ZnO Morphology Control by Pulsed Electrodeposition

ZnO films have been grown by pulsed electrochemical deposition between a reduction potential and an oxidation potential to improve their quality. Different morphologies like columns, platelets, flowers, and high-quality planar films are obtained changing the reduction potential without further addition of additives. The mechanism behind this control in morphology is ascribed to the OH- concentration at the electrode surface (pH) as a consequence of the reduction potential. The morphology, surface potential, and electrical conduction mechanism of high-quality ZnO films were simultaneously measured by kelvin probe force microscopy (KPFM). As a result of these measurements, one can conclude that the ZnO surface perpendicular to the [0001] direction is positively charged. Also, it becomes evident that the surface potential drop is mainly produced at the grain boundaries for the ZnO films grown by pulsing between -0.5 and 0.9 V, which indicates intergrain contact resistance.