Tunable metasurface absorber based on gallium oxide and graphene

Abstract

The invention relates to a tunable metasurface absorber based on gallium oxide and graphene, the tunable metasurface absorber is composed of a plurality of unit structure periodic arrays, each unit structure comprises a substrate, a metal reflecting layer, an intermediate dielectric layer, a metal array and a graphene layer which are sequentially arranged from bottom to top, the intermediate dielectric layer is made of gallium oxide, and the metal array is made of graphene. The metal arrays are the same in thickness, and structural parameters are set according to different functions. The device can realize single-wavelength absorption, multi-wavelength absorption and bandwidth absorption.

Description

Technical Field

[0001] The invention belongs to the field of microelectronic materials and micro-nano optical devices, and in particular relates to a tunable supersurface absorber based on gallium oxide and graphene. Background Art

[0002] From Maxwell's equations, we know that light is an electromagnetic wave. From Maxwell's equations in the medium, we can also know that, in principle, electromagnetic waves can be manipulated by arbitrarily controlling the dielectric constant and magnetic permeability of the material. These two parameters describe the response of different materials to electromagnetic waves. However, due to the limited atoms and their arrangement in natural materials, the range of variation of their dielectric constant and magnetic permeability is limited, and the control of electromagnetic waves is limited. Therefore, metasurfaces are created through artificial structures to break through the limitations of limited electromagnetic wave control. Metasurfaces not only have the advantages of arbitrary dielectric constants and magnetic permeabilities, but their two-dimensional form overcomes the limitations of three-dimensional systems, is easy to prepare, has low losses, and has a large degree of control freedom.

[0003] Metasurface absorbers are generally composed of resonant units and dielectric substrates. They absorb electromagnetic waves by reducing the loss of incident electromagnetic waves in the structure itself and converting electromagnetic waves into other forms of energy. Conventional absorption materials often have disadvantages such as being thick, heavy, and having poor stability. Metamaterial absorbers have outstanding advantages over traditional absorption materials, such as being thinner, having stronger absorption effects, and being lighter.

[0004] However, one of the limitations of traditional metasurface absorbers is that once the structural parameters are determined, the function cannot be changed. Graphene is a two-dimensional material with modulatable conductivity. By combining it with a metasurface, functional adjustability is achieved, which solves this limitation well. However, due to the material properties of graphene, the operating wavelengths of most graphene metasurfaces are limited to terahertz and mid-infrared, and the modulation effect in the near-infrared band is relatively limited. It is necessary to enhance its interaction with the near-infrared by designing the device structure.

[0005] Gallium oxide is mostly used in ultraviolet detection in optics due to its bandgap of 4.8eV. Gallium oxide is also a transparent oxide dielectric material with low loss, high refractive index, and good chemical and thermal stability. It should also have great application potential in other bands, but there are few reports on it. Summary of the invention

[0006] The object of the present invention is to provide a tunable metasurface absorber based on gallium oxide and graphene, which can realize single-wavelength absorption, multi-wavelength absorption and broadband absorption.

[0007] In order to achieve the above-mentioned purpose, the technical solution adopted by the present invention is: a tunable metasurface absorber based on gallium oxide and graphene, the device is composed of a plurality of periodic arrays of unit structures, the unit structure includes a substrate, a metal reflective layer, an intermediate dielectric layer, a metal array and a graphene layer arranged in sequence from bottom to top, the material of the intermediate dielectric layer is gallium oxide, the metal array has the same thickness, and the structural parameters are set according to different functions.

[0008] Furthermore, the material of the substrate is silicon; the material of the metal reflective layer is metal aluminum with a thickness of 40nm; the thickness of the intermediate dielectric layer is 30nm; the material of the metal array is gold with a thickness of 30nm; and the thickness of the graphene layer is 0.34nm.

[0009] Furthermore, when the device is to achieve single-wavelength absorption, the metal array of the unit structure of the device is composed of two identical gold rectangles, the width of the unit structure is 450nm, the length is 420nm, the width of the gold rectangle is 40nm, the length is 140nm, and the distance between the two gold rectangles is 70nm.

[0010] Furthermore, under a light source of 800nm-1600nm, the device can achieve an absorption rate of 99% at 1123nm; by changing the length of the gold cuboid, the absorption peak frequency of the device will change, while the absorption rate remains unchanged.

