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Jianchen Dang, Tongyao Wu, Shaohua Yan, [Kenji Watanabe](https://orcid.org/0000-0003-3701-8119), [Takashi Taniguchi](https://orcid.org/0000-0002-1467-3105), [Hechang Lei](https://orcid.org/0000-0003-0850-8514), [Xiao-Xiao Zhang](https://orcid.org/0000-0002-5447-3394)

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[Electrical switching of spin-polarized light-emitting diodes based on a 2D CrI3/hBN/WSe2 heterostructure](https://mdr.nims.go.jp/datasets/3482953d-fd77-4da6-be8e-8fd19530f1b3)

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Electrical switching of spin-polarized light-emitting diodes based on a 2D CrI3/hBN/WSe2 heterostructureArticle https://doi.org/10.1038/s41467-024-51287-9Electrical switching of spin-polarized light-emitting diodes based on a 2D CrI3/hBN/WSe2 heterostructureJianchen Dang1, Tongyao Wu1, Shuohua Yan2,3, Kenji Watanabe 4,Takashi Taniguchi 5, Hechang Lei 2,3 & Xiao-Xiao Zhang 1Spin-polarized light-emitting diodes (spin-LEDs) convert the electronic spininformation to photon circular polarization, offering potential applicationsincluding spin amplification, optical communications, and advanced imaging.The conventional control of the emitted light’s circular polarization requires achange in the external magnetic field, limiting the operation conditions ofspin-LEDs.Here,wedemonstrate an atomically thin spin-LEDdevicebasedonaheterostructure of a monolayer WSe2 and a few-layer antiferromagnetic CrI3,separated by a thin hBN tunneling barrier. The CrI3 and hBN layers polarize thespin of the injected carriers into theWSe2.With the valley optical selection rulein the monolayer WSe2, the electroluminescence exhibits a high degree ofcircular polarization that follows the CrI3 magnetic states. Importantly, weshow an efficient electrical tuning, including a sign reversal, of the electro-luminescent circular polarization by applying an electrostatic field due to theelectrical tunability of the few-layer CrI3 magnetization. Our results establish aplatform to achieve on-demand operation of nanoscale spin-LED and electricalcontrol of helicity for device applications.The spin states of materials are the building blocks of modern infor-mation technology. Most spintronics devices achieve the control anddetection of electronic spin based on electrical currents. In a spin-polarized light-emitting diode (spin-LED), the injection of spin-polarized carriers results in circularly polarized electroluminescence(EL), interfacing optoelectronics and photonicswith spintronics1. Spin-LEDs have been demonstrated using GaAs-based ferromagnet/semi-conductor structures2–4, organic semiconductors like chiralmolecules5and hybrid perovskites6, and two-dimensional (2D) layeredheterostructures7,8, with some showing capabilities of room-temperature operation. However, controlling the degree of polariza-tion in the EL signals for these spin-LEDdevices often requires a changein the temperature, magnetic field, or chemical composition. Efficientelectrical control of the ELpolarizationwill enable low-power andhigh-speed applications in spin-optoelectronics1, information processing9,and ellipsometry-based tomography10,11.The recent advances in 2D layered materials open up possibilitiesfor optoelectronics and spintronics device designs that are moreflexible and tunable. In a monolayer semiconducting transition metaldichalcogenide (TMD), the valley-spin coupling and the valley-dependent optical selection rule ensure that we can selectivelydetermine the circular polarization of the emitted light based on thecarriers’ and excitons’ valley and spin occupation12. In addition, 2DTMDs have remarkable optical properties due to their large excitonicinteractions, and their optoelectronic prototypes like photodetectorand light-emitting diodes have been demonstrated13. The van derReceived: 18 April 2024Accepted: 5 August 2024Check for updates1Department of Physics, University of Florida, Gainesville, FL, USA. 2Department of Physics and Beijing Key Laboratory of Opto-electronic Functional Materials& Micro-nano Devices, Renmin University of China, 100872 Beijing, China. 