Growth pathways in ultralow temperature Ge nucleation from Au

Device integration on flexible or low-cost substrates has driven interest in the low-temperature growth of semiconductor nanostructures. Using in situ electron microscopy, we examine the Au-catalyzed growth of crystalline Ge at temperatures as low as 150 °C. For this materials system, the model for low temperature growth of nanowires, we find three distinct reaction pathways. The lowest temperature reactions are distinguished by the absence of any purely liquid state. From measurements of reaction rates and parameters such as supersaturation, we explain the sequence of pathways as arising from a kinetic competition between the imposed time scale for Ge addition and the inherent time scale for Ge nucleation. This enables an understanding of the conditions under which catalytic Ge growth can occur at very low temperatures, with implications for nanostructure formation on temperature-sensitive substrates.