HfAlOx / graphene / HfAlOx heterojunction phase modulator, preparation method and phase modulation method

Abstract

The invention discloses an HfAlOx / graphene / HfAlOx heterojunction phase modulator, a preparation method and a phase modulation method, and according to an HfAlOx / graphene / HfAlOx heterojunction, HfAlOx is adopted as a dielectric material, and a good heterojunction structure is formed by the HfAlOx and graphene. The HfAlOx has a high dielectric constant and good stability, can effectively regulate and control the electrical properties of graphene, avoids the Fermi level pinning effect when graphene is in direct contact with metal, and improves the efficiency and flexibility of phase modulation. The length of the whole structure is only 800 nm and is far smaller than the free space wavelength of the middle infrared band, and sub-wavelength operation is achieved. The small-size structure is beneficial to high integration and miniaturization of devices, can be applied to the fields of high-density optical integrated chips, miniature optical sensors and the like, and is beneficial to improving the integration level and portability of a system.

Description

Technical Field

[0001] The invention belongs to the field of photoelectric conversion technology and relates to a HfAlO x / graphene / HfAlO x A heterojunction phase modulator, a preparation method and a phase modulation method. Background Art

[0002] In the mid-infrared band (usually with a wavelength range of 2.5μm-25μm), in optical communications, mid-infrared light can effectively reduce dispersion and loss in optical fiber transmission, greatly improve communication capacity and transmission distance, and provide key technical support for the construction of the next generation of high-speed, large-capacity optical communication networks; in the field of infrared imaging, the mid-infrared band has unique advantages in detecting the thermal radiation of objects, and can penetrate obstacles such as smoke and dust. It has extensive and indispensable applications in military reconnaissance, security monitoring, fire rescue, and medical thermal imaging. Phase modulation is one of the core operations of optical signal processing in the mid-infrared band. It is indispensable for realizing optical switches, optical signal encoding, optical computing, phase imaging in optical imaging, and optical microscope resolution improvement in optical communications. Traditional mid-infrared phase modulation methods are mainly based on the electro-optical effect or thermo-optical effect of crystal materials (such as lithium niobate, gallium arsenide, etc.). However, these traditional methods face many challenges. Modulators based on the electro-optical effect usually require a higher driving voltage, which not only increases energy consumption, but also puts higher requirements on the driving circuit, which is not conducive to the miniaturization and integration of equipment. Moreover, the growth and processing of crystal materials are complex and costly, which limits their large-scale application. Although the driving voltage of modulators based on the thermo-optical effect is relatively low, the response speed is slow and cannot meet the needs of high-speed optical communication and fast optical signal processing.

[0003] As a new type of two-dimensional carbon material, graphene has many excellent properties. Its chemical potential can be flexibly controlled by various means such as external electric field and chemical doping, which makes it possible to realize dynamically tunable optical devices. It also has a strong ability of light-matter interaction and can effectively support surface plasmon polaritons (SPPs) in the mid-infrared band. It can realize the localization and regulation of light fields at subwavelength scale, providing a new way for phase modulation in the mid-infrared band.

[0004] However, pure graphene also has some limitations in practical applications. For example, when graphene is in direct contact with the metal electrode layer, the Fermi level pinning effect is prone to occur, which will significantly limit 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 will lead to increased energy loss and affect the overall efficiency of the device. In order to overcome these problems, the graphene heterojunction structure has become a research hotspot. By combining graphene with other suitable materials to form a heterojunction, the advantages of each material can be comprehensively utilized to avoid the adverse effects of direct contact between graphene and metal, and to achieve more efficient and flexible mid-infrared phase modulation, 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 photothermal effect: Mid-infrared phase modulation is achieved by using the photothermal effect in the 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 thermo-optic effect: The refractive index of the material is changed by temperature change to achieve phase modulation. The disadvantages are: limited by the material, the modulation bandwidth is limited; (3) Double photoelastic difference frequency modulation: The difference frequency of two zinc selenide photoelastic modulators is used to reduce the system modulation frequency to generate 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 1 times difference frequency amplitude and 2 times difference frequency amplitude. This method can effectively suppress the influence of light intensity fluctuation and photoelastic modulator phase delay fluctuation on the measurement and improve 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 problems of 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 kind of HfAlO x / Graphene / HfAlO x Heterojunction, 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;

[0010] Preferably, 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 gold electrode is 50nm.

