Heterojunction photoelectric detector based on vertical built-in electric field regulation and control and preparation method and application thereof

Abstract

The invention belongs to the technical field of photoelectric detectors, and discloses a heterojunction photoelectric detector based on vertical built-in electric field regulation and control and a preparation method and application thereof. According to the photoelectric detector, a MoS2 thin film covers a WSe2 nanosheet on a SiO2 / Si substrate and a Cr / Au electrode, the WSe2 nanosheet is not in contact with the Cr / Au electrode, a source electrode-MoS2-drain electrode serves as a carrier transport channel layer, the WSe2 nanosheet serves as a sensitization layer, the electrodes are only in contact with the MoS2 thin film, and a heterojunction and a vertical built-in electric field are formed at the interface of the WSe2 nanosheet and the MoS2 thin film. The response time of the photoelectric detector is millisecond, the dark current is more than 3.4 pA, the current switch ratio is increased to 2.7 * 10 < 3 >, the responsivity is more than 4.2 * 10 < 3 > A / W, and the detection rate is more than 1.8 * 10 < 14 > Jones; the method can be applied to the field of optoelectronic integration and intelligent sensing.

Description

Technical Field

[0001] This invention belongs to the field of photodetector technology, and more specifically, relates to a heterojunction photodetector based on vertical built-in electric field modulation, its fabrication method, and its application. Background Technology

[0002] Photodetectors play a crucial role in high-speed imaging, optical communication, and real-time sensing, with core performance requirements including high sensitivity, low noise (dark current), and fast response. Two-dimensional transition metal chalcogenides (such as MoS2) are ideal detection materials due to their tunable bandgap, strong light-matter interaction, and potential for fabricating ultrathin flexible devices. However, MoS2 films grown by chemical vapor deposition (CVD) suffer from high-density trapped states due to lattice defects, which restricts carrier mobility and severely limits the ability to simultaneously optimize dark current, sensitivity, and response speed.

[0003] Current technologies primarily optimize performance through strategies such as constructing heterojunctions (e.g., lateral PN junctions), plasma enhancement, or dielectric environment modulation. However, these methods suffer from inherent limitations, including the need for precise doping in lateral heterojunctions and insufficient carrier separation efficiency; the tendency of plasma structures to introduce additional scattering losses; and the inherent limitations of grating-controlled gain mechanisms relying on deep-level traps, which, while improving responsivity, suffer from severe response hysteresis due to slow carrier release. Therefore, there is an urgent need to develop a novel mechanism for controlling an internal electric field to synergistically address the coupling challenges of dark current suppression, photoresponse gain, and carrier transport acceleration within the material, thereby overcoming existing performance bottlenecks. Summary of the Invention

[0004] This invention addresses the technical problems of high dark current (>1 nA), slow response (second-level), and limited sensitivity caused by numerous trapped states in chemical vapor deposition (CVD) MoS2 detectors. The primary objective of this invention is to provide a heterojunction photodetector based on vertical built-in electric field modulation. This photodetector forms a heterojunction by sequentially stacking WSe2 nanosheets and a CVD-grown MoS2 thin film on a silicon substrate. The electrodes are not connected to the WSe2 nanosheets and only contact the MoS2 thin film. An out-of-plane built-in electric field is generated at the MoS2 / WSe2 heterojunction interface due to the type II band alignment.

[0005] Another objective of this invention is to provide a method for fabricating the above-mentioned heterojunction photodetector based on vertical built-in electric field modulation. This method, through the out-of-plane built-in electric field engineered in the vertical heterojunction, is an efficient and universal strategy for realizing a new generation of high-sensitivity, low-dark-current, and fast-response photodetectors, laying the foundation for advanced optoelectronic applications.

[0006] Another object of the present invention is to provide the application of the above-mentioned heterojunction photodetector based on vertical built-in electric field modulation.

