Evolution of hydrogen-related defect states in amorphous In-Ga-Zn-O analyzed by photoelectron emission yield experiments

Total photoyield spectroscopy (TPYS) was applied to investigate the evolution of hydrogen-related defect states in amorphous In-Ga-Zn-O (a-IGZO) thin films. It was found that the defect states located at around 4.3 eV from the vacuum level were formed as a result of hydrogenation. After thermal annealing at 300 °C, the onset of the TPYS spectra shifted to 4.15 eV. As the annealing temperature was increased, the photoyield from the defect states decreased, implying that there was outdiffusion of hydrogen with Zn from the a-IGZO. These experiments produced direct evidence which shows the formation of defect states as a result of hydrogen incorporation into the a-IGZO thin films.