Synthesis of Vertical High‐Density Epitaxial Si(100) Nanowire Arrays on a Si(100) Substrate Using an Anodic Aluminum Oxide Template

Because of their unique electrical and optical properties, Si nanowires have attracted considerable attention, and already a number of devices based on Si nanowires as building blocks have been demonstrated. [1–4] Nanowires grown by using the vapor–liquid–solid (VLS) technique have been shown to have advantages compared with conventional lithographic techniques in terms of well-defined surface, small minimum size, and fabrication cost. Additionally, the VLS technique can be used to prepare epitaxially grown nanowires on single-crystal substrates. Vertically standing epitaxial nanowires as a device platform [3,4] avoid pick-and-place approaches or nanomanipulations. For vertical devices, control of growth direction and crystallographic orientation of the nanowire are important parameters. In order to combine vertically grown epitaxial Si nanowires with conventional Si micro/nanoelectronics manufactured on Si(100) wafers, the most important issue is the realization of vertically grown epitaxial Si nanowires, along the [100] direction, on Si(100) substrates. Epitaxial Si nanowires grown without any template on Si substrates reported up to now have three preferred growth directions, in particular , , and depending on the diameter of the wires. [5] Based on the present knowledge the preferred growth directions are for large diameter nanowires and and for small diameters, independent of the growth method, if no template is used. In this paper, we utilize an anodic aluminum oxide (AAO) template with vertical nanopores to grow epitaxial Si(100) nanowires on a Si(100) substrate. AAO is known to have ordered honeycomb nanopore arrays, perpendicular to the substrate. The diameter and the density of the nanopores can be controlled from a few nano