Wide tuning of the optical and structural properties of alternative plasmonic materials

Abstract

Alternative plasmonic materials have attracted considerable attention due to their advantages compared to conventional metals, including compatibility with Si processing, tunability of optical properties, and reduced losses. In this work, we demonstrate that post-deposition annealing of materials fabricated by magnetron sputtering allows large tuning of the structural and the optical dispersion properties of Indium Tin Oxide (ITO), Al-doped ZnO (AZO) and Titanium Nitride (TiN) nano-layers. By measuring their optical bandgaps, we show that thermal annealing treatments can dramatically modulate the carrier concentration in these materials, thus providing tunability of the optical losses and enabling the engineering of Epsilon-Near-Zero (ENZ) regime. Besides, we perform X-ray diffraction (XRD) measurements to show that thermal annealing can also effectively tune the materials grain sizes. Eventually, the effect of different annealing gases on the free carrier concentration has also been investigated. The wide tunability and control of the optical and structural properties that we demonstrated in this work is important to engineer resonant optical responses across a wide frequency spectrum for device applications to plasmonics, metamaterials and transformation-optics.