Study On The Preparation And Characteristics Of ZnO Quantum Dots And Their Ultraviolet Photodetectors

Ultraviolet detection technology has been proved to have broad application prospects in military and civilian fields.Traditional vacuum photomultiplier tubes and silicon-based photodiodes have been unable to meet the increasing demands of people.Ultraviolet detectors must continue to innovate,and the research of related fields is in the ascendant.As a wide bandgap semiconductor with direct band gap,ZnO QDs have visible-blind absorption characteristics.Miniaturized all-solid-state devices can be realized based on them.They are extremely suitable for applications in the field of ultraviolet detection.At the same time,they are non-toxic.The environmentally friendly characteristics of ZnO QDs also conform to the trend of green development.In addition,the preparation method of ZnO QDs is simple and the raw material cost of ZnO QDs is low,therefore,ZnO QDs UV detectors are expected to realize large-scale commercial application.However,the slow response speed is the main problem that hinders the further development of ZnO QDs UV detectors,and the reason for the slow response speed is still unclear.Because oxygen vacancy defects on the surface of ZnO QDs can trap/release electrons through the adsorption/desorption of oxygen during the device response process,some researchers believe that the slow response speed may be related to oxygen vacancy defects.Aiming at the problems in ZnO QDs UV detectors,this paper focuses on oxygen vacancy defects,and has carried out related research work and achieved certain results.The specific contents are as follows:(1)The oxygen vacancy defect concentration of ZnO QDs which is based on the traditional sol-gel method can be controlled by changing the ripening time.As the ripening time increases from 0 h to 2 h,the PL and PLE spectra of ZnO QDs are red-shifted,and the visible luminescence significantly becomes weak,indicating that the size of the quantum dots has increased,the crystal quality has been improved,and the oxygen vacancy defects have been reduced.(2)The ZnO QDs prepared in this paper have an ultraviolet detection light-dark suppression ratio of 10⁴,and the switching characteristics are stable.At the same time,the device has a fast response speed,and rise time and decay time of 1.00 s and 0.19 s,respectively.In addition,the device has a good thermal stability from room temperature to 110?.In the study of ZnO QDs detector,this device has outstanding performance advantages and it has the fastest decay speed.Compared with the devices reported in the same field,the device's fast response characteristics should inseparable from surface oxygen vacancies.(3)Oxygen vacancy defects in ZnO QDs and their devices have been further controlled by H₂O₂ solution treatment.It is proved that H₂O₂ solution treatment can effectively fill the oxygen vacancy defects in ZnO QDs by PL,PLE and XPS.In addition,with H₂O₂ solution treatment,the dark current of the device decreased,the photocurrent increased,and the responsivity increased by 8 times.In the variable atmosphere test,as the oxygen concentration increases,the response speed of the device after the H₂O₂ solution treatment has been significantly improved,while the improvement of the device before the treatment is small.At the same time,with the temperature rises,the decay speed of the device after the H₂O₂ solution treatment is significantly faster,and it hardly has effect on the decay speed of the device before the treatment.The surface oxygen vacancy defects are greatly reduced with the H₂O₂solution treatment,which weakens the adsorption ability of ZnO QDs for oxygen.Therefore,increasing the oxygen concentration or increasing the temperature can significantly improve the adsorption speed of ZnO QDs with treatment.These phenomena further clarify the oxygen vacancy defects in ZnO QDs detector plays an important role in the rapid response process.Our work in this paper provides a new idea for the realization of high-performance nanostructure UV detectors.