Effect of Zn Nitrate Hexahydrate Concentration on ZnO Nanorods Grown from an Electrochemically Oxidized ZnO Seed Layer

This study investigated the effect of precursor concentration on both the morphology and the structural, optical, and photoresponse properties of zinc-oxide (ZnO) nanorods when using a ZnO seed layer formed by using the electro-oxidation method. The ZnO nanorods were grown on the ZnO seed layer at various precursor concentrations. Field-emission scanning electron microscopy images revealed that most ZnO nanorods showed a pyramid-like top surface; however, those grown at a concentration of 40 mM showed a flat top surface. X-ray diffraction analysis revealed that the ZnO nanorods showed an improvement in orientation along the c-axis direction with increasing precursor concentration. Photoluminescence spectra showed that the full width at half maximum values of the near-band-edge emission peak and the ratio of the near-band-edge emission peak to the deep-level emission peak increased and decreased, respectively, with increasing precursor concentration, indicating the occurrence of many defects in the ZnO nanorods. In terms of the photoresponse properties, ZnO nanorods grown at a precursor concentration of 20 mM showed the highest responsivity.