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Thermoelectric power factor divergence close to phase transition in Co-doped epitaxial pnictide thin films
TL;DR: In this article, the authors show that the Seebeck coefficient can diverge in the vicinity of the metal-to-superconductor phase transition in two-dimensional (2D) systems.
Abstract: The bottleneck in state-of-the-art thermoelectric power generation and cooling is the low performance of thermoelectric materials. The main difficulty is to obtain a large thermoelectric power factor as the Seebeck coefficient and the electrical conductivity cannot be increased independently. Here, relating the thermoelastic properties of the electron gas that performs the thermoelectric energy conversion, to its transport properties, we show that the power factor can diverge in the vicinity of the metal-to-superconductor phase transition in two-dimensional systems. We provide experimental evidence of the rapid increase of the Seebeck coefficient without decreasing the electrical conductivity in a 100-nm Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ thin film with high structural quality, as the sample temperature approaches the critical temperature, resulting in a power factor enhancement of approximately 300. This level of performance cannot be achieved in a system with low structural quality as shown experimentally with our sample degraded by ion bombardment as defects preclude the strong enhancement of the Seebeck coefficient near the phase transition. We also theoretically discuss the thermoelectric conversion efficiency for a wide-range of model systems, and show that driving the electronic system to the vicinity of a phase transition may be an innovative path towards performance increase at the possible cost of a narrow temperature range of use of such materials.
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01 Jun 2010-Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms
TL;DR: SRIM as discussed by the authors is a software package concerning the stopping of ion/atom collisions, and individual interatomic potentials have been included for all ion and atom collisions in the SRIM package.
Abstract: SRIM is a software package concerning the S topping and R ange of I ons in M atter. Since its introduction in 1985, major upgrades are made about every six years. Currently, more than 700 scientific citations are made to SRIM every year. For SRIM-2010 , the following major improvements have been made: (1) About 2800 new experimental stopping powers were added to the database, increasing it to over 28,000 stopping values. (2) Improved corrections were made for the stopping of ions in compounds. (3) New heavy ion stopping calculations have led to significant improvements on SRIM stopping accuracy. (4) A self-contained SRIM module has been included to allow SRIM stopping and range values to be controlled and read by other software applications. (5) Individual interatomic potentials have been included for all ion/atom collisions, and these potentials are now included in the SRIM package. A full catalog of stopping power plots can be downloaded at www.SRIM.org . Over 500 plots show the accuracy of the stopping and ranges produced by SRIM along with 27,000 experimental data points. References to the citations which reported the experimental data are included.
6,906 citations
TL;DR: In this article, the authors proposed to use quantum-well superlattice structures to enhance the performance of thermoelectric coolers and showed that layering has the potential to increase significantly the figure of merit of a highly anisotropic material.
Abstract: Currently the materials with the highest thermoelectric figure of merit Z are ${\mathrm{Bi}}_{2}$${\mathrm{Te}}_{3}$ alloys. Therefore these compounds are the best thermoelectric refrigeration elements. However, since the 1960s only slow progress has been made in enhancing Z, either in ${\mathrm{Bi}}_{2}$${\mathrm{Te}}_{3}$ alloys or in other thermoelectric materials. So far, the materials used in applications have all been in bulk form. In this paper, it is proposed that it may be possible to increase Z of certain materials by preparing them in quantum-well superlattice structures. Calculations have been done to investigate the potential for such an approach, and also to evaluate the effect of anisotropy on the figure of merit. The calculations show that layering has the potential to increase significantly the figure of merit of a highly anisotropic material such as ${\mathrm{Bi}}_{2}$${\mathrm{Te}}_{3}$, provided that the superlattice multilayers are made in a particular orientation. This result opens the possibility of using quantum-well superlattice structures to enhance the performance of thermoelectric coolers.
3,202 citations
TL;DR: A delta-shaped transport distribution is found to maximize the thermoelectric properties, indicating that a narrow distribution of the energy of the electrons participating in the transport process is needed for maximum thermoelectedric efficiency.
Abstract: What electronic structure provides the largest figure of merit for thermoelectric materials? To answer that question, we write the electrical conductivity, thermopower, and thermal conductivity as integrals of a single function, the transport distribution. Then we derive the mathematical function for the transport distribution, which gives the largest figure of merit. A delta-shaped transport distribution is found to maximize the thermoelectric properties. This result indicates that a narrow distribution of the energy of the electrons participating in the transport process is needed for maximum thermoelectric efficiency. Some possible realizations of this idea are discussed.
1,441 citations
IBM1
TL;DR: In this article, the electric field is associated only with space charge but not with a current, and approximate space charge neutrality is restored, by adding a particular solution of the transport equation in which the electric fields are associated with a specific dipole field about each scatterer.
Abstract: Localized scatterers can be expected to give rise to spatial variations in the electric field and in the current distribution. The transport equation allowing for spatial variations is solved by first considering the homogeneous transport equation which omits electric fields. The homogeneous solution gives the purely diffusive motion of current carriers and involves large space charges. The electric field is then found, and approximate space charge neutrality is restored, by adding a particular solution of the transport equation in which the electric field is associated only with space charge but not with a current. The presence of point scatterers leads to a dipole field about each scatterer. The spatial average of a number of these dipole fields is the same as that obtained by the usual approach which does not explicitly consider the spatial variation. Infinite plane obstacles with a reflection coefficient r are also considered. These produce a resistance proportional to r/(1-r).
1,265 citations
Book•
01 Jan 1990TL;DR: The fundamental principles of carrier transport in semiconductors and semiconductor devices are discussed in this article, which is an accessible introduction to the behavior of charged carriers in semiconductor and semiconductor devices.
Abstract: Fundamentals of Carrier Transport is an accessible introduction to the behaviour of charged carriers in semiconductors and semiconductor devices. It is written specifically for engineers and students without an extensive background in quantum mechanics and solid-state physics. This second edition contains many new and updated sections, including a completely new chapter on transport in ultrasmall devices. The author begins by covering a range of essential physical principles. He then goes on to cover both low- and high-field transport, scattering, transport in devices, and transport in mesoscopic systems. The use of Monte Carlo simulation methods is explained in detail. Many homework exercises are provided and there are a variety of worked examples. The book will be of great interest to graduate students of electrical engineering and applied physics. It will also be invaluable to practising engineers working on semiconductor device research and development.
1,172 citations