A method for fabricating a fully depleted double heterojunction photodetector made of two-dimensional materials

Abstract

This application relates to the field of photoelectric detection technology, specifically disclosing a method for fabricating a fully depleted double heterojunction photodetector made of two-dimensional materials. The method comprises six core steps: composite substrate pretreatment, pre-electrode fabrication, two-dimensional material stripping and passivation, heterojunction transfer and stacking, electrode connection fabrication, and atmosphere annealing. Employing a step-by-step process of pre-fabricating electrodes before constructing the heterojunction effectively avoids irreversible damage to the lattice and interface of the two-dimensional material caused by high-energy fabrication processes such as photolithography and coating. The detector fabricated by this method has a core of a back-to-back double heterostructure consisting of a bottom p-type molybdenum ditelluride, a middle n-type molybdenum tetraselenide tungsten, and a top p-type molybdenum ditelluride stacked vertically. This structure achieves complete depletion of the middle absorption layer, significantly improving carrier separation and collection efficiency, while maintaining excellent photoelectric response sensitivity and speed. Furthermore, the fabrication process is highly compatible with existing silicon-based semiconductor processes, facilitating large-scale fabrication.

Description

Technical Field

[0001] This application relates to the field of photoelectric detection technology, and more specifically, to a method for fabricating a fully depleted double heterojunction photodetector made of two-dimensional material. Background Technology

[0002] As a core component for converting optical signals into electrical signals, photodetectors are widely used in optical communication, image sensing, remote sensing imaging, machine vision, and other fields, occupying an irreplaceable position in both military and civilian optoelectronic information systems. With the rapid development of the optoelectronic information industry, various application scenarios are placing increasingly higher demands on the core performance characteristics of photodetectors, such as response sensitivity and response speed.

[0003] Traditional photodetectors based on crystalline silicon are limited by the inherent physical properties of bulk materials, facing bottlenecks in carrier transport efficiency and device miniaturization, making them increasingly unsuitable for the development of high-performance photodetectors. Two-dimensional semiconductor materials, represented by transition metal chalcogenides, have become core materials for fabricating next-generation high-performance photodetectors due to their atomically flat interfaces, tunable band structures, and excellent carrier transport properties. Van der Waals heterojunctions based on two-dimensional materials have also become an important research direction in the field of photodetectors.

[0004] Currently, van der Waals heterojunction photodetectors based on two-dimensional materials mostly adopt a single pn heterojunction structure design. This type of structure makes it difficult to completely deplete the light absorption layer, and the transmission distance of photogenerated carriers is relatively long. Non-radiative recombination is prone to occur during the transmission process, resulting in insufficient carrier separation and collection efficiency. Ultimately, it is difficult for the device to simultaneously achieve high photoresponsivity and fast response speed, which cannot meet the requirements of high-performance photodetector systems for simultaneous improvement of core performance. Summary of the Invention

[0005] To address the challenges of achieving complete depletion of the light absorption layer and limited carrier separation and collection efficiency in existing two-dimensional van der Waals heterojunction photodetectors, which struggle to balance high photoresponsivity and fast response speed, this application provides a method for fabricating a fully depleted dual heterojunction photodetector made of two-dimensional materials.

[0006] A method for fabricating a fully depleted double heterojunction photodetector made of two-dimensional materials includes the following steps:

[0007] S1. Composite substrate pretreatment: Select a silicon / silicon dioxide composite substrate, and ultrasonically clean it sequentially with organic solvent and deionized water. After cleaning, dry it to obtain a clean substrate.

[0008] S2. Pre-electrode preparation: Photoresist is spin-coated onto the silicon dioxide layer of a clean substrate. After soft baking, exposure, and development, an electrode pattern is formed on the silicon dioxide layer. A chromium layer and a gold layer are deposited using an electron beam evaporation process. Then, the residual photoresist is stripped off to obtain a substrate with pre-electrodes.

[0009] S3. Material stripping and passivation: The molybdenum ditelluride bulk and the molybdenum tetraselenide tungsten bulk are mechanically stripped and screened to obtain multilayer two-dimensional materials; in an inert atmosphere, the interface to be contacted of the screened two-dimensional materials is subjected to low-energy plasma passivation treatment to obtain passivated two-dimensional materials.

[0010] S4. Heterojunction Transfer and Stacking: Using a dry transfer system, in the same inert atmosphere, firstly, passivated multilayer molybdenum ditelluride is transferred to the surface of the silicon dioxide layer of the substrate to form a bottom molybdenum ditelluride layer, ensuring that the bottom molybdenum ditelluride layer has no direct contact with the pre-fabricated electrode; then, passivated multilayer molybdenum tetraselenide is transferred to the top of the bottom molybdenum ditelluride layer; finally, another set of passivated multilayer molybdenum ditelluride is transferred to the top of the molybdenum tetraselenide layer to form a top molybdenum ditelluride layer, ensuring that the top and bottom molybdenum ditelluride layers have no direct contact, thus completing the fabrication of the dual heterojunction vertical stacking structure;

[0011] S5. Electrode connection fabrication: Photoresist is spin-coated onto the vertically stacked substrate surface. After exposure and development, electrode channels are defined. Chromium and gold layers are deposited using electron beam evaporation to electrically connect the bottom molybdenum ditelluride layer to the source electrode and the top molybdenum ditelluride layer to the drain electrode. Then, the residual photoresist is stripped off.

[0012] S6. Atmosphere Annealing: The device with completed electrode connections is placed in a vacuum annealing furnace and annealed under a chalcogen atmosphere in a vacuum environment. After natural cooling, the target photodetector is obtained.

[0013] By adopting the above technical solution, the entire process of substrate pretreatment, pre-electrode fabrication, material stripping and passivation, heterojunction transfer and stacking, electrode connection fabrication, and atmosphere annealing is carried out. The step-by-step process of first pre-fabricating electrodes, then constructing heterojunctions, and finally completing electrode connections can avoid irreversible damage to the two-dimensional material lattice and heterojunction interface caused by high-energy processes such as photolithography and coating. Through step-by-step interface passivation and symmetrical stacking control, a back-to-back vertical double heterojunction of "bottom p-type molybdenum ditelluride / n-type molybdenum tetraselenide / top p-type molybdenum ditelluride" is constructed, providing a structural basis for the full depletion state of the intermediate absorption layer. This allows photogenerated carriers to be confined to the two-dimensional material plane for transport, and can be efficiently controlled by a local electric field. Finally, a photodetector with wide spectral response, high sensitivity, and bipolar photoresponse characteristics is fabricated, and the entire process is compatible with existing silicon-based semiconductor processes, which is conducive to large-scale fabrication.

