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Fritz Kohlrausch Preis der Österreichischen Physikalischen Gesellschaft an Rinaldo Trotta

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Bildquelle: Robert Herbst, POINT OF VIEW (http://pov.at). ...  more of Fritz Kohlrausch Preis der Österreichischen Physikalischen Gesellschaft an Rinaldo Trotta (Titel)

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 Dietmar Pachinger

PhD thesis:

"Fabrication of SiGe Nanostructures for Infrared Devices"

Abstract

The molecular beam epitaxy (MBE) growth conditions for tensile strained silicon (Si) on germanium (Ge) substrates were investigated. The basic pre-conditions for the epitaxial growth were established with the development and optimization of a Ge cleaning procedure. Homoepitaxial growth of the Ge buffer layer was explored and resulted in a flat surface with monoand double-atomic steps only. The main focus, however, was put on the subsequent Stranski- Krastanow (SK) heteroepitaxial 3D-growth. Self-organized Si islands on Ge(001) substrates provide a confinement of Δ2-electrons, which is of special interest for conduction-electron spin manipulation or for photoluminescence in the near- or mid-infrared range. Under tensile strain, the wetting layer (WL) thickness is considerably increased to about 11 ML for the growth at 500°C. For comparison, under compressive strain 3D-growth commences already after 2-3 MLs. A further result of the experiments is the rather unusual coexistence of SK growth and plastic strain relaxation already at an early stage of 3D growth. SK growth is usually an equilibium process between the surface-, interface- and strain-energies with the driving force to minimize the total energy. Thus, modifying the surface energy in the total energy balance with the help of surfactants was analyzed. As surfactants, 0.1 ML of either carbon (C) or antimony (Sb) were deposited onto the Ge buffer layer just prior to Si deposition. Carbon or antimony pre-deposition significantly reduced the wetting layer thickness but could not prevent the whole system from plastic strain relaxation within the islands. Further, the use of pre-structured Ge substrates enhanced island nucleation and order. The growth of perfectly ordered Si islands is of special interest with respect to periodic arrays of localized electrons. Pre-structuring the Ge substrates was realized with e-beam lithography and subsequent reactive ion etching. After buffer layer growth on a pit-structure with a periodicity of 400 nm, an inverted dome-like structure with the characteristic {1 1 3}, {1 0 5} and {15 3 23} facets was found. For the following Si growth, the WL thickness was clearly reduced and preferred nucleation sites for the Si atoms were observed. Very shallow pits of a few nanometers seem to be promising for large-scale ordering of small Si islands. Finally, the growth of a modulation doped pure Si channel on Si1-xGex pseudo-substrates was investigated. The 2D electron gas within the tensile strained Si channel offers very high electron mobilities in the range of 420000cm2/Vs at low temperatures. The SK growth mode under tensile strain is astonishing in the Si/Ge materialsystem, but these structures offer exciting new possibilities in the field of infra-red optical information technology.

Diploma thesis:

"High Mobility Si/SiGe Heterostructures for spintronic Applications"

Abstract

Within this diploma work the fabrication of silicon-germanium (SiGe) heterostructures and their properties was investigated. The main focus was put on the growth of modulation doped heterostructures with different channel structures. These structures offer high electron mobilities in the low temperature limit. Also, the spin-lifetime within the channel is quite long, in the range of microseconds. Modulation-doped SiGe heterostructures provide therefore a suitable base for quantumbit (qubit) operations as needed in quantum information processing. A qubit can be switched on and off with externally applied microwaves using the Zeemann-splitting and a channel structure consisting of two layers with different g-factor. Initially, sample structures were simulated with the Turbo Pascal program PSISiGe. The user has only to determine the structure parameters; layer thicknesses, layer compositions, doping concentrations,... for instance. The program provides then the self-consistent solution of the Schr¨odinger- and Poisson-equation resulting from an iterative calculation. The most promising channel structures were a silicon channel with a 6% Ge step in it and a channel structure consisting of a Si channel and a Si0.95Ge0.05 channel next to it with a x=15% barrier in between. With the help of a front-gate and back-gate it is possible to move the wavefunction from the layer with g-factor 2 into the layer with lower g-factor and to keep the carrier concentration constant within the channel. In the case of g<2 the electron spin couples to the external field, which allows for a spin-flip with properly chosen microwave pulses. For g=2 the spin remains unaffected. Samples were grown by molecular beam epitaxy (MBE) which allows the production of thin crystalline films of very high quality. Afterwards, Hall-bars were fabricated on these structures and measurements were performed on them to get information about the electron mobility and carrier concentration in the channel. Mobilities around 200000cm2/Vs have been measured under optimized conditions at low temperatures. Also, quite long spin lifetimes can be expected. Additionally, the samples are characterized by electron spin resonance (ESR) measurements to find out their spin properties. These structures seem to be very promissing and they offer exciting new possibilities for the development of novel devices.

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