Sandwich plasma type high-photoresponse heterojunction photoelectric detector and preparation method thereof

Abstract

The embodiment of the invention relates to the technical field of photoelectrons, in particular to a preparation method of a sandwich plasma type high-photoresponse heterojunction photoelectric detector, which comprises the following steps of: transferring mechanically stripped WS2 to an interdigital electrode to construct a WS2 photoelectric detector; and constructing a ZnO / Au / ZnO sandwich plasma structure on the WS2 by adopting an atomic layer deposition technology and a spin-coating method to prepare the WS2 / ZnO / Au / ZnO heterojunction photoelectric detector. According to the preparation method of the high-photoresponse heterojunction photoelectric detector provided by the invention, the light absorption capability of a WS2 material is remarkably enhanced by utilizing a strong LSPR effect of a sandwich plasma structure in a visible band; the built-in electric field of the heterojunction interface not only promotes the separation of photon-generated carriers, but also improves the injection efficiency of high-energy hot electrons caused by the LSPR effect, realizes the dual optimization of light absorption and hot electron injection, and has important significance for the development of high-performance photoelectric devices.

Description

Technical Field

[0001] The invention relates to a sandwich plasma type high light response heterojunction photoelectric detector and a preparation method thereof, belonging to the field of low-dimensional hybrid heterojunction photoelectric devices. Background Art

[0002] Tungsten disulfide (WS2) two-dimensional materials, with their excellent electron mobility, tunable band gap (which varies with the number of layers), and excellent stability, have shown great potential for application in photodetectors, sensors, and solar cells. They are expected to play an increasingly important role in next-generation optoelectronic devices and novel functional materials. However, the atomic-scale thickness of two-dimensional WS2 limits its light absorption capacity, hindering the further development of high-performance WS2-based photodetectors. To address this issue, conventional approaches have involved constructing WS2-based heterostructures, which not only increase the total light absorption at the heterojunction, but also broaden the spectral absorption range and improve the efficiency of photogenerated carrier separation. Recent research suggests that incorporating noble metal nanoparticles (such as gold and silver nanoparticles, Au and Ag NPs) into heterostructures and exploiting their localized surface plasmon resonance (LSPR) effect can provide a new approach for developing highly photoresponsive heterojunction photodetectors.

[0003] The mechanisms by which metal nanoparticles enhance heterojunction photodetectors are primarily manifested in two aspects: First, the LSPR effect generates a high-intensity localized electromagnetic field around the metal nanoparticles, significantly enhancing the light absorption efficiency of adjacent materials through near-field coupling. Second, high-energy hot electrons generated by photoexcitation of the metal nanoparticles are injected into the two-dimensional material, directly enhancing the photocurrent of the photodetector. Currently, existing techniques integrate nanoparticles of varying metal types, sizes, and morphologies onto the surface or interface of heterojunctions through spin coating, evaporation, sputtering, and other methods to achieve varying LSPR enhancement effects. However, when metal nanoparticles are integrated onto the surface, the weak LSPR penetration depth limits their effect across the heterojunction. While integrating metal nanoparticles onto the interface overcomes the penetration depth issue, these common integration methods often cause lattice damage or introduce impurity defects, which in turn impair the transport of photogenerated carriers. Furthermore, the ultrashort lifetime and mean free path of the high-energy hot electrons, coupled with the high Schottky barrier resulting from the large work function of the metal, result in low utilization of the LSPR-induced hot electrons, thus undermining the full performance of plasmonic photodetectors.

