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Carmen Palacios-Berraquero, Matteo Barbone, Dhiren M. Kara, Xiaolong Chen, Ilya Goykhman, Duhee Yoon, Anna K. Ott, Jan Beitner, [Kenji Watanabe](https://orcid.org/0000-0003-3701-8119), [Takashi Taniguchi](https://orcid.org/0000-0002-1467-3105), Andrea C. Ferrari, Mete Atatüre

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[Atomically thin quantum light-emitting diodes](https://mdr.nims.go.jp/datasets/cdb23d06-31f7-4e1b-ad24-34dacf9b9643)

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Atomically thin quantum light-emitting diodesARTICLEReceived 19 Jul 2016 | Accepted 23 Aug 2016 | Published 26 Sep 2016Atomically thin quantum light-emitting diodesCarmen Palacios-Berraquero1,*, Matteo Barbone2,*, Dhiren M. Kara1, Xiaolong Chen2, Ilya Goykhman2,Duhee Yoon2, Anna K. Ott2, Jan Beitner1, Kenji Watanabe3, Takashi Taniguchi3, Andrea C. Ferrari2& Mete Atatüre1Transition metal dichalcogenides are optically active, layered materials promising for fastoptoelectronics and on-chip photonics. We demonstrate electrically driven single-photonemission from localized sites in tungsten diselenide and tungsten disulphide. To achieve this,we fabricate a light-emitting diode structure comprising single-layer graphene, thin hexagonalboron nitride and transition metal dichalcogenide mono- and bi-layers. Photon correlationmeasurements are used to confirm the single-photon nature of the spectrally sharp emission.These results present the transition metal dichalcogenide family as a platform for hybrid,broadband, atomically precise quantum photonics devices.DOI: 10.1038/ncomms12978 OPEN1 Cavendish Laboratory, University of Cambridge, J.J. Thomson Ave., Cambridge CB3 0HE, UK. 2 Cambridge Graphene Centre, University of Cambridge,Cambridge CB3 0FA, UK. 3 Advanced Materials Laboratory, National Institute for Materials Science, Tsukuba, Ibaraki 305-0034, Japan. * These authorscontributed equally to this work. Correspondence and requests for materials should be addressed to A.C.F. (email: acf26@cam.ac.uk) or to M.A.(email: ma424@cam.ac.uk).NATURE COMMUNICATIONS | 7:12978 | DOI: 10.1038/ncomms12978 | www.nature.com/naturecommunications 1mailto:acf26@cam.ac.ukmailto:ma424@cam.ac.ukhttp://www.nature.com/naturecommunicationsIncorporating single-photon sources into optoelectroniccircuits is a key challenge to develop scalable quantum-photonic technologies. Despite a plethora of single-photonsources reported to-date, all-electrical operation, desired forsystems integration, is reported for only a few1–4. Layeredmaterials (LMs) offer novel opportunities for next-generationphotonic and optoelectronic technologies5,6, such as lasers7,8,modulators9,10 and photodetectors11, and are compatible with thesilicon platform12.The attractiveness of single-photon sources in LMs13–18 stemsfrom their ability to operate at the fundamental limit of few-atomthickness, providing the potential to integrate into conventionaland scalable high-speed optoelectronic systems19,20. Transitionmetal dichalcogenides (TMDs), being optically active layeredsemiconductors, are particularly suitable for developingquantum-light generating devices.Here we demonstrate that LMs enable all-electrical single-photon generation over a broad spectrum. We use a light-emitting diode (LED) realized by vertical stacking of LMs andachieve charge injection into the active layer containing quantumemitters. We show that quantum emitters in tungsten diselenide(WSe2)13–17 can operate electrically. We further reportall-electrical single-photon generation in the visible spectrumfrom a new class of quantum emitters in tungsten disulfide(WS2). Our results highlight the promise of LMs as a newplatform for broadband