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Upcoming Conference: Mauterndorf Winterschool 2018

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20th International Winterschool on New Developments in Solid State Physics, Mauterndorf, Feb. 25 - March 2, 2018 ...  more of Upcoming Conference: Mauterndorf Winterschool 2018 (Titel)

Video zu Artikel "Free-running Sn precipitates..." (Gruppe Schäffler)

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Wir gratulieren Dr. Rinaldo Trotta zur Habilitation!

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"Zum Gral der Halbleitertechnik", in: Die Presse vom 8.4.2017

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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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Position Indication:


Dr. DI Heiko Groiss

PhD thesis: "Transmission Electron Microscopy of Semiconductor Nanostructures"


In this work transmission electron microscopy studies on different semiconductor nanostructures are presented. Common to all these structures are possible applications for opto-electronic devices in the near and mid infrared frequency range. This range is crucial for various actual and future applications, ranging from environmental monitoring over medical diagnosis to applications for security and military issues. The investigations of these structures by electron microscopy techniques reveal structural and compositional information and allow insight into dynamic processes of the systems. This requires an understanding of the used techniques, which are presented in detail in the first part of this thesis.

As a first material system investigated, coherent Ge islands on prepatterned Si substrates, which are grown in the Stranski-Krastanow growth mode, are presented. The investigated dots in shallow pits show an intermixing oscillation and can reach larger sizes compared to dots on flat substrates. Examples are presented, where these structures of site-controlled dots are used to demonstrate the possibility to perform shape transitions by annealing. By stacking these dots, one can produce large, Ge-rich islands, which could be used as strain sources for tensile strained Si in high-mobility Si devices. As strain relaxation in the Si-Ge system also occurs via dislocations, a study of dislocation engineering is presented. The possibilities of trench- and pit-patterned samples to control dislocation nucleation and their dynamics are discussed as well. The Si-Ge chapter is closed by an intense study of Si dots on Ge, where the defects of these structures are revealed and their origin is clarified.

The second part of this thesis covers the novel technique of lattice-type-mismatched epitaxy of immiscible materials that form self organized nanostructures. With PbTe layers embedded in CdTe two materials with different lattice types, but same lattices constants, are annealed and disintegrate into quantum dots with atomically sharp interfaces and highly symmetric shapes. The PbTe/CdTe structures show superior optical properties, because it is an ideal combination of a narrow band gap (PbTe) and a wide band gap (CdTe) material. One achieves a high controllability of the size distribution by choosing the thickness of the original epilayer. As the system is a combination of a polar zinc blende lattice and a neutral rock salt lattice, complex interface reconstructions occur. For several interfaces the atomic structure is revealed and compared to ab-initio calculations. The formation process of the structure is investigated by in-situ heating experiments, which allow an estimation of the occurring diffusion constants, revealing fast diffusion. The lattice-type-mismatched epitaxy can be expanded to further material classes and also dot formation after ion-implantation is presented.

Diploma thesis

"Transmission Electron Microscopy of self-organized PbTe/CdTe Nanocrystals"


Nano-structuring allows the manipulation of electronic and optical properties of semiconductors, which is useful for various applications. So-called quantumdots (QD) reveal optical properties comparable with atoms. They are a promising method for the production of material systems for opto-electronic devices in frequency ranges, which are not accessible with the standard materials.

A novel approach of QD formation was realized by decomposition of two immiscible semiconductors with different lattice structures. The experiments were carried out at CdTe/PbTe heterostructures. PbTe possesses the structure of rock salt (rs), CdTe has zincblende (zb) structure. A PbTe layer, embedded in CdTe, disintegrates into highly symmetrical nano-crystals with atomically sharp interfaces during an annealing step. The QDs show intense photoluminescence in the mid-infrared, an energy region, where the excitation energies of molecules are found. No efficient semiconductor lasers exist for this frequency range. The aim of this work was a concise characterisation of these QDs with transmission electron microscopy (TEM), for which different techniques were used. As will be shown, the PbTe nanocrystals have a thermodynamic equilibrium shape of small rhombi-cubo-octahedrons with {001}, {110} and {111} PbTe/CdTe interfaces. An insight into the processes during the annealing step is given. The size of the QDs can be controlled by the epi-layer thickness. The density of the dots depends strongly on their average size. The main part of this thesis is the atomic characterisation of the PbTe/CdTe interfaces and TEM image simulations, which are necessary for the interpretation. The different lattice structures of the two materials induce strong atomic displacement of single atoms or groups of atoms at the interfaces. The displacements end up in bonding configurations for the zb or rs lattice close to their respective bulk configuration. It was shown that two different {001} interfaces exist at the same QD, depending on the termination of the CdTe crystal half. The most remarkable effects can be found at the {110} interfaces, where the displacements lead to a shift of more than 10% of the two crystal halves against each other. The interface problem was also treated by R. Leitsman et al. with ab-initio calculations. The theoretical displacements and those obtained by high resolution TEM images show excellent agreement.

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