Search

Diameter-dependent compositions of Si(1-x)Ge(x) nanowires grown by a vapor-liquid-solid mechanism using SiH(4) and GeH(4) precursors are studied by transmission electron microscopy and X-ray energy dispersive spectroscopy. For the growth conditions studied, the Ge concentration in Si(1-x)Ge(x) nanowires shows a strong dependence on nanowire diameter, with the Ge concentration decreasing with decreasing nanowire diameter below approximately 50 nm. The size-dependent nature of Ge concentration in Si(1-x)Ge(x) NWs is strongly suggestive of Gibbs-Thomson effects and highlights another important phenomenon in nanowire growth.

There have been extensive studies of germanium (Ge) grown on planar silicon (Si) substrates by the Stranski-Krastanow (S-K) mechanism. In this study, we present S-K growth of Ge on Si nanowires. The Si nanowires were grown at 500 degrees C by a vapor-liquid-solid (VLS) method, using silane (SiH4) as the gaseous precursor. By switching the gas source from SiH4 to germane (GeH4) during the growth and maintaining the growth conditions, epitaxial Ge islands deposited on the outer surface of the initially formed Si nanowires. Transmission electron microscopy (TEM), scanning TEM, and energy-dispersive X-ray spectroscopy techniques were utilized to identify the thin wetting layer and the three-dimensional Ge islands formed around the Si core nanowires. Cross-sectional TEM verified the surface faceting of the Si core nanowires as well as the Ge islands.