hybrid all-integrated quantum-photoniccircuits.ResultsDesign and operation of a vertical TMD-based LED. We realizean LED based on a single tunnelling junction made of verticallystacked LMs (see ‘Methods’, Supplementary Figs 1–8 andSupplementary Notes 1–3). Figure 1a is a typical opticalmicroscope image of such a device. From bottom to top, threelayers form a heterostructure on a silicon/silicon dioxide (Si/SiO2)substrate: a single layer of graphene (SLG), a thin (2–6 atomiclayers) sheet of hexagonal boron nitride (hBN) and a mono- orbi-layer of TMD, such as WSe2. The WSe2, exfoliated from anaturally p-doped bulk crystal, is the optically activelayer hosting single-photon sources. Metal electrodesprovide electrical contact to the SLG and TMD layers. To obtainelectroluminescence (EL), we inject electrons from the SLGto the p-doped WSe2 through the hBN tunnel barrier(see Supplementary Fig. 9 for current–voltage characteristics ofthe devices). A vertically stacked heterojunction allows for ELfrom the whole device area, unlike lateral Schottky junction orsplit-gate p–n junction devices21–23, and provides the benefit ofatomically precise interfaces and barrier thicknesses24. We leavethe optically active TMD layer exposed at the top of the devicepurposefully to offer interfacing with other systems.Figure 1b illustrates the operational concept of our LED. Atzero bias between the SLG and the monolayer TMD contacts, theFermi energy (EF) of the system is constant across theheterojunction, preventing net charge flow (current) betweenthe layers (Fig. 1b, top). A negative bias applied to the SLGelectrode raises the SLG EF above the minimum of the conductionband (EC) of grounded WSe2. This induces electrons to tunnelfrom the SLG into the monolayer WSe2. This initiates photo-emission through radiative recombination between the tunnelledelectrons and the holes residing in the optically active WSe2 area(Fig. 1b, bottom). Figure 1c compares the EL and photolumines-cence (PL) spectra from this monolayer-WSe2-based LED devicefor two operation temperatures, room temperature (RT) and 10 K(see ‘Methods’ and Supplementary Fig. 10 for measurement set-up). PL at RT is given by the black curve in the lower panel with abroad peak at 750 nm corresponding to the monolayer WSe2unbound neutral exciton emission, X0 (ref. 25). Under electricalexcitation the main peak is shifted B20 nm to longerwavelengths, which is commensurate with the chargedexciton, X! (ref. 26), as shown in the blue curve. The blackand blue spectra in the upper panel of Fig. 1c show the device’sPL and EL emission at 10 K, respectively. Because of the increasedbandgap at low temperatures, the unbound exciton emission isshifted to shorter wavelengths by B30 nm (ref. 27). Consistentwith recent reports13–17,27, extra structure arising from localizedexciton state emission (L) appears at longer wavelengths in the PLspectrum. Critically, these features are also visible under electricalexcitation. In the low-current regime (o1 mA for this device) theydominate the EL spectrum, as shown in Fig. 1c, indicating thatlocalized exciton states respond more efficiently to chargeinjection than the delocalized ones.Electrically driven quantum light in a WSe2-based LED.Figure 2a is a spatial map of integrated EL from a WSe2-basedLED device at 10 K. The active region of this device consists ofadjacent monolayer and bilayer active areas, both in contactRT650Intensity700Wavelength (nm)750 800 85010 KELPLX0 X–LTMDhBNSLG10 µmSLG hBN TMDEcEvEFEFV = 0V < 0LEDa bcFigure 1 | Design and operation of a TMD-based LED. (a) Opticalmicroscope image of a typical device used in our experiments. The dottedlines highlight the footprint of the SLG, hBN and the TMD layersindividually. The