Study And Optimization Of 1D TiO₂ NWs Based UV Detector

Ultraviolet detectors have been widely used in ultraviolet astronomy,geospatial environmentdetection,environmentalmonitoring,firedetection,modern communication and biomedical research.One-dimensional semiconductor has great advantages in the application of optoelectronic devices due to its high surface-volume ratio,high carrier transportation efficiency and so on.TiO₂ nanowires prepared on FTO by low temperature bydrothermal have the characteristics of vertical growth and uniform distribution,which is helpful to the transportation of free carriers in the vertical direction.However,simple nanowires based device shows large dark current and low photo-to-dark current ratio,and the performance of the device tends to degrade after being placed in the air for some time.In this paper,these problems are studied and the performance of the device is optimized.Firstly,TiO₂ nanowires are prepared on FTO substrates by low temperature bydrothermal and FTO/TiO₂ heterjunction is obtained.Ag electrodes are then prepared on FTO and TiO₂ respectively and the FTO/TiO₂ based UV detector is obtained.The performance of the detector is measured at last and the results are analyzed together with the energy band structure of the materials related:the dark current of the device under reverse bias is not saturated and the photo current under UV radiation remains to be improved.Secondly,on the basis of FTO/TiO₂,MoO₃ nanolayer is prepared on TiO₂nanowires and then Ag electrodes is formed on FTO and MoO₃ respectively to form a UV detector.At last,the performance of the detector is measured.The results show that the dark current of the device is suppressed under reverse bias and reaches its lowest value under 2.2 V reverse bias,which is different from the unsaturation of the dark current of the FTO/TiO₂ based device without MoO₃.What's more,the photo current of the device increases and the responsivity is improved thereby.The results are analyzed together with the energy band structure of the materials related:there is electronic potential well formed when the FTO/TiO₂/MoO₃ heterojunction introduced in this paper is under reverse bias of specific region,which efficiently supresses the dark current of the device.While the photo current increases because of the increase of absorption and utilization of UV.In this paper,PMMA is used to modify the TiO₂ nanowires and Ag electrodes are fabricated to form the PMMA modified FTO/TiO₂ based UV detector.Then the performance of the detector is measured.Since the modification of PMMA blocks the absorption of water vapor molecules on TiO₂ nanowires in the air,the dark current in the device gets decreased efficiently.What's more,the photo current of the device gets increased due to the waterproof of PMMA,which can prevent the photo-excited carriers from being consumed by the dissociated water molecules.At last,the thesis is summarized.This paper paves a new way to supress the dark current and improve the performance of optoelectronic device.