Semiconductors that can be switched between their crystalline and amorphous phases by a pulse of light are the foundation for one of the most important optical data storage technologies. Technologically, the most important composition contains the elements, germanium, antimony, and tellurium, because this composition is the active component of re-writable DVD's. Previous results from this project have shown that the structures of the amorphous and crystalline phases are very different. A major focus of this project is to understand the microscopic mechanisms that drive the reversible phase-change process and produce the changes in structure. In addition to training several graduate students and postdoctoral research associates in areas of technological importance, such as materials for use in flat panel displays and re-writable DVD's, a textbook on disordered solids will be completed. The metastable, reversible change from a mostly crystalline to a mostly amorphous phase, and vice versa, is at the heart of both optically and electrically reprogrammable memories, but a basic physical understanding of these changes remains elusive. At both the undergraduate and graduate levels, women will play a prominent role in this project.
Disordered and amorphous semiconductors are important in many electronic and optical applications. This project will concentrate on understanding metastable effects, such as reversible amorphous-to-crystalline structural transformations or metastable shifts of the optical absorption edge after optical excitation. A major component is a study of Ge-Sb-Te alloys that are used in phase-change memory devices, with the ultimate aim of understanding the microscopic mechanisms that drive the reversible phase-change process. Theoretical tight-binding calculations will supplement the experimental results. In addition to training several graduate students and postdoctoral research associates in areas of technological importance, such as materials for use in flat panel displays and re-writable DVD's, the project will attempt to provide a basic understanding of the novel phase-change process itself. The metastable, reversible change from a mostly crystalline to a mostly amorphous phase, and vice versa, is at the heart of both optically and electrically reprogrammable memories, but a basic physical understanding of the microscopic mechanisms and the kinetics responsible for these changes remains elusive. A textbook entitled Introduction to Disordered Solids will be completed. At both the undergraduate and graduate levels, women will play a prominent role in this project.
