Preparation method of bismuth selenide film with adjustable defect concentration and application thereof in photoelectric synaptic device

Abstract

The application relates to a preparation method of a bismuth selenide film with adjustable defect concentration and application of the bismuth selenide film to a photoelectric synaptic device, and belongs to the technical field of two-dimensional photoelectric materials and photoelectric synaptic device preparation. The specific scheme is as follows: a Bi2Se3 film is prepared by adopting chemical vapor deposition, secondary treatment is conducted on the prepared Bi2Se3 film by in-situ heat treatment for avoiding air contact and keeping the original atmosphere to obtain a bismuth selenide film with adjustable defect concentration. The photoelectric synaptic device of the prepared bismuth selenide film is of an MSM structure, is simple in structure and has integration potential; the photoelectric response of the Bi2Se3 film photoelectric synaptic device has obvious basic synaptic behaviors of long-term potentiation, short-term potentiation and pulse enhancement, and can be applied to the field of artificial intelligence.

Description

Technical Field

[0001] This invention belongs to the field of two-dimensional optoelectronic materials and optoelectronic synaptic device fabrication technology, specifically relating to a method for preparing a bismuth selenide thin film with adjustable defect concentration and its application in optoelectronic synaptic devices. Background Technology

[0002] Traditional photodetectors separate their photodetection and storage functions, resulting in drawbacks such as high energy consumption and slow processing speed when performing image processing, which cannot meet the needs of the field of artificial intelligence. Photosynapses, on the other hand, have become a research hotspot in recent years because they simultaneously possess photodetection and storage functions.

[0003] The reported mechanisms of photoelectric synaptic devices mainly include: (1) the capture and detachment of free carriers caused by defects, gas molecules, band structure, etc.; and (2) the ferroelectric domain flipping caused by ferroelectric materials under illumination. Synapses based on ferroelectric materials often have complex structures, requiring source / drain electrodes, transport layers, ferroelectric layers, dielectric layers, and gates, which are difficult to integrate and are often used for basic research. However, photoelectric synaptic devices based on mechanism (1) can be composed of simple source / drain electrodes and transport layers, and have integration potential and industrialization potential. Therefore, the fabrication and research of such photoelectric synaptic devices are of great importance.

[0004] Currently reported two-dimensional double-ended photosynapses are mainly transition metal oxide sulfides such as MoS2 and ZnO. Due to the small number of defects in these materials and the difficulty of doping engineering, their sustainable photoconductive effect is not obvious.

[0005] Compared to transition metal oxides and sulfides, bismuth selenide possesses a large number of intrinsic selenium vacancy defects, theoretically making it an excellent candidate material for photoelectric synapses. However, due to the abundance of grain boundaries and low purity, the photoelectric response of a single bismuth selenide film is difficult to detect. Summary of the Invention

[0006] To address the problems existing in the background art, this invention provides a method for preparing a bismuth selenide thin film with adjustable defect concentration and its application in optoelectronic synaptic devices. The bismuth selenide thin film is prepared by chemical vapor deposition, and the defect concentration of the film is modulated by in-situ heat treatment. A metal material is used as an electrode to form a metal-semiconductor-metal (MSM) structure optoelectronic synaptic device.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for preparing a bismuth selenide thin film with adjustable defect concentration involves preparing a Bi2Se3 thin film by chemical vapor deposition, and then performing a secondary treatment on the prepared Bi2Se3 thin film by in-situ heat treatment that avoids air contact and maintains the original atmosphere to obtain a bismuth selenide thin film with adjustable defect concentration.

[0009] The specific steps are as follows:

[0010] Step 1: Using 0.1-0.3g of bismuth selenide powder as a precursor, place it in the center of a tube furnace, with fluorinated mica sheet (F-Mica) as a substrate, and place it 21-23cm downstream of the bismuth selenide powder. Seal the quartz tube and turn on the vacuum pump to extract the air in the tube until the air pressure is below 1Pa.

