The optical properties of In2S3 films in the far-infrared spectral range

Optical reflection spectra of In2S3 thin films (180 - 730 nm) deposited on glass substrates are measured by infrared spectroscopy using the synchrotron radiation of BESSY II storage ring in the spectral range of 30 - 8000 cm -1. The aim of the study is to find the influence of different substrate and post-annealing temperatures on the electron and phonon systems of In2S3 films deposited on glass. Clear features in the reflectance spectra for the studied films have been found mainly in the phonon excitation range 100 - 400 cm -1. The experimental dielectric functions epsilon(omega) of In2S3 films are found to be in good agreement with the calculated ones obtained for In2S3 crystals within the density functional theory. The dielectric functions epsilon(omega) of the films in the range of 100 - 400 cm -1 depend substantially on the post-annealing temperature. This indicates a transition of the film from the amorphous to the crystalline state. The thorough analysis of the frequency dependence of the reflection coeffi-cient R(omega) and optical conductivity sigma(omega) in the wavenumber range of 30 - 130 cm- 1 allowed us to reveal the distributed electron states in In2S3 films.