Electrochemical Deposition of (Bi,Sb) 2 Te 3 for Thermoelectric Microdevices
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Electrochemical Deposition of (Bi,Sb)2Te 3 for Thermoelectric Microdevices Jean-Pierre Fleurial, Jennifer A. Herman, G. Jeffrey Snyder, Margaret A. Ryan, Alexander Borshchevsky, and Chen-Kuo Huang Jet Propulsion Laboratory/California Institute of Technology 4800 Oak Grove Drive Pasadena, CA 91109, USA
ABSTRACT New experimental methods have been developed to electrochemically deposit p-type Sbrich Bi2-xSbxTe3, Pb-doped and Bi-doped Bi 2Te3, and PbTe thick films. Some of the deposited films were dense and had a smooth surface morphology. These films were deposited potentiostatically at room temperature in an acidic aqueous electrolyte. Experimental deposition of Bi 2Te3 alloys into various thick nanoporous templates made out of anodized alumina has also been achieved. Miniaturized thermoelements for microdevices (25 µm tall, 60 µm diameter) were grown by plating through thick photoresist templates. The experimental techniques developed, as well as the transport properties of some of the films and filled templates, will be presented. INTRODUCTION Electrochemical deposition (ECD) is a promising alternative technique to bulk synthesis for fabrication of thermoelectric microdevices. It is a simple, inexpensive, fast and safe technique, in which compounds are deposited on a substrate using an electrolyte and controlled current or potential. Deposition parameters determine the film composition, growth rate and morphology. Electrochemical deposition is a well-known technique for growth of metals, but is a relatively new method for growth of semiconductors [1]; nevertheless, it holds great promise for the fabrication of miniaturized thermoelectric elements and devices [2]. Our interests focus on n-type and p-type Bi2-xSbxTe3 materials as well as other known compounds such as PbTe, Zn4Sb3 and CoSb3. We have previously reported the successful development of ECD techniques for the growth of n-type Bi2Te3 and p-type Bi2-xSbxTe3 [3]. However, p-type films with thicknesses greater than 5 µm typically possess a rough morphology unsuitable for application to devices. This paper briefly reports progress in optimizing ECD experimental conditions to grow smooth p-type Bi2-xSbxTe3 films, the growth of microelements and nanostructures using templates, and the fabrication of complete thermoelectric devices using a combination of electrochemical deposition and integrated circuit techniques.
Z11.3.1 Downloaded from https:/www.cambridge.org/core. Cornell University Library, on 21 May 2017 at 21:06:07, subject to the Cambridge Core terms of use, available at https:/www.cambridge.org/core/terms. https://doi.org/10.1557/PROC-626-Z11.3
ELECTRODEPOSITION OF Bi2-xSb xTe 3 THERMOELECTRIC FILMS Experimental Method All experiments were run in a three electrode configuration (Pt counter electrode, Pt or Au working electrode and a Standard Calomel Electrode reference) using an EG&G Princeton Potentiostat/Galvanostat 273A. The standard electrolytes contained millimolar amounts of oxidized high purity elements, salts or chelating agents in aqueous 1 M
