BaTiO3 Integration with Nanostructured Epitaxial (100), (110), and (111) Germanium for Multifunctional Devices

ABSTRACT: Ferroelectric−germanium heterostructures have a strong potential for multifunctional devices. Germa-nium (Ge) is attractive due to its higher electron and hole mobilities while ferroelectric BaTiO3 is promising due to its high relative permittivity, which can make next-generation low-voltage and low-leakage metal-oxide semiconductor field-effect transistors. Here, we investigate the growth, structural, chemical, and band alignment properties of pulsed laser deposited BaTiO3 on epitaxial (100)Ge, (110)Ge, and (111) Ge layers. Cross-sectional transmission electron microscopy micrographs show the amorphous nature of the BaTiO3 layer and also show a sharp heterointerface between BaTiO3 and Ge. The appearance of strong Pendellösung oscillation fringes from high-resolution X-ray diffraction implies the presence of parallel and sharp heterointerfaces. The valence band offset relation of ΔEV(100) ≥ ΔEV(111)> ΔEV(110) and the conduction band offset relation of ΔEC(110)> ΔEC(111) ≥ ΔEC(100) on crystallographically oriented Ge offer significant advancement for designing new-generation ferroelectric−germanium-based multifunctional devices