Study On Photovoltaic Effect Of Polycrystalline BiFeO₃ Thin Film Prepared By Pulsed Laser Deposition

A multiferroic combines any two or more of the primary ferroic orderings(ferroelectric,ferromagnetic,ferroelastic)in the same phase.In recent years,multiferroic magnetoelectric materials have attracted widely attention because of their potential application value as multifunctional novel devices,such as date storage,spintronics and so on.As a star material,BiFeO₃ combining ferroelectric order and anti-ferromagnetic order in room temperature with large remnant polarization is one of the most widely studied lead-free multiferroic materials.Polycrystalline multiferroic BiFeO₃ thin film was grown on ITO/quartz transparent substrate by pulsed laser deposition.How the factors of temperature and oxygen pressure influence the basic properties BiFeO₃ thin film was studied in details and the best factors have been founded.We observed and investigated the switchable diode behavior and photovoltaic effect in pure high-quality BiFeO₃ polycrystalline thin film.The main results are listed as follows:1.Transparent and conductive ITO thin film was successfully prepared on quartz substrate as ITO coating quartz substrate.Four ITO films were fabricated at different temperature respectively range from 530?to 620?.XRD patterns indicate that all films present cubic ferromanganese ore structure with(222)_pc orientation.UV-Vis absorption result shows that the ITO film grown at 620?exhibits intense absorbance around 300nm and The band gap is 4.2e V which indicates that our ITO film prepared on quartz substrate almost do not absorb visible light2.Temperature influence was investigated in the thin film preparation procedure.XRD patterns indicate that low temperature is not helpful film crystallization with Bi-rich impurity phase.Meanwhile,high temperature enhances the leakage current of the thin film from the ferroelectric hysteresis loops.Oxygen pressure also plays an important role in the preparation procedure.UV-Vis absorption results indicate the band gap of BiFeO₃ thin film can be adjusted by the oxygen pressure,Appropriate increased oxygen pressure can reduce the oxygen vacancy concentration in BiFeO₃thin film.3.Under the condition of 540? and 7Pa oxygen pressure,polycrystalline BiFeO₃thin film is equipped with the best basic properties.Switchable diode behavior was observed in Au/BiFeO₃/ITO capacitor structure attributed to the modulation of Schottky-like barriers.Meanwhile,our observed ferroelectric photovoltaic effect in this film originated from the primary spontaneous remnant polarization.The switchable photoelectric effect was also investigated.We proposed that The built-in potential of schottky barriers and depolarization field of ferroelectric remnant polarization together dominate switchable photoelectric effect and the latter is the main role.