Na doping effects on the structural, conduction type and optical properties of sol–gel ZnO thin films

In this work we report on the sol–gel deposition of Na doped ZnO thin films on quartz substrates. The effects of Na doping concentrations (0, 3, 6 and 9 at.%) on structural, morphological, electrical and optical properties of the synthesized films were systematically investigated by X-ray diffraction (XRD), Raman spectroscopy, atomic force microscopy (AFM), Hall-effect measurements, UV–Vis–NIR spectrophotometry and photoluminescence (PL) spectroscopy. XRD patterns showed that the prepared films were highly c-axis oriented exhibiting hexagonal wurtzite structure of ZnO. Raman spectra of All the ZnO films exhibited similar scattering peaks corresponding to the Raman active modes of ZnO wurtzite hexagonal structure. AFM images indicated that grain size and surface roughness of the films were affected by Na doping. From the Hall-effect measurements, it was found that carrier type is dependent on Na content. The UV–Vis–NIR spectroscopy analyses revealed that all the films were highly transparent in the visible region. Room temperature PL spectra demonstrated that UV emission of the Na-doped ZnO thin films depends on the Na concentration. In particular, the undoped sample shows the highest emission intensity, while the p-type Na doped ZnO film at 3 at.% exhibits the lowest one.