Ultrafast carrier dynamics in two-dimensional transition metal dichalcogenides

Li, Yuanzheng; Shi, Jia; Mi, Yang; Sui, Xinyu; Xu, Haiyang; Liu, Xinfeng

doi:10.1039/c8tc06343e

Cited by 56 publications

(47 citation statements)

References 122 publications

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“…The fast decay time τ 1 of a few hundreds of femtoseconds should arise from the hot electron relaxation via electron-phonon interactions 44,45 . The slow decay time τ 2 could be related to nonradiative electron-hole recombinations (such as Auger recombination or many-body interactions) 46 . To analyze the results more quantitatively, we used the rate equation analysis (for details see Supplementary Note 1, Supplementary Fig.…”

Section: Resultsmentioning

confidence: 99%

Relaxation and transfer of photoexcited electrons at a coplanar few-layer 1 T′/2H-MoTe2 heterojunction

Liu

et al. 2020

Commun Mater

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Fundamental dynamic processes at the electronic contact interface, such as carrier injection and transport, become pivotal and significantly affect device performance. Time-resolved photoemission electron microscopy (TR-PEEM) with high spatiotemporal resolution provides unprecedented abilities of imaging the electron dynamics at the interface. Here, we implement TR-PEEM to investigate the electron dynamics at a coplanar metallic 1 T′-MoTe 2 /semiconducting 2H-MoTe 2 heterojunction. We find the non-equilibrium electrons in the 1 T′-MoTe 2 possess higher energy than those in the 2H-MoTe 2. The nonequilibrium photoelectrons collapse and relax to the lower energy levels in the order of picoseconds. The photoexcited electrons transfer from 1 T′-MoTe 2 to 2H-MoTe 2 with at a rate of~0.8 × 10 12 s −1 (as fast as 1.25 ps). These findings contribute to our understanding of the behavior of photoexcited electrons in heterojunctions and the design of in-plane optoelectronic devices.

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Section: Resultsmentioning

confidence: 99%

Relaxation and transfer of photoexcited electrons at a coplanar few-layer 1 T′/2H-MoTe2 heterojunction

Liu

et al. 2020

Commun Mater

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“…The corresponding data are plotted as a function of the temperature in Figure b. It is well known that the luminescence lifetime of semiconductors is an indication of the decay of the photogenerated carriers via both radiative and nonradiative processes . In our experiment, after injecting the photogenerated carriers into WSe 2 , the population of carriers at the excited‐state would gradually reduce or be removed completely by means of radiative and nonradiative processes with increasing time and would ultimately recover to an equilibrium state.…”

mentioning

confidence: 78%

Unveiling Bandgap Evolution and Carrier Redistribution in Multilayer WSe₂: Enhanced Photon Emission via Heat Engineering

Liu

et al. 2019

Advanced Optical Materials

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Semiconductor materials and relevant device technologies are important cornerstones for the rapid development of modern society. From the first generation of silicon and germanium semiconductors to the current third generation of silicon carbide and gallium nitride semiconductors, the applications of semiconductors have been widely expanded from initially integrated circuits and optical communications to advanced optoelectronic devices that are suitable for harsh working conditions (e.g., high temperature, high frequency, large power loading, and short wavelength emissions). [1,2] However, only the functionalities and performances of these traditional semiconductor materials have evolved; a breakthrough in reducing their dimensions and sizes has not yet been achieved. Obviously, such an evolution cannot push the boundaries of the stringent requirements of integrating electronic/optoelectronic components due to the quantum tunneling effect. Until 2004, the emergence of graphene has ushered in a new era of low-dimensional materials and technological innovations of high integration electronics and optoelectronics, [3,4] and has opened the door for 2D materials. Because graphene lacks an effective bandgap, recently, layered transition-metal dichalcogenides (TMDs) with optical bandgaps ranging from the visible to near-infrared spectral regions, [5][6][7][8] have been considered as a more promising candidate than graphene for 2D optoelectronic devices and digital electronic applications, [9][10][11][12][13] owing to their intriguing optical and electrical properties. [14][15][16][17][18] Monolayer TMDs with atomically thin thicknesses are direct bandgap semiconductors that possess superior lightemission characteristics. [15,19,20] However, the low optical density of states (DOS) and weak capacity for light absorption of these monolayer TMDs, [21,22] is limited by their ultrathin structure, which restricts their practical applications in the future. Compared to their monolayer counterparts, multilayer TMDs with an optically inactive indirect bandgap have a larger density of states and exhibit stronger photon absorption. Obviously, achieving the transformation of a bandgap structure from indirect bandgap to direct bandgap or propelling carriers in indirect bandgap to transform to direct bandgap in k-space Manipulating the bandgap structure and carrier distribution of multilayer transition metal dichalcogenides (TMDs) is crucial for improving their fluorescence efficiency and extending their optoelectronic applications. Herein, the evolution of the conduction band minimum of multilayer WSe 2 as a function of the temperature and thickness is experimentally demonstrated and an ≈70-fold fluorescence enhancement of the K-K direct emission is observed at 560 K in multilayer WSe 2 flakes (≈170 nm) by heat engineering. This abnormal enhancement is attributed to thermally driven carrier redistribution achieved via intervalley transfer, which is confirmed by the theoretical calculations and temperature-dependent time-resolved phot...

