TERAHERTZ QUANTUM CASCADE LASER UTILIZING LATTICE-MATCHED III-NITRIDE HETEROSTRUCTURES

利用晶格匹配iii -氮化物异质结构的太赫兹量子级联激光器普渡大学的michael J. Manfra和Oana Malis， ii -氮化物半导体具有独特的电子特性，使它们有希望将半导体光源的功能扩展到目前其他材料系统无法达到的光谱范围。我们建议展示和研究一类新的远红外半导体激光器，发射在1-10太赫兹范围（30-300 ìm波长范围）。这些激光器将利用晶格匹配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（qcl）的一般工作原理。我们的新方法涉及使用低al成分，晶格匹配的季氮化物（AlInGaN/GaN）和高质量的准块状GaN衬底来缓解过去阻碍氮化子带间器件进展的材料质量问题。我们选择的晶格匹配异质结构具有消除异质界面处压电场影响的额外优点，因此有利于导带工程。为了完全消除异质界面处的极化不连续，激光结构也将在非极性GaN衬底上生长。研究工作将是跨学科的，将涉及材料设计和生长，结构表征，器件制造和器件测试。智力优势：该项目研究了一种新型半导体激光器的可行性，以填补目前任何其他半导体技术无法实现的未充分利用的太赫兹间隙。如果成功，该项目将实现一种新型紧凑、相干、可调谐的太赫兹光源，其功率输出适用于技术应用（毫瓦级）。除了更宽的波长灵活性外，太赫兹氮化qcl预计在目前可用的GaAs太赫兹qcl的较长波长的工作温度和效率方面具有优越的性能。该研究项目的重点将放在使用晶格匹配氮化物的太赫兹激光器上，但所获得的知识也将与在其他光谱范围（如近红外（电信）范围）运行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）和其他材料系统也有价值。该项目将促进对晶格匹配iii -氮化物材料在复杂和厚的器件结构中的MBE生长的理解。在极性和非极性氮化镓衬底上材料生长的基本过程将进行详细的研究和比较。目标是实现对微观结构的充分理解和控制，以实现材料系统的理论潜力。这里提出的研究计划也将为理解氮化材料中的电荷输运和光跃迁的物理特性提供重要的贡献。本征极化场和导带偏移量等基本氮化物带结构参数将作为四元合金成分的函数来建立。指出了氮化物异质结构中共振隧穿的基本和实际限制。更广泛的影响：该项目将实现一种新型的紧凑、高效的太赫兹电源，将立即影响许多技术应用，为社会带来广泛的利益。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。该研究项目将为普渡大学不同群体的学生提供独特的跨学科研究机会。将特别关注为代表性不足的本科生提供动手制作经验。科学发现的兴奋将通过与学术界，工业界（Kyma Technologies）和联邦资助的实验室（麻省理工学院林肯实验室）的几个研究小组的合作来传达。PI将积极参与指导少数民族学生，特别是女性学生和有风险的学生。该项目的研究技术和成果将分别纳入分子束外延和光学材料生长基础的研究生/本科生课程中。外展活动将包括开发教育模块，介绍电磁波谱不可见范围内物质的基本光学特性，用于普渡大学“路上的物理学”项目的公开演示。这些私立学校还将举办面向中学女生的夏令营ScienceScape活动。这些活动将集中在一个有趣的、以项目为导向的环境中，通过要求学生创建视觉上引人注目的近红外和远红外图像，来说明光的产生、传播和检测的基本原理。

TERAHERTZ QUANTUM CASCADE LASER UTILIZING LATTICE-MATCHED III-NITRIDE HETEROSTRUCTURESMichael J. Manfra and Oana Malis, Purdue UniversityIII-nitride semiconductors have unique electronic properties that make them promising for extending the functionality of semiconductor light sources into spectral ranges currently inaccessible with other material systems. We propose to demonstrate and investigate a new class of far-infrared semiconductor lasers emitting in the 1-10 THz range (30-300 ìm wavelength range). These lasers will utilize intersubband transitions in the conduction band of lattice-matched III-nitride heterostructures and employ the general operating principles of quantum cascade lasers (QCLs). Our novel approach involves using low Al-composition, lattice-matched quaternary nitrides (AlInGaN/GaN) and high quality quasi-bulk GaN substrates to mitigate material quality issues that have hampered progress of nitride intersubband devices in the past. Our choice of lattice-matched heterostructures has the additional advantage of eliminating the effect of piezoelectric fields at hetero-interfaces, therefore facilitating conduction band engineering. To completely remove polarization discontinuities at hetero-interfaces, laser structures will also be grown on non-polar GaN substrates. The research effort will be interdisciplinary and will involve material design and growth, structural characterization, device fabrication, and device testing.Intellectual merit: This project investigates the feasibility of a new class of semiconductor lasers to fill the underutilized THz gap that is currently inaccessible with any other semiconductor technology. If successful, this project 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 QCLs are expected to have superior performance in terms of operating temperature and efficiency at the longer wavelengths currently available to GaAs THz QCLs. The focus of this research project will be on THz lasers using lattice-matched nitrides, but the knowledge acquired will also be relevant to nitride optoelectronic devices operating in other spectral ranges such as the near-infrared (telecom) range. Moreover, the acquired knowledge will also be valuable for other types of devices, such as transistors, and to other material systems. This project will advance the understanding of MBE growth of lattice-matched III-Nitride materials for complex and thick device structures. Underlying processes of material growth on polar and non-polar GaN substrates will be studied in detail and compared. The goal is to achieve adequate understanding and control of the microstructure in order to realize the theoretical potential of the material system. The research program proposed here will also give opportunities for major contributions to the understanding of the physics of charge transport and optical transitions in nitride materials. Basic nitride band structure parameters, such as conduction band offsets and intrinsic polarization fields, will be established as a function of composition for the quaternary alloys. The fundamental and practical limitations of resonant tunneling in nitride heterostructures will be identified.Broader Impact: This project will enable a new class of compact, efficient terahertz power sources that will immediately 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 will provide unique interdisciplinary research opportunities to a diverse group of students at Purdue University. Special attention will be given to providing hands-on fabrication experience to under-represented undergraduate students. The excitement of scientific discovery will be conveyed through collaborations with several research groups in academia, industry (Kyma Technologies) and a federally funded laboratory (MIT Lincoln Laboratories). The PI's will be actively involved in mentoring minority students, in particular females, and students at risk. The research techniques and findings of this project will be integrated into graduate/undergraduate courses on the fundamentals of material growth by Molecular Beam Epitaxy and Optics, respectively. Outreach activities will include development of educational modules about basic optical properties of matter in the invisible ranges of the electromagnetic spectrum for public demonstrations in the Purdue's Physics on the Road Program. The PIs will also host activities for ScienceScape, a summer camp for middle-school girls. These activities will be focused on illustrating fundamental principles of light generation, propagation, and detection in a fun, project-oriented environment by asking students to create visually-compelling near- and far-infrared images.