Photoelectric detector and preparation method thereof

Abstract

The invention relates to the technical field of photoelectric detection devices, and discloses a photoelectric detector and a preparation method thereof, the photoelectric detector comprises a heterojunction, and the heterojunction comprises a first layer, a second layer and a third layer which are stacked; the first layer is made of a transition metal chalcogenide; the second layer is made of graphene; the third layer is made of two-dimensional semiconductor materials, and energy band structures of the three materials are arranged in a step shape. The invention further provides a preparation method of the photoelectric detector, according to the photoelectric detector and the preparation method thereof, the photo-generated carrier dynamic process of a two-dimensional material heterojunction interface is regulated and controlled through the design of a three-layer heterojunction structure, the electric transport characteristic of the photoelectric detector is optimized, and then the response speed of the device is increased.

Description

Technical Field

[0001] This application relates to the technical field of optoelectronic detection devices, and particularly to an optoelectronic detector and a preparation method thereof. Background Art

[0002] In many scientific and technological fields, such as communication, imaging, biomedicine, environmental monitoring, etc., high-performance optoelectronic detectors play a crucial role due to their excellent properties such as high sensitivity, fast response, and low noise. With the continuous progress and development of modern technology, new requirements such as higher integration, lower power consumption, and stronger wearability have been put forward for optoelectronic detectors. However, optoelectronic detectors based on conventional bulk materials have defects such as cumbersome growth processes and great difficulty in hetero-integration, which severely restrict the improvement of their performance and the expansion of their applications.

[0003] In this context, two-dimensional materials represented by transition metal chalcogenides have emerged. Such materials can break through the lattice matching limit and construct hetero-structures with atomically flat interfaces due to their extremely high photon sensitivity and tunable optoelectronic response characteristics, providing a broad platform for the research and development of high-performance optoelectronic detectors. Benefiting from the strong absorption of light by their channel materials and efficient gain mechanisms, optoelectronic detectors based on transition metal chalcogenides can usually achieve high photoresponsivity and detectivity, and can effectively convert weak optical signals into electrical signals.

[0004] Despite the obvious advantages, there are still some problems to be solved urgently for such detectors at present. The trap states existing inside the materials and the relatively low carrier mobility jointly limit the separation and transport speed of photo-generated carriers, resulting in a slowdown of the device's optical response speed. Summary of the Invention

[0005] In view of the above problems, the embodiments of this application provide an optoelectronic detector, which can utilize the design of a three-layer hetero-junction structure to regulate the dynamic process of photo-generated carriers at the hetero-junction interface of two-dimensional materials, realize the optimization of the electrical transport characteristics of the optoelectronic detector, and further improve the device response speed.

[0006] This application provides an optoelectronic detector, which includes a hetero-junction, and the hetero-junction includes a first layer, a second layer, and a third layer stacked;

[0007] The first layer is made of a transition metal chalcogenide;

[0008] The second layer is made of graphene, and the second layer includes a first connection part and a second connection part. The first connection part covers the right side of the first layer, and the second connection part contacts the left side of the third layer. The second layer physically isolates the first layer from the third layer and prevents them from contacting;

[0009] The third layer is made of a two-dimensional semiconductor material. The left side of the third layer covers the right side of the second layer, and the right side of the third layer extends in a direction away from the second layer in the transverse direction.

[0010] In an alternative embodiment, the photodetector further includes a source electrode and a drain electrode. The source electrode is in contact with the third layer, and the drain electrode is in contact with the first layer.

[0011] In an alternative embodiment, the photodetector further includes a substrate. The drain electrode, the first layer, the second layer, the third layer, and the source electrode are sequentially disposed above the substrate from left to right.

[0012] In an alternative embodiment, the photodetector further includes a dielectric layer. The dielectric layer is disposed above the substrate, and the drain electrode, the first layer, the second layer, the third layer, and the source electrode are sequentially disposed above the dielectric layer from left to right.

[0013] The present application also provides a method for manufacturing a photodetector, including the following steps:

[0014] Obtain a two-dimensional transition metal sulfide layer by mechanical exfoliation or chemical vapor deposition. Prepare two-dimensional nanosheets from the two-dimensional transition metal sulfide layer by using a PDMS-assisted transfer method, and transfer them onto a substrate.

[0015] Obtain a graphene layer by mechanical exfoliation and transfer it onto a PDMS film.

[0016] Locate the graphene layer within a preset range by optical microscopy, and use a transfer platform to transfer the graphene layer on the PDMS film onto the two-dimensional nanosheets on the substrate.

[0017] Obtain a two-dimensional semiconductor layer by mechanical exfoliation and transfer it onto a PDMS film.

[0018] Locate the two-dimensional semiconductor layer within a preset range by optical microscopy, and use a transfer platform to transfer the two-dimensional semiconductor layer on the PDMS film onto the graphene layer on the substrate.

