Hydrothermal derived nanostructure rare earth (Er, Yb)-doped ZnO: structural, optical and electrical properties

The structural, optical and electrical properties of undoped and rare-earth (Er, Yb) doped zinc oxide (ZnO) nanopowder samples synthesized by hydrothermal method were investigated. The obtained samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive spectroscopy. The optical properties of undoped and rare-earth (Er, Yb) doped ZnO were carried out with UV-visible diffuse reflectance spectroscopy techniques. XRD results reveal that Yb and Er doped ZnO nanopowders have single phase hexagonal (Wurtzite) structure without any impurities. SEM analysis indicate that dopants with different radii affected the surface morphology of ZnO nanostructures. The optical band gap of all samples were calculated from UV-Vis diffuse reflectance spectroscopy data. We have obtained band gap values of undoped, Er and Yb doped ZnO as 3.24, 3.23, 3.22 eV, respectively. Electrical characterization of the samples were made in the 280-350 K temperature range using Van der Pauw method based on Hall effect measurement. The carrier concentrations decreased for both Er and Yb doping while the Hall mobility and electrical resistivity increased with Yb, Er doping compared to undoped ZnO nanopowder at room temperature. The temperature dependent resistivity measurements of Er doped ZnO showed a metal-semiconductor transition at about 295 K, while Yb doped ZnO showed characteristic semiconductor behavior.