Two-dimensional crystals such as graphene and transition-metal dichalcogenides1 demonstrate a range of unique and complementary optoelectronic properties2,3. Assembling different two-dimensional materials in vertical heterostructures4 enables the combination of these properties in one device, thus creating multifunctional optoelectronic systems with superior performance. Here, we demonstrate that graphene/WSe2/graphene heterostructures ally the high photodetection efficiency of transition-metal dichalcogenides5,6 with a picosecond photoresponse comparable to that of graphene7,8,9, thereby optimizing both speed and efficiency in a single photodetector. We follow the extraction of photoexcited carriers in these devices using time-resolved photocurrent measurements and demonstrate a photoresponse time as short as 5.5 ps, which we tune by applying a bias and by varying the transition-metal dichalcogenide layer thickness. Our study provides direct insight into the physical processes governing the detection speed and quantum efficiency of these van der Waals heterostuctures, such as out-of-plane carrier drift and recombination. The observation and understanding of ultrafast and efficient photodetection demonstrate the potential of hybrid transition-metal dichalcogenide-based heterostructures as a platform for future optoelectronic devices.
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The authors thank Q. Ma and P. Jarillo-Herrero for their instruction on the layer assembly technique, and M. Lundeberg for discussions. M.M. acknowledges support from the Natural Sciences and Engineering Research Council of Canada (PGSD3-426325-2012). F.V. acknowledges financial support from Marie-Curie International Fellowship COFUND and the ICFOnest programme. F.K. acknowledges support by Fundacio Cellex Barcelona, the ERC Career integration grant (294056, GRANOP), the ERC starting grant (307806, CarbonLight), the Mineco grants RYC-2012-12281 and FIS2013-47161-P, and support by the EC under the Graphene Flagship (contract no. CNECT-ICT-604391). P.S. acknowledges financial support from a scholarship from the ‘la Caixa’ Banking Foundation.
The authors declare no competing financial interests.
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Massicotte, M., Schmidt, P., Vialla, F. et al. Picosecond photoresponse in van der Waals heterostructures. Nature Nanotech 11, 42–46 (2016). https://doi.org/10.1038/nnano.2015.227
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