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理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），其中沉积物一次形成一个原子层。在 ALE 中，使用表面有限反应来形成每个原子层。表面限制的电化学反应通常在电势较低的情况下发生，电势低于在其自身上沉积元素所需的电势。该方法利用自动电化学流通池，有利于薄膜生长足够厚，以便通过 X 射线衍射 (XRD)、电子微探针分析 (EPMA)、红外 (IR) 和光学光谱进行分析。之前的 EC-ALE 研究主要集中在前几个原子层或完整薄膜的结构、成分和形态。该项目将解决沉积物形成过程中 EC-ALE 循环的表面化学问题。人们认为，最佳条件（潜力）会随着矿床的增长而变化，并且需要某种形式的反馈来更好地控制该过程。然而，在各个循环步骤期间测量的电流并不能提供沉积过程的准确图像。建议在沉积物形成时，在不同次数的循环后以及循环中的不同点研究表面化学，即跟踪第 2、5、10、25、-..200 次期间的表面化学，循环。表面敏感探针将用于跟踪薄膜生长过程中的 EC-ALE 循环化学过程。独特的电化学 STM 流通池将用于监测沉积过程中的表面结构和形态。该装置允许在受控环境中进行原子级成像，在该环境中可以轻松交换溶液并可以形成 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 循环的每个步骤中监测沉积物的质量。微量天平晶体将用作流通池中的基底。每个步骤的沉积物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。将构建电化学流通池沉积系统，用于特高压表面系统的前室，以便在任意次数的循环和任意循环步骤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，以便使用 AES、XPS、LEED、STM 和 LEIS 进行检查。提高对表面化学的了解，有望更好地控制沉积物结构、成分和形态。 InAs 和 InSb 正在使用 EC-ALE 进行生长，并且一般而言，III-V 族化合物的形成工作将继续进行。 CdSe/CdTe 和 InAs/InSb 超晶格已经形成，并将继续研究。%%%该项目解决具有高技术相关性的材料科学主题领域的基础研究问题。现在可以更全面地表征电化学原子层外延等新的创新实验技术，从而更好地理解和控制基本化学和扩散过程，从而促进基础材料科学和技术的进步。从研究中获得的基础知识和理解预计将有助于提高为电子和光子应用有效沉积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基础和技术重要领域对学生进行培训，将研究和教育融为一体。***