HfAlO x / graphene / HfAlO x Heterojunction phase modulator, method of manufacture and method of phase modulation

Abstract

The application discloses a kind of HfAlO x / graphene / HfAlO x Heterojunction phase modulator, preparation method and phase modulation method, the HfAlO x / graphene / HfAlO x Heterojunction, using HfAlO x As dielectric material, form good heterojunction structure with graphene.HfAlO x With high dielectric constant and good stability, can effectively regulate the electrical properties of graphene, while avoiding the Fermi level pinning effect when graphene is in direct contact with metal, improve the efficiency and flexibility of phase modulation.The whole structure length is only 800nm, much smaller than the free space wavelength of mid-infrared waveband, subwavelength operation is realized.This small size structure is conducive to the high integration and miniaturization of device, can be applied to high-density optical integrated chip, micro optical sensor and other fields, help to improve the integration and portability of system.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of photoelectric conversion, and relates to a HfAlO x / graphene / HfAlO x Heterojunction phase modulator, preparation method and phase modulation method. BACKGROUND

[0002] In the aspect of optical communication, mid-infrared waves (the wavelength range is generally 2.5 μm-25 μm) can effectively reduce the dispersion and loss in optical fiber transmission, greatly improve the communication capacity and transmission distance, and provide key technical support for the construction of the next generation of high-speed and large-capacity optical communication network; in the field of infrared imaging, the mid-infrared wave band has unique advantages in detecting the thermal radiation of objects, can penetrate obstacles such as smoke and dust, and has a wide and indispensable application in military reconnaissance, security monitoring, fire rescue and medical thermal imaging. Phase modulation is one of the core operations of mid-infrared wave optical signal processing, and is indispensable for realizing optical switching, optical signal coding, optical computing in optical communication, and phase imaging, optical microscope resolution enhancement in optical imaging. The traditional mid-infrared phase modulation method is mainly based on the electro-optic effect or the thermo-optic effect of crystal materials (such as lithium niobate, gallium arsenide, etc.). However, these traditional methods face many challenges. The modulator based on the electro-optic effect usually requires a high driving voltage, which not only increases the energy consumption, but also puts higher requirements on the driving circuit, which is not conducive to the miniaturization and integration of the device. Moreover, the growth and processing technology of crystal materials is complex and costly, which limits its large-scale application. The modulator based on the thermo-optic effect has a relatively low driving voltage, but the response speed is slow, which cannot meet the needs of high-speed optical communication and rapid optical signal processing.

[0003] Graphene, as a new type of two-dimensional carbon material, has many excellent properties. Its chemical potential can be flexibly adjusted by external electric field, chemical doping and other ways, which provides the possibility for realizing dynamically tunable optical devices. It also has strong light-matter interaction ability, which can effectively support surface plasmon polaritons (SPPs) in the mid-infrared wave band, and can realize the ability of subwavelength scale light field localization and control, which provides a new way for mid-infrared wave phase modulation.

[0004] However, pure graphene also has some limitations in practical applications. For example, when graphene is in direct contact with a metal electrode layer, the Fermi level pinning effect is prone to occur, which significantly limits the adjustable range of the graphene Fermi level, thereby weakening its phase modulation performance. In addition, the contact resistance between metal and graphene is large, which leads to increased energy loss and affects the overall efficiency of the device. To overcome these problems, graphene heterojunction structures have become a research hotspot. By combining graphene with other suitable materials to form a heterojunction, the advantages of each material can be comprehensively utilized, avoiding the adverse effects of direct contact between graphene and metal, achieving more efficient and flexible mid-infrared phase modulation, and promoting the further development of mid-infrared band optoelectronic technology.

[0005] At present, the research progress of existing technologies includes the following aspects: (1) Based on the photothermal effect: Mid-infrared phase modulation is achieved by using the photothermal effect in a hollow-core fiber filled with gas. For example, the phase modulator is placed on one arm of the Mach-Zehnder interferometer to further demonstrate mid-infrared intensity modulation. The disadvantages are: relatively slow response speed, thermal stability, and large energy loss; (2) Based on the thermo-optic effect: Phase modulation is achieved by changing the refractive index of the material through temperature changes. The disadvantages are: limited modulation bandwidth due to material limitations; (3) Double-photoelastic difference frequency modulation: The difference frequency of two zinc selenide-type photoelastic modulators is used to reduce the system modulation frequency, generating a low-frequency modulation signal carrying the measured phase delay. The phase delay of the measured wave plate can be obtained by dividing the modulated 1x difference frequency amplitude and 2x difference frequency amplitude. This method can effectively suppress the influence of light intensity fluctuations and photoelastic modulator phase delay fluctuations on the measurement, thereby improving the measurement accuracy. The disadvantages are: the required equipment is complex, limited by materials and frequency, and high-order harmonic interference is generated.

[0006] In summary, the existing technologies currently have the following problems: relatively slow response speed, large energy loss due to thermal stability, limited modulation bandwidth due to material limitations, and large interference. Summary of the Invention

[0007] In view of the problems existing in the prior art, the present invention provides a HfAlO x / graphene / HfAlO x The heterojunction phase modulator, preparation method and phase modulation method effectively solve the problems existing in the prior art, such as relatively slow response speed, large energy loss due to thermal stability, limited modulation bandwidth due to material limitations, and large interference.

[0008] The present invention is achieved through the following technical solutions:

[0009] A HfAlO x / graphene / HfAlO x heterojunction, the HfAlO x / graphene / HfAlO x The heterojunction comprises, from bottom to top, an SOI substrate, a HfAlO x an isolation layer, a graphene layer, a HfAlO x a dielectric layer and a metal electrode layer.

[0010] Preferably, the HfAlO x The thickness of the isolation layer is 100 nm; the thickness of the HfAlO x The thickness of the dielectric layer is 50-200 nm, and the thickness of the gold electrode is 50 nm.

