Numerical analysis of oxygen-related defects in amorphous in-w-o nanosheet thin-film transistor

The integration of 4 nm thick amorphous indium tungsten oxide (a-IWO) and a hafnium oxide (HfO₂ ) high-κ gate dielectric has been demonstrated previously as one of promising amorphous oxide semiconductor (AOS) thin-film transistors (TFTs). In this study, the more positive threshold voltage shift (∆V_TH ) and reduced I_ON were observed when increasing the oxygen ratio during a-IWO deposition. Through simple material measurements and Technology Computer Aided Design (TCAD) analysis, the distinct correlation between different chemical species and the corresponding bulk and interface density of states (DOS) parameters were systematically deduced, validating the proposed physical mechanisms with a quantum model for a-IWO nanosheet TFT. The effects of oxygen flow on oxygen interstitial (O_i ) defects were numerically proved for modulating bulk dopant concentration N_d and interface density of Gaussian acceptor trap N_GA at the front channel, significantly dominating the transfer characteristics of a-IWO TFT. Furthermore, based on the studies of density functional theory (DFT) for the correlation between formation energy E^f of O_i defect and Fermi level (E_F ) position, we propose a numerical methodology for monitoring the possible concentration distribution of O_i as a function of a bias condition for AOS TFTs.