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

We studied the effects of substrate temperature (Ts) on the surface roughness, resistivity (r), mobility (u), 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 300degC, n increased (2.6 x 1019 - 5.0 x 1019 /cm3), r decreased (7.0 x 10[?]3 - 4.7 x 10[?]3 O[?]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.