Transparent conductive aluminum-doped zinc oxide(AZO) thin films were synthesized by reactive RF magnetron co-sputtering system with metallic zinc and aluminum targets under oxygen atmosphere. Systematic study on the fixed sputtering power of the Zinc target (PZn) and the variation of the sputtering power of the Aluminum target (PAl) on structural, electrical and optical properties of AZO thin film was mainly investigated in this work. We found that the microstructure of AZO films would be obviously transformed from rice-like crystalline structure to nanocrystalline (nano-column) structure with the increasing of the sputtering power of the Aluminum target (PAl) . Nanocrystalline AZO films were formed at the specific sputtering power ratio of metallic targets (PAl/ PZn=1) . X-ray diffraction (XRD) spectra revealed that nanocrystalline AZO films highly preferred c-axis orientation (002) was growth in perpendicular to the substrate. The optical refractive index (n) of nanocrystalline AZO films had significantly lower values than others of microstructure AZO films, and this suggested the low optical dispersion in nano-column structure . Furthermore, the electronic properties of AZO films with the proper sputtering power of the Aluminum target (PAl) evidently improved under rapid temperature annealing (RTA) process. It suggested that both high annealing temperature(400¢J) and rapid cooling time(15min) are main factors to decrease the sheet resistances due to the maintenance of high temperature structural phase. The results of X-ray photoelectron spectroscopy (XPS) show that RTA process can decrease oxidized Al in order to decrease the sheet resistances.

For the purpose of creating a sustainable environment for the future generation, the government has recognized the importance of renewable resources, and actively takes on the strategies and measures by promoting the industries to recycling wastes in order to effectively improve the physical fitness of the industry. There are various ways to recycle waste materials, depends on the technology and the applications, one waste material can be classified into different ranks of recycled resource. Also, the market value of the recycled resource is judged by its ability to substitute the existing goods on the market. Because of the high proportion of galvanized steel in the steel scrap, zinc would vaporize during the high temperature process; as a result, the electric arc furnace dust (EAF dust) would contain high proportion of zinc. According to the existing recycling technology, the proportion of zinc in EAF dust is around 20% to 30%, which is a valuable secondary resource for producing zinc. This research focuses on the recycling industry; the aim of this research is to find out its future trend and the bottlenecks to be overcome. Hopefully come up with constructive suggestions and specific strategies and measures. The results suggest that the officials should set up standards for recycled products. What is also important is that the government should better plan the policies and regulations for recycling industry. Moreover, the results also show the users of the recycled materials care most about the quality of the product. Hence, the producers of crude zinc oxide should form strategic alliance in order to each the economic scales of production and develop recycling technology to elevate the quality of crude zinc oxide. Once the production meets the market demand, it will be able to expand the sales channels and establish a stable profit.

Nanowire structure plays an important role in the development of nanotechnology. However, further study shows that the shape of nanowires may not be the ideal morphology for some applications such as solar cells and sensors. Thus, the purpose of this thesis is to find a low cost and high yield approach to the synthesis of other morphologies of nanostructures in order to further improve the performance of these nanodevices. To this end, a chemical approach has been extended to the synthesis ZnO nanocones and platelets. With UV illumination, the synthesis of ZnO nanocones was achieved on GaN films on sapphire and gold films on silicon substrates. Both TEM and XRD results show that as-grown ZnO nanocones are single crystals. The formation of ZnO nanocones could be explained by the absorption process of photons. The UV light induced thermal gradient modifies the heat distribution as well as the reagent transport. The chemical reaction system is kinetically limited and results in ZnO nanocones. If the UV light is blocked, the ZnO nanowires result. In addition, the density of ZnO nanocones is higher than ZnO nanowires grown without UV illumination. By this chemical approach, ZnO platelets could also be obtained on GaN films deposited by PLD, whose c-axis is parallel to the surface of the substrate. The diameters and the thickness of the platelets depend on the quality and thickness of GaN film. TEM results illustrate that the obtained ZnO platelets are single crystals grown along the <0 1 1 0> direction within the {0 0 0 1} planes. Relative growth rates of various facets were altered by the presence of [1 0 0] textured GaN film. The suppression of the growth along c axis can also be achieved by citrate anions as a structure-directing agent to adsorb selectively on ZnO basal planes. Electrical measurement shows that the resistance of ZnO platelets is about 20-40 GΩ¸ and it is higher than that of ZnO nanowires. Piezoelectric potential calculation results also indicate that the piezoelectric potential is higher than for ZnO nanowires with the same external applied stress. These procedures and results demonstrate an easy and low cost way to fabricate ZnO nanocones and platelets, which may aid the utilization of nanostructures in solar cells, sensors and other applications to further improve their performance.

Thesis (M.S.)--University of North Texas, May, 2009. / Title from title page display. Includes bibliographical references.

Thesis (Ph. D.)--University of Hong Kong, 2010. / Includes bibliographical references. Also available online.

Thesis (Ph. D.)--University of Hong Kong, 2010. / Includes bibliographical references. Also available in print.

published_or_final_version / Physics / Master / Master of Philosophy

published_or_final_version / Physics / Doctoral / Doctor of Philosophy

published_or_final_version / Physics / Master / Master of Philosophy

Zinc oxide (ZnO), as a Ⅱ-Ⅵ compound semiconductor with a wide direct band gap, has attracted great attention from the worldwide researchers for its potential application in the fields of spintronics and optoelectronics. At present research about the defects in ZnO and ZnO-based materials is still far from complete. The deep level defects in melted grown ZnO single crystal induced by helium ions implantation and electron irradiation, as well as their thermal evolution, were studied in this research using the technique of deep level transient spectroscopy (DLTS) and photoluminescence (PL). DLTS results indicated that, besides E3 (????~0.28 ????) trap which was widely observed in the as-grown ZnO samples, the deep level with ????~0.92 ???? was also indentified in the helium-implanted ZnO samples, which was introduced by the ion implantation and tentatively assigned to be the oxygen vacancy (VO). This deep level was removed after 350 oC annealing in argon gas. Annealing at 350 oC also brought along a new deep level with ????~0.66???? into helium-implanted samples which could be annealed out by 650 oC annealing in argon gas. The electron irradiation induced a deep level with ????~0.59 ???? into ZnO, which was probably associated with the singly charged state of VO. This deep level also tended to be removed at 350 oC annealing in argon gas. The PL spectra revealed that both helium implantation and electron irradiation could improve the bound-exciton peak. Helium implantation also introduced defects emission at 1.90 eV , which was the red luminescence band, into the ZnO single crystal materials. This red luminescence band peak might be associated with DAP recombination. Electron irradiation might restrain the green luminescence in ZnO single crystal. The fine structures could disappear as the measurement temperature increased, leaving the green luminescence band only. / published_or_final_version / Physics / Doctoral / Doctor of Philosophy