A sandwich-type wide-spectrum optical detector and its preparation method

Abstract

The present application relates to the field of semiconductor devices, and specifically provides a sandwich-type wide-spectrum photodetector and a preparation method thereof. The photodetector includes a bottom electrode layer, a photosensitive layer, and a top electrode layer. The photosensitive layer is arranged on the bottom electrode layer, and the top electrode layer is arranged on the side of the photosensitive layer away from the bottom electrode layer. From the top electrode layer to the bottom electrode layer, the photosensitive layer includes a first tungsten ditelluride layer, a molybdenum disulfide nanotube layer, and a second tungsten ditelluride layer arranged in sequence. The preparation method includes the following steps: step 1, depositing a bottom electrode layer on a porous alumina substrate; step 2, depositing a second tungsten ditelluride layer on the bottom electrode layer; step 3, depositing a molybdenum disulfide nanotube layer on the second tungsten ditelluride layer; step 4, depositing a first tungsten ditelluride layer on the molybdenum disulfide nanotube layer; step 5, preparing a top electrode layer on the first tungsten ditelluride layer. In the sandwich structure of the present application, the absorption spectra of tungsten ditelluride and molybdenum disulfide are complementary, so that the response band of the photosensitive layer of the present application is extended to 400nm-2µm.

Description

Technical Field

[0001] The present application relates to the field of semiconductor devices, and in particular to a sandwich-type wide-spectrum optical detector and a method for preparing the same. Background Art

[0002] Semiconductor materials refer to materials with electrical conductivity between conductors and insulators, and their electrical conductivity can be adjusted by external conditions such as doping, temperature, and light. Semiconductor materials have excellent electronic and optoelectronic properties and can achieve high-frequency, high-power, and efficient photoelectric conversion. Therefore, semiconductor materials are widely used in photodetectors.

[0003] As a typical semiconductor, tungsten ditelluride has high carrier mobility, which can reach hundreds to thousands of cm² / V·s, making tungsten ditelluride photodetectors perform well in applications that require high response speed, such as high-speed optical communications and fast optical sensing, see the document entitled "Electronic properties of candidate type-II Weyl semimetalWTe2. A review perspective" (Electron. Struct. 1 (2019) 014003). Tungsten ditelluride has semi-metallic properties, and its band structure shows unique topological properties, with topologically protected surface states and edge states, and a linear dispersion relation near its Fermi surface. These topological properties can lead to high photoelectric conversion efficiency and low noise level, making it advantageous in photodetection applications. However, tungsten ditelluride has strong absorption and response in the infrared band (800 nm to 2 µm), and its absorption in the visible light band is limited, which limits the application of tungsten ditelluride in photodetectors in the visible light band. Summary of the invention

[0004] The purpose of the present invention is to provide a sandwich-type wide-spectrum photodetector and a method for preparing the same in view of the above-mentioned deficiencies in the prior art, so as to solve the problem in the prior art that tungsten ditelluride has limited absorption in the visible light band, resulting in its application in photodetectors in the visible light band being limited.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0006] The present application provides a sandwich-type wide-spectrum photodetector, which includes a bottom electrode layer, a photosensitive layer, and a top electrode layer. The photosensitive layer is arranged on the bottom electrode layer, and the top electrode layer is arranged on the side of the photosensitive layer away from the bottom electrode layer. From the top electrode layer to the bottom electrode layer, the photosensitive layer includes a first tungsten ditelluride layer, a molybdenum disulfide nanotube layer, and a second tungsten ditelluride layer arranged in sequence. When in use, a bias is applied between the bottom electrode layer and the top electrode layer, the bottom electrode layer is connected to the negative electrode, and the top electrode layer is connected to the positive electrode. The applied voltage is 1-10V, so that the photosensitive layer is in a uniform electric field, and the direction of the electric field is from the top electrode layer to the bottom electrode layer, so as to promote the separation of photogenerated electrons and photogenerated holes and reduce the recombination probability of carriers. The top electrode layer is a transparent structure. The light field is transmitted to the top electrode layer and irradiated on the photosensitive layer. The photosensitive layer absorbs photons and generates photogenerated electrons and photogenerated holes inside it. Under the action of the external electric field, the photogenerated electrons and photogenerated holes separate and move to the two electrode layers respectively. The photogenerated electrons move to the top electrode layer, and the photogenerated holes move to the bottom electrode layer. The directional movement of the photogenerated carriers forms an electrical signal. The change of light will cause the change of the electrical signal, thereby realizing light detection. In addition, the external electric field can accelerate the transmission of carriers, so that the photogenerated carriers reach the electrode faster, thereby improving the photoelectric response speed.

