HgCdTe-based quantum-well-heterostructures for mid-infrared heterodyne spectroscopy

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The common goal of the teams of this proposal is to investigate and to actively control the physical mechanisms determining the optical and optoelectronic properties of HgxCd1–xTe/CdyHg1–yTe-based multiple-quantum-well structures (MCT MQWs) towards applications in heterodyne spectroscopy in the mid-infrared (MIR, 9 - 30 micrometers) wavelength range. The mid-infrared spectral band covers many important molecular transitions, for example in the interstellar medium . Until now many MIR applications rely on MCT as material for detectors . The properties of this material can be varied and improved by design of state-of-the-art MCT MQWs in a targeted manner. Their spectral response, determined by bandgap, can be varied by chemical composition and lattice temperature, while designs of the charge carrier energy spectrum and presence of artificial point defects can control non-radiative relaxation of non-equilibrium carriers that determines electronic lifetimes. Controlling the lifetimes of an MCT heterostructure is the basis for designing and manufacturing fast and sensitive detectors as well as for mixers in heterodyne spectroscopy. In this project, we want to develop MCT MQWs optimized for the 9 – 30 µm MIR band with extended bandwidth or enhanced operation speed. Ultimately the project targets at sensitive prototype devices and demonstrating their performance for fast time-resolved spectroscopy as well as sensitive heterodyne spectroscopy. Standard optical characterization of the MQW heterostructures will be combined with time-resolved spectroscopy in order to obtain knowledge on the dynamics of IR excitations in the material and the fundamental limits for fast operation of the devices, which depends on the characteristic lifetimes of free electrons controlled dominantly by HgV centers. Finally the MCT MQWs will be will be implemented in the mixer prototypes for demonstrating and evaluating their performance in a heterodyne spectrometer