Terahertz detector based on circular metasurface and graphene composite structure and method

Abstract

The invention discloses a terahertz detector based on a circular metasurface and graphene composite structure and a method, and belongs to the technical field of semiconductor devices and micro-nano machining. The device comprises a substrate, a graphene layer, a circular metasurface layer, a first electrode and a second electrode, the graphene layer is arranged on the substrate; the first electrode and the second electrode are oppositely arranged on two side ends of the graphene layer; the circular metasurface layer is arranged on the graphene layer and located between the first electrode and the second electrode. According to the invention, the local field enhancement effect of the metasurface structure is combined with the photoelectric response of graphene, the frequency selective absorption of terahertz waves is realized, the signal-to-noise ratio and selectivity of the detector are improved, and the sensitivity and response speed of the detector are improved at the same time.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductor devices and micro-nano processing, and particularly relates to a terahertz detector and method based on a composite structure of a circular metasurface and graphene. Background Art

[0002] The terahertz band has a unique position in the electromagnetic spectrum, with a frequency range of 0.1 THz to 10 THz, located between the microwave and infrared bands. Due to its both microwave penetration ability and high resolution of optical waves, it shows great application potential in the fields of national defense security, astronomical detection, biomedical imaging, next-generation wireless communication, and non-destructive testing. However, traditional terahertz detectors have many limitations in performance and urgently need to be broken through. The sensitivity of terahertz detectors based on traditional materials is limited by the characteristics of the materials themselves, such as bandgap limitations, resulting in insufficient response ability to terahertz radiation and difficulty in meeting the requirements of high-precision detection. In addition, traditional terahertz detectors usually need to work in a low-temperature environment. This not only increases the complexity and cost of the system, but also limits its portability and popularity in practical applications. The low-temperature working conditions pose strict requirements on the materials and structures of the detectors. At the same time, the volume and energy consumption of the refrigeration system also greatly increase the overall size and operating cost of the detectors, which is not conducive to the large-scale application and promotion of terahertz technology.

[0003] Graphene, as a two-dimensional crystal composed of a single layer of carbon atoms arranged in a honeycomb structure, has a unique electronic structure and excellent physical properties. Its high carrier mobility is one of the most remarkable characteristics of graphene, and the carrier mobility can be as high as 200000 cm 2 / V·s, much higher than traditional semiconductor materials such as silicon and germanium. High carrier mobility means that in the terahertz band, graphene can achieve rapid charge transport, thereby improving the response speed and frequency characteristics of terahertz detectors, which is crucial for the application of terahertz detectors in fields such as high-speed communication and real-time imaging. However, the absorption rate of graphene in the terahertz band is relatively low, usually only about 2.3%, which limits its detection sensitivity to terahertz radiation. A low absorption rate means that the detector requires a larger incident power to generate a detectable signal, which may be limited in practical applications. Summary of the Invention

[0004] The purpose of the present invention is to address the above deficiencies in the prior art and provide a terahertz detector and method based on a composite structure of a circular metasurface and graphene to solve the problems of low sensitivity and slow response speed of traditional terahertz detectors.

[0005] To achieve the above object, the technical solution adopted by the present invention is:

[0006] In a first aspect, a terahertz detector based on a composite structure of a circular metasurface and graphene is provided, which includes a substrate, a graphene layer, a circular metasurface layer, a first electrode, and a second electrode;

[0007] The graphene layer is disposed on the substrate; the first electrode and the second electrode are oppositely disposed on two side ends of the graphene layer; the circular metasurface layer is disposed on the graphene layer and located between the first electrode and the second electrode.

[0008] Further, the substrate is silicon oxide; the graphene layer is made of single-crystalline graphene with a thickness of 1 to 5 layers.

[0009] Further, both the first electrode and the second electrode use 1 nm - 3 nm of metal Cr as a transition layer and 10 nm - 40 nm of metal Au.

[0010] Further, the circular metasurface layer includes 6×6 unit cells arranged at uniform intervals; the structure of a single unit cell is cylindrical;

[0011] The structural parameters of the cylindrical unit cell are:

[0012] The circular radius is 40 μm;

[0013] The height is 23 μm;

[0014] The lattice period is 137 μm.

