Observation of Optical Properties of Neodymium Oxide with Spectroscopic Ellipsometry

The annealing dependence of the optical properties of Nd2O3 films deposited by atomic layer deposition has been investigated by variable-angle spectroscopic ellipsometry (VASE). Based on VASE measurements, it is found that the refractive index and high-frequency dielectric constant decrease with increasing annealing temperature. The optical bandgap energy extracted using the Cody method varies from 4.13 eV for the as-grown state to 4.78 eV for the film annealed at 900°C. Moreover, three proposed physical models with corresponding optical models are applied to fit the experimental data to understand the possible structural change of the films with annealing temperature. Fitting results indicate that the interfacial interaction between the substrate and the film bulk occurs during the postdeposition annealing procedure and the surface properties of the Nd2O3 films are improved after annealing at 900°C. It is shown that the extracted VASE parameters well represented the characteristics of Nd2O3/SiO2/Si stacks with different annealing temperatures.