Nanopillar quantum cascade lasers

摘要标题：纳米柱量子级联激光器非技术性研究这项研究解决了在室温下在1-5 THz范围内工作的太赫兹半导体激光源的挑战。对于一系列光谱学和成像应用，期望以合理的高输出功率（毫瓦或更高）操作的紧凑芯片级太赫兹辐射源。例子包括天体物理学和大气科学领域中的分子气体传感（例如星星形成的研究）、生物和医学科学中的成像（例如烧伤和皮肤肿瘤成像）、安全筛查和非法材料检测（例如爆炸物和毒品识别）以及非破坏性评估（例如薄膜和涂层中的腐蚀监测、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，更大的尺寸和增加的功耗。这一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”，该系统有可能通过抑制电子与晶格振动的不必要的相互作用将工作温度提高到室温。更广泛的影响在几个层面上得到解决，包括本科生和研究生的研究经验，成果的传播，技术进步。将特别通过为征聘和留住代表性不足的少数族裔工程专业本科生而设计的课程制定研究项目，与代表性不足的少数族裔进行外联。技术说明该提案的智力价值在于两个创新组件：使用纳米柱量子点的子带间级联激光器，和无催化剂的选择性区域半导体纳米柱外延的量子点异质结构。使用量子点来产生离散能级可以显著地抑制电子被光学声子的非辐射散射。因此，基于量子点中的离散态的太赫兹激光器有望解决常规平面THz量子级联激光器的基本限制，其中非辐射声子辅助弛豫阻止室温操作。在这个提出的概念中，载流子将在级联的点到点隧穿机制中沿纳米线系综的长度纵向向下流动，而不与二维态耦合。无金属催化剂的选择性区域MOCVD外延将用于使用光刻定义的氧化物生长掩模生长高深宽比的InAs/InAsP半导体纳米柱阵列。横向量子限制由掩模特征尺寸和InP钝化壳异质结构的存在决定;纵向限制由轴向异质结构决定。一个合作的研究工作提出了三个重叠的阶段：（一）生长的轴向和核/壳异质结构的InAs/InAsP纳米柱形成耦合量子威尔斯和点，（二）调查的子带间的光学和输运性质，和（iii）调查的纳米柱级联设计电致发光，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.