Tailoring Surface Morphology of Epitaxial Layers on Silicon

9528513本研究项目采用超高真空显微镜的独特组合：低能电子显微镜和扫描隧道显微镜，对硅表面进行原位沉积和生长研究，以清楚地识别不同的生长模式，即Frank-van der Merwe、Volmer-Weber和STranski-Krastanov，并观察生长过程中表面的宏观变化，如刻面和阶跃聚束。研究的重点是在不同取向的硅表面上剪裁同质外延层和异质外延层的表面形貌。将研究Ge/Si(100)和Ge/Si(311)以及Si/Si(100)和Si/Si(311)的同质外延系统。将使用LEEM实时观察在有和没有表面活性剂的情况下生长过程中2D岛密度的发展，以评估表面活性剂的存在是否增加或减少了吸附原子的扩散长度，以促进逐层生长。%拟议的LEEM/STM研究有望查明高指数(311)基片表面所起的能量学和动力学作用。STM具有更好的空间分辨率，是研究成核初始阶段的理想工具；而LEEM特别适合于研究依赖于衬底温度、扩散速率和质量传输的生长动力学。这两种强大的横向空间分辨技术将能够识别定制生长形貌所需的关键参数，从而合成用于微电子应用的新的和改进的材料。从提高SiGe/Si超晶格载流子迁移率及其在异质结双极晶体管中应用的技术角度来看，Ge/Si系统具有重要意义，而Si/Si同质外延是研究控制生长动力学的基本机制的模型系统，特别是阶跃流生长的衬底温度最小化。从这一研究项目中获得的知识和理解有望通过为设计和生产改进材料提供基本的理解和基础，从而在总体上为提高用于计算、信息处理和电信的先进设备的性能做出贡献。该计划的一个重要特点是通过在一个具有根本意义和技术意义的领域对学生进行培训，将研究和教育结合起来。***

9528513 Tsong This research project uses a unique combination of ultrahigh vacuum (UHV) microscopies: low energy electron microscopy (LEEM) and scanning tunneling microscopy (STM), to conduct in situ deposition and growth studies on Si surfaces to clearly identify different growth modes, i.e. Frank-van der Merwe, Volmer-Weber, and Stranski-Krastanov, and also to observe gross changes of the surface during growth, such as faceting and step-bunching. The investigation focuses on tailoring the surface morphology of homoepitaxial and heteroepitaxial layers on Si surfaces with different orientations. Ge/Si(100) and Ge/Si(311) and the homoepitaxial systems of Si/Si(100) and Si/Si(311) will be studied. Real-time LEEM observations of the development of 2D-island density during growth with and without a surfactant will be used to assess whether or not the presence of surfactants increases or reduces the diffusion lengths of adatoms to promote layer-by-layer growth. %%% The proposed LEEM/STM investigations are expected to pinpoint the role of energetics versus kinetics played by the high-index (311) substrate surface. STM, with its better spatial resolution, is ideal for the study of the initial stages of nucleation; while LEEM is particularly suited to examine growth kinetics dependent upon substrate temperature, diffusion rates and mass transport. These two powerful lateral spatial resolving techniques will enable identification of critical parameters necessary to tailor growth morphologies, and hence the synthesis of new and improved materials for microelectronic applications. The Ge/Si system is significant from the technological point of view of enhanced carrier mobility in SiGe/Si superlattices and their application in heterojunction bipolar transistors, while Si/Si homoepitaxy is a model system to study fundamental mechanisms controlling growth kinetics, in particular the minimization of substrate temperature for step-flow growth. The knowledge and understanding gained from this research pr oject is expected to contribute in a general way to improving the performance of advanced devices used in computing, information processing, and telecommunications by providing a fundamental understanding and a basis for designing and producing improved materials. An important feature of the program is the integration of research and education through the training of students in a fundamentally and technologically significant area. ***