Boosting quantum yields in two-dimensional semiconductors via proximal metal plates

Yongjun Lee,Trang Thu Tran,Shrawan Roy,Jeongyong Kim,Andrey Chaves,Youngbum Kim,Johnathas D’Arf Severo Forte,Tony Low,Anshuman Kumar,Kenji Watanabe,Takashi Taniguchi,Alexey Chernikov,Joon I Jang

doi:10.1038/s41467-021-27418-x

Abstract

Monolayer transition metal dichalcogenides (1L-TMDs) have tremendous potential as atomically thin, direct bandgap semiconductors that can be used as convenient building blocks for quantum photonic devices. However, the short exciton lifetime due to the defect traps and the strong exciton-exciton interaction in TMDs has significantly limited the efficiency of exciton emission from this class of materials. Here, we show that exciton-exciton interaction in 1L-WS2 can be effectively screened using an ultra-flat Au film substrate separated by multilayers of hexagonal boron nitride. Under this geometry, induced dipolar exciton-exciton interaction becomes quadrupole-quadrupole interaction because of effective image dipoles formed within the metal. The suppressed exciton-exciton interaction leads to a significantly improved quantum yield by an order of magnitude, which is also accompanied by a reduction in the exciton-exciton annihilation (EEA) rate, as confirmed by time-resolved optical measurements. A theoretical model accounting for the screening of the dipole-dipole interaction is in a good agreement with the dependence of EEA on exciton densities. Our results suggest that fundamental EEA processes in the TMD can be engineered through proximal metallic screening, which represents a practical approach towards high-efficiency 2D light emitters.

Highlights

Monolayer transition metal dichalcogenides (1L-Transition metal dichalcogenides (TMDs)) have tremendous potential as atomically thin, direct bandgap semiconductors that can be used as convenient building blocks for quantum photonic devices
The presence of a large number of defects in 1L-TMDs can serve as nonradiative recombination centers leading to low QYs8–10
A near-unity quantum yield (QY) in sulfurbased 1L-MS2 has been reported through passivation of defectmediated nonradiative recombination by super-acid treatment[12] and atomic healing of sulfur vacancies were observed by scanning transmission electron microscopy[10]

Summary

Introduction

Monolayer transition metal dichalcogenides (1L-TMDs) have tremendous potential as atomically thin, direct bandgap semiconductors that can be used as convenient building blocks for quantum photonic devices. The presence of a large number of defects in 1L-TMDs (especially chalcogen vacancies, ~1012 cm−2) can serve as nonradiative recombination centers leading to low QYs8–10. Various methods such as defect passivation or charge transfer were proposed to improve the QY7,10–14. Even in the ideal pristine 2D MX2, the QY can still be quenched when the exciton-exciton interaction dominates to cause strong exciton Auger recombination, so-called excitonexciton annihilation (EEA)[15–19] This density-dependent fundamental process occurs at high exciton densities under strong light illumination. Since electroluminescence (EL) in 2D TMDs arises as a consequence of radiative excitonic transition[21], EEA practically determines the quantum efficiency of a light-emitting device at the exciton density under typical brightness[22,23]. EEA and the accompanying QY drooping at high exciton densities are of utmost importance to high-efficiency light-emitting devices

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Methods

Results