Tunnel Junction Based AlGaN Ultraviolet Lasers

虽然可见光蓝光激光器已经被证明具有优异的性能，但实现波长小于300 nm的紫外光激光器仍然具有挑战性，尽管各个研究小组在十多年的时间里做出了努力。电力激光器的主要问题是在激光材料中实现合理的p-电导性，电流将流经该电导。这使得在合理的电功率下操作激光变得具有挑战性。该项目提出了一种创新的方法，利用隧道结(TJ)，在不牺牲器件光学性能的情况下，缓解了激光材料的p-电导问题。这些短波紫外线激光最近被发现可用于对表面或物体进行消毒，作为防止冠状病毒(新冠肺炎)全球传播的预防措施之一。可以说，这种应用可以通过发光二极管(LED)在这种波长范围内实现。然而，迄今为止实现的节能LED体积大、结构复杂、价格昂贵，这从本质上限制了它们在这些关键领域的应用。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方面的跨学科教育活动。由于拟议的研究项目跨越不同的科学和工程学科，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动手学习活动，可以吸引不同背景的学生。此外，这项研究产生的科学见解和技术进步也将广泛影响光子学领域，使其能够在这一不发达的光谱区域运行。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，在紫外线(UV)-B(320-280 nm)和UV-C(280-200 nm)波长范围内，对电泵浦(EP)和连续波(CW)工作的基于AlGaN的二极管激光器有着巨大的需求。这项研究的主要目标是设计和演示隧道注入的EP和CW工作的紫外光激光器，发射波长从320 nm到280 nm。P型掺杂和形成低阻p欧姆接触是电泵浦紫外光激光二极管面临的关键挑战。这项工作建议使用新的带间隧道结来制备高达70%铝组分的超宽带隙AlGaN，以克服这一主要挑战。该项目的工作将产生关于AlGaN材料系统及其几个重要性质的新的基础知识，包括折射率、通过带尾态的载流子带间隧道和带隙收窄，以及具有量子限制的超薄层中的吸收。提出的研究涉及一种新的器件概念，以实现基于超宽带隙材料的这种高要求的光源。从这项研究中获得的器件知识将为展示在整个深紫外区发射的激光器件奠定基础。该项目的早期阶段旨在展示在有源区两侧使用高带隙nAlGaN包覆区的广域法布里-珀罗激光器。然后，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。在该项目的第二阶段，该项目旨在通过采用具有优化的外延结构的窄脊结构来演示适合应用的连续波操作激光器。这里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，并可能为新一类基于AlGaN的紫外激光技术建立平台。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.