Probing charge transfer excitons in a MoSe<sub>2</sub>–WS<sub>2</sub> van der Waals heterostructure

Ceballos, Frank; Bellus, Matthew Z.; Chiu, Hsin-Ying; Zhao, Hui

doi:10.1039/c5nr04723d

Cited by 101 publications

(95 citation statements)

References 46 publications

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“…Previously, some of us have shown that in graphene-WS 2 heterostructures, photocarriers excited in WS 2 can transfer to graphene in 1 ps with high efficiency [28]. In heterostructures formed by different types of TMD monolayers, interlayer charge transfer was also found to be highly efficient, as evident by pronounced photoluminescence quenching effect [29][30][31][32][33][34][35][36], and ultrafast, as revealed by ultrafast laser measurements [37][38][39][40][41]. However, the mechanism of such ultrafast transfer processes is still yet to be understood, given the weak van der Waal nature of the interlayer coupling.…”

Section: Introductionmentioning

confidence: 98%

Probing effect of electric field on photocarrier transfer in graphene-WS_2 van der Waals heterostructures

He¹,

He²,

Wang³

et al. 2017

Opt. Express

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We report spatially and temporally resolved measurements of photocarrier transfer process in van der Waals heterostructures. Graphene-WS₂ hetero-bilayers were fabricated by manually stacking monolayers of graphene and WS₂ obtained by mechanical exfoliation. Photocarriers were excited in WS₂ by an ultrafast laser pulse. Their transfer to graphene was monitored by measuring the differential reflection signal as a function of both time and space. Surprisingly, we found that the width of the photocarrier profile in graphene decreases with time. This counter-intuitive phenomenon suggests that the Coulomb field of the holes transferred from WS₂ to graphene can effectively drag the electrons to speed up their transfer. This effect illustrates that an externally applied electric field can be used to control the ambipolar photocarrier transfer in van der Waals heterostructures.

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Section: Introductionmentioning

confidence: 98%

Probing effect of electric field on photocarrier transfer in graphene-WS_2 van der Waals heterostructures

He¹,

He²,

Wang³

et al. 2017

Opt. Express

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“…Inset: Spatially resolved integrated PL intensity in the spectral range marked in the main panel around pillar A. e,f, Intensity-normalized PL spectra recorded from the HBL at different excitation powers at a position outside the pillar region (e) and on pillar A (f).Besides the power-dependent measurements shown in e,f all spectra were recorded at 10 K subject to strong continuous wave (cw) excitation at 633 nm using a power of 35 µW focused to a spot-size of ∼ 1 µm.4 over sub-picosecond timescales, faster than the exciton lifetime. [40][41][42] The most prominent emission feature from the HBL is at ∼1.38 eV and is attributed to IXs formed by an electron in the MoSe 2 and a hole in the WSe 2 .[7] This attribution is supported by the emission energy and the characteristically asymmetric lineshape featuring red-shifted emission from momentum-indirect IXs [23]. Fig.…”

mentioning

confidence: 99%

“…4 over sub-picosecond timescales, faster than the exciton lifetime. [40][41][42] The most prominent emission feature from the HBL is at ∼1.38 eV and is attributed to IXs formed by an electron in the MoSe 2 and a hole in the WSe 2 .…”

mentioning

confidence: 99%

Discrete interactions between a few interlayer excitons trapped at a MoSe2-WSe2 heterointerface (Conference Presentation)

