In the present thesis, dynamical processes during the epitaxial growth of self-catalyzed GaAs nanowires are investigated by means of time-resolved in-situ X-ray scattering methods at synchrotron radiation facilities. Comprehensive knowledge of their fundamental growth processes is pre-requisite for the optimized integration of GaAs nanowires into the complementary-metaloxide-semiconductor technology, e.g. as highly efficient vertical transistors.
First, growth studies employing a portable molecular-beam-epitaxy system specially designed for in-situ X-ray investigations are carried out. The aim is to epitaxially grow vertical GaAs nanowires onto silicon substrates with minimal parasitic GaAs island growth. Employing ex-situ scanning-electron-microscopy, the effect of the growth parameters on the growth and the properties of GaAs nanowires, as well as the liquid Ga-droplet is investigated. The growth parameters are comprised of the material fluxes of Ga and As, the substrate temperature as well as surface-oxide preparation.
Further, the microstructure of GaAs nanowires is investigated by means of ex-situ X-ray scattering methods. Employing highly focused X-ray radiation, the difference of the scattering signals from individual GaAs nanowires and parasitic GaAs islands is demonstrated. This allows the separation of the contributions of parasitic GaAs islands and GaAs nanowires in X-ray measurements averaging over a statistical ensemble of nanostructures and gives insight into the crystallographic properties of the nanowires.
On this basis, the evolution of the so-called wurtzite/zinc-blende polytypism during the growth of self-catalyzed GaAs nanowires is monitored by means of time-resolved in-situ X-ray scattering in symmetric geometry. Using a statistical model with time-dependent transitionprobabilities between the polytypes, insights into the evolution of key-parameters of polytypism, such as mean polytype segment length and polytype fraction, are obtained. Moreover, differences in the nucleation barriers are estimated.
The formation of microstructure and shape of GaAs nanowires during growth is monitored in-situ via time-resolved X-ray scattering at phase-sensitive Bragg reflections. Thereby, the separation of radial growth processes in non-catalytic and catalytic contributions is achieved. This allows for the direct comparison to theoretical models for catalytic radial growth. In dependence of the growth parameters, conclusions on the evolution of the liquid catalyst particle during growth become possible.