A method for realizing polarization ratio amplification of a photoelectric detector based on a two-dimensional semimetal material and a heterostructure

Abstract

This invention relates to a method for amplifying the polarization ratio of a photodetector based on a two-dimensional semi-metallic material and a heterostructure, belonging to the field of photodetection technology. Based on a strategy combining a two-dimensional semi-metallic material and a heterostructure, a BP / MoS2 / WTe2 heterojunction is constructed, where BP is the light-absorbing layer, MoS2 is the barrier layer, and WTe2 is the contact layer. This invention not only achieves selective carrier transport and reduces dark current, but also allows WTe2 to reduce contact resistance and provide a fast carrier extraction channel, realizing asymmetric amplification of the photocurrent, thereby achieving active amplification of the polarization ratio even at zero bias. This invention breaks the limitation of the inherent anisotropy of materials on the magnitude of the polarization ratio, and uses a completely dry transfer process to fabricate polarization detection photodetectors, eliminating the need for additional polarization elements and chemical solution treatment. It boasts advantages such as simple process, low cost, high repeatability, and no pollution.

Description

Technical Field

[0001] This invention belongs to the field of photoelectric detector technology, and relates to a method for amplifying the polarization ratio of a photoelectric detector based on two-dimensional semi-metallic materials and heterostructures. Background Technology

[0002] Polarization is one of the fundamental properties of light, and polarization-sensitive photodetectors have wide applications in remote sensing, imaging, spectral analysis, quantum communication, and biomedical detection. Traditional polarization detectors typically rely on complex optical elements (such as polarizers and waveplates) combined with broadband photodetectors, resulting in problems such as large system size, low integration, and low efficiency.

[0003] Two-dimensional materials, such as black phosphorus (BP), offer new avenues for developing miniaturized, integrated intrinsically polarization-sensitive detectors due to their unique layered structure and strong in-plane optical anisotropy. Black phosphorus exhibits significant differences in absorption rate for linearly polarized light with different directions, causing the photocurrent of black phosphorus-based optoelectronic devices to vary with the polarization direction of the incident light, i.e., they possess polarization sensitivity. The key parameter for measuring polarization sensitivity is the polarization ratio, defined as the ratio of the maximum photocurrent to the minimum photocurrent (I0). max / I min However, the polarization ratio of a simple BP field-effect transistor or metal-BP-metal detector is limited by the carrier injection efficiency at the electrode contact, the Schottky barrier, and the isotropic dark current background, making it difficult to achieve a high polarization ratio and thus limiting its sensitivity in practical applications. Therefore, how to effectively enhance the separation and extraction capabilities of photogenerated carriers through structural design, thereby significantly amplifying the photocurrent polarization ratio while maintaining the intrinsic polarization absorption characteristics of BP, is a key technical problem that urgently needs to be solved in this field.

[0004] In the prior art: (1) the metal-two-dimensional semiconductor structure is mainly limited by the Schottky barrier at the electrode contact, making it difficult to achieve efficient carrier extraction; (2) although the two-dimensional half-metal / semiconductor structure can reduce the contact resistance, it lacks a mechanism for regulating the carrier transport direction; therefore, the prior art cannot achieve a significant amplification of the polarization ratio while maintaining the intrinsic anisotropy of the material. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a method for amplifying the polarization ratio of a photodetector based on a two-dimensional semi-metallic material and a heterostructure. More specifically, it provides a heterostructure coupled with a semi-metallic material, which forms an asymmetric band arrangement and has carrier selective transport capabilities to reduce dark current and improve signal-to-noise ratio. Simultaneously, the two-dimensional semi-metallic material layer reduces contact resistance and provides a fast carrier extraction channel, forming a semi-metal-assisted asymmetric extraction mechanism in conjunction with the carrier selective transport structure. This mechanism, under incident light with different polarization directions, achieves asymmetric amplification of photocurrent through nonlinear extraction enhancement of the high carrier density direction, thereby enhancing the polarization ratio compared to devices made of a single anisotropic material, thus solving the problems existing in the prior art.