[0019] Deposit electrodes on the substrate: deposit a source electrode on one side of the two-dimensional semiconductor layer and deposit a drain electrode on one side of the transition metal chalcogenide layer.

[0020] In an alternative embodiment, the transverse dimension of the two-dimensional transition metal sulfide layer within the preset range and the graphene layer within the preset range is 10 - 50 μm, and the thickness is 1 - 10 nm. The transverse dimension of the two-dimensional semiconductor layer within the preset range is 30 - 80 μm, and the thickness is 10 - 50 nm.

[0021] In an alternative approach, depositing the electrodes on the substrate specifically includes the steps of: using a square copper mesh as a mask to design the metal electrodes, and successively depositing a titanium layer and a gold layer on the substrate by vacuum electron beam evaporation to prepare the metal electrodes.

[0022] In an alternative approach, the thickness of the titanium layer is 5 - 15 nm, and the thickness of the gold layer is 30 - 80 nm.

[0023] In an alternative approach, the method for preparing the photodetector further includes an annealing step: placing the prepared photodetector in an argon environment for annealing treatment.

[0024] In an alternative approach, the annealing temperature is 100 - 250 °C, and the annealing time is 0.5 - 3 h.

[0025] The photodetector of the present application adopts a three - layer van der Waals heterojunction structure and designs its energy band structure. This carefully designed heterojunction has a stepped energy band arrangement, which opens up an efficient path for the separation and collection of photo - generated electron - hole pairs, greatly optimizing the behavior of carriers. In terms of the rising and falling response speeds, the photodetector constructed with a three - layer vertical heterostructure having a stepped energy band arrangement shows a significant improvement. Particularly crucial is the introduction of the graphene intermediate layer, which significantly shortens the time for carriers to flow to the metal electrodes, endowing the device with an ultra - fast response ability to light. At the same time, the unique zero - bandgap property of the graphene intermediate layer enables it to detect optical signals in the range from ultraviolet to terahertz, providing a wider optical response wavelength range for the photodetector and broadening its application potential in different spectral regions.

[0026] In addition, the preparation process of the photodetector of the present application is simple and has good scalability, and can be flexibly applied to other two - dimensional semiconductor material systems, providing strong support for improving the response time of two - dimensional material van der Waals heterojunction photodetectors and promoting the development of high - performance photodetector technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The drawings constituting a part of this application are used to provide a further understanding of this application. The schematic embodiments and descriptions thereof of this application are used to explain this application and do not constitute an improper limitation of this application.

[0028] In order to more clearly illustrate the technical solutions in the embodiments of this application, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of this application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0029] Upon reading the following detailed description of the preferred embodiments, various other advantages and benefits will become clear to those of ordinary skill in the art. The accompanying drawings are only for the purpose of showing the preferred embodiments and are not considered to be a limitation of this application. Moreover, throughout the drawings, the same reference numerals are used to represent the same components. In the drawings:

[0030] Figure 1 is a schematic structural diagram of a photodetector provided by an embodiment of the present application.

[0031] Figure 2 is a comparison diagram of the Raman spectra of the MoTe2 / graphene / InSe van der Waals heterojunction of an embodiment of the present application and the Raman spectra of individual components.

[0032] Figure 3 is a PL characterization diagram of the MoTe2 / graphene / InSe van der Waals heterojunction and a comparison region of an embodiment of the present application.

[0033] Figure 4 is a KPFM diagram and a surface potential analysis result diagram of the MoTe2 / graphene / InSe van der Waals heterojunction of an embodiment of the present application.

[0034] Figure 5 is a time response test diagram of the MoTe2 / graphene / InSe van der Waals heterojunction of an embodiment of the present application.

[0035] Figure 6 is a time response test diagram of the MoTe2 / InSe van der Waals heterojunction prepared in the comparative example.

[0036] Figure 7 is a carrier mobility comparison diagram of the MoTe2 / graphene / InSe van der Waals heterojunction of an embodiment of the present application and the MoTe2 / InSe van der Waals heterojunction devices prepared in Comparative Examples 1-10.

[0037] Figure 8 is a relationship diagram of the optical responsivity of the MoTe2 / graphene / InSe van der Waals heterojunction of an embodiment of the present application varying with wavelength.

[0038] The reference numerals in the specific embodiments are as follows:

[0039] 1. Substrate, 2. Dielectric layer, 3. First layer, 4. Second layer, 5. Third layer, 6. Source electrode, 7. Drain electrode. Specific Embodiments

[0040] The embodiments of the technical solutions of the present application will be described in detail below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present application, so they are only examples and cannot be used to limit the protection scope of the present application. Many specific details are set forth in the following description in order to fully understand the present application. However, the present application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without departing from the connotation of the present application. Therefore, the present application is not limited by the specific embodiments disclosed below.

