Graphene is a promising material for ultrafast and broadband photodetection. Earlier studies have addressed the general operation of graphene-based photothermoelectric devices and the switching speed, which is limited by the charge carrier cooling time, on the order of picoseconds. However, the generation of the photovoltage could occur at a much faster timescale, as it is associated with the carrier heating time. Here, we measure the photovoltage generation time and find it to be faster than 50 fs. As a proof-of-principle application of this ultrafast photodetector, we use graphene to directly measure, electrically, the pulse duration of a sub-50 fs laser pulse. The observation that carrier heating is ultrafast suggests that energy from absorbed photons can be efficiently transferred to carrier heat. To study this, we examine the spectral response and find a constant spectral responsivity of between 500 and 1,500 nm. This is consistent with efficient electron heating. These results are promising for ultrafast femtosecond and broadband photodetector applications.
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The authors thank J. Song, L. Levitov and D. Brinks for discussions. K.J.T. acknowledges NWO for a Rubicon fellowship. L.P. acknowledges financial support from the Marie-Curie International Fellowship COFUND and the ICFOnest programme. F.K. acknowledges support by the Fundacio Cellex Barcelona, an ERC Career integration grant (294056, GRANOP) and ERC starting grant (307806, CarbonLight) and support by the EC under the Graphene Flagship (contract no. CNECT-ICT-604391). N.v.H. acknowledges support from an ERC advanced grant (ERC247330). Q.M. and P.J.H. have been supported by the AFOSR (grant no. FA9550-11-1-0225) and a Packard Fellowship. This work made use of the Materials Research Science and Engineering Center Shared Experimental Facilities supported by the National Science Foundation (NSF) (grant no. DMR-0819762) and Harvard's Center for Nanoscale Systems, supported by the NSF (grant no. ECS-0335765). Y.L., K.S.M. and C.N.L. are supported by the DOE BES division under grant no. ER 46940-DE-SC0010597. C.N.L. acknowledges support from the CONSEPT Center at UCR.
The authors declare no competing financial interests.
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Tielrooij, K., Piatkowski, L., Massicotte, M. et al. Generation of photovoltage in graphene on a femtosecond timescale through efficient carrier heating. Nature Nanotech 10, 437–443 (2015). https://doi.org/10.1038/nnano.2015.54
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