[0006] To achieve the above objectives, the first aspect of the present invention provides a photodetector with a high polarization ratio, comprising: a substrate, a metal electrode, a two-dimensional semi-metallic material layer, a two-dimensional semiconductor material layer I, and a two-dimensional semiconductor material layer II with anisotropy.

[0007] The substrate consists of two metal electrodes disposed at both ends of a substrate surface; a two-dimensional semi-metallic material layer disposed on the substrate surface and in contact with the metal electrode at one end of the substrate surface; a two-dimensional semiconductor material layer I disposed on the surface of the two-dimensional semi-metallic material layer; and a two-dimensional semiconductor material layer II disposed on the surface of the two-dimensional semiconductor material layer I and in contact with the metal electrode at the other end of the substrate surface. The two-dimensional semiconductor material layers I and II form a vertical van der Waals heterojunction between the metal electrodes, forming a unipolar barrier structure through asymmetric band arrangement, enabling selective separation and directional transport of different types of charge carriers. The two-dimensional semi-metallic material layer is used to suppress the Fermi level pinning effect, reduce contact resistance, and accelerate the carrier extraction process, thereby amplifying the photocurrent difference under illumination conditions with different polarization directions and achieving a high polarization ratio.

[0008] Furthermore, the semiconductor material used in the two-dimensional semiconductor material layer II is BP, with a conduction band bottom position of 4.4 eV and a valence band top position of 4.1 eV.

[0009] Furthermore, the semiconductor material used in the two-dimensional semiconductor material layer I is MoS2, with a conduction band bottom position of 4.2 eV and a valence band top position of 5.4 eV.

[0010] Furthermore, the semi-metallic material used in the two-dimensional semi-metallic material layer is WTe2, with a work function position of 4.7 eV.

[0011] Furthermore, the substrate is a SiO2 / Si substrate, wherein the thickness of SiO2 is 300 nm and the thickness of Si is 500 μm.

[0012] Furthermore, the metal electrode is a Cr / Au composite electrode with a thickness of 55 nm, wherein the thickness of Cr is 5 nm and the thickness of Au is 50 nm.

[0013] A second aspect of the present invention provides a method for amplifying the polarization ratio of the photodetector described in the first aspect based on a two-dimensional semi-metallic material and a heterostructure, the method comprising: First, obtain the substrate, and then ultrasonically clean it sequentially with acetone, anhydrous ethanol, and deionized water. After cleaning, dry it with a nitrogen gun and store it. Metal electrodes with target patterns are fabricated at both ends of a substrate surface using photolithography. Two-dimensional semi-metallic material layer, two-dimensional semiconductor material layer I, and anisotropic two-dimensional semiconductor material layer II were obtained by mechanical exfoliation. A two-dimensional semi-metallic material layer, a two-dimensional semiconductor material layer I, and a two-dimensional semiconductor material layer II of appropriate thickness are selected. Then, using PDMS, these three layers are sequentially transferred from bottom to top between metal electrodes at both ends of the substrate surface. The two-dimensional semi-metallic material layer is in contact with the metal electrode at one end of the substrate surface, and the two-dimensional semiconductor material layer II is in contact with the metal electrode at the other end of the substrate surface. Specifically, two-dimensional semiconductor material layers I and II form a vertical van der Waals heterojunction between the metal electrodes, used to construct a unipolar barrier structure. The two-dimensional semi-metallic material layer enhances carrier extraction efficiency and amplifies the photocurrent difference under illumination conditions with different polarization directions, thereby enhancing polarization detection capability.

[0014] Furthermore, the substrate was ultrasonically cleaned for 10 min each with acetone, anhydrous ethanol, and deionized water, and then dried with a nitrogen gun for preservation.

