Structure Control in Electrochemical Atomic Layer Eptiaxy

该项目的长期目标是获得对化合物半导体电沉积的基本理解，并实现具有形成光电器件所需的质量和控制的化合物半导体薄膜结构的沉积。为这些研究提出的方法是电化学原子层外延（ECALE），这是原子层外延（ALE）的电化学模拟物，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）是表面受限电化学反应的另一个名称。这是一种现象，一种元素的原子层以一个电位沉积在另一种元素上，而第一个元素需要在原子层上沉积。驱动力是表面化合物的形成，以及化合物形成的自由能。在ALE循环中使用upd，沉积物形成在或接近平衡状态，一次形成一层。每个元素的原子层依次沉积，形成一个循环，形成化合物的单层。旋回的次数决定了沉积物的厚度。ECALE的一个主要优点是它将复合电沉积分解为一系列基本步骤，允许他们独立调查和控制。ECALE研究是研究复合电沉积机理的最直接途径。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以用来创建一个ALE循环？是否可以通过使用不同的衬底或改变沉积参数来改变沉积习惯？三元化合物能形成吗？是否可以开发程序来形成渐变沉积物作为缓冲层，或帮助处理晶格匹配问题。什么类型的电化学反应可以用来创建一个ALE循环？复合电沉积中能控制掺杂吗？p型和n型材料都可以成型吗？自动流动沉积系统使用ECALE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）、用于研究沉积表面的超高真空电化学（UHV-EC），以及用于研究物理和电子性质的反射、吸收、发光、光电化学、光电导率和霍尔测量。该项目的一个重要特点是通过研究和教育的整合来进行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，并定期与首席研究员（PI）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。大多数PI的学生在毕业前在他们的简历上做过五次以上的演讲。同时也打算建立一个关于ECALE的网页，由学生设计和构建各个部分，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，在该领域工作的所有小组的出版物列表，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. ***