Salehi, Waheed AhmadWaheed AhmadSalehi2026-06-162026-06-162025-09-08https://dspace.ub.uni-siegen.de/handle/ubsi/9399Nanowires have emerged as a promising platform for the development of advanced hetero-structures, particularly where large lattice mismatches prevent coherent growth in planar configurations. In this thesis, strain and thermal behavior in GaAs and InxGa1-xAs core–shell nanowires are systematically investigated using both theoretical modeling and synchrotron-based experimental techniques. A theoretical approach is first established to model strain distributions in bent nanowires, revealing how mechanical deformation influences band structure and optoelectronic properties. Subsequently, strain relaxation in GaAs / InxGa1-xAs nanowires is experimentally examined through in-plane and axial X-ray diffraction. A critical transition from elastic to plastic strain relaxation is observed for indium concentrations exceeding 50%, with the formation of indium-rich surface mounds coexisting with coherent shells, confirmed by SEM and 3D strain mapping. The transient structural response of nanowires to femtosecond laser pulses is studied via an optical pump–X-ray probe setup. The results show that thermal expansion scales with laser power and is strongly dependent on nanowire geometry. Notably, zinc blende and Wurtzite phases exhibit distinct thermal behaviors under pulsed excitation. Finally, the axial distribution of beryllium dopants near the nanowire surface is probed using spatially resolved X-ray photoelectron spectroscopy (XPS). The Fermi level shifts are used to map local dopant concentrations, revealing a gradient along the nanowire growth axis attributed to flux shadowing effects during molecular beam epitaxy. Together, these findings provide a comprehensive understanding of strain, thermal dynamics, and dopant distribution in core–shell nanowires, offering insights critical for the design and optimization of nanoscale semiconductor devices.en530 PhysikGaAs nanowireSemiconductor nanowireSynchrotron radiationX-Ray diffractionPump-Prob techniqueX-Ray photoelectron spectroscopyGaAs-NanodrahtHalbleiter-NanodrahtSynchrotronstrahlungRöntgenbeugungPump-Probe-TechnikRöntgen-PhotoelektronenspektroskopieDoctoral ThesisPietsch, Ullrichurn:nbn:de:hbz:467-93997