Structural, optical and electrical properties of Hf-doped ZnO transparent conducting films prepared by sol-gel method

Hafnium doped zinc oxide (HZO) thin films with various Hf contents (0, 1, 3, 5, 7 at.%) at different solution concentrations (0.15-0.75 mol/L) were deposited on the glass substrates using sol-gel method. The structural, optical and electrical properties were investigated by means of XRD, PL and Hall-effect measurement. The results show that Hf ions could substitute Zn ions effectively and improve the crystallinity of ZnO significantly with highly preferred c-axis orientation. Based on photoluminescence and transmittance measurements, the strong ultraviolet emission band exhibits a blue shift and its intensity is found to rise with the increasing of Hf-doping density. Furthermore, the resistivity shows a bell curve and the minimum value is 5.6 × 10−3 Ω cm for the HZO film with 3 at.% Hf, which is lower than that of the typical Al-doped ZnO thin films using sol-gel method.