Plasmon enhanced self-driven photoelectric detector and preparation method thereof

Abstract

The invention discloses a plasmon enhanced self-driven photoelectric detector and a preparation method thereof. The photoelectric detector comprises a quartz substrate, a bottom-layer metal electrode, bottom-layer graphene, a WS layer, an h-BN insulating layer, a plasmon layer, top-layer graphene and a top-layer metal electrode from bottom to top. During preparation, the bottom layer metal electrode is firstly prepared on the quartz substrate by utilizing photoetching and electron beam evaporation technologies, then graphene and WS are sequentially transferred through mechanical stripping and dry transfer technologies, h-BN is transferred through a wet transfer technology, and then the plasmon layer is prepared through photoetching and magnetron sputtering technologies. Then transferring the top layer graphene through a mechanical stripping and dry transfer technology; and finally preparing a top layer metal electrode by utilizing a photoetching and electron beam evaporation technology. The device utilizes plasmon resonance and a vertical structure to enhance light absorption and carrier separation efficiency, and realizes broadband rapid self-driven photoelectric detection under zero bias voltage.

Description

Technical Field

[0001] This invention belongs to the field of photodetector technology, specifically relating to a plasmonic-enhanced self-driven photodetector and its fabrication method. Background Technology

[0002] Photodetectors are core devices that convert optical signals into electrical signals, and they have wide applications in imaging, sensing, and communication. With the development of flexible electronics and integrated optoelectronics, novel photodetectors based on two-dimensional materials have attracted much attention due to their excellent electrical and optical properties.

[0003] Currently, most common two-dimensional material photodetectors employ planar electrode structures. Photogenerated carriers need to travel a relatively long lateral path within the material plane before being collected by the electrodes, resulting in high carrier recombination rates, slow response speeds, and limited external quantum efficiency. Furthermore, many high-performance detectors require an external bias voltage to operate, which not only increases device power consumption and system complexity but may also introduce additional noise.

[0004] To address the self-powered problem, researchers have constructed detectors that do not require external bias voltage by utilizing the photovoltaic effect and photothermoelectric effect. However, these devices often face challenges such as limited light absorption, narrow response bands, and the difficulty in achieving both high responsivity and fast response speed. For example, the light absorption efficiency of photovoltaic detectors based solely on two-dimensional material heterojunctions is limited by the material thickness; while plasmon structures, although able to enhance the light field, typically have low coupling efficiency with photoactive materials and are complex to design.

[0005] Therefore, there is an urgent need to develop a new type of photodetector structure that combines high-efficiency light absorption, fast response, wide-spectrum operation capability, and no need for an external power supply. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a plasmonic-enhanced self-driven photodetector and its fabrication method. This detector, through a clever vertical stacking heterostructure design and the integration of plasmonic nanostructures, achieves significant improvements in light absorption efficiency, photoelectric conversion efficiency, and response speed, and can realize a wide-band optical response under zero bias.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A plasmon-enhanced self-driven photodetector, characterized in that it comprises, from bottom to top: Quartz substrate; A bottom metal electrode is disposed on the upper surface of the quartz substrate; A bottom graphene layer is disposed on the upper surface of the bottom metal electrode; A WS2 two-dimensional material layer is disposed on the upper surface of the underlying graphene layer; An h-BN insulating dielectric layer is disposed on the upper surface of the WS2 two-dimensional material layer; A plasmonic layer is disposed on the upper surface of the h-BN insulating dielectric layer; A top graphene layer is disposed on the upper surface of the plasmon layer; A top metal electrode is disposed on the upper surface of the top graphene layer; The bottom metal electrode and the top metal electrode are arranged in a non-overlapping manner in the vertical direction to form a vertical transmission channel.

[0008] Furthermore, the plasmonic layer is a gold island film, whose nanoscale island structure can excite local surface plasmonic resonance, effectively enhancing the light absorption of the device in the visible to near-infrared band.

