Valley engineering electron-hole liquids in transition metal dichalcogenide monolayers

Ray, Arnab Barman; Liang, Kevin; Vamivakas, Anthony Nicholas

doi:10.1103/physrevb.106.045206

Cited by 5 publications

(4 citation statements)

References 30 publications

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“…Hence, local strain can physically move excitons and trions toward or away from a strain apex, depending on the type of band bending that localized strain causes. If the band “pinches” together, it will collect quasi-particles and charge carriers, which is interesting for studying high-density phenomena such as crossover between an exciton gas and electron–hole liquid. , If on the other hand the bandgap decreases while both bands bend in the same direction (“type-II”), it may cause charge separation. A strong enough gradient in the band-bending will also separate the electron–hole pair in an exciton, collecting electrons and removing holes.…”

Section: Introductionmentioning

confidence: 99%

Charge Separation in Monolayer WSe₂ by Strain Engineering: Implications for Strain-Induced Diode Action

Chen

Luo

Liang

et al. 2022

ACS Appl. Nano Mater.

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Strain-engineering band structure in transition-metal dichalcogenides (TMDC) is a promising avenue toward capabilities in optoelectronics. For example, controlling the flow of optically generated quasiparticles can be achieved by a localized strain field which reduces the bandgap and generates an energy-band gradient that funnels neutral excitons to the strain apex. It would be even more advantageous to mimic a diode's internal field, where both conduction and valence bands bend in the same direction, to separate electrons and holes. This can be achieved if the strain in the TMDC layer lowers both the conduction band minimum as well as the valence band maximum during strain-induced band narrowing. Here, we have used density functional theory (DFT) calculations of monolayer WSe 2 electronic structure under biaxial strain to show that WSe 2 has this property. To test the band bending experimentally, we combined localized strain with electrostatic doping to follow photoluminescence from excitons and positive or negative trions. In unstrained WSe 2 , both positive and negative trion emissions dominate over excitons away from charge neutrality. In contrast, for strained areas, negative trions accumulate, while positive trion emission is near zero away from charge neutrality, indicating a lack of holes. Hence, strain bends both conduction and valence bands down, similarly to the band bending in a PN-diode depletion region, providing an opportunity to separate electrons and holes via localized strain.

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Section: Introductionmentioning

confidence: 99%

Charge Separation in Monolayer WSe₂ by Strain Engineering: Implications for Strain-Induced Diode Action

Chen

Luo

Liang

et al. 2022

ACS Appl. Nano Mater.

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“…Heterostructures, made by stacking monolayers of transition metal dichalcogenides [1][2][3][4][5][6][7] (TMDCs), as well as other materials, such as insulating hexagonal boron nitride(hBN), 8,9 have attracted significant scientific interest over the last decade. The possibilities of constructing different kinds of condensed matter systems [10][11][12] through the layer degree of freedom and the choice of material have been a cornerstone of research in this direction.…”

Section: Introductionmentioning

confidence: 99%

Interplay of trapped species and absence of electron capture in Moiré heterobilayers

Ray¹,

Mukherjee²,

Qiu³

et al. 2023

Preprint

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Moiré heterobilayers host interlayer excitons in a natural, periodic array of trapping potentials. Recent work has elucidated the structure of the trapped interlayer excitons and the nature of photoluminescence (PL) from trapped and itinerant charged complexes such as interlayer trions in these structures. In this paper, our results serve to add to the understanding of the nature of PL emission and explain its characteristic blueshift with increasing carrier density, along with demonstrating a significant difference between the interlayer exciton-trion conversion efficiency as compared to both localized and itinerant intra-layer species in conventional monolayers. Our results show the absence of optical generation of trions in these materials, which we suggest arises from the highly localized, near sub-nm confinement of trapped species in these Moiré potentials.

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“…Heterostructures, made by stacking monolayers of transition metal dichalcogenides − (TMDCs), as well as other materials, such as insulating hexagonal boron nitride (hBN), , have attracted significant scientific interest over the past decade. The possibilities of constructing different kinds of condensed matter systems − through the layer degree of freedom and the choice of material have been a cornerstone of research in this direction.…”

mentioning

confidence: 99%

“…The photoluminescence (PL) emission from interlayer excitons in MoSe 2 /WSe 2 Moiré heterobilayers has been studied in some detail, and three broad phases of excited state species were reported from diffusion-based studiestrapped excitons, itinerant excitons, and electron–hole plasmas at very high excitation intensities equivalent to carrier densities of the order of 10 13 cm –2 . , However, at intermediate carrier densities in the range 10 10 –10 11 cm –2 , when the spectral lines from individual trapped emitters are no longer isolatable due to power broadening and higher densities of trapped emitters, the dynamics between different species are not clear. This state of the system, which we call the quantum ensemble regime, represents emission from a collection of different trapped species across the excitation spot.…”

mentioning

confidence: 99%

Interplay of Trapped Species and Absence of Electron Capture in Moiré Heterobilayers

et al. 2023

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Moiréheterobilayers host interlayer excitons in a natural, periodic array of trapping potentials. Recent work has elucidated the structure of the trapped interlayer excitons and the nature of photoluminescence (PL) from trapped and itinerant charged complexes such as interlayer trions in these structures. In this paper, our results serve to add to the understanding of the nature of PL emission and explain its characteristic blueshift with increasing carrier density, along with demonstrating a significant difference between the interlayer exciton-trion conversion efficiency as compared to both localized and itinerant intralayer species in conventional monolayers. Our results show the absence of optical generation of trions in these materials, which we suggest arises from the highly localized, near subnanometer confinement of trapped species in these Moirépotentials.

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Valley engineering electron-hole liquids in transition metal dichalcogenide monolayers

Cited by 5 publications

References 30 publications

Charge Separation in Monolayer WSe₂ by Strain Engineering: Implications for Strain-Induced Diode Action

Charge Separation in Monolayer WSe₂ by Strain Engineering: Implications for Strain-Induced Diode Action

Interplay of trapped species and absence of electron capture in Moiré heterobilayers

Interplay of Trapped Species and Absence of Electron Capture in Moiré Heterobilayers

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Valley engineering electron-hole liquids in transition metal dichalcogenide monolayers

Cited by 5 publications

References 30 publications

Charge Separation in Monolayer WSe2 by Strain Engineering: Implications for Strain-Induced Diode Action

Charge Separation in Monolayer WSe2 by Strain Engineering: Implications for Strain-Induced Diode Action

Interplay of trapped species and absence of electron capture in Moiré heterobilayers

Interplay of Trapped Species and Absence of Electron Capture in Moiré Heterobilayers

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Charge Separation in Monolayer WSe₂ by Strain Engineering: Implications for Strain-Induced Diode Action

Charge Separation in Monolayer WSe₂ by Strain Engineering: Implications for Strain-Induced Diode Action