Thermal properties in semiconductors: first principles and phonon hydrodynamics
- Autores: Pol Torres
- Directores de la Tesis: Francesc Xavier Àlvarez Calafell (dir. tes.), Xavier Cartoixà Soler (codir. tes.)
- Lectura: En la Universitat Autònoma de Barcelona ( España ) en 2017
- Idioma: español
- Tribunal Calificador de la Tesis: David Jou i Mirabent (presid.), Riccardo Rurali (secret.), Konstantinos Termentzidis (voc.)
- Programa de doctorado: Programa de Doctorado en Física por la Universidad Autónoma de Barcelona
- Materias:
- Enlaces
- Tesis en acceso abierto en: TESEO
- Resumen
In this thesis, thermal transport is analyzed from the bulk to the nanoscale under different approaches using first principles. On one side, the bulk thermal conductivity is studied in the general kinetic-collective framework, where the Boltzmann Transport Equation (BTE) for phonons is solved under the Guyer and Krumhansl (GK) model and maximizing the entropy of the system. This solution is known as Kinetic Collective Model (KCM). On one side, the KCM, which splits the thermal conductivity into a kinetic and a collective contribution, has allowed obtaining the thermal conductivity of a large number of semiconductors, with excellent agreement to experimental results. On the other side, for reduced size samples, two approaches have been considered. In the first case, the GK boundary approach considers the boundaries as a microscopic scattering mechanism in the kinetic regime while in the collective contribution their effects are included from a hydrodynamic basis. The limitation of this approach for complex geometries has prompted the development of the second case: a full hydrodynamic thermal transport framework.
A hydrodynamic thermal transport equation has been developed based in the combination with the GK model and the Extended Irreversible Thermodynamics (EIT) framework and using a general hydrodynamic slip boundary condition. This has allowed to use the hydrodynamic KCM equation in finite elements calculations to study complex geometries.
Finally, an analysis of the phonon spectrum and its importance to deal with transient transport regimes is included.
Comparison of the KCM results with other current solutions concerting all the topics of the thesis are discussed.
Parallel to the development of the hydrodynamic model, the KCM expressions from the kinetic-collective boundary approach as well as hydrodynamic parameters have been implemented in an open source code. Sharing the model as a tool to predict thermal transport phenomena will allow bridging the physics of the heat transport from the microscopic to the macroscopic point of view.
