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HL: Halbleiterphysik

HL 6: Optische Eigenschaften

HL 6.1: Talk

Monday, March 26, 2001, 10:30–10:45, S9/10

Optical Properties of Nanocrystallites from ab initio Supercell Calculations — •Hans-Christian Weissker, Jürgen Furthmüller, and Friedhelm Bechstedt — IFTO, Friedrich–Schiller–Universität, Max–Wien–Platz 1, 07743 Jena

Spectral properties of nanocrystallites are described within Density Functional Theory (DFT) in Local Density Approximation (LDA) and by means of the Projector-Augmented Wave (PAW) Method. The dielectric function is calculated from transition matrix elements and band energies using a quadratically extrapolative tetrahedron method. First results of self–energy calculations within the GW approximation are also presented.
We study spherical Ge and Si nanocrystallites of 5 to 239 atoms embedded in cubic SiC as well as free, hydrogenated nanocrystallites to simulate embedding in a wide–gap semiconductor. The influence of the superzell size is considered. The localization, the overlap, and the occupation of dot–induced states give the information needed to determine the type of the respective heterostructures.

We investigate the interpretation of our results within different Effective Medium Approximations (EMA). The influence of the matrix material on the line shape and peak positions is discussed. The dielectric function is related to transmission spectra of Ge crystallites in Sapphire.