Excitonic resonance effects and Davydov splitting in circularly polarized Raman spectra of few-layer WSe
                    <sub>2</sub>

Kim, Sanghun; Kim, Kangwon; Lee, Jae-Ung; Cheong, Hyeonsik

doi:10.1088/2053-1583/aa8312

Cited by 35 publications

(50 citation statements)

References 63 publications

(174 reference statements)

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“…We assign the 0 , − , + peaks as the E"-phonon replica because the redshift energy (21.4 meV) matches the energy of the E" optical phonons (21.4 meV) in monolayer WSe2 [37,58,59]. Similar E" phonon replicas have been observed in quantum-dot excitons in monolayer WSe2 [37].…”

supporting

confidence: 52%

Valley-selective chiral phonon replicas of dark excitons and trions in monolayer WSe2

Liu

Baren

Taniguchi

et al. 2019

Phys. Rev. Research

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Monolayer WSe2 hosts long-lived dark excitonic states with robust valley polarization, but thus far lacks an experimental signature to identify their valley pseudospin. Here we reveal a set of three replica luminescent peaks at ~21.4 meV below the dark exciton, negative and positive dark exciton-polarons (or trions) in monolayer WSe2. The redshift energy matches the energy of the zone-center E" chiral phonons. The replicas exhibit parallel gate dependence and the same g-factors as the dark excitonic states, but follow the valley selection rules of bright excitonic states. While the dark states exhibit out-of-plane transition dipole and linearly polarized emission in the in-plane directions, their phonon replicas exhibit in-plane transition dipole and circularly polarized emission in the out-ofplane directions. Symmetry analysis shows that the K-valley dark exciton decays into a left-handed chiral phonon and a right-handed photon, whereas the K'-valley dark exciton decays into a right-handed phonon and a left-handed photon. Such chiral-phonon replicas can help identify the dark-state valley pseudospin and explore the intriguing excitonphonon interactions in monolayer WSe2.

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supporting

confidence: 52%

Valley-selective chiral phonon replicas of dark excitons and trions in monolayer WSe2

Liu

Baren

Taniguchi

et al. 2019

Phys. Rev. Research

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“…However, we disagree with ref. [17] on the interpretation of this mode, as they consider it to be Raman active but forbidden in backscattering for odd-layers WSe2, where its observation is explained invoking the significant portion of the incident and scattered light that is not normal to the sample plane due to the large numerical aperture (NA) of microscope objectives. Instead, we find that this mode is Raman active and forbidden in our geometry (i.e.…”

Section: First-order Raman Scatteringmentioning

confidence: 99%

New insights in the lattice dynamics of monolayers, bilayers, and trilayers of WSe₂ and unambiguous determination of few-layer-flakes’ thickness

Luca¹,

Cartoixà²,

Martín‐Sánchez³

et al. 2020

2D Mater.

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Among the most common few-layers transition metal dichalcogenides (TMDs), WSe2 is the most challenging material from the lattice dynamics point of view. Indeed, for a long time the main two phonon modes (A1g and E 1 2g) have been wrongly assigned. In the last few years, these two modes have been properly interpreted, and their quasi-degeneracy in the monolayer has been used for its identification. In this work, we show that this approach has a limited validity and we propose an alternative, more general approach, based on multi-phonon bands. Moreover, we show and interpret all the peaks (about 40) appearing in the Raman spectra of monolayers, bilayers, and trilayers of WSe2 by combining experimental wavelength-and polarization-dependent Raman studies with densityfunctional theory calculations providing the phonon dispersions, the polarization-resolved first-order Raman spectra, and the one-and two-phonon density of states. This complete study not only offers a method to distinguish between monolayers, bilayers, and trilayers with no need of optical images and atomic force microscopy, but it also sheds light on the interpretation of single and multi-phonon bands appearing in the inelastic light scattering experiments of layered WSe2; some of these bands were never observed before, and some were observed and uncertainly assigned. We promote the full understanding of the lattice dynamics of this material that is crucial for the realization of optoelectronics devices and of novel phononic metamaterials, such as TMDs superlattices.

