Berlin 2008 – wissenschaftliches Programm
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HL: Fachverband Halbleiterphysik
HL 31: Poster II
HL 31.50: Poster
Dienstag, 26. Februar 2008, 16:30–19:00, Poster D
Theoretical investigations of the photoluminescence from Si nanocrystals — •Davoud Pouladsaz1, Michael Schreiber1, and Reinhard Scholz2 — 1Institut für Physik, Technische Universität Chemnitz — 2Walter Schottky Institut, Technische Universität München
The photoluminescence (PL) of H-passivated tetrahedral silicon nanocrystals up to a diameter of 2.5 nm has been investigated by optimizing the geometries in the electronic ground state and in the relaxed excited state with density functional theory (DFT) and time-dependent DFT, respectively. In the excited state, the modified occupation numbers of the frontier orbitals define an anisotropic change of the electronic charge density, so that the deformation in the relaxed excited state consists of a symmetry conserving part and a tetragonal distortion. From a comparison of our calculations with measured PL bands obtained on clusters with known size distribution, we find an agreement of the PL energies within better than 0.2 eV. Moreover, our calculated PL lineshapes give clear evidence that the large linewidth of the PL band is an intrinsic property of each individual cluster, not the result of an average over an ensemble of different cluster geometries. In the relaxed excited geometries, some low-frequency e-symmetric vibrations are elongated so strongly that their broad Poisson progression inhibits the observation of distinct vibronic subbands of modes at high frequencies.