In situ control of Au-catalyzed chemical vapor deposited (CVD) Ge nanocone morphology by growth temperature variation

In situ control over the growth morphology of nanocones has important implications to their application in photovoltaic and thermoelectric devices. In this study, Ge nanocones were grown by an Au-catalyzed process in a chemical vapor deposition (CVD) chamber using germane (GeH4) as the source gas. The growth temperature was varied for different segments of the growth, and a corresponding variation of taper (angle of cone sidewalls relative to the axial direction) in the segments was observed. The structures obtained in these experiments reveal their temperature-dependent modes of growth. When the growth was conducted at an initial temperature of 350 °C then increased to 400 °C, faceted pillars consisting of a base segment of largely uniform diameter and a conical tapered tip were formed. When the growth was conducted at 395 and 375 °C, then at 350 °C, the nanocones featured a base with a wider taper and tips with a smaller taper. The dependence on temperature of the growth morphology is attributed to the relative influence of competing growth mechanisms at different temperature regimes: catalyzed unidirectional growth at lower temperatures approaching the Au–Ge eutectic point, and increasingly isotropic and facet-bounded epitaxial growth at higher temperatures up to 400 °C. The multi-step growth method also provides a reliable method of determining the rate and mode of catalyzed growth.