[0011] Furthermore, when the device is to achieve multi-wavelength absorption, the metal array of the unit structure of the device is composed of two different arrangements of gold cuboids, the width of the unit structure is 450nm, and the length is 420nm. One of the gold cuboids has a width of 40nm and a length of 120nm, and the other gold cuboid has a width of 40nm and a length of 140nm. The spacing between the two gold cuboids is 70nm, that is, the length of one of the gold cuboids is reduced by 20nm, and the other parameters remain unchanged, forming a metal array with an asymmetric structure.

[0012] Furthermore, under a light source of 800nm-1600nm, the device can reach absorption peaks with absorption rates of 78% and 91% at 996nm and 1109nm, respectively; by changing the reduced length of the gold cuboid, the absorption peak frequency with a lower absorption rate of the device will change.

[0013] Furthermore, when the device is to achieve broadband absorption, the metal array of the unit structure of the device is composed of four gold rectangles. The width of the unit structure is 400nm and the length is 400nm. The width of the gold rectangles is 180nm. The length of the upper left gold rectangle is 140nm, the length of the lower left gold rectangle is 110nm, the length of the upper right gold rectangle is 120nm, and the length of the lower right gold rectangle is 130nm.

[0014] Furthermore, under a light source of 800nm-1600nm, the device can achieve a broadband absorption with an absorption rate of more than 60% from 844nm to 1130nm, with an absorption rate of 78% at 1013nm.

[0015] Furthermore, in order to make the device tunable, a graphene layer is set on the top of the metal array of the unit structure. The graphene conductivity is changed by changing the graphene Fermi level, thereby changing the overall equivalent conductivity of the device to achieve the tuning function; when the graphene Fermi level is 0.7eV, the device can achieve a bandwidth absorption rate of more than 65% from 888nm to 1146nm; when the graphene Fermi level is 1.6eV, the device can achieve an absorption rate of 80% from 1097nm to 1254nm When the Fermi level of graphene is 1.9 eV, the device can achieve a broadband absorption with an absorption rate of more than 80% from 1133 nm to 1294 nm, and an absorption rate of 91% at 1230 nm; when the Fermi level of graphene is 2.3 eV, the device can achieve a broadband absorption with an absorption rate of more than 80% from 1178 nm to 1347 nm, and an absorption rate of 94% at 1282 nm.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a tunable metasurface absorber based on gallium oxide and graphene to solve the problems that the traditional metasurface absorber cannot be actively modulated, gallium oxide is rarely used in other light wavelengths, and graphene devices have limited modulation effects in the near-infrared. The present invention has a novel structure. By constructing a MIM structure and using different top metal array structures, single-wavelength absorption, multi-peak absorption, and broadband absorption are achieved at 800nm-1600nm. At the same time, a phase change material, graphene, is integrated on the top of the device. By changing the Fermi level to adjust the overall conductivity of the device, tunable broadband absorption is achieved, and the modulation range can reach 334.17nm. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 Schematic diagram of the structure of a tunable metasurface absorber based on gallium oxide and graphene in Example 1 of the present invention (the metal array of the unit structure is composed of two identical gold cuboids, and graphene has not yet been integrated on the top of the unit structure); wherein: (a) is a schematic diagram of the overall structure of the device, (b) is a schematic diagram of the unit structure, and (c) is a top view of the unit structure; Figure 2 The absorption spectra of the tunable metasurface absorber based on gallium oxide and graphene in Example 1 of the present invention (the metal array of the unit structure is composed of two identical gold cuboids, and graphene has not yet been integrated on the top of the unit structure) at different gold cuboid lengths; Figure 3 Schematic diagram of the structure of a tunable metasurface absorber based on gallium oxide and graphene in Embodiment 2 of the present invention (the metal array of the unit structure is composed of two different gold cuboids, and graphene has not yet been integrated on the top of the unit structure); wherein: (a) is a schematic diagram of the unit structure, and (b) is a top view of the unit structure; Figure 4 The absorption spectra of the tunable metasurface absorber based on gallium oxide and graphene in the second embodiment of the present invention (the metal array of the unit structure is composed of two different gold cuboids, and graphene has not yet been integrated on the top of the unit structure) at different reduced lengths of the gold cuboids; Figure 5 Schematic diagram of the structure of a tunable metasurface absorber based on gallium oxide and graphene in Example 3 of the present invention (the metal array of the unit structure is composed of four gold cuboids, and graphene has not yet been integrated on the top of the unit structure); wherein: (a) is a schematic diagram of the unit structure, and (b) is a top view of the unit structure; Figure 6 The broadband absorption spectrum of the tunable metasurface absorber based on gallium oxide and graphene in Example 3 of the present invention (the metal array of the unit structure is composed of four gold cuboids, and graphene has not yet been integrated on the top of the unit structure); Figure 7 This is a schematic structural diagram of a tunable metasurface absorber based on gallium oxide and graphene in Embodiment 4 of the present invention (the metal array of the unit structure is composed of four gold cuboids, and graphene is integrated on the top of the unit structure); Figure 8 This is the absorption spectrum of the tunable metasurface absorber based on gallium oxide and graphene in Example 4 of the present invention (the metal array of the unit structure is composed of four gold cuboids, and graphene is integrated on the top of the unit structure) at different graphene Fermi levels.

