Analysis of epitaxial fluoride-semiconductor interfaces

Abstract

It is known that the epitaxial quality of alkaline-earth fluorides on semiconductors is not simply related to the degree of lattice mismatch. The interfacial structure in two such systems has been examined by high-resolution electron microscopy. For the high-mismatch system (9%), BaF2 on (111) Ge, an ‘‘incommensurate’’ interface is observed. In contrast, the lower mismatch BaF2 on (100) InP system (5%), displays a locally ‘‘commensurate’’ interface with closely spaced misfit dislocations. These observations demonstrate that epitaxy can occur with or without strong bonding across the substrate overlayer interface, depending on the lattice mismatch. The discovery of a truly incommensurate, epitaxial interface [in the BaF2 on (111) Ge system] is furthermore quite unique.