Investigation Of Self-Powered Photodetectors Of Ternary Metal Oxides BiFeO₃ And CuBi₂O₄ And Its Application

Photodetectors that convert light signals into electrical signals are widely used in the fields of life,medical and industrial production,etc.Self-powered photodetectors based on the photovoltaic effect can achieve the detection of light signals without applied bias,meeting the requirements of low power consumption,miniaturization and integration of optoelectronic devices.The photoresponse characteristics of self-powered photodetectors are related to the processes of photogenerated carrier generation,separation,recombination,transportation and collection.The photoelectric conversion efficiency of devices can be improved by improving the crystalline quality of semiconductors to enhance the light absorption capacity or by constructing energy band structures and device structures that are conducive to the separation and transport of photogenerated carriers.In this thesis,self-powered photodetectors based on ternary metal oxides BiFeO₃（BFO）and CuBi₂O₄（CBO）were prepared using the sol-gel methods,respectively,and the photoresponse characteristics of the devices and applications were investigated,and the main research contents and results are as follows:（1）The photovoltaic and ferroelectric photovoltaic effects of the heterojunction are beneficial to enhance the performance of self-powered photodetectors.ZnO/BFO heterojunction devices are constructed using ZnO and BFO ferroelectric films,modulating the crystalline quality and energy band structure of the films by varying the thickness of the BFO films,and using ZnO nanorods to provide directional transport channels for photogenerated carriers.The synergistic effect of the built-in electric field in the ZnO/BFO heterojunction interface and the ferroelectric spontaneous polarization field of the BFO enhances the separation and transport of photogenerated carriers and strengthens the photocurrent of the device.The heterojunction device achieves Ultraviolet（UV）and visible dual-band photodetection under self-powered conditions,and the photoresponsivity and detectivity of the device reach 1.3 m A/W and 9.6×10¹¹Jones with a BFO thickness of 400 nm under 420 nm illumination,and the photoresponse rise/fall time is 12.6/44.9 ms.Polarization imaging applications of photodetector array units in UV and visible polarized light are explored by exploiting the dual-band polarization-sensitivity of the devices to UV and visible light at zero bias.（2）The transport ability of photogenerated carriers affects the performance of self-powered heterojunction photodetectors.The photoresponse range of Cu₂O/BFO/TiO₂devices is broadened to the red waveband,the stepped energy band structure of the heterojunction promotes the separation and transport of photogenerated carriers,and the self-powered photoresponse characteristics are enhanced by introducing Cu₂O layers with excellent optical absorption coefficients and hole mobility in the UV and visible bands in BFO/TiO₂ferroelectric heterojunction photodetectors.The self-powered photoresponsivity and detectivity of the device reached 3.0 m A/W and 9.4×10¹⁰Jones under 420 nm illumination,respectively.The device utilizes the ferroelectricity of the BFO films to switch between"AND"and"OR"logic gates in different BFO ferroelectricity states,expanding the application of ferroelectric heterojunction photodetectors in photo-controlled programmable logic gates.（3）The atomic ratios of the elements are crucial for the formation of stable phase structures of ternary compounds.The phase structure,optical band gap and Fermi energy level of CBO films are regulated by changing the Cu:Bi molar ratio in the precursor solution,which changes the optical and electrical properties of CBO and affects the self-powered photoresponse characteristics of Au/CBO/FTO devices.It is found that the CBO films prepared with a precursor Cu:Bi molar ratio of 0.5 have a single-phase structure,while the CBO films prepared with a Cu:Bi molar ratio less than or greater than 0.5 show Bi₂O₃or CuO and Cu₂O mixed precipitation phases,respectively.The single-phase CBO film forms a lower hole potential barrier at the interface with the FTO and Au electrodes,which facilitates the transport of hole carriers to the Au electrode and enhances the self-powered photoresponse characteristics of the device for the UV waveband.