Cr/Au electrodes contact the SLG and TMD layers toprovide an electrical bias. (b) Heterostructure band diagram. The topillustration shows the case for zero-applied bias and the bottom illustrationshows the case for a finite negative bias applied to the SLG. Tuning the SLGFermi level (EF) across the TMD conduction band edge (EC) allows electrontunnelling from the SLG to the TMD, resulting in light emission via radiativerecombination of the electrons with the holes residing in the p-doped TMDlayer. The appearance of valence-band holes below the Fermi level is due tothe natural p-doping of WSe2. (c) An example of layered LED emissionspectra for an optically active layer of WSe2. Top (bottom) spectracorrespond to 10 K (RT) operation temperature, where the black and bluespectra are obtained by optical excitation and electrical excitation,respectively.ARTICLE NATURE COMMUNICATIONS | DOI: 10.1038/ncomms129782 NATURE COMMUNICATIONS | 7:12978 | DOI: 10.1038/ncomms12978 | www.nature.com/naturecommunicationshttp://www.nature.com/naturecommunicationswith the ground electrode. The brighter area in Fig. 2acorresponds to the bilayer, suggesting that most of the injectedcurrent flows through this region (see Supplementary Fig. 11). Inaddition to the spatially uniform light emission from delocalizedexcitons, we observe quantum LED (QLED) operation in theform of highly localized light emission from both the monolayerand the bilayer WSe2, identified by the dotted circles (Fig. 2a).These localized states lie within the bandgap of WSe2, andtherefore emit at lower energies (longer wavelength) withrespect to the bulk exciton emission (see Fig. 2b)13–17. Figure 2cshows example emission spectra from these sites, where the top(bottom) spectrum belongs to a quantum emitter in themonolayer (bilayer) WSe2. We observe spectrally isolated peaksfrom multiple locations in most devices with linewidths rangingbetween 0.8 and 3 nm. We see on average 1–2 emitters perB40mm2 active device area. Electrically excited narrow linescoming from bilayer WSe2 regions are typically redshifted withrespect to those coming from the monolayer regions28. Theemission peaks of Fig. 2c are unpolarized, and the fine structuresplitting reported in PL experiments (B0.3 nm (refs 13–17)) isnot resolvable due to the broader linewidths we observe in EL.On the timescale of seconds, most emitters show spectralwandering, of up to 2 nm, similar to that seen in our PLmeasurements. Gating and encapsulation of the active layershould aid in reducing the broad linewidths observed here, whichwe attribute to charge noise in the device. Slow spectralfluctuations can further be reduced through active feedback,for example via the direct current Stark shift29,30. A fraction ofthe quantum emitters display blinking, discrete spectral jumpsor multiple spectral lines at similar timescales (see SupplementaryFig. 12). We also see that, as in PL, the electrically driven emittersdisplay robust operation, withstanding multiple (3–5) cooling/heating cycles and several hours of measurement underuninterrupted current flow.Figure 2d plots the current dependence of the integrated ELintensity from a quantum emitter, as well as from the unboundmonolayer WSe2 excitons. The latter shows a predominantlylinear relation between emission intensity and injected current;however, EL emission from the quantum emitter shows clearsaturation as a function of current, a universal behaviour seenwith single-photon sources31 (see Supplementary Fig. 13 for aplot of the unbound exciton and quantum emitter spectra as afunction of current). Figure 2e shows the measured intensity-correlation function, g(2)(t), of the integrated EL emission from aWSe2-based QLED using a Hanbury Brown and