Zno Growth Mechanism And Heterostructures On Gan And Diamond
| dc.contributor.author | Tneh, Sau Siong | |
| dc.date.accessioned | 2016-12-06T07:05:31Z | |
| dc.date.available | 2016-12-06T07:05:31Z | |
| dc.date.issued | 2016-05 | |
| dc.description.abstract | In this study, the physical properties of ZnO nanostructures and related devices have been investigated. Firstly, the growth via transformation of zinc to zinc oxide by thermal oxidation was discussed. The Zn completely has been found to transform to ZnO after 15 min of annealing. The x-ray diffraction (XRD) data suggest that the minimum surface energy of ZnO (002) < ZnO(100) < ZnO(101). Optical band gap of ZnO samples have been deduced in the range of 3.19 – 3.25 eV. The comparison of untraviolet (UV) near band edge and green emissions in photoluminescence (PL) analysis has also been discussed. The activation energies of this process are in the range of 76- 124 kJ/mol which correspond to the range of migration values for Zn interstitials, Zn vacancies, O interstitials and O vacancies. By comparing the reported values of the activation energy of these defects commonly found for ZnO in literature and the calculated values from XRD, it is observed that the transformation process can be attributed to these defects. By comparing the XRD and transmittance results, this transformation from Zn to ZnO is pre-dominantly a layer-by-layer process. Polycrystalline ZnO nanostructures were also produced from metallic Zn by dry thermal oxidation method at different annealing conditions. The XRD spectrum shows that the polycrystalline ZnO films are of good quality. The distributions of nano-wires and nano-sheets depend on oxygen gas concentration and also on the duration of annealing. Using XRD and current-voltage (I–V) measurements, the surface polarity of the zinc oxide thin film can be determined. After annealing at 800oC, the ZnO thin film shows a conversion from Ohmic to rectifying behavior which is indicative of a Zn-terminated surface. The rectifying behavior observed on the ZnO thin film is associated with the formation of nickel zinc oxide. The deposition of ZnO thin films on commercial p-type GaN is observed to demonstrate p-n junction properties. The I-V characteristics showed a rectifying behavior of the n-ZnO / p-GaN heterojunction before thermal oxidation. However, a different I-V behavior was observed after thermal oxidation due to the formation of Ga2O3 as an interfacial layer between ZnO/GaN heterojunction, creating a potential well to impede the electrons movement from ZnO to GaN during forward bias. The deposition of ZnO thin films on diamond was also observed to demonstrate p-n heterojunction behavior. The I-V measurements showed a change in electrical behavior under dark and UV exposure. Using a simple model, the donor level of 50 meV shifted closer to the conduction energy level of ZnO. The threshold voltage changes (0.4 V) could be estimated and was found to be consistent with the experimental results. Subsequently, the concentration of acceptor carriers of diamond and the sensitivity factor of the device were determined to be 2.82 x 1017 cm-3 and 3, respectively. | en_US |
| dc.identifier.uri | http://hdl.handle.net/123456789/3248 | |
| dc.subject | The physical properties of ZnO nanostructures | en_US |
| dc.subject | and related devices | en_US |
| dc.title | Zno Growth Mechanism And Heterostructures On Gan And Diamond | en_US |
| dc.type | Thesis | en_US |
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