[0007] The objective of this invention is achieved through the following technical solution: A heterojunction photodetector with a vertically built-in electric field is described, in which a MoS2 thin film is coated onto a WSe2 nanosheet, a source electrode, and a drain electrode on a SiO2 / Si substrate, with the WSe2 nanosheet and the source and drain electrodes not in contact, and the source and drain electrodes only in contact with the MoS2 thin film. The source electrode-MoS2 thin film-drain electrode serves as a carrier transport channel layer, and the WSe2 nanosheet serves as a sensitization layer. A heterojunction and a vertically built-in electric field are formed at the interface between the WSe2 nanosheet and the MoS2 thin film.

[0008] Preferably, both the source electrode and the drain electrode are electrodes composed of a Cr layer and an Au layer; the thickness of the Cr layer is 5~20 nm, and the thickness of the Au layer is 40~70 nm.

[0009] Preferably, the heterojunction photodetector exhibits a dark current exceeding 3.4 pA and an on / off ratio increasing to 2.7 × 10⁻⁶ when the gate voltage Vg = -20 V. 3 The above; at the source-drain voltage V sd = 10 V and gate voltage V g At 20 V, the responsivity reaches 4.2 × 10⁻⁶. 3 With an A / W ratio of over 1.8, the detectivity reaches 1.8 × 10⁻⁶. 14 Jones and above.

[0010] The fabrication method of the heterojunction photodetector based on vertical built-in electric field modulation includes the following specific steps: S1. The cut PDMS flexible material is peeled off the thin film layer using a mechanical peeling method, and then laid flat on an adhesive tape covered with WSe2 crystals for peeling. 1 to 50 layers of WSe2 nanosheets are selected. S2. Using a transfer platform, WSe2 nanosheets are transferred to the center of a cleaned SiO2 / Si substrate to prepare WSe2 nanosheets on the SiO2 / Si substrate, abbreviated as WSe2 nanosheets / SiO2 / Si; S3. Spin-coat photoresist onto WSe2 nanosheets / SiO2 / Si substrate and bake at 100~200 °C. Photolithographically etch electrodes on both sides outside the WSe2 channel region to serve as source and drain electrodes. S4. Place the SiO2 / Si substrate face down directly above a quartz boat, with MoO3 inside. Then, place a quartz crucible filled with sulfur powder independently in the upstream area of ​​the N2 flow direction. Place the crucible in the center of the constant temperature zone of the tube furnace and purge with 100~500 sccm N2 for 10~30 min. Introduce N2 at a flow rate of 50~200 sccm and heat to 300~400 ℃ after 5~10 min. Switch the flow rate to 5~20 sccm N2 and raise the temperature to 600~800 ℃, then hold for 5~20 min. Finally, allow it to cool naturally to room temperature. When the temperature drops below 500 ℃, increase the N2 flow rate to 200~500 sccm and open the furnace lid to accelerate cooling, thus obtaining a MoS2 thin film. S5. Transfer the MoS2 thin film onto WSe2, the source electrode, and the drain electrode to fabricate a heterojunction photodetector based on vertical built-in electric field modulation on a SiO2 / Si substrate, which is the MoS2 / WSe2 heterojunction photodetector.

[0011] Preferably, the spin coating speed in step S3 is 3000~5000 rpm, the spin coating time is 60~120 seconds, and the baking time is 3~5 minutes.

[0012] Preferably, the mass ratio of MoO3 to sulfur powder in step S4 is (1~10):(20~100); the thickness of the MoS2 film is 1~10 nm.

