Silicon-based metamaterial with enhanced absorption in near-infrared band

Abstract

The application discloses a silicon-based metamaterial with enhanced absorption in a near-infrared wave band, which is formed by arranging equal-thickness silicon material layers, each of which contains a silicon base doped with nano gold particles, and the doping concentration of the nano gold particles in the silicon base presents a uniform gradient distribution from low to high from a surface silicon material layer to a bottom silicon material layer, the particle size of the nano gold particles is less than one tenth of the wavelength of incident light entering the metamaterial, and the distribution interval of the nano gold particles in the silicon base is greater than five times the particle size. The application significantly enhances the absorption capacity of the material in the near-infrared wave band, and meanwhile, does not obviously increase the reflectivity.

Description

Technical Field

[0001] This invention belongs to the technical field of artificial electromagnetic metamaterials, and particularly relates to silicon-based metamaterials. Background Technology

[0002] Near-infrared photodetectors are widely used in fields such as low-light night vision, optoelectronic countermeasures, fire prevention, environmental monitoring, food safety, and autonomous driving. Currently, the fabrication of unit devices with near-infrared detection capabilities mainly utilizes non-silicon semiconductor materials such as germanium, germanium-silicon, germanium, indium gallium arsenide, and indium phosphide. However, these materials are expensive and difficult to integrate with silicon-driven circuits. In contrast, silicon-based photodetectors offer advantages such as CMOS process compatibility and low cost. Their applications in the visible light band are already mature, and further application in near-infrared photodetection can be considered. However, due to silicon's bandgap of 1.12 eV and photoelectric response cutoff wavelength of approximately 1100 nm, bulk silicon alone is difficult to use directly as a material for near-infrared photodetectors. Therefore, further exploration is needed to improve the absorption performance of silicon-based materials in the near-infrared band.

[0003] With the development of nanofabrication technology and plasmonic optics, nanostructured metal structures are often used to enhance the near-infrared absorption of silicon-based materials. The metal nanoparticles used in these structures exhibit a unique localized surface plasmon resonance (LSPR) phenomenon. When the frequency of the incident light is equal to the oscillation frequency of the free electrons on the metal surface, an enhanced local electromagnetic field will be generated on the surface of the metal nanoparticles, which is beneficial for enhancing light absorption. However, when enhancing near-infrared absorption through nanoparticles, it usually comes at the cost of increasing reflectivity, which greatly limits the use of the material. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the purpose of this invention is to provide a new silicon-based metamaterial with enhanced near-infrared absorption. The resulting metamaterial has significantly enhanced near-infrared absorption capability without significantly increasing reflectivity.

[0005] The technical solution of the present invention is as follows:

[0006] A near-infrared absorption-enhanced silicon-based metamaterial is formed by multiple silicon material layers of equal thickness arranged closely together. Each silicon material layer contains a silicon matrix and gold nanoparticles doped within the silicon matrix. The doping concentration of the gold nanoparticles within the silicon matrix is ​​uniformly distributed from low to high from the surface silicon material layer to the bottom silicon material layer. The particle size of the gold nanoparticles is less than one-tenth of the wavelength of the incident light entering the metamaterial, and the spacing between the gold nanoparticles is greater than five times their particle size.

[0007] In the above technical solutions of the present invention, the size of the gold nanoparticles is much smaller than the wavelength of the incident light, and the spacing between the gold nanoparticles is large enough to avoid resonance between particles. At the same time, the concentration of gold nanoparticles on the surface is low, and its refractive index does not change much compared with silicon, which can ensure that the reflectivity of the material surface does not undergo a large abrupt change. The concentration of gold nanoparticles in the bottom layer is higher, which can enhance the absorption capacity of silicon in the near-infrared band through the local surface plasmon resonance effect of gold nanoparticles. Meanwhile, the concentration of gold nanoparticles changes uniformly from the surface to the bottom layer, which can avoid abrupt changes in the reflectivity of the metamaterial due to significant refractive index changes between doped layers.

[0008] According to some preferred embodiments of the present invention, in the metamaterial, the volume doping concentration of gold nanoparticles in the surface silicon material layer is 0.25%, and the volume doping concentration of gold nanoparticles in the bottom silicon material layer is 5%.

[0009] According to some preferred embodiments of the present invention, the gradient volume concentration of the gradient distribution is 0.25%.

