Transmission Electron Microscopy Studies of GaN Multiple-section Nanorods and GaZnO Nanoneedles
| Autor: | Ta-Wei Chang, 張達瑋 |
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| Rok vydání: | 2014 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 102 We study the nanostructures of MOCVD-grown multiple-section GaN nanorods (NRs) and MBE-grown GaZnO nanoneedles (NNs) with transmission electron microscopy (TEM). In a multiple-section GaN NR, besides the discovery of a SiNx thin layer on the sidewall of an n-GaN NR when a high silane flow rate is applied for n-type doping, we focus the study on the growth process of a tapering section. It is found that during this process of reduced supply duration of TMGa in pulsed growth, the slant facets at the edge of an NR gradually turn from the {1-102}-plane in the uniform section into the {1-101}-plane. After the completion of the tapering growth, when a constant TMGa supply duration is used again for forming the next uniform section, the slant facets return to the {1-102}-plane. Because of the changing slant-facet angle in the tapering section, sidewall QW deposition in the tapering section can be achieved even though the QW growth on the {1-101}-plane in the pyramidal structure at the NR top is difficult. Regarding the study on GaZnO NN, the local crystal orientations in the GaZnO NNs and the simultaneously grown GaZnO thin film are investigated by analyzing the diffraction patterns of atomic-scale TEM images. It is found that the local c-axis varies slightly from place to place in the NNs and the thin film. At the boundary between the thin film and the “root” of an NN, the c-axis may rotate significantly. This structure is quite different from that in a GaZnO thin film without using Ag NPs as the catalyst, in which a column structure is observed. In this situation, the c-axis growth does not tilt, but twists in the c-plane. After the GaZnO growth with Ag NPs as the catalyst, Ag atoms distribute in the GaZnO NNs. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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