Broadband Terahertz Silicon Membrane Metasurface Absorber

Abstract

Metasurface absorbers are of particular interest in numerous photonic applications including detectors, photovoltaic cells, and emissivity coatings. We introduce a thin membrane silicon metasurface absorber with periodic elliptical holes that, as demonstrated theoretically and experimentally, achieves very high absorption (≥90%) over a ∼500 GHz bandwidth at normal incidence. Based on the analysis of the effective medium theory, the broadband absorption is attributed to proximal electric and magnetic dipole resonances. The absorption amplitude can also be tuned by ∼20% with above-gap photoexcitation. Due to the unit cell geometry, the carrier density on the top surface and sidewalls of the membrane must be taken into account. Our dynamic membrane silicon metasurface absorber is notably thin and CMOS-compatible, providing a promising platform to realize compact terahertz devices including detectors, modulators, and switches.

Review of Broadband Metamaterial Absorbers: From Principles, Design Strategies, and Tunable Properties to Functional Applications

“…Si, as high‐loss optical sensitive material, has been widely investigated for the design of optically tunable BMAs in the THz band due to its inherently low‐cost and easy availability. For example, Figure a depicts a thin‐film Si‐based BMA with a periodic elliptical hole array, [ 454 ] achieving high absorption of >90% in the frequency range of 1.1–1.6 THz, which is presented in Figure 13b. As shown in Figure 13c, the device's absorption decreases monotonically from 1.1 to 1.6 THz with increasing pump flux, with modulation amplitudes of up to 20%.…”

“…Reproduced with permission. [ 454 ] Copyright 2022, American Chemical Society. d) Illustration of a flexible tunable perfect absorber.…”

“…This section briefly discusses the recent research progress in the tunability and reconfiguration BMAs. According to the types of stimulus response, we here summarize six aspects of BMAs having tunable characteristics, which are: 1) Optically tunable BMAs; [112,454,455] 2) Thermally tunable BMAs; [93,452] 3) Electrically tunable BMAs; [453,456,457] 4) Magnetically tunable BMAs; [100][101][102] 5) Mechanically tunable BMAs; [106][107][108] and 6) Multi-parameter tunable BMAs. [223,267,[458][459][460][461][462][463][464][465][466][467][468][469] We expect that these modulation strategies could provide guidance and help for the design of tunable or reconfigurable BMAs and their applications.…”

“…The essence of optically tunable BMAs is to actively tune their absorbance and absorption bandwidth by controlling the intensity of the pump light to change the conductivity of active materials (for example, the photosensitive semiconductor materials) as well their effective dielectric constants and thus the absorption feature of BMAs. The most researched and readily available photosensitive material is Si, [110,111,259,325,454,[470][471][472] and some other materials, such as gallium arsenide (GaAs), [455] and VO 2 [112] have also been employed to design and achieve the optically modulated BMAs.…”

Complementary Vanadium Dioxide Metamaterials with Enhanced Modulation Amplitude at Terahertz Frequencies

“…This includes subwavelength imaging [1], the realization of a negative refractive index [2], near zero epsilon devices [3], and the demonstration of cloaks and metalenses [4,5]. Building on these capabilities, active control and tunability in metamaterials could lead to novel modulators, switches, and sensors over a vast span of the electromagnetic spectrum [6][7][8][9][10].…”