Making the Mid-IR nano with epitaxial plasmonic devices

We have extensively investigated heavily doped semiconductors as potential plasmonic metals at long wavelengths. The ability to control the doping level in a semiconductor material, both III-V´s (InAs/InSb) and Silicon, allows for control of the metal´s optical properties, and adds an intriguing additional controllable parameter to the design of plasmonic structures. These materials can be quite accurately modeled using the Drude formalism, even for energies larger than the band gap, and have a number of attractive qualities, including control of carrier concentration (and thus plasma frequency, ωρ), as well as single-crystal material quality, atomic-layer control of thicknesses, and the potential for integration with epitaxially-grown mid-IR optoelectronic devices. In this presentation, I will discuss recent developments in epitaxial plasmonic devices for mid-IR applications. First, the growth and characterization of our materials will be discussed, as well as the material limitations. Subsequently, I will demonstrate the doped semiconductors potential as epsilon-near-zero (ENZ) materials. At ENZ frequencies, we have demonstrated enhanced coupling to sub-wavelength waveguides, offering a potential route towards overcoming the mismatch between the micron-scale light of the mid-IR and the nano-scale. In addition, we have shown that near ENZ, these materials thin (d ≪ λo) loss-less dielectric films to serve as perfect absorbing layers, by controlling the metal/dielectric interface phase shift in thin film interference structures.