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

Abstract

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.

Hydrogen Behavior at Crystalline/Amorphous Interface of Transparent Oxide Semiconductor and Its Effects on Carrier Transport and Crystallization

“…Thus, we find that the structural, dynamic, and electronic properties reach their corresponding crystalline or amorphous bulk values within about 2 Å, making our choice of a 20 Å model sufficient to describe the c/a interface. The sharp c/a interface obtained in our calculations is in accord with the high-resolution TEM imaging of nanocrystallites in amorphous indium oxide …”

“…It must be stressed that the oxygen stoichiometry, cation composition, or density of amorphous indium oxide may influence the formation and concentration of stable In–OH, In–H–In, and O 2 defects and, hence, is likely to affect both the crystal grain size and the crystallization rate, explaining a wide variety of experimental observations reported in the literature. In addition, the film thickness and density and the oxygen environment during annealing are important control parameters of the crystallization process. , To address the effects of those parameters computationally, models of an amorphous oxide surface or a slab would be required in order to properly simulate surface defects, oxygen adsorption, diffusion, and defect passivation.…”

“…The sharp c/a interface obtained in our calculations is in accord with the high-resolution TEM imaging of nanocrystallites in amorphous indium oxide. 52 2.2. Properties of H Defects in c/a In 2 O 3 Interface.…”

“…In addition, the film thickness and density and the oxygen environment during annealing are important control parameters of the crystallization process. 52,57 To address the effects of those parameters computationally, models of an amorphous oxide surface or a slab would be required in order to properly simulate surface defects, oxygen adsorption, diffusion, and defect passivation. Because interfacial In−H−In defects are found to be unstable and have a strong tendency to switch to In−OH at elevated temperature during crystallization, the majority of stable In−H−In defects are expected to reside within disordered and/or oxygen-deficient parts of the structure: e.g., at grain boundaries.…”

Factors Determining the Resistive Switching Behavior of Transparent InGaZnO‐Based Memristors

“…Recently, Jia et al reported on the temporal evolution of microscopic structure and functionality during the crystallization of amorphous indium‐based oxides such as ITO and InGaO. [ 46 ] According to their work, nanocrystalline phases may be transformed out of the amorphous matrix of such AOSs, of which the process is facilitated by the support of oxygen vacancy migration, also known as structural relaxation. These potential instabilities of the amorphous phase and the associated change in the conduction path may be, at least in part, related to the demonstrated memristor performance issues regarding stability and endurance.…”