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

Abstract

The invention discloses a preparation method of a bismuth selenide film with adjustable defect concentration and application of the bismuth selenide film to a photoelectric synapse device, and belongs to the technical field of preparation of two-dimensional photoelectric materials and photoelectric synapse devices. According to the specific scheme, a Bi2Se3 film is prepared through chemical vapor deposition, and the prepared Bi2Se3 film is subjected to secondary treatment through in-situ heat treatment for avoiding air contact and keeping the original atmosphere to obtain the bismuth selenide film with the adjustable defect concentration. The bismuth selenide film photoelectric synapse device prepared by the invention 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 biological synaptic-like long-term enhancement, short-term enhancement, pulse enhancement and other basic synaptic behaviors, and the Bi2Se3 film photoelectric synaptic device can be applied to the field of artificial intelligence.

Description

Technical Field

[0001] The present invention belongs to the technical field of preparation of two-dimensional optoelectronic materials and optoelectronic synaptic devices, and specifically relates to a preparation method of a bismuth selenide film with adjustable defect concentration and its application in optoelectronic synaptic devices. Background Art

[0002] Traditional photodetectors have separate light detection and storage functions, which have disadvantages such as high energy consumption and slow processing speed when performing image processing, and cannot meet the needs of the field of artificial intelligence. Photoelectric synapses have become a research hotspot in recent years because they have both photodetection and storage functions.

[0003] The main mechanisms of optoelectronic synaptic devices reported so far are: (1) the capture and release of free carriers caused by defects, gas molecules, band structures, etc.; (2) the reversal of ferroelectric electromagnetic domains caused by ferroelectric materials under light. Synapses based on ferroelectric materials are often complex in structure, requiring source and drain electrodes, transport layers, ferroelectric layers, dielectric layers, and gates, etc., which are difficult to integrate and are often used for basic research. Optoelectronic synaptic devices based on mechanism (1) can be composed of simple source and drain electrodes and transport layers, and have the potential for integration and industrialization. Therefore, the preparation and research of such optoelectronic synaptic devices are extremely important.

[0004] The two-dimensional two-terminal photoelectric synapses reported so far are mainly made of transition metal oxide sulfides such as MoS2 and ZnO. Due to the few defects of these materials themselves and the difficulty of doping engineering, their sustainable photoconductivity effect is not obvious.

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

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

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A method for preparing a bismuth selenide film with adjustable defect concentration, wherein a Bi2Se3 film is prepared by chemical vapor deposition, and the prepared Bi2Se3 film is subjected to secondary treatment by in-situ heat treatment to avoid air contact and maintain the original atmosphere to obtain the bismuth selenide film with adjustable defect concentration.

[0009] The specific steps are as follows:

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

[0011] Step 2: Pass 200 sccm of argon gas to clean the quartz tube for ten minutes, adjust the argon gas flow rate to 6-10 sccm, and adjust the exhaust valve so that the pressure in the tube is maintained at 30-50 Pa suitable for the growth of bismuth selenide film;

[0012] Step 3: Heat the precursor to 480-520°C in a tube furnace for 30 minutes, and the substrate temperature to 300°C, and keep it warm for 1-5 minutes, and then cool it down naturally to 200°C;

[0013] Step 4: After the deposition is completed, 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 in the tube unchanged, and perform in-situ annealing on the Bi2Se3 film to obtain a bismuth selenide film with adjustable defect concentration. The purpose of keeping the argon flow rate and the pressure in the tube unchanged is to ensure that the bismuth selenide film is in the best film-forming environment and to ensure the excellent quality of the bismuth selenide film. The purpose of the in-situ annealing treatment is to modulate the selenium vacancy concentration of the bismuth selenide film, so as to obtain a bismuth selenide film suitable for preparing photoelectric synapses. The in-situ annealing treatment has the advantages of simple operation and low cost.

[0014] Furthermore, in step 4, the temperature of the in-situ annealing treatment is 260-380°C, preferably 350°C.

[0015] In step 1, the center of the tube furnace is the heat source location.

[0016] In step 1, the substrate used has no dangling bonds, and the film prepared using this substrate has the advantages of high crystallinity and good uniformity.

[0017] In step 1, the distance between the substrate and the precursor is determined by the furnace temperature curve.

