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

太赫兹频率范围（1-10 THz，1 THz = 1 E12 Hz）的电磁波由于其在许多重要应用中的潜力而引起了人们的强烈兴趣：仅举几例，生物化学物种检测、天文光谱学、太赫兹成像和光学无线通信。由于缺乏结构紧凑、低能耗、基于固态且易于操作的太赫兹源和探测器，阻碍了太赫兹技术的应用进展。这种情况最近开始发生变化，特别是在2002年报道的第一台工作在太赫兹频率范围内的半导体量子级联激光器发明之后。太赫兹量子级联激光器发展迅速，但要进一步提高器件性能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射和高功率运转可能是最大的挑战。该项目将通过实验和理论相结合的方法来解决技术挑战。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本物理学的全面知识库;（2）开发一个模拟软件包，可以数值计算量子异质结构的重要参数和量子级联激光器的总体性能，以便与实验结果进行比较; 3）探索新的量子结构（例如基于双声子弛豫的载流子注入和提取结构），其可以优于现有的量子有源区设计，以推动更高的工作温度; 4）制造和表征具有新结构的量子级联激光器，并将器件应用于实际应用。这项研究将提供太赫兹频率范围内广泛的新知识基础，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HQP提供了极好的培训机会，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.