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 (ACCU) 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 ACCU-FET is validated and clarified by carefully performed capacitance measurements. A depletion capacitance-quantum capacitance transition is observed. After the analysis of the MoS2 ACCU-FET, we have confirmed that most 2D FETs show an accumulation-mode behavior. The universal thickness scaling rule of 2D-FETs is then proposed, which provides guidance for future research on 2D materials.