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Homogeneious linewidth and relaxation of excited hole states in II–VI quantum dots



By use of differential absorption spectroscopy at different temperatures we investigate the homogeneous line broadening of small CdSxSe1 − x quantum dots embedded in glass. Our experiments show the strong correlation between the precipitation stages and characteristics optical parameters such as the saturation intensity and the longitudinal and transverse relaxation times. In samples grown in the diffusion-controlled regime to avoid coalescence, we find after strong laser excitation for the first time spectrally narrow holes in the non-linear differential absorption spectra. These sharp non-linear resonances with a halfwidth Γ of only 10 meV at T = 20 K allow us to investigate the energetic distance of the lowest hole levels and the temperature dependence of the line broadening. The different contributions of LO phonon coupling and temperature-independent scattering to the homogeneous linewidth will be analysed. The relaxation from the excited hole states has been investigated by exciting in the higher-energy hole states and measuring the resulting change in the ground state absorption.

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