A multi-layer heterojunction based near-infrared perfect absorber

Abstract

The application relates to a near-infrared perfect absorber based on a multilayer heterojunction, which comprises periodically and alternately stacked two-dimensional semiconductor layers and low-loss medium spacing layers; wherein the dielectric loss tangent of the low-loss medium is less than 0.005 in the near-infrared wave band, and the extinction coefficient is less than 0.001; the thickness of the single-layer two-dimensional semiconductor layer and the thickness of the single-layer low-loss medium spacing layer are both less than one tenth of the working wavelength. The application adopts periodically and alternately stacked two-dimensional semiconductor layers and low-loss medium spacing layers; based on the structure, the application can realize wide-angle and polarization-insensitive perfect absorption in the near-infrared wave band by adjusting the number of layers of the two-dimensional semiconductor layers and the chemical potential of the two-dimensional semiconductor layers; in addition, the application adopts low-loss medium instead of noble metal, avoids the ohmic loss of the noble metal, and significantly reduces the performance attenuation at room temperature.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic wave absorption, specifically relating to a near-infrared perfect absorber based on a multilayer heterojunction. Background Technology

[0002] Achieving perfect light absorption in the near-infrared band is crucial for thermal imaging, photoelectric detection, and optical camouflage. This requires simultaneously satisfying two key conditions: impedance matching and efficient dissipation. Surface plasmon resonance (SPR) has become a core physical mechanism for absorber design due to its ability to enhance light localization beyond the diffraction limit. However, traditional SPR excitation relies on noble metals (such as gold and silver), which have high intrinsic losses in the near-infrared band, limiting absorption efficiency. While emerging two-dimensional materials (such as graphene) possess tunable optical properties, their monolayer absorptivity is only 2.3%, and their short carrier relaxation time results in low hot electron collection efficiency.

[0003] Recent research has used effective dielectric theory to homogenize multilayer structures into anisotropic media, providing a new approach for impedance matching design. Existing solutions mainly include the following: First, microcavity-enhanced absorbers, which use distributed Bragg reflectors to form a Fabry-Perot cavity, embedding monolayer graphene in the cavity field enhancement region to achieve 60% absorption using interference effects. However, their operating bandwidth is only 20 nm, and the absorption rate decreases by more than 40% when the angle exceeds 15°. Second, plasmonic metamaterial absorbers, such as gold nanorod arrays stacked with dielectric layers, achieve over 90% absorption through magnetic resonance coupling. However, this relies on costly focused ion beam etching processes, and metal loss leads to significant thermal quenching at room temperature. Third, grating-coupled broadband absorbers, such as those using distributed Bragg reflector gratings (DBRs) (e.g., SiO2 / TiO2 periodic stacks) to achieve static absorption in the ultraviolet band (240–370 nm), but they lack dynamic tuning capabilities and are limited by precision photolithography processes.

[0004] These solutions generally suffer from three major drawbacks: First, the narrow-band characteristics (resonance peak half-width < 0.05 μm) of traditional microcavity and plasma structures make it difficult to meet the bandwidth requirements (> 0.1 μm) of multi-band applications (such as multicolor thermal imaging); second, the fabrication is highly complex, for example, plasma gratings require subwavelength groove etching, which has a low success rate and heterogeneous interface defects lead to scattering losses; third, ohmic losses in metal-based structures increase at room temperature, with absorption rates decreasing by more than 30%, while cryogenic cooling solutions significantly increase system complexity. Furthermore, traditional metallic materials (such as gold and silver) rely on localized surface plasmon resonance, exhibiting high angle sensitivity. When the incident angle exceeds 30°, the absorption rate drops sharply by more than 50%. Although plasma gratings can extend bandwidth to 18-70 μm, their reliance on fixed geometric parameters results in a lack of dynamic tuning capability and significant polarization dependence, severely limiting practical application performance. Summary of the Invention

[0005] To address the aforementioned problems in the prior art, this invention provides a near-infrared perfect absorber based on a multilayer heterojunction. The technical problem to be solved by this invention is achieved through the following technical solution:

[0006] A near-infrared perfect absorber based on a multilayer heterojunction includes: a two-dimensional semiconductor layer and a low-loss dielectric spacer layer that are periodically and alternately stacked.

