Studies On Photoelectric Properties Of BiFeO₃/γ-Fe₂O₃Granular Films

BiFeO3as a kind of typical single-phase multiferroic material attract much attention in recent years. BiFeO3is simultaneously ferroelectric and antiferromagnetic at room temperature. BiFeO3is a kind of narrow band gap semiconductor, which can fully absorb the visible light, and shows good photoelectric properties. Such special properties make BiFeO3having the potential application in dynamic random access memory, microcircuits, spin electronics devices and sensors, etc.In this paper, we study the structure and photoelectric properties of BiFeO3/γ-Fe2O3granular films. The main works are as follows:(1) BiFeO3/y-Fe2O3granular films were deposited on an n-type single crystal silicon (100) substrate by radio frequency magnetron sputtering method, and then the samples were annealed at various temperatures under vacuum conditions.(2) The crystal structure and surface morphology of BiFeO3/γ-Fe2O3granular films annealed at various temperatures were examined by X-ray diffraction (XRD) and scanning electron microscope (SEM). The results show that the samples annealed at600℃present a better crystallization, no impurity phase, and smooth surface.(3) The J-V characteristic of BiFeO3/γ-Fe2O3granular film exhibits diodelike rectifying behavior, which may be attributed to Schottky barrier between BiFeO3and Ag electrode.(4) The photoconductivity of BiFeO3/y-Fe2O3films was measured by CHI600D electrochemical analyzer. An ordinary incandescent lamp (power density about20mW/cm2) was used as the light source. We observed that the photoconductivity effect increases with increasing annealing temperature. The photoconductivity properties are more obvious under negative bias due to the Schottky barrier at the interface between the film and Ag electrode. At a reverse bias of2V, the dark current of the BiFeO3/γ-Fe2O3film annealed at600℃is0.5μA, and the light current can reach39.8μA.(5) The I-V and the photoresponses characteristics of BiFeO3film and BiFeO3/γ-Fe2O3granular film annealed at600℃were measured. We found that BiFeO3/γ-Fe2O3granular film show larger photoconductivity compare to BiFeO3. The enhanced photoconductivity in BiFeO3/γ-Fe2O3film should originate from γ-Fe2O3. γ-Fe2O3has a good absorption in visible light range due to the narrow energy band-gap (ca.2.2eV). The values of photo-dark current ratio for the BiFeO3/γ-Fe2O3film at-2V is86, which is Greater than that (35) of BiFeO3film. The band gap of2.48eV for BiFeO3/γ-Fe2O3is less than2.57for BiFeO3.(6) The influence of light on ferrelectric hysteresis loop is investigated by Precision LC unit. Light have an effect on electricity hysteresis loop of the BiFeO3and BiFeO3/γ-Fe2O3films annealed at600℃, the remanent polarization increase, and the coercive field is reduced. The result also show that BiFeO3/γ-Fe2O3film Have a more significant change, the optical storage efficiency can reach71%.