Surface-induced effects in GaN nanowires

Abstract

Semiconductor nanowires (NWs) are characterized by an extraordinarily large surface-to-volume ratio. Consequently, surface effects are expected to play a much larger role than in thin films. Here, we review a research focused on the impact of the surface on the electrical and optical properties of catalyst-free GaN NWs with growth direction <0001>. Using a combination of complementary experimental techniques, it has been shown that the Fermi level is pinned at the NW sidewall surfaces, resulting in internal electric fields and in full depletion for NWs below a critical diameter. Deoxidation of the surfaces unpins the Fermi level, leading to enhanced radiative recombination of excitons. Prominent absorption below the bandgap is caused by the Franz-Keldysh effect. Close to the surface, the ionization energy of donors is reduced. The consideration of surface-induced effects is mandatory for an understanding of the physical properties of NWs as well as their application in devices.

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Acknowledgment

We thank all the coauthors of our own papers reviewed in this work, and in particular C. Pfüller for helping with the figures. We acknowledge U. Jahn for the careful and critical reading of the manuscript. Our own research reviewed here has been partially supported by the EU Marie Curie Research Training Network "Interfacial Phenomena at Atomic Resolution and multiscale properties of novel III-V SEMiconductors" (PARSEM) under Grant MRTN-CT-2004-005583 and through the Information Society Technologies project "Nanowire-based One-Dimensional Electronics" (NODE) under Grant 015783 as well as by the German Federal Ministry of Education and Research joint research project "MONALISA - Epitaxie von monolithisch-integrierten III-V Materialien auf Sili-zium als Lichtemitter" (Contract No. 01BL0810).

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Correspondence to Lutz Geelhaar.

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Calarco, R., Stoica, T., Brandt, O. et al. Surface-induced effects in GaN nanowires. Journal of Materials Research 26, 2157–2169 (2011). https://doi.org/10.1557/jmr.2011.211

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