We present a spectroscopic ellipsometry study of Mo-doped VO2 thin films deposited on silicon substrates for the mid-infrared range. The dielectric functions and conductivity were extracted from analytical fittings of Ψ and Δ ellipsometric angles showing a strong dependence on the dopant concentration and the temperature. Insulator-to-metal transition (IMT) temperature is found to decrease linearly with increasing doping level. A correction to the classical Drude model (termed Drude-Smith) has been shown to provide excellent fits to the experimental measurements of dielectric constants of doped/undoped films and the extracted parameters offer an adequate explanation for the IMT based on the carriers backscattering across the percolation transition. The smoother IMT observed in the hysteresis loops as the doping concentration is increased, is explained by charge density accumulation, which we quantify through the integral of optical conductivity. In addition, we describe the physics behind a localized Fano resonance that has not yet been demonstrated and explained in the literature for doped/undoped VO2 films.

We report the design, fabrication, and characterization of a porous silicon-based omnidirectional mirror for the near infrared range. The structure consists of 300 porous silicon chirped dielectric layers, optimized to have omnidirectional reflectivity response from 1000 to 2000 nm wavelength range. Measurements of reflectivity spectra are presented for non-polarized light at several incident angles (range 8°–65°) with a reflectivity >95% covering a 1μm band-width. Transfer matrix method calculations were carried out to show the complete angular range for both TM and TE polarizations including a simple model to illustrate the interface scattering effects.

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