[0011] A HfAlO x / graphene / HfAlO x A method for preparing the heterojunction, comprising:

[0012] S1, after pretreatment of the SOI substrate, growing a HfAlO x isolation layer on the SOI substrate by atomic layer deposition technology;

[0013] S2, growing a graphene layer on the HfAlO x isolation layer of S1 by chemical vapor deposition method;

[0014] S3, preparing a HfAlO x dielectric layer on the graphene layer of S2 by physical vapor deposition method;

[0015] S4, defining an electrode pattern by electron beam lithography technology, and then depositing a metal electrode layer on the HfAlO x dielectric layer of S3 by metal evaporation or sputtering process, to finally obtain a HfAlO x / graphene / HfAlO x heterojunction.

[0016] Preferably, the pretreatment of the SOI substrate is specifically:

[0017] Chemical cleaning method is used to remove organic contaminants, particulate impurities and natural oxide layer on the surface of the SOI substrate;

[0018] Chemical mechanical polishing technology is used to polish the cleaned SOI substrate to obtain an SOI substrate with an atomic level flatness surface.

[0019] Preferably, the graphene layer is grown on the HfAlO x isolation layer by chemical vapor deposition method, and the specific conditions are:

[0020] The graphene layer is grown by chemical vapor deposition under the conditions of a growth temperature of 1000-1100℃, a copper foil or a nickel foil as a catalyst, a carbon source gas flow of 10-50sccm, a hydrogen flow of 100-500sccm, a reaction pressure of 1-10Torr, and a reaction time of 10-60 minutes; and the carbon source includes methane or ethylene.

[0021] After the graphene layer is grown, the graphene layer is transferred to a HfAlO x insulating layer on the SOI substrate by using a polymethyl methacrylate (PMMA) assisted transfer method.

[0022] Preferably, the graphene layer is transferred to a HfAlO x insulating layer on the SOI substrate by using a polymethyl methacrylate (PMMA) assisted transfer method.

[0023] A layer of PMMA is spin-coated on the surface of the graphene layer containing a copper foil as a support layer, then the copper foil with the PMMA / graphene is placed in an etching solution to remove the copper foil, and a PMMA / graphene film is obtained, and the PMMA / graphene film is transferred to a SOI substrate on which a HfAlO x insulating layer has been grown. x The graphene layer is grown on the insulating layer; and the etching solution is an ammonium sulfate solution.

[0024] Preferably, the HfAlO x dielectric layer is prepared on the graphene layer of S2 by a physical vapor deposition method.

[0025] The HfAlO x dielectric layer is prepared on the graphene layer by a physical vapor deposition method of electron beam evaporation or sputtering.

[0026] When the HfAlO x dielectric layer is prepared on the graphene layer by a physical vapor deposition method of electron beam evaporation, the HfAlO x is used as an evaporation source material, and the HfAlO x dielectric layer is deposited by controlling an electron beam current, an evaporation time, and a deposition rate of 0.1-0.5nm / s.

[0027] When the HfAlO x dielectric layer is prepared on the graphene layer by a physical vapor deposition method of sputtering, the HfAlO x is used as a target material, and the HfAlO x dielectric layer is deposited by sputtering under the conditions of a sputtering power of 100-300W and a gas pressure of 0.1-1Pa.

[0028] Preferably, the electrode pattern is defined by electron beam lithography, and then a metal electrode layer is deposited on the HfAlO of S3 by a metal evaporation or sputtering process x on the dielectric layer, specifically,

[0029] on the HfAlO x dielectric layer, a layer of electron beam resist is spin-coated, after soft baking, the designed pattern is exposed and developed by using an electron beam lithography device, and then a metal electrode layer is deposited in the area defined by the photoresist pattern through an electron beam evaporation or sputtering process, after removing the photoresist by using a stripping process, the metal electrode layer is deposited on the HfAlO x dielectric layer, and finally a HfAlO x / graphene / HfAlO x heterojunction is obtained.

[0030] The metal electrode layer is made of gold.

[0031] A HfAlO x / graphene / HfAlO x heterojunction phase modulator is provided. x / graphene / HfAlO x The HfAlO x / graphene / HfAlO x heterojunction phase modulator comprises, from bottom to top, an SOI substrate, a HfAlO x dielectric layer, and a metal electrode layer.

[0032] A phase modulation method of a HfAlO x / graphene / HfAlO g heterojunction phase modulator comprises,

[0033] by applying an external voltage V x to the metal electrode layer, the chemical potential of the graphene is regulated.

[0034] by the chemical potential of the graphene, the conductivity of the graphene is calculated according to the Kubo formula;

[0035] based on the conductivity of the graphene, the dispersion relation of the surface plasmon polariton wave in TM mode is obtained according to the Maxwell equations and the boundary conditions;

[0036] by solving the dispersion relation, the propagation constant β of the surface plasmon polariton wave is obtained.

[0037] by the TM mode wave equation, the phase shift is calculated based on the product of the real part of the propagation constant β of the surface plasmon polariton wave and the path length z of light propagation, thereby realizing the phase modulation of the HfAlO x / graphene / HfAlO x heterojunction phase modulator.

[0038] Compared with the prior art, the present invention has the following beneficial technical effects:

[0039] The present invention discloses a HfAlO x / graphene / HfAlO x Preparation method of heterojunction phase modulator, the HfAlO x / graphene / HfAlO x Heterojunction, using HfAlO x As a dielectric material, it forms a good heterojunction structure with graphene. x With a high dielectric constant and excellent stability, it can effectively manipulate graphene's electrical properties while avoiding the Fermi level pinning effect that occurs when graphene is in direct contact with metals, improving the efficiency and flexibility of phase modulation. The entire structure is only 800nm ​​long, far smaller than the free-space wavelength in the mid-infrared band, enabling subwavelength operation. This small size facilitates high-level device integration and miniaturization, and can be applied to high-density optical integrated chips, micro-optical sensors, and other fields, helping to improve system integration and portability.

