The typesetting of this document was done using LATEX. The illustrations were made using the TikZ package and the diagrams using the GNUPLOT program. All input files were created using the VI editor, synchronization and version management was handled using GIT.

This document owes its existence and quality to a large number of people and the following lines are solely devoted to adequately honor these extraordinary people.

Tibor Grasser’s wonderful lecture on semiconductor modeling has brought me to this fascinating field. His tireless scientific commitment and his deep fascination with physics and applied numerics is a constant motivation for his students. I would like to thank Tibor for giving me both freedom and advice, for the patience during my descent into the realm of quantum physics, and for hours of stimulating discussions.

From the many interesting discussions I had on conferences, I enjoyed the ones with Andreas Schenk most because of his in-depth knowledge of both semiconductor device simulation and multi-phonon transitions. I feel honored and grateful that he agreed to partake in my examination committee despite his enormously busy schedule.

Erasmus Langer and Siegfried Selberherr have founded and shaped the institute for microelectronics and the high quality of our research as well as the unique atmosphere at the institute are a credit to their efforts.

For the past five years, Paul-Jürgen Wagner and Phillipp Hehenberger were the best company one could ask for, and I enjoyed every of the hundreds of longer and shorter discussions in our office, both scientific and personal. I would like to thank Phillipp for his assistance in the solution of several tricky physics problems. Paul has contributed to the quality of many publications at the institute (including this one) by sharing his comprehensive and detailed knowledge of circuit engineering, typesetting and english grammar. Also, his manifold contributions to my world view are highly appreciated.

The most important thing I have learned during my doctoral studies is that the discussion with a competent person can save a hundred pages of reading. I therefore thank my colleagues Wolfgang Gös, Viktor Sverdlov, Oskar Baumgartner, and Zlatan Stanojevic for the numerous times they shared their expertise with me.

I would have never found my way into the enormously broad field of multi-phonon transitions without the invaluable input from Alex Shluger and Keith McKenna. Georg Kresse and Peter Blöchl have provided a lot of practical tips for my electronic structure calculations.

As I have the bad habit of losing track of signs and symbols during longer derivations, I thank Yannick Wimmer for heroically checking the formulae in Chap. 2.

During my time at the institute for microelectronics, Ewald Haslinger, Christoph Haslinger, Manfred Katterbauer, and Renate Winkler have competently handled all administrative tasks. In this context, I also thank Dietlinde Egger for her wonderful and friendly help with the bureaucratic aspects of my studies, and for lots of pleasant conversations.

Finally, I would like to acknowledge all the love and support I have received from my family. I thank my wife Nicole, from whom I learned more than from anyone else in the past 16 years, my daughter Lena, the Kung-Fu fighting piano virtuoso who takes every opportunity to make her parents the proudest on Earth1 , and my daughter Margarete, who is the most amazing almost two years old stunt girl in the world. This work is dedicated to these three wonderful women.

To Nicole, Lena, and Margarete