Kremser¹,

Brotons‐Gisbert²,

Meyer³

et al. 2020

2D Photonic Materials and Devices III

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1 arXiv:1907.08815v1 [cond-mat.mes-hall] 20 Jul 2019Bose quantum fluids of ultra-cold atoms [1] and exciton-polaritons[2] exhibit spectacular many-body phenomena, the physics of which can be captured by mean field theories in the weakly interacting regime. In contrast, dipolar quantum fluids interact more strongly over larger lengthscales and are, therefore, predicted to exhibit novel quantum, as well as classical multi-particle correlation effects that go far beyond mean field approaches [3][4][5][6]. Inter-layer excitons (IXs) in hetero-bilayers of transition metal dichalcogenides (TMDs) [7][8][9][10][11][12][13][14] represent an exciting emergent class of long-lived dipolar composite bosons in an atomically thin, near-ideal two-dimensional (2D) system [5,9,14]. The emergence of quantum correlations in finite 2D systems may open up tantalizing prospects of excitonic Bose-Einstein condensation [5,[14][15][16] and Wigner-crystal like phases[4] at sufficiently low temperatures and in confined geometries [17].Here, we trap a tunable number of dipolar IXs (N IX ∼ 1 − 4) within a nanoscale confinement potential induced by placing a MoSe 2 -WSe 2 hetero-bilayer (HBL) onto an array of SiO 2 nanopillars [18,19]. We control the mean occupation of the IX trap via the optical excitation level and observe discrete sharp-line emission from different configurations of interacting IXs. The intensities of these features exhibit characteristic near linear, quadratic, cubic and quartic power dependencies, [20] which allows us to identify them as different multiparticle configurations with N IX ∼ 1 − 4. We directly measure the hierarchy of dipolar and exchange interactions as N IX increases. The interlayer biexciton (N IX = 2) is found to be an emission doublet that is blue-shifted from the single exciton by ∆E = (8.4 ± 0.6) meV and split by 2J = (1.2 ± 0.5) meV. The blueshift is even more pronounced for triexcitons ((12.4 ± 0.4) meV) and quadexcitons ((17.0 ± 0.5) meV). These values are shown to be mutually consistent with numerical modelling of dipolar excitons moving in a harmonic trapping potential having a confinement lengthscale in the range ≈ 3 nm. [21,22] Our results contribute to the understanding of interactions between IXs in TMD heterobilayers at the discrete limit of only a few excitations and represent a key step towards exploring quantum correlations between IXs in TMD hetero-bilayers.HBLs of van-der-Waals bonded 2D TMDs feature an atomically sharp interface with a type-II band alignment and frontier orbital couplings defined by the mutual angular orienta-2 tion of the basal plane of the component layers.[7] Such atomically-thin 2D heterointerfaces can host IXs -Coulomb-bound states of electrons (e) and holes (h) located in the different component monolayers.[7] The spatial separation of e and h gives rise to a significantly increased lifetime compared to intralayer excitons [7, 9, 23] and a static electric out-of-plane dipole moment with a magnitude |p z |/e ∼ 0.7 nm for the MoSe 2 -WSe 2 heterointerface[7].The en...

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“…Except for the theoretical calculations, the band offset can be confirmed via microbeam X‐ray photoelectron spectroscopy, scanning tunneling spectroscopy, or submicrometer angle‐resolved photoemission spectroscopy in combination with photoluminescence (PL), such as in the MoS 2 /WSe 2 , MoS 2 /WS 2 , and MoSe 2 /WSe 2 heterojunctions . The shifts of PL and Raman spectra indicate that there is strong interlayer coupling between the two single layers in ultrathin vdW heterostructures regardless of mechanical exfoliated or chemical vapor deposition (CVD) samples, and such coupling can be affected by the atomic registry . The photoexcited electron–hole pairs should not dissociate effectively into free charge carriers within each separate layer of such heterostructures due to the large exciton binding energy, but efficient charge separation at heterojunctions can be realized via photoinduced electron and/or hole transfer.…”

Section: Heterostructures Between Different Tmdsmentioning

confidence: 99%

Novel Optoelectronic Devices: Transition‐Metal‐Dichalcogenide‐Based 2D Heterostructures