[0004] Therefore, in order to give full play to the LSPR effect of metal nanoparticles, it is of great significance to design a new type of sandwich plasmonic heterojunction photodetector. Summary of the Invention

[0005] To address the incomplete performance of existing plasmonic photodetectors, the present invention proposes a WS2 / ZnO / Au / ZnO sandwich plasmonic heterojunction photodetector based on the synergistic effect of the LSPR effect and heterojunction band engineering. This sandwich structure design not only protects the heterojunction interface quality and enhances the material's light absorption capacity, but also promotes carrier transport, achieving dual optimization of light absorption and hot electron injection efficiency. On the one hand, the ZnO layer in the sandwich structure prevents direct contact between the metal and the two-dimensional material, ensuring the material's lattice stability and maintaining the quality of the heterojunction interface. On the other hand, the Au nanoparticles in the sandwich structure are not limited by the LSPR effect's penetration depth, generating a strong localized electromagnetic field enhancement in the visible band, significantly improving the light absorption capacity of the WS2-based heterojunction. The WS2 also forms a built-in electric field within the heterojunction with the ZnO in the sandwich structure, promoting the separation of photogenerated electron-hole pairs and assisting the Au nanoparticle-induced hot electron injection, thereby improving the photoelectric conversion efficiency of the photodetector and achieving a plasmonic heterojunction photodetector with high light response.

[0006] The WS2 / ZnO / Au / ZnO heterojunction photodetector proposed in this invention comprises, from bottom to top, gold interdigitated electrodes, a WS2 layer, and a ZnO / Au / ZnO structure. The gold interdigitated electrodes have a finger width of 5 μm, a channel width of 3 μm, and a finger length of 1400 μm.

[0007] The preparation process of the WS2 / ZnO / Au / ZnO heterojunction photodetector specifically includes the following steps:

[0008] 1. Transfer the mechanically exfoliated 2D WS2 film onto pre-prepared gold interdigitated electrodes to fabricate a WS2 photodetector.

[0009] 2. The prepared WS2 photodetector was placed in the reaction chamber of the ALD equipment and a 2 nm thick ZnO film was deposited to construct a WS2 / ZnO heterojunction system.

[0010] 3. Place the WS2 / ZnO heterojunction photodetector on the stage of a spin coater. Maintain a vacuum using a mechanical pump to ensure stable substrate adsorption. Evenly drip 20 μL of the Au nanoparticle solution onto the WS2 / ZnO heterojunction photodetector. Operate the spin coater at 1000 rpm for 10 seconds, then 3000 rpm for 20 seconds.

[0011] 4. Heat the device at 80°C for 10 minutes to enhance heterojunction interface coupling.

[0012] 5. The WS2 / ZnO / Au heterojunction photodetector was placed in the reaction chamber of the ALD equipment, and a 2 nm ZnO film was deposited to encapsulate the Au NPs to ensure the long-term stability of the device.

[0013] Compared to traditional plasmonic photodetectors that focus solely on light absorption, this WS2 / ZnO / Au / ZnO sandwich plasmonic heterojunction successfully combines the local field enhancement effect induced by the LSPR effect with efficient hot electron injection, resulting in a highly responsive plasmonic heterojunction photodetector. This method offers a simple integration approach, strong process compatibility, and the absence of complex chemical modification, providing a promising approach for the fabrication of high-performance plasmonic heterojunction photoelectric devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 An accompanying diagram for the abstract;

[0015] Figure 2 Flow chart for the preparation of WS2 / ZnO / Au / ZnO heterojunction photodetectors;

[0016] Figure 3 (a) Dark current, (b) photocurrent, (c) responsivity, and (d) detectivity of WS2, WS2 / ZnO, and WS2 / ZnO / Au / ZnO photodetectors at different light power densities.

[0017] Figure 4 (a) is the response speed of WS2 / ZnO / Au / ZnO heterojunction photodetector at different frequencies under the same laser power density. Figure 4 (b) From Figure 4 (a) Extracted photoresponse cycle of one laser pulse;

[0018] Figure 5 is the energy band diagram of WS2 / ZnO / Au / ZnO heterojunction;

[0019] Figure 6 Raman spectra of WS2, WS2 / ZnO and WS2 / ZnO / Au / ZnO. DETAILED DESCRIPTION

[0020] In order to better illustrate the present invention, detailed embodiments are given below in conjunction with the accompanying drawings.

[0021] Example 1

[0022] This implementation involves the process of preparing WS2 photodetectors using a mechanical exfoliation method. The specific steps are as follows:

[0023] 1. Interdigital electrode preparation: Gold interdigital electrodes were prepared on a clean Si / SiO2 substrate using UV photolithography. The interdigital electrodes were made of gold, with a gap of 3 μm, a width of 5 μm, and a length of 1400 μm.

