Enhancement of carrier mobility in MoS₂ field effect transistors by a SiO₂ protective layer

Molybdenum disulfide is a promising channel material for field effect transistors (FETs). In this paper, monolayer MoS₂ grown by chemical vapor deposition (CVD) was used to fabricate top-gate FETs through standard optical lithography. During the fabrication process, charged impurities and interface states are introduced, and the photoresist is not removed cleanly, which both limit the carrier mobility and the source-drain current. We apply a SiO₂ protective layer, which is deposited on the surface of MoS₂, in order to avoid the MoS₂ directly contacting with the photoresist and the ambient environment. Therefore, the contact property between the MoS₂ and the electrodes is improved, and the Coulomb scattering caused by the charged impurities and the interface states is reduced. Comparing MoS₂ FETs with and without a SiO₂ protective layer, the SiO₂ protective layer is found to enhance the characteristics of the MoS₂ FETs, including transfer and output characteristics. A high mobility of ∼42.3 cm²/V s is achieved, which is very large among the top-gate CVD-grown monolayer MoS₂ FETs.