[0040] The present invention also provides a phase modulation method in which the optical path length is fixed at 800nm ​​by adjusting the voltage V g Changing within the range of 0-5V, the phase can be fully tuned from 0° to 360°; under specific parameter combinations (such as HfAlO x (When the dielectric thickness is 100nm, the driving voltage is 1V, and the operating wavelength is 6.55μm), the phase modulation range can reach 381°. This flexible phase modulation capability makes the graphene heterojunction structure have a wide range of application prospects in mid-infrared optoelectronic devices, such as it can be used to design high-performance optical switches, optical modulators, optical phased arrays and other devices. It can achieve continuous and wide-range tuning of the phase in the mid-infrared band, and the phase coverage range can reach 0°-360°, meeting the diverse needs of phase modulation in various complex optical signal processing and optoelectronic device applications. For example, in phase-shift keying modulation in optical communications, the phase change of the optical signal can be precisely controlled to achieve high-speed, large-capacity data transmission; in phase contrast enhancement technology in optical imaging, it can effectively improve the contrast and resolution of the image, which helps to observe microstructures and diseased tissues more clearly. Compared with traditional mid-infrared phase modulation methods and devices, the driving voltage required by the present invention is significantly reduced, and can be as low as 1V. Low driving voltage not only reduces energy consumption and improves energy utilization efficiency, which is especially suitable for portable and low-power devices with strict power consumption requirements, but also simplifies driving circuit design and reduces system cost and complexity. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1HfAlO x / graphene / HfAlO x A three-dimensional structure of the heterojunction.

[0042] Figure 2 HfAlO x / graphene / HfAlO x A plan view of the heterojunction. DETAILED DESCRIPTION

[0043] The present application will be further described in conjunction with specific examples, which are intended to explain but not limit the present application.

[0044] Specific technical solutions:

[0045] 1. Structure design: a HfAlO x / graphene / HfAlO x The structure of the heterojunction is shown in Figure 1 The proposed structure is composed of an SOI substrate, a 100 nm HfAlO x isolation layer, a single layer of graphene, a HfAlO x dielectric layer with a thickness of d, and a 50 nm thick gold electrode. Figure 1 is a perspective view, the length of the structure is L, which is also the optical path length, Figure 2 is a cross-sectional view. In this structure, when an external voltage (Vg) is applied between the graphene and the metal gate, the HfAlO x dielectric layer serves as an effective high-k dielectric for graphene chemical potential regulation. Here, the 100 nm HfAlO x isolation layer isolates the graphene from the environment, which is beneficial for maintaining the long-term stability of the graphene and preventing the accumulation of substances adsorbed on the graphene.

[0046] 2. Preparation method:

[0047] (1) SOI substrate selection and treatment: Select SOI silicon wafer as the substrate material to provide a stable support platform for the entire structure. The surface flatness and crystal quality of the substrate have important influence on the performance of the subsequent grown material layer, therefore, the substrate needs to be strictly pretreated. First, use chemical cleaning method (such as RCA cleaning method) to remove organic contaminants, particle impurities and native oxide layer on the surface of the substrate. Then, polish the cleaned substrate, which can adopt chemical mechanical polishing (CMP) technology to ensure that the surface roughness is less than a certain threshold value (such as 0.5 nm), so as to obtain an atomic level flatness surface, laying a foundation for high quality material growth.

[0048] (2) Isolation layer deposition: Grow a 100 nm thick HfAlO xIsolation layer. The growth of the isolation layer is carried out using atomic layer deposition (ALD) technology. By precisely controlling the pulse time of the precursor, reaction temperature and pressure and other process parameters, the uniform thickness and good quality of the isolation layer are ensured. HfAlO x The main role of the isolation layer is to isolate graphene from the substrate, reduce the diffusion of impurities and defects in the substrate to the graphene layer, and provide a flat and stable growth surface for graphene, which helps to maintain the structural integrity and electrical performance stability of graphene.

[0049] (3) Graphene growth and transfer: Single-layer high-quality graphene is grown on the isolation layer using chemical vapor deposition (CVD) method. During the CVD growth process, appropriate carbon sources (such as methane, ethylene, etc.), catalysts (such as copper foil, nickel foil, etc.) and reaction conditions (such as temperature, gas flow, reaction time, etc.) are selected to achieve high-quality, good uniformity and large-area graphene growth. For example, the growth temperature can be controlled between 1000°C-1100°C, the carbon source gas flow is 10-50sccm, the hydrogen flow is 100-500sccm, the reaction pressure is 1-10Torr, and the growth time is determined according to the required number of graphene layers and quality (such as 10-60 minutes). After growth, appropriate transfer technology (such as poly-methyl methacrylate (PMMA) assisted transfer method) is used to transfer graphene to the isolation layer. The specific operation includes spinning a layer of PMMA on the graphene surface as a support layer, then placing the copper foil with PMMA / graphene into etching solution (such as ammonium persulfate solution) to remove the copper foil, obtaining PMMA / graphene film. Finally, the PMMA / graphene film is transferred to the HfAlO x The substrate of the isolation layer, by heating or solvent treatment to remove PMMA, to obtain single-layer graphene transferred to the isolation layer, to ensure that the graphene is not damaged during the transfer process, and to maintain its excellent physical properties. High-quality graphene is a structure with complete and defect-free graphene structure;

[0050] (4) Preparation of dielectric layer: A layer of HfAlO x Dielectric layer. The dielectric layer is prepared by physical vapor deposition methods such as electron beam evaporation or sputtering. During the deposition process, parameters such as deposition rate, deposition time and working pressure are precisely controlled to achieve precise control of the thickness of the dielectric layer. For example, when electron beam evaporation is selected, HfAlO x is used as the evaporation source material, and the dielectric layer of the required thickness is deposited at an appropriate deposition rate (such as 0.1-0.5nm / s) by controlling the electron beam current and evaporation time; for sputtering process, HfAlO x target is used, and sputtering deposition is carried out at a certain sputtering power (such as 100-300W) and gas pressure (such as 0.1-1Pa). HfAlOx The medium layer and the graphene jointly constitute a capacitor structure under the action of an external voltage, and the chemical potential of the graphene can be effectively regulated by changing the voltage, thereby affecting the electrical and optical properties of the graphene and realizing the modulation of the phase of the mid-infrared light.

