Talk by Ullrich Pietsch
Solid state physics
University of Siegen, Germany
In-situ x-ray diffraction studies during III/V MBE nanowire growth
Catalyst-free MBE nanowire growth along the  crystallographic orientation suffers from Wurtzite-Zincblende polytypism. Typically X-ray diffraction studies of polytypism are performed ex-situ after removal of sample from MBE chamber. Therefore after growth modifications of the structure are not accessible. We report on in-situ x-ray diffraction experiments during InAs and GaAs MBE growth with the aim to explore the dynamic relation between the growth conditions and the structural composition of the nanowires. In the case of InAs NWs grown on Si(111) performed at MBE chamber at the Spring8 synchrotron radiation facility we studied the relation between the liquid Indium droplet and the phase composition of the growing NW. In the nucleation phase the InAs nanowires predominantly grow in the Wurtzite phase. The highly arsenic-rich growth conditions that we used limited the existence of the liquid indium to a short time interval. After the nucleation, the nanowires grow in the absence of liquid indium, and with a highly defective Wurtzite structure. This finding implies that pure Wurtzite nanowires may be obtained only if the growth is performed under the continuous presence of liquid indium at the growth interface, that is, in the vapor-liquid-solid mode.