Berlin 2012 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 98: Electronic Structure Theory

HL 98.10: Talk

Friday, March 30, 2012, 12:00–12:15, EW 202

Confinement effects on the vibrational properties of colloidal quantum dots — •Peng Han and Gabriel Bester — Max-Planck-Institut fuer Festkoerperforschung, Heisenbergstrasse 1, 70569 Stuttgart, Germany

Vibrational properties of colloidal III-V and II-VI quantum dots with thousand atoms are studied using first-principle density-functional theory (DFT) calculation. We describe the connection between the vibrational properties (including surface acoustic/optical modes, coherent acoustic modes, blue shifts for small radii and red shifts for large radii) and the structural changes induced by the surface. We can clearly ascribe most of these observations to the large relaxation of the clusters dominated by an inward relaxation of the surface penetrating deep inside the cluster of III-Vs and large distribution of bond length at the surface of II-VIs. These strong confinement effects tend to disappear for clusters with more than thousand atoms, where a small red shift of the Raman peak remains, due to a softening in response to undercoordination. The coherent acoustic modes, which have been viewed as the main cause for the bright-dark transition in the fine-structure splitting of quantum dots, are identified by our DFT calculation and found to agree well with the results from the Lamb model and experiment.