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

Bias-dependent effective channel length [L
_eff
(VG)] is empirically modeled with a channel conduction factor [α(VG)] 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
(VG) through the product of the empirical channel conduction factor [α(VG)] and the metallurgical channel length (Lm). We confirm that the gate bias-dependent channel conduction effect is significant in the subgap DOS far from the conduction band edge (EC) due to the low conductivity of the channel under subthreshold bias.