Berlin 2008 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 11: Time-Resolved Spectroscopy I
O 11.2: Vortrag
Montag, 25. Februar 2008, 13:45–14:00, MA 043
Combining density functional and density matrix theory: Optical excitation and electron relaxation at the Si(001) 2×1 surface — •Norbert Bücking1,3, Peter Kratzer2, Matthias Scheffler3, and Andreas Knorr1 — 1Institut für Theoretische Physik, Technische Universität Berlin, 10623 Berlin, Germany — 2Fachbereich Physik, 47048 Duisburg, Germany — 3Fritz-Haber-Institut der MPG, 14195 Berlin, Germany
A theoretical two-step approach to investigate the optical excitation and subsequent phonon-assisted relaxation dynamics at semiconductor surfaces is presented and applied to the Si (001) 2×1-surface: In the first step, the electronic band structure and the Kohn-Sham wave functions are calculated by density-functional-theory (DFT) within the LDA. In the second step, dynamical equations are derived from density-matrix theory (DMT), whereby an optical field is considered via A·p-coupling and phonon induced relaxation by a deformation potential coupling term. Into these equations, the numerical results of the DFT calculation (Kohn-Sham eigenvalues and wave functions) enter as coupling matrix elements. By numerically solving the dynamical equations, the time-resolved population of the excited states can be evaluated. The results for the Si (001) surface correspond to the findings of recent experiments, in particular a short (intra-surface-band scattering) and a long (bulk-surface band scattering) timescale are dominating the relaxation process. The value of the experimental short timescale is reproduced by our calculations, whereas the long timescale cannot be accurately described by our theory.