REDSHIFT IN THE OPTICAL BAND GAP OF AMORPHOUS NANOSTRUCTURE Se80Te20-xSnx FILMS

Ternary glasses of Se80Te20-xSnx (x=3 and 9 at.%) are prepared by melt quench technique. Thin films of Se80Te20-xSnx (x=3 and 9 at.%) of different thicknesses in the range of (25 nm -1450 nm) are prepared by the conventional thermal evaporation technique on glass substrate. X-ray diffraction measurements show that both bulk and thin films of Se80Te20-xSnx have amorphous natures. Optical transmission and reflection spectra of the studied thin films are measured in the wavelength range of 200−2500 nm at room temperature. The absorption coefficient (α) as an optical constant is determined as a function of film thickness. The width of localized states near the mobility edge increases with increasing the film thickness. The optical band gap is redshifted from 1.87 to 1.49 eV and from 1.85 to 1.35 eV with increasing the film thickness for both Se80Te20-xSnx (x=3 and 9 at.%) thin films respectively, due to quantum size effect.