Size effect on morphology and optical properties of branched ZnO/Si nanowire arrays

• Influence of reaction time on the morphology and optical properties was analyzed.
• Mechanisms for the growth and optical characteristics and their evolution were revealed.
• The system gave a reflectivity lower than 4% in the visible region.
• Band diagram of the branched ZnO/Si nanowire arrays was supplied.

Branched ZnO/Si nanowire arrays have been synthesized by integration of metal-assisted chemical etching and hydrothermal growth. Experiments for different etching duration and hydrothermal growth time were carried out to investigate their effect on the final morphology of the heterogeneous material as well as its photoluminescence and antireflectance. The results demonstrated that the Si nanowires got longer with extending etching period, on which the branched ZnO nanowires were shorter in length and smaller in diameter in the set time period. The branched ZnO nanowires became longer and gradually filled up the interval among Si nanowires with prolonging hydrothermal growth. The emission spectra indicated that the nanostructure became better with less defects and impurities for the long Si nanowires. The diffuse reflectance spectra of the ZnO/Si nanowires showed an optimal growth period for the reflectivity lower than 4% in the visible region. In this article, possible mechanisms for the nanowire arrays growth and optical properties and their evolution were also discussed, which might provide guidance for the architecture and application of the heterogeneous tree-like nanowire arrays.