Indium silicon oxide thin films for infrared metaphotonics

We demonstrate silicon-doped indium oxide (ISO) with tunable epsilon near-zero and plasmonic behavior and propose it as a Si-compatible alternative material for metaphotonic applications in the mid-infrared (MIR) spectral range. ISO thin films were grown using DC and RF magnetron cosputtering deposition. Post-deposition thermal annealing was performed that resulted in large tunability of the optical dispersion data, as measured directly by variable-angle ellipsometry. Screened plasma wavelengths in the range 1.7 mu m-5.8 mu m were experimentally obtained depending on the annealing conditions. Moreover, ISO films with 350 nm thickness were investigated by atomic force microscopy that reveals a maximum rms roughness of 1.9 nm, enabling high-quality nanofabrication. In order to demonstrate the suitability of ISO thin films for the fabrication of plasmonic structures, we have produced ISO nanoparticle disk arrays using electron-beam lithography on Al2O3 substrates and shown, using both finite element method simulations and Fourier transform infrared spectroscopy, distinctive plasmonic resonances at MIR wavelengths tuned by the nanoparticles' spacing and aspect ratio. A figure of merit based on Mie theory is computed for spheres whose radii are either lambda/10 or lambda/3 over a broad spectral range that enables quantitative comparison with alternative plasmonic materials and reveals the full potential of ISO for engineering localized surface plasmons across the MIR spectral range. The development of fully Si-compatible plasmonic materials with engineered optical dispersion is important to enable cost-effective photonic-plasmonic high-density device integration for metaphotonic research. Published under license by AIP Publishing.