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

Abstract

Abstract F-doped SnO 2 (FTO) thin films have been prepared by sputtering SnO 2 -SnF 2 target in Ar+H 2 atmosphere. The effects of H 2 /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 −2 Pa. The results show that introducing H 2 into sputtering atmosphere can lead to the formation of a FTO film with a (101) preferred orientation and produce oxygen vacancy ( V O ) at lower H 2 /Ar flow ratios, but SnO phase at higher H 2 /Ar flow ratios in the films. Accordingly, the resistivity of the films first decreases and then increases, but the transmittance decreases continuously with increasing H 2 /Ar flow ratio. When H 2 /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 ( E g ). 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 −3 Pa, 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 −2 Pa, the range of H 2 /Ar flow ratio for forming the SnO 2 phase and hence for obtaining high transparent conductive FTO films is widened at both substrate temperatures of 150 and 300 °C.