ROLE OF LATTICE MISMATCH AND SURFACE-CHEMISTRY IN THE FORMATION OF EPITAXIAL SEMICONDUCTOR-INSULATOR INTERFACES

The formation of SrF2/Si(111) and Ge/CaF2/Si(111) interfaces is studied with photoemission and compared to previous results for the CaF2/Si(111) interface. The interface between SrF2 and Si(111) is found to be nonstoichiometric, similar to the interface between CaF2 and Si(111): the bonding is between Si and the cation, with a layer of fluorine missing at the interface. In the case of Ge growth on CaF2/Si(111), a variety of effects are noted: The CaF2/Si(111) valence-band offset is reduced by about 1 eV upon deposition of Ge at room temperature. The sticking coefficient of the Ge is significantly increased by preparing the CaF2 surface with electron bombardment to remove the top layer of fluorine. For both the irradiated and nonirradiated cases, annealing of thin room-temperature-deposited films resulted in Ge island formation. © 1990 The American Physical Society.