[0018] In step 1, the bismuth selenide powder is a V-VI group compound, and the VI group atoms can easily escape to form n-type vacancy donor defects. The capture and de-capture of carriers by defects is the key to the synaptic behavior of the device.

[0019] In step 2, the argon gas is an inert gas, and using it as the atmosphere can effectively avoid the occurrence of irrelevant side reactions.

[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 film. If the precursor temperature is too high, the film preparation process is difficult to control, and if the temperature is too low, the required atoms cannot escape. If the substrate temperature is too high or too low, a film cannot be formed.

[0021] It should be noted that during the entire process of the preparation method, from the preparation of the Bi2Se3 film to the end of the in-situ annealing treatment, the quartz tube is kept sealed to avoid air contact and keep the atmosphere unchanged, thereby ensuring that the composition of the bismuth selenide film does not change.

[0022] The invention discloses an application of a bismuth selenide film with adjustable defect concentration in a photoelectric synaptic device. The bismuth selenide film with adjustable defect concentration is used as a substrate, a metal electrode is deposited on the substrate, and a metal-semiconductor-metal (MSM) photoelectric synaptic device is obtained.

[0023] Furthermore, electron beam evaporation was used to maintain the pressure in the chamber at 4.5×10 -4 Pa or less, with an electron beam current of 30 to 50, a metal electrode is deposited on the substrate.

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

[0025] Preferably, in the above method, the materials and atmosphere used are analytically pure.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. The present invention utilizes chemical vapor deposition supplemented by in-situ heat treatment to prepare a bismuth selenide film with adjustable defect concentration; chemical vapor deposition is an excellent method for preparing a bismuth selenide film, and in-situ heat treatment can effectively regulate the escape of selenium atoms in the bismuth selenide film; the prepared bismuth selenide film has good crystal quality, few grain boundaries, high purity, thin thickness, low roughness, and has a photoelectric response that ordinary bismuth selenide films do not have; using this material, a two-dimensional photoelectric synapse device with obvious photoelectric synapse behavior, simple preparation method and low cost is prepared.

[0028] 2. As a two-dimensional material, bismuth selenide has the advantages of high mobility, adjustable energy band 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 have.

[0029] 3. The bismuth selenide thin film photoelectric synaptic device prepared by the present invention is an MSM structure, which has a simple structure and has integration potential; the photoelectric response of the Bi2Se3 thin film photoelectric synaptic device of the present invention has obvious basic synaptic behaviors such as long-term potentiation (LTP), short-term potentiation (STP), and pulse enhancement (PPF) similar to biological synapses, and can be applied to the field of artificial intelligence. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

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

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

[0035] Figure 6 The PPF behavior of the bismuth selenide thin film optoelectronic synapse device with adjustable defect concentration prepared in Example 1 of the present invention;

[0036] Figure 7 IV curves of bismuth selenide films with adjustable defect concentration prepared in Examples 1-5 of the present invention and Comparative Example 1. DETAILED DESCRIPTION

[0037] The technical solution of the present invention will be clearly and completely described below in conjunction with the drawings and embodiments. Obviously, the described embodiments are only part of the embodiments of the invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0038] Embodiment 1:

[0039] A method for preparing a bismuth selenide film with adjustable defect concentration and its application in a photoelectric synapse device, comprising the following steps:

[0040] (1) 0.2 g of bismuth selenide powder was used as a precursor and placed in the center of a tube furnace. F-Mica was used as a substrate and placed downstream of the bismuth selenide powder. The quartz tube was sealed and the pressure in the tube was pumped down to below 1 Pa using a vacuum pump.

[0041] (2) Pass 200 sccm of argon gas to clean the quartz tube for ten minutes, adjust the argon flow rate to 8 sccm, and adjust the exhaust valve so that the pressure in the tube remains at 40 Pa;

[0042] (3) Heating in a tubular furnace to make the precursor temperature reach 500°C and the substrate temperature reach 300°C, keeping the temperature for one minute, and then cooling naturally;

[0043] (4) After the temperature of the precursor is naturally cooled to 200°C, the quartz tube is kept closed, the tube furnace is slid so that the deposited Bi2Se3 film is located in the center of the tube furnace, the argon gas flow rate and the pressure in the tube are kept constant, and the Bi2Se3 film is in-situ annealed at 350°C for 30 minutes to obtain a bismuth selenide film with adjustable defect concentration;

[0044] (5) Using electron beam evaporation method, the pressure in the chamber is maintained at 4.5×10 -4 Pa or less, the electron beam current is 40, and a silver electrode is deposited on the Bi2Se3 film prepared as above to obtain a Bi2Se3 thin film optoelectronic synapse device.

