Optical, X-ray absorption and photoelectron spectroscopy investigation of the Co site configuration in Zn1−xCoxO films prepared by pulsed laser deposition

In this paper, we investigate the Co site configuration in Zn1-xCoxO thin films by means of different spectroscopic techniques. Thin films were prepared by pulsed laser deposition with Co proportion from 1% to 30%. The Co 2p doublet observed in the X-ray photoelectron spectra exhibits the spin-orbit splitting and shake-up satellites typical of Co+2 ionization states. X-ray absorption spectra at the Co K-edge, taken in fluorescence mode, unambiguously show that Co atoms are in tetrahedral configuration substituting for Zn over the whole composition range. Optical absorption spectra provide further evidence of the tetrahedral coordination of Co cations, both through the internal transitions in the Co 3d shell and through the shift to higher energies of the band-to-band absorption edge with the increase of the Co proportion.