Abstract-The Role of Photo-Induced Exciton in the Transient Terahertz Conductivity of Few-Layer WS2 Laminate

Xiao Xing, Litao Zhao, Zeyu Zhang, Xiankuan Liu, Kailin Zhang, Yang Yu, Xian Lin, Huaying Chen, Jinquan Chen, Zuanming Jin, Jianhua Xu, and Guo-Hong Ma

http://pubs.acs.org/doi/abs/10.1021/acs.jpcc.7b05345?journalCode=jpccck

The exciton effect in two-dimensional (2D) transition metal dichalcogenides (TMDs) plays a dominated role in describing the optical and optoelectronic properties. However, the interplay between the excitons and free carriers has yet to be understood upon the photo excitation in 2D TMDs. Here we first present a study of the dynamical interplay of excitons and unbound electron-hole pairs using time-resolved terahertz (THz) spectroscopy (TRTS) in a few-layer WS2 laminate. Our experimental results demonstrate that the Auger recombination is observed only in the relaxation process of the mobile charge carriers rather than that of excitons upon photoexcitation. The transient complex THz photoconductivity spectroscopy of WS2 is well described by Lorentz oscillator model of free carriers modulated by the exciton polarization field. Our results provide a comprehensive understanding of non-equilibrium carrier kinetics (both excitons and free carriers) in WS2 laminate, and should be applicable to other 2D system.