[0013] This invention addresses the critical issues of high dark current and slow response speed in MoS2 thin films grown by chemical vapor deposition due to a large number of trapped states. Sensitization is achieved by constructing a vertical heterojunction between the MoS2 thin film and WSe2 nanosheets. An out-of-plane built-in electric field is generated between MoS2 and WSe2 due to the type II band alignment. This is enhanced by a grating control effect to achieve triple optimization: (1) By establishing a potential barrier and reducing the majority carriers (electrons) in the MoS2 channel, the dark current is suppressed to 3.4 pA, a reduction of more than two orders of magnitude compared to MoS2 photodetectors. The current on / off ratio is increased to 2.7 × 10⁻⁶. 3 (1) The responsivity is more than two orders of magnitude higher than that of the MoS2 photodetector; (2) The grating control effect makes the responsivity reach 4.2×10 3 A / W, with a detectivity of 1.8 × 10⁻⁶. 14 Jones; (3) The out-of-plane vertical electric field (E) generated in This technology promotes directional carrier separation, accelerating the time response from seconds to milliseconds. This heterojunction photodetector, based on vertically integrated electric field modulation, provides a core component for next-generation low-power, high-sensitivity photodetector systems, and has broad application prospects in optoelectronic integration and intelligent sensing.

[0014] Compared with the prior art, the present invention has the following beneficial effects: This invention utilizes the out-of-plane built-in electric field (E) generated by the type II band arrangement at the interface of the MoS2 / WSe2 heterojunction. in This mechanism drives a highly efficient grating, simultaneously establishing an energy barrier at a gate voltage of Vg = -20 V through an out-of-plane built-in electric field induced by type II band dislocation. This reduces the majority carriers (electrons) in the MoS2 channel, suppressing dark current to the pA level (3.4 pA), a reduction of more than two orders of magnitude compared to MoS2 photodetectors; the on / off ratio is increased to 2.7 × 10⁻⁶. 3 It is more than two orders of magnitude higher than the MoS2 photodetector. The built-in electric field enables rapid separation of photogenerated carriers, allowing holes to accumulate in WSe2 and gate the MoS2 channel, resulting in high responsivity and high photoconductivity gain. The directional carrier separation rate breaks through the deep-level trap limitation, achieving millisecond-level time response.

[0015] This invention is based on a heterojunction photodetector with a vertically built-in electric field modulated at the source-drain voltage V. sd = 10 V and gate voltage V g At 20 V, the electric field drives the rapid separation of photogenerated carriers, and holes accumulate in WSe2 to form a virtual gate voltage. Through efficient grating control effect, the conductance of the MoS2 channel is controlled, achieving a responsivity of 4.2 × 10⁻⁶. 3 A / W, detectivity up to 1.8×10 14 Jones' performance is three orders of magnitude better than that of the MoS2 photodetector.

[0016] This invention is based on the millisecond-level fast response of the vertical heterojunction photodetector. This is because the directional separation rate of photogenerated carriers at the MoS2 / WSe2 heterojunction interface breaks through the slow response speed bottleneck caused by deep-level trap capture. The response time is shortened from the second level to the millisecond level, which meets the requirements of high-speed imaging and optical communication.

[0017] 4. The present invention is based on a heterojunction photodetector with vertical built-in electric field control, which has a unique electrode isolation design (the electrode is not in contact with WSe2) and chemical vapor deposition-mechanical stripping integration process, providing synergistic protection for dark current suppression, grating control gain and fast response, and significantly improving performance indicators. Attached Figure Description

[0018] Figure 1 (a) An optical microscope image and (b) a schematic diagram of the photodetector based on a molybdenum disulfide / tungsten diselenide (MoS2 / WSe2) heterojunction regulated by a vertical built-in electric field, which are shown in Example 1.

[0019] Figure 2The transfer characteristic curves (I) of the photodetector based on the vertical built-in electric field-controlled MoS2 / WSe2 heterojunction of Example 1 and the molybdenum disulfide (MoS2) photodetector of Comparative Example 1 are shown in dark and light conditions. sd –V g ).

[0020] Figure 3 The photodetector (b) of Example 1 based on a vertically built-in electric field-controlled MoS2 / WSe2 heterojunction and the MoS2 photodetector (a) of Comparative Example 1 are compared at V sd = 10 V and dynamic photoresponse curves at different gate voltages.

