Energy consumption in our society is increasing rapidly. A significant fraction of the energy is lost in the form of heat. In this talk we introduce solid-state thermionic/ thermoelectric devices that allow direct conversion of heat into electricity. Novel metal-semiconductor nanocomposites are developed where the heat and charge transport are modified at the atomic level. Theory and experiment are compared for the case of rare-earth nanoparticles in a semiconductor matrix as well as in nitride metal/semiconductor multilayer films. High thermoelectric figure-of-merit >1 is achieved. Potential to reach energy conversion efficiencies exceeding 20% is discussed. We also describe how similar principles can be used to internally cool semiconductor lasers and to make micro refrigerators on a chip with cooling power densities exceeding 500W/cm2. The transition between diffusive thermoelectric and ballistic thermionic transport is studied using Monte Carlo simulations. Calculations show that non-linear Peltier and Seebeck effects can be observed in thin film samples and that they have the potential to improve the cryogenic solid-state cooling substantially. Finally, the fundamental Carnot limit for energy conversion efficiency and its, sometimes, inappropriate application to nanoscale devices will be discussed.
Ali Shakouri is a professor of electrical engineering at University of California Santa Cruz. He received his Ph.D. from California Institute of Technology in 1995. His current research is on nanoscale heat and current transport in semiconductor devices, high resolution thermal imaging, micro refrigerators on a chip and waste heat recovery. He is also working on a new sustainability curriculum in collaboration with colleagues in engineering and social sciences. He has initiated an international summer school on renewable energy sources in practice. He is the director of the Thermionic Energy Conversion center, a multi university research collaboration aiming to improve direct thermal to electric energy conversion technologies. He is the author or co-author of more than 200 journal and conference papers. He received the Packard Fellowship in Science and Engineering in 1999, the NSF CAREER award in 2000 and the UCSC School of Engineering FIRST Professor Award in 2004.