[0011] Step 2: Purge the quartz tube with 200 sccm of argon gas for ten minutes, adjust the argon gas flow rate to 6-10 sccm, and adjust the evacuation valve to keep the pressure inside the tube at 30-50 Pa, which is suitable for the growth of bismuth selenide thin films.

[0012] Step 3: Heat in a tube furnace for 30 minutes to bring the precursor to 480-520°C and the substrate to 300°C. Hold at this temperature for 1-5 minutes and allow to cool naturally to 200°C.

[0013] Step 4: After deposition, keep the quartz tube sealed and slide the tube furnace so that the deposited Bi₂Se₃ film is located in the center of the furnace. Maintain a constant argon flow rate and internal pressure, and perform in-situ annealing on the Bi₂Se₃ film to obtain a bismuth selenide film with adjustable defect concentration. Maintaining a constant argon flow rate and internal pressure ensures the bismuth selenide film is in the optimal film-forming environment, guaranteeing excellent film quality. The purpose of the in-situ annealing is to modulate the selenium vacancy concentration in the bismuth selenide film, thereby obtaining a suitable bismuth selenide film for preparing photoelectric synapses. In-situ annealing has advantages such as simple operation and low cost.

[0014] Furthermore, in step four, the in-situ annealing temperature is 260-380℃, preferably 350℃.

[0015] In step one, the heat source is located at the center of the tubular furnace.

[0016] In step one, the substrate used has no dangling bonds, and the thin film prepared on this substrate has advantages such as high crystallinity and good uniformity.

[0017] In step one, the distance between the substrate and the precursor is determined by the furnace temperature profile.

[0018] In step one, the bismuth selenide powder is a group V-VI compound. Group VI atoms are prone to escape to form n-type vacancy donor defects. The capture and decapture of charge carriers by defects are the key to the device having synaptic behavior.

[0019] In step two, the argon gas is an inert gas, and using it as an atmosphere can effectively prevent irrelevant side reactions from occurring.

[0020] In step three, the precursor temperature and substrate temperature are the appropriate evaporation temperature of the precursor and the appropriate deposition temperature of the prepared thin film. If the precursor temperature is too high, the thin film preparation process will be difficult to control; if the temperature is too low, the required atoms will not be able to escape; if the substrate temperature is too high or too low, a thin film cannot be formed.

[0021] It should be noted that: throughout the entire process of the preparation method, from the preparation of the Bi2Se3 thin film to the end of the in-situ annealing treatment, the quartz tube is kept in a sealed state to avoid air contact and maintain a constant atmosphere, which can ensure that the composition of the bismuth selenide thin film does not change.

[0022] The application of a bismuth selenide thin film with tunable defect concentration in optoelectronic synaptic devices involves using a bismuth selenide thin film with tunable defect concentration as a substrate, depositing metal electrodes on the substrate, and obtaining a metal-semiconductor-metal (MSM) optoelectronic synaptic device.

[0023] Furthermore, electron beam evaporation was used to maintain the intracavity pressure at 4.5 × 10⁻⁶. -4 Metal electrodes are deposited on a substrate at an electron beam current of 30–50 Pa below Pa.

[0024] Furthermore, the metal electrode is a silver electrode.

[0025] Preferably, in the above method, the materials and atmosphere used are of analytical grade.

[0026] Compared with the prior art, the beneficial effects of the present invention are:

[0027] 1. This invention utilizes chemical vapor deposition (CVD) combined with in-situ heat treatment to prepare bismuth selenide thin films with adjustable defect concentration. CVD is an excellent method for preparing bismuth selenide thin films, and in-situ heat treatment can effectively control the escape of selenium atoms from the bismuth selenide thin film. The prepared bismuth selenide thin film has good crystal quality, few grain boundaries, high purity, thin thickness, low roughness, and photoelectric response not found in ordinary bismuth selenide thin films. Using this material, a two-dimensional photoelectric synaptic device with obvious photoelectric synaptic behavior, simple preparation method, and low cost is prepared.

