Solution-processed lanthanum-zinc-tin-oxide thin films were fabricated with varying La content. A peak shift to small angles was observed in X-ray diffractometer spectra due to the expansion of the zinc-tin-oxide lattice originated from the larger ionic radius of La3+, while oxygen vacancies first increased, and then decreased with increasing La molar ratio. These results indicate that La, which has both low electronegativity and a large ionic radius, plays the role of either a generator or a suppressor of oxygen vacancies. Therefore, when choosing an additive to control the electrical properties of an oxide semiconductor, the ionic radius of the added atom should be carefully considered along with its electronegativity. (C) 2013 Elsevier B.V. All rights reserved.