Thin films of CdS:Cu, morphological, optical, structural and electrical properties

Abstract

Thin solid films of CdS:Cu were synthesized using a wet-chemical. Doping was by thermal diffusion. Films were obtained as a function of: precursor salts, deposition time and annealing temperature. Studies of transmittance, resistivity, photoluminescence at room temperature, X-ray diffraction, high-resolution scanning and transmission electron microscopies, were performed. The CdS and CdS:Cu films obtained had an average thickness of 130 nm and 160 nm, respectively. This study provides evidence of the greater effectiveness of sodium citrate than ammonium chloride as a complexing agent. The crystalline phase of the films was cubic and did not vary with deposition time or the precursor. Studies were consistent in showing a film made up of regularly spaced, asterisk-shaped entities of about 35 nm in size, which in turn were composed of nanocrystals smaller than 10 nm. The resulting films behaved as an n-type semiconductor with an energy gap of about 2.38 eV that varied only slightly with deposition time and the precursors’ nature, but increased to 2.93 eV with Cu doping. The resistivity achieved was 5.822 × 10-5 ?-cm. The PL emission spectra showed variation in optical quality and revealed a de-excitation mechanism due to the presence of cadmium vacancies, sulfur vacancies and interstitial cadmium.