[0007] The dielectric loss tangent of the low-loss medium is less than 0.005 in the near-infrared band (0.75μm-3μm), and the extinction coefficient is less than 0.001.

[0008] The thickness of the single-layer two-dimensional semiconductor layer and the thickness of the single-layer low-loss dielectric spacer layer are both less than one-tenth of the operating wavelength.

[0009] Optionally, the two-dimensional semiconductor layer is made of graphene or MoS2 and has a thickness of 0.35 nm.

[0010] Optionally, the low-loss dielectric spacer layer is made of lithium fluoride, SiO2, or MgF2.

[0011] Optionally, the thickness of the low-loss dielectric spacer layer ranges from 20 nm to 60 nm.

[0012] Optionally, the chemical potential of the two-dimensional semiconductor layer can be modulated by external gate voltage, chemical doping, or photocarrier injection.

[0013] Optionally, the absorption bandwidth of the absorber is extended by adjusting the number of layers in the two-dimensional semiconductor layer.

[0014] Optionally, the absorber can be used in near-infrared photodetectors, multispectral thermal imagers, and dynamic optical camouflage systems.

[0015] Optionally, the two-dimensional semiconductor layer is prepared by chemical vapor deposition, and the low-loss dielectric spacer layer is prepared by magnetron sputtering deposition.

[0016] This invention proposes a near-infrared perfect absorber based on a multilayer heterojunction, comprising periodically alternating stacked two-dimensional semiconductor layers and a low-loss dielectric spacer layer. Based on this structure, this invention can achieve wide-angle and polarization-insensitive perfect absorption in the near-infrared band by controlling the number of two-dimensional semiconductor layers and their chemical potential. Specifically, firstly, this invention can adjust the conductivity of a two-dimensional semiconductor layer by real-time control of its chemical potential, thus dynamically optimizing absorption characteristics without complex peripherals. Secondly, by increasing the number of two-dimensional semiconductor layers, the overall conductivity is improved, promoting surface plasmon resonance mode hybridization. Simultaneously, the multi-layer periodic stacked structure enhances the interference effect, synergistically broadening the absorption bandwidth to meet the requirements of multispectral applications. Furthermore, the thickness of both the single-layer two-dimensional semiconductor layer and the single-layer low-loss dielectric spacer layer in this invention is less than one-tenth of the operating wavelength. This means that the invention employs subwavelength stacking to satisfy the effective dielectric theory. The equivalent anisotropic dielectric tensor makes the structural equivalent impedance approach free-space impedance over a wide angular range, significantly reducing reflection and overcoming the angle dependence of the plasmon structure. Moreover, this invention simultaneously supports transverse magnetic polarization (dependent on anisotropic dielectric tensor excitation of surface plasmon resonance) and transverse electric polarization (dependent on waveguide modes and multi-layer interference effects), achieving perfect dual-polarization absorption. Additionally, this invention uses a low-loss dielectric instead of noble metals, avoiding the ohmic losses of noble metals and significantly reducing performance degradation at room temperature. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of a near-infrared perfect absorber based on a multilayer heterojunction provided in an embodiment of the present invention, wherein the material of the two-dimensional semiconductor layer is graphene and the material of the low-loss dielectric layer is lithium fluoride.

[0018] Figure 2 Subgraph (a) in the figure shows the experimental results of the real part of the effective dielectric constant of a near-infrared perfect absorber based on a multilayer heterojunction as a function of wavelength under different chemical potentials, provided by an embodiment of the present invention.

[0019] Figure 2 Subgraph (b) in the present invention provides experimental results showing the variation of the imaginary part of the effective dielectric constant of a near-infrared perfect absorber based on a multilayer heterojunction with wavelength under different chemical potentials.

[0020] Figure 3 Subgraph (a) in the figure shows the dispersion relation of the real part of the surface plasmon polariton wave vector of a near-infrared perfect absorber based on a multilayer heterojunction provided in the embodiment of the present invention under different chemical potentials;

[0021] Figure 3 Subgraph (b) in the present invention shows the loss characteristics of the imaginary part of the surface plasmon polariton wave vector of a near-infrared perfect absorber based on a multilayer heterojunction under different chemical potentials.

