Regensburg 2004 – wissenschaftliches Programm
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HL: Halbleiterphysik
HL 36: Quantenpunkte und -dr
ähte: Optische Eigenschaften I
HL 36.1: Vortrag
Donnerstag, 11. März 2004, 10:15–10:30, H17
Structural Relaxation and the Optical Properties of Ge and Si Nanocrystals – ab initio Calculations — •Weißker Hans-Christian1, Giancarlo Cappellini2, Jürgen Furthmüller1, and Friedhelm Bechstedt1 — 1IFTO, Friedrich-Schiller-Universität Jena, Max-Wien-Platz 1, 07743 Jena — 2Universitá di Cagliari, Cittadella Universitaria, Strada Prov.le Monserrato-Sestu, Km 0.700, Italy
Though much effort has been put into the description of the properties of nanocrystals, ab initio calculations of such systems are still a demanding task. The ionic degrees of freedom, i.e., the structural relaxation, have only recently become amenable to ab initio methods for larger clusters because of the large computational requirements. The use of ultrasoft pseudopotentials and of the projector-augmented-wave method helps to alleviate this problem. Size-dependent electron-hole pair excitation energies calculated by means of a DSCF method are presented.
The ionic relaxation is a twofold problem. First, there is the technical problem of finding reasonable model structures for the crystallites. This involves the question of the influence of the ground-state structural relaxation on the desired quantities. For the optical properties, we demonstrate that a proper account of the relaxation effects is indispensable for the quantitative, and in some cases even the qualitative, description. The second problem is the structural relaxation after electronic excitation, which results in a contribution of a single nanocrystal to the Stokes shift measurable for an experimental sample. Model calculations of the Stokes shift are presented and discussed.