[0015] In a second aspect, a preparation method of a terahertz detector based on a composite structure of a circular metasurface and graphene is provided, including the following steps:

[0016] S1. Ultrasonically clean the silicon oxide substrate;

[0017] S2. Grow multi-layer graphene by chemical vapor deposition;

[0018] S3. Transfer the multi-layer graphene onto the silicon oxide substrate layer to obtain the graphene layer;

[0019] S4. Fabricate a photolithography mask according to the pattern designed for the circular metasurface;

[0020] S5. Transfer the pattern on the photolithography mask onto the graphene layer;

[0021] S6. Perform thermal evaporation deposition on the graphene layer to form the first electrode, the second electrode, and the circular metasurface layer.

[0022] Further, in S2, using a copper foil as a substrate, methane as a carbon source, and growing graphene epitaxially by chemical vapor deposition; under the conditions of a temperature of 900 - 1000 °C and a pressure of 10 - 100 Pa, introducing hydrogen as a carrier gas to obtain multi-layer graphene on the copper substrate.

[0023] Further, in S3, the polymethyl methacrylate solution is spin-coated on the surface of the copper foil grown with graphene. After the polymethyl methacrylate is cured, the copper foil is put into hydrochloric acid or copper sulfate solution for etching to remove the copper foil. Then, the film attached with polymethyl methacrylate and graphene is transferred to the upper surface of the silicon oxide substrate. Next, acetone is used to remove the polymethyl methacrylate, and it is washed multiple times with deionized water and ethanol to obtain a graphene layer.

[0024] Further, in S6, the graphene layer sample is placed on the sample stage, and deposition is carried out by thermal evaporation to obtain the first electrode and the second electrode;

[0025] The sample deposited with metal is immersed in acetone to dissolve the photoresist, taken out and washed, and the surface of the sample is dried with a nitrogen gun to obtain a circular metasurface layer on the surface of the graphene layer.

[0026] The terahertz detector and method based on the composite structure of the circular metasurface and graphene provided by the present invention have the following beneficial effects:

[0027] 1. The present invention couples graphene with a resonant structure. By designing a specific resonant structure, the interaction between terahertz waves and graphene is enhanced, thereby improving the absorption efficiency of graphene for terahertz waves. In addition, the resonant structure can also achieve frequency-selective absorption of terahertz waves, thereby improving the signal-to-noise ratio and selectivity of the detector.

[0028] 2. The present invention combines the local field enhancement effect of the metasurface structure with the optoelectronic response of graphene. By carefully designing the geometric parameters, material composition of the circular metasurface structure, and the integration method with graphene, efficient absorption of terahertz waves and optoelectronic conversion are achieved.

[0029] 3. By optimizing the unit size, shape, and arrangement of the circular metasurface structure, the present invention can achieve resonant absorption of terahertz waves with a specific wavelength, thereby enhancing the response of graphene to terahertz radiation. At the same time, by using the local field enhancement effect of the circular metasurface structure, the generation and transport efficiency of carriers in graphene can be improved, further enhancing the optoelectronic conversion efficiency. This innovative combination can not only give full play to the advantages of the metasurface structure and graphene, but also overcome some key problems in traditional terahertz detectors, such as low sensitivity and slow response speed, providing a new solution for realizing high-performance terahertz detectors.

[0030] 4. When light waves of a specific wavelength are incident, the circular metasurface layer utilizes its local field enhancement effect to strengthen the absorption of light waves by graphene. Subsequently, graphene realizes the rapid migration and separation of photo-generated carriers by virtue of its high carrier mobility. Under the action of an electric field applied to the electrodes, a photocurrent signal is generated, thus completing the optoelectronic detection process, achieving efficient conversion of optical signals into electrical signals, and possessing efficient and rapid optoelectronic detection capabilities. Description of the Drawings

[0031] Figure 1 It is a schematic structural diagram of a terahertz detector based on a composite structure of a circular metasurface and graphene in Embodiment 1 of the present invention.

[0032] Among them, 1. Substrate; 2. Graphene layer; 3. Circular metasurface layer; 4. First electrode; 5. Second electrode.

[0033] Figure 2 It is an absorption rate diagram of the circular metasurface in Embodiment 1 of the present invention.

[0034] Figure 3 It is a top view of the local distribution of the terahertz wave electric field in the circular metasurface in Embodiment 1 of the present invention.

