Quasiparticle band structure calculation of monolayer, bilayer, and bulk MoS<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mrow /><mml:mn>2</mml:mn></mml:msub></mml:math>

Cheiwchanchamnangij, Tawinan; Lambrecht, Walter R. L.

doi:10.1103/physrevb.85.205302

Cited by 1,273 publications

(1,073 citation statements)

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“…3,26,27 Our results indicate that the direct gap does not change appreciably between 3TL and bulk. Furthermore, our results corroborate recent calculations that predict direct band gaps near 2.8 eV or higher for 1 and 2TL.…”

Section: Resonance Effects On Main First-order Peaksmentioning

confidence: 66%

Anomalous excitonic resonance Raman effects in few-layered MoS₂

et al. 2015

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ABSTRACT:The resonance effects on the Raman spectra from 5 to 900 cm −1 of few-layer MoS2 thin films up to 14-layers were investigated by using six excitation energies. For the main first-order Raman peaks, the intensity maximum occurs at ~2.8 eV for single layer and at ~2.5 eV for few-layer MoS2, which correspond to the band-gap energy. At the excitation energy of 1.96 eV, several anomalous behaviors are observed. Many second-order peaks are anomalously enhanced even though the main firstorder peaks are not enhanced. In the low-frequency region (<100 cm −1 ), a broad peak centered at ~38 cm −1 and its second order peak at 76 cm −1 appear for the excitation energy of 1.96 eV. These anomalous resonance effects are interpreted as being due to strong resonance with excitons or exciton-polaritons.2

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Section: Resonance Effects On Main First-order Peaksmentioning

confidence: 66%

Anomalous excitonic resonance Raman effects in few-layered MoS₂

et al. 2015

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“…Calculations have shown that the A and B excitons correspond to the expected energies of the gap energies at the K-point 130 , where the band splitting is due to spin-orbit coupling in monolayer MoS 2 (spin-orbit effects are described in more detail below). The calculations have also shown that the exciton binding energies are quite high owing to the decreased dielectric constants compared with the bulk, as well as the 2D confinement: about 0.897 eV for monolayer MoS 2 and 0.424 eV for bilayer 131 . We also note that in these calculations the transition energy of the excitons is offset by the exciton binding energy, and so the energy required to create an exciton would be much lower than the bandgap, and that the optical transition energies are not equivalent to the transport bandgap energies.…”

Section: Optoelectronicsmentioning

confidence: 96%

Electronics and optoelectronics of two-dimensional transition metal dichalcogenides

et al. 2012

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699M any two-dimensional (2D) materials exist in bulk form as stacks of strongly bonded layers with weak interlayer attraction, allowing exfoliation into individual, atomically thin layers 1 . The form receiving the most attention today is graphene, the monolayer counterpart of graphite. The electronic band structure of graphene has a linear dispersion near the K point, and charge carriers can be described as massless Dirac fermions, providing scientists with an abundance of new physics 2,3 . Graphene is a unique example of an extremely thin electrical and thermal conductor 4 , with high carrier mobility 5 , and surprising molecular barrier properties 6,7 .Many other 2D materials are known, such as the TMDCs 8,9 , transition metal oxides including titania-and perovskite-based oxides 10,11 , and graphene analogues such as boron nitride (BN) 12,13 . In particular, TMDCs show a wide range of electronic, optical, mechanical, chemical and thermal properties that have been studied by researchers for decades 9,14,15 . There is at present a resurgence of scientific and engineering interest in TMDCs in their atomically thin 2D forms because of recent advances in sample preparation, optical detection, transfer and manipulation of 2D materials, and physical understanding of 2D materials learned from graphene.The 2D exfoliated versions of TMDCs offer properties that are complementary to yet distinct from those in graphene. Graphene displays an exceptionally high carrier mobility exceeding 10 6 cm 2 V -1 s -1 at 2 K (ref. 16) and exceeding 10 5 cm 2 V -1 s -1 at room temperature for devices encapsulated in BN dielectric layers 5 ; because pristine graphene lacks a bandgap, however, fieldeffect transistors (FETs) made from graphene cannot be effectively switched off and have low on/off switching ratios. Bandgaps can be engineered in graphene using nanostructuring [17][18][19] , chemical functionalization 20 and applying a high electric field to bilayer graphene 21 , but these methods add complexity and diminish mobility. In contrast, several 2D TMDCs possess sizable bandgaps around 1-2 eV (refs 9,14), promising interesting new FET and optoelectronic devices.TMDCs are a class of materials with the formula MX 2 , where M is a transition metal element from group IV (Ti, Zr, Hf and so on), group V (for instance V, Nb or Ta) or group VI (Mo, W and so on), and X is a chalcogen (S, Se or Te). These materials form layered structures of the form X-M-X, with the chalcogen atoms in two hexagonal planes separated by a plane of metal atoms, as shown in Fig. 1a. Adjacent layers are weakly held together to form the bulk crystal in a variety of polytypes, which vary in stacking orders and metal atom coordination, as shown in Fig. 1e. The overall symmetry of TMDCs is hexagonal or rhombohedral, and the metal atoms have octahedral or trigonal prismatic coordination. The electronic properties of TMDCs range from metallic to semiconducting, as summarized in Table 1. There are also TMDCs that exhibit exotic behaviours such as charge density waves ...

