Ultraviolet-Assisted Atmospheric-Pressure Spatial Atomic Layer Depositions for Tuning ZnO Properties
This thesis investigates the development of UV-assisted Atmospheric Pressure Spatial Atomic Layer Deposition (UV-APSALD) as a technique for depositing ZnO films. A study of the current literature identifies the need for high-quality metal oxide thin films; metal oxides are near ubiquitous in modern day electronic applications, from optoelectronics and transistors, to superconductors and energy storage. As the electronic properties are strongly tied to the microstructure and chemistry of the metal oxides, it is vital to have a deposition method whereby these properties can be tuned. A review of the current deposition methods identifies a niche for an open-air, energy-assisted thin film deposition method. A significant proportion of this doctorate was devoted to the design, construct and assembly of the components to enable the UV-assisted depositions. These design and engineering considerations are discussed herein. A systematic study of the substrate-manifold distance *versus* film thickness indicates that changing the substrate-manifold distance is a key factor in determining whether the reactor operates in atomic layer deposition (ALD) mode or chemical layer deposition (CVD) mode. UV-assisted depositions are shown to alter the crystallographic and electrical properties of ZnO; *in-situ* UV light, is found to suppress ZnO growth in the (002) direction, and increase the resistivity by two orders of magnitude. When UV-assisted depositions are coupled with N doping, the films are approximately five orders of magnitude more resistive. It is proposed that the UV-light-assisted depositions increase the presence of charged reaction intermediates which sterically hinder the polar (002) facet, thereby promoting growth in the non-polar (100) direction. These resistive UV-ZnO:N films are incorporated as the channel layer into functioning thin-film transistors, further demonstrating the utility of the UV-APSALD deposition system. Finally, epitaxial ZnO is grown on c-sapphire at 250 oC; to the best of my knowledge, this is the first demonstration of open-air epitaxial growth of ZnO via CVD or ALD. Further, the degree of epitaxy is improved by reducing the growth rate to get a more controlled deposition.
Atmospheric Pressure ALD, Atmospheric Pressure CVD, Atomic Layer Deposition, Chemical Vapour Deposition, Metal Oxide, Spatial ALD, Spatial CVD, UV assisted ALD, UV assisted CVD, ZnO
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