Tailoring the Thickness-Dependent Optical Properties of Conducting Nitrides and Oxides for Epsilon-Near-Zero-Enhanced Photonic Applications

TL;DR

This paper demonstrates how the optical properties of conducting nitrides and oxides can be precisely controlled through film thickness to enhance epsilon-near-zero photonic applications, enabling tunable metasurfaces and nonlinear optical phenomena.

Contribution

It introduces a method to tailor the optical responses of TiN-AZO bilayers via thickness control, creating ENZ resonances and metasurfaces for advanced photonic functionalities.

Findings

TiN-AZO bilayers exhibit tunable ENZ resonances in the telecom range.

Bilayers act as strong ultraviolet light absorbers with ENZ and Fabry-Perot modes.

Optically-induced reflectance modulation reaches 15% with picosecond response.

Abstract

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.