The photoluminescence properties of undoped & Eu-doped ZnO thin films grown by RF sputtering on sapphire and silicon substrates

We have reported on the effects of the substrate type on the structural and photoluminescence properties of undoped and Eu-doped ZnO thin films, grown by RF sputtering on c-plane sapphire and silicon substrates. As revealed by the XRD, all films are highly textured and have a preferred orientation along the c-axis perpendicular to the substrate. XPS analysis confirms the incorporation of Eu ions into the ZnO matrix. Also, all thin films are O-rich, with increasing oxygen content after annealing in oxygen atmosphere. The annealed thin films on sapphire substrates are found to have more excess oxygen than those on silicon substrates. The AFM images showed that the substrate type and Eu-doping affect the surface morphology of the thin films. The photoluminescence measurements showed that the intensity ratio of the defect-related visible emission to the UV excitonic emission of ZnO, as well as the red emission intensity of Eu3+ ions were affected by the substrate type. Our results point out that, for luminescent devices based on the UV emission of ZnO thin films, silicon is a promising, cost-effective substrate. On the other hand, for efficient red emission of Eu3+ ions in Eu-doped ZnO thin films, c-plane sapphire substrate is more favorable.