[0015] The beneficial effects of this invention are as follows: (1) This invention achieves the transformation of carrier transport from bipolar to unipolar by constructing a two-dimensional semi-metallic contact control and unipolar barrier synergistic mechanism, which is conducive to controlling carrier transport, thereby controlling photocurrent and dark current, and forming a nonlinear amplification effect in the polarization-dependent carrier generation process, so that the photocurrent in the high absorption direction is enhanced by a super-proportional ratio, thereby significantly improving the polarization ratio, and the enhancement factor is not less than 3 times.

[0016] (2) Compared with the existing technology that requires precise adjustment of bias voltage (70-100 mV) to achieve infinite polarization ratio, the present invention adopts a zero bias voltage working mode, which does not require external voltage regulation and complex control circuits, significantly reducing system power consumption and complexity, and is more suitable for low power consumption and high integration application scenarios.

[0017] (3) The present invention uses a dry transfer process to prepare polarization detection optoelectronic devices. This process does not require the design of additional polarization elements, nor does it involve any chemical solution treatment. It has the advantages of simple process, low cost, high repeatability and no pollution.

[0018] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0019] To make the objectives, technical solutions, and advantages of the present invention clearer, the preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein: Figure 1 This is a schematic diagram of a photodetector structure provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the band structure of a BP / MoS2 / WTe2 heterojunction device. Figure 3 The diagram shows the polarization Raman test results of the BP / MoS2 / WTe2 heterojunction device, where (a) is the polarization Raman test of BP and (b) is the polarization Raman test of WTe2. Figure 4 The polarization current variation curves of the device in polar coordinates under zero bias voltage are shown; where (a) is the polarization characteristic of the BP material detector; (b) is the polarization characteristic of the BP / MoS2 heterojunction detector; (c) is the polarization characteristic of the BP / WTe2 heterojunction detector; and (d) is the polarization characteristic of the BP / MoS2 / WTe2 heterojunction detector. Figure 5 Polar coordinate curves of polarized photocurrent variation of BP / MoS2 / WTe2 heterojunction detector under 638 nm, 940 nm and 1550 nm lasers at zero bias. Figure 6 A schematic diagram showing the response time test results of the BP / MoS2 / WTe2 heterojunction detector under 0 V bias and 1550 nm laser excitation at zero bias.

[0020] Figure reference numerals: 1-substrate; 2-metal electrode; 3-two-dimensional semi-metallic material layer; 4-two-dimensional semiconductor material layer I; 5-two-dimensional semiconductor material layer II. Detailed Implementation

[0021] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0022] The accompanying drawings are for illustrative purposes only and are schematic diagrams, not actual pictures. They should not be construed as limiting the invention. To better illustrate the embodiments of the invention, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0023] In the accompanying drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components. In the description of the present invention, it should be understood that if terms such as "upper," "lower," "left," "right," "front," and "rear" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting the present invention. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0024] Example 1 like Figure 1 As shown, this embodiment provides a photodetector with a high polarization ratio based on a two-dimensional semi-metallic material and a heterostructure, which includes a substrate 1, a metal electrode 2, a two-dimensional semi-metallic material layer 3, a two-dimensional semiconductor material layer I 4 constituting a heterostructure, and a two-dimensional semiconductor material layer II 5 with anisotropy.

[0025] In this embodiment, substrate 1 is a SiO2 / Si substrate, wherein the thickness of SiO2 is 300 nm and the thickness of Si is 500 μm.

[0026] Metal electrode 2 is a Cr / Au composite electrode, which is disposed at both ends of the surface of substrate 1. The overall thickness of metal electrode 2 is 55 nm, of which the thickness of metallic Cr is 5 nm and the thickness of metallic Au is 50 nm.

[0027] The two-dimensional semi-metallic material layer 3 is made of semi-metallic material WTe2. The two-dimensional semi-metallic material layer 3 is disposed on the surface of the substrate 1 and is in contact with the metal electrode 2 at one end of the surface of the substrate 1. In this embodiment, the thickness of the semi-metallic material WTe2 is 10~30nm.

[0028] The two-dimensional semiconductor material layer I4 constituting the heterojunction is MoS2, and it is disposed on the surface of the two-dimensional semi-metallic material layer 3. In this embodiment, the thickness of MoS2 is 10~30 nm.

