Effect of Doping and Morphology on UV Emission in Low-Dimensional ZnO:Na Structures

Abstract

Band-edge photoluminescence of zinc oxide materials reveals a phonon-assisted ultraviolet emission enhanced by Na doping. We report the synthesis of ZnO and Na-doped ZnO, the changes in structure and optical properties as a function of doping concentration and synthesis temperature. The obtained samples are nanoneedles, microparticles, and microwires. The structural effect of Na doping is studied by X-ray diffraction and Raman spectroscopy. Room temperature photoluminescence reveals a contribution of band bending at the surface of the nanostructures, decreasing with Na concentration. Franz–Keldysh effect predicts strong electric field localized in the depletion region and appears to be the cause of red-shift in UV band emission of nanoneedles in comparison to microwires. Our results indicate that Na doping introduces an acceptor level between 150 and 200 meV above the valence band.