Structure to property relations of single MBE grown GaAs and InAs nanowires onto silicon (111) by X-ray nanodiffraction

III-V semiconductor nanowires (NWs) grown onto silicon substrate may become new building blocks of modern optoelectronic and electronic devices. For success in technical application it is necessary to explore their physical properties on the nanoscale. In MBE grown semiconductor NWs axial stacking faults separating zinc-blende and wurtzite entities are the major structural defects influencing the physical properties. Structural composition, phase arrangement and residual strain of individual GaAs NWs grown on Si(111) can be investigated X-ray nano-diffraction employing a focused synchrotron. It is found that even neighbouring NWs grown on the same sample under the same growth conditions differ significantly in their phase structure Moreover, the misfit strain at the substrate to NW interface releases within few monolayers due to relaxation towards the NW side planes [1]. The evolution of stacking faults is no constant but depends on growth time and the growth mode. In case of InAs NWs grown catalyst-free along the [111] we explored the dynamic relation between the growth conditions and the structural composition of the NWs using time-resolved X-ray scattering and diffraction measurements during the MBE growth. The spontaneous buildup of liquid indium droplet in the beginning of the growth process is accompanied by the simultaneous nucleation of InAs NWs predominantly grown in the wurtzite phase with low number of stacking faults. After nucleation the In droplets become consumed resulting in structural degradation of NWs due to the formation of densely spaced stacking faults [2]. For the first time the particular phase structure of single GaAs NWs could be correlated with their electrical properties. Here the V-I characteristics was measured in a dual Focused Ion Beam chamber the resistance and their effective charge carrier mobility was modeled in terms of thermo-ionic emission theory and space charge limited current model, respectively. Both resistance and inverse mobility show a qualitatively similar electric behavior comparing the inspected NWs. The same single NWs electrically measured have been inspected by X-ray nano-diffraction. The NWs were found to be composed by zinc-blende and twinned zinc-blende units separated by axial interfaces and a small plastic displacement. It turns out that the measured value of the extracted resistance and the inverse of effective mobility increases with the number of intrinsic axial interfaces, whereas the small plastic displacement has less influence on electrical properties [3]. We acknowledge support by BMBF and DFG.