Growth mechanisms and their effects on the opto-electrical properties of CdS thin films prepared by chemical bath deposition. (September 2016)

• Record Type: Journal Article
• Authors: Slonopas, Andre; Ryan, Herbert; Foley, Benjamin; Sun, Zeming; Sun, Keye; Globus, Tatiana; Norris, Pamela
• Is Part Of: Materials science in semiconductor processing. Volume 52(2016:Sep.)
• Page Start: 24
• Page End: 31
• Publication Date: 2016-09
• Subjects: Chemical bath deposition -- Thin films -- CdS -- Opto-electrical properties -- Growth mechanisms -- Spectroscopic ellipsometry; Semiconductors -- Periodicals; Integrated circuits -- Materials -- Periodicals; Semiconducteurs -- Périodiques; Circuits intégrés -- Matériaux -- Périodiques; Electronic journals; 621.38152
• DOI: 10.1016/j.mssp.2016.05.011
• Languages: English
• ISSNs: 1369-8001

Abstract

Abstract: 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 °C–95 °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 Ω cm. A noticeable decrease of, ~0.2 was observed in the refractive index and an increase of ~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.