Lanthanum concentration dependence of electrical properties in tin oxide thin films

Lanthanum doped tin oxide thin films were prepared on boron-silicon glass substrates by spray pyrolysis. Lanthanum concentration was varied from 0 to 1.0 wt%. The microstructures, sheet resistance and thermal stabilities of the lanthanum doped tin oxide thin films have been investigated in order to determine the role of this dopant on electrical properties. X-ray diffraction (XRD) result shows the deposited thin film is mainly rutile SnO₂. And atomic force microscopy (AFM) reveals that the thin film has smooth surface with no cracks and defects. And it exhibits a typical bimodal grain size distribution with an average grain size of 95 nm. The sheet resistances of the thin films have a complex dependence on the lanthanum concentration. With increasing lanthanum concentration, the sheet resistances of tin oxide thin films were slightly increased and then abruptly decreased. Moreover, when the lanthanum concentration of 0.5 wt% was reached, the specimen exhibits excellent electrical properties. Because of its effectiveness in improving homogeneity of operating surface temperature and thermal stability, lanthanum appears to be an attractive additive for the tin oxide thin films.