Molybdenum disulfide-polytetrafluoroethylene composite photodetector and its preparation method

Abstract

The present invention belongs to the field of photodetectors. Aiming at the disadvantage of low optical responsivity of existing molybdenum disulfide photodetectors, the present invention provides a preparation method of a photodetector composed of polytetrafluoroethylene and molybdenum disulfide. Molybdenum disulfide is grown on an insulating silicon wafer by chemical vapor deposition to prepare a molybdenum disulfide photodetector. A polytetrafluoroethylene film is prepared by spin coating, and the polytetrafluoroethylene film is polarized by corona. Finally, molybdenum disulfide and polytetrafluoroethylene are composited by wet transfer using a polymethyl methacrylate film. The present invention significantly improves the optical responsivity of the molybdenum disulfide photodetector. The prepared photodetector has good performance stability, simple operation and low requirements for preparation conditions.

Description

Technical Field

[0001] The present invention relates to the field of photodetectors, and particularly to a molybdenum disulfide-polytetrafluoroethylene composite photodetector and a preparation method thereof. Background Art

[0002] Two-dimensional materials, full name two-dimensional atomic crystal materials, can have an infinitely extendable size on the same plane with a huge surface area. At the same time, because the carrier migration and heat diffusion are both restricted within the two-dimensional plane, this material exhibits many peculiar properties. The prominent features are single atomic layer, high carrier mobility, linear energy spectrum, high strength, etc. Its adjustable bandgap characteristic is widely used in fields such as field effect transistors, optoelectronic devices, and thermoelectric devices. It is considered a revolutionary material in the future.

[0003] Among them, two-dimensional transition metal dichalcogenides have shown great potential as next-generation compound semiconductors. They combine various periodic table elements, various crystal and phase structures, nanometer thickness, and continuous rotational stacking order. As one of the earliest studied semiconductors, molybdenum disulfide photodetectors have long been maturely applied in a wide range of fields and have become one of the core device categories in modern industry and science. Monolayer molybdenum disulfide, as a typical two-dimensional semiconductor material, exhibits very excellent performance in the field of photodetection due to its direct bandgap with adjustable bandgap width, single molecular layer thickness, and environmental stability.

[0004] However, due to the low light absorption efficiency of thin layers and the existence of quenching effects, photodetectors prepared from pure molybdenum disulfide materials have low photoresponsivity, which hinders their further development in the optoelectronic field. Regulating the optoelectronic properties of molybdenum disulfide through physical and chemical methods not only can enrich the functions of existing devices, but also has important scientific significance for constructing new micro-nano optoelectronic devices and exploring new physical effects of molybdenum disulfide.

[0005] Molybdenum disulfide exhibits a strong photoluminescence effect in the visible light band. However, due to the nanometer-level thickness of monolayer molybdenum disulfide, it can only absorb 5 - 10% of visible light, and photodetectors prepared from monolayer molybdenum disulfide materials have low photoresponsivity, which limits its wide application in high-performance optoelectronic devices. Therefore, it is very necessary to study how to improve the photoresponsivity of molybdenum disulfide photodetectors. Summary of the Invention

[0006] In order to improve the photoresponsivity of molybdenum disulfide photodetectors, the present invention discloses a photodetector composed of a composite of molybdenum disulfide and polytetrafluoroethylene thin film and a preparation method thereof.

[0007] The preparation method of the molybdenum disulfide-polytetrafluoroethylene composite photodetector includes the following steps:

[0008] (1) Prepare molybdenum disulfide thin film;

[0009] (2) Prepare polytetrafluoroethylene thin film by spin coating;

[0010] (3) Polarize the polytetrafluoroethylene thin film by corona to make it store charges for a long time;

[0011] (4) Compound the prepared molybdenum disulfide thin film with the polytetrafluoroethylene thin film to obtain a molybdenum disulfide-polytetrafluoroethylene composite photodetector.

[0012] Preferably, the preparation method of the molybdenum disulfide thin film is as follows:

[0013] Use chemical vapor deposition (CVD) method to grow molybdenum disulfide thin film on the silicon dioxide layer of the first insulating silicon wafer.