[0011] A kind of HfAlO x / Graphene / HfAlO x A method for preparing a heterojunction, comprising:

[0012] S1. After pre-treating the SOI substrate, HfAlO is grown on the SOI substrate using atomic layer deposition technology. x Isolation layer;

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

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

[0015] S4, use electron beam lithography technology to define the electrode pattern, and then deposit the metal electrode layer on the HfAlO in S3 by metal evaporation or sputtering process. x On the dielectric layer, HfAlO is finally obtained. x / Graphene / HfAlO x Heterojunction.

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

[0017] Chemical cleaning methods are used to remove organic pollutants, particulate impurities and natural oxide layers on the surface of the SOI substrate;

[0018] The cleaned SOI substrate is polished by chemical mechanical polishing technology to obtain an SOI substrate with a surface flatness at the atomic level.

[0019] Preferably, HfAlO is deposited by chemical vapor deposition. x The graphene layer is grown on the isolation layer under the following specific conditions:

[0020] A graphene layer is grown by chemical vapor deposition under the conditions of a growth temperature of 1000° C. to 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;

[0021] After the growth of the graphene layer, the graphene layer was transferred to the HfAlO x On the isolation layer.

[0022] Preferably, the graphene layer is transferred to the HfAlO layer by using a polymethyl methacrylate assisted transfer method. x On the isolation layer, specifically:

[0023] A layer of PMMA is spin-coated on the surface of the graphene layer containing copper foil as a support layer, and 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 the surface of the HfAlO 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.

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

[0025] Preparation of HfAlO on graphene layer by physical vapor deposition method of electron beam evaporation or sputtering x dielectric layer;

[0026] When HfAlO is prepared on a graphene layer by physical vapor deposition using 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;

[0027] When HfAlO is prepared on the graphene layer by physical vapor deposition using a 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.

[0028] Preferably, the electrode pattern is defined by electron beam lithography, 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:

[0029] 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;

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

[0031] A kind of HfAlO x / Graphene / HfAlO x Heterojunction phase modulator, 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.

[0032] A kind of HfAlO x / Graphene / HfAlO x A phase modulation method for a heterojunction phase modulator, comprising:

[0033] By applying an external voltage V to the metal electrode layer g Manipulating the chemical potential of graphene;

[0034] The conductivity of graphene is calculated based on the chemical potential of graphene and the Kubo formula;

[0035] Based on the conductivity of graphene, according to Maxwell's equations and boundary conditions, the dispersion relation of surface plasmon waves in TM mode is obtained;

[0036] By solving the dispersion relation, the propagation constant β of the surface plasmon wave is obtained;

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

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

[0039] The 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 It has a high dielectric constant and good stability, can effectively regulate the electrical properties of graphene, and avoids the Fermi level pinning effect when graphene is in direct contact with metal, improving the efficiency and flexibility of phase modulation. The entire structure is only 800nm ​​long, which is much smaller than the free space wavelength in the mid-infrared band, and achieves subwavelength operation. This small-size structure is conducive to the high integration and miniaturization of devices, and can be applied to high-density optical integrated chips, micro optical sensors and other fields, helping to improve the integration and portability of the system.

[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 in the range of 0-5V, the phase can be fully tuned from 0° to 360°; under certain 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 broad application prospects in mid-infrared optoelectronic devices, such as the design of 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 optical signals can be accurately controlled to achieve high-speed and 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 3D structure diagram of heterojunction;

[0042] Figure 2 HfAlO x / Graphene / HfAlO x Plan view of the heterojunction; DETAILED DESCRIPTION

[0043] The present invention is further described in detail below in conjunction with specific embodiments, which are intended to explain the present invention rather than to limit it.

[0044] Specific technical solutions:

[0045] 1. Structural design: a HfAlO x / Graphene / HfAlO x The structure of the heterojunction is Figure 1 As shown in the figure, the proposed structure consists of a SOI substrate, 100nm HfAlO x Isolation layer, single-layer graphene, HfAlO with a thickness of d x The dielectric layer and the 50nm thick gold electrode. Figure 1 For a stereogram, 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 graphene and the metal gate, the HfAlO x The dielectric layer acts as an effective high-k dielectric for graphene chemical potential tuning. Here, 100 nm of HfAlO x The isolation layer isolates the graphene from the environment, which is beneficial to 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 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, use a chemical cleaning method (such as RCA cleaning method) 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.

