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

许多应用，如光电子和电力电子依赖于超宽带隙材料的功能。但是，为了充分发挥其潜力，有必要了解和实现新的工艺，以提高其性能，无论是电学还是光学性能。所提出的处理框架有机会使这些材料族发生革命性变化，从而提供实现否则将无法实现的特性。这是除了提供一个统一的概念方法与现代计算的努力，带来了一个非爱迪生的方法来设计的材料和工艺处理这类材料一致。这项研究将直接导致涉及自然资源保护和扩展的应用，包括：通过使用紫外线发光二极管进行消毒来提供清洁的饮用水，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（有些是专门针对少数民族学生的），特别是将材料特性和控制计划纳入处理为可持续性目的开发材料的需要的应用中。该计划将提供教育博士的机会。学生对这些材料的生长，表征和设备制造，同时参与一个既定的国际合作者网络。此外，这些想法融入新课程的设计，扩大了社区的学生和专家有关的主题，特别是那些处理计算方法。由此，研究生和小组成员将能够有效地讨论他们的研究，以实现富有成效的合作，同时加速他们的专业发展。化合物半导体中的带电点缺陷强烈地决定了电子和光学性质。点缺陷的形成能量是工艺条件和费米能的函数。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。对于掺杂n型或p型导电性的实际情况，能隙越大，与系统平衡的补偿点缺陷的浓度越高。这是这些材料的一个基本问题，将通过这些功能直接解决。在这种方法中，我们将扩展准费米能级的概念，努力量化的点缺陷的形成能量的外部激发的影响。在生长实验期间通过外部激发增加不需要的点缺陷的形成能量导致补偿点缺陷的减少和更高的器件效率。这项建议的研究目标是测试的假设，即形成的带电点缺陷的能量可以通过在生长过程中的稳态条件下的外部激励来操纵。方法包括引入带隙以上照明或电子束照射作为激发源。这个过程被称为费米能级控制的点缺陷。为了验证这一假设，我们设计了三个主要的研究任务：（1）在基于III族氮化物的UV LED结构的生长过程中，证明费米能级对技术上重要的点缺陷的控制;（2）点缺陷的光学和电学研究及其对器件性能的影响;（3）扩展到其他宽带隙系统和替代费米能级管理工艺，以显示该工艺的普遍性。这项研究将把这些能力扩展到AlGaN，以减少深紫外LED中的补偿和非辐射缺陷。预计该工艺通常适用于宽禁带材料的广泛类别，特别是几种氧化物系统。

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.