[0022] Figure 4 This invention provides a near-infrared perfect absorber based on a multilayer heterojunction with TM / TE polarization absorption spectra at different chemical potentials.

[0023] Figure 5 This invention provides a near-infrared perfect absorber based on a multilayer heterojunction with TM / TE polarization absorption spectra at different numbers of two-dimensional semiconductor layers. Detailed Implementation

[0024] To further illustrate the technical means and effects adopted by the present invention to achieve the intended purpose, the following detailed description of a near-infrared perfect absorber based on a multilayer heterojunction, in conjunction with the accompanying drawings and specific embodiments, is provided.

[0025] The foregoing and other technical contents, features, and effects of the present invention will be clearly presented in the following detailed description of specific embodiments in conjunction with the accompanying drawings. Through the description of the specific embodiments, a more in-depth and concrete understanding can be gained of the technical means and effects adopted by the present invention to achieve its intended purpose. However, the accompanying drawings are for reference and illustration only and are not intended to limit the technical solutions of the present invention.

[0026] Example 1

[0027] This embodiment provides a near-infrared perfect absorber based on a multilayer heterojunction, comprising periodically alternating stacked two-dimensional semiconductor layers and low-loss dielectric spacers. The low-loss dielectric has a dielectric loss tangent of less than 0.005 in the near-infrared band (0.75 μm - 3 μm) and an extinction coefficient of less than 0.001. The thickness of both the single-layer two-dimensional semiconductor layer and the single-layer low-loss dielectric spacer is less than one-tenth of the operating wavelength.

[0028] In one alternative implementation, the two-dimensional semiconductor layer is made of graphene or MoS2 with a thickness of 0.35 nm.

[0029] In one alternative implementation, the low-loss dielectric spacer layer is made of lithium fluoride, SiO2, or MgF2.

[0030] In one alternative implementation, the thickness of the low-loss dielectric spacer layer ranges from 20 nm to 60 nm.

[0031] Specifically, when the thickness of the low-loss dielectric spacer varies within a range, it is still necessary to satisfy the condition that the thickness of both the single-layer two-dimensional semiconductor layer and the single-layer low-loss dielectric spacer are less than one-tenth of the operating wavelength. In this case, high absorption can be achieved by optimizing optical phase matching (such as constructing a gradient refractive index metasurface or a Fabry-Perot resonator).

[0032] In one alternative implementation, the chemical potential of the two-dimensional semiconductor layer can be modulated by external gate voltage, chemical doping, or photocarrier injection.

[0033] Here, based on the fundamental principle of carrier modulation in two-dimensional semiconductor materials, absorption peaks can be dynamically switched through chemical doping or photocarrier injection, thereby enabling the modulation of chemical potential.

[0034] In one alternative implementation, the absorption bandwidth of the absorber is extended by adjusting the number of layers in the two-dimensional semiconductor layer.

[0035] For example, the number of layers in a two-dimensional semiconductor layer can be selected from 3 to 10.

[0036] In one alternative implementation, the absorber supports applications in near-infrared photodetectors, multispectral thermal imagers, and dynamic optical camouflage systems.

[0037] In one alternative implementation, the two-dimensional semiconductor layer is prepared by chemical vapor deposition, and the low-loss dielectric spacer layer is prepared by magnetron sputtering deposition.

[0038] Specifically, a two-dimensional semiconductor layer is prepared by chemical vapor deposition, a low-loss dielectric spacer layer is prepared by magnetron sputtering deposition, and the desired number of low-loss dielectric spacers and two-dimensional semiconductor layers are prepared by alternating stacking, without the need for photolithography and etching processes.

