Preparation And Study Of Wide Bandgap Oxide Semiconductors Ultraviolet Detectors

Ultraviolet（UV）photodetectors show wide applications in flame detection,biological analysis,UV irradiation detection,environmental monitoring and space communication.Wide bandgap semiconductors have the right band gap,combining high stability and strong radiation resistance,which are very suitable for short-wavelength optoelectronic devices,especially ultraviolet photodetectors.Compared with thin-film materials and bulk materials,low-dimensional micro-nano materials have good application prospects in the preparation of flexible,portable and wearable devices,because of large specific surface area,light weight,good flexibility,and low preparation cost.Wide-bandgap oxide semiconductor materials represented by zinc oxide（ZnO）and gallium oxide（Ga₂O₃）have rich and diverse micro-nano structures,and photodetectors based on their micro-nano materials have also made many progresses.However,wide bandgap oxide semiconductor micro-nano structure ultraviolet detectors generally have the problems of slow response speed and low UV/visible rejection ratio,which seriously restrict the further application and development of devices.That is due to the crystalline quality of the material and intrinsic defects such as oxygen vacancies.In view of the above problems,this thesis has carried out the preparation and research of ZnO and Ga₂O₃-based one-dimensional micro-nano structures and their UV detectors.The details are as follows:1.By regulating the concentration of oxygen vacancy defects,self-supporting ZnO one-dimensional nanowires were prepared by chemical vapor deposition（CVD）method.The one-dimensional ZnO nanowire ultraviolet detector shows a responsivity of～300 m A/W over a wide wavelength range from 254 nm to 365 nm and a high UV/visible rejection ratio of more than 10⁴.More interestingly,a short 90-10%decay time of<0.12 s can be observed in the air atmosphere,and the current can fully recover to its original dark value within 1 s after switching off the light.The effects of surface oxygen vacancy defects on their optical,electrical and photodetection properties were investigated,and the related mechanisms were clarified,it is found that surface oxygen vacancies can accelerate the adsorption and desorption of oxygen to a certain extent,thereby shortening the response time of the device.2.On the basis of the above work,in order to further control the defects and improve the crystal quality of the material,a CVD growth technology combining low-pressure high-temperature growth and in-situ atmospheric pressure annealing was invented.Theβ-Ga₂O₃ microribbons with widths of 5-40μm,thicknesses of 0.1-2μm and lengths of 1-12 mm were prepared.Selected area electron diffraction,Raman spectroscopy,X-ray photoelectron spectroscopy and other results show that the Ga₂O₃microband has high crystal quality and low oxygen vacancy defect density,which is mainly attributed to the slow growth under low pressure environment and the oxygen vacancy repair effect of high temperature annealing in in situ oxygen atmosphere.3.3.A singleβ-Ga₂O₃ micro-band solar-blind ultraviolet photodetector was prepared.The dark current of the device under 20 V bias is only 1 p A,the peak responsivity is 9.47 A/W,the UV-Vis rejection ratio can reach 8.8×10⁴,and the 90-10%fall time is only 1.37μs.In addition,the device has excellent working stability,and the device performance does not change significantly after multiple bending tests and repeated tests for a long time（three months）.The excellent solar-blind detection performance exhibited by this device is closely related to the high crystalline quality and low defect density of Ga₂O₃ microribbons.