3Key Laboratory of Quantum State Construction and Manipulation (Ministry ofEducation), Renmin University of China, 100872 Beijing, China. 4Research Center for Functional Materials, National Institute for Materials Science, 1-1 Namiki,Tsukuba, Japan. 5International Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba, Japan.e-mail: xxzhang@ufl.eduNature Communications |         (2024) 15:6799 11234567890():,;1234567890():,;http://orcid.org/0000-0003-3701-8119http://orcid.org/0000-0003-3701-8119http://orcid.org/0000-0003-3701-8119http://orcid.org/0000-0003-3701-8119http://orcid.org/0000-0003-3701-8119http://orcid.org/0000-0002-1467-3105http://orcid.org/0000-0002-1467-3105http://orcid.org/0000-0002-1467-3105http://orcid.org/0000-0002-1467-3105http://orcid.org/0000-0002-1467-3105http://orcid.org/0000-0003-0850-8514http://orcid.org/0000-0003-0850-8514http://orcid.org/0000-0003-0850-8514http://orcid.org/0000-0003-0850-8514http://orcid.org/0000-0003-0850-8514http://orcid.org/0000-0002-5447-3394http://orcid.org/0000-0002-5447-3394http://orcid.org/0000-0002-5447-3394http://orcid.org/0000-0002-5447-3394http://orcid.org/0000-0002-5447-3394http://crossmark.crossref.org/dialog/?doi=10.1038/s41467-024-51287-9&domain=pdfhttp://crossmark.crossref.org/dialog/?doi=10.1038/s41467-024-51287-9&domain=pdfhttp://crossmark.crossref.org/dialog/?doi=10.1038/s41467-024-51287-9&domain=pdfhttp://crossmark.crossref.org/dialog/?doi=10.1038/s41467-024-51287-9&domain=pdfmailto:xxzhang@ufl.eduWaals magnetic crystals have been shown to maintain magneticordering down to monolayer or few-layer limit, enabling the con-struction of nanoscale spintronic devices and easy integration withother 2D systems14,15. In particular, CrI3 crystals are A-type antiferro-magnets at the few-layer limit, with the spin easy axis along the out-of-plane direction. For an even or odd layer number, the correspondingmagnetic states in CrI3 are overall ferromagnetic or antiferromagnetic.The magnetic interactions, including the magnetic resonance fre-quency, in few-layer CrI3 can be efficiently tuned by either an out-of-plane electric field or doping density16–18, providing a unique oppor-tunity to develop electrically tunable magnetic devices.Here, we fabricated 2D LED structures based onmonolayerWSe2/hBN/few-layer CrI3, where the doping of WSe2 and CrI3 can be indivi-dually controlled by separate gating electrodes. TheCrI3/hBNserves asa spin-polarizing layer for carrier injection. We showed that the WSe2EL gained circular polarization due to the CrI3 spin filtering and spin-valley coupling. The EL light helicity switches with the layer-dependentmagnetization inCrI3. A large EL helicity of ~40%wasachieved inoneofthe devices, which infers a close-to-unity spin filtering efficiency. Wealso demonstrated an efficient electrostatic control of the EL helicitythrough the electrical control of the CrI3magnetization16,17. Our resultsestablished a 2D spin-LED prototype with programmable electricalcontrol of the helicity, which enables optoelectronic device designswith more tunable control and high-speed operation capabilities.ResultsEL characterizationThe dual-gated device geometry is shown in Fig. 1a. The back gate Vbgand top gate Vtg are used to control the doping of CrI3 and WSe2,respectively. When at appropriate bias voltages and doping levels,p-type carriers are injected through the CrI3/hBN into the n-dopedmonolayer WSe2, which gives rise to WSe2 electroluminescence sig-nals. In order to maintain the spin polarization during the carrierinjection, a thin hBN tunneling barrier (the thickness is confirmedwiththe atomic force microscope