Ambipolar MoS2 Thin Flake Transistors

Abstract

Field effect transistors (FETs) made of thin flake single crystals isolated from layered materials have attracted growing interest since the success of graphene. Here, we report the fabrication of an electric double layer transistor (EDLT, a FET gated by ionic liquids) using a thin flake of MoS₂, a member of the transition metal dichalcogenides, an archetypal layered material. The EDLT of the thin flake MoS₂ unambiguously displayed ambipolar operation, in contrast to its commonly known bulk property as an n-type semiconductor. High-performance transistor operation characterized by a large “ON” state conductivity in the order of ∼mS and a high on/off ratio >10² was realized for both hole and electron transport. Hall effect measurements revealed mobility of 44 and 86 cm² V^–1 s^–1 for electron and hole, respectively. The hole mobility is twice the value of the electron mobility, and the density of accumulated carrier reached 1 × 10¹⁴ cm^–2, which is 1 order of magnitude larger than conventional FETs with solid dielectrics. The high-density carriers of both holes and electrons can create metallic transport in the MoS₂ channel. The present result is not only important for device applications with new functionalities, but the method itself would also act as a protocol to study this class of material for a broader scope of possibilities in accessing their unexplored properties.