(Invited) Metallic Transport Behaviors in Monolayer and Multi-Layer MoS2 By Surface-Charge Transfer Interaction with Redox-Active Molecules

Abstract

In the last decade, transition metal chalcogenides (TMDCs), e.g., MoS2 and WSe2, have gathered attention as semiconducting 2D materials. Modulation of carrier concentrations in TMDCs is a crucial matter for applying to semiconductor devices. So far, we have developed a method to gain the carrier concentrations of MoS2 by a junction with organic molecules and achieved obtaining a degenerately doped state in the MoS2. The mechanism of the doping is a surface-charge transfer interaction at the interface. Although the transfer characteristic behaviors show the degenerately doped state (small ON/OFF ratio), the details of the transport behavior have not been well understood. In this presentation, I will discuss the details of the device characteristics of the monolayer and multilayer MoS2 metal-oxide-semiconductor field-effect-transistors (MOSFETs) with a junction of redox-active molecules in a manner of the surface-charge transfer interaction. The devices were fabricated via standard lithography (e-beam and photolithography) techniques to prepare each monolayer and multilayer MoS2 MOSFETs. Transport properties in the MoS2 MOSFETs were measured in the as-prepared device and the device after the molecular doping. The dopant molecule is benzyl viologen (BV) molecule which is known as a redox-active molecule with high-reduction potential. After the doping with BV molecules, the MoS2 MOSFET showed a small ON/OFF ratio in the transfer characteristic curves, indicating a degenerately doped state. The identical device further showed the metallic behavior in the temperature dependence (the conductivity increases with decreasing the temperature). Both monolayer and multilayer MoS2 MOSFETs showed similar metallic behavior. This metallic transport behavior changes to an insulative regime when applying gate-voltage to reduce the carrier concentrations in the channel MoS2. Therefore, the gate-electrostatic induced metal-insulator-transition was suggested. At the conference, I will discuss the details of the transport behaviors, gate-potential and temperature dependence of the contact resistance. In addition, I will also discuss potential candidates of other molecules for obtaining doping to TMDCs for going forward the 2D materials-based electronics.REF: Matsuyama, et al., "Metallic transport in monolayer and multilayer molybdenum disulfides by molecular surface-charge transfer doping", ACS Appl. Mater. Interfaces, 2022, 14, 8163-8170.