[0018] In the figure: W: width of the gold cuboid; L: length of the gold cuboid; g: spacing between the gold cuboids; Px: period width of the unit structure; Py: period length of the unit structure; td: thickness of the intermediate dielectric layer; tAl: thickness of the metal reflective layer; tAu: thickness of the metal array; d: reduced length of the gold cuboid. DETAILED DESCRIPTION

[0019] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0020] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0021] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0022] like Figure 1 As shown, this embodiment provides a tunable metasurface absorber based on gallium oxide and graphene. The device consists of a periodic array of multiple unit structures. The unit structure includes a substrate, a metal reflective layer, an intermediate dielectric layer, a metal array and a graphene layer arranged in sequence from bottom to top. The material of the intermediate dielectric layer is gallium oxide. The metal arrays have the same thickness, and the structural parameters are changed and set according to different functions.

[0023] Among them, the material of the substrate is silicon material; the material of the metal reflective layer is metal aluminum, and the thickness tAl is 40nm; the material of the intermediate dielectric layer is gallium oxide, and the thickness td is 30nm; the material of the metal array is gold, and the thickness tAu is 30nm; the thickness of the graphene layer is 0.34nm.

[0024] like Figure 1 As shown in the figure, when the device needs to achieve single-wavelength absorption, the metal array of the device periodic unit structure is composed of two identical gold cuboids, and the width of the unit structure is 450nm and the length is 420nm. The metal array is a symmetrical structure, the width of the gold cuboid is 40nm, the length is 140nm, and the distance between the two gold cuboids is 70nm. Under the light source of 800nm-1600nm, the device has an absorption peak with an absorption rate of 99% at 1123nm, achieving near-perfect absorption. This is due to the formation of electric dipole resonance between the top metal array and the bottom metal reflective layer. The top metal array and the bottom reflective metal layer form a pair of anti-parallel induced currents. Due to this pair of currents with opposite vectors, the intermediate dielectric layer forms a strong magnetic response. Due to the phase difference of π, the reflection in the far field will be eliminated by the interference of the two electric dipoles. Therefore, the strong absorption is attributed to these local magnetic dipole and electric dipole resonances. The energy absorbed by the absorber is mainly concentrated in the metal part, which is converted into heat through the ohmic loss generated by the metal. By changing the length of the gold cuboid (120nm-180nm), the absorption peak frequency of the device can be changed in the range of 1009nm to 1349nm (the longer the length, the greater the absorption peak frequency), while the absorption rate remains unchanged, such as Figure 2As shown, this is because under the action of the incident electromagnetic wave, the metal on the metasurface forms an induced current under dipole resonance, so they can be equivalent to inductors. The gap between the metal structures will accumulate a large amount of charge on both sides due to the action of the current, which can be equivalent to a capacitor. The entire metasurface device can be equivalent to an LC circuit. With the increase of the length of the Au rod, the equivalent inductance of the top metal array in the equivalent circuit model gradually increases. Since the resonant frequency is proportional to the inductance, the resonant frequency increases, the absorption curve gradually redshifts, and the increase of the equivalent inductance L leads to an increase in the electric dipole moment, a longer electron propagation path, an enhanced free oscillation effect of the Au rod, and a redshift in the spectrum.

