Optic properties of ZnO films grown by sol-gel technique

Abstract

Background. Zinc oxide (ZnO) is a promising material for designing the semiconductor radiation sources and detectors in the region of short wavelengths of the optical range. Films based on ZnO are considered as possible elements of optoelectronic devices that can be used to influence their optical properties. Nowadays, the methods of making such films are quite diverse, however, obtaining high-quality and inexpensive ZnO films remains an actual scientific and engineering task that needs to be solved. Thus, the research in this direction and the development of recommendations on the synthesis of ZnO films is urgent. Purpose of Work. The aim of the work is to obtain ZnO films by the sol-gel technique, to evaluate their structure and optical properties and to estimate the affect of ultraviolet radiation on the structure and optical characteristics of the obtained films. Techniques and Methodology. The process of obtaining ZnO films is considered. The process of obtaining such films by sol-gel technique is described. A visual analysis of the experimentally obtained films has been carried out. The optical properties of ZnO films were experimentally examined. In particular, the influence of ultraviolet radiation used at the stage of obtaining films on the features of their ability to absorb radiation in the optical range is analyzed. Results. ZnO films were grown experimentally by sol-gel technique. ZnO films were formed on quartz substrates. The formation of ZnO nanoparticles is observed in the films obtained without the influence of radiation. The usage of ultraviolet radiation at the stage of the final heat treatment at a temperature of 480 °C leads to the formation of a higher quality ZnO film and a decrease in the size of the granules. Analysis of the chemical composition of the films using X-ray fluorescence analysis shows the presence of zinc and oxygen in the formed films, as well as insignificant carbon content, which is associated with the use of quartz as substrates. The dependencies of the transmission capacity of ZnO films on the wavelength of radiation incident on the film in the range of 200-450 nm are obtained. It is shown that in films exposed to ultraviolet radiation at the stage of heat treatment, there is a shift in the value of the cut-off wavelength corresponding to the absorption edge and, accordingly, a decrease in the band gap calculated from the results of the experiment. Conclusions: To summarize the results of the research we can highlight that the influence of ultraviolet radiation at the stage of the final heat treatment on ZnO films formed by sol-gel method leads to an improvement in the quality of the films and to a change in their optical properties, in particular, a decrease in the energy corresponding to the absorption threshold.