[0007] The photosensitive layer of the sandwich structure in this application and the nanotube structure of molybdenum disulfide improve the ability of light absorption in terms of absorption wavelength range and absorption light intensity; thereby improving the response intensity of the photodetector under a wide spectrum. Specifically, on the one hand, the tungsten ditelluride material has a strong light absorption ability in the near-infrared spectral range (800 nm to 2 µm), and the molybdenum disulfide material has good light absorption characteristics in the visible light and near-infrared range (400 nm to 1 µm); the response band of the photosensitive layer formed by the two is from visible light (400 nm) to near-infrared (2 µm); that is, the light absorption spectra of tungsten ditelluride and molybdenum disulfide are complementary, and molybdenum disulfide can make up for the problem of insufficient absorption of tungsten ditelluride in the visible light range, thereby expanding the overall light absorption range. By combining these two materials, light response to a wider spectral range is achieved. On the other hand, the limiting effect of the sandwich structure on the light field and the effective capture of the light field by the molybdenum disulfide nanotubes further improve the light absorption efficiency. Specifically, the molybdenum disulfide nanotubes have a high light absorption efficiency, especially in the visible light and near-infrared spectral range. This allows it to effectively capture more photons and enhance the overall light absorption capacity. Structurally, the nanotube structure provides a large amount of surface area. The nanotube structure can guide photons into the tube and reflect multiple times on the tube wall, extending the path of light and increasing the scattering and multiple reflection paths of light. In other words, the MoS2 nanotube layer increases the path length and absorption probability of photon capture, further improving the light absorption efficiency. At the same time, the incident light is confined between the first tungsten ditelluride layer and the second tungsten ditelluride layer. In the sandwich structure, the light reflects back and forth between the two tungsten ditelluride layers, causing the photons to pass through the MoS2 nanotube layer multiple times, increasing the interaction time between light and the material and increasing light absorption.

[0008] A heterojunction is formed at the interface of tungsten ditelluride and molybdenum disulfide nanotubes. The formation of a heterojunction helps to separate and transmit photogenerated electrons and photogenerated holes, thereby improving the response speed of light detection and having a high sensitivity. Specifically, at the interface of tungsten ditelluride and molybdenum disulfide nanotube layers, due to the different energy band structures of the two materials, the energy levels of electrons and holes at the interface will be rearranged to form a heterojunction. At the heterojunction interface, a built-in electric field is formed due to the redistribution of electrons and holes. The built-in electric field exerts opposite forces on photogenerated electrons and photogenerated holes, effectively separating the photogenerated electrons and holes, reducing their recombination probability, and more incident photons can be converted into electrical signals, thereby improving the responsiveness of the photodetector. The built-in electric field not only helps to separate carriers, but also promotes their transmission. Driven by the built-in electric field, electrons and holes can quickly move to the corresponding electrodes to form a photocurrent. This improves the carrier mobility and photoelectric conversion efficiency. The built-in electric field enhances the separation and transmission of carriers, resulting in a higher photogenerated current. This enables the photodetector to generate a strong electrical signal even under low light intensity conditions, thereby improving the sensitivity of the device.

[0009] Furthermore, the thickness of the first tungsten ditelluride layer and the second tungsten ditelluride layer is 10-50nm. In this way, the thickness of 10-50nm can ensure that most of the incident near-infrared light is absorbed and generate enough photogenerated carriers; at the same time, the carrier transmission path is short, which reduces the recombination probability of photogenerated electrons and photogenerated holes and improves the photoelectric conversion efficiency; it also has a higher mobility, generates a higher photocurrent, increases the output signal of the detector, and thus improves the sensitivity.

[0010] Furthermore, the MoS2 nanotube layer is a single-layer nanotube. In this way, the single-layer MoS2 nanotube has a high light absorption coefficient, can effectively absorb incident light, generate a higher density of photogenerated carriers, and improve light absorption efficiency. It also has a high carrier mobility, which helps to improve photoelectric conversion efficiency and response speed. The interface quality between the single-layer MoS2 nanotube and the tungsten ditelluride layer is high, and the interface defects are relatively few, which is conducive to the efficient separation and transmission of carriers.

