Effect of Radius on Crystal Structure Selection in III-V Nanowire Growth

The radius of III-V nanowires is known to have an effect on the resulting crystal structure during particle-assisted growth; however, the causes behind this effect remain under debate. In this work, we use stochastic simulations of nanowire growth to evaluate how the radius (R) affects the growth dynamics and how this in turn affects the crystal structure selection. This is due to the geometry of the growing nanowire: the number of atoms in the seed particle scales with R-3, and the number of III-V pairs per layer scales with R-2. The influx of growth species to the seed can, for instance, scale with the surface area of the seed particle for direct impingement (proportional to R-2) or the perimeter of the nanowire for sidewall diffusion (proportional to R-1) or be radius-independent for substrate diffusion in some cases (proportional to R-0). These differences in radius dependencies cause the particle composition to change more rapidly for thinner nanowires, which in turn leads to nucleation at higher supersaturations and promotion of the wurtzite structure. In addition, the geometry can also make the influx V/III ratio dependent on the nanowire radius, which can influence the selection of crystal structure in different ways depending on the materials system and growth regime.