High-resolution terahertz semiconductor spectroscopy using quantum-cascade lasers: Develop-ment of appropriate laser sources for 2.7-3.3 and 5.0-5.7 THz

Paul-Drude-Institut（PDI）和柏林工业大学（TUB）的团队的共同目标包括演示一种光谱仪，用于太赫兹频率下半导体的高分辨率激光光谱学，该光谱仪基于多模窄线宽量子级联激光器（QCL）与光栅光谱仪的结合，以及对线宽、线形、以及杂质态的弛豫时间，特别是在同位素纯Ge和Si中。 PDI组的目标是基于适当的建模水平开发改进的设计工具，包括选择必要的理论组件，探索有效设计过程的原则和自动设计程序的介绍，将THz QCL的发射范围扩展到5 THz以上，并了解在更高频率下操作的限制物理过程，以及宽带，可调QCL的发展工作在2.7和3.3太赫兹（锗）和5.0和5.7太赫兹（硅）。最后，我们计划共同演示完整系统的操作和基于QCL的光谱仪的最佳分辨率的确定。 关于一个合适的模型的设计目的的发展，我们打算提高我们的近似子带间散射率，开始与纵向光学声子散射为例。横向势波动，界面配置文件，和相干效应对太赫兹QCL的操作性能的影响将被探讨。该模型将用于调查有效的设计过程和自动化设计过程的描述。这些知识将用于优化2.7和3.3 THz之间的适当QCL。THz QCL的发射范围超过5 THz的扩展和对在更高频率下操作的限制物理过程的理解以及几种可能结构的有效设计和相应激光器的制造将允许开发在5.0和5.7 THz之间操作的可调谐QCL。整个系统的演示将在与TUB小组密切互动的情况下进行，特别是在所需操作参数的定义方面。与TUB小组合作，我们还将使用高分辨率傅里叶变换红外光谱对同位素纯Ge和Si以及各自的杂质状态进行比较光谱研究。

The common goal of the groups at the Paul-Drude-Institut (PDI) and the Technische Universität Berlin (TUB) consists in the demonstration of a spectrometer for high-resolution laser spectroscopy of semiconductors at THz frequencies based on multi-mode, narrow-line-width quantum-cascade lasers (QCLs) combined with a grating spectrometer as well as the investigation of the line width, line shape, and the relaxation time of impurity states in particular in isotopepure Ge and Si. The objectives of the PDI group are the development of an improved design tool based on an appropriate level of modeling including the selection of necessary theoretical components, the exploration of principles for efficient design processes and the presentation of an automated design procedure, the extension of the emission range of THz QCLs beyond 5 THz and the understanding of the limiting physical processes for operation at higher frequencies, as well as the development of broad-band, tunable QCLs operating between 2.7 and 3.3 THz (for Ge) and 5.0 and 5.7 THz (for Si). Finally, we plan to jointly demonstrate the operation of the complete system and the determination of the best possible resolution of the QCL-based spectrometer. With regard to the development of a suitable model for design purposes, we intend to improve our approximation for the intersubband scattering rates, starting exemplarily with longitudinal optical phonon scattering. The influence of lateral potential fluctuations, interface profiles, and coherent effects on the operation properties of THz QCLs will be explored. The model will be used for the investigation of efficient design processes and the description of an automated design procedure. This knowledge will be used to optimize appropriate QCLs between 2.7 and 3.3 THz. The extension of the emission range of THz QCLs beyond 5 THz and the understanding of the limiting physical processes for operation at higher frequencies as well as the efficient design of several possible structures and the fabrication of the respective lasers will allow for the development of tunable QCLs operating between 5.0 and 5.7 THz. The demonstration of the complete system will be carried out in close interaction with the group at TUB, in particular with respect to the definition of the required operating parameters. In cooperation with the TUB group, we will also carry out comparative spectroscopic investigations using high-resolution Fourier transform infrared spectroscopy on isotopepure Ge and Si as well as on the respective impurity states.