Research On The Fabrications And Annealing Of ZnO Nanoflowers By A Hydrothermal Method And Their Ultraviolet Photodetectors

High-performance and low-cost ZnO ultraviolet（UV）photodetectors with simple structures will have wide applications and great development potential,but there are still many challenges for the developments of such UV photodetectors.In this thesis,ZnO nanoflowers were synthesized by a facile hydrothermal method,the ZnO nanoflowers UV photodetectors were built,their performances were investigated in detail.Also,the effects of the reaction temperature and time as well as annealing temperature on the device performances were systematically studied.The photoresponsive mechanisms of this device were illuminated.The main contents and results of this thesis are as follows:1.The fabrication of ZnO nanoflowers and the performance of ZnO nanoflowers UV photodetectors were investigated.ZnO nanoflowers were prepared using zinc acetate dehydrate,ammonia and D-mannitol as precursors,reaction temperature was 120℃,reaction time was 2 h.The results showed that the hollow ZnO nanorods assembled together to form single-crystalline ZnO nanoflowers,the diameters of the nanorods ranged from 96to 247 nm,and the nanoflowers were the hexagonal wurtzite ZnO.Furthermore,a photoconductive UV photodetector was prepared using ZnO nanoflowers.Under 77mW/cm²365 nm light irradiation,the responsivity,photocurrent gain,sensitivity,response time,decay time and detectivity for this device were 2.5 A/W（5 V）,8.3（5 V）,1369.7（-0.1 V）,35.3 s,35.2 s and 2.2′10¹³Jones,respectively.2.The effects of annealing temperature on the performance of ZnO nanoflowers UV photodetectors were studied.The as-preapred ZnO nanoflowers in the content（1）were annealed at 500～900℃for 1 h in air,respectively.The results displayed that the diameters of the nanorods in ZnO nanoflowers increased gradually and the crystallinity quality became better with increasing annealing temperatures.Also,UV photodetectors were fabricated using the annealed ZnO nanoflowers as the photosensitive layers,respectively.The results found that the photodetector based on the ZnO nanoflowers annealed at 800℃had better performance,and under 71mW/cm² 365 nm light irradiation,its responsivity,photocurrent gain,sensitivity,response time and decay time were 9.7 A/W（5 V）,33.2（5 V）,19991.3（-0.1 V）,17.1 s and 49.5 s,respectively.3.The effects of the hydrothermal reaction temperature and time on the performance of ZnO nanoflowers UV photodetectors were investigated.ZnO nanoflowers were synthetized at the different hydrothermal reaction temperature and time,many UV photodetectors were built using the as-synthetized ZnO nanoflowers,respectively.The results revealed that the UV photodetector based on the ZnO nanoflowers from the hydrothermal reaction temperature at 160℃had better responsivity and photocurrent gain,the responsivity of 20.7A/W（5 V）and photocurrent gain of 70.4（5 V）were obtained,respectively.And the results exhibited that the UV photodetector based on the ZnO nanoflowers from the hydrothermal reaction time for 1 h had better responsivity,photocurrent gain and sensitivity,they were 5.2A/W（5 V）,17.5（5 V）and 6117.7（-0.1 V）,respectively.4.The device mechanisms of ZnO nanoflowers UV photodetectors were investigated.The photoresponsive mechanisms of ZnOnanoflowews UV photodetectors were explained according to the adsorption-photodesorption theory of oxygen in ZnO nanoflowers,and transport process of the carriers in the ZnO nanoflowers UV photodetectors was also illuminated.