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Fritz Kohlrausch Preis der Österreichischen Physikalischen Gesellschaft an Rinaldo Trotta

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Video Online: "Embedding a Single Quantum Dot into a Photonic Crystal Cavity"

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Artikel OÖNachrichten: "Rinaldo Trotta: Der 1,5-Millionen-Euro-Forscher"

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Our recent work (Nature Comm.7, 10375, 2016) on tunable entangled photons from QDs has been recently highlighted in the Laser Focus World magazine!

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Back Cover of Phys. Status Solidi A 3/2016

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Winner of Science Slam Linz and the Austrian Final in Vienna 2016: Martyna Grydlik!!!

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"Wenn es in der Physik funkt...", Artikel in der PRESSE

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Dr. DI Herbert Lichtenberger

PhD thesis:

"Kinetic and Strain-Induced Self-Organization of SiGe Heterostructures"

Abstract

A kinetic growth instability of silicon-germanium molecular beam epitaxy (SiGe-MBE) was used to generate periodic Si-ripple-templates. By increasing the substrate miscut to 4° the ripple period could be tuned to smaller periods towards the nanometer scale. At Si growth rates of 0.2Å/s a ripple pattern with few defects develops within a small temperature window around 425°C. For our vicinal Si(001) substrates with 4° miscut along [110] this step-bunching instability provides undulations of about 100nm periodicity and 4nm amplitude.

In the first part of this work several aspects of self-organized growth in the Si/SiGe system could be addressed. The special morphology of step-bunching was used to investigate the interplay between kinetics, surface energy and strain. The step-bunching templates provide a one-dimensional pattern with preferable nucleation sites for SiGe-islands along the ripple flanks, and thus allow us to combine kinetic and strain-driven self-organization phenomena in the Si/SiGe heterosystem. At moderate temperatures around 425°C strain-driven ridges, which decorate the ripple flanks perpendicular to the step bunches, were observed. The whole morphology is only made up with (001)-surfaces and {105}-facets. These {105}-faceted ridges appear to be energetically preferable for geometrical reasons at slopes, which are close to {1 1 10}-planes. These structures show a fair degree of ordering entirely based on self-organization. Furthermore, such morphological features are the basis for understanding the mechanism of Ge-dot nucleation on 2D pit-patterned Si-templates.

In the second part magnetotransport measurements on p-modulation doped Si/SiGe heterostructures grown on top of a step-bunched Si-buffer are discussed. The short-scale periodic height fluctuations of the Si-buffer form well-defined undulations in the SiGe-channel. This should increase scattering in the remotely p-doped quantum well (p-MODQW). Thus an asymmetry in mobility perpendicular and parallel to the undulations is expected, which might help to uncouple the different scattering mechanisms. These, namely alloy scattering and interface-roughness related scattering, are conversely discussed as predominant hole-mobility limiting factors for p-modulation doped structures. Although still at the beginning, the first measurements confirm a decreased low-temperature mobility across the undulations by a remarkable factor of two. Further measurements combined with additional modeling are expected to provide a new approach toward settling the long-lasting dispute on the hole-mobility-limiting scattering mechanisms in p-MODQW structures.

Diploma thesis:

"Epitaxial Overgrowth of Patterned Si-Substrates"

Abstract

Within this work several investigation methods have been applied to study the the morphology of annealed and overgrown patterned Si-templates. The main interest has been directed to the vast Si-mass-transport on the Si-surface at usual oxide desorption temperatures of 900°C under UHV-conditions. Heat treatment of 5min transforms the initially rectangular profiles with a height of 250nm to flat (<100nm) and faceted triangular ridges. The periodic wire structures were generated by two-beam holographic exposure using an Ar+-Ion-Laser and reactive ion etching (RIE) with typical periods of 800nm. The homogeneity of the unprocessed samples and the wire shape were checked with the atomic force microscope (AFM).

After an elaborate cleaning procedure the Si wire templates were transferred into the UHV of the MBE-chamber (molecular beam epitaxy). The samples were heated radiatively within short annealing cycles ranging from 1 to 5min to temperatures of typical 900°C, which is a conventional step to desorb either the native SiO2 or the chemical oxide generated by the RCA-cleaning. This process is required to provide a clean and smooth Si-surface for epitaxial growth.

Wire templates were overgrown with a 4-fold Si/SiGe-superlattice at 550°C after oxide desorption for 5min at 900°C and 925°C respectively. Many more samples were systematically investigated after the annealing steps which were performed with variations in duration and maximum temperature.

Again the evolved wire structures were characterized mainly with the AFM but also with the scanning electron microscope (SEM) and the transmission electron microscope (TEM). It was observed that the wires develop during annealing to triangular-shaped ridges which exhibit thermodynamically preferred {111}- and {311}-facets.
It was found that the SiO2 on the wire surface must be responsible for the degradation of the wire structure. Removing the SiO2-layer from the Si wires ex situ with an HF-dip prevents the rectangular structures from significantly changing the shape during high temperature annealing.

The Si–SiO2-interface was investigated with the TEM at atomic resolution to image the Si wire surface in detail.

Simulations were applied to describe the Si-surface diffusion and the evolution of faceted Si-ridges starting from the rectangular wire profiles. The calculations reproduce very well the faceted wire profiles imaged with the TEM.

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