Bias-Dependent Effective Channel Length for Extraction of Subgap DOS by Capacitance-Voltage Characteristics in Amorphous Semiconductor TFTs

Abstract

Bias-dependent effective channel length [L-eff(V-G)] is empirically modeled with a channel conduction factor [alpha(V-G)] for a consistent capacitance-voltage (C-V) characterization of the intrinsic subgap density of states (DOS) over the bandgap with the sub-bandgap photoresponsive C-V technique in amorphous thin-film transistors. We define the effective channel length L-eff(V-G) through the product of the empirical channel conduction factor [alpha(V-G)] and the metallurgical channel length (L-m). We confirm that the gate bias-dependent channel conduction effect is significant in the subgap DOS far from the conduction band edge (E-C) due to the low conductivity of the channel under subthreshold bias.