Method for enhancing performance of WS2 photoelectric detector based on defect structured SU8 metasurface

Abstract

The invention belongs to the technical field of optical metasurfaces and two-dimensional photoelectric detectors, and particularly provides a method for enhancing the performance of a WS2 photoelectric detector based on a defect structured SU8 metasurface. The performance responsivity R, the detection rate D * and the quantum efficiency EQE of the WS2 photoelectric detector are effectively improved by about one order of magnitude; the preparation process is simple and convenient, and the scientific research production efficiency and the device preparation yield are improved; in the RIE etching process, the duration of introducing O2 can be changed according to specific conditions, and whether defects are introduced or not and the degree of introducing the defects are freely regulated and controlled, so that the performance of the device is improved to the maximum extent; the SU8 metasurface film has a certain packaging effect, can inhibit photooxidative degradation during WS2 testing, improves the stability of the WS2 photoelectric detector exposed in the air, and does not reduce the response speed of the WS2 photoelectric detector at the same time.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical metasurfaces and two-dimensional photoelectric detectors, and specifically relates to a method for enhancing the performance of WS2 photoelectric detectors based on defect-structured SU8 metasurfaces. Background Art

[0002] Photodetectors have been widely used in fiber-optic communications, digital imaging, flexible sensing, etc. In the past few years, two-dimensional materials, such as transition metal dichalcogenides (TMDs), have made significant breakthroughs in photodetection due to their well-developed semiconductor band gaps and stronger light-matter interactions.

[0003] As one of the TMDs materials, tungsten disulfide WS2 has excellent thermal stability and wide applications. Theoretical calculations show that the electron effective mass of WS2 is small, so it has a higher carrier mobility than other TMD materials. However, the response rate of detectors based on WS2 thin films is low because of its low optical absorbance. In order to improve the photoresponsivity, heterojunction photodetectors were subsequently proposed. However, the preparation process of a well-contacted heterojunction is usually complicated, with high process requirements and low efficiency.

[0004] Optical metasurface is a two-dimensional material composed of artificial structures of sub-wavelength size. It can flexibly control the polarization, amplitude, phase and other characteristics of electromagnetic waves. It has the advantages of being highly customized, easy to integrate, light, thin and efficient. It also has a certain packaging effect when using transparent materials. It is considered to be an effective way to improve the performance of optoelectronic devices. Summary of the invention

[0005] The main innovation of the present invention is to introduce defect-structured SU8 super-surface films in the field of WS2 photodetectors. This can solve the problem that the preparation process of heterojunction WS2 photodetectors is usually complicated, has high process requirements, and is relatively inefficient in order to improve the response performance of WS2 photodetectors, which is conducive to further improving device performance and device integration in the future. The structured SU8 super-surface film prepared by nanoimprinting in this method can more easily improve the response performance of WS2 photodetectors. At the same time, the structured SU8 super-surface film also has a certain packaging effect, which makes the performance of WS2 photodetectors more stable when exposed to air.

[0006] The method for enhancing the performance of WS2 photodetector based on defect structured SU8 metasurface includes the following steps: Step 1, cutting the polydimethylsiloxane (PDMS) film to size and attaching it to a glass slide to form a PDMS / glass slide structure; Step 2: Use a mechanical peeling method to transfer the over-layer WS2 to the above-mentioned PDMS film, use a blade to cut and remove the surrounding irrelevant PDMS film, reduce the PDMS area attached to the glass slide, and form a WS2 / PDMS / glass slide structure; Step 3, transfer the WS2 material to the substrate by dry transfer of the WS2 / PDMS / glass slide structure, fix the WS2 / PDMS / glass slide in the substrate card slot of the transfer platform, and fix the substrate on the sample stage by hot melt adhesive to form a WS2 / substrate structure; Step 4: Use a fine needle to pick up the electrode, and a thick needle to stick to the electrode to form an electrode / WS2 / substrate structure, and perform a photoelectric test; Step 5, using a spin coater to spin coat a layer of SU8 film on the electrode / WS2 / substrate structure to form a SU8 film / electrode / WS2 / substrate structure; Step 6, transferring the nanoarray structure to the SU8 film / electrode / WS2 / substrate structure by nanoimprinting to obtain a structured SU8 film / electrode / WS2 / substrate structure; Step 7, use RIE plasma etching to finally obtain a defective structured SU8 film / electrode / WS2 / substrate structure, and perform photoelectric testing.

