Novel mixed method for the electrochemical deposition of thick layers of Bi2+xTe3-x with controlled stoichiometry

A new method for the electrochemical deposition of Bi2+xTe3-x is presented, which combines voltage-controlled deposition pulses with current-controlled resting pulses. This method is based on results of a comprehensive electrochemical investigation including cyclic voltammetry, chronoamperometry and chronopotentiometry, which has been performed on the system Bi and Te on Pt in 2 M HNO3. The influence of electrolyte composition, deposition potential and deposition pulse duration on morphology and stoichiometry of the deposited material as well as the variation of the composition over the thickness of the layer has been investigated by means of SEM and EDX. The crystal structure was examined with XRD. Layers deposited with the new method show a constant and reproducible stoichiometry over their entire thickness. Layers of up to 800 mu m thickness deposited with deposition rates of up to 50 mu m/h have been achieved. The composition and hence the thermoelectric behavior may be adjusted via electrolyte composition or the deposition potential. Fabrication of n-type and, for the first time, p-type Bi2+xTe3-x is demonstrated and verified by measurements of the Seebeck coefficients. The suitability of the proposed method for low-cost fabrication of micro-thermoelectric devices is shown. The advantages of this method may also apply for electrochemical deposition of other binary or ternary compounds. (C) 2008 Elsevier Ltd. All rights reserved.