[0014] Preferably, in step S3, the molybdenum ditelluride is a p-type two-dimensional semiconductor material with a 2H phase, and the molybdenum tetraselenide is an n-type two-dimensional semiconductor material with a 2H phase; in step S4, the thickness of the bottom molybdenum ditelluride layer and the top molybdenum ditelluride layer are both 10-50 nm, and the thickness of the molybdenum tetraselenide layer is 10-40 nm.

[0015] By adopting the above technical solution, the 2H phase molybdenum ditelluride and molybdenum tetraselenide tungsten are thermodynamically stable semiconductor crystal phases, which can form stable p-type and n-type conductivity characteristics. The matched band structure of the two can form a clear type-II band shift and back-to-back built-in electric field at the heterojunction interface, providing a driving force for the efficient separation of photogenerated carriers, and at the same time providing an electric field basis for the complete depletion of the intermediate molybdenum tetraselenide tungsten layer. The precisely defined material thickness range not only ensures the effective absorption of incident light in the visible-near infrared band by the two-dimensional material, but also avoids the problems of extended photogenerated carrier transport path and increased non-radiative recombination probability caused by excessive material thickness. The upper and lower molybdenum ditelluride layers adopt the same crystal phase and thickness range, ensuring the structural and electrical symmetry of the double heterojunction, and providing the core structural basis for the device to achieve symmetrical bipolar photoresponse under positive and negative source-drain bias voltages.

[0016] Preferably, in step S2, the spin coating speed of the positive photoresist is 2800-3200 r / min, and the spin coating time is 30-60 seconds; the soft baking temperature is 100-120℃, and the soft baking time is 50-70 seconds; the exposure dose is 90-110 mJ / cm², and the exposure time is 25-35 seconds; the development time is 60-120 seconds, and the fixing time is 25-35 seconds; when depositing the chromium layer, the deposition rate is controlled at 0.08-0.2 nm / s, and the chromium layer thickness is 5-30 nm; when depositing the gold layer, the deposition rate is controlled at 0.2-0.6 nm / s, the gold layer thickness is 35-70 nm, and the total thickness of the metal electrode is 40-100 nm.

[0017] By employing the above technical solutions, the precise control of photoresist spin coating, soft baking, exposure, and development and fixing parameters can form a photoresist layer with uniform thickness and good adhesion on the substrate surface. After exposure and development, a regular morphology, clear edges, and precise dimensions of the electrode pattern are obtained, ensuring the pattern fidelity and positional accuracy of the pre-fabricated electrode. During the electron beam evaporation process, by limiting the deposition rate and thickness of the chromium and gold layers, the chromium layer can enhance the adhesion between the metal layer and the silicon dioxide substrate, preventing electrode detachment and providing a low barrier foundation for subsequent metal-semiconductor contact. The gold layer provides excellent conductivity and environmental stability for the electrode, ultimately forming a pre-fabricated electrode with strong adhesion, excellent conductivity, and dimensions that meet design requirements, providing a stable foundation for the electrical connection of subsequent devices.

[0018] Preferably, in step S4, the molybdenum tetraselenide tungsten layer is controlled to cover 70%-90% of the surface area of ​​the bottom molybdenum ditelluride layer, and the bottom molybdenum ditelluride layer, the molybdenum tetraselenide tungsten layer, and the top molybdenum ditelluride layer are in close contact through van der Waals forces.

[0019] By adopting the above technical solution, the coverage ratio of the molybdenum tetraselenide tungsten layer to the bottom molybdenum ditelluride layer is limited, ensuring that the double heterojunction has a sufficiently large effective photodetector area while reserving ample electrode connection area for the bottom molybdenum ditelluride layer, thus avoiding short-circuit problems in subsequent electrode connection processes. The layers achieve close contact through van der Waals forces, eliminating the need to consider lattice matching limitations between different two-dimensional materials. This results in a heterojunction interface with fewer interface defects and a clear bandgap arrangement, providing favorable conditions for rapid separation and cross-interface transport of photogenerated carriers. Simultaneously, it avoids the interface state surge problem caused by lattice mismatch, reducing interface recombination losses of photogenerated carriers and ensuring the photoelectric conversion efficiency of the device. Precise coverage ratio control ensures effective junction area matching between the upper and lower pn heterojunctions, providing a foundation for the symmetrical built-in electric field distribution of the double heterojunction.

[0020] Preferably, in step S5, the spin coating speed of the positive photoresist is 3500-4500 r / min, and the spin coating time is 40-80 seconds; the soft baking temperature is 160-200℃, and the soft baking time is 100-120 seconds; when depositing the chromium layer, the deposition rate is controlled at 0.08-0.2 nm / s, and the chromium layer thickness is 5-20 nm; when depositing the gold layer, the deposition rate is controlled at 0.2-0.6 nm / s, and the gold layer thickness is 50-80 nm.

[0021] By adopting the above technical solution, for the three-dimensional surface after vertical stacking, the optimized photoresist spin coating and soft baking parameters can form a uniformly covered photoresist layer without step fractures on the device surface with height differences, ensuring the accuracy of subsequent exposure and development. The electrode channels formed by exposure and development can accurately correspond to the reserved connection areas of the bottom and top molybdenum ditelluride layers, realizing independent electrical connection between the upper and lower p-type semiconductor layers and avoiding short circuits between the source and drain electrodes. The deposition parameters limited during electron beam evaporation can form a metal layer that is closely attached to the surface of the two-dimensional material in the electrode channel, effectively reducing the Schottky barrier and contact resistance between the metal and molybdenum ditelluride, reducing the transport loss of charge carriers at the electrode contact, and ensuring the stable realization of the device's bipolar operating mode.

[0022] Preferably, in step S6, the vacuum degree of the vacuum annealing furnace is 10. -3 -10 -5 Pa, annealing temperature is 180-220℃, and holding time is 5-10 minutes.

[0023] By employing the above technical solution, annealing in a high-vacuum environment can prevent the oxidation of the two-dimensional material and metal electrode during annealing. The set annealing temperature and holding time can effectively release the interlayer stress generated during the dry transfer stacking of two-dimensional materials, enhance the van der Waals interaction between layers, improve the contact tightness and uniformity of the heterojunction interface, reduce interlayer gaps and defects, and stabilize the built-in electric field distribution of the double heterojunction. The precisely controlled annealing time can not only fully release the interface stress and optimize the contact performance, but also avoid problems such as volatilization of chalcogen elements and lattice degradation in two-dimensional materials caused by prolonged high-temperature treatment. With the protection of the chalcogen element atmosphere, the generation of material defects can be further suppressed, ensuring the stability of the optoelectronic performance of the device and the repeatability of batch preparation.

