Study On Ultraviolet Lateral Photovoltaic Effect Of Ferric Spinel Oxide/SiC Heterojunctions

Transition metal oxides（TMOs）are widely applied in non-volatile storage,energy conversion,microwave devices due to their excellent magnetic,semiconducting and dielectric properties.Among them,ferric spinel oxide attracts many researchers in spintronics,energy conversion and abnormal semiconductors due to its complex crystal lattice and valence distribution of iron elements.It has great commercial application in the fields of miniaturization of electronic devices,high energy density storage and clean energy.However,the electrical insulation properties of most spinel oxides limit their application in the novel semiconducting materials and photoelectric devices.In this paper,the anomalous semiconducting properties of ferric spinel oxides with non-stoichiometric and then the application on the lateral photovoltaic effect are inverstigated in detail.Combined with wide bandgap semiconductor Si C,the oxide heterojunctions with huge photoresponse characteristics are studied for ultraviolet optoelectronic detectors,to realize the Si C-based photodetector with simple preparation and high cost-performance ratio.First,the lateral photovoltaic effect on half-metallic and spinel Fe₃O₄ films is investigated.The rectifying behavior suggests that the large build-in electric field was formed in the Schottky junctions.Moreover,the nonlinear current-voltage curves and the abnormal temperature dependence resistance behaviors all indicate that the inversion layer occurs on the surface of Si C.A near-ultraviolet sensitive lateral photovoltaic effect（LPE）in Fe₃O₄/3C-Si C Schottky junctions with a fast relaxation time（30 μs）is reported.This device has excellent position sensitivity as high as 67.8 m V mm-1 illuminated by a 405 nm laser.Furthermore,the MR was observed to be dependent upon both the applied voltage and the angle between the magnetic field and the current.A greatly magnified low field negative MR ～-4% was achieved at 300 K and 500 Oe up to 3.0 V in the Fe₃O₄ film,which originated from the release of charge accumulation at the interface under the applied magnetic field due to the negative MR of Fe₃O₄.Thus,the fast relaxation and high positional sensitivity of the LPE make the Fe₃O₄/3C-Si C junction a promising candidate for a wide range of ultraviolet/near-ultraviolet optoelectronic applications.Next,the anomalous semiconducting and ultraviolet photovoltaic characters of spinel NiFe₂O₄ epitaxial films are investigated.The change of growing pressure varies the Ni/Fe ratio for the obtained spinel NiFe₂O₄ films,showing that 4 orders of magnitude increases in DC resistivity,and the optical bandgap tunes between 2.25 and 2.71 e V.Especially,it shows that the fantastic p-type semiconductor behavior appears at the Fetet-loss NiFe₂O₄,which has been verified by firstprinciples calculations and electric and/or magnetic measurements experimentally.A largely sensitive LPE（about 103 m V mm-1）with ultrafast response（1.14 μs）was also observed.The physical mechanism of lateral transport of light-excited carriers of LPE in oxide/semiconductor heterojunction is firstly confirmed in our experiment by the huge difference sensitivity and response time of LPV and electrical resistance states for NiFe₂O₄ films grown on different substrates.Moreover,those junctions exhibited enhanced photoresponsivity as high as 3.2 m AW-1 and large on/off ratio under zero bias and excited with UV light,and an ultrafast response of 152 ns.Our results clearly address the pathway for the novel p-type semiconducting oxide,and self-powered ultraviolet optoelectronic（positional sensitive）detectors with simple structure,huge photoresponse and ultrafast response.Finally,the colossal ultraviolet photovoltaic effect of spinel FeAl₂O₄ oxides with non-stoichiometric is investigated in detail.The average free path of Fe/Al cations changes differently due to the various of the oxygen pressure,resulting in the non-stoichiometric FeAl₂O₄ epitaxial films are obtained experimentally.Also,the band alignments under thermal equilibrium combining with semiconductor Si C are studied.XPS valence band spectra and electrochemical measurements show that FeAl₂O₄ exhibits the abnormal transition from p-type to n-type semiconductor with the increase of Fe content,while its conductivity decreases rapidly.The lateral PV position sensitivity as high as 210.7 m V mm-1 and the rise time of only 0.86 μs were observed experimentally.