Einfluß von Strukturstörungen auf die optischen und elektronischen Eigenschaften von borreichen Festkörpern mit Ikosaederstruktur

Boron and boron rich solids are known to have a high concentration on intrinsic structural imperfections. From known structure data of real crystals and known band structure calculations of perfect ideal crystals a correlation between intrinsic structure defect concentration and electron deficit in the valence band is concluded. This correlation forms the basis for the following theses: 1. The electron deficit in the valence band of a perfect crystal is the driving force for the intrinsic structure defects in a real crystal. 2. The small electron deficit becomes compensated by the structure defects - this explains the semiconducting behavior. 3. The structure defects are the reason for the high density of localized electronic states in the band gap. The photoluminescence of beta-rhombohedral boron in the range 0.75eV to 1.4eV under interband excitation was investigated systematically and was interpreted using the one-dimensional Franck-Conden-Model. The only partially occupied B13-position in beta-rhombohedra l boron is suggested to be the reason for the localized electronic state, which is involved in the photoluminescence process. Together with an investigation of the time-depending photoconductivity under interband excitation the energy band schema of beta-rhombohedral boron is improved. The improved energy band schema is able to explain all known experimental data including the fatiguing of photoluminescence. An investigation of FIR-spectra of boron carbide and metal doped beta-rhombohedral boron by Kramers-Kronig-Analysis gives information on the main transport processes. Beside hopping conduction of localized electrons, band conduction of delocalized electrons were found. While holes in the valence band are the delocalized charge carriers in boron carbide, in vanadium doped beta-rhombohedral boron delocalized electrons in an extrinsic impurity band are suggested


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