[0011] Furthermore, the material of the top electrode layer is graphene, and the material of the bottom electrode layer is metallic molybdenum. The transmittance of graphene reaches more than 97%, which reduces the loss of light in the top electrode layer, enables the light to be measured to irradiate the photosensitive layer through the top electrode layer, increases the absorption of light by the photosensitive layer, and maximizes the light absorption and photoelectric conversion efficiency. As an electrode, graphene has extremely high conductivity, ensuring efficient collection and transmission of carriers. Metallic molybdenum has good electrical conductivity and can effectively collect and transmit photogenerated carriers; and molybdenum and tungsten ditelluride have good electrical contact characteristics, can form an ohmic contact with low contact resistance, reduce interface resistance, and improve carrier collection efficiency. The deposition technology of metallic molybdenum is mature, such as sputtering and chemical vapor deposition, and is easy to prepare. Metallic molybdenum and graphene also have excellent corrosion resistance and environmental stability, ensuring the stable performance of the device under various environmental conditions.

[0012] Furthermore, the photodetector further includes a substrate, the bottom electrode layer is arranged on the substrate, and the material of the substrate is porous alumina. Porous alumina has the advantages of good insulation, mechanical strength, and light weight; it also has good heat dissipation performance. Specifically, the porous structure allows air circulation and provides a channel for air flow. The air can naturally convect through the porous structure, thereby having a good heat dissipation effect, avoiding a rapid temperature rise when the photodetector is working, so as to keep the detector running at an optimal temperature.

[0013] Furthermore, the aperture on the side of the substrate close to the bottom electrode layer is smaller than the aperture on the side of the substrate away from the bottom electrode layer. The smaller aperture size on the side close to the molybdenum layer provides a smoother and uniform surface, which helps to deposit a uniform and high-quality molybdenum layer thereon, thereby achieving low contact resistance and efficient carrier transport. The gradient arrangement of the aperture size helps to alleviate stress concentration caused by thermal expansion and mechanical stress, and improve the stability and durability of the overall structure. The smaller gap size close to the molybdenum layer helps to effectively conduct heat to the larger gap area away from the molybdenum layer, and the larger aperture size on the side away from the molybdenum layer increases the air circulation channel, so that heat can be more easily discharged from the lower surface of the substrate through natural convection and heat dissipation mechanisms, thereby improving the heat dissipation effect. In addition, the gradient structure design alleviates the thermal stress concentration caused by temperature changes, reduces material fatigue and crack generation, and extends the service life of the device.

[0014] The present application also provides a method for preparing a sandwich-type wide-spectrum light detector, the method comprising the following steps:

[0015] Step 1, depositing a bottom electrode layer on a porous alumina substrate;

[0016] Step 2, depositing a second tungsten ditelluride layer on the bottom electrode layer;

[0017] Step 3, depositing a molybdenum disulfide nanotube layer on the second tungsten ditelluride layer;

[0018] Step 4, depositing a first tungsten ditelluride layer on the molybdenum disulfide nanotube layer;

[0019] Step 5: prepare a top electrode layer on the first tungsten ditelluride layer.

[0020] Furthermore, in step 1, the material of the bottom electrode layer is first obliquely deposited on the porous alumina substrate, and then the material of the bottom electrode layer is vertically deposited. After the deposition is completed, the porous alumina substrate and the bottom electrode layer are obtained.

[0021] Furthermore, the first tungsten ditelluride layer and the second tungsten ditelluride layer are prepared by chemical vapor deposition, and the molybdenum disulfide nanotube layer is prepared by liquid phase stripping, coating or spraying; before preparing the first tungsten ditelluride layer, the deposited molybdenum disulfide nanotube layer is plasma treated or heat treated.

[0022] Furthermore, the solution of the MoS2 nanotube layer is doped with CdS2 quantum dots.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The photosensitive layer in this application adopts a sandwich structure, with a nanotube layer of molybdenum disulfide set between two layers of tungsten ditelluride. Molybdenum disulfide materials have good light absorption characteristics in the visible light and near-infrared range (400 nm to 1 µm), and the light absorption spectra of tungsten ditelluride and molybdenum disulfide are complementary, which expands the response band of the photosensitive layer of this application from visible light (400nm) to near-infrared (2 µm), thereby achieving light response in a wide spectral range.