[0021] Figure 4 The net photocurrent of a 635 nm laser at different optical power densities is compared between the photodetector (a) of Example 1 based on a vertically built-in electric field-controlled MoS2 / WSe2 heterojunction and the MoS2 photodetector (a) of Comparative Example 1. I ph (a) , (b) responsiveness (R) and (c) detectivity (D*). Detailed Implementation

[0022] The technical solutions in the embodiments of the present invention will now be clearly and completely described with reference to the accompanying drawings. The described embodiments are merely some, not all, of the embodiments of the present invention. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention. Unless otherwise specified, the experimental methods described in the following embodiments are conventional methods; the reagents and materials, unless otherwise specified, can be obtained from publicly available commercial channels.

[0023] This specification uses spatially relative terms such as "below," "below," "down," "above," "over," and "above" to explain the positioning of one element relative to a second element. These terms are intended to cover different orientations of the device, except for those different from those shown in the figures. Furthermore, the use of terms such as "first" and "second" to describe individual elements, layers, regions, segments, etc., is not intended to be limiting. The use of terms such as "having," "containing," "including," and "comprising" are open-ended terms indicating the presence of the stated element or feature, but not excluding additional elements or features, unless the context clearly indicates otherwise.

[0024] The electrical characteristics of this invention were measured using a probe station (PSAICPB6A, Precision Systems Industrial Co., Ltd.) equipped with a Keithley 2636B semiconductor source meter. The WSe2 crystal and ARP-5350 positive photoresist used were purchased from Taizhou Sunano New Energy Co., Ltd. Example 1

[0025] 1. Rinse the SiO2 / Si substrate with anhydrous ethanol, and then soak and rinse it with distilled water to ensure that the substrate surface is free of dust and other impurities.

[0026] 2. Using a mechanical peeling method, a 0.5 cm² piece of PDMS flexible material was peeled off and laid flat on an adhesive tape covered with tungsten diselenide (WSe2) crystals. After standing for 15 seconds, the material was observed using an optical microscope. 1 to 50 layers of relatively flat WSe2 nanosheets were selected.

[0027] 3. Using a transfer platform, transfer the WSe2 nanosheets onto a 300 nm SiO2 / Si substrate, centering them on the substrate. Ensure the WSe2 nanosheets are firmly attached to the SiO2 / Si substrate, and adjust the heating stage temperature to 50 ℃. After heating for 1 min, the transfer is complete, resulting in WSe2 nanosheets on the SiO2 / Si substrate, abbreviated as WSe2 nanosheets / SiO2 / Si.

[0028] 4. Place the WSe2 nanosheet / SiO2 / Si substrate into a spin coater. Use a dropper to evenly apply ARP-5350 positive photoresist to the substrate surface. Set the spin coater to the correct operating steps. After spin coat is complete, place the WSe2 nanosheet / SiO2 / Si substrate on a heating stage and heat at 100 ℃ for 4 min to bake the photoresist. During the process, cover the substrate with an opaque cover to avoid the influence of light.

[0029] 5. Place the WSe2 nanosheet / SiO2 / Si substrate after photolithography in step 4 into a photolithography machine. Select the outer sides of the WSe2 nanosheet region to photolithographically print source and drain electrodes, respectively. Both source and drain electrodes are Cr / Au electrodes composed of Cr and Au layers; the thickness of the Cr layer is 5~20 nm, and the thickness of the Au layer is 40~70 nm. The Cr layer is in contact with the WSe2 nanosheet / SiO2 / Si substrate, and the Au layer is in contact with the MoS2 film. Neither the source nor drain electrode is connected to the WSe2 nanosheet. After photolithography, development is performed. The WSe2 nanosheet / SiO2 / Si substrate is placed in the developer. When black spots are observed on the silicon wafer, it is quickly placed in deionized water and stirred for 5 seconds. Then, the residual deionized water on the surface is blown off with a nitrogen gun. The developed WSe2 nanosheet / SiO2 / Si substrate is then subjected to electron beam evaporation. After the vapor deposition is completed, the WSe2 nanosheets / SiO2 / Si substrate is immersed in acetone solution, rinsed with distilled water, and then the residual distilled water on the surface is blown away with an air gun.

