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Modulating the intralayer and interlayer valley excitons in WS2 through interaction with AlGaN

利用AlGaN耦合作用调控WS2层内和层间谷激子

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Abstract

The fine-tuning of exciton transition and valley polarization process in two-dimensional materials have drawn tremendous research interest due to their rich valley-contrasting physics. Here, we demonstrate highly tunable exciton and valley characteristics in monolayer and bilayer WS2 through coupling to AlGaN with different doping levels. A notable redshift in exciton energy is observed by interfacing WS2 with n-type AlGaN. More interestingly, an interlayer exciton peak emerges as a result of the formation of type-II band alignment in bilayer WS2. Both the interlayer and intralayer exciton energies are tunable by the twist angle of bilayer WS2. A high valley polarization of 82.2% is achieved in monolayer WS2 at 13 K by coupling with n-type AlGaN, due to the faster exciton decay rate through electron-phonon interaction and the reduced intervalley scattering by doping-induced carrier screening. The valley polarization of interlayer exciton is higher than that of the intralayer exciton, due to the suppressed intervalley scattering resulting from the reduced electron-hole interaction. This work has presented a facile and efficient technique to modulate the excitonic properties of 2D materials. The reported high valley polarization in monolayer WS2 and the discovery of interlayer exciton in bilayer WS2 will trigger innovative study in valley exciton physics and facilitate emerging valleytronic applications.

摘要

二维材料中的激子跃迁和能谷极化过程具有丰富的能谷物理特 性, 因此具有极大的研究价值. 本文发现, 单层和双层WS2中激子和能谷 特性可以通过耦合不同掺杂浓度的AlGaN进行有效调控. 当WS2和n型 AlGaN耦合时, 会出现显著的激子能量红移. 值得一提的是, 来自AlGaN的层间电荷转移作用会促使双层WS2形成II型能带, 进而产生层间 激子跃迁. 层内激子峰和层间激子峰的能量和强度还可以通过双层 WS2中的转角进行调控. 在13 K条件下, 通过耦合n型AlGaN, 单层WS2 的谷极化率高达82.2%. 这是由于AlGaN的电子-声子相互作用会带来 更高的激子衰减速率, 且掺杂导致的载流子屏蔽效应会减少层间谷散 射. 层间激子的谷极化率明显高于层内激子, 这是由于在层间激子中电 子-空穴相互作用较弱, 导致层间谷散射受到抑制. 本文提出了一种简 便有效的方法来调控二维材料的激子特性, 在单层WS2中实现了极高 的谷极化, 并在双层WS2中诱导出层间激子. 这些发现将激发谷激子物 理学的创新探索, 并推动新兴的谷电子器件的应用研究.

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Acknowledgements

This work was supported by the National Natural Science Fund for Excellent Young Scholars (62022068), the National Key Research and Development Program of China (2018YFB0406603), the National Natural Science Foundation of China (61804129, 61974123 and 61874092), the Science and Technology Key Project of Xiamen (3502ZCQ20191001), the Science and Technology Project of Fujian Province, China (2019H0002), and the Natural Science Foundation of Jiangxi Province, China (20192BAB217013).

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  1. These authors contributed equally to this work.

Authors and Affiliations

  1. College of Physical Science and Technology, Key Laboratory of Semiconductors and Applications of Fujian Province, College of Chemistry and Chemical Engineering, Jiujiang Research Institute, Xiamen University, Xiamen, 361005, China

    Xinlong Zeng  (曾鑫龙), Wenyu Kang  (康闻宇), Xiaowen Zhou  (周小文), Yuanzheng Xia  (夏源政), Haiyang Liu  (刘海洋), Chengbiao Yang  (杨成彪), Yaping Wu  (吴雅苹), Zhiming Wu  (吴志明), Xu Li  (李煦) & Junyong Kang  (康俊勇)

  2. School of Physics, Southeast University, Nanjing, 211189, China

    Linglong Li  (李玲龙)

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  1. Xinlong Zeng  (曾鑫龙)
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Contributions

Zeng X designed and engineered the samples; Kang W provided AlGaN; Zhou X, Xia Y and Yang C helped with the characterizations of AFM and Raman; Li L helped with the characterization of KPFM; Liu H helped with the characterization of TRPL; Zeng X analyzed the data with support from Li X, Wu Y and Wu Z; Zeng X wrote the paper with support from Li X, Wu Y, Wu Z, Kang W and Kang J. All authors contributed to the general discussion.

Corresponding authors

Correspondence to Yaping Wu  (吴雅苹), Zhiming Wu  (吴志明) or Xu Li  (李煦).

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Conflict of interest

The authors declare that they have no conflict of interest.

Supplementary information

Supporting data are available in the online version of the paper.

Xinlong Zeng is currently a master candidate at Fujian Provincial Key Laboratory of Semiconductor Materials and Applications, Xiamen University. He received his BE degree (2019) from Nanchang Hangkong University. His research interests focus on 2D materials and devices and optoelectronic devices.

Wenyu Kang gained his PhD degree from the University of Adelaide, Australia. He currently works at the Department of Chemistry, Xiamen University as an associate research fellow engaging in material growth and equipment development.

Yaping Wu received her BSc and PhD degrees from Xiamen University. She is currently a full professor at Xiamen University. Her research interest includes wide-bandgap semiconductor devices, low-dimensional quantum structures and device applications, and 2D materials and devices.

Zhiming Wu received his BSc and PhD degrees from the East China Normal University. He joined Xiamen University in 2007 and was promoted to a full professor in 2015. He has been working as a visiting scholar at Oak Ridge National Laboratory. His current research interests focus on novel nanostructured solar cells, 2D materials and devices, wide-bandgap power-electronic devices, and surface physics and spin transport.

Xu Li received his BE degree from Zhejiang University in 2010. After graduation from the University of Chinese Academy of Sciences with a MSc degree, he obtained his PhD degree from the University of Hong Kong in 2017. He is currently an associate professor at the Department of Physics, Xiamen University. His research interest covers semiconductor materials, spintronic devices, and optoelectronic devices.

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Zeng, X., Kang, W., Zhou, X. et al. Modulating the intralayer and interlayer valley excitons in WS2 through interaction with AlGaN. Sci. China Mater. 66, 202–210 (2023). https://doi.org/10.1007/s40843-022-2138-x

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