Photon-accelerated negative bias instability involving subgap states creation in amorphous In–Ga–Zn–O thin film transistor

We investigated the visible photon accelerated negative bias instability (NBI) in amorphous In–Ga–Zn–O (a-IGZO) thin film transistor (TFT). As reported in previous works, the rigid shift in transfer curves with insignificant changes in field-effect mobility and subthreshold swing was observed. On the other hand, there is substantial change in capacitance-voltage characteristics caused by created subgap states. The suggested nature of created states is the ionized oxygen vacancy (VO2+) by the combination of visible light and negative bias. The generated VO2+ states enhance the NBI under illumination as increased deep hole trapping centers. Furthermore, the photoexcitation of VO to stable VO2+ yields excess free carriers in conduction band. The increased carrier density also enhances the negative shift in turn-on voltage of a-IGZO TFT.