Competition and Cooperation between Fluorine and Oxygen in SnO2:F Films

Abstract

The interaction of oxygen and fluorine (F&O) in an F-doped SnO2 film, prepared by regulating oxygen partial pressure and the content of doped fluorine from 2.5 at% to 10 at%, was investigated in the large perspective through characterization methods including XRD, Raman spectroscopy, photoluminescence spectroscopy, wettability measurement and a Hall effect test system. The results show that F&O’s competitive and cooperative relationship would be reflected in the structure and electrical characteristics of SnO2 films. The oxygen action is overwhelming and restricts fluorine, so a growing number of F atoms occupy the position by the order of co-edge oxygen of tin–oxygen octahedron chains > oxygen vacancies > segregation, which leads to that carrier concentration modestly increasing from ~1015 to ~1017/cm−3. As oxygen action is inadequate to restrain fluorine, more F atoms are likely to enter the SnO2 lattice in a solid-solution way to replace the O atoms at the co-edge position of the octahedron chains, causing a dramatic increase in carrier concentration from ~1016 to ~1019/cm−3. Furthermore, by continuing to weaken oxygen action, only 2.5 at% of fluorine content could bring about a carrier concentration augment from ~1016/cm−3 to ~1018/cm−3, then going up to ~1021/cm−3 by post-annealing. However, the impairment of oxygen action contributes to a more effective doping of fluorine on SnO2 film. Such mutual action between fluorine and oxygen provides a direction for highly efficient production and tunable regulation of SnO2 film on demand.