Epitaxial rare earth fluoride insulating layers on semiconductors: Structure, phase transitions, and interface reactions

Abstract

Layers of GdF3 were deposited on Ge(111) and GaAs(111)B surfaces, and the measurements compared with similar ones for HoF3 on Si(111) [C. L. Griffiths, J. E. Macdonald, and R. H. Williams, J. Appl. Phys. 70, 1858 (1991)]. It is shown that the trigonal structure normally only stable at higher temperatures is stable in all cases at room temperature, for thin layers. For thicker films a transition to the orthorhombic phase has been observed and studied by low-energy electron diffraction. Some interesting patterns are observed, and are interpreted in terms of a multidomain orthorhombic structure for HoF3 on Si(111) [C. L. Griffiths, J. E. Macdonald, and R. H. Williams, J. Appl. Phys. 70, 1858 (1991)], with the additional complexity of mirror planes for GdF3 on Ge(111). Interface reactions have also been studied in some detail, using x-ray photoelectron spectroscopy and soft x-ray photoemission spectroscopy. In all cases, except GdF3 on Ge, strong reactions are observed with rare earth silicide formation for HoF3 on Si and more complex products for GdF3 on GaAs. These reactions may be substantially reduced by the incorporation of a passivating interlayer. This is illustrated by the use of an ordered arsenic layer at the LaF3–Si interface.