Optical properties of thermally evaporated SnS thin films

Thermally evaporated SnS amorphous chalcogenide films undergo structural transformation upon annealing in the temperature range between 432-573 K. The optical properties of amorphous and annealed films were investigated using spectrophotometric measurements of the transmittance and reflectance at normal incidence in the wavelength range 250-2500 nm. The films are transparent for a wavelength > 1250 nm. The refractive index (n) and the absorption index (k) are independent of film thickness in the measured film thickness range (55-365 nm). The dispersion energy, E-d, of amorphous films increased from 20.2 to 23.85 eV for crystalline films. The types of optical transition responsible for optical absorption are indirect allowed and direct forbidden transitions with energy gaps of 1.4 and 2.18 eV for the amorphous films and of 1.38 and 2.33 eV for the crystalline films, respectively. (C) 2002 Elsevier Science B.V. All rights reserved.