[0028] 2. Bismuth selenide, as a two-dimensional material, has advantages such as high mobility, tunable band structure, and narrow band gap. In bismuth selenide, selenium atoms can easily escape to form selenium vacancies. As a donor defect, selenium vacancies can capture and decapture free electrons in the conduction band, thereby achieving sustainable photoconductivity that ordinary photodetectors do not possess.

[0029] 3. The bismuth selenide thin-film photoelectric synaptic device prepared by this invention has an MSM structure, which is simple and has integration potential. The photoelectric response of the Bi2Se3 thin-film photoelectric synaptic device of this invention has obvious biological synaptic basic synaptic behaviors such as long-term duration enhancement (LTP), short-term duration enhancement (STP), and pulse-to-pulse enhancement (PPF), which can be applied to the field of artificial intelligence. Attached Figure Description

[0030] Figure 1 This is an atomic force microscope (AFM) image of the bismuth selenide thin film with adjustable defect concentration prepared in Example 1 of the present invention;

[0031] Figure 2 The Raman spectrum of the bismuth selenide thin film with adjustable defect concentration prepared in Example 1 of the present invention;

[0032] Figure 3 The X-ray electron spectra (XPS) of the bismuth selenide thin film with adjustable defect concentration prepared in Example 1 of the present invention are shown.

[0033] Figure 4 The STP behavior of the bismuth selenide thin film photosynaptic device with adjustable defect concentration prepared in Example 1 of the present invention;

[0034] Figure 5 The LTP behavior of the bismuth selenide thin-film photosynaptic device with adjustable defect concentration prepared in Example 1 of this invention;

[0035] Figure 6 The defect concentration adjustable bismuth selenide thin film photosynaptic device prepared in Example 1 of this invention exhibits PPF behavior.

[0036] Figure 7 IV curves of bismuth selenide thin films with adjustable defect concentration prepared in Examples 1-5 and Comparative Example 1 of this invention. Detailed Implementation

[0037] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are only some embodiments of the invention, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0038] Example 1:

[0039] A method for preparing a bismuth selenide thin film with adjustable defect concentration and its application in optoelectronic synaptic devices includes the following steps:

[0040] (1) Using 0.2g of bismuth selenide powder as a precursor, place it in the center of a tube furnace, use F-Mica as a substrate, place it downstream of the bismuth selenide powder, seal the quartz tube, and use a vacuum pump to evacuate the gas pressure inside the tube to below 1Pa.

[0041] (2) Purge the quartz tube with 200 sccm of argon gas for ten minutes, adjust the argon gas flow rate to 8 sccm, and adjust the evacuation valve to keep the pressure inside the tube at 40 Pa.

[0042] (3) Heating in a tube furnace to bring the precursor temperature to 500°C and the substrate temperature to 300°C, holding for one minute, and then allowing it to cool down naturally.

[0043] (4) After the precursor temperature naturally cools down to 200℃, keep the quartz tube closed, slide the tube furnace, and place the deposited Bi2Se3 film in the center of the tube furnace. Keep the argon flow rate and the pressure inside the tube constant, and perform in-situ annealing treatment on the Bi2Se3 film at 350℃ for 30 minutes to obtain a bismuth selenide film with adjustable defect concentration.

[0044] (5) Electron beam evaporation is used to maintain the cavity pressure at 4.5 × 10⁻⁶. -4 With an electron beam current below Pa and an electron beam current of 40, a silver electrode is deposited on the Bi2Se3 thin film prepared above to obtain a Bi2Se3 thin film photoelectric synapse device.

