Controlled Epitaxial Growth of Vertically Well-Aligned ZnGa₂O₄ Nanowire Arrays on Sapphire via a Novel Vapor–Liquid–Solid Process

As a representative ternary oxide semiconductor, the epitaxial growth of uniaxially aligned ZnGa2O4 nanowire arrays on common substrates remains challenging, owing to their lattice mismatch and the differing volatility of zinc and gallium sources. Herein, we demonstrate the controllable epitaxial growth of vertically well-aligned ZnGa2O4 nanowire arrays on a c-plane sapphire substrate by the simple chemical vapor deposition method. To achieve the strategic control of the composition of ZnGa2O4, samples with different ratios of source materials were synthesized, and the preferred molar ratio of ZnO/Ga2O3/C for obtaining single-crystalline and ordered ZnGa2O4 nanowire arrays was found. Combined with the epitaxial relationship and the nucleation site analysis between ZnGa2O4 and c sapphire ([11̅2]ZnGa2O4//[112̅0]Al2O3 and [11̅0]ZnGa2O4//[11̅00]Al2O3), the special vapor–liquid–solid growth process was explored: the horizontal nanowires and the triangular pyramids of ZnGa2O4 frustums are formed successively at the early stage, which act as a buffer layer to progressively alleviate the large lattice mismatch between ZnGa2O4/sapphire and the subsequent formation of vertical nanowire arrays. In addition, the effects of oxygen concentration and Au film thickness are investigated. This work provides a facile referable strategy for epitaxial growth of other ternary compound nanowires, paving their way in potential applications.