Characterization of ferroelectric property of c-axis and non-c-axis oriented epitaxially grown bismuth layer-structured ferroelectric thin films with different m-numbers prepared by MOCVD

Epitaxial thin films of bismuth layer-structured ferroelectrics (BLSF) with different m-numbers, i.e., Bi₂VO_5.5 (BVO) (m=1), SrBi₂Ta₂O₉ (SBT) (m=2), and Bi₄Ti₃O₁₂ (BIT) (m=3), were grown by metalorganic chemical vapor deposition (MOCVD). (001)-oriented films were deposited on (100)SrTiO₃. (114)-oriented BVO, (116)-oriented SBT, and (118)-oriented BIT films were deposited on (110)SrTiO₃. Moreover, (102)-oriented BVO, (103)-oriented SBT, and (104)-oriented BIT films were deposited on (111)SrTiO₃. On (100), (110), and (111)SrTiO₃ substrates, c-axis of the deposited films was tilted about 0°, 45°, and 56°, respectively, against perpendicular to the surface of the substrates irrespective of m-number. This suggests the growth of crystallographic equivalent orientation. The distinctive surface morphology originated to the feature of the film orientation was observed. The dielectric constant and the leakage current of c-axis-oriented film was smaller than that of non-c-axis-oriented one, indicating smaller dielectric constant and leakage current along c-axis than a- or b-axes. A larger ferroelectric anisotropy was ascertained for SBT and BIT films. Furthermore, the evaluated spontaneous polarization along a- and c- axes of BIT from the data of the epitaxially grown BIT films well agreed with the reported one for the single crystal. This suggests the ferroelectric property was not strongly affected by the strain in the films.