[0035] Figure 4 It is a schematic diagram of the terahertz optoelectronic detection system in Embodiment 1 and Comparative Example 1 of the present invention.

[0036] Figure 5 It is the test result of the current response of the terahertz detector based on the composite structure of the circular metasurface and graphene in Embodiment 1 of the present invention to terahertz waves of 0.3 THz.

[0037] Figure 6 It is the test result of the current response of the graphene terahertz detector without a circular metasurface in Comparative Example 1 of the present invention to terahertz waves of 0.3 THz. Detailed Embodiments

[0038] The following describes the detailed embodiments of the present invention to facilitate those skilled in the art of the present technology to understand the present invention. However, it should be clear that the present invention is not limited to the scope of the detailed embodiments. For those of ordinary skill in the art of the present technology, as long as various changes are within the spirit and scope of the present invention defined and determined by the appended claims, these changes are obvious, and all inventions and creations using the concept of the present invention are within the scope of protection.

[0039] Embodiment 1,

[0040] This embodiment provides a terahertz detector based on a composite structure of a circular metasurface and graphene. This detector combines the electromagnetic field regulation ability of the metasurface structure and the high-sensitivity characteristics of graphene to meet the current major requirements for terahertz detectors. Specifically, it includes:

[0041] Substrate 1, graphene layer 2, circular metasurface layer 3, first electrode 4, and second electrode 5;

[0042] Among them, the graphene layer 2 is disposed on the substrate 1, the first electrode 4 and the second electrode 5 are oppositely disposed on two side ends of the graphene layer 2, and the circular metasurface layer 3 is disposed on the graphene layer 2 and located between the first electrode 4 and the second electrode 5.

[0043] As a preference of this embodiment, the substrate 1 is silicon oxide, and the graphene layer 2 is made of single-crystal graphene with a thickness of 1-5 layers.

[0044] As a preference of this embodiment, both the first electrode 4 and the second electrode 5 use 1nm-3nm metal Cr as the transition layer and 10nm-40nm metal Au.

[0045] As a preference of this embodiment, the circular metasurface layer 3 is made of highly conductive metals such as gold and silver, and the structure of the circular metasurface layer 3 is adjusted according to the detection band.

[0046] This embodiment further provides a specific implementation structure of the circular metasurface layer 3:

[0047] The circular metasurface layer 3 includes 6×6 unit cells arranged at uniform intervals; the structure of a single unit cell is cylindrical;

[0048] The structural parameters of the cylindrical unit cell are:

[0049] The circular radius is 40μm;

[0050] The height is 23μm;

[0051] The lattice period is 137μm.

[0052] Based on the above terahertz detector structure, this embodiment provides a preparation method of a terahertz detector based on a composite structure of a circular metasurface and graphene, which specifically includes the following steps:

[0053] S1. Ultrasonically clean the silicon oxide substrate;

[0054] Specifically, in this embodiment, the silicon oxide substrate is ultrasonically cleaned with acetone, isopropyl alcohol (IPA), and deionized water in sequence for 10 minutes each to remove organic pollutants.

[0055] S2. Grow multi-layer graphene by chemical vapor deposition;

[0056] In this embodiment, a copper foil is used as the substrate, methane (CH4) is used as the carbon source, and chemical vapor deposition is employed to epitaxially grow graphene. Under the conditions of a temperature of 900 - 1000 °C and a pressure of 10 - 100 Pa, an appropriate amount of hydrogen is introduced as the carrier gas, and growth is carried out for 20 minutes to obtain multi-layer graphene on the copper substrate.

[0057] S3. Transfer the multi-layer graphene onto a silicon oxide substrate to obtain a graphene layer;

[0058] In this embodiment, a polymethyl methacrylate solution is spin-coated on the surface of the copper foil on which multi-layer graphene has grown. After the polymethyl methacrylate is cured, the copper foil is placed in hydrochloric acid or copper sulfate solution for etching to remove the copper foil. Then, the film with attached polymethyl methacrylate and graphene is transferred to the surface of the silicon oxide substrate. Finally, the polymethyl methacrylate is removed using acetone, and the film is washed repeatedly with deionized water and ethanol to remove residual chemical reagents and impurities, obtaining a clean graphene layer.

