Uncovering edge states and electrical inhomogeneity in MoS2 field-effect transistors

Abstract

The understanding of various types of disorders in atomically thin transition metal dichalcogenides (TMDs), including dangling bonds at the edges, chalcogen deficiencies in the bulk, and charges in the substrate, is of fundamental importance for their applications in electronics and photonics. Because of the imperfections, electrons moving on these two-dimensional (2D) crystals experience a spatially non-uniform Coulomb environment, whose effect on the charge transport has not been microscopically studied. Here, we report the mesoscopic conductance mapping in monolayer and few-layer MoS2 field-effect transistors (FETs) by microwave impedance microscopy (MIM). The spatial evolution of the insulator-to-metal transition is clearly resolved. Interestingly, as the transistors are gradually turned on, electrical conduction emerges initially at the edges before appearing in the bulk of MoS2 flakes, which can be explained by our first-principles calculations. The results unambiguously confirm that the contribution of edge states to the channel conductance is significant under the threshold voltage but negligible once the bulk of the TMD device becomes conductive. Strong conductance inhomogeneity, which is associated with the fluctuations of disorder potential in the 2D sheets, is also observed in the MIM images, providing a guideline for future improvement of the device performance.

25 pages,5 figures, just accepted by Proceedings of the National Academy of Sciences 2016

References in corpus (7)

• The Valley Hall Effect in MoS2 Transistors
• Two-dimensional transition metal dichalcogenides under electron irradiation: defect production and doping
• Generation and Electric Control of Spin-Coupled Valley Current in WSe2
• Probing the Electron States and Metal-Insulator Transition Mechanisms in Atomically Thin MoS2 Based on Vertical Heterostructures
• Modeling of a Cantilever-Based Near-Field Scanning Microwave Microscope
• AFM-compatible near-field scanning microwave microscope with separated excitation and sensing probes
• Mesoscale Imperfections in MoS2 Atomic Layers Grown by Vapor Transport Technique

Cited by in corpus (6)

• Visualization of Local Conductance in MoS2/WSe2 Heterostructure Transistors
• Quasi-One-Dimensional Higher-Order Topological Insulators
• Edge states and spin-valley edge photocurrent in transition metal dichalcogenide monolayers
• Accuracy of Y-function methods for parameters extraction of two-dimensional FETs across different technologies
• Width-dependent Photoluminescence and Anisotropic Raman Spectroscopy from Monolayer MoS${}_2$ Nanoribbons
• Staircase-like transfer characteristics in multilayer MoS2 field-effect transistors