Berlin 2012 – wissenschaftliches Programm
Bereiche | Tage | Auswahl | Suche | Aktualisierungen | Downloads | Hilfe
DS: Fachverband Dünne Schichten
DS 33: Thermoelectric materials II: Reduced dimensionality (Focused session – Organizers: Meyer, Heiliger)
DS 33.1: Topical Talk
Donnerstag, 29. März 2012, 11:15–11:45, H 2032
Calculation of thermoelectric properties of nanostructured semiconductors — •Peter Kratzer and Gregor Fiedler — Fakultät für Physik and Center for Nanointegration (CeNIDE), Universität Duisburg-Essen, Duisburg, Germany
Epitaxial nanostructuring, e.g. in the form of superlattices, enables high figure of merit ZT even with perfectly crystalline samples of standard semiconductors. One decisive factor is the reduction of thermal conductivity, as demonstrated e.g. for an array of self-assembled SiGe quantum dots (QDs) in Si [Nature Materials 9, 491 (2010)]. Complementing these efforts, our work uses electronic structure + Boltzmann transport theory to explore the chances for increasing σ S2 in ZT.
We employ the tight-binding method to calculate the conduction-band states in an array of Ge QDs in Si. It is found that the strained Si between the QDs supports low-lying dispersive states, while the strongly compressed region between two vertically stacked QDs leads to a resonance in the conduction band. The consequences of the modified electronic structure for thermoelectric properties will be discussed.
In a more general framework, the role of transitions between bound and free states in a superlattice for the cross-plane transport relaxation time is investigated. If the mean free path of the phonons mediating these transitions exceeds the superlattice period, combined non-equilibrium effects of the electron and phonon system need to be considered. We predict an additional contribution to the thermopower that is similar to the phonon drag, but scales linearly with the number of superlattice periods and extends to higher temperatures.