期刊
NANO LETTERS
卷 22, 期 5, 页码 2016-2022出版社
AMER CHEMICAL SOC
DOI: 10.1021/acs.nanolett.1c04776
关键词
Terahertz nonlinearity; Metamaterials; Semiconductors; Impact ionization; Zener tunneling; Ultrafast mode switching
类别
资金
- National Center of Competence in Research - Molecular Ultrafast Science and Technology (NCCR MUST), a research instrument of the Swiss National Science Foundation
- European Union [FP-RESOMUS -MSCA 801459]
Researchers elucidate the details and timescales of mode switching in two-dimensional THz metamaterials consisting of metallic structures, and identify the dominant carrier generation mechanisms and dynamics.
Judiciously designed two-dimensional THz metamaterials consisting of resonant metallic structures embedded in a dielectric environment locally enhance the electromagnetic field of an incident THz pulse to values sufficiently high to cause nonlinear responses of the environment. In semiconductors, the response is attributed to nonlinear transport phenomena via intervalley scattering, impact ionization, or interband tunneling and can affect the resonant behavior of the metallic structure, which results, for instance, in mode switching. However, details of mode switching, especially time scales, are still debated. By using metallic split-ring resonators with nm-size gaps on intrinsic semiconductors with different bandgaps, we identify the most relevant carrier generation processes. In addition, by combining nonlinear THz time-domain spectroscopy with simulations, we establish the fastest time constant for mode switching to around hundred femtoseconds. Our results not only elucidate dominant carrier generation mechanisms and dynamics but also pave the route toward optically driven modulators with THz bandwidth.
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