Local lattice distortions in oxygen deficient Mn-doped ZnO thin films, probed by electron paramagnetic resonance

Abstract

The structure and functional properties of metal oxide films for device applications are largely affected by oxygen vacancies. While the macroscopic relationship between functionality and oxygen supply during growth is easy to access, the local influence of changing oxygen content on the incorporated metal atoms has been rarely investigated. As a model system, we use Mn as a local probe in hetero- and homoepitaxial ZnO thin films for electron paramagnetic resonance (EPR). Mn is expected to be incorporated as Mn²⁺ in the Zn-lattice site of ZnO films grown in a wide range of oxygen partial pressures. The zero field splitting (ZFS) parameter D depends on the crystallographic c/a ratio of ZnO : Mn lattice constants as it measures the trigonal distortion of oxygen tetrahedra at the Zn²⁺ site with respect to the Mn²⁺ site. The ZFS parameter D correlates linearly with displacement of Mn²⁺ ions along the c-axis in the MnO₄ tetrahedra and the corresponding bond lengths between the Mn²⁺ ions and the axial oxygen ion.