Thermoelectric Generators of Sequentially Deposited Si/Si+Ge Nano-layered Superlattices
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1181-DD02-04
Thermoelectric Generators of Sequentially Deposited Si/Si+Ge Nano-layered Superlattices C. Smith1, M. Pugh2, H. Martin2, R. Hill2, B. James2, S. Budak2, K. Heidary2, C. Muntele1, D. ILA1 1-Center for Irradiation of Materials, Alabama A&M University, Normal, AL USA 2-Department of Electrical Engineering, Alabama A&M University, Normal, AL USA
Abstract Effective thermoelectric materials have a low thermal conductivity and a high electrical conductivity. The performance of the thermoelectric materials and devices is shown by a dimensionless figure of merit, ZT = S2σ/ KTC, σ is the electrical conductivity T/ KTC, where S is the Seebeck coefficient, T is the absolute temperature and KTC is the thermal conductivity. In this study we have prepared the thermoelectric generator device of Si/Si+Ge multi-layer superlattice films using electron beam physical vapor deposition (EB-PVD). 5 MeV Si ion bombardment was performed in the multi-layer superlattice thin films to decrease the cross plane thermal conductivity, increase the cross plane Seebeck coefficient and cross plane electrical conductivity. Keywords: Ion bombardment, thermoelectric properties, multi-nanolayers, Figure of merit. *Corresponding author: C. Smith; Tel.: 256-372-5875; Fax: 256-372-5867; Email: [email protected] M. Pugh, R. Hill, B. James, H. Martin are 2008-2009 Senior Design Project Students in the Department of Electrical Engineering in Alabama A&M University. 1. Introduction The performance of a thermoelectric device is quantified by the dimensionless figure of merit ZT=S2σT/KTC. Our aim is to obtain high ZT values by increasing the Seebeck coefficient S and the electrical conductivity σ, and reducing the thermal conductivity KKTC by bombarding the structure with MeV Si ions. Ion bombardment induces the formation of quantum dots of Si and Ge. In addition to, the quantum well confinement of phonon transmission due to Bragg reflection at lattice interfaces [1,2] the defects and disorder in the lattice caused by ion bombardment and the grain boundaries of these nanoscale clusters increase phonon scattering and increase the chance of an inelastic interaction and phonon annihilation. All these effects inhibit heat transport perpendicular to the layer planes [4–7]. Thus, cross plane thermal conductivity will decrease. These quantum dot layers also increase the Seebeck coefficient and electric conductivity owing to the increase of the electronic density of states produced by the one dimensional periodic potential. We have already studied the improvement of thermoelectric properties for 10–
50 nm multilayers [8]. In this study we report on the growth of Si+Ge multi-layer superlattice films using co-electron beam physical vapor deposition (EB-PVD). Si and Ge materials were placed in separate electron guns and the shutters were manipulated to deposit the desired materials at the desired thickness. The deposition was followed by a 5 MeV Si ion bombardment at various fluences.
2. Sample preparation and characterization
Fig.1. Diagram of electrica
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