[0048] (2) Isolation layer deposition: A layer of HfAlO with a thickness of 100 nm is grown on the substrate. xIsolation layer. The atomic layer deposition (ALD) technology is used to grow the isolation layer. By precisely controlling the pulse time of the precursor, reaction temperature and pressure and other process parameters, the isolation layer is ensured to have uniform thickness and good quality. x The main function of the isolation layer is to isolate graphene from the substrate, reduce the diffusion of impurities and defects in the substrate into 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: A single layer of high-quality graphene is grown on the isolation layer using chemical vapor deposition (CVD). 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 rate, reaction time, etc.) are selected to achieve high-quality, uniform and large-area graphene growth. For example, the growth temperature can be controlled between 1000°C and 1100°C, the carbon source gas flow rate is 10-50sccm, the hydrogen flow rate is 100-500sccm, the reaction pressure is 1-10Torr, and the growth time is determined according to the required number and quality of graphene layers (such as 10-60 minutes). After the growth is completed, the graphene is transferred to the isolation layer using a suitable transfer technique (such as polymethyl methacrylate (PMMA) assisted transfer method). The specific operation includes spin coating 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), removing the copper foil, and obtaining a PMMA / graphene film. Finally, the PMMA / graphene film is transferred to a substrate with HfAlO grown on it. x On the base of the isolation layer, PMMA is removed by heating or solvent treatment to obtain a single layer of graphene transferred to the isolation layer, ensuring that the graphene is not damaged during the transfer process and maintains its excellent physical properties. High-quality graphene is a graphene structure with complete structure and no defects;

[0050] (4) Preparation of dielectric layer: Cover the graphene layer with a layer of HfAlO with a thickness of d (the value of d ranges from 50nm to 200nm) x Dielectric layer. The dielectric layer is prepared by physical vapor deposition methods such as electron beam evaporation or sputtering. During the deposition process, the 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 used, HfAlO x As the evaporation source material, 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; during the sputtering process, HfAlO x The target material is sputtered and deposited at a certain sputtering power (such as 100-300W) and gas pressure (such as 0.1-1Pa).x Under 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 regulated, thereby affecting its electrical and optical properties and achieving modulation of the phase of mid-infrared light.

[0051] (5) Preparation of electrode layer: Prepare a 50nm thick metal electrode layer 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 by 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 by electron beam evaporation or sputtering 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.

[0052] The HfAlO x / Graphene / HfAlO x A heterojunction phase modulator, the modulator comprising, from bottom to top, a SOI substrate, a HfAlO x Isolation layer, graphene layer, HfAlO x dielectric layer and metal electrode layer.

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

[0054] Example 1

[0055] (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, use a chemical cleaning method (such as RCA cleaning method) 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.

[0056] (2) Isolation layer deposition: A layer of HfAlO with a thickness of 100 nm is grown on the substrate. x Isolation layer. The atomic layer deposition (ALD) technology is used to grow the isolation layer. By precisely controlling the pulse time of the precursor, reaction temperature and pressure and other process parameters, the isolation layer is ensured to have uniform thickness and good quality. x The main function of the isolation layer is to isolate graphene from the substrate, reduce the diffusion of impurities and defects in the substrate into 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: A single layer of high-quality graphene is grown on the isolation layer using chemical vapor deposition (CVD). During the CVD growth process, appropriate carbon sources (such as methane), catalysts (such as copper foil) and reaction conditions (such as temperature, gas flow rate, reaction time, etc.) are selected to achieve high-quality, uniform and large-area graphene growth. For example, the growth temperature can be controlled between 1000°C, the carbon source gas flow rate is 10sccm, the hydrogen flow rate is 100sccm, the reaction pressure is 1Torr, and the growth time is determined according to the required number and quality of graphene layers (such as 10 minutes). After the growth is completed, the graphene is transferred to the isolation layer using an appropriate transfer technique (such as polymethyl methacrylate (PMMA) assisted transfer method). The specific operation includes spin coating a layer of PMMA on the graphene surface as a support layer, and then placing the copper foil with PMMA / graphene in an etching solution (such as ammonium persulfate solution), removing the copper foil, and obtaining a PMMA / graphene film. Finally, the PMMA / graphene film is transferred to a surface on which HfAlO has been grown. x On the base of the isolation layer, PMMA is removed by heating or solvent treatment to obtain a single layer of graphene transferred to the isolation layer, ensuring that the graphene is not damaged during the transfer process and maintains its excellent physical properties. High-quality graphene is a graphene structure with complete structure and no defects;

