Electrical and optical properties of the (N,Ga)-doped ZnO films have been studied. Three growth regions were identified to obtain ZnO films with different conduction types depending on the N/Ga flux ratio in doping process. The PL spectra show evident competition between neutral-donor bound exciton (D0X) and neutral-acceptor bound exciton (A0X) according to the N/Ga ratio. From the temperature-dependent PL spectra, the nitrogen acceptor level was identified to be about 126 meV in (N,Ga)-doped p-type ZnO. / For nitrogen doping of ZnO thin films, DMHy was used as the nitrogen dopant source. A narrow temperature window from about 500°C to 550°C for efficient nitrogen doping was identified. However, p-type ZnO was not obtained by nitrogen mono-doping, which results from the low solubility of N and the self-compensating effect of native defects, and/or N-induced complexes. By co-doping N with Ga in proper ratios, p-type ZnO films were successfully achieved with a high hole concentration of 3.51 x 1017 --2.41 x 1018cm-3, Hall mobility of 1.1 --4.29 cm2/V-s and resistivity of 0.6 -- 16.2 O cm. But the conduction type critically depends on the growth conditions. Based on the successfully fabrication of (N,Ga)-doped p-type ZnO, a p-ZnO:(N,Ga)/n-ZnO homojunction was fabricated. The I-V measurement shows clear rectifying behavior with a turn-on voltage of about 3.7 V. / Further investigation of the effect of N/Ga doping ratios on the conduction type of ZnO samples reveals that successful doping depends much on engineering a stable local chemical bonding environment. Under mono-doping conditions (via N-Zn4), nitrogen solubility is limited and nitrogen acceptors are readily compensated by native donors and/or N-related donors; under appropriate N/Ga flux ratios, cluster-doping (via Ga-N3O and Ga-N4) can be realized to achieve p-type ZnO; while excessively high N/Ga ratios cause the doped ZnO n-type conductivity again, which may be because that under excessively high N/Ga ratio range, N-Zn4 configuration dominates and thus cause more N-related donors and degrade the ZnO film quality, similar as the mono-doping case. By tuning the N/Ga ratio in doping, it is expected to create appropriate chemical environments to enhance the formation of desired dopant species for stable p-type ZnO. / In this work, Metal-organic chemical vapour deposition (MOCVD) growth of ZnO and its p-type doping have been studied. The group V element N was used as primary dopant to make ZnO p-type. In the growth of ZnO by MOCVD, it was found that the structural and morphological properties of deposited ZnO strongly depend on growth conditions. Low VI/II ratio and high growth rate favor the growth of ZnO nanostructures (nanowires, nanobelts); while high VI/II ratio and low growth rate favor the growth of ZnO thin films. / The semiconductor ZnO is currently gaining intense interest in the research community because of its prospect in optoelectronic applications, such as blue/ultraviolet emitters and detectors, and high speed electronic devices. However, making reliable and reproducible p-type ZnO is still a bottleneck, which impedes the practical application of ZnO-based devices. The difficulty is mainly due to the self-compensation effect of native defects and the low solubility limit of acceptor dopants. Although substantial research is currently being carried out worldwide towards this goal, the effective p-type dopant and its doping process have not yet been identified. / Wang, Hui. / "Apr 2008." / Adviser: Aaron H. P. Ho. / Source: Dissertation Abstracts International, Volume: 70-03, Section: B, page: 1860. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2008. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts in English and Chinese. / School code: 1307.
| Identifer | oai:union.ndltd.org:cuhk.edu.hk/oai:cuhk-dr:cuhk_344182 |
| Date | January 2008 |
| Contributors | Wang, Hui, Chinese University of Hong Kong Graduate School. Division of Electronic Engineering. |
| Source Sets | The Chinese University of Hong Kong |
| Language | English, Chinese |
| Detected Language | English |
| Type | Text, theses |
| Format | electronic resource, microform, microfiche, 1 online resource (xv, 110 p. : ill.) |
| Rights | Use of this resource is governed by the terms and conditions of the Creative Commons “Attribution-NonCommercial-NoDerivatives 4.0 International” License (http://creativecommons.org/licenses/by-nc-nd/4.0/) |
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