Extraction of Carrier Impact Ionization Rate in Poly-Si Films Based on TCAD Simulation of Thin-Film Transistors

Abstract

In this study, we propose a methodology to extract the carrier impact ionization rates ( $\alpha $ ) of poly-Si films with different crystallinity based on TCAD simulation of thin-film transistors (TFTs). The dependence of $\alpha $ on the total trap density was also investigated. First, the TCAD simulation model of TFTs was calibrated by precisely fitting the measured transfer and output characteristic curves of poly-Si TFTs, and the trap density of states (DOSs) in such poly-Si films was determined. Subsequently, by including the impact ionization model in TCAD simulation, $\alpha $ was successfully extracted by precisely fitting the kink current observed in the output characteristics. It is shown that $\alpha $ of poly-Si films strongly depends on their crystallinity, and the preexponential factor significantly increases with the trap density following a power-law dependency with an exponent of ~3.2. This work presents, for the first time, a quantitative analysis of $\alpha $ for poly-Si films of different crystallinity, and explicitly gives the dependency of $\alpha $ on the trap density of poly-Si films.