Au-assisted growth of GaAs nanowires by gas source molecular beam epitaxy: Tapering, sidewall faceting and crystal structure

GaAs nanowires grown by gas source molecular beam epitaxy for 3, 10, 30, and 40 min durations were studied by both scanning and transmission electron microscopy, providing a description of the time evolution of the nanowire morphology and structure. Tapered, “pencil-shaped” wires were observed in which a transformation of the sidewall orientation occurs from {1¯ 1 0 0} facets at the tip to {2¯ 1 1 0} facets at the base, providing evidence for a layer-by-layer radial growth model. The crystal structure of the nanowires, as well as the nature and frequency of stacking faults, was investigated. Local pseudo-periodicity of defects was observed in the vicinity of the wire base, while defect density decreased as the growth progressed.