[0030] 6. Using chemical vapor deposition (CVD), a SiO2 / Si substrate was placed face down directly above a quartz boat. The quartz boat contained 10 mg of molybdenum trioxide (MoO3) with a purity of ≥99.9%. A quartz crucible containing 200 mg of sulfur powder was placed independently in the upstream zone of the N2 flow direction. The quartz boat with the loaded components was placed in the center of the isothermal zone of a tube furnace. The furnace was purged with 500 sccm of N2 with a purity of ≥99.9% for 10 min. The furnace was then heated to 300 °C at a N2 flow rate of 100 sccm for 10 min, then the N2 flow rate was switched to 10 sccm, and the temperature was raised to 700 °C and held for 10 min. Finally, the furnace was allowed to cool naturally to room temperature. When the temperature dropped below 500 °C, the N2 flow rate was increased to 300 sccm, and the furnace lid was opened to accelerate cooling, thus obtaining a MoS2 thin film with a thickness of 1–10 nm. 7. The MoS2 thin film was transferred to WSe2 nanosheets and Cr / Au electrodes on a SiO2 / Si substrate using a transfer platform. The MoS2 thin film, WSe2 nanosheets and Cr / Au electrodes were attached tightly, and the heating stage temperature was adjusted to 50 ℃ and heated for 1 min to complete the transfer. A photodetector based on a vertical built-in electric field-controlled MoS2 / WSe2 heterojunction was fabricated on the SiO2 / Si substrate.

[0031] Comparative Example 1 The difference from Example 1 is that the MoS2 film was transferred to the Cr / Au electrode on the SiO2 / Si substrate using a transfer platform. The MoS2 film and the Cr / Au electrode were then attached tightly, and the heating stage temperature was adjusted to 50 °C and heated for 1 min to complete the transfer. A MoS2 photodetector was then fabricated on the SiO2 / Si substrate.

[0032] Figure 1 (a) An optical microscope image and (b) a schematic diagram of the photodetector structure of the molybdenum disulfide / tungsten diselenide (MoS2 / WSe2) heterojunction based on a vertically built-in electric field controlled according to Example 1. Figure 1 As can be seen in (a), the photodetector structure of this MoS2 / WSe2 heterojunction consists of a MoS2 thin film mounted on WSe2 nanosheets and a Cr / Au electrode. The electrode is not connected to WSe2 and only contacts MoS2. The overlapping shaded area represents the mounted MoS2 / WSe2 heterojunction. Figure 1As shown in (b), this photodetector consists of a MoS2 thin film covering a WSe2 nanosheet, a source electrode, and a drain electrode on a SiO2 / Si substrate. The WSe2 nanosheet is not in contact with the source and drain electrodes; the source and drain electrodes only contact the MoS2 thin film. The source electrode-MoS2 thin film-drain electrode layer serves as the carrier transport channel layer, and the WSe2 nanosheet serves as the sensitization layer. A heterojunction and a vertical built-in electric field are formed at the interface between the WSe2 nanosheet and the MoS2 thin film. Both the source and drain electrodes are composed of a Cr layer and an Au layer; the Cr layer is in contact with the substrate, and the Au layer is in contact with the MoS2 thin film. The thickness of the Cr layer is 5–20 nm, and the thickness of the Au layer is 40–70 nm.

