CN114465014A - Light adjustable broadband terahertz absorber based on intrinsic silicon metamaterial and regulation and control method - Google Patents

Abstract

The invention provides a light adjustable broadband terahertz absorber based on an intrinsic silicon metamaterial and a regulation and control method, which are used for solving the technical problems of complex preparation, low light tuning efficiency and strong reflection effect of a doped silicon absorber and comprise an antireflection layer and a substrate layer, wherein the antireflection layer is a resonance unit array, the resonance unit array is formed by periodically arranged cross columnar resonance units, and the cross columnar resonance units are formed by vertically intersecting the midpoints of a horizontal column and a vertical column; the antireflection layer and the substrate layer are both intrinsic silicon. According to the invention, through a brand-new terahertz absorption scheme and a metamaterial antireflection structure design, the optically adjustable broadband terahertz absorber based on the intrinsic silicon metamaterial is obtained, and under 1064nm continuous laser irradiation, the ultra-large range peak absorption rate adjustment of 0-99% and the broadband absorption of more than 1.3THz are realized; the device only needs a single silicon etching process for preparation, and has the advantages of simple structure, low manufacturing cost, good stability and the like.

Description

Optically tunable broadband terahertz absorber and control method based on intrinsic silicon metamaterial

technical field

The invention belongs to the fields of novel artificial electromagnetic materials and terahertz science and technology, and relates to a terahertz wave absorber, in particular to an optically tunable broadband terahertz absorber based on intrinsic silicon metamaterials and a control method.

Background technique

The electromagnetic wave absorbing material means that it has low reflectivity and transmittance at the same time, which is mainly realized by the ohmic loss, dielectric loss, and hysteresis loss of electromagnetic waves in the material. Absorbers are widely used in electromagnetic shielding, RCS reduction, etc. Traditional absorbing materials mainly include metal powder, graphite, ferrite, etc. Most of these materials are difficult to meet the application requirements of light weight, easy large-area preparation, broadband and high-efficiency absorption. Metamaterial absorbers mainly enhance ohmic loss or dielectric loss through electromagnetic resonance. The advantages of metamaterial absorbers are that they are thin in thickness and flexible in the design of absorption frequency bands. They can realize broadband absorption, and narrow-band or multi-band absorption can be designed. More importantly, metamaterial absorbers can realize more abundant absorption functions such as tunability and polarization selection.

Terahertz absorbers based on all-silicon metamaterials have also attracted interest in recent years. By appropriately doping crystalline silicon, a large number of defect carriers are introduced, and free carrier absorption will occur to the incident terahertz wave. The absorber based on doped silicon can use optical pumping to change the carrier concentration near the surface of the structure, and adjust the absorption efficiency by increasing the reflection. However, the doped silicon absorber needs to go through the steps of doping the intrinsic silicon and etching the metamaterial unit, and the higher carrier concentration after doping is difficult to achieve further efficient tuning after laser irradiation, especially for almost The inability to turn off the absorption function leads to many limitations in the production and application of doped silicon absorbers. For example, patent CN105609963B discloses an ultra-broadband terahertz wave absorber prepared by using doped silicon. The average absorption rate in the frequency range of 1.5THz-10THz exceeds 90%, but the absorption rate is lower below 1.5THz. At the same time, the preparation The terahertz wave absorbers lack the tunability of the absorption efficiency. In addition, in order to improve the absorption bandwidth, researchers have also developed a variety of absorbers with complex structures, multi-layer structures or multiple resonators. The surface structure design can significantly increase the absorption efficiency of terahertz waves; for example, patent CN207752171U discloses An absorber composed of a base layer, a silicon dioxide layer and a pattern with a cross structure, patent CN107942418B discloses an absorber composed of a metal reflective layer, a dielectric layer and a cross-shaped graphene pattern layer, but this The thickness of the pattern layer prepared by the method is relatively thin, which is only convenient for adjusting the position of the absorption peak, and it is difficult to improve the absorption efficiency in a wide frequency band.

