Surface Chemistry Studies During Thin-Film Growth Using Electrochemical Atomic Layer Epitaxy (EC-ALE)

使用电化学原子层外延 (EC-ALE) 进行薄膜生长过程中的表面化学研究

• 批准号: 0075868
• 负责人: John Stickney
• 金额: $ 37.66万
• 依托单位: University of Georgia Research Foundation Inc
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2000
• 资助国家: 美国
• 起止时间: 2000-08-01 至 2003-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0075868&HistoricalAwards=false
• 关键词: Surface; Chemistry; Studies; During; Thin

The goal of this project is greater understanding and control of electrochemical epitaxial processing of compound semiconductors. The focus of the project is atomic layer epitaxy (ALE), where deposits are formed an atomic layer at a time. In ALE, surface limited reactions are used to form each atomic layer. Surface limited electrochemical reactions generally occur at underpotentials, potentials below those needed to deposit the element on itself. The approach makes use of an automated electrochemical flow-cell, which facilitates growth of films thick enough for analysis by X-ray diffraction (XRD), electron microprobe analysis (EPMA), infrared (IR), and optical spectroscopies. Previous EC-ALE studies have focused either on the first few atomic layers or the structure, composition, and morphology of completed films. This project will address surface chemistry of the EC-ALE cycle as the deposit is being formed. It is thought that optimal conditions (potentials) change as the deposit grows, and some form of feedback is needed to better control the process. However, currents measured during various cycle steps do not provide an accurate picture of the deposition process. It is proposed to study the surface chemistry after various numbers of cycles, and at different points in the cycle, while deposits are forming, that is, to follow the surface chemistry during the 2nd , 5th , 10th , 25th , -..200th , cycles. Surface sensitive probes will be used to follow the EC-ALE cycle chemistry during film growth. A unique electrochemical STM flow-cell will be used to monitor surface structure and morphology during deposition. This apparatus allows atomic scale imaging in a controlled environment where solutions are easily exchanged and EC-ALE deposits can be formed. The mass of the deposits will be monitored at each step in the EC-ALE cycle using an electrochemical quartz crystal microbalance (EC-QCM) system. A microbalance crystal will be used as a substrate in a flow-cell. The mass of the deposit at each step will be compared with observed currents to elucidate interfacial processes and current efficiencies. An electrochemical flow-cell deposition system will be constructed for use in the antechamber of a UHV surface system, so that the composition of the surface can be monitored after any number of cycles and after any cycle step. Deposits will be transferred periodically from the flow cell directly to the analysis chamber for examination with AES, XPS, LEED, STM, and LEIS. Improved understanding of the surface chemistry, leading to better control over deposit structure, composition and morphology is expected. InAs and InSb are being grown using EC-ALE and work on the formation of III-V compounds in general will continue. CdSe/CdTe and InAs/InSb superlattices have been formed, and will continue to be studied.%%%The project addresses basic research issues in a topical area of materials science with high technological relevance. New, innovative experimental techniques such as electrochemical atomic layer epitaxy can now be characterized more fully leading to greater understanding and control of elementary chemical and diffusion processes which will allow advances in fundamental materials science and technology. The basic knowledge and understanding gained from the research is expected to contribute to improving the ability to efficiently deposit high crystal quality semiconductor films for electronic and photonic 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.***

该项目的目标是更好地了解和控制化合物半导体的电化学外延加工。该项目的重点是原子层外延(ALE)，即沉积一次形成一个原子层。在ALE中，表面受限反应被用来形成每个原子层。表面有限的电化学反应通常发生在低于电势的情况下，低于将元素沉积到自身所需的电势。该方法利用自动化的电化学流动池，便于生长足够厚的薄膜，以供X射线衍射(X射线衍射)、电子探针分析(EPMA)、红外(IR)和光学光谱分析。以前的EC-ALE研究要么集中在最初的几个原子层，要么集中在完成的薄膜的结构、组成和形态上。该项目将在矿床形成过程中解决EC-ALE循环的表面化学问题。人们认为，随着沉积的增长，最佳条件(电位)会发生变化，需要某种形式的反馈来更好地控制这个过程。然而，在不同的循环步骤中测量的电流并不能提供沉积过程的准确图像。建议在不同旋回次数后，在不同旋回的不同时间点研究沉积形成过程中的表面化学，即在第2、5、10、25、-200个旋回中进行表面化学研究。在薄膜生长过程中，将使用表面敏感探针来跟踪EC-ALE循环化学。一个独特的电化学STM流动池将被用来监测沉积过程中的表面结构和形貌。这种设备允许在受控环境中进行原子尺度成像，在这种环境中，溶液很容易交换，可以形成EC-ALE沉积物。将使用电化学石英晶体微天平(EC-QCM)系统在EC-ALE循环的每个步骤监测矿床的质量。在流动池中将使用微天平晶体作为衬底。每一步的沉积质量将与观察到的电流进行比较，以阐明界面过程和电流效率。将建造一个电化学流动电池沉积系统，用于特高压表面系统的前厅，以便在任何循环次数和任何循环步骤之后可以监测表面的成分。沉积物将定期从流动池直接转移到分析室，用俄歇电子能谱、X射线光电子能谱、LEED、STM和LEIS进行检测。更好地了解表面化学，从而更好地控制沉积物的结构、成分和形态是可望的。正在使用EC-ALE生长InAs和InSb，总体上将继续进行形成III-V化合物的工作。已经形成了CdSe/CdTe和InAs/InSb超晶格，并将继续进行研究。%该项目解决了材料科学中具有高度技术相关性的热门领域的基础研究问题。新的、创新的实验技术，如电化学原子层外延，现在可以更充分地表征，从而更好地理解和控制基本的化学和扩散过程，这将使基础材料科学和技术取得进步。从研究中获得的基本知识和理解有望有助于提高高效沉积用于电子和光子应用的高晶体质量半导体薄膜的能力。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。