[0039] Example 2

[0040] This embodiment provides a near-infrared perfect absorber based on a multilayer heterojunction, comprising periodically alternating stacked MoS2 layers (two-dimensional semiconductor layers) and MgF2 spacer layers. The number of MoS2 layers is 10, with a single MoS2 layer thickness of 0.35 nm. The MgF2 spacer layer has a thickness of 60 nm and a relative permittivity of 1.9-2.1. There are no gaps between the MoS2 layers and the MgF2 spacer layers. The thickness of both a single MoS2 layer and a single MgF2 spacer layer is less than one-tenth of the operating wavelength. Furthermore, MoS2 is chemically doped with KClO4 solution to alter its carrier density and achieve chemical potential modulation.

[0041] Example 3

[0042] This embodiment provides a near-infrared perfect absorber based on a multilayer heterojunction, comprising periodically alternating stacked graphene layers (two-dimensional semiconductor layers) and SiO2 spacer layers. The graphene layers consist of three layers, each with a thickness of 0.35 nm. The SiO2 spacer layers are 20 nm thick and have a relative permittivity of 1.9-2.1. There are no gaps between the graphene layers and the SiO2 spacer layers. The thickness of both the single-layer graphene layer and the single-layer SiO2 spacer layer is less than one-tenth of the operating wavelength. Furthermore, the chemical potential of the graphene layers is modulated using photocarrier injection, maintaining it between 0.1-0.9 eV. Specifically, ultraviolet light irradiation of the graphene layer excites electron-hole pairs, causing hole accumulation and increasing the chemical potential. The chemical potential recovers when the light source is turned off, thus achieving dynamic adjustment of the chemical potential.

[0043] Example 4

[0044] Please see Figure 1 The near-infrared perfect absorber based on a multilayer heterojunction provided in this embodiment includes periodically alternating stacked graphene layers (two-dimensional semiconductor layers) and lithium fluoride spacers. The graphene layers consist of 7 layers, with a single graphene layer thickness of 0.35 nm. The lithium fluoride spacers have a thickness of 40 nm and a relative permittivity of 2.2. There are no gaps between the graphene layers and the lithium fluoride spacers. The thickness of both the single graphene layer and the single lithium fluoride spacer is less than one-tenth of the operating wavelength.

[0045] In this embodiment, the chemical potential of the graphene layer is controlled by an external gate voltage. Specifically, an ITO electrode is deposited on top of the periodic structure, and a 20 nm Al2O3 gate dielectric layer is placed below it. A positive voltage is applied to the electrode, and the chemical potential of the graphene layer is controlled by adjusting the magnitude of the applied voltage, so that its chemical potential range is between 0.1 and 0.9 eV.

[0046] Lithium fluoride (LiF) exhibits low loss characteristics, with a dielectric loss tangent of less than 0.001. Replacing noble metals with LiF avoids the ohmic losses of noble metals, reduces performance degradation at room temperature, and achieves 100 hours of continuous operation at room temperature without performance degradation. Furthermore, the alternating stacking of LiF and graphene forms a periodic heterojunction. The thickness of both the single graphene layer and the single LiF spacer layer is less than one-tenth of the operating wavelength. This subwavelength design allows the periodic heterostructure to meet the theoretical conditions for an effective dielectric. Moreover, the interference effect in the graphene-LiF multilayer structure further enhances the light-matter interaction, while the layered structure maintains compatibility with scalable manufacturing methods. This makes this composite structure a strong contender for future reconfigurable terahertz (THz) and infrared optoelectronic devices. Additionally, the absorber uses chemical vapor deposition to prepare the graphene layer and magnetron sputtering to prepare the LiF spacer layer, simplifying the fabrication process and eliminating the need for photolithography or etching.

[0047] Example 5

[0048] This embodiment provides a near-infrared perfect absorber based on a multilayer heterojunction, comprising periodically alternating stacked graphene layers and lithium fluoride spacers. The graphene layers consist of five layers, each with a thickness of 0.35 nm. The lithium fluoride spacers have a thickness of 40 nm and a relative permittivity of 2.2. The thickness of both the single-layer graphene layer and the single-layer lithium fluoride spacer is less than one-tenth of the operating wavelength.

[0049] In this fifth embodiment, the chemical potential of the graphene layer is also controlled by an external gate voltage, so that the chemical potential of the graphene layer is 0.1-0.9 eV. For the specific control method, please refer to the fourth embodiment.