[0059] S4. Fabricate a photolithography mask according to the designed pattern of the circular metasurface;

[0060] In this embodiment, based on the wavelength of 1.55 THz and the local field enhancement effect, a circular metasurface is designed using electromagnetic simulation software. The circular radius is 40 μm, the height is 23 μm; the lattice period is 137 μm; the metasurface is located between the first electrode and the second electrode, and a photolithography mask is fabricated according to the designed pattern.

[0061] S5. Transfer the pattern on the photolithography mask onto the graphene layer;

[0062] In this embodiment, an appropriate amount of photoresist is dropped onto the surface of the graphene sample and spin-coated to form a uniform thin film on the graphene surface. It is pre-baked at 90 - 120 °C for 5 - 10 minutes. The pre-baked sample is placed on the sample stage of the photolithography machine, the designed mask is installed on the mask holder of the photolithography machine, and the pattern on the mask is aligned with the mark on the sample through the alignment system of the photolithography machine. Appropriate exposure dose and exposure time are set for exposure. The exposed sample is taken out of the photolithography machine and developed in the developer. After development is completed, the developer on the surface of the sample is rinsed clean with deionized water, and then dried with a nitrogen gun.

[0063] S6. Perform thermal evaporation deposition on the graphene layer to form the first electrode, the second electrode, and the circular metasurface layer.

[0064] The developed graphene layer sample is placed on the sample stage, and 3 nm of Cr and 30 nm of Au are deposited using thermal evaporation, that is, the first electrode and the second electrode are deposited.

[0065] The sample with the metal deposited is immersed in acetone to gradually dissolve the photoresist. The sample is taken out of the solvent, rinsed thoroughly with deionized water and ethanol to remove the residual photoresist and solvent on the surface, and then dried with a nitrogen gun to obtain a clear metal pattern deposited on the graphene surface, and then a circular metasurface layer is obtained.

[0066] Reference Figure 2 , the terahertz wave is incident from the top of the circular metasurface layer, and the absorption of the terahertz wave by the circular metasurface layer structure in the range of 1.4 THz to 2.0 THz is simulated. It can be seen that near 1.55 THz, the absorption of the designed circular metasurface layer for the terahertz wave is significantly improved.

[0067] Irradiate the circular metasurface layer with a 1.55 THz wave, and monitor the electromagnetic field distribution of the graphene structure on the circular metasurface layer. The results are as Figure 3 shown. Monitoring the electromagnetic field distribution on the circular metasurface layer at 1.55 THz shows that the resonance of the structural unit will cause local field enhancement and local absorption enhancement.

[0068] Reference Figure 4 , place the above-prepared terahertz detector in a terahertz optoelectronic detection system, and use a modulator to control the switching frequency of the 1.55 THz terahertz wave. Project the terahertz wave vertically onto the detector surface through the optical path. Connect the digital source meter to the two electrodes of the detector to extract and output the effective optoelectronic response signal. As Figure 5 shown, with the periodic change of the terahertz optical power, the detector can output a periodically changing electrical signal.

[0069] Comparative Example 1

[0070] Comparative Example 1 is a graphene terahertz detector without a circular metasurface layer in the structure of Example 1. The preparation process of Comparative Example 1 includes the following steps:

[0071] A1. Ultrasonically clean the silicon oxide substrate with acetone, isopropyl alcohol (IPA) and deionized water for 10 minutes each to remove organic pollutants

[0072] A2. Using a copper foil as a substrate, methane (CH4) as a carbon source, and using chemical vapor deposition to epitaxially grow graphene. Under the conditions of a temperature of 900 - 1000 °C and a pressure of 10 - 100 Pa, an appropriate amount of hydrogen is introduced as a carrier gas and grown for 20 minutes to obtain multi-layer graphene on the copper substrate.

[0073] A3. Spin-coat the polymethyl methacrylate solution on the surface of the copper foil grown with graphene. After the polymethyl methacrylate is cured, put the copper foil into hydrochloric acid or copper sulfate solution for etching to remove the copper foil. Then transfer the film with attached polymethyl methacrylate and graphene to the surface of the silicon oxide-based substrate. Finally, use acetone to remove the polymethyl methacrylate, and wash it with deionized water and ethanol multiple times to remove the residual chemical reagents and impurities, obtaining a clean graphene layer.

[0074] A4. Process a patterned mask. The hollow pattern of the mask is the detector electrode, and the electrode spacing is the same as that of the device in Example 1. Cover the mask on the graphene surface, and use thermal evaporation to deposit 3 nm of chromium and 30 nm of gold electrodes.

