Light Effect on Amorphous Tin Oxide Thin-Film Transistors

Abstract

Amorphous tin oxide (a-SnO_x) is a potential transparent oxide semiconductor candidate for future large-area electronic applications. The thin-film transistor (TFT) mobilities reach ≈100 cm² Vs⁻¹, a mobility higher than other multiple cation-based oxide semiconductor TFTs. Few optical properties have been reported so far and therefore both the effect of visible light and negative bias illumination stress (NBIS) on a-SnO_x TFT performances, known to dramatically impact oxide semiconductor-based TFTs, have been investigated. The variation of density of states (DOS) due to NBIS by device simulation is analyzed, and a fourfold increase of the donor-like states and a decrease in the band edge DOS from 2.3 to 2.0 × 10¹⁹ cm⁻³ eV⁻¹ are showed. The evaluation of the effect of neutral, singly, and doubly ionized oxygen vacancies by density functional theory using 95 atoms reveals not only states in the gap of SnO₂, but also variations in the electron density, and modifications in the crystal parameters compared to a structure without an oxygen vacancy. Material and device simulation analysis reveal that the oxygen vacancies have a dramatical impact on the DOS in the gap of SnO₂ and can explain the NBIS phenomenon observed in a-SnO_x TFT.