Twissinterferometer (see ‘Methods’). The value of the normalizedg(2)(0) drops to 0.29±0.08, well below the threshold value of 0.5,expected for a single-photon source1. We note that these data arenot corrected for background emission within the broad spectralwindow of detection or for the photon-counting detector darkcounts, which together contribute to the non-zero value of g(2)(0).While our results manifest the single-photon nature of theelectrically generated emission as proof-of-concept, theimmediate usability of these quantum emitters as single-photonsources would benefit from spectral filtering to suppress thebackground emission. Further technical improvements, such asCurrent (µA)0 1 2 3 4Integrated intensity050100150200IntensityWavelength (nm)LED QLED1 L2 LQLEDa b cdNormalized g2 (τ)Delay (ns)2 L1 L38,00002 µmEFV < 0–40 –20 0 20 4000.250.50.7511.25700 750 800 850QLEDLEDeIntegratedcounts/sFigure 2 | WSe2-based QLED operation in the near infrared spectrum. (a) A raster-scan map of integrated EL intensity from monolayer and bilayerWSe2 areas of the QLED for an injection current of 3 mA (12.4 V). The dotted circles highlight the submicron localized emission in this device.(b) A schematic energy band diagram, similar to that in Fig. 1b, including the confined electronic states of the quantum dots. EL emission fromquantum dots typically starts at lower bias than the conventional LED operation threshold. (c) Typical EL emission spectra for quantum dotsin the monolayer (top) and bilayer (bottom) WSe2. The shaded area highlights the spectral window for LED emission due to bulk WSe2 excitons,whereas QLED operation produces spectra at longer wavelengths. (d) Comparison of the integrated EL intensity for the WSe2 layer and for a quantumdot as a function of the applied current. The linear increase in WSe2 layer EL contrasts with the saturation behaviour of the QLED emission.(e) Intensity-correlation function, g(2)(t), for the same emitter displaying the antibunched nature of the EL signal, g(2)(0)¼0.29±0.08, anda rise-time of 9.4±2.8 ns.NATURE COMMUNICATIONS | DOI: 10.1038/ncomms12978 ARTICLENATURE COMMUNICATIONS | 7:12978 | DOI: 10.1038/ncomms12978 | www.nature.com/naturecommunications 3http://www.nature.com/naturecommunicationsoptimized designs for charge injection, may be possible once thenature of these emitters is identified.All-electrical generation of single-photon emission in WS2.In TMD-based quantum emitters, the host material influences thequantized energy levels and consequently their emission wave-length. Therefore, in order to obtain single-photon emission in acomplementary part of the spectrum, we replace the monolayer ofWSe2 with WS2 (exfoliated from an n-doped bulk crystal) as theactive layer; the rest of the QLED device structure remainsunchanged. Figure 3a,b displays the spatial maps of integrated ELemission from a WS2-based QLED device at high- (0.665mA) andlow- (0.570mA) current injection, respectively. At high current,the emission intensity is spatially uniform in the monolayer. Atlow currents, however, a spatially localized emission sitedominates, indicating that WS2 also hosts localized quantumemitters. Figure 3c shows the EL spectrum as a function ofinjection current, demonstrating that the low current(B0.570 mA) regime leads to a narrow (B4 nm) emission at640 nm, a line cut (in blue) of which is in the bottom right panel.Figure 3c (upper right plot) also shows how the EL spectrum isbroadened significantly when driven strongly at an injectioncurrent of 1.8 mA. The EL at 640 nm lies within the spectral regionof an emission band that appears, in addition to the unboundexciton emission, at low temperature (o10 K) under opticalexcitation (see Supplementary Figs 14 