Optical properties of the c-axis oriented LiNbO3 thin film

C-axis oriented Lithium Niobate (LiNbO₃) thin films have been deposited onto epitaxially matched (001) sapphire substrate using pulsed laser deposition technique. Structural and optical properties of the thin films have been studied using the X-ray diffraction (XRD) and UV-Visible spectroscopy respectively. Raman spectroscopy has been used to study the optical phonon modes and defects in the c-axis oriented LiNbO₃ thin films. XRD analysis indicates the presence of stress in the as-grown LiNbO₃ thin films and is attributed to the small lattice mismatch between LiNbO₃ and sapphire. Refractive index (n = 2.13 at 640 nm) of the (006) LiNbO₃ thin films was found to be slightly lower from the corresponding bulk value (n = 2.28). Various factors responsible for the deviation in the refractive index of (006) LiNbO₃ thin films from the corresponding bulk value are discussed and the deviation is mainly attributed to the lattice contraction due to the presence of stress in deposited film.