[0033] Figure 2 The transfer characteristics of the molybdenum disulfide (MoS2) photodetector in Comparative Example 1 and the MoS2 / WSe2 heterojunction photodetector based on vertical built-in electric field modulation in Example 1 under dark and light conditions (I) sd –V g ),from Figure 2 As can be seen, the MoS2 photodetector in Comparative Example 1 exhibits higher dark current and significant hysteresis. In contrast, the MoS2 / WSe2 heterojunction photodetector in Example 1 shows a significantly reduced dark current and a markedly weakened hysteresis. Furthermore, the photocurrent of this MoS2 / WSe2 heterojunction photodetector is much higher than that of the MoS2 photodetector in Comparative Example 1 across the entire gate voltage range, highlighting the gain improvement brought about by the grating control effect. Figure 3 The photodetector (b) of Example 1 based on a vertically built-in electric field-controlled MoS2 / WSe2 heterojunction and the MoS2 photodetector (a) of Comparative Example 1 are compared at V sd Dynamic photoresponse curves at 10 V and different gate voltages. From Figure 3 As can be seen, the response time of the MoS2 photodetector in Comparative Example 1 is on the order of seconds, while the MoS2 / WSe2 heterojunction photodetector in Example 1 accelerates the time response from seconds to milliseconds. Current switching ratio Through formula Calculate, where, I light This represents the current corresponding to the photodetector under illumination. I dark This represents the current corresponding to the photodetector in the unilluminated state. The heterojunction photodetector operates at a gate voltage V0. g At -20 V, an energy barrier is established through an out-of-plane built-in electric field induced by type II band dislocation, reducing the majority carriers (electrons) in the MoS2 channel and suppressing the dark current to 3.4 pA. This represents a reduction of more than two orders of magnitude compared to the MoS2 photodetector in Comparative Example 1, and the current on / off ratio is increased to 2.7 × 10⁻⁶. 3It is more than two orders of magnitude higher than the MoS2 photodetector in Comparative Example 1. Figure 4 The net photocurrent of a 635 nm laser at different optical power densities is compared between the photodetector (a) of Example 1 based on a vertically built-in electric field-controlled MoS2 / WSe2 heterojunction and the MoS2 photodetector (a) of Comparative Example 1. I ph (a) responsivity (R) and (b) detectivity (D*). From Figure 4 As can be seen from this, at the source-drain voltage V sd = 10 V and gate voltage V g At 20 V, the net photocurrent, responsivity, and detectivity of the MoS2 / WSe2 heterojunction photodetector are significantly higher than those of the MoS2 photodetector in Comparative Example 1 under different optical power densities. Due to the rapid separation of photogenerated carriers driven by the electric field, holes accumulate in WSe2 to form a virtual gate voltage. This voltage, through efficient grating control, controls the conductance of the MoS2 channel, enabling the MoS2 / WSe2 heterojunction photodetector to achieve a responsivity of 4.2 × 10⁻⁶. 3 A / W, with a detectivity of 1.8 × 10⁻⁶. 14 Jones's performance is three orders of magnitude better than a MoS2 photodetector of scale 1. Responsivity ( R ) and detection rate ( D The formula for calculating * is as follows:

[0034] in, I ph It is the net photocurrent, i.e., the same V sd Down I light minus I dark The value, I light It is photocurrent, which is the current measured under illumination. I dark It is dark current, that is, current measured under conditions of no light. P λ It is the optical power density of the incident light; S is the effective area of ​​the photodetector, and e is the electron charge, which has a value of 1.6 × 10⁻⁶. 19 C.

[0035] In summary, the photodetector based on a vertically integrated electric field-controlled molybdenum disulfide / tungsten diselenide (MoS2 / WSe2) heterojunction of the present invention exhibits excellent photoelectric performance, with a dark current exceeding 3.4 pA and an on / off ratio improved to 2.7 × 10⁻⁶ at a gate voltage Vg = -20 V. 3 The above; at the source-drain voltage V sd= 10 V and gate voltage V g At 20 V, the responsivity reaches 4.2 × 10⁻⁶. 3 With an A / W ratio of over 1.8, the detectivity reaches 1.8 × 10⁻⁶. 14 Jones and above have broad application prospects in fields such as optoelectronic integration and intelligent sensing.

