Electrical control of neutral and charged excitons in a monolayer semiconductor

Ross, Joel; Wu, Sanfeng; Yu, Hongyi; Ghimire, Nirmal; Jones, Aaron M.; Aivazian, Grant; Yan, Jiaqiang; Mandrus, David; Xiao, Di; Yao, Wang; Xu, Xiaodong

doi:10.1038/ncomms2498

Cited by 1,407 publications

(1,828 citation statements)

References 36 publications

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“…14 We can't see the p-transport transition in the unprocessed SLM sheet even at the gate voltage up to −150 V. This might be due to the hybridization of the defect states. However, such a tune can be achieved easily after the EDTA processing even at a very low back voltage.…”

Section: Resultsmentioning

confidence: 98%

“…This leads to the potential applications in optoelectronic devices, such as single-junction solar cells 18 and photoelectrochemical devices, based on single-layer MoSe 2 (SLM) with a direct bandgap and an even higher optical coupling strength. 14 Large SLM sheets with the dimension over 100 μm have been grown by chemical vapor deposition (CVD) method, 19 based on which the vertical Van der Waals heterostructure devices are fabricated with the demonstration of rapid charge transfer in 50 fs. 20 The field-effect transistors (FET) based on both exfoliated and CVD grown SLM sheets have been fabricated, whose on/off ratio reaches 10.…”

Section: Introductionmentioning

confidence: 99%

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Repairing atomic vacancies in single-layer MoSe2 field-effect transistor and its defect dynamics

et al. 2017

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Atomic defects are easily created in the single-layer electronic devices of current interest and cause even more severe influence than in the bulk devices since the electronic quantum paths are obviously suppressed in the two-dimensional transport. Here we find a drop of chemical solution can repair the defects in the single-layer MoSe 2 field-effect transistors. The devices' roomtemperature electronic mobility increases from 0.1 cm 2 /Vs to around 30 cm 2 /Vs and hole mobility over 10 cm 2 /Vs after the solution processing. The defect dynamics is interpreted by the combined study of the first-principles calculations, aberration-corrected transmission electron microscopy, and Raman spectroscopy. Rich single/double Selenium vacancies are identified by the highresolution microscopy, which cause some mid-gap impurity states and localize the device carriers. They are found to be repaired by the processing with the result of extended electronic states. Such a picture is confirmed by a 1.5 cm −1 red shift in the Raman spectra.

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Section: Resultsmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

Repairing atomic vacancies in single-layer MoSe2 field-effect transistor and its defect dynamics

et al. 2017

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“…The trion binding energy of 29 meV is very similar to that reported in other studies on MoSe 2 . 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 .…”

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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Probing Critical Point Energies of Transition Metal Dichalcogenides: Surprising Indirect Gap of Single Layer WSe₂

et al. 2015

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Experimental determinations of the electronic band structures in TMDs are quite non-trivial.Optical spectroscopies [1][2][3][4][5] are unsuitable to measure the quasi-particle band structures due to the existence of large exciton binding energies. Using angle resolved photoemission (ARPES), it is difficult to probe the conduction band structures 6,7 . In principle, scanning tunneling spectroscopy (STS) would be an ideal probe to determine both the valence and conduction band structures.However, the reported results have been controversial thus far, even for the determination of the quasi-particle band gaps [8][9][10] . As we will show, this is due primarily to the intriguing influence of the lateral momentum in the tunneling process, making certain critical points difficult to access in the conventional scanning tunneling spectroscopy acquired at a constant tip-to-sampledistance (Z). By using a comprehensive approach combining the constant Z and variable Z spectroscopies, as well as state-resolved tunneling decay constant measurements, we have shown 3 that detailed electronic structures, including quasi-particle gaps, critical point energy locations and their origins in the BZs in TMDs can be revealed.The TMD samples are grown using chemical vapor deposition (CVD) for WSe 2 11 or molecular beam epitaxy (MBE) for MoSe 2 on highly-oriented-pyrolytic-graphite (HOPG)substrates. In addition, MoSe 2 has also been grown on epitaxial bi-layer graphene to investigate the environmental influences on the quasi-particle band structures. Figures 1a and b show scanning tunneling microscopy (STM) images of MoSe 2 and WSe 2 , respectively. Due to a nearly 4:3 lattice match with the graphite, the TMD samples also show Moiré patterns with a periodicity of ~ 1nm. An example is shown as an inset in Fig. 1b, similar to those reported earlier 9 . In Fig. 1c we show a generic electronic structure for SL-TMD materials. We first discuss the result of MoSe 2 due to the availability of experimentally determined E vs. k dispersion in the valence band which can be used to cross-check with our results. 4Such a large difference in the decay constant is responsible for the difficulty in detecting the states near the VBM. The lack of the sensitivity in the constant-Z STS can be overcome by acquiring spectra at variable Z as described before 14 . Here we adopt a form of variable Z spectroscopy by performing STS at constant current. In this mode, as the sample bias is scanned across different thresholds, Z (the dependent variable) will respond automatically in order to keep the current constant. The differential conductivity (I/V) I is measured by using a lock-in amplifier (Fig. 2b). In the meantime, the acquired Z-value is used to deduce (Z/V) I which can be used to identify individual thresholds (Fig. 2c).For the valence band (left panel), the state at the  point also appears as a prominent peak in the (I/V) I spectrum. Moreover, spectroscopic features above  are observed due to the significant enhancement of the sensitivity. A shoul...

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Electrical control of neutral and charged excitons in a monolayer semiconductor

Cited by 1,407 publications

References 36 publications

Repairing atomic vacancies in single-layer MoSe2 field-effect transistor and its defect dynamics

Repairing atomic vacancies in single-layer MoSe2 field-effect transistor and its defect dynamics

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

Probing Critical Point Energies of Transition Metal Dichalcogenides: Surprising Indirect Gap of Single Layer WSe₂

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Electrical control of neutral and charged excitons in a monolayer semiconductor

Cited by 1,407 publications

References 36 publications

Repairing atomic vacancies in single-layer MoSe2 field-effect transistor and its defect dynamics

Repairing atomic vacancies in single-layer MoSe2 field-effect transistor and its defect dynamics

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

Probing Critical Point Energies of Transition Metal Dichalcogenides: Surprising Indirect Gap of Single Layer WSe2

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

Probing Critical Point Energies of Transition Metal Dichalcogenides: Surprising Indirect Gap of Single Layer WSe₂