Electron transport and device physics in monolayer transition-metal dichalcogenides

Two-dimensional transition-metal dichalcogenides (TMDs) represent a promising class of materials for electronic and photonic devices, benefiting from their sizable bandgap of 1-2eV and ultrathin body. However, one of the major issues is that the experimental mobility is much lower than the theoretical phonon limit. It is speculated that the mobility is degraded by many extrinsic factors. In this talk I will present our systematic investigations on the electron transport and field-effect transistors of monolayer TMDs (including MoS$_{\mathrm{2}}$ and WS$_{\mathrm{2}})$. We find that the major extrinsic mobility limiting factors are charged impurities, traps and point defects. We develop a facile low-temperature thiol chemistry to repair the sulfur vacancies and improve the interface quality, resulting in significant reduction of the charged impurities and traps. In combination with high-k dielectrics that further screens the charged impurities, we are able to achieve record-high room-temperature mobilities of \textasciitilde 150cm$^{\mathrm{2}}$/Vs and 83cm$^{\mathrm{2}}$/Vs for monolayer MoS$_{\mathrm{2}}$ and WS$_{\mathrm{2}}$, repectively. We further develop a theoretical model to quantitatively correlate these extrinsic scattering sources to measured electrical data. Our study shows that interface engineering is critical for high-performance transistors based on 2D semiconductors. \begin{enumerate} \item []References \item Hao Qiu, Lijia Pan, Zongni Yao, Junjie Li, Yi Shi* and Xinran Wang*, \textit{Appl. Phys. Lett.}, 100, 123104 (2012). \item Hao Qiu, Tao Xu, Zilu Wang, Wei Ren, Haiyan Nan, Zhenhua Ni, Qian Chen, Shijun Yuan, Feng Miao, Fengqi Song, Gen Long, Yi Shi, Litao Sun, Jinlan Wang* {\&} Xinran Wang*, \textit{Nature Comm.} 4, 2642 (2013). \item Zhihao Yu, Yiming Pan, Yuting Shen, Zilu Wang, Zhun-Yong Ong, Tao Xu, Run Xin, Lijia Pan, Baigeng Wang, Litao Sun, Jinlan Wang, Gang Zhang, Yongwei Zhang, Yi Shi* {\&} Xinran Wang*\textit{, Nature Comm. 5, 5290 (2014)}. \item Yang Cui, Run Xin, Zhihao Yu, Yiming Pan, Zhun-Yong Ong, Xiaoxu Wei, Junzhuan Wang, Haiyan Nan, Zhenhua Ni, Yun Wu, Tangsheng Chen, Yi Shi*, Baigeng Wang, Gang Zhang*, Yong-Wei Zhang {\&} Xinran Wang*, \textit{Adv. Mater. 27, 5230 (2015)}. \item Zhihao Yu, Zhun-Yong Ong, Yiming Pan, Yang Cui, Run Xin, Yi Shi*, Baigeng Wang, Yong-Wei Zhang, Gang Zhang* {\&} Xinran Wang*, \textit{Adv. Mater. 28, 547 }(2016). \end{enumerate}