Tunnel Junction Based AlGaN Ultraviolet Lasers

虽然可见蓝色激光器已被证明具有优异的性能，但实现波长短于300纳米的紫外激光器仍然具有挑战性，尽管各研究小组已经努力了十多年。电动激光器的主要问题是如何使激光材料具有合理的p导电性，从而使电流流过。这使得在合理的电力功率下操作激光器具有挑战性。本项目提出了一种利用隧道结（TJs）的创新方法，该方法在不牺牲器件光学性能的情况下缓解了激光材料的p-电导率问题。最近发现，作为防止冠状病毒（COVID-19）全球传播的预防措施之一，这些短波紫外激光器可用于对表面或物体进行消毒。可以说，这种应用可以通过发光二极管（led）在这个波长范围内实现。然而，迄今为止实现的节能led体积大、结构复杂、价格昂贵，这从根本上限制了它们在这些关键领域的适用性。除了高影响力的研究进展外，该项目还将支持纳米科学和纳米技术的跨学科教育活动。由于拟议的研究项目跨越了科学和工程的不同学科，如光学、材料科学、电气工程、物理和化学，它将导致一系列潜在的、实践的学习活动，可以吸引不同背景的学生。此外，该研究的科学见解和技术进步也将广泛影响光子学领域，使这一不发达光谱区域的操作成为可能。由于广泛的新兴应用，包括植物生长照明、水杀菌、微量气体传感、固化聚合物和刺激抗癌物质的形成，对紫外(UV) -B （320-280 nm）和紫外-c （280-200 nm）波长范围内的电泵浦（EP）和连续波（CW）操作gan基二极管激光器的需求巨大。该研究的主要目标是设计和演示隧道注入EP和cw操作的紫外激光器，发射波长从320 nm到280 nm。p型掺杂和低阻p欧姆触点的形成是电泵浦紫外激光二极管面临的关键挑战。为了克服这一主要挑战，本工作提出使用新型带间隧道结用于铝成分高达70%的超宽带隙AlGaN。在这个项目中进行的工作将产生关于algan材料系统及其几个重要特性的新基础知识，包括折射率，通过带尾状态的载流子带间隧道和带隙缩小，以及在量子约束的超薄层中的吸收。提出了一种基于超宽带隙材料实现高要求光源的新器件概念。从本研究中获得的器件知识将为在整个深紫外光谱范围内展示具有发射的激光器件奠定基础。该项目的早期阶段旨在展示广域法布里-帕姆罗特激光器，在有源区两侧使用高带隙n-AlGaN包层区域。这些器件将在脉冲模式下进行测试，这将有助于确定高铝成分结构的各种未知材料特性。在项目的第二阶段，该项目旨在通过采用具有优化外延结构的窄脊结构来演示适合应用的cw操作激光器。本文提出的全新方法将在超宽带隙材料和光学器件领域实现新的科学理解，并为新型基于algan的紫外激光技术建立平台。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

While visible blue lasers have been demonstrated with excellent performance, realizing ultraviolet lasers at wavelengths shorter than 300 nm is still challenging despite efforts over more than a decade by various research groups. The principal problem for electrically-powered lasers is related to achieving a reasonable electrical p-conductivity in laser materials through which electrical current will flow. This makes it challenging to operate lasers at a reasonable electrical power. This project proposes an innovative approach that utilizes tunnel junctions (TJs) which alleviates the p-conductivity problem of laser materials without sacrificing optical performance of the device. These short-wavelength ultraviolet lasers are recently found to be useful for sterilizing surfaces or objects, as one of the precautionary steps to prevent the global spread of the coronavirus (COVID-19). Arguably, this application could be enabled by light emitting diodes (LEDs) in this wavelength regime. However, energy-inefficient LEDs achieved to-date are large, complicated, and expensive, which essentially limits their applicability in these key areas. In addition to high impact research advancement, this project will also support interdisciplinary education activities in nanoscience and nanotechnology. Because the proposed research project crosses different disciplines of science and engineering, such as optics, materials science, electrical engineering, physics, and chemistry, it will lead to a range of potential, hands-on learning activities that can engage students of varying backgrounds. In addition, the scientific insights and technological advances stemming from the research will also broadly impact the field of photonics by enabling operation in this underdeveloped spectral region. There is a tremendous need for electrically-pumped (EP) and continuous-wave (CW) operating AlGaN-based diode lasers in the ultraviolet (UV)­B (320­280 nm) and UV-C (280–200 nm) wavelength regimes due to a wide range of emerging applications including plant growth lighting, water sterilization, trace gas sensing, curing polymers, and stimulating the formation of anti-cancerogenic substances. The primary objective of the proposed research is to design and demonstrate tunnel-injected EP and CW-operating UV lasers with wavelengths of emission ranging from 320 nm to 280 nm. P-type doping and formation of low-resistive p-ohmic contacts are the key challenges for electrically-pumped UV laser diodes. This work proposes to use novel interband tunnel junctions for ultra-wide band gap AlGaN up to 70% aluminum composition in order to overcome this principal challenge. The work performed within this project will generate new fundamental knowledge on the AlGaN-material system and its several important properties including refractive index, carrier interband tunneling through band-tail states and bandgap narrowing, as well as absorption in ultra-thin layers with quantum confinement. The proposed research involves a novel device concept to realize such highly demanding light sources based on the ultra-wide band gap materials. The device knowledge gained from this research will establish a foundation for demonstrating laser devices with emission in the entire deep-UV spectral regime. The early stage of the project aims to demonstrate broad-area Fabry-Pérot lasers using high-bandgap n­AlGaN cladding regions on both sides of the active region. The devices will then be tested in pulsed mode, which will help determine various unknown material properties of high Al composition structures. In the second stage of the project, this project aims to demonstrate application-suited CW-operating lasers by employing narrow­ridge structures with optimized epitaxial structures. The radically new approach proposed here will enable new scientific understanding in the areas of ultra-wide band gap materials and optical devices as well as could establish the platform for a new class of AlGaN-based UV laser technology.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.