and 15 for details andSupplementary Fig. 16 for a comparison between the raster-scanmaps of integrated EL intensity from WS2 and WSe2 at RT and10 K). Operating in the low-current range ensures that the full ELspectrum is dominated by single-photon emission from thequantum emitter, obviating any need for tailored spectral filter-ing. The intensity-correlation measurement for EL in this regime,without spectral filtering, yields the g(2)(t) data in Fig. 3d. Similarto the WSe2 emitters, the uncorrected, but normalized, g(2)(0)falls below 0.5 to 0.31±0.05, indicating that WS2 supports stableQLED operation, generating single photons in the visible spectralrange.DiscussionOur TMD-based QLEDs rely on a single tunnelling heterojunc-tion design, where a wide range of TMDs can be active materials.Other designs, employing a back gate to tune EF of the activeTMD layer and providing electrostatic tuning of the EL emissionspectrum, can enhance the versatility of these devices. Onepossibility is the deterministic control over the charging states ofconfined excitons32, en route to spin control33 and entangledphoton generation34. We also note that the emission wavelengthrange for WSe2 emitters can match rubidium transitions(B780 nm) for exploring quantum storage possibilities.Similarly, silicon-vacancy centres (B737 nm) and nitrogen-vacancy centres (B637 nm) in diamond can have matchingtransitions with the WSe2 and WS2 QLEDs, respectively, forinterfacing hybrid quantum systems via distributed or on-chipphotonic channels. Other TMDs are likely to yield similar resultsdecorating different spectral windows. Our results demonstratethat LMs are a platform for fully integrable and atomically precisedevices for quantum photonics technologies.0900 kadDelay (ns)020 kb1 µm1 µmcWavelength (nm)600 650 7000.60.81.01.21.41.61.8Wavelength (nm)501002,000Intensity (cts)04,000Current (µA)–40 –20 0 20 4000.250.500.751.001.25Normalized g2 (τ)600 650 7000Integratedcounts/sIntegratedcounts/sFigure 3 | WS2-based QLED operation in the visible spectrum. A raster-scan map of integrated EL intensity from the monolayer WS2 area of the device:(a) at 0.665mA injection current (bias 2.08 V), where the emission is delocalized and roughly uniform, and (b) at 0.570mA (1.97 V), where the highlylocalized QLED emission dominates over the unbound WS2 exciton emission. (c) A map of the EL spectrum, displaying the evolution of the WS2 QDemission spectrum as a function of current. The spectrum at the top (bottom) of the panel is a line cut for injection current of 1.8mA (0.578mA).(d) Intensity-correlation function, g(2)(t), for the same quantum dot displaying the antibunched nature of the EL signal, g(2)(0)¼0.31±0.05, and arise-time of 1.4±0.15 ns.ARTICLE NATURE COMMUNICATIONS | DOI: 10.1038/ncomms129784 NATURE COMMUNICATIONS | 7:12978 | DOI: 10.1038/ncomms12978 | www.nature.com/naturecommunicationshttp://www.nature.com/naturecommunicationsMethodsDevice fabrication. We exfoliate the LMs on oxidized Si wafers by micro-mechanical cleavage of bulk crystals of graphite (NGS Naturgraphit), TMDs (HQGraphene) and hBN single crystals, grown by the temperature-gradient methodunder high pressure and high temperature35. Mono-, bi- and few-layer samplesare identified by a combination of optical contrast (see Supplementary Figs 1, 3and 5)36, Raman spectroscopy (see Supplementary Figs 2, 4a, 6 and 7a)37, PL(see Supplementary Figs 4b and 7b) and atomic force microscopy (AFM)(see Supplementary Fig. 8). Single crystals are assembled into heterostructuresvia a dry-transfer technique38. A transparent stack comprising a glass slide, apolydimethylsiloxane layer attached to the glass and polycarbonate (PC) as anexternal film is mounted on a micromanipulator