1D n–p Heterojunctions of Zinc Oxide on Gallium Nitride: A Structural Characterization

Abstract

Recently, we showed lateral growth of ZnO nanowires and nanowalls on single crystal GaN and formation of bi- and tridirectional assembly of nanowires and nanowalls using a surface-directed vapor–liquid–solid process (SVLS). Taking advantage of this growth technique, planar arrays of electrically addressable n–p heterojunctions were fabricated. Each n–p heterojunction is formed at the interface of a nanowire or nanowall with the underlying substrate. In the present work, we further investigated the coherency of the crystal structure of the heterojunctions both along their width and length using focused-ion beam microscopy and high-resolution transmission electron microscopy (HRTEM). We explain the anisotropic growth of ZnO in multi directions using a SVLS mechanism, whereas conventional crystal growth techniques only anticipate an isotropic island formation of ZnO on GaN. During the SVLS process, a ZnO nanocrystal forms inside a Au nanodroplet, and elongates via a sequential ZnO island formation during whi...