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Thermal engineering in an epitaxial nanostructured germanium semiconductor

Lundi 16 novembre 2015 14:00 - Duree : 2 heures
Lieu : Salle des séminaires - bât A - Campus CNRS, 25 rue des martyrs - 38000 Grenoble

Orateur : Soutenance de Thèse de Yanqing LIU (Institut Néel - CNRS)

For the development of thermal engineering in semiconductor (SC) based devices, the requirement of new materials under the idea of "electron crystal - phonon glass" model stays always a great challenge. In this work, a new germanium based SC model has been studied and experimentally characterized regarding its thermal conductivity for thermal engineering. The materials are thin films of an epitaxial germanium matrix embedded with randomly distributed Ge3Mn5 nano-inclusions (5-50 nm in diameter), grown on a Germanium-on-insulator (GOI) substrate. The Ge matrix is demonstrated to be highly single-crystalline doped p-type by manganese atoms. TEM characterizations revealed that the nano-inclusions are nearly spherical and their geometries and diameter distributions are tunable depending on the growth parameters in molecular beam epitaxy, i.e. the Mn concentration and the annealing temperature.

The thermal conductivities of the Ge:Mn thin films have been measured using both a highly sensitive technique based on the 3-omega method, and the scanning thermal microscopy (SThM). The measurement results revealed dramatically reduced thermal conductivities (compared to Ge bulk), 3-15 Wm−1K−1, for Ge:Mn thin films containing different Mn% (6%-14%) at room temperature. The minimum value of 3.3 Wm−1K−1 for Ge:Mn thin film containing 10% Mn was found to have beaten the “alloy limit” of thermal conductivity set by Si1-xGex at room temperature (6 Wm−1K−1). The low thermal conductivities for all Ge:Mn/GOI samples have also been confirmed by SThM results. These remarkable results have demonstrated the significant effects of the nano-inclusions on the phonon transport in the crystalline Ge matrix. Numerical simulations based on Boltzmann transport equation have been performed, and different models have been tried. Further modeling work will be continued to try to achieve a fully interpretation of the experimental results on these Ge:Mn thin films, and to understand the understand the phonon scattering mechanisms in this nano-structured SC material.

Contact : yanqing.liu@neel.cnrs.fr

Discipline évènement : (Physique)
Entité organisatrice : (Institut Néel)
Nature évènement : (Soutenance de thèse)
Site de l'évènement : Polygone scientifique

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