Showing papers by "Gehong Zeng published in 2007"
TL;DR: In this article, the cross-plane and in-plane Seebeck coefficients for ErAs:InGaAs∕InGaAlAs superlattices with different carrier concentrations using test patterns integrated with microheaters were characterized.
Abstract: We characterize cross-plane and in-plane Seebeck coefficients for ErAs:InGaAs∕InGaAlAs superlattices with different carrier concentrations using test patterns integrated with microheaters. The microheater creates a local temperature difference, and the cross-plane Seebeck coefficients of the superlattices are determined by a combination of experimental measurements and finite element simulations. The cross-plane Seebeck coefficients are compared to the in-plane Seebeck coefficients and a significant increase in the cross-plane Seebeck coefficient over the in-plane Seebeck coefficient is observed. Differences between cross-plane and in-plane Seebeck coefficients decrease as the carrier concentration increases, which is indicative of heterostructure thermionic emission in the cross-plane direction.
65 citations
TL;DR: In this article, the Boltzmann transport equation is solved self-consistently to include the effect of charge transfer and band bending in the potential profile of superlattices.
Abstract: Low dimensional and nanostructured materials have shown great potential to achieve much higher thermoelectric figure of merits than their bulk counterparts. Here, we study the thermoelectric properties of superlattices in the cross-plane direction using the Boltzmann transport equation and taking into account multiple minibands. Poisson equation is solved self-consistently to include the effect of charge transfer and band bending in the potential profile. The model is verified with the experimental data of cross-plane Seebeck coefficient for a superlattice structure with different doping concentrations. The simulations show that thermoelectric properties of superlattices are quite different from those of bulk materials because the electronic band structure is modified by the periodic potential. The Lorenz numbers of superlattices are surprisingly large at low carrier concentrations and deviate far away from the Wiedemann-Franz law for bulk materials. Under some conditions, the Lorenz number could be reduced by 50% compared to the bulk value. Most significantly, the Seebeck coefficient and the Lorenz number of superlattices do not change monotonically with doping concentration. An oscillatory behavior is observed. The effects of temperature and well and barrier thicknesses on the cross-plane Seebeck coefficient and Lorenz number are also investigated.
64 citations
TL;DR: In this article, a wafer scale approach for the fabrication of 400 element power generator modules composed of 200 n-type ErAs (InGaAs) 0.8(InAlAs)0.2 and 200 p-type InGaAs alloy thermoelectric elements was described.
Abstract: We report a wafer scale approach for the fabrication of 400 element power generator modules composed of 200 n-type ErAs:(InGaAs)0.8(InAlAs)0.2 and 200 p-type ErAs:InGaAs alloy thermoelectric elements. The thermoelectric properties of the materials were characterized. Two sets of generator modules with the element thicknesses of 20 and 10μm, respectively, were fabricated. The 20μm module had an output power density of 2.5W∕cm2 and 3.5V open circuit voltages, and the 10μm generator modules had an output power density of 1.12W∕cm2 and open circuit voltage of 2.1V. The performance of thermoelectric generator modules can further be improved by increasing the thicknesses of the elements and reducing the electrical and thermal parasitic resistances.
37 citations
01 Jan 2007
TL;DR: In this paper, a thermoelectric module of 200 N-P pairs of InGaAlAs with embedded ErAs metallic nanoparticles has been fabricated, and the combination of this new representation of the dynamic behavior of the packaged device with high resolution thin film temperature measurement allows us to obtain information about heat transfer within the module.
Abstract: Embedded metallic nanoparticles in semiconductors have recently been proven to be of great interest for thermoelectric applications. These metallic nanoparticles play the role of scattering centers for phonons and a source of doping for electrons; they reduce simultaneously the thermal conductivity and increase the thermoelectric power factor of the semiconductor. It has also shown that metal/semiconductor heterostructures can be used to break the crystal momentum symmetry for hot electrons in thermionic devices, then increasing the number of electrons participating in transport. A thermoelectric module of 200 N-P pairs of InGaAlAs with embedded ErAs metallic nanoparticles has been fabricated. Network Identification by Deconvolution (NID) technique is then applied for transient thermal characterization of this thermoelectric module. The combination of this new representation of the dynamic behavior of the packaged device with high resolution thin film temperature measurement allows us to obtain information about heat transfer within the thermoelectric module. This is used to extract the thermal resistances and heat capacitances of the module.Copyright © 2007 by ASME
TL;DR: In this paper, the fabrication and characterization of segmented element power generator modules of 254 thermoelectric elements was reported, where Erbium arsenide metallic nanoparticles are incorporated to create scattering centers for middle and long wavelength phonons, provide charge carriers and form local Schottky barriers for electron filtering.
Abstract: We report the fabrication and characterization of segmented element power generator modules of 254 thermoelectric elements. The element is 1 mm × 1 mm in area, which consists of 300 µm thickness Bi 2 Te 3 and 50 µm thickness ErAs:(InGaAs) 1-x (InAlAs) x , so that each segment can work at different temperature ranges. Erbium arsenide metallic nanoparticles are incorporated to create scattering centers for middle and long wavelength phonons, provide charge carriers, and form local Schottky barriers for electron filtering. The thermoelectric properties of ErAs:InGaAlAs were characterized by variable temperature measurements of thermal conductivity, electrical conductivity and Seebeck coefficient from 300 K to 600 K. Generator modules of Bi 2 Te 3 and ErAs:InGaAlAs segmented elements were fabricated and an output power over 5.5 W was measured. The performance of the thermoelectric generator modules can further be improved by improving the thermoelectric properties of the element material, and reducing the electrical and thermal parasitic losses.