove the quartz tube to obtain the Bi ₁₂ O ₁₅ Cl ₆ /Bi ₃ O ₄ Cl/Bi ₁₂ O Two-dimensional nanosheets or thin films of ₁₇ Cl ₂ .

There are three kinds of bismuth oxyhalides synthesized in the present invention: Bi ₃ O ₄ Cl, Bi ₁₂ O ₁₇ Cl ₆ , Bi ₁₂ O ₁₇ Cl ₂ . After in-situ analysis by AFM, it was found that the thickness of the nanosheets after the phase transition was thinned and the surface was bubbling. These phenomena are all due to the decomposition of BiOCl to produce BiCl ₃ gas during the high-temperature conversion process, and the gas escapes (see Figure 3). The chemical reactions involved are as follows:

15BiOCl _(s) → 3BiCl _3(g) +Bi ₁₂ O ₁₅ Cl _6(s) #(1)

4BiOCl _(s) →BiCl _3(g) +Bi ₃ O ₄ Cl _(s) #(2)

17BiOCl _(s) → 5BiCl _3(g) +Bi ₁₂ O ₁₇ Cl _2(s) #(3)

As shown in Figure 4, the XRD results after heat treatment at different temperatures show that the BiOCl material undergoes three different stoichiometric phase structures: Bi ₁₂ O ₁₅ Cl ₆ , Bi ₃ O ₄ Cl, and Bi ₁₂ O ₁₇ Cl ₂ . Diffraction peaks showing two phase structures, this is because there will be a nano-continuous film when transferring the material, and the thickness of the continuous film is between 0.1 μm and 5 μm, so there will be incomplete high-temperature conversion at the continuous film, making XRD The spectrum shows that the diffraction peaks of the previous phase structure remain.

Example 3: Phase inversion in gas phase and preparation of carbon-doped Bi ₃ O ₄ Cl

Except that the mica with BiOCl nanosheets grown in step (1) was replaced by the substrate with BiOCl nanosheets transferred by the polymer sacrificial layer method, the rest was the same as in Example 2, and carbon-doped Bi ₃ O ₄ Cl two-dimensional nanosheets were prepared. piece. Since carbon residues will be left on the surface of BiOCl when excess polymer is removed, the phase structure transformation will take place during the high-temperature heat treatment process, and the carbon element will diffuse and implant into the sample under the action of high temperature on the one hand, and finally the carbon element doped Heterogeneous two-dimensional layered bismuth oxyhalide materials. The prepared carbon-doped Bi ₃ O ₄ Cl samples were tested and characterized as follows:

(1) As shown in Figure 17(d)(e)(f), the converted nanosheets after heat treatment at 440-460°C were compared with the simulated diffraction lattice in the direction of Bi ₃ O ₄ Cl[001] in TEM analysis, and it was found that the same It shows regular Bi ₃ O ₄ Cl [001] direction diffraction spots, which can also correspond to {220} and {200} interplanar spacings in high-resolution TEM images. However, there are some periodic miscellaneous spots, as shown in Figure 17(e), we guess that these periodic diffraction spots may be due to the doping of C element during the heat treatment process. At the same time, in the high-resolution TEM images, it was found that some bright spots that should be bismuth atoms were missing, and it was speculated that it might be due to the doping of C element into the crystal to replace the bismuth atoms.

Since the converted nanosheets are disturbed by some periodic impurities in the [001] direction TEM analysis, and in order to further prove that the converted nanosheets are Bi ₃ O ₄ Cl structure and carbon doped, we performed FIB slice processing on the samples. Analyze the crystal structure information at the cross-section of the nanosheet. As shown in Figure 18, the main spots and

The direction simulation lattice is very well matched, and the spherical aberration high-resolution TEM diagram can also correspond

Interplanar spacing of {002}. Atomic resolution is also achieved in high-resolution TEM images, where the atomic arrangement corresponds to

The crystal structure of the facets. In the EDS analysis of the FIB samples, it was proved that the carbon elements were uniformly distributed in the Bi ₃ O ₄ Cl nanosheets.