[0014] Preferably, the process of the chemical vapor deposition (CVD) method is as follows: Place molybdenum trioxide powder downstream of the quartz tube of the tube furnace, place sulfur powder upstream of the quartz tube of the tube furnace, and increase the temperature of molybdenum trioxide to 900 °C at a heating rate of 50 °C·min -1 and keep it for 2 min. When the temperature rises to 600 °C, increase the temperature of sulfur powder to 180 °C at a rate of 30 °C·min -1 During the reaction, introduce argon as the carrier gas; after the reaction, naturally cool the tube heating furnace to room temperature.

[0015] Preferably, the step (2) includes the following steps: Place the second insulating silicon wafer on the spin coater, drop 60 wt% polytetrafluoroethylene dispersion liquid on its surface, set the spin coating speed to be first low speed 500 r·min -1 , then high speed 2000 r·min -1 , and then put it into a vacuum drying oven at 100 °C for drying for 2 hours to obtain polytetrafluoroethylene thin film.

[0016] Preferably, the specific process of the corona polarization in the step (3) is as follows:

[0017] Place the second insulating silicon wafer with the polytetrafluoroethylene thin film on the polarization platform, supply power by a high-voltage power supply, and perform corona discharge through a discharge needle clamped by an iron stand. Lay copper foil paper on the bakelite as the grounding electrode. Adjust the clamping bracket of the iron stand to make the tip of the discharge needle 2-3 cm away from the polytetrafluoroethylene thin film, and slowly increase the output voltage of the high-voltage power supply to charge the polytetrafluoroethylene thin film, and the charging voltage is 2 kv - 6 kv.

[0018] Preferably, the specific process of the step (4) is as follows:

[0019] Transfer the metal electrode to the molybdenum disulfide thin film prepared in the step (1);

[0020] Place the first silicon-on-insulator (SOI) wafer carrying the molybdenum disulfide thin film on a spin coater, spin-coat a polymethyl methacrylate (PMMA) solution on its surface, and then heat it to form a PMMA film.

[0021] Seal the edge of the PMMA film on the first SOI wafer with tape, and then place it in a sodium hydroxide solution to etch away the silicon dioxide layer.

[0022] Tear off the tape together with the PMMA thin film adhered to the tape from the first SOI wafer and place it in deionized water for cleaning.

[0023] Transfer the PMMA thin film to the second SOI wafer with the polarized polytetrafluoroethylene (PTFE) thin film prepared in step (3), heat to remove moisture, and then place it in an acetone solution for fumigation to remove PMMA, obtaining a PTFE thin film and molybdenum disulfide thin film composite photodetector.

[0024] Preferably, silver paste is dotted on the metal electrodes of the obtained PTFE thin film and molybdenum disulfide thin film composite photodetector.

[0025] The present invention also provides a molybdenum disulfide-polytetrafluoroethylene composite photodetector, which is composed of three layers: a metal electrode, a molybdenum disulfide film, and an electret film. Among them, the electret film is located at the bottom layer.

[0026] Preferably, the electret film is a polarized polytetrafluoroethylene thin film.

[0027] The principle of the present invention:

[0028] Polytetrafluoroethylene is one of the substrates with negative electricity, and it shows great advantages in chemical stability and flexibility. The PTFE thin film has a low surface energy. When the ion beam generated by corona discharge bombards the PTFE thin film, the charges of some ions will be deposited in the PTFE material, thereby realizing charge storage. The polarized PTFE thin film is then compounded with molybdenum disulfide, which can regulate the electrical transport properties of molybdenum disulfide. And there are a large number of sulfur vacancy defects in as-grown molybdenum disulfide, forming deep energy level traps for excitons, increasing the collision and recombination rate of excitons in the material, resulting in a short lifetime of molybdenum disulfide on silicon dioxide. In contrast, PTFE can passivate defects by rearranging sulfur atoms on the surface to reduce existing sulfur vacancies and eliminate the influence of defect-mediated non-radiative recombination, thereby prolonging the lifetime of molybdenum disulfide. At the same time, the interfacial formation energy between molybdenum disulfide and PTFE can reduce the exciton binding energy, which is beneficial to electron-hole separation and prolongs the fluorescence lifetime, improving the photoelectric sensitivity of molybdenum disulfide.

[0029] The present invention constructs a new structure by introducing the composite of polytetrafluoroethylene and molybdenum disulfide to improve the light responsivity of the molybdenum disulfide photodetector. By using the regulation of polytetrafluoroethylene after corona polarization on molybdenum disulfide, the overall charge transport of molybdenum disulfide is improved, thereby enhancing the responsivity.

