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Auto Feeding Epitaxial Growth of Oxide Thin Film without Oxidant Kazuo Shimoyama, Kousuke Kubo, 1Tatsuro Maeda and Kikuo Yamabe Institute of Applied Physics, University of Tsukuba Tsukuba, Ibaraki 305-8573, Japan 1 Electrotechnical Laboratory Tsukuba, Ibaraki 305-8568, Japan ABSTRACT High-quality thin films of BaTiO3 and SrTiO3 on SrTiO3 substrate were obtained by shutting off the oxygen supply during growth. Epitaxial growths were carried out with molecular-beam epitaxy (MBE) under extremely low oxygen partial pressure (pO2 < 1×10-8 Pa). Although only Ba(Sr) and Ti metals were supplied without introducing oxidant during the growth, clear reflection high-energy electron diffraction (RHEED) intensity oscillations from layer-by-layer growth were observed. The deposited films were found to have approximately stoichiometric compositions of BaTiO3 and SrTiO3. Oxygen was automatically fed from the substrate during the growths. It was found that the BaTiO3/SrTiO3 interface was abrupt without intermixing, despite a considerable amount of oxygen seems to have moved from the substrate to the film through the interface.

INTRODUCTION Thin films of perovskite oxide Ba1-xSrxTiO3 have attracted much attention for their applications in advanced microelectronics such as dynamic random access memories (DRAMs) and nonvolatile memories. It is known that the lattice strain of BaTiO3 induced by the lattice mismatch between film and substrate strongly influences the electrical properties such as dielectric constant, ferroelectricity and Curie temperature [1-3]. The misfit factor between BaTiO3 and SrTiO3 is ~2.3%. If BaTiO3 film grows coherently on the SrTiO3 substrate without misfit strain relaxation, the c-axis length elongates to accommodate the in-plane lattice mismatch. Therefore, precise control techniques of the lattice misfit strain are strongly needed. The authors have reported that the oxygen partial pressure during the growth plays a crucial role in the lattice strain relaxation. Lowering the oxygen partial pressure during the heteroepitaxy of BaTiO3/SrTiO3 leads to a larger critical thickness of the BaTiO3 film [4,5]. Understanding of growth mechanisms of the oxides is of significance for a new class of material with artificially layered structure whose layer thickness and interface are controlled on an atomic scale. In this study, we demonstrate that SrTiO3 and BaTiO3 grow epitaxially on SrTiO3 substrate in extremely low oxidizing ambient. As an extreme case of a low oxidizing ambient, the component metals (Ba, Sr and Ti) were deposited to the SrTiO3 substrate while shutting off the oxygen supply in a ultra high vacuum (UHV) growth chamber. The deposited film was evaluated by reflection highenergy electron diffraction (RHEED), Auger electron spectroscopy (AES) and X-ray diffraction (XRD). Growth mechanisms of perovskite oxides on oxide substrate in the extremely low oxygen partial pressure are discussed. F11.2.1

EXPERIMENTAL Ba and Ti metals were coevaporated with an MBE apparatus for epitaxial growth of BaTiO3, and Sr and