High-quality MoS2 monolayers with largely enhanced electrical properties by plasma-treated SiO2/Si substrates based chemical vapor deposition

The atomic chalcogen vacancies are generally considered to be intrinsic defects of two-dimensional transition metal dichalcogenides prepared either by chemical vapor deposition or mechanical exfoliation, which could be detrimental to the intrinsic properties and device performance. Here we report a plasma-pretreated SiO2/Si substrate based chemical vapor deposition strategy for the synthesis of high quality MoS2 single crystal monolayers with largely enhanced electrical properties. First, the plasma-pretreated SiO2/Si substrate possesses much better hydrophilicity than the pristine one, and this promotes the adsorption of sodium molybdate solution (metal source) via spin coating, and thus facilitates the growth of high quality and large size MoS2 single crystal monolayers with fewer sulfur vacancies. As a result, the as-fabricated MoS2 FETs exhibit enhanced ON-state current density by nearly three order of magnitude, improved carrier mobility by around 70-fold up to 38.8 cm2 V-1 s- 1. Second, the treated SiO2 surface have active oxygen bonds, which can bond with S atoms of the subsequently growing MoS2 monolayers, introducing n-type doping to the final sample, as verified by optical and electrical measurements. Our work provides a non-destructive but effective strategy towards reducing intrinsic defect density and tuning carrier density through engineering the growing substrate surface.