[0007] The beneficial effects achieved by the present invention are: (1) This method uses nanoimprint technology and RIE etching process to prepare defect-structured SU8 super-surface films, which can effectively improve the performance of WS2 photodetector responsivity R, detection rate D*, and quantum efficiency EQE by about an order of magnitude; (2) The preparation process of the super-surface film prepared by this method is simple and convenient, which improves the scientific research production efficiency and device preparation yield. It only needs to use a spin coater to spin-coat a layer of SU8 film on the WS2 photodetector, then heat it, and use a stamp to stamp to form a structured SU8 film; (3) The metasurface film prepared by this method can autonomously control whether to use the RIE etching process to introduce defects and the degree of defects introduced according to the specific situation of the WS2 photodetector, so as to maximize the device performance improvement; (4) The SU8 supersurface film prepared by this method has a certain encapsulation effect, which can inhibit the photo-oxidative degradation of WS2 during testing to a certain extent and improve the stability of the WS2 photodetector when exposed to air; (5) The SU8 supersurface film prepared by this method does not reduce the response speed of the WS2 photodetector and has almost no effect on its response time. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1is a flow chart of a method in an embodiment of the present invention; Figure 2 This is a flow chart of device nanoimprinting in an embodiment of the present invention; Figure 3 This is a 100x optical microscope image of the WS2 material transferred onto a silicon oxide substrate in an embodiment of the present invention; Figure 4 This is a 100x optical microscope image of the WS2 material after spin coating with SU8 and structuring in an embodiment of the present invention; Figure 5 This is the AFM characterization image of WS2 in the embodiment of the present invention; Figure 6 The SEM characterization images of the top view and cross section of the structured SU8 super surface treated with RIE for 0s and 90s in the embodiment of the present invention; Figure 7 It is the differential reflection spectra of WS2, structured SU8 film / WS2, and defective structured SU8 film / WS2 in the embodiment of the present invention; Figure 8 WS2 and defective structured SU8 film / WS2 in the embodiment of the present invention at different V g The output curve below: Fig. 9 Comparison of response time of WS2 and defect structured SU8 film / WS2 in the embodiment of the present invention; Fig.10 Comparison of the performance R, D*, and EQE of WS2 and defective structured SU8 film / WS2 in the embodiments of the present invention; Fig.11 This is an error diagram of the improvement degree of the defect structured SU8 film / WS2 performance R, D*, and EQE prepared in an embodiment of the present invention. DETAILED DESCRIPTION

[0009] The technical solutions of the embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings.

[0010] The method for enhancing the performance of WS2 photodetectors based on defect-structured SU8 supersurface in this embodiment includes the following steps.

[0011] Step 1: Cut the commercial PDMS film into strips of approximately 1 cm × 2 cm, attach it to a glass slide wiped clean with ethanol, and treat it with ozone for 2-5 minutes to reduce its surface viscosity, so that the WS2 mechanically peeled off from it can be more easily transferred to the silicon oxide substrate in the subsequent process.

[0012] Step 2: Use mechanical peeling to tear the WS2 material onto the PDMS film. Use an optical microscope to observe the transparency of the WS2 material under the 10x eyepiece transmitted light field to roughly determine its thickness. Look for multilayer WS2 materials with suitable thickness and shape. Then switch to the 100x eyepiece to carefully observe whether the material thickness is flat and uniform. After selection, use a blade to cut and remove the surrounding irrelevant PDMS films to further reduce the PDMS area attached to the glass slide, making it easier to find the target WS2 material in the field of view of the CCD microscope camera on the transfer system platform in the subsequent process.

