High Conductivity Tunnel Junctions for Next-Generation UV Emitters

紫外线光源可以通过实现水的快速净化和生物传感，极大地影响健康和福祉。然而，目前可用的光源过于昂贵，体积庞大，效率低下，无法广泛采用。基于半导体的紫外光源理论上可以克服这些挑战，实现紧凑高效的紫外光源，但它们面临一些根本性的挑战。紫外线光源是基于宽禁带半导体，而这些半导体的正电荷载流子（空穴）导电性很差。在过去的几十年里，这些孔的导电性差一直是一个挑战，导致固态发射器的效率低、功率低。提议的项目将通过使用量子力学隧道，允许注入带正电荷的载流子来解决这个问题。这项研究有望实现一种新型的紧凑、高效、明亮的紫外线光源，这种光源将直接应用于水处理厂、疾病预防和许多其他关键应用。研究者将开发用于学习和教授半导体器件物理的触摸敏感应用程序（app），重点是直观和视觉的概念学习。此外，研究员将继续开展外联活动，让高中生和本科生参与研究项目，以及促进国际交流和经验。在提出的工作中，提出了一种变革性的紫外发光二极管新设计，其中使用非平衡隧道输运将空穴注入发光二极管的有源区域。由于AlGaN等宽禁带材料的独特挑战，短波长紫外线发射器（350 nm）的效率较低。空穴掺杂和输运仍然是基于algan的紫外线发射器面临的主要挑战之一，并且占损失的很大一部分。高受体电离能导致低空穴浓度和高电阻率，以及电子和空穴注入不平衡，导致电子溢出。制造p型接触的挑战需要吸收p型氮化镓接触层，这会导致进一步的损失。孔洞隧道注入消除了热电离的限制，增强了孔洞注入，从而提高了注入效率。先进的建模和生长技术将用于设计和演示超宽带隙AlGaN材料的高效隧道。隧道结将与紫外线发射器集成，以显示隧道注入的有效性，并使器件没有任何p接触。所提出的实验工作将得到详细的理论和模拟的支持，以验证和预测装置的运行，并将导致对iii -氮化物系统隧道输运的详细了解。在隧道输运和非平衡载流子注入的纳米尺度工程上提出的想法将为iii -氮化物紫外发射器带来更高的效率和新的设计范例，并且也可能与基于其他几种宽带隙半导体的双极器件相关。

Ultra violet light sources can greatly impact health and well-being by enabling rapid water purification, biological sensing. However, the light sources available today are too costly, bulky, and inefficient for widespread adoption. Semiconductor based ultra-violet sources can in theory overcome these challenges and enable compact and efficient ultra-violet sources, but they face some fundamental challenges. Ultra-violet light sources are based on wide band gap semiconductors, and these semiconductors have very poor conductivity of positive charge carriers (holes). The poor conductivity of these holes has been a challenge for the last several decades, leading to poor efficiency and low power in solid state emitters. The proposed project will circumvent this problem through the use of quantum mechanical tunneling that allows positively charged carriers to be injected. The research proposed is expected to enable a new class of compact, efficient, and bright ultra-violet light sources that would find direct applications in water treatment plants, disease prevention, and many other critical applications. The investigator will develop touch sensitive applications (apps) for learning and teaching semiconductor device physics, with an emphasis on intuitive and visual learning of concepts. In addition, the investigator will continue outreach activities by engaging high school students and undergraduates in research projects, as well as by promoting international exchange and experiences. In the proposed work, a transformative new design is proposed for ultra violet light emitting diodes where non-equilibrium tunneling transport is used to inject holes into the active region of the light emitting diode. Short wavelength ultra-violet emitters (350 nm) have low efficiency due to the unique challenges presented by wide band gap materials such as AlGaN. Hole doping and transport remain one of the main challenges for AlGaN-based ultra-violet emitters and account for a large portion of the losses. High acceptor ionization energy leads to low hole concentration and high resistivity, as well as imbalance between electron and hole injection, leading to electron overflow. The challenges of making p-contact necessitate absorbing p-type GaN contact layers that lead to further losses. Tunneling injection of holes removes constraints due to thermal ionization, enhances hole injection, thereby increasing the injection efficiency. Advanced modeling and growth techniques will be used to design and demonstrate highly efficient tunneling for the first time in ultra-wide band gap AlGaN materials. Tunnel junctions will be integrated with ultra-violet emitters to show the efficacy of tunneling injection, and to enable devices without any p-contacts. The proposed experimental work will be supported by detailed theory and simulation to verify and predict device operation, and will lead to detailed understanding of tunneling transport in the III-nitride system. The ideas proposed on nanometer scale engineering of tunneling transport and non-equilibrium carrier injection will lead to higher efficiency and new design paradigms for III-nitride ultra-violet emitters, and could also be relevant for bipolar devices based on several other wide band gap semiconductors.