Characteristics and Uniformity Improvement of Ga-doped ZnO Thin Films Deposited by Atmospheric Pressure Plasma Jet

• Main Authors: Tung-Sheng Chou, 周東陞
• Other Authors: Jia-Yang Juang
• Format: Others
• Language: zh-TW
• Published: 2014
• Online Access: http://ndltd.ncl.edu.tw/handle/18717930059054498298

碩士 === 國立臺灣大學 === 機械工程學研究所 === 102 === Indium tin oxide (ITO) is one of the most widely used transparent conductive oxide (TCO) materials owing to its low resistivity (about 10-4 Ω&;#8729;cm) and excellent transmittance at visible light range (over 80%). However, its principal component, indium, is scarce and expensive. Many researchers are searching for substitutive materials for ITO aggressively. Polycrystalline ZnO films on glass have been extensively developed. By doping different metal atoms, Ga doped ZnO (GZO) deposited by sputtering can now compete with ITO both in cost and quality. Althrough sputtering has many advantedges, it must work in vacuum and, hence, raises the cost. In addition, it is not suitable for mass production when integrating with other processes is required. In this study we use atmospheric pressure plasma jet (APPJ) to deposit GZO thin films in atmospheric pressure environment without a vacuum chamber. Deposition of thin films on large area substrate is achieved by moving the nozzle with respect to the substrate, and the material is continuously sprayed during the scanning process. In this thesis we use APPJ generated by a DC pulse source to deposit GZO thin films on the glass substrate with a raster scanning trajectory. We discuss the effects of several key process parameters on the film deposited on smaller substrate with a dimension of 50 mm × 50 mm × 0.5 mm, and study the effects of electrical properties and uniformity of GZO thin films influenced by different trajectories and external flows on larger substrate, 185 mm × 117 mm × 0.5 mm in dimension. For the smaller sample, we adjust the parameters, including scanning recipe, Ga concentration, substrate temperature, gap, main gas flow rate and mixed carrier gas ratio, to understand the correlations between those parameters and photoelectric properties of the films, and as a result, obtain optimized recipes. In small samples, the films with about 150 nm thickness have better optoelectronic properties. By adjusting scanning repcipe on large area samples, we find that the sheet resistance is proportional to the air annealing time for samples experiencing single scan (refered as single-pass sample); Two-pass samples, in which the scan begins from one edge to the opposite edge and returns to the original edge so that the entire film enssentially consist of two layers, exhibit better uniformity in general, but show highest sheet resistance near the center of the substrate. In the external flow experiments, the pumping flow, caused by a fan designed to remove undeposited materials, alters the sheet resistance distribution, in particular the region with the highest sheet resistance. We apply α-step, equivalent circuit models, XRD, SEM, residual stress measurement and Hall measurement to analyze the reason of nonuniform electrical properties.