[0024] Preferably, in step S1, the organic solvent is acetone and isopropanol, the ultrasonic cleaning power is 70-90W, and each cleaning session lasts 10-15 minutes; the drying process involves blowing with nitrogen gas followed by drying at 110-130℃ for 20-40 minutes; the silicon layer of the silicon / silicon dioxide composite substrate is a high-resistivity silicon substrate with a resistivity not lower than... The thickness of the silicon dioxide layer is 300-400nm.

[0025] By adopting the above technical solution, a stepwise ultrasonic cleaning process using acetone, isopropanol, and deionized water can be used to sequentially remove organic oil, particulate impurities, and inorganic residues from the substrate surface. Combined with the set ultrasonic power and cleaning time, deep cleaning of the substrate surface is achieved, preventing surface impurities from affecting the subsequent photoresist film formation quality and interlayer contact of the two-dimensional materials. Nitrogen blowing combined with vacuum high-temperature drying can thoroughly remove residual moisture from the substrate surface and micropores, preventing moisture residue from adversely affecting subsequent processes. Using a high-resistivity silicon substrate with a silicon dioxide insulating layer of a set thickness provides stable mechanical support for the entire device and achieves excellent electrical isolation, significantly reducing leakage current and ensuring the accuracy and operational stability of the device's electrical tests.

[0026] Preferably, in step S3, the number of multilayer molybdenum ditelluride layers obtained by mechanical peeling is 20-30 layers, and the number of multilayer molybdenum tetraselenide tungsten layers is 15-25 layers.

[0027] By adopting the above technical solutions, through mechanical peeling and optical screening, the number of layers in two-dimensional materials can be precisely controlled, which can stably match the designed material thickness and ensure that the material has stable semiconductor band characteristics and light absorption capabilities. Two-dimensional materials with uniform number of layers can form a heterojunction interface with an ultra-smooth surface, avoiding problems such as interface wrinkles, interlayer gaps, and poor contact caused by uneven number of layers. This ensures that the built-in electric field of the heterojunction is uniformly distributed throughout the entire effective area, providing a uniform electric field environment for the full depletion state of the intermediate absorption layer, and at the same time providing a stable material basis for the efficient separation and long-distance transport of photogenerated carriers.

[0028] Preferably, in step S3, the inert atmosphere is a high-purity argon atmosphere with a water oxygen content of less than 0.1 ppm; the low-energy plasma passivation treatment and the heterojunction transfer and stacking process in step S4 are continuously completed in the same glove box environment without being exposed to the atmospheric environment in between.

[0029] By employing the above technical solutions, the high-purity argon atmosphere with extremely low water and oxygen content can prevent the two-dimensional materials from being oxidized by atmospheric water and oxygen during passivation and transfer, reducing the generation of defects on the material surface and interface. Passivation treatment with the same parameters is applied to the interfaces of the upper and lower molybdenum ditelluride layers and the middle molybdenum tetraselenide tungsten layer, achieving symmetrical passivation of the two heterojunction interfaces. This ensures a high degree of consistency in the interface characteristics of the two pn junctions, providing an interface basis for the symmetry of the device's bipolar response. Low-energy plasma passivation is completed in an inert atmosphere and operates continuously in the same environment as the subsequent dry transfer and stacking, preventing the passivated material interfaces from being exposed to the atmosphere again and causing secondary pollution. This maximizes the cleanliness and low defect state density of the heterojunction interface, reduces the trapping effect of the interface on photogenerated carriers, and improves carrier transport efficiency and the device's photoelectric response performance.

[0030] Preferably, in step S4, during the dry transfer process, after each layer of two-dimensional material is transferred, the transfer is carried out only after confirming with an optical microscope that there are no bubbles or wrinkles between the layers.

[0031] By adopting the above technical solution, after the transfer of each layer of two-dimensional material is completed, real-time in-situ confirmation can be performed using an optical microscope. This allows for the timely detection and removal of interlayer bubbles, interface wrinkles, and other interface defects that may affect the performance of the heterojunction. At the same time, the stacking position of each layer of material can be checked in real time to ensure that the stacking accuracy of the three-layer two-dimensional material meets the design requirements. This avoids problems such as insufficient effective detection area, misalignment of electrode connection areas, and asymmetry of upper and lower heterojunctions caused by positional deviations. It ensures the structural integrity of the single device and the consistency of devices fabricated in batches, thereby reducing the defect rate of device fabrication.

[0032] In summary, this application has the following beneficial effects:

[0033] 1. This application adopts a vertically stacked dual heterostructure consisting of a bottom p-type molybdenum ditelluride, a middle n-type molybdenum tetraselenide, and a top p-type molybdenum ditelluride. Through the synergistic effect of the back-to-back heterojunctions, the middle absorption layer is completely depleted, which significantly shortens the transmission distance of photogenerated carriers, greatly improves the carrier separation and collection efficiency, and obtains better photoelectric response sensitivity and response speed.

[0034] 2. In this application, a symmetrical double heterojunction design with molybdenum ditelluride of the same material and specification for the upper and lower layers is preferred. Combined with symmetrical interface passivation and stacking process control, the consistency of the electrical characteristics of the double heterojunction is ensured, so that the device has similar photoresponse characteristics under positive and negative source and drain voltages, and excellent bipolar photoresponse effect is obtained.

[0035] 3. The method of this application, by combining 2H phase p-type molybdenum disiteride and n-type molybdenum tetraselenide tungsten semiconductor materials, and with optimized material thickness and layer number design, effectively expands the spectral response range of the device, realizes stable photoelectric detection in the visible to near-infrared band, and breaks through the spectral response limitation of traditional silicon-based detectors.

[0036] 4. This application adopts a stepwise fabrication process of first prefabricating electrodes and then constructing heterojunctions, combined with dry transfer stacking, in-situ interface passivation, and annealing in a chalcogenide atmosphere, which effectively avoids lattice damage to two-dimensional materials caused by high-energy processes, ensures the quality of heterojunction interfaces, and obtains devices with stable performance and good batch consistency. Moreover, the fabrication process is highly compatible with existing silicon-based semiconductor processes.

[0037] 5. By precisely limiting the thickness and number of layers of the two-dimensional material, this application ensures the material's light absorption capacity and structural stability while avoiding the decrease in carrier transport efficiency and material waste caused by excessive material thickness, thus achieving an optimized balance between device optoelectronic performance and fabrication cost. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of the cross-sectional structure of the molybdenum ditelluride / molybdenum tetraselenide / molybdenum ditelluride van der Waals heterojunction of the two-dimensional material fully depleted double heterojunction photodetector provided in this application; wherein, 1 is the substrate layer, 2 is the insulating layer, 3 is the molybdenum ditelluride layer, 4 is the molybdenum tetraselenide layer, 5 is the chromium layer, and 6 is the gold layer; the metal electrode is composed of the chromium layer and the gold layer;

[0039] Figure 2 This is a graph showing the response current variation of the photodetector provided in this application under 532nm laser wavelength illumination at different optical power densities when Vds=1V and Vds=-1V.

