Effect of growth conditions on the composition and structure of Si_1-xGe_x nanowires grown by vapor-liquid-solid growth

The effect of growth conditions on the composition and structure of Si_1-xGe_x nanowires grown by the vapor-liquid-solid method using gaseous precursors (SiH₄, and GeH₄) was investigated. Transmission electron microscopy was used to characterize the structural properties and elemental composition of the nanowires. At higher growth temperatures (>425°C), Ge thin film deposition on the nanowire surface resulted in Au loss during growth and the formation of tapered structures. By simultaneously reducing the growth temperature from 425 to 325 °C to suppress the rate of Ge film deposition and increasing the GeH₄/(GeH₄ + SiH₄) gas ratio, Si_1-xGe_x nanowires were produced with Ge fractions spanning the entire composition range. The Ge fraction follows that predicted from the elemental nanowire growth rates in the Ge-rich (x > 0.5) regime, but deviates to higher Ge fractions in Si-rich (x < 0.5) nanowires. A mechanism was proposed whereby surface diffusion provides an additional pathway to Ge incorporation in Si-rich Si_1-xGe_x. nanowires.