[0009] The present invention also provides a method for fabricating the photodetector, characterized by comprising the following steps: S1. Clean the quartz substrate; S2. The bottom metal electrode is prepared on the substrate by photolithography and electron beam evaporation. S3. The bottom graphene layer and the WS2 layer are transferred sequentially using mechanical exfoliation and dry transfer techniques; S4. Transfer the h-BN insulating dielectric layer using wet transfer technology; S5. Gold island plasmonic layers were prepared by photolithography and magnetron sputtering. S6. The top graphene layer is transferred using mechanical exfoliation and dry transfer techniques; S7. The top metal electrode is prepared by photolithography and electron beam evaporation.

[0010] The beneficial effects of this invention are as follows: High-efficiency light absorption and field enhancement: The gold island film plasmon layer in the structure can generate a strong local electromagnetic field enhancement near the WS2 photoactive layer through the local surface plasmon resonance effect, which greatly improves the light-harvesting ability and effective light absorption cross section of the device.

[0011] Highly efficient carrier separation and rapid vertical transport: A built-in electric field can be formed between WS2 and the two layers of graphene, enabling efficient separation of photogenerated electron-hole pairs under illumination. The vertically stacked "electrode-graphene-WS2-h-BN-graphene-electrode" structure provides carriers with extremely short and direct tunneling or drift transport paths, significantly reducing transport time and recombination probability, thereby improving response speed and quantum efficiency.

[0012] Wideband self-driven response: The plasmon resonance peak can be tuned by the size and morphology of the gold island film, thereby extending the spectral response range of the device from the visible light to the near-infrared band. At the same time, the device operates by relying on the built-in electric field of the WS2 / graphene heterojunction, generating significant photocurrent under zero applied bias voltage, achieving true self-driven operation and reducing power consumption.

[0013] Compact structure and integration potential: All functional layers are integrated through van der Waals forces, avoiding lattice mismatch problems. The fabricated devices have a compact structure, high interface quality, and good compatibility with silicon-based processes, and have the potential for large-scale integrated applications. Attached Figure Description

[0014] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0015] Figure 1 This is a flowchart of a method for fabricating a plasmonic-enhanced self-driven photodetector according to an embodiment of the present invention; Figure 2 and Figure 3 The images are a structural diagram and an optical microscope top view of the plasmon-enhanced self-driven photodetector provided in the embodiments of the present invention. Figure 4 The above are simulation data of the optical absorption spectra of self-driven photodetectors with and without plasmon layers provided in the embodiments of the present invention. Figure 5 The current-voltage (IV) characteristic curves of the plasmonic-enhanced self-driven photodetector provided in the embodiments of the present invention under dark and illuminated (λ=405nm) conditions; Figure 6 The photocurrent-time (IT) response curve of the plasmon-enhanced self-driven photodetector provided in this embodiment of the invention is shown in the figure. The light source (λ=405nm) is periodically turned on and off at zero bias (0V) and the incident light power density is increased. Figure 7 The self-driven transient response curve of the plasmon-enhanced self-driven photodetector according to an embodiment of the present invention is shown under 405nm wavelength illumination and zero bias voltage (0V). Figure 8 The self-driving time response curves of the plasmon-enhanced self-driven photodetector according to an embodiment of the present invention under illumination of wavelengths of 405-1310 nm are shown. Figure 9 The self-driven time response curves of the self-driven photodetectors with and without plasmon layers provided in the embodiments of the present invention under 405nm wavelength illumination are shown. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art. Unless otherwise stated, the reagents, methods, and equipment used in this invention are conventional reagents, methods, and equipment in this technical field.

[0017] refer to Figure 1 A specific embodiment of the present invention discloses a plasmonic-enhanced self-driven photodetector and its fabrication method, comprising the following steps S101 to S103: S101: The bottom metal electrode is prepared on a clean quartz substrate by photolithography and electron beam evaporation. The bottom graphene and WS2 materials are stacked sequentially by mechanical exfoliation and dry transfer technology. Then, the h-BN insulating layer is covered by wet transfer technology to form a graphene / WS2 / h-BN heterojunction.

