GOALI/FRG: Nanoscale Morphological Control of Strained Semiconductor Surfaces

这个FRG/GOALI项目是弗吉尼亚大学和位于纽约约克敦高地的IBM的研究人员共同努力的成果。与伊利诺伊州立大学厄巴纳-香槟分校、弗吉尼亚州法姆维尔的朗伍德学院、联合大学和桑迪亚国家实验室建立了更多的合作关系。我们的方法是研究晶格失配异质外延薄膜的应变松弛途径，目的是充分从根本上了解外延层松弛时表面粗化和界面位错所起的作用，从而实现异质外延薄膜的形态编程。研究人员试图通过在初始生长表面上引入扰动--表面台阶、界面位错和/或光刻定义的图案--来获得定义外延层最终形态的知识和能力。还将探索这种编程表面在后续纳米结构(如图案化量子点阵列和功能生物分子)模板化方面的应用。这种可编程性完全不依赖于自发自组装或光刻。相反，它寻求协同效应，可能在实际纳米结构制造方面提供突破。最初，实验将集中在GeSi/Si系统上。将研究一系列生长技术(分子束外延、气源分子束外延和超高真空化学气相沉积)，以推断一般机制，而不是特定于特定生长化学或结构的机制。对均匀(即非扰动)表面演化的研究将集中在应变释放的微观机制和总体应变状态的宏观测量上。形态演化和失配位错注入的竞争和相互依赖将被详细研究。实验技术包括非原位和原位透射电子显微镜(TEM)、原位低能电子显微镜(LEEM)、X射线衍射的二维倒易晶格映射、原位晶片曲率和光谱光散射测量、有限元分析(FEA)计算，以及使用TEM成像和衍射的局部应变映射。外延层粗化应变松弛的定量测量将被合并到现有的模拟器中，该模拟器是在之前的NSF拨款下开发的，该模拟器模拟失配的位错注入到晶格失配的异质结构中。该组合模拟器将提供一系列异质外延系统中应变松弛、形态演变和位错产生的完整描述。后续对微扰机制和可编程表面的研究将应用许多相同的工具，重点是局部敏感的探头，如基于TEM、LEEM和FEA的技术。%该项目解决具有高度技术相关性的材料科学主题领域的基础研究问题。从研究中获得的基本知识和理解有望有助于提高半导体材料在当前和未来器件和电路应用中的性能。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。该计划的多学科(材料科学、电气工程、物理)和与工业相关的性质为学生提供了独特的教育机会，让他们从学术和工业的角度体验以团队合作为导向的研究环境。

This FRG/GOALI project is a collaborative effort between researchers at the University of Virginia and IBM, Yorktown Heights, NY. Additional collaborations are established with U. IL, Urbana-Champaign; Longwood College, Farmville, VA; UCB; and Sandia National Laboratories. The approach is to investigate pathways for strain-relaxation of lattice mismatched heteroepitaxial films with the goal of gaining sufficient fundamental understanding of the roles that surface roughening and interfacial dislocations play as the epilayer relaxes to allow morphological 'programming' of heteroepitaxial films. The investigators seek to acquire the knowledge and ability to define the final morphology of an epilayer by introducing perturbations--surface steps, interfacial dislocations and/or lithographically defined patterns--onto the initial growth surface. Applications of such programmed surfaces for templating of subsequent nanoscale structures such as patterned quantum dot arrays and functional biological molecules will also be explored. This programmability places total reliance on neither spontaneous self-assembly nor lithography. Instead, it seeks out synergistic effects that may provide breakthroughs in practical nanostructure fabrication. Initially, experiments will concentrate upon the GeSi/Si system. A range of growth techniques (molecular beam epitaxy, gas source molecular beam epitaxy, and ultra-high vacuum chemical vapor deposition) will be studied, to enable general mechanisms to be inferred, rather than those particular to a particular growth chemistry or configuration. Studies on the evolution of uniform (i.e. non-perturbed) surfaces will focus upon both microscopic mechanisms of strain relief and macroscopic measurements of the overall strain state. The competition and inter-dependence of morphological evolution and misfit dislocation injection will be examined in detail. Experimental techniques will include ex-situ and in-situ transmission electron microscope (TEM), in-situ low energy electron microscope (LEEM), two dimensional reciprocal lattice mapping with X-Ray diffraction, in-situ wafer curvature and spectroscopic light scattering measurements, finite element analysis (FEA) calculations, and local strain mapping using TEM imaging and diffraction. Quantitative measurements of strain relaxation by epilayer roughening will be incorporated into an existing simulator, developed under a previous NSF grant, that models misfit dislocation injection into lattice-mismatched heterostructures. The combined simulator will provide a complete description of strain relaxation, morphological evolution and dislocation generation in a range of heteroepitaxial systems. Subsequent studies of perturbation mechanisms and programmable surfaces will apply many of the same tools, with emphasis on locally sensitive probes such as TEM-, LEEM- and FEA-based techniques.%%%The project addresses basic research issues in a topical area of materials science with high technological relevance. The basic knowledge and understanding gained from the research is expected to contribute to improving semiconductor materials performance in current and future device and circuit applications. 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. The multidisciplinary (materials science, electrical engineering, physics) and industrially-connected nature of this GOALI program offers unique educational opportunities for students to experience a teamwork-oriented research environment from both academic and industrial perspectives.***