[0025] like Figure 3 As shown in FIG. 1 , when the device needs to achieve multi-wavelength absorption, the metal array of the unit structure of the device is composed of two different arrangements of gold cuboids. The width of the unit structure is 450nm and the length is 420nm. One of the gold cuboids has a width of 40nm and a length of 120nm. The width of the other gold cuboid is 40nm and the length is 140nm. The distance between the two gold cuboids is 70nm. That is, the length of one of the gold cuboids in the unit structure is reduced (reduced by 20nm), and other parameters remain unchanged, forming an asymmetric metal array. Figure 4 As shown in the figure, under the light source of 800nm-1600nm, the device has absorption peaks with absorption rates of 78% and 91% at 996nm and 1109nm respectively. This is because as the symmetry of the structure is broken, a non-uniform electromagnetic field appears, creating an effective coupling path for the bright film that can directly couple with the incident light field and the dark film that cannot couple with the incident light field, Fano resonance is excited, and the asymmetric structure produces strong coupling; from the equivalent circuit model, the destruction of symmetry makes the distribution of capacitance and inductance in the equivalent LC circuit of the resonant cavity no longer uniform, so two resonance peaks with different frequencies appear. As the length d increases, the asymmetry is greatly increased, the broadening of the spectrum line is also continuously increased, and the modulation depth of the middle U-shaped spectrum line is gradually increased, indicating that the absorption of the stray frequency is less, and the resonance frequency appears blue shifted with the increase of asymmetry. This is because the reduction of the material size reduces the capacitance and inductance that determine the peak, and the resonance frequency will decrease.

[0026] like Figure 5 As shown in FIG. 1 , when the device needs to achieve broadband absorption, the metal array of the device periodic unit structure is composed of four gold cuboids arranged in an array, the width of the unit structure is 400nm, the length is 400nm, the width of the gold cuboid is 180nm, the length of the upper left cuboid is 140nm, the length of the lower left cuboid is 110nm, the length of the upper right cuboid is 120nm, and the length of the lower right cuboid is 130nm, constructing an asymmetric array structure. Figure 6As shown in the figure, under the light source of 800nm-1600nm, the device can achieve an absorption rate of more than 60% from 844nm to 1130nm, forming broadband absorption, and the absorption rate can reach 78% at 1013nm. This is because the asymmetric structure produces a multi-peak absorption phenomenon. If the frequencies of these peaks are close enough, they can overlap, thus widening the absorption spectrum and achieving broadband absorption.

[0027] like Figure 7 As shown in the figure, when the device needs to achieve tunable bandwidth absorption, based on the periodic unit structure of the bandwidth absorption device, graphene is added on the top of the device, and the conductivity of graphene is changed by changing the Fermi level of graphene, resulting in changes in the overall equivalent impedance of the device and the resonant frequency. The real part of the graphene conductivity is in μ c =0.7-2.3eV, while the imaginary part increases significantly with the increase of Fermi level; Figure 8 As shown, when the Fermi level of graphene is 0.7eV, the device achieves a broadband absorption rate of more than 65% at 888nm to 1146nm; when the Fermi level of graphene is 1.6eV, the device achieves a broadband absorption rate of more than 80% at 1097nm to 1254nm, and the absorption rate can reach 88% at 1202nm; when the Fermi level of graphene is 1.9eV, the device can achieve a broadband absorption rate of more than 80% at 1133nm to 1294nm, and the absorption rate can reach 91% at 1230nm; when the Fermi level of graphene is 2.3eV, the device can achieve a broadband absorption rate of more than 80% at 1178nm to 1347nm, and the absorption rate can reach 94% at 1282nm. Compared with the absorption spectrum without graphene layer, the bandwidth frequency is red-shifted by 334nm; similar to the structure without graphene, the enhanced magnetic field is confined to the dielectric, and the electric field vectors of the top and bottom metals form a closed current loop, causing a strong dipole resonance. Not only does the device metal participate in the energy absorption of the asymmetric structure device containing graphene, but the energy absorption of the top graphene layer is also very significant, where the metal absorption energy is lower than that of the asymmetric structure device without graphene.

