Electrochemical and structural investigation of BixTey thin films electrodeposited on ITO substrate

Abstract

Bismuth telluride films with various stoichiometries BixTey have been successfully elaborated by potentiostatic deposition on indium tin oxide (ITO) substrate from an acidic solution containing a mixture of different concentrations of Bi3+ and HTeO2+ ions. The electrochemical study using cyclic voltammetry and chronoamperometry shows that the electrodeposition of bismuth telluride is a quasi-reversible reaction controlled by the diffusion process and the composition of the reaction mixture controls the BixTey stoichiometry. It was found, from electrochemical and EDS analysis, that a mixture in stoichiometric proportions leads to the formation of bismuth tellurium Bi2Te3, an excess of telluryl ion HTeO2+ gives a product rich in tellurium Bi2-xTe3+x, but a high concentration of Bi3+ (compared to the stoichiometry) gives rise to the electrodeposition of a compound rich in bismuth Bi2+xTe3-x. The chronoamperometric analysis of current density-time transients using Scharifker-Hills model showed that the mechanism of deposition and growth of BixTey on ITO substrate takes place according to a progressive 3D nucleation for low Bi3+ concentration and 3D instantaneous nucleation for higher concentration. The morphology of the BixTey films is strongly depending to the electrolytes composition. The X-ray diffraction characterization shows that the crystalline structure of bismuth tellurium BixTey produced is of the rhombohedral type.