Abstract:

We successfully prepared ZnO thin films through spin-coating a mixture of zinc acetate dihydrate, poly(ethylene oxide) (PEO) and deionized H2O. Smooth and pure ZnOthin films were obtained by using PEO, because of its low thermal decomposition temperature. The morphology, crystallinity, band gap energy (Eg), and conductivity of the ZnO thin films annealed at different temperatures were determined. Atomic force microscopy (AFM) showed that the rootmean square (rms) surface roughness of films annealed at 400, 450, and 500 ℃ was 3.3, 2.7, and 3.6 nm, respectively. TEMimages showed that the ZnOfilms were composed of ZnOnanocrystals. The band gap energy (Eg) for the films was calculated as 3.3 eV from the absorption edge at 373 nm. From their current-voltage (I-V) curves the resistivities of ZnO thin films annealed at 400, 450, and 500 ℃ were calculated as 3.3×109, 2.7×109, and 6.6×109 Ω·cm, respectively. High annealing temperature is useful in improving purity and density of the film and increasing adsorbed oxygen on the film. The film with high purity and density will exhibit low resistivity. The film with more adsorbed oxygen will exhibit high resistivity, due to higher grain boundary barrier. Consequently, the ZnO thin film annealed at 450 ℃ exhibited the lowest resistivity, while the ZnO thin filmannealed at 500 ℃ had the highest resistivity.

Key words: ZnO, Solution process, Water solution, Band gap energy, Conductivity