Probing the Electron States and Metal-Insulator Transition Mechanisms in Atomically Thin MoS2 Based on Vertical Heterostructures

摘要

The metal-insulator transition (MIT) is one of the remarkable electricaltransport properties of atomically thin molybdenum disulphide (MoS2). Althoughthe theory of electron-electron interactions has been used in modeling the MITphenomena in MoS2, the underlying mechanism and detailed MIT process stillremain largely unexplored. Here, we demonstrate that the verticalmetal-insulator-semiconductor (MIS) heterostructures built from atomically thinMoS2 (monolayers and multilayers) are ideal capacitor structures for probingthe electron states in MoS2. The vertical configuration of MIS heterostructuresoffers the added advantage of eliminating the influence of large impedance atthe band tails and allows the observation of fully excited electron states nearthe surface of MoS2 over a wide excitation frequency (100 Hz-1 MHz) andtemperature range (2 K- 300 K). By combining capacitance and transportmeasurements, we have observed a percolation-type MIT, driven by densityinhomogeneities of electron states, in the vertical heterostructures built frommonolayer and multilayer MoS2. In addition, the valence band of thin MoS2layers and their intrinsic properties such as thickness-dependence screeningabilities and band gap widths can be easily accessed and precisely determinedthrough the vertical heterostructures.