[0025] At the same time, the sandwich structure's limiting effect on the light field and the effective capture of the light field by MoS2 nanotubes improve the light absorption efficiency. A heterojunction is formed at the interface between tungsten ditelluride and MoS2 nanotubes. The formation of the heterojunction helps separate and transmit photogenerated electrons and photogenerated holes, thereby improving the response speed of light detection and achieving higher sensitivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 A schematic diagram of a sandwich-type wide-spectrum optical detector provided by the present invention;

[0027] Figure 2 A schematic diagram of obliquely depositing metal molybdenum on a substrate in a method for preparing a sandwich-type wide-spectrum optical detector provided by the present invention;

[0028] Figure 3 A schematic diagram of vertically depositing metal molybdenum on a substrate in a method for preparing a sandwich-type wide-spectrum optical detector provided by the present invention.

[0029] Icon: 1-top electrode layer; 2-photosensitive layer; 21-first tungsten ditelluride layer; 22-molybdenum disulfide nanotube layer; 23-second tungsten ditelluride layer; 3-bottom electrode layer. DETAILED DESCRIPTION

[0030] In order to make the implementation process of the present invention clearer, it will be described in detail below with reference to the accompanying drawings.

[0031] Embodiment 1:

[0032] The present invention provides a sandwich-type wide-spectrum optical detector, such as Figure 1As shown, the photodetector includes a bottom electrode layer 3, a photosensitive layer 2, and a top electrode layer 1 from top to bottom. That is, the photosensitive layer 2 is arranged on the bottom electrode layer 3, and the top electrode layer 1 is arranged on the side of the photosensitive layer 2 away from the bottom electrode layer 3. The top electrode layer 1 is a transparent conductive material, and the material of the top electrode layer 1 can be graphene; the bottom electrode layer 3 is a conductive material, which can be metal molybdenum. The geometric centers of the bottom electrode layer 3, the photosensitive layer 2, and the top electrode layer 1 are collinear and perpendicular to the plane where the bottom electrode layer 3 is located. The area of ​​the bottom electrode layer 3 is larger than that of the photosensitive layer 2. The photosensitive layer 2 is arranged in the middle of the bottom electrode layer 3, so that the edge area of ​​the bottom electrode layer 3 can be used to connect wires, etc., and will not affect the structure of the photosensitive layer 2. Light is transmitted through the top electrode layer 1 to the photosensitive layer 2, and the photosensitive layer 2 converts the optical signal into an electrical signal.

[0033] When in use, a bias voltage is applied between the bottom electrode layer 3 and the top electrode layer 1. The bottom electrode layer 3 is connected to the negative electrode, and the top electrode layer 1 is connected to the positive electrode, so that the photosensitive layer 2 is in an electric field. The external electric field promotes the separation of photogenerated electrons and photogenerated holes and reduces the recombination probability of carriers.

[0034] The photosensitive layer 2 includes, from top to bottom, a first tungsten ditelluride layer 21, a molybdenum disulfide nanotube layer 22, and a second tungsten ditelluride layer 23. Preferably, the molybdenum disulfide nanotube layer 22 is a single-layer nanotube. The material of the first tungsten ditelluride layer 21 and the second tungsten ditelluride layer 23 is tungsten ditelluride, which can be a single layer or a multilayer; the thickness of the first tungsten ditelluride layer 21 and the second tungsten ditelluride layer 23 is 10-50nm. The thickness of the first tungsten ditelluride layer 21 and the second tungsten ditelluride layer 23 can be the same or different; the thickness of the first tungsten ditelluride layer 21 and the second tungsten ditelluride layer 23 are the same. During preparation, the deposition time and deposition rate of the two are the same, and there is no need to optimize the corresponding parameters; preferably, the thickness of the first tungsten ditelluride layer 21 is less than the thickness of the second tungsten ditelluride layer 23, the thickness of the first tungsten ditelluride layer 21 is 10-20nm, and the thickness of the second tungsten ditelluride layer 23 is 20-50nm, so that the thinner first tungsten ditelluride layer 21 absorbs less light field, so that more light is irradiated on the molybdenum disulfide nanotube layer 22 on its lower side, so that the absorption of the light field by the molybdenum disulfide nanotube layer 22 is enhanced, maximizing light absorption. The thicker second tungsten ditelluride layer 23 fully absorbs the transmitted light, achieving a balance between light absorption and transmission.