The 1064nm CW laser has good penetrability to intrinsic silicon, generates photogenerated carriers in the entire thickness range of the absorber, and achieves efficient absorption of terahertz waves, which provides a new idea for the preparation of broadband tunable broadband terahertz absorbers. However, the reflection effect of terahertz waves at the silicon interface is strong, resulting in limited absorption efficiency. By reducing the reflection effect of terahertz waves at the silicon interface, the application of intrinsic silicon in the field of terahertz wave absorption can be increased.

SUMMARY OF THE INVENTION

Aiming at the technical problems of complex preparation, low optical tuning efficiency and strong reflection effect of the existing doped silicon absorber, the present invention proposes an optically tunable broadband terahertz absorber based on intrinsic silicon metamaterial, which realizes the preparation of the absorber. simplicity, optical tunability and high absorption efficiency.

In order to achieve the above object, the technical scheme of the present invention is achieved in this way:

An optically tunable broadband terahertz absorber based on intrinsic silicon metamaterial, comprising an anti-reflection layer and a substrate layer, wherein the anti-reflection layer is a resonant unit array, and the resonant unit array is composed of periodically arranged cross-column resonator units, The cross-column-shaped resonance unit is composed of a horizontal column and a vertical column intersecting vertically at a midpoint; the anti-reflection layer and the substrate layer are both intrinsic silicon.

A cross-shaped columnar periodic structure metamaterial is designed as an antireflection layer. According to Snell's law in optical theory, when the electromagnetic wave is vertically incident on the interface of different media, the relative refractive index is defined as n=n2/n1, then the reflectance is

，

,

Obviously, when the terahertz wave is incident from the air to the smooth silicon interface, its relative refractive index is 3.45, and the reflectivity reaches about 0.3 at this time, which cannot meet the performance requirements of the absorber. When a metamaterial unit of appropriate size is etched on the silicon surface, the effective refractive index of its equivalent interface will decrease, which means that n in the above formula will be closer to 1, that is, the reflectivity will decrease. The anti-reflection performance of the cross-shaped metamaterial array was simulated and optimized by electromagnetic simulation software, and the structural parameters of the optically tunable broadband terahertz absorber were determined.

The horizontal and vertical columns have the same length and width, and the electrical conductivity in the optically tunable broadband terahertz absorber reaches 80 S/m.

The length of the horizontal column and the vertical column are both 90-110 μm, and the width is 20-30 μm.

Preferably, the length of the horizontal column and the vertical column are both 100 μm and 25 μm in width.

The height of the anti-reflection layer is 50-70 μm, and the thickness of the substrate layer is 430-450 μm.

Preferably, the height of the anti-reflection layer is 60 μm, and the thickness of the substrate layer is 440 μm.

The period length of the cross-columnar resonance unit is 110-130 μm.

Preferably, the period length of the cross-columnar resonator unit is 120 μm.

The control method of an optically tunable broadband terahertz absorber based on intrinsic silicon metamaterials, using a 1064 nm continuous laser to irradiate the optically tunable broadband terahertz absorber, the irradiation power is 0-1.1W.

The device obtained in step 1 is irradiated with a continuous laser with a wavelength of 1064 nm, and the tunable terahertz absorption function is turned on. In the case of laser irradiation of intrinsic silicon, when the photon energy is greater than the band gap of silicon by 1.12 eV, the dielectric constant of silicon in the terahertz band can be described by the Drude model:

=11.9，

为等离子频率，N为硅中的实际载流子浓度，mopt为载流子的光学有效质量，τd为弛豫时间。可以看出，硅的介电特性主要由光激发的载流子浓度决定，即由激光功率决定。而1064nm激光的光子能量为1.16eV，仅略大于本征硅带隙，表现为微弱吸收和良好的穿透性。in

=11.9,

is the plasma frequency, N is the actual carrier concentration in silicon, mopt is the optically effective mass of the carrier, and τd is the relaxation time. It can be seen that the dielectric properties of silicon are mainly determined by the photo-excited carrier concentration, that is, by the laser power. The photon energy of the 1064nm laser is 1.16eV, which is only slightly larger than the intrinsic silicon band gap, showing weak absorption and good penetration.

Preferably, the transmission power is 1.1W.