[0058] (4)HfAlO x Preparation of dielectric layer: Cover the graphene layer with a layer of HfAlO with a thickness of d (the value of d is 50nm) x The dielectric layer is prepared by the physical vapor deposition method of electron beam evaporation. During the deposition process, the 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 used, HfAlO x As the evaporation source material, the dielectric layer of the required thickness is deposited at an appropriate deposition rate (such as 0.1 nm / s) by controlling the electron beam current and evaporation time; 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 regulated, thereby affecting its electrical and optical properties and achieving modulation of the phase of mid-infrared light.

[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 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 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 by electron beam evaporation process. Finally, the photoresist is removed by stripping process to obtain a metal electrode layer structure that is well electrically connected to graphene. The main function of the electrode is to apply external voltage, thereby realizing the regulation of the electrical state of the graphene heterojunction structure.

[0060] Prepare a HfAlO x / Graphene / HfAlO x A heterojunction phase modulator, the phase modulator comprising, from bottom to top, an SOI substrate, a 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, use a chemical cleaning method (such as RCA cleaning method) 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: A layer of HfAlO with a thickness of 100 nm is grown on the substrate x Isolation layer. The atomic layer deposition (ALD) technology is used to grow the isolation layer. By precisely controlling the pulse time of the precursor, reaction temperature and pressure and other process parameters, the isolation layer is ensured to have uniform thickness and good quality. xThe main function of the isolation layer is to isolate graphene from the substrate, reduce the diffusion of impurities and defects in the substrate into 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.

[0064] (3) Graphene growth and transfer: Chemical vapor deposition (CVD) was used to grow graphene on HfAlO x A single layer of high-quality graphene is grown on the isolation layer. During the CVD growth process, appropriate carbon sources (such as ethylene), catalysts (such as nickel foil, etc.) and reaction conditions (such as temperature, gas flow rate, reaction time, etc.) are selected to achieve high-quality, uniform and large-area graphene growth. For example, the growth temperature can be controlled between 1100°C, the carbon source gas flow rate is 50sccm, the hydrogen flow rate is 500sccm, the reaction pressure is 10Torr, and the growth time is determined according to the required number and quality of graphene layers (such as 60 minutes). After the growth is completed, the graphene is transferred to the isolation layer using a suitable transfer technology (such as polymethyl methacrylate (PMMA) assisted transfer method). The specific operation includes spin coating a layer of PMMA on the graphene surface as a support layer, and then placing the copper foil with PMMA / graphene in an etching solution (such as ammonium persulfate solution), removing the copper foil, and obtaining a PMMA / graphene film. Finally, the PMMA / graphene film is transferred to a HfAlO-containing film that has been grown. x On the base of the isolation layer, PMMA is removed by heating or solvent treatment to obtain a single layer of graphene transferred to the isolation layer, ensuring that the graphene is not damaged during the transfer process and maintains its excellent physical properties. High-quality graphene is a graphene structure with complete structure and no defects;

[0065] (4) Preparation of dielectric layer: Cover the graphene layer with a layer of HfAlO with a thickness of d (the value of d is 200 nm) x The dielectric layer is prepared by the physical vapor deposition method of electron beam evaporation. During the deposition process, the 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 used, HfAlO x As the evaporation source material, the dielectric layer of the required thickness is deposited at an appropriate deposition rate (such as 0.5 nm / s) by controlling the electron beam current and evaporation time; HfAlO x Under 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 regulated, thereby affecting its electrical and optical properties and achieving modulation of the phase of mid-infrared light.

[0066] (5) Electrode layer preparation: 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 by 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 by 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.

[0067] The HfAlO x / Graphene / HfAlO x A heterojunction phase modulator, the phase modulator comprising, from bottom to top, an SOI substrate, a HfAlO x Isolation layer, graphene layer, HfAlO x dielectric layer and metal electrode layer.

[0068] Example 3

[0069] (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, use a chemical cleaning method (such as RCA cleaning method) 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.

