Heteroepitaxial growth of the δ-Ta2O5 films on α-Al2O3 (0001)

The heteroepitaxial δ-Ta2O5 films were deposited on α-Al2O3 (0001) by MOCVD. As the growth temperature increases from 650 °C to 800 °C, the structure of δ-Ta2O5 films changes from amorphous to single crystal, and finally to mixed phase structure. The film deposited at 750 °C exhibited the highest crystallinity and the corresponding epitaxial relationship were determined as δ-Ta2O5 (101¯1\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$10\overline{1 }1$$\end{document}) ‖ α-Al2O3 (0001) with δ-Ta2O5⟨1¯21¯0⟩\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\langle \overline{1 }2\overline{1 }0\rangle$$\end{document} ‖ α-Al2O3⟨101¯0⟩\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\langle 10\overline{1 }0\rangle$$\end{document}. A simplified diagram was proposed to illustrate the growth mechanism. The optical bandgap of the prepared films was within 4.20–4.22 eV. The refractive index of the amorphous and heteroepitaxial films was within 2.1–2.5.