GeSn as a group-IV material opens up new possibilities for realizing photonic device concepts in Si-compatible fabrication processes. Here we present results of the ellipsometric characterization of highly p- and n-type doped Ge0.95Sn0.05 alloys deposited on Si substrates investigated in the wavelength range from 1 to 16 μm. We discuss the suitability of these films for integrated plasmonic applications in the infrared region.