Structural, electrical and optical properties of SnO 2-x:F-layers deposited by DC-reactive magnetron-sputtering from a metallic target in Ar–O 2/CF 4 mixtures

Abstract

F-doped SnO x films have been prepared by DC-reactive magnetron sputtering in Ar-O 2/CF 4 mixtures at a deposition temperature of 180°C. The optical and electrical parameters (specific resistance, charge carrier concentration, mobility) were correlated with the chemical composition and the structural properties (phases, grain size). Small concentrations of F increase both the charge carrier concentration and the mobility. Higher fluorine incorporation into the films does not improve the electrical properties, which is attributed to the formation of tin fluorides. The maximum fluorine concentration in the SnO 2−x:F-films, measured by RBS, is 7×10 21 cm −3 (corresponding to 8 at.%). Comparison of the charge carrier concentrations with the fluorine content shows that the electrical activation of the fluorine is smaller than 3.4%. The low electrical activation of the fluorine is tentatively explained by the formation of tin fluorides, leading to low charge carrier concentrations (N D≈1.4× 10 20cm −3). This limits the specific resistivities to values >7×10 −3 Ωcm.