Non-Equilibrum Svnthesis and Growth of Silicon Micro-and Nano-Columns

该项目的目的是探索微米和纳米柱的形成、生长和物理性质。通过使用脉冲准分子激光在硅片表面生长高纵横比的纳米硅柱阵列，产生“活性尖端”，气相中硅的沉积显著增加。将研究纳米柱阵列的初始形成和随后生长的机制，并测量硅纳米柱的电学和光电性质。硅微纳米柱结构的可控生长在太阳能电池、场发射针尖和传感器中具有重要的应用价值。先前的工作表明，脉冲激光照射下的硅微柱生长与气-液-固(VLS)法生长硅晶须的早期研究之间存在联系。这一链接为更好地理解这两种方法开辟了新的途径，并为生产降维的半导体结构提供了新的工具。在第一阶段的研究中，微柱的顶端将被熔化以激活纳米柱的生长。在第二个研究阶段，基于对激光辅助化学气相沉积的已有知识，将避免熔化，以主要使用光解激活生长来生长纳米级尖端。在这两个阶段中，使用先前生长的微柱作为模板来生长纳米柱。预计纳米柱将笔直生长，保持充当其基座的微柱的晶体取向，并将直接连接到下面的晶片上。这使得对纳米柱结构和性质的控制和表征成为可能。利用直的、相互连接的纳米柱，可以实现较短的载流子路径和对电信号的较短传播/响应时间。脉冲激光生长还允许控制掺杂原子的含量，以及从气相简单地形成钝化层。我们将研究生长条件对微米和纳米柱长度、直径和演化的影响。在现场，包括离子探针测量和发射和吸收光谱在内的纳秒分辨率诊断将被用来确定在烧蚀过程中靠近硅表面的物种及其时间行为。将使用HRSEM、HRTEM和AFM显微镜来确定各个柱和阵列的形态、成分和结构特征，以及它们的生长动力学。计算机模拟还将用于指导对柱子形成和生长过程的理解。%该项目解决具有潜在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通过为设计和生产改进的纳米结构材料提供基本的理解和基础，从而有助于提高当前和新的电子/光子应用的性能。在这些调查中要解决各种基本问题。该项目的核心是培训研究生和本科生使用最先进的设备和适当的科学方法进行研究，因为他们使用具有有趣和重要应用的材料来促进对材料生长现象的基本理解。因此，该计划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。***

The aim of this project is to explore the formation, growth, and physical properties of micro- and nano-columns. Arrays of high aspect ratio silicon nanocolumns will be grown on the surface of a silicon wafer by using a pulsed excimer laser to generate "active tips" where the deposition of silicon from the vapor phase is dramatically augmented. Mechanisms of initial formation and subsequent growth of nanocolumn arrays will be studied, and electronic and optoelectronic properties of silicon nano-columns measured. Controlled growth of silicon micro- and nano-column structures could find significant applications in solar cells, field emission tips and sensors. Prior work indicates a connection between silicon microcolumn growth during pulsed-laser irradiation and earlier studies of silicon whisker growth by the vapor-liquid-solid (VLS) method. This link opens new avenues for greater understanding of both methods and provides new tools for the production of semiconductor structures with reduced dimensionality. In the first stage of research the tips of microcolumns will be melted to activate nanocolumn growth. In a second research stage, melting will be avoided in order to grow nanometer scale tips using primarily photolytic activation of growth, based on established knowledge of laser-assisted CVD. In both stages the nanocolumns are grown using previously grown microcolumns as a template. Nanocolumns are expected to grow straight, maintaining the crystal orientation of the microcolumns that serve as their pedestals, and will be directly connected to the wafer beneath. This makes possible control and characterization of nanocolumn structure and properties. With straight, interconnected nanocolumns a short carrier path and short propagation/response time to electrical signals can be achieved. Pulsed-laser growth also permits control of the dopant-atom content as well as simple formation of a passivation layer from the gas phase. The effects of growth conditions on the length, diameter, and evolution of micro- and nano-columns will be investigated. In situ, nanosecond resolution diagnostics including ion probe measurements and emission and absorption spectroscopy will be used to determine the species present close to the silicon surface during ablation and their temporal behavior. Morphological, compositional, and structural features of the individual columns and arrays, and their growth kinetics, will be determined using HRSEM, HRTEM, and AFM microscopies. Computer modeling also will be used to guide understanding of the column formation and growth processes.%%%The project addresses basic research issues in a topical area of materials science having potential technological relevance. The basic knowledge and understanding gained from the research is expected to contribute to improving the perform-ance of current and new electronic/photonic applications by providing a fundamental understanding and a basis for designing and producing improved nanostructured materials. A variety of fundamental issues are to be addressed in these investigations. Central to the project is the training of graduate and undergraduate students to conduct research using state-of-the-art equipment and appropriate scientific methodology as they advance basic understanding of materials growth phenomena using materials having interesting and important applications. Thus the program integrates research and education through the training of students in a fundamentally and technologically significant area. ***