[0018] The specific preparation method in this step is as follows: (1) Substrate cleaning: Select a double-sided polished quartz sheet as the substrate. Place it in acetone, anhydrous ethanol and deionized water in sequence, and ultrasonically clean each for 5 minutes. After cleaning, blow the surface liquid with high-purity nitrogen gas, and then place it on a hot plate to dry at 110°C for 5 minutes to obtain a clean and dry quartz substrate.

[0019] (2) Preparation of the underlying metal electrode: In a clean environment in the photolithography chamber, the quartz substrate was fixed on a spin coater. Positive photoresist (ARP-5350) was dropped onto its surface. First, the photoresist was spin-coated at 500 rpm for 5 seconds to spread, and then at 4000 rpm for 60 seconds to make it uniform. Then, the substrate was pre-baked on a hot plate at 105℃ for 4 minutes. The pre-baked sample was placed in a UV lithography machine, and a single-sided electrode pattern was designed to expose the quartz substrate. After exposure, the sample was immersed in tetramethylammonium hydroxide developer for about 20 seconds, then fixed with deionized water for 30 seconds, and finally the sample surface was gently dried with a nitrogen gun. The patterned substrate was placed on the sample stage of an electron beam evaporation coating machine, and a titanium (Ti) adhesion layer with a thickness of 10 nm and a gold (Au) layer with a thickness of 50 nm were deposited successively. After vapor deposition, the sample is immersed in acetone solution for lift-off to remove the photoresist and excess metal, leaving the patterned Ti / Au (10nm / 50nm) as the bottom metal electrode. The sample is then soaked in anhydrous ethanol solution and finally dried with a nitrogen gun.

[0020] (3) Transfer of the underlying graphene and WS2 layer: Few-layer graphene and WS2 flakes were obtained using a mechanical exfoliation method. Specifically, the graphene and WS2 crystals were repeatedly peeled off with adhesive tape, and then the tape with the thin layer of material was attached to a polydimethylsiloxane (PDMS) elastomer film and slowly peeled off to transfer the material to the PDMS surface. With the assistance of an optical microscope and a micromanipulation platform, a few-layer (1-5 layers) graphene sheet on the PDMS was first aligned and attached to a designated area of ​​the underlying metal electrode. Subsequently, it was kept at 80°C for 3 minutes on a heating stage, and then slowly cooled and the PDMS was peeled off to complete the dry transfer of graphene. Next, using the same dry transfer technique, a few-layer (30-40 nm thick) WS2 flake was aligned and transferred to a designated area on the surface of the underlying graphene to ensure good van der Waals contact between the two. To optimize interface contact and remove any residues that may be introduced during the transfer process, the resulting heterojunction sample was placed on a heating stage at 150°C and annealed for 30 minutes after the dry transfer was completed.

[0021] (4) Transfer of h-BN insulating dielectric layer: A few-layer h-BN film grown on copper foil by chemical vapor deposition (CVD) was transferred using a wet transfer technique. First, a layer of polymethyl methacrylate (PMMA) was spin-coated onto the h-BN surface on the copper foil as a support layer. Subsequently, the copper foil substrate was etched away using a copper chloride solution. The PMMA / h-BN film floating on the solution was washed several times with deionized water and then lifted with the target substrate (i.e., the quartz plate on which WS2 has been transferred) so that the h-BN film was aligned and covered on the WS2 area. After the sample dried, it was immersed in an acetone solution to dissolve and remove the PMMA support layer, then rinsed with isopropanol and dried with nitrogen to obtain a 2.5 nm thick h-BN insulating dielectric layer covering WS2.

[0022] S102: A gold island plasmon layer is patterned on the surface of the heterojunction using photolithography and magnetron sputtering techniques, so that it only contacts the h-BN layer, thus forming a graphene / WS2 / h-BN / gold island composite structure.

