Effect of Mn substitution on the electronic structure for Mn-doped indium-tin oxide films studied by soft and hard x-ray photoemission spectroscopy

We report the electronic structure of In1.8-xMnxSn0.2O3 (x = 0.0, 0.2, and 0.3), which combines transparency, ferromagnetism, and semiconducting properties, by means of hard x-ray photoemission spectroscopy (HAXPES), soft x-ray resonant photoemission spectroscopy (RPES), and x-ray absorption spectroscopy (XAS). The spectral shape of the Mn L-edge XAS spectra indicates that the valence of the substitutional Mn ions is divalent. The peak position of the In 3d and O 1s core-level spectra shifts toward lower binding energy with Mn concentration suggest the hole doping due to the Mn2+ ions. The valence-band spectra exhibit the well-defined features associated with the donor states across the Fermi level E-F and the valence-band edge. The valence-band maximum (VBM) shifts to lower binding energy and the spectral weight near E-F decreases with increasing Mn concentration, which is consistent with the hole doping nature observed in the core-level shift. The Mn 2p-3d RPES reveals that the hump structure around 1.9 eV above the VBM originates from the Mn 3d impurity band and the valence-band state consists of the O 2p band strongly hybridized with the Mn 3d orbital. Furthermore, there is no contribution of the Mn 3d orbital to the spectral weight close to E-F. Our results reveal the entire valence-band structure of In1.8-xMnxSn0.2O3 and the effect of the Mn substitution, which provides the important information related to the physical properties such as transparency, electrical conductivity, and ferromagnetism for the functional materials.