Two-dimensional Van der Waals heterojunction photoelectric detector and preparation method thereof
By using the GaS-WSe2 heterojunction structure, the environmental stability and dark current problems of the TMD heterojunction photodetector were solved, achieving wide spectral response, fast response and high linear dynamic range, thus improving the overall performance of the photodetector.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- THE HONG KONG POLYTECHNIC UNIV SHENZHEN RES INST
- Filing Date
- 2024-10-24
- Publication Date
- 2026-04-24
AI Technical Summary
Existing TMD heterojunction photodetectors exhibit poor performance in terms of environmental stability and dark current, have a small linear dynamic range, and cannot maintain good performance under varying light conditions.
A two-dimensional van der Waals photodetector was fabricated by using a GaS-WSe2 heterojunction structure, which is formed by GaS nanosheets and WSe2 nanosheets of a specific thickness. The two-dimensional van der Waals photodetector was fabricated by combining tape transfer and annealing techniques.
It achieves wide spectral response capability, fast response speed, low dark current and high linear dynamic range, covering a wide spectral range from 275nm to 1064nm, with a response speed of up to 625μs and a dark current as low as fA, exhibiting excellent environmental stability and durability.
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Figure CN121924853A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of photodetector technology, and in particular to a two-dimensional van der Waals heterojunction photodetector and its fabrication method. Background Technology
[0002] Photodetectors (PDs) are widely used in various fields, such as imaging, environmental monitoring, communication, and security. In recent years, two-dimensional material photodetectors based on van der Waals heterojunctions have attracted considerable attention, particularly those made of transition metal sulfides (TMDs), such as MoS2 / WSe2 heterojunctions. These materials exhibit excellent photoelectric properties and tunable band structures, demonstrating good broadband optical response, fast response speed, and high detectivity. These devices typically possess high photoelectric conversion efficiency and can cover a wide wavelength range from ultraviolet to near-infrared. However, existing photodetectors based on these materials still suffer from some significant drawbacks.
[0003] On the one hand, many TMD-based heterojunction photodetectors exhibit poor environmental stability, especially when exposed to air or moisture, where their performance is prone to degradation. Furthermore, these devices typically perform poorly in terms of dark current; high dark current not only affects the detector's signal-to-noise ratio but also limits its application under low-light conditions. On the other hand, while existing heterojunction devices demonstrate good performance in terms of wide-band optical response and high detectability, the performance of many devices is heavily dependent on specific structural optimizations, and their performance degrades significantly when operating conditions change. Simultaneously, some heterojunction photodetectors have a small linear dynamic range, failing to maintain linear response across a wide range of light intensities, thus limiting their application in variable lighting environments.
[0004] Therefore, existing technologies still need to be improved and developed. Summary of the Invention
[0005] In view of the shortcomings of the prior art, the purpose of this invention is to provide a two-dimensional van der Waals heterojunction photodetector and its fabrication method, aiming to solve the problems of small linear dynamic range and poor environmental stability of existing TMD heterojunction photodetectors.
[0006] The technical solution of the present invention is as follows:
[0007] In a first aspect, the present invention provides a two-dimensional van der Waals heterojunction photodetector, comprising, from bottom to top, a substrate, a hexagonal boron nitride layer, a bottom two-dimensional semiconductor, a top two-dimensional semiconductor, and metal source and metal drain electrodes covering the non-overlapping ends of the bottom two-dimensional semiconductor and the top two-dimensional semiconductor; the bottom two-dimensional semiconductor is located at the center of the hexagonal boron nitride layer, the top two-dimensional semiconductor covers a portion of the bottom two-dimensional semiconductor and extends onto the hexagonal boron nitride layer, and the overlapping region between the top two two-dimensional semiconductor and the bottom two-dimensional semiconductor forms a heterojunction through van der Waals forces;
[0008] The bottom two-dimensional semiconductor includes WSe2 nanosheets, and the top two-dimensional semiconductor includes GaS nanosheets.
