Urbach energy and dispersion parameters of CdS chemically deposited thin films on the effect of thickness

Optical transmittance spectra of CdS thin films were recorded from UV-Visible spectrophotometer in the range 380-900 nm. The films were prepared by chemical spray pyrolysis by spraying an aqueous solution of cadmium chloride (CdCl2) and thiourea [(NH2)2CS] with de-ionized water. UV-Visible spectrophotometer used to recording the transmittance spectra in the range of 380-900 nm. The transmittance decreased with the increasing of CdS film thickness, while the reflectance increases. The energy gap decreased with the increasing of film thickness, while Urbach energy increased. Dispersion parameters such as; Ed, Eo, ε∞, n(0), So, λo, M-1, and M-3 are studied.