传统GaAs系太赫兹量子级联激光器THz-QCL受限于固有特性，局限于0.8-5.4THz，工作温度一直未突破200K，严重制约该领域发展。对比鲜明，GaN声子能量是GaAs的2.5倍，用于制备THz-QCL具有两个明显优势：能极大抑制热激发导致的非辐射复合，维持室温粒子数反转，有潜力开发室温THz-QCL；又能避免声子吸收带对THz波的强烈吸收，拓宽至5.4-12THz空白频段。本项目提议试制GaN新型THz-QCL原型器件。针对氮化物强极化大失配的特点，研究有源区子能级布局规律、THz波导设计、有源区分子束外延生长规律这三个关键基础问题。以室温GaN系THz-QCL为最终目标。为该领域提供新思路和新途径，拓展科学前沿。室温THz-QCL将极大推动THz技术的发展与应用。本研究处于早期探索阶段，是当前国际上具有战略性的前沿领域。申请人长期从事氮化物和太赫兹领域研究，具备良好的工作基础。

THz-QCLs have attracted much attention for their wide applications. However, the operation frequency of the traditional GaAs based THz QCLs has been limited between 0.8 and 5.4 THz, and the progress of raising operation temperature stopped at 200 K since 2012. GaN has a much larger LO-phonon energy (~90 meV), 2.5 times of GaAs LO-phonon (36 meV). For GaN based THz-QCL, the depopulation of the upper lasing level through thermally activated LO-phonon scattering and back-filling effect are expected to be significantly suppressed. The forbidden Reststrahlen band of GaN lies at 17-22 THz, far away from THz range, and potentially can fill the 5.5~12 THz gap for solid-state coherent light sources. Therefore, the GaN based THz-QCLs has been expected to be able to operate at room temperature and cover the gap frequencies. ..This research proposes using Ga(Al)N materials to fabricate novel THz-QCLs. III-nitride materials are characterized by the large lattice/thermal mismatch to foreign substrates and even between GaN/InGaN/AlGaN themselves, and by the strong built-in polarization fields due to both spontaneous and piezoelectric polarization charges at the hetero-interfaces. These two features make the design and simulation much more complicated. Taking these two important feature into account, we focus on three key fundamental issues: (1) suitable subband arrangement in one module and between upper/lower modules in the strong polarization fields; (2) design and fabricate low loss and high confinement THz waveguides with complicated substrates and buffer layers; (3) establish optimal epitaxial technology for thick QCL growth by a nitride MBE. This research is seeking to establish new routes and ideas to overcome the difficulty of 200 K operation temperature limitation for THz-QCLs, and push the frontier forward. High temperature or room temperature THz-QCLs will pave the way for their wide applications in the THz field. The proposed research is still in its very early stage and the THz-QCL field is a strategically important research frontier worldwide. ..The proposer and research team have accumulated extensive experience and knowledge on the III nitride field, especially nitride MBE technologies, and the proposer has been investigating the potential of III nitrides for THz-QCLs in recent 3 years. The strong background in the related field is a solid foundation for the team to conduct the proposed research.