[0009] Optionally, the substrate is a SiO2 / Si substrate composed of silicon dioxide covering a silicon surface.
[0010] Optionally, the thickness of the WSe2 nanosheet is 3-4 nm.
[0011] Optionally, the thickness of the GaS nanosheet is 8-9 nm.
[0012] Preferably, the thickness of the WSe2 nanosheet is 3 nm, and the thickness of the GaS nanosheet is 8.5 nm.
[0013] Optionally, the thickness of the hexagonal boron nitride layer is 8-10 nm.
[0014] Optionally, both the metal source and the metal drain are Ag / Au electrodes with a thickness of 20-100 nm.
[0015] A second aspect of the present invention provides a method for fabricating the aforementioned two-dimensional van der Waals heterojunction photodetector, comprising the steps of:
[0016] S1. After mechanically peeling off hexagonal boron nitride with adhesive tape, transfer it to polydimethylsiloxane. Using an optical microscope, select a hexagonal boron nitride sheet with a thickness of 8-10 nm from the polydimethylsiloxane and transfer the hexagonal boron nitride sheet to a SiO2 / Si substrate to form a hexagonal boron nitride layer.
[0017] S2. Use adhesive tape to peel the WSe2 crystal material onto the WSe2 nanosheets, transfer the WSe2 nanosheets from the adhesive tape onto polydimethylsiloxane, and transfer WSe2 nanosheets of a target thickness onto the hexagonal boron nitride layer.
[0018] S3. Use adhesive tape to peel the GaS crystal material onto GaS nanosheets, transfer the GaS nanosheets from the adhesive tape onto polydimethylsiloxane, stack GaS nanosheets of target thickness onto WSe2 nanosheets to form van der Waals heterojunctions, and perform annealing treatment.
[0019] S4. Using photolithography and electron beam evaporation techniques, metal source and metal drain electrodes are deposited at the non-overlapping ends of GaN nanosheets and WSe2 nanosheets, respectively, to finally obtain the two-dimensional van der Waals heterojunction photodetector.
[0020] Optionally, the thickness of the WSe2 nanosheet is 3-4 nm.
[0021] Optionally, the thickness of the GaS nanosheet is 8-9 nm.
[0022] Optionally, the annealing temperature is 200-300℃, and the annealing time is 3-5 hours.
[0023] Beneficial effects:
[0024] This invention provides a two-dimensional van der Waals heterojunction photodetector and its fabrication method. The GaS-WSe2 heterojunction exhibits superior photoelectric performance, possessing a wide spectral response, fast response speed, low dark current, and high linear dynamic range. The GaS-WSe2 heterostructure not only responds in the ultraviolet and visible light bands but also extends to the near-infrared band, covering a wide spectral range from 275 nm to 1064 nm. Furthermore, the two-dimensional van der Waals heterojunction photodetector has a linear dynamic range exceeding 100, a response speed as high as 625 μs, and a dark current as low as fA, exhibiting excellent environmental stability and durability, making the photodetector highly competitive in photoelectric detection applications. Attached Figure Description
[0025] Figure 1 This is a schematic diagram of the structure of a two-dimensional van der Waals heterojunction photodetector in an embodiment of the present invention.
[0026] Figure 2 This is a graph showing the relationship between the logarithm of the open-circuit voltage (VOC) and short-circuit current (ISC) and the logarithm of the power density for a two-dimensional van der Waals heterojunction photodetector in an embodiment of the present invention.
[0027] Figure 3 This is a test graph showing the switching stability of a two-dimensional van der Waals heterojunction photodetector under 405nm illumination after 200 switching cycles in an embodiment of the present invention.
[0028] Figure 4 This is a stability test diagram of a two-dimensional van der Waals heterojunction photodetector stored under atmospheric conditions for 3 months in an embodiment of the present invention.
[0029] Figure 5 This refers to the response time of the two-dimensional van der Waals heterojunction photodetector near the cutoff frequency in this embodiment of the invention.
