MBE Growth of Fe3O4 and Fe2O3 for Both Spin Injection Layers and Templates for Spinel Complex Oxides

Effective integration of functional oxides (magnetic, ferroelectric, piezoelectric and other multi-functional
materials) with semiconductors will lead to next-generation devices such as: new architectures that enable
multiple and simultaneous interactions with the environment for multifunctional active sensors and
controllers; energy harvesting and conversion devices as part of everyday items from clothing to
sidewalks; integrated nonvolatile memories for harsh environments; and paradigm-shifting spintronicsbased
circuits. Many of the functional properties of complex oxides are directional, thus requiring a
specific plane alignment in a device, and most oxides have multiple stable structures for a given
stoichiometry. In addition, small changes in stoichiometry with the same unit cell structure can produce
easily measurable differences in performance properties. While this sensitivity enables the possibility of
tuning complex oxides for different and novel applications, precise control of stoichiometry and structure
(practically at the atomic-level for nanoscale thin film heterostrucutres) is required. This is particularly
true for the interfaces and near-interface layers between the semiconductor and oxide as well as between
subsequent functional oxide layers, because surface quality impacts chemistry, structure, and morphology
of next-layer film deposition that, in turn, impacts the functionality of the film layer and the coupling
effects across layers through critical interfaces. Through molecular beam epitaxy (MBE), the use of a
magnesium oxide (MgO) template layer and the interface formation mechanisms of an oxygen bridge
have been investigated for effective heteroepitaxy of high-quality ferroelectric barium titanate (BTO) and
ferrimagnetic barium hexaferrite (BaM) on 6H-SiC. The results suggest strategies applicable to many
functional oxide integrations and many processing techniques.  Particular emphasis will be on the magnetic BaM and various forms of iron oxide.