[0050] Furthermore, based on Example 5, the beneficial effects of the present invention in achieving wide-angle and polarization-insensitive perfect absorption in the near-infrared band by controlling the number of layers and the chemical potential of the two-dimensional semiconductor layer will be explained.

[0051] First, the variation of the effective dielectric constant of the near-infrared perfect absorber with wavelength under different chemical potentials was analyzed through simulation. The parameter settings were consistent with those in Example 5. See [link to example]. Figure 2 , Figure 2 Subplot (a) shows the experimental results of the effective real part of the dielectric constant of the near-infrared perfect absorber as a function of wavelength at different chemical potentials. The horizontal axis represents wavelength (micrometers), and the vertical axis represents the effective real part of the dielectric constant. Different colored curves correspond to different chemical potentials. .like Figure 2 As shown in subfigure (a), when the wavelength starts from 0.5 μm, the initial values ​​of the parallel component (solid line) and perpendicular component (dashed line) of the real part of the effective dielectric constant are between 0 and 5. As the wavelength increases, the curve of the real part of the effective dielectric constant first rises to a peak value and then turns negative. This characteristic of the real part of the effective dielectric constant turning from positive to negative indicates the onset of hyperbolic dispersion, indicating that the present invention can support high momentum light modes and provide a physical basis for perfect absorption. Figure 2 Subplot (b) shows the experimental results of the imaginary part of the effective dielectric constant of the near-infrared perfect absorber varying with wavelength at different chemical potentials, with the vertical axis representing the imaginary part of the effective dielectric constant. Figure 2 As shown in subgraph (b), with increasing wavelength, the imaginary part of the effective dielectric constant exhibits a characteristic of first increasing linearly and then decreasing sharply. Its peak position coincides with the critical point where the real part of the effective dielectric constant turns from positive to negative. This position corresponds to the region of maximum light energy dissipation. Here, the imaginary part value decreases with increasing chemical potential, indicating that the enhanced conductivity of graphene improves the dissipation efficiency.

[0052] Secondly, the variation of the surface plasmon polariton (SPP) wave vector of the near-infrared perfect absorber with wavelength under different chemical potentials was analyzed through simulation. The parameter settings were consistent with those in Example 5. See [link to example]. Figure 3 , Figure 3 Subplot (a) shows the dispersion relation of the real part of the surface plasmon wave vector of the near-infrared perfect absorber at different chemical potentials. The horizontal axis represents wavelength (micrometers), and the vertical axis represents the real part of the surface plasmon wave vector (unit: per meter). Figure 3 As shown in subfigure (a), a sharp resonance peak appears at a specific wavelength. This peak reflects the localization ability of surface plasmon polaritons. The larger the real part value, the smaller the optical field is compressed to. As the chemical potential increases, the peak blue shifts and increases, which verifies that gate voltage modulation can enhance the optical field confinement strength. Figure 3 Subplot (b) shows the loss characteristics of the imaginary part of the surface plasmon polariton wave vector of the near-infrared perfect absorber at different chemical potentials. The vertical axis represents the imaginary part of the surface plasmon polariton wave vector (unit: per meter). Figure 3 As shown in subgraph (b), the peak positions of the imaginary and real parts of the surface plasmon polariton wave vector move synchronously. Their numerical values ​​characterize the propagation loss of the surface plasmon polariton (i.e., the efficiency of light energy conversion into heat energy). When the chemical potential is 0.9 eV, the imaginary part reaches its maximum value, several times higher than when the chemical potential is 0.1 eV, demonstrating a significant enhancement in energy dissipation at high chemical potentials. Combined with… Figure 2 The phenomenon of reduced peak value of the imaginary part of the effective dielectric constant in subgraph (b) indicates that although the loss per unit distance is reduced, the strong localization effect actually improves the overall absorption efficiency.

