Thursday, January 14, 2016

Intrinsic photo-conductance triggered by the plasmonic effect in graphene for terahertz detection

Terahertz (THz) technology is becoming more prominent for applications including biomedical imaging, communication, security and astronomy. However, THz technology still possesses some challenges due to the lack of sources and detectors available. Although the terahertz wavelength ranges from 0.1~100 mm, this exceeds the dimensions of the nanoscale. Reporting in Nanotechnology, researchers Dr Lin Wang, Professor Xiaoshuang Chen, and colleagues at Shanghai Institute of Technical Physics explain an even stronger response of graphene with only a single carbon atomic layer at terahertz region. They find that the terahertz-induced potential wells or barriers trapping or detrapping carriers in graphene FET channel make it very promising for photo-detection. This property combined with its 2D nature offer a new route for future compact graphene-based integration and high performance flexible focal plane array in the field of terahertz imaging and security.
“The stronger response is due to the carrier dynamics at the timescale around terahertz frequency in graphene,” says Dr. Wang, “The motion of electron bunch at this frequency behaves like a fluid or sound wave, which leads to plasmonic resonances when Dirac fermions are ac excited.” The researchers find that the near-field of the grating coupler leads to enhanced localised nonlinearity of Dirac fermions and change the conductance ultimately, which is obviously different from mechanisms discovered before including photothermoelectric (PTE) bolometric effects.
The researchers point out that controlling the distribution of the THz field enables the freedom of controlling the transport of carriers in any fantastic way, and leads to the appearance of more intriguing phenomena such as photogalvanic, helicity-sensitive and photovoltaic detections.
More information about this research can be found in the journal Nanotechnology 27 035205.

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