Photoluminescence of ZnO nanowires dependent on O2 and Ar annealing

High-purity ZnO nanowires have been synthesized on Si substrates without the presence of a catalyst at 600 °C by a simple thermal vapor technique. Photoluminescence (PL) spectra of the annealed samples at 900 °C under oxygen and argon gases have been investigated. After O2 or Ar annealing, the PL visible-emission intensity that is related to intrinsic defects (oxygen vacancies) is greatly reduced compared with as-grown ZnO nanowires because the oxygen-gas ions or oxygen interstitials diffuse into the oxygen vacancies during annealing process. The blue-band peak of the O2- or Ar-annealed ZnO naonowires is also smaller than the green-band peak in the visible broadband because of the reduction of oxygen vacancies. Therefore, the main intrinsic defects (oxygen vacancies) of as-grown ZnO nanowires can be reduced by O2 or Ar annealing, which is an important procedure for the development of advanced optoelectronic ZnO nanowire devices.