Electrooptical modulator of graphene indium tin oxide P-N heterojunction and preparation method

Abstract

The invention relates to the technical field of electro-optical modulators, in particular to a graphene indium tin oxide P-N heterojunction electro-optical modulator and a preparation method thereof, and the graphene indium tin oxide P-N heterojunction electro-optical modulator comprises an electrode, a graphene layer, an ITO layer, an Al2O3 spacing layer, a silicon waveguide layer, a light input port and a light output port; the graphene layer of the electro-optical modulator has extremely high carrier mobility, the ITO layer also has good electrical performance, and the heterojunction formed by the graphene layer and the ITO layer can quickly respond to the change of an electric field, so that high-speed electro-optical modulation is realized, and the extinction ratio can be effectively improved by optimizing the structure and electrical parameters of the graphene-ITO heterojunction. For example, the appropriate number of graphene layers and the appropriate thickness of the ITO layer can enable the contrast ratio of optical signals in the 0 state and the 1 state to be remarkably increased, due to the synergistic effect of the optical performance and the electrical performance of the graphene layers and the ITO layer, the energy loss of the optical signals is small when the optical signals pass through the modulator, and the insertion loss is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of electro-optic modulators, and in particular to an electro-optic modulator of a graphene indium tin oxide PN heterojunction and a preparation method thereof. Background Art

[0002] PN heterojunction electro-optic modulator is a device that uses the electro-optic effect generated by the PN junction in semiconductor materials under the action of an electric field to modulate optical signals. PN heterojunction electro-optic modulator plays an important role in modern communication technology and is widely used in optical fiber communication systems to achieve the conversion of electrical signals to optical signals, as well as high-speed modulation and signal processing of optical signals.

[0003] Traditional electro-optic modulators usually refer to modulators made of bulk lithium niobate materials. These modulators have some technical limitations in the development of photonic integrated circuits, including: large size, difficulty in improving performance, and poor light field binding ability. PN heterojunction electro-optic modulators usually have higher performance indicators, especially in terms of integration and response speed, which makes them more suitable for high-speed optical communication systems.

[0004] Combining the many advantages of heterojunction design, the electro-optic modulator of heterojunction design can be miniaturized and integrated through micro-nano processing technology, making the overall size smaller and more suitable for application in limited space. Its structure and performance can also be adjusted as needed, with greater flexibility and adjustability, and can adapt to different application scenarios and needs. By optimizing the design to achieve higher transmittance and conductivity, it can be controlled and transmitted more accurately. More energy-saving and environmentally friendly materials and processes can also be used in the manufacturing process. At the same time, due to its small size, it can also reduce energy consumption and resource waste. Summary of the invention

[0005] The purpose of the present invention is to provide an electro-optic modulator of a graphene indium tin oxide PN heterojunction and a preparation method thereof, aiming to change the material structure of the electro-optic modulator of the heterojunction to achieve low-loss transmission.

[0006] To achieve the above objectives, in a first aspect, the present invention provides an electro-optic modulator of a graphene indium tin oxide PN heterojunction, comprising an electrode, a graphene layer, an ITO layer, an Al2O3 spacer layer, a silicon waveguide layer, an optical input port and an optical output port; the optical input port is arranged on one side of the silicon waveguide layer, the optical output port is arranged on the opposite side of the optical input port, the Al2O3 spacer layer is arranged on the top of the silicon waveguide layer, the ITO layer is arranged on the side of the Al2O3 spacer layer away from the silicon waveguide layer, the graphene layer is arranged on the side of the ITO layer away from the Al2O3 spacer layer, and the electrode is arranged on the side of the graphene layer away from the ITO layer.

[0007] In a second aspect, the present invention further provides a method for preparing an electro-optic modulator of a graphene indium tin oxide PN heterojunction, which is used to prepare the electro-optic modulator of a graphene indium tin oxide PN heterojunction as described in the first aspect above, comprising the following steps:

[0008] Prepare ITO layer, graphene layer, Al2O3 spacer layer, silicon waveguide layer and electrode respectively;

[0009] Connecting the optical input port and the optical output port, and assembling the electrode, the graphene layer, the ITO layer, the Al2O3 spacer layer and the silicon waveguide layer in sequence from top to bottom to form an electro-optic modulator;

[0010] A performance test is performed on the electro-optic modulator.

