Ge in-plane nanowires grown by MBE: influence of surface treatment

Abstract

We present a detailed study of morphological phenomena during molecular beam epitaxy (MBE) of Ge nanowires on Ge substrates by means of the vapor–liquid–solid mechanism. Different wet chemical surface passivation methods were tested for their effect on Ge nanowire growth. Clean, smooth and well-passivated surfaces enable the preferential formation of in-plane nanowires, instead of conventional out-of-plane nanowires. Depending on the type of passivation, different growth directions of the self-aligned in-plane wires were observed: exclusively -grown wires on substrates with a very stable passivation layer, both and growth on substrates with a less stable passivation. The morphology of the wires was studied by means of transmission electron microscopy (TEM), scanning electron microscopy (SEM) and atomic force microscopy (AFM). For the -grown in-plane wires, nanofaceting of the top and side walls was observed. Based on the analysis, a coherent hypothesis is formulated to explain the experimental findings.