Investigation of the Properties of Electrochemically Deposited Semiconductor Materials for Thermoelectric Applications
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Investigation of the Properties of Electrochemically Deposited Semiconductor Materials for Thermoelectric Applications C.-K. Huang, J.A. Herman, N. Myung, J. R. Lim and J.-P. Fleurial, Jet Propulsion Laboratory/California Institute of Technology 4800 Oak Grove Drive, Pasadena, CA 91109 USA [email protected] ABSTRACT At JPL, it is our desire to fabricate thermoelectric micro-devices for power generation and cooling applications using an electrochemical deposition (ECD) technique. We believe that the performance of our current micro-device developed is limited by the properties of the ECD materials. Therefore, the objective of this study is to develop ECD methods for obtaining n-type Bi2Te3 and p-type Bi2-xSbxTe3 thermoelectric materials with near bulk properties, as well as optimizing morphology and transport properties. The films of Bi2Te3 and Bi2-xSbxTe3 were initially obtained under various ECD conditions. Seebeck coefficients and transport properties were then measured along the direction parallel to the substrates before and after annealing at 250oC for 2hrs. From the data obtained, ECD n-Bi2Te3 material can achieve a high Seebeck coefficient (-189 µV/K) when it is deposited at –200 mV vs. SCE. The in-plane resistivity, in-plane mobility, and carrier concentration are 3.0 mohm-cm , 31 cm2 V-1 S-1, and 6.79 x 1019 cm-3, respectively. As for the p-type Bi2-xSbxTe3, it is possible to achieve a high Seebeck coefficient (+295 µV/K) when it is deposited at 0.3 mA/cm2. The in-plane resistivity, in-plane mobility, and carrier concentration are 9.8374 mohm-cm, 66.58 cm2 V-1 S-1, and 9.54 x 1018 cm-3, respectively. From the results of our preliminary study, we have found the conditions for depositing high quality Bi2Te3 and Bi2-xSbxTe3 materials with thermoelectric properties comparable to those of their state-of-the-art bulk samples. INTRODUCTION Advances in the microelectronics industry have made it possible to miniaturize components and devices. With the miniaturization of electronic devices, there has also been a tremendous focus on developing miniaturized power conversion and thermal management systems [1,2]. For example, in the optoelectronics industry, thermal management is a significant factor in optimizing device performance. Thermoelectric devices make use of the Seebeck effect for power generation and can also utilize the Peltier effect for active cooling [3]. A thermoelectric module generally consists of several n- and p-type leg elements connected in series electrically and in parallel thermally. Thermoelectric microdevices can convert rejected or waste heat into usable electric power, at moderate (200-500K) temperatures and often with small temperature differentials. For the temperature range of 200-500K, alloys based on n-type Bi2Te3 and p-type Bi2-xSbxTe3 are the best materials for numerous applications. These materials can also be used as the basic materials for electronic and sensor building of nanowires and nanotubes. At the Jet Propulsion Laboratory (JPL), we are currently studying t
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