Influence of low energy Ag ion irradiation for formation of Bi2Se3 phase from Bi/GeSe2 heterostructure thin films

The manuscript reports on the influence of 40 keV Ag -ve ion bombardment with different fluences on the microstructural and optical properties of thermally evaporated Bi/GeSe2 bilayer thin films. Two different fluences (5x10(14) ions cm(-2) and 1x10(15) ions cm(-2)) of Ag -ve ions were used to irradiate the thin films that changed the microstructure and optical properties as studied by different spectroscopic methods like X-ray diffraction method (XRD), Energy dispersive X-ray spectroscopy (EDS), Field emission scanning electron microscopy (FESEM), Atomic force microscopy (AFM), Raman spectroscopy, and UV-Vis spectroscopy. The evolution of topological Bi2Se3 phase occurs after ion irradiated diffusion of Bi into GeSe2 matrix. The optical parameters as calculated from the transmission spectra infers the indirect allowed transition with reduction of E-g on ion irradiation. The various optical parameters like absorption coefficient (alpha), optical energy gap (E-g), Tauc parameter (B-1/2), Urbach energy (E-e), extinction coefficient (k), refractive index (n) were modified with ion irradiation. The surface morphology is being changed after irradiation as probed by AFM and FESEM. The Raman spectra support the formation of Bi2Se3 phase with irradiation. The obtained results have been explained on the basis of increase in band tailing of valence band due to defect states caused by the irradiation.