Ferroelectric Filed Effect And Photovoltaic Effect Of Pr And Mn Co-substituted BiFeO₃Thin Films

Ferroelectric thin films show important ferroelectric, pyroelectric, piezoelectric and photoelectric effects, which have various potential applications in microelectronic and optoelectronic fields. Multiferroic materials are compounds with two or more primary ferroic characteristics. Only a few materials are multiferroics and their magnetoelectric effects can only be observed at very low temperature. Recently, multiferroic materials have attracted much attention due to their interesting magnetoelectric coupling. BiFeO3, as the only room temperature multiferroic material, exhibits superior ferroelectric properties, and have many applications in nonvolatile memories, sensors, catalysis and green energy. We prepared Pr and Mn co-substituted BiFeO3(Bi1-x%Prx%Feo.95Mno.o5O3) thin films, abbreviated as BPFMOx, by a sol-gel method and studied their ferroelectric filed effect and photovoltaic effect. The results are summarized as follows.1. The effect of Pr concentration on the ferroelectric field effect in Pt/BPFMOx/Si structures was studied. Well-crystallized BPFMOx thin films were obtained as characterized by X-ray diffraction. It is found that the grain size decreases with the increase of Pr concentration. Counterclockwise C-V hysteresis loops using p-type Si substrates were observed when Pr concentration is less than5%, indicating strong charge injection. As Pr concentration increases, clockwise hysteresis loops appear, demonstrating the ferroelectric field effect. The largest memory window observed is0.92V in Pt/BPFMO15/Si.2. The effect of the insertion of Al2O3and HfO2insulating layer on the ferroelectric field effect in Pt/BPFMO15/Si was studied. Memory window in Pt/BPFMO15/Al2O3/Si is increased to1.4V compared with Pt/BPFMO15/Si. With the increase of sweep voltage, memory window increases to a maximum value and then decreases. The Al2O3insulating layer helps to suppress the charge injection. However, the application of HfO2insulating layer is not successful. The memory window decreases to0.6V. With the increase of sweep voltage, it decreases further.3. The photovoltaic effect of BPFMOx thin film under the irradiation of white light was studied. Through the Ⅰ-Ⅴ measurement, a maximum photo voltage of21.6mV is observed. When the Pr doping content is15%, the film shows the largest photovoltage. Because the largest ferroelectric polarization appears at15%Pr concentration, it is inferred that the ferroelectric photovoltaic effect can be controlled by the polarization.