Magnetoexcitons in large area CVD-grown monolayer<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>MoS</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:math>and<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>MoSe</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:math>on sapphire

Mitioglu, Anatolie; Gałkowski, Krzysztof; Surrente, Alessandro; Kłopotowski, Ł.; Dumcenco, Dumitru; Kis, András; Maude, D. K.; Plochocka, P.

doi:10.1103/physrevb.93.165412

Cited by 72 publications

(69 citation statements)

References 46 publications

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“…1(c) has a peak at 1.637 eV, which corresponds well to the high energy shoulder of the µPL spectrum and hence is assigned to A exciton. As in our previous study, 34 we are unable to resolve the B exciton in reflectivity contrast measurements on as grown MoSe 2 .…”

Section: Defect Healingcontrasting

confidence: 68%

Defect Healing and Charge Transfer-Mediated Valley Polarization in MoS₂/MoSe₂/MoS₂ Trilayer van der Waals Heterostructures

et al. 2017

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Monolayer transition metal dichalcogenides (TMDC) grown by chemical vapor deposition (CVD) are plagued by a significantly lower optical quality compared to exfoliated TMDC. In this work we show that the optical quality of CVD-grown MoSe 2 is completely recovered if the material is sandwiched in MoS 2 /MoSe 2 /MoS 2 trilayer van der Waals heterostructures. We show by means of density-functional theory that this 1 arXiv:1703.00806v2 [cond-mat.mes-hall] 14 Jun 2017 remarkable and unexpected result is due to defect healing: S atoms of the more reactive MoS 2 layers are donated to heal Se vacancy defects in the middle MoSe 2 layer. In addition, the trilayer structure exhibits a considerable charge-transfer mediated valley polarization of MoSe 2 without the need for resonant excitation. Our fabrication approach, relying solely on simple flake transfer technique, paves the way for the scalable production of large-area TMDC materials with excellent optical quality. KeywordsChemical Vapor Deposition, transition metal dichalcogenides, van der Waals heterostructures, defect healing, charge transfer mediated valley polarization Monolayer transition metal dichalcogenides (TMDC) have a direct bandgap situated in the visible range, which makes them ideal building blocks for novel electronic and optoelectronic devices. [1][2][3][4][5][6][7][8][9][10] The bandgap of monolayer TMDCs occurs at the inequivalent (but degenerate) K and K' points of the hexagonal Brillouin zone. The broken inversion symmetry of a TMDC monolayer combined with the time reversal symmetry imposes opposite magnetic moments at the K and K' valleys. This in turn determines the characteristic circular dichroism exhibited by these materials, wherein each valley can be addressed separately with circularly polarized light of a given helicity. 11-13 Additionally, optical spectra are influenced by the strong spin-orbit coupling, which lifts the degeneracy of band states at the valence band edges, resulting in well-resolved A and B resonances, as observed in reflectivity or absorption spectra. 2,14-16 The interplay of spin-orbit coupling with broken inversion symmetry and time reversal symmetry locks the valley and spin degrees of freedom, making TMDC attractive candidates for valleytronics. 17 The spin-valley index locking along with the large 2 distance in the momentum space between K and K' valleys preserves the valley polarization observed in the degree of circular polarization (DCP) in helicity resolved photoluminescence emission. [18][19][20][21][22] Applications require a scalable fabrication platform providing high-quality large-area monolayer TMDC. Unfortunately, the most promising approach today, namely chemical vapor deposition (CVD) growth 23-27 struggles to compete with exfoliated TMDC in terms of sample quality. Low temperature PL spectroscopy of CVD-grown MoS 2 and MoSe 2 reveals broad emission from defect bound excitons, which is significantly more intense than the free exciton peak [28][29][30] and is related to chalcogen vacancies induced...

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Section: Defect Healingcontrasting

confidence: 68%

Defect Healing and Charge Transfer-Mediated Valley Polarization in MoS₂/MoSe₂/MoS₂ Trilayer van der Waals Heterostructures

et al. 2017

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“…This phenomenon has been confirmed during a hightemperature optical spectroscopy of ML WS 2 [72]. Here, the role of strain cannot be ruled out for the CVDgrown MLs of WSe 2 on sapphire (see supporting information), although it is claimed in [73] that strain may not be the reason for the difference between exfoliated and CVD-grown MoS 2 following a calculated small contribution of strain to spectral shifts.…”

