Time-resolved ultrafast photocurrents and terahertz generation in freely suspended graphene

Leonhard Prechtel, Li Song, Dieter Schuh, Pulickel Ajayan, Werner Wegscheider and Alexander W. Holleitner ()
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Leonhard Prechtel: Technische Universität München, Am Coulombwall 4a, 85748 Garching, Germany.
Li Song: Research Center for Exotic Nanocarbons, Faculty of Engineering, Shinshu University, 4-17-1 Wakasato, Nagano-shi 380-8553, Japan.
Dieter Schuh: Institut für Experimentelle und Angewandte Physik, Universität Regensburg, D-93040 Regensburg, Germany.
Pulickel Ajayan: Rice University
Werner Wegscheider: Solid State Physics Laboratory, ETH Zurich
Alexander W. Holleitner: Technische Universität München, Am Coulombwall 4a, 85748 Garching, Germany.

Nature Communications, 2012, vol. 3, issue 1, 1-7

Abstract: Abstract Graphene, a two-dimensional layer of carbon atoms, is a promising building block for a wide range of optoelectronic devices owing to its extraordinary electrical and optical properties, including the ability to absorb ~2% of incident light over a broad wavelength range. While the RC-limited bandwidth of graphene-based photodetectors can be estimated to be as large as 640 GHz, conventional electronic measurement techniques lack for analysing photocurrents at such frequencies. Here we report on time-resolved picosecond photocurrents in freely suspended graphene contacted by metal electrodes. At the graphene–metal interface, we demonstrate that built-in electric fields give rise to a photocurrent with a full-width-half-maximum of ~4 ps and that a photothermoelectric effect generates a current with a decay time of ~130 ps. Furthermore, we show that, in optically pumped graphene, electromagnetic radiation up to 1 THz is generated. Our results may prove essential to build graphene-based ultrafast photodetectors, photovoltaic cells and terahertz sources.

Date: 2012
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DOI: 10.1038/ncomms1656

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