[0041] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above drawings are intended to cover non-exclusive inclusion.

[0042] In the description of the embodiments of this application, technical terms such as "first", "second", "third", etc. are only used to distinguish different objects and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity, specific order or primary-secondary relationship of the indicated technical features. The mention of "embodiment" in this article means that the specific features, structures or characteristics described in connection with the embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various positions in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art explicitly and implicitly understand that the embodiments described herein can be combined with other embodiments.

[0043] In the description of the embodiments of this application, the orientation or positional relationship indicated by technical terms such as "length", "width", "thickness", "upper", "lower", "left", "right", "vertical", "horizontal", "top", "bottom", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the embodiments of this application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the embodiments of this application.

[0044] In the description of the embodiments of the present application, unless otherwise clearly defined and limited, technical terms such as "connected", "connected to", "fixed" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or integrated; it can also be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to specific situations.

[0045] In the present application, unless otherwise clearly defined and limited, the first feature being "on" or "under" the second feature can be that the first and second features are in direct contact, or the first and second features are indirectly in contact through an intermediate medium. Moreover, the first feature being "above", "over" and "on top of" the second feature can be that the first feature is directly above or obliquely above the second feature, or merely indicates that the first feature has a higher horizontal height than the second feature. The first feature being "under", "below" and "beneath" the second feature can be that the first feature is directly below or obliquely below the second feature, or merely indicates that the first feature has a lower horizontal height than the second feature.

[0046] In the present application, "covering" means a vertical alignment with direct contact. The term "vertical" refers to the direction perpendicular to the substrate plane, and the term "lateral" can be used to represent a direction or area parallel to the substrate plane. When the second layer "covers" the first layer, the second layer and the first layer are vertically aligned and they are in direct contact with each other. In other words, the two layers have been sequentially disposed on a given area of the substrate. They are vertically aligned because the first layer is first disposed on the area, and then the second layer is disposed on the same area. Therefore, within this area, the first layer is located below the second layer in the vertical direction.

[0047] In the present application, "overlying" means a vertical alignment without direct contact. When the second layer "overlies" the first layer, the second layer and the first layer are vertically aligned, but they are not in direct contact with each other. In other words, both layers have been disposed on a given area of the substrate, but an intermediate layer has been disposed between them. The three layers are all vertically aligned. The first layer is first disposed on the area, then the intermediate layer is disposed on the same area, and then the second layer is disposed on the same area. Within this area, the first layer is thus located below the intermediate layer and the second layer. The intermediate layer is located above the first layer but below the second layer in the vertical direction.

[0048] It should be noted that the expressions "partially covering" and "partially overlying" are used to refer to a partial vertical alignment, where the area of the first layer is not completely covered or overlaid by the second layer. Open-ended qualifying expressions such as "at least partially covering" and "at least partially overlying" are used to refer to a partial vertical alignment.

[0049] In addition, the expression that an object is "on a substrate" can mean that the object covers the substrate partially or entirely (or is deposited to cover it), or that the object covers a part or all of the substrate on the substrate. In other words, the electrode "on the substrate" can be an electrode in direct contact with the substrate, or an electrode in direct contact with one or more intermediate layers covering the substrate. In other words, the electrode "on the substrate" can cover or cover a part of the substrate. In the case of a deposition method, it can be specified that a plurality of layers are deposited in sequence "on the substrate". Specifying the order of such deposition steps corresponds to the order in which the layers are deposited on the substrate or on certain areas of the substrate. Therefore, this order determines which (preceding) layers a given layer covers or covers in a specific area of the substrate, and which (subsequent) layers will cover or cover the given layer in a specific area of the substrate in sequence.

[0050] As Figure 1 shown, this application provides a photodetector, which includes a heterojunction, and the heterojunction includes a first layer 3, a second layer 4, and a third layer 5 arranged in a stack. Among them: the first layer 3 is made of a transition metal chalcogenide. Specifically, the transition metal chalcogenide is at least one of MoTe2, MoSe2, WS2, WSe2, ReS2, PdSe2; preferably, the transition metal chalcogenide is two-dimensional MoTe2, and its thickness is 5-15 nm; further, the preferred thickness of two-dimensional MoTe2 is 5 nm, 7 nm, or 9 nm. The second layer 4 is made of graphene. Specifically, the left side of the second layer 4 is in contact with the right side of the first layer 3, and the right side of the second layer 4 is in contact with the left side of the third layer 5. The second layer 4 physically isolates the first layer 3 and the third layer 5 and prevents them from contacting; preferably, the thickness of the graphene layer is 1-10 nm; preferably, the thickness of the graphene is 2 nm, 3 nm, or 4 nm.

