Reduction of Parasitic Losses to Improve Quantum Well Efficiency

Huge renewable heat sources are continuously being generated but are not being used. For cars and trucks, two thirds of the gasoline consumed is converted to waste heat and thrown away. Within the basic materials industries (aluminum plants, steel mills, oil refineries, etc.), about the same amount of waste heat also is being generated and lost. Combined, the amount of waste heat is equivalent to 300-1,000 million barrels of oil/year. This project will develop a waste heat recovery technique, based on new, more efficient thermoelectric materials, in which quantum well (QW) layers, 100 Å thick, are deposited on a substrate. The research will focus on overcoming a parasitic heat leak problem associated with the substrate. In Phase I, the heat leak problem was separated into temperatures above and below 300oC, the temperature at which organic materials (such as Kapton) can no longer be used. Below 300oC, N and P type Si/SiGe QW films were deposited on Kapton. The N and P films were joined with the metal molybdenum, producing very low resistance contacts, and the power produced was very close to the anticipated values. Above 300oC, the Si/SiGe QW films were successfully deposited on a 25 µm thick SiGe substrate. The a, ¿, and ¿ parameters for the film show that QW behavior was obtained in the films, and a figure of merit (ZT) of 3 to 5 was obtained at room temperature. The plans for Phase II also differ for the two temperature regimes. Below 300oC, the deposition of the Si buffer coat and the QW films on Kapton will be improved, so that it can be scaled up to yield 15 ¿ 20% at ~ 300oC. Above 300oC, the promising SiGe buffer coat, deposited on mica or glass, will be evaluated with Si/SiGe, as well as with the high temperature QW films Si/SiC and B4C/B9C, for use up to 1000oC. At 800oC, an efficiency of ~ 40% is expected. Commercial Applications and other Benefits as described by the awardee: Vehicles fitted with the new waste heat recovery device should expect an increase in mileage by ~10%. In addition, the high temperature, basic materials industries should be able to recover appreciable waste heat when their processes are fitted with the QW thermoelectric generators. Other applications include geothermal wells. The total market could be in the range of a billion dollars per year