Optical Characterization of Mn doped ITO Nano films*

Determination of the band structure evolution of Indium Tin Oxide (ITO) with increasing Mn concentration is a key factor in understanding the origin of ferromagnetism in this sample. Thin films of ITO with various Mn concentrations are deposited on glass substrate with various thicknesses from a few tens of nanometer up to around a micrometer using a DC magnetron sputtering coating method. We then investigate these samples with room temperature photoluminescence (PL), ellipsometry, scanning electron microscopy (SEM-EDX), and x-ray diffraction (XRD). Topography measured with SEM-EDX of the thin films, show well-defined particles with similar elongated geometries with aspect ratio>3, which are on average 50 nm wide and ~150 nm long. The chemical composition measured with SEM EDX spectrum shows all the constituent elements are present in the Mn doped ITO films. Structural measurements performed with XRD shows a decrease in lattice constant as Mn concentration increases.  The PL and fluorometry measurements of the Mn doped films reveal blue and blue-green emission peaks. The peaks are tentatively attributed to the vacancies or surface defects in our films. The PL intensity decreases by increasing Mn concentration which is tentatively attributed to upward shift of the valence band.