[0070] (2) Isolation layer deposition: A layer of HfAlO with a thickness of 100 nm is grown on the substrate. x Isolation layer. The atomic layer deposition (ALD) technology is used to grow the isolation layer. By precisely controlling the pulse time of the precursor, reaction temperature and pressure and other process parameters, the isolation layer is ensured to have uniform thickness and good quality. x The main function of the isolation layer is to isolate graphene from the substrate, reduce the diffusion of impurities and defects in the substrate into 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.

[0071] (3) Graphene growth and transfer: A single layer of high-quality graphene is grown on the isolation layer using chemical vapor deposition (CVD). 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 rate, reaction time, etc.) are selected to achieve high-quality, uniform and large-area graphene growth. For example, the growth temperature can be controlled between 1050°C, the carbon source gas flow rate is 30sccm, the hydrogen flow rate is 300sccm, the reaction pressure is 5Torr, and the growth time is determined according to the required number and quality of graphene layers (such as 40 minutes). After the growth is completed, the graphene is transferred to the isolation layer using an appropriate transfer technique (such as polymethyl methacrylate (PMMA) assisted transfer method). The specific operation includes spin coating a layer of PMMA on the graphene surface as a support layer, and then placing the copper foil with PMMA / graphene into an etching solution (such as ammonium persulfate solution), removing the copper foil, and obtaining a PMMA / graphene film. Finally, the PMMA / graphene film was transferred to the HfAlO x On the base of the isolation layer, PMMA is removed by heating or solvent treatment to obtain a single layer of graphene transferred to the isolation layer, ensuring that the graphene is not damaged during the transfer process and maintains its excellent physical properties. High-quality graphene is a graphene structure with complete structure and no defects;

[0072] (4) Preparation of dielectric layer: A layer of HfAlO with a thickness of d (the value of d is 100 nm) is covered on the graphene layer. x The dielectric layer is prepared by the physical vapor deposition method of sputtering. During the deposition process, the deposition rate, deposition time and working pressure are precisely controlled to achieve precise control of the thickness of the dielectric layer. For example, when using HfAlO x The target material is sputtered and deposited at a certain sputtering power (such as 100W) and gas pressure (such as 0.1Pa). x Under 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 regulated, thereby affecting its electrical and optical properties and achieving modulation of the phase of mid-infrared light.

[0073] (5) Electrode layer preparation: 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 by 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, a 50nm thick metal electrode layer is deposited in the area defined by the photoresist pattern by sputtering 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.

[0074] The HfAlO x / Graphene / HfAlO x A heterojunction phase modulator, the phase modulator comprising, from bottom to top, an SOI substrate, a HfAlO x Isolation layer, graphene layer, HfAlO x dielectric layer and metal electrode layer.

[0075] Example 4

[0076] (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, use a chemical cleaning method (such as RCA cleaning method) 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.

[0077] (2) Isolation layer deposition: A layer of HfAlO with a thickness of 100 nm is grown on the substrate. x Isolation layer. The atomic layer deposition (ALD) technology is used to grow the isolation layer. By precisely controlling the pulse time of the precursor, reaction temperature and pressure and other process parameters, the isolation layer is ensured to have uniform thickness and good quality. x The main function of the isolation layer is to isolate graphene from the substrate, reduce the diffusion of impurities and defects in the substrate into 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.

[0078] (3) Graphene growth and transfer: A single layer of high-quality graphene is grown on the isolation layer using chemical vapor deposition (CVD). 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 rate, reaction time, etc.) are selected to achieve high-quality, uniform and large-area graphene growth. For example, the growth temperature can be controlled between 1080°C, the carbon source gas flow rate is 10-50sccm, the hydrogen flow rate is 400sccm, the reaction pressure is 6Torr, and the growth time is determined according to the required number and quality of graphene layers (such as 45 minutes). After the growth is completed, the graphene is transferred to the isolation layer using a suitable transfer technology (such as polymethyl methacrylate (PMMA) assisted transfer method). The specific operation includes spin coating a layer of PMMA on the graphene surface as a support layer, and then placing the copper foil with PMMA / graphene into an etching solution (such as ammonium persulfate solution), removing the copper foil, and obtaining a PMMA / graphene film. Finally, the PMMA / graphene film was transferred to the HfAlO x On the base of the isolation layer, PMMA is removed by heating or solvent treatment to obtain a single layer of graphene transferred to the isolation layer, ensuring that the graphene is not damaged during the transfer process and maintains its excellent physical properties. High-quality graphene is a graphene structure with complete structure and no defects;

