Optogeometric study of multimode TiO2 waveguide thin films elaborated by reactive magnetron sputtering

TiO2 thin films were deposited by reactive magnetron sputtering with increasing thickness T1, T2, T3 and T4. The μ-Raman spectra showed the presence of anatase TiO2 in all films. The phonon confinement model revealed the crystallite size ranging between 5.1 and 6.1 nm. The optical gap energy was found to decrease from 3.45 eV to 3.37 eV. Scanning electron microscopy and energy dispersive X-ray spectroscopy analysis showed enhancement of crystallinity and stoichiometry over the films’ thickness in accordance with the μ-Raman measurements. The m-lines spectroscopy confirmed the normal behavior of the films as multimode waveguides by the increase of propagation modes’ number with the films’ thickness for each transverse electric and transverse magnetic polarization. Both ordinary and extraordinary refractive indices decreased over the films’ thickness. The birefringence however had an opposite behavior. The cut-off thickness experienced an increment as a function of thickness. In comparison, m-lines and Swanepoel’s method were relatively compatible.