[0040] Figure 3 The output characteristic curves of the photodetector provided in this application under different laser bands of 532nm, 650nm, 976nm, 1310nm, and 1550nm are shown.

[0041] Figure 4 This is a graph showing the responsivity and specific detectivity of the photodetector provided in this application under the conditions of 532nm laser and Vds=1V.

[0042] Figure 5This is a photoresponse time curve of the photodetector provided in this application under the conditions of 532nm laser, laser frequency 500Hz, and Vds=1V. Detailed Implementation

[0043] The present application will be further described in detail below with reference to embodiments and comparative examples. Unless otherwise specified, the experimental methods used below are conventional methods. Unless otherwise specified, the materials, reagents, methods and instruments used are all conventional materials, reagents, methods and instruments in the art, which can be obtained by those skilled in the art through commercial channels or prepared according to literature methods.

[0044] Technical Concept: In the field of photoelectric detection technology, van der Waals heterojunctions based on two-dimensional materials are currently the core research and development direction for high-performance photoelectric detectors. Existing related technologies mostly adopt device structures with a single pn heterojunction. The built-in electric field coverage of this type of structure is limited, making it difficult to achieve complete depletion of the light absorption layer. This results in a long transport distance for photogenerated carriers, and non-radiative recombination easily occurs during transport, significantly limiting the separation and collection efficiency of carriers. At the same time, existing fabrication processes mostly involve building the heterojunction first and then fabricating the electrodes. High-energy processes such as photolithography and coating can easily cause irreversible damage to the lattice of the two-dimensional material and the heterojunction interface, further degrading the photoelectric performance of the device. Ultimately, this makes it difficult for existing detectors to simultaneously achieve high photoresponsivity and fast response speed.

[0045] This technical solution addresses the aforementioned technical challenges by simultaneously focusing on two core dimensions: device structure design and fabrication process optimization. In terms of structure design, a vertically stacked back-to-back dual heterostructure is constructed, consisting of a bottom p-type molybdenum ditelluride, a middle n-type molybdenum tetraselenide tungsten, and a top p-type molybdenum ditelluride. Through the synergistic effect of the built-in electric fields of the two heterojunctions, complete depletion of the middle absorption layer is achieved, significantly shortening the photogenerated carrier transport distance and reducing carrier recombination losses. In terms of fabrication process, a step-by-step process is adopted, first prefabricating electrodes and then constructing the heterojunctions. This is combined with processes such as early passivation of the two-dimensional material interface, precise dry transfer stacking, and annealing in a chalcogenide atmosphere. This effectively avoids damage to the two-dimensional materials caused by high-energy processes, ensuring the quality of the heterojunction interface and ultimately achieving a balance between high photoelectric response sensitivity and fast response speed.

[0046] Example 1: This example provides a method for fabricating a fully depleted double heterojunction photodetector made of two-dimensional materials. The core material parameters are as follows:

[0047] Molybdenum ditelluride is a p-type two-dimensional semiconductor material with a 2H phase. The thickness of both the bottom and top molybdenum ditelluride layers is 30 nm. The number of multilayer molybdenum ditelluride layers obtained by mechanical exfoliation is 25.

[0048] Molybdenum tetraselenide (MTL) is an n-type two-dimensional semiconductor material with a 2H phase. The thickness of the MTL layer is 25 nm, and the number of MTL layers obtained by mechanical exfoliation is 20.

[0049] The fabrication method of the above-mentioned two-dimensional material fully depleted double heterojunction photodetector includes the following steps:

[0050] S1. Composite substrate pretreatment: Select a silicon / silicon dioxide composite substrate, and ultrasonically clean it sequentially with organic solvent and deionized water. After cleaning, dry it to obtain a clean substrate.

[0051] In this case, the silicon layer of the silicon / silicon dioxide composite substrate is a high-resistivity silicon substrate with a resistivity of not less than [missing information]. The thickness of the silica layer is 350nm; the organic solvents are acetone and isopropanol; the ultrasonic cleaning power is 80W, and the cleaning time is 12 minutes each time; the drying process is to blow dry with nitrogen and then place it in a vacuum drying oven at 120℃ for 30 minutes.

[0052] S2. Pre-electrode preparation: Photoresist is spin-coated onto the silicon dioxide layer of a clean substrate. After soft baking, exposure, and development, an electrode pattern is formed on the silicon dioxide layer. A chromium layer and a gold layer are deposited using an electron beam evaporation process. Then, the residual photoresist is stripped off to obtain a substrate with pre-electrodes.

[0053] The photoresist used in the spin coating was a positive photoresist, with a spin coating speed of 3000 r / min and a spin coating time of 45 seconds; the soft baking temperature was 110℃, and the soft baking time was 60 seconds; the exposure dose was 100 mJ / cm. 2 The exposure time was 30 seconds; the development time was 90 seconds; the fixing time was 30 seconds; the deposition rate of the chromium layer was controlled at 0.15 nm / s, and the thickness of the chromium layer was 18 nm; the deposition rate of the gold layer was controlled at 0.4 nm / s, and the thickness of the gold layer was 52 nm, with a total metal electrode thickness of 70 nm.

[0054] S3. Material stripping and passivation: The molybdenum ditelluride bulk and the molybdenum tetraselenide tungsten bulk are mechanically stripped and screened to obtain multilayer two-dimensional materials; in an inert atmosphere, the interface to be contacted of the screened two-dimensional materials is subjected to low-energy plasma passivation treatment to obtain passivated two-dimensional materials.

[0055] The inert atmosphere is a high-purity argon atmosphere with a water oxygen content of less than 0.1 ppm; the low-energy plasma passivation treatment uses argon plasma, with the argon flow rate controlled at 7 sccm, the plasma power at 7 W, and the treatment time at 1.5 seconds; the low-energy plasma passivation treatment and the subsequent heterojunction transfer and stacking process in step S4 are completed continuously in the same glove box environment without being exposed to the atmospheric environment.

