Abstract
Controlling the diameter of self-catalyzed III-V nanowires is important for tailoring their performance in optoelectronic applications. Here, we investigate the impact of abrupt or gradual increase of the V/III flux ratio on the GaAs nanowire diameter. A dynamic model of nanowire diameter is developed to explain the changes induced by flux ratio modulation: (i) shrinkage of the catalyst droplet under elevated As flux and (ii) convergence toward a critical diameter governed by the flux ratio during subsequent nanowire elongation. The different diameter behaviors observed under abrupt or gradual flux increase are elucidated by this relationship, through which we present a quantitative analysis of the relationship between the nanowire diameter and the V/III flux ratio. Epitaxial Ge shells were grown around the modulated-diameter GaAs cores to investigate any impact on the morphology and quality of the group-IV shell. The Ge shell is found to maintain a uniform thickness, regardless of the diameter of the GaAs core. High-resolution annular dark-field scanning transmission electron microscopy reveals Ge shell sidewalls indexed to the {112} planes and rotated by 47° relative to the GaAs core facets, while energy-dispersive X-ray spectroscopy confirms slight Ge interdiffusion into the GaAs core. This work provides a predictive framework for controlling the diameter evolution under varying flux ratios and provides insights into III-V/IV heterointegration.