[0051] (5) Electrode layer preparation: a 50 nm thick metal electrode layer is prepared on the medium layer. The metal electrode layer is made of gold (Au). Electron beam lithography technology is used to define the electrode pattern, and then metal is deposited on the medium layer through metal evaporation or sputtering process to form an electrode structure that is in good electrical connection with the graphene layer. The specific operation includes: spin-coating an electron beam resist on the medium layer, soft baking, and then exposing according to the design pattern using an electron beam lithography device. After development, a 50 nm thick metal electrode layer is deposited in the area defined by the photoresist pattern through electron beam evaporation or sputtering process. Finally, the photoresist is removed using a stripping process to obtain a metal electrode layer structure that is in good electrical connection with the graphene. The main function of the electrode is to apply an external voltage, thereby realizing the regulation of the electrical state of the graphene heterojunction structure.

[0052] The HfAlO x / graphene / HfAlO x Heterojunction phase modulator, the modulator includes, from bottom to top, an SOI substrate, an HfAlO x isolation layer, graphene layer, HfAlO x medium layer and metal electrode layer.

[0053] In order to enable those skilled in the art to better understand the technical scheme of the present application, the technical scheme in the embodiments of the present application will be described clearly and completely below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor should be within the scope of protection of the present application.

[0054] Example 1

[0055] (1) SOI substrate selection and treatment: an SOI silicon wafer is selected as the substrate material to provide a stable support platform for the entire structure. The surface flatness and crystal quality of the substrate have an important influence on the performance of the material layer grown subsequently, so the substrate needs to be strictly pretreated. First, chemical cleaning methods (such as RCA cleaning method) are used to remove organic contaminants, particulate impurities and native oxide layer on the surface of the substrate. Then, the cleaned substrate is polished, and chemical mechanical polishing (CMP) technology can be used to ensure that the surface roughness is less than a certain threshold (such as 0.5 nm) to obtain an atomic-level flat surface, laying a foundation for high-quality material growth.

[0056] (2) Isolation layer deposition: Grow a layer of HfAlO with a thickness of 100 nm on the substrate x Isolation layer. The growth of the isolation layer is carried out using atomic layer deposition (ALD) technology, by precisely controlling the pulse time, reaction temperature and pressure of the precursor, etc. Process parameters to ensure that the isolation layer has uniform thickness and good quality. HfAlO x The main role of the isolation layer is to isolate graphene from the substrate, reduce the diffusion of impurities and defects in the substrate to the graphene layer, and provide a flat and stable growth surface for graphene, which helps to maintain the structural integrity and electrical performance stability of graphene.

[0057] (3) Graphene growth and transfer: Use chemical vapor deposition (CVD) method to grow single-layer high-quality graphene on the isolation layer. During the CVD growth process, select appropriate carbon source (such as methane), catalyst (such as copper foil) and reaction conditions (such as temperature, gas flow, reaction time, etc.) to achieve high-quality, good uniformity and large-area graphene growth. For example, the growth temperature can be controlled between 1000°C, the carbon source gas flow is 10sccm, the hydrogen flow is 100sccm, the reaction pressure is 1Torr, and the growth time is determined according to the required number of graphene layers and quality (such as 10 minutes). After growth, use appropriate transfer technology (such as poly-methyl methacrylate (PMMA) assisted transfer method) to transfer graphene to the isolation layer. The specific operation includes spinning a layer of PMMA on the graphene surface as a support layer, then placing the copper foil with PMMA / graphene into etching solution (such as ammonium persulfate solution) to remove the copper foil, obtaining PMMA / graphene film. Finally, transfer the PMMA / graphene film to the HfAlO x The substrate of the isolation layer, by heating or solvent treatment to remove PMMA, to obtain single-layer graphene transferred to the isolation layer, to ensure that the graphene is not damaged during the transfer process, and to maintain its excellent physical properties. High-quality graphene is a structure with complete and defect-free structure;

[0058] (4) HfAlO x Dielectric layer preparation: Cover a layer of HfAlO with a thickness of d (d is 50 nm) on the graphene layer x Dielectric layer. The dielectric layer is prepared by physical vapor deposition method of electron beam evaporation, and the deposition rate, deposition time and working pressure, etc. Parameters are precisely controlled during the deposition process to achieve precise control of the thickness of the dielectric layer. For example, when electron beam evaporation, select HfAlO x as the evaporation source material, by controlling the electron beam current and evaporation time, to deposit the dielectric layer with the required thickness at an appropriate deposition rate (such as 0.1 nm / s); HfAlO xUnder the action of external voltage, the dielectric layer forms a capacitor structure together with graphene. By changing the voltage, the chemical potential of graphene can be effectively controlled, thereby affecting its electrical and optical properties and realizing the modulation of the mid-infrared light phase.

[0059] (5) Fabrication of metal electrode layer: On HfAlO x A 50nm thick metal electrode layer is prepared on the dielectric layer. Gold (Au) is selected for the metal electrode layer. Electron beam lithography technology is used to define the electrode pattern, and then the metal is deposited on the dielectric layer through metal evaporation or sputtering process to form an electrode structure that is well electrically connected to the graphene layer. The specific operation includes spin-coating a layer of electron beam photoresist on the dielectric layer, using electron beam lithography equipment to expose the design pattern after soft baking, and after development, depositing a 50nm thick metal electrode layer in the area defined by the photoresist pattern through electron beam evaporation process. Finally, the photoresist is removed by a stripping process to obtain a metal electrode layer structure that is well electrically connected to the graphene. The main function of the electrode is to apply an external voltage to achieve the regulation of the electrical state of the graphene heterojunction structure.

[0060] Prepared a HfAlO x / graphene / HfAlO x Heterojunction phase modulator, the phase modulator includes SOI substrate, HfAlO x Isolation layer, graphene layer, HfAlO x dielectric layer and metal electrode layer.

[0061] Example 2

[0062] (1) SOI substrate selection and processing: SOI silicon wafers are selected as the substrate material to provide a stable support platform for the entire structure. The surface flatness and crystal quality of the substrate have an important impact on the performance of the subsequently grown material layer, so the substrate needs to be strictly pretreated. First, a chemical cleaning method (such as RCA cleaning method) is used to remove organic pollutants, particulate impurities and natural oxide layers on the surface of the substrate. Then, the cleaned substrate is polished. Chemical mechanical polishing (CMP) technology can be used to ensure that the surface roughness is less than a certain threshold (such as 0.5nm) to obtain an atomically flat surface, laying the foundation for high-quality material growth.