Beneficial effects of the present invention: The intrinsic silicon absorber does not need to dope silicon first, and uses a continuous laser with a wavelength of 1064 nm to excite photogenerated carriers in the intrinsic silicon as an absorption mechanism, so as to realize the device in a completely closed state and efficient absorption The switching between states is easier to prepare and more flexible and controllable; and a periodically arranged cross-shaped silicon column is designed as an anti-reflection layer. By changing the laser irradiation power, the peak absorption rate adjustment of 0%-99% is realized, and the effective absorption bandwidth is Greater than 1.3THz. The device preparation only needs a single silicon etching process, and has the advantages of simple structure, low manufacturing cost, good stability and the like.

Description of drawings

In order to explain the embodiments of the present invention or the technical solutions in the prior art more clearly, the following briefly introduces the accompanying drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only These are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can also be obtained according to these drawings without creative efforts.

Fig. 1 is the partial scanning electron microscope picture of the sample prepared in Example 1, in the figure 1, the anti-reflection layer, 2, the substrate layer;

Fig. 2 is the optical photograph and partial scanning electron microscope picture of the preparation sample of embodiment 1;

Figure 3(a) is a comparison of the time-domain transmission signal between the sample prepared in Example 1 and an ordinary intrinsic silicon wafer, and Figure 3(b) is a comparison of the first-order pulse transmission frequency-domain signal of the two;

Figure 4 shows the change of the absorptivity of the device under the same laser power (equivalent to the conductivity in the device) of the sample prepared in Example 1, Figure 4(a) is the simulated value, and Figure 4(b) is the measured value.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

An optically tunable broadband terahertz absorber based on intrinsic silicon metamaterial, as shown in Figure 1-2, includes an anti-reflection layer 1 and a substrate layer 2, the anti-reflection layer 1 is a resonant unit array, and the resonant unit array It is composed of cross-column-shaped resonance units arranged periodically, and the cross-column-shaped resonance unit is composed of a horizontal column and a vertical column intersecting vertically at the midpoint; the anti-reflection layer 1 and the substrate layer 2 are both intrinsic silicon, and the intrinsic silicon material cross The column array is used as the antireflection layer of the absorber, and the intrinsic silicon terahertz dielectric constant is 11.9, achieving broadband and high-efficiency antireflection performance.

The length and width of the horizontal column and the vertical column are the same, the length of the horizontal column and the vertical column are both 90-110 μm, and the width is 20-30 μm.

Preferably, the lengths are both 100 μm and the widths are 25 μm.

The height of the anti-reflection layer 1 is 50-70 μm, and the thickness of the substrate layer 2 is 430-450 μm.

Preferably, the height of the antireflection layer 1 is 60 μm, and the thickness of the substrate layer 2 is 440 μm.

The period length of the cross-columnar resonance unit is 110-130 μm.

Preferably, the period length of the cross-columnar resonator element is 120 μm.

The optically tunable broadband terahertz absorber was irradiated with a 1064 nm continuous laser with an irradiation power of 0-1.1 W.

Preferably, the irradiation power is 1.1 W, and the conductivity in the optically tunable broadband terahertz absorber is 80 S/m. The CW laser excites photogenerated carriers in intrinsic silicon as an absorption mechanism, enabling the device to switch between a fully off state and an efficient absorption state, while the absorption peak of the absorber can be controlled.

Example 1

An optically tunable broadband terahertz absorber based on intrinsic silicon metamaterial, as shown in Figure 1-2, the thickness of the substrate layer 2 is 440 μm, the height of the anti-reflection layer 1 composed of the cross column part is 60 μm, and the cross The period length of the columnar resonance unit is 120 μm, the length of the horizontal column and the vertical column is 100 μm, the width is 25 μm, and the actual sample size is 1.4 cm × 1.4 cm; 1.1W 1064 nm continuous laser is used to irradiate the absorber, and the optically tunable broadband is obtained. Terahertz absorber, the conductivity in optically tunable broadband terahertz absorber is 80 S/m.

The reflection situation of the fabricated optically tunable broadband terahertz absorber was tested in the range of 0.5-2 THz, as shown in Fig. The anti-reflection layer was seen to reduce the reflected signal in the 0.6-1.9 THz range to less than 10%.

