Optical dielectric properties of HfO2-based films

Abstract

We report the dielectric Properties of HfO2-based films in the optical–high frequency range. The demonstrated tunability of the optical dielectric constant of HfO2-based compounds is of great relevance for optoelectronic applications, e.g., high-refractive index dielectrics for nanoantenna and optical coatings for electronic displays. Since the optical dielectric constant of HfO2 is determined by the electronic structure and its crystal environment, we tune the physical properties of HfO2 films on MgO by adding different dopants. In this work, we aim to determine the influence of doping together with the resulting crystal structure on the optical dielectric constant. Hence, we studied 20 mol. % Y-doped HfO2 (HYO), Hf0.5Zr0.5O2 (HZO), and Hf0.5Ce0.5O2 (HCO). Among the dopants, Y2O3 has the lowest, ZrO2 an intermediate, and CeO2 the highest real part of the optical dielectric constant. The optical dielectric constant is found to be lowest in the cubic HYO films. An intermediate dielectric constant is found in HZO films that is predominantly in the monoclinic phase, but additionally hosts the cubic phase. The highest dielectric constant is observed in HCO films that are predominantly in the cubic phase with inclusions of the monoclinic phase. The observed trend is in good agreement with the dominant role of the dopant type in setting the optical dielectric constant.