measurement, as shown in Supplemen-tary Fig. 1) is used to overcome the impedance mismatch19 and also toavoid the Schottky barrier at the interfaces. Two graphite stripescontact theWSe2 and CrI3 separately and serve as the source and draincontacts. Fig. 1b shows themicroscopic imageof a devicewith a bilayerCrI3. The Methods section provides detailed information on materialpreparation and heterostructure fabrication.When applying a bias voltage between the CrI3 and WSe2, thetunneling current I starts to flow for both positive and negative appliedbias voltages, as shown in Fig. 1d. The EL from the WSe2 can only beobserved for the positive bias region, and the onset EL thresholdcurrent decreases with an increasing top gate voltage, and therefore ata higher n-type doping density in WSe2 (The back gate Vbg for the CrI3doping is kept at zero for this part of the experiment). Combined withthe expected type-II band alignment between the WSe2 and CrI320 and-3 -2 -1 0 1 2 3-4-2024I bias(A)Vbias(V)Vtg= -1V   ThresholdVtg= -0.5VVtg= 0VVtg= 0.5VVtg= 1V1.55 1.60 1.65 1.70 1.75 1.8001234)stinu.bra(ytisnetnIEnergy(eV)Vbias=3.2 VVbias=3 VVbias=2.8 VVbias=2.6 VVbias=2.4 VVbias=2.2 VVbias=2 V1.6 1.801)stinu.bra(IEnergy(eV)PLELd fbaVtgVbiasWSe2CrI3hBNhBNGrGrGrGrhBNVbgceWSe2 CrI3hBNVbias > 0Vbias < 0Fig. 1 | Electroluminescence based on WSe2/hBN/CrI3 heterostructure.a Schematic of the device structure. The back gate Vbg and top gate Vtg are used tocontrol the doping of CrI3 and WSe2. The bias voltage Vbias is applied across thevertical junction going through the hBN tunneling barrier. hν indicates the emittedphoton with circular polarization σ±. b The whitelight microscopic image of amonolayer WSe2/hBN/bilayer CrI3 device. The scale bar is 10μm. The monolayerWSe2 is outlined by red dashed lines, blue dashed lines outline CrI3, the thin hBN(~2.5 nm) tunneling layer is denoted by the green dashed lines, and the source anddrain contacts (from graphite stripes) are denoted by the gray lines. c Spatially-resolved electroluminescence (EL) image of the device. The notation of dashedlines is the same as b. The scale bar is 10 μm. The EL signal comes from theoverlapped area of the source and drain contacts. d I–V characteristics of theheterostructure at different top gate voltages while keeping Vbg = 0V. The redtriangles denote the extracted threshold point for EL generation. e Band alignmentschematics of the heterostructure under different bias voltages during EL genera-tion with a positive Vbias (upper panel, WSe2 n-doped) and no EL generation with anegative Vbias (lower panel). The arrows indicate the direction of carrier tunnelingand the dashed ellipse represents the exciton. f EL spectra at different Vbias withVtg = 1 V and Vbg = 0V. The inset shows the comparison of the normalized photo-luminescence (PL) and EL spectra. The PL spectra was taken with a 633nm con-tinuous wave laser (10μW). The EL spectrum was measured under Vbias = 2.5 V,Ibias = 0.49μA with Vtg = 1 V.Article https://doi.org/10.1038/s41467-024-51287-9Nature Communications |         (2024) 15:6799 2the measured doping level shift from the WSe2 photoluminescence(PL) (see Supplementary Fig. 2), the I-V characteristic and the EL biasdependence can be understood by considering the type-II to type-Iband alignment transition when applying a negative bias voltage, asdepicted in Fig. 1e. With a positive bias voltage, p-type carriers flowfrom theCrI3/hBN layer intoWSe2. They can recombinewith the n-typecarriers in WSe2 and generate EL signals. On the other hand, with anegative bias voltage, there is no EL signal in WSe2 when tuning theWSe2 doping level fromp- to n-type doping. It thus indicates that thereis no carrier injection into WSe2 with a negative Vbias (when there issignificant tunneling current). This is likely due to the shift in CrI3bands under the bias voltage, which converts the type-II to a type-Iband alignment. The p-type carriers can flow fromWSe2 to CrI3 layersand give rise to tunneling currents without EL generation.Fromthe spatially-resolved EL imaging inFig. 