Synthesis ZnO Transparent Conductive Oxide by Electrospray Deposition
New York State College of Ceramics at Alfred University. Kazuo Inamori School of Engineering.
The objective of this thesis was to synthesize ZnO-based transparent oxide (TCO) thin film by using an economically-versatile fabrication technique called electrospray deposition (ESD). A co-doping approach was employed to enhance optoelectronic properties of undoped ZnO, which is a non-toxic and abundant material for flat display panels and energy-harvesting applications. Firstly, ESD process parameters were investigated in order to optimize the quality of thin film, namely, deionized water content in precursor, applied voltage, deposition temperature, flow rate, deposit distance, and deposit time. Regression plots revealed the tendency of individual process parameter towards % film coverage area. In addition, the factorial design of the experiment was performed to determine significant process parameters (P-value < 0.05), which showed a strong influence to film quality at R2 of 87.61%. Secondly, 0-3%wt of Aluminum (Al) concentration were co-doped with 3%wt of Lithium (Li). The aim was to synthesize p-type ZnO-based TCO by a co-doping approach. Li (acceptor) and Al (donor) at different ratios of acceptor-to-donor (A/D) were investigated effects on defect diffusion mechanism, film’s crystallinity, microstructure, and topography by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). Hall effect measurement and UV-Visible spectrometer studies were carried out to evaluate optoelectronic properties of as-annealed film. The lowest resistivity of 2.51x10-3 Ohm∙cm of p-type ZnO-based TCO was obtained without optical properties degradation by employing A/D of 2:1 due to the scattering effect of ionized defect and was minimized by A-D-A defect cluster. Lastly, 3%wt of gallium (donor) and 3%wt of lithium (acceptor) were co-doped with 0- 3%wt of Aluminum concentration in order to compare effects of co-dopant types on defect diffusion mechanism. A small variation of lattice distortion as %Al increased, which suggested that dopant solubility was improved by substitutional mechanism. As a result, the film’s crystallinity and microstructure were improved due to the minimization of disturbing stress and enhanced diffusibility. Consequently, UV-Visible spectrometer and 4-point probe measurement showed that optoelectronic properties of the film improved in co-doped samples.
Advisory committee members: S.K. Sundaram, Nathan Mellot. Dissertation completed in partial fulfillment of the requirements for the degree of Masters of Science in Ceramic Engineering at the Kazuo Inamori School of Engineering, New York State College of Ceramics at Alfred University