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This work presents experimental results on intersubband transitions in p-type SiGe heterostructures, where time-resolved photocurrent studies allow the determination of intersubband relaxation times of relevance for the development of a silicon-based quantum cascade laser. Inter-valence band relaxation by the emission of LO phonons leads to ultra-short lifetimes of the excited hole state around 500 fs for transition energies above the LO phonon energy, as determined in the course of this work by photocurrent pump-pump experiments employing a free-electron-laser. In contrast, for transition energies below the LO phonon energy, intersubband relaxation times are in the range of ten picoseconds. The concept of diagonal transitions poses a means of increasing these relaxation times. This work demonstrates a voltage-induced change between a spatially direct and a diagonal intersubband transition and a consequential bias tuning of the associated decay times by a factor of two. In addition, this thesis covers novel SiGe quantum well infrared photodetector concepts as well as an innovative approach for the fabrication of blocked-impurity band detectors operating in the terahertz regime.

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studied physics at the University of Linz, Austria, andreceived the Dipl.-Ing. (M.Sc.) and Ph.D. degrees in 2003 and2010, respectively. He performed his research at the Institute ofSemiconductor and Solid State Physics in Linz, and partly at thefree electron laser FELIX at the FOM Institute for Plasma PhysicsRijnhuizen in the Netherlands.

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