Investigation of the Characteristics of Undoped and Sn-Doped ZnO Films Prepared by an Acidic Sol.

Transparent conducting thin films of undoped and Sn-doped zinc oxide films w~re prepared on glass substrate by a dip-coating method using an acidic sot. The effect of metal sources, zinc chloride (ZnCl₂) and zinc acetate dihydrate [Zn(OAc)₂·2H₂O], on the crystalline structure and properties of the films was investigated in detail. X-ray diffraction analysis reveals that the acidic sol leads to ZnO crystals with a hexagonal wurtzite structure after annealing treatment. Transmission electron microscopy results evidence that the Sn-doped ZnO thin films are a mixed phase of wurtzite ZnO and tetragonal Sn₂, nanocrystals. Field-emission scanning electron microscopy shows that the morphology of the films is largely affected by the zinc metal sources, and optical and electrical properties of the films are closely related to their microstructure. The undoped films prepared with the zinc chloride source exhibit a lower transmittance in the visible wavelength between 600 and 800 nm, compared with that using the zinc acetate dihydrate source. The electrical resistivity of the undoped films is high (p > 2.0 X 10⁴ Ω cm) but can be reduced by a Sn doping treatment. The optimum electrical resistivity of the Sn-doped films can reach to about 1.5 X 10¹ Ω cm. [ABSTRACT FROM AUTHOR]