Fabrication and characterization of high refractive index optical coatings by sol-gel method for photonic applications

The deposition and characterization of thin Ta2O5, TiO2 and Nb2O5 film, obtained by the sol-gel methods using tantalum ethoxide, titanium isopropoxide and niobium chloride as precursors and specially developed water free sol-gel procedure are presented. Structure and morphology of the obtained layers are inspected through XRD and SEM measurements. Refractive index, extinction coefficient and thickness of the films are determined from reflectance spectra using non-linear curve fitting method. Refractive index values as high as 1.9, 2.28 and 2.39 are obtained for Ta2O5, TiO2 and Nb2O5 film, respectively at wavelength of 500 nm. The possibility of controlled tuning of optical properties by appropriate annealing is demonstrated. The application of coatings as high refractive index building blocks of one dimensional photonic crystals is discussed.