Enhancement of carrier mobility in MoS_2 field effect transistors by a SiO_2 protective layer

摘要

Molybdenum disulfide is a promising channel material for field effect transistors (FETs). In this paper, monolayer MoS_2 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 SiO_2 protective layer, which is deposited on the surface of MoS_2, in order to avoid the MoS_2 directly contacting with the photoresist and the ambient environment. Therefore, the contact property between the MoS_2 and the electrodes is improved, and the Coulomb scattering caused by the charged impurities and the interface states is reduced. Comparing MoS_2 FETs with and without a SiO_2 protective layer, the SiO_2 protective layer is found to enhance the characteristics of the MoS_2 FETs, including transfer and output characteristics. A high mobility of ～42.3 cm~2/V s is achieved, which is very large among the top-gate CVD-grown monolayer MoS_2 FETs.