Atomic-Scale Structure and Surface Kinetics of Semiconductor Heteroepitaxy

本项目探讨了用表面活性剂介导的工艺生长IV族外延材料的几个关键问题。原位研究将集中于IV-VI族元素在Si和Ge单晶（001）表面的吸附，以探索异质外延的一般重要性问题。方法是首先确定相关单元素吸附剂的平衡和亚稳表面相的结构。接下来，将研究假晶层上的吸附，以了解晶格应变、立体效应和相对化学键强度等因素，这些因素决定了特定表面异相的结构。然后将探索表面活性剂对表面过程动力学的修饰，并利用表面活性剂促进亚稳外延合金结构的生长。所制备的异质外延薄膜的结构完善性和晶格应变将作为所研究的生长技术有效性的敏感监视器进行检查。研究采用x射线驻波、表面x射线衍射和表面扩展x射线吸收精细结构光谱，重点研究应变层异质外延的初始相和次级相，以及外延生长动力学。要研究的异质外延生长的具体方面有：(1)由单层（或更少）异质层沉积引起的表面结构，(2)与生长相关的吸附物（如表面活性剂或掺杂剂）在衬底表面的表面结构，(3)薄应变异质层表面的结构，以及(4)表面活性剂物种的存在对表面动力学的改变。该项目涉及具有技术相关性的材料科学主题领域的基础研究问题。该项目的一个重要特点是通过在一个基础和技术上重要的领域培养学生，将研究和教育结合起来。* * *

This project explores several key issues related to growth of group IV epitaxial materials by surfactant mediated processes. In situ studies will center on adsorption of elements from groups IV-VI on the (001) surface of Si and Ge single crystals to explore issues of general importance for heteroepitaxy. The approach is to first determine the structure of equilibrium and metastable surface phases of relevant monoelemental adsorbates. Next, adsorption on pseudomorphic layers will be studied to gain an understanding of factors such as lattice strain, steric effects, and relative chemical bond strength that determine the structure of a particular surface heterophase. The modification of the kinetics of surface processes by surfactants will then be explored, and exploited to facilitate growth of metastable epitaxial alloy structures. The structural perfection and lattice strain of the heteroepitaxial thin films produced will be examined as a sensitive monitor of the efficacy of the investigated growth technique. The study features x-ray standing waves, surface x-ray diffraction, and surface extended x-ray absorption fine structure spectroscopy, and focuses on the initial and secondary phases of strained-layer heteroepitaxy, as well as the kinetics of epitaxial growth. Specific aspects of heteroepitaxial growth to be examined are: (1)surface structure resulting from the deposition of a monolayer (or less) of a heterolayer, (2)surface structure of growth-related adsorbates (e.g., surfactants or dopants) on the surface of the substrate, (3)structure found on the surface of a thin strained heterolayer, and (4)alteration of surface kinetics by the presence of a surfactant species.%%%The project addresses basic research issues in a topical area of materials science having technological relevance. An important feature of the project is the integration of research and education through the training of students in a fundamentally and technologically significant area. ***