[0030] Figure 6 This is the frequency response diagram of the two-dimensional van der Waals heterojunction photodetector in an embodiment of the present invention.
[0031] Figure 7 This is a performance comparison chart of two-dimensional van der Waals heterojunction photodetectors of different thicknesses (device 1: 10 nm and device 2: 20 nm) under similar illumination conditions. Detailed Implementation
[0032] This invention provides a two-dimensional van der Waals heterojunction photodetector and its fabrication method. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.
[0034] This invention provides a two-dimensional van der Waals heterojunction photodetector, comprising, from bottom to top, a substrate, a hexagonal boron nitride layer, a bottom two-dimensional semiconductor, a top two-dimensional semiconductor, and metal source and metal drain electrodes covering the non-overlapping ends of the bottom and top two-dimensional semiconductors. The bottom two-dimensional semiconductor is located at the center of the hexagonal boron nitride layer, and the top two-dimensional semiconductor covers a portion of the bottom two-dimensional semiconductor and extends onto the hexagonal boron nitride layer. The overlapping region between the top and bottom two-dimensional semiconductors forms a heterojunction through van der Waals forces.
[0035] The bottom two-dimensional semiconductor includes WSe2 nanosheets, and the top two-dimensional semiconductor includes GaS nanosheets.
[0036] In the two-dimensional van der Waals heterojunction photodetector designed in this invention, the underlying two-dimensional semiconductor WSe2 has a suitable bandgap (approximately 1.2 eV), making it suitable for detecting photons in the visible to near-infrared spectrum. It exhibits strong light absorption at longer wavelengths, resulting in high sensitivity during high-wavelength operation. However, WSe2 has a high dark current, which can reduce the signal-to-noise ratio in the photon detector. Simultaneously, WSe2 possesses suitable electronic structure and mobility characteristics, which are beneficial for forming a type II heterojunction, thereby enhancing the performance of the photodetector.
[0037] The top-layer two-dimensional semiconductor GaS possesses a high bandgap (approximately 2.5 eV), resulting in very high absorption efficiency at short wavelengths (such as ultraviolet and blue light). Compared to GaN, which has a wider bandgap (approximately 3.4 eV), GaS in heterojunctions can more effectively reduce dark current to extremely low levels (fA), thereby significantly improving detector sensitivity and signal-to-noise ratio. This is achieved by regulating the transport and recombination of photogenerated charge carriers, thus enabling the device to maintain stable performance even in low-light environments. Therefore, using GaS semiconductor materials not only demonstrates superior technical effects in reducing dark current and expanding the response range, but also achieves fast response and higher detection sensitivity through optimized carrier transport mechanisms.
[0038] GaS achieves a large linear dynamic range in van der Waals heterojunctions. The type II heterojunction formed by combining GaS with WSe2 further expands the response range of the photodetector, covering a broad spectral response range from 275 nm to 1064 nm, achieving a wider detection wavelength range and a lower detection limit. Mechanistically, the thermoelectric properties and good electron mobility of GaS enhance the effective separation and transport efficiency of charge carriers. GaS and WSe2 work synergistically to provide a high-mobility hole channel, jointly promoting the rapid response of the self-powered photodetector, enabling the device to achieve efficient photoelectric conversion without an external power supply. The GaS / WSe2 heterojunction effectively promotes the separation of photogenerated electron-hole pairs and suppresses electron-hole recombination, thereby significantly improving photoresponse while reducing photoresponse time.
[0039] Traditional WSe2 photodetectors typically have response times ranging from several seconds to tens of seconds, while the two-dimensional van der Waals heterojunction photodetector designed in this invention, based on a GaS / WSe2 heterojunction, exhibits response times in the microsecond range for both ultraviolet and visible light. Traditional photodetectors based on transition metal chalcogenides generally have visible light responsivity in the order of mA / W, while the two-dimensional van der Waals heterojunction photodetector designed in this invention achieves responsivity in the tens to hundreds of A / W range for both ultraviolet and visible light. GaS, as a wide-bandgap semiconductor, possesses low dark current characteristics, which can significantly reduce noise in the detection system. Forming a heterojunction between GaS two-dimensional semiconductor materials and other transition metal chalcogenides can significantly optimize and improve the performance of traditional photodetectors.