[0030] Advantages of the present invention: A new structure is constructed by using the composite of polytetrafluoroethylene and molybdenum disulfide, which is simple to operate and has low requirements for preparation conditions; through the interfacial regulation of polytetrafluoroethylene on molybdenum disulfide, the light responsivity of the molybdenum disulfide photodetector is significantly improved, and the light responsivity can reach 180R (A·W -1 ); The storage of charge by polytetrafluoroethylene is very stable, and the performance of the photodetector prepared by compounding with molybdenum disulfide can be maintained for a long time. Description of the Drawings

[0031] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the specific embodiments or the prior art. Subsequently, some specific embodiments of the present invention will be described in detail with reference to the drawings in an exemplary rather than restrictive manner. The same reference numerals in the drawings denote the same or similar components or parts. Those skilled in the art should understand that these drawings are not necessarily drawn to scale. In the drawings:

[0032] Figure 1 is a schematic structural diagram of a photodetector composed of a composite of molybdenum disulfide and polytetrafluoroethylene film of the present invention. Among them, 1 is an insulating substrate, 2 is a polytetrafluoroethylene film, 3 is a metal electrode, and 4 is a monolayer molybdenum disulfide.

[0033] Figure 2 is a schematic diagram of the corona polarization platform of the polytetrafluoroethylene film.

[0034] Figure 3 is a flowchart of the preparation method of the photodetector composed of a composite of molybdenum disulfide and polytetrafluoroethylene film of the present invention.

[0035] Figure 4 is an optical microscope picture of the composite of molybdenum disulfide and polytetrafluoroethylene film in the embodiment of the present invention (the triangles in the figure are molybdenum disulfide).

[0036] Figure 5 is a scanning electron microscope picture of the composite of molybdenum disulfide and polytetrafluoroethylene film in the embodiment of the present invention, and the triangles in the figure are molybdenum disulfide.

[0037] Figure 6 is a comparison of the light responsivity between the photodetector composed of a composite of molybdenum disulfide and polytetrafluoroethylene film and the photodetector based on molybdenum disulfide film in the embodiment of the present invention. Specific Embodiments

[0038] To make the objectives, technical solutions and advantages of the present application more clearly understood, the present application will be further described in detail below with reference to the accompanying drawings and embodiments. In the present invention, unless otherwise specified, the raw materials and equipment used can be purchased from the market or are commonly used in the art. The methods in the embodiments are conventional methods in the art unless otherwise specified. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0039] Example 1:

[0040] (1) Prepare a monolayer molybdenum disulfide film: Use chemical vapor deposition (CVD) method to grow a two-dimensional molybdenum disulfide film on a silicon dioxide substrate, and the preparation temperature is 550 - 900 °C;

[0041] (2) Prepare a polytetrafluoroethylene film: Spin-coat a polytetrafluoroethylene dispersion on the surface of a silicon wafer, and then place it in a vacuum drying oven for 2 hours to obtain a polytetrafluoroethylene film.

[0042] (3) Corona polarization of the polytetrafluoroethylene film: Place the polytetrafluoroethylene film obtained in step (2) on a polytetrafluoroethylene polarization platform, supply power by a high-voltage power supply, and perform corona discharge through a discharge needle clamped by an iron stand, and slowly increase the output voltage of the high-voltage power supply to charge the polytetrafluoroethylene film.

[0043] (4) Prepare a composite of the polytetrafluoroethylene film and the molybdenum disulfide film and a photodetector: Transfer a metal electrode onto the molybdenum disulfide obtained in step (1), then spin-coat a polymethyl methacrylate solution on the surface of the silicon wafer in step (1), etch away the silicon dioxide in a sodium hydroxide solution, transfer the peeled-off polymethyl methacrylate film onto the polytetrafluoroethylene film obtained in step (3), then fumigate with acetone solution to remove the polymethyl methacrylate, and finally dot silver paste on the metal electrode to prepare a photodetector.

[0044] Example 2: An example of polarizing polytetrafluoroethylene film with a voltage of 2 kV

[0045] See Figure 1 , the structural diagram of a photodetector with a composite of molybdenum disulfide and a polytetrafluoroethylene film, including a molybdenum disulfide layer (4) stacked from top to bottom in sequence, metal electrodes (3) arranged at intervals on the molybdenum disulfide layer, a polytetrafluoroethylene film layer (2), and an insulating dielectric layer (1).

