Many of the common NW synthesis techniques can be used for the III-V NW synthesis of GaAs, such as Vapor-Liquid-Solid (VLS), molecular beam epitaxy (MBE), metal organic chemical vapor deposition (MOCVD). There also exist many techniques that improve on these earlier methods such as laser ablation.
Vapor-Liquid-Solid growth (VLS) is common for nanowire synthesis and has been used for GaAs nanowire growth.\cite{Hu_1999} A catalytic liquid phase droplet is formed (in the case of GaAs NW, the catalyst could be Cu, Ag or Au) on the solid surface of the substrate, the droplet quickly absorbs the vapor containing precursors then becomes supersaturated to the point that crystal growth begins.\cite{9781420067828} Historically it is known that the radius limit of nanowires grown this way depends on the formation and stability of the liquid catalyst cluster beads, for which the minimum radius (\(r_{min}\)) of the wire is given by equation \ref{eq:vls_limit} and is limited by equilibrium conditions (\(T\) is growth temperature, \(V_l\) is the liquid molar volume, \(\sigma\) is the degree of vapor pressure saturation and \(\sigma_{LV}\) is the liquid-vapor interfacial energy) .\cite{9781420067828} \[\label {eq:vls_limit} r_{min}=\frac{2\sigma_{LV}V_{L}}{RT \sigma}\] Using typical values of GaAs nanowire growth for equation \ref{eq:vls_limit} a limit of \(2 \mu m\) is found. \cite{Hu_1999} Laser ablation can overcome the limitation of equilibrium clusters sizes to prepare catalyst clusters to subsequently produe nanowires via VLS.\cite{Morales_1998} The mechanism works as follows...First a phase diagram must be examined to find the conditions necessary for the catalyst to be in liquid phase and for the material to precipitate out. The desired elements and catalyst are placed in a quartz furnace tube to control the temperature, pressure and residence time. Then a laser is used to ablate the precursors and catalyst. The vapor phase species condenses into small clusters, then nanowire growth begins once the liquid becomes supersaturated and continues as long as the nanoclusters remains in the liquid phase. Growth ends when the NW are cooled.\cite{Morales_1998}