Preparation And Photoelectric Properties Of BiFeO₃-base Thin Films

BiFeO₃ is a kind of multiferroic material that has both ferroelectric and ferromagnetic properties at room temperature,but the higher leakage current is still the primary problem faced by BiFeO₃.Several reasons result in this challenge:?1?Bismuth is very unstable.During the process of film deposition and annealing,bismuth often combines with oxygen in the film and then volatilizes,leaving vacancies of bismuth and oxygen served as spaces charges.As these space charges could move in the direction of the applied electric field,the leakage current of film increases;?2?Fe³⁺is unstable,which tends to change into Fe²⁺.The electron transfer during this process generates current.Moreover,oxygen vacancies induced by valence change of iron ions could also increase leakage currents.In this paper,doping of bismuth by rare earth elements in BiFeO₃ is explored.The effect of Zn O by forming ZnO/BiFeO₃ thin films on leakage is investigated.Besides,the electrical and optical properties of these films are also studied.Bi_1-xGd_xFeO₃?x=0.00,0.05,0.10,0.15?films are prepared on Pt/Ti/SiO₂/Si substrates and FTO glass substrates by sol-gel method,respectively.The dielectric behavior,ferroelectric properties,leakage current performance and optical properties of the films are studied at room temperature.The leakage current test shows that doping of Gd effectively limits the leakage current of BiFeO₃ film.Further studies show that the ferroelectric properties of Bi_1-xGd_xFeO₃ thin films prepared on Pt/Ti/SiO₂/Si substrates and FTO glass substrates are both enhanced by appropriately doping?x=0.05?of Gd.Polarization intensity 2Pr are 115?C cm^-2 and 170?C cm^-2,respectively.ZnO/BiFeO₃ composite films are prepared on FTO glass substrates by sol-gel method.The leakage currents,I-V characteristics and optical properties of the composite films are studied.Compared with pure BiFeO₃ films,the leakage current of ZnO/BiFeO₃ films has been significantly improved.Obvious diode effects could be observed from the composite films by I-V tests.Photoelectric tests show that the composite ZnO/BiFeO₃ film exhibits obvious photovoltaic effect.