PACS 63.50.+x, 78.30.Fs We report results of Infrared and Raman spectra studies of bulk Zn 1-x Cd x Se. The obtained concentration dependences of oscillator parameters, reveals an unusual behavior. Besides two transverse optical (TO) and longitudinal optical (LO) branches, which are typical for a one-mode behavior, an additional branch getting into TO-LO splitting region was observed. We explained the nature of these "inserted modes" on the basis of the microscopic theory, which well describes the quasi-local mode frequency and the sign of splitting.

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The phonon modes of self-assembled Ge/Si quantum dots grown by molecular-beam epitaxy in an apparatus integrated with a chamber of the scanning tunneling microscope into a single high-vacuum system are investigated using Raman spectroscopy. It is revealed that the Ge-Ge and Si-Ge vibrational modes are considerably enhanced upon excitation of excitons between the valence band Λ 3 and the conduction band Λ 1 (the E 1 and E 1 + ∆ 1 transitions). This makes it possible to observe the Raman spectrum of very small amounts of germanium, such as one layer of quantum dots with a germanium layer thickness of ≈ 10 Å. The enhancement of these modes suggests a strong electron-phonon interaction of the vibrational modes with the E 1 and E 1 + ∆ 1 excitons in the quantum dot. It is demonstrated that the frequency of the Ge-Ge mode decreases by 10 cm -1 with a decrease in the thickness of the Ge layer from 10 to 6 Å due to the spatial-confinement effect. The optimum thickness of the Ge layer for which the size dispersion of quantum dots is minimum is determined.

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