Exciton band structure in layered MoSe<sub>2</sub>: from a monolayer to the bulk limit

Arora, Ashish; Nogajewski, Karol; Molas, Maciej R.; Koperski, Maciej; Potemski, M.

doi:10.1039/c5nr06782k

Cited by 196 publications

(265 citation statements)

References 59 publications

(87 reference statements)

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“…29,46 The high optical quality of the MoSe 2 embedded in the heterostructure enabled us to resolve an additional peak at 1.87 eV in the reflectivity contrast spectrum, assigned to the B exciton of MoSe 2 . 43,47 The vastly improved optical properties suggest a defect healing process, in which the contact with MoS 2 is enough to drastically reduce the number of defects in MoSe 2 . The quenching of the intralayer emission 32,37 in the trilayer is manifestation of a fast charge transfer mechanism 36,48 related to the type II band alignment in MoS 2 /MoSe 2 heterostructures.…”

Section: Defect Healingmentioning

confidence: 99%

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 Healingmentioning

confidence: 99%

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

et al. 2017

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“…In the singlelayer configuration, the TMDs offer a unique platform to explore not only the carrier transport in an ultrathin channel but also the control of 2D excitonic systems and the spinvalley physics [4][5][6]. These may be achieved owing to their electronic structure and spatialinversion symmetry that give rise to a strong spin-obit coupling, i.e.…”

Section: Introductionmentioning

confidence: 99%

Millimeter-scale layered MoSe2 grown on sapphire and evidence for negative magnetoresistance

Dau

Vergnaud

Marty

et al. 2017

Applied Physics Letters

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Molecular beam epitaxy technique has been used to deposit a single layer and a bilayer of MoSe2 on sapphire. Extensive characterizations including in-situ and ex-situ measurements show that the layered MoSe2 grows in a scalable manner on the substrate and reveals characteristics of a stoichiometric 2H-phase. The layered MoSe2 exhibits polycrystalline features with domains separated by defects and boundaries. Temperature and magnetic field dependent resistivity measurements unveil a carrier hopping character described within two-dimensional variable range hopping mechanism. Moreover, a negative magnetoresistance was observed, stressing a fascinating feature of the charge transport under the application of a magnetic field in the layered MoSe2 system. This negative magnetoresistance observed at millimeter-scale is similar to that observed recently at room temperature inWS2 flakes at a micrometer scale [Zhang et al., Appl. Phys. Lett. 108, 153114 (2016)]. This scalability highlights the fact that the underlying physical mechanism is intrinsic to these two-dimensional materials and occurs at very short scale.

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“…1 and 2, whereas in ML WSe 2 , the discrete emitters can overlap with broad peaks linked to localized 2D excitons and/or their phonon replica. 30 (ii) The 2D neutral exciton states in ML MoSe 2 are optically bright, whereas the lowest energy transition in ML WSe 2 is optically dark, [30][31][32][33][34][35] which will impact carrier relaxation and recombination dynamics. The MoSe 2 ML flakes are obtained by micro-mechanical cleavage of a bulk crystal using viscoelastic stamping.…”

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confidence: 99%

Discrete quantum dot like emitters in monolayer MoSe2: Spatial mapping, magneto-optics, and charge tuning

Branny

Wang

Kumar

et al. 2016

Applied Physics Letters

118

110

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Transition metal dichalcogenide monolayers such as MoSe2,MoS2 and WSe2 are direct bandgap semiconductors with original optoelectronic and spin-valley properties. Here we report spectrally sharp, spatially localized emission in monolayer MoSe2. We find this quantum dot like emission in samples exfoliated onto gold substrates and also suspended flakes. Spatial mapping shows a correlation between the location of emitters and the existence of wrinkles (strained regions) in the flake. We tune the emission properties in magnetic and electric fields applied perpendicular to the monolayer plane. We extract an exciton g-factor of the discrete emitters close to -4, as for 2D excitons in this material. In a charge tunable sample we record discrete jumps on the meV scale as charges are added to the emitter when changing the applied voltage.

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Exciton band structure in layered MoSe₂: from a monolayer to the bulk limit

Cited by 196 publications

References 59 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

Millimeter-scale layered MoSe2 grown on sapphire and evidence for negative magnetoresistance

Discrete quantum dot like emitters in monolayer MoSe2: Spatial mapping, magneto-optics, and charge tuning

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Exciton band structure in layered MoSe2: from a monolayer to the bulk limit

Cited by 196 publications

References 59 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

Millimeter-scale layered MoSe2 grown on sapphire and evidence for negative magnetoresistance

Discrete quantum dot like emitters in monolayer MoSe2: Spatial mapping, magneto-optics, and charge tuning

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Product

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Exciton band structure in layered MoSe₂: from a monolayer to the bulk limit

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