[0045] The prepared samples were characterized by AFM, Raman and XPS. Figure 1-3 The thickness of the prepared bismuth selenide film is 7.13nm, and the roughness Ra is 1.03nm. It is thin and has a small roughness. Figure 1 It can be seen from the figure that the bismuth selenide film is composed of a large number of triangular and hexagonal crystals. Triangles and hexagons are the standard shapes of bismuth selenide nanosheets, indicating that the prepared bismuth selenide film has good quality. Figure 2 The three Raman vibration peaks corresponding to bismuth selenide can be clearly observed, with small half-peak width and obvious characteristic peaks, indicating good crystallinity and high purity of bismuth selenide film. Figure 3 The characteristic peaks corresponding to the selenium-bismuth bond of selenium and bismuth can be clearly observed, indicating that the purity of bismuth selenide is high. Figure 3 Obvious characteristic peaks corresponding to bismuth oxygen bonds can also be observed in the bismuth element. The bismuth atoms are located inside the five molecular layers of bismuth selenide. Therefore, the formation of bismuth oxygen bonds is inseparable from selenium vacancies, indicating that the prepared bismuth selenide film has a large number of selenium vacancies. The photoelectric synaptic behavior of the sample is detailed in the attached Figure 4-6 , at an intensity of 5.2mW / cm 2 Under the light of wavelength 450nm, the sample showed obvious STP, LTP and PPF behaviors. The feasibility of bismuth selenide thin film optoelectronic synaptic device was confirmed. The IV curve test of the sample was carried out, see the attached Figure 7 .

[0046] In order to confirm the modulation effect of in-situ heat treatment on the selenium vacancy defect concentration of bismuth selenide film, five control experiments were also conducted, see Examples 2-6 for details.

[0047] Comparative Example 1:

[0048] A method for preparing a bismuth selenide film and its application in a photoelectric synapse device, comprising the following steps:

[0049] (1) 0.2 g of bismuth selenide powder was used as a precursor and placed in the center of a tube furnace. F-Mica was used as a substrate and placed downstream of the bismuth selenide powder. The quartz tube was sealed and the pressure in the tube was pumped down to below 1 Pa using a vacuum pump.

[0050] (2) Pass 200 sccm of argon gas to clean the quartz tube for ten minutes, adjust the argon flow rate to 8 sccm, and adjust the exhaust valve so that the pressure in the tube remains at 40 Pa;

[0051] (3) heating in a tubular furnace to make the precursor temperature reach 500° C. and the substrate temperature reach 300° C., maintaining the temperature for one minute, and cooling naturally to obtain a bismuth selenide film;

[0052] (4) Using electron beam evaporation method, the pressure in the chamber is maintained at 4.5×10 -4 Pa or less, the electron beam current is 40, and a silver electrode is deposited on the Bi2Se3 film prepared as above to obtain a Bi2Se3 thin film optoelectronic synapse device.

[0053] (5) The IV curve test was carried out on the samples. See the attached Figure 7 .

[0054] Embodiment 2:

[0055] A method for preparing a bismuth selenide film with adjustable defect concentration and its application in a photoelectric synapse device, comprising the following steps:

[0056] (1) 0.2 g of bismuth selenide powder was used as a precursor and placed in the center of a tube furnace. F-Mica was used as a substrate and placed downstream of the bismuth selenide powder. The quartz tube was sealed and the pressure in the tube was pumped down to below 1 Pa using a vacuum pump.

