An Ultra-Wideband THz/IR Metamaterial Absorber Based on Doped Silicon.

Huafeng Liu,Liangcheng Tu,Shihao Tang,Danhua Peng,Kai Luo,Fangjing Hu

doi:10.3390/ma11122590

Abstract

Metamaterial-based absorbers have been extensively investigated in the terahertz (THz) range with ever increasing performances. In this paper, we propose an all-dielectric THz absorber based on doped silicon. The unit cell consists of a silicon cross resonator with an internal cross-shaped air cavity. Numerical results suggest that the proposed absorber can operate from THz to far-infrared regimes, having an average power absorption of ∼95% between 0.6 and 10 THz. Experimental results using THz time-domain spectroscopy show a good agreement with simulations. The underlying mechanisms for broadband absorption are attributed to the combined effects of multiple cavities modes formed by silicon resonators and bulk absorption in the doped silicon substrate, as confirmed by simulated field patterns and calculated diffraction efficiency. This ultra-wideband absorption is polarization insensitive and can operate across a wide range of the incident angle. The proposed absorber can be readily integrated into silicon-based photonic platforms and used for sensing, imaging, energy harvesting and wireless communications applications in the THz/IR range.

Highlights

Terahertz (THz) absorbers with broadband operations are essential components for various applications such as sensing, imaging, energy harvesting and wireless communications
Metamaterial-based perfect absorbers (MPAs) have been extensively studied since it was first proposed in the microwave range by Landy et al [6]
We propose an ultra-wideband absorber based on a standard 400-μm thick doped silicon substrate and demonstrate its EM responses in the THz and far-infrared spectra (e.g., 0.1–10 THz)

Summary

Introduction

Terahertz (THz) absorbers with broadband operations are essential components for various applications such as sensing, imaging, energy harvesting and wireless communications. Either complicated unit cell shapes, or composite and multilayer structures are required, limiting the applications for the increased fabrication and design complexities. To tackle this problem, Materials 2018, 11, 2590; doi:10.3390/ma11122590 www.mdpi.com/journal/materials. Materials 2018, 11, 2590 doped silicon substrates have been used to create broadband MPAs. Different unit cells patterns, including circular holes [12], rectangular cubes [13,14,15], cross-cave patches [16] sawtooth structures [17], crosses [18,19] and dumbbell shapes [20], have been demonstrated. With a wider operating spectrum, applications such as bolometric imaging, stealth applications and energy harvesting can be fully explored It is still in great demand for designing ultra-wideband absorbers within the THz/IR spectral ranges. When compared with previous studies, the proposed design has advantages such as single-layer resonating structure, low fabrication complexity and ultra-wide bandwidth, and can be readily integrated into silicon-based photonic platforms

Design and Simulations

Fabrication and Experimental Results

Findings

Conclusions