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Effects of Au catalyst geometry on Ge films grown laterally on Si using the vapor–liquid–solid mechanism

A lateral epitaxial growth technique has been demonstrated to grow high-quality Ge micro-films on Si at low temperatures using the vapor–liquid–solid mechanism. These Ge films were grown within a confined structure to foster horizontal growth in the presence of Au catalyst. In this work the size and geometric shape of the Au catalyst were shown to impact the film size and morphology. In particular, a general trend was observed, as the size of Au catalyst increased the Ge film size initially increased as well until the Ge film size plateaued and eventually decreased. This phenomenon is described by a model, which is a function of Au catalyst size and GeH4 dose and can be used to estimate the final Ge film size. In general, a large-sized Au catalyst absorbs more Ge because of its large vapor–liquid interface but it also requires more Ge to saturate the liquid, and therefore this fact results in a peak in the plot of the Ge film size versus the Au size. In addition, a large GeH4 dose due to more absorption of GeH4 leads to multiple nucleation sites in a small Au catalyst, while a micro-crucible with a larger Au volume or reduced vapor–liquid interface can help to realize single nucleation. These results helped in designing two-opening Au catalysts with asymmetric sides, which preferentially nucleates a large crystal near the wider side.