[0045] The prepared samples were characterized by AFM, Raman, and XPS, as detailed in the appendix. Figure 1-3 The prepared bismuth selenide film had a thickness of 7.13 nm and a roughness Ra of 1.03 nm, exhibiting both thinness and low roughness. (From the attached...) Figure 1 As can be seen, the bismuth selenide film is composed of numerous triangular and hexagonal wafers. Triangular and hexagonal shapes are standard shapes for bismuth selenide nanosheets, indicating that the prepared bismuth selenide film is of good quality. (From the attached...) Figure 2 Three Raman vibration peaks corresponding to bismuth selenide can be clearly observed in the film. The small half-peak width and obvious characteristic peaks indicate the good crystallinity and high purity of the bismuth selenide film. (From the attached image...) Figure 3 The characteristic peaks corresponding to the selenium-bismuth bond between selenium and bismuth can be clearly observed, indicating that bismuth selenide has high purity. (See attached image.) Figure 3 The study also revealed distinct characteristic peaks corresponding to bismuth-oxygen bonds. Since bismuth atoms are located within the five-layered structure of bismuth selenide, the formation of bismuth-oxygen bonds is inextricably linked to selenium vacancies, indicating that the prepared bismuth selenide film possesses a large number of selenium vacancies. For details on the photosynaptic behavior of the samples, please refer to the appendix. Figure 4-6 At a strength of 5.2 mW / cm 2 Under 450nm illumination, the sample exhibited distinct STP, LTP, and PPF behaviors, confirming the feasibility of bismuth selenide thin-film photosynaptic devices. IV curve testing was performed on the sample; see attached image for details. Figure 7 .

[0046] To verify the effect of in-situ heat treatment on the modulation of selenium vacancy defect concentration in bismuth selenide thin films, five control experiments were also conducted, as detailed in Examples 2-6.

[0047] Comparative Example 1:

[0048] A method for preparing a bismuth selenide thin film and its application in optoelectronic synaptic devices includes the following steps:

[0049] (1) Using 0.2g of bismuth selenide powder as a precursor, place it in the center of a tube furnace, use F-Mica as a substrate, place it downstream of the bismuth selenide powder, seal the quartz tube, and use a vacuum pump to evacuate the gas pressure inside the tube to below 1Pa.

[0050] (2) Purge the quartz tube with 200 sccm of argon gas for ten minutes, adjust the argon gas flow rate to 8 sccm, and adjust the evacuation valve to keep the pressure inside the tube at 40 Pa.

[0051] (3) Heating in a tube furnace to bring the temperature of the precursor to 500°C and the temperature of the substrate to 300°C, holding for one minute, and then cooling naturally to obtain a bismuth selenide film.

[0052] (4) Electron beam evaporation is used to maintain the cavity pressure at 4.5 × 10⁻⁶. -4 With an electron beam current below Pa and an electron beam current of 40, a silver electrode is deposited on the Bi2Se3 thin film prepared above to obtain a Bi2Se3 thin film photoelectric synapse device.

[0053] (5) IV curve tests were performed on the samples. See Appendix for details. Figure 7 .

[0054] Example 2:

[0055] A method for preparing a bismuth selenide thin film with adjustable defect concentration and its application in optoelectronic synaptic devices includes the following steps:

[0056] (1) Using 0.2g of bismuth selenide powder as a precursor, place it in the center of a tube furnace, use F-Mica as a substrate, place it downstream of the bismuth selenide powder, seal the quartz tube, and use a vacuum pump to evacuate the gas pressure inside the tube to below 1Pa.

[0057] (2) Purge the quartz tube with 200 sccm of argon gas for ten minutes, adjust the argon gas flow rate to 8 sccm, and adjust the evacuation valve to keep the pressure inside the tube at 40 Pa.

[0058] (3) Heating in a tube furnace to bring the precursor temperature to 500°C and the substrate temperature to 300°C, holding for one minute, and then allowing it to cool down naturally.

[0059] (4) After the precursor temperature naturally cools down to 200℃, keep the quartz tube closed, slide the tube furnace, and place the deposited Bi2Se3 film in the center of the tube furnace. Keep the argon flow rate and the pressure inside the tube constant, and perform in-situ annealing treatment on the Bi2Se3 film at 260℃ for 30 minutes to obtain a bismuth selenide film with adjustable defect concentration.

