OPTICAL AND STRUCTURAL PROPERTIES OF 100 MeV Ag SWIFT HEAVY ION IRRADIATED AMORPHOUS Ge24Se61Sb15 THIN FILMS

Abstract

Present study reports about change in structural and linear/nonlinear optical properties of amorphous Ge24Se61Sb15 thin films using 100 MeV silver (Ag) swift heavy ion (SHI) irradiation. The thin films were irradiated under 100 MeV Ag SHI for six different fluences (3x1010, 1x10 11, 3x1011, 1x1012, 3x1012, and 1x1013 ions/cm2 ). The XRD images of the pristine and irradiated (3x1012 ions/cm2 ) thin films confirm the amorphous nature of thin films. The scanning electron microscopy (SEM) micrograph reveals that the fluence 1x1013 ions/cm2 is the upper limit of ion fluence. The loss of energy and stopping range of 100 MeV Ag SHI was calculated using SRIM-2006. The electronic energy loss dominates over nuclear energy loss, hence is mainly responsible for optical and structural changes. The optical transmission spectra of the pristine and irradiated thin films were recorded within the spectral range from 300 nm to 900 nm. The optical absorption coefficient was calculated by using the Lambert-Beer law. The optical band gap (Eg) was calculated by extrapolating the Tauc’s plot. The optical band gap (Eg) reduces from 1.59 eV (pristine) to 1.38 eV (3x1012 ions/cm2 ) and further increases to 1.48 eV (1x1013 ions/cm2 ). Linear and nonlinear refractive index were calculated using semi-empirical relations and both increases till fluence 3x1012 ions/cm2 , which is the consequence of bonding rearrangement as explained using Raman measurement.