Characterization of indium-doped zinc oxide films deposited by pyrolytic spray with different indium compounds as dopants

The results of a systematic study of the electrical, optical, structural and surface properties of thin ZnO:In films are presented. The films were deposited by the spray pyrolysis technique. The spraying solution was zinc acetate diluted in methanol and the indium doping was achieved by adding indium acetate, indium nitrate and indium sulfate at different concentrations up to [In] / [Zn] = 3 at%. The films grown at low temperature show regular and uniformly smooth surfaces with no texturization. Films grown at high temperature show rough surfaces. All the films are polycrystalline and grow with a (101) preferred orientation. The electrical resistivity measured at room temperature shows a minima in all cases as a function of the substrate temperature. The lowest value, ρ = 2 × 10^-3 Ω cm, was obtained by doping with indium acetate at a [In] / [Zn] =3 at% concentration. For films about 0.6 μm thick the average transmittance was better than 85%. A shift in the energy gap due to a variation in the carrier concentration was observed. This shift is explained with a model in which the Burstein-Moss effect and the electron-electron exchange interaction are considered.