Investigation of the Effects of Electroplating Parameters on Electoplated Zinc Oxide

• Main Authors: Kung-Cheng Li, 李公正
• Other Authors: Ching-An Huang
• Format: Others
• Language: en_US
• Published: 2005
• Online Access: http://ndltd.ncl.edu.tw/handle/91229957775292383088

博士 === 長庚大學 === 機械工程研究所 === 93 === ABSTRACT Presently, ZnO thin film is attracting much attention for its particular optical and electrical properties and the wide applications to optoelectronic devices. The structural, optical, and electrical properties of ZnO film are closely related to the preparation methods. Electroplating has the potential for obtaining the large area deposition of films with low cost. Since the electrodepositon of ZnO films were developed from Japanese and French researchers with nitrate and chloride base solutions in 1996, this field has attracted considerable attention for the improvement of film properties and the possible application to various substrates. In this study the ZnO films were electroplated on ITO films from zinc nitrate solution. First, the effects of different cathodic current densities on the initial growth of ZnO film were studied. Galvanostatic deposition and pulsed current electrolysis were further applied to prepare the ZnO films with different electroplating parameters, such as bath temperature, additive, and post-annealing. It is well known that the surface properties of substrate are strongly related to the growth of electrodeposits. Based on this point of view, this thesis first investigated the electrochemical behavior of ITO films by using CVs (Cyclic Voltammetry stripping) test in 0.3 M HCl solution. The variations of surface conditions of tested ITO films were examined by SEM and EDS analysis. The results can be the recommendations for pretreatments of ITO films used in ZnO electroplating. It also can be a valuable reference for the etching process applied in the manufacture of optoelectronic devices, such as organic light emitting diodes (OLEDs). Experimental results show that a significant reduction-current peak was observed during the first negative potential scanning test when ITO films were tested in 0.3 M HCl solution. Numerous spherical In-Sn particles on the ITO’s surface formed concurrently with the occurrence of this reduction-current peak. Formation of the spherical reduction In-Sn particles was confirmed by FESEM examinations and EDS analyses. A schematic diagram illustrating the processes related with the formation of this In-Sn reduction particle was postulated. For discussing the effects of different cathodic current densities on the initial growth of ZnO film, the ZnO films were electroplated with the different cathodic current densities and electroplating times at 30 and 60OC based on the constant electric charge. The results indicate that the improvement of optical transmittance at visible wavelength range was obtained from the ZnO-coated ITO films. An addition of Ga(NO3)2 would slightly etch the surfaces of the ZnO thin films but a superior transparency was obtained to that of the ZnO thin films prepared with 0.1 M DMAB. This could be applied as the activation treatment for the two-step ZnO deposition. Besides, post-annealing resulted in the decrease of surface roughness and the formation of tiny crack for the ZnO films prepared without and with additives. The effects of electroplating parameters on the properties of the electroplated ZnO films were also studied. The ZnO films were prepared with galvanostatic deposition and pulsed current electrolysis. The wavelike films, probably zinc hydroxide or amorphous, and many tiny crystallized particles were formed at bath temperature of 30OC with both galvanostatic deposition and pulsed current electrolysis. The quantity of the crystallized particles was changed with the addition of DMAB and the pulsed on time. An excellent optical transmittance, close to 100%, was obtained for the 30OC-prepared ZnO films, and the optical energy band gap was shifted with the preparation methods. The relatively high carrier concentrations were achieved for the ZnO films prepared at 45 and 60OC due to the formation of more interstitial zinc during electroplating. Besides, many tiny pores were formed on the grains of the 60OC-prepared ZnO films after post-annealing. The crystallite orientation of the 60OC-prepared films was also altered with post-annealing. Keywords: electroplating parameter, ZnO electroplating, pulsed current electrolysis, additive, and post-annealing