Effect of Bismuth on Structural and Optical Properties of Ge30Se70 Amorphous Thin Film

The present paper emphasizes on the structural and optical properties change in thermally evaporated Bi doped Ge30Se70 thin film. Thin films of Ge30Se70 and Ge30Se60Bi10 were prepared by thermal evaporation technique from the bulk material under high vacuum condition. X-ray diffraction study (XRD) revealed the amorphous nature of both the films as no sharp peak was found. Scanning electron microscopy (SEM) study indicated the smooth surface for both the films. The elemental presence was confirmed from Energy Dispersive X-ray spectroscopy (EDXS). The optical transmission was recorded by Fourier Transform Infra Red (FTIR) spectroscopy in the range 500-1100 nm. The optical band gap calculated by Tauc's relation shows a large decrease in band gap from 1.67 eV (Ge30Se70) to 1.05 eV (Ge30Se60Bi10) with Bi incorporation. This decrease in band gap is discussed in terms of defect states and degree of disorderness in the film. After incorporation of Bi, the increase in width of localized states in the band gap region reduces the optical band gap