Preparation and characterization of ZnO-based layered thin films

In this thesis, Co doped and Al/Co co-doped ZnO thin film sample structures were deposited on ZnO buffer layer by ultrasonic spray pyrolysis (USP) technique. The structural, optical and electrical properties of the doped and layered ZnO materials produced according to the determined preparation conditions were investigated at room tempearture. Doped-layered ZnO thin film samples were determined as (002) oriented hexagonal wurtzite crystal structure. Co ions narrow the optical band gap of the ZnO structure, make the sample opaque by reducing the optical transmittance of the sample and give it a dark-green appearance. Adding Al to the Co-doped ZnO structure changes the optical properties again. It slightly expands the optical band gap, increases optical transmittance, thus making it more transparent and transforming it into a light-green color. ZnO, Co:ZnO/ZnO and (Al,Co):ZnO/ZnO samples all have AC-conductivity of the order of 10-5 (ohm.cm)-1 at high frequencies. It was observed that the sample with a top layer of Co:ZnO was more resistive. At low frequencies, the sample structure with the highest alternative current (AC)-conductivity is ZnO, while the lowest sample structure is Co:ZnO/ZnO. In this study, it was observed that Al ions in the ZnO base material created a setting effect by rearranging the effect created by Co ions.