Dispersive optical constants of thermally evaporated Se_70-xTe₃₀Pb_x thin films

Thin films of amorphous Se_70-xTe₃₀Pb_x (x= 0, 2, 4, 6 and 8) are deposited on glass substrate by thermal evaporation technique. Transmittance measurements were used to calculate refractive index n and the extinction coefficient k using Swanepole’s method. The oscillator energyE₀, dispersion energy Ed, and other parameters have been determined by Wemple - DiDomenico single oscillator approach. The optical band gap E_g is estimated using Tauc’s relation and is found to decrease with the increasing Pb content. The decrease in optical band gap is interpreted in terms of electronegativity difference of constituent atoms and average bond energy difference of the system.