Berlin 2012 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 24: Poster Session: Ge/Si/SiC / III - V Semiconductors

HL 24.19: Poster

Montag, 26. März 2012, 16:00–19:00, Poster D

Isotopically modulated silicon and its thermoelectric properties — •Soizic Eon¹, Nadine Wehmeier¹, Hartmut Bracht¹, Georg Bastian², Arne Vogelsang², Saeed M. Ullah², Anton Plech³, Christian Heiliger⁴, and Dietrich Wolf⁵ — ¹WWU Münster — ²U Rhine-Waal — ³KIT Karlsruhe — ⁴U Giessen — ⁵U Duisburg-Essen

In order to use silicon (Si) for thermoelectric applications, it is necessary to increase the figure of merit ZT for example by decreasing the thermal conductivity. A promising approach is the use of isotopically modulated Si structures. Isotopically enriched Si multilayers were grown on natural Si substrates by means of molecular beam epitaxy. Homogeneously p- and n-type samples were fabricated and assembled to a thermoelectric module. Information about the thermal stability was gained by depth profiling before and after thermal treatments. The electrical conductivity was determined by Van de Pauw and current-voltage measurements after ohmic contact formation. Various methods were applied to determine the thermal conductivity of the multilayer structures. This includes measurements with time-domain thermoreflectance, time-resolved X-Ray scattering and the 3-ω-method. Our investigations reveal a reduced conductance due to phonon scattering at the isotopes interface while the electrical conductivity remains unchanged. Molecular dynamics and ab-initio calculations confirm a reduced thermal conductivity between Si layers of different isotopic composition. Further reduction is expected by optimizing the arrangement of the isotope layers and by an additional lateral confinement.