[0028] In this embodiment, the method for preparing the tunable metasurface absorber based on gallium oxide and graphene comprises the following steps: S1: Electron beam evaporation is used to deposit an aluminum (Al) layer on a silicon substrate as a metal reflective layer.

[0029] S2: A gallium oxide (Ga2O3) layer is deposited on the aluminum layer using atomic layer deposition as an intermediate dielectric layer.

[0030] S3: Spin-coat two layers of electron beam resist on the gallium oxide layer, one layer of polymethyl methacrylate and another layer of methyl methacrylate on top of it.

[0031] S4: On top of the resist, a very thin layer of chromium (Cr) is deposited as a charge dissipation layer.

[0032] S5: Patterning the double layer resist using electron beam lithography.

[0033] S6: After patterning, the sample is developed in a solution containing 1 part methyl isobutyl ketone and 3 parts isopropyl alcohol at low temperature to remove the exposed resist.

[0034] S7: Deposit a gold (Au) layer using thermal evaporation.

[0035] S8: Stripping was performed by soaking the sample in hot acetone for 12 hours, followed by rinsing with acetone and IPA.

[0036] S9: Using the CVD graphene sample on copper foil (covering both sides), cut a small piece, large enough to cover the entire area where the device is to be fabricated, and place it on a glass slide. Then place a drop of water on the glass slide to fix the small piece in its original position. We then spin-coat a layer of 950 K A4 PMMA on top of the graphene piece (at 2500 rpm for 1 min) to protect the graphene layer on this side from the following processing steps. The small piece is then flipped over to reveal the bare graphene side of the copper foil. This small piece is fixed to the glass slide by taping it on all four sides with Kapton tape.

[0037] S10: The glass slide is placed in an oxygen (O2) plasma chamber for 15 minutes in order to etch the graphene away from this side of the copper foil.

[0038] S11: Remove the graphene covered copper foil (now on one side) and cut off the four edges of the foil. Put the graphene covered copper foil into copper etchant to separate the graphene and copper foil.

[0039] S12: Use a small piece of wafer to scoop out the floating graphene sheet from the etchant and place it in deionized water to remove all the copper etchant.

[0040] S13: Scoop out the graphene sample from the deionized water and transfer it to the device. We then blow gently with a nitrogen (N2) gun to remove any water droplets under the graphene and let it dry on its own for 24 hours. After that, put the sample in acetone for 5 minutes and then rinse with acetone and IPA to remove all PMMA on top. Then use a nitrogen gun to blow dry the sample.

[0041] S14: Ti (10 nm) and Au (40 nm) were evaporated and deposited onto the graphene sample in vacuum through a template mask for source, drain, and gate.

[0042] S15: Preparation of PEO electrolyte. In a glove box, polyethylene oxide (PEO, Mw = 600000, ACROSORGANICS) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI, Aladdin 99%) were placed in a blue-capped bottle at an oxygen-lithium ratio of EO:Li=18:1, and an appropriate amount of acetonitrile (Innochem, 99.9%) was added to make the polymer concentration 50 mg / mL. The mixture was sealed in a blue-capped bottle and heated and stirred at 55°C for 12 hours until a uniform solution was formed. The resulting slurry was then transferred to a stirring tank and stirred at 1500 rpm in a revolution and rotation stirrer in a defoaming mode for 10 minutes to obtain a bubble-free solution. It was cast onto the device in a glove box and spin dried for 12 hours to form a film, and dried at 55°C for 24 hours under vacuum conditions to completely remove the acetonitrile solvent.

[0043] S16: Apply different voltages V to the electrolyte gate eg , immediately cool the sample (< 1 min) to below 250 K to avoid electrochemically induced sample degradation. At this temperature, Li+ and The ions are "frozen" out and no longer move in the electrolyte, pinning the charge accumulated in the Debye layer to the graphene surface. The induced charge carrier density does not change significantly with time and temperature until the sample is warmed up again.

[0044] The operation methods of electron beam evaporation, atomic layer deposition, electron beam lithography, thermal evaporation deposition, etc. in this embodiment are all existing technologies and will not be described in detail here.

[0045] The above is only a preferred embodiment of the present invention, and does not limit the present invention in other forms. Any technician familiar with the profession may use the above disclosed technical content to change or modify it into an equivalent embodiment with equivalent changes. However, any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention without departing from the technical solution of the present invention still belongs to the protection scope of the technical solution of the present invention.

