Thickness Dependence of the Optical properties of Vacuum Evaporated YF3 Thin Films

Abstract

Rare earth oxides and fluorides are well known for their refractory nature and chemical stability and so they find considerable application in electronic and optical devices. The present investigation deals with the optical properties of vacuum evaporated Yttrium fluoride thin films. The thicknesses of the films deposited on cleaned glass substrates were measured by a multiple beam interferometer. XRD technique has been used for structural analysis and dependence of film thickness on structure has also been discussed. Transmittance measurements were made over the wavelength range 400-800 nm. It has been observed that the transmittance decreases with the increase of film thickness. From the transmittance data the absorption index kf and refractive index nf were evaluated for the films of different thicknesses (78 to 136 nm). For a film of thickness 103 nm kf and nf were calculated as 0.007 and 1.23 respectively at a wavelength of 500 nm. From alpha /sup2/ versus hv plot the optical band gap-energy has been estimated as 2.0 eV and the type of transition was found to be allowed and direct