It was found that O-vacancy (VO) acted as a hole trap and played a role in negative bias illumination stress instability in amorphous In–Ga–Zn–O thin film transistors. Photo-excited holes drift toward the channel/dielectric interface due to small potential barriers and could be captured by VO in the dielectrics. While some of VO+2 defects were very stable at room temperature, their original deep states were recovered via electron capture upon annealing. It was also found that VO+2 could diffuse in amorphous phase, inducing hole accumulation near the interface under negative gate bias.

O-Vacancy as the Origin of Negative Bias Illumination Stress Instability in Amorphous In–Ga–Zn–O Thin Film Transistors. B.Ryu, H.K.Noh, E.A.Choi, K.J.Chang: Applied Physics Letters, 2010, 97[2], 022108