[0029] The anisotropic two-dimensional semiconductor material layer II5 is made of black scale (BP), which is disposed on the surface of the two-dimensional semiconductor material layer I4 and is in contact with the metal electrode 2 at the other end of the surface of the substrate 1. In this embodiment, the thickness of BP is 80~150nm.

[0030] The physical mechanism by which the above-described photodetector achieves polarization ratio amplification is based on the synergistic effect of the following two points: First, the inherent in-plane crystal structure anisotropy of photoactive layers (such as BP, WTe2, etc.) is the source of polarization response. These materials exhibit fundamentally different absorption rates for polarized light in different directions, providing a crystallographic basis for the generation of polarization-sensitive photocurrents.

[0031] Secondly, a structure capable of selective carrier transport was constructed. This structure features a gradient-distributed energy band, enabling directional electron transport while simultaneously blocking holes. A two-dimensional semi-metallic layer (WTe2) provides a rapid carrier extraction channel, reducing carrier recombination in high absorption directions and thus amplifying photocurrent differences. The semi-metallic material, as an efficient carrier transport channel, significantly suppresses photogenerated carrier recombination. In low absorption directions, the intrinsic light absorption of the material is weak, resulting in a low density of photogenerated carriers and relatively small recombination losses. Therefore, the rapid extraction by the semi-metallic layer only leads to a limited increase in photocurrent. Conversely, in high absorption directions, strong light absorption leads to a high density of photogenerated carriers. Without the semi-metallic layer, these carriers are highly susceptible to severe recombination. The semi-metallic material provides a crucial rapid pathway, efficiently collecting and extracting carriers before recombination, resulting in a significant relative increase in photocurrent in high absorption directions. This nonlinear extraction enhancement in high carrier density directions achieves asymmetric amplification of the photocurrent, thereby realizing active amplification of the polarization ratio.

[0032] like Figure 2 The diagram shows the band structure of the BP / MoS2 / WTe2 device in this embodiment. Figure 2As can be seen, the structure forms an asymmetric band arrangement, and the constructed unipolar barrier dominates the selective transport of charge carriers. Electrons are transported to one side without hindrance, while holes in BP move to the other side. Holes on the WTe2 side are blocked by the barrier layer and do not contribute current. WTe2, on the other hand, serves as a semi-metallic contact layer to provide an efficient channel for charge carrier extraction.

[0033] Figure 3 The results of polarization Raman spectroscopy (PRS) measurements of the BP / MoS2 / WTe2 heterostructure in this embodiment are shown, with a focus on analyzing the variation of characteristic peak intensities of WTe2 and BP with the incident light polarization angle. By rotating the polarization direction (0°~360°) to record the Raman signal intensity, a significant periodic variation in the main vibrational modes can be observed. This angle dependence stems from the anisotropy of the material's Raman tensor, reflecting the differences in vibrational response of the crystal along different crystal axes. The test results verify the anisotropy of WTe2 and BP materials, providing a basis for subsequent research on anisotropic photoelectric properties.

[0034] Figure 4 This is the polar coordinate form of the polarized photocurrent variation curve of the device in this embodiment under zero voltage. From... Figure 4 As can be seen from (a), the polarization ratio of the pure BP material detector is 2.3, and the anisotropic BP produces basic polarization detection capability. From Figure 4 As can be seen from (b), the polarization ratio of the BP / MoS2 heterojunction detector is 5.2. The heterojunction structure has the ability to effectively separate charge carriers and simultaneously improves polarization sensitivity. Figure 4 As can be seen in (c), the polarization ratio of the WTe2 / BP detector is only 2.6, indicating that the direct amplification effect of the half-metallic material on the anisotropic action of BP is weak. From Figure 4 As shown in (d), the polarization ratio of the BP / MoS2 / WTe2 heterojunction detector is 7.8, and the device achieves enhanced polarization detection capability. Experimental results indicate a synergistic effect between the two-dimensional semi-metallic material layer and the carrier-selective transport structure, which cannot be expected from the simple superposition of single structures. Figure 4 As shown in (c), when only the WTe2 half-metal is introduced into contact with the BP (without the MoS2 interlayer), the polarization ratio is only 2.6, which is a limited improvement compared to the 2.3 of the pure BP device; Figure 4 As shown in (b), when constructing a BP / MoS2 heterojunction alone (without the WTe2 half-metal layer), the polarization ratio is 5.2, which shows an improvement, but the magnitude is limited. Only when both the WTe2 half-metal layer and the MoS2 interlayer are introduced simultaneously does the device polarization ratio reach 7.8, achieving a super-additive effect (an improvement of approximately 3.4 times, exceeding simple addition). This synergistic effect proves that the technical solution of this invention is not a simple superposition of half-metal contacts and heterojunctions, but rather produces unexpected technical effects.

