Optical Properties of amorphous Ge-Se-Tl System Films

Abstract

The optical properties of Ge SeŽ9 x . Tl x thin-film samples of different thicknesses are studied as a function of the thallium contents. Transmittance and reflectance measurements in the range of Ž400 2600 nm. of various thicknesses range of Ž114 618.3 nm. were used to calculate the optical band gap Egopt, the width of localised states and optical constants n and k. It is shown that the optical band-gap decreases and the width of the tail increases with the increase in the Tl content. The allowed optical transitions were found to be indirect transitions. From the transmission spectra, the relationship between the refractive index n and the wavelength Ž . at different Tl contents is derived. The increase in the refractive index with the increase in the Tl content is attributed to the increase in the valency density of the current carriers. Analysis of the refractive indices has yielded optical dielectric constant Ž ..