Ion beam analysis of VLS grown Ge nanostructures on Si

A rich variety of nanostructures can be synthesized by varying pressure and temperature during vapor-liquid-solid (VLS) epitaxy on Si. The chemical vapor deposition (CVD) growth by VLS of epitaxial Ge nanowires and nanopillars seeded by metallic nanodots on (1 1 1) and (1 0 0) oriented Si is reported with an emphasis on analyses by ion backscattering and channeling in combination with scanning electron microscopy. The nanostructures are grown using digermane in an Ultra High Vacuum (UHV) system at pressures from 10^-6 to 10 ^-2 Torr and temperatures between 400 and 600 °C. Au nanodots with diameters of 10-50 nm are formed by vapor deposition on H-terminated Si surfaces. The Ge growth kinetics and morphology are observed to depend strongly on pressure. At lower pressures the Au seeds the growth of layered heteroepitaxial islands (referred to here as nanopillars) which grow both vertically and laterally. At higher pressures a transition to rapid 〈1 1 1〉 axial nanowire epitaxial growth occurs with a growth rate that scales linearly with pressure. We contrast quantitative measurements of the kinetics for VLS nanowire growth with that for uniform CVD layer growth.