[0013] Step 3, use the E1-T multifunctional high-precision two-dimensional material transfer system platform to transfer the target WS2 material on the cut PDMS to a clean area on the oxidized silicon wafer, fix the WS2 material / PDMS / glass slide prepared in the above steps in the substrate card slot of the glass slide moving platform, use the CCD microscope camera of the transfer system platform to find the target WS2 material on the cut PDMS, align it with the clean area on the silicon oxide substrate fixed on the substrate carrier platform, control the electric axis to slowly drop the glass slide moving platform, and finally let the WS2 material / PDMS / glass slide fit with the silicon oxide substrate on the substrate carrier platform, wait for 1 minute to allow the target WS2 material to better adsorb to the silicon oxide wafer (because the PDMS film is treated with ozone in step 1, the adhesion of the PDMS film will be less than that of the silicon oxide wafer), control the electric axis to slowly lift the glass slide moving platform to complete the transfer of the target WS2 material. The purpose of this step is to obtain a relatively clean WS2 material / silicon oxide wafer structure. The thickness of the WS2 material is as follows: Figure 5 As shown in the AFM image, it is necessary to avoid the existence of too much defective WS2 material that does not meet the requirements around the target WS2 material, which will affect the electrode bonding and SU8 film spin coating in the subsequent process.

[0014] For the oxide silicon wafer substrate, the SiO2 layer thickness is 285nm and the Si layer thickness is 500um ， Cut it into 1.5cm×1.5cm squares, and use RIE to introduce O2, with a gas flow of 50sccm, a power of 30W, a high valve of 100%, and a duration of 5s. Such pretreatment can increase the hydrophilicity of the surface of the silicon oxide wafer, making the SU8 spin coating more uniform in the subsequent process.

[0015] Step 4, use a fine needle with a 1um tip to cut the 120nm thick Au film strip to the required length under optical microscope observation through a customized platform, then use a thick needle with a 15um tip, apply adhesive on the needle tip, pick up the Au film strip cut by the fine needle in the previous step, and stick the Au film strip on the target WS2 material on the silicon oxide substrate. These two Au film strips serve as the source and drain of the WS2 photoelectric detection device. Use a diamond pen to gently scratch the corners of the silicon oxide substrate to expose the Si layer under the oxide layer as the gate of the WS2 photoelectric detection device, and obtain the electrode / WS2 / substrate structure, such as Figure 3 As shown. In a room temperature environment, the electrical and optoelectronic tests were performed using the Fs-Pro semiconductor device analyzer to perform relevant tests on the WS2 photodetector. When testing the output curve, the gate voltages were set to -30V, -20V, -10V, 0V, 10V, 20V, and 30V respectively. The light source used a 532nm laser. In order to measure the photocurrent related to the photon energy and the incident power, the incident power of the laser was adjusted by using an attenuation plate. The applied bias voltage was 3V and the gate voltage was -30V. In a room temperature environment, the optical spectral analysis used a QE-pro ocean spectrometer with a response band of 200-950nm. The light source used a halogen lamp to test the reflectivity of the silicon oxide substrate. , reflectivity of WS2 / silicon oxide substrate , through the formula The differential reflection of WS2 can be obtained; the reflectivity of the silicon oxide substrate is tested separately , Reflectivity of structured SU8 film / WS2 / silicon oxide substrate , through the formula The differential reflection of structured SU8 film / WS2 can be obtained; the reflectivity of silicon oxide substrate is tested respectively , reflectivity of defect structured SU8 film / WS2 / silicon oxide substrate , through the formula The differential reflection of the defect structured SU8 film / WS2 can be obtained.