[0023] In this step, a positive photoresist (ARP-5350) is spin-coated onto the surface of a quartz wafer containing a graphene / WS2 / h-BN / structure. The photoresist is first spread by spin-coating at 500 rpm for 5 seconds in a spin coater, then by spin-coating at 4000 rpm for 60 seconds to ensure uniformity. The substrate is then pre-baked at 105°C for 4 minutes. After pre-baking, the sample is placed in a UV lithography machine, and the designed pattern is exposed in the area corresponding to the h-BN layer using the lithography system. After exposure, the sample is immersed in tetramethylammonium hydroxide developer for approximately 20 seconds, then fixed with deionized water for 30 seconds, and finally gently dried with a nitrogen gun. The sample is then placed in a magnetron sputtering apparatus to deposit a 15 nm thick gold island film. The sample was then soaked in acetone to remove the photoresist and excess gold island film attached to it, and finally a plasmonic layer (i.e., gold island film) composed of discrete gold nano islands was formed on the h-BN surface.

[0024] S103: A top layer of graphene is stacked on the surface of the gold island film as a transparent electrode by mechanical exfoliation and dry transfer technology, and a top layer of metal electrode is photolithographically etched and vapor-deposited on top of it. The top layer of metal electrode does not overlap with the bottom layer of metal electrode in vertical projection to form a plasmonic-enhanced self-driven photodetector.

[0025] The specific preparation method in this step is as follows: (1) Transfer of the top graphene layer: The graphene crystal was repeatedly peeled off with tape, and then the tape with a thin layer of material was attached to the polydimethylsiloxane (PDMS) elastomer film and slowly peeled off to transfer the material to the PDMS surface. With the assistance of an optical microscope and a micromanipulation platform, a few-layer (1-5 layers) graphene sheet on the PDMS was aligned and attached to a designated area on the surface of the gold island film. Then, it was kept at 80°C for 3 minutes on a heating stage, and then slowly cooled and peeled off the PDMS to complete the dry transfer of graphene. Finally, the obtained heterojunction sample was placed on a heating stage at 90°C and annealed for 10 minutes.

[0026] (2) Preparation of the top metal electrode: In a clean environment of the photolithography chamber, the quartz substrate with the prepared graphene / WS2 / h-BN / gold island film / graphene structure was fixed on a spin coater. Positive photoresist (ARP-5350) was dropped onto its surface. First, the photoresist was spin-coated at 500 rpm for 5 seconds to spread, and then at 4000 rpm for 60 seconds to make it uniform. Then, the substrate was pre-baked on a hot plate at 105℃ for 4 minutes. The pre-baked sample was placed in a UV lithography machine, and a single-sided electrode pattern was designed on the designated area of ​​the top graphene surface to expose the quartz substrate. After exposure, the sample was immersed in tetramethylammonium hydroxide developer for about 20 seconds, then fixed with deionized water for 30 seconds, and finally the sample surface was gently dried with a nitrogen gun. The patterned substrate was placed on the sample stage of an electron beam evaporation coating machine, and a titanium (Ti) adhesion layer with a thickness of 10 nm and a gold (Au) layer with a thickness of 50 nm were deposited successively. After vapor deposition, the sample is immersed in acetone solution for a photoresist stripping process to remove the photoresist and excess metal, leaving the patterned Ti / Au (10nm / 50nm) as the top metal electrode. The sample is then soaked in anhydrous ethanol solution and finally dried using a nitrogen gun. A key design feature is that the pattern of the top metal electrode must be completely offset from the bottom metal electrode in vertical space, without overlapping, to ensure that photogenerated carriers must pass vertically through the intermediate heterostructure to form a circuit and complete photoelectric conversion.

[0027] The final fabricated device structure is as follows Figure 2 As shown, its optical microscope top view is as follows Figure 3 As shown, the stacking of each material layer and the arrangement of the metal electrodes can be clearly seen. To compare the performance improvement effect of the plasmonic-enhanced self-driven photodetector with a plasmonic layer, a self-driven photodetector without a plasmonic layer can be fabricated simultaneously. This self-driven photodetector, used as a comparison sample, only lacks a plasmonic layer in its structure. Compared with the plasmonic-enhanced self-driven photodetector fabricated in the example, its fabrication method only lacks the step of fabricating the plasmonic layer in step S102. The top graphene layer transferred in step S103 is in direct contact with the h-BN layer.

