The study of crystallization of phase change materials and their applications for data storage

Phase change recording materials are amorphous semiconductors with large rates of crystallization. These materials are composed mainly of elements from Groups IV A, V A and VI A of the periodic table. Phase change materials can be reversibly transformed between amorphous and crystalline states. Both of these states can be retained at room temperature for long periods of time (>10 years). Due to the difference in the physical properties (such as reflectivity and electric: conductivity), the amorphous and the crystalline states can be distinguished by optical or electrical methods. Therefore, phase change materials have wide application in data storage.; In order to find the appropriate recording materials for phase change recording, it is necessary to understand the crystallization mechanism of these types of materials. In this thesis, we used both experimental and computational methods to study the crystallization kinetics of phase change recording materials. First, in-situ annealing experiments in the column of a transmission electron microscope (TEM) were carried out to understand the crystallization process and to measure the crystallization parameters at relatively low temperature. High temperature crystallization parameters can be obtained by extrapolating these low-temperature values. We also built an atomic random network model to study the atomic arrangements in different amorphous states of the phase change materials. This model enables us to understand the crystallization process from the atomic scale. Based on the studies of crystallization kinetics, we constructed models to simulate the recording processes for both phase change optical recording and phase change electric recording. Using these models, we investigated the optimal operation conditions for phase change devices.