[0035] Preferably, the photodetector of the present application further comprises a substrate, the bottom electrode layer 3 is arranged on the substrate, and the area of ​​the substrate is larger than the area of ​​the bottom electrode layer 3, and the material of the substrate is porous alumina; the thickness of the substrate can be 0.1-2 mm. The aperture of the substrate close to the bottom electrode layer 3 is smaller than the aperture of the substrate away from the bottom electrode layer 3. The size of the smaller aperture on the substrate is 50-200 nm, and the size of the larger aperture is 10-200 μm, which is conducive to the rapid circulation of air and better heat dissipation effect.

[0036] The present application also provides a method for preparing the above-mentioned sandwich-type wide-spectrum light detector, the method comprising the following steps:

[0037] Step 1, depositing a bottom electrode layer 3 on a porous alumina substrate;

[0038] First, clean the porous alumina substrate to ensure that the surface of the porous alumina substrate is clean and free of impurities. Specifically, use isopropanol, ethanol, and deionized water to perform ultrasonic cleaning in sequence to remove surface contaminants; each cleaning ultrasonic time is greater than 10 minutes for thorough cleaning. After cleaning, the porous alumina substrate needs to be dried at a temperature of 50-60°C for a drying time of not less than 1 hour to ensure that the moisture inside the porous structure is completely evaporated. After cleaning, the deposition surface of the substrate is plasma treated or ultraviolet ozone treated. This embodiment uses plasma treatment, and the gas source used is argon gas. The treatment time is 5-10 seconds, which increases the hydroxyl content on the surface of the substrate, improves the adhesion of the substrate, and allows for better bonding between the metal molybdenum and the substrate.

[0039] Next, deposit metal molybdenum on the treated substrate surface; the deposition of metal molybdenum can be carried out by physical vapor deposition, chemical vapor deposition, or sputtering. Since the deposition angle can be better controlled and the tilt angle of the sample can be changed during the deposition process, this embodiment adopts sputtering to prepare the metal molybdenum film. It can be deposited directly vertically, or it can be deposited obliquely first and then vertically. Preferably, the latter method is used for deposition in the embodiment of the present application. Specifically, first, as Figure 2 As shown, the deposition is performed at an angle of 30-60° between the deposition direction and the substrate surface. Before deposition, a glass or PVC template is used to cover the area outside the small hole to ensure that metal molybdenum is not deposited in other areas. Metal molybdenum is deposited only on the sidewalls of the small hole edges. More metal molybdenum is deposited on the sidewalls of the small hole edges of the substrate. At the same tilt angle, 360° deposition is performed around the normal direction of the substrate. In this way, metal molybdenum is deposited around the sidewalls of the small hole. Then, the template is removed, and then Figure 3As shown, vertical deposition is performed in the direction perpendicular to the substrate to form a metal molybdenum film. The time for oblique deposition is one tenth of the vertical deposition time; in this way, no large bulge will be generated during oblique deposition. The thickness of the metal molybdenum is controlled by the deposition time. The material of the bottom electrode layer 3 is first obliquely deposited on the porous alumina substrate, and then the material of the bottom electrode layer 3 is vertically deposited. After the deposition is completed, the porous alumina substrate and the bottom electrode layer 3 are obtained. Metal molybdenum is also deposited on the inner sidewall of the hole. In terms of conductivity, the contact area between the metal molybdenum and the porous alumina substrate is increased. The larger contact area helps to improve the interface contact quality and reduce the contact resistance, thereby improving the carrier transmission efficiency, and also improves the collection and transmission path of carriers, improves the separation efficiency of photogenerated electrons and holes, and thus improves the photoelectric conversion efficiency. In terms of heat dissipation, the deposition of metal molybdenum in the hole increases the heat conduction path, helps to evenly distribute and dissipate heat, reduces the risk of local overheating, and more effectively conducts heat to the porous alumina substrate and dissipates it through it, thereby improving the overall heat dissipation performance. Mechanically, more contact points and a larger contact area form an anchoring effect, which enhances the adhesion of the molybdenum layer to the substrate. At the same time, it disperses the mechanical stress at the interface, reduces stress concentration, and prevents the molybdenum layer from peeling off during subsequent processing or work.