[0079] (4) Preparation of dielectric layer: Cover the graphene layer with a layer of HfAlO with a thickness of d (the value range of d is 150 nm) x Dielectric layer. The dielectric layer is prepared by physical vapor deposition method of sputtering. During the deposition process, the 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 used, HfAlO x As the evaporation source material, the dielectric layer of the required thickness is deposited at an appropriate deposition rate (such as 0.4nm / s) by controlling the electron beam current and evaporation time; during the sputtering process, HfAlO x The target material is sputtered and deposited at a certain sputtering power (such as 300W) and gas pressure (such as 1Pa). x Under 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 regulated, thereby affecting its electrical and optical properties and achieving modulation of the phase of mid-infrared light.

[0080] (5) Electrode layer preparation: 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 by 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, a 50nm thick metal electrode layer is deposited in the area defined by the photoresist pattern by sputtering 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.

[0081] The HfAlO x / Graphene / HfAlO x A heterojunction phase modulator, the phase modulator comprising, from bottom to top, an SOI substrate, a HfAlO x Isolation layer, graphene layer, HfAlO x dielectric layer and metal electrode layer.

[0082] By treating a HfAlO x / Graphene / HfAlO x Phase modulation method of heterojunction phase modulator:

[0083] The steps for implementing phase modulation include: applying an external voltage to regulate the chemical potential of graphene; deriving the conductivity from the chemical potential according to the Kubo formula; then obtaining the dispersion relation from the conductivity; then deriving the propagation constant β from the dispersion relation, and the product of the real part of the propagation constant β and the length of the transmission path to obtain the phase shift.

[0084] (1) Chemical potential regulation:

[0085] By applying an external voltage V to the metal electrode layer g To change the chemical potential of the graphene layer. The chemical potential formula of the graphene layer is as follows. By changing the voltage V g , the chemical potential of graphene can be precisely controlled in a wide range. 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, v0 is the bias voltage caused by natural doping, and e is the charge of the electron.

[0086]

[0087] (2) Conductivity calculation:

[0088] After obtaining the chemical potential, the surface conductivity of graphene can be calculated according to the Kubo formula. By accurately calculating the conductivity, we can gain a deep understanding of the light transmission characteristics (including phase and light intensity) of the graphene heterojunction under different chemical potentials, providing key parameters for subsequent phase modulation analysis. For example, at a given working wavelength (such as 1550nm), as the chemical potential changes, the real and imaginary parts of the conductivity will change accordingly. This change is closely related to the optical properties of graphene such as absorption, reflection and transmission of mid-infrared light, which in turn affects the phase modulation effect.

[0089] (3) Determination of dispersion relation:

[0090] After obtaining the conductivity, the dispersion relation of the surface plasmon polaritons (SPPs) wave in the TM mode was derived based on Maxwell's equations and boundary conditions. where ε 1＝ ε 2＝ ε r (HfAlO x Relative dielectric constant), k m 2 =β 2 -ε m k0 2 (m=1,2), k0 is the electromagnetic wave propagation constant in air, η0 is the free space impedance. By solving the dispersion relation, the propagation constant β of SPPs wave can be obtained, so that different graphene chemical potential and dielectric layer parameters will lead to changes in the propagation constant β, which in turn affects the propagation speed and phase change of SPPs wave in the structure, which is an important basis for realizing phase modulation.

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

[0092] Substituting β into the wave equation gives the phase shift. According to the TM mode wave equation H x (y) = A m e iβz e -kmy , it can be seen that 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 the external voltage V g , the dielectric layer thickness d and the wavelength of the incident light. Therefore, adjusting these parameters can change β, and thus achieve continuous tuning of the optical phase.

[0093] A HfAlO x / Graphene / HfAlO x The heterojunction phase modulator, preparation method and phase modulation method have the following improvements:

[0094] (1) Wide phase modulation range: The present invention can achieve continuous and wide-range tuning of the phase in the mid-infrared band, with a phase coverage range of up to 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 optical signals can be precisely controlled to achieve high-speed, large-capacity data transmission; in phase contrast enhancement technology in optical imaging, the contrast and resolution of images can be effectively improved, which helps to observe microstructures and diseased tissues more clearly.

