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27 August 2014 Off-axis sputter deposition of ZnO films on c-sapphire substrates by utilizing nitrogen-mediated crystallization method
Naho Itagaki, Kazunari Kuwahara, Koichi Matsushima, Daisuke Yamashita, Hyunwoong Seo, Kazunori Koga, Masaharu Shiratani
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Optical Engineering, Vol. 53, Issue 8, 087109 (August 2014). https://doi.org/10.1117/1.OE.53.8.087109
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.
CC BY: © The Authors. Published by SPIE under a Creative Commons Attribution 4.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.
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Naho Itagaki, Kazunari Kuwahara, Koichi Matsushima, Daisuke Yamashita, Hyunwoong Seo, Kazunori Koga, and Masaharu Shiratani "Off-axis sputter deposition of ZnO films on c-sapphire substrates by utilizing nitrogen-mediated crystallization method," Optical Engineering 53(8), 087109 (27 August 2014). https://doi.org/10.1117/1.OE.53.8.087109
Published: 27 August 2014
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Cited by 10 scholarly publications.
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KEYWORDS
Zinc oxide
Crystals
Sputter deposition
Sapphire
Particles
Oxygen
Gallium nitride
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