Effects of Substrate Temperature on Structural, Electrical and Optical Properties of Amorphous In-Ga-Zn-O Thin Films

Abstract

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.