1c, the ELgenerationis most efficient at the overlapping region of the source and draingraphite strips, where the tunneling currents go through the verticalheterostructure without further diffusion or drift. Fig. 1f shows theevolution of the EL signals at different bias voltages and tunnelingcurrents when Vtg = 1 V and Vbg = 0 V. The top gate dependence of theEL spectra is plotted in Supplementary Fig. 2a. The EL signal quencheswhen the WSe2 is tuned to p-doped, which can be deduced from thegate-dependent PL in Supplementary Fig. 2b, consistent with theexpected EL generationprocess in Fig. 1e. The I-V curves and EL spectraat different back gate voltages were summarized in SupplementaryFig. 2, which do not show significant back gate dependence. Thecomparison of the EL and PL (at Vtg = 0) spectra is plotted in the insetof Fig. 1f. The EL emission peak is redshifted with no obvious defect-related peaks, which may be attributed to the additional carrierscreening and the charge-related defect states being filled up. A moredetailed comparison and analysis of the EL exciton contributions canbe found in Supplementary Fig. 3.Spin-dependent circularly polarized ELWe measured the magnetic field-dependent EL to reveal the spinsensitivity of this structure. Under an out-of-plane magnetic field, thefew-layer CrI3 will go through layer-dependent spin-flip transitions.When the CrI3 layer is spin-polarized, the CrI3/hBN will serve as a spin-filtering layer for the injected holes into theWSe2 layer. The valley-spincoupling and valley-dependent optical selection rule in WSe2 sub-sequentially generate circularly polarized light emission based on theinjected hole spin polarization (Fig. 2a). The large spin-orbit couplingsplitting in theWSe2 valencebands and long valley lifetime of the holesfurther facilitate the generation of the circularly polarized EL. Fig. 2bshows the oppositely circularly polarized EL spectra at oppositemagnetic fields from a bilayer CrI3/hBN/WSe2 device (± 1.8 T is a fullypolarizing field for bilayer CrI3). As shown in Fig. 2c, d, we measuredand compared the magnetic state switching of the CrI3 layer throughthe reflective magnetic circular dichroism (RMCD) and the EL lighthelicity switching with different magnetic field ramping directions.Here, the EL polarization is characterized by the helicity as defined byðIσ + � Iσ�Þ=ðIσ + + Iσ�Þ. The RMCD shows the spin-flip transition thatcorresponds to the layer-dependent spin switching in bilayer CrI321, asindicated by the schematic plot in Fig. 2c. The EL helicity follows theRMCD magnetic field dependence and shows a jump to ~±10% at thespin-flip fields. This phenomenonwas further confirmed bymeasuringthree additional devices with bilayer CrI3. In all cases, the EL helicityfollowed the RMCD traces (see Supplementary Fig. 4). As the tem-perature was increased to be close to the Neel temperature of CrI3(~45 K), the EL helicity also dropped to zero (see Supplementary Fig. 5).Depending on the layer number of the CrI3, we can further tunethe EL helicity field dependence. A trilayer CrI3 is ferromagnetic at zerofields and goes through layer dependent spin-flip transitions with anincreasing out-of-plane magnetic field (Fig. 2e). The corresponding ELhelicity of a trilayer CrI3/hBN/WSe2 device also shows zero field helicityand spin-flip fields consistent with the RMCD signals, as shown inFig. 