Nanopillar quantum cascade lasers

摘要题目：纳米柱量子级联激光器非技术描述本研究解决了在室温下工作在1-5太赫兹范围内的太赫兹半导体激光源的挑战。紧凑的芯片级太赫兹辐射源，具有相当高的输出功率（毫瓦或更高），适用于一系列光谱学和成像应用。例子包括天体物理学和大气科学领域的分子气体传感（例如恒星形成的研究）、生物和医学领域的成像（例如烧伤和皮肤肿瘤成像）、安全筛查和非法材料检测（例如爆炸物和药物识别）以及非破坏性评估（例如腐蚀监测、薄膜和涂层中的分层和空隙检测）。现有的太赫兹量子级联激光器只能在低温下工作，这需要额外的冷却、更大的尺寸和更高的功耗。这项提议的智力价值在于为这种激光器开发了一种新的材料系统“纳米柱量子点”，它有可能通过抑制电子与晶格振动之间不必要的相互作用，将工作温度提高到室温。更广泛的影响涉及几个层面，包括本科生和研究生的研究经验，成果的传播，技术进步。向代表性不足的少数民族伸出援手的具体方式是，为一门旨在招募和留住代表性不足的少数民族工程本科生的课程制定研究项目。本提案的知识价值在于两个创新组成部分：使用纳米柱量子点用于亚带间级联激光器，以及量子点异质结构的无催化剂选择区半导体纳米柱外延。使用量子点来创建离散能级可以显著地抑制光学声子对电子的非辐射散射。因此，基于量子点离散态的太赫兹激光有望解决传统平面太赫兹量子级联激光器的基本限制，其中非辐射声子辅助弛豫妨碍了室温操作。在这个提出的概念中，载流子将在级联的点对点隧道机制中沿着纳米线整体的长度纵向流动，而不会与二维状态耦合。无金属催化剂的选择性面积MOCVD外延将用于使用光刻定义的氧化物生长掩膜生长高纵横比的InAs/InAsP半导体纳米柱阵列。横向量子约束由掩模特征尺寸和InP钝化壳异质结构的存在决定；纵向约束是由轴向异质结构决定的。我们将在三个重叠的阶段进行合作研究：(i) InAs/InAsP纳米柱中轴向和核壳异质结构的生长，以形成耦合量子阱和量子点；（ii）研究子带间光学和输运性质；（iii）研究纳米柱级联设计，用于电致发光、受激发射和量子级联激光演示。

Abstract Title: Nanopillar quantum cascade lasersNon-technical descriptionThis research addresses the challenge of making terahertz semiconductor laser sources that operate at room temperature in the 1-5 THz range. Compact chip-scale sources of terahertz radiation that operate with both reasonably high output power (milliwatts or more) are desired for a range of spectroscopy and imaging applications. Examples include molecular gas sensing in the field of astrophysics and atmospheric science (for example investigation of star formation), imaging in the biological and medical sciences (for example burn and skin tumor imaging), security screening and illicit material detection (for example explosive and drug identification), and non-destructive evaluation (for example corrosion monitoring, delamination and void detection in films and coatings). Existing THz quantum-cascade lasers only operate at cryogenic temperatures which requires extra cooling, larger size, and increased power consumption. The intellectual merit of this proposal lies in the development of a new material system for such lasers "nanopillar quantum dots" that has the potential to increase operating temperatures to room temperature by suppressing unwanted interactions of the electrons with lattice vibrations. The broader impacts are addressed at several levels including undergraduate and graduate research experiences, dissemination of results, technology advancement. Outreach to underrepresented minorities will specifically occur through the development of research projects for a course designed for the recruitment and retention of underrepresented minority engineering undergraduates. Technical DescriptionThe intellectual merit of this proposal resides in two innovative components: the use of nanopillar quantum-dots for intersubband cascade lasers, and catalyst-free selective area semiconductor nanopillar epitaxy of quantum dot heterostructures. Use of quantum dots to create discrete energy levels can dramatically suppress nonradiative scattering of electrons by optical-phonon. Hence, a terahertz laser based discrete states in quantum-dots is expected to solve a fundamental limitation of conventional planar THz quantum-cascade lasers, where non-radiative phonon-assisted relaxation prevents room temperature operation. In this proposed concept, carriers would flow longitudinally down the length of a nanowire ensemble in a cascaded dot-to-dot tunneling regime without coupling with two-dimensional states. Selective-area MOCVD epitaxy without metal catalysts will be used to grow high-aspect ratio InAs/InAsP semiconductor nanopillar arrays using lithographically defined oxide growth masks. Lateral quantum confinement is determined by the mask feature dimension and the presence of an InP passivating shell heterostructure; longitudinal confinement is determined by the axial heterostructure. A collaborative research effort is proposed in three overlapping stages: (i) growth of axial and core/shell heterostructures in InAs/InAsP nanopillars for the formation of coupled-quantum wells and dots, (ii) investigation of the intersubband optical and transport properties, and (iii) investigation of nanopillar cascade designs for electroluminescence, stimulated emission, and quantum cascade laser demonstration.