Optical and structural modification in amorphous Ge24Se61Sb15 thin films under 80 MeV Silicon swift heavy ions for telecom and optical applications

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Present study reports about the effect of 80 MeV Silicon swift heavy ions irradiation on linear and nonlinear optical properties of amorphous Ge24Se61Sb15 thin films. Optical changes are correlated with structural modifications for their utilization in telecom and optical applications. Optical transmission spectra were recorded from 200 nm to 1100 nm. Linear refractive index is calculated by optical transmission using Swanepoel envelope method. Dispersion in the linear refractive index of the thin films is described using Wemple-DiDomenico model. Nonlinear optical parameters are determined using semi-empirical relations. Optical band gap is calculated by extrapolating the Tauc's plot. The investigation shows that optical band gap decreases from 1.64 eV to 1.47 eV and linear refractive index increases from 2.50 to 2.59 till fluence 1 × 1012 ions/cm2. In addition, third-order nonlinear susceptibility increases from 8.178 × 10−10 [esu] to 11.43 × 10−10 [esu] and nonlinear refractive index increases from 1.742 × 10−10 [esu] to 2.698 × 10−10 [esu] till fluence 1 × 1012 ions/cm2. Raman measurements reveal that swift heavy ion irradiation converts homopolar Ge–Ge, Sb–Sb bonds into hetropolar Ge–Sb and Se–Sb bonds, which is responsible for observed optical changes. The changes are understood in terms of glass network structure and electronic energy loss for application point of view.