Temporal Evolution of Microscopic Structure and Functionality during Crystallization of Amorphous Indium-Based Oxide Films

Understanding the crystallization mechanism of amorphous metal-oxide thin films remains of importance to avoid the deterioration of multifunctional flexible electronics. We derived the crystallization mechanism of indium-based functional amorphous oxide films by using in situ X-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements. Crystallization begins with surface nucleation, especially at low annealing temperatures, and proceeds simultaneous nucleation and growth in the bulk. Three-dimensional crystal growth in the film was observed when the crystallite size was sufficiently smaller than the film thickness. When the growing crystallites reached the film surface, the crystallization was dominated by two- or lower-dimensional growth. Such crystallization can be explained within the framework of the modified Avrami theory and can be varied for tailoring the electrical properties of the amorphous In₂O₃ film. After tailoring the film crystallinity and crystallite size, the carrier mobility was improved to >100 cm²/V·s in 30 min. Our results show that a carrier mobility of >90 cm²/V·s can be implemented for the In₂O₃ film with a crystallinity of >40% and a crystallite size of >70 nm by an optimized annealing process. The incorporation of Ga element into amorphous In₂O₃ films obviously increases the activation energy of nucleation and migration. In contrast, Sn dopants can promote the crystal growth. This is attributed to two kinds of migration mechanisms during the annealing in air, one of which is the dominant migration mechanism of oxygen interstitials in crystallized indium-tin oxide (ITO) films and the other dominated by oxygen vacancies in In₂O₃ and IGO films. Combining the modified Avrami theory with TEM observations, we predicted the structural evolution kinetics for indium-based amorphous oxide films and gained new insights for understanding the temporal structure-functionality relationship during crystallization.