Hafnium silicate films with pure HfO2 and SiO2 samples as references were fabricated by atomic layer deposition (ALD) in this work. The optical properties of the films as a function of the film composition were measured by vacuum ultraviolet (VUV) ellipsometer in the energy range of 0.6 to 8.5 eV, and they were investigated systematically based on the Gaussian dispersion model. Experimental results show that optical constants and bandgap of the hafnium silicate films can be tuned by the film composition, and a nonlinear change behavior of bandgap with SiO2 fraction was observed. This phenomenon mainly originates from the intermixture of d-state electrons in HfO2 and Si-O antibonding states in SiO2.
Yang, W., Fronk, M., Geng, Y., Chen, L., Sun, Q. Q., Gordan, O. D., … Zhang, D. W. (2015). Optical properties and bandgap evolution of ALD HfSiOx films. Nanoscale Research Letters, 10(1). https://doi.org/10.1186/s11671-014-0724-z