Influence of the Metal-MoS$_{2}$ interface on MoS$_{2}$ Transistor Performance

We compare the electrical characteristics of MoS$_{2}$ field-effect transistors (FETS) with Ag source/drain contacts with transistors with Ti contacts, and we demonstrate that the metal-MoS$_{2}$ interface is crucial to the final device performance. The topography of 5nm Au/5nm Ag (contact layer) and 5nm Au/5nm Ti metal films deposited onto mono- and few-layer MoS$_{2}$ was characterized by using scanning electron microscopy and atomic force microscopy. The surface morphology of the Au/Ti films on MoS$_{2}$ shows a rough, dewetting pattern while Au/Ag forms smooth, dense films. These smoother and denser Au/Ag contacts lead to improved carrier transport efficiency. FETs with Ag contacts show more than 60 times higher on-state current and a steeper subthreshold slope. Raman spectroscopy of MoS$_{2}$ covered with Au/Ag or Au/Ti films revealed that the contact layer is Ag or Ti, respectively. In addition, there is a dramatic difference in the heat transfer between the MoS$_{2}$ and the two metals: while laser heating is observed in Au/Ti covered MoS$_{2}$, no heating effects are seen in Au/Ag covered MoS$_{2}$. It is reasonable to conclude that the smoother and denser Ag contact leads to higher carrier transport efficiency and contributes to the improved thermal properties.