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Ge/SiGe quantum wells (QWs) are a new system characterized by optical and electronic properties different from those commonly observed in the more widely studied QWs based on III-V semiconductors. These peculiar properties are due to the type-I band alignment for both the Γ- and the L-type states and to the small energy distance between the direct and the indirect bad gap in Ge, which provides Ge/SiGe QWs with a so-called quasi-direct optical behavior. Moreover, these systems are of potential interest for the integration of good optical properties on the CMOS platform: indeed, room temperature electroluminescence, optical gain and an efficient Quantum Confined Stark Effect have all been demonstrated on Ge/SiGe QWs. This thesis is aimed at a detailed and systematic study of the recombination processes and of the carrier dynamics of compressively strained Ge/SiGe QWs with Ge-rich barriers. Different optical spectroscopy techniques have been employed and measurements as a function of different parameters have been performed. The origin and the decay of the direct and the indirect emission, the thermalization paths, and the scattering phenomena that occur in Ge/SiGe QWs have all been analyzed. An overall picture of carrier dynamics in these systems summarizes all the experimental evidences, and the typical times of the different processes are provided. These results enable a deeper understanding of the intricate and rich carrier dynamics that characterize Ge/SiGe QWs. |
