Mobility Enhancement of Strained MoS2 Transistor on Flat Substrate

Strain engineering has been proposed as a promising methodto boostthe carrier mobility of two-dimensional (2D) semiconductors. However,state-of-the-art straining approaches are largely based on putting2D semiconductors on flexible substrates or rough substrate with nanostructures(e.g., nanoparticles, nanorods, ripples), where theobserved mobility change is not only dependent on channel strain butcould be impacted by the change of dielectric environment as wellas rough interface scattering. Therefore, it remains an open questionwhether the pure lattice strain could improve the carrier mobilitiesof 2D semiconductors, limiting the achievement of high-performance2D transistors. Here, we report a strain engineering approach to fabricatehighly strained MoS2 transistors on a flat substrate. Bymechanically laminating a prefabricated MoS2 transistoronto a custom-designed trench structure on flat substrate, well-controlledstrain can be uniformly generated across the 2D channel. In the meantime,the substrate and the back-gate dielectric layer remain flat withoutany roughness-induced scattering effect or variation of the dielectricenvironment. Based on this technique, we demonstrate the MoS2 electron mobility could be enhanced by tension strain and decreasedby compression strain, consistent with theoretical predictions. Thehighest mobility enhancement is 152% for monolayer MoS2 and 64% for bilayer MoS2 transistors, comparable to thatof a silicon device. Our method not only provides a compatible approachto uniformly strain the layered semiconductors on flat and solid substratebut also demonstrates an effective method to boost the carrier mobilitiesof 2D transistors.