Gold Catalyzed Germanium Nanowires on Titanium

Germanium nanowires have been grown successfully on titanium. The wires are single crystal, with some low angle stacking faults and other defects. Growth of nanowires on metal substrates offers reduced cost over single crystal substrates, while still offering an electrical contact to the wire core for core-shell junction structures. Summary of Research: Figure 1: 80 nm germanium nanowires on a 200 nm titanium metal film. Nanowires have received considerable interested as a material for photovoltaics (PV) [1-3]. In many proposed systems, the nanowire and a radial cladding on the nanowire serve as an inorganic pn junction. These nanowire PVs suffer from a variety of problems, including electrical parasitic effects, doping control, poor contacts and material quality issues related to the use of metal catalysts. In order to achieve the highest quality material, nanowires are often grown on single crystal substrates. This allows for the possibility of epitaxial growth on matched substrates. Indeed, it has been shown that wires have preferred orientations of growth in such conditions [4]. One of the principle reasons to use nanowires for PV applications is possible cost reduction. Therefore, the need for a single crystal substrate is a significant drawback. Indeed, if such a substrate is used, one may reasonably inquire—why not simply use the substrate itself as the PV? In order to get around this problem, some groups have shown that it is possible to reuse a single crystal substrate many times over, thus reducing this cost, while preserving the integrity of the growth [5]. Others have grown wires directly on metal films, which are relatively inexpensive [6]. This second route is appealing if growth of high quality wires can be achieved. We have used thin sheets of evaporated titanium on a silicon substrate, and grown nanowires on them. While silicon wafers are still used in this process they