Optical properties of amorphous and crystalline Sb 2S 3 thin films

Abstract

The optical constants of amorphous thin films of Sb 2S 3 prepared by vacuum evaporation were determined. After deposition the films were crystallized by baking in a vacuum and their optical constants were re-determined. The amorphous and crystalline states of the films were determined by means of transmission electron microscopy. The amorphous material shows the exponential absorption tail characteristic of most amorphous materials. At higher photon energies near the absorption edge a linear dependence of (α E) 1 2 on photon energy is observed from which the extrapolated optical gap is found to be 1.7 eV. The optical constants in the amorphous films are rather structureless but on crystallization several structures are observed in ε 2 at energies of 1.88, 2.88, 3.48, 3.86 and 5.25 eV. The band gap in the crystalline material is 1.88 eV and is considered to be direct. On crystallization the magnitudes of the optical constants ε 2 and n increase to a great extent. The establishment of long range order in the material is likely to increase the weaker bonding by the chalcogen p electrons. This would probably increase the effective number of electron contributing to interband optical transitions and give rise to the observed change in optical properties.