Identification of a donor-related recombination channel in ZnO thin films

An excitonic recombination line is observed in photoluminescence spectra of ZnO thin films at 3.3465 eV. The line is labeled I-12. Its appearance was only observed in samples grown on a MgO or heavily aluminum-doped ZnO buffer layer. The properties of the recombination mechanism were probed by photoluminescence and photoluminescence-excitation spectroscopy. The recombination was classified to be an exciton bound to a neutral donor. Both an ionized state and a two-electron satellite transition were observed and could be correlated with the central transition. The excitation channels are similar to those of the well-known I-6 transition related to Al-Zn. The localization energy was calculated to be 29.4 meV. A donor activation energy of 90.8 meV was extrapolated using the Haynes rule for ZnO.