2f. The measured EL helicity varies across different devices, pos-sibly due to variations in device quality. We discussed the variability ofEL helicity and present data for multiple bilayer and trilayer CrI3devices in Supplementary Table 1. The maximum saturation polariza-tion obtainedwas ~40%, as shown in this trilayer device. This helicity inEL is intrinsically limited mainly by the exciton depolarization, whicharises from the efficient intervalley exciton exchange interactions22.Supplementary Fig. 7 is the measured circular polarization of neutraland charged excitons in PL with a near-resonant valley-polarizedoptical excitation, with trion states showing a maximum of ~37% cir-cular polarization, close to the highest circular polarization observedin EL devices. We therefore infer the spin filter efficiency was close tounity with these 2D magnetic tunneling junctions in the device withobserved maximum EL helicity, and the helicity was mostly con-strained by the intervalley exciton depolarization.Notably, the EL helicity is determined by the overall magnetiza-tionof theCrI3, insteadof the topmost layer adjacent to theWSe2 layer,which is distinctly different from the previously reported circularlypolarized PL quenching in CrI3/WSe223. In a CrI3/WSe2 structure, spin-dependent charge transfer is mostly determined by the adjacent CrI3layer spin polarization. In comparison, the hBN barrier here (Fig. 1a)ensures that the tunneling carriers’ spin is set by the overall magneti-zation of the CrI3 layer. The EL helicity does not show observabledependence on the WSe2 layer doping level (Fig. 3a) and the appliedbias voltage (Fig. 3b) within the EL generation ranges. These are con-sistent with the expectation of spin tunneling behavior, which is notsensitive to the relative shifts of Fermi levels across the hetero-structure. To reveal the impact of the tunneling junction, we alsomeasured EL signals with CrI3/WSe2 devices without the hBN tunnelingbarrier. While EL signals can still be observed, there is no obviouscircular dichroism that depends on the CrI3 magnetization (see Sup-plementary Fig. 6), which highlights the importance of tunneling bar-riers to reduce conductance mismatch and increase spin filterefficiency in 2D heterostructures.To further illustrate the differences in the tunneling spin injectionand spin-dependent charge transfer, we further compared the helicityof PL in a CrI3/WSe2 heterostructure and EL spectra in a CrI3/hBN/WSe2device. Fig. 3d shows the circularly polarized PL taken with a linearlypolarized excitation in CrI3/WSe2 under a 2 T magnetic field. Theenhanced PL polarization is caused by charge transfer, consistent withprevious work20,23. In comparison, the EL polarization (Fig. 3c) isoppositely polarized. This is consistent with the expectation of theband alignments and transfer processes. During EL generation,the polarization is determined and aligned by the CrI3 spin direction.As shown in Fig. 3e, injected spin-polarized carriers will reside in, e.g.,the K valley because of the valley-spin coupling inmonolayer TMDandgives rise to σ+ emission. On the other hand, the PL polarization ina CrI3/WSe2 heterostructure arises from the spin-dependent chargetransfer23,24, which quenches the valley/spin-polarized exciton withcarriers’ spin aligned with the CrI3 spin orientation. In the depictedscenario in Fig. 3f, under the same CrI3 spin alignment as Fig. 3e, the Kvalley exciton will be quenched due to electron interlayer transfer,giving rise to an overall σ- polarization in light emission.Electrical switching of EL helicityEfficient electrical tuning of magnetic interactions has beendemonstrated in few-layer CrI3 in prior studies16–18,25. Here, we utilizethe electrical tunability of CrI3 to control the spin-dependent ELsignals. To this end, we use the back gate to electrostatically tune thedoping level in CrI3 (Fig. 1a) while observing the EL helicity switch-ing.When varying the doping in CrI3, the spin-flip transition field canshow significant shifting16,17 and gives rise to spin switching, andtherefore EL helicity switching, at certain fixed magnetic fields. InFig. 