[0011] Wherein, the Al2O3 spacer layer is prepared by using physical vapor deposition technology to deposit the Al2O3 spacer layer on the silicon waveguide layer.

[0012] Wherein, the ITO layer is prepared by using physical vapor deposition technology to deposit the ITO layer on the Al2O3 spacer layer.

[0013] The graphene layer is prepared by chemical vapor deposition, with methane as the carbon source and hydrogen as the carrier gas, and the graphene layer is grown on the ITO layer under the conditions of 800-1000° C. and 1-10 Torr.

[0014] In the electro-optic modulator of the graphene indium tin oxide PN heterojunction of the present invention, the graphene layer and the ITO layer are sequentially arranged on the silicon waveguide layer to form a graphene-ITO heterojunction. The silicon waveguide layer is made of a material with good optical and electrical properties, such as a SiO2 substrate, and the electrodes are arranged on both sides of the graphene-ITO heterojunction. The electrodes are used to apply an electric field to achieve modulation of the optical signal. The electrode material can be made of a metal material, such as gold (Au) or silver (Ag), to ensure good conductivity. The optical input port and the optical output port are respectively arranged at both ends of the modulator. The optical signal enters the modulator through the input port and is output from the output port after being modulated by the graphene-ITO heterojunction. Figure 2As shown, when an electric field is applied to the electrode, the electrical properties of the graphene layer, such as the Fermi level, etc., will change due to the heterojunction effect between the graphene layer and the ITO layer. This change in electrical properties will affect the absorption and refraction characteristics of graphene to light. When the optical signal passes through the silicon waveguide, due to the change in the electrical properties of graphene, the polarization state, phase and other characteristics of the light will change accordingly, thereby realizing electro-optical modulation of the optical signal. The graphene layer of the electro-optic modulator has an extremely high carrier mobility, and the ITO layer also has good electrical properties. The heterojunction formed by the two can quickly respond to changes in the electric field, thereby realizing high-speed electro-optical modulation. By optimizing the structure and electrical parameters of the graphene-ITO heterojunction, the extinction ratio can be effectively improved. For example, the appropriate number of graphene layers and the thickness of the ITO layer can significantly increase the contrast of the optical signal in the "0" and "1" states. Graphene is a p-type semiconductor, and the typical electron affinity value X G is 0.073eV, and the power value is Φ G is 4.5eV. ITO is an n-type semiconductor, and its typical electron affinity is X ITO is 4.1eV, and the power value is Φ ITO The band gap values ​​of graphene and ITO are 0 ev and 3.39 eV respectively. The conduction band and valence band of the graphene / ITO heterojunction form a staggered gap at the interface, as shown in the attached Figure 1 As shown in Figure 1. Therefore, when the Fermi levels of the two materials are aligned, the valence band of the graphene layer bends downward, while the valence band of the ITO layer bends upward. In the heterojunction, the unique heterostructure of the graphene / semiconductor junction breaks the traditional epitaxial growth limitations such as interatomic diffusion and lattice mismatch. Figure 2 The electro-optic modulator is designed with a three-dimensional structure, and the thickness of the graphene layer is set to 10nm, the thickness of the ITO layer is set to 10nm, and the thickness of the silicon waveguide layer is set to 250nm, and the thickness of the Al2O3 spacer layer is set to 10nm, wherein the thickness of the SiO2 layer in the silicon waveguide layer is 2.25μm. Due to the synergistic effect of the optical and electrical properties of the graphene layer and the ITO layer, the energy loss of the optical signal when passing through the modulator is small, the insertion loss is reduced, and the size is reduced compared to the traditional electro-optic modulator. At the same time, analogous to the electro-optic modulator of a single material, the graphene-ITO heterojunction material layer is added, and the low-loss photoelectric propagation of the electro-optic modulator can be achieved. The transmittance of the heterojunction in the electro-optic modulator structure is significantly better than that of single graphene and ITO. The effect of the transmittance is shown in the attached figure. Figure 5As shown in Figure 5-a, Figure 5-b is the transmittance of graphene, Figure 5-c is the transmittance comparison of graphene, ITO and heterojunction at the same thickness. The carrier concentration of the heterojunction in the electro-optic modulator structure is significantly higher than the carrier concentration of the two. The effect of the change of carrier concentration with voltage is shown in the attached figure. Figure 6 As shown, Figure 6-a shows the variation of the carrier concentration of graphene with voltage, Figure 6-b shows the variation of the carrier concentration of ITO with voltage, and Figure 6-c shows the variation of the carrier concentration of the heterojunction with voltage. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0016] Figure 1 Schematic diagram of the band gap arrangement of graphene / ITO heterojunction designed using the electron affinity model.