[0051] The third layer 5 is made of a two-dimensional semiconductor material, and the third layer 5 is made of a two-dimensional semiconductor with high mobility, specifically at least one of InSe, Te, BP, Bi2O2Se. Preferably, the high-mobility semiconductor is two-dimensional InSe, and its thickness is 10-50 nm; preferably, the thickness of two-dimensional InSe is 10 nm, 12 nm, or 16 nm.

[0052] Specifically, the left side of the third layer 5 covers the right side of the second layer 4, and the right side of the third layer 5 extends in a direction away from the second layer 4 in the lateral direction.

[0053] The photodetector of the present application, by setting three layers of van der Waals heterojunctions and designing the energy band structure of the heterojunctions, enables the heterojunctions to have a stepped energy band arrangement structure, which can effectively promote the separation and collection of photo-generated electron-hole pairs at the heterojunction interface. On the one hand, the rise and fall response speeds of the photodetector constructed by the three-layer vertical heterostructure are improved. The introduction of the graphene middle layer greatly reduces the time for carriers to flow to the metal electrodes, making the device's response to light extremely fast. On the other hand, the graphene middle layer adopted in the present application has a zero bandgap and can detect optical signals in the range from ultraviolet to terahertz, with a wider optical response wavelength range. In addition, the preparation of the present application is simple and can be extended to other two-dimensional semiconductor material systems, providing better support for improving the response time of two-dimensional material van der Waals heterojunction photodetectors.

[0054] In some embodiments of the present application, the photodetector further includes a source electrode 6 and a drain electrode 7. The source electrode 6 is in contact with the third layer 5, and the drain electrode 7 is in contact with the first layer 3. This design is beneficial for constructing an efficient carrier transport channel. Specifically, there is no overlapping area in the lateral projection of the source electrode 6 and the drain electrode 7, that is, there is a gap in the lateral projection of the source electrode 6 and the drain electrode 7. Photo-generated carriers can be quickly transported between the source electrode 6 and the drain electrode 7, reducing the recombination probability, making the photoelectric conversion process more efficient, improving the ability to convert optical signals into electrical signals, and further enhancing the detection sensitivity of the detector to light, enabling it to more accurately identify weak optical signals.

[0055] Among them, the source electrode 6 and the drain electrode 7 are metal electrodes. Optionally, the metal electrode is at least one of chromium, titanium, gold, silver, platinum, and copper. Preferably, in some embodiments of the present application, the metal electrode is a titanium-gold bilayer metal electrode. This preferred scheme is based on the many significant advantages brought by the combination of titanium and gold. The titanium layer can provide good adhesion and a stable contact interface, helping to ensure a tight connection between the electrode and other functional layers of the photodetector, thereby reducing the contact resistance and improving the stability of electrical properties. The gold layer, on the other hand, performs excellently in conductivity and oxidation resistance, can effectively conduct current and maintain good electrical properties for a long time, and can prevent oxidation and performance degradation even under complex environmental conditions. The design of the titanium-gold bilayer metal electrode not only optimizes the electrical properties of the photodetector but also improves its reliability and durability.

[0056] In addition, this contact configuration of the source electrode 6 and the drain electrode 7 can optimize the rise and fall response speeds of the photodetector. Photo-generated carriers can be quickly collected and transported by the source electrode 6 and the drain electrode 7, making the detector's response to optical signals more rapid and sensitive, shortening the signal response time, helping to improve the real-time and dynamic performance of the detector, and enabling it to perform better in scenarios of detecting rapidly changing optical signals.

[0057] Furthermore, the source electrode 6 and the drain electrode 7 are respectively arranged at the left and right ends on the top of the photodetector. The source electrode 6 and the drain electrode 7 are designed to be easily integrated with other electronic components or circuits, improving the integratability and compatibility of the detector, facilitating the construction of complex photodetection systems, meeting the requirements of modern technology for miniaturized and high-performance photodetection devices, and promoting the application and development of related technologies in fields such as communication and imaging.

[0058] In some embodiments of the present application, the photodetector further includes a substrate 1. The drain electrode 7, the first layer 3, the second layer 4, the third layer 5, and the source electrode 6 are sequentially arranged above the substrate 1 from left to right. Specifically, the drain electrode 7 covers the substrate 1, the first layer 3 covers the substrate 1, the second layer 4 partially covers the substrate 1, the third layer 5 partially covers the substrate 1, and the source electrode 6 covers the substrate 1.

