Nature of Electronic States in Ultrathin MoS$_{2}$ Field Effect Transistor

Molybdenum disulphide (MoS$_{2})$ is a layered transition metal dichalcogenide with a Mo layer sandwiched between two S layers (S-Mo-S), which forms its basic unit. Each basic unit is attached to other units only with weak Van der Waals force. This enables to make an atomically thin single layer of MoS$_{2}$ with a bandgap 1.9 eV. The presence of bandgap has made it an interesting material in thin film transistors. It has been reported [1] recently that very high on/off ratio ($\sim $10$^{8})$ can be obtained in single layer MoS$_{2}$ transistor due to the presence of this bandgap. Though the on/off ration is very high, mobility in these transistors are considerably low. Here we have investigated the origin of such low mobility. From our temperature dependent study we find that atomically thin MoS$_{2}$ layer becomes highly disordered in the presence of the substrate and electron got localised in the traps created by the charge impurities at substrate-MoS$_{2}$ interface. We propose that high mobility can be obtained in these transistors by removing the charge impurity background. \\[4pt] [1] Radisavljevic, B. \textit{et al}. Nature Nanotechnology \textbf{2011}, 6, 147--150. \\[0pt] [2] Ghatak, S. \textit{et al}. ACS Nano \textbf{2011}, 5, 7707.