Picosecond photoresponse in van der Waals heterostructures


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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Figure 1: Photocurrent generation in the G/WSe2/G heterostructure.
Figure 2: Extraction of the photoresponse time of a G/2.2 nm WSe2/G heterostructure by time-resolved photocurrent measurements.
Figure 3: Tuning of photoresponse time τ by variation of the WSe2 layer thickness L and bias voltage VB.
Figure 4: Dynamic processes governing the photoresponse of G/WSe2/G heterostructures.


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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.

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M.M. and F.H.L.K. conceived and designed the experiments. M.M., P.S. and F.V. fabricated the samples, carried out the experiments and performed the data analysis. K.W. and T.T. provided boron nitride crystals. K.G.S. and A.R.P. provided assistance for the photoluminescence measurements. M.M., F.V., K.J.T., P.S. and F.H.L.K co-wrote the manuscript, with the participation of K.G.S. and A.R.P.

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Correspondence to F. H. L. Koppens.

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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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