Andreas Witzig

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The computation of optical modes inside axisymmetric cavity resonators with a general spatial permittivity profile is a formidable computational task. In order to avoid spurious modes the vector Helmholtz equations are discretised by a mixed finite element approach. We formulate the method for first and second order Nédélec edge and Lagrange nodal elements.(More)
High PV utilization ratios in buildings, i.e. the consumption of most of the PV energy within the building premises, can reduce the energy losses in distribution networks, and mitigate overvoltages and transformer overloadings. For this reason, some countries have adopted, or are discussing, regulatory instruments to motivate local utilization of PV energy.(More)
2000 Acknowledgements I wish to thank Prof. Wolfgang Fichtner for his guidance and assistance during my years at IIS, and Prof. Klaus Ensslin for reading and co-examining this thesis. Special thanks goes to PD Andreas Schenk for supervising the scientific aspects of this work.
Ahmed Al-Mogbel, Patrick Ruch, Abdulrahman Al-Rihaili, Saleh Al-Ajlan, Paul Gantenbein, Andreas Witzig, Bruno Michel 1 King Abdulaziz City for Science and Technology (KACST), Riyadh, Saudi Arabia Phone: +966 1 481 4323, Fax: +966 1 481 3880 E-Mail: aalmogbel@kacst.edu.sa Internet: http://www.kacst.edu.sa/ 2 IBM Research – Zurich, Säumerstrasse 4, 8803(More)
The computation of optical modes inside axisymmetric cavity resonators with a general spatial permittivity profile is a formidable computational task. In order to avoid spurious modes the vector Helmholtz equations are discretised by a mixed finite element approach. We formulate the method for first and second order Nédélec edge and Lagrange nodal elements.(More)
Topic of this doctoral thesis are the correlation effects between the charge carriers in semiconductors which originate from the long-range Coulomb interaction. In particular, their relevance to the operation of silicon devices is considered. In the first part, the formation of bound states and the plasmainduced band gap narrowing are investigated. A(More)
Self-sufficiency of systems with photovoltaic (PV) energy production gets more and more important. Demand side management with the use of heat pump and thermal energy storage has proven to be an efficient and effective means for increasing the PV self-consumption ratio [1, 2]. Accurate prediction of the self-consumption and the resulting self-sufficiency(More)
This thesis deals with the optical characterization of single quantum dot devices emitting at 1300nm. Thanks to the development and optimization of the growth technique we were able to achieve at the same time emission at 1300nm and ultra low QD densities. Our single QD devices present clear and reproducible spectral signatures in which we can identify(More)
The analysis of filter devices based on eigenmodes provides a facile and fast means to simulate the reflection and transmission function and shows good agreement with the measurements. The computing time is proportional to the number of eigenmodes, and the analysis yields an analytical expression for the transfer functions. The method can be easily applied(More)
Penetration of the waveguide mode into the substrate has some effects in Nitride-based semiconductor lasers grown on Silicon Carbide while it is usually not a problem in Arsenide-based devices. We observe oscillations in the red part of the measured gain spectrum of an (Al,In)GaN semiconductor lasers. These have been attributed to the presence of a standing(More)