Zinc oxide (ZnO) is a II–VI compound semiconductor with a wide direct band-gap of 3.3 eV and a hexagonal structure. ZnO is often used in the paint, paper, rubber, food and drug industries. It is also a promising material in nanotechnology applications, for example in nano-electronics and nano-robotic technology. With its wide band-gap, high exciton binding energy and high breakdown strength, ZnO can be utilized for electronic and photonic devices, as well as for high-frequency applications. To produce such optoelectronic devices, control of electronic properties, such as the nature of conduction and carrier density, is required. However, such control has proved difficult for ZnO. Much research has been done to pursue p type ZnO using different processing techniques, however, there are few reports addressing the relationships of microstructure on optical and electrical properties, ion implantation doping of ZnO and nano-ZnO polymer composites. The objectives of this project are to study the processing, composition, microstructure, electronic, optical, UV and electromagnetic shielding properties of ZnO thin films and composites; to explore ion implantation as a method to dope Al, Ag, Sb, Sn and TiN into ZnO thin films or single crystals; to develop conducting, transparent oxide films and/or p-type semiconductor for potential device applications; and to study the relationships of doping, microstructure and electro-optical properties of ZnO thin films and nano-ZnO polymer composites. The experimental work included annealing, characterizing and implantation of magnetron sputtering ZnO thins films and ZnO single crystals. Ion implantation was employed to dope ZnO thin films or single crystals with Ti, N, Sb, Al, Sn and Ag. The diffusion behaviour of implanted and annealed ZnO and the ellipsometry of implanted ZnO thin films were investigated. The relationship of microstructure and properties of as-deposited, annealed and implanted ZnO was studied. The results show that compared to direct current (d.c.) sputtering, the films produced using radio frequency (r.f.) have significantly lower resistivity, porosity and stress. The residual stress can change the band gap of ZnO thin films. Conductivity experiments suggest that the conduction mechanism of sputtered ZnO thin films involves charge transport in the conduction band and electronic hopping between the nearest neighbour donor levels. Furthermore, the optical transmission of ZnO thin films is high in the visible, with excellent UV absorption properties. It is also found that annealing alters the grain size and composition, and reduces the stress of ZnO thin films. Moreover, ion implantation causes partial amorphousness of ZnO films in the implantation zone and introduces stress and interstitial dopants. Transport of Ions in Matter (TRIM) modelling and Secondary Ion Mass Spectrometer (SIMS) analysis confirm that lighter elements implant deeper than heavy elements. The implanted ZnO shows some p type tendency and evidence of photoluminescence. Lastly, the nano-ZnO and polymer composites show excellent mechanical, good UV barrier properties.
| Identifer | oai:union.ndltd.org:ADTP/276635 |
| Date | January 2006 |
| Creators | Lee, Jim, 1963- |
| Publisher | ResearchSpace@Auckland |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated., http://researchspace.auckland.ac.nz/docs/uoa-docs/rights.htm, Copyright: The author |
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