Soft X-ray photoelectron spectroscopic investigation of Au-deposited amorphous In–Ga–Zn–O thin-film surface

• Au was deposited on a-IGZO thin film and the chemical state changes were investigated by HR-XPS.
• At initial stage, some amounts of Au atoms exist as Au-oxide, while most of them are in metallic state.
• Au atoms interact more strongly with Indium atoms than with other element atoms.
• The deposited Au layer shows clear long-range metallic feature at thicker deposition.

Thin Au layers (0.04 nm, 0.06 nm, 0.08 nm, 0.21 nm) were deposited on an amorphous In–Ga–Zn–O (a-IGZO) thin-film surface by thermal evaporation in an ultrahigh vacuum. The chemical-state changes of the Au layer and the a-IGZO surface were investigated by measuring the Au 4f, O 1s, In 3d, Ga 3d and Zn 3d peaks as well as the valence bands by soft X-ray photoelectron spectroscopy. Upon initial deposition, an oxidized Au component formed, whereas a metallic Au component was dominant. At the later deposition stages, the metallic Au component dominated the spectral features. When the Au thickness was thicker than 0.08 nm, a split Au 5d feature was apparent. And as the Au thickness continued to increase, In 3d showed a strong lower-binding-energy (lower-BE) component; the Ga 3d and Zn 3d also showed lower-BE components, but of much reduced intensities relative to In 3d. These results seem to imply that compared with other elements, Au atoms prefer to occupy oxygen vacancies and strongly interact with In atoms.