Accumulation-mode two-dimensional field-effect transistor: Operation mechanism and thickness scaling rule

Understanding the operation mode of a two-dimensional (2D) material-based field-effect transistor (FET) is one of the most essential issues in the study of electronics and physics. The existing Schottky barrier-FET model for devices with global back gate and metallic contacts overemphasizes the metal-2D contact effect, and the widely observed residual conductance cannot be explained by this model. Here, an accumulation-mode FET model, which directly reveals 2D channel transport properties, is developed based on a partial top-gate MoS2 FET with metallic contacts and a channel thickness of 0.65~118 nm. The operation mechanism of an accumulation-mode FET is validated and clarified by carefully performed capacitance measurements. A depletion capacitance-quantum capacitance transition is observed. After the analysis of the MoS2 accumulation-mode FET, we have confirmed that most 2D-FETs show accumulation-mode behavior. The universal thickness scaling rule of 2D-FETs is then proposed, which provides guidance for future research on 2D materials.