Fabrication of Transparent ZnO Thick Film with Unusual Orientation by the Chemical Bath Deposition

Abstract

We report a fabrication of transparent ZnO thick films by a chemical bath deposition using zinc acetate ethanolic− aqueous solutions with cetyltrimethylammonium chloride (CTAC). In this system, CTAC plays a particular role in nucleation and crystal growth of ZnO, and the micrometer-thick ZnO films formed on ZnO-buffered glass substrates. The resultant ZnO thick films show a high transmittance of around 80% in the visible region. An orientation of ZnO nuclei formed on the substrates in the early stage is different from a c-axis orientation of the ZnO-buffer layer, and the resultant ZnO thick films also show the unusual orientation. The detailed information on the orientation of these ZnO films was analyzed based on X-ray diffraction (XRD) 2θ/θ scan measurements at angles between in-plane and out-of-plane geometries. According to the results, the c-axis of ZnO is tilted at around 40−50°with respect to the film normal, and the micrometer-thick ZnO films exhibit the (112)-plane orientation by adjusting the CTAC concentration of reaction solutions. ■ INTRODUCTIONZinc oxide (ZnO) is an important material attracting considerable research interest due to its wide-ranging applications such as in photoluminescence, 1−3 photocatalysis, 4,5 dye-sensitized solar cells, 6−9 and sensors. 10−12 Moreover, Aland Ga-doped ZnO are potential candidates for transparent conductive oxide (TCO) materials, 13−15 which are used in various electronic devices such as flat-panel displays and solar cells. Indium tin oxide films are representative TCO films used in these electronic devices, 16−18 though alternative materials are needed due to the problem of acquiring indium resources. Since zinc is a ubiquitous element, ZnO is an appropriate alternative.High-quality TCO films are generally fabricated by a sputtering process, 14−16 which requires a large equipment with a vacuum system and is a high energy-cost process as well as an atomic layer deposition process and chemical vapor deposition process. 18,19 In contrast, direct deposition methods such as a chemical bath deposition (CBD) and a liquid phase deposition are attracting attention as low-cost film formation processes. In these processes, nucleation and crystal growth on substrate in solution result in the formation of metal−oxide and metal−chalcogenide films. 19−21 Fabrication processes of microstructured ZnO films have been intensively studied by many researchers. 22−29 For application to TCO films, it is necessary to prepare ZnO thick films to reduce the resistivity, though the thick films prepared by solution processes tend to cause severe light scattering due to the formation of internal pores or voids. In the present study, we attempted to fabricate transparent ZnO thick films by the CBD method. Although there are a number of reports for controlling the morphology of ZnO films by the CBD method, the fabrication of transparent ZnO thick films is not easy. The transparency of thick films fabricated in solutions has been discussed in some studies in recent years. 30−34 As seen in ref ...

Investigations on the Crystallographic Orientation Induced Surface Morphology Evolution of ZnO Thin Films and Their Wettability and Conductivity

“…In general, ZnO columnar nanostructures with c -axis crystallographic orientation are most commonly obtained in several nanosynthesized methods including wet and physical–chemical vapor deposition techniques. A lot of models have been developed to explain crystal growth mechanism including preferential nucleation, sticking probability on each plane, surface diffusion of adatoms, and growth rate anisotropy of the different crystallographic planes. − Here, we deduce a growth mechanism to interpret the crystallographic orientation evolution of ZnO thin film depending on the synthesized temperature, which is on the basis of the DEZn as a precursor that could be decomposed into different chemical species such as metal zinc, ethyl groups, and its fragments under different synthesized temperatures and then further influence the nucleation and growth of grains . For verifying and better understanding this growth mechanism in our case, the in situ OES analysis was used to monitor plasma chemical composition during the synthesis process as shown in Figure , and Figure depicts a schematic drawing for the proposed growth mechanisms.…”

The Effects of Deposition Time and Seed Layer on Morphological Properties of Zinc Oxide by Chemical Bath Deposition

“…The presence of nucleation sites from the seeding process that enhanced binding will determine the success of any uniform growth [10]. A hexagonal rod morphology, which originates from a wurtzite-type crystal structure of ZnO with a hexagonal symmetry is frequently found in CBD [11].…”

Fabrication of transparent conductive zinc oxide films by chemical bath deposition using solutions containing Zn²⁺ and Al³⁺ ions

“…28) Figure 2 shows the wide range RSM of the ZnO films obtained from the solutions with 02.0 mol % AlCl 3 . A horizontal axis and a vertical axis correspond to the diffraction angle of 2ª and the inclination angle of ¼, respectively.…”

“…24)26) We have demonstrated recently that the morphology of solution-processed ZnO materials can be highly controlled by using a surfactant having a cationic head group, cetyltrimethylammonium chloride (CTAC). 27), 28) That is, the formation reaction of ZnO in zinc acetate solutions with CTAC leads to the evolution of unique morphologies as nanostructured particles or oriented thick films with high transparency. In the present work, we further added aluminum chloride (AlCl 3 ) to zinc acetate solutions with CTAC to investigate the influence of foreign metal cations on the growth of ZnO films.…”