Preparation And Performance Of Ultraviolet Photoelectric Detector Based On TiO₂ Nanotree Arrays

Ultraviolet photoelectric detection technology has been widely used in military and civil fields,such as missile guidance,fire monitoring,biomedicine and so on.At present,semiconductor materials commonly used in UV detectors include Zn O,Ga₂O₃,Si C,Ga N and TiO₂,among which,TiO₂ materials are widely used in the construction of high-performance UV detectors due to their chemical inertia,low manufacturing cost,environmental friendliness,high UV absorption coefficient and many other advantages.It’s photocurrent of the device is low due to the low mobility and high recombination rate of photogenerated carriers in TiO₂ nanoparticles.Therefore,in recent years,three-dimensional arrays（NAs）integrated with one-dimensional TiO₂ nanostructures（nanowires,nanotubes,etc.）are usually used to construct high-performance ultraviolet photoelectric detectors.However,the device prepared by TiO₂ nanoarray has the problem of slow response speed,which seriously limits its practical application.In order to improve the response speed of TiO₂array device,the"tree-like"nanoarray（nano-tree）was prepared by hydrothermal method,and the single TiO₂ nanoarray was modified by composite materials and heterojunction preparation,and achieves the purpose of improving the detector performance by optimizing the device structure.The research content and main conclusions of this paper are as follows:（1）Anatase TiO₂ nanoarrays with different growth and annealing temperatures were prepared by hydrothermal method.Through the characterization and comparison of the structure and properties of the sample materials,it is concluded that growth at 180℃and annealed at 500℃are the best growth conditions of TiO₂ array devices,and the devices have larger switching ratio and faster response speed under these conditions.（2）The effect of SiO₂ dielectric layer on the structure and photoelectrical performance of TiO₂ nanoarray was studied.Composite device was prepared by spin-coating method for TiO₂ array composite SiO₂.After optimization,a high-performance device with fast response speed（1.13 s/0.75 s）under-5 V voltage was obtained.The main reason is that the existence of SiO₂ layer broadens the depletion layer on TiO₂ surface and increases the loss rate of photogenerated carriers,thus reducing the response time of the device.（3）The effect of the position of NiO layer on the performance of TiO₂ nanoarray photodetector was studied.Two NiO/TiO₂ composite devices with different structures were prepared by spin-coating method and electrodeposition method respectively.By comparison,it is found that the device with NiO layer at the bottom has lower dark current,larger switching ratio and faster light response speed（0.1 s）,and also has self-powered performance.This is mainly because the dense and uniform NiO layer deposited on the FTO substrate not only has greater uniformity and stability,but also can form a built-in potential field with TiO₂.（4）The preparation process and properties of NiO/SiO₂/TiO₂ composite（NST）devices were studied.Combined with electrodeposition,spin coating and hydrothermal method,the NiO/TiO₂ composite device was inserted with SiO₂ layer to obtain an integrated device that can work under high pressure.At-40 V bias voltage,the device still has very low dark current（0.29μA）and high responsivity(R₃₆₅=1.745 A/W),and the response speed reaches the millisecond level（2.91/0.95 s）.This is mainly because the space charge region of the semiconductor system is widened by applying reverse bias and inserting SiO₂ layer,thus inhibiting the generation of current.To sum up,in this paper,through compound modification of TiO₂ nanoarray ultraviolet photoelectric detector,a high-performance ultraviolet photoelectric detector with low dark current,fast response speed,self-powered supply and high working voltage can be obtained,which lays a certain foundation for promoting its future practical application.