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Optical Engineering • Open Access

Off-axis sputter deposition of ZnO films on c-sapphire substrates by utilizing nitrogen-mediated crystallization method
Author(s): Naho Itagaki; Kazunari Kuwahara; Koichi Matsushima; Daisuke Yamashita; Hyunwoong Seo; Kazunori Koga; Masaharu Shiratani

Paper Abstract

High-quality epitaxial ZnO films on c-plane sapphire substrates have been obtained by utilizing an off-axis sputtering configuration together with buffer layers prepared via nitrogen-mediated crystallization (NMC). The role of NMC buffer layers is to provide high density of nucleation site and, thus, to reduce the strain energy caused by the large lattice mismatch (18%) between ZnO and sapphire. The NMC buffer layers allow two-dimensional growth of subsequently grown ZnO films, being particularly enhanced by employing an off-axis sputtering configuration in which the substrate is positioned out of the high-energy particles, such as negative oxygen ions originating from the targets. As a result, ZnO films with smooth surfaces (root-mean-square roughness: 0.76 nm) and a high electron mobility of 88  cm2/V·s are fabricated. Photoluminescence spectra of the ZnO films show strong near-band-edge emission, and the intensity of the orange-red defect emission significantly decreases with increasing horizontal distance between the target and the substrate. From these results, we conclude that off-axis sputtering together with NMC buffer layers is a promising method for obtaining high-quality epitaxial ZnO films.

Paper Details

Date Published: 27 August 2014
PDF: 6 pages
Opt. Eng. 53(8) 087109 doi: 10.1117/1.OE.53.8.087109
Published in: Optical Engineering Volume 53, Issue 8
Show Author Affiliations
Naho Itagaki, Kyushu Univ. (Japan)
Japan Science and Technology Agency (Japan)
Kazunari Kuwahara, Kyushu Univ. (Japan)
Koichi Matsushima, Kyushu Univ. (Japan)
Daisuke Yamashita, Kyushu Univ. (Japan)
Hyunwoong Seo, Kyushu Univ. (Japan)
Kazunori Koga, Kyushu Univ. (Japan)
Masaharu Shiratani, Kyushu Univ. (Japan)

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