Cathodoluminescent proreties of ZnO nanobranches on Si nanowire backbones by catalyst-free metalorganic vapor deposition

Abstract

One-dimensional (1D) semiconductor nanocrystals are of interest due to their efficient transport of electrons and optical excitations. The ability to control the structure, morphology, and composition of these building blocks could provide the potential to design their electrical and optical properties. In particular, branched nanocrystals allow for the assembly of three-dimensionally interconnected nanowire networks, and can be exploited as active components in a wide range of device applications. Recently, self-organized dendritic nanowire structures have been synthesized by a thermal vapor transportation and condensation approach, but this method has the limited control over the composition and structure. Multi-step metal-catalyzed vapor-liquid-solid (VLS) technique has also been introduced to grow branched and hyperbranched nanowire structures. However, the strategy for sequential seeding of catalysts on the nanowire backbones to grow the nanowire branches is not well established even though this is very crucial to control the position and density of the nanowire branches. At the same time, the introduction of a large amount of metal catalysts on the backbones could result in the incorporation of the metal impurities into both backbones and branches, which might significantly affect on the electrical and optical properties of semiconductor nanowires. Catalyst-free synthesis provides the growth of high quality 1D nanostructures on various substrates, but the synthesis of the branched nanostructures on the 1D nanowire backbones is not well established. Here, we report the synthesis of ZnO/Si branched heterostructures by employing catalyst-free metalorganic vapor deposition. The formation of single-crystalline ZnO nanobranches on Si backbones with an abrupt heterointerface was conformed by transmission electron microscopy (TEM) (Fig. 1). By adjusting the growth conditions, the size and density of the ZnO nanobranches have been tuned. Moreover, it is demonstrated that ZnO nanorods can be grown on laterally aligned Si nanowire arrays selectively, suggesting the potential of these hierarchical heterostructures for creating multi-dimensionally interconnected nanoelectronic and photonic systems. Furthermore, cathodoluminescent properties of ZnO nanobranches on Si nanowire backbones depending on the position and size will be discussed (Fig. 2).