Growth mechanisms and their effects on the opto-electrical properties of CdS thin films prepared by chemical bath deposition

Chemically deposited CdS exhibits high sensitivity in the opto-electrical performance to the growth mechanisms. Hence it is of a great interest to study the effects of growth mechanisms on the opto-electrical performance in such films. Studies were carried out by the means of spectroscopic ellipsometry, and coupled with structural, optical, and electrical characterization. A range of bath temperatures (55 degrees C-95 degrees C) were used as the means to alter the growth mechanisms. Ion-by-ion process dominated deposition at lower bath temperatures throughout the length of the deposition. This mechanism produced films composed of single phase cubic crystals with corresponding opto-electrical properties inherent to such structures. Complex formations at higher bath temperatures supplement the sole ion-by ion mechanisms with the cluster-by-cluster mechanism. This results in a mixed cubic/hexagonal structure, and deviation from stoichiometry. As a result, carrier concentrations and mobility increased nearly eight and four fold respectively. Resistivity decreased more than four times from 33.2 to 7.5 Omega cm. A noticeable decrease of, similar to 0.2 was observed in the refractive index and an increase of similar to 0.07 eV in the band gap is also reported. Nuclear magnetic resonance analysis confirms deviation from stoichiometry in the cluster-by-cluster mechanisms, resulting in interstitially trapped Cd+2 and S-2 ions. The trapped ions act as donors in the film enhancing its electrical performance. (C) 2016 Elsevier Ltd. All rights reserved.