Ambipolar MoS₂ Thin Flake Transistors

Abstract

Field effect transistors (FETs) made of thin flake single\ncrystals\nisolated from layered materials have attracted growing interest since\nthe success of graphene. Here, we report the fabrication of an electric\ndouble layer transistor (EDLT, a FET gated by ionic liquids) using\na thin flake of MoS₂, a member of the transition metal\ndichalcogenides, an archetypal layered material. The EDLT of the thin\nflake MoS₂ unambiguously displayed ambipolar operation,\nin contrast to its commonly known bulk property as an <i>n</i>-type semiconductor. High-performance transistor operation characterized\nby a large “ON” state conductivity in the order of ∼mS\nand a high on/off ratio >10² was realized for both hole\nand electron transport. Hall effect measurements revealed mobility\nof 44 and 86 cm²V^–1s^–1 for electron and hole, respectively. The hole mobility\nis twice the value of the electron mobility, and the density of accumulated\ncarrier reached 1 × 10¹⁴ cm^–2, which\nis 1 order of magnitude larger than conventional FETs with solid dielectrics.\nThe high-density carriers of both holes and electrons can create metallic\ntransport in the MoS₂ channel. The present result is not\nonly important for device applications with new functionalities, but\nthe method itself would also act as a protocol to study this class\nof material for a broader scope of possibilities in accessing their\nunexplored properties.