Example 2

An optically tunable broadband terahertz absorber based on intrinsic silicon metamaterials, the main difference from Example 1 is that a 0.83W 1064nm continuous laser is used to irradiate the absorber to obtain an optically tunable broadband terahertz absorber. The conductivity in the tuned broadband terahertz absorber is 50 S/m.

Example 3

An optically tunable broadband terahertz absorber based on intrinsic silicon metamaterials, the main difference from Example 1 is that a 0.61W 1064nm continuous laser is used to irradiate the absorber to obtain an optically tunable broadband terahertz absorber. The conductivity in the tuned broadband terahertz absorber is 30 S/m.

Example 4

An optically tunable broadband terahertz absorber based on intrinsic silicon metamaterials, the main difference from Example 1 is that a 0.28W 1064nm continuous laser is used to irradiate the absorber to obtain an optically tunable broadband terahertz absorber. The conductivity in the tuned broadband terahertz absorber is 10 S/m.

Example of experimental effect

The absorptivity changes of the optically tunable broadband terahertz absorbers prepared in Examples 1-4 were tested, as shown in Figures 4(a) and 4(b). The absorption efficiency is gradually improved, and the absorption peak is as high as 99%. The absorption bandwidth also gradually widens, and the frequency range where the absorption rate is greater than 90% gradually increases to above 1.3THz. According to the theoretical calculation of the Drude model and the comparison of the simulation and test absorption performance in the figure, when the laser power is 1.1W, the conductivity in silicon increases to about 80S/m, and the absorber has the best wave absorption performance at this time.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the scope of the present invention. within the scope of protection.

Claims (10)

1. An optically tunable broadband terahertz absorber based on intrinsic silicon metamaterial, characterized in that it comprises an anti-reflection layer (1) and a substrate layer (2), wherein the anti-reflection layer (1) is an array of resonant elements, and the resonant The unit array is composed of periodically arranged cross-column-shaped resonant units, and the cross-column-shaped resonance unit is composed of a horizontal column and a vertical column intersecting vertically at a midpoint; the anti-reflection layer (1) and the substrate layer (2) are both intrinsic silicon. 2. The optically tunable broadband terahertz absorber of intrinsic silicon metamaterial according to claim 1, wherein the horizontal column and the vertical column have the same length and width, and the optically tunable broadband terahertz absorber has the same length and width as the vertical column. The conductivity is 0-80S/m. 3 . The optically tunable broadband terahertz absorber of intrinsic silicon metamaterial according to claim 2 , wherein the length of the horizontal column and the vertical column are both 90-110 μm, and the width is 20-30 μm. 4 . 4 . The optically tunable broadband terahertz absorber of intrinsic silicon metamaterial according to claim 3 , wherein the length of the horizontal column and the vertical column are both 100 μm and 25 μm in width. 5 . 5 . The optically tunable broadband terahertz absorber of intrinsic silicon metamaterial according to claim 1 , wherein the height of the anti-reflection layer ( 1 ) is 50-70 μm, and the thickness of the substrate layer ( 2 ) is 50-70 μm. 6 . 430-450μm. 6 . The optically tunable broadband terahertz absorber of intrinsic silicon metamaterial according to claim 1 , wherein the height of the anti-reflection layer ( 1 ) is 60 μm, and the thickness of the substrate layer ( 2 ) is 440 μm. 7 . 7 . The optically tunable broadband terahertz absorber of intrinsic silicon metamaterial according to claim 1 , wherein the period length of the cross-columnar resonance unit is 110-130 μm. 8 . 8 . The optically tunable broadband terahertz absorber of intrinsic silicon metamaterial according to claim 1 , wherein the period length of the cross-columnar resonance unit is 120 μm. 9 . 9. the control method of the optically tunable broadband terahertz absorber based on the intrinsic silicon metamaterial according to any one of claims 1-8, it is characterized in that: utilize 1064nm continuous laser to irradiate the optically tunable broadband terahertz absorber, The irradiation power is 0-1.1W. 10 . The control method for an optically tunable broadband terahertz absorber based on intrinsic silicon metamaterials according to claim 9 , wherein the irradiation power is 1.1W. 11 .

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