Coherent control of electron spin dynamics in nano-engineered semiconductor structures

The research presented in this thesis aimed at improving the understanding of, and abilities to control the evolution of spin ensembles in semiconductor device structures. Various fundamental aspects of spin ensemble evolution like dephasing, decoherence, relaxation, diusion and drift are addressed. All experiments used GaAs or GaAs/AlGaAs-based semiconductor materials and devices that were engineered at the nanoscale for obtaining properties that are advantageous for controlling coherent spin dynamics. These GaAs-based systems provide interesting test systems since they combine the highest available material quality, a very advanced level of possibilities for device processing and engineering, and strong optical transitions across the semiconductor bandgap that obey clear selection rules with respect to optical polarization and spin. Progress with this research is relevant for realizing new spintronic- and quantum-information functionalities. The work aimed at answering questions and realizing new proof-of-principle demonstrations in this field. The focus was on using the advantages of ultrafast optical pump-probe studies, which was a well-established technique at the start of this thesis work. Thus, the goal was to apply this for the first time to studies of the spin dynamics that is specific for devices structures, rather than studies on bulk materials, and several interesting results in this direction were obtained. However, in the course of this work, several experiments led to observations that pointed out that the fundamental understanding of the underlying physical mechanisms was {despite the large body of earlier work on bulk materials{ in fact incomplete, or even to observations that were in conflict with the established descriptions. On these occasions the reported work aimed at characterizing and understanding these new observations.