Epitaxial growth of barium titanate thin films on germanium via atomic layer deposition

•Barium titanate (BTO) thin films were epitaxially grown on Ge(001) via ALD.•The epitaxial BTO films have a c-axis out-of-plane orientation.•No Ge native oxide is observed between BTO films and Ge substrates.•Ge surface reconstruction was preserved throughout the growth process. Barium titanate BaTiO3 (BTO) thin films were epitaxially grown at 225°C on 2×1-reconstructed Ge(001) surfaces via atomic layer deposition (ALD). Approximately 2nm of BTO film was grown directly on Ge(001) as an amorphous film. Electron diffraction confirmed the epitaxy of the BTO films after post-deposition annealing at 650°C. Additional BTO layers grown on the crystalline BTO/Ge(001) film were crystalline as-deposited. X-ray diffraction indicated that the epitaxial BTO films had a c-axis out-of-plane orientation, and the abrupt BTO/Ge interface was preserved with no sign of any interfacial germanium oxide. Scanning transmission electron microscopy provided evidence of Ba atoms occupying the troughs of the dimer rows of the 2×1-reconstructed Ge(001) surface, as well as preservation of the 2×1-reconstructed Ge(001) surface. This study presents a low-temperature process to fabricate BTO/Ge heterostructures.