Epsilon-near-Zero Modes and Surface Plasmon Resonance in Fluorine-Doped Cadmium Oxide Thin Films

• DOI: 10.1021/acsphotonics.7b00429
• Publication Date: 2017-07-18T13:18:31Z
• Authors: Evan L. Runnerstrom; Kyle P. Kelley; Edward Sachet; Christopher T. Sh...; Jon-Paul Maria
• Keywords: 02 engineering and technology; 0210 nano-technology; 7. Clean energy

In this report we demonstrate fluorine-doped CdO as a model infrared plasmonic material by virtue of its tunable carrier density, high mobility, and intense extreme-subwavelength plasmon–polariton coupling. Carrier concentrations ranging from 1019 to 1020 cm–3, with electron mobility values as high as 473 cm2/V·s, are readily achieved in epitaxial CdO films over a thickness range spanning 50 to 500 nm. Carrier concentration is achieved by reactive sputtering in an Ar/O2 atmosphere with trace quantities of CF4. Infrared reflectometry measurements demonstrate the possibility of near-perfect plasmonic absorption through the entire mid-IR spectral range. A companion set of reflectivity simulations are used to predict, understand, and optimize the epsilon-near-zero plasmonic modes. In the context of other transparent conductors, CdO exhibits substantially higher electron mobility values and thus sharp and tunable absorption features. This highlights the utility of high-mobility transparent conducting oxides as...