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

许多应用，如光电子和电力电子，都依赖于超宽带隙材料的功能。但为了充分发挥它们的潜力，有必要了解和实现新的工艺，以提高它们的性能，无论是电气上还是光学上。拟议的加工框架有机会使这些材料家族发生革命性变化，从而实现否则无法实现的性能。这是除了提供与现代计算努力相一致的统一概念方法之外，该方法带来了处理这类材料的材料和工艺的非爱迪生方法的设计。这项研究将直接导致涉及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。在该项目中提出的新概念也可用于教育和外联工作(有些是专门针对少数族裔学生的)，特别是将材料表征和控制计划纳入处理可持续发展材料开发需要的应用。该项目将为博士生提供有关这些材料的生长、表征和器件制造的教育机会，同时参与已建立的国际合作者网络。此外，将这些想法整合到新课程的设计中，扩大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，以进行富有成效的合作，同时加速他们的专业成长。化合物半导体中的荷电点缺陷强烈地决定着电子和光学性质。点缺陷的形成能是工艺条件和费米能量的函数。在超宽带隙材料或绝缘体中，费米能对电荷点缺陷的形成能有很大的贡献。对于n型或p型电导掺杂的实际情况，能隙越大，与系统处于平衡状态的补偿点缺陷浓度越高。这是这些材料的一个根本问题，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，以努力量化外部激发对点缺陷形成能的影响。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，从而减少补偿点缺陷，提高器件效率。这一建议的研究目的是验证一个假设，即在生长过程中，在稳态条件下，电荷点缺陷的形成能量可以通过外部激发来操纵。方法包括引入带隙以上照明或电子束照射作为激发源。这个过程被称为点缺陷的费米能级控制。设计了三个主要的研究任务来验证这一假设：(1)展示了在基于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)点缺陷及其对器件性能的影响的光学和电学研究，(3)扩展到其他宽带隙系统和替代的费米能级管理工艺，以显示该过程的普遍性。这项研究将把这些能力扩展到AlGaN，以工程方式减少深紫外光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.