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 Bi_2+xTe_3-x solid solution have been prepared from E = -200 to +80mV (versus Ag/AgCl). The films prepared at +20 ≤ E ≤ +60mV exhibit strong {1 1 0} orientation, while those prepared at +60 < E ≤ +80mV show remarkable {1 0 5} orientation. Both the a-axis and c-axis lengths are almost independent of the cathodic potential for E < -100mV. Above -100mV, the a-axis length gradually decreases and the c-axis length increases with cathodic potential, implying the Bi concentration in the Bi_2+xTe_3-x solid solution moves from the stoichiometric value. The films prepared at E < +20mV show p-type conduction, while those prepared at +20 ≤ E ≤ +80mV show n-type conduction. The largest Seebeck coefficient, S = -63 μVK^-1 (300 K), has been observed for the film deposited at E = +20mV.