Author : Xinyi Chen
Release : 2017-01-26
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Wide Band-Gap Nanostructure Based Devices - read free eBook in online reader or directly download on the web page. Select files or add your book in reader. Download and read online ebook Wide Band-Gap Nanostructure Based Devices write by Xinyi Chen. This book was released on 2017-01-26. Wide Band-Gap Nanostructure Based Devices available in PDF, EPUB and Kindle. This dissertation, "Wide Band-gap Nanostructure Based Devices" by Xinyi, Chen, 陈辛夷, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Wide band gap based nanostructures have being attracting much research interest because of their promise for application in optoelectronic devices. Among those wide band gap semiconductors, gallium nitride (GaN) and zinc oxide (ZnO) are the most commonly studied and optoelectronic devices based on GaN and ZnO have been widely investigated. This thesis concentrates on the growth, optical and electrical properties of GaN and ZnO nanostructures, plus their application in solar cells and light emitting diodes (LEDs). GaN-nanowire based dye sensitized solar cells were studied. Different post-growth treatments such as annealing and coating with a TiOx shell were applied to enhance dye absorption. It was found that TiOx increased the dye absorption and the performance of the dye sensitized solar cell. ZnO nanorods were synthesized by vapor deposition and electrodeposition. Post-growth treatments such as annealing and hydrothermal processing were used to modify the defect chemistry and optical properties. LEDs based on GaN/ZnO heterojunctions were studied. The influence of ZnO seed layers on GaN/ZnO LEDs was investigated. GaN/ZnO LEDs based on ZnO nanorods with MgO and TiOx shells were also prepared in order to modify the LED performance. The coating condition of the shell was found to influence the current-voltage (I-V) characteristics and device performance. Moreover, high brightness LEDs based on GaN with InGaN multiple quantum wells were also fabricated. The origin of the emission from GaN/ZnO LEDs was studied using different kinds of GaN substrates. Direct metal contacts on bare GaN substrates were also employed to investigate the optical emission and electrical properties. It is found that the emission from the GaN/ZnO LEDs probably originated from the GaN substrate. GaN/ZnO LEDs with MgO as an interlayer were also fabricated. The MgO layer was expected to modify the band alignment between the GaN and the ZnO. It was shown that GaN/MgO/ZnO heterojunctions (using both ZnO nanorods and ZnO films) have quite different emission performance under forward bias compared to those that have no MgO interlayer. An emission peak was around 400 nm could originate from ZnO. Nitrogen doped ZnO nanorods on n-type GaN have been prepared by electrodeposition. Zinc nitrate and zinc acetate were used as ZnO precursors and NH4NO3 was used as a nitrogen precursor. Only the ZnO nanorods made using zinc nitrate showed obvious evidence of doping and coherent I-V characteristics. Cerium doped ZnO based LEDs were fabricated and showed an emission that depended on the cerium precursor that was employed. This indicates that the choice of precursor influences the growth, the materials properties and the optical properties of ZnO. DOI: 10.5353/th_b4979929 Subjects: Gallium nitride Zinc oxide Wide gap semiconductors - Materials Nanostructured materials Solar cells Light emitting diodes