Section: Resultsmentioning

confidence: 75%

Influence of the substrate material on the optical properties of tungsten diselenide monolayers

et al. 2017

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Monolayers of transition-metal dichalcogenides such as WSe 2 have become increasingly attractive due to their potential in electrical and optical applications. Because the properties of these 2D systems are known to be affected by their surroundings, we report how the choice of the substrate material affects the optical properties of monolayer WSe 2 . To accomplish this study, pump-density-dependent micro-photoluminescence measurements are performed with time-integrating and time-resolving acquisition techniques. Spectral information and power-dependent mode intensities are compared at 290K and 10K for exfoliated WSe 2 on SiO 2 /Si, sapphire (Al 2 O 3 ), hBN/Si 3 N 4 /Si, and MgF 2 , indicating substrate-dependent appearance and strength of exciton, trion, and biexciton modes. Additionally, one CVD-grown WSe 2 monolayer on sapphire is included in this study for direct comparison with its exfoliated counterpart. Time-resolved micro-photoluminescence shows how radiative decay times strongly differ for different substrate materials. Our data indicates exciton-exciton annihilation as a shortening mechanism at room temperature, and subtle trends in the decay rates in correlation to the dielectric environment at cryogenic temperatures. On the measureable time scales, trends are also related to the extent of the respective 2D-excitonic modes' appearance. This result highlights the importance of further detailed characterization of exciton features in 2D materials, particularly with respect to the choice of substrate.

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“…V). The low-temperature linewidth in our capped samples is more than 1 order of magnitude smaller than the one observed for the usual broad peak reported in most studies for MoS 2 [9,14,16,[29][30][31][32][33][34]. This transition usually attributed to the neutral exciton is possibly merged with a broad charged exciton and/or defect contribution, as discussed recently [40].…”

Section: Neutral Exciton Transition In Pl and Reflectivitymentioning

confidence: 67%

“…3(a) and 4(d). This is a major improvement on the usually reported emission linewidth of ≈50 meV at low temperature [9,14,16,[29][30][31][32][33][34]. The high-quality van der Waals heterostructures [35] we investigate here allow us to access new information on their optical and spin-valley properties.…”

Section: Introductionmentioning

confidence: 97%

“…In the literature, only a few reported experimental values exist for the exciton g factor on MoS 2 MLs [33,34] between g X ¼ −4 and g X ¼ −4.5, obtained with magnetoreflectivity measurements on CVD-grown MoS 2 MLs. In order to rule out any possible modification of the g factor induced by the hBN encapsulation, we perform magneto-PL on uncapped MoS 2 MLs deposited directly onto SiO 2 substrates.…”

Section: B Valley Zeeman Splitting and Field-induced Valley Polarizamentioning

confidence: 99%

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Excitonic Linewidth Approaching the Homogeneous Limit in MoS2 -Based van der Waals Heterostructures

et al. 2017

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The strong light-matter interaction and the valley selective optical selection rules make monolayer (ML) MoS 2 an exciting 2D material for fundamental physics and optoelectronics applications. But, so far, optical transition linewidths even at low temperature are typically as large as a few tens of meV and contain homogeneous and inhomogeneous contributions. This prevented in-depth studies, in contrast to the bettercharacterized ML materials MoSe 2 and WSe 2 . In this work, we show that encapsulation of ML MoS 2 in hexagonal boron nitride can efficiently suppress the inhomogeneous contribution to the exciton linewidth, as we measure in photoluminescence and reflectivity a FWHM down to 2 meV at T ¼ 4 K. Narrow optical transition linewidths are also observed in encapsulated WS 2 , WSe 2 , and MoSe 2 MLs. This indicates that surface protection and substrate flatness are key ingredients for obtaining stable, high-quality samples. Among the new possibilities offered by the well-defined optical transitions, we measure the homogeneous broadening induced by the interaction with phonons in temperature-dependent experiments. We uncover new information on spin and valley physics and present the rotation of valley coherence in applied magnetic fields perpendicular to the ML.

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Magnetoexcitons in large area CVD-grown monolayerMoS2andMoSe2on sapphire

Cited by 72 publications

References 46 publications

Defect Healing and Charge Transfer-Mediated Valley Polarization in MoS₂/MoSe₂/MoS₂ Trilayer van der Waals Heterostructures

Defect Healing and Charge Transfer-Mediated Valley Polarization in MoS₂/MoSe₂/MoS₂ Trilayer van der Waals Heterostructures

Influence of the substrate material on the optical properties of tungsten diselenide monolayers

Excitonic Linewidth Approaching the Homogeneous Limit in MoS2 -Based van der Waals Heterostructures

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Magnetoexcitons in large area CVD-grown monolayerMoS2andMoSe2on sapphire

Cited by 72 publications

References 46 publications

Defect Healing and Charge Transfer-Mediated Valley Polarization in MoS2/MoSe2/MoS2 Trilayer van der Waals Heterostructures

Defect Healing and Charge Transfer-Mediated Valley Polarization in MoS2/MoSe2/MoS2 Trilayer van der Waals Heterostructures

Influence of the substrate material on the optical properties of tungsten diselenide monolayers

Excitonic Linewidth Approaching the Homogeneous Limit in MoS2 -Based van der Waals Heterostructures

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Defect Healing and Charge Transfer-Mediated Valley Polarization in MoS₂/MoSe₂/MoS₂ Trilayer van der Waals Heterostructures

Defect Healing and Charge Transfer-Mediated Valley Polarization in MoS₂/MoSe₂/MoS₂ Trilayer van der Waals Heterostructures