Tuning the infrared dielectric and plasmonic properties of ZnO thin films on glass

Abstract

Infrared reflectivity measurements are performed on c-axis oriented zinc oxide thin films deposited on glass by the pulsed laser deposition technique at 350 °C and 700 °C and for different deposition times to examine the effect of deposition temperature and film thickness on the physical properties of the grown zinc oxide material. The recorded infrared reflectivity spectra are fitted, using the least-squares method, to a formalism derived from the transfer matrix method for a multilayer system and the Lorentz-Drude harmonic oscillator model to determine the infrared dielectric and plasmonic properties of the films along the c-axis and perpendicular to it. It is found that the film thickness has a significant effect on the ratio of the high-frequency dielectric constant parallel to the c-axis to the high-frequency dielectric constant perpendicular to the c-axis, and the oscillator damping factor decreases as the film thickness increases. It is also found that zinc oxide films deposited on glass exhibit a significant density of free carriers with high mobility. However, for a deposition temperature of 350 °C and a film thickness between 110 and 150 nm, the free carrier density reaches values close to those of highly doped zinc oxide films. The results highlighted in this paper demonstrate that the infrared dielectric and plasmonic properties of zinc oxide films deposited on a glass substrate can be tuned by the deposition temperature and film thickness to meet the requirements of materials suitable for technological applications such as transparent electrical conductors, hyperbolic materials, and infrared plasmonic sensors. © 2022