Over the last two decades, the development of plasmonics for operation around the visible spectral window has heavily relied on gold as the preferred material, mainly because of its excellent properties in terms of stability, easy chemical synthesis, and biocompatibility.1–6 Already in these high-frequency ranges, however, other metals have sometimes been preferred when it comes to specific spectral regions, in particular, Ag and Al for the blue region and, more recently, the near-UV region.7,8 Longer midinfrared (mid-IR) wavelengths have also been approached by exploiting gold,9–13 which in the IR range behaves as a very good conductor, with low penetration depths for the electromagnetic fields. Strictly speaking, however, the equivalent of a plasmonic metal in the mid-IR would possess carrier densities in the to range, something that can be achieved by heavily doping the semiconductor. Indeed, a few seminal works have already outlined the very interesting possibilities that will be opened by the use of such materials for mid-IR plasmonics.14–16 The idea of turning attention to semiconductors as “metals” in the mid-IR comes from the dependence of the plasma frequency (marking the onset of conducting behavior) on the carrier density , according to the relation , where represents the effective mass of the free carriers involved in the plasma oscillations. Another relevant issue when it comes to the use of plasmonic interfaces in optoelectronics and integrated devices is the compatibility with the existing Si photonics and CMOS platforms, something that cannot be solved with Au-based nanostructures. A natural choice in terms of semiconductor materials, from the point of view of integration, points toward Si and Ge.17–19 Between these two, Ge should be preferred both in standard mid-IR photonic devices, due to its inherently lower losses, and for plasmonic applications based on heavy doping, since the lower effective mass ( for Ge compared to for Si) allows a higher plasma frequency to be reached for a given doping level.