Nature of electronic states in atomically thin MoS₂ field-effect transistors

We present low-temperature electrical transport experiments in five field-effect transistor devices consisting of monolayer, bilayer and trilayer MoS₂ films, mechanically exfoliated onto Si/SiO₂ substrate. Our experiments reveal that the electronic states in all films are localized well up to room temperature over the experimentally accessible range of gate voltage. This manifests in two-dimensional (2D) Variable Range Hopping (VRH) at high temperatures, while below ∼30 K, the conductivity displays oscillatory structures in gate voltage arising from resonant tunneling at the localized sites. From the correlation energy (T₀) of VRH and gate voltage dependence of conductivity, we suggest that Coulomb potential from trapped charges in the substrate is the dominant source of disorder in MoS₂ field-effect devices, which leads to carrier localization, as well