Diffusion-controlled growth of semiconductor nanowires: Vapor pressure versus high vacuum deposition

Theoretical model of nanowire formation is presented, that accounts for the adatom diffusion from the sidewalls and from the substrate surface to the wire top. Exact solution for the adatom diffusion flux from the surface to the wires is analyzed in different growth regimes. It is shown theoretically that, within the range of growth conditions, the growth rate depends on wire radius R approximately as 1/R2, which is principally different from the conventional 1/R performance. The effect is verified experimentally for the MBE grown GaAs and AlGaAs wires. The dependences of wire length on the drop density, surface temperature and deposition flux during vapor pressure deposition and high vacuum deposition are analyzed and the differences between these two growth techniques are discussed.