[0040] The two-dimensional van der Waals heterojunction photodetector provided by this invention achieves wide-band photoresponse, low dark current, high linear dynamic range, and good environmental stability. Especially in the spectral range of 275 nm to 1064 nm, the device exhibits excellent photovoltaic response characteristics, along with extremely high detectivity and fast response speed. These advantages significantly improve the overall performance of the photodetector, particularly in terms of broadband optical response, low noise, high linear dynamic range, and environmental adaptability, demonstrating broad application potential.
[0041] In some embodiments, the substrate is a SiO2 / Si substrate composed of silicon dioxide covering a silicon surface.
[0042] In some embodiments, the thickness of the WSe2 nanosheet is 3-4 nm.
[0043] The thickness of the underlying two-dimensional semiconductor WSe2 is controlled within the range of 3nm to 4nm, forming an ultrathin material with a bandgap of 1.6eV to 1.7eV. This thickness of WSe2 exhibits p-type conductivity, making it suitable for constructing pn junctions in heterojunctions. The WSe2 layer absorbs light in the wavelength range of 500nm to 800nm. However, under illumination with wavelengths below 500nm, the WSe2 response decreases significantly because this wavelength exceeds the bandgap response range of WSe2. With increasing thickness, WSe2 gradually transforms into n-type conductivity, thereby disrupting the band structure of the van der Waals heterojunction.
[0044] In some embodiments, the thickness of the GaS nanosheet is 8-9 nm.
[0045] The top-layer two-dimensional semiconductor GaS exhibits stable n-type conductivity within a thickness range of 8-9 nm, with a band gap of 2.5 eV and an optical response range of 275 nm to 550 nm. As the thickness of GaS decreases, the band gap increases, its n-type conductivity weakens, and it gradually transforms into p-type characteristics.
[0046] In some preferred embodiments, the thickness of the WSe2 nanosheet is 3 nm, and the thickness of the GaS nanosheet is 8.5 nm.
[0047] In the two-dimensional van der Waals heterojunction photodetector of the present invention, the thick n-type semiconductor GaS and p-type semiconductor WSe2 form a strong pn van der Waals heterojunction, providing a reliable and efficient mechanism for charge separation, effectively promoting the separation of photogenerated electron-hole pairs, suppressing recombination between electrons and holes, and thus significantly improving the photoresponsivity while reducing the photoresponse time, thereby significantly improving the performance of the photodetector.
[0048] In some embodiments, the thickness of the hexagonal boron nitride layer is 8-10 nm.
[0049] In some embodiments, both the metal source and the metal drain are Ag / Au electrodes with a thickness of 20-100 nm.
[0050] A second aspect of the present invention provides a method for fabricating the aforementioned two-dimensional van der Waals heterojunction photodetector, comprising the steps of:
[0051] S1. After mechanically peeling off hexagonal boron nitride with tape, transfer it to polydimethylsiloxane (PDMS). Using an optical microscope, select a hexagonal boron nitride sheet with a thickness of 8-10 nm from the PDMS and transfer the hexagonal boron nitride sheet to a SiO2 / Si substrate to form a hexagonal boron nitride layer.
[0052] S2. Use adhesive tape to peel the WSe2 crystal material onto the WSe2 nanosheets, transfer the WSe2 nanosheets from the adhesive tape onto polydimethylsiloxane, and transfer WSe2 nanosheets of a target thickness onto the hexagonal boron nitride layer.
[0053] S3. Use adhesive tape to peel the GaS crystal material onto GaS nanosheets, transfer the GaS nanosheets from the adhesive tape onto polydimethylsiloxane, stack GaS nanosheets of target thickness onto WSe2 nanosheets to form van der Waals heterojunctions, and perform annealing treatment.
