Semiconducting nanowires have unique properties that are distinct from their bulk counterparts, but realization of their full potential will be ultimately dictated by the ability to control nanowire structure, composition, and size with high accuracy. Here, we report a simple, yet versatile, approach to modulate in situ the diameter, length, and composition of individual segments within (In,Ga)N nanowires by tuning the seed particle supersaturation and size via the supply of III and V sources during the growth. By elucidating the underlying mechanisms controlling structural evolution, we demonstrate the synthesis of axial InN/InGaN nanowire heterojunctions in the nonpolar m-direction. Our approach can be applied to other materials systems and provides a foundation for future development of complex nanowire structures with enhanced functionality.
Controlled modulation of diameter along the axis of nanowires can enhance nanowire-based device functionality, but the potential for achieving such structures with arbitrary diameter ratios has not been explored. Here, we use a theoretical approach that considers changes in the volume, wetting angle, and three-dimensional morphology of seed particles during nanowire growth to understand and guide nanowire diameter modulation. We use our experimental results from diameter-modulated InN and GaN nanowires and extend our analysis to consider the potential and limitations for diameter modulation in other materials systems. We show that significant diameter modulations can be promoted for seed materials that enable substantial compositional and surface energy changes. Furthermore, we apply our model to provide insights into the morphology of the liquid/solid interface. Our approach can be used to understand and guide nanowire diameter modulation, as well as probe fundamental phenomena during nanowire growth.
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