Structural, Chemical and Optical Properties of Cerium Dioxide Film Prepared by Atomic Layer Deposition on TiN and Si Substrates

TL;DR

This study investigates the structural, chemical, and optical properties of CeO2 thin films deposited by atomic layer deposition on Si and TiN substrates, highlighting differences in crystallographic orientation, interface roughness, and oxygen vacancy content.

Contribution

It provides detailed comparison of CeO2 films on different substrates, revealing substrate-dependent properties and advancing understanding for applications of ALD-deposited CeO2.

Findings

CeO2 films are polycrystalline with specific orientations depending on substrate.

Oxygen vacancies are present, with Ce3+ concentrations around 18-22%.

Optical properties such as bandgap and refractive index are characterized.

Abstract

Thin films of cerium dioxide (CeO2) were deposited by atomic layer deposition (ALD) at 250 {\deg}C on both Si and TiN substrates. The ALD growth produces CeO2 films with polycrystalline cubic phase on both substrates. However, the films show a preferential orientation along <200> crystallographic direction for CeO2/Si or <111> for CeO2/TiN, as revealed by X-ray diffraction. Additionally, CeO2 films differ in interface roughness depending on the substrate. Furthermore, the relative concentration of Ce3+ is 22.0% in CeO2/Si and around 18% in CeO2/TiN, as obtained by X-ray photoelectron spectroscopy (XPS). Such values indicate a ~10% off-stoichiometry and are indicative of the presence of oxygen vacancies in the films. Nonetheless, CeO2 bandgap energy and refractive index at 550 nm are 3.54+/-0.63 eV and 2.3 for CeO2/Si, and 3.63+/-0.18 eV and 2.4 for CeO2/TiN, respectively. Our results extend the knowledge on the structural and chemical properties of ALD-deposited CeO2 either on Si or TiN substrates, underlying films differences and similarities, thus contributing to boost the use of CeO2 through ALD deposition as foreseen in a wide number of applications.