Design, fabrication and characterization of high-performance terahertz quantum cascade lasers

太赫兹频率范围内的电磁波（1-10太赫兹，1THz = 1E12赫兹）由于其在许多重要应用方面的潜力而引起了人们的强烈兴趣：生物化学物种探测，天文光谱，太赫兹成像和光学无线通信，仅举几例。由于缺乏紧凑、低能耗、固态和易于操作的太赫兹源和探测器，太赫兹技术的应用进展一直受到阻碍。这种情况最近开始发生变化，特别是在2002年报道了在太赫兹频率范围内工作的第一个半导体量子级联激光器的发明之后。太赫兹量子级联激光器的发展进展迅速，但在进一步提高器件性能方面仍存在许多技术挑战。其中，实现太赫兹量子级联激光器的室温激光和高功率运行可能是最大的挑战。本项目将采用实验与理论相结合的方法来解决技术难题。该提案的目标包括：1)建立一个关于量子半导体异质结构中子带间跃迁和载流子动力学的基础物理的综合知识库；2)开发能够对量子异质结构重要参数和量子级联激光器整体性能进行数值计算的仿真包，并与实验结果进行对比；3)探索新的量子结构（如基于双声子弛豫的载流子注入和提取结构），以超越现有的量子有源区设计，从而提高工作温度；4)制作和表征新结构的量子级联激光器，并将器件应用于实际。这项研究将为太赫兹频率范围内的新知识提供广泛的基础，并对电信、生物和医学科学以及安全领域产生潜在影响。它还为HQPs提供了良好的培训机会，以获得强大的光子知识和高要求的实践技能。

Electromagnetic waves in the terahertz frequency range (1-10 THz, 1THz = 1E12 Hz) have attracted intense interest because of their potential for many important applications: bio-chemical species detection, astronomical spectroscopy, terahertz imaging and optical wireless communication, to name a few. Application progress of terahertz technologies has been hampered by the lack of compact, low-energy-consumption, solid-state based and easily-operational terahertz sources and detectors. The situation has started to change recently, particularly after the invention of the first semiconductor quantum cascade laser working in the terahertz frequency range reported in 2002. The development of terahertz quantum cascade lasers has proceeded rapidly, nevertheless, there are still many technical challenges to further improve device performance. Among them, to achieve room-temperature lasing and high-power operation of terahertz quantum cascade lasers might be the biggest challenge. This proposed project will tackle the technical challenges by means of combined experimental and theoretical approaches. The objectives of the proposal include 1) to develop a comprehensive knowledge base on the underlying physics of intersubband transition and carrier dynamics in the quantum semiconductor heterostructures; 2) to develop a simulation package that can numerically calculate the important parameters of the quantum heterostructures and the overall performance of the quantum cascade lasers for comparison to experimental results; 3) to explore new quantum structures (such as a structure based on double phonon relaxation for carrier injection and extraction) that could outperform the existing quantum active-region designs in order to push higher the operating temperature; 4) to fabricate and characterize quantum cascade lasers with new structures and to apply the devices for practical applications. This research will provide a broad base of new knowledge in the THz frequency range with potential impacts in the areas of telecommunication, biological and medical sciences and security. It also brings in excellent training opportunities for HQPs to acquire strong photonic knowledge and highly-demanded hands-on skills.