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.