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LPEM seminar : Raja Sen, Thursday November 23 at 2:00 pm (Paris time)}
ESPCI, Room Boreau, building C
Study and engineer the coupled dynamics of electrons and phonons in semiconductors at transient and equilibrium regimes : A first-principles approach
In this seminar, I will shed light on the crucial role played by the coupled dynamics between electrons and phonons in influencing the transport properties of semiconductors and, consequently, the efficiency of the associated energy-harvesting devices. When subjected to a temperature gradient and/or an electric field, the electric and heat currents experience a mutual drag on each other via electron-phonon interactions, which, in turn, control the transport coefficients of materials. For instance, the phonon-drag effect, a phenomenon where electrons are dragged from the hot to the cold side of a sample by out-of-equilibrium phonons, leads to significant enhancement of the Seebeck coefficient of some materials and, therefore, presents a potential interest for thermoelectric devices.
However, given the impossibility of experimentally quantifying the contribution of phonon-drag to the total Seebeck coefficient, the role of phonon-drag in semiconductor nanostructures at room temperature, including silicon, remains a subject of debate, with a commonly held view suggesting its limited impact on the nanoscale due to increased phonon-boundary scatterings. In the first part of my presentation, I will discuss the theoretical results of our systematic study examining how dimensionality, size reduction, and heat transport direction influence the phonon-drag contribution to the Seebeck coefficient of silicon nanostructures [1].
In the final part of my talk, I will share a glimpse of our ongoing research work, which aims to develop an efficient ab initio approach to find the time-dependent solution of the Boltzmann transport equation with DFT-calculated electron-phonon scattering probabilities, for exploring the dynamics of excited electrons in semiconductors at the transient regimes [2].
References :
[1] R. Sen, N. Vast, and J. Sjakste, Phys. Rev. B (Letter) 108, L060301 (2023) [Editors’ Suggestion].
[2] R.Sen, N. Vast, and J. Sjakste, Appl. Phys. Lett. 120, 082101 (2022).