[0095] (2) Advantages of small-size structure: The entire structure is only 800 nm long, which is much smaller than the free-space wavelength in the mid-infrared band, thus achieving sub-wavelength operation. This small-size structure is conducive to the high integration and miniaturization of devices, and can be applied to high-density optical integrated chips, micro optical sensors and other fields, helping to improve the integration and portability of the system.

[0096] (3) Low driving voltage characteristics: Compared with the traditional mid-infrared phase modulation method and device, 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 particularly suitable for portable and low-power devices with strict power consumption requirements, but also simplifies the driving circuit design and reduces system cost and complexity.

[0097] (4) Excellent material and structural performance: using HfAlO x As a dielectric material, it forms a good heterojunction structure with graphene. x It has a high dielectric constant and good stability, 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, thereby improving the efficiency and flexibility of phase modulation.

[0098] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any ordinary technician in the industry can smoothly implement the present invention as shown in the drawings and described above. However, any equivalent changes, modifications and evolutions made by technicians familiar with the profession without departing from the scope of the technical solution of the present invention using the technical content disclosed above are all equivalent embodiments of the present invention. At the same time, any equivalent changes, modifications and evolutions made to the above embodiments based on the essential technology of the present invention are still within the protection scope of the technical solution of the present invention.

Claims

1. A HfAlO x / Graphene / HfAlO x A heterojunction, characterized in that The HfAlO x / Graphene / HfAlO x The heterojunction includes SOI substrate, HfAlOx isolation layer, graphene layer, HfAlO x dielectric layer and metal electrode layer.

2. A HfAlO according to claim 1 x / Graphene / HfAlO x A heterojunction, characterized in that 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 gold electrode is 50nm.

3. A HfAlO according to any one of claims 1 to 2 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 in S1 x growing a graphene layer on the isolation layer; S3, preparing HfAlO on the graphene layer of S2 by physical vapor deposition method x Dielectric layer, S4, use electron beam lithography technology to define the electrode pattern, and then deposit the metal electrode layer on the HfAlO in S3 by metal evaporation or sputtering process. x On the dielectric layer, HfAlO is finally obtained. x / Graphene / HfAlO x Heterojunction.

4. A HfAlO according to claim 3 x / Graphene / HfAlO x A method for preparing a heterojunction, characterized in that: The pretreatment of the SOI substrate is specifically: 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 by chemical mechanical polishing technology to obtain an SOI substrate with a surface flatness at the atomic level.

5. A HfAlO according to claim 3 x / Graphene / HfAlO x A method for preparing a heterojunction, characterized in that: HfAlO was prepared by chemical vapor deposition. x The graphene layer is grown on the isolation layer under the following specific conditions: A graphene layer is grown by chemical vapor deposition under the conditions of a growth temperature of 1000° C. to 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 growth of the graphene layer, the graphene layer was transferred to the HfAlO x On the isolation layer.

6. 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 layer of PMMA is spin-coated on the surface of the graphene layer containing copper foil as a support layer, and 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 the surface of the HfAlO 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.

7. A HfAlO according to claim 3 x / Graphene / HfAlO x A method for preparing a heterojunction, characterized in that: Prepare HfAlO on the graphene layer of S2 by physical vapor deposition method x The dielectric layer is: Preparation of HfAlO on graphene layer by physical vapor deposition method of electron beam evaporation or sputtering x dielectric layer; When HfAlO is prepared on a graphene layer by physical vapor deposition using 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 using a 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.

8. A HfAlO according to claim 3 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.

9. A HfAlO according to any one of claims 1 to 2 x / Graphene / HfAlO x A heterojunction phase modulator, 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.

10. A HfAlO as claimed in claim 9 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 conductivity of the graphene layer is calculated according to the Kubo formula through the chemical potential of the graphene layer; Based on the conductivity of the graphene layer, the dispersion relation of the surface plasmon wave in the TM mode is obtained according to Maxwell's equations and boundary conditions. By solving the dispersion relation, the propagation constant β of the surface plasmon wave is obtained; Through the TM mode wave equation, the phase shift is calculated based on the real part of the propagation constant β of the surface plasmon wave and the path length z of the light propagation, thereby realizing the HfAlO x / Graphene / HfAlO x Phase modulation of heterojunction phase modulator.

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