Spatiotemporal Study of Charge Transport in Amorphous Semiconductor Transistors

Due to the absence of long-range order, charge transport and carrier dynamics in amorphous semiconductors such as InGaZnO (a-IGZO) are different from conventional crystalline materials. In this work, we combine transport measurements and time-resolved microwave impedance microscopy (MIM) to study the underlying mechanisms of charge transport in a-IGZO field-effect transistors (FETs). By gradually turning on the FETs, we observed strong conductivity fluctuations near the sub-threshold regime. The typical domain size of this inhomogeneous electronic landscape is on the order of several hundred nanometers, consistent with the percolation model. We also studied the transient behavior of the MIM signals by applying square-wave-shaped gate voltages. The intrinsic charge mobility and carrier lifetime can be estimated through the purely diffusion-driven process. Our results demonstrated the crucial role of localized states and trapping/releasing process in amorphous semiconductors.