Homogeneity of sol-gel derived silica-titania waveguide films – Spectroscopic and AFM studies

Abstract

This work discusses optical homogeneity of high refractive index silica-titania waveguide layers fabricated using sol-gel method and dip-coating technique. Tetraethyl orthosilicate Si(OC2H5)4 (TEOS) and titanium(IV) ethoxide Ti(OC2H5)4, were used as precursors of silica and titania, respectively. Optical homogeneity was determined from reflectance characteristics of thin layers. Interference minima and maxima of reflectance spectra were used to calculate refractive indices and thickness of fabricated layers. Refractive indices were further approximated with Cauchy function to determine the dispersion characteristic. Calculated parameters of thin layers were compared with those obtained via laser ellipsometry and spectroscopic ellipsometry. Excellent agreement between both results was achieved. Dispersion characteristics were used for the reconstruction of reflectance spectra via 2 × 2 transfer matrix formalism. Again, excellent agreement between reconstructed (theoretical) and measured characteristics was obtained. Chemical profiling performed via Auger Electron Spectroscopy (AES) method demonstrated homogeneity in concentrations of oxygen, titanium, and silicon atoms, which was as expected [Si]:[Ti] = 1:1. Surface morphology determined via Auger Electron Spectroscopy (AES) method and atomic force microscopy demonstrated high smoothness and measured root mean square surface roughness was 0.328(3) nm.