[0059] Specifically, the substrate 1 serves as the basic support structure of the heterojunction, providing a solid physical foundation for the multi-layer structure of the entire photodetector. It ensures the structural stability of the photodetector during manufacturing, assembly, use, and transportation, preventing misalignment or damage of the layers of materials caused by external forces, vibrations, or other mechanical factors. From the perspective of the manufacturing process, arranging the layers of materials on the substrate 1 in sequence simplifies the manufacturing process and improves production efficiency. This arrangement makes the alignment and integration between the layers relatively easy, reducing the complexity and errors in the manufacturing process. At the same time, the presence of the substrate 1 also facilitates subsequent packaging and integration, being conducive to the large-scale production and application of the photodetector. In addition, the substrate 1 can serve as a platform for integration with other electronic components or circuits, enabling the photodetector to be closely combined with other functional modules (such as signal processing circuits, amplifiers, etc.) to construct a more compact and efficient photodetection system. This integrated design not only reduces the volume and weight of the system but also improves the performance and reliability of the system, meeting the requirements of modern technology for miniaturized and high-performance photodetection devices.

[0060] Furthermore, in some embodiments of the present application, the substrate 1 is made of at least one of sapphire, silicon, mica, quartz, and flexible substrates, having certain chemical stability and thermal stability, and being able to protect the active materials of the photodetector from the erosion and influence of environmental factors (such as moisture, oxygen, temperature changes, etc.).

[0061] In some embodiments of the present application, the photodetector further includes a dielectric layer 2, which is disposed above the substrate 1, and the drain 7, the first layer 3, the second layer 4, the third layer 5, and the source 6 are sequentially disposed above the dielectric layer 2 from left to right. Specifically, the drain 7 covers the dielectric layer 2, the first layer 3 covers the dielectric layer 2, the second layer 4 partially covers the dielectric layer 2, the third layer 5 partially covers the dielectric layer 2, and the source 6 covers the dielectric layer 2. The dielectric layer 2 provides a flat and uniform deposition surface for the upper functional layers, which helps the growth and transfer of two-dimensional materials and reduces the damage and contamination of the materials during the preparation process.

[0062] Furthermore, the dielectric layer 2 has good dielectric properties and can effectively adjust the electric field distribution. In addition, the dielectric layer 2 can also play a certain insulating role to prevent short circuits or leakage between different electrodes and ensure the normal operation of the device.

[0063] Specifically, a van der Waals heterojunction with a sandwich structure is constructed on the substrate 1. The heterojunction from bottom to top is the substrate 1, MoTe2, graphene, and InSe. The above three materials are all transferred to the substrate 1 by dry method of directional transfer, and the energy band structure of the vertical heterojunction is arranged in a stepped manner. The heterojunction is assembled into a photodetector, and the metal electrodes are prepared by dry etching mask and vacuum electron beam evaporation method. The source 6 and the drain 7 are respectively in contact with two two-dimensional semiconductors. In addition, the lower-layer transition metal dichalcogenide MoTe2 and the upper-layer high-mobility two-dimensional semiconductor InSe do not contact each other. The source 6 is in contact with the upper-layer high-mobility two-dimensional semiconductor InSe, the drain 7 is in contact with the lower-layer transition metal dichalcogenide MoTe2, and neither the source 6 nor the drain 7 is in contact with the graphene layer.

[0064] The present application also provides a method for preparing a photodetector, including the following steps:

[0065] Obtain a two-dimensional transition metal sulfide layer by mechanical exfoliation or chemical vapor deposition method, prepare two-dimensional nanosheets from the two-dimensional transition metal sulfide layer by PDMS-assisted transfer method, and transfer the prepared two-dimensional nanosheets to the substrate 1;

[0066] Obtain a graphene layer by mechanical exfoliation method and transfer the graphene layer to the PDMS film;

[0067] Find the graphene layer within a preset range through an optical microscope, and transfer the graphene layer on the PDMS film to the two-dimensional nanosheets on the substrate 1 by using a transfer platform;

[0068] Obtain a two-dimensional semiconductor layer by mechanical exfoliation method and transfer it to the PDMS film;

[0069] Find a two-dimensional semiconductor layer within a preset range through an optical microscope, and use a transfer platform to transfer the two-dimensional semiconductor layer on the PDMS film to the graphene on Substrate 1;

[0070] Deposit electrodes on Substrate 1: deposit the source electrode 6 on one side of the two-dimensional semiconductor, and deposit the drain electrode 7 on one side of the transition metal dichalcogenide.

[0071] In some embodiments of the present application, the lateral dimension of the two-dimensional transition metal sulfide layer within the preset range and the two-dimensional graphene thin layer within the preset range is in the range of 10 - 50 μm, and the thickness is in the range of 1 - 10 nm. The lateral dimension of the two-dimensional semiconductor layer within the preset range is in the range of 30 - 80 μm, and the thickness is in the range of 10 - 50 nm.

[0072] In some embodiments of the present application, depositing electrodes on Substrate 1 specifically includes using a square copper mesh as a mask to design metal electrodes, and preparing metal electrodes by successively depositing a titanium layer and a gold layer using vacuum electron beam evaporation.

