Regensburg 2013 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 16: Theory: Metal-insulator transitions / Electronic structure calculations
HL 16.4: Talk
Monday, March 11, 2013, 16:15–16:30, H13
Dynamical processes and temperature effects in semiconductor nanoclusters — Peng Han and •Gabriel Bester — Max-Planck-Institut für Festkörperforschung, Heisenbergstraße 1, 70569 Stuttgart, Germany.
Electron-phonon interactions in colloidal semiconductor quantum dots consisting of thousands of atoms are calculated using first principles density functional theory (DFT) and the frozen-phonon approach. In the computation, the electronic states and the change of the potentials caused by a phonon induced distortion of the lattice are self-consistently calculated using DFT; the electron-phonon interaction matrix elements are then obtained using perturbation theory. Using the electron-phonon coupling matrix elements obtained from this approach, we study the electronic relaxation processes in colloidal semiconductor nanoclusters (NCs) via the Liouville-von Neumann equation including a phenomenological Lindblad decay term. We observe a decaying Rabi oscillation with a period of tens of fs, corresponding to emission/absorption of a phonon, and with a decay rate that is dominated by the phonon lifetime. To estimate the phonon lifetime in NCs, we perform ab initio molecular dynamics simulations of a Si10H16 cluster and extract the time evolution of the energy of selected vibrational modes from the energy auto-correlation functions. We find vibrational cooling times of are around 1 ps for pure Si modes, which are close to the phonon lifetimes in bulk Si.