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Issue 16, 2019
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Photo-induced selective etching of GaN nanowires in water

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Nanowire (NW) based devices for solar driven artificial photosynthesis have gained increasing interest in recent years due to the intrinsically high surface to volume ratio and the excellent achievable crystal qualities. However, catalytically active surfaces often suffer from insufficient stability under operational conditions. To gain a fundamental understanding of the underlying processes, the photochemical etching behavior of hexagonal and round GaN NWs in deionized water under illumination are investigated. We find that the crystallographic c-plane remains stable, whereas the m-planes are photochemically etched with rates up to 11 nm min−1, depending on the applied UV light intensity. By investigating nanowalls, we achieve control of the exposed crystallographic facets and find an enhanced stability of the a-plane compared to the m-plane. Photo-excited holes, which drift to the side facets due to the upward surface band bending in nominally n-type (not intentionally doped) GaN, are identified as the driving force of the process, which allows the development of concepts for the stabilization of the nanostructures. A geometrically enhanced absorption of periodic NW arrays is correlated with a dependence of the etch rate on the NW pitch and diameter. Further, we find selective photochemical etching of the NW base in the presence of sub-band gap illumination, which is attributed to defect-related absorption in this region. These results provide improved understanding of the roles of inhomogeneous defect distribution, light excitation profiles, and different surface facets on the photochemical stability of nanostructures and provide viable strategies for improving stabilities under light-driven reaction conditions.

Graphical abstract: Photo-induced selective etching of GaN nanowires in water

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Publication details

The article was received on 11 Dec 2018, accepted on 01 Apr 2019 and first published on 02 Apr 2019

Article type: Paper
DOI: 10.1039/C8NR10021G
Nanoscale, 2019,11, 7967-7975

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    Photo-induced selective etching of GaN nanowires in water

    M. Kraut, F. Pantle, J. Winnerl, M. Hetzl, F. Eckmann, I. D. Sharp and M. Stutzmann, Nanoscale, 2019, 11, 7967
    DOI: 10.1039/C8NR10021G

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