[0073] In some embodiments of the present application, the thickness of the titanium layer is 5 - 15 nm, and the thickness of the gold layer is 30 - 80 nm.

[0074] In some embodiments of the present application, the preparation method of the photodetector finally further includes an annealing step: annealing the prepared photodetector in an argon environment.

[0075] In some embodiments of the present application, the annealing temperature is 100 - 250 °C, and the annealing time is 0.5 - 3 h.

[0076] The preparation method of the photodetector of the present application specifically includes the following steps:

[0077] (1) Obtain a two-dimensional transition metal sulfide MoTe2 thin layer by mechanical exfoliation. Further, use the PDMS-assisted transfer method to prepare two-dimensional MoTe2 nanosheets from a MoTe2 single crystal block and transfer them to Substrate 1. This method has the advantages of simple operation and no lattice matching limitation. Further, Substrate 1 is a silicon substrate 1 with an oxide layer of 10 - 500 nm on its surface. Further still, Substrate 1 is an N-type silicon substrate 1 with an oxide layer of 300 nm on its surface;

[0078] (2) Obtain a graphene thin layer by mechanical exfoliation and transfer it onto the PDMS film;

[0079] (3) Find graphene with a lateral dimension distribution in the range of 10 - 50 μm and a thickness distribution in the range of 1 - 10 nm through an optical microscope, and use a micro-region transfer platform to transfer the graphene thin layer on the PDMS to the two-dimensional MoTe2 thin layer on the target silicon substrate 1 to form a MoTe2 / graphene heterojunction;

[0080] (4) A two-dimensional InSe thin layer is obtained by mechanical exfoliation and transferred onto a PDMS film.

[0081] (5) Two-dimensional InSe with a lateral size distribution in the range of 30 - 80 μm and a thickness distribution in the range of 10 - 50 nm is found through an optical microscope. The InSe nanosheets on the PDMS are transferred onto the graphene thin layer on the silicon substrate 1 using a micro-area transfer platform to form a MoTe2 / graphene / InSe sandwich structure.

[0082] (6) A square copper mesh is used as a mask to design metal electrodes. Titanium and gold are successively deposited by vacuum electron beam evaporation to prepare the metal electrodes. Optionally, the thickness of the titanium layer is 5 - 15 nm, and the thickness of the gold layer is 30 - 80 nm.

[0083] (7) The fabricated photodetector is annealed in an environment of high-purity argon. Optionally, the annealing temperature is 100 - 250 °C, and the annealing time is 0.5 - 3 h.

[0084] The beneficial effects of the photodetector and its preparation method of the present application are described in detail below in combination with comparative examples:

[0085] As Figure 1 shown, a photodetector and its preparation method are provided in the present application, which is a sandwich-structured van der Waals heterojunction photodetector, including, from bottom to top in sequence: a heavily doped N-type low-resistance (0.001 - 0.005 Ω·cm) silicon substrate 1, a 300-nm-thick silicon dioxide layer on the surface, a lower-layer MoTe2 nanosheet, a middle-layer graphene, an upper-layer InSe nanosheet, a source electrode 6, and a drain electrode 7. The MoTe2 / graphene / InSe heterojunction is prepared by the following method:

[0086] (1) Using MoTe2, graphene, and InSe bulk single crystals as raw materials respectively, the materials are thinned by repeatedly folding a blue film tape multiple times. Then, the two-dimensional materials on the blue film tape are transferred onto a PDMS film, and the PDMS with the transferred materials is attached to a glass slide with the front side facing up.

[0087] (2) The silicon substrate 1 is placed on the sample pedestal of the transfer stage and fixed by vacuum adsorption. Then, the PDMS / glass slide prepared in step (1) is fixed in the hole at the front end of the transfer arm with the front side facing down. By controlling the micro-area transfer platform, the PDMS with two-dimensional MoTe2 nanosheets is pressed onto the silicon substrate 1. After complete adhesion, the transfer arm is slowly lifted to leave the two-dimensional MoTe2 nanosheets on the silicon substrate 1. The selected thickness of the MoTe2 nanosheets is 7 nm.

[0088] (3) Use an optical microscope to find graphene nanosheets with appropriate size and thickness, and transfer them to the target MoTe2 nanosheets according to the method in step (2), so that the graphene and the two-dimensional MoTe2 nanosheets partially overlap to form a MoTe2 / graphene heterojunction. The thickness of the selected graphene is 3 nm.

[0089] (4) Use an optical microscope to find InSe nanosheets with appropriate size and thickness, and transfer them to the target graphene nanosheets according to the method in step (2), so that the InSe nanosheets and the graphene partially overlap, while ensuring that the InSe nanosheets do not contact the bottom-layer MoTe2 nanosheets, to obtain a MoTe2 / graphene / InSe heterojunction with a sandwich structure. The thickness of the selected InSe nanosheets is 16 nm.