[0028] The prepared device is connected to a test platform (such as a probe station) for photoelectric performance testing. The test content includes: (1) IV characteristics: The current-voltage (IV) curves of the device were measured in a dark environment and under laser irradiation with a wavelength of 405 nm. The results are as follows: Figure 5 As shown, a significant photocurrent exists at the zero bias (0V) point, demonstrating that the device possesses excellent self-driven (photovoltaic) operation capability.

[0029] (2) Time response characteristics: Under zero bias, the device is irradiated with a 405nm pulsed laser, and the change of its photocurrent over time is measured to obtain the IT curve. For example... Figure 6 The figure shows the change of photocurrent over time as the incident light power density increases. The photocurrent of the device increases with increasing incident light power density. The device exhibits a stable and repeatable switching photocurrent response, with rise and fall times both on the order of microseconds, demonstrating rapid response capability. The self-driven transient response curve at zero bias (0V) is shown below. Figure 7 As shown.

[0030] (3) Spectral response range: By illuminating the device with monochromatic light of different wavelengths and measuring its zero-bias photocurrent, it was found that the device has a significant response in a wide range from visible light (e.g., 450 nm) to near-infrared light (e.g., 1310 nm), such as Figure 8 As shown. This is mainly due to the plasmon resonance effect of the gold island film, whose resonance peak range covers this band, effectively enhancing the device's absorption of light of different wavelengths.

[0031] (4) Comparison of Plasmon Enhancement Effect: To clarify the contribution of the plasmon layer to the device performance, under zero bias conditions, a plasmon-enhanced self-driven photodetector with a gold island plasmon layer and a control device without a plasmon layer were respectively irradiated with a 405nm pulsed laser of the same power, and the response curves (IT curves) of their photocurrent as a function of time were measured. The comparison results show that the saturation photocurrent of the plasmon-enhanced self-driven photodetector with the introduction of the plasmon layer is increased by more than two orders of magnitude compared with the control device, such as... Figure 9 As shown in the figure. This experiment directly confirms that the gold island plasmon structure significantly improves the light absorption and carrier generation efficiency of the device through the local field enhancement effect, thereby achieving an order-of-magnitude increase in photocurrent.

[0032] In summary, this embodiment successfully fabricated a high-performance plasmonic-enhanced self-driven photodetector. This device combines the short-range transmission advantages of vertical heterojunctions with the optical field enhancement effect of plasmonic nanostructures, achieving wide-band, high-speed, and high-response photodetection capabilities under zero bias.

[0033] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A plasmonic-enhanced self-driven photodetector, characterized in that, From bottom to top, they include: Quartz substrate; A bottom metal electrode is disposed on the upper surface of the quartz substrate; A bottom graphene layer is disposed on the upper surface of the bottom metal electrode; A WS2 two-dimensional material layer is disposed on the upper surface of the underlying graphene layer; An h-BN insulating dielectric layer is disposed on the upper surface of the WS2 two-dimensional material layer; A plasmonic layer is disposed on the upper surface of the h-BN insulating dielectric layer; A top graphene layer is disposed on the upper surface of the plasmon layer; A top metal electrode is disposed on the upper surface of the top graphene layer; The bottom metal electrode and the top metal electrode are arranged in a non-overlapping manner in the vertical direction.

2. The plasmon-enhanced self-driven photodetector according to claim 1, characterized in that, The bottom and top metal electrodes are made of titanium / gold composite layers, with the titanium layer having a thickness of 10 nm and the gold layer having a thickness of 50 nm.

3. The plasmon-enhanced self-driven photodetector according to claim 1, characterized in that, The bottom and top graphene layers are few-layer graphene obtained by mechanical exfoliation, with 1-5 layers.

4. The plasmon-enhanced self-driven photodetector according to claim 1, characterized in that, The WS2 two-dimensional material layer is a few-layer WS2 obtained by mechanical exfoliation, with a thickness of 30-40 nm.

