Investigation of O2- and Air-Exposure Effects on Amorphous In–Ga–Zn–O Thin-Film Surface by X-ray Photoelectron Spectroscopy
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A sputter-cleaned amorphous In–Ga–Zn–O thin-film surface was exposed to O2 and air, and the spectral changes at the O 1s, In 3d, Ga 3d, Zn 3d, and the valence band were investigated by soft-X-ray photoelectron spectroscopy. Both exposures reduced the density of the oxygen-vacancy-representing deep subgap state, which was located above the maximum of the valence band. The exposures also reduced the densities of the metallic states, which were observed near the Fermi energy and at In 3d. A higher oxidation state than that of the unexposed metal oxide was negligibly observed at the metal 3d orbitals. These results imply that O2 and air exposures effectively fill oxygen vacancies and decrease the number of free electrons.
KeywordsIn–Ga–Zn–O IGZO Threshold voltage shift Transparent semiconducting oxides Oxygen-exposure effect Air-exposure effect
The authors would like to acknowledge the financial support of the Basic Science Research Program (2009-0087060 and No. 2008-0062606, CELA-NCRC) through the National Research Foundation of Korea (NRF) and by the Converging Research Center Program (2013K000306), funded by the Korea government Ministry of Science, ICT and Future Planning (MSIP).