positioned under an opticalmicroscope with a temperature-controlled stage. After adjusting the alignment andbringing the transfer stack into contact with the exfoliated TMD flakes, these arepicked up due to their higher adhesion to PC. The process is repeated for the hBNtunnel barrier. Finally, after aligning and bringing in contact hBN and TMD on PCwith exfoliated SLG on Si/SiO2, the temperature is raised to B100 !C, releasing thePC with hBN/TMD onto SLG. Then, the sample is soaked in chloroform todissolve the PC film, leaving the SLG/hBN/TMD heterostructure on the Si/SiO2substrate. Finally, Cr/Au (3/50 nm) contacts both to SLG and TMD are patternedby e-beam lithography following a standard lift-off process. Heterostructures arecharacterized by Raman spectroscopy to ensure no degradation (see SupplementaryNotes 1–3 for further details).Confocal microscopy. PL and EL measurements are performed using a home-built confocal microscopy mounted on a three-axis stage (Physik InstrumenteM-405DG) with a 5-cm travel range and 200-nm resolution for coarse alignmentand a piezo scanning mirror (Physik Instrumente S-334) for high resolution rasterscans (see Supplementary Fig.10 for a diagram of the optical set-up). PL and EL arecollected using a 1.7-mm working distance objective with a numerical aperture of0.7 (Nikon S Plan Fluor 60# ) and detected on a fibre-coupled single-photon-counting module (PerkinElmer SPCM-AQRH). A variable-temperature heliumflow cryostat (Oxford Instruments Microstat HiRes2) is used to perform PL and ELmeasurements. A controlled bias is applied to the QLED devices by a sourcemeasurement unit (Keithley 2,400) for EL experiments. Intensity correlations fromthe Hanbury Brown and Twiss interferometer are recorded with a time-to-digitalconverter (quTAU). A double-grating spectrometer (Princeton Instruments) isused for acquiring spectra. For PL measurements, the excitation laser (700/520 nm,Thorlabs MCLS1) is suppressed with a long pass filter (715 nm, Semrock FF01-715/550 nm Thorlabs FEL0550).Data availability. The data that support the findings of this study are availablefrom the corresponding authors upon request.References1. Yuan, Z. et al. Electrically driven single-photon source. Science 295, 102–105(2002).2. Mizuochi, N. et al. Electrically driven single-photon source at roomtemperature in diamond. Nat. Photonics 6, 299–303 (2012).3. Lohrmann, A. et al. Single-photon emitting diode in silicon carbide.Nat. Commun. 6, 7783 (2015).4. Nothaft, M. et al. Electrically driven photon antibunching from a singlemolecule at room temperature. Nat Commun. 3, 628 (2012).5. Bonaccorso, F., Sun, Z., Hasan, T. & Ferrari, A. C. Graphene photonics andoptoelectronics. Nat. Photonics 4, 611–622 (2010).6. Ferrari, A. C. et al. Science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems. Nanoscale 7, 4598–4810 (2014).7. Ye, Y. et al. Monolayer excitonic laser. Nat. Photonics 9, 733–737 (2015).8. Sun, Z. et al. Graphene mode-locked ultrafast laser. ACS Nano 4, 803–810(2010).9. Liu, M. et al. A graphene-based broadband optical modulator. Nature 474,64–67 (2011).10. Phare, C. T., Daniel Lee, Y.-H., Cardenas, J. & Lipson, M. Graphene electro-optic modulator with 30 GHz bandwidth. Nat. Photonics 9, 511–514 (2015).11. Koppens, F. H. L. et al. Photodetectors based on graphene, other two-dimensional materials and hybrid systems. Nat. Nanotechnol. 9, 780–793(2014).12. Xia, F., Wang, H., Xiao, D., Dubey, M. & Ramasubramaniam, A. Two-dimensional material nanophotonics. Nat. Photonics 8, 899–907 (2014).13. Srivastava, A. et al. Optically active quantum dots in monolayer WSe2.Nat. Nanotechnol. 10, 491–496 (2015).14. He, Y.-M. et al. Single quantum emitters in monolayer semiconductors.Nat. Nanotechnol. 