The structure of charge-compensated Fe3+ ions in ZnO

The properties of charge-compensated Fe3+ centers in hydrothermally grown ZnO single crystals were investigated by electron paramagnetic resonance (EPR) in X- and Q-band. The EPR angular dependences of the three types of Fe3+ centers were fitted using spin Hamiltonians appropriate for S  =52 centers with Ci symmetry. The analysis of the results, and in particular the determination of the second rank fine structure tensors, suggests that Fe3+ substitutes Zn2+ with a significant distortion of the initial C3v symmetry of the Zn site. The centers are interpreted as Fe3+ substitutional on the Zn site with (i) an oxygen vacancy in one of the nearest non-axial anionic positions, (ii) a Zn vacancy in one of the six positions lying in the basal plane and (iii) a Zn vacancy in one of the nearest six cationic positions which form a trigonal prism.