[0046] Figure 2 is the polarization platform of the polytetrafluoroethylene film.

[0047] The process flow is shown in Figure 3 :

[0048] (1) Preparation of two-dimensional molybdenum disulfide film: Using chemical vapor deposition (CVD) method, grow a two-dimensional molybdenum disulfide film on the silicon dioxide layer of the first insulating silicon wafer. Place 5 mg of molybdenum trioxide powder downstream in the quartz tube of the tube furnace, and place 500 mg of sulfur powder upstream in the quartz tube of the tube furnace. Raise the temperature of molybdenum trioxide to 900 °C at a heating rate of 50 °C·min -1 and keep it for 2 min. When the temperature rises to 600 °C, raise the temperature of sulfur powder to 180 °C at a rate of 30 °C·min -1 During the reaction, introduce 80 sccm of argon gas as the carrier gas. After the reaction, naturally cool the tube furnace to room temperature.

[0049] (2) Preparation of polytetrafluoroethylene film: Place a 2 cm * 2 cm second insulating silicon wafer on the spin coater, drop 5 - 8 drops of 60 wt% polytetrafluoroethylene dispersion on its surface, and the spin coating speed is 500 r·min -1 at low speed and 2000 r·min -1 at high speed. Then put it into a vacuum drying oven and dry it at 100 °C for 2 hours to obtain a polytetrafluoroethylene film.

[0050] (3) Corona polarization of polytetrafluoroethylene film: Place the second insulating silicon wafer with the polytetrafluoroethylene film on the Figure 2 polytetrafluoroethylene polarization platform, powered by a high-voltage power supply, and perform corona discharge through a discharge needle clamped by an iron stand. Lay copper foil paper on the bakelite as the grounding electrode, and adjust the clamping bracket of the iron stand so that the tip of the discharge needle is 2 - 3 cm away from the polytetrafluoroethylene film. After ensuring that the wiring is correct and the grounding is good, slowly increase the output voltage of the high-voltage power supply to charge the polytetrafluoroethylene film, and the charging voltage is 2 kv - 6 kv for 15 minutes.

[0051] (4) Preparation of the composite of polytetrafluoroethylene film and molybdenum disulfide film and photodetector:

[0052] Transfer the metal electrode to the molybdenum disulfide in step (1):

[0053] Then place the first insulating silicon wafer carrying the molybdenum disulfide film on the spin coater, spin coat poly(methyl methacrylate) solution on its surface, and then heat it to form a poly(methyl methacrylate) film.

[0054] Seal the four sides of the first insulating silicon wafer with tape, and then place it in sodium hydroxide solution for 2 hours. After the silicon dioxide layer on the surface of the silicon wafer is corroded by sodium hydroxide,

[0055] Use tweezers to hold the tape and tear off the tape together with the poly(methyl methacrylate) film adhered to the tape from the first insulating silicon wafer, and place it in deionized water, changing the water every 15 minutes for four times.

[0056] Then transfer the polymethyl methacrylate film to the second insulating silicon wafer with the polarized polytetrafluoroethylene film prepared in step (3), place it on a heating plate and heat for 2 hours to remove moisture, then place it above the acetone solution and heat and fumigate for 1 hour to remove polymethyl methacrylate. Finally, apply silver paste at both electrode points to obtain a photodetector composed of a polytetrafluoroethylene film and a molybdenum disulfide film. For the optical microscope image and scanning electron microscope image, see Figure 4 , Figure 5 , and its photosensitivity is shown in Figure 6 . There is a significant improvement in the photosensitivity compared with that of the molybdenum disulfide film-based photodetector.

[0057] As described above, only some specific embodiments of the present invention are given, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. Preparation method of molybdenum disulfide polytetrafluoroethylene composite photodetector, characterized in that, It includes the following steps: (1) Prepare a molybdenum disulfide thin film; (2) Spin-coat to prepare a polytetrafluoroethylene thin film; (3) Polarize the polytetrafluoroethylene thin film by corona to make it store charges for a long time; (4) Compound the prepared molybdenum disulfide thin film with the polytetrafluoroethylene thin film to obtain a molybdenum disulfide-polytetrafluoroethylene composite photodetector. The molybdenum disulfide-polytetrafluoroethylene composite photodetector includes, from top to bottom, a molybdenum disulfide layer (4), metal electrodes (3) spaced apart from each other on the molybdenum disulfide layer, and a polytetrafluoroethylene thin film layer (2).

