Controlled Epitaxial\nGrowth of Vertically Well-Aligned\nZnGa<sub>2</sub>O<sub>4</sub> Nanowire Arrays on Sapphire via a Novel\nVapor–Liquid–Solid Process

As a representative ternary oxide semiconductor, the\nepitaxial\ngrowth of uniaxially aligned ZnGa<sub>2</sub>O<sub>4</sub> nanowire\narrays on common substrates remains challenging, owing to their lattice\nmismatch and the differing volatility of zinc and gallium sources.\nHerein, we demonstrate the controllable epitaxial growth of vertically\nwell-aligned ZnGa<sub>2</sub>O<sub>4</sub> nanowire arrays on a <i>c</i>-plane sapphire substrate by the simple chemical vapor\ndeposition method. To achieve the strategic control of the composition\nof ZnGa<sub>2</sub>O<sub>4</sub>, samples with different ratios of\nsource materials were synthesized, and the preferred molar ratio of\nZnO/Ga<sub>2</sub>O<sub>3</sub>/C for obtaining single-crystalline\nand ordered ZnGa<sub>2</sub>O<sub>4</sub> nanowire arrays was found.\nCombined with the epitaxial relationship and the nucleation site analysis\nbetween ZnGa<sub>2</sub>O<sub>4</sub> and <i>c</i> sapphire\n([11̅2]<sub>ZnGa<sub>2</sub>O<sub>4</sub></sub>//[112̅0]<sub>Al<sub>2</sub>O<sub>3</sub></sub> and [11̅0]<sub>ZnGa<sub>2</sub>O<sub>4</sub></sub>//[11̅00]<sub>Al<sub>2</sub>O<sub>3</sub></sub>), the special vapor–liquid–solid growth process\nwas explored: the horizontal nanowires and the triangular pyramids\nof ZnGa<sub>2</sub>O<sub>4</sub> frustums are formed successively\nat the early stage, which act as a buffer layer to progressively alleviate\nthe large lattice mismatch between ZnGa<sub>2</sub>O<sub>4</sub>/sapphire\nand the subsequent formation of vertical nanowire arrays. In addition,\nthe effects of oxygen concentration and Au film thickness are investigated.\nThis work provides a facile referable strategy for epitaxial growth\nof other ternary compound nanowires, paving their way in potential\napplications.