1.Introduction

Transparent conductive oxide film (TCO) refers to a class of important optoelectronic materials with high conductivity, high transparency in the visible light range. In nature, transparent materials are usually not conductive (such as glass, crystal, etc.), while materials with conductivity or good conductivity are often opaque (such as metal materials, graphite, etc.). Transparent conductive oxide film breaks the traditional concept, combining transparency with conductivity, and has become a unique type of functional film material. Common TCO films are mainly divided into ITO films, AZO films, FTO films, ATO films, etc., and have been widely used in different fields such as photovoltaic cell modules, flat panel displays, touch panels, light-emitting diodes (LEDs), gas sensors and so on.

2.TCO Thin Film Characterization Analysis

The physical structure of TCO thin films plays a decisive role in the quality of their products. Through phase analysis, we can gain in-depth understanding of the key characteristics of TCO thin films, such as crystal structure, lattice parameters, grain size, and preferred orientation of crystal growth, which are closely related to the optoelectronic properties of the film, such as transparency, conductivity, and long-term stability.

X-ray diffraction (XRD) technology is a key tool for analyzing TCO thin films, which can provide detailed information about the crystal structure and microstructure of the film. The data such as lattice parameters, grain size, and preferred orientation obtained by XRD analysis are extremely important for the optoelectronic behavior of FTO thin films and improving their performance stability. Through these analyses, researchers can optimize the preparation process of TCO thin films, thereby improving their performance in various applications.

Identify the crystal structure and phase composition of the TCO film. By analyzing the diffraction peaks in the XRD spectrum, it can be determined whether the FTO film is a rutile structure and whether there are other phases, such as tetragonal or cubic phases. This information helps to understand the crystal quality of the film, which in turn affects its conductivity and transparency.

We need to detect the lattice parameters of TCO films, including lattice constant and interplanar spacing. Changes in these parameters may be related to the stress state during film growth, thus affecting the electronic properties and mechanical stability of the film.

We need to evaluate the grain size and crystal orientation of TCO films. The grain size can be calculated from the width of the diffraction peak, while the relative intensity of the diffraction peak can provide information on the preferred orientation of the crystal by using the Scherrer formula. These data are important for optimizing the preparation process of the film and improving its perform.

3.Application Case

In this experiment, the FRINGE benchtop X-ray diffractometer from LANScientific Co., Ltd. was used to characterize the phase structure of TCO thin film samples provided by a company.

(1)Sample Preparation

(2)Test parameter settings

(4)Test Results and Conclusion

After GIXRD testing, it was determined that the film sample was a FTO (SnO₂:F) film with a (200) preferred orientation. FTO (SnO₂:F) film is the abbreviation of fluorine-doped tin oxide (Fluorine-doped Tin Oxide), which is a wide bandgap semiconductor material. Its main component is SnO₂ and it is doped with fluorine element F. FTO film has excellent transparency and conductivity because fluorine atoms replace part of the oxygen atoms to form a SnO₂-xFx structure, thereby adjusting the bandgap width and carrier concentration of the material, making the film both transparent and conductive. FTO film usually presents a tetragonal rutile structure with the characteristics of high carrier concentration and low resistivity.

References:

Fan Lin, Xu Kejing, Shi Xiaohui, Jia Yuhui, Zhang Heng, Wei Chuncheng. Effects of different fluorine sources on the properties of FTO films and their mechanisms. Materials Engineering, 2018, 46(9): 59-64.