Preparation of Bi2Te3 films by electrodeposition

Bismuth telluride films have been electrochemically deposited from solutions of Bi2O3 and TeO2 in diluted HNO3 (pH = 0.50) onto Ti sheet working electrodes at 293 K. A conventional three-electrode cell was used with a platinum wire counter electrode and Ag/AgCl (saturated KCl) reference electrode. Single-phase films of Bi2+xTe3-x solid solution have been prepared from E = -200 to +80 mV (versus Ag/AgCl). The films prepared at +20 less than or equal to E less than or equal to +60 mV exhibit strong {1 1 0} orientation, while those prepared at +60 < E less than or equal to +80 mV show remarkable {1 0 5} orientation. Both the a-axis and c-axis lengths are almost independent of the cathodic potential for E < -100 mV. Above -100 mV, the a-axis length gradually decreases and the c-axis length increases with cathodic potential, implying the Bi concentration in the Bi2+xTe3-x solid solution moves from the stoichiometric value. The films prepared at E < +20 mV show p-type conduction, while those prepared at +20 less than or equal to E less than or equal to +80 mV show n-type conduction. The largest Seebeck coefficient, S = -63 mu VK-1 (300 K), has been observed for the film deposited at E = +20 mV. (C) 2001 Elsevier Science B.V. All rights reserved.