Metal-insulator crossover in monolayer MoS₂

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Monolayer molybdenum disulfide (MoS₂) is a promising 2D material for electronic applications.
• Understanding charge transport mechanisms is crucial for optimizing MoS₂-based devices.

Purpose of the Study:

• To investigate the electronic transport properties of monolayer MoS₂ devices near the conduction band edge.
• To characterize the transition from insulating to metallic behavior in these devices.
• To identify the underlying transport mechanisms and scattering processes.

Main Methods:

• Fabrication of monolayer MoS₂ devices using chemical vapor deposition (CVD).
• In situ annealing for improved ohmic contact formation.
• Four-probe electrical transport measurements to determine conductivity and mobility.
• Analysis of temperature-dependent conductivity data.

Main Results:

• Achieved high effective mobility (up to 180 cm²V^-1s^-1) in CVD-grown MoS₂.
• Observed an insulating regime below 1.4e²/h and 1.7 × 10¹² cm^-2, transitioning to a metallic regime at higher values.
• Identified Efros-Schklovskii variable range hopping as the dominant low-temperature transport mechanism in the insulating phase.
• Demonstrated that high-temperature transport can be modeled by Boltzmann equation considering phonon and impurity scattering.

Conclusions:

• Monolayer MoS₂ exhibits a metal-insulator transition (MIT) with distinct transport regimes.
• Efros-Schklovskii variable range hopping suggests non-phonon-mediated transport at low temperatures.
• While phonon scattering explains some aspects, a genuine 2D MIT cannot be excluded due to observed scaling behavior.