[0057] (2) Pass 200 sccm of argon gas to clean the quartz tube for ten minutes, adjust the argon flow rate to 8 sccm, and adjust the exhaust valve so that the pressure in the tube remains at 40 Pa;

[0058] (3) Heating in a tubular furnace to make the precursor temperature reach 500°C and the substrate temperature reach 300°C, keeping the temperature for one minute, and then cooling naturally;

[0059] (4) After the temperature of the precursor is naturally cooled to 200°C, the quartz tube is kept closed, the tube furnace is slid so that the deposited Bi2Se3 film is located in the center of the tube furnace, the argon gas flow rate and the pressure in the tube are kept constant, and the Bi2Se3 film is in-situ annealed at 260°C for 30 minutes to obtain a bismuth selenide film with adjustable defect concentration;

[0060] (5) Using electron beam evaporation method, the pressure in the chamber is maintained at 4.5×10 -4 Pa or less, the electron beam current is 40, and a silver electrode is deposited on the Bi2Se3 film prepared as above to obtain a Bi2Se3 thin film optoelectronic synapse device.

[0061] (6) The IV curve test was carried out on the samples. See the attached Figure 7 .

[0062] Embodiment 3:

[0063] A method for preparing a bismuth selenide film with adjustable defect concentration and its application in a photoelectric synapse device, comprising the following steps:

[0064] (1) 0.2 g of bismuth selenide powder was used as a precursor and placed in the center of a tube furnace. F-Mica was used as a substrate and placed downstream of the bismuth selenide powder. The quartz tube was sealed and the pressure in the tube was pumped down to below 1 Pa using a vacuum pump.

[0065] (2) Pass 200 sccm of argon gas to clean the quartz tube for ten minutes, adjust the argon flow rate to 8 sccm, and adjust the exhaust valve so that the pressure in the tube remains at 40 Pa;

[0066] (3) Heating in a tubular furnace to make the precursor temperature reach 500°C and the substrate temperature reach 300°C, keeping the temperature for one minute, and then cooling naturally;

[0067] (4) After the temperature of the precursor is naturally cooled to 200°C, the quartz tube is kept closed, the tube furnace is slid so that the deposited Bi2Se3 film is located in the center of the tube furnace, the argon gas flow rate and the pressure in the tube are kept constant, and the Bi2Se3 film is in-situ annealed at 290°C for 30 minutes to obtain a bismuth selenide film with adjustable defect concentration;

[0068] (5) Using electron beam evaporation method, the pressure in the chamber is maintained at 4.5×10 -4 Pa or less, the electron beam current is 40, and a silver electrode is deposited on the Bi2Se3 film prepared as above to obtain a Bi2Se3 thin film optoelectronic synapse device.

[0069] (6) The IV curve test was carried out on the samples. See the attached Figure 7 .

[0070] Embodiment 4:

[0071] A method for preparing a bismuth selenide film with adjustable defect concentration and its application in a photoelectric synapse device, comprising the following steps:

[0072] (1) 0.2 g of bismuth selenide powder was used as a precursor and placed in the center of a tube furnace. F-Mica was used as a substrate and placed downstream of the bismuth selenide powder. The quartz tube was sealed and the pressure in the tube was pumped down to below 1 Pa using a vacuum pump.

[0073] (2) Pass 200 sccm of argon gas to clean the quartz tube for ten minutes, adjust the argon flow rate to 8 sccm, and adjust the exhaust valve so that the pressure in the tube remains at 40 Pa;

[0074] (3) Heating in a tubular furnace to make the precursor temperature reach 500°C and the substrate temperature reach 300°C, keeping the temperature for one minute, and then cooling naturally;

[0075] (4) After the temperature of the precursor is naturally cooled to 200°C, the tube furnace is kept closed, and the tube furnace is slid so that the deposited Bi2Se3 film is located in the center of the tube furnace. The argon gas flow rate and the pressure in the tube are kept constant, and the Bi2Se3 film is in-situ annealed at 320°C for 30 minutes to obtain a bismuth selenide film with adjustable defect concentration;

[0076] (5) Using electron beam evaporation method, the pressure in the chamber is maintained at 4.5×10 -4 Pa or less, the electron beam current is 40, and a silver electrode is deposited on the Bi2Se3 film prepared as above to obtain a Bi2Se3 thin film optoelectronic synapse device.

[0077] (6) The IV curve test was carried out on the samples. See the attached Figure 7 .

