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John O | January 2019

Researchers create graphene-based terahertz detector, potential for use in wireless data transfer

By Josh Perry, Editor


Researchers from the Moscow (Russia) Institute of Physics and Technology (MIPT), in collaboration with scientists from the U.K., Japan, and Italy, developed a terahertz radiation photodetector from bilayer graphene sandwiched between crystals of boron nitride and attached to a terahertz antenna.


The transistor channel, made of bilayer graphene (BLG), is sandwiched between two crystals of hexagonal boron nitride (hBN). (@tsarcyanide/MIPT Press Office)


According to a report from MIPT, this configuration pushes impurities to the edges of the graphene flakes and enables plasmons to propagate freely in the material. “The graphene sheet confined by metal leads forms a plasmon resonator, and the bilayer structure of graphene enables wave velocity tuning in a wide range,” the report explained.


The scientists were able to build a terahertz spectrometer that was only several microns in size and used voltage tuning to control resonant frequency. The tuning of frequencies and electron densities allowed researchers to better understand plasmon properties.


Terahertz radiation, which exists between microwaves and infrared light, have the potential for faster Wi-Fi, medical diagnostics, and radio telescopes but has required too much power and intense cooling to be viable.


“The reason for the inefficiency of the existing terahertz detectors is the mismatch between the size of the detecting element, the transistor — about one-millionth of a meter — and the typical wavelength of terahertz radiation, which is some 100 times greater,” the article added. “This results in the wave slipping past the detector without any interaction.”


Using graphene, the researchers were able to overcome the damping of plasmons that hindered previous efforts.


The research was recently published in Nature Communications. The abstract stated:


“Plasmons, collective oscillations of electron systems, can efficiently couple light and electric current, and thus can be used to create sub-wavelength photodetectors, radiation mixers, and on-chip spectrometers. Despite considerable effort, it has proven challenging to implement plasmonic devices operating at terahertz frequencies. The material capable to meet this challenge is graphene as it supports long-lived electrically tunable plasmons.


“Here we demonstrate plasmon-assisted resonant detection of terahertz radiation by antenna-coupled graphene transistors that act as both plasmonic Fabry-Perot cavities and rectifying elements. By varying the plasmon velocity using gate voltage, we tune our detectors between multiple resonant modes and exploit this functionality to measure plasmon wavelength and lifetime in bilayer graphene as well as to probe collective modes in its moiré minibands.


“Our devices offer a convenient tool for further plasmonic research that is often exceedingly difficult under non-ambient conditions (e.g. cryogenic temperatures) and promise a viable route for various photonic applications.”

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