(2) As shown in Figure 19, X-ray photoelectron spectroscopy (XPS) shows that the main elemental composition of the material has not changed before and after heat treatment, but the Bi _4f peak has a blue shift and the Cl _2p peak has a red shift after heat treatment. And the XPS atomic content analysis shows that the atomic content ratio of Bi and Cl in the sample after heat treatment is close to 3:1 (see Table 1). This is due to the

The chemical bond length and bond angle changed after being transformed into Bi ₃ O ₄ Cl.

Table 1 Estimation of atomic content percentage by XPS data of samples before and after heat treatment

the	Bi atomic content%	Cl atom content%	Bi, Cl atomic content ratio
Before annealing	26.74	27.4	0.98:1
After annealing	2.02	0.78	2.6:1

(3) The Raman spectrum characterization results are shown in Figure 20, the BiOCl material

The vibration mode Raman peak is at 144cm ^-1 , which is the vibration mode between Bi-Cl atoms. After heat treatment at 440～460℃

The blue shift of the peak to 155cm ^-1 is due to the change of the relative positions of Bi and Cl atoms in the crystal structure after the transformation of BiOCl to Bi ₃ O ₄ Cl, resulting in

Vibration pattern enhanced.

(4) Before and after phase inversion, the results of UV-Vis spectrophotometer (UV-Vis spectrophotometer) show that the optical band gap of BiOCl is E _g ~ 3.21eV, and the optical band gap of Bi ₃ O ₄ Cl after heat treatment is E _g ~ 2.88eV (see Figure 21), and the absorption of the sample after heat treatment in the 200-350nm band is about 26% stronger than that before heat treatment.

Embodiment 4: Preparation of ultraviolet detection device and FET performance test

Taking two-dimensional layered BiOCl and C-doped Bi ₃ O ₄ Cl nanosheets as examples, the preparation process of the ultraviolet detection device using the n-type doped two-dimensional layered bismuth oxyhalide material of the present invention is described in detail.

(1) The fabricated device structure is shown in Fig. 6 . Put the BiOCl or C-doped Bi ₃ O ₄ Cl nanosheet sample transferred onto the silicon substrate into isopropanol for 3 minutes of ultrasonication to remove the thick accumulation layer and impurity particles generated during the growth of the nanosheet, and then plated on A layer of hexamethyldisilazane (HMDS) was uniformly coated on the sample surface with Lor 5A (MicroChem) and S1805 (Dow) positive photoresist. The homogenized sample was naturally cooled to room temperature, and then placed on a manual UV exposure machine (Karl Suss MJB4Mask Aligner) for exposure, since the distribution of BiOCl or C-doped Bi ₃ O ₄ Cl nanosheets on the substrate is wide enough and The range is large enough to randomly cover the device electrodes in the reticle pattern on the BiOCl or C-doped Bi ₃ O ₄ Cl nanosheets without alignment during exposure.

(2) After the exposure was completed, the sample was put into MF-26 developer solution for 40s for development. Immediately after the development was completed, it was soaked in water for 3 minutes, dried with high-purity nitrogen, and then put into the reactive ion etching system (Vision 322, Advanced Vaccum) to remove the incompletely developed residual glue to ensure sufficient contact between the metal and the sample during the next film deposition. 80nm Au and 1.5nm Cr were plated on the substrate using PRO Line PVD75, Kurt J. Lesker electron beam evaporation coating machine. Soak the sample in the PG Remover solution at 80°C for 10 minutes, and then use a syringe to flush the sample in the solution. At this time, most of the photoresist will be dissolved, and the metal on it will also be removed. Stripped down. Then soak in PG Remover at 80°C for 10 minutes for the second time, repeat the previous step, and finally put it in a new PG Remover to heat at 80°C, soak for 12 hours and take it out. According to the actual effect of peeling, the sample can be soaked in PG Remover Gently wipe the surface of the device with a cotton swab to facilitate the metal stripping of the small line width device part. Finally, the sample was taken out, rinsed with isopropanol, and then rinsed with deionized water and dried. The final results of device preparation are shown in Figure 7 and Figure 8.

