Fully Current-Based Sub-Bandgap Optoelectronic Differential Ideality Factor Technique and Extraction of Subgap DOS in Amorphous Semiconductor TFTs

A sub-bandgap optoelectronic differential ideality factor technique is proposed for extraction of the intrinsic density-of-states (DOS) over the bandgap in amorphous semiconductor thin-film transistors (TFTs). In the proposed technique, the gate bias-dependent differential change in the difference of ideality factors (dAη(V_GS)/dV_GS) between dark and sub-bandgap photonic excitation condition is employed. With the sub-bandgap photons (hν <; E_g), the photonic excitation of electrons is confined only from the localized DOS over the bandgap. We applied the proposed technique to a-InGaZnO TFTs with W/L = 50/25 μm/μm and extracted the energy distribution of the intrinsic DOS for the localized states over the bandgap.