First, I would like to thank my advisor Prof. Siegfried Selberherr for providing me with a perfect working environment, allowing me the freedom to pursue my own ideas, and giving me the opportunity to attend several international conferences.
I am also very grateful to my colleagues Johann Cervenka and Franz Schanovsky for their support concerning the computer cluster, Paul-Jürgen Wagner for helping me with many LaTeX issues, and Lado Filipovi
for proofreading this work.
Finally, I would like to thank Stefan Halama, who gave me the opportunity to gain a lot of experience during an internship with an impressive company.