Tunable Transport Gap in Phosphorene

In this paper, we experimentally demonstrate that the transport gap of phosphorene can be tuned monotonically from ~0.3 to ~1.0 eV when the flake thickness is scaled down from bulk to a single layer. As a consequence, the ON current, the OFF current, and the current ON/OFF ratios of phosphorene field effect transistors (FETs) were found to be significantly impacted by the layer thickness. The transport gap was determined from the transfer characteristics of phosphorene FETs using a robust technique that has not been reported before. The detailed mathematical model is also provided. By scaling the thickness of the gate oxide, we were also able to demonstrate enhanced ambipolar conduction in monolayer and few layer phosphorene FETs. The asymmetry of the electron and the hole current was found to be dependent on the layer thickness that can be explained by dynamic changes of the metal Fermi level with the energy band of phosphorene depending on the layer number. We also extracted the Schottky barrier heights for both the electron and the hole injection as a function of the layer thickness. In conclusion, we discuss the dependence of field effect hole mobility of phosphorene on temperature and carrier concentration.. Authors: Das, Saptarshi [Argonne National Lab. (ANL), Argonne, IL (United States). Center for Nanoscale Material]; Zhang, Wei [Argonne National Lab. (ANL), Argonne, IL (United States). Materials Science Division]; Demarteau, Marcel [Argonne National Lab. (ANL), Argonne, IL (United States). Division of High Energy Physics]; Hoffmann, Axel [Argonne National Lab. (ANL), Argonne, IL (United States). Materials Science Division]; Dubey, Madan [Army Research Lab., Adelphi, MD (United States)]. DOE Contract: AC02-06CH11357. Subjects: 74 ATOMIC AND MOLECULAR PHYSICS; Phosphorene; field effect transistor; mobility; transport gap