Optical and Structural Properties of Copper Doped CdS Thin Films Prepared by Pulsed Laser Deposition

This paper presents the study of the structural and optical properties of copper doped cadmium sulfide thin films prepared by pulsed Nd:YAG laser. The copper concentration in the targets was varied from 0.05% to 5% in weight and they were heated at a temperature of 500 degrees C in air for one hour. It was observed that annealing un-doped and doped thin films at temperatures above 160 degrees C leads to an abrupt increase in the optical transmission, changing from dark brownish to transparent yellowish. For annealed samples at 300 degrees C, increasing Cu concentration from 0.0% to 2%, leads to an increase in the optical transmission up to 80%, at a wavelength of about 700 nm. XRD patterns showed the hexagonal phase of cadmium sulfide and a number of CdO peaks relating to the partial oxidation of cadmium. The XPS spectra of the annealed samples indicate an accumulation of Cu at the surface. Therefore, Cu impurity can enhance CdS oxidation and the size of the crystallites. The highest value of the photo-current for the samples is related to the lowest Cu concentration, i.e: 0.05%.