Effect of Sn addition on the optical gap and far-infrared reflectivity spectra of amorphous Sb-Se films

This paper reports the spectroscopic studies on the thermally evaporated Sn_xSb₂₀Se_{80 - x} (2 ≤ x ≤ 8) films. Optical gap and band tailing parameter decreases except for x = 8, where it increases. The red shift in peak reflectivity spectrum in the interband transition region (200-800 nm) has been observed. The position and shape of the reflectivity bands (80-378 cm^{- 1}) indicate the change in the local structure of the films. The Kramer-Kronig transformations have been used to evaluate the dielectric constants from the far-infrared reflectivity spectrum. Splitting of the longitudinal optic and transverse optic mode characterizes the partial ionic character for Sn-Sb-Se system. The relationship between the optical properties and structure has been revealed.