Zeng

Liu

2018

Adv Elect Materials

112

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as intriguing building blocks for optoelectronic applications due to their unique properties. First, TMDs have a layered structure with strong in-plane covalent bonds and weak interlayer van der Waals (vdW) interaction, [1] allowing almost effortless exfoliation into monolayer or thin layers. [2,3] Their optical transparency and mechanical flexibility make the fabrication of TMDs based devices more easy and flexible. Second, the bandgap of most semiconducting TMDs is inversely proportional to the number of layers, and crosses over from in-direct to direct as the layer number decreases to single layer, due to the interlayer decoupling and quantum confinement effects. [4][5][6][7] Furthermore, valley-selective excitation is observed in 2H monolayer TMDs due to the splitting of the valence band driven by spin−orbit interactions, which are ascribed to the breaking of inversion symmetry. [8][9][10][11][12] Similar phenomena are also observed in bilayer samples when a perpendicular electric field is applied, [13,14] and even in bulk 3R MoS 2 . [15] Finally, semiconducting TMDs have strong light−matter interaction and photon absorption, [16,17] and relatively high charge carrier mobility, [18,19] opening up the possibility of utilizing few-layer TMDs in a wide range of applications like ultrathin field effect transistors (FETs), [20][21][22][23][24][25] photodetectors, [26][27][28][29][30][31] light-emitting FETs or diodes, [32][33][34] and solar cells. [35,36] At the same time, research on TMD based heterostructure, an essential component for electronic and optoelectronic devices, is gaining more and more attention. The rapid development of these 2D devices can be mainly ascribed to the multifunction of various 2D materials and the exploiting of manufacture technologies. To date, the optoelectronic research in TMDs heterostructures focuses on the Mo-and W-based compounds with optical bandgaps in the range of 1.1−1.9 eV for the single layer. [3] Besides bandgap, the absolute band edge positions of each material (band offset) are also critical for predicting the performances of heterostructures. A wide range of heterojunctions can be created by using different TMDs because their band alignments cover type I, type II, and even type III structures. [37][38][39][40] Simultaneously, numerous other photoactive 2D materials have been studied, such as black phosphorus (bP), [41][42][43][44][45] III-VI (e.g., InSe, α-In 2 Se 3 , GaSe, and GaTe) [46][47][48][49][50][51][52][53][54] or IV-VI compounds (e.g., SnS, SnS 2 , and SnSe 2 ), [55][56][57][58][59] and transition metal trichalcogenides (e.g., TiS 3 ), [60] providing more flexible combinations with TMDs for the optoelectronic applications. Additionally, as a zero bandgap Over the past decade, graphene and other 2D materials have attracted much attention in both fundamental studies and potential applications due to their extraordinary properties. In particular, heterostructures based on these van der Waals (vdW) materials have become one of the leading hot topics in the elect...

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Probing charge transfer excitons in a MoSe₂–WS₂ van der Waals heterostructure

Cited by 101 publications

References 46 publications

Probing effect of electric field on photocarrier transfer in graphene-WS_2 van der Waals heterostructures

Probing effect of electric field on photocarrier transfer in graphene-WS_2 van der Waals heterostructures

Discrete interactions between a few interlayer excitons trapped at a MoSe2-WSe2 heterointerface (Conference Presentation)

Novel Optoelectronic Devices: Transition‐Metal‐Dichalcogenide‐Based 2D Heterostructures

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Probing charge transfer excitons in a MoSe2–WS2 van der Waals heterostructure

Cited by 101 publications

References 46 publications

Probing effect of electric field on photocarrier transfer in graphene-WS_2 van der Waals heterostructures

Probing effect of electric field on photocarrier transfer in graphene-WS_2 van der Waals heterostructures

Discrete interactions between a few interlayer excitons trapped at a MoSe2-WSe2 heterointerface (Conference Presentation)

Novel Optoelectronic Devices: Transition‐Metal‐Dichalcogenide‐Based 2D Heterostructures

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Probing charge transfer excitons in a MoSe₂–WS₂ van der Waals heterostructure