Microstructure and Optical Properties of Electrochemical Deposited Zinc Oxide

• Main Authors: Shao-Sian Li, 李紹先
• Other Authors: 林招松
• Format: Others
• Language: zh-TW
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/74550386469955234259

碩士 === 國立臺灣大學 === 材料科學與工程學研究所 === 94 === Zinc oxide (ZnO) was electrodeposited from zinc chloride electrolyte on ITO glass. The potentials at which ZnO can be plated from a specific electrolyte were determined using cyclic voltammetry. The effects of electrolyte composition and electroplating parameters on the materials and optical properties of ZnO films were then systematically studied. Experimental results indicate that ZnO films can be plated at potentials ranging from -0.6 to -1.0V (vs. Ag/AgCl). The deposition rate was relatively small at low overpotentials, while metallic zinc was likely to form at high overpotentials. During potentiostatic deposition, the resultant current decreased with continued electroplating, and gradually reached a saturated value, signifying the semiconductor characteristic of ZnO. The ZnO electrodeposits consisted of columnar grains, which grew with c axis perpendicular to the substrate. Consequently, this polycrystalline ZnO film displayed a (002) texture as characterized by XRD. Dense ZnO crystals reduced the surface roughness of ZnO film, which, in turn, enhances the transmittance of the film due to less scattering effects. Although more dense ZnO films were plated by increasing overpotential, solution H2O2 concentration, and deposition time, these ZnO films exhibited insignificant improvement in optical properties. A two-step electroplating process was thus employed to prepare the ZnO film. This process enhanced the population density of columnar ZnO crystals, while reduced the size of the crystals. Both contributed to the enhanced transparency of ZnO films. The PL peak, absorption edge, and energy band gap of ZnO prepared by one-step process was found to have blue shift in PL and PLE spectrums, suggesting that the ZnO crystals contained significant amounts of interstitial zinc vacancies. The ZnO film fabricated by the two-step process showed less blue shift in PL and PLE spectrums. Apparently, the ZnO film with improved optical properties can be deposited using this two-step electroplating process.