[0060] (5) Electron beam evaporation is used to maintain the cavity pressure at 4.5 × 10⁻⁶. -4 With an electron beam current below Pa and an electron beam current of 40, a silver electrode is deposited on the Bi2Se3 thin film prepared above to obtain a Bi2Se3 thin film photoelectric synapse device.

[0061] (6) IV curve tests were performed on the samples; see Appendix for details. Figure 7 .

[0062] Example 3:

[0063] A method for preparing a bismuth selenide thin film with adjustable defect concentration and its application in optoelectronic synaptic devices includes the following steps:

[0064] (1) Using 0.2g of bismuth selenide powder as a precursor, place it in the center of a tube furnace, use F-Mica as a substrate, place it downstream of the bismuth selenide powder, seal the quartz tube, and use a vacuum pump to evacuate the gas pressure inside the tube to below 1Pa.

[0065] (2) Purge the quartz tube with 200 sccm of argon gas for ten minutes, adjust the argon gas flow rate to 8 sccm, and adjust the evacuation valve to keep the pressure inside the tube at 40 Pa.

[0066] (3) Heating in a tube furnace to bring the precursor temperature to 500°C and the substrate temperature to 300°C, holding for one minute, and then allowing it to cool down naturally.

[0067] (4) After the precursor temperature naturally cools down to 200℃, keep the quartz tube closed, slide the tube furnace, and place the deposited Bi2Se3 film in the center of the tube furnace. Keep the argon flow rate and the pressure inside the tube constant, and perform in-situ annealing treatment on the Bi2Se3 film at 290℃ for 30 minutes to obtain a bismuth selenide film with adjustable defect concentration.

[0068] (5) Electron beam evaporation is used to maintain the cavity pressure at 4.5 × 10⁻⁶. -4 With an electron beam current below Pa and an electron beam current of 40, a silver electrode is deposited on the Bi2Se3 thin film prepared above to obtain a Bi2Se3 thin film photoelectric synapse device.

[0069] (6) IV curve tests were performed on the samples; see Appendix for details. Figure 7 .

[0070] Example 4:

[0071] A method for preparing a bismuth selenide thin film with adjustable defect concentration and its application in optoelectronic synaptic devices includes the following steps:

[0072] (1) Using 0.2g of bismuth selenide powder as a precursor, place it in the center of a tube furnace, use F-Mica as a substrate, place it downstream of the bismuth selenide powder, seal the quartz tube, and use a vacuum pump to evacuate the gas pressure inside the tube to below 1Pa.

[0073] (2) Purge the quartz tube with 200 sccm of argon gas for ten minutes, adjust the argon gas flow rate to 8 sccm, and adjust the evacuation valve to keep the pressure inside the tube at 40 Pa.

[0074] (3) Heating in a tube furnace to bring the precursor temperature to 500°C and the substrate temperature to 300°C, holding for one minute, and then allowing it to cool down naturally.

[0075] (4) After the precursor temperature naturally cools down to 200℃, keep the tube furnace closed, slide the tube furnace so that the deposited Bi2Se3 film is located in the center of the tube furnace, keep the argon flow rate and the pressure inside the tube constant, and perform in-situ annealing treatment on the Bi2Se3 film at 320℃ for 30 minutes to obtain a bismuth selenide film with adjustable defect concentration.

[0076] (5) Electron beam evaporation is used to maintain the cavity pressure at 4.5 × 10⁻⁶. -4 With an electron beam current below Pa and an electron beam current of 40, a silver electrode is deposited on the Bi2Se3 thin film prepared above to obtain a Bi2Se3 thin film photoelectric synapse device.

[0077] (6) IV curve tests were performed on the samples; see Appendix for details. Figure 7 .

[0078] Example 5:

[0079] A method for preparing a bismuth selenide thin film with adjustable defect concentration and its application in optoelectronic synaptic devices includes the following steps:

[0080] (1) Using 0.2g of bismuth selenide powder as a precursor, place it in the center of a tube furnace, use F-Mica as a substrate, place it downstream of the bismuth selenide powder, seal the quartz tube, and use a vacuum pump to evacuate the gas pressure inside the tube to below 1Pa.

