Research On Characteristic Of Vertical Structure MgZnO:Ga/NiO Ultraviolet Detector

Compared with the traditional herejunction structure type ultraviolet photodetector,there are many advantages of vertical structure ultraviolet photodetector.For example,the electric field,which is relatively uniform distributed among the area,is directly assembled to the both sides of the junction,and is helpful for the separation of photogenerated electron and hole pairs in the junction region.And the small electrode spacing is always good for reduce the loss of free carrier in the transmission process.Futhermore,it can help the detector avoiding the influence of the watervapor or any other external adverse factor on the performance of the device.At present,most of the common vertical structure photodetectors are based on two-dimensional materials,such as MoS₂ and single layer graphene.However,there also exist many defects on two-dimensional materials at present,such as,harsh manufacture conditions,high cost of the preparation.And with the decrease of number of material layers,the carrier mobility will increases,however,the light absorption capacity of the material will also decreases.So this article chooses the wide band-gap semiconductor materials MgZnO:Ga and NiO,which have been widely studied and have achieved some degree of success,to fabricate the vertical structure heterojunction type ultraviolet photodetector.We hope the device could not only inherit the advantages of the vertical structure photoelectric detector,but also avoid the difficulties in application of two-dimensional material,resulting in gaining a photodetector which play an excellent performance.At the very beginning,we prepared a series of NiO thin films grown on the quartz substrate under different technological parameters（sputtering pressure,sputtering power,argon-oxygen ratio and the annealing temperature）by using the radio frequency magnetron sputtering.And we made use of X ray diffraction,UV transmission and absorption spectra test,atomic force scanning and other method to find out the influence of different technological parameters on the NiO thin films’crystal quality,surface morphology and optical properties.The results showed the NiO thin film has the trend to grow on the crystal phase（200）.The optimized parameters of sputtering pressure is 2.0Pa,and the sputtering power is 140 W,the argon-oxygen ratio is 30:10 and the annealing temperature is 500°C.Secondly,with the goal of having the herejunction structure device of good performance,we optimized the technological parameters of preparing MgZnO:Ga/NiO thin films.On the basis of previous optimized parameters of preparing NiO thin films,we grown a series of NiO with the same quality.And we grown a range of MgZnO:Ga on the NiO thin films under different sputtering pressure,sputtering power,argon-oxygen ratio and the annealing temperature.Analyses of crystal quality,optical and electrical properties are finished by the characterization of composition,structure,morphology.EDS and XPS test confirmed the exist of elements in MgZnO:Ga/NiO.After all the optimization procedure,we fabricated a set photodetector devices with different electrode,which all showed good rectification characteristic.Device with the Au electrode showed the best performance and had the peak response at 221nm with the responsivity of0.78mA/W and peak response at 336nm with the responsivity of 0.63mA/W,which had a good dual-band detect capacity in ultraviolet range.Finally,we fabricated the vertical structure herejunction MgZnO:Ga/NiO ultraviolet photodetector with the specific shape and size.When the electrode sapcing is too large,the devices did not show any characteristic of optics and electricity by test on optical and photoelectric property.However,the performance of the device improved with the decrease of electrode spacing.When the distance between the electrodes is 0.5mm,the spectral response peak of the device was at 204nm with the responsivity of 14.1mA/W and the cut-off edge is 237nm,which showed a good inhibition ratio.And the spectral response peak was at 336nm with the responsivity of 12.3mA/W.The external quantum efficiency of the device reaches 8.57%and 4.54%,respectively.