Electrical Contact Resistance of Electroless Nickel to Nanocrystalline Silicon and the Fabrication of a Thermoelectric G
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Electrical Contact Resistance of Electroless Nickel to Nanocrystalline Silicon and the Fabrication of a Thermoelectric Generator V. Kessler1, M. Dehnen1, R. Chavez1, M. Engenhorst1, J. Stoetzel1, N. Petermann1, K. Hesse2, T. Huelser3, M. Spree3, G. Schierning1 and R. Schmechel1 1
Faculty of Engineering and Center for Nanointegration Duisburg-Essen (CENIDE), University of Duisburg-Essen, 47057 Duisburg, Germany 2 GSI - Gesellschaft für Schweißtechnik International mbH, Niederlassung SLV Duisburg, 47057 Duisburg, Germany 3 Institute of Energy and Environmental Technology e.V. (IUTA), 47229 Duisburg, Germany ABSTRACT We present the fabrication of a high-temperature stable thermoelectric generator based on nanocrystalline silicon. Highly doped silicon nanoparticles were sintered by a current activated sintering technique to get nanocrystalline bulk silicon. The metalization of silicon was realized by (electro-)chemical plating and the specific electrical contact resistance ρc of the semiconductor-metal interface was measured by a transfer length method. Values as low as ρ C < 1⋅10 −6 Ωcm 2 were measured. The metalized nanocrystalline silicon legs were sintered to metalized ceramic substrates using a silver-based sinter paste. The device figure of merit of the thermoelectric generator was determined by a Harman measurement with a maximum ZT of approximately 0.13 at 600 °C. INTRODUCTION
Thermoelectric Generators (TEGs) are used for energy harvesting applications and, if actively powered, as cooling systems exploiting the Peltier effect. In order to achieve higher efficiencies of TEGs, it is not only important to improve the thermoelectric figure of merit
α 2σ zT = T κ
(1)
of the employed material, but also to successfully contact the material for device implementation purposes. Here, α is the Seebeck coefficient, σ the electrical conductivity, к the thermal conductivity and T the absolute temperature. Increasing zT can be achieved by many strategies [1,2], whereas a nanostructuring approach allows for partly decoupled optimization of the electrical and thermal conductivity, which has been done successfully for nanostructured bulk silicon [3,4]. Additional loss mechanisms, like the electrical and thermal contact resistance at the interfaces, will lower the overall efficiency with implementation of the material into a device. Therefore the device figure of merit ZT is distinguished from the material figure of merit zT. However, ZT can be conveniently measured by a Harman measurement [5], thus allowing an evaluation of the efficiency. In this study, we present the fabrication of a TEG based on nanostructured bulk silicon including thermoelectric characterization of the device and measurement of the specific electrical contact resistance at the semiconductor metal interface. Starting with a gas phase synthesis of
highly doped silicon nanoparticles, a subsequent current activated sintering yields bulk nanocrystalline silicon (nc-Si) with a density of > 97% of single crystalline silicon. Although silicon is known to show
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