[0063] (2)HfAlO x Isolation layer deposition: grow a 100nm thick HfAlO layer on the substrate x Isolation layer. Atomic layer deposition (ALD) technology is used to grow the isolation layer. By precisely controlling the pulse time of the precursor, reaction temperature, pressure and other process parameters, the isolation layer is ensured to have uniform thickness and good quality. xThe main role of the isolation layer is to isolate graphene from the substrate, reduce the diffusion of impurities and defects in the substrate to the graphene layer, and provide a flat and stable growth surface for graphene, which helps to maintain the structural integrity and electrical stability of graphene.

[0064] (3) Graphene growth and transfer: using chemical vapor deposition (CVD) method to grow single-layer high-quality graphene on HfAlO x The isolation layer is grown on the substrate. During the CVD growth process, appropriate carbon source (such as ethylene), catalyst (such as nickel foil, etc.) and reaction conditions (such as temperature, gas flow, reaction time, etc.) are selected to realize the growth of high-quality, good uniformity and large-area graphene. For example, the growth temperature can be controlled between 1100℃, the carbon source gas flow is 50sccm, the hydrogen flow is 500sccm, the reaction pressure is 10Torr, and the growth time is determined according to the required number of graphene layers and quality (such as 60 minutes). After growth, appropriate transfer technology (such as polymethyl methacrylate (PMMA) assisted transfer method) is used to transfer graphene to the isolation layer. The specific operation includes spinning a layer of PMMA on the surface of graphene as a support layer, then putting the copper foil with PMMA / graphene into etching solution (such as ammonium persulfate solution) to remove the copper foil, and obtaining PMMA / graphene film. Finally, the PMMA / graphene film is transferred to the HfAlO x The PMMA is removed from the substrate of the isolation layer by heating or solvent treatment, and single-layer graphene transferred to the isolation layer is obtained, ensuring that the graphene is not damaged during the transfer process and maintaining its excellent physical properties. High-quality graphene is a structure with complete structure and no defects;

[0065] (4) Preparation of dielectric layer: a layer of HfAlO x with a thickness of d (d is 200nm) is covered on the graphene layer. The dielectric layer is prepared by physical vapor deposition method of electron beam evaporation. During the deposition process, parameters such as deposition rate, deposition time and working pressure are accurately controlled to realize accurate control of the thickness of the dielectric layer. For example, when electron beam evaporation is selected as the evaporation source material, the required thickness of the dielectric layer is deposited at an appropriate deposition rate (such as 0.5nm / s) by controlling the electron beam current and evaporation time; HfAlO x The dielectric layer is prepared by physical vapor deposition method of electron beam evaporation. During the deposition process, parameters such as deposition rate, deposition time and working pressure are accurately controlled to realize accurate control of the thickness of the dielectric layer. For example, when electron beam evaporation is selected as the evaporation source material, the required thickness of the dielectric layer is deposited at an appropriate deposition rate (such as 0.5nm / s) by controlling the electron beam current and evaporation time; HfAlO x The dielectric layer and graphene together form a capacitor structure under the action of external voltage, which can effectively regulate the chemical potential of graphene, and then affect its electrical and optical properties, realizing the modulation of mid-infrared light phase.

[0066] (5) Electrode layer fabrication: A 50nm thick metal electrode layer is prepared on the dielectric layer. The metal electrode layer is selected to be gold (Au). Electron beam lithography technology is used to define the electrode pattern, and then the metal is deposited on the dielectric layer through metal evaporation or sputtering process, forming an electrode structure that is well electrically connected with the graphene layer. The specific operation includes spin-coating a layer of electron beam resist on the dielectric layer, after soft baking, using an electron beam lithography equipment to expose according to the design pattern, after development, depositing a 50nm thick metal electrode layer in the area defined by the photoresist pattern through electron beam evaporation process. Finally, the photoresist is removed using a stripping process to obtain a metal electrode layer structure that is well electrically connected with the graphene, and the main function of the electrode is to apply an external voltage, thereby realizing the regulation of the electrical state of the graphene heterojunction structure.

[0067] The HfAlO x / graphene / HfAlO x Heterojunction phase modulator, the phase modulator comprises, from bottom to top, an SOI substrate, an HfAlO x isolation layer, graphene layer, HfAlO x dielectric layer and metal electrode layer.

[0068] Example 3

[0069] (1) SOI substrate selection and treatment: Select SOI silicon wafer as the substrate material to provide a stable support platform for the whole structure. The surface flatness and crystal quality of the substrate have important influence on the performance of the material layer grown subsequently, therefore the substrate needs to be strictly pretreated. First, use chemical cleaning method (such as RCA cleaning method) to remove organic contaminants, particle impurities and native oxide layer on the surface of the substrate. Then, polish the cleaned substrate, which can adopt chemical mechanical polishing (CMP) technology to ensure that the surface roughness is less than a certain threshold value (such as 0.5nm), so as to obtain an atomic level flatness surface, laying a foundation for high quality material growth.

[0070] (2) Isolation layer deposition: A 100nm thick HfAlO x isolation layer is grown on the substrate. Atomic layer deposition (ALD) technology is used for the growth of the isolation layer, by accurately controlling the pulse time, reaction temperature and pressure of the precursor, etc. Process parameters to ensure that the isolation layer has uniform thickness and good quality. HfAlO x The main function of the isolation layer is to isolate the graphene from the substrate, reduce the diffusion of impurities and defects in the substrate to the graphene layer, and at the same time provide a flat and stable growth surface for the graphene, which helps to maintain the structural integrity and electrical performance stability of the graphene.

