CAREER: Engineering point defect formation in UWBG-based optoelectronic devices

光电子和电力电子等许多应用都依赖于超宽带隙材料的功能。但为了充分发挥其潜力，有必要了解和实现新的工艺来提高其性能，无论是电学还是光学。所提出的加工框架有机会彻底改变这些材料家族，从而实现否则无法实现的特性。除此之外，还提供了一种统一的概念方法，与现代计算努力相一致，为处理这类材料的材料和过程的设计带来了一种非爱迪生方法。这项研究将直接导致处理自然资源保护和扩展的应用，允许：通过使用紫外线发光二极管消毒获得清洁饮用水，以及检测污染物和其他流出物。在这个项目中开发的新概念也可以在教育和推广工作中实施（其中一些专门针对少数民族学生），特别是将材料特性和控制方案整合到处理可持续发展材料需求的应用中。该项目将为博士生提供机会，让他们了解这些材料的生长、表征和设备制造，同时参与一个已建立的国际合作网络。此外，将这些想法整合到新课程的设计中，拓宽了与该主题相关的学生和专家的社区，特别是那些处理计算方法的学生和专家。由此，研究生和小组成员将能够有效地讨论他们的研究成果合作，同时加速他们的专业成长。在化合物半导体中，带电点缺陷对电子和光学性质有很大的影响。点缺陷的形成能量是过程条件和费米能量的函数。在超宽带隙材料或绝缘体中，费米能对带电点缺陷形成能的贡献是显著的。对于n型或p型电导率掺杂的实际情况，能隙越大，与体系平衡的补偿点缺陷浓度越高。这是这些材料的一个基本问题，将通过这些能力直接解决。在这种方法中，我们将扩展准费米能级的概念，以量化外部激发对点缺陷形成能量的影响。在生长实验中，通过外部激励增加不需要的点缺陷的形成能量，可以减少对点缺陷的补偿，提高器件效率。本课题的研究目的是验证在生长过程中带电点缺陷的形成能量可以在稳态条件下通过外部激励来控制的假设。方法包括引入带隙以上照明或电子束辐照作为激发源。这个过程称为点缺陷的费米能级控制。为了验证这一假设，设计了三个主要的研究任务：(1)证明在基于iii -氮化物的UV LED结构生长过程中技术上重要的点缺陷的费米能级控制；(2)点缺陷的光学和电学研究及其对器件性能的影响；(3)扩展到其他宽禁带系统和替代费米能级管理过程，以显示该过程的普遍性。这项研究将这些能力扩展到AlGaN，用于减少深紫外led中的补偿和非辐射缺陷。预计该工艺一般适用于一类宽禁带材料，特别是几种氧化物体系。

Many applications such as optoelectronics and power electronics rely on the functionality of ultra wide bandgap materials. But to reach their full potential, it is necessary to understand and realize novel processes to enhance their performance, either electrically or optically. The proposed processing framework has the opportunity of revolutionizing these family of materials, thus providing for the achievement of properties that otherwise will not be attainable. This is in addition to providing a unifying conceptual approach consistent with modern computational efforts that bring about a non-Edisonian approach to the design of materials and processes dealing with this class of materials. This research will directly lead to applications that deal with the preservation and extension of natural resources by allowing for: the availability of clean potable water through disinfection by the use of ultraviolet light emitting diodes, and the detection of pollutants and other effluents. The novel concepts developed within this project can also be implemented in the educational and outreach efforts (some specifically targeted at minority students), especially integrating materials characterization and control schemes to applications dealing with the need for the development of materials for sustainability purposes. This program will provide the opportunity to educate Ph.D. students on the growth, characterization and device fabrication of these materials while participating on an established international collaborators network. Furthermore, integration of these ideas into design of new courses broadens the community of students and experts related to the topic, especially those dealing with computational methods. From this, graduate students and group members will be able to effectively discuss their research for fruitful collaborations while accelerating their professional growth.Charged point defects in compound semiconductors strongly determine electronic and optical properties. The energy of formation of a point defect is a function of the process conditions and the Fermi energy. In ultra wide bandgap materials or insulators, the contribution of the Fermi energy to the formation energy of charged point defects is significant. For the practical case of doping for n- or p-type conductivity, the larger the energy gap, the higher the concentration of compensating point defects that is at equilibrium with the system. This is a fundamental problem of these materials that will be directly addressed with these capabilities. In this approach, we will extend the concept of the quasi-Fermi level in an effort to quantify the impact of external excitation in the formation energy of the point defect. Increasing the formation energy of unwanted point defect through external excitation during a growth experiment leads to a reduction in compensating point defects and higher device efficiencies. The research objective of this proposal is to test the hypothesis that the energy of formation of charged point defects could be manipulated by an external excitation in a steady-state condition during growth. Approaches include the introduction of above-bandgap illumination or e-beam irradiation as excitation sources. This process is referred to as Fermi level control of point defects. Three main research tasks are designed to test the hypothesis: (1) demonstration of Fermi level control of technologically important point defects during the growth of III-nitrides based UV LED structures, (2) optical and electrical study of point defects and their influence on the device performance, (3) extension to other wide bandgap systems and alternative Fermi level management processes to show universality of the process. This research will extend these capabilities to AlGaN for the engineered reduction of compensating and non-radiative defects in deep UV LEDs. It is expected that this process is generally applicable to a broad class of wide bandgap materials, in particular, several oxide systems.