Sputtering deposition of transparent conductive F-doped SnO2 (FTO) thin films in hydrogen-containing atmosphere

F-doped SnO2 (FTO) thin films have been prepared by sputtering SnO2-SnF2 target in Ar+H2 atmosphere. The effects of H2/Ar flow ratio on the structural, electrical and optical properties of the films were investigated at two substrate temperatures of 150 and 300°C and two base pressures of 3.5×10−3 and 1.5×10−2Pa. The results show that introducing H2 into sputtering atmosphere can lead to the formation of a FTO film with a (101) preferred orientation and produce oxygen vacancy (VO) at lower H2/Ar flow ratios, but SnO phase at higher H2/Ar flow ratios in the films. Accordingly, the resistivity of the films first decreases and then increases, but the transmittance decreases continuously with increasing H2/Ar flow ratio. When H2/Ar flow ratio is increased above a certain value, more amorphous SnO phase forms in the films, resulting in a big decrease in conductivity, transmittance, and band gap (Eg). Increasing substrate temperature can increase the Hall mobility due to the improvement of film crystallinity, but decrease the carrier concentration due to outward-diffusion of fluorine in the films. At a base pressure of 3.5×10−3Pa, high substrate temperature (300°C) can hinder the formation of SnO and thus improve the transparent conductive properties of the films. At a base pressure of 1.5×10−2Pa, the range of H2/Ar flow ratio for forming the SnO2 phase and hence for obtaining high transparent conductive FTO films is widened at both substrate temperatures of 150 and 300°C.