Structure Control in Electrochemical Atomic Layer Eptiaxy

本计画的长期目标是获得化合物半导体电沉积的基本了解，并达成化合物半导体薄膜结构的沉积，其品质与控制是形成光电子元件所必须的。为这些研究提出的方法是电化学原子层外延（ECALE），原子层外延（ALE）的电化学模拟，其中使用表面限制反应来形成材料，一次一个原子层。欠电位沉积，upd，是表面限制电化学反应的另一个名称。这是一种现象，其中一种元素的原子层在其自身上存款第一种元素所需的电势之前沉积在第二种元素上。驱动力是表面化合物的形成和化合物形成的自由能。在ALE循环中使用upd，沉积物在平衡或接近平衡时形成，一次形成一个单层。每种元素的原子层在一个循环中依次沉积，以形成化合物的单层。循环次数决定了存款的厚度。ECALE的一个主要优点是它将化合物电沉积分解为一系列基本步骤，允许独立的调查和控制。ECALE研究是研究复合电沉积机理最直接的途径。 要解决的问题包括：在化合物半导体器件结构的电化学形成中可以获得多少控制？什么类型的电化学反应可用于创建ALE循环？可以通过使用不同的基底或通过改变沉积参数来改变存款习惯吗？ 可以形成三元化合物吗？是否可以开发程序来形成梯度沉积物作为缓冲层，或帮助解决晶格匹配问题。什么类型的电化学反应可用于创建ALE循环？ 在复合电沉积中掺杂可以控制吗？p型和n型材料都能形成吗？ 使用ECALE的自动流动沉积系统用于形成沉积物，其中电位和溶液变化由计算机控制。 表征方法包括原位电化学扫描隧道显微镜（ECSTM），电化学石英晶体微天平（EQCM），超真空电化学（UHV-EC）用于存款表面的研究，以及反射，吸收，发光，光电化学，光电导和霍尔测量的物理和电子性能的研究。该项目的一个重要特点是通过研究和教育的结合，促进教育和人力资源开发。该项目涉及研究生和本科生，各级参与者相互交流，并定期与主要研究者（PI）进行交流。在PI小组工作的五名学生中有两名来自代表性不足的群体，并将获得该奖项的支持。学生们积极参与发表论文，并在专业协会会议上发表演讲和海报。PI的大部分学生在毕业前的简历上都有超过五次的陈述。本课程还打算在ECALE上建立一个网页，学生们在此设计和建立各个部分，目的是形成一个可以找到ECALE现状的页面。该页面将包括如何使用ECALE形成沉积物的描述，该领域所有工作组的出版物列表，方法，仪器设计，以及在实验室视图中编写的控制沉积的程序，任何对该方法感兴趣的人都可以访问。***

The long term objective of this project is to gain fundamental understanding of compound semiconductor electrodeposition and to achieve deposition of compound semiconductor thin film structures with the quality and control necessary to form optoelectronic devices. The methodology proposed for these studies is electrochemical atomic layer epitaxy (ECALE), the electrochemical analog of atomic layer epitaxy (ALE), where surface limited reactions are used to form a material, one atomic layer at a time. Underpotential deposition, upd, is another name for a surface limited electrochemical reaction. It is a phenomenon where an atomic layer of one element is deposited on a second at a potential prior to that needed to deposit the first on itself. The driving force is formation of a surface compound, and the free energy of compound formation. Using upd in an ALE cycle, deposits are formed at or near equilibrium, a monolayer at a time. An atomic layer of each element is deposited in turn, in a cycle, to form a monolayer of the compound. The number of cycles determines the thickness of the deposit. A major benefit of ECALE is that it breaks compound electrodeposition into a series of fundamental steps, allowing their independent investigation and control. ECALE studies are the most direct route to the mechanisms of compound electrodeposition. Questions to be addressed include: How much control can be obtained in the electrochemical formation of compound semiconductor device structures? What types of electrochemical reactions can be used to create an ALE cycle? Can the deposit habit be altered by using different substrate or by changing the deposition parameters? Can ternary compounds be formed? Can programs be developed to form graded deposits as buffer layers, or to help with lattice matching issues. What types of electrochemical reactions can be used to create an ALE cycle? Can doping be controlled in compound electrodeposition? Can both p and n type materials be formed? An automated flow deposition system is used to form deposits using ECALE, where potentials and solution changes are controlled by computer. Methodologies for characterization include in-situ electrochemical scanning tunneling microscopy (ECSTM), electrochemical quartz crystal microbalance (EQCM), ultrahigh vacuum electrochemistry (UHV-EC) for studies of deposit surfaces, as well as reflection, absorption, luminescence, photoelectrochemical, photoconductivity, and Hall measurements for studies of physical and electronic properties. %%% An important feature of the project is in education and human resource development through the integration of research and education. The project involves graduate and undergraduate students with participants at all levels interacting with each other and the principal investigator (PI) on a regular basis. Two of the five students working in the PI's group are from under-represented groups, and will be supported by this award. Students are actively involved in publishing papers and presenting talks and posters at professional society meetings. Most of the PI's students have over five presentations on their vitae before they graduate. It is also intended to construct a web page on ECALE, where students design and build various sections, with the intent of forming a page where the present status of ECALE can be found. The page will include descriptions of how to form deposits using ECALE, listings of publications by all groups working in the area, methodologies, instrument designs, as well as programs written in lab view for controlling deposition, accessible by anyone interested in the method. ***