Structures and textures of transparent conducting pulsed laser deposited In₂O₃-ZnO thin films revealed by transmission electron microscopy

Thin films of composition belonging to the In₂O₃-ZnO binary system were made by pulsed laser deposition, and characterized by means of X-ray and transmission electron microscopy (TEM) measurements to obtain phase purity and textural/microstructural information. Collected TEM images together with their analysis clearly show that three different types of films could be obtained, depending on the In₂O₃-ZnO target composition and film growth parameters. The first type, obtained from indium-rich pellets, is made of polyhedral grains having a bixbyite-type structure. The second type, obtained from zinc-rich pellets, presents a classic columnar texture consisting of grains having a wurtzite-type structure, occasionally faulted. The last type of thin films is made of a multitude of Zn_kIn₂O_k+3 polytypes forming a fibrous texture. The overall EDS analysis evidences that the composition is nearly constant between the target and the film, except for the Zn amount that is always slightly lower in the films. High-resolution electron microscopy studies on films formed of polytypes enable, after a complete image analysis, a simulation of the X-ray diffraction patterns that fit well with the experimental patterns, justifying the validity of our random intergrowth model.