Bandgap engineering and structure analysis of ZnO/ Al$_{\mathrm{2}}$O$_{\mathrm{3}}$ superlattices grown by atomic layer deposition.

ORAL

Abstract

ALD-grown ZnO/Al$_{\mathrm{2}}$O$_{\mathrm{3}}$ superlattices (SLS) as analyzed by XRR assisted with GenX fittings exhibit a consistent mass density for the ZnO layers of 5.6 g/cm$^{\mathrm{3}}$, largely that of the bulk crystal. However, for Al$_{\mathrm{2}}$O$_{\mathrm{3}}$, the value is \textasciitilde 2.95 g/cm$^{\mathrm{3}}$ versus the ideal 3.95 g/cm$^{\mathrm{3}}$. This discrepancy suggests a highly porous Al$_{\mathrm{2}}$O$_{\mathrm{3}}$, possibly due to the presence of hydrogen in an AlO(OH) amorphous boehmite phase. TEM imaging portrays the periodic structures consistent with the XRR findings. The ZnO layers are c-textured while Al$_{\mathrm{2}}$O$_{\mathrm{3}}$ amorphous. Room-temperature CL measurements showed decreasing ZnO bandgap as the Al$_{\mathrm{2}}$O$_{\mathrm{3}}$ cycles increased, hinting at feasible bandgap engineering through SLS structural variations. Amorphous Al$_{\mathrm{2}}$O$_{\mathrm{3}}$ is known to have a smaller bandgap of 5.7-7.1 eV as compared to 7.1-8.8 eV for bulk crystals. CL also showed a peak at \textasciitilde 5.1 eV, thus consistent with our conjecture of the am-Al$_{\mathrm{2}}$O$_{\mathrm{3}}$.

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Authors

  • W.C. Hsieh

    • Department of Physics, National Sun Yat-Sen University

  • Q.Y. Chen

    • Department of Physics, National Sun Yat-Sen University

  • P.V. Wadekar

    • Department of Physics, National Sun Yat-Sen University

  • C.F. Chang

    • Department of Physics, National Sun Yat-Sen University

  • H.C. Huang

    • Department of Material Science and Optoelectronics, National Sun Yat-Sen University

  • C.M. Shiau

    • Department of Physics, National Sun Yat-Sen University

  • Y.P. Cheng

    • Department of Physics, National Sun Yat-Sen University

  • Y.S. Hong

    • Department of Physics, National Sun Yat-Sen University

  • C.Y. Dang

    • Department of Physics, National Sun Yat-Sen University

  • P.C. Kung

    • Department of Physics, National Sun Yat-Sen University

  • C.H. Lee

    • Department of Physics, National Sun Yat-Sen University

  • S.H. Huang

    • Department of Physics, National Sun Yat-Sen University

  • Z.Y. Wu

    • Department of Physics, National Sun Yat-Sen University

  • Y.Y. Liang

    • Department of Physics, National Sun Yat-Sen University

  • C.M. Lin

    • Department of Physics, National Sun Yat-Sen University

  • S.T. You

    • Department of Physics, National Sun Yat-Sen University

  • L.W. Tu

    • Department of Physics, National Sun Yat-Sen University

  • N.J. Ho

    • Department of Material Science and Optoelectronics, National Sun Yat-Sen University

  • H.W. Seo

    • Department of Physics, Jeju National University

  • W.K. Chu

    • Texas Center of Superconductivity and Department of Physics, University of Houston