Crystal phase of III-V ternary nanowires: Control parameters and open questions

Compositional trends in III-V ternary nanowires grown by the vapor-liquid-solid method were extensively studied over the past decade. Conversely, the wurtzite-zincblende polytypism was investigated mainly for binary III-V nanowires. The crystal phase changes in III-V ternary nanowires and even the key parameters determining the preferred crystal structure of such nanowires remain largely unknown. Here, we try to fill the gap by presenting a model for the crystal phase in vapor-liquid-solid III-V ternary nanowires based on the surface energy analysis. Our approach is based on the known phase diagram of GaAs nanowires, and allows one to identify the crystal phase as a function of the droplet contact angle and composition. We show a qualitative trend agreement of the phase diagrams with the available experimental data on $\mathrm{I}{\mathrm{n}}_{x}\mathrm{G}{\mathrm{a}}_{1\ensuremath{-}x}\mathrm{As}, \mathrm{A}{\mathrm{l}}_{x}\mathrm{G}{\mathrm{a}}_{1\ensuremath{-}x}\mathrm{As}$, and $\mathrm{Ga}{\mathrm{P}}_{x}\mathrm{A}{\mathrm{s}}_{1\ensuremath{-}x}$ nanowires. We also discuss the general crystal phase trends and the remaining uncertainties that should be circumvented to enable the full description and compositional control of these complex growth systems.