Characterization of Bi₂Te₃Thin Films Grown by Pulse Electroplating

Abstract

Abstract:The preparation of bismuth telluride deposits has been performed by galvanostatic pulsed electrolysis from nitric solutions on gold layer deposited on glass. The influence of the chemical conditions and pulsed parameters has been investigated on the stoichiometry and on thermoelectric behaviour for deposited and annealed films. The results demonstrated that improvements of the transport properties in bismuth telluride films can be generated by a pulsed electroplating mode. Boikov et al. [3], the lattice thermal conductivity of chalcogenide films is considerably lower than that of bulk crystals of similar compositions, leading to an increase of the figure of merit of films. Furthermore the current tendency towards miniaturization has increased the interest in micro-thermoelectric devices (sensors or generators). Electrochemical deposition (ECD) also opens up opportunities for thin film microsystems since this method is considerably simpler and cheaper than dry processes such as molecular-beam epitaxy, sputtering and metalorganic chemical vapor deposition. Moreover ECD allows growing of uniform films with a thickness ranging from the nanoscale to a few millimeters over large areas, on irregular shaped surfaces and compositionally modulated structures or non-equilibrium alloys. Electrodeposition has been successfully applied to the production of bismuth telluride binaries [4-10] Se-ternary [11], and Sb-ternary [12]. Recently, pulse current plating was investigated [13,14] in order to improve the morphology and properties of bismuth telluride electrodeposits. This process is known to have positive effects on mass transport, electrode kinetics and the nucleation of growth centres. Pulse plating also offers a larger number of parameters (i.e., on-time, off-time, cathodic-and anodic-pulse current density and frequency) than does direct current plating to improve deposit quality [15,16]. The present work concerns the characterization of bismuth telluride films synthesized by pulse electroplating. The evolution of roughness as a function of the stoichiometry was studied. Thermoelectric properties (Seebeck coefficient, resistivity) were measured and correlated to the stoichiometry of the films. Finally, the influence of the annealing on the physical properties was studied. All these results were compared to results obtained by direct electrodeposition in order to identify the influence of pulse electroplating.