Annealing effects on electrical and optical properties of ZnO thin films synthesized by the electrochemical method

Microstructural and electrical properties of potentiostatically electrodeposited ZnO thin films from an aqueous bath were investigated after annealing at different temperatures in Ar and 5% H2/Ar atmospheres. It is confirmed that the bandgap energy of ZnO thin films decreased with annealing from 3.42 to 3.27–3.29 eV by calculating the wavelength of the absorption region. The annealing at temperatures as low as 200 °C decreased the sheet resistance of ZnO thin films because of the extinction of Zn(OH)2 in the atmosphere. In addition, the sheet resistance of ZnO thin films decreased by annealing in a 5% H2 atmosphere, which caused an increase of carrier concentration by hydrogen reduction.