Exploring Si/SiGe quantum-well thin-film thermoelectric devices using TCAD simulation

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Title: Exploring Si/SiGe quantum-well thin-film thermoelectric devices using TCAD simulation
Author: Hu, Shaoting
Abstract: There is an increasing demand for energy as a result of industrial development and rapid growth in global population. To date, most energy supply comes from traditional sources like coal and gas, which are nonrenewable energy sources. The combustion of fossil fuels produces greenhouse gases and pollution, which deteriorates our ecosystem. Extensive attention and research has been given to the development of renewable energy sources, including solar, wind, tides, geothermal heat, hydroelectricity, thermoelectricity and <italic>et al<italic>. Thermoelectric (TE) applications can be categorized mainly into power generation and cooling operation utilizing Seebeck and Peltier effects, respectively. The further development of TE devices is limited by the low TEG efficiency and the low cooling coefficient of performance due to the limitation of the material figure of merit (<italic>ZT<italic>). In the 1990s, the advent of low dimensional (quantum well and quantum wire) thermoelectric systems triggered the breakthrough of improved <italic>ZT<italic> via two basic mechanisms: 1) increased density of states near Fermi level, and 2) deceased thermal conductivity by increased phonon scattering at material boundaries [1], [2]. Despite theoretical and experimental success using low dimensional TE systems reported by different universities or laboratories, the efficiency and coefficient of performance of commercially available bulk thermoelectric devices remain at a mere 5%-10%. The Silvaco Inc. device simulator (ATLAS) is used to explore the physics and evaluate the performance of quantum well TE devices on single crystalline silicon-on- glass (SiOG). Owing to the distinguish features of SiOG substrate, including lower thermal conductivity, microfabrication compatibility, good template for QW layers epitaxially grown atop, Corning Incorporated are especially interested in Si/SiGe quantum well thermoelectrical devices for automobile waste heat recovery application. In this thesis, model adjustments were implemented to calibrate bulk Si & SiGe parameters, and capture the electrical and thermal effects from quantum-sized dimensions. Design parameters, which optimize the thermal power and <italic>ZT<italic> for <italic>n<italic>- and <italic>p<italic>- type Si/SiGe QW structures were established. The electrical and thermal parasitic effects from SOI and SiOG to QW layers were studied. Moreover, equivalent circuit model was developed which demonstrates the performance advantage of SiOG as a low-loss substrate.
Record URI: http://hdl.handle.net/1850/15348
Date: 2012-05-22

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