Abstract
We report on morphology-controlled remote epitaxy via hydrothermal growth of ZnO micro- and nanostructure crystals on graphene-coated GaN substrate. The morphology control is achieved to grow diverse morphologies of ZnO from nanowire to microdisk by changing additives of wet chemical solution at a fixed nutrient concentration. Although the growth of ZnO is carried out on poly-domain graphene-coated GaN substrate, the direction of hexagonal sidewall facet of ZnO is homogeneous over the whole ZnO-grown area on graphene/GaN because of strong remote epitaxial relation between ZnO and GaN across graphene. Atomic-resolution transmission electron microscopy corroborates the remote epitaxial relation. The non-covalent interface is applied to mechanically lift off the overlayer of ZnO crystals via a thermal release tape. The mechanism of facet-selective morphology control of ZnO is discussed in terms of electrostatic interaction between nutrient solution and facet surface passivated with functional groups derived from the chemical additives.
Highlights
We report on morphology-controlled remote epitaxy via hydrothermal growth of ZnO micro- and nanostructure crystals on graphene-coated GaN substrate
Remote heteroepitaxial growth of ZnO was begun with transfer of the chemical vapor deposition (CVD)-grown single-layer graphene (SLG) onto GaN/Al2O3(0001) wafer through the poly(methyl methacrylate) (PMMA)-supported etching–transfer technique
ZnO micro- and nanostructured crystals were hydrothermally grown on the SLG-coated GaN substrate in four different nutrient solutions, described in (i)–(iv) of Fig. 1a, at 95 °C for 4 h
Summary
We report on morphology-controlled remote epitaxy via hydrothermal growth of ZnO micro- and nanostructure crystals on graphene-coated GaN substrate. In the bottom-up approach for fabricating non-planar overlayer, morphological control is essential to apply them to functional devices because size, shape, and geometry of the as-synthesized semiconductor crystal overlayers determine the physical properties and device performances (e.g., carrier confinement, mobility, laser Q factor, light extraction efficiency, energy storage capacity, depletion geometry at the junction of nanostructure/ substrate, etc.)[18,19,20,21,22,23,24,25]. We discuss the mechanism of morphology control in terms of facet-dependent growth rate determined by electrostatic interaction between nutrient solution and facet surface passivated with functional groups derived from the chemical additives. The ability of remote epitaxy to mass-release of ZnO microarrays from the original substrate is demonstrated, based on a sticky tape delamination technique
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