[0090] (5) Use a square copper mesh with 100-200 mesh as a mask to design metal electrodes, so that the electrodes are located on the individual InSe and MoTe2 layers respectively, and then deposit metals by vacuum electron beam evaporation. The selected metal type is a titanium-gold bilayer metal electrode, where the thicknesses of titanium and gold are 10 nm and 50 nm respectively.

[0091] (6) Place the MoTe2 / graphene / InSe heterojunction photodetector on a heating stage in a glove box, and set the heating temperature to 200 °C to anneal the device for 2 h.

[0092] Examples 2-10: The preparation steps are the same as those in the example, where the thickness of the MoTe2 nanosheets is selected to be 5-10 nm, the thickness of the graphene is selected to be 1-5 nm, and the thickness of the InSe nanosheets is selected to be 10-30 nm.

[0093] Comparative Examples 1-10:

[0094] The preparation steps of the comparative example photodetector are the same as those in the above example, except that: the comparative example is a bilayer heterojunction composed of MoTe2 and InSe, without introducing a graphene intermediate layer. The thicknesses of the selected InSe and MoTe2 nanosheets are the same as those in the above example respectively, forming a control group lacking only the graphene layer, and the electrode connected to InSe is still the source electrode, and the electrode connected to MoTe2 is the drain electrode.

[0095] Figure 2 It is the Raman spectrum of the MoTe2 / graphene / InSe three-layer van der Waals heterojunction and the individual components in the examples of this application. The Raman characteristic peaks of the three components in the heterojunction region are clearly visible, indicating the effective formation of a high-quality heterojunction;

[0096] Figure 3It is the PL spectral characterization of the MoTe2 / graphene / InSe three-layer van der Waals heterojunction, as well as the separate InSe region, InSe / graphene heterojunction region, and InSe / MoTe2 heterojunction region in the embodiments of this application. It can be seen that compared with the separate InSe region, the PL intensities of the other three heterojunction regions are significantly reduced. Among them, the PL intensity quenching of InSe in the MoTe2 / graphene / InSe heterojunction region is the most obvious, indicating that the charge transfer process between the interfaces of the three-layer heterojunction is more effective, and the introduction of the graphene intermediate layer can significantly enhance the separation and transport of photo-generated carriers.

[0097] Figure 4 It is the KPFM characterization of the MoTe2 / graphene / InSe three-layer van der Waals heterojunction in the embodiments of this application. The surface potentials of the upper InSe, middle graphene, and lower MoTe2 show a stepped distribution. Among them, the surface potential of the upper InSe is higher than that of the middle graphene (the potential difference is 293 mV), and the surface potential of the middle graphene is higher than that of the lower MoTe2 (the potential difference is 117 mV). Correspondingly, the Fermi levels of the upper InSe, middle graphene, and lower MoTe2 are sequentially distributed in a stepped manner. Thus, under the action of an external field, photo-generated carriers can be effectively separated and transported.

[0098] Figure 5 It is the test result graph of the optical response time of the MoTe2 / graphene / InSe van der Waals heterojunction photodetector in the embodiments of this application. The measured rise and fall response times of the device are 362 ns and 405 ns respectively;

[0099] Figure 6 It is the test result graph of the optical response time of the MoTe2 / InSe van der Waals heterojunction photodetector in the comparative example. The measured rise and fall response times of the device are 485 μs and 539 μs respectively; It can be seen that the response time of the photodetector prepared with the MoTe2 / graphene / InSe heterojunction in the embodiments of this application has increased by three orders of magnitude compared with the optical response time of the MoTe2 / InSe heterojunction device without the graphene intermediate layer.

[0100] Figure 7 It is the test result graph of the carrier mobility of the MoTe2 / graphene / InSe van der Waals heterojunction device in 10 embodiments of this application. Compared with the MoTe2 / InSe heterojunction devices in 10 comparative examples, the carrier mobility of the MoTe2 / graphene / InSe device has increased by 1-2 orders of magnitude.

[0101] Figure 8It is a graph showing the relationship between the optical responsivity of the MoTe2 / graphene / InSe van der Waals heterojunction photodetector in the embodiments of the present application and the wavelength change. Due to the introduction of the graphene intermediate layer, the response wavelength range of the heterojunction device can reach 1400 nm.

