OP: Terahertz Lasers Using Intersubband Transitions in non-polar III-nitrides

摘要非技术描述：该项目研究了一种新型紧凑、高效的激光光源，工作在红外和微波之间的长波长光谱范围内，被称为太赫兹（THz）间隙。由于常用半导体的基本限制，这个范围是目前无法与任何其他半导体激光器。这个项目利用了氮化半导体的独特特性。然而，氮化物也提出了一些独特的挑战，涉及到它们的原子结构和内置电场。为了克服这些挑战，研究人员采用复杂的建模工具来设计新的激光结构。然后使用分子束外延（一种可以在纳米尺度上控制氮化物厚度的技术）来生长材料，并使用结构和光学技术来表征。最后，制作并测试了激光器件，研究了其在不同工作条件下的性能，并进一步完善了设计参数。这些新型激光器具有影响许多技术应用的潜力，对社会有广泛的好处。这些应用大致可分为两大类：太赫兹光谱学和太赫兹成像。太赫兹光谱学目前广泛应用于天文学、大气科学、等离子体聚变诊断和生化武器探测等领域。太赫兹成像具有广泛的应用，从机场安检到医学成像。这个研究项目也为普渡大学的不同学生群体提供了独特的跨学科研究机会。特别注意为代表性不足的学生，特别是妇女提供实践研究经验。外展活动将提高印第安纳州中部经济背景较差的7-12年级学生和教师对光子学的科学内容和方法的认识和曝光。技术描述：该项目开发和研究了1-10太赫兹范围内的新型远红外半导体发射器，特别是在砷化镓（30-40微米波长）的抑制波段工作。这些激光器利用非极性iii -氮化物异质结构导带中的子带间跃迁，并采用量子级联激光器的一般工作原理。该技术方法涉及在高质量的独立m平面GaN衬底上生长低al成分，非极性氮化物异质结构（AlInGaN/GaN），以缓解迄今为止阻碍氮化物子带间器件进展的材料质量和设计问题。选择无偏振的m面异质结构具有消除异质界面内嵌电场影响的巨大优势。研究工作本质上是跨学科的，涉及材料设计和生长，结构和光学材料表征，波导设计和制造，最后是器件测试。这项研究将使一种新型的紧凑、相干、可调谐的太赫兹光源具有适合技术应用的功率输出（毫瓦级）。除了更宽的波长灵活性外，太赫兹氮化物激光器在工作温度和效率方面也有望具有优越的性能，目前GaAs太赫兹量子级联激光器可以在更长的波长上使用。该研究的重点是使用非极性氮化物的太赫兹激光器，但所获得的知识也与在其他光谱范围（如近红外（电信）范围）工作的氮化物光电器件相关。此外，所获得的知识对其他类型的器件（如晶体管）和其他材料系统也是有价值的。本研究项目在氮化材料的光学跃迁和垂直电荷输运物理学方面也做出了重要贡献。精心设计的建模工具和技术被开发来预测和解释真实的设备行为。此外，该项目大大提高了iii -氮化物材料分子束外延的知识，具有复杂红外器件所需的原子层精度和精确再现性。

Title: Novel compact terahertz lasers utilizing polarization-free nitride semiconductors for sensing and imaging AbstractNon-technical description: This project investigates a new class of compact, efficient laser light sources operating in the long-wavelength spectral range between the infrared and the microwave ranges, known as the terahertz (THz) gap. Due to fundamental limitations of commonly used semiconductors, this range is currently inaccessible with any other semiconductor lasers. This project exploits the unique properties of nitride semiconductors. However, the nitrides also present some unique challenges related to their atomic structure and built-in electric fields. To overcome these challenges the researchers employ sophisticated modeling tools to design new laser structures. The materials are then grown using molecular beam epitaxy, a technique that allows control of the nitride thicknesses at the nanoscale, and characterized with structural and optical techniques. Finally, laser devices are fabricated and tested to study their performance under different operating conditions and to further refine the design parameters.These novel lasers have the potential to impact a number of technological applications with broad benefits to society. The applications loosely fit into one of two main categories: THz spectroscopy, and THz imaging. THz spectroscopy is currently used in fields ranging from astronomy, and atmospheric science, to plasma fusion diagnostics and bio-chemical weapons detection. THz imaging has broad applications from airport security to medical imaging. This research program also provides unique interdisciplinary research opportunities to a diverse group of students at Purdue University. Special attention is given to providing hands-on research experience to under-represented students, especially women. Outreach activities will increase the awareness and exposure of Grade 7-12 students and teachers from economically disadvantaged backgrounds in Central Indiana to the scientific content and methods of photonics.Technical description: This project develops and studies a new class of far-infrared semiconductor emitters for the 1-10 THz range, specifically operating in the reststrahlen band of GaAs (30-40 micron wavelength). These lasers utilize intersubband transitions in the conduction band of non-polar III-nitride heterostructures and employ the general operating principles of quantum cascade lasers. The technical approach involves using low Al-composition, non-polar nitride heterostructures (AlInGaN/GaN) grown on high quality free-standing m-plane GaN substrates to mitigate material quality and design issues that have, so far, impeded progress of nitride intersubband devices. The choice of polarization-free m-plane heterostructures has the tremendous advantage of eliminating the effect of built-in electric fields at hetero-interfaces. The research effort is interdisciplinary in nature and involves material design and growth, structural and optical material characterization, waveguide design and fabrication, and finally device testing.This research will enable a novel compact, coherent, tunable THz light source with power output suitable for technological applications (milliwatt level). In addition to broader wavelength flexibility, the THz nitride lasers are expected to have superior performance in terms of operating temperature and efficiency at the longer wavelengths currently accessible with GaAs THz quantum cascade lasers. The research focuses on THz lasers using non-polar nitrides, but the knowledge acquired is also relevant to nitride optoelectronic devices operating in other spectral ranges such as the near-infrared (telecom) range. Moreover, the acquired knowledge is valuable for other types of devices, such as transistors, and to other material systems. This research program also brings about important contributions to the physics of optical transitions and vertical charge transport in nitride materials. Elaborate modeling tools and techniques are developed to predict and explain real device behavior. Moreover, this project considerably advances knowledge regarding molecular beam epitaxy of III-nitride materials with the atomic-layer precision and exact reproducibility necessary for complex infrared devices.