The prepared optoelectronic device was tested for FET performance. The carrier mobility of BiOCl was measured to be 6.31×10 ^-5 cm ² V ^-1 s ^-1 . The carrier mobility of Bi ₃ O ₄ Cl is shown in Table 2. Calculation The formula is as follows formula 4:

Where L and W are the length and width of the conductive channel respectively, C _i =11.3nF/cm ² is the dielectric constant of the gate insulating layer with a thickness of 300nm SiO ₂ , I _ds is the source-drain current of the device, and V _ds is the device Source-drain voltage, V _g is the device gate voltage.

As shown in Figure 9, it is found from the FET transfer characteristic curve that the grown BiOCl exhibits the properties of a p-type semiconductor, and the transformed Bi ₃ O ₄ Cl exhibits the properties of an n-type semiconductor. DFT theoretical calculations (as shown in Figure 13(a) and (b)) use the crystal model in which carbon atoms are replaced by bismuth atoms. It is found that the bottom of the conduction band is split in the energy band structure of Bi ₃ O ₄ Cl after carbon doping, so that Shown as n-type semiconductor properties. It can be predicted that the same sample can realize n-type and p-type conversion through heat treatment, which may be able to realize the application of special functions in many semiconductor devices.

Table 2 Bi ₃ O ₄ Cl photosensitive performance parameters and FET electrical parameters

Example 5: Photogenerated carrier lifetime test

In the invention, an ultrafast femtosecond transient absorption test is performed on a sample to fit the carrier lifetime of the sample under 266nm ultraviolet light. Femtosecond transient absorption spectroscopy (fs-TAS) of the samples were performed using a commercial femtosecond titanium/sapphire regenerative amplifier laser system (Coherent) (800nm, 35fs, 7mJ/pulse and 1kHz repetitionrate), nonlinear frequency mixing technique and automated data acquisition Transient absorption spectrometer (Ultrafast, Helios). The pump wavelength of fs-TAS is 266nm, the detection wavelength range is 320nm-730nm, and all experiments are carried out at room temperature.

By performing ultrafast femtosecond laser transient absorption spectroscopy tests on three different samples of carbon-doped Bi ₃ O ₄ Cl, undoped Bi ₃ O ₄ Cl and BiOCl nanosheets, it can be further proved that C doping leads to The lifetime of photogenerated electron-hole pairs is increased, which leads to a significant enhancement of Bi ₃ O ₄ Cl's absorption of ultraviolet light.

From the transient absorption spectrum (Figure 22), it can be seen that the absorption intensity of carbon-doped Bi ₃ O ₄ Cl is significantly stronger than that of BiOCl, and the kinetic fitting carrier lifetime of carbon-doped Bi ₃ O ₄ Cl is also much longer than BiOCl, which proves that under _{266nm laser} irradiation, the carriers in the excited state in _Bi3O4Cl can last longer _to enhance the photoelectric response of _Bi3O4Cl , while comparing carbon-doped _Bi3O4 Cl and undoped Bi ₃ O ₄ Cl samples found that the carbon-doped Bi ₃ O ₄ Cl carrier lifetime is also greater than that of undoped Bi ₃ O ₄ Cl. This can prove that the doping of carbon elements can help the carriers in the excited state to obtain a longer lifetime, and further enhance the photoelectric performance of Bi ₃ O ₄ Cl.

