Guided
Growth of Horizontal GaN Nanowires on Spinel
with Orientation-Controlled Morphologies
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Abstract
We report the guided growth of horizontal
GaN nanowires (NWs) on
spinel (MgAl<sub>2</sub>O<sub>4</sub>) substrates with three different
orientations: (111), (100), and (110). The NWs form ordered arrays
with distinct morphologies on the surface of the substrates, controlled
by the interaction with the substrate. The geometry of the NWs matches
the symmetry of the spinel surfaces: on MgAl<sub>2</sub>O<sub>4</sub>(111), (100), and (110) the NWs grow in six, four, and two directions,
respectively. The epitaxial relations and morphologies of the NW–substrate
interface were characterized by cross-sectional transmission electron
microscopy. The substrate was found to be mobilized during the growth
and either climb up or recede on/under one or two sides of the NW,
depending on the substrate orientation. Possible reasons for the similarity
and differences between the orientations of the NWs and thin GaN films
grown on MgAl<sub>2</sub>O<sub>4</sub> are proposed. These results
demonstrate the generality and flexibility of the guided growth phenomenon
in NWs and specifically show that MgAl<sub>2</sub>O<sub>4</sub>(111)
could be a low-mismatch substrate for the growth of high-quality GaN
layers and NWs