[0056] S4. Heterojunction Transfer and Stacking: Using a dry transfer system, in the same inert atmosphere, firstly, passivated multilayer molybdenum ditelluride is transferred to the surface of the silicon dioxide layer of the substrate to form a bottom molybdenum ditelluride layer, ensuring that the bottom molybdenum ditelluride layer has no direct contact with the pre-fabricated electrode; then, passivated multilayer molybdenum tetraselenide is transferred to the top of the bottom molybdenum ditelluride layer; finally, another set of passivated multilayer molybdenum ditelluride is transferred to the top of the molybdenum tetraselenide layer to form a top molybdenum ditelluride layer, ensuring that the top and bottom molybdenum ditelluride layers have no direct contact, thus completing the fabrication of the dual heterojunction vertical stacking structure;

[0057] In this process, the molybdenum tetraselenide tungsten layer covers 80% of the surface area of ​​the bottom molybdenum ditelluride layer; the bottom molybdenum ditelluride layer, the molybdenum tetraselenide tungsten layer, and the top molybdenum ditelluride layer are in close contact through van der Waals forces; during the dry transfer process, after each layer of two-dimensional material is transferred, the transfer of the next layer of material is carried out only after confirming with an optical microscope that there are no bubbles or wrinkles between the layers.

[0058] S5. Electrode connection fabrication: Photoresist is spin-coated onto the vertically stacked substrate surface. After exposure and development, electrode channels are defined. Chromium and gold layers are deposited using electron beam evaporation to electrically connect the bottom molybdenum ditelluride layer to the source electrode and the top molybdenum ditelluride layer to the drain electrode. Then, the residual photoresist is stripped off.

[0059] The photoresist used in the spin coating is a positive photoresist, with a spin coating speed of 4000 r / min and a spin coating time of 60 seconds; the soft baking temperature is 180℃ and the soft baking time is 110 seconds; the deposition rate of the chromium layer is controlled at 0.15 nm / s and the chromium layer thickness is 12 nm; the deposition rate of the gold layer is controlled at 0.4 nm / s and the gold layer thickness is 65 nm.

[0060] S6. Atmosphere annealing: The device with completed electrode connection is placed in a vacuum annealing furnace and annealed in a vacuum environment by introducing a chalcogen element atmosphere. After natural cooling, the target photodetector is obtained.

[0061] The vacuum degree of the vacuum annealing furnace is... The introduced chalcogen element atmosphere is a high-purity tellurium-selenium mixed vapor, prepared by sublimation of high-purity tellurium powder and high-purity selenium powder in a molar ratio of 1:1 at 200°C in the preheating zone of the annealing furnace; the partial pressure of the atmosphere in the annealing chamber is controlled at 7.5 × 10⁻⁶. -3 Pa; the annealing temperature is 200℃, and the holding time for annealing is 7 minutes.

[0062] Example 2: This example provides a method for fabricating a fully depleted double heterojunction photodetector made of two-dimensional materials. The core material parameters are as follows:

[0063] Molybdenum ditelluride is a p-type two-dimensional semiconductor material with a 2H phase. The thickness of both the bottom and top molybdenum ditelluride layers is 10 nm. The number of multilayer molybdenum ditelluride layers obtained by mechanical peeling is 20.

[0064] Molybdenum tetraselenide (MTL) is an n-type two-dimensional semiconductor material with a 2H phase. The thickness of the MTL layer is 10 nm, and the number of MTL layers obtained by mechanical exfoliation is 15.

[0065] The fabrication method of the above-mentioned two-dimensional material fully depleted double heterojunction photodetector includes the following steps:

[0066] S1. Composite substrate pretreatment: Select a silicon / silicon dioxide composite substrate, and ultrasonically clean it sequentially with organic solvent and deionized water. After cleaning, dry it to obtain a clean substrate.

[0067] In this case, the silicon layer of the silicon / silicon dioxide composite substrate is a high-resistivity silicon substrate with a resistivity of not less than [missing information]. The thickness of the silica layer is 300 nm; the organic solvents are acetone and isopropanol; the ultrasonic cleaning power is 70 W, and the cleaning time is 10 minutes each time; the drying process is to blow dry with nitrogen and then place it in a vacuum drying oven at 110°C for 20 minutes.

[0068] S2. Pre-electrode preparation: Photoresist is spin-coated onto the silicon dioxide layer of a clean substrate. After soft baking, exposure, and development, an electrode pattern is formed on the silicon dioxide layer. A chromium layer and a gold layer are deposited using an electron beam evaporation process. Then, the residual photoresist is stripped off to obtain a substrate with pre-electrodes.

[0069] The photoresist used in the spin coating was a positive photoresist, with a spin coating speed of 2800 r / min and a spin coating time of 30 seconds; the soft baking temperature was 100℃ and the soft baking time was 50 seconds; the exposure dose was 90 mJ / cm² and the exposure time was 25 seconds; the development time was 60 seconds and the fixing time was 25 seconds; the deposition rate of the chromium layer was controlled at 0.08 nm / s and the chromium layer thickness was 5 nm; the deposition rate of the gold layer was controlled at 0.2 nm / s and the gold layer thickness was 35 nm, with a total metal electrode thickness of 40 nm.

[0070] S3. Material stripping and passivation: The molybdenum ditelluride bulk and the molybdenum tetraselenide tungsten bulk are mechanically stripped and screened to obtain multilayer two-dimensional materials; in an inert atmosphere, the interface to be contacted of the screened two-dimensional materials is subjected to low-energy plasma passivation treatment to obtain passivated two-dimensional materials.

[0071] The inert atmosphere is a high-purity argon atmosphere with a water oxygen content of less than 0.1 ppm; the low-energy plasma passivation treatment uses argon plasma, with the argon flow rate controlled at 6 sccm, the plasma power at 6W, and the treatment time at 1 second; the low-energy plasma passivation treatment and the subsequent heterojunction transfer and stacking process in step S4 are completed continuously in the same glove box environment without being exposed to the atmospheric environment.

[0072] S4. Heterojunction Transfer and Stacking: Using a dry transfer system, in the same inert atmosphere, firstly, passivated multilayer molybdenum ditelluride is transferred to the surface of the silicon dioxide layer of the substrate to form a bottom molybdenum ditelluride layer, ensuring that the bottom molybdenum ditelluride layer has no direct contact with the pre-fabricated electrode; then, passivated multilayer molybdenum tetraselenide is transferred to the top of the bottom molybdenum ditelluride layer; finally, another set of passivated multilayer molybdenum ditelluride is transferred to the top of the molybdenum tetraselenide layer to form a top molybdenum ditelluride layer, ensuring that the top and bottom molybdenum ditelluride layers have no direct contact, thus completing the fabrication of the dual heterojunction vertical stacking structure;

[0073] In this process, the molybdenum tetraselenide tungsten layer covers 70% of the surface area of ​​the bottom molybdenum ditelluride layer; the bottom molybdenum ditelluride layer, the molybdenum tetraselenide tungsten layer, and the top molybdenum ditelluride layer are in close contact through van der Waals forces; during the dry transfer process, after each layer of two-dimensional material is transferred, the transfer of the next layer of material is carried out only after confirming with an optical microscope that there are no bubbles or wrinkles between the layers.