We also compared carbon-doped Bi ₃ O ₄ Cl with commercial TiO ₂ crystals, both of which were tested using the above-mentioned femtosecond transient absorption test conditions, and found that carbon-doped Bi ₃ O ₄ Cl flows under excitation at 266nm The sub-lifetime is also greater than commercial _TiO2 crystals (41 ps). This shows that the carbon-doped Bi ₃ O ₄ Cl low-power avalanche ultraviolet photodetector device prepared by the present invention has abundant commercial value, which is comparable to the ultraviolet detectors currently on the market.

The fitting results are shown in Table 3.

Table 3 Comparison of carrier lifetimes of C-doped Bi ₃ O ₄ Cl, undoped Bi ₃ O ₄ Cl, and BiOCl

the	τ 1	τ 2	τ 3
C-doped Bi 3 O 4 Cl	3ps	419 ps	91ns
Undoped Bi 3 O 4 Cl	5ps	660ps	37ns
BiOCl	3ps	284ps	11ns
TiO 2	3ps	41ps	-

The above-mentioned embodiments only illustrate the principles and effects of the present invention, but are not intended to limit the present invention. Anyone skilled in the art can modify or change the above-mentioned embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes made by those skilled in the art without departing from the spirit and technical ideas disclosed in the present invention shall still be covered by the claims of the present invention.

Claims (15)

1. An n-type doped two-dimensional layered bismuth oxyhalide material is characterized in that its general chemical formula is Z _i -Bi _l O _m X _n , wherein X is a halogen, and Z is a group IVA element; the element stoichiometric ratio ( The value of i+l):m:n is 12:15:6, 3:4:1, or 12:17:2, i/(i+l+m+n)≤7%; the two-dimensional layer The bismuth oxyhalide material is a single crystal nanosheet or a single crystal continuous film.
2. The n-type doped two-dimensional layered bismuth oxyhalide material according to claim 1, characterized in that its general chemical formula is C _i -Bi _3-i O ₄ X, wherein X is a halogen, and i≤0.56.
3. The n-type doped two-dimensional layered bismuth oxyhalide material as claimed in claim 2 is characterized in that, when the resistive device has a voltage ≤ 1V and an ultraviolet light intensity ≥ 100mW/cm ² , photocarriers avalanche multiplication phenomenon.
4. The n-type doped two-dimensional layered bismuth oxyhalide material according to claim 3, characterized in that the lifetime of the photocarriers is ≥ 91 ns.
5. The preparation method of the n-type doped two-dimensional layered bismuth oxyhalide material according to any one of claims 1 to 4, characterized in that, the two-dimensional layered BiOX is used as a precursor, and the phase transformation is carried out simultaneously in the gas phase and doping.
6. The preparation method of n-type doped two-dimensional layered bismuth oxyhalide material according to claim 5, characterized in that, the phase transformation comprises the following steps: in 10-80% nitrogen mixed with oxygen, the pressure is 0.01- 1atm, temperature 350～700℃ for thermal annealing treatment of BiOX; through thermal annealing treatment at different temperatures, different degrees of dehalogenation and phase transformation can be controlled to obtain Bi ₁₂ O ₁₅ X ₆ , Bi ₃ O ₄ X, or Bi ₁₂ O ₁₇ X ₂ two-dimensional layered nanomaterials.
7. The preparation method of an n-type doped two-dimensional layered bismuth oxyhalide material according to claim 6, wherein the phase transformation specifically comprises the following steps:

   Step 1. Place the substrate loaded with BiOX in a quartz boat, and put the quartz boat into the quartz tube of the tube furnace;

   Step 2. Vacuumize the quartz tube of the tube furnace, remove impurity gases in the system, feed the carrier gas, program the temperature to the required reaction temperature, feed the carrier gas and reaction gas to adjust the chamber pressure, and carry out phase inversion;

