Wachstum und Charakterisierung von nitrid-basierten Halbleiterstrukturen für optoelektronische Anwendungen: Nanosäulen, Bragg-Reflektoren und Laserdioden

Solid state light sources are present in applications such as Bluray-Players and they are used for communication via optical fiber networks. To achieve or to optimze these devices and to understand the physical properties of the group-III-nitride system fundamental research as well as device-orientated investigations are necessary. The work presented in this thesis was developed in this context. Four different epitaxial growth-topics were attended to. In all cases the final coal was to understand and to improve the growth mechanisms behind the optical devices of our future life. These topics range from the growth in non-polar direction to the realisation of catalyst- and mask-free grown, high quality nanorods. Besides, the work was concentrated on edge-emitting laser-structures, which were deposited on freestanding GaN-substrates and featured quantum dots as active material. Finally, the growth of AlInN-layers for an application in distributed Bragg mirrors was investigated

Optical Properties and Modal Gain of InGaN Quantum Dot Stacks

We present investigations of the optical properties of stacked InGaN quantum dot layers and demonstrate their advantage over single quantum dot layer structures. Measurements were performed on structures containing a single layer with quantum dots or threefold stacked quantum dot layers, respectively. A superlinear increase of the quantum dot related photoluminescence is detected with increasing number of quantum dot layers while other relevant GaN related spectral features are much less intensive when compared to the photoluminescence of a single quantum dot layer. The quantum dot character of the active material is verified by microphotoluminescence experiments at different temperatures. For the possible integration within optical devices in the future the threshold power density was investigated as well as the modal gain by using the variable stripe length method.Comment: 9 Pages, 4 Figure

Growth and characterisation of nitrid-based semiconductors for opto-electronic applications: Nanorods, Bragg-reflectors and laserdiodes

Solid state light sources are present in applications such as Bluray-Players and they are used for communication via optical fiber networks. To achieve or to optimze these devices and to understand the physical properties of the group-III-nitride system fundamental research as well as device-orientated investigations are necessary. The work presented in this thesis was developed in this context. Four different epitaxial growth-topics were attended to. In all cases the final coal was to understand and to improve the growth mechanisms behind the optical devices of our future life. These topics range from the growth in non-polar direction to the realisation of catalyst- and mask-free grown, high quality nanorods. Besides, the work was concentrated on edge-emitting laser-structures, which were deposited on freestanding GaN-substrates and featured quantum dots as active material. Finally, the growth of AlInN-layers for an application in distributed Bragg mirrors was investigated

Improved survival of patients with coronary artery disease and low ejection fraction with ICD implantation versus conventional therapy in a real world survey

Abstract Background Coronary artery disease (CAD) is associated with an increased risk for sudden cardiac death. Randomized controlled trials have shown that implantable cardioverter defibrillators (ICD) improve life expectancy unless they are implanted within the first days after an acute myocardial infarction and guidelines recommend their use. We aimed to validate that these results also apply to patients of a typical community hospital in Germany. Methods This was a retrospective analysis of patients undergoing coronary angiography in the Lippe-Detmold Hospital between 2003 and 2006. They had to have significant CAD and an ejection fraction (EF) ≤ 35% and no acute myocardial infarction within 28 days of implantation and no history of ventricular fibrillation. Results 213 patients were included; 70 of which received an ICD. Patients with an ICD implantation were younger (64.8 ± 9.9 vs. 67.9 ± 9.8 years; p = 0.034), had single vessel CAD more frequently (22.9 vs. 11.2%; p = 0.025) and a lower EF (26.7 ± 6.3 vs. 29.1 ± 4.6%; p = 0.006). Hospital readmissions were comparable between the ICD and the control group (68.6 vs. 72.0%; p = 0.602). ICD therapy was associated with a considerable survival benefit compared to conventional therapy (HR 0.52; 95%CI 0.29-0.93; p = 0.027) in a Cox-Proportional Hazards Regression analysis. Conclusions Appreciating the potential limitations of retrospective studies, we found that ICD use was associated with improved survival in patients with significant CAD and an EF <= 35% typical for a large tertiary hospital.</p

HemaCAM® - a computer assisted microscopy system for hematology

Cost and competition force modern hematology laboratories to further automate their processes. To that respect the examination and analysis of the peripheral blood is of central importance as it is relevant to a large variety of diseases while on the other hand financial reimbursement is low. Over the past eight years, the HemaCAM system has been developed by the Fraunhofer IIS, which supports the assessment of peripheral blood samples and the so-called white blood differential. Since 2010, HemaCAM has been available on the market as a certified medical product, to be more specific as an in vitro diagnostic device. This contribution provides an overview of the key components of the HemaCAM system

Influence of Static Atomic Displacements on Composition Quantification of AlGaN/GaN Heterostructures from HAADF-STEM Images

AbstractIn an earlier publication Rosenauer et al. introduced a method for determination of composition in AlGaN/GaN heterostructures from high-angle annular dark field (HAADF) images. Static atomic displacements (SADs) were neglected during simulation of reference data because of the similar covalent radii of Al and Ga. However, SADs have been shown (Grillo et al.) to influence the intensity in HAADF images and therefore could be the reason for an observed slight discrepancy between measured and nominal concentrations. In the present study parameters of the Stillinger–Weber potential were varied in order to fit computed elastic constants, lattice parameters and bonding energies to experimental ones. A reference data set of HAADF images was simulated, in which the new parameterization was used to account for SADs. Two reference samples containing AlGaN layers with different Al concentrations were investigated and Al concentrations in the layers determined based on the new data set. We found that these concentrations were in good agreement with nominal concentrations as well as concentrations determined using alternative techniques such as strain state analysis and energy dispersive X-ray spectroscopy.</jats:p