We report on the Au-free molecular beam epitaxy growth of coherent GaAs nanowires directly on Si(111) substrates. The growth is catalyzed by liquid Ga droplets formed in the openings of a native oxide layer at the initial growth stage. Transmission electron microscopy studies demonstrate that the nanowires are single crystals having the zincblende structure along their length (apart from a thin wurtzite region directly below the Ga droplet), regardless of their diameter (70\char21{}80 nm) and the growth temperature range (560\char21{}630\,\ifmmode^\circ\else\textdegree\fi{}C). We attribute the observed phase purity to a much lower surface energy of liquid Ga than that of Au-Ga alloys, which makes triple line nucleation energetically unfavorable. The change in growth catalyst to a liquid metal with a lower energy suppresses the (more usual) formation of wurtzite nuclei on surface energetic grounds. These results can provide a distinct method for the fabrication of chemically pure and stacking-fault-free zincblende nanowires of III-V compounds on silicon.

We present a general model for the vapor-liquid-solid nanowire (NW) growth rates which accounts for adatom diffusion from the substrate and sidewalls into the Au catalyst drop as well as the Gibbs-Thomson effect of elevated chemical potential in the drop with a curved surface. The growth model is compared with the experimental length-diameter dependences for InP and Si NWs grown via metal organic chemical vapor deposition (MOCVD) and GaAs nanowires grown via molecular beam epitaxy (MBE). We show that MBE growth is affected mainly by adatom diffusion from the substrate, whereas MOCVD growth is affected mainly by direct Au drop impingement and sidewall diffusion. The Gibbs-Thomson effect is shown to limit growth for smaller diameter nanowires. Fits for diffusion lengths and the Gibbs-Thomson radii are determined which explain the experimental length-diameter dependence observed.

Recent results of studying the semiconductor’s whisker nanocrystals are reviewed. Physical grounds of growing whisker nanocrystals using the mechanism vapor-liquid-crystal are given and the main epitaxial technologies of synthesis of whisker nanocrystals are described. Thermodynamic and kinetic factors controlling the morphological properties, composition, and crystal structure of whisker nanocrystals are considered in detail. The main theoretical models of the growth and structure of whisker nanocrystals are described. The data on physical properties of whisker nanocrystals and possibilities of their use in nanophotonics, nanoelectronics, and nanobiotechnology are presented.

The Au-assisted molecular beam epitaxial growth of InAs nanowires is discussed. In situ reflection high-energy electron diffraction observations of phase transitions of the catalyst particles indicate that they can be liquid below the eutectic point of the Au-In alloy. The temperature range where the catalyst can be liquid covers the range where we observed nanowire formation $\left(380–430°\text{C}\right)$ . The variation of nanowire growth rate with temperature is investigated. Pure axial nanowire growth is observed at high temperature while mixed axial/lateral growth occurs at low temperature. The change of the InAs nanowire shape with growth duration is studied. It is shown that significant lateral growth of the lower part of the nanowire starts when its length exceeds a critical value, so that their shape presents a steplike profile along their axis. A theoretical model is proposed to explain the nanowire morphology as a result of the axial and lateral contributions of the nanowire growth.