Self-assembled and ordered growth of silicon and germanium nanowires

Self-assembled and ordered silicon and germanium nanowires grown by physical vapor deposition (PVD) via vapor-liquid-solid (VLS) mechanism are presented. The morphology of the nanowires has been investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Differences in the orientation of the homoepitaxially grown nanowires between silicon and germanium were observed. Most silicon nanowires grew in [111] direction on the (111) Si substrate whereas germanium nanowires grew in < 1110 > direction on the (111) Ge substrate. Nucleation energies as a function of supersaturation were considered. The results of these calculations could explain the behavior of Si and Ge wires in terms of growth direction. A method to position nanodroplets and thus to obtain a regular arrangement of nanowires is also presented. For this purpose, substrates were structured with nanopores by focused ion beams (FIB) before inserting them into the growth chamber. Gold droplets have been successfully ordered both on silicon and on germanium substrates. A regular array of epitaxial silicon nanowires has been obtained as well. (C) 2008 Elsevier Ltd. All rights reserved.