[0075] Place the terahertz detector prepared in this comparative example in a terahertz optoelectronic detection system, as Figure 2 shown. Use a modulator to control the switching frequency of the 1.55 THz terahertz wave, project the terahertz wave vertically onto the detector surface through the optical path, connect the digital source meter to the two electrodes of the detector, and extract and output the effective optoelectronic response signal.

[0076] As Figure 6 shown, with the periodic change of the terahertz optical power, the detector can output an electrically periodic signal. Since the device does not contain a circular metasurface and cannot effectively absorb terahertz waves, the optoelectronic response performance of the device is significantly lower than that of Example 1.

[0077] Although the specific implementation mode of the invention has been described in detail in conjunction with the drawings, it should not be construed as a limitation on the protection scope of this patent. Within the scope described in the claims, various modifications and deformations that can be made by those skilled in the art without creative labor still fall within the protection scope of this patent.

Claims

1. A terahertz detector based on a composite structure of a circular metasurface and graphene, characterized in that: It includes a substrate, a graphene layer, a circular metasurface layer, a first electrode, and a second electrode; The graphene layer is disposed on the substrate; the first electrode and the second electrode are oppositely disposed on two side ends of the graphene layer; the circular metasurface layer is disposed on the graphene layer and located between the first electrode and the second electrode.

2. The terahertz detector based on the composite structure of a circular metasurface and graphene according to claim 1, wherein: The substrate is silicon oxide; the graphene layer is made of single-crystal graphene with a thickness of 1 - 5 layers.

3. The terahertz detector based on the composite structure of a circular metasurface and graphene according to claim 1, wherein: Both the first electrode and the second electrode use 1nm - 3nm metal Cr as a transition layer and 10nm - 40nm metal Au.

4. The terahertz detector based on the composite structure of circular metasurface and graphene according to claim 1, characterized in that: The circular metasurface layer includes 6×6 unit cells arranged at uniform intervals; the structure of a single unit cell is cylindrical; The structural parameters of the cylindrical unit cell are: The circular radius is 40μm; The height is 23μm; The lattice period is 137μm.

5. A preparation method for a terahertz detector based on a composite structure of a circular metasurface and graphene according to any one of claims 1 to 4, characterized in that, It includes the following steps: S1. Ultrasonically clean the silicon oxide substrate; S2. Grow multi-layer graphene by chemical vapor deposition; S3. Transfer the multi-layer graphene onto the silicon oxide substrate to obtain the graphene layer; S4. Fabricate a photolithography mask according to the pattern of the circular metasurface design; S5. Transfer the pattern on the photolithography mask onto the graphene layer; S6. Perform thermal evaporation deposition on the graphene layer to form the first electrode, the second electrode, and the circular metasurface layer.

6. The preparation method of the terahertz detector based on the composite structure of the circular metasurface and graphene according to claim 5, wherein, In step S2, using a copper foil as a substrate, methane as a carbon source, and growing graphene epitaxially by chemical vapor deposition; under the conditions of a temperature of 900 - 1000°C and a pressure of 10 - 100 Pa, introducing hydrogen as a carrier gas to obtain multi-layer graphene on the copper substrate.

7. The preparation method of the terahertz detector based on the composite structure of the circular metasurface and graphene according to claim 5, characterized in that, In step S3, spin-coat a polymethyl methacrylate solution on the surface of the copper foil grown with graphene. After the polymethyl methacrylate is cured, put the copper foil into hydrochloric acid or copper sulfate solution for etching to remove the copper foil. Then transfer the film with attached polymethyl methacrylate and graphene onto the upper surface of the silicon oxide substrate layer, and then use acetone to remove the polymethyl methacrylate, and wash it with deionized water and ethanol multiple times to obtain the graphene layer.

8. The preparation method of the terahertz detector based on the composite structure of a circular metasurface and graphene according to claim 5, characterized in that, In step S6, place the graphene layer sample on the sample stage and perform deposition using thermal evaporation to obtain the first electrode and the second electrode; Immerse the sample deposited with metal in acetone to dissolve the photoresist, take out and wash the sample, and use a nitrogen gun to blow dry the surface of the sample to obtain the circular metasurface layer on the surface of the graphene layer.

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