[0024] 2. WS2 thin film preparation: Use 3M tape to peel off the surface of WS2 crystal to obtain micron-thick sheets. The tape is periodically folded to weaken the interlayer van der Waals forces to obtain a thin layer of WS2 material. The thin layer of WS2 material on the 3M tape is transferred to blue film tape and folded and peeled multiple times to obtain a few layers of WS2.

[0025] 3. Preparation of WS2 photodetectors: The mechanically exfoliated two-dimensional few-layer WS2 film was transferred to pre-prepared gold interdigital electrodes and heat-treated at 80°C for about 10 minutes on a heating table to strengthen the adhesion between the WS2 material and the interdigital electrodes to prepare a WS2 photodetector.

[0026] Example 2

[0027] This implementation involves the process of fabricating WS2 / ZnO heterojunction photodetectors using ALD technology. The specific steps are as follows:

[0028] 1. Interdigital electrode preparation: Gold interdigital electrodes were prepared on a clean Si / SiO2 substrate using UV photolithography. The interdigital electrodes were made of gold, with a gap of 3 μm, a width of 5 μm, and a length of 1400 μm.

[0029] 2. WS2 thin film preparation: Use 3M tape to peel off the surface of WS2 crystal to obtain micron-thick sheets. The tape is periodically folded to weaken the interlayer van der Waals forces to obtain a thin layer of WS2 material. The thin layer of WS2 material on the 3M tape is transferred to blue film tape and folded and peeled multiple times to obtain a few layers of WS2.

[0030] 3. Preparation of WS2 photodetectors: The mechanically exfoliated two-dimensional few-layer WS2 film was transferred to pre-prepared gold interdigital electrodes and heat-treated at 80°C for about 10 minutes on a heating table to strengthen the adhesion between the WS2 material and the interdigital electrodes to prepare a WS2 photodetector.

[0031] 4. Preparation of WS2 / ZnO heterojunction photodetector: Place the WS2 photodetector in the ALD equipment reaction chamber, set the deposition recipe and cycle, and deposit a 2 nm ZnO film. After deposition, remove the sample to obtain a WS2 / ZnO heterojunction photodetector.

[0032] Example 3

[0033] This embodiment involves the process of preparing WS2 / ZnO / Au / ZnO heterojunction photodetector by spin coating. Figure 2 As shown, the specific steps are as follows.

[0034] 1. Interdigital electrode preparation: Gold interdigital electrodes were prepared on a clean Si / SiO2 substrate using UV photolithography. The interdigital electrodes were made of gold, with a gap of 3 μm, a width of 5 μm, and a length of 1400 μm.

[0035] 2. WS2 thin film preparation: Use 3M tape to peel off the surface of WS2 crystal to obtain micron-thick sheets. The tape is periodically folded to weaken the interlayer van der Waals forces to obtain a thin layer of WS2 material. The thin layer of WS2 material on the 3M tape is transferred to blue film tape and folded and peeled multiple times to obtain a few layers of WS2.

[0036] 3. Preparation of WS2 photodetectors: The mechanically exfoliated two-dimensional few-layer WS2 film was transferred to pre-prepared gold interdigital electrodes and heat-treated at 80°C for about 10 minutes on a heating table to strengthen the adhesion between the WS2 material and the interdigital electrodes to prepare a WS2 photodetector.

[0037] 4. Preparation of WS2 / ZnO heterojunction photodetector: Place the WS2 photodetector in the ALD equipment reaction chamber, set the deposition recipe and cycle, and deposit a 2 nm ZnO film. After deposition, remove the sample to obtain a WS2 / ZnO heterojunction photodetector.

[0038] 5. Preparation of Au NPs Solution: Accurately prepare 1 mmol·L⁻¹ chloroauric acid solution and 1% trisodium citrate solution. Inject 4 mL of chloroauric acid solution into 96 mL of deionized water, stir magnetically at 700 rpm, and heat to boiling. Subsequently, inject 15 mL of trisodium citrate solution, maintain boiling, and stir continuously at 700 rpm for 30 min to obtain a wine-red Au NPs solution.