[0040] Step 2, depositing a second tungsten ditelluride layer 23 on the bottom electrode layer 3;

[0041] The second tungsten ditelluride layer 23 is prepared by chemical vapor deposition. Specifically, the structure obtained in step 1 is used as a substrate, which is placed downstream of the precursor powder and deposited thereon. The precursors are tungsten chloride and tellurium powder, the deposition temperature is 650-750°C to ensure that the precursors evaporate into gas at the same time, the deposition time is 1-2h, the carrier gas during the deposition process is argon or nitrogen, and the flow rate of the carrier gas is 90-110 sccm; the thickness of the deposited second tungsten ditelluride layer 23 can be adjusted by adjusting the deposition time and the deposition temperature. It should be noted that since the temperature required for tungsten chloride to evaporate into gas is lower than the temperature required for tellurium powder to evaporate into gas, the tellurium powder is placed in the middle of the quartz heating tube, that is, in the middle of the heating area, and the tungsten chloride is placed upstream of the carrier gas. During deposition, the two are in the gaseous state at the same time, reacting inside the quartz heating tube to generate tungsten ditelluride, which is deposited on the downstream substrate with the carrier gas. The obtained second tungsten ditelluride layer 23 has uniform thickness and good film quality. It interacts with the bottom electrode layer 3 material at the atomic level and is stably combined, which can further optimize the growth conditions of the tungsten ditelluride layer to ensure its crystal quality and surface flatness.

[0042] Step 3, depositing a molybdenum disulfide nanotube layer 22 on the second tungsten ditelluride layer 23;

[0043] The molybdenum disulfide nanotube layer 22 can be prepared by liquid phase stripping, coating or spraying. Specifically, first use the liquid phase stripping method to prepare a molybdenum disulfide nanotube suspension, dissolve the molybdenum disulfide nanotube powder in isopropanol or N-methylpyrrolidone, the concentration can be 1-10 mg / mL, and perform ultrasonic stripping. During the ultrasonic process, a water bath method is used to prevent the solution temperature from being too high. The ultrasonic time is greater than 1h, and the molybdenum disulfide nanotubes are dispersed and stripped from the powder into a single layer or a few layers. Then centrifuge again, centrifuge at a speed of 4000-5000rpm for 15-20min to remove large particle samples, and take the upper clear liquid, which is the molybdenum disulfide nanotube solution. Molybdenum disulfide nanotube powder can be purchased or prepared by a hydrothermal method. The specific preparation method is not repeated here. Then, the molybdenum disulfide nanotube solution is spin-coated, drip-coated or sprayed on the surface of the second tungsten ditelluride 23 layer obtained in step 2. The specific thickness is controlled by the concentration of the solution, the spin coating speed or the spraying speed. Finally, set the temperature to 50°C in a vacuum drying oven and dry for 30 minutes, so that the interlayer bonding is tighter.

[0044] Step 4, depositing a first tungsten ditelluride layer 21 on the molybdenum disulfide nanotube layer 22;

[0045] Chemical vapor deposition is performed again to deposit the first tungsten ditelluride layer 21 on the surface of the sample obtained in step 3. The process of chemical vapor deposition is the same as step 2, except that the deposition time is 20min-1h, so that the thickness of the obtained film is thinner. Preferably, before preparing the first tungsten ditelluride layer 21, the surface of the deposited molybdenum disulfide nanotube layer 22 is plasma treated or heat treated. Plasma treatment introduces active groups on the surface of the molybdenum disulfide nanotube layer 22 to increase the chemical activity of the surface and enhance the interface bonding force; at the same time, it reduces interface defects and makes it easier for carriers to migrate at the interface.

[0046] Step 5: preparing a top electrode layer 1 on the first tungsten ditelluride layer 21 .

[0047] Since the temperature of preparing graphene by chemical vapor deposition is relatively high, generally above 1000°C, high temperature will destroy the prepared structure. Therefore, the graphene is transferred to the surface of the first tungsten telluride layer 21 by liquid phase transfer method as the top electrode layer 1. Finally, the prepared device is annealed. The annealing temperature range is between 350-450°C, and the time is controlled to be 30min-2h. Annealing promotes atomic diffusion between layers, improves interface bonding quality, reduces defects and interface stress, and makes carrier transmission more efficient.

