Molecular beam epitaxy growth of epitaxial barium silicide, barium oxide, and barium titanate on silicon

Abstract

Thin‐film epitaxial structures of BaSi₂, BaO, and BaTiO₃, have been grown on the (001) face of silicon using ultrahigh vacuum, molecular beam epitaxy (MBE) methods. Source shuttering for the metal species coordinated with a pulsed, or cyclic, oxygen arrival at the growing oxide surfaces significantly improves film quality. The epitaxial growth of BaO is accomplished without silica formation at the BaO/Si interface by stabilizing BaSi₂ as a submonolayer template structure. In situ ellipsometric measurements of the indices of refraction for BaO and for BaTiO₃ in a BaTiO₃/BaO/Si multilayer gave n=1.96 for BaO and n=2.2 for the BaTiO₃, within 10% of their bulk values. These values suggest that this structure can be developed as an optical waveguide. BaO is impermeable to silicon for films as thin as 10 nm at temperatures as high as 800 °C, and good epitaxy can be obtained from room temperature to 800 °C. The epitaxy is such that BaTiO₃(001)∥BaO(001)∥Si(001) and BaTiO ₃〈110〉∥BaO〈100〉∥Si〈100〉.