As the library of potential materials with plasmonic behavior in the infrared (IR) grows, we must carefully assess their suitability for nanophotonic applications. This assessment relies on knowledge of the materials' optical constants, best determined via spectroscopic ellipsometry (SE). Transparent conductive oxides are great candidates for IR plasmonics due to their low carrier concentration (compared to noble metals) and the ability to tailor their carrier concentration by manipulating the defect composition. When the carrier concentration becomes low enough, phonon and defect states become the dominant mechanisms of absorption in the IR spectral range, leading to near-IR (NIR) tailing effects. These NIR tailing effects can be misinterpreted for free carrier absorption, rendering NIR-visible-ultraviolet-SE (NIR-VIS-UV-SE) incapable of reliably extracting the carrier transport properties. In this work, we report the limitations of NIR-VIS-UV and IR-SE (in terms of carrier concentration) by investigating the transport mechanisms of indium tin oxide, aluminum-doped zinc oxide and gallium-doped zinc oxide. We find regions of carrier concentration where NIR-VIS-UV-SE cannot reliably determine the transport properties and we designate material-dependent and application-specific confidence factors for this case. For IR-SE, the story is more complex, and so we investigate the multifaceted influences on the limitations, such as phonon behavior, grain size, presence of a substrate, film thickness, and measurement noise. Finally, we demonstrate the importance of identifying the IR optical constants directly via IR-SE (rather than by extrapolation from NIR-VIS-UV-SE) by means of comparing specific figures of merits (Faraday and Joule numbers), deemed useful indicators for plasmonic performance.

SrTiO3 as a disruptive technological solution to the inflated expectations of plasmonics, targeting the mid and far infrared wavelengths.

The unique structural transition of VO2 between dielectric and metallic phases has significant potential in optical and electrical applications ranging from volatile switches and neuromorphic computing to smart devices for thermochromic control and radiative cooling. Critical condition for their widespread implementation is scalable deposition method and reduction of the phase transition to near room temperature. Here, a W:VO2 process based on atomic layer deposition (ALD) is presented that enables precise control of W‐doping at the few percent level, resulting in a viable controllable process with sufficient W incorporation into VO2 to reduce the phase transition to room temperature. It is demonstrated that the incorporation of 1.63 at.% W through ALD growth leads to a state‐of‐the‐art phase transition at 32 °C with emissivity contrast between the low‐temperature and high‐temperature phase exceeding 40% in a metasurface‐based radiative cooling device configuration. The process is shown to be viable on 200 mm silicon substrates as well as flexible polyimide films. The full and self‐consistent temperature‐dependent characterization of the W‐doped VO2 using spectroscopic ellipsometry, electrical conductivity, mid‐wave infrared camera, and Fourier transform infrared emissivity, allows for a fully validated material model for the theoretical design of various smart and switchable device applications.

Transparent conductive oxides are appealing materials for optoelectronic and plasmonic applications as, amongst other advantages, their properties can be modulated by engineering their defects. Optimisation of this adjustment is, however, a complex design problem. This work examined the modification of the carrier transport properties of sputtered tin-doped indium oxide (ITO) via laser annealing in reactive environments. We relate the optical modifications to the structural, compositional, and electronic properties to elucidate the precise mechanisms behind the reactive laser annealing (ReLA) process. For sufficiently high laser fluence, we reveal an ambient-dependent and purely compositional modulation of the carrier concentration of ITO thin films. Hereby, we demonstrate that ReLA utilises the precise energy delivery of photonic processing to enhance the carrier mobility and finely tune the carrier concentration without significantly affecting the crystal structure. Exploitation of this phenomena may enable one to selectively engineer the optoelectronic properties of ITO, promising an alternative to the exploration of new materials for optoelectronic and photonic applications.

We demonstrate a novel material integration scheme for the realisation of wave-length division multiplexing devices in the O-band and discuss advanced fabrication meth-ods for the realisation of nonlinear devices for all-optical processing in the C-band.