Electronic structure of Cu-doped ZnO thin films by x-ray absorption, magnetic circular dichroism, and resonant inelastic x-ray scattering

Abstract

The electronic structure of Cu-doped ZnO thin films, synthesized with a nominal composition of Zn1-xCuxO (x = 0.03, 0.05, 0.07, and 0.10) by using spray pyrolysis method, has been investigated using near-edge x-ray absorption fine structure (NEXAFS) experiments at the O K- and the Cu L-3.2-edges and resonant inelastic x-ray scattering (RIXS) measurements at Cu L-3,L-2 edge. The Zn1-xCuxO thin films showed single phase wurtzite-hexagonal like crystal structure and ferromagnetic behavior at room temperature (RT). The intensity of the pre-edge spectral feature at the O K- edge increases with the Cu concentration, which clearly reveals that there is strong hybridization of O 2p-Cu 3d orbitals in the ZnO matrix. Spectral features of the Cu L-3,L-2-edge NEXAFS exhibit multiple absorption peaks and appreciable x-ray magnetic circular dichroism signal that persists even at RT. These results demonstrate that Cu is in mixed valence state of Cu-2+,Cu-3+/Cu1+, substituting at the Zn site and Cu2+/ 3+ ions are magnetically polarized. RIXS experiments at Cu L-3 edge show strong d-d excitations due to localized nature of Cu ions in the ZnO matrix. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3372758]