[0078] Embodiment 5:

[0079] A method for preparing a bismuth selenide film with adjustable defect concentration and its application in a photoelectric synapse device, comprising the following steps:

[0080] (1) 0.2 g of bismuth selenide powder was used as a precursor and placed in the center of a tube furnace. F-Mica was used as a substrate and placed downstream of the bismuth selenide powder. The quartz tube was sealed and the pressure in the tube was pumped down to below 1 Pa using a vacuum pump.

[0081] (2) Pass 200 sccm of argon gas to clean the quartz tube for ten minutes, adjust the argon flow rate to 8 sccm, and adjust the exhaust valve so that the pressure in the tube remains at 40 Pa;

[0082] (3) Heating in a tubular furnace to make the precursor temperature reach 500°C and the substrate temperature reach 300°C, keeping the temperature for one minute, and then cooling naturally;

[0083] (4) After the temperature of the precursor is naturally cooled to 200°C, the quartz tube is kept closed, the tube furnace is slid so that the deposited Bi2Se3 film is located in the center of the tube furnace, the argon gas flow rate and the pressure in the tube are kept constant, and the Bi2Se3 film is in-situ annealed at 380°C for 30 minutes to obtain a bismuth selenide film with adjustable defect concentration;

[0084] (5) Using electron beam evaporation method, the pressure in the chamber is maintained at 4.5×10 -4 Pa or less, the electron beam current is 40, and a silver electrode is deposited on the Bi2Se3 film prepared as above to obtain a Bi2Se3 thin film optoelectronic synapse device.

[0085] The IV curve of the sample was tested, see the attached Figure 7 .

[0086] When only the annealing temperature is changed, the IV curve slope (conductance) of the prepared bismuth selenide film changes significantly, and the surface resistance also changes significantly. Conductance and resistance are closely related to the carrier concentration of the device. For n-type bismuth selenide, the carriers are mainly provided by selenium vacancies. Therefore, the changes in conductivity and resistance imply the 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] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A method for preparing a bismuth selenide film with adjustable defect concentration, characterized in that: The Bi2Se3 thin film is prepared by chemical vapor deposition, and the prepared Bi2Se3 thin film is subjected to secondary treatment by in-situ heat treatment to avoid air contact and maintain the original atmosphere to obtain a bismuth selenide thin film with adjustable defect concentration.

2. The preparation method according to claim 1, characterized in that: The specific steps are as follows: Step 1: Use bismuth selenide powder as a precursor and place it in the center of a tube furnace. Use a fluorine crystal mica sheet as a substrate and place it downstream of the bismuth selenide powder. Seal the quartz tube and turn on the vacuum pump to extract the air in the tube. Step 2: introduce argon gas to clean the quartz tube, adjust the argon gas to a suitable flow rate, and adjust the exhaust valve so that the pressure in the tube is suitable for the growth of bismuth selenide film; Step 3: Heat the precursor in a tubular furnace to 480-520°C, keep it warm for a certain period of time, and then cool it down naturally; Step 4: After the deposition is completed, keep the quartz tube closed, slide the tubular furnace so that the deposited Bi2Se3 film is located in the center of the tubular furnace, keep the argon gas flow rate and the pressure in the tube unchanged, and perform in-situ annealing on the Bi2Se3 film to obtain a bismuth selenide film with adjustable defect concentration.

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

4. The preparation method according to claim 2, characterized in that: In step 2, the argon gas flow rate used for the growth of the bismuth selenide film is 6-10 sccm, and the pressure in the tube is maintained at 30-50 Pa.

5. The preparation method according to claim 2, characterized in that: In step 3, the insulation time is 1 to 5 minutes.

6. The preparation method according to claim 2, characterized in that: In step 4, the temperature of the in-situ heat treatment is 260-380°C.

7. Application of a bismuth selenide film with adjustable defect concentration in a photoelectric synapse device, characterized in that: A bismuth selenide film with adjustable defect concentration is used as a substrate, and a metal electrode is deposited on the substrate to obtain a metal-semiconductor-metal optoelectronic synapse device.

8. The use according to claim 7, characterized in that: The metal electrode is deposited on the substrate by electron beam evaporation with a suitable electron beam current.

9. The use according to claim 7 or 8, characterized in that: The metal electrode is a silver electrode.

10. The use according to claim 8, characterized in that: The metal electrode is evaporated using an electron beam current of 30 to 50.

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