Contact pinning induced abnormal short-channel effects in monolayer MoS2 transistors

Two-dimensional (2D) semiconductors are widely regarded as promising channel materials for future transistors. The primary motivation is that 2D transistors could minimize the short-channel effects, which remain a critical issue in state-of-the-art silicon transistors. However, in this article, we report the observation of abnormal short-channel effects in monolayer MoS2 transistors. In great contrast to previous theory, monolayer MoS2 transistors indeed exhibit a much larger off-state current and stronger short-channel effects compared to thicker devices. This unexpected behavior is modeled using technology computer aided design (TCAD) simulations and confirmed through detailed capacitance–voltage measurement and is further explained by the Schottky barrier-based nature of 2D transistors. Finally, we applied van der Waals metal lamination technique to mitigate the contact pinning effect, hence recovering the ability to suppress short-channel effects in a monolayer device. Our work reports the observation of abnormal short-channel effects in monolayer 2D semiconductors, indicating that the well-known scaling advantage of two-dimensional transistors for suppressing short-channel effects cannot be effectively demonstrated due to the Fermi level pinning effect in the contact area. Hence, our study highlights the critical role of contact engineering to fully realize the scaling advantage and device potential of 2D transistors in future integrated circuits.