Al2O3 buffer-facilitated epitaxial growth of high-quality ZnO/ZnS core/shell nanorod arrays

Abstract

II–VI semiconductor heterojunctions show huge potential for application in nanodevice fabrication due to their type-II alignments owing to the better spatial separation of electrons and holes. However, the hetero-epitaxial growth of high-quality heterostructures is still a challenge, especially for materials with large lattice mismatch. In this work, well-aligned single-crystalline ZnO/ZnS core/shell nanorod arrays were obtained by introducing an Al₂O₃ buffer layer. It is interesting that the nature of the ZnS layer varies with the thickness of the Al₂O₃ layer. When Al₂O₃ is less than 2 nm, the interaction between the substrate and epilayer is strong enough to penetrate through the buffer layer, enabling the growth of ZnS on Al₂O₃-coated ZnO nanorod arrays. On the basis of detailed characterization, a rational growth mechanism of the core/shell heterostructure is proposed, in which the Al₂O₃ interlayer can eliminate voids due to the Kirkendall effect around the interface and accommodate a misfit dislocation between the inner ZnO and outer ZnS, resulting in more sufficient strain relaxation in the epitaxy. In addition, cathodoluminescence measurements demonstrate that the optical properties of the ZnO/ZnS heterostructure could be effectively improved by taking advantage of the thin Al₂O₃. The I–V curves characterized by PeakForce tunneling atomic force microscopy reveal that the heterostructure shows a typical rectifying behavior and good photoresponse to ultraviolet light. These findings may provide a reasonable and effective strategy for the growth of highly lattice-mismatched heterostructure arrays buffered by the Al₂O₃ layer, broadening the options for fabricating heterojunctions and promoting their applications in optoelectronic devices.