[0048] Embodiment 2:

[0049] Based on Example 1, this embodiment has the following differences. The molybdenum disulfide nanotube layer 22 in the photodetector is doped with cadmium sulfide quantum dots, and the doping concentration is 1-5 wt%; during preparation, the cadmium sulfide quantum dot solution is added to the molybdenum disulfide nanotube solution in step 3. In this way, on the one hand, the cadmium sulfide quantum dots have a high absorption cross section, which can capture more incident photons and transfer their energy to the molybdenum disulfide nanotubes, thereby improving the overall light absorption efficiency and thus increasing the photocurrent; the cadmium sulfide quantum dots have a unique quantum confinement effect, which can generate multiple electron-hole pairs after absorbing photons. After the introduction of cadmium sulfide quantum dots, the photodetector can generate more electrical signals under the same incident photon energy, thereby improving the sensitivity of the photodetector. On the other hand, cadmium sulfide quantum dots have energy band advantages. Cadmium sulfide quantum dots have a wide band gap (~2.4 eV). When they are doped in the MoS2 nanotube layer 22, a heterojunction interface can be formed, which is conducive to the separation of photogenerated electrons and holes, reduces the recombination probability, and improves the separation efficiency and transmission efficiency of photogenerated carriers. The conduction band position of cadmium sulfide is relatively close to that of MoS2, which is conducive to the transfer of photogenerated electrons. Doping with cadmium sulfide quantum dots can passivate the surface defects and interface states of MoS2 nanotubes, reduce surface recombination centers, and increase the carrier lifetime, thereby improving the responsivity of the photodetector. From the perspective of the response spectrum, cadmium sulfide quantum dots can absorb photons from the ultraviolet to the visible light range, which enables the photodetector to effectively detect in a wider spectral range. Especially in the ultraviolet and blue light bands, cadmium sulfide quantum dots have strong absorption capacity, which significantly expands the spectral response range of the photodetector.

[0050] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A sandwich-type wide-spectrum photodetector, comprising a bottom electrode layer, a photosensitive layer, and a top electrode layer, wherein the photosensitive layer is disposed on the bottom electrode layer, and the top electrode layer is disposed on a side of the photosensitive layer away from the bottom electrode layer, characterized in that: From the top electrode layer to the bottom electrode layer, the photosensitive layer includes a first tungsten ditelluride layer, a molybdenum disulfide nanotube layer, and a second tungsten ditelluride layer arranged in sequence.

2. The sandwich-type wide-spectrum optical detector according to claim 1, characterized in that: The thickness of the first tungsten ditelluride layer and the second tungsten ditelluride layer is 10-50 nm.

3. The sandwich-type wide-spectrum optical detector according to claim 2, characterized in that: The molybdenum disulfide nanotube layer is a single-layer nanotube.

4. The sandwich-type wide-spectrum optical detector according to claim 3, characterized in that: The material of the top electrode layer is graphene, and the material of the bottom electrode layer is metal molybdenum.

5. The sandwich-type wide-spectrum optical detector according to claim 4, characterized in that: The photodetector further comprises a substrate, the bottom electrode layer is arranged on the substrate, and the material of the substrate is porous aluminum oxide.

6. The sandwich-type wide-spectrum optical detector according to claim 5, characterized in that: The aperture of the substrate on a side close to the bottom electrode layer is smaller than the aperture of the substrate on a side away from the bottom electrode layer.

7. A method for preparing a sandwich-type wide-spectrum optical detector, characterized in that: The method comprises the following steps: Step 1, depositing a bottom electrode layer on a porous alumina substrate; Step 2, depositing a second tungsten ditelluride layer on the bottom electrode layer; Step 3, depositing a molybdenum disulfide nanotube layer on the second tungsten ditelluride layer; Step 4, depositing a first tungsten ditelluride layer on the molybdenum disulfide nanotube layer; Step 5: preparing a top electrode layer on the first tungsten telluride layer.

8. The method for preparing the sandwich-type wide-spectrum optical detector according to claim 7, characterized in that: In the step 1, the material of the bottom electrode layer is firstly obliquely deposited on the porous alumina substrate, and then the material of the bottom electrode layer is vertically deposited. After the deposition is completed, the porous alumina substrate and the bottom electrode layer are obtained.

9. The method for preparing the sandwich-type wide-spectrum optical detector according to claim 8, characterized in that: The first tungsten ditelluride layer and the second tungsten ditelluride layer are prepared by chemical vapor deposition, and the molybdenum disulfide nanotube layer is prepared by liquid phase stripping and coating. Before preparing the first tungsten ditelluride layer, the deposited molybdenum disulfide nanotube layer is subjected to plasma treatment or heat treatment.

10. The method for preparing the sandwich-type wide-spectrum optical detector according to claim 9, characterized in that: Cadmium sulfide quantum dots are doped into the solution of the molybdenum disulfide nanotube layer.

Images