Localized Electronic States in Amorphous Semiconductors

可以通过光脉冲在晶体和非晶相之间切换的半导体是最重要的光学数据存储技术之一的基础。从技术上讲，最重要的成分包括锗、锑和碲等元素，因为这些成分是可重写DVD的有效成分。该项目先前的结果表明，非晶相和结晶相的结构有很大的不同。这个项目的一个主要焦点是了解驱动可逆相变过程和产生结构变化的微观机制。除了在重要的技术领域（如用于平板显示器和可重写DVD的材料）培训几名研究生和博士后研究助理外，还将完成一本关于无序固体的教科书。从晶态到非晶态的亚稳态可逆变化（反之亦然）是光学和电可重编程存储器的核心，但对这些变化的基本物理理解仍然难以捉摸。在本科和研究生两级，妇女将在这个项目中发挥突出作用。无序和非晶半导体在许多电子和光学应用中都很重要。该项目将集中于理解亚稳效应，如可逆的非晶到晶体的结构转变或光激发后光学吸收边缘的亚稳位移。一个主要组成部分是研究用于相变存储器件的Ge-Sb-Te合金，其最终目的是了解驱动可逆相变过程的微观机制。理论紧束缚计算将补充实验结果。除了在重要的技术领域（如用于平板显示器和可重写DVD的材料）培训几名研究生和博士后研究助理外，该项目还将尝试提供对新型相变过程本身的基本理解。从晶态到非晶态的亚稳态可逆变化（反之亦然）是光学和电可重编程存储器的核心，但对这些变化的微观机制和动力学的基本物理理解仍然难以捉摸。将完成一本名为《无序固体导论》的教科书。在本科和研究生两级，妇女将在这个项目中发挥突出作用。

Non-Technical AbstractSemiconductors 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. Technical AbstractDisordered 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.