Infrared metamaterial by RF magnetron sputtered ZnO/Al:ZnO multilayers

Kevin C Santiago,Curtis White,Rajeh Mundle,Aswini K Pradhan,Messaoud Bahoura

doi:10.1063/1.5024900

Kevin C Santiago, Curtis White + Show 3 more

Open Access

https://doi.org/10.1063/1.5024900

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Abstract

Hyperbolic metamaterials create artificial anisotropy using metallic wires suspended in dielectric media or alternating layers of a metal and dielectric (Type I or Type II). In this study we fabricated ZnO/Al:ZnO (AZO) multilayers by the RF magnetron sputtering deposition technique. Our fabricated multilayers satisfy the requirements for a type II hyperbolic metamaterial. The optical response of individual AZO and ZnO films, as well as the multilayered film were investigated via UV-vis-IR transmittance and spectroscopic ellipsometry. The optical response of the multilayered system is calculated 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 fabricated multilayers undergo a hyperbolic transition at a wavelength of 2.2 μm. To our knowledge this is the first AZO/ZnO type II hyperbolic metamaterial system fabricated by magnetron sputtering deposition method.

Highlights

Metamaterials (MMs) are man-made materials that exhibit properties nonexistent in nature.[1]MMs have an abundance of applications, fabrication schemes, and designs, all of which depend of the particular bandwidth of interest, and desired functionality
We investigated the optical properties of the constituent AZO and ZnO, and calculated the hyperbolic dispersion transition wavelength using the nonlocal corrected Maxwell-Garnett Effective Medium Approximation (EMA).[24]
The thickness of the constituent AZO/ZnO films, and AZO/ZnO Multi-Layer (ML) samples were confirmed via cross-sectional scanning electron microscopy (SEM) and atomic force microscopy (AFM) scans

Summary

INTRODUCTION

Metamaterials (MMs) are man-made materials that exhibit properties nonexistent in nature.[1]. The real permittivity of AZO is negative in the near infrared, satisfying the requirements for the hyperbolic dispersion relation and subsequent MM behavior. The resistivity is higher for the thinner AZO films, the carrier concentration is still high enough to see a positive – to – negative transition in the real permittivity. A thickness of ∼ 40 nm the free carrier concentration greatly diminishes, and no positive – to – negative transition in the real permittivity is observed from the visible to NIR. A minimum layer thickness of 45-50 nm is required to observe the negative permittivity in sputtered AZO films.

EXPERIMENTAL DETAILS

RESULTS AND DISCUSSION

ML model

CONCLUSION