Dresden 2011 – scientific programme
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DS: Fachverband Dünne Schichten
DS 59: Thermoelectric Materials, Thin Films, and Nanostructures I (Focused Session -- Organisers: Nielsch, Rastelli, Balke)
DS 59.4: Topical Talk
Friday, March 18, 2011, 12:30–13:00, GER 37
Theoretical studies of electrical cross-plane transport in semiconductor multilayer heterostructures — •Peter Kratzer1 and Vladimir M. Fomin2 — 1Faculty of Physics and CeNIDE, University Duisburg-Essen, 47048 Duisburg, Germany — 2Institute for Integrative Nanosciences, IFW Dresden, 01069 Dresden, Germany
Using epitaxially grown multilayer heterostructures, it has been demonstrated experimentally that low lattice thermal conductivity κph can be realized in crystalline samples made from standard semiconductors. In particular, built-in self-assembled quantum dot (QD) stacks offer the possibility to affect both the thermal and the electrical cross-plane transport in a way favorable for thermoelectrics. In this talk, we employ Boltzmann transport theory to explore the role of the electronic structure for further enhancement of the figure of merit Z by increasing its numerator σ S2. For a stack of quantum dots separated by nanometer-thin spacer layers, miniband transport may be used to realize an electronic transport regime with large σ S2 but still low κel. The geometry-dependent miniband dispersion is obtained from atomistic calculations of the electronic structure of QD arrays. Moreover, due to different quantum states available for scattering, the mean free path of carriers in low-dimensional transport differs strongly from bulk transport. Interesting effects are to be expected if the layer thickness in the structures is reduced below the mean free path. As one example, we predict values of ZT > 2 at room temperature for an array of InAs QDs in GaAs for suitably chosen geometry and doping level [Phys. Rev. B 82, 045318 (2010)].