[0010] According to some preferred embodiments of the present invention, the metamaterial is formed by closely arranging 20 layers of silicon material, each with a thickness of 50 nm.

[0011] According to some preferred embodiments of the present invention, the metamaterial is formed by 20 layers of silicon material, each with a thickness of 50 nm, arranged closely together. In each silicon material layer, the particle size of the gold nanoparticles is less than 20 nm, the interparticle spacing is greater than 100 nm and less than 10 μm, the volume doping concentration of the gold nanoparticles in the surface silicon material layer is 0.25%, the volume doping concentration of the gold nanoparticles in the bottom silicon material layer is 5%, and the gradient volume concentration is 0.25%.

[0012] The present invention has the following beneficial effects:

[0013] (1) The silicon-based metamaterial of the present invention has significantly enhanced near-infrared absorption capacity compared with ordinary silicon materials. In some specific embodiments, its absorption capacity in the near-infrared band can be enhanced by up to 10.4 dB compared with silicon materials.

[0014] (2) The silicon-based metamaterial of the present invention enhances absorption in the near-infrared band without significantly increasing reflectivity, which greatly improves the application capability and application range of the material.

[0015] (3) The silicon-based metamaterial of the present invention has polarization-independent properties and still has good absorption performance when the light source is incident at a large angle. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the material structure according to an embodiment of the present invention.

[0017] Figure 2 It is the equivalent refractive index of the metamaterial in this embodiment of the invention.

[0018] Figure 3 This is a comparison chart of the reflectivity of the metamaterial and Si according to an embodiment of the present invention.

[0019] Figure 4 This is a comparison diagram of the transmittance of metamaterials and Si in an embodiment of the present invention.

[0020] Figure 5 This is a comparison chart of the absorption rates of metamaterials and Si in embodiments of the present invention.

[0021] Figure 6 This refers to the improvement in absorption rate of the metamaterial in this embodiment of the invention.

[0022] Figure 7 This is a wide-angle incident performance spectrum of the metamaterial according to an embodiment of the present invention. Detailed Implementation

[0023] The present invention will now be described in detail with reference to embodiments and accompanying drawings. However, it should be understood that the embodiments and drawings are for illustrative purposes only and do not constitute any limitation on the scope of protection of the present invention. All reasonable modifications and combinations included within the inventive spirit of the present invention fall within the scope of protection of the present invention.

[0024] See attached document Figure 1 In some specific embodiments, the near-infrared absorption-enhanced silicon-based metamaterial of the present invention has the following structure:

[0025] The metamaterial is formed by multiple silicon material layers of equal thickness arranged closely one on the top and bottom. Each silicon material layer contains a silicon matrix formed of silicon and gold nanoparticles uniformly doped in the silicon matrix. The doping concentration of the gold nanoparticles in the silicon matrix is ​​uniformly distributed from low to high from the surface silicon material layer to the bottom silicon material layer. The particle size of the gold nanoparticles is less than one-tenth of the wavelength of the incident light into the metamaterial, and the spacing between the gold nanoparticles is more than five times their particle size.

[0026] In some more specific embodiments, the metamaterial has a volume doping concentration of 0.25% for the gold nanoparticles in the outer silicon layer and a volume doping concentration of 5% for the gold nanoparticles in the inner silicon layer.

[0027] In one specific embodiment, the near-infrared absorption-enhanced silicon-based metamaterial of the present invention has the following structure:

[0028] This metamaterial is formed by closely arranged 20 silicon material layers, each 50 nm thick. Each silicon material layer contains a silicon matrix and gold nanoparticles doped within the silicon matrix. The gold nanoparticles have a particle size of less than 20 nm and an interparticle spacing of greater than 100 nm and less than 10 μm. The volume doping concentration of the gold nanoparticles in the silicon matrix is ​​distributed in a gradient of 0.25% from the top silicon material layer to the bottom silicon material layer. The volume doping concentration of the gold nanoparticles in the top silicon material layer is 0.25%, and the volume doping concentration of the gold nanoparticles in the bottom silicon material layer is 5%.

