Photonic I-V Technique With Photogating Effect for Extended Extraction of Subgap Density of States in Amorphous Oxide Semiconductor TFTs

Abstract

The extraction of the subgap density of states (DoS, gDoS) is crucial in modeling, characterization, and simulation of amorphous oxide semiconductor thin-film transistors (AOS TFTs). Previous photonic current-voltage (I-V) methods were primarily focused on the photoconductive effect (PCE), often leading to erroneous gDoS. They are also limited to the subthreshold region with narrow energy range for gDoS. This study reports an enhanced photonic I-V technique expanding the energy range and refines the energy mapping with both the photovoltaic effect (PVE) and PCE. The method was experimentally validated using an amorphous In-Ga-Zn-O thin-film transistors (TFTs), yielding tail DoS parameters with NTA = 2.9 × 1017 eV-1⋅cm -3 and ETA = 0.06 eV. These results are consistent with those of technology computer-aided design (TCAD) simulations and are further confirmed with those of a previous method, along with various wavelengths of photons. © 2025 IEEE.