Using a Statistical Experimental Design Method to Confirm the Optimization of Al/Al Doped ZnO Double Layers
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https://doi.org/10.1007/s11664-020-08323-3 Ó 2020 The Minerals, Metals & Materials Society
Using a Statistical Experimental Design Method to Confirm the Optimization of Al/Al Doped ZnO Double Layers SHAO-HWA HU,1 YEN-SHENG LIN,2,3 YI-TING LIN,2 SHUI-HSIANG SU,2 and LI-CHUN WU1 1.—Department of Logistics Engineering, Dongguan Polytechnic, Dongguan, Guangdong, China. 2.—Department of Electronic Engineering, I-Shou University, Kaohsiung, Taiwan, ROC. 3.—e-mail: [email protected]
A conductive metal thin film Al is deposited as a buffer to form Al/AZO double layers. The Taguchi method, based on the Al thickness, annealing temperature and duration, is used to determine the optimum synthesis conditions. The quality and thickness of the layers are analyzed by field emission scanning electron microscopy. The atomic resolution microstructures and the interface between Al/AZO are observed using high resolution transmission electronic microscopy. The optoelectronic properties of the layers are measured using a four-point probe and UV–VIS-NIR spectrophotometer. Using the appropriate parameters as derived by the Taguchi method, it is verified that the optimized results correspond with the experimental results for this study. The thickness of the Al metal layer is about 10 nm and the double layers are thermally annealed for 10 min at 500°C; the best figure of merit (FOM) is calculated as 0.0375 (X1). Key words: Al-doped ZnO, Taguchi method, transparent conductive oxide, RF magnetron sputtering, rapid thermal annealing, high resolution transmission electronic microscopy
INTRODUCTION Transparent conductive films (TCF) have been the subject of many studies. The basic characteristics of a TCF are a visible range having a high transmittance (80% or more) and low resistivity (below 103 X cm).1,2 Indium tin oxide (ITO) is popularly used, but indium is rare, toxic and unstable in high temperature processes, so lessexpensive zinc oxide (ZnO) has an opportunity to replace ITO in applications requiring a transparent conductive film. Un-doped ZnO thin film, however, has a lower carrier concentration than ITO, so treating ZnO with an effective dopant such as aluminum (Al) or gallium (Ga) becomes very important. Many studies confirm that AZO (Al-doped ZnO) thin films have a good basic nature,3–5 but the
(Received March 21, 2020; accepted July 8, 2020)
resistivity of the resulting AZO thin film is still not as low as ITO, so new materials and different film structures have been studied. A conductive metal layer was sputtered as a buffer to form a Al/AZO double-layer structure, and the conductivity increased,6–8 but visible transmittance was low and needed to be improved. For a metal layer with a thickness of less than 10 nm, the resistance of a thin film increases due to the formation of islands and discontinuities in the film, but greater thickness of the metal layer will reduce the transmittance. If the thickness of the metal could be adjusted to give higher transmittance and also improve the quality of the layer, this would substantial
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