[0054] S4. Using photolithography and electron beam evaporation techniques, metal source and metal drain electrodes are deposited at the non-overlapping ends of GaN nanosheets and WSe2 nanosheets, respectively, to finally obtain the two-dimensional van der Waals heterojunction photodetector.
[0055] In some embodiments, the thickness of the WSe2 nanosheet is 3-4 nm.
[0056] In some embodiments, the thickness of the GaS nanosheet is 8-9 nm.
[0057] In some embodiments, the annealing temperature is 200-300°C and the annealing time is 3-5 hours.
[0058] In some embodiments, both the metal source and the metal drain are Ag / Au with a thickness of 20-100 nm.
[0059] The following detailed description uses specific examples.
[0060] Example 1
[0061] GaS crystal growth
[0062] Gallium sulfide (GaS) crystals were obtained using chemical vapor transport (CVT) technology. 0.25 grams of gallium (Ga: 99.999% purity) and 0.25 grams of sulfur (S: 99.999% purity) were mixed and encapsulated in a quartz tube with a diameter of 22 mm and a length of 20 cm, under a pressure of approximately 10... -4 Gallium was transported using iodine (I₂) (0.1 g) as a carrier. The powder was heated to 900 °C and maintained in a single-zone furnace for 7 days, then cooled to room temperature. Gallium reacted with sulfur and deposited as yellow crystals at the cold end of the tube.
[0063] WSe2 crystal growth
[0064] Tungsten diselenide (WSe2) crystals were obtained using chemical vapor transport (CVT). Tungsten (W: 99.999% purity) and selenium (Se: 99.999% purity) were mixed in a 1:2 molar ratio and encapsulated in a quartz tube with a diameter of 22 mm and a length of 20 cm, filled with argon gas at one-third atmosphere pressure. The mixture was heated to 850°C in a tube furnace at a rate of 20°C per hour and maintained for 3 days before the furnace was shut off. Approximately 2.98 g of WSe2 powder and 0.25 g of iodine (I2) were encapsulated in another quartz tube at a pressure of approximately 10... -4 The tube was heated in a two-zone furnace for 14 days, with the hot zone at 1050°C and the cold zone at 1000°C, and finally cooled to room temperature. Crystals formed at the cold end of the tube, resulting in lustrous, plate-like WSe2 crystals.
[0065] A van der Waals heterostructure was obtained from an externally sourced crystal using a traditional micromechanical pyrolysis and directional transfer technique based on transparent tape / PDMS. Hexagonal boron nitride (h-BN) was peeled off using transparent tape and transferred to PDMS. Thin sheets of suitable thickness (10 nm) were identified and selected under a microscope using optical contrast, and then transferred to a SiO2 / Si substrate. The SiO2 / Si substrate was previously ultrasonically cleaned with acetone (2 min), IPA (3 min), and deionized water (3 min), followed by plasma treatment (O2 plasma, 100 W, 5 min). PDMS was then brought into contact with the target region on the SiO2 substrate and heated to 60 °C. After waiting 3 min, the PDMS was slowly withdrawn at a certain angle, leaving the h-BN layer on top of the SiO2. Similarly, WSe2 and GaS crystal materials were peeled off with tape to obtain WSe2 (3nm) nanosheets and GaS (8.5nm) nanosheets, respectively, which were then transferred to PDMS and sequentially stacked on top of the h-BN layer at the same temperature to form a van der Waals heterojunction. The heterojunction was then annealed in a tube furnace at 200°C for 3 hours with an Ar gas flow rate of 50 sccm.
