Unravelling the doping mechanism and origin of carrier limitation in Ti-doped In2O3 films

Ti-doped In2O3 thin films with varying Ti contents are prepared by partial reactive co-sputtering using ceramic In2O3 and metallic Ti targets and characterized by in situ x-ray photoelectron spectroscopy, electrical conductivity, and Hall-effect measurements. For a substrate temperature of 400°C, the carrier concentration increases faster than the Ti content and saturates at ≈7.4×1020cm−3. Based on these results, it is suggested that Ti does not directly act as donor in In2O3 but is rather forming TiO2 precipitates and that the related scavenging of oxygen generates oxygen vacancies in In2O3 as origin of doping. Neutralization of oxygen vacancies is, therefore, suggested to be origin of the limitation of the carrier concentration in Ti-doped In2O3 films.