[0074] S5. Electrode connection fabrication: Photoresist is spin-coated onto the vertically stacked substrate surface. After exposure and development, electrode channels are defined. Chromium and gold layers are deposited using electron beam evaporation to electrically connect the bottom molybdenum ditelluride layer to the source electrode and the top molybdenum ditelluride layer to the drain electrode. Then, the residual photoresist is stripped off.

[0075] The photoresist used in the spin coating is a positive photoresist, with a spin coating speed of 3500 r / min and a spin coating time of 40 seconds; the soft baking temperature is 160℃ and the soft baking time is 100 seconds; the deposition rate of the chromium layer is controlled at 0.08 nm / s and the chromium layer thickness is 5 nm; the deposition rate of the gold layer is controlled at 0.2 nm / s and the gold layer thickness is 50 nm.

[0076] S6. Atmosphere annealing: The device with completed electrode connection is placed in a vacuum annealing furnace and annealed in a vacuum environment by introducing a chalcogen element atmosphere. After natural cooling, the target photodetector is obtained.

[0077] The vacuum degree of the vacuum annealing furnace is 10. -3 Pa; the introduced chalcogen element atmosphere is a high-purity tellurium-selenium mixed vapor, prepared by sublimation of high-purity tellurium powder and high-purity selenium powder in a molar ratio of 1:1 at 200℃ in the preheating zone of the annealing furnace; the partial pressure of the atmosphere in the annealing chamber is controlled at 5×10 Pa. -3Pa; the annealing temperature is 180℃, and the holding time for annealing is 5 minutes.

[0078] Example 3: This example provides a method for fabricating a fully depleted double heterojunction photodetector made of two-dimensional materials. The core material parameters are as follows:

[0079] Molybdenum ditelluride is a p-type two-dimensional semiconductor material with a 2H phase. The thickness of both the bottom and top molybdenum ditelluride layers is 50 nm. The number of multilayer molybdenum ditelluride layers obtained by mechanical peeling is 30.

[0080] Molybdenum tetraselenide (MTL) is an n-type two-dimensional semiconductor material with a 2H phase. The thickness of the MTL layer is 40 nm, and the number of MTL layers obtained by mechanical exfoliation is 25.

[0081] The fabrication method of the above-mentioned two-dimensional material fully depleted double heterojunction photodetector includes the following steps:

[0082] S1. Composite substrate pretreatment: Select a silicon / silicon dioxide composite substrate, and ultrasonically clean it sequentially with organic solvent and deionized water. After cleaning, dry it to obtain a clean substrate.

[0083] In this case, the silicon layer of the silicon / silicon dioxide composite substrate is a high-resistivity silicon substrate with a resistivity of not less than [missing information]. The thickness of the silica layer is 400 nm; the organic solvents are acetone and isopropanol; the ultrasonic cleaning power is 90 W, and the cleaning time is 15 minutes each time; the drying process is to blow dry with nitrogen and then place it in a vacuum drying oven at 130°C for 40 minutes.

[0084] S2. Pre-electrode preparation: Photoresist is spin-coated onto the silicon dioxide layer of a clean substrate. After soft baking, exposure, and development, an electrode pattern is formed on the silicon dioxide layer. A chromium layer and a gold layer are deposited using an electron beam evaporation process. Then, the residual photoresist is stripped off to obtain a substrate with pre-electrodes.

[0085] The photoresist used in the spin coating was a positive photoresist, with a spin coating speed of 3200 r / min and a spin coating time of 60 seconds; the soft baking temperature was 120℃, and the soft baking time was 70 seconds; the exposure dose was 110 mJ / cm. 2 The exposure time was 35 seconds; the development time was 120 seconds; the fixing time was 35 seconds; the deposition rate of the chromium layer was controlled at 0.2 nm / s, and the thickness of the chromium layer was 30 nm; the deposition rate of the gold layer was controlled at 0.6 nm / s, and the thickness of the gold layer was 70 nm, with a total metal electrode thickness of 100 nm.

[0086] S3. Material stripping and passivation: The molybdenum ditelluride bulk and the molybdenum tetraselenide tungsten bulk are mechanically stripped and screened to obtain multilayer two-dimensional materials; in an inert atmosphere, the interface to be contacted of the screened two-dimensional materials is subjected to low-energy plasma passivation treatment to obtain passivated two-dimensional materials.

[0087] The inert atmosphere is a high-purity argon atmosphere with a water oxygen content of less than 0.1 ppm; the low-energy plasma passivation treatment uses argon plasma, with the argon flow rate controlled at 8 sccm, the plasma power at 8W, and the treatment time at 2 seconds; the low-energy plasma passivation treatment and the subsequent heterojunction transfer and stacking process in step S4 are completed continuously in the same glove box environment without being exposed to the atmospheric environment.

[0088] S4. Heterojunction Transfer and Stacking: Using a dry transfer system, in the same inert atmosphere, firstly, passivated multilayer molybdenum ditelluride is transferred to the surface of the silicon dioxide layer of the substrate to form a bottom molybdenum ditelluride layer, ensuring that the bottom molybdenum ditelluride layer has no direct contact with the pre-fabricated electrode; then, passivated multilayer molybdenum tetraselenide is transferred to the top of the bottom molybdenum ditelluride layer; finally, another set of passivated multilayer molybdenum ditelluride is transferred to the top of the molybdenum tetraselenide layer to form a top molybdenum ditelluride layer, ensuring that the top and bottom molybdenum ditelluride layers have no direct contact, thus completing the fabrication of the dual heterojunction vertical stacking structure;

[0089] In this process, the molybdenum tetraselenide tungsten layer covers 90% of the surface area of ​​the bottom molybdenum ditelluride layer; the bottom molybdenum ditelluride layer, the molybdenum tetraselenide tungsten layer, and the top molybdenum ditelluride layer are in close contact through van der Waals forces; during the dry transfer process, after each layer of two-dimensional material is transferred, the transfer of the next layer of material is carried out only after confirming with an optical microscope that there are no bubbles or wrinkles between the layers.

[0090] S5. Electrode connection fabrication: Photoresist is spin-coated onto the vertically stacked substrate surface. After exposure and development, electrode channels are defined. Chromium and gold layers are deposited using electron beam evaporation to electrically connect the bottom molybdenum ditelluride layer to the source electrode and the top molybdenum ditelluride layer to the drain electrode. Then, the residual photoresist is stripped off.

