Growth of CdF2/CaF2Si(111) heterostructure with abrupt interfaces by using thin CaF2 buffer layer

The minimum thickness of CaF2 buffer layer in CdF2/CdF2/Si(111) heterostructure to grow CdF2 epitaxialy on Si(111) under less stringent vacuum conditions (similar to 10(-8) Torr) was found to be 0.9 nm. Chemical reaction and growth mode at the initial stage of growth of CdF2 layer on Si(111) and on CaF2/Si(111) were studied with the in-situ X-ray photoelectron spectroscopy method. It was found that oxygen-related, chemical reaction of the CdF2 occurred on the Si(111) surface, but not on the CaF2(111) surface, Two-dimensional growth of CdF2 layer from the initial stage was observed on the CaF2 buffer layer, These results indicate that the CaF2 buffer layer plays a role as a barrier layer to chemical reaction between the CdF2 and the Si substrates. A short-period CdF2/CaF2 superlattice was grown on CaF2/Si(111) and the XRD showed satellite peaks which is consistent with the growth rate. This result shows that the structure has abrupt interfaces with less than a few monolayers.