Metallic band structure of CaF2 thin films grown on silicon(1 1 1): Possible formation of CaSi2

Abstract

We grew epitaxial 10 monolayer (ML) CaF2 films on a Si(111) substrate and measured its electronic structure with angle-resolved photoemission spectroscopy. Reflection high-energy electron diffraction measurements showed the 1×1 streaks of the grown film with no sign of the formation of the Ca-Si surface superstructure at the growth temperature of 400–500 °C. The band dispersion of the films was metallic in contrast to the highly insulating nature of bulk CaF2. The metallic band dispersion did not change with additional Si deposition (1–10 ML) on the CaF2 film. We suggest that CaSi2 may be formed near the surface layers and this shows that the CaF2/Si is not an ideal insulator/semiconductor heterostructure for application in atomically thin electronic devices.