Introduction. In the late 1990s, the success of SrTiO3 epitaxial growth on Si by molecular beam epitaxy (MBE) opened a path for integrating complex oxides on Si-based platforms. In particular, ferroelectric perovskite oxides offer promising perspectives to improve or add functionalities on-chip like low power logic devices or integrated photonics [1]. BaTiO3, the prototypical ferroelectric perovskite oxide, is a good candidate for these applications [2, 3]. However, regarding practical devices, integrating a perovskite oxide epitaxially on Si by MBE is still in its infancy. One key point is the control of the crystalline orientation, which determines the polarization orientation within the thin film. Playing with experimental parameters of growth and the composition of the Si xGe1-x semiconductor substrate are means to manipulate the competition between compressive stress from epitaxy and tensile stress from thermal expansion. In order to support MBE growth strategies, aberration-corrected scanning transmission electron microscopy has been investigated to determine both the strain and the chemical state of epitaxial BaTiO3 thin films.
Experiment. BaTiO3 was epitaxially grown on Si xGe1-x (x=1 and x = 0.20) substrates either using an SrTiO3 buffer layer to reduce both thermal and lattice mismatches between BaTiO3 and Si or without any buffer on Si0;2Ge0.8. The complex oxides were grown by MBE using Sr, Ba and Ti effusion cells. Details on the growth are given in refs [1,4]. BaTiO3 was grown directly on strained Si0.8Ge0.2/Si substrates using a barium passivation. STEM-HAADF images were collected on a FEI Titan Low-Base 60-300 probe corrected microscope and the data treated using the geometric phase analysis (GPA). STEM-EELS data were also acquired with a special attention to Ba, Ti and O elements.
Main results. In a first part, we will first describe the crystalline structure and cationic composition studied at the nanoscale in BaTiO3/SrTiO3/Si heterostructures. The effect of oxygen pressure will be discussed. We show that the lattice parameter profile evolution within the thickness of the BaTiO3 films is clearly associated with modifications of the cation stoichiometry within the thickness and that there is a clear impact of the oxygen pressure on both lattice parameter and composition profiles. In a second part, we will discuss the particular epitaxial state of BaTiO3 grown directly on Ba-passivated strained Si0.8Ge0.2.
References.
Figures:
Fig. 1 Atomic structure image of an epitaxial BaTiO3 (BTO) crystal grown on a SrTiO3 (STO)-buffered Si substrate and corresponding lattice parameters maps determined by GPA analysis.
Fig. 2 Lattice parameters profiles obtained by integration of the maps shown in figure 1 and elemental profiles from a crystal of the same film.
To cite this abstract:
Sylvie Schamm-Chardon, Cesar Magen, Lucie Mazet, Robin Cours, Martin Frank, Vijay Narayanan, Catherine Dubourdieu; Epitaxial BaTiO3 on Si and SiGe for low power devices: nanoscale characterization of the film and its interface with the semiconductor by HAADF and EELS in STEM. The 16th European Microscopy Congress, Lyon, France. https://emc-proceedings.com/abstract/epitaxial-batio3-on-si-and-sige-for-low-power-devices-nanoscale-characterization-of-the-film-and-its-interface-with-the-semiconductor-by-haadf-and-eels-in-stem/. Accessed: December 4, 2023« Back to The 16th European Microscopy Congress 2016
EMC Abstracts - https://emc-proceedings.com/abstract/epitaxial-batio3-on-si-and-sige-for-low-power-devices-nanoscale-characterization-of-the-film-and-its-interface-with-the-semiconductor-by-haadf-and-eels-in-stem/