Elsevier

Physics Letters A

Volume 404, 19 July 2021, 127404
Physics Letters A

Optical capture capability enhancement by right-angled triangular visible absorber

https://doi.org/10.1016/j.physleta.2021.127404Get rights and content

Highlights

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    A visible enhanced absorber by the right-angled triangular grating on thin film.

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    Polarization independent characteristics under TE and TM polarizations absorbing.

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    Absorption efficiency >90% with bandwidth of 380 nm and angle approaching 50Ā°.

Abstract

Polarization-insensitive thin-film absorber is proposed by right-angled triangular grating. Combining the electric field distribution under two polarizations, the physical mechanism of absorption is analyzed using the finite element method. The presented results show that the average absorption efficiency exceeds 90.10% with a spectral range of 300-680 nm, and the incident angle can reach 50Ā°. Compared with reference planar and triangular structures, the thin-film visible absorber presented has better absorption characteristics. Furthermore, compared with the reported visible absorber by rectangular grating, the visible absorber designed in this work has enhanced absorption spectrum bandwidth of 380 nm and wide angle of 50Ā°. It is believed that the novel absorber has great potential in the field of visible light absorber.

Introduction

Many absorbers have been reported based on microstructures [1], [2], [3], [4], [5]. From the perspective of absorption bandwidth, absorbers are divided into narrow-band absorbers [6], [7], [8] and wide-band absorbers [9], [10], [11]. According to the absorption spectrum, absorbers can be divided into infrared absorbers [12], microwave absorbers [13], terahertz absorbers [14], and visible light absorbers [15]. Among them, due to the widespread use of visible light in visible absorber and other fields, visible wavelength spectral absorption has become one of the research hotspots [16], [17], [18], [19]. In addition, the addition of metamaterials is the main way to achieve polarization-independent and high-efficiency absorption characteristics of light absorbers at visible wavelengths [20], [21]. In order to realize the function of wide absorption spectrum and high efficiency, some researchers have done a lot of work. Lee et al. proposed a polarization-sensitive tunable visible absorber [22]. The proposed absorber consists of a metal-dielectric multilayer medium and a plasma grating. Nguyen et al. analyzed a perfect visible absorber by plasmonic grating [23]. Broadband absorptivity is above 90% in the wavelength range of 0.4 um to 1.4 um. Wan et al. designed a polarization-insensitive visible absorber by rectangular grating [24]. The polarization-insensitive absorber is designed to achieve a wide band absorption of 300 nm and an incident angle width of 45Ā° for TE and TM modes.

In this paper, in order to improve the absorption of absorbers, a polarization-insensitive thin-film absorber is proposed based on a right-angled triangular grating structure. The presented results show that the average absorption efficiency greater than 90.10% with a spectral range of 300-680 nm and the incident angle can reach 50Ā°. In addition, the changes of groove depth, groove width and coating thickness have a relatively small influence on the absorption rate. Furthermore, compared with the reference planar absorber, the reference triangular absorber, and the reported rectangular visible absorber [24], the designed visible light absorber in this work has better absorption bandwidth and incident angle.

Structure sizes of thin-film absorber are on the order of nanometers, which need to be studied by electromagnetic theory. Theories for studying visible absorbers include modal method [25], rigorous coupled-wave analysis method [26], finite element method [27] and finite time domain difference method [28]. The energy distribution of the electromagnetic field intensity of the absorber is clearly analyzed by finite element method [27]. By determining the boundary conditions, the transmittance and reflectance of the absorber are obtained. The incident energy minus the reflectance and transmittance is the absorbance. The original parameters of the right-angled triangular absorber are optimized by rigorous coupled-wave analysis method [26].

In order to improve the light absorption of the absorber, it is a better method to use a chirped grating [29], [30], [31] combined with a triangular structure. The traditional rectangular grating achieves broadband absorption enhancement by depositing Ni on Si3N4 [24]. However, the production cost of one-dimensional ordered gratings also increases. Wen et al. proposed the concept of adding cascaded rectangular nanometer gratings over the nanometer active layer to achieve broadband absorption enhancement [32]. It is due to the strong coupling between the local surface plasmon resonance and photon mode of the cascaded rectangular grating at the top of the absorption layer. However, there are few studies on chirped period gratings, which need further research. This paper designs a thin-film light absorber in the visible light band. The chirped period absorber absorbing layer composed of right-angled triangles in this paper not only makes up for the loss of metal but also outperforms the reference absorber with planar and triangular structures in the visible wavelength band. In addition, the finite element method [27] is used to analyze and discuss absorber parameters. The presented absorber has a high absorption of visible light in a wide-angle range.

Section snippets

Structure of right-angled triangular grating absorber

The 2D and 3D views of the schematic diagram of the proposed thin-film absorber based on a periodically chirped right-angled triangular grating are shown in Fig. 1. Such a structure is composed of an ITO layer, a right-angle triangular a-Si layer, a planar a-Si absorption layer, and a metal back reflection Ag layer. The structure is composed of ITO material with the refractive index of n=12.00. The ITO material in the structure is made up of indium tin oxide. Indium tin oxide (ITO) can control

Characteristics and discussions

The comparison of the power absorptivity of different types is shown in Fig. 7. The reference plane structure is composed of the planar a-Si layer and the Ag back reflection layer, and the reference triangular structure is composed of the triangular a-Si layer and the Ag back reflection layer. Obviously, plane a-Si layer and triangular a-Si layer play an important role in the absorption of incident light. As shown in Fig. 7 (b) and (c), the reference plane structure has the characteristics of

Conclusions

A visible light trapping structure capable of enhancing absorption of the absorber is proposed. The presentation of the absorption layer with the cascade right-angled triangular a-Si layer, the plane a-Si layer and the ITO layer make the absorber visible light absorption. The electric field distribution of the absorber is analyzed to explain the absorption mechanism. The average absorption efficiency more than 90.10% in the incident spectral range of 300-680 nm with wide angle of 50Ā°.

CRediT authorship contribution statement

Jimin Fang: Conceptualization, Data curation, Formal analysis, Writing - Original draft preparation. Bo Wang: Supervision, Project administration, Investigation, Writing- Reviewing and Editing.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This work is supported by the Science and Technology Program of Guangzhou City (202002030284, 202007010001).

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