GISAXS and asymmetric X-ray diffraction on Ga droplets on Si substrates and on top of GaAs nanowires grown by MBE

GaAs nanowires (NWs) are often fabricated by molecular beam epitaxy using the self-catalyzed vapour-liquid-solid mode, where a liquid Ga catalyst droplet at the apex of the NW drives the axial crystal growth. The wetting angle of the droplet determines the crystal structure of the NWs which mainly consists of the zinc blende (ZB) and wurtzite (WZ) crystal phases when grown along the [111] crystallographic direction. Regardless of the achieved high degree of control over the crystal phase of GaAs NWs during latter growth stages, it is challenging to control the polytypism at the beginning of the NW growth due to transients in the droplet contact angle. Here, we aim to correlate the crystal structure of as-grown GaAs NWs with the wetting angle of their catalyst liquid Ga droplets at the nucleation phase, by performing (1) grazing incidence small angle X-ray scattering on the Ga droplets, and (2) asymmetric X-ray diffraction of polytype sensitive reflections on the NWs underneath.