Publication
Semiconductor quantum wires (QWRs) and quantum dots (QDs) are nanoscale heterostructures, which form fascinating low-dimensional systems for fundamental studies of quantum-mechanical effects and are attractive candidates for integration into optoelectronic semiconductor devices. With plenty of already established technologies for their fabrication, extensive research efforts are concentrated nowadays on achieving precise control of their position, geometry and heterostructure potential, which provides a tool for tailoring their electron transport and light emission properties. Tuning of the quantum confining potential in a given system offers the possibility of realization of complex nanostructure configurations. In particular, it allows to design and control transfer paths within the surrounding potential landscape, energy relaxation, capture and radiative recombination of charge carriers generated through a non-resonant optical excitation of the QWR-QD structure. This Thesis is devoted to investigation of these processes in tailored-potential GaAs/Alx Ga1−x As QWR-QD structures, which are formed along the vertical axis of pyramidal recesses etched in a (111)B GaAs substrate and regrown with AlGaAs. The reproducibility and controllability characteristic to this system make it particularly suitable for realization of mixed-dimensionality and intermediate-dimensionality 1D-0D structures. An important feature exploited here is the fact that a QWR structure with well-controlled lateral confinement and tunable length can be obtained by a growth of an AlxGa1−xAs/AlyGa1−yAs heterostructure (x < y). The system offers also the possibility of precise bandgap engineering by modification of the chemical composition x during the growth: as shown before, single or multiple QDs can be embedded in the QWR by creating sharp heterointerfaces along the growth direction. In this work, a continuous axial modulation of the QWR potential was realized, which yields novel 1D and quasi-1D systems. The work was started with systematic investigation of carrier dynamics in a QD-QWR system, emphasizing the effect of reduced barrier dimensionality on the efficiency of carrier trapping into the QD. By combining temperature-dependent and time-resolved spectroscopy with theoretical modeling, it was shown that the carrier distribution in the QD and its QWR barriers is determined by different temperature-dependent processes: phonon-assisted capture, limited at low temperatures by diffusion in the 1D barriers (defined by the fraction of the exciton population, which is delocalized) and thermal activation from the QD to the QWR (equivalent to thermalization of carrier population over the available higher-energy states). A V-shaped potential modulation was then used to fabricate QD structures with intermediate (quasi-1D) dimensionality. It was demonstrated that such a potential profile induces additional energy quantization in the vertical direction, which gives rise to multiple conf