Self-formed silicon quantum wires on ultrasmooth sapphire substrates

We have observed step-flow growth of Si on sapphire, for the first time, by gas-source molecular beam epitaxy using ultrasmooth sapphire substrates, and self-formed Si quantum wires were fabricated on the substrates. The wires were aligned along the substrate steps and formed uniformly with 50 nm width and 1 nm height. Visible photoluminescence from the wires was observed at 9 and 300 K. The optical properties of the wires were very similar to those observed in conventional porous silicon and other nanostructured silicon.