Regensburg 2013 – scientific programme
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DS: Fachverband Dünne Schichten
DS 24: Thermoelectric Materials
DS 24.4: Talk
Wednesday, March 13, 2013, 15:30–15:45, H32
Thermal conductivity of SiGe-based nanostructures — •Katrin Bertram1, Bodo Fuhrmann1, Nadine Geyer2, Alexander Tonkikh2, Nicole Wollschläger2, Peter Werner2, and Hartmut S. Leipner1 — 1Interdisziplinäres Zentrum für Materialwissenschaften, Martin-Luther-Universität Halle- Wittenberg, 06120 Halle, Germany — 2Max Planck Institute of Microstructure Physics, Weinberg 2, 06120 Halle, Germany
A low thermal conductivity of thermoelectric materials is necessary to achieve enhanced figure of merits ZT for thermoelectric generators and Peltier coolers. Regarding theoretical predictions, nanostructured materials such as superlattices, quantumdot superlattices or nanowires, are able to show a higher figure of merit than bulk materials. The reduction of thermal conductivity in superlattices is achieved by diffuse interface scattering of the phonons at the interfaces. With a mismatch of the phonon dispersions the scattering of short-wavelength phonons is enhanced due to localized phonon states. Some theoretical work predicted a further decrease in thermal conductivity with nonperiodic superlattice structures. In this study, we have investigated the thermal conductivities of Si-Ge based superlattices. Periodic and nonperiodic Sim-Gen superlattices with stacks of m Si and n Ge layers of various thicknesses were grown by molecular beam epitaxy on (111) Si substrates. The influence of periodicity was investigated. Further investigations were done on nanowire arrays grown from these superlattices. A comparison between the different approaches for the reduction of thermal conductivity will be presented.