10, 497–502 (2015).15. Koperski, M. et al. Single photon emitters in exfoliated WSe2 structures.Nat. Nanotechnol. 10, 503–506 (2015).16. Chakraborty, C., Kinnischtzke, L., Goodfellow, K. M., Beams, R. & Vamivakas, A. N.Voltage-controlled quantum light from an atomically thin semiconductor. Nat.Nanotechnol. 10, 507–511 (2015).17. Tonndorf, P. et al. Single-photon emission from localized excitons in anatomically thin semiconductor. Optica 2, 347 (2015).18. Tran, T. T., Bray, K., Ford, M. J., Toth, M. & Aharonovich, I. Quantumemission from hexagonal boron nitride monolayers. Nat. Nanotechnol. 11,37–41 (2015).19. Yin, Z. et al. Single-layer MoS2 phototransistors. ACS Nano 6, 74–80 (2011).20. Wang, H., Zhang, C., Chan, W., Tiwari, S. & Rana, F. Ultrafast response ofmonolayer molybdenum disulfide photodetectors. Nat. Commun. 6, 8831(2015).21. Ross, J. S. et al. Electrically tunable excitonic light-emitting diodes based onmonolayer WSe2 p-n junctions. Nat. Nanotechnol. 9, 268–272 (2014).22. Baugher, B. W. H., Churchill, H. O. H., Yang, Y. & Jarillo-Herrero, P.Optoelectronic devices based on electrically tunable p-n diodes in a monolayerdichalcogenide. Nat. Nanotechnol. 9, 262–267 (2014).23. Pospischil, A., Furchi, M. M. & Mueller, T. Solar-energy conversion and lightemission in an atomic monolayer p-n diode. Nat. Nanotechnol. 9, 257–261(2014).24. Withers, F. et al. Light-emitting diodes by band-structure engineering in vander Waals heterostructures. Nat. Mater. 14, 301–306 (2015).25. Zhou, B. et al. Evolution of electronic structure in atomically thin sheets of WS2and WSe2. ACS Nano 7, 791–797 (2013).26. Jones, A. M. et al. Optical generation of excitonic valley coherence inmonolayer WSe2. Nat. Nanotechnol. 8, 634–638 (2013).27. Wang, G. et al. Valley dynamics probed through charged and neutral excitonemission in monolayer WSe2. Phys. Rev. B 90 (2014).28. Kumar, S., Kaczmarczyk, A. & Gerardot, B. D. Strain-induced spatial andspectral isolation of quantum emitters in mono- and bilayer WSe2. Nano Lett.15, 7567–7573 (2015).29. Hansom, J., Schulte, C. H. H., Matthiesen, C., Stanley, M. J. & Atatüre, M.Frequency stabilization of the zero-phonon line of a quantum dot via phonon-assisted active feedback. Appl. Phys. Lett. 105, 172107 (2014).30. Acosta, V. M. et al. Dynamic stabilization of the optical resonances of singlenitrogen-vacancy centers in diamond. Phys. Rev. Lett. 108, 206401 (2012).31. Eisaman, M. D., Fan, J., Migdall, A. & Polyakov, S. V. Invited review article:single-photon sources and detectors. Rev. Sci. Instrum. 82, 071101 (2011).32. Warburton, R. et al. Optical emission from a charge-tunable quantum ring.Nature 405, 926–929 (2000).33. Nowack, K. C., Koppens, F. H. L., Nazarov, Y. V. & Vandersypen, L. M. K.Coherent control of a single electron spin with electric fields. Science 318,1430–1433 (2007).34. Salter, C. L. et al. An entangled-light-emitting diode. Nature 465, 594–597(2010).35. Watanabe, K., Taniguchi, T. & Kanda, H. Direct-bandgap properties andevidence for ultraviolet lasing of hexagonal boron nitride single crystal.Nat. Mater. 3, 404–409 (2004).36. Casiraghi, C. et al. Rayleigh imaging of graphene and graphene layers. NanoLett. 7, 2711–2717 (2007).37. Ferrari, A. C. & Basko, D. M. Raman spectroscopy as a versatile tool forstudying the properties of graphene. Nat. Nanotechnol. 8, 235–246 (2013).38. Bonaccorso, F. et al. Production and processing of graphene and 2d crystals.Mater. Today 15, 564–589 (2012).AcknowledgementsWe acknowledge the financial support from the EU Graphene Flagship (no. 604391),ERC Grants Hetero2D and PHOENICS, EPSRC Grants EP/K01711X/1, EP/K017144/1,EP/N010345/1, EP/M507799/1, EP/L016087/1, EP/M013243/1 and the EPSRCCambridge NanoDTC, EP/G037221/1. We are grateful to J. Barnes, C. Le Gall and H.S.Knowles for technical assistance.Author contributionsM.A., A.C.F. and I.G. devised and managed the project. K.W. and T.T. provided high-quality hBN material, M.B., X.C. and I.G. fabricated the devices, C.P.