Device Physics of Contact Issues for the Overestimation and Underestimation of Carrier Mobility in Field-Effect Transistors

Cutting-edge field-effect and thin-film transistors (FETs and TFTs) reportedly offer very high carrier mobilities, but the reliability of these values is controversial. This study reveals the complicated evolution of band bending and actual carrier concentrations in three-terminal devices with non-Ohmic contacts, and its effect on the estimation of carrier mobility. The widely used method is shown to be unreliable: In FETs or TFTs with gated Schottky contacts, mobility can be overestimated by a factor of 10 or more, while in those with resistive contacts it can be underestimated. Fortunately, this analysis also shows how to determine mobilities accurately.