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“…[40][41][42] Figure 4b shows the low frequency Raman spectra from the same TMD channels, as conducted to confirm the identities of the three TMDs. [43][44][45] As our last application using n-IGZO and TMD channels on a common gate, we present n-IGZO/p-MoTe 2 CMOS inverter and AC frequency doubler. Figure 5a shows the individual transfer curve characteristics of p-MoTe 2 and n-IGZO FETs, along with another transfer curve from p-channel/n-channel combined FET.…”

Section: Resultsmentioning

confidence: 99%

Advanced Multifunctional Field Effect Devices Using Common Gate for Both 2D Transition‐Metal Dichalcogenide and InGaZnO Channels

Cho

Lim

et al. 2019

Adv Elect Materials

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p-and n-channel FETs, homogeneous and heterogeneous complementary metal oxide semiconductor (CMOS) inverters have been reported. [15][16][17][18][19][20] Moreover, PN junction-and Schottky junction-based FETs were even reported using 2D TMD semiconductors. [21,22] However, in a practical view, devices based on only 2D materials are not easy to fabricate and seldom reproducible. Very recently, researchers have attempted other approaches combining 2D materials and conventionally proven ones to fabricate more practical type of classical devices such as CMOS inverters and hetero PN junction diodes. [23][24][25][26][27][28][29][30][31][32] Those could be regarded as practical approaches in consideration that one could use conventionally proven semiconductors for functional electron devices. However, such approaches are still very rare.In the present study, we approach to combine 2D n-/or p-TMD FET and conventional InGaZnO (IGZO) FET, presenting advanced non-classical functions: multivalue (MV) FETs for logic and photodetecting function, and signal frequency doubler. Multivalue logic would be important in the future for minimizing the power consumption which emerges as challenging issues in the present Si-based binary logic circuitry. [33][34][35] Frequency doubling is also an interesting and beneficial technique in alternating current (AC) circuit. [36,37] For these purposes, we have initially fabricated n-IGZO channel FET on glass substrate, which is followed by n-channel TMD (n-ReSe 2 , n-WSe 2 , p-, or ambipolar-MoTe 2 ) FETs. Although top-MoTe 2 /bottom-IGZO combination approach was once introduced for basic classical devices, [26] present study displays more advanced novel functions based on unique device architecture; we use a long and unique-shape gate pattern, so that n-or p-channel TMD and n-IGZO channels may be located side by side sharing a gate metal in common. Atomic layer deposited (ALD) Al 2 O 3 dielectric is located on the patterned gate. According to individual transfer characteristics of two FET devices, our n-IGZO FET always shows higher drain current (I D ) and more positive-side turn-on voltage (V t ) than those of n-TMD channel FETs. As a result, a combined transfer characteristics presented two-step drain current levels, so that their load-resistance inverter might demonstrate three value output Various functions are introduced from a unique field-effect device structure which combines or merges transition metal dichalcogenide (TMD) and InGaZnO (IGZO) channels together on one common gate: multivalue field effect transistors (FETs), photodetecting devices, and signal frequency doublers. Judging by the individual transfer characteristics of two FET devices, the n-IGZO FET always shows higher drain current and more positive-side turn-on voltage than those of n-TMD channel FETs. As a result, a combined transfer characteristic presents two-step drain current levels, so that their load-resistance inverter might demonstrate three value output voltage signals. Those ternary value inverter devices with n...

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Excitonic resonance effects and Davydov splitting in circularly polarized Raman spectra of few-layer WSe ₂

Cited by 35 publications

References 63 publications

Valley-selective chiral phonon replicas of dark excitons and trions in monolayer WSe2

Valley-selective chiral phonon replicas of dark excitons and trions in monolayer WSe2

New insights in the lattice dynamics of monolayers, bilayers, and trilayers of WSe₂ and unambiguous determination of few-layer-flakes’ thickness

Advanced Multifunctional Field Effect Devices Using Common Gate for Both 2D Transition‐Metal Dichalcogenide and InGaZnO Channels

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Excitonic resonance effects and Davydov splitting in circularly polarized Raman spectra of few-layer WSe 2

Cited by 35 publications

References 63 publications

Valley-selective chiral phonon replicas of dark excitons and trions in monolayer WSe2

Valley-selective chiral phonon replicas of dark excitons and trions in monolayer WSe2

New insights in the lattice dynamics of monolayers, bilayers, and trilayers of WSe2 and unambiguous determination of few-layer-flakes’ thickness

Advanced Multifunctional Field Effect Devices Using Common Gate for Both 2D Transition‐Metal Dichalcogenide and InGaZnO Channels

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Excitonic resonance effects and Davydov splitting in circularly polarized Raman spectra of few-layer WSe ₂

New insights in the lattice dynamics of monolayers, bilayers, and trilayers of WSe₂ and unambiguous determination of few-layer-flakes’ thickness