[0071] (3) Graphene growth and transfer: Single-layer high-quality graphene is grown on the isolation layer using the chemical vapor deposition (CVD) method. During the CVD growth process, appropriate carbon sources (such as methane, etc.), catalysts (such as copper foil, etc.), and reaction conditions (such as temperature, gas flow, reaction time, etc.) are selected to achieve high-quality, good uniformity, and large-area graphene growth. For example, the growth temperature can be controlled between 1050°C, the carbon source gas flow is 30 sccm, the hydrogen flow is 300 sccm, the reaction pressure is 5 Torr, and the growth time is determined according to the required number of graphene layers and quality (such as 40 minutes). After growth is complete, a suitable transfer technique (such as the polymethyl methacrylate (PMMA) assisted transfer method) is used to transfer the graphene to the isolation layer. The specific operation includes spinning a layer of PMMA on the graphene surface as a support layer, then placing the copper foil with PMMA / graphene into an etching solution (such as ammonium persulfate solution) to remove the copper foil, and obtaining a PMMA / graphene film. Finally, the PMMA / graphene film is transferred to the HfAlO x substrate on which the isolation layer has been grown, and the PMMA is removed by heating or solvent treatment to obtain single-layer graphene transferred to the isolation layer, ensuring that the graphene is not damaged during the transfer process and maintaining its excellent physical properties. High-quality graphene is a graphene structure that is structurally complete and defect-free;

[0072] (4) Dielectric layer preparation: A HfAlO x dielectric layer with a thickness of d (d is 100 nm) is covered on the graphene layer. The dielectric layer is prepared by physical vapor deposition method of sputtering, and during the deposition process, parameters such as deposition rate, deposition time, and working gas pressure are accurately controlled to achieve precise control of the thickness of the dielectric layer. For example, in the sputtering process, a HfAlO x target is used to perform sputtering deposition under a certain sputtering power (such as 100 W) and gas pressure (such as 0.1 Pa). The HfAlO x dielectric layer, under the action of an external voltage, together with the graphene forms a capacitor structure, and by changing the voltage, the chemical potential of the graphene can be effectively regulated, thereby affecting its electrical and optical properties and achieving modulation of the phase of mid-infrared light.

[0073] (5) Electrode layer fabrication: A 50nm thick metal electrode layer is prepared on the dielectric layer. The metal electrode layer is selected to be gold (Au). Electron beam lithography technology is used to define the electrode pattern, and then the metal is deposited on the dielectric layer by metal evaporation or sputtering process to form an electrode structure that is well electrically connected with the graphene layer. The specific operation includes spin-coating a layer of electron beam resist on the dielectric layer, soft baking, and then using an electron beam lithography equipment to expose according to the design pattern, after development, a 50nm thick metal electrode layer is deposited in the area defined by the photoresist pattern through sputtering process. Finally, the photoresist is removed using a stripping process to obtain a metal electrode layer structure that is well electrically connected with the graphene, and the main function of the electrode is to apply an external voltage, thereby realizing the regulation of the electrical state of the graphene heterojunction structure.

[0074] The HfAlO x / graphene / HfAlO x Heterojunction phase modulator, the phase modulator comprises, from bottom to top, an SOI substrate, an HfAlO x isolation layer, graphene layer, HfAlO x dielectric layer and metal electrode layer.

[0075] Example 4

[0076] (1) SOI substrate selection and treatment: Select SOI silicon wafer as the substrate material to provide a stable support platform for the whole structure. The surface flatness and crystal quality of the substrate have important influence on the performance of the material layer grown subsequently, therefore the substrate needs to be strictly pretreated. First, use chemical cleaning method (such as RCA cleaning method) to remove organic contaminants, particle impurities and native oxide layer on the surface of the substrate. Then, polish the cleaned substrate, which can adopt chemical mechanical polishing (CMP) technology to ensure that the surface roughness is less than a certain threshold value (such as 0.5nm), so as to obtain an atomic level flatness surface, laying a foundation for high quality material growth.

[0077] (2) Isolation layer deposition: A 100nm thick HfAlO x isolation layer is grown on the substrate. Atomic layer deposition (ALD) technology is used for the growth of the isolation layer, by accurately controlling the pulse time, reaction temperature and pressure of the precursor, etc. Process parameters to ensure that the isolation layer has uniform thickness and good quality. HfAlO x The main function of the isolation layer is to isolate the graphene from the substrate, reduce the diffusion of impurities and defects in the substrate to the graphene layer, and at the same time provide a flat and stable growth surface for the graphene, which helps to maintain the structural integrity and electrical performance stability of the graphene.

[0078] (3) Graphene growth and transfer: Single-layer high-quality graphene is grown on the isolation layer using the chemical vapor deposition (CVD) method. During the CVD growth process, appropriate carbon sources (such as methane, ethylene, etc.), catalysts (such as copper foil, nickel foil, etc.), and reaction conditions (such as temperature, gas flow, reaction time, etc.) are selected to achieve high-quality, good uniformity, and large-area graphene growth. For example, the growth temperature can be controlled between 1080°C, the carbon source gas flow is 10-50 sccm, the hydrogen flow is 400 sccm, the reaction pressure is 6 Torr, and the growth time is determined according to the required number of graphene layers and quality (such as 45 minutes). After growth is complete, a suitable transfer technique (such as the polymethyl methacrylate (PMMA) assisted transfer method) is used to transfer the graphene to the isolation layer. The specific operation includes spinning a layer of PMMA on the graphene surface as a support layer, then placing the copper foil with PMMA / graphene into an etching solution (such as ammonium persulfate solution) to remove the copper foil, and obtaining a PMMA / graphene film. Finally, the PMMA / graphene film is transferred to the HfAlO x base of the isolation layer, the PMMA is removed by heating or solvent treatment, and single-layer graphene transferred to the isolation layer is obtained, ensuring that the graphene is not damaged during the transfer process and maintaining its excellent physical properties. High-quality graphene is a structurally complete and defect-free graphene structure;

[0079] (4) Dielectric layer preparation: A HfAlO x dielectric layer with a thickness of d (d is in the range of 150 nm) is covered on the graphene layer. The dielectric layer is prepared by physical vapor deposition method of sputtering, and during the deposition process, parameters such as deposition rate, deposition time, and working gas pressure are precisely controlled to achieve precise control of the thickness of the dielectric layer. For example, when electron beam evaporation is used, HfAlO x is selected as the evaporation source material, and the dielectric layer with the required thickness is deposited at an appropriate deposition rate (such as 0.4 nm / s) by controlling the electron beam current and evaporation time; for sputtering process, HfAlO x target is used for sputtering deposition under certain sputtering power (such as 300 W) and gas pressure (such as 1 Pa). HfAlO x The dielectric layer, under the action of an external voltage, together with the graphene forms a capacitor structure, and by changing the voltage, the chemical potential of the graphene can be effectively regulated, thereby affecting its electrical and optical properties and achieving modulation of the phase of mid-infrared light.

