Diffraction studies for stoichiometry effects in BaTiO3 grown by molecular beam epitaxy on Ge(001)

作者：Hsu Min Hsiang Mark^*; Merckling Clement; El Kazzi Salim; Pantouvaki Marianna; Richard Oliver; Bender Hugo; Meersschaut Johan; Van Campenhout Joris; Absil Philippe; Van Thourhout Dries

来源：Journal of Applied Physics, 2016, 120(22): 225114.

DOI：10.1063/1.4972101

In this work, we present a systematic study of the effect of the stoichiometry of BaTiO3 (BTO) films grown on the Ge(001) substrate by molecular-beam-epitaxy using different characterization methods relying on beam diffraction, including reflection high-energy electron diffraction (RHEED), X-ray diffraction (XRD), and selected-area electron diffraction in transmission electron microscopy. Surprisingly, over a wide range of [Ba]/[Ti] ratios, as measured by the Rutherford backscattering spectrometry, all the BTO layers exhibit the same epitaxial relationship < 100 > BTO(001)//< 110 > Ge(001) with the substrate, describing a 45 degrees lattice rotation of the BTO lattice with respect to the Ge lattice. However, varying the [Ba]/[Ti] ratio does change the diffraction behavior. From RHEED patterns, we can derive that excessive [Ba] and [Ti] generate twinning planes and a rougher surface in the non-stoichiometric BTO layers. XRD allows us to follow the evolution of the lattice constants as a function of the [Ba]/[Ti] ratio, providing an option for tuning the tetragonality of the BTO layer. In addition, we found that the intensity ratio of the 3 lowest-order Bragg peaks I-(001)/I-(002), I-(101)/I-(002), and I-(111)/I-(002) derived from omega - 2 theta scans characteristically depend on the BTO stoichiometry. To explain the relation between observed diffraction patterns and the stoichiometry of the BTO films, we propose a model based on diffraction theory explaining how excess [Ba] or [Ti] in the layer influences the diffraction response. Published by AIP Publishing.

• 出版日期2016-12-14