Effect of pH value on the optical and electrical properties of Al-doped ZnO thin films by sol-gel process

Al-doped ZnO transparent conducting thin films oriented along the c-axis have been prepared by the sol-gel process on glasses and the effect of pH value of precursor sol on the microstructures, surface morphologies, electrical and optical properties of thin films was investigated. The results show that the grain sizes of films increase with the decrease of pH value of the precursor sol, the resistivities decrease at first and then increase with decrease of pH value from 8.4 to 6.8, and the minimum resistivity is obtained at the pH=7.2. Further analysis indicated that the variation of pH value of the precursor sol results in the change of carrier mobility which is relative to the grain boundary scattering. Within the visible wavelength region, the transmission of the films increased as the pH value decrease, while the band gap decrease from 3.36 eV to 3.32 eV.