Fe charge state adjustment in ZnO upon ion implantation

The influence of the ion implantation process on the charge state of dilute 57Fe impurities implanted as radioactive 57Mn in ZnO is investigated by 57Fe emission Mössbauer spectroscopy. One sample is additionally implanted with stable 23Na impurities. Both Fe2+ and Fe3+ charge states are observed, and the Fe3+/Fe2+ ratio is found to increase with the fluence of both 57Mn/57Fe and 23Na ions, demonstrating that the build-up of Fe3+ is not related to the chemical nature of the implanted ions. The results are interpreted in terms of radiation damage induced changes of the Fermi level, and illustrate that the Fe3+/Fe2+ ratio can be adjusted by ion implantation. The spin-lattice relaxation time for Fe3+ in ZnO is found to be independent of the implantation fluence, and is evidently an intrinsic property of the system.