[0016] Step 5: Place the electrode / WS2 / silicon oxide substrate structure on the sample stage of the spin coater, drop a drop of SU8 photoresist solution with a mass concentration ratio of 1:1 on its surface, and spin coat at a speed of 5000 r / min and an acceleration of 300 r / s. 2 , and spin coating for 30 s to obtain a SU8 film / electrode / WS2 / silicon oxide substrate structure.

[0017] Step 6, place it on a 65℃ hot stage for 1 minute, place it on a 95℃ hot stage for 1 minute, and after cooling to room temperature, press the micro-nanostructure stamp on it, place it on a 95℃ hot stage for 45 seconds, and after cooling to room temperature, remove the micro-nanostructure stamp to obtain a structured SU8 film / electrode / WS2 / silicon oxide substrate structure, such as Figure 4 In this embodiment, a single micro-nano pillar of the micro-nano structure stamp is designed to have a height of 330 nm, a diameter of 620 nm, and a period of 1020 nm.

[0018] Step 7: Place the structured SU8 film / electrode / WS2 / silicon oxide substrate structure into a RIE electron beam etcher, introduce O2, with a gas flow rate of 30 sccm, a power of 30 W, a high valve of 100%, and an etching time of 90 s. Under these conditions, defects can be introduced while retaining the structured SU8 photoresist. Figure 6 , forming a defective structured SU8 film / electrode / WS2 / silicon oxide substrate structure, and this defect level can maximize the performance of the WS2 photodetector in this embodiment. The electrical and photoelectric tests and optical spectrum analysis in room temperature environment are consistent with those in step 4, and comparative analysis is performed.

[0019] In this embodiment, from Figure 7 In the reflectivity spectrum, it can be seen that the reflectivity of the defective structured SU8 film / electrode / WS2 / silicon oxide substrate structure is greatly reduced compared to the electrode / WS2 / silicon oxide substrate structure, which also means that more light is absorbed. Compared with the structured SU8 film / electrode / WS2 / silicon oxide substrate structure, while ensuring similar reflectivity, the reflectivity of light in a specific band can be regulated.

[0020] from Figure 8 In the comparison of the output curve before and after structuring, it can be seen that the defective structured SU8 film / electrode / WS2 / silicon oxide substrate structure is different from the electrode / WS2 / silicon oxide substrate structure at different V g Under the gate voltage, the output current is improved to a certain extent, especially under the horizontal axis bias voltage V ds This is especially evident at =-2V and 2V.

[0021] from Fig. 9 From the comparison of response time before and after, it can be seen that the switching time of the defect structured SU8 film / electrode / WS2 / silicon oxide substrate structure is not affected by the addition of the defect structured SU8 film compared to the electrode / WS2 / silicon oxide substrate structure.

[0022] from Fig.10 Comparison chart of the device's responsivity R before and after structuring, comparison chart of the external quantum efficiency EQE before and after structuring, comparison chart of the detection rate D* before and after structuring, and Fig.11 From the responsivity R improvement ratio error diagram, external quantum efficiency EQE improvement ratio error diagram, and detection rate D* improvement ratio error diagram of multiple devices under different light intensities, it can be seen that the defect structured SU8 film / electrode / WS2 / silicon oxide substrate structure photodetector has a D* improvement of up to 14 times, EQE improvement of up to 9.4 times, and R improvement of up to 5.6 times compared with the electrode / WS2 / silicon oxide substrate structure photodetector.

[0023] The above description is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above embodiment. Any equivalent modifications or changes made by ordinary technicians in this field based on the contents disclosed by the present invention should be included in the protection scope recorded in the claims.