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“…The photocarrier dynamics in 2D semiconductors have been actively investigated in recent years, which has been covered in a number of reviews [21][22][23] . Once optically injected into the samples, the non-equilibrium photocarriers typically undergo relaxation processes, including rapid thermalization through carrier-carrier scattering, cooling to the band edges through interaction with phonons, and electron-hole recombination either directly or via the assistance of defects or phonons (Fig.…”

Section: Photocarrier Relaxation Dynamics In 2d Semiconductorsmentioning

confidence: 99%

“…Since there have been a number of review articles on the ultrafast photocarrier dynamics in 2D semiconductors [21][22][23] , in this review, we focus on summarizing recent efforts in identifying methods to modulate the photocarrier relaxation behavior. We start with a brief introduction to the photocarrier relaxation dynamics in 2D semiconductors and then devote a section to discussing modulation of Coulomb interactions and the resulting effects on the transient properties of 2D semiconductors.…”

Section: Introductionmentioning

confidence: 99%

Modulation of photocarrier relaxation dynamics in two-dimensional semiconductors

2020

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Due to strong Coulomb interactions, two-dimensional (2D) semiconductors can support excitons with large binding energies and complex many-particle states. Their strong light-matter coupling and emerging excitonic phenomena make them potential candidates for next-generation optoelectronic and valleytronic devices. The relaxation dynamics of optically excited states are a key ingredient of excitonic physics and directly impact the quantum efficiency and operating bandwidth of most photonic devices. Here, we summarize recent efforts in probing and modulating the photocarrier relaxation dynamics in 2D semiconductors. We classify these results according to the relaxation pathways or mechanisms they are associated with. The approaches discussed include both tailoring sample properties, such as the defect distribution and band structure, and applying external stimuli such as electric fields and mechanical strain. Particular emphasis is placed on discussing how the unique features of 2D semiconductors, including enhanced Coulomb interactions, sensitivity to the surrounding environment, flexible van der Waals (vdW) heterostructure construction, and non-degenerate valley/spin index of 2D transition metal dichalcogenides (TMDs), manifest themselves during photocarrier relaxation and how they can be manipulated. The extensive physical mechanisms that can be used to modulate photocarrier relaxation dynamics are instrumental for understanding and utilizing excitonic states in 2D semiconductors.

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Ultrafast carrier dynamics in two-dimensional transition metal dichalcogenides

Cited by 56 publications

References 122 publications

Relaxation and transfer of photoexcited electrons at a coplanar few-layer 1 T′/2H-MoTe2 heterojunction

Relaxation and transfer of photoexcited electrons at a coplanar few-layer 1 T′/2H-MoTe2 heterojunction

Unveiling Bandgap Evolution and Carrier Redistribution in Multilayer WSe₂: Enhanced Photon Emission via Heat Engineering

Modulation of photocarrier relaxation dynamics in two-dimensional semiconductors

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Ultrafast carrier dynamics in two-dimensional transition metal dichalcogenides

Cited by 56 publications

References 122 publications

Relaxation and transfer of photoexcited electrons at a coplanar few-layer 1 T′/2H-MoTe2 heterojunction

Relaxation and transfer of photoexcited electrons at a coplanar few-layer 1 T′/2H-MoTe2 heterojunction

Unveiling Bandgap Evolution and Carrier Redistribution in Multilayer WSe2: Enhanced Photon Emission via Heat Engineering

Modulation of photocarrier relaxation dynamics in two-dimensional semiconductors

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Unveiling Bandgap Evolution and Carrier Redistribution in Multilayer WSe₂: Enhanced Photon Emission via Heat Engineering