Effect of the pH on the growth and properties of sol–gel derived boron-doped ZnO transparent conducting thin film

Boron-doped zinc oxide transparent conducting thin films have been deposited from the solution of zinc acetate and trimethyl borate by a sol–gel process. The effect of pH of precursor sol on the crystallization, microstructure, electrical and optical properties of thin films were investigated. The pH of the precursor sol is found to have a significant influence on the surface morphology, electrical and optical properties of the thin films. X-ray diffractograms and field emission scanning electron microscopy reveal that the grain size is increased with the increase in pH of the precursor sol. The resistivity of the film was also found to decrease from 1.6×10−2 to 4.2×10−3 Ω cm with increase in the pH of the precursor sol from 5.0 to 6.2 and then started to increase as pH was further increased to 6.8. The experimentally observed dependence of the resistivity on the pH of precursor sol is correlated to the dependence of the carrier mobility on grain boundary scattering. The optical studies show that the band gap decreases from 3.38 to 3.23 eV with increase in the pH.