The local structure of Co-doped ZnO films studied by X-ray absorption spectroscopy

The Zn0.95Co0.05O films were deposited under different oxygen partial pressure (PO2PO2) by inductively coupled plasma enhanced physical vapor deposition. The effect of PO2PO2 on the local structure of Zn0.95Co0.05O films was investigated by X-ray absorption spectroscopy (XAS) at Co K-edge and L-edge. The Co L-edge XAS spectra show the spin-orbit splitting and typical shake-up satellites of the Co2+ ionization states. The XAS spectra at the Co K-edge indicate that Co ions substitute for Zn2+ sites in the tetrahedral configuration without changing the wurtzite structure. The qualitative analyses of X-ray absorption near edge structure (XANES) reveal that the main defects are oxygen vacancies when Zn0.95Co0.05O films were deposited under very low PO2PO2. The extended X-ray absorption fine structure (EXAFS) analyses provide no significant bond length deviation from the pure ZnO structure. The coordination number varies slightly with different samples. The correlation between the coordination number and the pseudo Debye–Waller factor implies that the disorder is increased in samples prepared under low PO2PO2.