Effect of preheating process on crystallization and optical properties of sol-gel derived ZnO semiconductor thin films

Abstract

Highly transparent ZnO semiconductor thin films were deposited onto alkali-free glass substrates by a sol-gel spin coating process. This research investigated the effects of different preheating rates (4 or 10°C/min) on the various surface morphologies, crystallization characteristics, and optical properties of these thin films. The ZnO sol was synthesized by dissolving the zinc acetate dihydrate in isopropanol (IPA), and then adding monoethanolamine (MEA). These as-coated films were preheated at 300°C for 10 min and annealed in an air ambiance at 500°C for 1 h. Experimental results revealed that the as-prepared films had a hexagonal wurtzite structure, and that the heating rates of the preheating process obviously affected the surface morphologies, crystallization qualities, and transparency levels of the thin films. A ZnO thin film preheated at 10°C/min exhibited preferential orientation along the (002) plane, a flat surface, and also achieved a high transmittance value, 92.5%, for light with a wavelength of 550 nm.

Evaluation of the Tauc method for optical absorption edge determination: ZnO thin films as a model system

“…As noted above, we collected a large number of published Tauc analyses of undoped ZnO that included plots of the absorbance data against the photon energy . This was critical, as our assessment of the application of the Tauc method required the consistent application of a fitting method, as described below.…”

Microstructure evolution and photoluminescence in nanocrystalline MgxZn1 −xO thin films

“…The process of formation of polycrystalline thin films by sol-gel processing involves three steps: solvent evaporation, precursor decomposition and crystallization. Various factors that affect the structure of these films are pre-firing temperature, composition, firing or annealing temperature, and rate of heating [40][41][42][43]. Ohyama et al [43] reported that low heating rates result in dense ZnO films, because the film is given enough time for structural relaxation before crystallization.…”

Molecular Structures of ZnO by Aggregates of Atoms and Interaction of Two Monolayers

“…This material is currently considered a semiconductor synthesized through a process of new techniques, where growth brings new physical properties, as well as technological applications [7][8][9][10]. Zinc oxide has different electronegativities of zinc and oxygen, and the most stable crystalline structure is the hexagonal wurzite type [11][12][13][14]. Zinc oxide has technological interest and especially in nanometer-level structures, because it is possible to obtain nanostructures in the form of nanoparticles, where different structures are observed in both form and type, generating various nanostructures in the form of nanoparticles, nanowires, nanofiber, as the main ones.…”