[0066] Photoresist (PR) (AZ5214E) was spin-coated onto a 1cm x 1cm Si substrate at 5000 rpm, resulting in a 1.25μm thickness. The PR-coated photoresist was then baked in an electric furnace at 110°C for 1 minute. A chromium photomask with electrode patterns was then mounted onto a mask aligner (SUSS MA-6, Microtek), and the PR-coated substrate was exposed to 375nm UV light for 5 seconds. The exposed substrate was then immersed in developer (AZ300MIF) for 30 seconds, gently agitated, thoroughly rinsed with deionized water, and dried using a nitrogen gun. Metal deposition was performed via electron beam evaporation (Denton E-beam Explorer) at a rate of [missing information - likely a specific velocity value]. The working pressure is 4.2*10 -7 To, covering layer The deposition rate, at 6.1 x 10⁻⁶ -7 A 20 nm layer was deposited under the operating pressure of the substrate. The metal-deposited substrate was peeled off by placing it in an acetone bath and gently agitating it, followed by immersion in water for 3 hours. Finally, the patterned substrate was rinsed sequentially with IPA and deionized water.
[0067] To integrate the patterned electrode onto the van der Waals heterojunction, PVA thermoplastic was used for pick-and-place. A PVA-DI aqueous solution (0.083 g / ml) was spin-coated onto the top of the patterned electrode at 3000 rpm and then dried on a hot plate at 60°C for 10 minutes. The electrode, encased in the PVA film, was released from the sacrificial substrate using tweezers, and then precisely transferred to the top of the heterojunction region using PDMS as a carrier and aligned with a micrometer on the same transfer stage. The substrate was heated to 50°C, at which point the electrode / PVA / PDMS was precisely in contact with the heterojunction, held for 3 minutes, and finally the PDMS was released at a specific angle. The PVA-electrode-heterojunction was immersed in a deionized water bath for 1 hour and then dried with nitrogen to complete the two-dimensional van der Waals heterojunction photodetector, as shown in the schematic diagram below. Figure 1 As shown.
[0068] The two-dimensional van der Waals heterojunction photodetector was comprehensively tested using an Agilent B1500 parameter analyzer. During the test, various light sources were used, including lasers with wavelengths of 405nm, 450nm, 532nm, 660nm and 1064nm, and LEDs with wavelengths of 275nm, 325nm, 375nm, 810nm and 940nm.
[0069] like Figure 2As shown, the maximum open-circuit voltage of the device is 0.36V, indicating high photoresponse efficiency under illumination. The linear dynamic range (LDR) of the two-dimensional van der Waals heterojunction photodetector is 106.7dB, reflecting its wide detection range, while the power index reaches a maximum of 0.96, indicating that the device has minimal trapping and recombination effects. In the wavelength range of 375nm to 940nm, the power index consistently remains above 0.9, indicating that the two-dimensional van der Waals heterojunction photodetector exhibits consistent high performance in this band (see...). Figure 2 ).
[0070] like Figure 3 and Figure 4 As shown, the two-dimensional van der Waals heterojunction photodetector prepared in this embodiment of the invention maintains its performance unchanged after 200 operating cycles and 3 months of atmospheric storage, demonstrating excellent operational stability and durability.
[0071] like Figure 5 and Figure 6 As shown, the two-dimensional van der Waals heterojunction photodetector has a good response speed, with a rise time of 685 microseconds and a fall time of 657 microseconds, and a cutoff frequency of 697 Hz.
[0072] like Figure 7 As shown, both devices exhibited strong photoresponse characteristics, including significant Voc and Isc values, when tested under the same illumination conditions. However, the device with a slightly larger thickness showed a slightly lower light conversion efficiency, indicating that the effective layer thickness of the device has a synergistic effect on carrier separation, extraction, and recombination, and any deviation from the optimal thickness will lead to performance degradation.
[0073] In summary, the GaS-WSe2 van der Waals heterojunction of this invention exhibits superior photoelectric performance, possessing broad spectral response, fast response speed, low dark current, and high linear dynamic range. By designing GaS nanosheets and WSe2 nanosheets of specific thicknesses, this invention enables the GaS-WSe2 heterojunction to achieve performance far exceeding that of individual monolayer materials. The GaS-WSe2 heterostructure not only exhibits response in the ultraviolet and visible light bands but also extends to the near-infrared band, covering a broad spectral range from 275 nm to 1064 nm. Furthermore, the two-dimensional van der Waals heterojunction photodetector fabricated in this embodiment of the invention has a linear dynamic range exceeding 100, a response speed as high as 625 μs, and a dark current as low as fA, making this photodetector highly competitive in photoelectric detection applications.
