Transport properties and electronic structure of fluorine-doped SnO₂ prepared by ultrasonic assisted mist deposition

We have investigated the relationship between the transport properties and electronic states of fluorine-doped tin dioxide (FTO) films prepared by ultrasonic assisted mist deposition. The resistivity of the films has the minimum against F/Sn ratios caused by the saturation of carrier concentration. The core-level and valence band PES spectra revealed that there were fluorine ions with two different chemical states and excess fluorine ions tended to form impurity states in band gap, which would not contribute to the conduction of the films. These spectroscopic results well explain the saturated tendency of the carrier concentration of the FTO films.