Cd(Zn)O on SiC: epsilon-near-zero modes and plasmon-phonon coupling

TL;DR

This study explores Cd(Zn)O on SiC as a new platform for mid-IR plasmonic applications, demonstrating epsilon-near-zero modes and strong plasmon-phonon coupling with improved optical properties.

Contribution

Introduces SiC as a novel, highly polar, dopable substrate for Cd(Zn)O, analyzing its plasmonic and epsilon-near-zero properties compared to sapphire.

Findings

Cd(Zn)O/SiC exhibits two surface polariton modes: a plasmonic ENZ mode and a hybridized plasmon-phonon mode.

Alloy with 10% Zn shows optimal crystalline and plasmonic quality with optical losses of 13% of plasma frequency.

The SiC substrate enhances epsilon-near-zero behavior due to its high dielectric constant.

Abstract

Cd(Zn)O stands out as probably the best plasmonic material in the mid-IR, but it is usually grown on sapphire or other passive substrates. In this work we introduce SiC as a novel, highly polar, dopable substrate for Cd(Zn)O. The Cd(Zn)O/SiC system is analyzed as a function of the Zn concentration and thin film thickness, and the results are compared to those obtained in the Cd(Zn)O/sapphire system. XRD and reflectance measurements show that the alloy with 10 % Zn nominal concentration has the best crystalline and plasmonic quality, with optical losses as good as 13 % of the plasma frequency. The thin films show two surface polariton modes: a purely plasmonic symmetric mode at higher energies with negligible frequency dispersion and pinning at the plasma frequency for the thinnest films, characteristic of an ideal epsilon-near-zero mode; and a plasmonic-phononic hybridized antisymmetric mode at lower energies, which thanks to the large value of the higher frequency dielectric constant of SiC compared to sapphire, shows much lower frequency dispersion, indicative of the stronger epsilon-near-zero character. Hence, Cd(Zn)O/SiC offers a promising platform for the development of ENZ devices on an active substrate.