4a, we prepared a bilayer device in the “up” state by applying aArticle https://doi.org/10.1038/s41467-024-51287-9Nature Communications |         (2024) 15:6799 3magnetic field of 2 T. Subsequently, we swept the back gate voltagewhile maintaining the system at 0.8, 0.71, and 0.5 T, correspondingto traces 1 to 3 in Fig. 4b, respectively.When atmagnetic fields (0.8 Tand 0.5 T) away from the spin-flip field, themagnetization remains inferromagnetic and antiferromagnetic states, respectively, as shownin the RMCD measurements. Near the spin-flip field (trace 2), arepeatable switching between the ferromagnetic and anti-ferromagnetic states can be achieved, consistent with previousreports16,17. The measured EL helicity shows corresponding repea-table switching between 7% and 21% (Fig. 4c), with switching gatevoltage hysteresis similar to that observed in RMCD. We note thatthe incomplete AFM to FM switching here is due to the limited backgate voltages applied in this device. Alternatively, we also examinedthe switching capability with a trilayer CrI3 device (Fig. 4d). Thedevice was initially prepared at 2 T and then subjected to a fixedmagnetic field just below its coercive force at −0.68 T. As the gatevoltage scanned from negative to positive values, it induces a signswitch in the magnetism of CrI3 (Fig. 4e) because of the decrease inthe spin-flip field. Notably, this is a one-time-only switching event, asthe device remains in the negative sign state afterward due to itbeing the low-energy state under a negative magnetic field. Due tothe spin reversal in CrI3, it thus gives rise to a sign reversal in the ELhelicity that is triggered by electrical signals, as shown in Fig. 4f. Inaddition, we investigated the repeatable switching behavior near thespin-flip transition field of 1.73 T, as shown in Supplementary Fig. 8.DiscussionIn conclusion, we showed robust spin-LEDdevice operation composedof CrI3/hBN/WSe2 van der Waals heterostructures, where the spin-polarized carriers tunneled through the CrI3/hBN layer and resulted invalley polarized and circularly polarized light emission. A close-to-unity spin transfer efficiencywas achievedwith our tunneling contacts.Importantly, we demonstrate an effective modulation and control ofEL helicity through electrical signals due to the electrical tunability ofmagnetization in CrI3. Our results provide an approach to having on-demand, electrically tunable helicity in 2D spin-LED, opening updirections to combine optoelectronics, spintronics, valleytronics, andadvanced imaging.1.6 1.7)stinu.bra(ytisnetni LEEnergy(eV) + B= 1.8T1.6 1.7Energy(eV) + B= -1.8T-2 0 2-2-1012)%(DCMRMagnetic field (T) down up-2 0 2-40-2002040)%(yticile h L EMagnetic field (T) down up-2 -1 0 1 2-15-10-50510)%(yticileh LEMagnetic field (T) down upa bc de fWSe2CrI3hBNTunnelingK-2 -1 0 1 2-101)%(DCMRMagnetic field (T) down upFig. 2 | Spin-dependent EL. a The spin dependence in EL signals originated fromthe spin-polarized carrier injection through CrI3/hBN and the coupled spin andvalley indexes inmonolayer transitionmetal dichalcogenide (TMD).b Polarization-resolved EL spectra under ±1.8 T out-of-plane magnetic fields, showing oppositehelicity. c The reflective magnetic circular dichroism (RMCD) signals as a functionof magnetic fields for a bilayer CrI3/hBN/WSe2 device. The spin switching for eachlayer is sketched. The red and blue arrows indicate the spin-up and spin-downdirections. The up and down indicates the magnetic field sweeping directions.d The corresponding extracted EL helicity as a function when sweeping the mag-netic field. e The RMCD signals and f corresponding EL helicity of a trilayer CrI3/hBN/WSe2 device as a function of magnetic fields.Article https://doi.org/10.1038/s41467-024-51287-9Nature Communications |         (2024) 15:6799 4MethodsCrystal growthCrI3 single crystals were grown by the chemical vapor transportmethod. Chromium powder (99.99% purity) and iodine flakes(99.999%) in a 1:3molar ratio are put into a silicon tubewith