[0017] Figure 2 It is a schematic diagram of the three-dimensional structure of the heterojunction electro-optic modulator.

[0018] Figure 3 This is the end view of the heterojunction electro-optic modulator.

[0019] Figure 4 It is a schematic diagram of the output light intensity change curve after the optical signal passes through the modulator under different electric field intensities, among which 4-a has high loss and 4-b has low loss.

[0020] Figure 5 It is the transmittance curve, where 5-a is the transmittance of graphene with different thicknesses, 5-b is the transmittance of ITO with different thicknesses, and 5-c is the transmittance of 20 nm graphene, 20 nm ITO and 20 nm graphene-ITO heterojunction.

[0021] Figure 6 It is the variation of carrier concentration of materials and structures with voltage, 6-a the variation of carrier concentration of graphene with voltage, 6-b the variation of carrier concentration of ITO with voltage, 6-c the variation of carrier concentration of graphene-ITO heterojunction with voltage.

[0022] Figure 7 The present invention provides a flow chart of a method for preparing an electro-optic modulator of a graphene indium tin oxide PN heterojunction.

[0023] In the figure: 1-electrode, 2-graphene layer, 3-ITO layer, 4-Al2O3 spacer layer, 5-silicon waveguide layer, 6-light input port, 7-light output port. DETAILED DESCRIPTION

[0024] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0025] See also Figures 1 to 7 In a first aspect, the present invention provides an electro-optic modulator of a graphene indium tin oxide PN heterojunction, comprising an electrode 1, a graphene layer 2, an ITO layer 3, an Al2O3 spacer layer 4, a silicon waveguide layer 5, an optical input port 6 and an optical output port 7;

[0026] The light input port 6 is arranged on one side of the silicon waveguide layer 5, the light output port 7 is arranged on the opposite side of the light input port 6, the Al2O3 spacer layer 4 is arranged on the top of the silicon waveguide layer 5, the ITO layer 3 is arranged on the side of the Al2O3 spacer layer 4 away from the silicon waveguide layer 5, the graphene layer 2 is arranged on the side of the ITO layer 3 away from the Al2O3 spacer layer 4, and the electrode 1 is arranged on the side of the graphene layer 2 away from the ITO layer 3.

