Abstract
The p–n junction is the functional element of many electronic and optoelectronic devices, including diodes, bipolar transistors, photodetectors, light-emitting diodes and solar cells. In conventional p–n junctions, the adjacent p- and n-type regions of a semiconductor are formed by chemical doping. Ambipolar semiconductors, such as carbon nanotubes1, nanowires2 and organic molecules3, allow for p–n junctions to be configured and modified by electrostatic gating. This electrical control enables a single device to have multiple functionalities. Here, we report ambipolar monolayer WSe2 devices in which two local gates are used to define a p–n junction within the WSe2 sheet. With these electrically tunable p–n junctions, we demonstrate both p–n and n–p diodes with ideality factors better than 2. Under optical excitation, the diodes demonstrate a photodetection responsivity of 210 mA W–1 and photovoltaic power generation with a peak external quantum efficiency of 0.2%, promising values for a nearly transparent monolayer material in a lateral device geometry. Finally, we demonstrate a light-emitting diode based on monolayer WSe2. These devices provide a building block for ultrathin, flexible and nearly transparent optoelectronic and electronic applications based on ambipolar dichalcogenide materials.
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Acknowledgements
The authors are grateful for experimental assistance provided by K. Akkaravarawong, T. Andersen, N. Gabor, Q. Lin, Q. Ma, W. Fang and J. Sanchez-Yamagishi, as well as for discussions with P. Brown. This work was primarily funded by the Office of Naval Research Young Investigator Award (N00014-13-1-0610) and partly by the Office of Naval Research Graphene Approaches to Terahertz Electronics Multidisciplinary University Research Initiative 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) (award no. DMR-0819762) and of Harvard's Center for Nanoscale Systems, supported by the NSF (grant ECS-0335765).
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B.W.H.B., H.O.H.C. and Y.Y. fabricated the samples. B.W.H.B., H.O.H.C. and Y.Y. performed the measurements. All authors analysed the data and co-wrote the paper.
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Baugher, B., Churchill, H., Yang, Y. et al. Optoelectronic devices based on electrically tunable p–n diodes in a monolayer dichalcogenide. Nature Nanotech 9, 262–267 (2014). https://doi.org/10.1038/nnano.2014.25
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DOI: https://doi.org/10.1038/nnano.2014.25
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