Effect of gold migration on the morphology of germanium nanowires grown by a two-step growth method with temperature modulation

Germanium nanowires (Ge NWs) grown at high temperatures (HTs) are investigated because of the demand for impurity doping. However, gold agglomeration, which occurs at HTs, results in undesired moundlike structures. A two-step growth technique with temperature modulation from low temperatures (LTs) to HTs was adopted to prevent gold agglomeration, thus revealing high-yield HT Ge NWs on top of LT Ge NWs. These Ge NWs can be classified into two groups on the basis of their shape. The timing of gold migration plays a crucial role in determining the shape of these NWs. Fat core-shell-like Ge NWs, where gold migration occurs as temperature increases, are due to the enhanced radial growth at HTs generated from the migrated gold nanoparticles on the NW sidewalls. However, for thin NWs, because Au seeds were stabilized on top of NWs until synthesis ended, the axial growth of Ge NWs continued at HTs. (C) 2016 The Japan Society of Applied Physics