[0027] In the embodiment of the present invention, the graphene layer 2 and the ITO layer 3 are sequentially arranged on the silicon waveguide layer 5 to form a graphene-ITO heterojunction. The silicon waveguide layer 5 is made of a material with good optical and electrical properties, such as a SiO2 substrate, and the electrodes 1 are arranged on both sides of the graphene-ITO heterojunction. The electrodes 1 are used to apply an electric field to achieve modulation of the optical signal. The electrode material can be made of metal materials, such as gold (Au) or silver (Ag), to ensure good conductivity. The optical input port 6 and the optical output port 7 are respectively arranged at the two ends of the modulator. The optical signal enters the modulator through the input port and is output from the output port after being modulated by the graphene-ITO heterojunction. Figure 2As shown, when an electric field is applied to the electrode 1, the electrical properties of the graphene layer 2, such as the Fermi level, will change due to the heterojunction effect between the graphene layer 2 and the ITO layer 3. This change in electrical properties will affect the absorption and refraction characteristics of graphene to light. When the optical signal passes through the silicon waveguide, due to the change in the electrical properties of graphene, the polarization state, phase and other characteristics of the light will change accordingly, thereby realizing electro-optical modulation of the optical signal. The graphene layer 2 of the electro-optic modulator has an extremely high carrier mobility, and the ITO layer 3 also has good electrical properties. The heterojunction formed by the two can quickly respond to changes in the electric field, thereby realizing high-speed electro-optical modulation. By optimizing the structure and electrical parameters of the graphene-ITO heterojunction, the extinction ratio can be effectively improved. For example, the appropriate number of graphene layers 2 and the thickness of the ITO layer 3 can significantly increase the contrast of the optical signal in the "0" and "1" states. Graphene is a p-type semiconductor, and the typical electron affinity value X G is 0.073eV, and the power value is Φ G is 4.5eV. ITO is an n-type semiconductor, and its typical electron affinity is X ITO is 4.1eV, and the power value is Φ ITO The band gap values ​​of graphene and ITO are 0 ev and 3.39 eV respectively. The conduction band and valence band of the graphene / ITO heterojunction form a staggered gap at the interface, as shown in the attached Figure 1 As shown in Figure 1. Therefore, when the Fermi levels of the two materials are aligned, the valence band of the graphene layer 2 bends downward, while the valence band of the ITO layer 3 bends upward. In the heterojunction, the unique heterostructure of the graphene / semiconductor junction breaks the traditional epitaxial growth limitations such as interatomic diffusion and lattice mismatch. Figure 2 The electro-optic modulator is designed with a three-dimensional structure, and the thickness of the graphene layer 2 is set to 10nm, the thickness of the ITO layer 3 is set to 10nm, and the thickness of the silicon waveguide layer 5 is set to 250nm, and the thickness of the Al2O3 spacer layer 4 is set to 10nm, wherein the thickness of the SiO2 layer in the silicon waveguide layer 5 is 2.25μm. Due to the synergistic effect of the optical and electrical properties of the graphene layer 2 and the ITO layer 3, the energy loss of the optical signal when passing through the modulator is small, the insertion loss is reduced, and the size is reduced compared to the traditional electro-optic modulator. At the same time, analogous to the electro-optic modulator of a single material, the graphene-ITO heterojunction material layer is added, and the low-loss photoelectric propagation of the electro-optic modulator can be realized. The transmittance of the heterojunction in the electro-optic modulator structure is significantly better than that of single graphene and ITO. The effect of the transmittance is shown in the attached figure. Figure 5As shown in Figure 5-a, Figure 5-b is the transmittance of graphene, Figure 5-c is the transmittance comparison of graphene, ITO and heterojunction at the same thickness. The carrier concentration of the heterojunction in the electro-optic modulator structure is significantly higher than the carrier concentration of the two. The effect of the change of carrier concentration with voltage is shown in the attached figure. Figure 6 As shown, Figure 6-a shows the variation of the carrier concentration of graphene with voltage, Figure 6-b shows the variation of the carrier concentration of ITO with voltage, and Figure 6-c shows the variation of the carrier concentration of the heterojunction with voltage.

[0028] In a second aspect, the present invention further provides a method for preparing an electro-optic modulator of a graphene indium tin oxide PN heterojunction, which is used to prepare the electro-optic modulator of a graphene indium tin oxide PN heterojunction as described in the first aspect above, comprising the following steps:

[0029] S1 prepares ITO layer 3, graphene layer 2, Al2O3 spacer layer 4, silicon waveguide layer 5 and electrode 1 respectively;

[0030] In the embodiment of the present invention, the graphene layer 2 is prepared by chemical vapor deposition (CVD). With methane (CH4) as the carbon source and hydrogen (H2) as the carrier gas, the graphene layer 2 is grown on the ITO layer 3 under the conditions of high temperature (800-1000°C) and low pressure (1-10Torr). By controlling parameters such as reaction time and gas flow rate, the graphene layer 2 with a suitable number of layers, such as 1-3 layers of graphene, can be obtained.