[0091] The photoresist used in the spin coating is a positive photoresist, with a spin coating speed of 4500 r / min and a spin coating time of 80 seconds; the soft baking temperature is 200℃ and the soft baking time is 120 seconds; the deposition rate of the chromium layer is controlled at 0.2 nm / s and the chromium layer thickness is 20 nm; the deposition rate of the gold layer is controlled at 0.6 nm / s and the gold layer thickness is 80 nm.

[0092] S6. Atmosphere annealing: The device with completed electrode connection is placed in a vacuum annealing furnace and annealed in a vacuum environment by introducing a chalcogen element atmosphere. After natural cooling, the target photodetector is obtained.

[0093] The vacuum degree of the vacuum annealing furnace is 10.-5 Pa; the introduced chalcogen element atmosphere is a high-purity tellurium-selenium mixed vapor, prepared by sublimation of high-purity tellurium powder and high-purity selenium powder in a molar ratio of 1:1 at 200℃ in the preheating zone of the annealing furnace; the partial pressure of the atmosphere in the annealing chamber is controlled at 1×10⁻⁶. -2 Pa; the annealing temperature is 220℃, and the holding time for annealing is 10 minutes.

[0094] Example 4: Device Performance Testing and Result Analysis

[0095] This embodiment conducts comprehensive photoelectric performance tests on the fully depleted double heterojunction photodetector based on two-dimensional materials prepared in Example 1. The test conditions are as follows: the test environment is room temperature 25℃ and atmospheric atmosphere; the light source uses continuous wave lasers with wavelengths of 532nm, 650nm, 976nm, 1310nm and 1550nm, and the optical power density can be adjusted as needed; the electrical test uses a semiconductor characteristic analyzer, and the applied source-drain voltage (Vds) during the test ranges from -1V to 1V.

[0096] (1) Bipolar photoresponse characteristics test

[0097] Under laser irradiation at a wavelength of 532 nm, source-drain voltages of Vds=1V and Vds=-1V were applied to the device, respectively, and the laser power density was adjusted from 50 μW / mm². 2 Up to 400 μW / mm 2 Gradient change, test the change law of response current of the device, the test results are as follows Figure 2 As shown.

[0098] Test results show that the device exhibits significant photoresponse characteristics under both positive and negative source-drain voltages, and that the response current amplitudes corresponding to the positive and negative voltages are highly similar under the same optical power density. When the optical power density is 363 μW / mm²... 2 When Vds=1V, the response current is 2.8μA, and when Vds=-1V, the response current is -2.7μA, which fully demonstrates that the device has excellent bipolar optical response characteristics and can fully meet the detection requirements in bidirectional voltage operation scenarios.

[0099] (2) Broad spectrum response characteristics test

[0100] Lasers with wavelengths of 532nm, 650nm, 976nm, 1310nm, and 1550nm were used to test the output characteristic curves of the device at different wavelengths. The test results are as follows: Figure 3 As shown.

[0101] The results show that the device exhibits stable optical responses in both the visible light band (532 nm, 650 nm) and the near-infrared band (976 nm, 1310 nm, 1550 nm). In the 1550 nm near-infrared band, the response current reaches 0.5 μA when the optical power density is 2611 μW / mm², proving that the device has successfully achieved broadband visible-near-infrared detection with a complete spectral response range covering 532 nm to 1550 nm.

[0102] (3) Response sensitivity and response speed test

[0103] The core performance indicators of the device were characterized under test conditions of 532nm wavelength and Vds=1V, and the results are as follows: Figure 4 , Figure 5 As shown in the figure. Test results show that the device's photoresponsivity can reach 40.49 A / W, and its specific detectivity is as high as 7.48 × 10⁻⁶. 10 Jones; at the same time, the device has excellent response speed, with a light response rise time of only 0.757ms and a fall time of 2.627ms, which can fully meet the application requirements of high-speed photoelectric detection.

[0104] Example 5: Comparative Experiment on Optimization of Preparation Parameters

[0105] To verify the rationality of the core parameter design of this invention and to clarify the influence of key process and material parameters on device performance, this embodiment sets up a single-variable control experiment. The specific verification content is as follows:

[0106] (1) The effect of two-dimensional material thickness on device performance

[0107] Based on the core fabrication process of this invention, only the thickness of the molybdenum ditelluride layer was adjusted, while all other process parameters and environmental conditions remained completely consistent. A control device was fabricated and its performance was tested. Test results show that when the thickness of the molybdenum ditelluride layer decreased to 10 nm, the material's light absorption capacity weakened, and the device responsivity decreased significantly. When the thickness of the molybdenum ditelluride layer increased to 60 nm, the photogenerated carrier transport path lengthened, the device response speed decreased, and the response time increased significantly. The preferred thickness range of 10–50 nm in this invention achieves the optimal balance between light absorption capacity and carrier transport efficiency.

[0108] (2) The influence of electrode materials and structure on device performance

[0109] Based on the core fabrication process of this invention, only the material structure of the electrode was adjusted, while all other process parameters and environmental conditions remained completely consistent. A control device was fabricated and its performance was tested. The test results showed that when only the gold layer was used as the electrode, the contact resistance between the metal and the molybdenum distellide layer increased significantly, leading to an increase in the device's dark current. However, by using the chromium and gold composite electrode structure designed in this invention, the contact resistance can be effectively reduced, the dark current can be suppressed, and the detection sensitivity of the device can be significantly improved.

[0110] (3) The impact of transfer process on device performance

[0111] Based on the material system and structural design of this invention, only the transfer process of the two-dimensional material was changed. Control devices were fabricated using both the wet transfer process and the dry transfer process of this invention, while all other process parameters and environmental conditions remained completely consistent. Test results show that the wet transfer process easily leads to residual organic solvents on the surface of the two-dimensional material, causing poor interlayer contact in the heterojunction and a significant decrease in the optical response stability of the device. In contrast, the dry transfer process used in this invention effectively ensures interlayer cleanliness and tight contact, resulting in more stable device performance and better batch-to-batch consistency.

[0112] The technical solutions can be summarized as follows:

[0113] The above-described fabrication examples, performance tests, and parameter optimization experiments demonstrate that this invention, through a rationally designed symmetrical double heterojunction structure, precise material parameter control, and optimized fabrication process, successfully fabricates a fully depleted double heterojunction photodetector with broad spectral response, high detection sensitivity, fast response speed, and excellent bipolar photoresponse characteristics. This device has broad application prospects in fields such as integrated sensing and computing imaging and encrypted communication. Furthermore, the fabrication method is highly compatible with existing silicon-based semiconductor processes, facilitating large-scale integration and industrial application.

