To model the infrared reflectance spectrum of a conductive multiple layer stack, one needs the plasma frequency and damping parameter of every constitutive material. In this work we show how they can be linked to the resistivity or doping level of the different layers. From a typical application performed in the case of Schottky diode structures, we find that between 1000 and 4000 cm(-1), the interference shape of the resulting infrared spectrum is mostly sensitive to the doping level and thickness of the buried buffer layer.