-B. and D.M.K.performed the optical measurements, assisted by M.B., X.C. and I.G., and analysed thedata. M.B., C.P.-B., D.Y. and A.K.O. performed Raman, PL, optical contrasts and AFMmeasurements and analysis. J.B. developed part of the data acquisition software for theconfocal microscope. All authors participated in the writing of the manuscript.Additional informationSupplementary Information accompanies this paper at http://www.nature.com/naturecommunicationsNATURE COMMUNICATIONS | DOI: 10.1038/ncomms12978 ARTICLENATURE COMMUNICATIONS | 7:12978 | DOI: 10.1038/ncomms12978 | www.nature.com/naturecommunications 5http://www.nature.com/naturecommunicationshttp://www.nature.com/naturecommunicationshttp://www.nature.com/naturecommunicationsCompeting financial interests: The authors declare no competing financialinterests.Reprints and permission information is available online at http://npg.nature.com/reprintsandpermissions/How to cite this article: Palacios-Berraquero, C. et al. Atomically thinquantum light-emitting diodes. Nat. Commun. 7, 12978 doi: 10.1038/ncomms12978(2016).This work is licensed under a Creative Commons Attribution 4.0International License. The images or other third party material in thisarticle are included in the article’s Creative Commons license, unless indicated otherwisein the credit line; if the material is not included under the Creative Commons license,users will need to obtain permission from the license holder to reproduce the material.To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/r The Author(s) 2016ARTICLE NATURE COMMUNICATIONS | DOI: 10.1038/ncomms129786 NATURE COMMUNICATIONS | 7:12978 | DOI: 10.1038/ncomms12978 | www.nature.com/naturecommunicationshttp://npg.nature.com/reprintsandpermissions/http://npg.nature.com/reprintsandpermissions/http://creativecommons.org/licenses/by/4.0/http://www.nature.com/naturecommunications title_link Results Design and operation of a vertical TMD-based LED Electrically driven quantum light in a WSe2-based LED Figure™1Design and operation of a TMD-based LED.(a) Optical microscope image of a typical device used in our experiments. The dotted lines highlight the footprint of the SLG, hBN and the TMD layers individually. The CrsolAu electrodes contact the SLG and  Figure™2WSe2-based QLED operation in the near infrared spectrum.(a) A raster-scan map of integrated EL intensity from monolayer and bilayer WSe2 areas of the QLED for an injection current of 3thinspmgrA (12.4thinspV). The dotted circles highlight the subm All-electrical generation of single-photon emission in WS2 Discussion Figure™3WS2-based QLED operation in the visible spectrum.A raster-scan map of integrated EL intensity from the monolayer WS2 area of the device: (a) at 0.665thinspmgrA injection current (bias 2.08thinspV), where the emission is delocalized and roughly uni Methods Device fabrication Confocal microscopy Data availability YuanZ.Electrically driven single-photon sourceScience2951021052002MizuochiN.Electrically driven single-photon source at room temperature in diamondNat. Photonics62993032012LohrmannA.Single-photon emitting diode in silicon carbideNat. Commun.677832015Notha We acknowledge the financial support from the EU Graphene Flagship (no. 604391), ERC Grants Hetero2D and PHOENICS, EPSRC Grants EPsolK01711Xsol1, EPsolK017144sol1, EPsolN010345sol1, EPsolM507799sol1, EPsolL016087sol1, EPsolM013243sol1 and the EPSRC Cambri ACKNOWLEDGEMENTS Author contributions Additional information