Thermodynamics of GaAs nanowire MBE growth with gold droplets

The thermodynamics of growth conditions of GaAs nanowires using gold droplets is analyzed. Equilibrium conditions for steady-state growth using experimental molecular beam epitaxy (MBE) impinging molecular flows, as previously published, are calculated in the range 793–893 K. These show that: (i) the tie line for Ga liquidus composition in equilibrium with GaAs(s) is in the 0.4–0.6 mole fraction range, close to the GaAu–GaAs pseudo-binary section, (ii) the As content of the droplet is in the 0.2–0.4×10⁻³ mole fraction range and (iii) the growth rate is mainly governed by the contact angle that determines the droplet section. Different cooling conditions are analyzed using the Scheil–Guliver assumptions to compare final phases after solidification, as analyzed by X-ray diffraction (XRD), with our calculations. The agreement is very good and this feature demonstrates that quasi-equilibrium conditions prevail in the growth process of nanowires.