[0114] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

[0115] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for fabricating a fully depleted double heterojunction photodetector made of two-dimensional materials, characterized in that: Includes the following steps: S1. Composite substrate pretreatment: Select a silicon / silicon dioxide composite substrate, and ultrasonically clean it sequentially with organic solvent and deionized water. After cleaning, dry it to obtain a clean substrate. S2. Pre-electrode preparation: Photoresist is spin-coated onto the silicon dioxide layer surface of a clean substrate, and after soft baking, exposure, and development, an electrode pattern is formed on the silicon dioxide layer. A chromium and gold layer was deposited using an electron beam evaporation process, and then the residual photoresist was stripped off to obtain a substrate with pre-fabricated electrodes. S3. Material exfoliation and passivation: The molybdenum ditelluride bulk and the molybdenum tetraselenide tungsten bulk are mechanically exfoliated and screened to obtain multilayer two-dimensional materials; In an inert atmosphere, the interface of the selected two-dimensional material to be contacted is subjected to low-energy plasma passivation treatment to obtain the passivated two-dimensional material. S4. Heterojunction Transfer and Stacking: Using a dry transfer system, in the same inert atmosphere, firstly, passivated multilayer molybdenum ditelluride is transferred to the surface of the silicon dioxide layer of the substrate to form a bottom molybdenum ditelluride layer, ensuring that the bottom molybdenum ditelluride layer has no direct contact with the pre-fabricated electrode; then, passivated multilayer molybdenum tetraselenide is transferred to the top of the bottom molybdenum ditelluride layer; finally, another set of passivated multilayer molybdenum ditelluride is transferred to the top of the molybdenum tetraselenide layer to form a top molybdenum ditelluride layer, ensuring that the top and bottom molybdenum ditelluride layers have no direct contact, thus completing the fabrication of the dual heterojunction vertical stacking structure; S5. Electrode connection fabrication: Photoresist is spin-coated onto the vertically stacked substrate surface, and after exposure and development, electrode channels are defined. A chromium and gold layer is deposited using an electron beam evaporation process, which electrically connects the bottom molybdenum ditelluride layer to the source and the top molybdenum ditelluride layer to the drain. Then, the residual photoresist is stripped off. S6. Atmosphere Annealing: The device with completed electrode connections is placed in a vacuum annealing furnace and annealed under a chalcogen atmosphere in a vacuum environment. After natural cooling, the target photodetector is obtained.

2. The method for fabricating a fully depleted double heterojunction photodetector of a two-dimensional material according to claim 1, characterized in that: In step S3, the molybdenum ditelluride is a p-type two-dimensional semiconductor material with a 2H phase, and the molybdenum tetraselenide tungsten is an n-type two-dimensional semiconductor material with a 2H phase. In step S4, the thickness of the bottom molybdenum ditelluride layer and the top molybdenum ditelluride layer are both 10-50 nm, and the thickness of the molybdenum tetraselenide tungsten layer is 10-40 nm.

3. The method for fabricating a two-dimensional material fully depleted double heterojunction photodetector according to claim 1, characterized in that: In step S2, the spin coating speed of the positive photoresist is 2800-3200 r / min, and the spin coating time is 30-60 seconds; the soft baking temperature is 100-120℃, and the soft baking time is 50-70 seconds; the exposure dose is 90-110 mJ / cm², and the exposure time is 25-35 seconds; the development time is 60-120 seconds, and the fixing time is 25-35 seconds; when depositing the chromium layer, the deposition rate is controlled at 0.08-0.2 nm / s, and the chromium layer thickness is 5-30 nm; when depositing the gold layer, the deposition rate is controlled at 0.2-0.6 nm / s, the gold layer thickness is 35-70 nm, and the total thickness of the metal electrode is 40-100 nm.

4. The method for fabricating a fully depleted double heterojunction photodetector of a two-dimensional material according to claim 1, characterized in that: In step S4, the molybdenum tetraselenide tungsten layer is controlled to cover 70%-90% of the surface area of ​​the bottom molybdenum ditelluride layer, and the bottom molybdenum ditelluride layer, the molybdenum tetraselenide tungsten layer and the top molybdenum ditelluride layer are in close contact through van der Waals forces.

5. The method for fabricating a fully depleted double heterojunction photodetector of a two-dimensional material according to claim 1, characterized in that: In step S5, the spin coating speed of the positive photoresist is 3500-4500 r / min, and the spin coating time is 40-80 seconds; the soft baking temperature is 160-200℃, and the soft baking time is 100-120 seconds; when depositing the chromium layer, the deposition rate is controlled at 0.08-0.2 nm / s, and the chromium layer thickness is 5-20 nm; when depositing the gold layer, the deposition rate is controlled at 0.2-0.6 nm / s, and the gold layer thickness is 50-80 nm.

6. The method for fabricating a fully depleted double heterojunction photodetector of a two-dimensional material according to claim 1, characterized in that: In step S6, the vacuum degree of the vacuum annealing furnace is 10. -3 -10 -5 Pa, annealing temperature is 180-220℃, and holding time is 5-10 minutes.

7. The method for fabricating a fully depleted double heterojunction photodetector of a two-dimensional material according to claim 1, characterized in that: In step S1, the organic solvents are acetone and isopropanol; the ultrasonic cleaning power is 70-90W; and each cleaning session lasts 10-15 minutes. The drying process involves blowing with nitrogen gas followed by drying at 110-130℃ for 20-40 minutes. The silicon layer of the silicon / silicon dioxide composite substrate is a high-resistivity silicon substrate with a resistivity not lower than [value missing]. The thickness of the silicon dioxide layer is 300-400nm.

8. The method for fabricating a fully depleted double heterojunction photodetector of a two-dimensional material according to claim 1, characterized in that: In step S3, the number of multilayer molybdenum ditelluride layers obtained by mechanical stripping is 20-30, and the number of multilayer molybdenum tetraselenide tungsten layers is 15-25.

9. The method for fabricating a fully depleted double heterojunction photodetector of a two-dimensional material according to claim 1, characterized in that: In step S3, the inert atmosphere is a high-purity argon atmosphere with a water oxygen content of less than 0.1 ppm; the low-energy plasma passivation treatment and the heterojunction transfer and stacking process in step S4 are completed continuously in the same glove box environment without being exposed to the atmospheric environment.

10. The method for fabricating a fully depleted double heterojunction photodetector of a two-dimensional material according to claim 1, characterized in that: In step S4, during the dry transfer process, after each layer of two-dimensional material is transferred, the transfer is confirmed by an optical microscope to ensure that there are no bubbles or wrinkles between the layers before the next layer of material is transferred.

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