[0053] Next, the complete absorption of the near-infrared perfect absorber under different chemical potentials was analyzed. The parameter settings were consistent with those in Example 5. See [link to example]. Figure 4 , Figure 4 The TM / TE polarization absorption spectra of the near-infrared perfect absorber at different chemical potentials are shown. The horizontal axis represents the incident angle, and the vertical axis represents the wavelength (μm). The blue area represents low reflectance (i.e., near-complete absorption), and the red area represents high reflectance and low absorption. Figure 4 Subgraphs (a), (c), and (e) in the figure are TM polarization absorption spectra. Figure 4Subgraphs (b), (d), and (f) in the figure show the TE polarization absorption spectra. Experimental results show that when the number of graphene layers is fixed at 5, the absorption center is located at 2.48 μm under a chemical potential of 0.3 eV. When the chemical potential is increased to 0.9 eV, the absorption band blue-shifts to 0.82 μm. This continuous tuning covers the infrared communication and sensing bands, breaking through the wavelength locking defect of traditional static structures. The absorption band positions of TM polarization and TE polarization are completely consistent, and the reflectivity can be maintained at less than 1% in a wide angle range of 0°-70°. This excellent performance is due to the low loss characteristics of lithium fluoride and the synergistic optimization of the anisotropic dielectric tensor, which makes the absorber of this invention highly robust to incident conditions. At the same time, the phenomenon of the absorption band narrowing with increasing chemical potential is similar to... Figure 3 The sharpening of the peak value of the mid-surface plasmon polariton wave vector corresponds to the narrowing of the resonance peak due to the enhanced field localization effect.

[0054] Finally, the complete absorption of the near-infrared perfect absorber under different numbers of two-dimensional semiconductor layers was analyzed. The parameter settings, except for the number of graphene layers, were consistent with those in Example 5, where the number of graphene layers ranged from 1 to 5. Figure 5 The TM / TE polarization absorption spectra of the near-infrared perfect absorber with different numbers of graphene layers are shown, where GL represents the number of graphene layers. Experimental results show that the number of graphene layers has a significant modulating effect on the static bandwidth. When the chemical potential is fixed at 0.5 eV, monolayer graphene (GL=1) produces only a narrow band absorption of 0.03 μm, while increasing the number of graphene layers to 5 (GL=5) can extend the bandwidth to 0.15 μm. This phenomenon is mainly due to two mechanisms: first, increasing the number of graphene layers significantly improves the overall conductivity, broadening the surface plasmon resonance dispersion curve; second, the graphene-lithium fluoride multilayer structure enhances the interference effect, effectively widening the optical response range of the resonant cavity.

[0055] In summary, this fifth embodiment achieves perfect absorption based on a light field-coordinated impedance matching and dynamic tuning mechanism. Specifically, firstly, impedance matching is achieved by the anisotropic dielectric properties of the composite material. Both the parallel and perpendicular components of the effective dielectric constant of the graphene-lithium fluoride multilayer structure can be obtained from the material thickness and its own dielectric constant. This anisotropy allows the overall impedance of the material to approximate the air impedance; therefore, when incident light enters the absorber from air, reflection loss is suppressed, and more light energy enters the material's interior. Secondly, the dynamic tuning mechanism is based on chemical potential regulation. Increasing the chemical potential enhances the conductivity of graphene and increases the real part of the interfacial electromagnetic coupling mode (see...). Figure 3 The subgraph (a) in the image causes a blue shift of the absorption peak (see subgraph (a)). Figure 4For example, the center wavelength is 2.48 μm at a chemical potential of 0.3 eV, and shifts to 0.82 μm at a chemical potential of 0.9 eV, covering the 0.82–2.48 μm range. Furthermore, the number of graphene layers provides static bandwidth tuning; with monolayer graphene, the absorption bandwidth is only 0.03 μm (see...). Figure 5 When the number of graphene layers increases to 5 (GL=5), the bandwidth expands to 0.15 μm, an improvement of 400%. Increasing the number of graphene layers enhances the overall conductivity and interference effect, and broadens the dispersion curve. This invention maintains an absorptivity >99% at incident angles of 0°-70° and under TM / TE polarization, and can operate continuously at room temperature for 100 hours without performance degradation. It is suitable for near-infrared photodetectors (such as those in the 1.55 μm communication band), multispectral thermal imagers, and dynamic optical camouflage systems.

