Growth and application of epitaxial heterostructures with polymorphous rare-earth oxides

Abstract Cubic lanthanide sesquioxides consisting of cations with an atom radius larger that promethium could be used as a buffer layer for growth of semiconductors with a cubic structure (Ge, GaAs or SiGe) on Si due to the close matching of a lattice constant between the oxides and the semiconductors. However, the oxides have a stable hexagonal structure at temperatures higher than 600 °C, which is typical for the epitaxy process. According to our ab initio density functional theory calculations, energy of molecular unit of hexagonal lanthanum oxide is lower than that of the cubic structure by 127 meV. In this paper, we demonstrate epitaxial stabilization of pseudomorphic cubic structure of lanthanum oxide grown on a cubic template. The oxide layer can serve as a buffer for growth of Ge or GaAs layers on Si substrate. On the other hand, gadolinium oxide, which according to many studies has a stable cubic structure, was grown on hexagonal GaN. The single crystal monoclinic Gd 2 O 3 could be used as a gate dielectric layer for GaN based electronic devices.