Observation of Hydrogen-Related Defect in Subgap Density of States and Its Effects Under Positive Bias Stress in Amorphous InGaZnO TFT

In amorphous oxide semiconductors, hydrogen-related defects have been unable to be observed from the electrical characteristics of thin-film transistors (TFTs) in comparison to oxygen-related defects. Here, the hydrogen-related defect is observed as the Gaussian distributed density of states (DoS) in E-C - 0.6 eV level by using the photoresponse of C-V characteristics in In-Ga-Zn-O (IGZO) TFTs. Coupled with X-ray photoelectron spectroscopy (XPS), it is identified as hydroxide ion (OH-), which both passivates oxygen vacancy defects and supplies the carriers as shallow donors. Furthermore, the evolution of DoS under positive bias stress and its origin are comparatively investigated for IGZO TFTs with three types of gate insulators (GIs), such as low-temperature atomic layered deposited Al2O3, thermally grown SiO2, and double-layered GIs.