[0080] (5) Electrode layer fabrication: 50nm thick metal electrode layer is prepared on the dielectric layer. The metal electrode layer is selected from gold (Au). Electron beam lithography technology is used to define the electrode pattern, and then metal is deposited on the dielectric layer by metal evaporation or sputtering process to form an electrode structure that is well electrically connected with the graphene layer. The specific operation includes spin-coating an electron beam resist on the dielectric layer, soft baking, and then using an electron beam lithography device to expose according to the design pattern, developing, and then depositing a 50nm thick metal electrode layer in the area defined by the photoresist pattern through sputtering process. Finally, the photoresist is removed using a stripping process to obtain a metal electrode layer structure that is well electrically connected with the graphene. The main function of the electrode is to apply an external voltage, thereby realizing the regulation of the electrical state of the graphene heterojunction structure.

[0081] The HfAlO x / graphene / HfAlO x heterojunction phase modulator, which comprises, from bottom to top, an SOI substrate, an HfAlO x isolation layer, graphene layer, HfAlO x dielectric layer and metal electrode layer.

[0082] The HfAlO x / graphene / HfAlO x heterojunction phase modulator of embodiment 1 is prepared.

[0083] The implementation steps of phase modulation include: regulating the chemical potential of graphene by applying an external voltage; deriving the conductivity from the chemical potential according to the Kubo formula; obtaining the dispersion relation from the conductivity; deriving the propagation constant β from the dispersion relation; and obtaining the phase shift by multiplying the real part of the propagation constant β and the transmission path length.

[0084] (1) Chemical potential regulation:

[0085] The chemical potential of the graphene layer is changed by applying an external voltage V g to the metal electrode layer. The chemical potential of the graphene layer is as follows. By changing the voltage V g , the chemical potential of the graphene can be accurately regulated in a wide range. ε0 and ε r are the dielectric constant in free space and the relative dielectric constant of the substrate material, respectively. d is the thickness of the dielectric, and v0 is the deviation voltage caused by natural doping, and e is the charge amount of an electron.

[0086]

[0087] (2) Conductivity calculation:

[0088] After the chemical potential is obtained, the surface conductivity of graphene can be calculated according to the Kubo formula, and by accurately calculating the conductivity, the light transmission characteristics (including phase and light intensity) of the graphene heterojunction under different chemical potentials can be deeply understood, thereby providing key parameters for subsequent phase modulation analysis. For example, under a given working wavelength (such as 1550 nm), the real part and the imaginary part of the conductivity will change accordingly with the change of the chemical potential, and this change is closely related to the optical properties of graphene, such as absorption, reflection and transmission of mid-infrared light, thereby affecting the phase modulation effect.

[0089] (3) Dispersion relationship determination:

[0090] After the conductivity is obtained, the dispersion relationship of surface plasmon polaritons (SPPs) in TM mode is derived according to Maxwell's equations and boundary conditions where ε 1＝ ε 2＝ ε r (HfAlO x , k m 2 = β 2 -ε m k0 2 (m = 1, 2), k0 is the electromagnetic wave propagation constant in air, and η0 is the free space impedance. By solving the dispersion relationship, the propagation constant β of SPPs can be obtained, so that the change of the propagation constant β caused by different chemical potentials of graphene and medium layer parameters can be mastered, thereby affecting the propagation speed and phase change of SPPs in the structure, which is an important basis for realizing phase modulation.

[0091] (4) Phase shift calculation and modulation:

[0092] The phase shift is obtained by bringing β into the wave equation H x (y) = A m e iβz e -kmy It can be seen that the light accumulates different phase shifts after propagating different path lengths z. The phase shift is calculated by multiplying the optical path length z and the real part of the propagation constant β. Because β is related to external voltage V g , medium layer thickness d and incident light wavelength, etc., adjusting these parameters can change β, thereby realizing continuous tuning of the light phase.

[0093] The HfAlO x / graphene / HfAlO x heterojunction phase modulator, preparation method and phase modulation method of the present application have the following improvements:

[0094] (1) Wide phase modulation range: the present application can realize continuous and wide-range tuning of the phase in the mid-infrared band, and the phase coverage range can reach 0°-360°, meeting the diversified demand for phase modulation in various complex optical signal processing and optoelectronic device applications. For example, in the phase-shift keying modulation in optical communication, the phase change of the optical signal can be accurately controlled to realize high-speed and high-capacity data transmission; in the phase contrast enhancement technology in optical imaging, the contrast and resolution of the image can be effectively improved, which helps to observe the microstructure and pathological tissue more clearly.

[0095] (2) Small size structure advantage: the entire structure length is only 800 nm, which is much smaller than the free space wavelength in the mid-infrared band, realizing subwavelength operation. This small size structure is conducive to the high integration and miniaturization of the device, and can be applied to high-density optical integrated chips, miniature optical sensors and other fields, which helps to improve the integration and portability of the system.

[0096] (3) Low driving voltage characteristic: compared with traditional mid-infrared phase modulation methods and devices, the driving voltage required by the present application is significantly reduced, which can be as low as 1V. Low driving voltage not only reduces energy consumption and improves energy utilization efficiency, but also is especially suitable for portable and low-power devices with strict power consumption requirements, and simplifies the design of the driving circuit, reduces the system cost and complexity.

[0097] (4) Excellent material and structure performance: HfAlO x is used as the dielectric material, and a good heterojunction structure is formed with graphene. HfAlO x has high dielectric constant and good stability, which can effectively regulate the electrical properties of graphene, and at the same time avoids the Fermi level pinning effect when graphene is in direct contact with metal, improving the efficiency and flexibility of phase modulation.

