Solid-State and Vacuum Thermionic Energy Conversion
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0886-F07-01.1
Solid-State and Vacuum Thermionic Energy Conversion A. Shakouri, Z. Bian, R. Singh, Y. Zhang, D. Vashaee, T. E. Humphrey and H. Schmidt Baskin School of Engineering University of California at Santa Cruz J. M. Zide, G. Zeng, J-H. Bahk, A. C. Gossard and J. E. Bowers Materials Department, Electrical and Computer Engineering University of California at Santa Barbara V. Rawat and T. D. Sands Materials Engineering, Electrical and Computer Engineering Purdue University W. Kim, S. Singer and A. Majumdar Mechanical Engineering Department University of California at Berkeley P. M. Mayer and R. J. Ram Research Laboratory of Electronics Massachusetts Institute of Technology K. J. Russel and V. Narayanamurti Division of Engineering and Applied Sciences Harvard University F.A.M. Koeck, X. Li, J.-S. Park, J.R. Smith, G.L. Bilbro, R.F. Davis, Z. Sitar, R.J. Nemanich Departments of Physics, Materials Science and Engineering and Electrical and Computer Eng. North Carolina State University
ABSTRACT A brief overview of the research activities at the Thermionic Energy Conversion (TEC) Center is given. The goal is to achieve direct thermal to electric energy conversion with >20% efficiency and >1W/cm2 power density at a hot side temperature of 300-650C. Thermionic emission in both vacuum and solid-state devices is investigated. In the case of solid-state devices, hot electron filtering using heterostructure barriers is used to increase the thermoelectric power factor. In order to study electron transport above the barriers and lateral momentum conservation in thermionic emission process, the currentvoltage characteristic of ballistic transistor structures is investigated. Embedded ErAs nanoparticles and metal/semiconductor multilayers are used to reduce the lattice thermal conductivity. Cross-plane thermoelectric properties and the effective ZT of the thin film are analyzed using the transient Harman technique. Integrated circuit fabrication techniques are used to transfer the n- and p-type thin films on AlN substrates and make power generation modules with hundreds of thin film elements. For vacuum devices, nitrogen-doped diamond and carbon nanotubes are studied for emitters. Sb-doped highly oriented diamond and low electron affinity AlGaN are investigated for collectors. Work functions below 1.6eV and vacuum thermionic power generation at temperatures below 700C have been demonstrated.
0886-F07-01.2
INTRODUCTION Direct thermal to electrical energy conversion systems that could operate at lower temperatures (300-650C) with high efficiencies (>15-20%) provide an attractive compact alternative to internal combustion engines for many applications in the W-MW range. They will also expand the possibilities for waste heat recovery applications. The Thermionic Energy Conversion Center’s goal is to design, fabricate, and characterize direct energy conversion systems that meet the above requirements. The core of the solution is an integrated approach to engineer electrical and thermal properties of nanostructured materials a
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