[0056] This invention proposes a near-infrared perfect absorber based on a multilayer heterojunction, comprising periodically alternating stacked two-dimensional semiconductor layers and a low-loss dielectric spacer layer. Based on this structure, this invention can achieve wide-angle and polarization-insensitive perfect absorption in the near-infrared band by controlling the number of two-dimensional semiconductor layers and their chemical potential. Specifically, firstly, this invention can adjust the conductivity of a two-dimensional semiconductor layer by real-time control of its chemical potential, thus dynamically optimizing absorption characteristics without complex peripherals. Secondly, by increasing the number of two-dimensional semiconductor layers, the overall conductivity is improved, promoting surface plasmon resonance mode hybridization. Simultaneously, the multi-layer periodic stacked structure enhances the interference effect, synergistically broadening the absorption bandwidth to meet the requirements of multispectral applications. Furthermore, the thickness of both the single-layer two-dimensional semiconductor layer and the single-layer low-loss dielectric spacer layer in this invention is less than one-tenth of the operating wavelength. This means that the invention employs subwavelength stacking to satisfy the effective dielectric theory. The equivalent anisotropic dielectric tensor makes the structural equivalent impedance approach free-space impedance over a wide angular range, significantly reducing reflection and overcoming the angle dependence of the plasmon structure. Moreover, this invention simultaneously supports transverse magnetic polarization (dependent on anisotropic dielectric tensor excitation of surface plasmon resonance) and transverse electric polarization (dependent on waveguide modes and multi-layer interference effects), achieving perfect dual-polarization absorption. Additionally, this invention uses a low-loss dielectric instead of noble metals, avoiding the ohmic losses of noble metals and significantly reducing performance degradation at room temperature.

[0057] In the description of this invention, the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0058] In the description of this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0059] In the description of this invention, unless otherwise expressly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature being directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature being directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0060] It should be noted that the terms "first," "second," etc., are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. Rather, they are merely examples of apparatuses and methods consistent with some aspects of the invention.

[0061] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Furthermore, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.

[0062] Although the invention has been described herein in conjunction with various embodiments, those skilled in the art will understand and implement other variations of the disclosed embodiments by reviewing the accompanying drawings and the disclosure in carrying out the claimed invention. In the description of the invention, the word "comprising" does not exclude other components or steps, "a" or "an" does not exclude a plurality, and "a plurality" means two or more, unless otherwise explicitly specified. Furthermore, while different embodiments may describe certain measures, this does not mean that these measures cannot be combined to produce good results.

[0063] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A multi-layer heterojunction based near-infrared perfect absorber, characterized in that, The two-dimensional semiconductor layer and the low-loss dielectric spacer layer are periodically alternately stacked; The low-loss dielectric has a dielectric loss tangent less than 0.005 and an extinction coefficient less than 0.001 in a near-infrared waveband (0.75 μm-3 μm); The thickness of the two-dimensional semiconductor layer and the thickness of the low-loss dielectric spacer layer are both less than one-tenth of the working wavelength; The two-dimensional semiconductor layer is graphene with a thickness of 0.35 nm; The low-loss dielectric spacer layer is lithium fluoride with a thickness of 20 nm-40 nm; The composite of graphene and lithium fluoride has anisotropic dielectric properties.

2. The multi-layer heterojunction based near-infrared perfect absorber of claim 1, wherein, The chemical potential of the two-dimensional semiconductor layer is regulated by an external gate voltage, chemical doping or photo-carrier injection.

3. The multi-layer heterojunction based near-infrared perfect absorber of claim 1, wherein, The absorption bandwidth of the absorber is expanded by adjusting the number of layers of the two-dimensional semiconductor layer.

4. The multi-layer heterojunction based near-infrared perfect absorber of claim 1, wherein, The absorber supports applications in near-infrared photodetectors, multispectral thermal imagers and dynamic optical camouflage systems.

5. The multi-layer heterojunction based near-infrared perfect absorber of claim 1, wherein, The two-dimensional semiconductor layer is prepared by a chemical vapor deposition process, and the low-loss dielectric spacer layer is prepared by a magnetron sputtering deposition process.

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