Xuefeng Liu1,2, Hongyi Yu3, Qingqing Ji4, Zhihan Gao1,2, Shaofeng Ge1,2, Jun Qiu1,2, Zhongfan Liu4,Yanfeng Zhang4,5 and Dong Sun1,2
http://iopscience.iop.org/article/10.1088/2053-1583/3/1/014001/meta
We investigate the dynamical formation of an exciton from photo-excited electron-hole plasma and its subsequent decay dynamics in monolayer MoS2 grown by chemical vapor deposition (CVD) using ultrafast pump and terahertz probe spectroscopy. Different photo-excited electron-hole states are resolved based on their distinct responses to THz photon and decay lifetimes. The observed transient THz transmission can be fitted with two decay components: a fast component with a decay lifetime of 20 ps, which is attributed to the exciton lifetime, including its formation and subsequent intra-exciton relaxation; a slow component with an extremely long decay lifetime of several ns, possibly due to a long-lived dark exciton state. The relaxation dynamics are further supported by temperature and pump-fluence-dependent studies of the decay time constants. The sign of the transient THz observed in this experiment is the opposite of that measured in a recent parallel transient THz work on MoS2 [1]. The observed decay dynamics are also different, and the possible reasons for these discrepancies are discussed.
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