a length of200mmand an inner diameter of 14mm. The tube was pumped downto 0.01 Pa and sealed under vacuum, and then placed in a two-zonehorizontal tube furnace. The twogrowth zones are raised slowly to 903and 823 K for two days and are then held there for another seven days.Shiny, black, plate-like crystals with lateral dimensions of up to severalmillimeters can be obtained from the growth. In order to avoiddegradation, the CrI3 crystals are stored in an inert-gas glovebox.Device fabricationThe few layer graphite, hBN, bilayer/trilayer CrI3 and monolayer WSe2were first mechanically exfoliated from bulk crystals and identified bytheir color contrast under an optical microscope. The heterostructurewas built by using the dry transfer technique with a PC stamp26 andreleased onto a substrate with pre-patterned gold electrodes. Thetransfer steps were performed in a nitrogen-filled glove box.Optoelectronic measurementsThe devices were mounted onto a 3D piezoelectric stage in an opticalcryostat (attoDry1000) with a base temperature of 4 K. The cryostatwas equipped with a superconducting solenoid magnet, which cansupply amagnetic field from −9T to 9 T. For EL and PLmeasurements,the emission was collected by an objective lens with a numericalaperture of 0.82 and detected by a grating spectrometer and CCD(Princeton Instruments SpectraPro HRS300+ PIXIS). The polarizationof the emission was measured by using a λ∕4 plate followed by apolarizer. For PL measurement, the sample was excited by a 633-nmcontinuous wave laser with a focal spot diameter ~1μm.Fig. 3 | Characterization of EL helicity. a The evolution of EL helicity (bilayer CrI3/hBN/WSe2) under different Vtg,measured under 2 Tout-of-planemagnetic field andwith Vbias = 2.5 V.b ELhelicity dependencewhen varying Vbias (after reaching the ELthreshold conditions), as measured with 2 T out-of-plane field and Vtg = 1 V.c,d compares the circular polarization of the EL and PL signals at 2 Tmagneticfield.The PL was measured at a WSe2/CrI3 heterostructure region without hBN barrier,excited by linearly polarized 633 nm laser. The EL spectra weremeasured in a CrI3/hBN/WSe2 device. EL and PL possess opposite circular polarizations. e Theexemplary schematics illustrate the spin-polarized carrier injection process, wherethe spin polarization results in K valley and σ + EL emission. The solid and dashedarrows indicate the allowed and forbidden carrier injection. B┴ represents the out-of-planemagnetic field. fUnder the same CrI3 spin alignment, the interlayer chargetransfer favors the quenching of K valley electrons and therefore results in a higher-K exciton population and σ- PL emission.Article https://doi.org/10.1038/s41467-024-51287-9Nature Communications |         (2024) 15:6799 5RMCD measurementsForRMCDmeasurements, the 633-nmcontinuouswave laserwasused.The laser was modulated at 50 kHz between the left and right circularpolarization using a photoelastic modulator (Hinds PEM). The reflec-ted light was focused onto a photodiode. The RMCD was determinedas the ratio of the a.c. component of the photodiode signal measuredby a lock-in amplifier at the polarizationmodulation frequency and thed.c. component of the photodiode signalmeasuredbyanoscilloscope.Data availabilityThe data that support the findings of this study are available within thepaper and its Supplementary Information. Additional data are availablefrom the corresponding authors upon request.References1. Žutić, I., Fabian, J. & Das Sarma, S. Spintronics: Fundamentals andapplications. Rev. Mod. Phys. 76, 323–410 (2004).2. Fiederling, R. et al. Injection and detection of a spin-polarized cur-rent in a light-emitting diode. Nature 402, 787–790 (1999).3. Ohno, Y. et al. Electrical spin injection in a ferromagnetic semi-conductor heterostructure. Nature 402, 790–792 (1999).4. Nishizawa, N., Nishibayashi, K. & Munekata, H. Pure circular polar-ization electroluminescence at room temperature with spin-polarized light-emitting diodes. Proc. Natl Acad. Sci. 114,1783–1788 (2017).5. Yang, Y., da Costa, R. C., Smilgies, D.