ZnO:Al thin films obtained by chemical spray: effect of the Al concentration

Aluminum-doped zinc oxide thin films, ZnO:Al, were deposited on soda-lime glass substrates by the chemical spray technique. The effect of the Al concentration and the type of solvent (methanol, ethanol and isopropanol) in the starting solution, on the resistivity, structure, surface morphology and optical transmittance of the ZnO:Al thin films was studied. The substrate temperature used was of 500 °C. The resistivity of the films was in all cases below 0.4 Ω cm. The smallest resistivity values, around 1.3×10−2 Ω cm, were obtained using a [Al]/[Zn] ratio of 3 at.% in the starting solution and methanol as solvent. All the films were polycrystalline and their surface morphology changed with the type of solvent employed. Films prepared with methanol and isopropanol showed a broad distribution of particle size. On the contrary, films prepared with ethanol showed an uniform particle size, around 110 nm in average. The optical transmittance was higher than 85% at 550 nm. An increase in the Al concentration produced a shift in the adsorption edge to higher energies.