Green luminescent center in undoped zinc oxide films deposited on silicon substrates

The photoluminescence (PL) spectra of the undoped ZnO films deposited on Si substrates by dc reactive sputtering have been studied. There are two emission peaks, centered at 3.18 eV (UV) and 2.38 eV (green). The variation of these peak intensities and that of the $\mathrm{I–V}$ properties of the ZnO/Si heterojunctions were investigated at different annealing temperatures and atmospheres. The defect levels in ZnO films were also calculated using the method of full-potential linear muffin-tin orbital. It is concluded that the green emission corresponds to the local level composed by oxide antisite defect ${\mathrm{O}}_{\mathrm{Zn}}$ rather than oxygen vacancy ${\mathrm{V}}_{\mathrm{O}},$ zinc vacancy ${\mathrm{V}}_{\mathrm{Zn}},$ interstitial zinc ${\mathrm{Zn}}_i,$ and interstitial oxygen ${\mathrm{O}}_i.$