-M., Campbell, A. J. & Fuchter,M. J. Induction of Circularly Polarized Electroluminescence from anAchiral Light-Emitting Polymer via a Chiral Small-Molecule Dopant.Adv. Mater. 25, 2624–2628 (2013).6. Kim, Y.-H. et al. 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The up and down inb indicates the sweeping direction of Vbg. c The repeatable switching of EL helicitywhen varying the back gate voltage at a fixed 0.71 T, which corresponds to trace 2position in a and b. d RMCD of trilayer CrI3 as a function of magnetic field underzero back gate voltage at 4 K. e Back gate voltage control of RMCD of trilayer CrI3.The sample was prepared by a magnetic field first at 2 T and then biased at −0.68 T(trace 4). fTheELhelicity of the corresponding trilayer CrI3 devicewhenvaryingVbgat a fixed −0.68 T (trace 4 position).Article https://doi.org/10.1038/s41467-024-51287-9Nature Communications |         (2024) 15:6799 6https://doi.org/10.1063/1.3582917https://doi.org/10.1063/1.358291716. Huang, B. et al. Electrical control of 2D magnetism in bilayer CrI3.Nat. Nanotechnol. 13, 544–548 (2018).17. Jiang, S., Li, L.,Wang, Z.,Mak, K. F. &Shan, J. Controllingmagnetism in2DCrI3byelectrostatic doping.Nat. Nanotechnol. 13, 549–553 (2018).18. Jiang, S., Shan, J. & Mak, K. 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Commun. 11, 6021 (2020).25. Zhang, X.-X. et al. Gate-tunable spin waves in antiferromagneticatomic bilayers. Nat. Mater. https://doi.org/10.1038/s41563-020-0713-9 (2020).26. Wang, L. et al. One-Dimensional Electrical Contact to a Two-Dimensional Material. Science 342, 614 (2013).AcknowledgementsX-X.Z. acknowledge the support from the Department of Energy (DOE)award DE-SC0022983. This work was partly conducted at the ResearchService Centers of the Herbert Wertheim College of Engineering at theUniversity of Florida. H.C.L. was supported by Beijing Natural ScienceFoundation (Grant No. Z200005), National Key R&D Program of China(Grants Nos. 2022YFA1403800, 2023YFA1406500), and National Nat-ural Science Foundation of China (Grants Nos. 12274459).Author contributionsX-X.Z. and J. D. designed the study. J.D. and T.W. fabricated the deviceand performed the measurements. K.W. and T.T. grew the bulk hBNcrystals. S.Y. andH.C.L. grew the bulk CrI3 crystals. X-X.Z. and J.D. wrotethemanuscript. All authors discussed the results andcommentedon themanuscript.Competing interestsThe authors declare no competing interests.Additional informationSupplementary information The online version containssupplementary material available athttps://doi.org/10.1038/s41467-024-51287-9.Correspondence and requests for materials should be addressed toXiao-Xiao Zhang.Peer review information Nature Communications thanks the anon-ymous reviewers for their contribution to the peer review of this work. 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To view a copy of this licence, visit http://creativecommons.org/licenses/by-nc-nd/4.0/.© The Author(s) 2024Article https://doi.org/10.1038/s41467-024-51287-9Nature Communications |         (2024) 15:6799 7https://doi.org/10.1038/s41563-020-0713-9https://doi.org/10.1038/s41563-020-0713-9https://doi.org/10.1038/s41467-024-51287-9http://www.nature.com/reprintshttp://creativecommons.org/licenses/by-nc-nd/4.0/http://creativecommons.org/licenses/by-nc-nd/4.0/ Electrical switching of spin-polarized light-emitting diodes based on a 2D CrI3/hBN/WSe2 heterostructure Results EL characterization Spin-dependent circularly polarized EL Electrical switching of EL helicity Discussion Methods Crystal growth Device fabrication Optoelectronic measurements RMCD measurements Data availability References Acknowledgements Author contributions Competing interests Additional information