Gain engineering for terahertz quantum cascade lasers

本研究计划的目的是研究和论证新型的有源区设计策略，用于制造具有高光学增益的太赫兹量子级联激光器（THz QCL）。高光学增益将转化为更好的激光器性能，即高能量转换效率、高光输出功率和器件的高工作温度。这三个方面对于太赫兹光源的未来技术和应用的发展至关重要，太赫兹光源位于光学和电子学之间的边界。太赫兹QCL代表了迄今为止在太赫兹光谱范围内发射的激光器中功率和紧凑性的最佳组合。在2002年首次展示，发射频率在1-10 THz之间的THz QCL从那时起就被报道在2-5 THz范围内具有最佳性能。然而，THz QCL的最新性能仅限于低光功率（< 1 W）和低于200 K的工作温度。在本项目的范围内，驱动激光增益的激光物理问题，包括激光能级的设计、电子注入、电子提取和粒子数反转将得到解决。首先，我们将制定一个现实的模型，电子输运太赫兹QCL，包括界面粗糙度散射和热电子效应。半导体异质结构中粗糙晶体界面引起的微扰势引起界面粗糙散射。热电子效应产生于电子系统和晶格之间的缓慢热交换。这两种机制都降低了激光增益并恶化了激光性能。其次，我们将研究不同的方法来工程师界面粗糙度散射在太赫兹QCL，以提高光学增益。我们还将研究通过设计热电子的传输来减少THz QCL中载流子泄漏的方法。最后，我们将提出并展示基于成熟的GaAs/AlGaAs异质结和新型半导体异质结（如InGaAs/InAlAs和InGaAs/InGaAs）的高增益THz QCL的新型有源区设计。

The objective of this research project is the investigation and demonstration of novel active-region-design strategies for the fabrication of terahertz quantum cascade lasers (THz QCLs) with high optical gain. High optical gain will translate into better laser performance in terms of a high energy conversion efficiency, high light output power and high operation temperature of devices. All three aspects are crucial for the development of future technology and applications using terahertz light sources, which lie at the boundary between optics and electronics.THz QCLs represent by far the best combination of power and compactness in lasers emitting within the THz spectral range. First demonstrated in 2002, THz QCLs with emission frequencies between 1-10 THz have been reported since then with best performance in the 2-5 THz range. The state of the art performance of THz QCLs is however limited to low optical powers (< 1 W) and operation temperatures below 200 K.Within the scope of this project laser physics issues driving the laser gain including the design of laser levels, electron injection, electron extraction, and population inversion will be addressed. First, we will formulate a realistic model for electron transport in THz QCLs, including interface-roughness scattering and hot electron effects. Interface-roughness scattering arises from the perturbation potential induced by rough crystal interfaces in semiconductor heterostructures. Hot electron effects arise from the slow heat exchange between the electron system and the crystal lattice. Both mechanisms reduce laser gain and deteriorate laser performance. Second, we will investigate different approaches to engineer interface-roughness scattering in THz QCLs in order to enhance optical gain. We will also investigate approaches to reduce carrier leakage in THz QCLs by engineering the transport of hot electrons. Finally, we will propose and demonstrate novel active region designs for high-gain THz QCLs based on the well-established GaAs/AlGaAs heterosystem and on novel semiconductor heterosystems as InGaAs/InAlAs and InGaAs/InGaAs.