Ambipolar MoS₂ Thin Flake Transistors

TLDR

Field‑effect transistors made from thin flakes of layered materials have attracted growing interest since the success of graphene. The authors aim to fabricate an electric double‑layer transistor using a thin MoS₂ flake. They fabricate an EDLT gated by ionic liquids with a thin MoS₂ flake as the channel. The EDLT shows ambipolar operation with high‑performance transistor behavior, achieving ON conductivities of ~mS, on/off ratios >10², electron and hole mobilities of 44 and 86 cm² V⁻¹ s⁻¹, carrier densities up to 10¹⁴ cm⁻², and metallic transport, underscoring its promise for new device functionalities and as a protocol for studying transition‑metal dichalcogenides.

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.