We studied the effects of substrate temperature (Ts) on the surface roughness, resistivity (ρ), mobility (μ), charge carrier concentrations (n), transmission and optical bandgap (Eg) of amorphous In-Ga-Zn-O thin films (∼250 nm thickness) deposited by radio-frequency magnetron sputtering. As Ts increased from RT to 300°C, n increased (2.6 × 1019 → 5.0 × 1019 /cm3), ρ decreased (7.0 × 10−3 → 4.7 × 10−3 Ω−cm), and Eg (3.9 → 3.7 eV) along with the average transmission (89 → 82%) in the visible region decreased. Investigation of the O 1s core level and the Ga 3d, In 4d, and Zn 3d shallow-core levels spectra obtained by high-resolution X-ray photoelectron spectroscopy revealed that as Ts increased, an O 1s component representing the oxygen vacancies increased in amount and that the intensity ratio of In/Ga increased but that of Zn/Ga decreased. The analysis suggests that the increase of oxygen vacancies could explain the increase of charge carrier concentration and that the compositional change could explain the change of Eg.

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The chemical states of Ne + -ion-sputtered amorphous Ga-In-Zn-O ͑a-GIZO͒ thin films were investigated by high-resolution X-ray photoelectron spectroscopy. The sputtering reduced the Zn and In contents relative to that of Ga and generated a subgap state above the valence band maximum. Further sputtering resulted in metallic states at the In3d and In4d orbitals and at the Fermi energy edge, more so for the lower Zn-and In-content film. Locally generated metallic In is suggested to contribute to the metallic states.

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