[0035] Figure 5 The polarization current variation curves of the BP / MoS2 / WTe2 heterojunction detector under zero bias voltage with 638 nm, 940 nm, and 1550 nm lasers are shown in polar coordinates. Figure 5 As can be seen, the polarization ratios of the BP / MoS2 / WTe2 heterojunction detector under 638 nm, 940 nm and 1550 nm lasers are 3.0, 2.9 and 7.8 respectively, demonstrating a wide-spectrum polarization detection capability. The polarization difference comes from the different light absorption rates of the materials under different lasers and the different injection efficiencies caused by the interfacial band arrangement.

[0036] Figure 6 The response time of the BP / MoS2 / WTe2 heterojunction detector under 0 V bias and 1550 nm laser excitation was measured at zero bias. It can be seen that the rise time of the BP / MoS2 / WTe2 heterojunction detector is 273 μs and the fall time is 713 μs, both less than 1 ms, demonstrating the device's fast response capability.

[0037] Example 2 This embodiment provides a method for amplifying the polarization ratio of a photodetector based on two-dimensional semi-metallic materials and heterostructures, as described below: 1. Pre-treat the SiO2 / Si substrate before use.

[0038] Specifically, the samples were ultrasonically cleaned with acetone, anhydrous ethanol, and deionized water for 10 minutes in sequence, and then dried with a nitrogen gun for storage.

[0039] 2. Cr / Au electrodes with target patterns are prepared on SiO2 / Si substrates using standard photolithography processes such as coating, exposure, development, magnetron sputtering, and lift-off.

[0040] 3. Obtain two-dimensional semi-metallic materials, two-dimensional semiconductor materials constituting heterojunctions, and two-dimensional semiconductor materials with anisotropy through mechanical exfoliation.

[0041] In this embodiment, the mechanical peeling method specifically involves obtaining a small amount of half-metal material WTe2 and semiconductor materials MoS2 and BP, placing these materials on a blue film, and repeatedly folding them to perform mechanical peeling, thereby obtaining two-dimensional half-metal material and two-dimensional semiconductor material.

[0042] 4. Select WTe2, MoS2 and BP material layers of appropriate thickness, and then transfer them sequentially between the two metal electrodes on the SiO2 / Si substrate using PDMS to complete the device fabrication.

[0043] The sequential transfer of WTe2, MoS2, and BP material layers to the SiO2 / Si substrate via PDMS includes: first, loading selected WTe2, MoS2, and BP material layers onto PDMS; then, inverting the PDMS containing the two-dimensional semi-metallic material WTe2 onto the surface of the SiO2 / Si substrate, making it contact the metal electrode at one end of the substrate surface, and finally peeling off the PDMS to complete the transfer of the two-dimensional semi-metallic material WTe2. Using the same method, the two-dimensional semiconductor material MoS2 is transferred to the WTe2 surface, and the two-dimensional semiconductor material BP is transferred to the MoS2 surface, making BP contact the metal electrode at the other end of the substrate surface.

