PULSED LASER DEPOSITION OF ZINC OXIDE THIN FILMS ON SILICON: AN INVESTIGATION OF GROWTH, DIELECTRIC, AND PLASMONIC PROPERTIES

Abstract

This thesis investigates the pulsed laser deposition (PLD) of zinc oxide (ZnO) thin films on silicon (100) substrates, following up on previous work performed in our department on the growth of ZnO on sapphire and glass substrates. A pulsed KrF excimer laser was thus used to ablate a polycrystalline ZnO target, and experimental parameters such as deposition temperature and deposition time were varied. The crystalline quality, stoichiometry, and morphology of the resulting thin films were studied by X-Ray Diffraction (XRD), Energy Dispersive X-Ray Spectroscopy (EDS), and Scanning Electron Microscopy (SEM), respectively. Surface profilometry and SEM were used to measure the thickness of the layers, and their optical properties in the Infra-Red range were determined by infrared reflectivity measurements using Fourier Transform Infrared Spectroscopy (FTIR). The recorded infrared reflectivity spectra, performed as a function of temperature, were fitted to a formalism derived from the transfer matrix method for a multilayer system and the Lorentz-Drude model to determine the infrared dielectric and plasmonic properties of the films along the c-axis and the basal plane. The successful growth of highly crystallized ZnO thin films on Si revealed a strong preferential orientation along the c-axis for temperatures as low as 350◦C. As deposition temperature is increased, a noticeable enhancement in the crystallinity of the films is observed, as inferred from a narrowing of the XRD peaks. From the XRD, the size of the crystalline grains was found to be in the range of ∼25 nm and ∼50 nm for deposition temperatures of 350 and 700◦C, respectively. A slight dependence of crystalline grain size on the film’s thickness was also detected. SEM imaging showed that sharp and clear hexagonal grain shapes are obtained at 700◦C. Various surface morphologies (pyramid-like or rectangular-like) are observed for lower deposition temperatures and different thicknesses. The fitting of the IR reflectivity data led to the determination of crucial dielectric and plasmonic properties of the thus obtained films, including the dielectric constant, the electron density, and the electron mobility. It was found, through temperature-dependent IR reflectivity measurements, that the dielectric and plasmonic properties of the PLD ZnO films on Si are stable up to operating temperatures of ∼450◦C. This is very encouraging for the potential use of these films in plasmonic applications.