Comparison of Modeling Strategies for the Growth of Heterostructures in III-V Nanowires

We present two models of the vapor liquid solid growth of nanowires of alloyed compound semiconductors. These models are tested against experiments on axial heterostructures in self-catalyzed (A1,Ga)As nanowires. They make use of the available bulk thermodynamic functions for this system. With a growth rate set by the group V dynamics, the crucial question is to determine the relationship between the compositions of liquid catalyst nanoparticle and solid. The first model assumes the equilibrium relationship. It predicts heterostructure profiles in excellent agreement with the experiments. The second model acknowledges that nanowires grow via nucleation at the solid liquid interface. We find the size and composition of the critical nucleus at the saddle point of the surface describing the work of formation of the nucleus. Assuming a fixed nucleus edge energy, the critical composition is virtually independent of the As concentration in the liquid and therefore close to the equilibrium composition. This model thus predicts equally well the interface profiles. With a composition-dependent edge energy, the profiles may differ significantly. We clarify why the effects of group III and group V atoms may be decoupled and why the reservoir effect is weak. Finally, we discuss how these findings could be extended to other systems.