[0044] In summary, this invention proposes a method for amplifying the polarization ratio of a photodetector based on a two-dimensional semi-metallic material and a heterostructure. By adding the semi-metallic material WTe2, which effectively alleviates contact problems and extracts charge carriers, polarization-enhanced photodetection can be achieved without bias voltage or other conditions, solely through the assistance of the two-dimensional semi-metallic material. This breaks the limitations imposed by the inherent anisotropic dichroism of the material on the polarization response direction and polarization ratio. Furthermore, this invention employs a completely dry transfer process to fabricate the photodetector, eliminating the need for additional polarization elements and chemical solution treatment. It boasts advantages such as simple process, low cost, high repeatability, and no pollution.

[0045] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A zero-bias high polarization-ratio photodetector, characterized in that, It includes a substrate, metal electrodes, a two-dimensional semi-metallic material layer, a two-dimensional semiconductor material layer I, and an anisotropic two-dimensional semiconductor material layer II; wherein, the metal electrodes are disposed at both ends of the substrate surface; the two-dimensional semi-metallic material layer is disposed on the substrate surface and is in contact with the metal electrode at one end of the substrate surface; the two-dimensional semiconductor material layer I is disposed on the surface of the two-dimensional semi-metallic material layer; the two-dimensional semiconductor material layer II is disposed on the surface of the two-dimensional semiconductor material layer I and is in contact with the metal electrode at the other end of the substrate surface, forming a vertical van der Waals heterojunction.

2. The photodetector of claim 1, wherein, The anisotropic two-dimensional semiconductor material layer II is BP.

3. The photodetector of claim 1, wherein, The two-dimensional semiconductor material layer I is MoS2.

4. The photodetector of claim 1, wherein, The two-dimensional semi-metallic material layer is WTe2.

5. The photodetector of claim 1, wherein, The substrate is a SiO2 / Si substrate, wherein the thickness of SiO2 is 300 nm and the thickness of Si is 500 μm.

6. The photodetector of claim 1, wherein, The metal electrode is a Cr / Au composite electrode with a thickness of 55 nm, of which Cr has a thickness of 5 nm and Au has a thickness of 50 nm.

7. The photodetector of claim 1, wherein, The vertical van der Waals heterojunction has a gradient band distribution to impede hole transport; at the same time, the valence band barrier height of the vertical van der Waals heterojunction is set to 0.7-1 eV to impede hole transport, while no barrier is set in the conduction band to ensure smooth electron transport.

8. A method for realizing polarization ratio amplification of the photodetector according to any one of claims 1-7 based on a two-dimensional semimetal material and a heterostructure, characterized in that, First, obtain the substrate, and then ultrasonically clean it sequentially with acetone, anhydrous ethanol, and deionized water. After cleaning, dry it with a nitrogen gun and store it. Metal electrodes with target patterns are fabricated at both ends of a substrate surface using photolithography. Two-dimensional semi-metallic material layer, two-dimensional semiconductor material layer I, and anisotropic two-dimensional semiconductor material layer II were obtained by mechanical exfoliation. Two-dimensional semi-metallic material layers, two-dimensional semiconductor material layer I, and two-dimensional semiconductor material layer II of appropriate thickness are selected. Then, the two-dimensional semi-metallic material layer, two-dimensional semiconductor material layer I, and two-dimensional semiconductor material layer II are transferred from bottom to top between the metal electrodes at both ends of the substrate surface using PDMS. The two-dimensional semi-metallic material layer is in contact with the metal electrode at one end of the substrate surface, and the two-dimensional semiconductor material layer II is in contact with the metal electrode at the other end of the substrate surface. Among them, the two-dimensional semiconductor material layer I and the two-dimensional semiconductor material layer II form a vertical van der Waals heterojunction between the metal electrodes, which is used to construct a unipolar barrier structure. The two-dimensional semi-metallic material layer is used to enhance the carrier extraction efficiency and amplify the photocurrent difference under illumination conditions with different polarization directions, so as to enhance the polarization detection capability.

9. The method of claim 8, wherein, The substrate was ultrasonically cleaned for 10 min each with acetone, anhydrous ethanol, and deionized water, and then dried with a nitrogen gun for storage.

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