   Step 3. Cool naturally after the reaction, and take out the substrate to obtain two-dimensional layered nanomaterials that have been phase-transformed into Bi ₁₂ O ₁₅ X ₆ , Bi ₃ O ₄ X , or Bi ₁₂ O ₁₇ X ₂ on the surface of the substrate.
8. The method for preparing an n-type doped two-dimensional layered bismuth oxyhalide material according to claim 7, wherein the phase transformation further includes one or more of the following features:

   1) The carrier gas introduced in step 2 is specifically nitrogen with a flow rate of 100-300 sccm;

   2) When the carrier gas and reaction gas are introduced in step 2, specifically when the temperature is about to reach the target temperature, the oxygen flow rate of one path is set to 50-150 sccm, and the nitrogen flow rate of the other path is set to 50-150 sccm;

   3) The required temperature in step 2 is 390-410°C, 440-460°C or 490-510°C;

   4) The phase inversion time in step 2 is 50-150 min.
9. The method for preparing an n-type doped two-dimensional layered bismuth oxyhalide material according to claim 5, wherein the method for preparing the two-dimensional layered BiOX comprises: using BiX ₃ , water vapor or oxygen as a precursor source, at a pressure of 0.1-0.8atm and a temperature of 260-400°C, the BiOX single-crystal nanosheet or single-crystal continuous film is prepared by chemical vapor deposition.
10. The method for preparing an n-type doped two-dimensional layered bismuth oxyhalide material according to claim 5, wherein the doping is carbon element doping, comprising the steps of: using a polymer sacrificial layer method to transfer two A two-dimensional layered BiOX material sample is produced, and carbon residues are generated on the surface, and then the carbon element is diffused and implanted into the sample by high-temperature phase transformation, and a carbon-doped two-dimensional layered Bi ₃ O ₄ X material is obtained.
11. Application of the n-type doped two-dimensional layered bismuth oxyhalide material in any one of claims 1 to 4 on an ultraviolet detector.
12. The application according to claim 11, wherein the ultraviolet detector comprises a high temperature resistant substrate or a flexible substrate, and the n-type doped two-dimensional layered bismuth oxyhalide material is applied to a high temperature resistant substrate or a flexible substrate superior.
13. The application according to claim 12, characterized in that it includes one or more of the following features:

    (1) The method for applying the n-type doped two-dimensional layered bismuth oxyhalide material to a high-temperature-resistant substrate is: using the polymer sacrificial layer method to transfer the two-dimensional layered BiOCl material to any high-temperature-resistant substrate, Thermally driven phase transition to produce Zi _{-Bi 12-i} O ₁₅ Cl ₆ , Zi _{-Bi 3-i} O ₄ Cl or Zi _{-Bi 12-i} O ₁₇ Cl ₂ nanosheets or thin films;

    (2) The method for applying the n-type doped two-dimensional layered bismuth oxyhalide material to a flexible substrate is: using a polymer sacrificial layer method to transfer the two-dimensional layered BiOCl material to a high-temperature resistant silicon substrate, first Thermally driven phase transition, producing Z _i -Bi _12-i O ₁₅ Cl ₆ , Zi _{-Bi 3-i} O ₄ Cl or Zi _{-Bi 12-i} O ₁₇ Cl ₂ nanosheets or thin films, and then Z _i -Bi _12-i O ₁₅ Cl ₆ , Zi _- Bi _3-i O ₄ Cl or Zi _- Bi _12-i O ₁₇ Cl ₂ nanosheets or films are transferred onto flexible substrates.
14. An ultraviolet detection device, comprising a substrate, an ultraviolet sensitive layer and an electrode layer; the ultraviolet sensitive layer is arranged on the substrate, and the electrode layer is arranged on the ultraviolet sensitive layer; the ultraviolet The sensitive layer is the n-type doped two-dimensional layered bismuth oxyhalide material described in any one of 1-4.
15. The ultraviolet detection device according to claim 14, characterized in that, when the operating voltage is ≤1V and the intensity of 266nm ultraviolet light is ≥100mW/cm ² , an avalanche photocurrent phenomenon occurs.

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