Large Area Deposition of Si/SiC Quantum Well Films for Thermoelectric Generator Applications
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Large Area Deposition of Si/SiC Quantum Well Films for Thermoelectric Generator Applications
Tianhua Yu, Harry Efstathiadis, Richard Matyi, and Pradeep Haldar College of Nanoscale Science and Engineering, University at Albany – State University of New York, Albany, NY Saeid Ghamaty and Norbert Elsner Hi-Z Technology, Inc., San Diego, CA ABSTRACT Recent development in thermoelectric conversion, especially in the area of quantum well (QW) thin film materials, have demonstrated the potential to achieve the high efficiency and power density to fabricate future power supplies. In this study, we develop the large area QW films of N-type Si/SiC integrated with P-type B4C/B9C, which can be used as thermoelectric devices for waste heat recovery. The approach is to fabricate thick large area film stacks (up to 11 μm) deposited by sputter deposition technique on 6” n-type (100) silicon substrates, which might be proven to be a suitable method for potentially manufacturing large area thermoelectric devices in a cost effective manner. These more basic studies are being carried out to better understand variables such as film thickness, deposition rate and other important parameters of these ~10 nm films. The resulting as deposited and annealed multilayer stacks were characterized in terms of thin film uniformity, thickness, growth rate, composition, and thermoelectric performance, by Spectroreflectometry, atomic force microscopy (AFM), Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), X-ray reflectivity (XRR), and electrical measurements. Issues, which could cause film stack degradation, such as interface layer formation, film delamination, and crack formation lowering the device performance will be presented and correlated to device efficiency.
INTRODUCTION The recovery of waste heat from internal combustion engines, truck exhausts, furnaces, etc., requires high performance power-generating thermoelectric devices to meet the challenging cost goals. Advantages of thermoelectrics include reversible devices (changing between cooling and heating), no moving parts, environmental friendly materials (ceramics), long life time (exceed 100,000 hrs. of steady state operation), easy to control temperature (within fractions of a degree), and low cost for volume production devices. The cost is estimated to be for quantum well based devices about $0.20/Watt and bulk for Bi2Te3 about $1/Watt [1-3]. The efficiency of thermoelectric energy conversion devices is determined by the thermoelectric figure of merit Z, given by Z = S2σ/k, where σ is the electrical
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conductivity, k is the total thermal conductivity due to lattice (kL) and electronic (ke) contributions, and S is the Seebeck coefficient [2]. Increasing Z is the subject of intense research. Encouraging results have been achieved for thin film superlattice and quantum well structures [4-6]. In addition to quantum confinement, which becomes significant when the active layer thickness is below ~20 nm, improvement in Z may result from t
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