Evidence for the influence of interfacial atomic structure on electrical properties at the epitaxialCaF2/Si(111) interface

The atomic structure at the epitaxial ${\mathrm{CaF}}_2$/Si(111) interface has been determined by high-resolution electron microscopy. As-grown layers reveal only direct Ca-Si bonding at the interface, with eightfold coordinated Ca atoms. Fluorine is preferentially removed from the interface during a rapid thermal anneal leaving fivefold coordinated Ca atoms. Removal of F results in a dramatic improvement in the electrical properties of the interface. The measured interface state density is reduced from ≳${10}^{13}$ ${\mathrm{cm}}^{\mathrm{-}2}$ to ≲${10}^{11}$ ${\mathrm{cm}}^{\mathrm{-}2}$.