The Reseach On High Efficiency Photodetector Based On Ferroelectric Photovoltaic Effect

Low power consumption,high sensitivity and high responsivity of photodetectors have been the focus of researchers’attention.The ferroelectric photovoltaic effect can realize the self-driven characteristic of photodetectors,but its own small photocurrent density limits the sensitivity and responsivity of the photodetectors.It is worthwhile for researchers to explore how to enhance the photocurrent density under the realization of self-driven characteristics of photodetectors.In this paper,self-driven photodetectors based on two ferroelectric polycrystalline ceramic film materials,Ba(Zr_0.2Ti_0.8)O₃-x(Ba_0.7Ca_0.3)Ti O₃（BZT-x BCT）and bismuth ferrate（Bi Fe O₃）,were constructed.The strength of the built-in electric field was improved by depolarization field,flexoelectric field and the Schottky barrier caused by the asymmetric electrodes.The photocurrent density was improved by increasing the strength of the built-in electric field,optimizing the light absorption performance,and optimizing the device thickness to enhance the performance of the photodetectors.The specific work is as follows.Firstly,BZT-x BCT（x=0.3,0.4,0.5,0.6,0.7）polycrystalline ceramic films and Bi_（1-x）Sm_xFe_（1-y）Co_yO₃（x=0 or 0.05,y=0、0.025、0.05 or 0.1）polycrystalline ceramic films were successfully prepared by the conventional solid-phase reaction method and hydrothermal method for the construction of self-driven photodetectors based on ferroelectric photovoltaic effect.The phase structure and microscopic morphology of the materials were investigated by XRD,SEM,and EDX,and it was found that the materials were pure and crystalline.When the elemental doping is excessive,it leads to the impurity phase in Bi Fe O₃.Compared with the BZT-0.5BCT ceramic film,the Bi_0.95Sm_0.05Fe O₃ ceramic film has lower densities and a certain amount of porosity.Secondly,the effects of different compositions of the samples on the light absorption properties,ferroelectric properties and dielectric properties were investigated.It was found that the response range of Bi_（1-x）Sm_xFe_（1-y）Co_yO₃was wider than BZT-x BCT,and the absorption coefficient in the visible region was larger.In the BZT-x BCT system,the ferroelectric ceramic film has the largest residual polarization intensity and the largest dielectric properties when x=0.5.Due to the volatilization of Bi elements,Bi_（1-x）Sm_xFe_（1-y）Co_yO₃has high carrier concentration and high leakage current,reducing the ferroelectric and dielectric properties.Finally,the photocurrent response of the samples with different compositions was investigated and the ceramic films with different compositions were able to respond to 405 nm light.In the BZT-x BCT system,the Pt/BZT-0.5BCT/Pt photodetector has the highest response current to 405 nm light,which confirms that the largest residual polarization intensity,the highest efficiency in separating photogenerated carriers,exhibits the highest photocurrent.In the system of Bi_（1-x）Sm_xFe_（1-y）Co_yO₃,the Pt/5-BSFO/Pt photodetector has the largest photocurrent response.The asymmetric Schottky barrier formed by using the Ag-Pt asymmetric surface electrodes which was beneficial to the carrier extraction and optimization of the thickness were used to further enhance the photocurrent response of the devices.The Ag/BZT-0.5BCT/Pt photodetector produced a pyroelectric-photovoltaic coupling current density of 67.3n A/cm² when detecting 405 nm light with a power density of 154.6 m W/cm²,and the sensitivity of the device reached 0.38 n A/m W.Under the same conditions,the photocurrent density of the Ag/5-BSFO/Pt device reached 78.86μA/cm²,which is three orders of magnitude greater than that of the Ag/BZT-0.5BCT/Pt photodetector.The sensitivity of the Ag/5-BSFO/Pt photodetector reached 2.71μA/m W,which is four orders of magnitude larger than that of the Ag/BZT-0.5BCT/Pt photodetector.The structural distortion in the thickness direction of the 5-BSFO ceramic film was investigated by Raman,and it was found that there is a strain gradient due to the Bi/Sm composition gradient in the thickness direction,and thus flexoelectric field generated in the ceramic film.