Tailorable Near-Perfect Absorption in Ferrel Berreman Metasurfaces Utilizing The Thickness Dependent ENZ Characteristics Of Aluminum Doped Zinc Oxide and Titanium Nitride

The tailorable optical properties of transition metal nitrides and transparent conducting oxides have raised them to be one of the top candidates in technologically relevant nanophotonic research. In this work, the thickness-dependent properties of thin layers of aluminum-doped zinc oxide(AZO) and titanium nitride(TiN) are investigated with a special interest in their epsilon near zero (ENZ) region. Lithography-free metasurfaces with bilayer stacks of TiN and AZO are shown to possess two highly absorptive modes with strong field enhancements. These absorption peaks are associated with the excitation of the radiative modes (Ferrel-Berreman mode) near the ENZ regions of AZO and TiN. The thickness tunable material properties of AZO provide an additional degree of freedom to engineer the spectral position of the resonance over a 200 nm wavelength range spanning the telecom regime. The metasurfaces show all-optical reflection modulation of 15% with picosecond temporal response. The thickness-dependent characteristics enable tailorability of optical devices like absorbers and modulators, while the high field enhancement near the ENZ regime induces strong light-matter interactions enabling nonlinear optical applications like time refraction studies, all optical switching, and high harmonic generation.