[0074] It should be understood that the application of the present invention is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.
Claims
1. A two-dimensional van der Waals heterojunction photodetector, characterized in that, The structure, from bottom to top, includes a substrate, a hexagonal boron nitride layer, a bottom two-dimensional semiconductor, a top two-dimensional semiconductor, and metal source and drain electrodes covering the non-overlapping ends of the bottom and top two-dimensional semiconductors. The bottom two-dimensional semiconductor is located at the center of the hexagonal boron nitride layer, and the top two-dimensional semiconductor covers a portion of the bottom two-dimensional semiconductor and extends onto the hexagonal boron nitride layer. The overlapping region between the top and bottom two-dimensional semiconductors forms a heterojunction through van der Waals forces. The bottom two-dimensional semiconductor includes WSe2 nanosheets, and the top two-dimensional semiconductor includes GaS nanosheets.
2. The two-dimensional van der Waals heterojunction photodetector according to claim 1, characterized in that, The substrate is a SiO2 / Si substrate composed of silicon dioxide covering the silicon surface.
3. The two-dimensional van der Waals heterojunction photodetector according to claim 1, characterized in that, The thickness of the WSe2 nanosheets is 3-4 nm.
4. The two-dimensional van der Waals heterojunction photodetector according to claim 1, characterized in that, The thickness of the GaS nanosheets is 8-9 nm.
5. The two-dimensional van der Waals heterojunction photodetector according to claim 3 or 4, characterized in that, The WSe2 nanosheets have a thickness of 3 nm, and the GaS nanosheets have a thickness of 8.5 nm.
6. The two-dimensional van der Waals heterojunction photodetector according to claim 1, characterized in that, The thickness of the hexagonal boron nitride layer is 8-10 nm.
7. The two-dimensional van der Waals heterojunction photodetector according to claim 1, characterized in that, Both the metal source and the metal drain are Ag / Au electrodes with a thickness of 20-100 nm.
8. A method for fabricating a two-dimensional van der Waals heterojunction photodetector as described in any one of claims 1-7, characterized in that, Including the following steps: S1. After mechanically peeling off hexagonal boron nitride with adhesive tape, transfer it to polydimethylsiloxane. Using an optical microscope, select a hexagonal boron nitride sheet with a thickness of 8-10 nm from the polydimethylsiloxane and transfer the hexagonal boron nitride sheet to a SiO2 / Si substrate to form a hexagonal boron nitride layer. S2. Use adhesive tape to peel the WSe2 crystal material onto the WSe2 nanosheets, transfer the WSe2 nanosheets from the adhesive tape onto polydimethylsiloxane, and transfer WSe2 nanosheets of a target thickness onto the hexagonal boron nitride layer. S3. Use adhesive tape to peel the GaS crystal material onto GaS nanosheets, transfer the GaS nanosheets from the adhesive tape onto polydimethylsiloxane, stack GaS nanosheets of target thickness onto WSe2 nanosheets to form van der Waals heterojunctions, and perform annealing treatment. S4. Using photolithography and electron beam evaporation techniques, metal source and metal drain electrodes are deposited at the non-overlapping ends of GaN nanosheets and WSe2 nanosheets, respectively, to finally obtain the two-dimensional van der Waals heterojunction photodetector.
9. The method for fabricating a two-dimensional van der Waals heterojunction photodetector according to claim 8, characterized in that, The thickness of the WSe2 nanosheets is 3-4 nm, and the thickness of the GaS nanosheets is 8-9 nm.
10. The method for fabricating a two-dimensional van der Waals heterojunction photodetector according to claim 8, characterized in that, The annealing temperature is 200-300℃, and the annealing time is 3-5 hours.