[0098] The above is only a preferred embodiment of the present application, and does not limit the present application in any form; any ordinary skilled person in the industry can easily implement the present application according to the drawings and the above description; however, any equivalent changes, modifications and evolution of the above-mentioned technical content within the scope of the technical solutions of the present application are equivalent embodiments of the present application; at the same time, any equivalent changes, modifications and evolution of the above-mentioned technical content within the scope of the technical solutions of the present application are equivalent embodiments of the present application.

Claims

1. HfAlO X / graphene / HfAlO X A method for preparing a heterojunction, characterized in that: include: S1. After pre-treating the SOI substrate, HfAlO is grown on the SOI substrate using atomic layer deposition technology. X Isolation layer; S2, using chemical vapor deposition method on the HfAlO X growing a graphene layer on the isolation layer; S3, using physical vapor deposition method to prepare HfAlO on the graphene layer of S2 X dielectric layer; S4, use electron beam lithography technology to define the electrode pattern, and then deposit the metal electrode layer on the HfAlO layer of S3 by metal evaporation or sputtering process. X On the dielectric layer, HfAlO is finally obtained X / graphene / HfAlO X heterojunction; HfAlO was prepared on the graphene layer of S2 by physical vapor deposition method. X The dielectric layer is: HfAlO was prepared on graphene layers by physical vapor deposition methods such as electron beam evaporation or sputtering. X dielectric layer; When HfAlO is prepared on a graphene layer using physical vapor deposition by electron beam evaporation X When the dielectric layer is used, HfAlO X As the evaporation source material, HfAlO was deposited by controlling the electron beam current, evaporation time and deposition rate of 0.1-0.5 nm / s. X dielectric layer; When HfAlO is prepared on the graphene layer by physical vapor deposition method using sputtering process X When the dielectric layer is used, HfAlO X As the target material, HfAlO was obtained by sputtering deposition under the conditions of sputtering power of 100-300W and gas pressure of 0.1-1Pa. X dielectric layer; The HfAlO X / graphene / HfAlO X The heterojunction includes SOI substrate, HfAlO X Isolation layer, graphene layer, HfAlO X dielectric layer and metal electrode layer; The HfAlO X The thickness of the isolation layer is 100nm; HfAlO X The thickness of the dielectric layer is 50nm-200nm, and the thickness of the metal electrode layer is 50nm.

2. A HfAlO according to claim 1 X / graphene / HfAlO X A method for preparing a heterojunction, characterized in that: The pretreatment of the SOI substrate is specifically as follows: Chemical cleaning methods are used to remove organic pollutants, particulate impurities and natural oxide layers on the surface of the SOI substrate; The cleaned SOI substrate is polished using chemical mechanical polishing technology to obtain an SOI substrate with a surface flatness at the atomic level.

3. A HfAlO according to claim 1 X / graphene / HfAlO X A method for preparing a heterojunction, characterized in that: HfAlO was deposited by chemical vapor deposition X The graphene layer is grown on the isolation layer under the following conditions: Growing a graphene layer by chemical vapor deposition at a growth temperature of 1000°C-1100°C, a catalyst of copper foil or nickel foil, a carbon source gas flow rate of 10-50 sccm, a hydrogen flow rate of 100-500 sccm, a reaction pressure of 1-10 Torr, and a reaction time of 10-60 minutes; the carbon source comprises methane or ethylene; After the graphene layer is grown, the graphene layer is transferred to the HfAlO X On the isolation layer.

4. A HfAlO according to claim 3 X / graphene / HfAlO X A method for preparing a heterojunction, characterized in that: The polymethyl methacrylate-assisted transfer method is used to transfer the graphene layer to the HfAlO X On the isolation layer, specifically: A PMMA layer is spin-coated on the surface of the graphene layer containing copper foil as a support layer. Then the copper foil with PMMA / graphene is placed in an etching solution to remove the copper foil to obtain a PMMA / graphene film. The PMMA / graphene film is transferred to a substrate where HfAlO has been grown. X On the SOI substrate of the isolation layer, HfAlO is obtained by removing PMMA X A graphene layer is grown on the isolation layer; and the etching solution is an ammonium sulfate solution.

5. A HfAlO according to claim 1 X / graphene / HfAlO X A method for preparing a heterojunction, characterized in that: Electron beam lithography is used to define the electrode pattern, and then the metal electrode layer is deposited on the HfAlO layer of S3 by metal evaporation or sputtering. X On the dielectric layer, specifically: In HfAlO X A layer of electron beam photoresist is spin-coated on the dielectric layer. After soft baking, it is exposed and developed according to the design pattern using electron beam lithography equipment. The metal electrode layer is deposited in the area defined by the photoresist pattern by electron beam evaporation or sputtering process. After the photoresist is removed by stripping process, the metal electrode layer is deposited on the HfAlO X On the dielectric layer, HfAlO is finally obtained X / graphene / HfAlO X heterojunction; The metal electrode layer is made of gold.

6. A HfAlO X / graphene / HfAlO X Heterojunction phase modulator based on a HfAlO according to any one of claims 1 to 5 X / graphene / HfAlO X HfAlO prepared by heterojunction preparation method X / graphene / HfAlO X Heterojunction, characterized in that The HfAlO X / graphene / HfAlO X The heterojunction phase modulator includes SOI substrate, HfAlO X Isolation layer, graphene layer, HfAlO X dielectric layer and metal electrode layer.

7. A HfAlO as claimed in claim 6 X / graphene / HfAlO X The phase modulation method of a heterojunction phase modulator is characterized in that: include, By applying an external voltage V to the metal electrode layer g Manipulating the chemical potential of graphene layers; The electrical conductivity of the graphene layer is calculated based on the Kubo formula through the chemical potential of the graphene layer; Based on the conductivity of the graphene layer, Maxwell's equations and boundary conditions, the dispersion relation of the surface plasmon wave in the TM mode is obtained; By solving the dispersion relation, the propagation constant β of the surface plasmon wave is obtained; Through the TM mode wave equation, based on the real part of the propagation constant β of the surface plasmon wave and the path length of light propagation z The phase shift is calculated by multiplication, thus realizing the HfAlO X / graphene / HfAlO X Phase modulation of heterojunction phase modulator.

Images