Infrared metamaterials by RF sputtered ZnO/Al:ZnO multilayers

TL;DR

This paper reports the fabrication and optical characterization of ZnO/Al:ZnO multilayers that exhibit hyperbolic metamaterial properties at near-infrared wavelengths, validated through experimental and theoretical analysis.

Contribution

It introduces RF sputtered ZnO/Al:ZnO multilayers as a new hyperbolic metamaterial platform with validated optical properties.

Findings

Multilayers satisfy conditions for type I hyperbolic metamaterials.

Hyperbolic transition occurs at 2.2 μm wavelength.

Experimental and theoretical results are in agreement.

Abstract

Hyperbolic metamaterials create artificial optical anisotropy using metallic wires suspended in a dielectric medium, or alternating layers of a metal and dielectric. Here we fabricated ZnO/Al:ZnO (AZO) multilayers by the RF magnetron sputtering deposition technique. Our fabricated multilayers satisfy the conditions required for a type I hyperbolic metamaterial. The optical response of individual AZO and ZnO films, as well as the multilayered film were investigated via angular transmittance and spectroscopic ellipsometry measurements. The optical response of the multilayered system is predicted using the nonlocal-corrected Effective Medium Approximation (EMA). The spectroscopic ellipsometry data of the multilayered system was modeled using a uniaxial material model and EMA model. Both theoretical and experimental studies validate the multilayers undergo a hyperbolic transition at a wavelength of 2.2 {\mu}m.