Photoelectric Response Characteristics Of ZnGa₂O₄/NiO Heterojunction

As a popular semiconductor in recent years,ZnGa₂O₄ is a promising candidate for solar-blind UV detection material due to its ultra-wide bandgap of about 5.0 e V at room temperature.Although many properties were observed in UV detectors with photoconductive structures,their slow response speed still limited future applications.Photosensitive diodes based on pn junction have drawn many researchers'attention because of their fast response speed.So far,p-type doping of ZnGa₂O₄ was still under investigation,which made photosensitive diodes based on hetero-pn junction a possible candidate.As an oxide with a 3d electronic configuration,NiO is a translucent p-type semiconductor material with a bandgap of 3.6 e V.The properties made it a possible choice for the construction of the ZnGa₂O₄/NiO hetero-pn junction.Therefore,based on NiO growth research,this thesis fabricates the p-NiO/n-ZnGa₂O₄ heterojunction diode and studied its photoelectric response characteristics.The results show significant improvement in the photoelectric response time characteristics of the device.First,this thesis used radio frequency magnetron sputtering technology to fabricate NiO film.Using NiO ceramics as the target material,the NiO thin films were grown on c-plane sapphire substrates.Then the effects of different substrate temperatures and argon-oxygen ratio on the surface morphology and crystal quality of NiO thin films were investigated by X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS),atomic force microscopy(AFM),UV-Vis spectrometer,et al.The results show that under the growth conditions of substrate temperature of 400?and the argon-to-oxygen ratio of 2:1,high-quality NiO thin films that fabricate on c-plane sapphire substrates could provide technical support for the construction of heterostructures.Secondly,we successfully prepared the NiO/ZnGa₂O₄ heterojunction UV photodetector based on the ZnGa₂O₄ thin film growth process.The ZnGa₂O₄ thin films were grown on the surface of the NiO thin films and we used electron beam evaporation technology to deposit Ti/Au electrodes.The NiO/ZnGa₂O₄ heterojunction showed obvious rectification characteristics in the dark state.The turn-on voltage is about 3V,and under the positive and negative 5V bias,the rectification ratio of the device is 15,as well as the dark current of the device is about 9.4p A under the 5V bias.Under the irradiation of 255nm ultraviolet light,the photocurrent is about 20.5 n A at 5 V bias,and the light-dark current ratio is larger than 10~3.The photoresponsivity of the device is0.64A/W,and the detection rate can reach 9.2×10¹².Even under zero bias voltage,the photoresponsivity of the NiO/ZnGa₂O₄ heterojunction device is 0.047 A/W and the detection rate is 9.8×10¹² Jones.The results show an obvious photovoltaic effect,which basically meets the technical demand of static response characteristics.Though the quality of the NiO film and the interface characteristics of the NiO/ZnGa₂O₄heterojunction still can be optimized,the response speed of the NiO/ZnGa₂O₄heterojunction photodetector is improved obviously.The rise time of the NiO/ZnGa₂O₄heterojunction photodetector is 47 ms and 40 ms respectively under 5 V bias and zero bias voltage.As for the case of fall time,the experimental results show 32ms and 24 ms under the above condition.Both rise time and fall time meet the application requirements.In general,the thesis's results have shown that the NiO/ZnGa₂O₄heterojunction is a feasible technical solution for the development of solar-blind UV detection devices.