Epitaxial thin-film growth enables novel functionalities, particularly if significant barriers to integration with existing technologies, scalability and excessive temperature of films, can be addressed. Here, we demonstrate a step toward addressing both challenges by combining hybrid molecular beam epitaxy and atomic layer deposition to epitaxially integrate BiFeO3 on Si wafers via a SrTiO3 metamorphic buffer layer. The solid-solid transformation of atomic-layer-deposited amorphous Bi-Fe-O films into epitaxial BiFeO3 thin films is investigated by in situ annealing utilizing transmission electron microscopy. The amorphous Bi-Fe-O layer undergoes a very complex crystallization process, encompassing phenomena such as reorientation, recrystallization, and grain growth. Our in situ transmission electron microscopy study revealed that a growth front of epitaxial crystallites emerged from the interface with the (001)-oriented SrTiO3 as temperature increased, whereas randomly oriented BiFeO3 crystallites formed simultaneously away from the interface. Structural rearrangement and recrystallization of crystallites took place at temperatures below 400 °C. At the final stage, above 400 °C, epitaxial crystallites larger than 60 nm merged into a single crystalline film. Our results demonstrate that this approach permits high-quality epitaxial integration of BiFeO3 thin films at back-end-of-line-compatible temperatures below 500 °C on metamorphic SrTiO3 buffer layers on Si.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films