  The n-type Ge-on-Si epitaxial material platform enables a novel paradigm for
plasmonics in the mid-infrared, prompting the future development of
lab-on-a-chip and subwavelength vibrational spectroscopic sensors. In order to
exploit this material, through proper electrodynamic design, it is mandatory to
retrieve the dielectric constants of the thin Ge epilayers with high precision
due to the difference from bulk Ge crystals. Here we discuss the procedure we
have employed to extract the real and imaginary part of the dielectric
constants from normal incidence reflectance measurements, by combining the
standard multilayer fitting procedure based on the Drude model with
Kramers-Kronig transformations of absolute reflectance data in the
zero-transmission range of the thin film.
