Regensburg 2013 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 3: Focus Session: Electron-phonon interaction and ultrafast processes in semiconductors
HL 3.2: Talk
Monday, March 11, 2013, 10:00–10:15, H13
Zero-point motion and temperature effects on the band gap renormalization of semiconductor nanoclusters — Peng Han and •Gabriel Bester — Max-Planck-Institut für Festkörperforschung, Heisenbergstraße 1, 70569 Stuttgart, Germany.
Using the frozen-phonon approach based on ab initio density functional theory (DFT), we calculate the zero-point motion band gap renormalization and the temperature dependent of the band gap in semiconductor nanoclusters. Our method avoids the large computational costs (especially the slow convergence with respect to the number of unoccupied bands) associated with the calculation of the Fan- (self-energy-) and the Debye-Waller terms. A band gap reduction in silicon clusters with a magnitude of hundreds of meV induced by the quantum zero-point atomic motion is obtained; this quantum effect is found to increase with decreasing cluster size. Based on the Bose-Einstein distribution, we further study the temperature dependence of the band gap in semiconductor nanoclusters and find a reduction of 580 meV and 270 meV at room temperature for silicon clusters with radius of 9.6 and 11.9 Å, respectively. Furthermore, we find that the Si-H rotation and shear modes play an important role on the zero-point band gap renormalization of hydrogen passivated silicon clusters. By analyzing the mode dependence of the band gap reduction, we also see that the zero-point renormalization of the band gap is dominated by the optic-like vibrations with Γ4 point group symmetry.