SEM images of SiGe NW grown during 40 mins at 400 °C with R = 0.15. The HCl flow rate has been varied: (a) Φ HCl = 0 sccm, (b) Φ HCl = 40 sccm, (c) Φ HCl = 60 sccm, (d) Φ HCl = 90 sccm (scale bars = 500 nm except when specified otherwise). The density and morphology of the NW is drastically improved at low HCl flow (40 sccm). A higher HCl flow (60 sccm) slows the NW growth and induces V-shaped NWs (SEM image, inset of (c)). At 90 sccm HCl, the NW density is extremely poor and the growth rate is very low. (e) shows a  zone axis HRTEM image of a NW grown in the condition of the sample b) and the corresponding FFT diffraction pattern.
(Color online) (a) STEM image and (b) EDX profile from a high Ge fraction SiGe NW grown at 400 °C, R = 0.15, and Φ HCl = 40 sccm. The graph includes two profiles: the Ge profile around 70 atomic %, and the Si profile around 30 atomic %.
(Color online) (a) Variation of the Ge fraction of the SiGe alloy NWs grown at 400 °C as a function of the ratio R without (▴) or with 40 sccm HCl (Δ) during the growth. Without HCl, the Ge fraction for R = 0.15 does not seem to follow (red arrow) the linear tendency highlighted for low R (dashed line). When using a 40 sccm flow of HCl, the Ge fraction seems to follow a linear increase (dashed-dot line) as a function of R. (b) Variation of the NWs’ growth rate (nm/min) as a function of R without HCl (♦) and with 40 sccm HCl (⋄).
(Color online) SEM images of SiGe NW grown at 450 °C with R = 0.15 (a) without HCl and (b) with 40 sccm HCl (scale bar = 1 μm). (c) shows the variation of Ge fraction of the SiGe alloy NWs grown without HCl at different gas flow ratio R without or with 40 sccm HCl as a function of temperature. The cross at the upper right-hand corner represents the Ge fraction of NW grown with R = 0.15 and Φ HCl = 90 sccm.
(Color online) Schematic of the system without or with HCl: (a) without HCl, the gas phase is composed of hydrides and by-products, and the droplet and NW surface are passivated by H atoms; (b) with HCl, chlorides appear in the gas phase and the surfaces are mainly passivated by Cl atoms.
Ge fraction x (%) in Si1−xGex NW as a function of the HCl flow (sccm) at T = 400 °C and constant R = 0.15 (Ф GeH4 = 4.5 sccm, Ф SiH4 = 25 sccm).
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