Showing papers by "Daryoosh Vashaee published in 2005"
TL;DR: In this article, composite epitaxial materials that consist of semimetallic ErAs nanoparticles embedded in a semiconducting In0.53Ga0.47As matrix were grown as superlattices and randomly distributed throughout the matrix.
Abstract: We have grown composite epitaxial materials that consist of semimetallic ErAs nanoparticles embedded in a semiconducting In0.53Ga0.47As matrix both as superlattices and randomly distributed throughout the matrix. The presence of these particles increases the free electron concentration in the material while providing scattering centers for phonons. We measure electron concentration, mobility, and Seebeck coefficient of these materials and discuss their potential for use in thermoelectric power generators.
134 citations
TL;DR: In this article, the model and optimization of bulk SiGe thin-film coolers are described, and important parameters in the design of such cooling systems are investigated theoretically and compared with experimental data.
Abstract: Modeling and optimization of bulk SiGe thin-film coolers are described. Thin-film coolers can provide large cooling power densities compared to commercial thermoelectrics. Thin-film SiGe coolers have been demonstrated with maximum cooling of 4°C at room temperature and with cooling power density exceeding 500 W/cm2. Important parameters in the design of such coolers are investigated theoretically and are compared with experimental data. Thermoelectric cooling, joule heating, and heat conduction are included in the model as well as non-ideal effects such as contact resistance, geometrical effects, and three-dimensional thermal and electrical spreading resistance of the substrate. Simulations exhibit good agreement with experimental results for bulk Si and SiGe thin-film coolers. It turned out that in many spot cooling applications using two n- and p-elements electrically in series and thermally in parallel does not give significant improvement over single leg elements. This is in contrast to conve...
31 citations
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TL;DR: In this paper, the authors explore electron filtering as a technique to increase Seebeck coefficient and the thermoelectric power factor of heterostructured materials over that of the bulk.
Abstract: In this letter, we explore electron filtering as a technique to increase Seebeck coefficient and the thermoelectric power factor of heterostructured materials over that of the bulk. We present a theoretical model in which Seebeck coefficient and the power factor can be increased in an InGaAs based composite material. Experimental measurements of the cross-plane Seebeck coefficient are presented and confirm the importance of the electron filtering technique to decouple the electrical conductivity and Seebeck coefficient to increase the thermoelectric power factor.
14 citations
TL;DR: In this article, a brief overview of the research activities at the Thermionic Energy Conversion (TEC) Center is given, where 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.
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 current-voltage 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.
2 citations