Preparation And Visible Photoconductive Modulation Of LaCoO₃ Epitaxial Films

Visible-photoconductive materials for utilizing rich-visible light(accounting for?43%of the total sunlight)for optical information storage and signal transmission,and play a very important role in optoelectronic technology.Perovskite-type LaCoO₃has a unique 3d electronic structure and rich optical and electromagnetic properties.It has a broad application prospect in the field of visible photoconductive materials.In this paper,LaCoO₃epitaxial film is prepared by polymer assisted deposition method.The crystal structure distortion can be controlled by adjusting the epitaxial stress and crystal plane orientation,in order to explore the influence mechanism of structural distortion on the visible photoconductivity response of LaCoO₃.The experimental results show that:the lattice relaxation effect existing in LaCoO₃epitaxial film makes the epitaxial stress and Jahn-teller like tetragonal distortion of Co O₆octahedron decrease with the increase of film thickness,affects the t_2g-e_genergy level and band gap width of 3d electrons of cobalt ions,and leads to the decrease of visible photoconductivity of the film.Under tensile strain,the order of photoconductive activities of LaCoO₃/Sr Ti O₃films with different orientations are as follows:(111)>(110)>(100);Under compressive strain,the order of photoconductive activity driven by visible light of LaCoO₃/La Al O₃with different orientations is(100)>(110)>(111);It is closely related to the Jahn-teller like tetragonal distortion degree of Co O₆octahedron,the crystal plane energy and the anisotropy of photogenerated carrier transmission.Yttrium(Y³⁺)was doped at A site of LaCoO_3,due to lattice mismatch,the epitaxial strain along c-axis as well as the strain-induced tetragonal distortion of La_1-xY_xCo O₃films increase with the content of doped yttrium.As-prepared films have higher degree of Co O₆stetragonal distortion,which result in lower crystal field splitting energy and narrower band gap energy,thereby elevating the charge transition.The introduction of yttrium can restrain recombination of the photo-generated electron-hole pairs,expand the visible light absorption range,and improve the photoconductive performance of LaCoO₃epitaxial films.La_1-xY_xCo O₃films under visible light irradiation(96 m W/cm~2,1 voltage bias),it is observed that La_0.85Y_0.15Co O₃film shows a significant photocurrent(0.48?A),as compared to the undoped LCO film(0.05?A).