Raman and photoluminescence properties of highly Cu doped ZnO nanowires fabricated by vapor-liquid-solid process

Abstract

Highly Cu doped ZnO nanowires have been fabricated by vapor-liquid-solid (VLS) process. The average concentration of Cu in the ZnO nanowires is estimated to be 6 at. %. The ultrafine synthesized nanowires have diameters nearly 80 nm, while their average length lies in the range of 40 to 90 mum. Raman spectroscopy shows that the Cu doped ZnO nanowires have a typical wurtzite structure. High resolution transmission electron microscopy (HRTEM) investigations of individual nanowires demonstrate that the nanowires have single crystalline structure in which the growth direction is oriented along the c axis. Room temperature photoluminescence spectrum of as prepared nanowires shows two emissions in UV and visible regions that can be ascribed to the near band edge (NBE) transition and defects respectively, while the spectrum of the annealed nanowires exhibits a red shift in UV and a suppression in visible bands. Furthermore, the low temperature (10 K) PL spectrum illustrates a novel dominant blue emission relating to the different valence states of Cu atoms in ZnO, which is explained on the basis of Dingle model.