Investigation of Electrostatic Gating in Two-Dimensional Transitional Metal Dichalcogenide (TMDC) Field Effect Transistors (FETs)

In the active and growing explorations of the rapidly emerging two-dimensional (2D) electronic and optoelectronic devices based upon atomically thin semiconductors and their heterostructures, developing better understanding of electrostatic gating is very important, especially for realizing logic and switching devices by employing 2D field effect transistors (FETs) with low subthreshold swing (SS) and high on-off ratio (I-On/I-Off). In this study, we propose and demonstrate a method that includes a combination of two-probe and four-probe I-V measurements on 2D transition metal dichalcogenide (TMDC) FETs to uncover the evolution of resistance of channel and contacts separately, upon change of gate voltage during switching between On and Off states. In 2D TMDC FETs with Schottky barrier (SB) contacts, we demonstrate that switching between On and Off states is primarily attained by modulating SBs due to change of electric field via electrostatic gating. Therefore, transistor characteristics is mostly determined by the contact resistance change upon the application of gate voltage. We present our method for 2D TMDC (MoS2, MoTe2) FETs. In addition, we also perform C-V measurements to investigate the presence of interface trap states and quantum capacitance in TMDC FETs.