Co-occurrence of Dominant Direct and Indirect Transitions in Low Temperature Sputtered Indium Tin Oxide Thin Films on Polymers

Indium tin oxide (ITO) layers are prepared on polymethylmethacrylate and polyethylene terephthalate by rf-magnetron sputtering at room temperature. Their 3D-AFM images and visible transmittance spectra are contrastively characterized and studied. An interesting morphological effect of the polymer substrates on their top ITO layers is observed. Dominant direct and indirect transition types deduced from optical spectra are surprisingly found in ITO films on different polymers. Furthermore, qualitative band structures are figured, and some theoretical discussions about the correlation of optical band structure, interface/surface morphology and carrier density are also presented.