[0081] (2) Purge the quartz tube with 200 sccm of argon gas for ten minutes, adjust the argon gas flow rate to 8 sccm, and adjust the evacuation valve to keep the pressure inside the tube at 40 Pa.

[0082] (3) Heating in a tube furnace to bring the precursor temperature to 500°C and the substrate temperature to 300°C, holding for one minute, and then allowing it to cool down naturally.

[0083] (4) After the precursor temperature naturally cools down to 200℃, keep the quartz tube closed, slide the tube furnace, and place the deposited Bi2Se3 film in the center of the tube furnace. Keep the argon flow rate and the pressure inside the tube constant, and perform in-situ annealing treatment on the Bi2Se3 film at 380℃ for 30 minutes to obtain a bismuth selenide film with adjustable defect concentration.

[0084] (5) Electron beam evaporation is used to maintain the cavity pressure at 4.5 × 10⁻⁶. -4 With an electron beam current below Pa and an electron beam current of 40, a silver electrode is deposited on the Bi2Se3 thin film prepared above to obtain a Bi2Se3 thin film photoelectric synapse device.

[0085] IV curves were tested on the samples; see attached document for details. Figure 7 .

[0086] By simply changing the annealing temperature, the slope (conductivity) of the IV curve of the prepared bismuth selenide film changed significantly, as did the surface resistivity. Conductivity and resistance are closely related to the carrier concentration of the device. For n-type bismuth selenide, carriers are mainly provided by selenium vacancies; therefore, changes in conductivity and resistance suggest changes in the selenium vacancy concentration of the bismuth selenide film, indicating that in-situ heat treatment can modulate the concentration of selenium vacancy defects.

[0087] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. The application of a bismuth selenide thin film with adjustable defect concentration in photoelectric synaptic devices, characterized in that, Bi₂Se₃ thin films were prepared by chemical vapor deposition. A secondary treatment, which avoided air contact and maintained the original atmosphere, was then applied to the prepared Bi₂Se₃ thin films to obtain bismuth selenide thin films with adjustable defect concentrations. The specific steps are as follows: Step 1: Using bismuth selenide powder as a precursor, place it in the center of a tube furnace, with fluorinated mica sheet as a substrate, placed downstream of the bismuth selenide powder, seal the quartz tube, and turn on the vacuum pump to extract the air from the tube. Step 2: Introduce argon gas to clean the quartz tube, adjust the argon gas flow rate to a suitable level, and adjust the evacuation valve to make the pressure inside the tube suitable for bismuth selenide film growth; the argon gas flow rate used for bismuth selenide film growth is 6~10 sccm, and the pressure inside the tube is maintained at 30~50 Pa. Step 3: Heat the precursor in a tube furnace to 480~520℃, hold it at that temperature for a certain time, and then allow it to cool naturally; the holding time is 1~5 minutes. Step 4: After deposition, keep the quartz tube closed, slide the tube furnace so that the deposited Bi2Se3 film is located in the center of the tube furnace, keep the argon flow rate and the pressure inside the tube constant, and perform in-situ annealing of the Bi2Se3 film for 30 minutes to obtain a bismuth selenide film with adjustable defect concentration; the temperature of the in-situ heat treatment is 260~380℃. Using a bismuth selenide thin film with adjustable defect concentration as a substrate, metal electrodes are deposited on the substrate to obtain a metal-semiconductor-metal opto-synaptic device.

2. The application according to claim 1, characterized in that: In step one, the mass of bismuth selenide powder used is 0.1~0.3g, and the substrate is located 21~23cm downstream of the precursor.

3. The application according to claim 1, characterized in that: Metal electrodes are deposited on a substrate using an electron beam evaporation method with a suitable electron beam current.

4. The application according to claim 1 or 3, characterized in that: The metal electrode is a silver electrode.

Images