Nanowires provide an attractive platform for nanoscale integration of III-V semiconductors on silicon. Their optoelectronic applications are ongoing research topics and benefit from the unique accessibility to the combination of materials not realizable in planar geometry. InAs nanowires, in particular, are highly attractive systems due to their small effective mass and low bandgap energy offering benefits for nanoelectronic and mid-infrared optoelectronic applications. Due to the onset of quantum confinement at relatively large nanowire diameters, InAs nanowires can also exploit strong quantized effects in charge carrier dynamics of such applications. The electronic properties of InAs nanowires suffer though from surface effects with strong influence on, e.g. the optical emission and electrical transport. In the past approaches of epitaxial passivation were limited by large lattice mismatch of chosen materials causing strain issues and associated defects that hamper the performance of these nanowires. A suited material system for the epitaxial overgrowth of InAs nanowires and the formation of advanced core-shell heterostructures is AlAsSb which can be grown under lattice matching conditions, but has not been investigated so far as core-shell nanowire system. Small variations of As molar fraction of AlAsSb could at the same time tune the bandgap energy of the InAs core via strain and open the door for tunable optical transitions between type-I and type-II band alignment. Together with quantum confinement the effects of strain and tunable band lineup could therefore tune the bandgap and nature of recombination dynamics over a wide range. Moreover, such InAs-AlAsSb based systems exploiting quantum confinement effects are also a powerful candidate for the realization of hot carrier solar cells, which become efficient in quantized systems while also benefiting from a type-II alignment. The central objective of this thesis was therefore to establish a suited nanowire based system for potential application in mid-infrared nano-optoelectronics and hot carrier solar cells. For this purpose, ultrathin InAs nanowire cores and InAs-AlAsSb core-shell nanowires were grown by molecular beam epitaxy and characterized within the framework of this thesis. In the first part of this thesis the diameters of InAs nanowires were tuned down well below 30nm by catalyst-free growth via molecular beam epitaxy for the first time. In a first approach bottom-up growth under sophisticated parameter settings generated ultrathin InAs nanowires with diameters down to 17nm at reasonable aspect ratios. In a second approach, top-down reverse-reaction growth was investigated to achieve InAs nanowires with lengths of 2 μm and diameters down to 12nm. Specific low-temperature transport measurements and simulations of the electron density distribution in the subbands proved the 1D character of these nanowires. The second part introduces the overgrowth of InAs nanowires with Sb based compounds. For the first time InAs-AlAsSb core-shell nanowires with tunable As fraction were grown. The compositions of the AlAsSb shells were probed and quantified by TEM-EDX, XRD and Raman spectroscopy measurements with complementary SEM investigations to correlate effects of As molar fraction on morphology evolution, microstructure and strain. The well-known complex microstructure of the InAs cores alternating between dominantly hexagonal and cubic crystal stacking was found to be transferred to the epitaxially overgrown shells, too. Arsenic fractions in the shells were tuned from pure AlSb compounds up to 54% As content. At the same time, Raman spectroscopy and particularly the phonon mode shifts of the InAs-related modes revealed strain applied to the InAs nanowire cores. The strain reached from a tensile regime (13% As) over nearly lattice matched conditions (18% As) to a strongly compressively strained regime (from 25% As on). Correlations between Raman and SEM led to the assumption of partially relaxed shells for As fractions above 25%. Finally, in the last part of this thesis the optical properties are characterized systematically in these InAs-AlAsSb based nanowires using steady-state confocal microphotoluminescence spectroscopy. The photoluminescence of bare InAs nanowires showed Auger dominated characteristics with strongly blue shifted peak position energies (towards 0.46 eV) due to the wurtzite dominated microstructure. InAs-AlAsSb core-shell nanowires exhibited shifts in the emission peak energy up to 90 meV (compared to the bare InAs nanowires). These findings correlated again strongly with the findings from Raman spectroscopy regarding strain applied to the InAs core from tensile to compressive strained regimes. In addition, the tunability between type-I and type-II like band alignment was found for very small As molar fraction (13%). Moreover, first hints towards the generation of hot carriers were found by fitting and analysis of excitation power dependent PL spectra with the tendency of higher temperatures for core-shell nanowires compared to bare InAs nanowires. Eventually, InAs-AlAsSb core-shell nanowires with ultrathin InAs core exhibited optical characteristics that clearly point to the regime of radial quantum confinement.weiterlesen