Wavelength-scale features lead to fast practical graphene light sensing


The work is published in Nature Light Science & Applications in the paper ‘Gold-patched graphene nano-stripes for high-responsivity and ultrafast photodetection from the visible to infrared regime‘, whose title explains just about all you need to know.

Photo-carrier generation is mostly confined to the graphene stripes and conduction mostly to the gold patches, meaning that the structures gets the broadband optical absorption and photo-carrier multiplication of graphene, without being defeated by graphene’s short photo-carrier lifetime because the gold patches (100nm wide in diagram) provide fast photo-carrier transport before recombination occurs.

“We specifically designed the dimensions of the graphene stripes and their metal patches such that incoming visible and infrared light is tightly confined inside them,” said researcher Dr Semih Cakmakyapan. “This design efficiently produces an electrical signal that follows ultra-fast and subtle variations in the light’s intensity over the entire spectral range, from visible to infra-red.”

Photoelectric sensitivity from the visible to infra-red is said to be 0.6A/W at 0.8μm and 11.5A/W at 20μm, with operation exceeding 50GHz, claimed by the researchers in the paper to “demonstrate improvement of the response times by more than seven orders of magnitude and an increase in bandwidths of one order of magnitude compared to those of higher-responsivity graphene photodetectors based on quantum dots and tunnelling barriers”.

The substrate is silicon dioxide over a silicon wafer.

“Our photodetector could extend the scope and potential uses of photodetectors in imaging and sensing systems,” said Professor Mona Jarrahi. “It could dramatically improve thermal imaging in night vision or in medical diagnosis applications where subtle differences in temperatures can give doctors a lot of information. It could also be used t  identify the concentration of pollutants.”

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