Claims

1. Enhanced WS based on defect-structured SU8 metasurface 2 Photodetector Performance Methods, Features: The method comprises the following steps: Step 1, cutting the polydimethylsiloxane (PDMS) film to size and attaching it to a glass slide to form a PDMS / glass slide structure; Step 2: Use mechanical stripping to remove the multi-layer tungsten disulfide WS 2 Transfer to the above PDMS film, use a blade to cut and remove the surrounding irrelevant PDMS film, reduce the PDMS area attached to the slide, and form a WS 2 / PDMS / glass slide structure; Step 3: Set WS 2 / PDMS / glass slide structure uses dry transfer method to transfer WS 2 Material transfer to substrate, WS 2 The / PDMS / glass slide is fixed in the substrate slot of the transfer platform, and the substrate is fixed on the sample stage using hot melt adhesive to form a WS 2 / substrate structure; Step 4: Use a fine needle to pick up the electrode and a thick needle to stick to the electrode to form an electrode / WS 2 / substrate structure, and conduct optoelectronic testing; Step 5: Use a spin coater to coat the electrode / WS 2 / Spin-coat a layer of SU8 film on the substrate structure to form SU8 film / electrode / WS 2 / substrate structure; Step 6: Transfer the nanoarray structure to the SU8 film / electrode / WS by nanoimprinting 2 / substrate structure, a structured SU8 film / electrode / WS 2 / substrate structure; Step 7, use RIE plasma etching to finally obtain a defective structured SU8 film / electrode / WS2 / substrate structure, and perform photoelectric testing.

2. The defect-structured SU8 supersurface-enhanced WS according to claim 1 2 Photodetector Performance Methods, Features: In step 2, the multi-layer WS used 2 The thickness is 5nm-20nm.

3. The defect-structured SU8 supersurface-enhanced WS according to claim 1 2 Photodetector Performance Methods, Features: In step 3, the substrate used is an oxidized silicon wafer.

4. The defect-structured SU8 supersurface-enhanced WS according to claim 1 2 Photodetector Performance Methods, Features: In step 3, an RIE plasma etcher is used to pass O 2 Treat the surface of the silicon oxide substrate to increase its hydrophilicity; The specific parameters of the RIE plasma etching process are as follows: 2 , the gas flow rate is 50sccm, the power is 50W, the high valve is 100%, and the etching time is 5s.

5. The defect-structured SU8 supersurface-enhanced WS according to claim 1 2 Photodetector Performance Methods, Features: In step 4, the tip of the fine needle is 1 um and the tip of the thick needle is 15 um.

6. The defect-structured SU8 supersurface-enhanced WS according to claim 1 2 Photodetector Performance Methods, Features: In step 4, the electrode used is Au with a thickness of 120 nm.

7. The defect-structured SU8 supersurface-enhanced WS according to claim 1 2 Photodetector Performance Methods, Features: In step 5, place the electrode / WS 2 The silicon oxide substrate structure was placed on the sample stage of the spin coater, and a drop of SU8 photoresist solution with a mass concentration ratio of 1:1 was dropped on its surface. The spin coating speed was 5000r / min and the acceleration was 300r / s. 2 , spin coating for 30 s to obtain SU8 film / electrode / WS 2 / Silicon oxide substrate structure.

8. The defect-structured SU8 supersurface-enhanced WS according to claim 1 2 Photodetector Performance Methods, Features: In step 6, the stamp nanoarray structure used is a columnar structure, with a single structure diameter of 620 nm and a period of 1020 nm.

9. The defect-structured SU8 supersurface-enhanced WS according to claim 1 2 Photodetector Performance Methods, Features: In step 7, the specific parameters of the RIE plasma etching process are set as follows: 2 , the gas flow rate is 30sccm, the power is 30W, the high valve is 100%, and the etching time is 0-120s. Under this condition, defects are introduced while retaining the structured SU8 photoresist.

10. The defect-structured SU8 supersurface-enhanced WS according to claim 9 2 Photodetector Performance Methods, Features: In step 7, O 2 The length of time regulates the lateral size and longitudinal depth of the structure, while regulating the degree of defects introduced. The length of time is controlled to avoid excessive defects that destroy the enhancement effect of the structured SU8 film.

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