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Abstract <p>Epitaxial growth of (ZnO)<sub><i>x</i></sub>(InN)<sub>1−<i>x</i></sub> films by sputtering has been achieved by suppressing In–N decomposition through reduced substrate temperature while ensuring adatom migration on O-polar ZnO substrates with smooth surfaces characterized by Gaussian height distribution. The root-mean-square roughness of films prepared between room temperature and 300°C are 0.22–0.33&#xa0;nm, significantly lower than 0.59&#xa0;nm observed at 450°C. Surface height distribution analysis indicates that growth of pit components, triggered by In–N decomposition, is suppressed at these temperatures. Notably, films fabricated at 150–300°C exhibit atomically flat surfaces with straight step edges, indicating crystal growth in step-flow mode. They possess minimal tilt mosaicity and excellent out-of-plane alignment, with (0002) x-ray rocking curves showing full&#xa0;width at half&#xa0;maximum as low as 0.04–0.07°. Our findings highlight a critical substrate temperature range that promotes step-flow growth while preventing In–N decomposition, offering potential advantages for other material systems constrained by similar substrate temperature limitation. Our findings advance the understanding of crystal-growth behaviors at reduced temperatures and pave the way for fabricating high-quality compound films at lower temperatures, which offers potential benefits for crystal growth of various materials where thermal sensitivity is a concern.</p> Graphical abstract <p></p> Impact statement <p>This study demonstrates a significant advancement in compound material systems by demonstrating low-temperature epitaxial growth of (ZnO)<sub><i>x</i></sub>(InN)<sub>1−<i>x</i></sub> films on ZnO substrates by sputtering. Our findings identify a critical substrate temperature range of 150–300°C that avoids In–N decomposition while promoting step-flow growth. Here, despite the low temperature, adatom migration is assured on O-polar substrates with smooth surfaces characterized by minimal skewness of surface height distribution. Films grown at these temperatures exhibit high crystal qualities with the full&#xa0;width at half&#xa0;maximum of the (0002) plane x-ray rocking curves as low as 0.04–0.07°, which are typically observed at higher temperatures. By avoiding In–N decomposition and carefully selecting the substrate temperatures, we have not only reduced the root-mean-square roughness to 0.22–0.33&#xa0;nm, but also achieved step-flow growth. Transmission electron microscopy further confirms that (ZnO)<sub><i>x</i></sub>(InN)<sub>1−<i>x</i></sub> films fabricated within this temperature range have homogeneous compositions and nearly uniform lattice spacings, highlighting the importance of precise substrate temperature control in achieving film uniformity.</p>

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Low-temperature step-flow growth of (ZnO)x(InN)1−x films by magnetron sputtering

  • 期刊论文

  • 发表日期：

    2025年6月18日

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  • Ryota Narishige,
  • Shotaro Hata,
  • Hiroki Otsuyama,
  • Yoshiharu Wada,
  • Yutaro Nakano,
  • Naoto Yamashita,
  • Kunihiro Kamataki,
  • Takamasa Okumura,
  • Kazunori Koga,
  • Masaharu Shiratani,
  • Naho Itagaki

摘要

Abstract

Epitaxial growth of (ZnO)x(InN)1−x films by sputtering has been achieved by suppressing In–N decomposition through reduced substrate temperature while ensuring adatom migration on O-polar ZnO substrates with smooth surfaces characterized by Gaussian height distribution. The root-mean-square roughness of films prepared between room temperature and 300°C are 0.22–0.33 nm, significantly lower than 0.59 nm observed at 450°C. Surface height distribution analysis indicates that growth of pit components, triggered by In–N decomposition, is suppressed at these temperatures. Notably, films fabricated at 150–300°C exhibit atomically flat surfaces with straight step edges, indicating crystal growth in step-flow mode. They possess minimal tilt mosaicity and excellent out-of-plane alignment, with (0002) x-ray rocking curves showing full width at half maximum as low as 0.04–0.07°. Our findings highlight a critical substrate temperature range that promotes step-flow growth while preventing In–N decomposition, offering potential advantages for other material systems constrained by similar substrate temperature limitation. Our findings advance the understanding of crystal-growth behaviors at reduced temperatures and pave the way for fabricating high-quality compound films at lower temperatures, which offers potential benefits for crystal growth of various materials where thermal sensitivity is a concern.

Graphical abstract

Impact statement

This study demonstrates a significant advancement in compound material systems by demonstrating low-temperature epitaxial growth of (ZnO)x(InN)1−x films on ZnO substrates by sputtering. Our findings identify a critical substrate temperature range of 150–300°C that avoids In–N decomposition while promoting step-flow growth. Here, despite the low temperature, adatom migration is assured on O-polar substrates with smooth surfaces characterized by minimal skewness of surface height distribution. Films grown at these temperatures exhibit high crystal qualities with the full width at half maximum of the (0002) plane x-ray rocking curves as low as 0.04–0.07°, which are typically observed at higher temperatures. By avoiding In–N decomposition and carefully selecting the substrate temperatures, we have not only reduced the root-mean-square roughness to 0.22–0.33 nm, but also achieved step-flow growth. Transmission electron microscopy further confirms that (ZnO)x(InN)1−x films fabricated within this temperature range have homogeneous compositions and nearly uniform lattice spacings, highlighting the importance of precise substrate temperature control in achieving film uniformity.