In-situ TEM observation of in-plane silicon nanowires growth via solid-liquid-solid process: reactive wetting of indium droplets on a-Si:H

We consider the solid-liquid-solid (SLS) process of in-plane silicon nanowire growth from a point of view of spontaneous motion of indium (In) droplets on hydrogenated amorphous silicon (a-Si:H) coated substrates, and intermixing with the a-Si:H layer and precipitating crystalline silicon (c-Si) nanowires (NWs). Detailed SEM studies of the nanowires system (drop diameter, trench width, and a-Si:H thickness) and their interdependence unveils a reactive-wetting behaviour of In droplets on a-Si:H, which is in perfect agreement with the in-situ TEM observation. We propose that this reactive wetting process transforms a-Si:H to c-Si, so that establishes a substrate energy gradient between the In contacts with a-Si:H at its advancing edge and with the substrate at its receding edge. This energy gradient activates the spontaneous movement of the drop which thereby maintains its contact with a-Si:H and allows a continuous nanowire growth. We suggest that the anisotropic wetting profile of In droplets results in the random growth of nanowires, which cannot be avoided on flat substrate. Thus, we study the mechanism and stability of step-guided growth approach, aiming at high yield self-organisation of in-plane silicon nanowires.