The modulation of Si_1-xGe_x nanowires by correlation of inlet gas ratio with H₂ gas content

Si_1-xGe_x nanowires (NWs) were prepared by a Vapor-Liquid-Solid (VLS) procedure using Au as the catalyst at a fixed growth temperature of 400 °C. The alloy composition was adjusted and the growth rate of the Si_1-xGe_x NWs was achieved by varying the inlet gas ratio and the H₂ flow rate. The growth of Si _1-xGe_x NWs can be explained by two mechanisms that are related to growth kinetics; first, collisional activation is a dominant factor at flow rates of H₂ 100 sccm and second, in the case of a H ₂ flow rate of 200 sccm, the reaction is unimolecular. In addition, a Ge concentration (0.56 < x < 0.91) in Si_1-xGe_x NWs is observed at a relatively high growth temperature of 400 °C as compared with data reported in the literature. The findings herein indicate that the high Ge concentration (x) can be attributed to the presence of interstitial Ge atoms in the Si_1-xGe_x NWs, when they are grown under non-equilibrium conditions. This was confirmed by comparing the measured Ge concentration between EDX and XRD, Raman and strongly demonstrated by XPS results indicating the development of Ge interstitial states at lower binding energy, rather than bulk-like bonding.