Role of oxygen in green emission from ZnO thin films

To confirm the role of oxygen in green emission from ZnO thin films on Si(100) substrates, we deposited thin films sputtering with a ZnO target. The O-2 content, as a reactive gas was changed, and a sequential annealing was done in a N-2 or an O-2 atmosphere. The photoluminescence spectra, showed that thermal annealing in an O-2 ambient, rather than increasing the content of O-2 gas during the deposition process, was very effective in increasing the green emission from the ZnO thin films. This may be associated with the fact that the number of interstitial Zn (Zn-i) and O vacancies (Vo) is reduced by the effective incorporation of oxygen atoms during the annealing process. We also found from the results of Fourier transform infrared and X-ray diffraction measurements that zinc silicate (Zn2SiO4) was generated at the interface during thermal annealing. However, we could not find any evidence that the green emission (520 nm) originated from zinc silicate.