5. The plasmon-enhanced self-driven photodetector according to claim 1, characterized in that, The h-BN insulating dielectric layer is a few-layer h-BN with a thickness of 2.5 nm, obtained by growing and transferring it using copper-based chemical vapor deposition.

6. The plasmon-enhanced self-driven photodetector according to claim 1, characterized in that, The plasmon layer is a gold island film obtained by magnetron sputtering technology, with a thickness of 15 nm.

7. A method for fabricating a plasmonic-enhanced self-driven photodetector as described in any one of claims 1-6, characterized in that, Includes the following steps: S1. Substrate cleaning: The quartz substrate was ultrasonically cleaned for 5 minutes each with acetone solution, anhydrous ethanol solution and deionized water, then dried with a nitrogen gun and dried at 110°C for 5 minutes. S2. Fabrication of the bottom metal electrode: In the photoluminescence chamber, photoresist is spin-coated onto a clean quartz wafer. The pattern of the bottom metal electrode is defined by photolithography. A 60nm thick metal layer is deposited by electron beam evaporation. Then, a photoresist stripping process is performed to form the bottom metal electrode. S3. Transfer of the underlying graphene and WS2 layer: Few-layer graphene sheets and few-layer WS2 sheets are obtained on a polydimethylsiloxane film by mechanical exfoliation, and then transferred sequentially to the surface of the underlying metal electrode and the surface of the underlying graphene layer by dry transfer technology. S4. Transfer of h-BN insulating dielectric layer: Using a wet transfer technique, polymethyl methacrylate is used as a support layer to transfer a few-layer h-BN grown on a copper substrate by chemical vapor deposition to the surface of the WS2 two-dimensional material layer. S5. Preparation of plasmonic layer: In the yellow light chamber, photoresist is spin-coated on the h-BN insulating dielectric layer, and the pattern is defined by photolithography; a 15nm thick gold island film is deposited by magnetron sputtering. The adhesive removal process is then performed to form the plasmonic layer. S6. Transfer of the top graphene layer: A few-layer graphene sheet is obtained by mechanical exfoliation, and then precisely aligned and transferred to the surface of the plasmon layer by dry transfer technology; S7. Fabrication of the top metal electrode: In the photoluminescence chamber, photoresist is spin-coated onto the top graphene layer, and the top metal electrode pattern is defined by photolithography. A 60nm thick metal layer is deposited using electron beam evaporation technology to ensure that it does not overlap with the bottom metal electrode in the vertical projection. Then, a photoresist removal process is performed to form the top metal electrode, and finally the plasmon-enhanced self-driven photodetector is obtained.

8. The preparation method according to claim 7, characterized in that, The mechanical peeling and dry transfer techniques described in steps S3 and S6 specifically include the following operations: The graphene or WS2 crystals were repeatedly mechanically peeled off using adhesive tape, and the thin-layer material was picked up using a polydimethylsiloxane film. Under a microscope, the polydimethylsiloxane film carrying the material is aligned and covered onto the target substrate or layer surface; The material is heated and residual polymer is removed to ensure stable contact and thorough drying between the transferred material and the lower layer. The heating temperature is 150°C and the time is 30 minutes.

9. The preparation method according to claim 7, characterized in that, The photolithography and magnetron sputtering techniques described in step S5 specifically include the following operations: The substrate coated with photoresist and pre-baked is subjected to ultraviolet exposure to define the plasmonic layer pattern. After exposure, the substrate is placed in a developer solution prepared with tetramethylammonium hydroxide solution. After development for 20 seconds, the device is quickly transferred to a deionized water solution and immersed for 30 seconds for fixing. Then, the surface of the deionized water is gently dried with a nitrogen gun. A patterned substrate was placed in a magnetron sputtering coating machine to sputter a gold island film with a thickness of 15 nm. After the coating is completed, the device is first immersed in an acetone solution, and then transferred to an anhydrous ethanol solution for a photoresist stripping process to remove the photoresist and excess metal. Finally, a nitrogen gun is used to gently blow away any remaining solution on the surface.

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