[0031] Preparation of the ITO layer 3: The ITO layer 3 is deposited on the Al2O3 spacer layer 4 by using a physical vapor deposition (PVD) technique, such as a magnetron sputtering method. The deposition process parameters, such as sputtering power, gas flow rate, deposition time, etc., are controlled to obtain the ITO layer 3 with suitable thickness and electrical properties. For example, the sputtering power can be set to 100-200W, the argon gas flow rate to 20-50sccm, and the deposition time to 10-30 minutes to obtain an ITO layer 3 with a thickness of 50-150nm.

[0032] Preparation of the Al2O3 spacer layer 4: The Al2O3 spacer layer is deposited on the substrate using PVD technology. The deposition process parameters, such as sputtering power, gas flow rate, deposition time, etc., are controlled to obtain the Al2O3 spacer layer 4 with suitable thickness and electrical properties. The Al2O3 spacer layer 4 isolates the upper layer material from the lower layer material to prevent potential carriers from being injected from the upper layer material into the lower layer material.

[0033] Preparation of the silicon waveguide layer 5: The silicon waveguide layer 5 is formed on the SiO2 substrate by a CVD method. The specific steps are as follows:

[0034] 1. Substrate pretreatment

[0035] Cleaning: Place the SiO2 substrate in a cleaning solution, which can be a solution of deionized water, hydrogen peroxide, and sulfuric acid mixed in a certain ratio (e.g., 1:1:5). Soak for 10-20 minutes at 80-100°C to remove organic matter and impurities on the substrate surface. Then rinse the substrate with a large amount of deionized water to ensure that there is no residual cleaning solution on the surface.

[0036] Drying: Use nitrogen to blow dry or dry in a vacuum drying oven, set the drying temperature at 60-80°C, and the drying time is 30 minutes to 1 hour to make the substrate surface dry and clean.

[0037] 2. CVD process

[0038] Reaction gas preparation: Select silicon source gas, such as silane (SiH4), and hydrogen H2 can be selected as carrier gas. Mix silane and hydrogen in a gas mixing device at a certain flow ratio (for example, silane flow is 10-50 sccm, hydrogen flow is 100-500 sccm).

[0039] Deposition reaction: Place the pretreated SiO2 substrate into the reaction chamber of the CVD equipment. Set the temperature of the reaction chamber to 300-800°C and the pressure to 1-100Torr. Turn on the gas mixing device to allow the mixed gas to flow into the reaction chamber. In the reaction chamber, silane undergoes a decomposition reaction at high temperature and a certain pressure: SiH4→Si+2H2, and silicon atoms are deposited on the surface of the SiO2 substrate, gradually forming a silicon layer. The deposition time depends on the thickness of the required silicon layer. For example, if a silicon layer with a thickness of 1-5μm is to be prepared, the deposition time may be 30 minutes to 5 hours.

[0040] 3. Waveguide Patterning

[0041] Photoresist coating: Spin-coat the photoresist on the SiO2 substrate with the silicon layer deposited thereon. The thickness of the photoresist can be selected according to the specific photolithography process requirements, for example, 1-3 μm. The spin-coating speed is 1000-5000 rpm and the time is 30-60 seconds.

[0042] Exposure and development: Use a photolithography mask to expose the substrate coated with photoresist. The exposure energy depends on the characteristics of the photoresist and the mask pattern, and is generally 10-100mJ / cm 2 The substrate is then placed in a developer for development for 30-90 seconds to remove the photoresist in the exposed area (if it is a positive photoresist) or the unexposed area (if it is a negative photoresist), thereby obtaining a photoresist mask of a waveguide pattern.

[0043] Etching: Reactive ion etching (RIE) or other suitable etching techniques are used to etch the silicon layer using a photoresist mask as a template. Fluorine-based gases, such as CF4, can be selected as etching gases. Etching power, gas flow rate, and etching time are optimized according to the etching depth and waveguide size requirements. For example, the etching power is 100-500W, the CF4 flow rate is 20-100sccm, and the etching time is 10-60 minutes. The etching depth reaches the predetermined thickness of the silicon layer to form a silicon waveguide structure.

[0044] Photoresist removal: Finally, the remaining photoresist is removed by a suitable method, such as organic solvent immersion or plasma ashing, to obtain a silicon waveguide structure on the SiO2 substrate.

