On the optical properties of CdS thin films

Cadmium sulfide thin films (d = 0. 12 - 1.25 mu m) were deposited onto glass substrates by the quasi-closed volume technique under vacuum. The investigations shown that the films are polycrystalline and have a hexagonal (wurtzite) structure. Reflection, transmission and absorption spectra were studied in spectral range 300 - 1400 nm. Energy bandgap calculated from absorption spectra (assuming that allowed direct band-to-band transitions are predominant) ranged between 2.30 and 2.60 eV. The effect of the heat treatment (consisting of several heating/cooling cycles within a temperature range Delta T = 300 500 K) on the optical properties has been studied. The heat treated samples are characterized by higher values of transmission coefficient. This fact is probably due to the increase of crystallite size (the decrease of intercrystallite boundaries).