2. The preparation method of the molybdenum disulfide polytetrafluoroethylene composite photodetector according to claim 1, characterized in that, The method for preparing the molybdenum disulfide thin film is as follows: Use the chemical vapor deposition (CVD) method to grow a molybdenum disulfide thin film on the silicon dioxide layer of the first insulating silicon wafer.

3. The preparation method of the molybdenum disulfide polytetrafluoroethylene composite photodetector according to claim 2, characterized in that, The process of the chemical vapor deposition (CVD) method is as follows: Take molybdenum trioxide powder and place it downstream in the quartz tube of the tube furnace, and take sulfur powder and place it upstream in the quartz tube of the tube furnace. Increase the temperature of molybdenum trioxide to 900 °C at a heating rate of 50 °C·min -1 , and hold for 2 minutes. When the temperature rises to 600 °C, increase the temperature of sulfur powder to 180 °C at a rate of 30 °C·min -1 . During the reaction, introduce argon as the carrier gas. After the reaction, naturally cool the tube heating furnace to room temperature.

4. The preparation method of the molybdenum disulfide polytetrafluoroethylene composite photodetector according to claim 1, wherein, Step (2) includes the following steps: Place a second insulating silicon wafer on a spin coater, drop a 60 wt% polytetrafluoroethylene dispersion liquid on its surface, and set the spin coating speed to be first low speed of 500 r·min -1 , then high speed of 2000 r·min -1 , and then place it in a vacuum drying oven at 100 °C for drying for 2 hours to obtain a polytetrafluoroethylene film.

5. The preparation method of the molybdenum disulfide polytetrafluoroethylene composite photodetector according to claim 1, characterized in that, The specific process of polarizing the polytetrafluoroethylene thin film by corona in step (3) is as follows: Place the second insulating silicon wafer with the polytetrafluoroethylene thin film on a polarization platform, supply power by a high-voltage power supply, and perform corona discharge through a discharge needle clamped by an iron stand. Lay copper foil paper on the bakelite as a grounding electrode. Adjust the clamping frame of the iron stand to make the tip of the discharge needle 2 - 3 cm away from the polytetrafluoroethylene thin film, and slowly increase the output voltage of the high-voltage power supply to charge the polytetrafluoroethylene thin film. The charging voltage is between 2 kV and 6 kV.

6. The preparation method of the molybdenum disulfide polytetrafluoroethylene composite photodetector according to claim 5, wherein, The specific process of step (4) is as follows: Transfer the metal electrodes to the molybdenum disulfide thin film prepared in step (1); Place the first insulating silicon wafer carrying the molybdenum disulfide thin film on a spin coater, spin-coat a polymethyl methacrylate solution on its surface, and then heat to form a polymethyl methacrylate film; Seal the edge of the polymethyl methacrylate film on the first insulating silicon wafer with tape, and then place it in a sodium hydroxide solution to etch away the silicon dioxide layer; Tear off the tape together with the polymethyl methacrylate thin film adhered to the tape from the first insulating silicon wafer, and place it in deionized water for cleaning; Transfer the polymethyl methacrylate thin film to the second insulating silicon wafer with the polarized polytetrafluoroethylene thin film prepared in step (3), heat to remove moisture, and then place it in an acetone solution for fumigation to remove the polymethyl methacrylate, obtaining a molybdenum disulfide-polytetrafluoroethylene composite photodetector.

7. The preparation method of the molybdenum disulfide polytetrafluoroethylene composite photodetector according to claim 6, characterized in that, Dot silver paste on the metal electrodes of the obtained molybdenum disulfide-polytetrafluoroethylene composite photodetector.

8. A molybdenum disulfide polytetrafluoroethylene composite photodetector, characterized in that, It is composed of a three-layer composite of a metal electrode, a molybdenum disulfide film, and an electret film. Among them, the electret film is the polarized polytetrafluoroethylene thin film; the molybdenum disulfide-polytetrafluoroethylene composite photodetector includes, from top to bottom, a molybdenum disulfide film, metal electrodes spaced apart from each other on the molybdenum disulfide film, and a polytetrafluoroethylene thin film.

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