Screening fermi-level pinning effect through van der waals contacts to monolayer MoS2

Nano-electronic devices incorporating Van der Waals electrical contact, particularly on two-dimensional semiconductor, offer exceptional electrical performance. However, the fabrication of Van der Waals electrical contact is still a challenge. Here, layered reduced graphene oxide (rGO) flakes are employed as buffer to construct the Van der Waals electrical contact in monolayer molybdenum disulfide (MoS2) transistors, and screen the Fermi-level pinning effect. The results show that the work function of monolayer MoS2 would increase by 0.12 eV and its electron concentration would decrease by 0.74 × 1012 cm−2, demonstrating the p-type doping role of rGO flakes. To quantitatively reveal the role of rGO buffer layer during the electrode fabrication, the MoS2 transistors w/o rGO buffer layer were fabricated on single monocrystalline MoS2 domain. Though comparatively studying the electrical properties at room/low temperature, it has been demonstrated the rGO buffer layer would contribute to forming van der Waals contacts and lead the dramatically decrease of Schottky barrier resulting in about ten times device mobility enhancement in MoS2 transistor.