[0102] For the photodetector of the present application, the three-layer van der Waals heterojunction adopted has a stepped energy band arrangement structure, which can effectively promote the separation and collection of photo-generated electron-hole pairs at the heterojunction interface. On the one hand, the rise and fall response speeds of the photodetector constructed by the MoTe2 / graphene / InSe vertical heterostructure reach 362 ns and 405 ns respectively. In comparison, the rise and fall response speeds of the photodetector constructed by the MoTe2 / InSe vertical heterostructure are 485 μs and 539 μs respectively. Therefore, the introduction of the graphene intermediate layer greatly reduces the time for carriers to flow to the metal electrode, making the device's response to light extremely fast. On the other hand, the graphene intermediate layer adopted in the present application has a zero bandgap and can detect optical signals in the range from ultraviolet to terahertz. Compared with the InSe / MoTe2 heterojunction device, the photodetector constructed by the InSe / graphene / MoTe2 vertical heterostructure has a wider optical response wavelength range.

[0103] The present application uses the van der Waals heterointegration technology to construct a three-layer van der Waals heterojunction. This technical means is simple to operate and can be extended to other two-dimensional semiconductor material systems, providing an effective way to improve the response time of two-dimensional material van der Waals heterojunction photodetectors.

[0104] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application. In particular, as long as there is no structural conflict, the technical features mentioned in each embodiment can be combined in any way.

[0105] The technical features of the above embodiments can be combined arbitrarily. For the sake of concise description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope recorded in this specification.

[0106] The above embodiments merely represent several implementation manners of the present application. The description thereof is relatively specific and detailed, but it should not be construed as a limitation to the scope of the patent application. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several modifications and improvements can still be made, and these all fall within the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the appended claims.

Claims

1. A photodetector, characterized in that, It includes a heterojunction, and the heterojunction includes a first layer, a second layer, and a third layer that are stacked; The first layer is made of a transition metal chalcogenide; The second layer is made of graphene, and the second layer includes a first connection part and a second connection part. The first connection part covers the right side of the first layer, and the second connection part contacts the left side of the third layer. The second layer physically separates the first layer from the third layer and prevents them from contacting; The third layer is made of a two-dimensional semiconductor material. The left side of the third layer covers the right side of the second layer, and the right side of the third layer extends in a direction away from the second layer in the lateral direction.

2. The photodetector according to claim 1, wherein It further includes a source electrode and a drain electrode. The source electrode contacts the third layer, and the drain electrode contacts the first layer.

3. The photodetector according to claim 2, wherein It further includes a substrate, and the drain electrode, the first layer, the second layer, the third layer, and the source electrode are sequentially arranged above the substrate from left to right.

4. The photodetector according to claim 3, characterized in that, It further includes a dielectric layer. The dielectric layer is arranged above the substrate, and the drain electrode, the first layer, the second layer, the third layer, and the source electrode are sequentially arranged above the dielectric layer from left to right.

5. A method for preparing a photodetector, characterized in that, It includes the following steps: Obtain a two-dimensional transition metal sulfide layer by mechanical exfoliation or chemical vapor deposition. Use the PDMS-assisted transfer method to prepare two-dimensional nanosheets from the two-dimensional transition metal sulfide layer and transfer them to a substrate; Obtain a graphene layer by mechanical exfoliation and transfer it onto a PDMS film; Find the graphene layer within a preset range through an optical microscope, and use a transfer platform to transfer the graphene layer on the PDMS film onto the two-dimensional nanosheets on the substrate; Obtain a two-dimensional semiconductor layer by mechanical exfoliation and transfer it onto a PDMS film; Find the two-dimensional semiconductor layer within a preset range through an optical microscope, and use a transfer platform to transfer the two-dimensional semiconductor layer on the PDMS film onto the graphene layer on the substrate; Deposit electrodes on the substrate: deposit a source electrode on one side of the two-dimensional semiconductor layer and deposit a drain electrode on one side of the two-dimensional transition metal chalcogenide layer.

6. The manufacturing method of the photodetector according to claim 5, characterized in that, The lateral dimensions of the two-dimensional transition metal sulfide layer and the graphene layer within the preset range are 10 - 50 μm, and the thickness is 1 - 10 nm. The lateral dimensions of the two-dimensional semiconductor layer within the preset range are 30 - 80 μm, and the thickness is 10 - 50 nm.

7. The manufacturing method of the photodetector according to claim 6, characterized in that, The step of depositing electrodes on the substrate specifically includes: using a square copper mesh as a mask to design metal electrodes, and using vacuum electron beam evaporation to deposit a titanium layer and a gold layer on the substrate in sequence to prepare metal electrodes.

8. The manufacturing method of the photodetector according to claim 7, wherein, The thickness of the titanium layer is 5 - 15 nm, and the thickness of the gold layer is 30 - 80 nm.

9. The manufacturing method of the photodetector according to claim 5, characterized in that, It further includes an annealing step: place the prepared photodetector in an argon environment for annealing treatment.

10. The manufacturing method of the photodetector according to claim 9, characterized in that, The temperature used for annealing is 100 - 250 °C, and the annealing time is 0.5 - 3 h.

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