Optically initialized robust valley-polarized holes in monolayer WSe2

Hsu, Wei-Ting; Chen, Yen Lun; Chen, Chiang Hsiao; Liu, Po–Tsun; Hou, Tuo‐Hung; Li, Lain‐Jong; Chang, Wen‐Hao

doi:10.1038/ncomms9963

Cited by 179 publications

(142 citation statements)

References 34 publications

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“…As mentioned earlier, TMDCs can exhibit valley and spin selective interaction with light. WSe 2 is one such example which has spin-polarized valleys [137][138][139][140]. For example, all the electrons in the K-valley are spin-up and in the K'-valley are spin-down in ML WSe 2 .…”

Section: Light Emitting Devicesmentioning

confidence: 99%

Optoelectronic and photonic devices based on transition metal dichalcogenides

Thakar

Lodha

2020

Mater. Res. Express

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Transition metal dichalcogenides (TMDCs) are a family of two-dimensional layered materials (2DLMs) with extraordinary optical properties. They present an attractive option for future multifunctional and high-performance optoelectronics. However, much remains to be done to realize a mature technology for commercial applications. In this review article, we describe the progress and scope of TMDC devices in optical and photonic applications. Various photoresponse mechanisms observed in such devices and a brief discussion on measurement and analysis methods are described. Three main types of optoelectronic devices, namely photodetectors, photovoltaics and lightemitting devices are discussed in detail with a focus on device architecture and operation. Examples showing experimental integration of 2DLM-based devices with silicon photonics are also discussed briefly. A wide range of data for key performance metrics is analysed with insights into future directions for device design, processing and characterization that can help overcome present gaps and challenges. While the field is still in its infancy and requires significant efforts toward standardizing various approaches towards a mature technology, it has already shown promising results in broader aspects of compatibility, integration and performance for future electronics. Sensors are increasingly becoming an integrated part of the global electronic eco-system with the rise of data-driven technologies. There is a growing need for networks of cost-effective, robust and reliable sensors and their integration with present technologies. Optoelectronic and photonic devices are of importance for both sensing as well as high-speed optical communication applications. 2DLMs demonstrate significant light-matter interaction that is tunable with external physical and electronic parameters such as pressure, strain, electric and magnetic field [1-6]. Moreover, 2DLMs show strong dependence of their band structure on thickness with a transition to direct bandgap in monolayers in most of the known 2DLMs [7][8][9]. Graphene has been the most studied material since its discovery in 2004 [10][11][12]. Apart from graphene, there are nearly 1500 possible 2DLMs with a wide range of material properties as predicted by first principle simulations [13]. Transition metal dichalcogenides (TMDCs) are a family of 2DLMs in the form of MX 2 compounds, where M is a transition metal (Mo, W, Re) and X is a chalcogen (S, Se, Te). TMDCs are promising for electronic applications due to their semiconducting behaviour as opposed to semi-metallic graphene, and better thermal stability than materials such as black phosphorus and silicene [14][15][16][17][18][19]. Optoelectronic devices based on TMDCsTMDCs have been the most studied 2DLMs, apart from graphene and black phosphorus, for electronic and optoelectronic device applications [20,21]. They have a sizeable bandgap in the visible and near infrared (NIR) range (∼1-2 eV) that is optimal for optoelectronic sensors and light-emitting sources for short-ran...

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Section: Light Emitting Devicesmentioning

confidence: 99%

Optoelectronic and photonic devices based on transition metal dichalcogenides

Thakar

Lodha

2020

Mater. Res. Express

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“…The trion valley polarization (probing at 1.71 eV) relaxes significantly slower than that of A excitons, qualitatively consistent with the previous reports. [24][25][26] A two-section exponential fit gives time constants of 5 ± 1 ps and 80 ± 14 ps, respectively. The valley polarization of free carriers (probing at 2.318 eV) experiences a rapid decay near zero time delay followed by an even slower decay, with time constants of 5 ± 2 ps and 2.4 ± 1 ns, respectively.…”

mentioning

confidence: 98%

“…A spin resolved photocurrent measurements estimated the valley/spin lifetime in the range of 10 0 ∼ 10 2 nanoseconds in monolayer WS 2 , while optical pump-probe spectroscopy and time-resolved photoluminescence (PL) experiments gave a very short valley lifetime of several picoseconds [16][17][18][19][20][21][22][23] with a few exceptions where long valley lifetime of bound excitons were reported. [24][25][26] The huge discrepancy lies in that the excitonic effect is prevalent in optical responses of monolayer TMDs. [27][28][29][30][31][32][33] The giant exciton binding energy implies a short effective radius of excitons, a close separation between electrons and holes, enhancing the exchange interactions.…”

mentioning

confidence: 99%

Long valley relaxation time of free carriers in monolayer WSe2

Yan

Yang

et al. 2017

Phys. Rev. B

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Monolayer transition metal dichalcogenids (TMDs) feature valley degree of freedom, giant spinorbit coupling and spin-valley locking. These exotic natures stimulate efforts of exploring the potential applications in conceptual spintronics, valleytronics and quantum computing. Among all the exotic directions, a long lifetime of spin and/or valley polarization is critical. The present valley dynamics studies concentrate on the band edge excitons which predominates the optical response due to the enhanced Coulomb interaction in two dimensions. The valley lifetime of free carriers remains in ambiguity. In this work, we use time-resolved Kerr rotation spectroscopy to probe the valley dynamics of excitons and free carriers in monolayer tungsten diselinide. The valley lifetime of free carriers is found around 2 ns at 70 K, about 3 orders of magnitude longer than the excitons of about 2 ps. The extended valley lifetime of free carriers evidences that exchange interaction dominates the valley relaxation in optical excitation. The pump-probe spectroscopy also reveals the exciton binding energy of 0.60 eV in monolayer WSe2.

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“…Due to strong spin-orbit coupling, the valley pseudospin is locked to the real spin orientation6. Since flipping an electron spin requires a simultaneous flip of a valley pseudospin, free carrier spin-valley polarization at the band edge is expected to be robust and long lived, which has recently been measured to be on order of 1–100 ns (refs 7, 8). Large spin-valley polarizations associated with excitons have been generated by circularly polarized light excitation through a valley dependent optical selection rule3691011.…”

mentioning

confidence: 99%

Directional interlayer spin-valley transfer in two-dimensional heterostructures

et al. 2016

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Van der Waals heterostructures formed by two different monolayer semiconductors have emerged as a promising platform for new optoelectronic and spin/valleytronic applications. In addition to its atomically thin nature, a two-dimensional semiconductor heterostructure is distinct from its three-dimensional counterparts due to the unique coupled spin-valley physics of its constituent monolayers. Here, we report the direct observation that an optically generated spin-valley polarization in one monolayer can be transferred between layers of a two-dimensional MoSe2–WSe2 heterostructure. Using non-degenerate optical circular dichroism spectroscopy, we show that charge transfer between two monolayers conserves spin-valley polarization and is only weakly dependent on the twist angle between layers. Our work points to a new spin-valley pumping scheme in nanoscale devices, provides a fundamental understanding of spin-valley transfer across the two-dimensional interface, and shows the potential use of two-dimensional semiconductors as a spin-valley generator in two-dimensional spin/valleytronic devices for storing and processing information.

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Optically initialized robust valley-polarized holes in monolayer WSe2

Cited by 179 publications

References 34 publications

Optoelectronic and photonic devices based on transition metal dichalcogenides

Optoelectronic and photonic devices based on transition metal dichalcogenides

Long valley relaxation time of free carriers in monolayer WSe2

Directional interlayer spin-valley transfer in two-dimensional heterostructures

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