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Graphene pushes the speed limit of light-to-electricity conversion

15 April 2015

Researchers have developed a graphene-based photodetector capable of converting absorbed light into an electrical voltage at extremely high speeds.

Ultra-fast photo-voltage creation after light absorption at the interface of two graphene areas with different Fermi energy (image courtesy ICFO/Achim Woessner)

Graphene is an excellent material for the ultra-fast conversion of light into electrical signals, but so far it was not known how fast graphene responds to ultra-short flashes of light.

The research team, from the Institute of Photonic Sciences (ICFO) in Barcelona, and MIT and the University of California, Riverside in the US, has now demonstrated that a graphene-based photodetector converts absorbed light into an electrical voltage at an extremely high speed - in less than 50 femtoseconds.

The ultra-fast creation of a photo-voltage in graphene is possible due to the extremely fast and efficient interaction between all conduction band carriers in the material. This interaction leads to a rapid creation of an electron distribution with an elevated electron temperature.

The energy absorbed from light is therefore efficiently and rapidly converted into electron 'heat'. Next, the electron heat is converted into a voltage at the interface of two graphene regions with different doping. This photo-thermoelectric effect turns out to occur almost instantaneously.

The results of this work, which are published in the journal, Nature Nanotechnology, could open a new pathway towards ultra-fast optoelectronic conversion applications.

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