[0029] Furthermore, the performance of the silicon-based metamaterial obtained in this embodiment was simulated and tested. The testing process included:

[0030] The equivalent dielectric constant of a single silicon material layer can be calculated using the following formula:

[0031]

[0032] Where, ε e ε represents the equivalent dielectric constant of a single silicon material layer. h ε represents the dielectric constant of silicon. m denoted by ρ, which represents the dielectric constant of the gold particles, and p represents the volume fraction of the gold nanoparticles.

[0033] The dielectric constants of silicon and gold nanoparticles can both be obtained using existing technologies.

[0034] Based on the equivalent dielectric constant, the equivalent refractive index of a single silicon material layer is obtained by the following formula;

[0035] ε e =n e 2 ;

[0036] Where, n e This represents the equivalent refractive index of the silicon material layer.

[0037] Furthermore, taking a silicon material layer with a gold particle volume doping concentration of 1% as an example, the calculated equivalent refractive index of a single silicon material layer is shown in the attached figure. Figure 2 As shown, n represents the real part of the equivalent refractive index, and k represents the imaginary part of the equivalent refractive index.

[0038] By substituting different volume fractions into the formula using the above method, the equivalent refractive index of each silicon material layer can be obtained.

[0039] The calculated equivalent refractive index of each metamaterial layer was imported into Finite-Difference Time Domain (FDTD) software to model the metamaterial and perform simulation analysis. The simulation yielded the reflectivity and transmittance curves of the metamaterial (i.e., the composite material shown in the figure) relative to Si, as shown in the figure. Figure 3 , 4 As shown, compared with pure silicon, the reflectivity of metamaterials only changes slightly around the 820nm wavelength, still maintaining a reflectivity similar to that of silicon. In the 610-1450nm band, the transmittance is lower than that of pure silicon, and the transmittance is 0 in the 783-892nm range, showing a good near-infrared anti-reflection effect.

[0040] Furthermore, the absorption rate of metamaterials is obtained through the following methods:

[0041] A = 1 - RT (2)

[0042] Where A represents the absorptivity of the metamaterial, R represents the reflectivity of the metamaterial, and T represents the transmittance of the metamaterial. Based on the obtained reflectivity and transmittance curves, the absorptivity curve of the metamaterial can be further obtained as follows: Figure 5 As shown.

[0043] The improvement effect of metamaterials on absorption rate, i.e., the improvement rate, is calculated according to the following formula:

[0044] Improvement rate = 10log 10 (A2 / A1)

[0045] Where A1 and A2 represent the absorptivity of the silicon substrate without gold nanoparticles and the absorptivity of the entire metamaterial after gold nanoparticle doping, respectively, and the resulting absorptivity improvement effect is as follows: Figure 6 As shown, this metamaterial can enhance absorption in a wide wavelength range of 610–1450 nm, with a peak at 980 nm, and the enhancement effect can reach 10.4 dB.

[0046] In practical applications, it's often not just a single vertically incident plane wave; therefore, studying the near-infrared enhancement effect of materials under oblique incidence is equally important. Using the same simulation software FDTD and the same model, by changing the incident angle of the light source, the wide-angle near-infrared enhancement characteristics of this material were studied. The difference in absorptivity (A2-A1) before and after doping with gold nanoparticles is shown below. Figure 7 As shown, absorption is enhanced across a wavelength range greater than 620 nm at different incident light angles. The difference lies in the slight decrease in absorption enhancement at larger angles. The material exhibits excellent wide-angle incident light performance.

[0047] The above embodiments are merely preferred embodiments of the present invention, and the scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A silicon-based metamaterial with enhanced near-infrared absorption, characterized in that, It is formed by closely arranging 20 silicon material layers, each 50 nm thick. Each silicon material layer contains a silicon substrate and gold nanoparticles doped within the silicon substrate. The doping concentration of the gold nanoparticles within the silicon substrate is uniformly distributed from low to high from the top silicon material layer to the bottom silicon material layer. The particle size of the gold nanoparticles is less than one-tenth of the wavelength of the incident light entering the metamaterial, and the spacing between the gold nanoparticles is greater than five times their particle size. The volume doping concentration of the gold nanoparticles in the top silicon material layer is 0.25%, and the volume doping concentration of the gold nanoparticles in the bottom silicon material layer is 5%. The gradient volume concentration is 0.25%. The particle size of the gold nanoparticles in each silicon material layer is less than 20 nm, and the particle spacing is greater than 100 nm and less than 10 μm.

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