Chinese Optics Letters, Volume. 20, Issue 10, 100002(2022)

Layer-dependent photoexcited carrier dynamics of WS2 observed using single pulse pump probe method

Author Affiliations
• 1State Key Laboratory of Digital Manufacturing Equipment and Technology, Huazhong University of Science and Technology, Wuhan 430074, China
• 2Optics Valley Laboratory, Wuhan 430074, China
• show less

Understanding the ultrafast carrier dynamics and the mechanism of two-dimensional (2D) transition metal dichalcogenides (TMDs) is key to their applications in the field of optoelectronic devices. In this work, a single pulse pump probe method is introduced to detect the layer-dependent ultrafast carrier dynamics of monolayer and few-layer $WS2$ excited by a femtosecond pulse. Results show that the ultrafast carrier dynamics of the layered $WS2$ films can be divided into three stages: the fast photoexcitation phase with the characteristic time of 2–4 ps, the fast decay phase with the characteristic time of 4–20 ps, and the slow decay phase lasting several hundred picoseconds. Moreover, the layer dependency of the characteristic time of each stage has been observed, and the corresponding mechanism of free carrier dynamics has been discussed. It has been observed as well that the monolayer $WS2$ exhibits a unique rising time of carriers after photoexcitation. The proposed method can be expected to be an effective approach for studying the dynamics of the photoexcited carriers in 2D TMDs. Our results provide a comprehensive understanding of the photoexcited carrier dynamics of layered $WS2$, which is essential for its application in optoelectronics and photovoltaic devices.

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1. Introduction

Transition metal dichalcogenides (TMDs) have attracted tremendous attention and played an important role in the development of two-dimensional (2D) semiconductor materials in the past decade due to their unique physical properties and outstanding photoelectric performance[13]. The extraordinary physical properties of the TMDs can be attributed to their unique physical structure. TMDs are layered structures, in which monolayer materials are stacked together through weak van der Waals forces between layers[4]. As a result, the optical and physical properties of TMDs will always exhibit striking layer-dependent evolutions[5,6]. Peculiarly, when the material is thinned from multiple layers to an atomically thin monolayer, the indirect band gap semiconductor will be transformed into a direct band gap semiconductor[7]. Due to its fascinating and layer-dependent photoelectronic and mechanical properties, 2D TMDs have promising potential applications in the field of optoelectronics, electronics, and flexible devices[811].

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Lin Zhang, Jiamin Liu, Hao Jiang, Honggang Gu, Shiyuan Liu. Layer-dependent photoexcited carrier dynamics of WS2 observed using single pulse pump probe method[J]. Chinese Optics Letters, 2022, 20(10): 100002

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Category: Ultrafast Optics: fundamentals and applications