| Summary: | 博士 === 國立成功大學 === 材料科學及工程學系碩博士班 === 100 === Fabrication of high-performance ZnO nanowire-based photodetectors through low temperature processes is the main purpose of this dissertation. For this purpose, a wet chemical process was employed as the main technique for synthesizing ZnO nanowires. Besides, the morphology and size of ZnO nanowires were tuned by the addition of PVA with varied amount. PVA acts as a structure-directing agent for growing the ultra-long ZnO nanowires. Then, the ZnO UV photdetectors were fabricated by aligning ZnO nanowires between the interdigitated electrodes via a dielectrophoresis process. Based on decreasing the reflection of UV light on ZnO surface, the signal to noise ratio can be improved via capping PMMA micro-lens arrays. Then Ag nanoparticles were loaded onto the surface of ZnO nanowires by a photoreduction process, for the purpose of decreasing the response time. By investigating the Ag/ZnO interface, a non-stoichiometric AgOx phase is observed by HRTEM images and SAED patterns. Ag2O nanoparticles were also decorated onto the surface of ZnO nanowires. Photogenerated electrons and holes can be separated by the built-in potential induced by Ag2O/ZnO p-n junction. After decorating Ag2O nanoparticles onto ZnO surface, the maximum signal to noise ratio is larger than 105, accomplishing both a short rise time and a decay time of less than 1 s. After turning off UV irradiation, the current of Ag2O/ZnO heterostructured UV detector is recovered to the initial value within around 10~13s.
The aqueous solution processes were also used to self-assemble ZnO nanobridge photodetcors. By investigation with XPS and PL, singly ionized oxygen vacancies induce the persistence photoconductivity of ZnO-nanowire-based UV photdetectors. A hydrothermal process was used to passivate the surface states and singly ionized oxygen vacancies on the ZnO nanowires. The photoresponse time decreases significantly after extending the hydrothermal duration.
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