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.