Regensburg 2007 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 31: Quantum dots and wires: Optical properties III
HL 31.10: Talk
Wednesday, March 28, 2007, 17:15–17:30, H17
Calculation of the vibronic progressions observed in the photoluminescence of Si nanocrystals — •Davoud Pouladsaz1,2 and Reinhard Scholz1 — 1Walter Schottky Institut, Technische UniversitätMünchen, Am Coulombwall 3, 85748 Garching — 2Institut für Physik, Technische UniversitätChemnitz, 09107 Chemnitz, Germany
The optical properties of H-passivated silicon nanocrystals are determined by the energetics of the frontier orbitals and their dependence on the deformation in the relaxed excited state. For tetrahedral nanocrystals up to a diameter of 1.5 nm, we have optimized 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. Therefore, the deformation in the relaxed excited state consists of a symmetry conserving part and of a symmetry-breaking distortion from Td towards D2d. The projection of these different parts of the deformation pattern onto the vibrational modes in the electronic ground state generates the vibronic progressions observed in photoluminescence (PL). The lineshapes obtained from this projection scheme are compared with available experimental data, resulting in similar PL energies and linewidths.