[0036] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations and simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A heterojunction photodetector based on vertical built-in electric field modulation, characterized in that, The heterojunction photodetector consists of a MoS2 thin film covering a WSe2 nanosheet, a source electrode, and a drain electrode on a SiO2 / Si substrate. The WSe2 nanosheet and the source and drain electrodes are not in contact; the source and drain electrodes only contact the MoS2 thin film. The source electrode-MoS2 thin film-drain electrode layer serves as a carrier transport channel layer, and the WSe2 nanosheet serves as a sensitization layer. A heterojunction and a vertical built-in electric field are formed at the interface between the WSe2 nanosheet and the MoS2 thin film.

2. The heterojunction photodetector based on vertical built-in electric field modulation according to claim 1, characterized in that, Both the source electrode and the drain electrode are electrodes composed of a Cr layer and an Au layer; the thickness of the Cr layer is 5~20 nm, and the thickness of the Au layer is 40~70 nm.

3. The heterojunction photodetector based on vertical built-in electric field modulation according to claim 1 or 2, characterized in that, The heterojunction photodetector exhibits a dark current exceeding 3.4 pA and an on / off ratio increasing to 2.7 × 10⁻⁶ at a gate voltage Vg = -20 V. 3 The above; at the source-drain voltage V sd = 10 V and gate voltage V g At 20 V, the responsivity reaches 4.2 × 10⁻⁶. 3 With an A / W ratio of over 1.8, the detectivity reaches 1.8 × 10⁻⁶. 14 Jones and above.

4. The method for fabricating a heterojunction photodetector based on vertical built-in electric field modulation according to any one of claims 1-3, characterized in that, The specific steps include the following: S1. The cut PDMS flexible material is peeled off the thin film layer using a mechanical peeling method, and then laid flat on an adhesive tape covered with WSe2 crystals for peeling. 1 to 50 layers of WSe2 nanosheets are selected. S2. Using a transfer platform, WSe2 nanosheets are transferred to the center of a cleaned SiO2 / Si substrate to prepare WSe2 nanosheets on the SiO2 / Si substrate, abbreviated as WSe2 nanosheets / SiO2 / Si; S3. Spin-coat photoresist onto WSe2 nanosheets / SiO2 / Si substrate and bake at 100~200℃. Photolithographically etch electrodes on both sides outside the WSe2 channel region to serve as source and drain electrodes. S4. Place the SiO2 / Si substrate face down directly above a quartz boat, with MoO3 inside. Then, place a quartz crucible filled with sulfur powder independently in the upstream area of ​​the N2 flow direction. Place the crucible in the center of the constant temperature zone of a tube furnace and purge with 100~500 sccm N2 for 10~30 min. Introduce N2 at a flow rate of 50~200 sccm and heat to 300~400 ℃ after 5~10 min. Switch the flow rate to 5~20 sccm N2 and raise the temperature to 600~800 ℃, then hold for 5~20 min. Finally, allow it to cool naturally to room temperature. When the temperature drops below 500 ℃, increase the N2 flow rate to 200~500 sccm and open the furnace lid to accelerate cooling, thus obtaining a MoS2 thin film. S5. Transfer the MoS2 thin film onto WSe2, the source electrode, and the drain electrode to fabricate a heterojunction photodetector based on vertical built-in electric field modulation on a SiO2 / Si substrate, which is the MoS2 / WSe2 heterojunction photodetector.

5. The fabrication method of the heterojunction photodetector based on vertical built-in electric field modulation according to claim 4, characterized in that, In step S3, the spin coating speed is 3000~5000 rpm, the spin coating time is 60~120 seconds, and the baking time is 3~5 minutes.

6. The fabrication method of the heterojunction photodetector based on vertical built-in electric field modulation according to claim 4, characterized in that, In step S4, the mass ratio of MoO3 to sulfur powder is (1~10):(20~100); the thickness of the MoS2 film is 1~10 nm.

7. The application of the heterojunction photodetector based on vertical built-in electric field modulation as described in any one of claims 1-3 in the field of optoelectronic integration or intelligent sensing.

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