[0039] 6. Preparation of WS2 / ZnO / Au / ZnO heterojunction photodetector: The WS2 / ZnO heterojunction device was placed on the stage of a spin coater, and a vacuum environment was maintained by a mechanical pump to achieve stable substrate adsorption. The prepared Au NPs solution was then evenly dripped onto the WS2 / ZnO heterojunction photodetector. The spin coater was controlled to operate at 1000 rpm for 10 s and then at 3000 rpm for 20 s. The device was heated at 80°C for 10 min to enhance heterojunction interface coupling. Finally, a 2 nm thick ZnO thin film was deposited on the WS2 / ZnO / Au heterojunction photodetector using ALD technology to obtain a WS2 / ZnO / Au / ZnO heterojunction photodetector.

[0040] Figure 3The key parameters of WS2, WS2 / ZnO, and WS2 / ZnO / Au / ZnO devices, such as dark current, photocurrent, responsivity, and detectivity, were compared, and their photoelectric enhancement effects were systematically evaluated. Figure 3 As shown in (a), in the dark state, the maximum dark current of the WS2 / ZnO / Au / ZnO heterojunction photodetector is 46.4 μA, which is 193.3 times that of the WS2 photodetector, while the dark current of the WS2 / ZnO QDs@Au device is 429 times that of the WS2 photodetector. This proves that the non-contact plasmonic structure can effectively solve the dark current surge problem of traditional LSPR structures. Figure 3 (b) shows that, under 447 nm laser (power density 0.2-196 mW / cm 2 ) irradiation, the photocurrents of the three devices increase linearly with the increase of power density, among which the WS2 / ZnO / Au / ZnO heterojunction photodetector increases linearly with the increase of power density at 196 mW / cm 2 The photocurrent reaches 716.2 μA, which is 208.8 times that of WS2 device. However, the responsivity shows a typical attenuation trend with the increase of laser power density. 2 When the laser power density increases to 196 mW / cm 2 The responsivity drops to 33 A / W when the injection pressure is high, which is attributed to the exponential increase in the carrier recombination rate under high injection conditions. The detectivity has the same trend as the responsivity. 2 The detection rate is as high as 1.45×10 13 Jones, and when the laser power density increased to 196 mW / cm 2 When the detection rate drops to 9.1×10 10 Jones, e.g. Figure 3 As shown in (c) and (d).

[0041] Figure 4 (a) WS2 / ZnO / Au / ZnO device under 447 nm laser (power density of 196 mW / cm 2 ) excitation, corresponding to the optical response signal output from 1000 to 3000 Hz. When the laser pulse frequency is increased from 1000 Hz to 3000 Hz, the device exhibits excellent optical response reproducibility, indicating that its signal output has good stability. Figure 4 (b) The optical response period of the WS2 / ZnO / Au / ZnO device under one laser pulse. The rise time of the device is 90.82 μs and the decay time is 125.31 μs.

[0042] Figure 5The energy band diagram of the WS2 / ZnO / Au / ZnO heterojunction shows the charge transfer in the heterojunction and deeply analyzes the enhancement mechanism of the device's photoelectric performance. WS2 and ZnO form a Type-Ⅱ band alignment. Under the action of the built-in electric field, the carriers are quickly separated and their recombination is suppressed. The photoelectric performance of the WS2 / ZnO heterojunction photodetector is therefore improved. After the introduction of Au NPs, LSPR is achieved under laser irradiation. Since the ultra-thin ZnO layer does not hinder the LSPR from directly acting on WS2, the WS2 / ZnO / Au / ZnO heterojunction photodetector obtains an ultra-high light response. At the same time, the non-contact plasma structure hinders the free electrons in the metal nanoparticles, suppresses the growth of dark current, and the device obtains a higher detection rate. As Figure 5 As shown in (c), under the energy band arrangement of WS2-ZnO-Au-ZnO, the high-energy hot electrons generated by Au NPs through LSPR will overcome the influence of the potential barrier and directly participate in charge transfer. More importantly, the WS2 / ZnO heterojunction interface will assist the hot electron injection and improve the efficiency of hot electron injection, thereby obtaining a high-performance WS2 / ZnO / Au / ZnO heterojunction photodetector.

