Photovoltaic Effect And Reproducible Resistive Switching Effect In BiFeO₃ Based Epitaxial Films

As one of the most popular materials studied by many researchers around the world,ferroelectric material has many special properties,such as ferroelectricity,piezoelectricity,pyroelectricity,photovoltaic effect and resistive switching effect.BiFeO₃ as a typical ferroelectric material came into the view of researchers due to its relatively high Curie temperature.Up to now,ferroelectricity,piezoelectricity and domain switching mechanism of BiFeO₃ have been widely studied.In this paper,the photovoltaic effect in BiFeO₃ thin films was studied.The photovoltaic effect in BiFeO₃ can be regulated by the ferroelectric polarization,which enables BiFeO₃ being used in the electro-optic sensor field in the future.What’s more,with the rapid development of the information technology,it is vital to find new materials which have potential in the information technology application.As a result,Bi₂FeCrO₆,a relatively new ferroelectric material,has been prepared by doping Cr in BiFeO₃,then the microstructure and resistive switching effect of Bi₂FeCrO₆ films was studied.In this paper,multilayer ferroelectric thin films with different structures have been prepared on the SrTiO₃ substrates using pulse laser deposition system.After that,X-ray diffraction,atomic force microscopy,scanning tunneling microscopy,ultraviolet spectrophotometer and Keithley digital-source meter were used to characterize the prepared films,including morphology,crystal structure,transmission spectrum,photovoltaic effect and resistive switching effect.This paper mainly contains the following three aspects:（1）the preparation of high-quality ferroelectric thin films（2）research concerning the photovoltaic effect in BiFeO₃ thin film;（3）research concerning the resistive switching effect in the Bi₂FeCrO₆ thin films.The specific contents are as follow:BiFeO₃ and Bi₂FeCrO₆ thin films with high quality were prepared by the pulse laser deposition system.Through adjusting the preparation parameters during the film growth,such as laser energy,oxygen pressure in the growth chamber,the distance between sample and target,high-quality ferroelectric thin films with various multilayer structures were prepared.And the high-quality thin films are the guarantees of the accuracy in the subsequent measurements.The photovoltaic effect in SrTiO₃/La_0.7Sr_0.3MnO₃/BiFeO₃/ITO（In₂O₃:SnO₂=9:1）thin film was studied with the Keithley digital-source meter.It is found that there exists photovoltaic effect in this structure.Furthermore,the direction of open-circuit voltage and short-circuit current changes with the ferroelectric polarization switching;the value of short-circuit current increases with the increase of source light intensity and ferroelectric polarization;with the temperature rising from 25 ℃ to 130 ℃,the short-circuit current increases from 180 nA to 480 nA.The resistive switching effect of SrTiO₃/SrRuO₃/Bi₂FeCrO₆ was studied using both the conductive atomic force microscopy and the scanning tunneling microscopy,and the diameters of the tips used in the measurements are 100 nm and 1 nm,respectively.A stable and repeatable bipolar resistive switching effect was observed in SrTiO₃/SrRuO₃/Bi₂FeCrO₆ with conductive atomic force microscopy.What’s more,a stable resistive switching effect at negative bias was observed using scanning tunneling microscopy.The ON/OFF ratios（the ratio between the high and low resistance values of the film）in both measurrements are between 15 and 122.In a word,the results concerning ferroelectricity,photovoltaic effect and resistive switching effect of BiFeO₃ based films in this paper are significant in both scientific research and the application in information technology.