  The unique properties of the emerging photonic materials - conducting
nitrides and oxides - especially their tailorability, large damage thresholds,
and the so-called epsilon-near-zero (ENZ) behavior, have enabled novel photonic
phenomena spanning optical circuitry, tunable metasurfaces, and nonlinear
optical devices. This work explores direct control of the optical properties of
polycrystalline titanium nitride (TiN) and aluminum-doped zinc oxide (AZO) by
tailoring the film thickness, and their potential for ENZ-enhanced photonic
applications. We demonstrate that TiN-AZO bilayers act as Ferrell-Berreman
metasurfaces with thickness-tailorable epsilon-near-zero resonances in the AZO
films operating in the telecom wavelengths spanning from 1470 to 1750 nm. The
bilayer stacks also act as strong light absorbers in the ultraviolet regime
employing the radiative ENZ modes and the Fabry-Perot modes in the constituent
TiN films. The studied Berreman metasurfaces exhibit optically-induced
reflectance modulation of 15% with picosecond response-time. Together with the
optical response tailorability of conducting oxides and nitrides, utilizing the
field-enhancement near the tunable ENZ regime could enable a wide range of
nonlinear optical phenomena, including all-optical switching, time refraction,
and high-harmonic generation.
