Scaling-up charge injection to nanowire p-n heterojunctions: From individual nanowires to their large size arrays

One-dimensional nanocrystals and nanowires due to their high crystal quality, ease of growth, control and diversity in their composition have become promising building blocks in a number of technologies including photovoltaic, chemical sensing and light sources. One of the technological barriers to integrate such nanostructures to devices is the inability in controlling their hierarchical order on a scalable fashion. An ordered structure is needed because charge transport must be done at the individual nanowire level. In this presentation, we use a crystal growth technique for wafer scale growth of planar nanowires. We discuss a surface-directed vapor-liquid-solid (SVLS) growth technique in which horizontal nanowires grow from individual Au nanodroplets, and their alignment is dictated by the underlying substrate. SVLS process maintains the strength of the traditional VLS-based methods in growth of nanowires, while enabling excellent control over their hierarchical assemblies. We discuss the concept of “smart surfaces” for planar growth of some semiconductor oxides such as ZnO and TiO₂ and present results on growth morphology of other II-VI semiconductors. In this presentation we show the impact of the substrate on growth direction of nanowires and formation of bi- and tri-directional assemblies as well as n-p heterojunctions (Figure 1a, b).