Substrate temperature dependent structural, optical and electrical properties of amorphous InGaZnO thin films

The effects of substrate temperature (Ts) on the electrical and optical properties of amorphous InGaZnO thin films deposited by sputtering have been investigated. As Ts increased from RT to 400 °C, all the films remained amorphous, the transmission in the visible region increased from 92.8% to 93.54%, and the band gap decreased from 3.42 eV to 3.31 eV. Based on Cauchy-Urbach model, the optical properties of all samples were analyzed by spectroscope ellipsometry (SE) and increase in refractive index has been detected with the increase in Ts. Results of Hall measurement showed that substrate temperature have remarkable influence on the resistivity (ρ), carrier concentration (n), and carrier mobility (μ) of IGZO films. As Ts increased from RT to 400 °C, ρ decreased from 46.6 to 0.24 Ω cm, and then increased to 1.11 Ω cm at Ts of 400 °C, and n increase from 5.67 × 1015 to 7.33 × 1018 cm−3. Investigation of X-ray photoelectron spectroscopy (XPS) indicated 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 in n and reduction in ρ and that the compositional change could explain the change of Eg.