Facile synthesis and enhanced luminescent properties of ZnO/HfO2 core–shell nanowires

Abstract

The morphological, structural and photoluminescence properties of one-dimensional ZnO/HfO₂ core–shell nanowires (NWs) with various thicknesses of HfO₂ shell layers are studied in detail in this work. The ZnO NWs have been fabricated by a simple hydrothermal method, which are then coated by thin HfO₂ shell layers using atomic layer deposition (ALD). The morphological and structural characterization demonstrates that the HfO₂ shells with polycrystalline structures grow on the single-crystalline ZnO NWs conformally. Moreover, the ZnO/HfO₂ core/shell NWs show remarkable enhanced ultraviolet (UV) emission with increasing thickness of the HfO₂ shell layer compared with bare ZnO NWs. The UV emission intensity for the sample with HfO₂ shell thickness of ∼16 nm is about 9 times higher than that of bare ZnO NWs. It mainly results from the decreased surface states by surface passivation of the HfO₂ shell layer as well as a typical type-I band alignment in the ZnO/HfO₂ core/shell structure. A model is also proposed to explain the evolution of the wide visible emission band with the relatively low intensity of the core/shell structures. Our results suggest that the ZnO/HfO₂ core/shell structures have potential applications for high-efficiency optoelectronic devices such as UV light-emitting diodes and lasers.