Claims

1. A tunable metasurface absorber based on gallium oxide and graphene, characterized in that: The device is composed of a periodic array of multiple unit structures, wherein the unit structure includes a substrate, a metal reflective layer, an intermediate dielectric layer, a metal array and a graphene layer arranged in sequence from bottom to top. The material of the intermediate dielectric layer is gallium oxide. The metal array has the same thickness, and the structural parameters are set according to different functions.

2. The tunable metasurface absorber based on gallium oxide and graphene according to claim 1, characterized in that: The material of the substrate is silicon; the material of the metal reflective layer is metal aluminum with a thickness of 40nm; the thickness of the intermediate dielectric layer is 30nm; the material of the metal array is gold with a thickness of 30nm; and the thickness of the graphene layer is 0.34nm.

3. The tunable metasurface absorber based on gallium oxide and graphene according to claim 1, characterized in that: When the device is to achieve single-wavelength absorption, the metal array of the device's unit structure is composed of two identical gold cuboids. The width of the unit structure is 450nm and the length is 420nm. The width of the gold cuboid is 40nm and the length is 140nm. The distance between the two gold cuboids is 70nm.

4. The tunable metasurface absorber based on gallium oxide and graphene according to claim 3, characterized in that: Under a light source of 800nm-1600nm, the device can achieve an absorption rate of 99% at 1123nm; by changing the length of the gold cuboid, the absorption peak frequency of the device will change, while the absorption rate remains unchanged.

5. The tunable metasurface absorber based on gallium oxide and graphene according to claim 1, characterized in that: When the device is to achieve multi-wavelength absorption, the metal array of the device's unit structure is composed of two different arrangements of gold cuboids. The width of the unit structure is 450nm and the length is 420nm. One of the gold cuboids has a width of 40nm and a length of 120nm, and the other gold cuboid has a width of 40nm and a length of 140nm. The spacing between the two gold cuboids is 70nm, that is, the length of one of the gold cuboids is reduced by 20nm, and the other parameters remain unchanged, forming a metal array with an asymmetric structure.

6. The tunable metasurface absorber based on gallium oxide and graphene according to claim 5, characterized in that: Under a light source of 800nm-1600nm, the device can reach absorption peaks with absorption rates of 78% and 91% at 996nm and 1109nm respectively; by changing the reduced length of the gold cuboid, the absorption peak frequency with a lower absorption rate of the device will change.

7. The tunable metasurface absorber based on gallium oxide and graphene according to claim 1, characterized in that: When the device is to achieve broadband absorption, the metal array of the device's unit structure is composed of four gold rectangles. The width of the unit structure is 400nm and the length is 400nm. The width of the gold rectangles is 180nm. The length of the upper left gold rectangle is 140nm, the length of the lower left gold rectangle is 110nm, the length of the upper right gold rectangle is 120nm, and the length of the lower right gold rectangle is 130nm.

8. The tunable metasurface absorber based on gallium oxide and graphene according to claim 7, characterized in that: Under a light source of 800nm-1600nm, the device can achieve a broadband absorption with an absorption rate of more than 60% from 844nm to 1130nm, and an absorption rate of 78% at 1013nm.

9. The tunable metasurface absorber based on gallium oxide and graphene according to claim 1, characterized in that: In order to make the device tunable, a graphene layer is set on the top of the metal array of the unit structure. The graphene conductivity is changed by changing the graphene Fermi level, thereby changing the overall equivalent conductivity of the device to achieve the tuning function; when the graphene Fermi level is 0.7eV, the device can achieve a bandwidth absorption rate of more than 65% from 888nm to 1146nm; when the graphene Fermi level is 1.6eV, the device can achieve an absorption rate of more than 80% from 1097nm to 1254nm Broadband absorption, with an absorption rate of 88% at 1202nm; when the Fermi level of graphene is 1.9eV, the device can achieve broadband absorption with an absorption rate of more than 80% at 1133nm to 1294nm, and an absorption rate of 91% at 1230nm; when the Fermi level of graphene is 2.3eV, the device can achieve broadband absorption with an absorption rate of more than 80% at 1178nm to 1347nm, and an absorption rate of 94% at 1282nm.

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