[0045] Substrate preparation: For SiO2 substrates, standard semiconductor substrate preparation processes are used, including but not limited to substrate cleaning, chemical mechanical polishing (CMP), thermal oxidation, photolithography, etching, ion implantation and metallization. These steps together ensure the flatness, cleanliness and suitable electrical properties of the substrate surface.

[0046] S2 connects the optical input port 6 and the optical output port 7, and assembles the electrode 1, the graphene layer 2, the ITO layer 3, the Al2O3 spacer layer 4 and the silicon waveguide layer 5 in sequence from top to bottom to form an electro-optic modulator;

[0047] In the embodiment of the present invention, the prepared electrode 1 material is made into an electrode 1 by processes such as photolithography and metal evaporation, and is accurately arranged on both sides of the graphene-ITO heterojunction. The size and spacing of the electrode 1 are adjusted according to specific design requirements, for example, the spacing of the electrode 1 can be set to 5-15 μm. The optical input port 6 and the optical output port 7 are connected, and optical fiber coupling technology is used to ensure that the optical signal can be efficiently input and output from the modulator.

[0048] S3 performs a performance test on the electro-optic modulator.

[0049] In the embodiment of the present invention, an optical signal generator is used to generate optical signals of different frequencies and intensities, which are input into an electro-optic modulator, and a photodetector is used to detect the characteristics of the output optical signal, such as light intensity, polarization state, phase, etc. According to the test results, the structure and parameters of the electro-optic modulator are further optimized to achieve the best modulation performance.

[0050] The above disclosure is only a preferred embodiment of the electro-optic modulator and preparation method of the graphene indium tin oxide PN heterojunction of the present invention. Of course, this cannot be used to limit the scope of rights of the present invention. Ordinary technicians in this field can understand that all or part of the processes of the above embodiments and equivalent changes made according to the claims of the present invention still fall within the scope of the invention.

Claims

1. Graphene indium tin oxide PN heterojunction electro-optic modulator, characterized in that ； It includes an electrode, a graphene layer, an ITO layer, an Al2O3 spacer layer, a silicon waveguide layer, an optical input port and an optical output port; The light input port is arranged on one side of the silicon waveguide layer, the light output port is arranged on the opposite side of the light input port, the Al2O3 spacer layer is arranged on the top of the silicon waveguide layer, the ITO layer is arranged on the side of the Al2O3 spacer layer away from the silicon waveguide layer, the graphene layer is arranged on the side of the ITO layer away from the Al2O3 spacer layer, and the electrode is arranged on the side of the graphene layer away from the ITO layer.

2. A method for preparing an electro-optic modulator of a graphene indium tin oxide PN heterojunction, for preparing the electro-optic modulator of a graphene indium tin oxide PN heterojunction as claimed in claim 1, characterized in that: The steps include: Prepare ITO layer, graphene layer, Al2O3 spacer layer, silicon waveguide layer and electrode respectively; Connecting the optical input port and the optical output port, and assembling the electrode, the graphene layer, the ITO layer, the Al2O3 spacer layer and the silicon waveguide layer in sequence from top to bottom to form an electro-optic modulator; A performance test is performed on the electro-optic modulator.

3. The method for preparing the graphene indium tin oxide PN heterojunction electro-optic modulator according to claim 2, It is characterized by: The Al2O3 spacer layer is prepared by using a physical vapor deposition technique to deposit an Al2O3 spacer layer on the silicon waveguide layer.

4. The method for preparing an electro-optic modulator of a graphene indium tin oxide PN heterojunction according to claim 2, characterized in that ； The ITO layer is prepared by using physical vapor deposition technology to deposit an ITO layer on the Al2O3 spacer layer.

5. The method for preparing the electro-optic modulator of the graphene indium tin oxide PN heterojunction according to claim 2, It is characterized by: The graphene layer is prepared by adopting a chemical vapor deposition method, using methane as a carbon source and hydrogen as a carrier gas, and growing the graphene layer on the ITO layer under the conditions of 800-1000° C. and 1-10 Torr.

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