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Electrically tunable excitonic light-emitting diodes based on monolayer WSe2 p–n junctions


The development of light-emitting diodes with improved efficiency, spectral properties, compactness and integrability is important for lighting, display, optical interconnect, logic and sensor applications1,2,3,4,5,6,7,8. Monolayer transition-metal dichalcogenides have recently emerged as interesting candidates for optoelectronic applications due to their unique optical properties9,10,11,12,13,14,15,16. Electroluminescence has already been observed from monolayer MoS2 devices17,18. However, the electroluminescence efficiency was low and the linewidth broad due both to the poor optical quality of the MoS2 and to ineffective contacts. Here, we report electroluminescence from lateral p–n junctions in monolayer WSe2 induced electrostatically using a thin boron nitride support as a dielectric layer with multiple metal gates beneath. This structure allows effective injection of electrons and holes, and, combined with the high optical quality of WSe2, yields bright electroluminescence with 1,000 times smaller injection current and 10 times smaller linewidth than in MoS2 (refs 17,18). Furthermore, by increasing the injection bias we can tune the electroluminescence between regimes of impurity-bound, charged and neutral excitons. This system has the required ingredients for new types of optoelectronic device, such as spin- and valley-polarized light-emitting diodes, on-chip lasers and two-dimensional electro-optic modulators.

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Figure 1: Monolayer WSe2 p–n junctions.
Figure 2: Photoresponse of monolayer p–n junction at 100 K.
Figure 3: Photoluminescence and electroluminescence.
Figure 4: Tuning valley-exciton electroluminescence at 60 K.


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This work was mainly supported by the US Department of Energy, Basic Energy Sciences, Materials Sciences and Engineering Division (DE-SC0008145). N.G., J.Y. and D.M. are supported by the US DoE, BES, Materials Sciences and Engineering Division. W.Y. is supported by the Research Grant Council of Hong Kong (HKU705513P), the University Grant Committee (AoE/P-04/08) of the government of Hong Kong and the Croucher Foundation under the Croucher Innovation Award. D.C. is supported by the US DoE, BES, Materials Sciences and Engineering Division (DE‐SC0002197). Device fabrication was performed at the Washington Nanofabrication Facility and National Science Foundation-funded Nanotech User Facility.

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X.X. conceived the experiments. J.S.R. fabricated the devices and performed the measurements, assisted by P.K. and A.M.J. J.S.R. and X.X. performed data analysis, with input from D.C. and W.Y. N.G., J.Y. and D.G.M. synthesized and performed bulk characterization measurements on the WSe2 crystals. T.T., K.W. and K.K. provided boron nitride crystals. X.X, D.C., J.S.R and W.Y. wrote the paper. All authors discussed the results.

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Correspondence to Xiaodong Xu.

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Ross, J., Klement, P., Jones, A. et al. Electrically tunable excitonic light-emitting diodes based on monolayer WSe2 p–n junctions. Nature Nanotech 9, 268–272 (2014).

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