[0043] Figure 6 The Raman spectra of WS2, WS2 / ZnO, and WS2 / ZnO / Au / ZnO confirm the LSPR effect in the heterojunction. The figure shows that the introduction of Au NPs significantly increases the Raman peak intensity of the WS2 / ZnO / Au / ZnO heterojunction. This confirms the presence of the Au NP-induced LSPR effect in the WS2 / ZnO / Au / ZnO heterojunction.

[0044] This invention designs a sandwich plasmonic heterojunction photodetector based on the LSPR effect and band alignment. It successfully achieves the synergistic effect of LSPR-induced local field enhancement and efficient hot electron injection, improving the photoelectric conversion efficiency of the WS2 / ZnO / Au / ZnO heterojunction photodetector. This invention is simple to operate and has a high success rate. It effectively solves the problem of incomplete performance of existing plasmonic photodetectors and meets the current demand for high-performance low-dimensional hybrid heterojunction photoelectric devices.

[0045] The above-described embodiments are preferred versions of the present invention. However, in actual practice, they are not set in stone and may be adjusted in form and detail as needed. Professionals may make appropriate modifications and improvements without violating the core concepts and principles. Therefore, the scope of protection of the present invention shall be based on the formal claims, which include all reasonable variations and alternatives within the spirit and scope of the invention.

Claims

1. A method for fabricating a sandwich-type plasmonic WS2 / ZnO / Au / ZnO heterojunction photodetector. From bottom to top, the fabrication process consists of gold interdigitated electrodes, a WS2 layer, and a ZnO / Au / ZnO sandwich structure. This sandwich structure not only maintains the heterojunction interface quality and enhances the material's light absorption capacity, but also facilitates carrier transport, achieving dual optimization of light absorption and hot electron injection efficiency.

2. According to the WS2 / ZnO / Au / ZnO heterojunction photodetector described in claim 1, gold interdigital electrodes are photolithographically prepared on a clean Si / SiO2 substrate using ultraviolet photolithography technology. The interdigital electrodes are made of gold, with a finger gap of 3 μm, a finger width of 5 μm, and a finger length of 1400 μm.

3. Use 3M tape to peel off the surface of WS2 crystals to obtain micron-thick sheets. The tape is then periodically folded to weaken the interlayer van der Waals forces, resulting in thin layers of WS2 material. This method is also applicable to other two-dimensional transition metal sulfides (TMDs), such as MoS2, WSe2, and MoSe2.

4. Preparation of WS2 / ZnO / Au / ZnO heterojunction photodetector, including the following steps: (1) Place the WS2 photodetector in the ALD equipment reaction chamber, set the deposition recipe and cycle, deposit a 2 nm ZnO film, and remove the sample after the deposition is completed to obtain a WS2 / ZnO heterojunction photodetector; (2) Accurately configure 1 mmo1·L -1 1% chloroauric acid solution and 1% trisodium citrate solution were prepared for later use; 4 mL of chloroauric acid solution was injected into 96 mL of deionized water, and the mixture was heated to boiling with magnetic stirring at 700 rpm; then 15 mL of trisodium citrate solution was injected, and the mixture was kept boiling and stirred at 700 rpm for 30 min to obtain a wine-red Au NPs solution. (3) Place the WS2 / ZnO heterojunction device on the stage of a spin coater and maintain a vacuum environment by a mechanical pump to achieve stable adsorption of the substrate; then drop the prepared Au NPs solution evenly onto the WS2 / ZnO heterojunction photodetector and control the spin coater to run at 1000 rpm for 10 s and then at 3000 rpm for 20 s; (4) Heating the device at 80 °C for 10 min to enhance heterojunction interface coupling; (5) Finally, a 2 nm ZnO thin film was deposited on the WS2 / ZnO / Au heterojunction photodetector using ALD technology to obtain a WS2 / ZnO / Au / ZnO heterojunction photodetector.

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