Amorphous Semiconductor Mobility Physics and TFT Modeling

Four topics are addressed. First, the mobility physics of an amorphous semiconductor (or insulator) is found to be dominated by carrier trapping in conjunction with diffusive carrier transport resembling Brownian motion. Second, a new method is proposed for measuring mobility in a thin-film transistor (TFT) based on use of the Enz–Krummenacher–Vittoz (EKV) compact model. Third, a new procedure is developed for accurately fitting mobility versus gate voltage trends based on use of a Gompertz function. Fourth, physics-based simulations of amorphous indium–gallium–zinc oxide ( a -IGZO) TFTs are performed that closely reproduce measured mobility trends. Accurate simulation requires accounting for extrinsic effects associated with defects and/or impurities, as well as intrinsic properties involving band tail and conduction band states.