Photoluminenscence property of ferromagnetic ZnMnO thin films

High quality Mn doped ZnO thin films were grown on c-plane Al2O3 by oxygen plasma assisted molecular beam epitaxy. Photoluminescence spectra were investigated on the ferromagnetic ZnMnO films. An additional emission located at ∼3.32 eV was observed on these ferromagnetic films for both as-grown and oxygen-annealed samples. It is assigned to the recombination of neutral acceptor bound excitons. The ionization energy of the acceptor was estimated to be 53-80 meV. The observed ferromagnetism was explained to relate with acceptor-type defects.