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“…The electronic structure of group 6 TMD monolayers has been studied extensively. 10,11,13,[15][16][17]37 The valence band maximum (VBM) and conduction band minimum (CBM) are located at the K point of the Brillouin zone (BZ) and are mostly contributed by the d orbitals of the transition metal atoms. 9 The large spin−orbit coupling splits the VBM into two states with a well-defined spin projection, S z , in the out-of-plane direction.…”

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confidence: 99%

“…8 We employ fully relativistic pseudopotentials and treat the sp semicore states of the transition metal atoms as valence electrons. 8,16 The quasiparticle bandstructures are computed using the GW approach as implemented in the Yambo code. 32 We employ the "one-shot" G 0 W 0 approximation, 26 a plasmonpole model for the dielectric function in the GW self-energy, cutoff energies of 60 and 10 Ry for the exchange and correlation parts of the GW self-energy, respectively, and up to 300 empty bands.…”

mentioning

confidence: 99%

Exciton Radiative Lifetimes in Two-Dimensional Transition Metal Dichalcogenides

Palummo¹,

2015

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Light emission in two-dimensional (2D) transition metal dichalcogenides (TMDs) changes significantly with the number of layers and stacking sequence. While the electronic structure and optical absorption are well understood in 2D-TMDs, much less is known about exciton dynamics and radiative recombination. Here, we show firstprinciples calculations of intrinsic exciton radiative lifetimes at low temperature (4 K) and room temperature (300 K) in TMD monolayers with the chemical formula MX 2 (X = Mo, W, and X = S, Se), as well as in bilayer and bulk MoS 2 and in two MX 2 heterobilayers. Our results elucidate the time scale and microscopic origin of light emission in TMDs. We find radiative lifetimes of a few picoseconds at low temperature and a few nanoseconds at room temperature in the monolayers and slower radiative recombination in bulk and bilayer than in monolayer MoS 2 . The MoS 2 /WS 2 and MoSe 2 /WSe 2 heterobilayers exhibit very long-lived (∼20−30 ns at room temperature) interlayer excitons constituted by electrons localized on the Mo-based and holes on the W-based monolayer. The wide radiative lifetime tunability, together with the ability shown here to predict radiative lifetimes from computations, hold unique potential to manipulate excitons in TMDs and their heterostructures for application in optoelectronics and solar energy conversion. KEYWORDS: Monolayer materials, transition metal dichalcogenides, luminescence, radiative lifetime, excitons, optoelectronics T wo-dimensional (2D) transition metal dichalcogenides (TMDs) are promising materials for ultrathin electronic, optoelectronic, photocatalytic, and photovoltaic devices. 1−8 Out of approximately 40 existing TMDs, 9,10 some have received particular attention due to their semiconducting nature and tunable band gap. In particular, group 6 monolayer TMDs with chemical formula MX 2 (M = Mo, W and X = S, Se) are direct gap semiconductors with relatively intense photoluminescence (PL), while bilayers and thicker multilayers exhibit indirect gap and weaker PL. 1,10−17 The peculiar nature of the excited states has stimulated intense research efforts to investigate exciton dynamics and radiative/nonradiative lifetimes in TMDs. 13,18−24 Recent time-resolved experiments found a range of characteristic times for exciton dynamics in monolayer TMDs, including fast (1−10 ps) recombination attributed to exciton trapping at defects, and slower processes on a 0.1−1 ns time scale interpreted as radiative exciton recombination. 18,20−22 However, the attribution of the observed signals to radiatiave and nonradiative processes can be ambiguous in time-resolved spectroscopies since defects and impurities can modulate the excited state dynamics. In TMDs, the interpretation of time signals and comparison among different experiments is further complicated by the use of micrometer-size flakes where the edges can play a significant role in exciton recombination. This situation has stimulated an ongoing quest for the intrinsic time scale of exciton recombinatio...

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Quasiparticle band structure calculation of monolayer, bilayer, and bulk MoS2

Cited by 1,273 publications

References 18 publications

Anomalous excitonic resonance Raman effects in few-layered MoS₂

Anomalous excitonic resonance Raman effects in few-layered MoS₂

Electronics and optoelectronics of two-dimensional transition metal dichalcogenides

Exciton Radiative Lifetimes in Two-Dimensional Transition Metal Dichalcogenides

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Quasiparticle band structure calculation of monolayer, bilayer, and bulk MoS2

Cited by 1,273 publications

References 18 publications

Anomalous excitonic resonance Raman effects in few-layered MoS2

Anomalous excitonic resonance Raman effects in few-layered MoS2

Electronics and optoelectronics of two-dimensional transition metal dichalcogenides

Exciton Radiative Lifetimes in Two-Dimensional Transition Metal Dichalcogenides

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Product

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Anomalous excitonic resonance Raman effects in few-layered MoS₂

Anomalous excitonic resonance Raman effects in few-layered MoS₂